JP7748610B2 - Base station for cordless telephone device, and cordless telephone device - Google Patents

Description

The present invention relates to a base station for a cordless telephone device that uses the DECT wireless communication system, which is suitable for use with digital cordless telephones, and to the cordless telephone device itself.

In Japan, key telephone system terminals include not only key telephones connected directly to the main unit via a wired transmission line, but also digital cordless telephones (handsets) connected to the main unit via a wireless base station. These digital cordless telephones are highly valued as telephones that can be used anywhere, and are expected to have the same functionality as key telephones.

Digital cordless phones in Japan have traditionally used the second-generation cordless telephone system standard (RCR STD-28), but in 2011 a new standard for broadband digital cordless phones (ARIB STD-T101) was established, making it possible to develop digital cordless phones that comply with J-DECT. J-DECT is a DECT standard localized for Japan, and specifies six frequencies (F1 to F6) within the 1.9 GHz private band (1893.5 MHz to 1906.1 MHz).

In a key telephone system, the required number of telephone lines are connected to the main unit according to the call volume (the number of communication lines occupied per unit time) in the user's installation environment, and these can be shared and used by each key telephone. For example, in an office with 80 employees, if an average of 10 people make 5-minute calls per hour, the call volume is 0.833 Erlangs. In this case, if the call loss rate (the probability that a call cannot be made because there are no available lines when a call is made) is to be kept below 0.1, then, according to the Erlang B formula, three or more telephone lines should be provided.

In such a system, if all or some of the key telephones are replaced with digital cordless telephones, wireless base stations can be arranged so that the calling area of one or more wireless base stations covers the entire service area (office).

For example, if an office has four wireless base stations and accommodates 80 digital cordless telephones (handsets), then on average each wireless base station should accommodate around 20 handsets. When a call comes in from the telephone line, it is desirable for the incoming call to be notified to all handsets via each wireless base station, and for the first handset to answer to be able to start talking.

It is also desirable to notify each handset of an incoming call as quickly as possible, preferably within 1-2 seconds of the call coming in on the telephone line.

Also, unlike key telephones, digital cordless telephones (handsets) are not installed in fixed locations but are mobile, so there may be cases where a large number of handsets (for example, 40 handsets) are concentrated around a specific wireless base station. Even in such cases, it is desirable to notify each handset of an incoming call within 1 to 2 seconds, if possible.

Patent Document 1 describes a cordless telephone device and wireless communication method that uses a method for transmitting data in transmission units having an A field for transmitting control data and a B field for transmitting voice data; that when the control unit of the radio transmission circuit of the base unit determines that the unit is in a call, the control unit controls the TDMA modulation/demodulation unit to transmit control data using the A field and voice data using the B field; and that when the control unit determines that the unit is not in a call, the control unit controls the TDMA modulation/demodulation unit to transmit control data using at least the B field, thereby enabling control data to be transmitted without delay in a wireless communication system that uses a TDMA/TDD wireless communication method.

Patent Document 2 describes a telephone system, a telephone control device, and a base unit of a cordless telephone device, in which the main unit has a base unit-specific handset management table formed based on information in a handset management table provided by the base unit, and a control circuit in the main unit supplies a control signal to the base unit to control the on/off of a broadcast mode in which information to be sent to all handset units connected to the base unit is sent to all of the handset units by transmitting the information. The control circuit references the base unit-specific handset management table and controls base units with a predetermined number of connected handset units or less to turn on the broadcast mode, and controls base units with more than the predetermined number of connected handset units to turn off the broadcast mode, thereby reducing communication time loss that occurs when more handset units than the number capable of simultaneous communication are connected to the base unit of the cordless telephone device.

JP 2015-177239 A Japanese Patent Application Laid-Open No. 2019-146054

A base station for a digital cordless telephone system using DECT generally has one DECT transceiver installed, and in principle can communicate with up to 12 handsets using up to 12 slots. However, in practice, the maximum number of handsets that can communicate simultaneously is limited to 10 or less, to allow for slot switching to accommodate handover handsets and to avoid interference.

In the cordless telephone device and wireless communication method described in Patent Document 1, control data for a handset is transmitted using the A field when the handset is in a call and the B field when the handset is not in a call. Here, control data transmission in the A field refers to data transmission over the Cs channel, and control data transmission in the B field refers to data transmission over the Cf channel. In both cases, the base station and handset establish a bearer (bidirectional data link) and a data link layer link, and data is transmitted bidirectionally. Therefore, when the number of handset units accommodated by a base station is 10 or fewer, the maximum number of handset units that can communicate simultaneously, transmitting control data using this technology allows control based on that control data to be executed at the appropriate time. However, when the number of handset units accommodated by a base station exceeds the maximum number of handset units that can communicate simultaneously, there is a problem in that control data cannot be transmitted to all of those handset units. Patent Document 1 does not describe control when the number of handset units accommodated by a base station exceeds the maximum number of handset units that can communicate simultaneously.

In the telephone system, telephone control device, and cordless telephone base unit described in Patent Document 2, if the number of handsets accommodated by a base station exceeds the maximum number of handsets capable of simultaneous communication, the bearer (bidirectional data link) between the base station and each handset must be reconnected. This is necessary to prevent large delays in control data transmission to the last handset to be controlled, given that the handset authentication and encryption procedures take more than one second. Ultimately, the telephone system, telephone control device, and cordless telephone base unit described in Patent Document 2 are unable to notify all handsets of an incoming call. Furthermore, if the number of handsets connected to the base station changes over time, the same handset may sometimes be notified of an incoming call and sometimes not, which may appear to the user to be malfunctioning with the handset.

The object of the present invention is to solve the above problem by enabling a base station for a cordless telephone device using the DECT wireless communication system, and for the cordless telephone device, to notify all handsets of an incoming call without significant delay, even when the number of handsets accommodated by the base station exceeds the maximum number of handsets that can communicate simultaneously.

To solve the above problem, the present invention provides a base station for a cordless telephone device that selectively uses one base station and one handset out of one or more base stations connected to a telephone control device connected to a wide area network and multiple handset devices connected to the base station wirelessly. The base station extracts information that needs to be transmitted to the handset device from a handset control command transmitted from the telephone control device to generate a handset control signal, and further includes: DECT control signal generation means that selects the optimal transmission channel for wirelessly transmitting the handset control signal in the DECT system according to the type of the handset control command; and DECT transmission/reception control means that performs wireless transmission/reception in the DECT system and assembles/disassembles DECT TDMA/TDD frames, and transmits the handset control signal provided by the DECT control signal generation means using the optimal transmission channel selected by the DECT control signal generation means.

The present invention is also characterized in that, when the handset control command transmitted from the telephone control device is a line lamp display command, the DECT control signal generation means selects a broadcast channel as the optimal transmission channel for wirelessly transmitting the handset control signal generated from the handset control command using the DECT system, and the DECT transmission/reception control means transmits the handset control signal using the broadcast channel without establishing a link.

The present invention also includes a base station status management means for generating, as base station status information, information on the number of handset devices in communication and the number of connected handset devices, and two-bit information indicating whether the number of handset devices in communication and the number of connected handset devices have reached their respective upper limits, and for generating a base station status notification signal that instructs the base station status information to be notified in the MAC information of a beacon, and for notifying the base station status notification signal via the DECT transmission/reception control means.

The present invention also relates to a cordless telephone device that is connected to a wide area network and is configured by selectively using one base station and one handset out of one or more base stations connected to a telephone control device of a digital cordless telephone system and a plurality of handset units connected to the base station by wireless communication, and the base station extracts information that needs to be transmitted to the handset unit from a handset control command transmitted from the telephone control device and generates a handset control signal, and further includes DECT control signal generation means that selects the optimal transmission channel for wirelessly transmitting the handset control signal in the DECT system according to the type of the handset control command, and a .... The system includes a DECT transmission/reception control means that performs TDMA/TDD frame synthesis/decomposition and transmits the handset control signal provided by the DECT control signal generation means using the optimum transmission channel selected by the DECT control signal generation means, and a per-handset paging group number storage means that transmits the handset control signal to the handset only on the Bs channel of the multi-frame corresponding to the handset's paging group number, and the handset has a paging group number storage unit that, during discontinuous reception at a 640 ms cycle, performs reception operations only on the multi-frame corresponding to the paging group number stored in the paging group number storage unit.

Furthermore, in the cordless telephone device of the present invention, when the handset control command transmitted from the telephone control device is a line lamp display command, the DECT control signal generation means provided in the base station selects a broadcast channel as the optimal transmission channel for wirelessly transmitting the handset control signal generated from the handset control command in the DECT system, and the DECT transmission/reception control means transmits the handset control signal using the broadcast channel without establishing a link.

Here, the paging group number for the handset can be determined by the base station during the location registration sequence with the base station, taking load balancing into consideration, and notified to the handset.

Alternatively, the paging group number of the handset can be determined independently by the base station and the handset based on system-specific handset identification information assigned when the handset is added to the digital cordless telephone system.

Furthermore, the present invention is characterized in that the base station generates, as base station status information, information on the number of calling handsets and the number of connected handsets of the base station, and 2-bit information on whether the number of calling handsets and the number of connected handsets have each reached their upper limit, and further comprises base station status management means for generating a base station status report signal that instructs the base station status information to be reported in the MAC information of the beacon, and the handset comprises a handset control unit that operates to select a base station to connect to from among base stations for which the number of calling handsets has not reached its upper limit in the base station status information reported in the beacon during a base station search immediately before link establishment, and to select a base station to connect to from among base stations for which the number of connected handsets has not reached its upper limit in the base station status information reported in the beacon during other base station searches.

According to the present invention, a base station for a cordless telephone device using the DECT wireless communication system and the cordless telephone device select the optimal transmission channel for wirelessly transmitting a handset control signal using the DECT system depending on the type of handset control command, and transmit the handset control signal using the optimal transmission channel. Furthermore, if the handset control command is a line lamp display command, a notification channel is selected as the optimal transmission channel, and the handset control signal is transmitted using this notification channel without establishing a link. Therefore, even if the number of handset devices accommodated by the base station exceeds the maximum number of handset devices that can communicate simultaneously, all handset devices can be notified of incoming calls and other notifications without significant delay.

In addition, the base station manages the number of active and connected handsets at that base station based on handset control commands, and generates and reports a base station status notification signal indicating whether the number of active and connected handsets has reached its respective upper limit. This allows the handset to check the base station status information and select a base station to connect to, thereby achieving optimal load balancing and reducing the increase in call delay time at the base station until the external call incoming lamp display is completed for all handsets.

FIG. 2 is a block diagram showing a basic configuration of an example of a main device. FIG. 1 is a diagram illustrating an example of a frame format for signal transmission by a TDD (ping-pong transmission) method on a base station transmission line. 10A and 10B are diagrams illustrating an example of transmission of child device control data having a multi-frame configuration. FIG. 10 is a diagram illustrating an example of slave unit management in a control unit. FIG. 1 is a block diagram showing a basic configuration of an embodiment of a base station according to the present invention. 1 is a block diagram showing a basic configuration of an embodiment of a slave unit according to the present invention; FIG. 10 is a block diagram showing the basic configuration of another embodiment of a base station according to the present invention. FIG. 10 is a block diagram showing the basic configuration of another embodiment of a slave unit according to the present invention. 1 shows an example of the form of a slave unit. FIG. 2 is a diagram illustrating an example of a slave device state and a state transition. FIG. 1 is a diagram showing the relationship between the communication distance and the average reception level and the fading drop level in indoor radio wave propagation. FIG. 2 is a diagram showing the relationship between a callable area and a location registerable area. FIG. 10 is a diagram illustrating an example of a location registration sequence. FIG. 10 is a diagram illustrating an example of a call sequence from a handset. FIG. 10 is a diagram showing an example of a line lamp display sequence. 10 is a diagram showing an example of a line lamp display message broadcast from a base station using the Bs channel. FIG. FIG. 10 is a diagram showing an example of an external call incoming call sequence. FIG. 10 is a diagram illustrating an example of a control sequence in the case of handover. FIG. 10 is a diagram illustrating an example of a keep-alive sequence from a slave device. FIG. 10 is a diagram illustrating an example of a transmission operation of paging frames for four paging groups. FIG. 10 is a diagram showing another example of the transmission operation of paging frames for four paging groups. FIG. 1 is a diagram showing one form of station placement design for a cordless telephone device. FIG. 1 is a diagram showing the arrangement of radio resources in J-DECT. 1 shows the frame format of a DECT frame, where (a) shows a short frame and (b) shows a long frame. FIG. 1 is a diagram illustrating an example of a frame format of a DECT multiframe. FIG. 10 is a diagram showing a frame format of base station ID information Nt. FIG. 10 is a diagram showing the frame format of system information Qt. FIG. 10 is a diagram illustrating an example of the correspondence between a Qt header and system information. FIG. 10 is a diagram showing a frame format of MAC control information Mt. FIG. 10 is a diagram illustrating an example of the correspondence between an Mt header and a message type. FIG. 10 is a diagram illustrating an example of the correspondence between Mt commands and MAC control messages. FIG. 10 is a diagram showing a frame format of paging information Pt. FIG. 10 is a diagram illustrating an example of the correspondence between a Pt header and Bs channel information. 10 is a diagram showing an example of the correspondence between information types of Pt short pages and MAC information. FIG. 10A and 10B are diagrams illustrating an example of power-saving wireless operation of a DECT slave unit in a communication state. FIG. 10 is a diagram illustrating an example of power-saving wireless operation of a DECT slave unit in an idle lock state. FIG. 10 is a diagram illustrating an example of power-saving wireless operation of a DECT handset when receiving multiple paging frames.

The present invention will now be described with reference to the drawings.

Since this invention relates to the control of digital cordless telephones that use the DECT wireless communication system, we will first provide a brief explanation of the DECT standard for control related to this invention.

Figure 23 shows the allocation of radio resources in J-DECT.

The DECT standard uses the TDMA-TDD method. As shown in Figure 23, J-DECT's radio resource allocation has a frame structure with a 10 ms period on the time axis, with 12 slots for downlink (base station → handset) and 12 slots for uplink (handset → base station). Six frequencies (F1 to F6) are specified on the frequency axis. While it shares the same frequency band as privately operated second-generation cordless telephone (PHS) systems, the PHS control channel is a fixed frequency, and interference with this could cause PHS handsets to become uncontrollable. Therefore, the ARIB STD-T101 PHS protection regulations stipulate that after powering on, J-DECT base stations check for the presence or absence of PHS control channel signals before transmitting, and if signals are detected, do not use channels F3 and F4.

Channels other than F3 and F4, which overlap in frequency band with the PHS control channel, are shared with PHS for free channel detection. However, the time interval for free channel detection in PHS systems is often around 300 μs, which means that dummy bearers can slip through this and cause interference that is invisible to the PHS side. Therefore, the PHS protection regulations of ARIB STD-T101 stipulate that after powering up, J-DECT base stations must check for the presence of PHS control channel signals before transmitting, and if they determine that signals are present, they must avoid transmitting dummy bearers on F2 and F6 channels as much as possible. This is because, while many PHS products take measures to avoid using the F1 and F5 channel bands to avoid market interference, they do use the F2 and F6 channel bands, and if a J-DECT base station were to transmit a dummy bearer in these bands, there is a risk of market interference.

When transmitting wirelessly in DECT, the handset and base station detect available channels and select and use the channel (combination of frequency channel and slot) with the lowest reception (interference) level.

Figure 24 shows the frame format of a DECT frame.

As shown in Figures 24(a) and (b), DECT has short frames called dummy bearers, which have a duration of 83.3 us, and long frames called traffic bearers, which have a duration of 368.1 us. The former are frames used by base stations in an idle (non-communicating) state to transmit beacons, and the latter are frames used during one-to-one communication between a base station and a handset.

The beacon (dummy bearer) transmitted by an idle base station is a one-way broadcast channel for downlink only, and is transmitted using one or two downlink radio resources (channels) per base station. Two beacons are transmitted per base station to avoid a situation where a mobile device is unable to handover to that base station if the beacon transmission slot of the destination base station matches the mobile device's call slot when handing over. The two beacons are transmitted in different slots. On the other hand, the traffic bearer used for one-to-one communication between a base station and a mobile device is a bidirectional channel, using a pair of slots spaced 5 ms apart (for example, slot 1 and slot 13). A base station in communication can transmit both a dummy bearer for beacons and a traffic bearer, and can also transmit beacon control data using the A-Field in the traffic bearer.

In digital cordless telephone systems using DECT, traffic bearers are transmitted for the number of one-to-one communications between base stations and handsets, and up to twice the number of base stations or dummy bearers. The right to transmit both dummy bearers and traffic bearers is acquired in the same way through free channel detection. From the perspective of efficient frequency utilization, the free channel detection level is set so that channels used by surrounding base stations and their handsets can be reused and used. During times of traffic congestion, there is a possibility that some handsets will be unable to receive dummy bearers due to co-channel interference from traffic bearers from surrounding base stations, so it is desirable to use traffic bearers only to the minimum extent necessary.

Figure 25 shows an example of a frame format for a DECT multiframe.

DECT uses beacons to broadcast tail data (40 bits) using this multiframe structure. One multiframe is 160 ms long and consists of 16 frames (frame 0 to frame 15).

The tail data (40 bits) broadcast in the beacon is classified into base station ID information Nt, system information Qt, MAC control information M, paging information Pt, and upper layer control information Ct depending on its type. This beacon type information is stored in the header information of the dummy bearer A-Field.

Figure 26 shows the frame format of base station ID information Nt, which broadcasts base station ID information.

The base station ID information Nt includes the equipment manufacturer ID (EIC), system ID (FPN), and base station ID (RPN). Each user is assigned a different system ID, and the base station within the user's system is identified by the base station ID.

Figure 27 shows the frame format of system information Qt, which reports system information, and Figure 28 shows an example of the correspondence between the Qt header and system information.

System information Qt includes basic information such as available RF carrier information, RF carrier/slot information for the Qt frame, and primary scan frequency information, which is the base station's free channel detection frequency information, as well as extended RF carrier information, multiframe number information, base station transmission power information, and unique system information.

Figure 29 shows the frame format of MAC control information Mt, which reports MAC control information, and Figure 30 shows an example of the correspondence between Mt headers and message types. Furthermore, Figure 31 shows an example of the correspondence between Mt commands and MAC control messages.

Figure 32 shows the frame format of paging information Pt that reports paging information, and Figure 33 shows an example of the correspondence between the Pt header and Bs channel information. Figure 34 shows an example of the correspondence between the information type of a Pt short page and MAC information.

The paging information Pt broadcasts data from the Bs channel (slow broadcast channel) and MAC information. The Bs channel can broadcast paging information and unique information to notify that there is downlink data addressed to a specific mobile station. MAC information includes blind slot information (unavailable slots for the base station), base station status (BUSY, etc.), and available frequency channel information. The type of MAC information broadcast in the frame is stored in the information type of the dummy bearer A-Field.

Paging information Pt frames include short pages (Figure 32(a)) that broadcast 20 bits of Bs channel data and MAC information, and full pages (Figure 32(b)) that broadcast only 36 bits of Bs channel data. Long pages can also be used, which combine multiple full pages to broadcast 36 x N bits of Bs channel data. The frame type information for paging information Pt is transmitted in the Pt header.

In the DECT standard, the frame number is specified as 28 bits, incremented by one for each frame, and goes through a cycle approximately once a month. The upper 24 bits are called the multi-frame number.

In digital cordless telephone systems using the DECT standard, frame numbers and multiframe numbers are generally synchronized between base stations.

Paging information Pt is transmitted in frame 0, and battery-powered, power-saving handset devices can receive only frame 0 intermittently at 160 ms intervals. The DECT standard stipulates that base stations transmit the same beacon information in four consecutive multi-frames to enable intermittent reception at 640 ms intervals. In other words, power-saving handset devices can receive only frame 0 intermittently at 640 ms intervals.

If there are multiple pieces of paging information Pt, up to six pieces of paging information Pt can be transmitted within one multiframe. The presence or absence of subsequent paging information Pt within the same multiframe is indicated by the first bit of the Pt header, and the power-saving slave device transitions to sleep mode after receiving all paging information Pt.

Figure 35 shows an example of power-saving wireless operation of a DECT handset in a communicating state, Figure 36 shows an example of power-saving wireless operation of a DECT handset in an idle-locked state, and Figure 37 shows an example of power-saving wireless operation of a DECT handset when receiving multiple paging frames.

In addition, if there is no particular paging information, the base station can transmit base station ID information Nt instead of paging information Pt. The base station ID information Nt is used by the handset when searching for a base station. In addition, system information Qt is always transmitted in frame 8, and base station ID information Nt is always transmitted in frame 14.

In addition, during one-to-one communication between a base station and a mobile device, even-numbered frames (frame 1, frame 3, ... frame 11) are used as upper layer control information Ct, a data link is established between the base station and the mobile device on the upper layer control information Ct, and low-speed control information can be transmitted in both directions using the bidirectional low-speed control channel Cs on the data link. Note that the upper layer control information Ct is a bidirectional channel, and the upper layer control information Ct is also transmitted using the A-Field for the uplink traffic bearer.

A traffic bearer is used for one-to-one communication between a base station and a handset. The Cs channel is a low-speed channel that uses the tail (40 bits) of the traffic bearer's A-field, but the high-speed Cf channel that uses the traffic bearer's B-field (320 bits) can also be used. For example, during a call, voice data is transmitted in the B-field, so control data is transmitted over the A-field Cs channel, and when not in a call, control data can be transmitted at high speed using the B-field Cf channel.

Note that even-numbered frames (frame 1, frame 3, etc.) are also used for bidirectional transmission of MAC control information Mt for MAC access control. When conducting one-to-one communication between a base station and a mobile device, it is first necessary to establish a bearer (bidirectional data link) using the MAC control information Mt. The MAC control information Mt is also used in encryption procedures and handovers.

In a dummy bearer, if there is no MAC control information, base station ID information Nt can be transmitted in even-numbered frames (frame 1, frame 3, etc.). The base station ID information Nt is used by the mobile device when searching for a base station.

This invention takes into account the above DECT standard and enables the transmission of incoming call and incoming call lamp information to all handsets without significant delay, even when the number of handsets accommodated by a base station exceeds the maximum number of handsets that can communicate simultaneously.

The present invention will now be described with reference to the drawings.

The present invention particularly relates to a cordless telephone device configured by selectively using one base station and one handset among one or more base stations connected to a telephone control device (main unit) connected to a wide area network and multiple handset units connected to the base station via a wireless communication system, and the base station. First, we will explain the main unit connected to the wide area network.

Figure 1 is a block diagram showing the basic configuration of an example of a main device connected to a wide area network.

The main unit 10 comprises a central office interface unit (central office I/F unit) 11, an internal line interface unit (internal line I/F unit) 12, a clock generation unit 13, a circuit switching unit 14, and a control unit 15. For simplicity, only the necessary components are shown here. This also applies to the following diagrams.

The central office I/F unit 11 is connected to L telephone lines (central office lines) (L is a natural number greater than or equal to 1), allowing for simultaneous central office call origination and central office call termination on up to L lines. The internal line I/F unit 12 is connected to M base station transmission lines (M is a natural number greater than or equal to 1), allowing for the accommodation of up to M base stations (M is a natural number greater than or equal to 1) via these.

The audio data inside the main unit 10 is, for example, an audio encoded signal such as a PCM codec signal. A PCM codec signal is 64 kbps audio data that is quantized to 14 bits at 8 kHz (125 us intervals) and then nonlinearly compressed to 8 bits.

The clock generation unit 13 generates an audio multiplex clock that is fast enough to circuit-switch the telephone line and internal line audio signals, and supplies it to the central office I/F unit 11 and internal line I/F unit 12, respectively. The multiplexed audio signal generated using this is applied to the line switching unit 14, where circuit switching is performed based on control information for external and internal line outgoing and incoming calls. The clock generation unit 13 also generates an audio codec frame pulse with a 125 μs period, which is supplied to the central office I/F unit and internal line I/F unit, respectively, allowing circuit switching on a per-sample basis for the audio signal. Furthermore, the clock generation unit 13 generates an inter-base station synchronization timing pulse for DECT inter-base station synchronization. This inter-base station synchronization timing signal is supplied to each base station via the base station transmission path, thereby achieving inter-base station synchronization.

In addition, digital cordless telephone systems using the DECT wireless communication method require not only multi-frame synchronization between base stations but also frequency channel synchronization for detecting available channels, so timing synchronization with a period of 160 ms x (number of frequency channels) is required. If the number of frequency channels is 6, timing information with a period of 960 ms is supplied.

The base station transmission path transmits two-way voice data with the handset connected to that base station for calls, two-way control data for all handset connected to that base station, and timing information for synchronization between DECT base stations.

Figure 2 shows an example of a frame format for signal transmission using the TDD (ping-pong) method on a base station transmission line.

Here, downstream and upstream transmissions are provided, and a guard period is provided between the upstream and downstream transmissions to take into account the transmission delay time on the base station transmission path.

The TDD system's period (frame time length) is set to an integer multiple of 125 μs to match the division of audio data. Downstream transmission data consists of synchronization bits, one or more channels of audio data, downstream common control data, and DECT inter-base station synchronization bits (not shown). The same applies to upstream transmission data.

The control data for the slave device is usually several to several tens of bytes long, and a transmission delay of several hundred milliseconds is acceptable. Therefore, multiple TDD frames can be concatenated to form a multiframe, and control data can be transmitted in multiframe units. In this case, a multiframe synchronization bit can be used. The time length of the multiframe is set to, for example, several tens of milliseconds.

Figure 3 shows an example of transmission of handset control data in a multi-frame configuration.

Here, a multiframe is constructed with 50 bytes of control data per multiframe.

Frame synchronization is an integer multiple of 125us, multi-frame synchronization is on the order of several tens of ms, and DECT inter-base station synchronization has a period of, for example, 960ms. DECT inter-base station synchronization timing information may be transmitted using a frame synchronization bit pattern.

The control data is generated by the control unit 15. The bidirectional control data contains control commands for each control sequence between the main unit 10 and the base station. The control data can also include ID information for identifying the handset to be controlled, and can also include information such as the call number assigned when making or receiving a call.

The control unit 15 manages and sequentially updates the connected base station information, call status, whether or not a ringing sound is specified, the station line key assignment, and the lamp status of the assigned station line key for all handset units in the system. If the lamp status of the station line key of a handset unit changes, a line lamp display command is issued to that handset unit.

Figure 4 shows an example of handset management in the control unit 15.

Here, base station 1 accommodates handset units with handset IDs "100" to "105", and these handset units can communicate through base station 1, while base station 2 accommodates handset units with handset IDs "106" to "107", and these handset units can communicate through base station 2. Also, handset unit with handset ID "100" is assigned lines "5239" and "5396", but its current call control state is "idle", and the line lamps for lines "5239" and "5369" are both "off". Also, handset unit with handset ID "101" is assigned lines "5211" and "5169", but its current call control state is "in call", and the line lamp for line "5169" is "green" (in call). This indicates that the user of the handset with handset ID "101" is making a call through line "5169."
Furthermore, handset units with handset IDs "102" to "107" are assigned line "5169," but because the user of handset unit with handset ID "101" is already in a call on that line, the line lamps on those handset units are "lit red," indicating that the line is being used by another handset. Handset units with handset IDs "101" to "107" are also assigned line "5211." The call control status for that line is currently "incoming call," and the line lamp is "flashing red" (incoming call), indicating that an incoming call is coming through line "5211."

Figure 5 is a block diagram showing the basic configuration of an embodiment of a base station according to the present invention.

Here, only the basic configuration of base station 1 (20) is shown, but other base stations have a similar basic configuration. The digital telephone device of the present invention is configured by selectively using one of these base stations and one of the handset units described below, and functions as a single cordless telephone.

The base station 20 includes a base station transmission path termination unit 21, a DECT transmission/reception control unit 22, a DECT control signal generation unit 23, and a base station status management unit 24.

The base station transmission path termination unit 21 decomposes and combines TDD frames transmitted over the base station transmission path. K (K is a natural number greater than or equal to 1) pieces of bidirectional audio data are transmitted over the base station transmission path, and this bidirectional audio data is serially transmitted to the DECT transmission/reception control unit 22, for example, via a codec interface.

For the codec interface, the multiplexed audio codec clock and audio codec frame pulse are also generated in the base station transmission path termination unit 21 and applied to the DECT transmission/reception control unit 22.

In addition, predetermined timing information (inter-base station synchronization timing pulses) for DECT inter-base station synchronization, for example, with a period of 960 ms, is also output from the base station transmission path termination unit 21 and applied to the DECT transmission/reception control unit 22.

In addition, the base station transmission path termination unit 21 synthesizes or decomposes bidirectional control data into handset control commands in multiframe units of the base station transmission path, and applies the data to the DECT control signal generation unit 23, for example, via a bidirectional serial interface.

The DECT control signal generator 23 analyzes the command type of the handset control command received from the base station transmission path termination unit 21 via the serial interface, determines the optimal DECT transmission channel based on the command type, and notifies the DECT transmission/reception controller 22 of this as a DECT transmission channel selection signal. At the same time, the DECT control signal generator 23 applies the control information of the handset control command to the DECT transmission/reception controller 22 as a handset control signal either directly or by converting it into a format compatible with the DECT transmission channel.

Conversely, the DECT transmission/reception control unit 22 receives control information from the handset via the wireless transmission path and applies it as a handset control signal to the DECT control signal generation unit 23. The DECT control signal generation unit 23 converts this into a format for a handset control command specified by the main unit 10, and applies it to the base station transmission path termination unit 21. The handset control command is then notified to the main unit 10 via the base station transmission path.

DECT transmission channels include the Cs and Cf channels, which transmit control data after establishing a one-to-one link between the base station and handset, and the Bs channel, which broadcasts control data using beacons without establishing a link. The Bs channel can broadcast paging information and unique information to notify that there is downlink data addressed to a specific handset. Therefore, for line lamp display messages and incoming call messages, which require information to be communicated to all handset units connected to the base station, the Bs channel is selected, which can broadcast control data using beacons without establishing a link and without being limited by the maximum number of handset units that can communicate simultaneously. For other control information, the Cs or Cf channel is selected.

The base station status management unit 24 acquires handset control commands sent and received between the base station transmission path termination unit 21 and the DECT control signal generation unit 23, and also acquires keep-alive signals from the DECT transmission/reception control unit 22 that the handset periodically sends to the base station to indicate that it is in range. Based on these, the base station status management unit 24 manages the base station status and applies a base station status notification signal to the DECT transmission/reception control unit 22.

For example, if a response command to a handset is detected in an outgoing call sequence from the handset, the number of handsets may be increased by one, and if a disconnect command is detected, the number of handsets may be decreased by one. Similarly, if a response command from a handset is detected in an incoming call sequence to the handset, the number of handsets may be increased by one, and if a disconnect command is detected, the number of handsets may be decreased by one. Furthermore, if a handset is handed over, the base station from which it moved may decrease the number of handsets by one if it detects a call disconnect command from the main unit, and the base station to which it moved may increase the number of handsets by one if it detects a response command from the main unit.

Similarly, for example, the number of connected handset devices may be increased by one when a location registration acceptance command from the main unit is detected in the location registration sequence from the handset. Furthermore, the number of connected handset devices may be decreased by one when a keep-alive signal, transmitted from the handset at a fixed period T1, for example, every 30 seconds, cannot be received for a fixed period T2, for example, three minutes. Furthermore, when a handset hands over, the source base station may decrease the number of connected handset devices by one when it detects a call disconnection command from the main unit, and the destination base station may increase the number of connected handset devices by one when it detects a response command from the main unit. Furthermore, although not shown, when an idle handset device that is not making a call roams between base station areas, after accepting location registration from the destination base station, the main unit may instruct the source base station to delete the handset's location registration, and the base station that receives this instruction may decrease the number of connected handset devices by one.

As a result, the base station status management unit 24 manages the number of calling handsets and the number of connected handsets at the base station 20, and based on this, generates 2-bit information indicating whether the number of calling handsets and the number of connected handsets have reached their respective upper limits. From this, a base station status notification signal is generated that instructs notification in the MAC information of the beacon and applied to the DECT transmission/reception control unit 22, allowing the base station status to be reported in the MAC information of the beacon transmitted from the base station 20.

When searching for a base station immediately before establishing a link, the handset checks the base station status information in the MAC information broadcast in the beacon and selects a base station to connect to from among base stations where the number of handset devices in communication has not reached the upper limit. When searching for base stations at other times, the handset checks the base station status information in the MAC information broadcast in the beacon and selects a base station to connect to from among base stations where the number of connected handset devices has not reached the upper limit. This allows for optimal load balancing. This reduces the increase in call delay time, which is the time it takes for the incoming call lamp to display for all handset devices at that base station when a large number of handset devices are connected to a specific base station.

Figure 6 is a block diagram showing the basic configuration of an embodiment of handset 1 (30) according to the present invention.

Although only the basic configuration of one handset is shown here, N handset units (N is a natural number greater than or equal to 1) are provided per system, and the other handset units have the same basic configuration. This allows each handset to make and receive calls via any of the base stations.
The handset 30 of this embodiment includes a DECT transmission/reception control unit 31, a handset control unit 32, an audio codec 33, an office line key 34, a ringer 35, an LCD display unit 36, a microphone 37, a speaker 38, and a numeric keypad 39.

The DECT transmission/reception control unit 31 performs functions such as transmitting and receiving DECT radio signals, GFSK or differential PSK modulation/demodulation, TDMA frame synthesis, TDMA frame disassembly, search processing when searching for base stations, and radio status management.

The handset control unit 32 sends and receives handset control commands to and from the DECT transmission/reception control unit 31, and controls each part of the handset 30.

The audio codec 33 transmits and receives audio codec signals to and from the DECT transmission/reception control unit 31, and also receives an audio codec clock and audio codec frames from the DECT transmission/reception control unit 31 to encode/decode audio. A microphone 37 and a speaker 38 are connected to the audio codec 33. The audio signal uttered by the handset is converted into an electrical signal by the microphone 37, sampled at a predetermined rate, for example, 8 kHz, by an AD converter provided in the audio codec 33, and the transmission bandwidth is further compressed by the audio codec 33. For example, a linear PCM signal that has been AD converted at 14 bits may be compressed to 8 bits using u-law PCM or A-law PCM, and then further compressed to 4 bits using ADPCM.

The DECT standard supports audio codecs such as 32 kbps ADPCM for narrowband audio, and 64 kbps u-law PCM and 64 kbps G.722 for wideband audio. Narrowband audio uses one slot each for upstream and downstream, while wideband audio uses two slots each for upstream and downstream. Handset 30 may use either narrowband or wideband audio.

The voice signal uttered by the other party in the call is converted to an analog signal by a DA converter provided in the voice codec 33 and output from the speaker 38. The voice codec 33 receives an voice codec clock and a voice codec frame pulse indicating the start point of one sample of data from the DECT transmission/reception control unit 31, and bidirectional voice codec signals are transmitted between the voice codec 33 and the DECT transmission/reception control unit 31.

The handset control unit 32 is connected to the station line keys 34, ringer 35, LCD display unit 36, numeric keypad 39, and other devices, and displays the station line key lamps, sounds the ringer, and displays information on the LCD in response to handset control signals. Information on pressing the station line keys 34 or numeric keypad 39 is also applied to the DECT transmission/reception control unit 31 as handset control signals and processed within the control sequence. The control sequence is explained later.

Figure 7 is a block diagram showing the basic configuration of another embodiment of base station 1 (20) according to the present invention. In Figure 7, the same components as in Figure 5 are designated by the same reference numerals.

In this embodiment, the base station 20 includes a per-handset paging group number storage unit 25. The per-handset paging group number storage unit 25 stores paging group numbers for all handset units connected to the base station 20 and applies them to the DECT control signal generation unit 23. The DECT control signal generation unit 23 then applies handset control signals for each handset unit to the DECT transmission/reception control unit 22 at multi-frame timing corresponding to the paging group. The base station 20 also includes a base station status management unit 24. Similar to the base station status management unit 24 in FIG. 5, this base station status management unit 24 acquires base station status signals from handset control commands and further acquires keep-alive signals that handset units periodically transmit to the base station from the DECT transmission/reception control unit 22 to indicate that they are within range. Based on these, the base station status management unit 24 manages the base station status and generates a base station status notification signal, which it then applies to the DECT transmission/reception control unit 22.

In addition, the DECT control signal generator 23 is supplied with a multi-frame timing pulse indicating the start timing of a 160 ms multi-frame and information on the lowest two bits of the multi-frame number.

The lowest two bits of the multiframe number have a repetition period of 640 ms, and the DECT control signal generator 23 performs control such that, for example, handset control signals to be transmitted using the Bs channel to handset units in paging group 1 are applied to the DECT transmission/reception controller 22 in multiframes where the lowest two bits of the multiframe number are "00", and handset control signals to be transmitted using the Bs channel to handset units in paging group 2 are applied to the DECT transmission/reception controller 22 in multiframes where the lowest two bits of the multiframe number are "01". This allows handset units belonging to different paging groups to be notified of handset control signals transmitted on the Bs channel to all handset units within 640 ms using different multiframes.

In each paging group, up to six Bs channels can be transmitted within one multiframe period. In other words, for up to 24 handset units, each Bs channel can be transmitted within 640 ms.

Figure 8 is a block diagram showing the basic configuration of another embodiment of handset 1 (30) according to the present invention. In Figure 8, the same parts as in Figure 6 are designated by the same reference numerals.

The handset 30 in this embodiment operates in conjunction with the base station 20 in Figure 7 and is equipped with a paging group number storage unit 40 for storing the paging group number of the handset 30, and the paging group number information stored therein is applied to the handset control unit 32.

When receiving intermittently at a 640 ms cycle, the handset control unit 32 references the multiframe number broadcast in the beacon and controls the DECT transmission/reception control unit 31 to receive only the multiframe corresponding to the paging group number of the handset at a 640 ms cycle.

Figure 9 shows an example of the handset configuration.

The handset here has eight line keys, LK1 to LK8, each associated with a telephone line.

As with key telephones, each line key is equipped with an LED that displays the line's status (free, in use, etc.), allowing users to see the status of free lines at a glance. For example, if the line key for a free line is unlit and the line key for a line currently in use is lit, the user can select the unlit free line to make an outside call.

In addition, when an outside call comes in, the line key on all handsets that have that telephone line assigned to it will flash to notify you of the incoming call, and only the handset that answers first will be able to talk. Also, just like with key telephones, calls can be put on hold or transferred after the call is made.

Furthermore, just like with key telephones, when an outside call comes in, not only will the corresponding line key flash to notify you of the call, but a handset previously designated as a ringing terminal will also ring. However, it is desirable to establish a link with the ringing handset so that the call can be made immediately when the user answers.

However, during times of traffic congestion, there is a possibility that some handset units may be unable to receive dummy bearers due to co-channel interference from traffic bearers. Therefore, it is desirable to limit the use of traffic bearers to the minimum necessary, and from this perspective, it is also desirable to limit the number of ringing handset units to the minimum necessary.

Figure 10 shows an example of the slave device state and state transitions.

In the initial state after powering on, each handset performs a base station search at regular intervals. During the base station search, for example, it can receive base station ID information Nt broadcast by each base station using a dummy bearer, select the base station with the highest reception level, and connect to it.

When each handset registers its location with a base station, it enters an idle lock state. The idle lock state means that the handset is connected to a base station, but is only receiving beacons and is not engaged in two-way communication with the base station.

As described above, after powering on, each handset registers its location with one of the base stations and becomes able to make and receive calls through that base station. This is called connecting the handset to a base station. In other words, each handset becomes able to make and receive calls through the base station to which it is connected.

When a handset communicates with a base station, it establishes a link and transitions to a communication locked state. In the communication locked state, two-way communication with the base station is performed using a traffic bearer.

Even in a communication locked state, a search for a communicating base station can be performed when communication quality deteriorates or at specified time intervals. If a new base station with better wireless communication capabilities is discovered, a link is established with the new base station, transitioning to a handover state with a double link established, and then the old link is severed and transitioning to a communication locked state with the new base station. In other words, as a handset in an idle locked state moves, it may reconnect to a base station with better wireless communication capabilities. Even during a call, as a handset moves, it may reconnect to a base station with better wireless communication capabilities. The former is called roaming, and the latter is called handover.

Before registering its location, the handset searches for nearby base stations and generally registers its location with the base station that provides the highest reception level for the beacons transmitted every 160 ms. Cordless phones use radio waves in the 1.9 GHz band, but indoor propagation of microwave radio waves generally causes multipath fading, and the reception level is known to fluctuate over time by around 10 to 20 dB.

Figure 11 shows the relationship between communication distance and average reception level and fading drop level in indoor radio wave propagation. Note that in Figure 11, the average reception level was calculated using the Rec. ITU-R P.1238-6 indoor propagation model. This model takes into account loss due to partitions in an office, etc.

To ensure good call quality, it is desirable to maintain a minimum receiving sensitivity or higher, even when the reception level drops due to fading, so that communication can be carried out without radio transmission errors. Regarding location registration, however, location registration is possible if the minimum receiving sensitivity or higher is maintained when the reception level is high even when the reception level fluctuates due to fading.

If we consider the former to be the area where calls can be made and the latter to be the area where location registration is possible, the radius of the area where location registration is possible is generally much larger than the area where calls can be made. In a typical indoor propagation model, the average reception level drops by 6 dB when the communication distance doubles. In this propagation model, a difference of 10 to 20 dB in reception level translates to a communication distance of approximately four times or more.

Usually, with cordless phones, base stations are placed (base station placement design) so that the entire service area is covered by multiple calling areas. In this case, each location registration area includes surrounding calling areas, and a search for surrounding base stations often finds all or most of the base stations that are available for location registration.

Figure 12 shows the relationship between call areas and location registration areas.

This shows the communication areas of the central base station and the six surrounding base stations (shown by solid lines), as well as the location registration area of the central base station (shown by dashed lines).

When registering, the base station with the highest beacon reception level is generally selected from among the base stations capable of location registration found in the surrounding base station search, and location registration is performed. If location registration is not possible with the base station with the highest beacon reception level, location registration will be performed with a surrounding base station capable of location registration. However, wireless communication is generally possible between base stations capable of location registration and the handset, so call origination and incoming call control is possible.

If location registration is not possible with the base station with the highest beacon reception level and location registration is performed with a nearby base station that allows location registration, it is possible that the device will be outside the calling area of the base station with which it has registered its location. However, if such a handset makes or receives a call and enters a call state, and the call status is not good, it will hand over to an adjacent base station and enter the calling area.

Next, we will explain the control sequence in the cordless telephone device according to the present invention. In this explanation, we will refer to Figures 1, 5 (Figure 7), and 6 (Figure 8) as appropriate.

Figure 13 shows an example of a location registration sequence.

The location registration sequence uses the Cs channel or Cf channel to establish a one-to-one link between the base station 20 and the handset 30 and then transmit control data. The location registration sequence is performed by the handset 30 immediately after powering on, or by the handset 30 after moving into an adjacent base station zone, by establishing a wireless link.

The handset 30 attempting to register its location first sends an access request, as defined in the DECT MAC layer standard (ETSI EN 300-175-3), to the base station 20 it is attempting to register its location with in order to establish a bearer. The base station 20 it is attempting to register its location with is, for example, the base station 20 with the highest beacon reception level in the most recent base station search.

After receiving bearer confirmation from base station 20 as specified in the DECT MAC layer standard, handset 30 establishes a link at the data link layer according to the procedure specified in the DECT DATA LINK layer standard (ETSI EN 300-175-4), and then transmits a location registration request message to base station 20 using the Cs channel or Cf channel.

In the base station 20, the message is output from the DECT transmission/reception control unit 22 as a handset control signal and applied to the DECT control signal generation unit 23. The DECT control signal generation unit 23 converts the received location registration request message into a handset control command for the main unit 10, and then transmits it to the main unit 10 over the base station transmission line via the base station transmission line termination unit 21.

The location registration request message generated by the handset 30 may be the same as the handset control command from the main unit 10, or may have unnecessary headers removed to reduce the transmission data size.

When the main unit 10 receives a location registration request from the handset 30, it issues an authentication request command to the handset 30. This command is transmitted to the base station 20 via the base station transmission path. The authentication request command is output from the base station transmission path termination unit 21 and applied to the DECT control signal generation unit 23 as a handset control command.

The DECT control signal generator 23 outputs the authentication request command itself, or a command with a reduced transmission data size excluding headers, etc., as a handset control signal and applies it to the DECT transmission/reception controller 22. At the same time, the DECT control signal generator 23 also outputs a DECT channel selection signal instructing the selection of the Cs channel or the Cf channel, and applies it to the DECT transmission/reception controller 22.

The DECT transmission/reception control unit 22 transmits an authentication request message to the handset 30 using the Cs channel or the Cf channel based on the DECT channel selection signal. Note that the DECT channel selection signal may be any signal that can specify the channel to be used for DECT transmission. For example, the handset control signal may include information specifying the channel to be used for DECT transmission.

When the main unit 10 receives a correct authentication response from the handset 30, it issues a location registration acceptance command to the handset 30. This command is transmitted to the base station 20 via the base station transmission path.

A location registration acceptance command is output from the base station transmission path termination unit 21 and applied to the DECT control signal generation unit 23 as a handset control command.

The DECT control signal generator 23 outputs the location registration acceptance command itself, or a command with a reduced transmission data size obtained by removing the header, etc., as a handset control signal and applies it to the DECT transmission/reception controller 22. At the same time, the DECT control signal generator 23 also outputs a DECT channel selection signal instructing the selection of the Cs channel or the Cf channel, and applies it to the DECT transmission/reception controller 22.

In response to this, the DECT transmission/reception control unit 22 transmits a location registration acceptance message to the handset 30 using the Cs channel or Cf channel based on the DECT channel selection signal.

Figure 14 shows an example of a call sequence from a handset.

The call sequence is used when making an outside call from the handset 30, and uses the Cs channel or Cf channel to transmit control data after establishing a one-to-one link between the base station 20 and the handset 30.

When the call processing is accepted by the main unit 10, a line lamp display command is issued to change the station line lamp (the lamp currently being used for outgoing calls) of the handset 30 from "off" to "in use." The line lamp display command may be transmitted using the Bs channel, which uses a beacon to broadcast control data without establishing a link, or, like other control data, may be transmitted using the Cs or Cf channel.

When an unused (off) line key on the handset 30 is pressed to make a call, this information is notified to the DECT transmission/reception control unit 31 as a handset control signal, and an access request specified in the DECT MAC layer standard to establish a bearer is sent to the registered base station 20.

After receiving a bearer confirmation from base station 20 as specified in the DECT MAC layer standard, handset 30 establishes a link at the data link layer according to the procedure specified in the DECT DATA LINK layer standard, and then transmits a call setup message to base station 20 using the Cs channel or Cf channel.

In the base station 20, the message is output from the DECT transmission/reception control unit 22 as a handset control signal and applied to the DECT control signal generation unit 23. The DECT control signal generation unit 23 converts the received call setup message into a handset control command for the main unit 10, and then transmits it over the base station transmission line to the main unit 10 via the base station transmission line termination unit 21. The call setup message generated on the handset 30 side may be the same as the handset control command for the main unit 10, or may have unnecessary headers removed to reduce the transmission data size.

When the main unit 10 receives a call setup command from the handset 30, it issues a call setup acceptance command to the handset 30. This command is transmitted to the base station 10 via the base station transmission path.

A call setup acceptance command is output from the base station transmission path termination unit 21 and applied to the DECT control signal generation unit 23 as a handset control command.

The DECT control signal generator 23 outputs the call setup acceptance command itself, or a command with a reduced transmission data size excluding headers, etc., as a handset control signal and applies it to the DECT transmission/reception controller 22. At the same time, the DECT control signal generator 23 also outputs a DECT channel selection signal instructing the selection of the Cs channel or the Cf channel, and applies it to the DECT transmission/reception controller 22.

The DECT transmission/reception control unit 22 transmits a call setup acceptance message to the handset 30 using the Cs channel or the Cf channel based on the DECT channel selection signal.

The main unit 10 then issues an authentication request command to the handset 30 to verify that the handset 30 is a legitimate handset for its own system, and the handset 30 responds by sending an authentication response message. These commands are the same as those in the location registration sequence, so a detailed explanation is omitted.

When the main unit 10 accepts the call request, it issues a line lamp display command to change the station line lamp (used for outgoing calls) of the handset 30 from "off" to "in use." This command is transmitted to the base station 20 via the base station transmission path.

A line lamp display command is output from the base station transmission path termination unit 21 and applied to the DECT control signal generation unit 23 as a handset control command.

The DECT control signal generator 23 outputs the line lamp display command itself, or a command with a reduced transmission data size obtained by removing the header, etc., as a handset control signal and applies it to the DECT transmission/reception controller 22. At the same time, the DECT control signal generator 23 also outputs a signal instructing the selection of the Bs channel as a DECT channel selection signal, which is applied to the DECT transmission/reception controller 22.

The DECT transmission/reception control unit 22 transmits a line lamp display message to the handset 30 using the Bs channel based on the DECT channel selection signal. Since the line lamp display message in the call sequence is intended for only the handset 30, the Cs channel or Cf channel may be used, as with other control data.

The main unit 10 then issues a call command to the handset 30, notifying it that the other party is being called. The call command is sent to the handset 30 via the base station 20 using the Cs channel or Cf channel. At the same time, an audio path is established for the handset 30, and a ring back tone is transmitted over this audio path.

The ring tone for the handset 30 is transmitted using one of the downlink audio data channels of the base station transmission path. In the base station 20, the ring tone is output as a multiplexed audio codec signal from the base station transmission path termination unit 21 and applied to the DECT transmission/reception control unit 22.

The base station transmission path termination unit 21 also outputs a clock for the multiplexed audio codec and an audio codec frame pulse to the DECT transmission/reception control unit 22, which stores the ring tone addressed to the handset 30 in the B-Field of the DECT traffic bearer and transmits it.

When the handset 30 receives the call message, it forms an audio path, supplies the audio codec signal of the ring tone received in the B-Field of the DECT traffic bearer to the audio codec, and outputs the ring tone from the speaker.

When the other party goes off-hook, this information is transmitted from the telephone network via the telephone line to the main unit 10, which then issues a response command to notify the handset 30 and transitions to a call state.

Figure 15 shows an example of a line lamp display sequence.

This sequence is a control sequence that, for example, when one key telephone or handset makes an outside call, notifies other handsets that the central office line is busy.

When the main unit 10 detects that a new call has been placed and the central office line has become busy, it issues a line lamp display command to all other handset units, notifying them that the line is in use. This command is transmitted to the base station 20 via the base station transmission line. The line lamp display command is output from the base station transmission line termination unit 21 and applied to the DECT control signal generation unit 23 as a handset control command.

The DECT control signal generator 23 outputs the line lamp display command itself, or a command with a reduced transmission data size obtained by removing the header, etc., as a handset control signal and applies it to the DECT transmission/reception controller 22. At the same time, the DECT control signal generator 23 also outputs a signal instructing the selection of the Bs channel as a DECT channel selection signal, which is applied to the DECT transmission/reception controller 22.

Based on the DECT channel selection signal, the DECT transmission/reception control unit 22 transmits a line lamp display message to the handset 30 using the Bs channel.

Figure 16 shows an example of a line lamp display message broadcast from a base station using such a Bs channel. The message may include message type information, intra-base station handset identifier information, and line key status information. Here, the message type may include, for example, "line lamp display information for a handset with eight station line keys." Furthermore, the intra-base station handset identifier information may be, for example, paging group information and intra-base station handset identifier information determined by the base station in a location registration acceptance message received by the handset at the end of the location registration sequence. Here, the intra-base station handset identifier information may be the same as the paging group information. It is desirable that the intra-base station handset identifier information be different for each handset at the base station.

Specifically, for example, if the maximum number of connected handset devices at a base station is 32, the intra-base station handset identifier information may be a natural number between 0 and 31. Furthermore, a single Bs channel may be used to broadcast line lamp display messages for two or more handset devices. In this case, the two or more handset devices may belong to the same paging group and be identified by the intra-base station handset identifier information. The line key status information may include status information for multiple line keys, for example, eight. The line key status may be three-bit information identifying states such as "idle," "own communication," "other communication," "other call on hold," "incoming external call," and "internal call." The line key status information may be broadcast for all line keys, for example, eight line keys, or may broadcast only the status information for line keys whose status has changed. Furthermore, the base station may retain status information for all line keys, and periodically broadcast the line key status information even if the line key status has not changed.

On the handset 30 side, the DECT transmission/reception control unit 31 outputs a line lamp display message as a handset control signal, which is applied to the handset control unit 32. The line lamp display message can include information specifying the station line key to be controlled and information indicating the state of that station line key, i.e., whether it is in use by another unit. In response to this, the handset control unit 32 controls the station line key to display a busy signal, for example, to a lit state.

In the example of Figure 15, a line lamp display command is issued to each of five handset devices 30, but even if there are more handset devices 30, a line lamp display command is issued to each of all handset devices 30. Also, for simplicity, Figure 15 shows a case where all handset devices 30 are connected to the same base station, but if there are handset devices connected to different base stations 30, a line lamp display command is sent to the base station 20 to which each handset device 30 to be controlled is connected, and then transmitted to each handset device 30 via each base station 20.

Figure 17 shows an example of an external call sequence.

This shows the control sequence when an external call is received by handset 1, which is connected to base station 1 and has a designated ring tone, and handset 2 through handset 5, which do not. For handset 1, not only is the incoming call lamp (blinking) displayed on the corresponding line key, but a ring tone is also sounded to notify the call. This also shows the operation when handset 1 answers the call and enters a call state. Note that in Figure 17, handsets with a designated ring tone are indicated by an "*" above them.

The main unit 10 issues a call setup command to handset 1 for which a sound has been specified to notify it of an incoming call. It also issues line lamp display commands not only to handset 1 but also to handset units 2-5 for which a sound has not been specified, thereby notifying them of the incoming call by displaying the lamps. These commands are transmitted via the base station transmission path to the base station 20 to which handset units 1-5 are connected. The base station transmission path termination unit 21 of the base station 20 outputs the call setup command and line lamp display commands for each handset unit 1-5, which are applied to the DECT control signal generation unit 23 as handset control commands.

The DECT control signal generator 23 generates an incoming call message based on the information on the called handset ID included in the call setup command and applies it to the DECT transmission/reception controller 22 as a handset control signal. At the same time, the DECT control signal generator 23 also outputs a signal instructing the selection of the Bs channel as a DECT channel selection signal, which is applied to the DECT transmission/reception controller 22. Based on the DECT channel selection signal, the DECT transmission/reception controller 22 transmits the incoming call message to handset 1 using the Bs channel.

The DECT control signal generator 23 further outputs the line lamp display command itself for each handset 1 to 5, or a reduced transmission data size excluding headers, etc., as a handset control signal, and applies it to the DECT transmission/reception controller 22. At the same time, the DECT control signal generator 23 also outputs a signal instructing the selection of the Bs channel as a DECT channel selection signal for each handset control signal, and applies it to the DECT transmission/reception controller 22.

Based on the DECT channel selection signal, the DECT transmission/reception control unit 22 uses the Bs channel to transmit line lamp display messages for each of the handsets 1 to 5.

Next, when handset 1 receives the incoming call message, a one-to-one link is established between base station 10 and handset 1, and control data transmission takes place using the Cs channel or Cf channel. Specifically, handset 1 first sends an access request, as specified in the DECT MAC layer standard, to the connected base station 10 to establish a bearer. Then, upon receiving a bearer confirmation, as specified in the DECT MAC layer standard, from base station 10, handset 1 establishes a link at the data link layer according to the procedure specified in the DECT DATA LINK layer standard.

The DECT control signal generator 23 also outputs the call setup command itself, or the call setup command minus the called handset ID information, or the call setup command minus the header and other information to reduce the transmission data size, as a handset control signal and applies it to the DECT transmission/reception controller 22. At the same time, the DECT control signal generator 23 also outputs a DECT channel selection signal instructing the selection of the Cs channel or the Cf channel, which is applied to the DECT transmission/reception controller 22. After a link is established in the data link layer, the call setup message is transmitted using the Cs channel or the Cf channel.

When handset 1 receives the call setup message, it generates a call setup acceptance message and sends it to main unit 10 using the Cs channel or Cf channel. The authentication request and authentication response may conform to the DECT NETWORK layer standard (ETSI EN 300-175-5) or may be based on any authentication procedure using an authentication key.

Main unit 10 then issues an authentication request command to handset 1 to verify that it is a legitimate handset for its own system, and the handset responds by sending an authentication response message. These commands are the same as those in the location registration sequence, so a detailed explanation is omitted.

When main unit 10 receives the authentication response command from handset 1, it determines that the central office line is in use and issues a line lamp display command to each of handsets 1-5 to notify them of this state. A line lamp display command is issued to handset 1 to indicate that it is in use by itself, for example, to flash green, and a line lamp display command is issued to handsets 2-5 to indicate that it is in use by another device, for example, to light red.

These commands are transmitted via the base station transmission path to the base station 20 to which the handsets 1-5 are connected. The base station transmission path termination unit 21 of the base station 20 outputs line lamp display commands for each of the handsets 1-5, which are applied to the DECT control signal generation unit 23 as handset control commands.

The DECT control signal generator 23 generates a line lamp display message based on the line lamp display information included in each line lamp display command, and applies this to the DECT transmission/reception controller 22 as a handset control signal. At the same time, the DECT control signal generator 23 also outputs a signal instructing the selection of the Bs channel as a DECT channel selection signal, which is applied to the DECT transmission/reception controller 22.

The DECT transmission/reception control unit 22 transmits a line lamp display message to each handset 1 to 5 using the Bs channel based on the DECT channel selection signal.

After sending the authentication response message, handset 1 uses the ringer to ring the incoming call, and then sends a call message to base station 20 using the Cs channel or Cf channel to notify main unit 10 that the ringing has begun. The call message is converted into a call command by DECT control signal generator 23 and notified to main unit 10.

When the handset 1 responds by pressing a line key after sending the call message, a response message is generated and transmitted to the base station 20 using the Cs or Cf channel. The response message is converted into a response command by the DECT control signal generator 23 and notified to the main unit 10.

When the main unit 10 receives a response command from the handset 1, it issues a response confirmation command and enters a call state. When the handset 1 receives a response confirmation message from the base station 10, it enters a call state.

As explained above, with this invention, when an external call arrives, the incoming call information and incoming line lamp information are transmitted to all handsets assigned to that line without establishing a link, so all handsets can be notified of the incoming call without being limited by the maximum number of simultaneous calls.

FIG. 18 shows an example of a sequence in the case of a handover.
If communication quality deteriorates while handset 1 is performing two-way communication with base station 1, and a new base station 2 with better wireless communication capabilities is discovered as a result of searching for a base station in communication, handset 1 establishes a link with the new adjacent base station 2, transitions to a handover state, and then disconnects the old link and transitions to a communication locked state with the adjacent base station 2. In other words, if handset 1 moves and needs to reconnect to an adjacent base station 2 with better wireless communication capabilities, even during a call, handset 1 will reconnect to the adjacent base station 2 with better wireless communication capabilities and enter its call area.

FIG. 19 shows an example of a keep-alive sequence from a slave device.
Since a handset may move out of service area or may be turned off, the handset transmits a keep-alive signal at a regular interval (T1), for example, every 30 seconds, to the base station to which it is connected to notify that the handset is in service and ready to make and receive calls. The base station monitors the keep-alive signal from the handset, and if it does not receive a keep-alive signal for a predetermined period of time, for example, three minutes, it determines that the handset is outside the communication area of the base station, deletes the handset's location registration, decrements the number of handset units connected to the base station by one, and notifies the main unit that the handset is out of service area.

Below, we will further explain the technology that allows incoming call information to be notified to all handset devices within 1 to 2 seconds.

The base station 20 in Figures 5 and 7 is equipped with a base station status management unit 24, which manages the number of terminals connected to the base station 20 and the number of terminals connected to the base station that are currently performing call connections.

As shown in Figure 32, a short page paging frame Pt can broadcast 12 bits of MAC information, and when the transmitted MAC information type is set to "4b'1010", base station status information can be broadcast. When broadcasting MAC information using a short page paging frame Pt, 4 bits of base station status information can be broadcast. Specifically, setting the base station status information to "XXX1" (X is 0 or 1) can be used to notify that the number of communicating terminal devices has reached the upper limit, and setting the base station status information to "XX1X" (X is 0 or 1) can be used to notify that the number of connected terminal devices has reached the upper limit.

The base station status management unit 24 applies information about the number of handset devices connected to the base station 20 or whether the number of handset devices connected to the base station has reached a predetermined upper limit, and information about the number of handset devices connected to the base station 20 that are currently connected to a call or whether the number of handset devices currently connected to a call has reached a predetermined upper limit, as a base station status notification signal to the DECT transmission/reception control unit 22. Notification by the base station status notification signal may be made when the base station status changes, or at predetermined time intervals, for example, every 5 seconds.

When the DECT transmission/reception control unit 22 receives a base station status notification signal from the base station status management unit 24, it uses the MAC information notification of the short page frame to notify the base station 20 of the number of connected terminals or whether the number of connected terminals has reached its upper limit, and the number of call connected terminals or whether the number of call connected terminals connected to the base station 20 has reached its upper limit.

A handset 30 that has registered its location with one of the base stations 20 enters an idle-lock state and intermittently receives paging frames Pt at 160 ms or 640 ms intervals. At this time, the handset 30 receives the paging frame Pt transmitted in frame 0, the first frame of each multiframe. If multiple paging frames Pt are transmitted within a single multiframe, the first bit of the paging header indicates whether there is a subsequent paging frame Pt. If it is notified that there is no subsequent paging frame Pt, the handset 30 transitions to a sleep state for approximately 160 ms or 640 ms after receiving the paging frame Pt.

If notified that a subsequent paging frame Pt is available, the handset 30 operates to receive the subsequent paging frame Pt after receiving the paging frame Pt, and continues receiving paging frames Pt until notified that there is no subsequent paging frame Pt.

When the DECT transmission/reception control unit 22 receives a base station status notification signal, it adds a short page frame to another paging frame Pt to notify the base station status information, and the handset 30 that receives this notifies it and performs a control sequence taking this into consideration. For example, a handset 30 that attempts to make a call to a base station 20 where the number of connected handset 30s has reached the upper limit, or a handset 30 that receives a call, first performs roaming processing, and then performs the outgoing or incoming call operation with the new base station 20.

Furthermore, when registering the location of the handset 30 after powering on or searching for a base station during roaming, the base station 20 with the highest beacon reception level may be selected after excluding base stations 20 for which the number of connected handset units has reached the upper limit. The upper limit on the number of call-connected handset units may be the number of voice channels in the base station transmission path. It is also desirable to limit the number of connected handset units to the number that can transmit incoming call information in 1 to 2 seconds or less.

The DECT standard stipulates that the maximum intermittent reception period is 640 ms, and that frame 0 in one multiframe is intermittently received. Furthermore, as already explained, one multiframe can transmit up to six Pt frames, i.e., lamp information or incoming call information.

DECT base stations 20 constantly search for available channels using unused channels that are not being used for communication, and may change the beacon transmission frequency or transmission slot over time based on the results.

Changes in the beacon transmission frequency or transmission slot at each base station 20 are notified to all handset 30 connected to that base station using MAC information broadcast in short page frames. Handset 30 receiving intermittently at a 640 ms cycle receives the paging frame Pt for frame 0 once every four multiframes. However, DECT base stations 20 generally do not know which multiframes handset 30 receiving intermittently will receive, and instead transmit the same paging frame Pt four times in four consecutive multiframes, allowing all handset 30 to receive the information in that paging frame Pt.

On the other hand, from the perspective of accommodating as many handset devices as possible in one base station and notifying all of these handset devices of incoming call information as quickly as possible, it is desirable to notify incoming call information for different handset devices in each of the four multi-frames transmitted within a 640 ms cycle.

For this reason, when each handset 30 registers its location with the base station 20, the base station 20 notifies the handset 30 of the multi-frames that the handset 30 should receive intermittently from among the four multi-frames transmitted at 640 ms intervals. Furthermore, each handset 30 connected to the base station 20 operates to intermittently receive the multi-frames specified at the time of location registration from among the four multi-frames transmitted at 640 ms intervals.

Figure 20 shows an example of paging frame transmission behavior when there are four paging groups.

Here, of the four multiframes transmitted within a 640 ms cycle, there are four paging groups: paging group 1, which receives the first multiframe; paging group 2, which receives the second multiframe; paging group 3, which receives the third multiframe; and paging group 4, which receives the last multiframe. The base station assigns one of the paging groups to each handset.

The lamp information and incoming call information for handsets belonging to paging group 1 are transmitted in the first of four multiframes transmitted at 640 ms intervals, and the handsets belonging to paging group 1 receive this information intermittently at this timing. For handsets belonging to paging groups 2, 3, and 4, the information is transmitted in the second, third, and fourth multiframes, respectively, and the handsets belonging to each paging group receive this information intermittently at this timing.

The paging group assignment method may be any method that allows the base station and handset to share the paging group assignment results. For example, the paging group may be determined by the base station and notified to the handset in a location registration acceptance message in the location registration sequence. Alternatively, the paging group may be uniquely determined based on system-specific identification information, such as the handset ID, assigned when the handset registers with the cordless telephone device. Specifically, the paging group may be determined based on the remainder modulo 4 of the handset ID. Information that needs to be notified to all handset devices connected to the base station, such as MAC information, may be transmitted a total of four times in each of the four multiframes transmitted at a 640 ms cycle.

Figure 21 shows another example of paging frame transmission behavior when there are four paging groups.

Here, the transmission operation of the paging frame Pt is shown in the case where four paging groups each have two mobile terminals, for a total of eight mobile terminals connected.
For example, in a multi-frame assigned to paging group 1, lamp information or incoming call information for handset 1 and handset 2 is transmitted in two paging frames Pt, and handset 1 and handset 2 first intermittently receive the paging frame Pt transmitted in frame 0.

At this time, the first bit of the Pt header is 1, indicating that there is another paging frame Pt in the same multiframe, and frame 2 is also intermittently received. The first bit of this Pt header is 0, and handset 1 and handset 2 will enter sleep mode until the next intermittent reception timing, approximately 640 ms later.

Figure 22 shows one form of station design for cordless telephone devices.

In this example, the office has three outside lines assigned to it. Office employees can make outside calls using any one of the lines. If all three lines are in use, they cannot make an outside call until one of the lines is no longer in use.

In this example, four base stations are installed in the office, and the entire office is covered by the coverage areas of these four base stations. Each handset is connected to one of the base stations, and in this example, 20 handset units are connected to each base station. It is possible that a concentration of handset units may connect to a specific base station, but to ensure that station line key status information and incoming call information can be notified within 640 ms, the upper limit for the number of connected handset units is set to 32, for example. When a base station reaches this number of connected handset units, it will notify this fact via a beacon, preventing more than 32 handset units from concentrating on a specific base station.

The line's usage status can be confirmed by checking the light on the line key on the handset. If the line key light is off, the line is free and can be used. If the line key light is lit, for example, the line is in use (a call is in progress) and cannot be used. On the other hand, if an outside call comes into the office, all employees' handsets will be notified of the call within one second and their line key will flash. Furthermore, handsets that have been designated to ring will not only display the line key light but will also ring to indicate the incoming call.

When an external call is received, the main unit issues a line lamp display command to all handsets that have that line assigned to their line key to indicate the incoming call. It also issues a call setup command to all handsets that have been designated to ring on that line. As a result, when an incoming call is received, the line keys of all handsets assigned to that line will flash to notify of the incoming call, and only the handsets that have been designated to ring will ring, achieving the same functionality as a key telephone.

As mentioned above, each handset registers its location in advance via one of the base stations, and the control unit of the main unit manages information about the base station with which each handset has registered its location. It then transmits line lamp display commands and call setup commands indicating incoming calls addressed to each handset to the base station with which the handset has registered its location over the base station transmission path.

Although the above describes an embodiment, the present invention is not limited to the above. For example, when an external call comes in, it is necessary to notify all of the intended recipient devices of the incoming call. If it takes too long to notify the call, the caller may assume there is no answer and disconnect the call. Therefore, the time it takes to notify all recipient devices of the incoming call should be as short as possible, preferably within 1 to 2 seconds.

When multiple handset devices are registered at a specific base station, incoming calls are notified to many of them via that base station. However, handset devices are typically battery-powered and perform intermittent reception at relatively long intervals, such as 640 ms, to reduce power consumption, so it takes time to notify many handset devices of incoming calls and distribute line lamp information.

For this reason, an upper limit can be set on the number of location registration terminals per base station, and if this limit is exceeded, location registration requests can be rejected or a beacon can be used to notify that location registration is not possible, and any additional terminals can be forced to register their locations with other nearby base stations. Specifically, the base station terminal status management unit in each base station manages the number of location registration terminals, and if this reaches the upper limit, the base station can reject any further location registration requests.

10...Main device
11...Station line I/F section
12...Internal line I/F section
13...Clock generation unit
14...Circuit switching unit
15...Control unit
20...Base station
21...Base station transmission line termination unit
22...DECT transmission/reception control unit
23...DECT control signal generation unit
24...Base station status management unit
25: Paging group number storage section for each handset
30... Sub-unit
31...DECT transmission/reception control unit
32... Child unit control unit
33...Audio codec
34...Station line key
35...Lingam
36...LCD display section
37...Mike
38...Speaker
39...numeric keypad
40: Paging group number storage section

Claims (8)

A base station for a cordless telephone device is configured by selectively using one base station and one handset among one or more base stations connected to a telephone control device connected to a wide area network and a plurality of handset units connected to the base station by wireless communication,
a DECT control signal generating means for extracting information that needs to be transmitted to the handset from a handset control command transmitted from the telephone control device, to generate a handset control signal, and for selecting an optimum transmission channel for wirelessly transmitting the handset control signal in the DECT system according to the type of the handset control command;
A base station for a cordless telephone device, comprising: a DECT transmission/reception control means for performing DECT radio transmission/reception and DECT TDMA/TDD frame synthesis/decomposition, and transmitting the handset control signal provided by the DECT control signal generation means using the optimum transmission channel selected by the DECT control signal generation means. when the handset control command transmitted from the telephone control device is a line lamp display command, the DECT control signal generation means selects a broadcast channel as an optimum transmission channel for wirelessly transmitting the handset control signal generated from the handset control command in the DECT system;
2. The base station for a cordless telephone device according to claim 1, wherein said DECT transmission/reception control means transmits said handset control signal using said broadcast channel without establishing a link. The cordless telephone base station of claim 1 further comprises a base station status management means for generating base station status information including information on the number of handset handsets in communication and the number of connected handset handsets, and two-bit information indicating whether the number of handset handsets in communication and the number of connected handset handsets have reached their respective upper limits, and for generating a base station status notification signal that instructs the base station status information to be reported in the MAC information of a beacon, and for reporting the base station status notification signal via the DECT transmission/reception control means. A cordless telephone device is configured by selectively using one base station and one handset among one or more base stations connected to a telephone control device of a digital cordless telephone system connected to a wide area network and a plurality of handset units connected to the base stations by wireless communication, the cordless telephone device comprising:
The base station
a DECT control signal generating means for extracting information that needs to be transmitted to the handset from a handset control command transmitted from the telephone control device, to generate a handset control signal, and for selecting an optimum transmission channel for wirelessly transmitting the handset control signal in the DECT system according to the type of the handset control command;
a DECT transmission/reception control means for performing DECT radio transmission/reception and DECT TDMA/TDD frame synthesis/decomposition, and transmitting the handset control signal provided by the DECT control signal generation means using the optimum transmission channel selected by the DECT control signal generation means;
A paging group number storage means for each handset is provided,
transmitting the handset control signal to the handset only on a Bs channel of a multiframe corresponding to a paging group number of the handset;
The slave unit is
A paging group number storage unit is provided,
A cordless telephone device characterized in that, during intermittent reception at a cycle of 640 ms, reception is performed only in multiframes corresponding to the paging group numbers stored in said paging group number storage section. when the handset control command transmitted from the telephone control device is a line lamp display command, the DECT control signal generation means selects a broadcast channel as an optimum transmission channel for wirelessly transmitting the handset control signal generated from the handset control command in the DECT system;
5. The cordless telephone device according to claim 4, wherein the DECT transmission/reception control means transmits the handset control signal using the broadcast channel without establishing a link. A cordless telephone device according to claim 4 or 5, characterized in that the paging group number of the handset is determined by the base station during the location registration sequence with the base station, taking load balancing into consideration, and is notified to the handset. A cordless telephone device according to claim 4 or 5, characterized in that the paging group number of the handset is determined by the base station and the handset, respectively, based on system-specific handset identification information assigned when the handset is added to the digital cordless telephone system. The base station
a base station status management means for generating, as base station status information, information on the number of handset terminals and the number of connected handset terminals of the base station, and two-bit information on whether the number of handset terminals and the number of connected handset terminals have reached their respective upper limits, and further for generating a base station status report signal for instructing that the base station status information be reported in MAC information of a beacon;
The slave unit is
A cordless telephone device as described in any one of claims 4 to 7, characterized in that it is provided with a handset control unit that operates to select a base station to connect to from among base stations for which the number of handsets in communication has not reached the upper limit in the base station status information reported by the beacon in a base station search immediately before link establishment, and to select a base station to connect to from among base stations for which the number of handsets connected has not reached the upper limit in the base station status information reported by the beacon in other base station searches.