JP7795702B2 - Base station for cordless telephone device, base station and handset for cordless telephone device, and telephone control device and base station for cordless telephone system - Google Patents

Description

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

In Japan, key telephone system terminals include not only key telephones that are directly connected to the main unit via a wired transmission line, but also digital cordless telephones (handsets) that are 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 depending on the call volume (the amount of communication lines occupied per unit time) in the user's installation environment, and these can be shared and used by each key telephone.

In such a system, if all or some of the key telephones are replaced with digital cordless telephones, wireless base stations can be positioned so that the calling area of one or more wireless base stations covers the entire service area (office). This is expressed as covering the entire service area (office) by expanding the base station zone, which is the calling area of one base station, into a surface area.

Like key telephones, it is desirable for such digital cordless telephones (handsets) to be able to make and receive calls reliably at all times, except when there are no available telephone lines. Furthermore, specifically, even when traffic on digital cordless telephones (handsets) becomes congested and the number of handsets making simultaneous calls increases, it is desirable for such telephones to be able to make and receive calls reliably at all times, except when there are no available telephone lines.

Patent Document 1 discloses a technology for preventing co-channel interference in a TDMA-TDD digital cordless telephone device. When a call is being made on another nearby digital cordless telephone device, the technology detects the timing of the slots in which the other digital cordless telephone device transmits and receives, calculates a slot position that does not overlap in time with the detected slot position for transmission and reception, and transmits and receives at this calculated slot position. By applying this technology, the effects of co-channel interference from surrounding base station zones can be reduced when base station zones are deployed to cover the entire service area.

Non-Patent Document 1 describes the carrier sense regulations for the J-DECT system. The J-DECT system defines two carrier sense levels (first level: -82 dBm, second level: -62 dBm) and two carrier groups (first carrier group: F1, F2, F5, F6, second carrier group: F3, F4), and specifies that before a base station or a mobile device starts transmission, it performs carrier sense for two or more consecutive frames and selects the channel to be used in the following order of priority:
・1st priority: Channels in the 1st carrier group with an interference level of 1st level or lower ・2nd priority: Channels in the 2nd carrier group with an interference level of 1st level or lower ・3rd priority: Channels in the 1st carrier group with an interference level of 2nd level or lower ・4th priority: Channels in the 2nd carrier group with an interference level of 2nd level or lower ・Transmission is not possible if there are no channels with an interference level of 2nd level or lower

Non-Patent Document 1 also specifies protection regulations for time division multiple access narrowband digital cordless telephones in the J-DECT system (hereinafter referred to as private PHS protection regulations). The regulations stipulate that J-DECT base stations determine whether or not radio waves are present at the frequencies of the two control channels of the private PHS system (1,899.072 MHz and 1,900.8 MHz), and if radio waves are determined to be present, that only the first carrier group is usable, and that when a DECT base station is idle, i.e., not communicating, it is permitted to use only F1 or F5 to the greatest extent possible for transmitting dummy bearers.

The former provision was enacted because the radio waves from the second carrier group are in the same band as the control channels for privately operated PHS systems, and interference with these channels could cause the privately operated PHS systems to become uncontrollable.

On the other hand, the basic idea for the radio waves of the first carrier group is to share them with the private PHS system through vacant channel detection. However, while the time interval for vacant channel detection for private PHS systems is often around 300 us, the time length of the dummy bearer is 83.3 us, as shown in Figure 16 (details will be given later). This means that there is a possibility that interference that is invisible to the private PHS system may occur by bypassing the vacant channel detection, making it difficult to share the dummy bearer with the private PHS system through vacant channel detection.

As a result, many privately operated PHS products have taken measures to avoid using the F1 and F5 channel bands to avoid market disruption, but they do use the F2 and F6 channel bands, and there is a risk of market disruption occurring if J-DECT base stations transmit dummy bearers in these bands. As a result, the latter regulation was enacted, limiting the transmission of dummy bearers by J-DECT base stations to F1 or F5.

Figure 16 shows the frame format of a DECT frame, where (a) shows a short frame and (b) shows a long frame. As shown in Figure 16, DECT uses short frames with a duration of 83.3 us called dummy bearers and long frames with a duration of 368.1 us called traffic bearers.

The former is a downlink (base station → handset) transmission frame sent as a beacon by an idle (non-communicating) base station, and is used to notify handset of base station identifier information, system information, paging information, etc. The latter is a bidirectional (base station ⇔ handset) frame used during one-to-one communication between a base station and handset, and can transmit 320 bits of information stored in the B-Field in both directions between the base station and handset.

In this way, when J-DECT base stations near a private PHS system transmit beacons, priority is given to using channels F1 or F5 with interference levels of level 1 or lower, but if no channels with interference levels of level 1 or lower exist, channels with interference levels of level 2 or lower will also be used.

Non-Patent Document 2 describes how the effectiveness of reducing co-channel interference in a wireless LAN can be evaluated in terms of throughput by increasing the interference distance through the use of different frequency channels between adjacent APs.

In addition, in mobile telephone systems, four-cell repeat arrangements, seven-cell repeat arrangements, etc. are used to spatially reuse the same frequency channel. In wireless systems with small zone configurations like this, it is a commonly known technique to increase the interference distance and reduce co-channel interference by using different radio frequencies between adjacent base stations.

Japanese Patent Application Publication No. 4-286431

Standard for Radio Equipment of Time Division Multiple Access Wideband Digital Cordless Telephone Stations (ARIB STD-T101) Dynamic Channel Allocation in Wireless LAN Systems, IEICE Technical Report. RCS, Wireless Communication Systems 97(266), 27-32, 1997-09-24

However, while the carrier sense provisions described in Non-Patent Document 1 can reduce co-channel interference in systems with a small number of base stations or low traffic, in systems with a large number of base stations or high traffic during busy periods, there are insufficient channels using only level 1 or lower, and channels at level 2 or lower must also be used, which can result in co-channel interference. This issue is explained below.

Figure 17 shows the relationship between communication distance and reception level of DECT wireless signals, calculated based on the ITU-R P.1238-6 indoor propagation model, which is commonly used as an indoor radio wave propagation model.

Generally, in indoor radio wave propagation, the reception level fluctuates by approximately 10 to 15 dB over time due to the effects of multipath fading. Figure 17 shows the average reception level, the reception level when it drops due to fading, along with the carrier sense first level and carrier sense second level. Note that the fading depth is set to 15 dB, assuming non-line-of-sight propagation.

Assuming that the minimum receiving sensitivity of a DECT transceiver (the receiving level required to achieve a specified transmission quality, for example, a bit error rate of ^10-3 or less) is -86 dBm, with a 20 dB margin for shadowing effects caused by human bodies and other factors, in order to ensure communication within the base station zone even when there are drops in signal due to fading, Figure 17 shows that the base station zone radius must be 30 m or less.It can also be seen that the receiving level is almost at or above Level 1 even at a communication distance of 120 m, which is four times the base station zone radius.

Figure 18 is a diagram explaining the impact of co-channel interference when base station zones are deployed in a planar configuration using regular hexagonal zones. This diagram shows six adjacent base stations and 12 second-neighboring base stations relative to a centrally located base station. It can also be seen that if the base station zone radius is r, then the distance between the centrally located base station and the adjacent base stations is 2r, and the distance between the centrally located base station and the second-neighboring base station is 4r. In this example of a planar deployment of base stations, there are approximately 20 base stations in an area four times the base station zone radius, including the second-neighboring base stations. Therefore, if carrier sensing is performed at the first level, approximately 20 base stations will share the channel.

Furthermore, if the distance between base stations in adjacent zones is 60 m, as shown in Figure 17, the range of fluctuation in the reception level of radio waves from adjacent base stations is -60 dBm to -75 dBm, and will probabilistically fall below the second level (-62 dBm). Therefore, if there are insufficient channels below the first level, adjacent base stations may transmit simultaneously, resulting in co-channel interference.

In a digital cordless telephone system using J-DECT, each base station transmits one or two beacons at 10 ms intervals. The reason two beacons are transmitted at 10 ms intervals is so that if one beacon cannot be received due to co-channel interference, the other beacon can be received instead, and the two beacons broadcast the same information.

Another reason for transmitting two beacons at 10 ms intervals is that when a mobile device in a call moves between base station zones and performs a handover, it searches for a base station. Even if one of the beacons from the destination base station is transmitted in the same slot as the mobile device is using for the call, the mobile device can still receive the beacon from the other base station, which is transmitted in a different slot. This ensures that the beacon from an adjacent base station can be received regardless of its transmission slot.

As such, in a digital cordless telephone system capable of handover, it is desirable to transmit two beacons every 10 ms. However, as mentioned above, wireless channels are shared between neighboring base stations. Therefore, when there are a large number of installed base stations, the increased number of channels used by beacons increases the likelihood of co-channel interference occurring, which is an issue. The issues with digital cordless telephone systems are explained below.

If the total number of base stations in a digital cordless telephone system is M (M is a natural number greater than or equal to 1), and the maximum number of simultaneous calls in the entire system is K (K is a natural number greater than or equal to 1), then a maximum of (M + K) or (2M + K) downstream channels can be used simultaneously.

Also, as mentioned above, if a private PHS system exists near a digital cordless telephone system using DECT, the private PHS protection provisions of the ARIB standard (ARIB STD-T101) require that beacon transmissions use the two frequency channels F1 and F5 whenever possible, effectively limiting the number of usable channels to 24.

For example, in a digital cordless telephone system in which each base station transmits two beacons at 10 ms intervals, if there are 12 base stations, the beacons alone will occupy 24 channels, and when making further calls, channels at level 2 or lower will also have to be used, which can result in co-channel interference. Furthermore, if there are more than 12 base stations, beacons will be transmitted using channels at level 2 or lower, which can result in co-channel interference between beacons. Furthermore, even if there are fewer than 12 base stations, if there are a large number of simultaneous calls during peak hours, channels at level 2 or lower will also have to be used, which can result in co-channel interference.

The following provides a more detailed explanation of an example in which a regular hexagonal base station zone, as shown in Figure 18, is deployed to cover the entire service area.

As shown in Figure 18, when a regular hexagonal base station zone is deployed in an area to cover the entire service area, a maximum of six adjacent zones and 12 second-neighboring zones are generated. Therefore, with this area deployment of base station zones, even if only interference from adjacent zones is considered, for example, the central base station zone will receive a maximum of 14 beacons in a 10 ms cycle.

For this reason, for example, if more than 10 simultaneous calls are taking place in the current base station zone or an adjacent base station zone, it becomes impossible to select a slot that does not overlap in time with slots where transmission and reception are already taking place. In such cases, the technology described in Patent Document 1 cannot be applied, and a base station in an adjacent base station zone may use the same frequency channel and slot used for beacon transmission in the current base station zone for a call, which could result in a handset being unable to receive the beacon due to co-channel interference.

If the traffic bearer used during one-to-one communication between a base station and a mobile device is subject to co-channel interference, the deterioration in communication quality can be used as a trigger to implement interference avoidance processing, such as frequency channel switching, slot switching, or handover.

On the other hand, the dummy bearer transmitted as a beacon by an idle base station is a broadcast channel transmitted by the base station, and no interference avoidance processing is performed. This poses a particular issue, as handset devices experiencing co-channel interference near the base station zone boundary will be unable to receive the beacon.

The following section explains co-channel interference with beacons transmitted by base stations in more detail.

In digital cordless telephone systems using DECT, 10 ms frame synchronization is typically performed between base stations to ensure communication capacity. The timing signal for this frame synchronization can be generated by the main unit and distributed to each base station via the base station transmission path. Each base station can also receive beacons broadcast from surrounding base stations when it starts up, and then synchronize wirelessly in sequence.

In this case, the downlink transmission period (base station → client device) in the first half of the 10 ms frame and the uplink transmission period (client device → base station) in the second half are synchronized between base stations, and in this case, the only thing that will interfere with the beacon transmitted by the base station is a beacon from another adjacent base station.

In an area deployment using a regular hexagonal base station zone, the distance between the base station in question and an adjacent base station is 2r, where r is the zone radius. According to Figure 17, the minimum reception level during fading fluctuations at a communication distance of 60m, which corresponds to 2r, is -75dBm, which is below the carrier sense level 2 (-62dBm). Therefore, if there are no available channels below carrier sense level 1, the frequency and slot on which the beacon is being received may be used to transmit the beacon of the adjacent base station or the traffic bearer for the call.

Furthermore, with regard to the impact of co-channel interference from adjacent base stations, if the handset is located near the zone boundary with the adjacent base station, in the worst case scenario, the distance from the base station to the handset and the distance from the adjacent base station to the handset will be nearly equal. As a result, the average reception level of the beacon from the base station and the average reception level of the interference wave will be nearly equal, and there is a high probability that the beacon will not be received.

On the other hand, with regard to co-channel interference from the next-neighboring base station, in an area deployment using a regular hexagonal base station zone, the distance between the base station in question and the next-neighboring base station is 4r, where r is the zone radius.

According to Figure 17, the average reception level during fading fluctuations at a communication distance of 120 m, equivalent to 4r, is -68 dBm, which is below the second carrier sense level of -62 dBm. Therefore, the next-neighboring base station will not be able to detect the beacon from that base station, and may transmit the next-neighboring base station's beacon or a traffic bearer for a call using the same frequency and slot as the beacon.

However, in the example of area deployment using regular hexagonal base station zones shown in Figure 18, as shown in Figure 19, with regard to the impact of co-channel interference from second-neighboring base stations, even when the mobile device is near the zone boundary with that adjacent base station, the worst-case distance from the second-neighboring base station to the mobile device is three times the zone radius.According to Figure 17, the average reception level of fading fluctuations at a communication distance of 90 m, equivalent to 3r, is -66 dBm, which is 14 dB lower than the average signal reception level of -52 dBm near the zone boundary.Therefore, it can be said that the beacon from that base station is hardly affected by co-channel interference from second-neighboring base stations.

As explained above, when area deployment is performed in a digital cordless telephone system using DECT, there is a risk that during times of traffic congestion, there will be a shortage of channels below the first carrier sense level, resulting in co-channel interference from adjacent base stations and resulting in some handset units being unable to receive beacons.

Non-patent document 2 describes the evaluation of the effectiveness of reducing co-channel interference in wireless LANs by using different frequency channels between adjacent APs to increase the interference distance, using throughput. Furthermore, in mobile telephone systems, four-cell repeat layouts, seven-cell repeat layouts, etc. are used to spatially reuse the same frequency channel. In wireless systems with small zone configurations like this, the use of different radio frequencies between adjacent base stations to increase the interference distance and reduce co-channel interference is a commonly known technique.

However, as mentioned above, in a digital cordless telephone system using DECT, when installed near a privately operated PHS system, the only wireless channels that can be used are essentially two, F1 and F5, and area expansion through frequency channel allocation cannot reduce the interference distance.

The present invention aims to solve the above problems by preventing co-channel interference between adjacent base stations in base stations for cordless telephone devices that use the DECT wireless communication system, base stations and handsets for cordless telephone devices, and telephone control devices and base stations for cordless telephone systems, and by increasing the interference distance to reduce the effects of co-channel interference, thereby enabling beacons, which are control signals, to be received without interference.

In order to solve the above problems, the present invention provides a base station for a TDMA-TDD cordless telephone device, which is configured by connecting one or more base stations, each capable of connecting a plurality of handset units, to a telephone control device connected to a wide area network, the base station comprising: slot group information storage means for storing slot group information, which is information for identifying one or more slot groups to be used by the base station from among L slot groups (L is a natural number equal to or greater than 3) into which a plurality of slots used in wireless transmission are classified; blind slot information generation means for identifying a slot to be used by the base station from all slots specified by the TDMA-TDD system based on the slot group information, and generating blind slot information, which is information on whether each slot is usable; and a DECT transmission/reception control unit that embeds the blind slot information in MAC information of a short page frame of the DECT standard, or in unique information of a system information frame of the DECT standard , and reports the blind slot information in a beacon, and transmits and receives wireless transmissions using the slot selected based on the blind slot information.

The slot group information can also be information identifying the slot group used by the base station. Alternatively, the slot group information can be information about a slot group calculated in the cordless telephone device from the identification information of the base station according to predetermined rules, and the blind slot information generation means can generate blind information from the slot group information.

Furthermore, in order to calculate the slot group information from the base station identification information, the remainder obtained by dividing the base station identification information by L (L is a natural number greater than or equal to 3) can be referenced.

The present invention also provides a base station and a handset for a cordless telephone device, which comprises one or more base stations connected to a telephone control device connected to a wide area network and a plurality of handset units connectable to the base stations, the base station comprising slot group information storage means for storing slot group information, which is information for specifying one or more slot groups to be used by the base station from among L slot groups (L is a natural number of 3 or more) into which a plurality of slots used in radio transmission are classified; blind slot information generation means for specifying a slot to be used by the base station from all slots specified by the TDMA-TDD system based on the slot group information, and generating blind slot information, which is information on whether each slot is available; and a DECT transmission/reception control section for embedding the blind slot information in MAC information of a short page frame of the DECT standard or in unique information of a system information frame of the DECT standard, and announcing the blind slot information in a beacon, and transmitting and receiving radio transmissions in a slot selected based on the blind slot information, The blind slot information is embedded in the MAC information of a short page frame of the DECT standard, or embedded in the unique information of a system information frame of the DECT standard, and notified to the handset by a beacon, and wireless transmission is performed using a slot selected based on the blind slot information. The handset is characterized by comprising: a per-base station slot group table storage means for generating a per-base station slot group table based on the base station search information and blind slot information acquired during base station search, and storing this table; and a handset control means for managing the handset state and state transition, for referencing the per-base station slot group table, for acquiring information on a slot group to be used at a base station with which a wireless link is established, and for controlling the establishment of a wireless link and communication over the wireless link using a slot selected based on the slot group information.

Furthermore, the present invention provides a telephone control device and a base station for a cordless telephone system configured by connecting one or more base stations to which a plurality of handset units can be connected to a telephone control device connected to a wide area network, the telephone control device and the base station comprising: L slots used in radio transmission; and the telephone control device is characterized in that it classifies the base stations into slot groups of L (L is a natural number of 3 or more) for use by each base station, and the telephone control device is provided with per-base-station slot group information storage means for storing slot groups to which one or more slot groups are assigned so that different slot groups are assigned to adjacent base stations, and the base station is provided with slot group information storage means for storing slot group information of the base station which is acquired via the base station transmission path when the base station is started up and stored in the per-base-station slot group information storage means, blind slot information generation means for specifying a slot to be used by the base station from all slots specified by the TDMA- TDD system based on the slot group information and generating blind slot information which is information on whether each slot is usable, and a DECT transmission/reception control section for embedding the blind slot information in MAC information of a short page frame of the DECT standard or in unique information of a system information frame of the DECT standard, and announcing the blind slot information by a beacon, and for transmitting and receiving radio transmissions using a slot selected based on the blind slot information.

According to this invention, in a digital cordless telephone system using the DECT wireless communication system, slots are classified into L slot groups (L is a natural number greater than or equal to 3) and adjacent base stations are assigned different slot groups. This prevents co-channel interference between downstream signals from adjacent base stations (base station → handset), and limits co-channel interference to interference from the next-neighboring base station only, allowing handset units to receive beacons, which are downstream control signals from the base station, with almost no interference.

Furthermore, according to the present invention, available slots are classified into L slot groups (L is a natural number equal to or greater than 3), adjacent base stations use different slot groups, the available slots at each base station are embedded in the MAC information of a short page frame of the DECT standard, or embedded in the unique information of a system information frame of the DECT standard, and are notified to the handset by a beacon, the handset stores the information on the available slots for each base station it receives, and when establishing a link with a base station, it transmits an access request using the available slot of that base station, thereby avoiding the occurrence of co-channel interference between adjacent base stations, including traffic bearers, and by increasing the interference distance, the effects of co-channel interference are reduced, and it becomes possible to receive the beacon, which is a downlink control signal, without the effects of interference.

Furthermore, according to the present invention, adjacent base stations use different slot groups, so that during handover, the beacon from the adjacent base station is always transmitted in a slot different from the slot used by the handset in question for the call. This allows the base station to transmit only one beacon every 10 ms, significantly reducing co-channel interference. Even when digital cordless telephone (handset) traffic becomes congested and the number of handsets making simultaneous calls increases, calls can be made and received reliably at all times, except when there are no available telephone lines.

FIG. 10 is a diagram showing an example of classification of slot groups (when L=3) in the present invention. 2 is a diagram showing an example of a surface expansion (when L=3) of base station zones for the slot group of FIG. 1. FIG. FIG. 10 is a diagram showing another example of classification of slot groups in the present invention (when L=4). 4 is a diagram showing an example of a surface expansion (when L=4) of base station zones for the slot group of FIG. 3. FIG. 1 is a block diagram showing the basic configuration of an embodiment of a digital cordless telephone system using the DECT wireless communication system according to the present invention; 1 is a block diagram showing the basic configuration of an embodiment of a main device of a digital cordless telephone system using the DECT wireless communication system according to the present invention. FIG. 1 is a diagram illustrating an example of a frame format for signal transmission in a TDD (ping-pong) system on a base station transmission line. FIG. 10 is a diagram illustrating an example of transmission of common control data having a multi-frame configuration. 1 is a block diagram showing the basic configuration of an embodiment of a base station in a digital cordless telephone system using the DECT wireless communication system according to the present invention. FIG. 10 is a block diagram showing the basic configuration of another embodiment of a base station in a digital cordless telephone system that uses the DECT wireless communication system according to the present invention. 1 is a block diagram showing the basic configuration of an embodiment of a handset in a digital cordless telephone system that uses the DECT wireless communication system according to the present invention. FIG. 2 is a diagram illustrating an example of a slave device state and a state transition. FIG. 10 is a diagram illustrating an example of a slot group table for each base station. FIG. 10 is a diagram showing an example of a location registration sequence of a slave unit to a main unit. 10A and 10B are diagrams illustrating an example of a call sequence when a key operation for making a call is performed on a handset. 1A and 1B are diagrams showing the frame format of a DECT frame, where (a) shows a short frame and (b) shows a long frame. FIG. 1 is a diagram showing the relationship between the communication distance and reception level of a DECT radio signal calculated based on the ITU-R P.1238-6 indoor propagation model, which is generally used as an indoor radio wave propagation model. FIG. 10 is an explanatory diagram of the influence of co-channel interference when base station zones are deployed in a plane using regular hexagonal zones. FIG. 10 is an explanatory diagram of the influence of co-channel interference when base station zones are deployed in a plane using regular hexagonal zones. FIG. 1 is a diagram showing the arrangement of radio resources in J-DECT. FIG. 1 is a diagram illustrating an example of a frame format of a DECT multiframe. 10 is a diagram showing a frame format of base station ID information Nt that broadcasts base station ID information. FIG. 10 is a diagram showing the frame format of system information Qt that notifies system information. FIG. FIG. 10 is a diagram illustrating an example of the correspondence between a Qt header and system information. 10 is a diagram showing a frame format of MAC control information Mt that broadcasts MAC control information. FIG. 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. 10 is a diagram showing a frame format of paging information Pt that notifies paging information. FIG. 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 MAC information types and MAC information of a Pt short page. FIG.

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

The DECT standard uses the TDMA-TDD method. Figure 20 shows the allocation of radio resources in J-DECT, which 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 Privately Operated PHS Protection Regulations stipulate that after powering on, J-DECT base stations check for the presence of PHS control channel signals before transmitting, and if they determine that signals are present, they will not use channels F3 and F4.

For channels other than F3 and F4, which overlap in frequency band with the PHS control channel, the band is 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. For this reason, the PHS protection regulations of ARIB STD-T101 stipulate that J-DECT base stations, after powering up, check for the presence of PHS control channel signals before transmitting, and if they determine that signals are present, avoid transmitting dummy bearers on F2 and F6 channels as much as possible. This is because many PHS products already have measures in place to avoid using the F1 and F5 channel bands to avoid market interference, but the F2 and F6 channel bands are in use, and if a J-DECT base station were to transmit dummy bearers in these bands, there is a risk of market interference.

When transmitting wirelessly via 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.

The dummy bearer transmitted as a beacon 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.

The traffic bearer used for one-to-one communication between a base station and a handset is a bidirectional channel, using a pair of slots spaced 5 ms apart (for example, slot 1 and slot 13).

In addition, a base station in communication status can transmit both a dummy bearer for beacons and a traffic bearer, and can also transmit beacon information using the A-Field in the traffic bearer.

In a digital cordless telephone system using DECT, traffic bearers are transmitted for the number of one-to-one communications between the base station and the handset, as well as dummy bearers up to the number of base stations or twice that number.

The transmission rights of both dummy bearers and traffic bearers are 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 slave devices can be reused and used. During times of traffic congestion, there is a possibility that some slave devices will be unable to receive dummy bearers due to co-channel interference from traffic bearers from surrounding base stations. For this reason, it is desirable to use traffic bearers only to the extent necessary.

Figure 21 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 broadcast in the beacon is classified into base station ID information Nt, system information Qt, MAC control information Mt, 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 22 shows the frame format of base station ID information Nt, which broadcasts base station ID information.

The base station ID information Nt includes a fixed access right code of "0001", an equipment manufacturer ID (EIC), a system ID (FPN), and a 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 23 shows the frame format of system information Qt, which reports system information, and Figure 24 shows an example of the correspondence between the Qt header and system information.

System information Qt includes basic information such as the carrier number and slot number of the Qt frame, as well as information on the number of available carriers, multiframe number information, the base station's transmission power information, and unique system information.

Figure 25 shows the frame format of MAC control information Mt that reports MAC control information, and Figure 26 shows an example of the correspondence between Mt headers and message types. Furthermore, Figure 27 shows an example of the correspondence between Mt commands and MAC control messages.

Figure 28 shows the frame format of paging information Pt that reports paging information, and Figure 29 shows an example of the correspondence between the Pt header and Bs channel information. Furthermore, Figure 30 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 that broadcast 20 bits of Bs channel data and MAC information, and full pages 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.

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 a 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 Cs channel in the A-Field, and when not in a call, control data can be transmitted at high speed using the Cf channel in the B-Field.

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 Mt, 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.

Taking the above DECT standard into consideration, this invention provides a digital cordless telephone system that uses the DECT wireless communication method. It classifies available slots into L slot groups (L is a natural number greater than or equal to 3), with adjacent base stations using different slot groups. Each base station notifies the handset of its available slots via a beacon. The handset stores the information on available slots received from each base station, and when establishing a link with a base station, transmits an access request using the available slot of that base station. This avoids co-channel interference between adjacent base stations, and by increasing the interference distance, reduces the effects of co-channel interference, allowing the beacon, which is a control signal, to be received without interference.

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

Figure 1 shows an example of slot group classification (when L=3) in this invention. Here, the downlink slots (SL0-SL11) and uplink slots (SL12-SL23) in DECT radio resources are each classified into three slot groups (slot groups SL0-SL3 and SL12-SL15, slot groups SL4-SL7 and SL16-SL19, and slot groups SL8-SL11 and SL20-SL23).

In Figure 1, consecutive slots are assigned to each slot group, but for example, every third slot may be assigned to the same slot group, and any slot group can be assigned as long as there is no overlap. Furthermore, the number of slots assigned to each slot group does not necessarily have to be the same; for example, five or more slots may be assigned to a slot group of a base station where high traffic is expected, taking into account the expected traffic at each base station. As shown here, uplink and downlink paired slots belong to the same slot group.

Figure 2 shows an example of the area expansion of base station zones for the slot groups in Figure 1. Here, the slot groups used by each base station are shown in the same gray scale as in Figure 1, corresponding to Figure 1. As shown here, by categorizing slots as in Figure 1, it is possible to make the slot groups used by adjacent base stations different from each other. This makes it possible for the central white zone to avoid interference from adjacent base station zones (light gray or dark gray), and to only experience interference from the next adjacent white zone; by increasing the interference distance, the effects of co-channel interference can be reduced.

Furthermore, when a handset in the central white zone that is currently in a call moves and performs a handover, the adjacent base station zone to which it will move is a light gray or dark gray zone, and since it uses a different set of slots than the base station from which it moved, the slots used for the call and the beacon transmission slots of the destination base station are different, so it is guaranteed that the beacon of the destination base station will be found when searching for a base station in use during a handover. This eliminates the need to send two beacons every 10 ms, and allows it to send one beacon every 10 ms, which halves the channels used by idle base stations and reduces the impact of co-channel interference.

Figure 3 shows another example of slot group classification in the present invention (when L=4). Here, the downlink slots (SL0-SL11) and uplink slots (SL12-SL23) in DECT radio resources are each classified into four slot groups (slot groups SL0-SL2, SL12-SL14, slot groups SL3-SL5, SL15-SL17, slot groups SL6-SL8, SL18-SL20, and slot groups SL9-SL11, SL21-SL23).

Note that while Figure 3 shows consecutive slots assigned to each slot group, it is also possible to assign every third slot to the same slot group, and any slot group can be assigned as long as there are no overlaps. Furthermore, the number of slots assigned to each slot group does not necessarily have to be the same; for example, taking into account the traffic expected at each base station, four or more slots can be assigned to a slot group of a base station where high traffic is expected.

FIG. 4 is a diagram showing an example of the area expansion of base station zones for the slot groups of FIG. 3, where the slot groups used by each base station are shown in the same gray scale as in FIG. 3. As shown here, by classifying the slots as in FIG. 3, it is possible to make the slot groups used by adjacent base stations different from each other. Also, the number of slot group classifications L
is arbitrary as long as it is 3 or more, but by making L larger, the interference distance can be made larger and the influence of co-channel interference can be further reduced.

Figure 5 is a block diagram showing the basic configuration of one embodiment of a digital cordless telephone system using the DECT wireless communication system according to the present invention.

The digital cordless telephone system of this embodiment comprises a telephone control device (hereinafter referred to as the main device) 10, M (M is a natural number greater than or equal to 1) base stations 20, and N (N is a natural number greater than or equal to 1) handsets 30. One base station 20 and one handset 30 are selectively used from among the M base stations 20 and N handsets 30 to form the digital cordless telephone system.

P (P is a natural number greater than or equal to 1) telephone lines (office lines) are connected to the main unit 10, allowing simultaneous outgoing and incoming calls on up to P lines. In addition, M (M is a natural number greater than or equal to 1) base stations 20 are connected to the main unit 10, allowing N (N is a natural number greater than or equal to 1) handset units 30 to make and receive calls via these.

After powering on, each handset 30 registers its location with one of the base stations 20 and becomes able to make and receive calls through that base station 20. This is referred to as the handset 30 connecting to the base station 20. In other words, each handset 30 becomes able to make and receive calls through the base station 20 to which it is connected.

As the handset 30 moves, it may reconnect to a base station 20 that offers better wireless communication. This is called roaming. Even during a call, as the handset 30 moves, it may reconnect to a base station 20 that offers better wireless communication. This is called handover.

The specific configuration of the main unit, base station, and handset is explained below.

Figure 6 is a block diagram showing the basic configuration of one embodiment of a main unit in a digital cordless telephone system that uses the DECT wireless communication method according to the present invention. For simplicity, only the necessary components are shown here. This also applies to the following figures.

The main unit 10 of this embodiment includes 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, a control unit 15, and a base station slot group information storage unit 16.

P (P is a natural number greater than or equal to 1) telephone lines (office lines) are connected to the central office interface unit 11, allowing for simultaneous outgoing and incoming calls on up to P lines. M (M is a natural number greater than or equal to 1) base station transmission lines are connected to the internal line interface unit 12, allowing for the accommodation of up to M (M is a natural number greater than or equal to 1) base stations via these lines.

The audio data inside the main unit 10 is, for example, an audio coded signal such as a PCM codec. 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 a sufficiently high-speed voice multiplex clock and a 125-us-cycle voice codec frame pulse to circuit-switch the voice signals on the telephone line and extension lines, and supplies these to the central office I/F unit 11 and extension I/F unit 12, respectively. The multiplexed voice signal generated using these is applied to the circuit switching unit 14. The circuit switching unit 14 performs circuit switching in one-sample units based on the circuit switching control signals for external and extension line outgoing and incoming calls provided by the control unit 15.

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 pulse 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 inter-base station synchronization timing pulses for synchronization between DECT base stations.

Figure 7 shows an example of a frame format for TDD (ping-pong) signal transmission 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 cycle (frame time length) is set to an integer multiple of 125 μs to match the division of audio data. Downstream transmission data consists of a frame synchronization bit, a multi-frame synchronization bit, common control data, and one or more channels of audio data (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 8 shows an example of transmission of common 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 the connected base station information, call status, whether or not a ring tone is specified, the station line key assignment, and the lamp status of the assigned station line key for all handset units in the system, and updates them accordingly. 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.

The base station slot group information storage unit 16 stores slot group information for each base station. The base station slot group information specifies, for example, the slot groups available for use by the base station for each base station identification information.

The base station identification information can be, for example, the base station ID (RPN) of the base station ID information defined in the DECT standard shown in Figure 22, or base station identification information defined on the system (main unit) side, such as the base station number. Furthermore, the slot group information for the base station can be any L-number of numbers for identifying L slot groups (L is a natural number greater than or equal to 3), or the remainder obtained by dividing the base station ID by L.

By using the base station ID to derive the slot group information for a base station, there is no need to store slot group information for each base station in the main unit. This has the advantage that the slot group information for that base station can be obtained directly at the base station, as in another embodiment of the base station described below (Figure 10). For example, the slot group information for that base station can be calculated from the base station ID information displayed on the back of the base station. When a construction company installs a base station for a cordless telephone system, by appropriately setting the base station ID of adjacent base stations, the slot groups of adjacent base stations can easily be arranged to be different from each other.

Figure 9 is a block diagram showing the basic configuration of an embodiment of a base station in a digital cordless telephone system that uses the DECT wireless communication method according to the present invention. While only the basic configuration of base station 1 (20) is shown here, the other base stations also have a similar basic configuration.

The base station 20 of this embodiment includes a base station transmission path termination unit 21, a DECT transmission/reception control unit 22, a slot group information storage unit 23, and a blind slot information generation 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.

The base station transmission path termination unit 21 also combines or decomposes the bidirectional control data into handset control commands in multiframe units of the base station transmission path, and applies them to the DECT transmission/reception control unit 22, for example, via a bidirectional serial interface.

Conversely, the DECT transmission/reception control unit 22 applies control information received from the handset via the wireless transmission path to the base station transmission path termination unit 21 as a handset control command, and the handset control command is notified to the main unit 10 via the base station transmission path.

During the control data exchange sequence with the main unit when the base station is started, the slot group information storage unit 23 acquires the slot group information of the base station stored in the base station slot group information storage unit 16 of the main unit 10 and stores it in the slot group information storage unit 23.

The blind slot information generator 24 generates blind slot information, which is information on whether each slot in the base station 20 is available for use, based on the relationship between the slot group information and the blind slot information, and applies this information to the DECT transmission/reception controller 22. For example, if slots 1 to 4 are available for use and slots 5 to 12 are unavailable, the blind slot information generated would be {1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0}.

When the DECT transmission/reception control unit 22 receives blind slot information, it uses a beacon to broadcast the blind slot information to all handset devices connected to the base station 20.

Blind slot information can be reported by beacon by storing it in the MAC information of the short page Pt, or it can be reported as unique information in the system information Qt.

Figure 10 is a block diagram showing the basic configuration of another embodiment of a base station 20 in a digital cordless telephone system that uses the DECT wireless communication method according to the present invention.

The base station 20 of this embodiment comprises a base station transmission path termination unit 21, a DECT transmission/reception control unit 22, a base station number information storage unit 25, a slot group information generation unit 26, and a blind slot information generation unit 24. It differs from the base station 20 of FIG. 9 in that it calculates slot group information from base station number information that is individually set and stored in the base station 20, without acquiring slot group information from the main unit. Therefore, in the case of the base station 20 of this embodiment, the main unit does not need to comprise a slot group information storage unit for each base station.

The base station number information storage unit 25 stores the base station number, for example, as a base station ID. The slot group information generation unit 26 calculates slot group information from the base station number by performing a predetermined process, such as calculating the remainder when the base station number is divided by L (L is a natural number greater than or equal to 3). Furthermore, the blind slot information generation unit 24 generates blind slot information, which is information on whether each slot at the base station is available or unavailable, from the relationship between the slot group information and the blind slot information. This information is applied to the DECT transmission/reception control unit 22, which broadcasts the blind slot information as a beacon.

Figure 11 is a block diagram showing the basic configuration of one embodiment of a handset in a digital cordless telephone system that uses the DECT wireless communication method according to the present invention.

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, a numeric keypad 39, and a base station slot group table storage unit 40.

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 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 code/decode the audio. A microphone 37 and speaker 38 are connected to the audio codec 33. The audio signal uttered by the handset 30 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, etc., 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 is processed within the control sequence.

The base station slot group table storage unit 40 stores a base station slot group table created based on the base station search information and blind slot information acquired during base station searches. This base station slot group table is updated sequentially.

Figure 12 shows an example of the slave unit state and state transitions. Below, we will explain the operation of the slave unit, referring to Figure 12 and Figure 11 as appropriate.

When each handset is powered on, it switches from its initial state to a base station search state, performs base station search operations at regular intervals, and acquires base station search information and blind slot information.

Specifically, the device receives base station ID information Nt broadcast by each base station using a dummy bearer, acquires base station search information consisting of the base station ID information and beacon reception level information from that base station, and further receives system information Qt broadcast by each base station using a dummy bearer to acquire blind slot information from that base station. It is also possible to receive blind slot information broadcast as system information Qt from the base station during base station search, and acquire blind slot information and reception level information. When a handset searches for base stations, it may select a base station where the number of location registration handset units has not reached the upper limit, and perform location registration.

Based on the acquired base station search information and blind slot information, a slot group table for each base station is created, and this information is stored in the slot group table for each base station storage unit 40.

Figure 13 shows an example of a slot group table for each base station. This slot group table for each base station is composed of a list of base station ID information discovered during base station search, beacon reception level information from each base station, and blind slot information for each base station.

The list of base station ID information can use all or part of the base station identification information contained in the base station ID information Nt. For example, if the system ID information (FPN) contained in the base station ID information Nt matches the system ID of the local system, the base station ID (RPN) and reception level information can be retained.

In addition, instead of the base station ID (RPN), base station identification information defined on the system (main unit) side, such as the base station number, can be used, or this can be used in combination with the base station ID (RPN). Furthermore, the base station identification information defined on the system (main unit) side can be broadcast as system information Qt, which can be received when searching for a base station to obtain the base station identification information and reception level information.

As explained using Figure 21, the base station ID information Nt, system information Qt, and paging information Pt are each broadcast using the same frequency channel and the same slot within one multiframe.

As shown in Figures 23 and 24, system information Qt includes not only basic system information but also RF carrier information, multiframe number information, and unique system information, and the type of system information transmitted in the Qt frame is stored in the Qt header. Such different system information is broadcast using multiple multiframes, and a slave device can acquire these different system information by receiving multiple multiframes. The base station can broadcast its own system information, such as base station identification information or blind slot information defined on the system (main device) side, by adding it to system information Qt, and the slave device can receive multiple multiframes and acquire base station identification information or blind slot information.

As shown in Figure 28, paging information Pt includes short pages that include MAC information such as blind slot information, and full pages and long pages that do not include MAC information. Furthermore, as shown in Figure 30, even in short pages, several different pieces of MAC information are broadcast using multiple multi-frames. The handset can also receive multiple multi-frames to obtain the blind slot information broadcast using short pages. As described above, by receiving multiple multi-frames on the same frequency channel and in the same slot, it is possible to obtain base station search information and blind slot information.

Blind slot information for each base station can be obtained from the blind slot information, which is one piece of MAC information that is intermittently broadcast from the base station using paging information Pt.

Next, we will explain in more detail the operation of the handset during the location registration sequence.

Figure 14 shows an example of the location registration sequence of handset 30 with the main unit.

In the location registration sequence, the mobile device first sends an access request to the base station with which it is attempting to register its location, in order to prepare a bearer (MAC layer) that establishes a link in the data link layer.

The handset control unit 32 of a handset in a base station search state references the base station slot group table stored in the base station slot group table storage unit 40, selects, for example, the base station with the highest reception level, and then acquires the blind slot information of that base station from the base station slot group table. Alternatively, the blind slot information may be acquired by intermittently receiving the paging information Pt of that base station over multiple multiframes.

When a handset is searching for a base station, the handset control unit 32 selects a base station to register its location with and acquires the blind slot information of that base station. Based on the blind slot information, the handset control unit 32 generates a handset control signal for transmitting a MAC access request using an available slot at that base station and applies this to the DECT transmission/reception control unit 31. In response, the DECT transmission/reception control unit 31 transmits the MAC access request using an available slot at that base station.

When a base station receives a MAC access request, it uses a paired slot to transmit a MAC bearer confirmation message to the mobile station. A paired slot refers to an uplink slot and a downlink slot that are spaced 5 ms apart on the same frequency channel, and both paired slots belong to the same slot group. In other words, the MAC bearer confirmation message is transmitted using a slot that belongs to the slot group available to the base station.

After that, wireless transmission is performed in accordance with the data link layer link establishment procedure and location registration procedure using the same pair of slots, i.e., slots belonging to the group of slots available for use by the base station, and location registration is performed.

When a handset registers its location with a base station, it enters an idle lock state. Idle lock 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.

When a handset in idle lock state communicates with a base station, it must establish a link and transition to communication lock state. In communication lock state, two-way communication with the base station is performed using a traffic bearer.

Figure 15 shows an example of a call sequence when a key operation to make a call is performed on the handset.

When a key operation to make a call is performed on a handset in the idle-locked state, the handset control unit 32 detects this and generates a handset control signal for transmitting a MAC access request to the connected base station that performed location registration, using a slot belonging to the slot group allowed for use by that base station, based on the blind slot information of that base station, and applies this signal to the DECT transmission/reception control unit 31. In response, the DECT transmission/reception control unit 31 transmits the MAC access request using a slot belonging to the slot group allowed for use by that base station.

When a base station receives a MAC access request, it uses the paired slot to send a MAC bearer confirmation message to the device. Since both paired slots belong to the same slot group that is available for use by the base station, the MAC bearer confirmation message is sent using that slot.

From then on, wireless transmission of data link layer link establishment procedures, call procedures, and communication procedures is carried out using paired slots belonging to the same slot group, i.e., using slots belonging to the slot group that is available for use by the base station.

Even in a communication locked state, pre-communication base station searches can be performed when communication quality deteriorates or at predetermined time intervals. If a new base station with better wireless communication capabilities is discovered, a link can be established with the new base station, and the communication can transition to a communication locked state with the new base station. In other words, handover can be performed.

When performing a handover in a communication locked state, it is necessary to continue communication with the currently connected base station while simultaneously searching for a base station in communication. When searching for a base station in communication, the base station search is performed in slots other than the slot currently being used for communication.

When a handover is performed by moving between two base station zones while a mobile device is communicating, with conventional technology, if the transmission slot of the beacon of the destination base station matches the slot currently being used for communication, the beacon of the destination base station cannot be found by searching for the communicating base station, and the destination base station must be selected from among base stations other than the destination base station whose beacon does not match the slot currently being used for communication.

It's fine if a suitable base station other than the destination base station can be found for handover, but if no suitable base station can be found, even though there is a base station at the destination, the handover cannot be carried out because the base station cannot be found, resulting in a deterioration in communication quality and, in the worst case, a disconnection of communication.

To avoid this situation, two beacons are sent from each base station at 10 ms intervals to transmit the same information. However, this poses the problem of congestion and co-channel interference becoming more likely because the beacons occupy twice the number of slots as the number of base stations. On the other hand, if each base station sends one beacon at 10 ms intervals, as mentioned above, there is a risk that the beacon from the destination base station cannot be received during handover.

In contrast, according to the present invention, different slot groups are assigned to adjacent base stations. Therefore, even if one beacon is transmitted from each base station at a 10 ms interval, the slots currently in use for communication and the slot group used by the destination base station are different, so there is no chance that the beacon from the destination base station will not be received during handover. Therefore, it is possible to use only one beacon at a 10 ms interval, which is advantageous from the perspective of co-channel interference.

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
16...Slot group information storage unit for each base station
20...Base station
21...Base station transmission line termination unit
22...DECT transmission/reception control unit
23...Slot group information storage unit
24: Blind slot information generation unit
25...Base station number information storage unit
26...Slot group information generation unit
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...Base station slot group table storage unit

Claims (6)

A base station for a TDMA-TDD cordless telephone device, configured by connecting one or more base stations to which a plurality of handset terminals can be connected to a telephone control device connected to a wide area network, comprising:
a slot group information storage means for storing slot group information, which is information for specifying one or more slot groups to be used in the base station from among L slot groups (L is a natural number of 3 or more) into which a plurality of slots used in wireless transmission are classified;
a blind slot information generating means for specifying slots to be used in the base station from among all slots defined by the TDMA-TDD system based on the slot group information, and generating blind slot information which is information on whether each slot is available for use;
A base station for a cordless telephone device, characterized in that the blind slot information is embedded in the MAC information of a short page frame of the DECT standard, or embedded in the unique information of a system information frame of the DECT standard, and is broadcast by a beacon, and is equipped with a DECT transmission/reception control unit that transmits and receives radio transmissions in a slot selected based on the blind slot information. 2. The base station for a cordless telephone device according to claim 1 , wherein said slot group information is information for identifying said slot group used by said base station. The base station for a cordless telephone device according to claim 1 or 2, characterized in that the slot group information is information on a slot group calculated in the cordless telephone device from identification information of the base station in accordance with a predetermined rule, and the blind slot information generating means generates blind slot information from the slot group information. The base station of the cordless telephone device according to claim 3 , characterized in that in order to calculate the slot group information from the base station identification information, the remainder obtained by dividing the base station identification information by L (L is a natural number equal to or greater than 3) is referenced. A base station and a handset of a cordless telephone device comprising one or more base stations connected to a telephone control device connected to a wide area network and a plurality of handset units connectable to the base stations,
The base station
a slot group information storage means for storing slot group information, which is information for specifying one or more slot groups to be used in the base station from among L slot groups (L is a natural number of 3 or more) into which a plurality of slots used in wireless transmission are classified;
a blind slot information generating means for specifying slots to be used in the base station from among all slots defined by the TDMA-TDD system based on the slot group information, and generating blind slot information which is information on whether each slot is available for use;
a DECT transmission/reception control unit that embeds the blind slot information in MAC information of a short page frame of the DECT standard or embeds the blind slot information in unique information of a system information frame of the DECT standard, and notifies the beacon, and performs transmission and reception of wireless transmissions in a slot selected based on the blind slot information;
The blind slot information is embedded in MAC information of a short page frame of the DECT standard, or embedded in unique information of a system information frame of the DECT standard, and notified to a slave unit by a beacon, and wireless transmission is performed using a slot selected based on the blind slot information;
The slave unit is
a base station slot group table storage means for generating a base station slot group table based on base station search information and blind slot information acquired during base station search and storing the table;
A base station and a handset of a cordless telephone device, characterized in that they comprise handset control means for managing handset states and state transitions, for obtaining information on slot groups to be used by a base station with which a radio link is to be established by referring to the slot group table for each base station, and for controlling the establishment of a radio link and communication over the radio link by using slots selected based on the slot group information. A telephone control device and a base station of a cordless telephone system, which is configured such that one or more base stations to which a plurality of handset units can be connected are connected to a telephone control device connected to a high-bandwidth network,
A plurality of slots used in wireless transmission are classified into L slot groups (L is a natural number equal to or greater than 3),
The telephone control device
a slot group information storage means for storing slot groups to which one or more slot groups to be used by each base station are assigned, so that different slot groups are assigned to adjacent base stations;
The base station
slot group information storage means for storing slot group information of the base station, which is acquired via a base station transmission line when the base station is started and stored in said slot group information storage means for each base station;
a blind slot information generating means for identifying slots to be used by the base station from among all slots defined by the TDMA-TDD system based on the slot group information, and generating blind slot information which is information on whether each slot is available for use;
A telephone control device and a base station for a cordless telephone system, characterized in that the blind slot information is embedded in the MAC information of a short page frame of the DECT standard, or in the unique information of a system information frame of the DECT standard, and is announced by a beacon, and the telephone control device and base station are provided with a DECT transmission/reception control unit that transmits and receives radio transmissions in a slot selected based on the blind slot information.