JP7433736B2 - wireless communication system - Google Patents

Description

The present invention relates to a wireless communication system that performs wireless communication using time division multiple access frames.

Transmission from the HUB station to each terminal station (i.e., downlink) follows the time division multiplexing (TDM) method, and transmission from each terminal station to the HUB station (i.e., uplink) uses time division multiple access. In a wireless communication system that uses frames compliant with a radio frame format that follows the Time Division Multiple Access (TDMA) method, each terminal station transmits a frame to a HUB station by At the HUB station, frames (in other words, bursts) are transmitted while adjusting the transmission timing so as not to collide with each other. Therefore, time synchronization is required between the HUB station and each terminal station. If the time synchronization accuracy is high, the space between frames (that is, the idle time inserted between each time slot) can be minimized, and a system with high line utilization and transmission efficiency can be built. can. As a specific method, there is a method of using time information of GPS (Global Positioning System), but this method cannot be said to be optimal considering the constraints such as GPS receivable area and cost.

As a conventional mobile communication technology that employs communication access methods such as time division multiple access (TDMA), a time adjustment request command is set in advance to request current time information from a base station that transmits control information via a control channel. a transmission control unit that automatically outputs the time adjustment request command in response to the timing of the transmission; a transmission unit that transmits the time adjustment request command output from the transmission control unit to the base station; It includes a receiving unit that receives and outputs current time information transmitted via a control channel, and a time adjustment unit that automatically adjusts the time of a built-in clock based on the current time information output from the receiving unit. Mobile communication devices are known (see Patent Document 1).

Re-publication No. 01/028132

By the way, in a satellite communication system with a large coverage area, there is a large difference in propagation delay between the HUB station and the terminal station, so accurate absolute time synchronization cannot be achieved. Therefore, the space between frames (i.e., It is necessary to increase the amount of non-communication time inserted between each time slot. For this reason, there is a problem in that the utilization efficiency and transmission efficiency of the uplink are reduced. Furthermore, since periodic transmission of time synchronization information is required, there is a problem in that downlink transmission efficiency decreases.

Therefore, the present invention makes it possible to perform efficient data transmission by using a frame that conforms to a radio frame format that follows the time division multiplexing (TDM) method in the downlink and the time division multiple access (TDMA) method in the uplink. The purpose is to provide a wireless communication system that is possible.

In order to solve the above problems, a wireless communication system according to the present invention follows a time division multiplexing method in transmission from a HUB station to each terminal station, and uses a time division multiple access method in transmission from each terminal station to the HUB station. a HUB station and a terminal station that perform two-way wireless communication via a communication satellite using frames compliant with a radio frame format according to and the time of the transmission timing of the head of the header of the subsequent frame , and the difference between the reception timing of the head of the header of the frame at the terminal station and the time of the header of the header of the subsequent frame. It is characterized by comprising a frequency synchronization unit that synchronizes the frequency of the HUB station timer of the HUB station and the frequency of the terminal station timer of the terminal station using a ratio of the difference between the first reception timing and the time.

In the wireless communication system according to the present invention, the terminal station has a time adjustment unit that adjusts the time of the terminal station timer using a difference between the transmission timing and the reception timing. You can.

In the wireless communication system according to the present invention, the HUB station calculates a time error that is a difference between a scheduled time at which a frame is received and an actual reception time for each time slot conforming to time division multiple access. The terminal station may include a time error adjustment unit that adjusts the timing of transmitting frames to the HUB station based on the time error.

In the wireless communication system according to the present invention, the HUB station includes a time error comparison unit that determines whether the time error is greater than or equal to a predetermined threshold, and the terminal station has a time error comparison unit that determines whether or not the time error is greater than or equal to the threshold. The information processing apparatus may further include a readjustment unit that adjusts the transmission timing of frames to the HUB station based on the time error.

In the wireless communication system according to the present invention, a spare slot is provided in addition to a communication slot within one slot cycle of a time slot conforming to time division multiple access, and before processing by the frequency synchronization unit is performed. The terminal station may use the reserved slot to transmit a frame to the HUB station.

According to the wireless communication system according to the present invention, the frequency of the HUB station timer of the HUB station and the frequency of the terminal station timer of each terminal station are synchronized, so that frames are transmitted from each terminal station to the HUB station. It becomes possible to realize frequency synchronization between the HUB station and the terminal station, which is a prerequisite for adjusting the transmission timing.

According to the wireless communication system according to the present invention, when the time of the HUB station timer and the time of the terminal station timer are adjusted, the prerequisites for adjusting the frame transmission timing from each terminal station to the HUB station are It becomes possible to realize time adjustment between the HUB station and the terminal station.

According to the wireless communication system according to the present invention, from each terminal station to the HUB station based on the propagation delay between each terminal station and the HUB station based on the reception timing at the HUB station of a frame transmitted from each terminal station. If the timing of frame transmission to each terminal is adjusted, it is possible to absorb/compensate for the time error due to the propagation delay of each terminal station (in other words, the variation in propagation delay of each terminal station). It becomes possible to transmit frames in accordance with the timing of the time slots assigned to the station, which in turn reduces the space between uplink frames (i.e., the idle time inserted between each time slot). This makes it possible to improve line usage efficiency and transmission efficiency by reducing the number of lines.

According to the wireless communication system according to the present invention, the frame transmission timing from each terminal station to the HUB station is changed only when the time error, which is the difference between the scheduled frame reception time and the actual reception time, is greater than or equal to a predetermined threshold. If the holding process is performed, the increase in data transmission amount related to the holding process of frame transmission timing between the HUB station and each terminal station is suppressed, and the line usage efficiency and transmission efficiency are reduced. It is possible to avoid this.

According to the wireless communication system according to the present invention, when a spare slot is provided in addition to a communication slot within one slot period, the timing of transmitting a frame from a terminal station to a HUB station is adjusted. It is possible to prevent collisions between frames (in other words, between bursts) at the HUB station before processing is performed.

1 is a functional block diagram showing a schematic configuration of a wireless communication system according to an embodiment of the present invention. (A) is a diagram schematically showing a frame transmitted from each terminal station to each terminal station in the wireless communication system of FIG. 1, and (B) is a diagram schematically showing frames transmitted from each terminal station to each terminal station in the wireless communication system in FIG. FIG. 2 is a diagram schematically showing a frame to be transmitted. FIG. 2 is a diagram illustrating a process of synchronizing the frequency of a HUB station timer of a HUB station and a frequency of a terminal station timer of a terminal station in the wireless communication system of FIG. 1, and is a diagram illustrating the contents of processing in the HUB station. 4 is a diagram illustrating processing contents at a terminal station corresponding to processing contents at the HUB station in FIG. 3. FIG. FIG. 2 is a diagram illustrating a process for adjusting the time of a HUB station timer of a HUB station and a time of a terminal station timer of a terminal station in the wireless communication system of FIG. 1, and is a diagram illustrating the content of processing at the terminal station. FIG. 2 is a diagram illustrating adjustment processing of frame transmission timing from a terminal station to a HUB station in the wireless communication system of FIG. 1. FIG. FIG. 3 is a diagram illustrating a configuration in which a communication slot and a spare slot are provided within one slot period.

The present invention will be described below based on the illustrated embodiments.

FIG. 1 is a functional block diagram showing a schematic configuration of a wireless communication system 1 according to an embodiment of the present invention.

The wireless communication system 1 is a communication satellite ( In other words, using a satellite communication line), the transmission from the HUB station 2 to each terminal station 3A, 3B, 3C (i.e., downlink) follows a time division multiplexing (TDM) method, and each terminal station 3A, 3B , 3C to the HUB station 2 (ie, uplink), two-way wireless communication is performed using frames conforming to a wireless frame format according to the time division multiple access (TDMA) system. Although the illustrated example shows three terminal stations, the number of terminal stations may be two or four or more. Further, the configurations of the terminal stations 3B and 3C are the same as that of the terminal station 3A, so illustration thereof is omitted. In the following, when describing operations common to each of the plurality of terminal stations 3A, 3B, and 3C, the term "terminal station 3" will be used to include the plurality of terminal stations 3A, 3B, and 3C.

The HUB station 2 communicates with each terminal station 3 via a communication satellite 4 (in other words, using a satellite communication line) in accordance with a time division multiplexing (TDM) method in the downlink, and in the uplink. It is a mechanism that performs bidirectional wireless communication using frames compliant with the wireless frame format according to the connection (TDMA) method, and mainly includes a control section 21, a buffer memory 22, a transmitting section 23, a receiving section 24, and the like. , a duplexer 25, an antenna 26, and a HUB station timer 27.

The control unit 21 has a function of controlling the operation of each unit constituting the HUB station 2, and includes a central processing unit 211 (CPU), an input/output unit 212 (I/O), and a storage unit. Contains 213.

The control section 21 is connected to each section of the HUB station 2 via an input/output section 212, and controls the start, content, and end of processing of each section constituting the HUB station 2. To avoid complication, signal lines from the input/output section 212 to each section are omitted.

The storage unit 213 serves as a work area for temporarily storing data and information generated when the central processing unit 211 performs communication processing, and stores various information, programs, and data. It has the function of serving as a storage area for storage, etc., and is composed of storage media such as RAM (Random Access Memory), ROM (Read Only Memory), and storage.

A control program for the control unit 21 to control the overall operation of the HUB station 2 is stored in the storage unit 213 . The control unit 21 controls the overall operation of the HUB station 2 according to a control program stored in the storage unit 213 and realizes each function.

The buffer memory 22 receives input of data to be transmitted output from a transmission source (not shown), and uses a first-in, first-out (FIFO) system for adjusting the timing of transmitting data/frames from the HUB station 2. Out) function.

The transmitter 23 receives input of the data to be transmitted outputted from the buffer memory 22, time-division multiplexes a plurality of data sequences based on the time division multiplexing (TDM) method, and transmits the multiplexed data to each terminal station 3. Equipped with a processing function.

The receiving unit 24 has a function of receiving the signal output from the duplexer 25 and receiving and processing frames/data transmitted from each terminal station 3 in accordance with the time division multiple access (TDMA) system.

The transmitter/receiver duplexer 25 has a function of switching between transmitting and receiving, and receives the input of the signal output from the transmitter 23 and outputs it to the antenna 26, or receives the input of the signal output from the antenna 26 and outputs it to the receiver. 24.

The antenna 26 has a function of transmitting and receiving wireless signals.

The HUB station timer 27 has a clock function and is configured to be able to supply time.

In the HUB station 2, when data to be transmitted outputted from a transmission source (not shown) is sent to the buffer memory 22, the transmission unit 23 converts it into a time division multiplexing (TDM) wireless frame format. Accordingly, the data to be transmitted is divided into predetermined time periods, multiplexed, and transmitted to each terminal station 3.

For example, as shown in FIG. 2A, a signal is a signal consisting of successive frames (including header H and data D) that are temporally divided in accordance with the time division multiplexing (TDM) wireless frame format. is transmitted from the HUB station 2 to each terminal station 3.

The terminal station 3 communicates with the HUB station 2 via the communication satellite 4 (in other words, using a satellite communication line) in accordance with the time division multiplexing (TDM) method in the downlink and in the uplink. It is a mechanism for performing bidirectional wireless communication using frames compliant with a wireless frame format according to the (TDMA) system, and mainly includes a control section 31, a buffer memory 32, a transmitting section 33, a receiving section 34, It has a duplexer 35, an antenna 36, and a terminal timer 37.

The control section 31 has a function of controlling the operations of each section constituting the terminal station 3, and includes a central processing unit 311 (CPU), an input/output section 312 (I/O), and a storage section 313.

The control section 31 is connected to each section of the terminal station 3 via an input/output section 312, and controls the start, content, and end of processing of each section constituting the terminal station 3. To avoid complication, signal lines from the input/output section 312 to each section are omitted.

The storage unit 313 serves as a work area for temporarily storing data and information generated when the central processing unit 311 performs communication processing, and stores various information, programs, and data. It has a function of serving as a storage area for storing data, and is composed of storage media such as RAM, ROM, and storage.

A control program for the control unit 31 to control the overall operation of the terminal station 3 is stored in the storage unit 313 . The control unit 31 controls the overall operation of the terminal station 3 according to a control program stored in the storage unit 313 and realizes each function.

The buffer memory 32 receives input of data to be transmitted output from a transmission source (not shown) and has a first-in first-out (FIFO) function for adjusting the timing of transmitting data/frames from the terminal station 3. .

The transmitter 33 has a function of receiving data to be transmitted output from the buffer memory 32 and transmitting the data string to the HUB station 2 in accordance with the time division multiple access (TDMA) method.

The receiving unit 34 receives the input of the signal output from the duplexer 35, receives and processes frames/data that are time-division multiplexed and transmitted from the HUB station 2 in accordance with the time division multiplexing (TDM) method. Equipped with functions.

The transmitter/receiver duplexer 35 has a function of switching between transmitting and receiving, and receives the input of the signal output from the transmitter 33 and outputs it to the antenna 36, and receives the input of the signal output from the antenna 36 and outputs it to the receiver. 34.

The antenna 36 has a function of transmitting and receiving wireless signals.

The terminal timer 37 is constituted by a self-running timer, has a clock function, and is configured to be able to supply time.

In the terminal station 3, when the data to be transmitted outputted from the transmission source (not shown) is sent to the buffer memory 32, the transmitter 33 transmits the data to the buffer memory 32 according to the time division multiple access (TDMA) method. The data to be transmitted is transmitted to the HUB station 2.

In other words, burst signals that are temporally divided in accordance with the radio frame format of the time division multiple access (TDMA) system and are intermittent in time in frame units are transmitted at predetermined intervals (in other words, burst signals that conform to the TDMA system) (at the signal transmission timing) from the terminal station 3 to the HUB station 2.

Then, in the HUB station 2, as shown in FIG. 2B, for example, a frame transmitted from the terminal station 3A (including a header Ha and data Da), a frame transmitted from the terminal station 3B (including (including header Hb and data Db) and frames transmitted from terminal station 3C (including header Hc and data Dc) are received in the time slots assigned to each terminal station 3. be done.

At this time, the smaller the space between uplink frames (i.e., the non-communication time inserted between each time slot) when the HUB station 2 receives frames transmitted from each terminal station 3, the more the line Usage efficiency and transmission efficiency will improve.

The wireless communication system 1 according to the embodiment follows a time division multiplexing (TDM) method in transmission from the HUB station 2 to each of the terminal stations 3A, 3B, and 3C (that is, downlink), and A HUB that performs bidirectional wireless communication via a communication satellite 4 using a frame compliant with a wireless frame format according to time division multiple access (TDMA) in transmission (i.e., uplink) from 3B and 3C to a HUB station 2. The terminal station 3 has a station 2 and a terminal station 3, and the terminal station 3 calculates the difference in time th between the transmission timing of the header of the frame transmitted from the HUB station 2 and the reception timing of the header of the frame at the terminal station 3. A frequency synchronization unit 314 synchronizes the frequency of the HUB station timer 27 of the HUB station 2 and the frequency of the terminal station timer 37 of the terminal station 3 using the ratio Δf between the difference between the time ts and the time ts of the transmission timing and the reception timing. The HUB station 2 has a time adjustment unit 315 that adjusts the time of the terminal station timer 37 using the difference between the timing and the time ts. The terminal station 3 has a time error calculation unit 214 that calculates a time error Δtd that is the difference between the scheduled time of receiving the frame and the actual reception time, and the terminal station 3 determines the transmission timing of the frame to the HUB station 2 based on the time error Δtd. A time error adjustment section 316 is provided to adjust the time error adjustment section 316.

First, the frequency of the HUB station timer 27 of the HUB station 2 and the frequency of the terminal station timer 37 of each terminal station 3 are synchronized.

Specifically, as shown in FIG. 3, the HUB station 2 inputs the time supplied from the HUB station timer 27 into the FEC frame at the transmission timing of the header H of the FEC (Forward Error Correction) frame. It is added as time stamp information TS and transmitted to each terminal station 3.

In the example shown in FIG. 3, when transmitting an FEC frame from the HUB station 2 to each terminal station 3, the time th_i supplied from the HUB station timer 27 at the transmission timing of the header H of the <i>th FEC frame is The time th_i+1 added to the <i+2>th FEC frame as time stamp information TS and supplied from the HUB station timer 27 at the transmission timing of the header H of the <i+1>th FEC frame is <i+3>. The time stamp information TS is added to the second FEC frame.

In the example shown in FIG. 3, in consideration of the time required to acquire the time supplied from the HUB station timer 27 and add it as time stamp information TS, the time stamp information TS for each FEC frame is set two times later. Although the time stamp information TS for each FEC frame is added to the FEC frame, it may be added to the FEC frame in question or to the next FEC frame.

Furthermore, in the example shown in FIG. 3, the timestamp information TS for the <i>th FEC frame and the timestamp information TS for the <i+1>th FEC frame are added to the FEC frame and transmitted to the terminal station 3. However, for example, the timestamp information TS for the <i>th FEC frame and the timestamp information TS for the <i+2>th FEC frame are added to the FEC frame and sent to the terminal station 3. It may also be transmitted. That is, it is sufficient that the time stamp information TS regarding a plurality of FEC frames that are sequential in time is transmitted from the HUB station 2 to the terminal station 3.

When the time stamp information TS is transmitted from the HUB station 2 to each terminal station 3, for example, a flag indicating that the frame is an FEC frame including the time stamp information TS is included in the header H. The terminal station 3 recognizes that the frame includes time stamp information TS.

When the terminal station 3 receives the FEC frame transmitted from the HUB station 2, it acquires the time supplied from the terminal station timer 37 at the reception timing of the beginning of the header H of the FEC frame, and stores it in the storage unit 313 or the like. At the same time, if time stamp information TS is added to the FEC frame, the time stamp information TS is acquired and stored in the storage unit 313 or the like.

In the example shown in FIGS. 3 and 4, when the terminal station 3 receives the FEC frame transmitted from the HUB station 2, the signal is supplied from the terminal station timer 37 at the reception timing of the beginning of the header H of the <i>th FEC frame. The time ts_i is acquired and stored in the storage unit 313 or the like, and the time ts_i+1 supplied from the terminal timer 37 at the reception timing of the head of the header H of the <i+1>th FEC frame is acquired and stored. The information is stored in the section 313 or the like.

In the examples shown in FIGS. 3 and 4, the time th_i added to the <i+2>th FEC frame as time stamp information TS is also acquired and stored in the storage unit 313, and Time th_i+1 added to the FEC frame as time stamp information TS is acquired and stored in the storage unit 313 or the like.

Then, the frequency synchronization unit 314 of the control unit 31 of the terminal station 3 determines the ratio of the elapsed time in the HUB station timer 27 of the HUB station 2 to the elapsed time in the terminal station timer 37 of the terminal station 3 (in other words, The frequency error Δf between the HUB station timer 27 and the terminal station timer 37 is calculated from the ratio of the rate of time lapse between the terminal station timer 37 and the terminal station timer 37 according to Equation 1 below.
(Math. 1) Δf = (ts_i+1−ts_i)/(th_i+1−th_i)

The above formula 1 is applied taking into consideration which FEC frame the timestamp information TS attached to each FEC frame corresponds to. For example, in the examples shown in FIGS. 3 and 4, it is considered that the timestamp information TS added to each FEC frame is the timestamp information TS for the two previous FEC frames.

Specifically, in the examples shown in FIGS. 3 and 4, in the above formula 1, "th_i" is set by the HUB station timer 27 at the transmission timing of the beginning of the header H of the <i>th FEC frame in the HUB station 2. In the example shown in the figure, this is the time stamp information TS added to the <i+2>th FEC frame. "ts_i" is a time supplied from the terminal station timer 37 at the terminal station 3 at the reception timing of the head of the header H of the <i>th FEC frame.

Moreover, "th_i+1" is the time supplied from the HUB station timer 27 at the transmission timing of the head of the header H of the <i+1>th FEC frame in the HUB station 2, and in the example shown in the figure, the This is time stamp information TS added to the FEC frame. "ts_i+1" is a time supplied from the terminal timer 37 at the terminal station 3 at the reception timing of the head of the header H of the <i+1>th FEC frame.

The frequency synchronization unit 314 of the control unit 31 of the terminal station 3 uses the times (here, ts_i, ts_i+1) supplied from the terminal station timer 37 stored in the storage unit 313 etc. and the times added to the FEC frame. The time stamp information TS (here, th_i, th_i+1) is read out, the frequency error Δf is calculated according to the above equation 1, and the frequency of the terminal station timer 37 is corrected based on the frequency error Δf. That is, the frequency synchronization unit 314 changes the frequency by multiplying the frequency of the terminal timer 37 by the reciprocal of the frequency error Δf obtained as a result of calculation using Equation 1 above.

As described above, the frequency of the HUB station timer 27 of the HUB station 2 and the frequency of the terminal station timer 37 of each terminal station 3 are synchronized. In the example shown in the figure, the time in the terminal station timer 37 at the timing when frequency synchronization is achieved is tf.

Next, the time of the HUB station timer 27 of the HUB station 2 and the time of the terminal station timer 37 of each terminal station 3 are adjusted.

Specifically, the time adjustment unit 315 of the control unit 31 of the terminal station 3 calculates the difference between the time of the HUB station timer 27 of the HUB station 2 and the time of the terminal station timer 37 of the terminal station 3 according to the following formula 2. A time difference Δt between the HUB station timer 27 and the terminal station timer 37 is calculated.
(Math. 2) Δt = ts_j−th_j

The above formula 2 is applied taking into consideration which FEC frame the timestamp information TS attached to each FEC frame corresponds to. For example, in the example shown in FIG. 5, similarly to the example shown in FIG. 3, it is considered that the timestamp information TS added to each FEC frame is the timestamp information TS about the two previous FEC frames. .

Specifically, in the example shown in FIG. 5, in the above formula 2, "th_j" is supplied from the HUB station timer 27 at the transmission timing of the beginning of the header H of the <j>th FEC frame in the HUB station 2. In the example shown in the figure, this is the time stamp information TS added to the <j+2>th FEC frame. "ts_j" is a time supplied from the terminal timer 37 at the terminal station 3 at the reception timing of the head of the header H of the <j>th FEC frame. Time ts_j is a time later than time tf at which frequency synchronization was achieved. The above-mentioned times “th_j” and “ts_j” are stored in the storage unit 313 or the like.

The time adjustment unit 315 of the control unit 31 of the terminal station 3 uses the time (here, ts_j) supplied from the terminal station timer 37 stored in the storage unit 313 etc. and the time stamp information TS added to the FEC frame. (here, th_j) is read out, a time difference Δt is calculated according to the above equation 2, and the time of the terminal station timer 37 is corrected based on the time difference Δt. In other words, the time adjustment unit 315 changes the time by subtracting the time difference Δt obtained as a result of calculation using Equation 2 above from the time of the terminal station 3.

As described above, the time of the HUB station timer 27 of the HUB station 2 and the time of the terminal station timer 37 of the terminal station 3 are adjusted. In the example shown in the figure, the time in the terminal station timer 37 at the timing when the time adjustment is made is tt.

After the time adjustment process is completed, the HUB station 2 stops adding and transmitting the time stamp information TS. For example, the addition and transmission of the time stamp information TS may be performed until a predetermined time has elapsed from the start of the addition and transmission of the time stamp information TS, or the The process may continue until a predetermined stop signal is sent to the machine.

Next, adjustment processing of the frame transmission timing from each terminal station 3 to the HUB station 2 is performed.

Specifically, the HUB station 2 receives an FEC frame (in other words, an uplink burst signal) transmitted from each of the terminal stations 3A, 3B, and 3C, and determines the reception completion timing of the information in the header H of the FEC frame. The time supplied from the HUB station timer 27 (referred to as "reception completion time of header H of the FEC frame") is acquired and stored in the storage unit 213 or the like.

In the example shown in FIG. 6, in the HUB station 2, the FEC frame <A> transmitted from the terminal station 3A is received in the time slot <k> allocated to the terminal station 3A, and the FEC frame The reception completion time of header H of frame <A> is th_a. Further, in the HUB station 2, the FEC frame <B> transmitted from the terminal station 3B is received in the time slot <k+1> assigned to the terminal station 3B, and the FEC frame <B> is The reception completion time of header H is th_b. Furthermore, in the HUB station 2, the FEC frame <C> transmitted from the terminal station 3C is received in the time slot <k+2> assigned to the terminal station 3C, and the FEC frame <C> is The reception completion time of header H is th_c.

The reception start timing (" The "scheduled reception start time of the header H of the FEC frame") is predetermined.

In the example shown in FIG. 6, the scheduled reception start time of the header H of the FEC frame in time slot <k> allocated to the terminal station 3A at the HUB station 2 is th_k, and the time slot allocated to the terminal station 3B is The scheduled time to start receiving header H of the FEC frame in time slot <k+1> assigned to the terminal station 3C is th_k+1, and reception of header H of the FEC frame in time slot <k+2> allocated to terminal station 3C starts. The scheduled time is th_k+2.

The time error calculation unit 214 of the control unit 21 of the HUB station 2 calculates the scheduled reception start time and the actual reception start time of the header H of the FEC frame for each time slot, in other words, for each terminal station 3 assigned to the relevant time slot. The difference between the reception completion time and the reception completion time (referred to as "time error Δtd") is calculated. The time error Δtd corresponds to the deviation of the propagation delay assumed by the HUB station 2 from the reference value.

The time error Δtd calculated by Equation 3A below is the difference between the scheduled reception start time th_k of the header H of the FEC frame in the time slot <k> assigned to the terminal station 3A and the actual reception of the FEC frame <A>. The time error Δtda is the difference from the completion time th_a, and corresponds to the deviation from the reference value of the propagation delay assumed by the HUB station 2 for the terminal station 3A.
(Math. 3A) Δtda = th_k−th_a

The time error Δtd calculated by Equation 3B below is the difference between the scheduled reception start time th_k+1 of the header H of the FEC frame in the time slot <k+1> assigned to the terminal station 3B and the actual time of the FEC frame <B>. The time error Δtdb is the difference from the reception completion time th_b, and corresponds to the deviation from the reference value of the propagation delay assumed by the HUB station 2 for the terminal station 3B.
(Math 3B) Δtdb = th_k+1−th_b

The time error Δtd calculated by Equation 3C below is based on the estimated reception start time th_k+2 of the header H of the FEC frame in the time slot <k+2> assigned to the terminal station 3C and the actual time of the FEC frame <C>. The time error Δtdc is the difference from the reception completion time th_c of the terminal station 3C, and corresponds to the deviation from the reference value of the propagation delay assumed by the HUB station 2 for the terminal station 3C.
(Math 3C) Δtdc = th_k+2−th_c

The time error calculation unit 214 of the control unit 21 of the HUB station 2 transmits to each terminal station 3 the time error Δtd obtained as the calculation result of the above formulas 3A, 3B, and 3C. In the example shown in FIG. 6, the time error Δtda calculated according to the above formula 3A is the <n>th time error regarding time slot <k> (or regarding the terminal station 3A assigned to time slot <k>). The time error Δtdb, which is added to the FEC frame of The time error Δtdc added to the n+1>th FEC frame and further calculated according to the above formula 3C is the time related to time slot <k+2> (or related to the terminal station 3C assigned to time slot <k+2>). The error is added to the <n+2>th FEC frame and transmitted from the HUB station 2.

The time error adjustment unit 316 of the control unit 31 of the terminal station 3 acquires the time error Δtd regarding the time slot assigned to itself, which is added to the FEC frame transmitted from the HUB station 2, and adjusts the time The frame transmission timing to the HUB station 2 is adjusted based on the error Δtd.

In the example shown in FIG. 6, based on the time error Δtda regarding the time slot <k> added to the <n>th FEC frame (in other words, regarding the terminal station 3A assigned to the time slot <k>) , the timing of frame transmission from the terminal station 3A to the HUB station 2 is adjusted. Specifically, when the scheduled transmission timing of the frame from the terminal station 3A to the HUB station 2 is Tsa, T'sa calculated according to the following formula 4A is the frame transmission timing from the terminal station 3A to the HUB station 2. This is the scheduled time after adjusting the transmission timing.
(Math 4A) T'sa = Tsa + Δtda

Also, based on the time error Δtdb regarding the time slot <k+1> added to the <n+1>th FEC frame (in other words, regarding the terminal station 3B assigned to the time slot <k+1>), The timing of transmitting frames to the HUB station 2 is adjusted. Specifically, when the scheduled transmission timing of the frame from the terminal station 3B to the HUB station 2 is Tsb, T'sb calculated according to the following formula 4B is the transmission timing of the frame from the terminal station 3B to the HUB station 2. This is the scheduled time after adjusting the transmission timing.
(Math. 4B) T'sb = Tsb + Δtdb

Furthermore, based on the time error Δtdc regarding the time slot <k+2> added to the <n+2>th FEC frame (in other words, regarding the terminal station 3C assigned to the time slot <k+2>), The timing of transmitting frames to the HUB station 2 is adjusted. Specifically, when the scheduled transmission timing of the frame from the terminal station 3C to the HUB station 2 is Tsc, T'sc calculated according to the following formula 4C is the transmission timing of the frame from the terminal station 3C to the HUB station 2. This is the scheduled time after adjusting the transmission timing.
(Math. 4C) T'sc = Tsc + Δtdc

Here, since there is a time lag between the scheduled reception start time of the header H of the FEC frame and the actual reception completion time, all terminal stations 3 use this reference time as the reference time after a certain time lag from the scheduled reception start time. By adjusting the time difference with respect to the time, the transmission timing of frames from each terminal station 3 to the HUB station 2 is adjusted as a result, and collisions between frames (in other words, bursts) at the HUB station 2 are prevented. Ru.

As described above, the transmission timing of frames from each terminal station 3 to the HUB station 2 is adjusted.

Next, processing for holding the frame transmission timing from each terminal station 3 to the HUB station 2 is performed.

Specifically, even after the transmission timing of frames from each terminal station 3 to the HUB station 2 is once adjusted as described above, the HUB station 2 continues to transmit the frames to the terminal stations 3A and 3B as in the example shown in FIG. , 3C, and stores the reception completion time of the header H of the FEC frame (in other words, an uplink burst signal) transmitted from each of the FEC frames (in other words, uplink burst signals) in the storage unit 213, etc., and the time error calculation unit 214 of the control unit 21 calculates the time For each slot, in other words, for each terminal station 3 assigned to the relevant time slot, a time error Δtd, which is the difference between the scheduled reception start time of the header H of the FEC frame and the actual reception completion time, is calculated.

The time error comparison unit 215 of the control unit 21 of the HUB station 2 determines whether the time error Δtd for each time slot (in other words, for each terminal station 3) is greater than or equal to a predetermined time error threshold Tthr, When the time error Δtd is greater than or equal to the time error threshold Tthr, the time error Δtd associated with the time slot that is greater than or equal to the time error threshold Tthr is transmitted to the terminal station 3 assigned to the time slot.

Specifically, for example, to explain using the example shown in FIG. 6, the scheduled reception start time th_k of the header H of the FEC frame of the time slot <k> allocated to the terminal station 3A and the FEC frame <A>. When the time error Δtda (see formula 3A above), which is the difference from the actual reception completion time th_a, is greater than or equal to the time error threshold Tthr, the time error Δtda relates to time slot <k> (or This is added to the <n>th FEC frame and transmitted from the HUB station 2 as a time error (regarding the terminal station 3A assigned to >).

Also, the time that is the difference between the scheduled reception start time th_k+1 of the header H of the FEC frame in the time slot <k+1> assigned to the terminal station 3B and the actual reception completion time th_b of the FEC frame <B> When the error Δtdb (see Equation 3B above) is greater than or equal to the time error threshold Tthr, the time error Δtdb is a time error related to time slot <k+1> (or related to the terminal station 3B assigned to time slot <k+1>) This is added to the <n+1>th FEC frame and transmitted from the HUB station 2.

The time error threshold Tthr is not limited to a specific value, and for example, the space between uplink frames when the HUB station 2 receives frames transmitted from each terminal station 3 (i.e., the space between each time slot). It is set to an appropriate value, taking into account that collisions between frames (in other words, between bursts) can be avoided while minimizing the non-communication time inserted between frames.

The readjustment unit 317 of the control unit 31 of the terminal station 3 adjusts the time slot transmitted from the HUB station 2 and assigned to itself after the time error adjustment unit 316 adjusts the frame transmission timing. If a time error Δtd is added to the FEC frame received at the FEC frame, the time error Δtd is acquired, and the timing of transmitting the frame to the HUB station 2 is adjusted based on the time error Δtd.

Specifically, for example, to explain using the example shown in FIG. 6, at the terminal station 3A, the When a time error Δtda is added to the frame, the transmission timing of the frame from the terminal station 3A to the HUB station 2 is adjusted based on the time error Δtda (see Equation 4A above).

In addition, in the terminal station 3B, if a time error Δtdb is added to the <n+1>th FEC frame received in the time slot <k+1> allocated to the terminal station 3B, the time error Δtdb Based on the error Δtdb, the frame transmission timing from the terminal station 3B to the HUB station 2 is adjusted (see Equation 4B above).

Note that the time error calculation unit 214 of the HUB station 2 and the time error adjustment unit 316 of the terminal station 3 adjust the transmission timing of frames from each terminal station 3 to the HUB station 2 at first. The explanation above assumes that this is done for all (in-use) time slots (in other words, for all communicating terminal stations 3) regardless of the size of the error Δtd, but from the beginning, The process may be performed only when the time error Δtd is greater than or equal to the time error threshold Tthr. In this case, the time error calculation unit 214 of the HUB station 2 does not perform the process of transmitting the time error Δtd to each terminal station 3. Further, the time error adjustment section 316 and the readjustment section 317 of the terminal station 3 are configured as one unit (specifically, it is sufficient to be configured as one having a function equivalent to the readjustment section 317).

In addition, when the frame transmission timing from each terminal station 3 to the HUB station 2 is being maintained, the time error Δtd for each time slot (in other words, for each terminal station 3) is the predetermined maximum error. When it is equal to or greater than the threshold Tmax, or when the time error Δtd for each time slot (in other words, for each terminal station 3) is frequently equal to or greater than the predetermined time error threshold Tthr, the above-mentioned HUB station 2 Synchronization processing of the frequency of the HUB station timer 27 and the frequency of the terminal station timer 37 of each terminal station 3, and adjustment processing of the time of the HUB station timer 27 of the HUB station 2 and the time of the terminal station timer 37 of the terminal station 3 is performed again, and then the process of adjusting the frame transmission timing from each terminal station 3 to the HUB station 2 and the process of holding the frame transmission timing from each terminal station 3 to the HUB station 2 are performed again. Good too.

The maximum error threshold Tmax is not limited to a specific value; for example, the size of the time error Δtd, which corresponds to the criticality at which collisions between frames (in other words, between bursts) occur, is taken into consideration. After that, it is set to an appropriate value.

In addition, before the above-mentioned adjustment process between the time of the HUB station timer 27 of the HUB station 2 and the time of the terminal station timer 37 of each terminal station 3 is performed, the terminal station 3 sends a frame to the HUB station 2 (in other words, When transmitting an uplink burst signal), there is a possibility that it will collide with another terminal station's frame (uplink burst signal). Therefore, as shown in FIG. 7, a spare slot may be provided in addition to the communication slot within one slot period.

In the example shown in FIG. 7, within one slot period, slots 0001 to 1000 are provided as communication slots, and slots 1001 to 1005 are further provided as reserve slots. The number of spare slots is not limited to five in the example shown in FIG. 7, but is appropriately set to an appropriate number, taking into consideration that the transmission efficiency will not be excessively deteriorated.

In the spare slot, for example, before the frequency of the HUB station timer 27 of the HUB station 2 and the frequency of the terminal station timer 37 of each terminal station 3 are synchronized, the terminal station 3 transmits the FEC frame to the HUB station 2. used when sending to. For example, the HUB station 2 sends an instruction to the terminal station 3A to use slot 1002 (in other words, to transmit a frame at the timing of slot 1002), and the terminal station 3A transmits the FEC frame at the timing of slot 1002. Transmit to HUB station 2.

That is, in the wireless communication system 1 in this case, a spare slot is provided in addition to a communication slot within one slot cycle of a time slot conforming to time division multiple access (TDMA), and the timing for transmitting a frame is determined. The terminal station 3 uses a spare slot to transmit a frame to the HUB station 2 before the adjustment process (for example, the process by the frequency synchronization unit 314) is performed.

At this time, if adjacent slots are used, there is a risk of collision between frames (in other words, between bursts), so it is preferable to use a spare slot that is not adjacent to the communication slot. In the example shown in FIG. 7, it is preferable to use slot 1002, which is not adjacent to slot 1000, which is a communication slot, instead of slot 1001, which is adjacent to slot 1000, which is a communication slot, among the spare slots. In addition, if there are two terminal stations 3 that have not yet undergone the process of adjusting the frame transmission timing and use two of the spare slots at the same time, slot 1000 of the communication slots among the spare slots. It is preferable to use slots 1002 that are not adjacent to each other, and slots 1004 that are not adjacent to said slots 1002. This makes it possible to more reliably prevent collisions between frames (in other words, between bursts) at the HUB station 2.

To set and use the spare slot, the HUB station 2 and terminal station 3 perform the above-mentioned timer frequency synchronization processing, timer time adjustment processing, frame transmission timing adjustment processing, and frame transmission timing holding processing. This is not limited to cases where That is, in a wireless communication system in which (some kind of processing) is performed to adjust the timing of transmitting a frame from the terminal station 3 to the HUB station 2, before the processing for adjusting the timing of transmitting the frame is performed, the terminal station 3 Setting and using a spare slot is useful when transmitting a frame to the HUB station 2.

According to the wireless communication system 1 according to the embodiment, since the frequency of the HUB station timer 27 of the HUB station 2 and the frequency of the terminal station timer 37 of each terminal station 3 are synchronized, each terminal station 3 It becomes possible to realize frequency synchronization between the HUB station 2 and the terminal station 3, which is a prerequisite for adjusting the transmission timing of frames from the HUB station 2 to the HUB station 2.

According to the wireless communication system 1 according to the embodiment, since the time of the HUB station timer 27 and the time of the terminal station timer 37 are adjusted, the transmission of frames from each terminal station 3 to the HUB station 2 is It becomes possible to realize the time adjustment between the HUB station 2 and the terminal station 3, which is a prerequisite for timing adjustment.

According to the wireless communication system 1 according to the embodiment, the transmission delay between each terminal station 3 and the HUB station 2 is based on the reception timing at the HUB station 2 of a frame transmitted from each terminal station 3. Since the transmission timing of frames from each terminal station 3 to the HUB station 2 is adjusted, time errors due to propagation delays of each terminal station 3 (in other words, variations in propagation delays of each terminal station 3) are absorbed. / compensation, it becomes possible to transmit frames in accordance with the timing of the time slot assigned to each terminal station 3, and by extension, the space between uplink frames (i.e., each time slot It is possible to improve line usage efficiency and transmission efficiency by reducing the amount of non-communication time inserted between

According to the wireless communication system 1 according to the embodiment, once the transmission timing of frames from each terminal station 3 to the HUB station 2 is adjusted, the difference between the scheduled frame reception time and the actual reception time is determined. Since the frame transmission timing from each terminal station 3 to the HUB station 2 is maintained only when a certain time error Δtd is greater than or equal to the time error threshold Tthr, the transmission timing between the HUB station 2 and each terminal station 3 is This makes it possible to suppress an increase in the amount of data transmission associated with frame transmission timing holding processing during the interval, thereby avoiding a decrease in line usage efficiency and transmission efficiency.

According to the wireless communication system 1 according to the embodiment, when a spare slot is provided in addition to a communication slot within one slot cycle, a frame is transmitted from the terminal station 3 to the HUB station 2. It is possible to prevent collisions between frames (in other words, between bursts) at the HUB station 2 before the timing adjustment process is performed, and for this reason, the space between frames (i.e. between each time slot) can be prevented from colliding with each other (in other words, between bursts). This makes it possible to reduce the amount of non-communication time inserted into the network, which in turn makes it possible to improve line usage efficiency and transmission efficiency.

Although the embodiments of this invention have been described above, the specific configuration is not limited to the above embodiments, and even if there are changes in the design within the scope of the gist of this invention, Included in invention.

For example, in the above embodiment, the frequency synchronization unit 314 of the terminal station 3 synchronizes the frequency of the HUB station timer 27 of the HUB station 2 with the frequency of the terminal station timer 37 of each terminal station 3, the time of the terminal station 3, The adjustment unit 315 adjusts the time of the terminal station timer 37 of each terminal station 3, and the time error calculation unit 214 of the HUB station 2 and the time error adjustment unit 316 of the terminal station 3 adjust the time from each terminal station 3 to the HUB station 2. and frame transmission from each terminal station 3 to the HUB station 2 by the time error calculation unit 214 and time error comparison unit 215 of the HUB station 2 and the readjustment unit 317 of the terminal station 3. Although the timing holding process is performed, each of the four processes described above may be used alone or in combination with other processes as necessary. That is, for example, only the frequency synchronization process described above may be performed, or other time adjustment processes may be performed after the frequency synchronization process is performed, as necessary.

1 Wireless communication system 2 HUB station 21 Control unit 211 Central processing unit 212 Input/output unit 213 Storage unit 214 Time error calculation unit 215 Time error comparison unit 22 Buffer memory 23 Transmission unit 24 Receiving unit 25 Transmission/reception duplexer 26 Antenna 27 HUB station timer 3, 3A, 3B, 3C Terminal station 31 Control section 311 Central processing unit 312 Input/output section 313 Storage section 314 Frequency synchronization section 315 Time adjustment section 316 Time error adjustment section 317 Readjustment section 32 Buffer memory 33 Transmission section 34 Receiving section 35 Transmitter/receiver duplexer 36 Antenna 37 End station timer 4 Communication satellite

Claims (5)

Transmission from the HUB station to each terminal station follows the time division multiplexing method, and transmission from each terminal station to the HUB station uses a frame that conforms to a radio frame format that follows the time division multiple access method. It has a HUB station and a terminal station for wireless communication in the direction,
The terminal station determines the difference between the transmission timing of the beginning of the header of the frame transmitted from the HUB station and the transmission timing of the beginning of the header of the subsequent frame , and the difference in the transmission timing of the header of the frame at the terminal station. The frequency of the HUB station timer of the HUB station and the frequency of the terminal station timer of the terminal station are calculated using the ratio of the difference between the time of the first reception timing and the time of the first reception timing of the header of the subsequent frame. It has a frequency synchronization section that synchronizes the frequency.
A wireless communication system characterized by: The terminal station has a time adjustment unit that adjusts the time of the terminal station timer using the difference between the transmission timing and the reception timing.
The wireless communication system according to claim 1, characterized in that: The HUB station has a time error calculation unit that calculates a time error that is a difference between a scheduled time to receive a frame and an actual reception time for each time slot conforming to time division multiple access,
The terminal station has a time error adjustment unit that adjusts the timing of transmitting frames to the HUB station based on the time error.
The wireless communication system according to claim 1 or 2, characterized in that: The HUB station has a time error comparison unit that determines whether the time error is greater than or equal to a predetermined threshold;
The terminal station has a readjustment unit that adjusts the transmission timing of the frame to the HUB station based on the time error that is equal to or greater than the threshold value.
The wireless communication system according to claim 3, characterized in that: A spare slot is provided in addition to a communication slot within one slot period for a time slot conforming to time division multiple access,
The terminal station transmits a frame to the HUB station using the spare slot before processing by the frequency synchronization unit is performed.
The wireless communication system according to any one of claims 1 to 4.