JP6959580B2 - Wireless communication system, simulcast controller, relay station and communication method - Google Patents

Description

The present invention relates to communication technology, and relates to a simulcast wireless communication system, a simulcast controller, a relay station, and a communication method.

A simulcast wireless communication system is a wireless system in which a plurality of sites transmit at the same frequency to expand the coverage area. To expand the coverage area, it is necessary to synchronize the radio waves transmitted from each site.
For this reason, the system is such that the time of each site is synchronized and simultaneous transmission is possible from each site. For example, time data called a time stamp message can be used to enable simultaneous transmission of each site (US Patent Publication No. 5867488).

U.S. Pat. No. 5,867,488

In US Pat. No. 5,867,488, received data (inbound data) is transferred to a time stamp server via a network. The time stamp server transfers packet data including the outbound transmission start-up time calculated based on the time of the received inbound data to each site via the networm. The site controller of each site starts transmission according to the outbound transmission start-up time. This system can manage the time with a single device (time stamp server), but there is a demerit that the system becomes complicated because it is necessary to provide a time stamp server.

Further, when transmitting by a simulcast system to a terminal device located at a position where signals can be received from a plurality of sites, it is necessary to consider the time difference of radio wave propagation from each site. Simultaneous transmission may cause interference.

The present invention has been made in view of these circumstances, and an object of the present invention is to provide a simulcast wireless communication system, a simulcast controller, a relay station, and a communication method having a simple system configuration that does not require a time stamp server.

In order to solve the above problems, the wireless communication system of a certain aspect of the present invention is a wireless communication system that performs communication by simulcast in which an uplink signal received from a terminal device is transmitted as a downlink signal from a plurality of relay stations. The relay station includes a plurality of terminal devices, a plurality of relay stations, and a simulcast controller connected to all of the relay stations by a network, and the relay station supplies time-synchronized pulse data every second. The first is provided with a server and a symbol counter that counts the symbol period used in the communication based on the pulse data, and the relay station is a count value of the symbol counter at the timing when synchronization with the uplink signal is established. The second uplink signal including the count value is transferred to the simulcast controller, and the simulcast controller is at a timing when the relay station transmits a downlink signal addressed to the terminal device based on the first count value. The count value is calculated, and the downlink signal for transmitting the signal to the terminal device by the relay station including the second count value is transmitted to all the relay stations, and the relay station performs the second count. It is characterized in that transmission of the downlink signal is started based on the value.

Another aspect of the present invention is a relay station. It is a relay station of a wireless communication system that performs wireless communication by a simulcast method that transmits an uplink signal received from a terminal device as a downlink signal from a plurality of relay stations, and the relay station is a time-synchronized pulse every second. A time server that supplies data, a symbol counter that counts the symbol period used in the communication based on the pulse data, a wireless communication unit that wirelessly communicates with the terminal device, and synchronization with the uplink signal have been established. The uplink signal is transferred to the simulcast controller including the first count value which is the count value of the symbol counter of the timing, and the relay station is sent from the simulcast controller to the terminal device based on the first count value. The network communication unit that receives the downlink signal for the relay station to transmit to the terminal device, including the second count value calculated as the timing for transmitting the downlink signal, and the wireless communication unit are the second. It is characterized in that transmission of the downlink signal is started based on the count value.

Another aspect of the present invention is a communication method. This is a communication method in which multiple relay stations relay communication between terminal devices by the simulcast method. The symbol period used in communication by multiple relay stations in the previous term based on the timing of pulse data every second synchronized with the time. A step in which one of the relay stations receives an uplink signal from the terminal device, and a step in which a first count value, which is a count value of a symbol cycle at a timing synchronized with the uplink signal, is determined. , The step of transferring the uplink signal to the simulcast controller including the first count value, and the timing of the downlink signal transmitted by the relay station to the terminal device based on the first count value included in the uplink signal. A step of calculating a second count value, which is a count value of the symbol period, a step of the simulcast controller transferring the downlink signal to the plurality of relay stations including the second count value, and the relay. It is characterized in that the station includes a step of starting transmission of a downlink signal at a timing based on the second count value.

It should be noted that any combination of the above components and the conversion of the expression of the present invention between methods, devices, systems, recording media, computer programs and the like are also effective as aspects of the present invention.

According to the present invention, it is possible to provide a simulcast wireless communication system, a simulcast controller, a relay station, and a communication method having a simple system configuration.

It is a figure which shows the structure of the wireless communication system of the Example of this invention. It is a block diagram which shows the structure of the relay station 20 of FIG. It is a figure which shows the relationship of the count value of a symbol counter. It is a figure which shows the message sequence between the message of DSP and Host with respect to the received data. It is a figure which shows the relationship of the timing which the received data is transmitted from a relay station. It is a figure which shows the message sequence between DSP and Host of a repeater 24 which received a frame synchronization request. It is an area map when the cell radii of a plurality of relay stations 20 are different. It is a figure which shows the state in which the interference between symbols occurs. It is a figure when the offset time is set in the symbol count of a relay station 20.

FIG. 1 shows the configuration of the wireless communication system 100 according to the embodiment of the present invention. The wireless communication system 100 includes a plurality of terminal devices 10 (10A, 10B, 10C), a plurality of relay stations 20 (20A, 20B, 20C), and a simulcast controller 30. The number of terminal devices 10 is arbitrary, and the number of relay stations 20 is also arbitrary.

The terminal device 10 is a half-duplex wireless communication device. The wireless digital protocol of the wireless communication device will be described by taking the NXDN Very Now system as an example.

FIG. 2 shows the configuration of the relay station 20. The relay station 20 includes a repeater (repeater 24) compatible with the above-mentioned NXDN system and a GPS reference machine (time server 22) that synchronizes time based on a signal from a GPS (Global Positioning System) satellite or the like. The repeater 24 includes a symbol counter 242, a Host (control unit 243), a DSP (signal processing unit 244), a wireless communication unit 245, and an IP network communication unit 246.

The simulcast controller 30 is connected to the plurality of relay stations 20 via an IP network.

Returning to FIG. 1, the flow of communication signals by the simulcast method is shown. The arrows a to d in the figure indicate the direction of communication. Here, a case where the terminal device 10B and the terminal device 10C receive the signal transmitted from the terminal device 10A by using the simulcast method of the present invention will be described.
a: The signal (uplink signal) transmitted from the terminal device 10A is received by the relay station 20A.
b: The uplink signal received by the relay station 20A is sent to the simulcast controller 30 via the IP network.
c: The simulcast controller 30 generates a downlink signal for synchronously transmitting the uplink signal at each relay station 20, and transfers the uplink signal to each relay station 20.
d: Each relay station 20 transmits based on the transmission timing included in the downlink signal transferred from the simulcast controller 30, and the terminal device 10 receives the transmitted downlink signal when it can be received.

Next, the operation at the time of starting the relay station 20 will be described with reference to FIG. The time server 22 of the relay station 20 is in a time / frequency synchronized state with GPS based on the GPS signal received by the GPS antenna 221 and outputs a 1 pps signal and a 10 MHz reference signal to the repeater 24. The 1 pps signal is a pulse signal synchronized with each second of time. When the repeater 24 is started, the control unit 243 in the repeater 24 queries the time server 22 for the time. The time server 22 notifies the control unit 243 of the repeater 24 in response to the inquiry, and the control unit 243 informs the signal processing unit 244 of the repeater 24 that the 1 pps signal is an odd number of seconds or an even number of seconds from that time. Notify if it is.

FIG. 3 shows a symbol count (Simul Symbol Count) and a frame count (Simul Frame Count) based on the time number (Time-Pulse Number) of the 1 pps signal notified from the time server 22 whether it is an odd number of seconds or an even number of seconds. ) Is shown. Since the wireless digital protocol is taken as an example of the NXDN system, it is 4800 symbols / sec, 12.5 frames / sec, and the time divisible by the number of frames is a 2-second cycle. In FIG. 3, the symbol count values are 1 to 4800 symbols for odd-numbered seconds and 4801 to 9600 symbols for even-numbered seconds. In FIG. 3, the frame number, which is the value of the frame count, has 1 at the start of odd-numbered seconds and 25 at the end of even-numbered seconds. In the case of other wireless digital protocols, the time corresponding to the symbol rate or frame rate of the wireless digital protocol may be counted. If 1 second is divisible by the number of frames, it is not necessary to distinguish between odd-numbered seconds and even-numbered seconds.

The signal processing unit 244 sets each count value of the counter having the configuration shown in FIG. 3 in the symbol counter 242 and starts counting. In FIG. 3, the symbol counter 242 sets the rising edge of the 1 pps signal for odd seconds as the start of the symbol count and the frame count. When it is necessary to provide a time difference (delay) in each relay station 20 to be described later, the start of the symbol count and the frame number count may be offset from the rise of 1 pps when the relay station 20 is started.

Next, processing for a signal (uplink signal) transmitted from the terminal device 10 in the relay station 20 will be described. The repeater 24 of the relay station 20 receives the signal transmitted by the terminal device 10 by using the antenna 241. The wireless communication unit 245 of the repeater 24 inputs the signal received by the antenna 241 to the signal processing unit 244. The signal processing unit 244 performs symbol synchronization and frame synchronization with respect to the received signal.

FIG. 4 shows a message sequence between the messages of the signal processing unit 244 (DSP) and the control unit 243 (Host) for the received signal (RX) received by the relay station 20 in the signal transmitted from the terminal device 10. The "P" at the beginning of the received signal is a preword "P" that is prefixed to the synchronization word "FSW" only at the start of communication in order to facilitate the detection of the start of reception. The preword "P" facilitates the establishment of symbol synchronization. The preword "P" also facilitates frame synchronization by detecting the synchronization word "FSW" after symbol synchronization. The signal processing unit 244 receives the synchronization word "FSW", and when synchronization is detected, outputs a frame detection notification (S301) to the control unit 243. This notification signal includes the symbol count value and the frame number of FIG.

Further, the signal processing unit 244 demodulates the received signal and outputs the received information notification (S310a-S310e) to the control unit 243 according to each logical channel of the demodulated received data. These notification signals also include the symbol count value of the Simul Symul Count and the frame number of the Simul Frame Count in FIG. Similarly, the received voice data notification (S320a-S320b) includes the symbol count value of the Simul Symul Count and the frame number of the Simul Frame Count in FIG. If the operation of the simulcast can be managed only by the symbol count value, only the symbol count value may be notified.

The control unit 243 that has received the frame detection notification signal outputs the received data including various notification signals to the simulcast controller 30 via the IP network.

FIG. 5 shows the timing relationship for transmitting the received data from the relay station 20. The simulcast controller 30 calculates the timing (downlink start timing) for transmitting the downlink signal from the relay station 20 based on the symbol count value included in the frame detection notification signal output from the relay station 20. FIG. 5 shows the case where the frame number at the time of frame synchronization detection of the received signal is “1” and the symbol count value is “1” as “1-1”. In this embodiment, it is the result of calculation so that the downlink start timing is set after 3.5 frames of the frame, and the simulcast controller 30 is "4-1345" (frame number) after 3.5 frames, which is the downlink start timing. (4), symbol count value “1345”) is transferred to all relay stations 20 of the system via the IP network. As described above, if the operation can be managed only by the symbol count value, the downlink start timing may be set only by the symbol count value. The control unit 243 of the repeater 24 that has received the downlink start timing notifies the signal processing unit 244 of the downlink start timing by a frame synchronization request.

FIG. 6 shows a message sequence between the control unit 244 (DSP) and the control unit 243 (Host) of the repeater 24 that received the frame synchronization request. Upon receiving the frame synchronization request, the signal processing unit 244 notifies the frame synchronization completion one frame before the transmission start timing, that is, at the timing of the frame number “3” and the symbol count “961” which are “3-961” shown in FIG. The signal is output to the control unit 243. Although the frame synchronization completion notification signal is set to one frame before in the embodiment, it may be at any timing on the assumption that there is no problem in synchronization.

Return to FIG. The control unit 243 to which the frame synchronization completion notification signal is input outputs various setting signals for starting transmission by downlink the transmission start setting to the signal processing unit 244. The signal processing unit 244 outputs a transmission power switching, transmission data setting timing notification signal, and the like in accordance with the transmission start timing notified by the frame synchronization request. The control unit 243 that has received the transmission data setting timing notification signal sets the transmission data setting to the signal processing unit 244. This is the data to be transmitted in the downlink (downlink data). The signal processing unit 244 starts the transmission of the downlink signal by matching the downlink data received in the transmission data setting with the count value of the frame synchronization request. By managing these processes with a counter, it is possible to realize simultaneous transmission of downlink signals from each relay station (each site).

The symbol counter 242 continues to count repeatedly unless the repeater 24 restarts and inquires about the time to the time server 10. The communication system of the present invention grasps the upstream reception timing based on the count value of the symbol counter, calculates the downlink transmission timing, and starts the downlink transmission according to the calculated count value. Further, the system does not need to make a time inquiry to the time server 10 unless the repeater 24 is restarted. Therefore, it is possible to provide a simulcast wireless communication system having a simple system configuration.

In the above-mentioned simulcast wireless communication system, when the influence of radio wave propagation from each site is small, even if the terminal device receives signals transmitted from a plurality of sites, in order to prevent interference between the sites. It is an effective means.

The case where the influence of radio wave propagation from each site is small is, for example, the case where the transmission power output from each site is relatively low and the radio wave propagation distance is short. When the radio wave propagation distance is short, even if the terminal device is in a position where signals from a plurality of sites can be received, the interference due to the delay in radio wave propagation from each site can be almost ignored. Even when the transmission power from each site is relatively high, if the transmission power between each site is the same, the distance of radio wave propagation from each site is the same, and it can be said that there is little interference due to delay. ..

The case where the influence of radio wave propagation from each site is large is the case where the transmission power output from each site is relatively high, the distance of radio wave propagation is long (for example, several tens of km), and the transmission power between sites is different. That is, the distance of radio wave propagation differs between sites.

In the commercial radio, the transmission power of the wireless communication unit 245 of the relay station 20 provided in each site is relatively high (for example, 50 W). Therefore, the distance (hereinafter referred to as the cell radius) at which the terminal device 10 can secure a practical reception level for the signal transmitted by the relay station 20 is several tens of km, and when signals from a plurality of sites are received. Can be the distance to be interfered with.

If the transmission outputs of adjacent sites are the same, it can be said that there is no effect of radio wave propagation even if the terminal device is in a position where it can receive the signals of both adjacent sites.
It is ideal to arrange each relay station with the same cell radius, but it is often difficult to arrange the relay stations ideally (cell arrangement) due to the influence of topography and the like. In addition, as the city develops, it is possible to add sites that will be small areas with small cell radii adjacent to areas with large cell radii. That is, the relay station is arranged so as to cover the required area, and its transmission power is also set to cover the required area.

FIG. 7 shows an example of an area map when the cell radii of the relay stations are different. In FIG. 7, two relay stations 20A and 20B are arranged, and the area of the relay station 20A is designated as area A1 and the area of relay station 20B is designated as area A2. The terminal device 10A is located in an area where the area A1 and the area A2 overlap.
Since the relay station 20 is arranged so as to cover the required area and its transmission power is also set to cover the required area, in the case of FIG. 7, the area A1 covered by the relay station 20A is relatively relatively large. The area A2, which is a wide area and is covered by the relay station 20B, is narrower than the area A1.
For example, the cell radius R1 of the area A1 is 20 km, and the cell radius R2 of the area A2 is 10 km. Since the electric field strength is inversely proportional to the square of the distance, the propagation distance is 0.5 times, and in order to obtain the same electric field strength, the transmission output is 0.25 times. The transmission output for the relay station 20B to cover the area A2 is 25% of that of the relay station 20A.
When the cell radii of the adjacent relay stations 20 are different, that is, when the transmission power of the radio communication unit 245 of the adjacent relay stations 20 is different, the terminal device 10A is in a position where the signals from both relay stations can be received. If so, the electric field strengths received from both are theoretically the same, but the radio waves from the distant relay station are delayed, causing interference.
Since radio waves propagate at the speed of light, assuming a speed of light of 300,000 km / S, it takes about 66.6 μS to propagate a distance of 20 km, and about 33.3 μS to propagate a distance of 10 km. And. Therefore, when the terminal device 10 is in a position where signals from both the relay station 20A and the relay station 20B can be received, the terminal device 10 receives the signal from the relay station 20A and the signal from the relay station 20B. On the other hand, the signal is received with a delay of 33.3 uS, which is the difference in radio wave propagation. Even if the same signal has the same electric field strength, if there is a difference in radio wave propagation between the two signals, they will interfere and the quality of the received signal will deteriorate.
FIG. 8 shows the waveform when the terminal device 10A receives and demodulates the signals simultaneously transmitted from the relay stations 20A and 20B, respectively. This is an example of a waveform when the modulation method used for communication is 4-value FSK and the terminal device 10A demodulates it by FM. It can be said that the timing that can be detected as a four-value symbol value (-3, -1, +1, +3) from the demodulated waveform is the symbol timing. Assuming that the symbol rate is 4800 symbols / sec, the time between one symbol is about 208 μS. The demodulated waveform interferes with the time between one symbol (208 μS) due to the time difference (33.3 μS) from the two base stations to the arrival of the signal due to the propagation delay, and the symbol timing is not determined. Further, the interference has a delay time (33.3 μS) of 10% or more with respect to the time between one symbol (208 μS), which is not a negligible value and is in a state where intersymbol interference occurs. Such intersymbol interference is an unfavorable phenomenon in which the preceding and following codes act as a kind of noise, and the quality of the received signal is deteriorated, so that the reliability of communication is lowered.

Therefore, when installing a new relay station, the propagation time in the area bordering the surrounding area is measured, and when the relay station is started, the symbol count value and frame value are counted from the rising edge of 1 pps. The offset time may be set based on the above and the counting may be started. Even in an environment where the terminal device receives signals from multiple relay stations by setting the offset time, what is the radio wave delay from each relay station? ?? ?? ?? ?? ??
FIG. 9 shows an example in which the relay station 20B of FIG. 7 starts by setting an offset time for the symbol count. In the case of the embodiment, since the start of the odd-numbered seconds is used as the reference, the symbol count cannot be started before the start of the first odd-numbered seconds. Offset forward and start symbol counting. After starting the repeater 24, the control unit 243 inquires the time server 22 about the time. Based on the time obtained from the time server 22, the symbol count is started after the offset time T1 elapses from the rise of odd seconds. Similarly, the counting of the frame value also starts with the offset time T1. Once the relay station is installed, it cannot be easily moved, so it is not necessary to change this offset time unless the transmission main force of the relay station is changed.
As a result, the wireless communication system of the present invention can set the transmission timing in consideration of the time difference of radio wave propagation, and the simulcast controller does not need to consider the offset time of each relay station, so that it is simple. It is possible to provide a wireless communication system by simulcasting the system configuration.

As described above, the larger the transmission output set in the wireless communication unit 245 of the relay station 20, the longer the propagation distance. In an environment where the propagation distance is uniquely determined by the transmission output, the offset time of each adjacent relay station may be set based on the relationship between the propagation distance and the transmission output.

FIG. 10 shows the configuration of the simulcast controller 30.

Further, although the present invention describes the wireless digital protocol as the case of NXDN Very Now, other wireless digital protocols may be used.

100 wireless communication system 10 terminal device 10A, 10B, 10C
20 relay stations 20A, 20B, 20C
22 Time server 221 GPS antenna 24 Repeater 241 Antenna 242 Symbol counter 243 Control unit 244 Signal processing unit 245 Wireless communication unit 246 IP network communication unit 30 Simulcast controller

Claims (6)

A wireless communication system that communicates by a simulcast method in which an uplink signal received from a terminal device is transmitted as a downlink signal from a plurality of relay stations.
With multiple terminal devices,
With multiple relay stations
A simulcast controller connected to all of the relay stations via a network,
With
The relay station
A time server that supplies time-synchronized pulse data every second,
A symbol counter for counting the symbol period used in the communication based on the pulse data is provided.
The relay station transfers the uplink signal to the simulcast controller, including a first count value which is a count value of the symbol counter at the timing when synchronization is established with the uplink signal.
The simulcast controller
Based on the first count value, the second count value, which is the timing at which the relay station transmits a downlink signal addressed to the terminal device, is calculated, and the relay station includes the second count value and signals to the terminal device. The downlink signal for transmitting is transmitted to all the relay stations,
The relay station is a wireless communication system that starts transmitting the downlink signal based on the second count value. A simulcast controller that controls transmission of an uplink signal transmitted from a terminal device and received by a relay station as a downlink signal from a plurality of relay stations including the relay station.
A network interface that receives the transmitted uplink signal including the count value at the timing when the uplink synchronization is established, which is the count value of the symbol counter that counts based on the time-synchronized pulse data of each second provided in the relay station. When,
A transmission signal generation unit that calculates the symbol timing for transmitting the downlink signal based on the count value and generates a downlink signal including the calculated symbol value information.
With
The network interface transmits a downlink signal including the calculated symbol value information to the plurality of relay stations.
A simulcast controller that features that. A relay station of a wireless communication system that performs wireless communication by a simulcast method in which an uplink signal received from a terminal device is transmitted as a downlink signal from a plurality of relay stations.
The relay station
A time server that supplies time-synchronized pulse data every second,
A symbol counter that counts the symbol period used in the communication based on the pulse data, and
A wireless communication unit that performs wireless communication with the terminal device,
The uplink signal is transferred to the simulcast controller including the first count value which is the count value of the symbol counter at the timing when synchronization with the uplink signal is established, and the simulcast controller is based on the first count value. The network communication unit that receives the downlink signal for the relay station to transmit to the terminal device, including the second count value calculated as the timing for the relay station to transmit the downlink signal to the terminal device.
The wireless communication unit is a relay station characterized by starting transmission of the downlink signal based on the second count value. The relay station according to claim 1, wherein the symbol counter determines an offset time determined based on the timing of the pulse data and starts counting. The offset time is a time defined to reduce interference when a terminal device located in an area capable of receiving downlink signals from the plurality of relay stations receives downlink signals from the plurality of relay stations. The relay station according to claim 4 , wherein the relay station is characterized in that. This is a communication method in which multiple relay stations relay communication between terminal devices by the simulcast method.
A step in which multiple relay stations count the symbol period used in communication based on the timing of pulse data every second synchronized in time.
When one of the relay stations receives the uplink signal from the terminal device,
The step of determining the first count value, which is the count value of the symbol cycle at the timing synchronized with the uplink signal, and
The step of transferring the uplink signal to the simulcast controller including the first count value, and
Based on the first count value included in the uplink signal, a step of calculating a second count value which is a count value of a symbol cycle which is a timing of a downlink signal transmitted by the relay station to a terminal device, and a step of calculating the second count value.
A step in which the simulcast controller transfers the downlink signal to the plurality of relay stations, including the second count value.
A step in which the relay station starts transmitting a downlink signal at a timing based on the second count value, and
Communication methods including.

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