JP2018166293A - Wireless communication system, mobile station and base station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid reception interruption due to beat interference between base stations in a broadcast type wireless communication system using quadrature FSK (Frequency Shift Keying) modulation. SOLUTION: A wireless communication device 102a of a first base station 101a performs quaternary FSK modulation based on a first mapping, and a wireless communication device 102b of a second base station 101b has a quaternary value based on a second mapping different from the first mapping. FSK modulation is performed, and the wireless communication devices of the first base station and the second base station each transmit the broadcast communication data to the mobile station 111 at the timing when the network timing signal from the central control device 120 is delayed by the delay adjustment circuit 201. The delay amount of the delay adjustment circuit of the first base station and the second base station for transmission is defined so that the transmission timing of the first base station and the transmission timing of the second base station are synchronized with each other. [Selection diagram] Fig. 2

Description

  The present invention relates to a radio communication system, and more particularly to a radio communication system that avoids interference between signals from adjacent base stations, and a mobile station and a base station used therefor.

  In a train radio system, a plurality of base stations using the same frequency are arranged along a track, and a radio area is constructed. A radio communication device (referred to as an “on-board station”) mounted on each of a plurality of trains moving on a track receives a signal from a base station in a broadcast manner. In the train radio system, the radio radio wave arrival ranges from adjacent base stations are arranged so as to overlap each other. This is to allow radio waves from the base station to be received wherever the onboard station is on the track. However, if it is arranged so that radio waves from a plurality of base stations can be received satisfactorily, an area where radio waves from the plurality of base stations interfere with each other occurs. In a place where such interference occurs, there arises a problem that data received by the on-board station cannot be reproduced accurately, that is, a problem called identical wave interference or beat interference.

  Patent Document 1 relates to a train radio system, and in each of a plurality of base stations, from a common data sequence to be transmitted using a space-time block code (STBC) or a differential space-time block code (DSTBC). A plurality of data strings orthogonal to each other are generated. The base station assigns a directional antenna to each data stream so that a mobile station located in the middle of adjacent base stations receives a transmission wave of a different coded stream, thereby preventing interference. Even if it occurs, the original transmission data series can be reproduced.

JP, 2006-34147, A

  In Patent Literature 1, interference is prevented by applying a special encoding method for generating a plurality of data sequences orthogonal to each other in a broadcast radio system that transmits signals from a plurality of base stations using a single frequency. I am trying.

  In contrast, in such a wireless communication system, it is considered to apply four-value FSK (Frequency Shift Keying) modulation. Beat interference is a phenomenon in which identical modulated waves of the same frequency transmitted from two adjacent base stations that are indistinguishable are combined with each other and cancel each other out, so that the mobile station cannot receive.

  On the other hand, if the modulated waves transmitted from two adjacent base stations are different, that is, the modulated wave transmitted from one base station is the frequency f1, and the modulated wave transmitted from the other base station is the frequency f2. If so, the respective frequency components can be separated from the combined radio signal from the two base stations and demodulated. However, due to circumstances such as effective use of frequencies and restrictions on allocation, a system in which the frequency of modulated waves from adjacent base stations is the same is often constructed, and the problem of beat interference cannot be avoided.

  A plurality of base stations including a first base station and a second base station adjacent to each other, and a central control device connected to the plurality of base stations, each of the plurality of base stations from the central control device The wireless communication apparatus has a four-value FSK modulation and transmits the communication data to the mobile station. The wireless communication apparatus of the first base station performs four-value FSK modulation based on the first mapping, and the wireless communication apparatus of the second base station Performs quaternary FSK modulation based on a second mapping different from the first mapping, and the wireless communication devices of the first base station and the second base station respectively transmit communication data to the mobile station.

  In a wireless communication system using quaternary FSK (Frequency Shift Keying) modulation, reception interruption due to beat interference between base stations can be avoided.

It is a system outline figure of a train radio system. It is a figure explaining the system which avoids interference between adjacent base stations. It is a functional block diagram of a base station. It is a figure explaining the method of carrying out transmission synchronization between base stations. It is a functional block diagram of an on-board station. It is an example of the frequency allocation in A mapping and B mapping. This is a combination of frequencies when the on-board station receives signals from two base stations.

  FIG. 1 shows a schematic diagram of a train radio system according to an embodiment. The central controller 120 is connected to a plurality of base stations 101 (represented here as a base station A 101a and a base station B 101b) by a transmission medium 140 such as an optical fiber. A wireless communication device 102 is mounted on the base station 101. Further, an on-board station 111 is mounted on the train 110, and a wireless communication device 112 is mounted on the on-board station 111. Thereby, the on-board station 111 performs wireless communication with the base station 101. The downlink 141 is a downlink from the base station 101 to the onboard station 111, and its radio (carrier) frequency is F1. The uplink 142 is an uplink from the onboard station 111 to the base station 101, and its radio (carrier) frequency is F2.

  As a modulation method of the wireless communication apparatuses 102 and 112, four-value FSK (Frequency Shift Keying) is applied. The 4-value FSK is a method of transmitting 2-bit data for one symbol, and data “00”, “01”, “10”, and “11” are assigned to four frequency shifts, respectively.

  The central controller 120 transmits data to be transmitted to the onboard station 111 to the base station 101 via the transmission medium 140. Here, the data is an audio data signal from the communication console 130 or other digital data signal. A control signal for communication between the base station 101 and the on-board station 111 is also transmitted from the central control device 120 to the base station 101 via the transmission medium 140.

  In the train radio system, the transmission (radio transmission) timing from the onboard station 111 is controlled from the base station 101 side, and a plurality of onboard stations do not transmit at the same timing. For this reason, signals from a plurality of on-board stations do not interfere with each other on the uplink 142. On the other hand, the plurality of base stations 101 arranged so that the wireless radio wave coverages overlap each other broadcasts the data signal transmitted from the central controller 120 to the on-board station 111. The present embodiment is configured to avoid that the on-board station 111 cannot receive the downlink 141a from the base station A 101a and the downlink 141b from the base station B 101b due to interference.

  A method for avoiding interference between adjacent base stations in this embodiment will be described with reference to FIG. Base stations are arranged linearly along the track 200. Therefore, the base stations that can be received by the on-board station 111 on the track are only from two adjacent base stations. In this embodiment, adjacent base stations differ in data assigned to 4 frequency shifts in 4-level FSK (this is called “mapping”). In the example of FIG. 2, the base station A 101a and the base station C 101c apply A mapping, and the base station B 101b and the base station D 101d apply B mapping. In addition, in order to accurately synchronize the transmission timing (radio transmission) of each base station to the onboard station, a network clock is supplied from the central controller 120 to each base station, and a delay adjustment circuit 201 is provided in each base station. It has been.

  An onboard station existing between the base station A and the base station B will be described as an example. As shown in FIG. 2, the adjacent base station A and base station B transmit signals to the on-board station in synchronization. Since the adjacent base stations use different mappings and the transmission from the base station to the onboard station is broadcast communication, the frequency of the transmission signal from the base station A (here, f1) and the base station The frequency of the transmission signal from B (here, f2) is always different. Further, the received signal strength at which the signal from the base station is received by the on-board station becomes smaller as the distance from the base station increases.

  In the on-board station 111a located at the point X from the base station A, the signal of the frequency f1 is received with a large received signal strength, and the signal of the frequency f2 is not received or is received as compared with the signal of the frequency f1. Much weaker. In such a case, it is only necessary to receive a signal of frequency f1 and determine whether this signal is modulated by A mapping or B mapping. On the other hand, at the onboard station 111b located at a point Y near the middle between the base station A and the base station B, the signal of the frequency f1 and the signal of the frequency f2 are received with substantially the same received signal strength. In this case, both the signal of the frequency f1 and the signal of the frequency f2 are received, and the data corresponding to the combination is demodulated using the fact that it is uniquely determined.

  FIG. 3 shows a functional block diagram of the base station 101. In addition, it is a block diagram only of the main functions relevant to a present Example, and others are abbreviate | omitted. The base station 101 receives a voice signal, a data signal, a network clock signal, and a network timing signal from the central controller 120 via the transmission medium 140. These signals are input to the input terminals 321 to 324, respectively. In the base station 101, a clock signal synchronized with the network clock signal is distributed to the radio communication apparatus 102 and the delay adjustment circuit 201 which are internal circuits of the base station, and these circuits operate in synchronization with the clock signal. The clock signal inside the base station may be used by regenerating and amplifying the received network clock, or by providing a highly stable crystal in the base station 101 and appropriately multiplying the oscillation signal generated by the highly stable crystal. The clock signal may be distributed to the internal circuit in synchronization with the network clock. Since it is well known that generation and distribution of such a clock signal can be realized by a PLL (Phase Locked Loop) circuit or a DLL (Delay Locked Loop) circuit, detailed description thereof is omitted here.

  First, the transmission function will be described. The input audio signal is converted from an analog signal to a digital signal in the audio interface unit 301. In order to compress the wide dynamic range of the audio signal, digital conversion should be performed using the μ-law algorithm. The audio compression unit 302 compresses and encodes the digitized audio signal. The encoding / decoding unit 304 performs error correction encoding and further interleaving on the audio data signal output from the audio compression unit or the data signal from the central control unit 120 to construct a radio frame. With respect to digital data constituting a radio frame arranged in a serial bit arrangement, data “00”, “01”, “10”, and “11” are predetermined by the four-value FSK processing unit 306 or the four-value FSK processing unit 307. Of frequency data. A VCO (Voltage-controlled Oscillator) 309 generates intermediate frequency band transmission data in accordance with frequency data attached to digital data constituting a radio frame. Specifically, when the VCO performs voltage / frequency conversion, intermediate frequency band transmission data whose frequency changes according to the data series is generated. The high frequency circuit 310 amplifies the high frequency by adding the radio frequency band (F1) signal to the input intermediate frequency band transmission data, and outputs it to the antenna 311. The high frequency circuit 310 has a power amplifier for amplifying radio frequency band transmission data. In the present embodiment, since it is FSK modulation, a class C amplifier with good amplification efficiency can be used. The control unit 300 performs predetermined control on the functional blocks of the wireless communication apparatus 102.

  As shown in FIG. 2, in this embodiment, the base station performs 4-level FSK modulation using A mapping or B mapping. For this reason, a 4-level FSK processing unit 306 that performs 4-level FSK modulation / demodulation based on A mapping and a 4-level FSK processing unit 307 that performs 4-level FSK modulation / demodulation based on B mapping are provided. Selection / distribution units 305 and 308 Thus, switching of signal input / output can be set. Switching of signal input / output is performed by the control unit 300. When the base station 101 is installed, it is fixed whether A mapping or B mapping is used for modulation of transmission data of the base station. The modulation / demodulation unit 312 includes the selection / distribution units 305 and 308, the four-value FSK processing units 306 and 307, and the VCO 309.

In addition, transmission from the base station is performed in synchronization with a network timing signal from the central controller 120 by a plurality of base stations connected to the central controller 120. This will be described with reference to FIG. 4 shows a clock signal waveform 401 (common to base stations A and B), a network timing signal waveform 402 received by the base station A, a transmission timing waveform 403 transmitted by the base station A, and a network received by the base station B. A timing signal waveform 404 and a transmission timing waveform 405 transmitted from the base station B are shown. A network timing signal, which is a signal for controlling the transmission timing of the base station from the central controller 120, is received at each base station due to a difference in propagation distance from the central controller 120 to each base station. There is a phase difference in timing. For this reason, the base station is provided with a delay adjustment circuit 201 so as to remove this phase difference and to transmit the downlink signal in synchronization with each base station. That is, the delay adjustment circuit 201 of the base station A causes the delay time D _A delay network timing signal received, the delay adjustment circuit 201 of the base station B by the delay time D _B delays the network timing signal received, the base station The transmission timing of A and the transmission timing of the base station B can be synchronized. In each base station, the delay amount for delaying the network timing signal may be set by measuring the delay amount of each base station of the network timing signal at the stage where the base station is installed.

  Next, the reception function will be described. The radio frequency band (F2) signal received by the antenna 311 is down-converted by the high frequency circuit 310 into an intermediate frequency band received signal. In the modulation / demodulation unit 312, the VCO 309 performs frequency / voltage conversion on the received signal in the intermediate frequency band, and the quaternary FSK processing unit 306 or the quaternary FSK processing unit 307 detects the frequency, and data “00” “01” “ By assigning to “10” and “11”, the radio frame is converted into a serial bit array. Received data can be obtained by inversely transforming (deinterleaving and error decoding) the radio frame having the serial bit arrangement in the encoding / decoding unit 304. When the received data is audio data, the audio decompression unit 303 decodes the received data, and the audio interface unit 301 converts it into an analog audio signal.

  Since the onboard station does not transmit simultaneously, it is determined in advance in the train radio system whether A mapping or B mapping is used when the onboard station performs four-value FSK modulation on the transmission signal. For this reason, the received signal is input by the selection / distribution units 305 and 308 so that the received signal is input to the 4-level FSK processing unit 306 or the 4-level FSK processing unit 307 corresponding to the mapping used by the onboard station. Output switching can be set.

  FIG. 5 shows a functional block diagram of the on-board station 111. Signal processing for transmission / reception between the base station radio communication apparatus 102 and the on-board station radio communication apparatus 112 is equivalent, and the same functional blocks are denoted by the same reference numerals as those in FIG. The difference from the base station in terms of functions is that, unlike the base station, it is not necessary to synchronize with the control signal from the central controller, so there is no related functional block, and there is no base station even in the interference area between the two base stations. This is the point that a control unit 500 that performs inherent control for accurately receiving a signal from a station is provided.

  Transmission from the on-board station 111 is performed by performing four-level FSK modulation at a timing designated by the base station and by mapping predetermined in the train radio system. The control unit 500 sets the switching of the selection / distribution units 305 and 308 so that the transmission signal is input to the 4-level FSK processing unit 306 or the 4-level FSK processing unit 307 corresponding to the predetermined mapping.

  The reception of signals from the base station in the onboard station 111 will be described. First, the case where the on-board station 111 is located at the point X shown in FIG. 2 will be described. In this case, in the on-board station, only the signal from the base station A having a strong received signal strength is subjected to frequency / voltage conversion by the VCO 309 and is sent to the selection / distribution unit 308. At this stage, the onboard station does not know whether this signal is modulated by A mapping or B mapping, so that the demodulated received signal is processed by 4-level FSK processing unit 306 and 4-level FSK processing. It is input to both of the unit 307. In order to determine at an early stage which mapping the received signal has been modulated, modulation information about whether the radio frame has been modulated by A mapping or B mapping has been stored in the header portion of the radio frame. It is desirable to include it. When the control unit 500 decodes the header part and determines whether the data is modulated by either mapping, the received data is input to either the corresponding 4-level FSK processing unit 306 or 4-level FSK processing unit 307. The selection / distribution units 305 and 308 are switched.

  Next, the case where the on-board station 111 is located at the point Y shown in FIG. 2 will be described. FIG. 6 shows an example of A mapping 61 and B mapping 62. Assume that f1 to f4 are used as the frequencies of the four-value FSK mapping. As the frequency of quaternary FSK mapping, for example, according to the mapping specified in ARIB STD-T102, the frequency deviation of f1 is +990 Hz, the frequency deviation of f2 is +330 Hz, and the frequency deviation of f3 is − The frequency is set so that the frequency deviation of 330 Hz and f4 is −990 Hz. When the mapping as shown in FIG. 6 is adopted, the on-board station located at the point Y receives signals of two frequencies, and the two base stations transmit the same signal synchronously. The combination of frequency signals received by the upper station is limited to (f1, f4), (f2, f3), (f1, f3), (f2, f4) as shown in FIG. Even if the two base stations transmit the same signal in synchronization, if the distance between the onboard station and each base station is different, a phase difference occurs in the signal when it is received at the onboard station. However, signals of two frequencies are received simultaneously only when the onboard station is in the vicinity of the middle between the base stations, and the distance between the onboard station and the two base stations is substantially equal to each other. For this reason, even if there is a phase difference between the signals of two frequencies, if the phase difference is small, the onboard station can properly demodulate the signals of the two frequencies, that is, the frequency of the same symbol. The signal can be detected.

  The control unit 500 of the wireless communication device 112 of the onboard station 111 holds a combination table of frequency signals received by the onboard station as shown in FIG. In the example shown in FIGS. 6 and 7, the modulation / demodulation unit 312 detects data “01” when the combination (f1, f4) is detected, and data “00” when the combination (f2, f3) is detected. ”Is converted to data“ 10 ”if a combination of (f1, f3) is detected, and is converted to data“ 11 ”if a combination of (f2, f4) is detected. Convert to frame. The radio frame having the serial bit arrangement is input to the encoding / decoding unit 304, and the subsequent processing is the same.

  The four-value FSK mapping is not limited to that shown in FIGS. 6 and 7, but it is desirable that the frequencies of the two received signals received by the on-board station are as far apart as possible. It is desirable that at least one symbol is set so as not to have an adjacent frequency. In the example of FIG. 7, three of the four symbols (corresponding to data “01”, “00”, “10”, and “11”) are set so as not to be adjacent frequencies. As the frequency of the two received signals received by the on-board station is farther, more robust communication is possible.

  Although the present embodiment has been described by taking a train radio system as an example, the present embodiment can also be applied to radio communication systems other than train radio. In this case, the onboard station is widely read as a mobile station.

  In the above-described embodiment, the plurality of base stations are configured to synchronize with the network clock signal of the central control apparatus. However, the synchronization method between the plurality of base stations is not limited to this, and various methods are possible. May be adopted. For example, each base station may be provided with a GPS (Global Positioning System) receiver, and may be synchronized based on a 1 ppm signal from GPS or time information. Furthermore, according to the present invention, the base stations do not have to be synchronized with high accuracy, and even in this case, the mobile station can receive more reliably in the interference area between the plurality of base stations.

101: base station, 102: wireless communication device, 110: train, 111: on-board station, 112: wireless communication device, 120: central control device, 130: communication console, 140: transmission medium, 200: track, 201: delay Adjustment circuit, 300, 500: control unit, 301: audio interface unit, 302: audio compression unit, 303: audio decompression unit, 304: encoding / decoding unit, 305, 308: selection / distribution unit, 306, 307: Four-value FSK processing unit, 309: VCO, 312: modulation / demodulation unit, 310: high frequency circuit, 311: antenna.

Claims (8)

A plurality of base stations including a first base station and a second base station adjacent to each other;
A central controller connected to the plurality of base stations,
Each of the plurality of base stations has a wireless communication device that performs four-value FSK modulation on communication data from the central control device and transmits the modulated data to a mobile station,
The wireless communication device of the first base station performs quaternary FSK modulation based on a first mapping, and the wireless communication device of the second base station performs quaternary FSK modulation based on a second mapping different from the first mapping. Done
The wireless communication system in which the wireless communication devices of the first base station and the second base station respectively transmit the communication data to the mobile station. In claim 1,
Each of the plurality of base stations has a delay adjustment circuit,
The wireless communication device and the delay adjustment circuit operate in synchronization with a clock signal synchronized with a network clock signal from the central control device,
The wireless communication devices of the first base station and the second base station respectively transmit broadcast data as the communication data to the mobile station,
Wireless communication in which the delay amounts of the delay adjustment circuits of the first base station and the second base station are determined so that the transmission timing of the first base station and the transmission timing of the second base station are synchronized. system. In claim 1 or 2,
In 4-level FSK modulation, any one of the first to fourth frequencies is assigned to each of the four symbols,
The first mapping and the second mapping assign four different frequencies of the first to fourth frequencies to four symbols, respectively.
The radio communication system including at least one of the first to fourth frequencies different from the frequency allocated by the first mapping and the frequency allocated by the second mapping in at least one symbol. In any one of Claims 1-3,
The mobile station
An antenna,
A high-frequency circuit that down-converts a high-frequency signal received by the antenna into an intermediate frequency band received signal;
A demodulator that performs four-level FSK demodulation of the intermediate frequency band reception signal output from the high-frequency circuit;
A radio communication system that demodulates to one symbol based on a combination of two detected frequencies when the demodulator detects two frequencies. A mobile station that transmits and receives a four-value FSK modulated high-frequency signal,
An antenna,
A high-frequency circuit that down-converts a high-frequency signal received by the antenna into an intermediate frequency band received signal;
A demodulator that performs four-level FSK demodulation of the intermediate frequency band reception signal output from the high-frequency circuit;
A mobile station that demodulates to one symbol based on a combination of two detected frequencies when two frequencies are detected by the demodulator. In claim 5,
The high-frequency signal is broadcast communication from a plurality of base stations to a mobile station, and a transmission signal that is quaternary FSK modulated based on a first mapping at a first base station and a first signal adjacent to the first base station. A mobile station that is a combined signal of a transmission signal that has been subjected to 4-level FSK modulation based on a second mapping different from the first mapping at two base stations. In claim 6,
When one frequency is detected by the demodulator, whether the intermediate frequency band reception signal output from the high frequency circuit is mapped by the first mapping or the second mapping. Mobile station to judge. A base station connected to a central controller,
A wireless communication device for performing four-value FSK modulation on the broadcast data from the central control device and transmitting it to a mobile station;
A delay adjustment circuit,
The wireless communication device and the delay adjustment circuit operate in synchronization with a clock signal synchronized with a network clock signal from the central control device,
The wireless communication device performs quaternary FSK modulation based on either a predetermined first mapping or second mapping,
The radio communication apparatus is a base station that transmits the broadcast data at a timing obtained by delaying a network timing signal from the central control apparatus by a predetermined delay amount.

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