JP4396928B2 - Communications system - Google Patents

Description

The present invention relates to a communication system that enables adaptive modulation by determining propagation path conditions and the like.

In wireless communication between a fixed wireless device (hereinafter referred to as a base station) and a mobile wireless device (hereinafter referred to as a mobile station), the propagation environment that receives multipath fading and the like varies depending on the moving speed of the mobile station and the surrounding environment.
FIG. 6 is a diagram showing an example of a communication area for indicating such an environmental situation. Now, when the mobile station 2 moving in the areas A, B, and C communicates with the base station 1 wirelessly, if the mobile station 2 is moving in the area A or B, it propagates from the surrounding environment such as a building. The condition is relatively good and high quality communication is possible. On the other hand, while the mobile station 2 is in the area C, the propagation state is likely to deteriorate from the surrounding environment such as a building, and the SN of the received signal deteriorates and the error rate increases.

  Conventionally, techniques such as adaptive modulation that reduce the error rate by lowering the transmission rate when the propagation condition is bad are known in order to realize error-free communication even if the propagation condition is bad. There is no established method and various studies are underway.

  As another means, in the case of data communication, the transmission side transmits at a high transmission rate, and the reception side issues a retransmission request to the transmission side by an automatic repeat request (ARQ) signal if the error rate is high. Also, a method is known in which when the transmission side receives ARQ, it retransmits at a reduced transmission rate.

In addition, the following patent document is known as a technique relevant to the said prior art example (for example, refer patent document 1, 2).
Japanese Patent Laid-Open No. 10-56420 JP 2002-290246 A

  However, the technique using ARQ has a problem that the process of retransmission by ARQ is complicated, and if the modulation method is the same, the error rate cannot be improved.

The present invention has been made in view of the above-described circumstances. For example, the present invention is applied between a base station and a mobile station, and in a time zone in which communication is not performed, a wireless propagation test is automatically performed, so that a wireless propagation state is real-time. We investigate from time to time, and when the propagation situation is poor, lower the data transmission rate (modulation method) to achieve error-free communication, and when the propagation situation is good, increase the data transmission rate to achieve high quality and effective communication. An object is to provide a communication system that can be enabled.

In order to solve the above-described problems, a communication system according to the present invention is a communication system that determines a propagation path condition between a base station and a mobile station and switches a modulation scheme. (Press To Talk) off time and squelch close time are monitored to determine whether or not communication with the mobile station is performed, and when it is determined that communication is not being performed, propagation to and from the mobile station The present invention is characterized in that determination of a propagation path condition is performed by transmitting / receiving data for determining a road condition, and switching a modulation method of communication in the communication section based on the determination result.
Here, when the base station determines that communication has not been performed for a predetermined time, the base station performs transmission / reception of propagation path status data to / from the mobile station to determine the propagation path status It is characterized by.

  In the embodiment, the propagation path condition is determined by transmitting random data such as a PN code from a wireless device (for example, a base station) to a transmission partner (for example, a mobile station). The demodulated data is returned to the radio as modulated data. On the wireless device side, the received data is demodulated and compared with the original random data, and the state of wireless propagation between the wireless device and the transmission partner is determined based on the error rate.

  Further, in the embodiment, the determination of the time zone during which communication with the communication partner is not performed is performed by monitoring the off time of PTT (Press To Talk) on the base station side when the wireless device is a base station, In the case of a mobile station, the closing time of the squelch of the analog demodulation unit on the base station side is monitored, and it is determined on the condition that no transmission act has been performed from the base station or the mobile station for a predetermined time.

  The communication system between the base station and the mobile station in the embodiment determines a non-communication time zone in the base station, modulates a predetermined test signal when the time zone is determined, and transmits the modulated test signal to the mobile station. The test signal returned after receiving, demodulating and remodulating the test signal is demodulated, the test signal before transmission is compared, and the modulation method for communication with the mobile station is selected based on the comparison result To do.

As described above in detail, according to the present invention, it is possible to provide a communication system that can always perform good communication regardless of the propagation path condition by using the modulation method in which the propagation path condition is considered. it can.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing an overall configuration of the present embodiment. In the figure, 1 is a base station, 2 is a mobile station capable of communicating with the base station 1, and 1a and 2a are provided in the base station 1 and the mobile station 2, respectively, and perform wireless communication between the base station 1 and the mobile station 2 This is an antenna for wireless communication. Reference numeral 4 denotes a data flow at the time of the propagation state test (at the time of the loopback test).

  The base station 1 and the mobile station 2 perform wireless communication via the antennas 1a and 2a. The state of radio propagation between the base station 1 and the mobile station 2 varies from time to time depending on the surrounding environment. A propagation state test is performed between the base station 1 and the mobile station 2 as needed, and wireless communication is performed at a transmission rate optimum for the propagation state.

  According to the data flow at the time of the propagation state test indicated by 4, at the time of the propagation test, random data such as a PN code is modulated from the base station 1 and transmitted from the antenna 1 a to the mobile station 2. The mobile station 2 demodulates the data received via the antenna 2a, compares the demodulated data with the original random transmission data, and determines the radio propagation status between the base station 1 and the mobile station 2 based on the error rate. When the propagation situation is bad, the data transmission rate is lowered to realize error-free communication, and when the propagation situation is good, the data transmission rate is raised to enable effective communication.

  FIG. 2 is a block diagram of the base station 1 in the embodiment of the present invention. In FIG. 2, reference numeral 101 denotes a transmission data input unit during normal wireless operation (except during a propagation state test). A pseudo data (random data) input unit 121 generates random data during a propagation state test. A communication system switching control unit 122 controls the normal communication / propagation test. SW1 is a switch for switching input data and output data under the control of the communication system switching control unit, and either a1 or b1 is selected. 103 indicates transmission data for one block from input data from the input unit 101 or the pseudo data input unit 121, communication system information from the communication system switching control unit 122, modulation system information of the system switching control unit and other control data. This is a channel coding unit to be generated. SW2 is a switch for switching the modulation method and the demodulation method under the control of the method switching control unit indicated by 123, and any one of a2, b2, and c2 is selected.

  Reference numeral 105 denotes a 16QAM modulation unit that performs baseband 16QAM modulation on transmission data from the channel coding unit 103. Reference numeral 106 denotes a QPSK modulation unit that performs baseband QPSK modulation on transmission data from the channel coding unit 103. Reference numeral 107 denotes a BPSK modulation unit that performs baseband BPSK modulation on transmission data from the channel coding unit 103. An analog modulation unit 108 performs modulation processing such as AM on the baseband modulated wave, and outputs an analog modulated wave. Reference numeral 109 denotes a transmitter that converts the analog modulated wave (intermediate frequency band) into a radio frequency band. Reference numeral 110 denotes a power amplifying unit that amplifies a radio frequency band signal to a radio output level, which is transmitted from the transmitting antenna 1a-1 to the mobile station after power amplification.

  Reference numeral 1a-2 denotes a reception antenna, and reference numeral 113 denotes a reception unit that converts a reception signal (radio frequency band) received from the mobile station 2 via the reception antenna 1a-2 into an intermediate frequency. Reference numeral 114 denotes an analog demodulation unit having a squelch function for performing analog demodulation on the intermediate frequency. Reference numeral 115 denotes a 16QAM demodulator that performs 16QAM demodulation in the baseband. Reference numeral 116 denotes a QPSK demodulator that performs QPSK demodulation in the baseband. Reference numeral 117 denotes a BPSK demodulator that performs baseband BPSK demodulation.

  Reference numeral 118 denotes a channel decoding unit that separates data such as communication system information and system information from 16QAM, QPSK, or BPSK demodulated data. Reference numeral 119 denotes a reception data output unit when the channel decoding unit is in normal radio operation (except during the propagation state test). A pseudo data determination unit 120 at the time of the propagation state test compares data with the pseudo data input unit 121, and determines a modulation method at the next block transmission from the error rate.

  Hereinafter, as the operation of the base station, the operation during the propagation state test will be described. The propagation state test is performed by monitoring the time when wireless communication is not performed between the base station and the mobile station. For example, transmission from the base station is performed by monitoring the PTT (Press To Talk) OFF time on the base station side, and transmission from the mobile station is performed by monitoring the squelch closing time of the analog demodulation unit 114 on the base station side.

  As a result, a propagation state test is performed when transmission from the mobile station is not performed from the base station for a fixed time (for example, 15 minutes). The propagation state test is performed by switching SW1 to the b1 side by the communication system switching control unit 122. At this time, random data such as PN is generated from the pseudo data input unit 121 and used as transmission data. The channel coding unit 103 creates transmission data to which data from the pseudo data input unit 121 and communication system information, modulation scheme information, and other control parameters are added. An example of a transmission data format created by the channel coding unit is shown in FIG.

  In this transmission format, modulation of the 16QAM modulation baseband for high-speed transmission is performed on the transmission 1 block data under the control of the system switching control unit 123, and analog modulation such as AM modulation is performed by the analog modulation unit 108. After being converted to a radio frequency band by unit 109, the power is amplified by power amplifying unit 110 and transmitted from antenna 1 a 1 to mobile station 2.

  On the receiving side, when the data returned from the mobile station 2 is received by the antenna 1a-2, the frequency-converted signal by the receiving unit 113 is demodulated into a baseband modulated wave by the analog demodulating unit 114, and then the 16QAM demodulating unit 115 is obtained. Is output to the channel decoding unit 118. The channel decoding unit 118 divides data, communication system information, system information, and other control parameters. During the propagation state test, the data divided by the channel decoding unit 118 is output to the pseudo data determination unit 120 and compared with the data generated and transmitted by the pseudo data input unit 121. The above operation is repeated until pseudo data of about 10 9 bits is generated, and the propagation status is determined based on the error rate.

  If there is an error, SW2 is switched to b2 and the above is repeated with QPSK modulation baseband modulation. FIG. 4 shows the relationship between test results and propagation conditions. The transmission rate (baseband modulation system) during normal operation is determined by the above propagation condition test.

FIG. 5 shows a block diagram of the mobile station in the embodiment.
In FIG. 5, the last two digits of each symbol are the same as those in FIG. That is, the basic configuration of the mobile station is almost the same as the configuration of the base station described with reference to FIG. On the mobile station side, the pseudo data input unit 121 and the pseudo data determination unit 120 included in the base station 1 are not provided, and a communication system determination unit 220 ′ is provided separately. The communication system determination unit 220 ′ is a communication system determination unit that obtains communication system information from the channel decoding unit 218 and switches SW1.

The operation during the propagation status test of the mobile station will be described below.
Since it is basically the same as the base station of FIG. 3, only the different parts will be described.
The channel decoding unit 218 of the mobile station divides demodulated data after baseband demodulation into data, modulation scheme information, communication system information, and other control parameters. If it is determined from the communication system information that the propagation status test is being performed, SW1 is switched to the b1 side, and the demodulated data is used as input data on the transmission side to be returned to the base station (the data at this time is a pseudo data input unit) Random data generated at 121). Thus, a test system for a radio loopback test (propagation state) is constructed with a data flow from the base station 1 to the mobile station 2 and from the mobile station 2 to the base station 1.

It is a systematic diagram of an embodiment of the invention. It is a block diagram of a base station in an embodiment. It is a figure which shows the format of 1 transmission block in embodiment. It is a figure which shows the relationship between a propagation condition test result, and a transmission rate. It is a block diagram of the mobile station in embodiment. It is a figure which shows an example of a communication area.

Explanation of symbols

    1 base station, 2 mobile station, 101, 201 input unit, 103, 203 channel coding unit, 105, 205 16QAM modulation unit, 106, 206 QPSK modulation unit, 107, 207 BPSK modulation unit, 115, 215 16QAM demodulation unit, 116 , 216 QPSK demodulation unit, 117, 217 BPSK demodulation unit, 118, 218 channel decoding unit, 119, 219 output unit, 120 pseudo data determination unit, 121 pseudo data input unit, 122 communication system switching control unit, 123, 223 Switching control unit, 220 ′ communication system determination unit.

Claims (2)

In a communication system that determines a propagation path condition between a base station and a mobile station and switches a modulation method,
  The base station determines whether it is communicating with the mobile station by monitoring its own PTT (Press To Talk) off time and squelch closing time, and determines that communication is not being performed. When performing transmission / reception data transmission / reception data transmission / reception with the mobile station to determine the propagation path condition, the communication modulation method in the communication section is switched based on the determination result. A communication system. When the base station determines that communication has not been performed for a predetermined time, the base station performs transmission / reception data transmission / reception data transmission / reception with the mobile station to determine the propagation path condition. The communication system according to claim 1.

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