JP2008131093A - Transmission reception device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission reception device capable of prohibiting transmission of its own station to prevent collision by easily detecting that another station is in transmission, using a function equivalent to measurement of transmission power, even if the device has no function of carrier sense. <P>SOLUTION: A demodulating section 3 is added with a reception quality measurement output function for measuring the signal quality of a reception signal, and a transmission reception control section 4 is added with a transmission prohibiting function for comparing the signal quality measurement output from the demodulating section 3 with a previously set threshold value and stopping transmission from its own device when the quality of a reception signal is satisfactory. With this configuration, the device can easily obtain a function equal to the measurement of a reception signal, even if it has no function of carrier sense. In this way, the device can detect that another station is performing transmission to prohibit transmission of its own device, thereby preventing collision. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transmission / reception apparatus that detects whether or not another station is transmitting, and prohibits the transmission of the own station to prevent a collision while detecting that the other station is transmitting.

  In the case of a CSMA transmission / reception apparatus in which a plurality of radio stations share the same frequency and communicate, stations other than the transmitting station detect whether or not the other station is transmitting by carrier sense, and the other station is transmitting. While detecting the existence, a multiple access method is used in which transmission of the own station is prohibited to prevent collision. For this carrier sense, a reception power measuring function called RSSI is generally used. On the other hand, the transmitter / receiver uses a transmitter / receiver that performs radio transmission / reception with a desired modulation method with an audio band signal as an input, or a radio transmitter and a radio receiver. In transmission, digital information to be transmitted is temporarily stored in the audio band signal. A configuration may be used in which a modulated signal is input to a wireless transmitter, and in reception, a receiver output is received in the form of an audio band signal and demodulated to restore digital information.

  However, as described above, the conventional transmission / reception apparatus using the voice band signal often does not have a function of measuring the receiver input power for carrier sense, and the input / output of the wireless transceiver is an intermediate frequency. There are configurations that use signals but do not have a carrier sense function, and in such a configuration, a transmission / reception device detects whether another station is transmitting or not while detecting that another station is transmitting Cannot prohibit the transmission of its own station and prevent the collision.

  An object of the present invention is to prevent a collision by prohibiting the transmission of the own station by detecting that another station is transmitting by a function equivalent to the measurement of received power even in a configuration without a carrier sense function. It is an object of the present invention to provide a transmission / reception device that can perform the above-mentioned.

  In order to achieve the above object, the present invention achieves the above-described object by transmitting and receiving a voice band signal or an intermediate frequency signal as an input / output signal for transmission and reception, and modulating transmission data into a voice band signal or an intermediate frequency signal and transmitting it to the transmitter and receiver A transmission / reception apparatus comprising: a modulation unit that performs reception; a demodulation unit that receives and demodulates an audio band signal or an intermediate frequency signal from the transmission / reception unit during a period of no transmission; and a transmission / reception control unit that performs transmission / reception control. A reception quality measurement output function for measuring the signal quality of the reception signal is added, and the signal quality measurement output from the demodulation unit is compared with a preset threshold value in the transmission / reception control unit, so that the quality of the reception signal is good In this case, a transmission prohibiting function for stopping transmission from the own station is added.

  In carrying out the present invention, the demodulator determines a detector for detecting according to the modulation method, a determiner for determining the detection output to obtain data, and an error from a correct signal point of the output of the detector. Or an error determining unit for obtaining a signal quality measurement output, or the demodulating unit demodulates output data from the equalizer that compensates for distortion of the transmission path by the equalization processing. The detection determination unit includes an error determination unit that measures the error between the signal point of the output of the equalizer and the signal point of the reference signal that is the reference signal for the equalization process and obtains a signal quality measurement output.

  In implementing the present invention, each radio station always performs a receiving operation when the own station is not transmitting, measures the signal quality of the received signal, compares it with a preset threshold value, When the signal quality is better than the threshold as a comparison result when starting transmission, a communication control method is adopted in which the transmission start of the own station is prohibited and the signal quality waits as the comparison result becomes worse than the threshold.

  The transmission / reception apparatus according to the present invention compares the signal quality measurement output by the reception quality measurement output function of the demodulation unit with a preset threshold value, and stops transmission from the own station when the received signal quality is good Since this function is added, even in a configuration that does not have a carrier sense function, it is easily detected that another station is transmitting by a function equivalent to the measurement of received power, and the transmission of its own station is prohibited and a collision is detected. Can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a system diagram of a transmission / reception apparatus according to an embodiment of the present invention.
A CSMA transmission / reception apparatus in which a plurality of radio stations communicate by sharing the same frequency includes a transmission / reception unit 1 that inputs and outputs voice band signals or intermediate frequency signals. After the transmission data to the station is converted into a transmission frame necessary for transmission by the modulation unit 2, it is modulated into a voice band signal or an intermediate frequency signal by a desired modulation method and passed to the transmission / reception unit 1 and received by the transmission / reception unit 1 In the case of reception, the radio frequency signal received by the transmission / reception unit 1 is converted into a voice band signal or an intermediate frequency signal, and the demodulating unit 3 that receives the signal performs demodulation processing. The output data is returned to the received data. The demodulator 3 not only demodulates data but also has a reception quality measurement output function for measuring reception quality corresponding to S / N, and inputs the reception quality measurement output to the transmission / reception controller 4. Upon receiving this reception quality measurement output, the transmission / reception control unit 4 compares the reception quality measurement output value with a preset threshold value to determine the presence / absence of a received signal, and the result of determination by this determination function is reception. When there is a signal, that is, when it is determined that the other station is transmitting, the transmission prohibiting function that stops the transmission of the own station and waits until the transmission of the other station is completed, and on the other hand, the determination result in the transmission / reception control unit 4 And a transmission function for transmitting data by determining that there is no received signal and transmitting data to another station by operating the modulation unit 2 to switch the operation of the transmission / reception unit 1 to transmission. ing.

  The demodulator 3 that performs demodulation processing may or may not use an equalizer, and the equalizer is used when propagation or signal distortion at the transceiver is large. Next, the configuration of the demodulator 3 in these two usage modes will be described.

FIG. 2 is a configuration example of the demodulator 3 when no equalizer is used.
The voice band signal or intermediate frequency signal from the transmission / reception unit 1 is detected by the detection unit 5 using a detection method corresponding to the modulation method, and is determined by the determination unit 6 that has received the detection output and demodulated as reception data. The detection output of the detection unit 5 is also supplied to an error detection unit 7 corresponding to the reception quality measurement output function. The error detection unit 7 detects the magnitude of an error vector between the detection output and a correct signal point, and smoothes the error vector. Is processed and passed to the transmission / reception control unit 4 as a reception quality measurement output. As will be described later, this reception quality measurement output is a measurement value corresponding to N / S, and when this is small (the difference between S and N is large), it can be determined that the other station is transmitting. it can. Therefore, the part corresponding to the determination function of the transmission / reception control unit 4 compares this with an appropriate threshold and determines that the signal reception quality is poor when the error is large, and that the signal reception quality is good when the error is small, In the portion corresponding to the transmission prohibition function, when it is determined that the reception quality is good, even if there is transmission data to other stations, the transmission from the own station is prohibited, and it waits until the reception quality deteriorates.

  Taking the four-phase PSK as an example of modulation, the signal point of the four-phase PSK takes one of four points indicated by 00, 01, 11, and 10 on the signal phase space as shown in FIG. Noise is superimposed on the signal received through the space. For example, if the noise of the arrow is superimposed on the signal at signal point 00, the signal is received at signal point A. The magnitude of the fluctuation of the signal point due to the noise component is a power value equal to N / S when the signal power is 1. Therefore, this error voltage is proportional to the reciprocal of the received electric field strength of the signal component because the noise power is constant in normal wireless communication. If the error from the correct signal point is measured in this way, the measurement equivalent to the measurement of the receiver input voltage by RSSI can be performed, and this is used to determine whether the transmission / reception control unit 4 stops the transmission of the own station. By doing so, collision in space can be avoided.

FIG. 3 is a configuration example of the demodulator 3 when an equalizer is used.
An equalizer is used for demodulation when there is a factor that distorts a signal such as multipath due to propagation, or when there is a distortion factor such as delay distortion in the characteristics of the transceiver. In such a case, the audio band signal or the intermediate frequency signal from the transmission / reception unit 1 is input to the equalizer 8, and the distortion generated in the propagation path and the distortion generated in the radio unit due to the equalization process of the equalizer 8 are reduced. After that, the signal is detected and determined by the detection determination unit 9 and demodulated as received data. The equalized output of the equalizer 8 is also supplied to an error detection unit 7 corresponding to the reception quality measurement output function, and the error detection unit 7 uses a signal point of a standard signal used as a reference signal for equalization processing. The error vector magnitude is measured, smoothed, and passed to the transmission / reception control unit 4 as a reception quality measurement output. In the part corresponding to the determination function of the transmission / reception control unit 4, the error between the signal point of the output equalized by the equalizer 8 and the signal point of the reference signal is compared with an appropriate threshold value. If the reception quality is poor and the error is small, it is determined that the signal reception quality is good, and if it is determined that the reception quality is good in the part corresponding to the transmission prohibition function, even if there is transmission data to other stations Prohibit transmission from the station and wait until reception quality deteriorates. Here, as the equalizer 8, various known ones can be used.

  When the equalizer 8 is used, in general, a signal called a unique word having a predetermined waveform (code string) is transmitted at an appropriate interval on the transmission side, and a waveform of this unique word and the received signal is transmitted on the reception side. Comparison is performed, and equalization processing is performed so that the error becomes zero at the signal determination timing. In this equalization processing, the distortion component in the received signal generally compensates because it fluctuates slowly. On the other hand, the noise component does not compensate because it varies randomly at almost the same speed as the modulation rate. Will remain as it is. The error power between the signal point of the unique word after the equalization process and the signal point of the standard unique word that becomes the reference signal for the equalization process is called an equalization error, and this value can be understood from the above description. Thus, an output that is inversely proportional to S / N is obtained. In this way, by using the error between the signal point of the equalized output of the equalizer 8 and the signal point of the reference signal as the reception quality measurement output, it is equivalent to the case of measuring the received input voltage by RSSI. Can be used for collision avoidance.

  FIG. 5 is a characteristic diagram showing an example of the equivalent error. The relationship between the equivalent error of the equalizer 8 and the received input power is represented by a modulation rate of 6K symbols / second, and the modulation method is a test apparatus of two-phase PSK. It is a measured value. The equivalent error is the average value of the error from the correct signal point of the equalizer output expressed as a ratio (dB) to the signal power, and the fact that the equivalent error is large means that the ratio of the equivalent error and the signal power is large. It corresponds to that. As can be seen from the figure, the equivalent error in terms of the ratio to the signal power and the received input power correspond to each other almost in a straight line, and even if the equivalent error is used in place of the received signal power, carrier sense is achieved. It can be seen that an equivalent function can be obtained.

  Regardless of the configuration, the presence / absence of a received signal from another station is determined by comparing the reception quality measurement output with an appropriate threshold set in advance. This threshold is used when only noise is received. It is desirable to set the level so as to reduce the probability of erroneous determination as being present, and it is generally appropriate to set the level to about 6 dB in S / N.

  According to such a transmission / reception device, a reception quality measurement output function for measuring the signal quality of the reception signal is added to the demodulation unit 3, and the signal quality measurement output from the demodulation unit 3 is preset in the transmission / reception control unit 4. Since the transmission prohibition function for stopping transmission from the local station is added when the received signal quality is good by comparing the threshold values, the reception power measurement can be simply performed as shown in FIG. 5 even in the configuration without the carrier sense function. Thus, it is possible to detect that another station is transmitting, thereby prohibiting the transmission of the own station and preventing a collision. In addition, such a transmission / reception device always performs a reception operation when each wireless station is not transmitting, measures the signal quality of the received signal, compares it with a preset threshold value, If the signal quality is better than the threshold as a comparison result when starting transmission, a communication control method is adopted that prohibits the start of transmission of the own station and waits until the signal quality becomes worse than the threshold as a comparison result This can be easily realized.

  The transmission / reception apparatus according to the present invention can be applied to a configuration other than the configuration shown in FIG.

It is a systematic diagram which shows schematic structure of the transmitter / receiver by one Embodiment of this invention. It is a block diagram which shows the specific structure of the demodulation part of the transmission / reception apparatus shown in FIG. It is a block diagram which shows the other specific structure of the demodulation part of the transmission / reception apparatus shown in FIG. It is explanatory drawing which shows arrangement | positioning of a signal point. It is a characteristic view which shows the relationship between an equivalent error and input electric power.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission / reception part 2 Modulation part 3 Demodulation part 4 Transmission / reception control part 5 Detection part 6 Determination part 7 Error detection part 8 Equalizer 9 Detection determination part

Claims (1)

  A transmission / reception unit that uses an audio band signal or an intermediate frequency signal as an input / output signal for transmission / reception, a modulation unit that modulates transmission data into an audio band signal or an intermediate frequency signal during transmission, and inputs to the transmission / reception unit; In a transmission / reception apparatus including a demodulation unit that receives and demodulates an audio band signal or an intermediate frequency signal from the transmission / reception unit, and a transmission / reception control unit that controls transmission / reception, the reception unit measures the quality of the received signal in the demodulation unit A transmission prohibition function that adds an output function and stops transmission from the own station when the quality of the received signal is good by comparing the signal quality measurement output from the demodulator with a preset threshold value to the transmission / reception controller A transmission / reception apparatus characterized by adding

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