JP2010263511A - Communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the increase of transmission latency time caused by an erroneous detection and noise in determination of a carrier when the receiving strength per communication apparatus varies a lot and noise whose strength is larger than the receiving strength is received in the CSMA (Carrier Sense Multiple Access)/CA (Collision Avoidance) access method of the communication apparatus. <P>SOLUTION: A process to compare the receiving strength with a threshold value to decide the carrier and another process to detect a synchronous signal at the head of communication signals are simultaneously operated. A transmission timing control section detects the continuance after the existence of the carrier is decided. If no synchronous detection is detected in a certain time of period after the existence of the carrier is decided, a process to subtract the continuance after the decision of the carrier existence from a CW (Contention Window) period is provided. From the above, the increase of the transmission latency time when a noise larger than the threshold value is received is suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a communication apparatus that constitutes a communication network, and relates to a communication apparatus that employs an access method suitable when a plurality of communication apparatuses communicate using a single communication medium such as wireless or wired communication.

  A carrier that uses CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) as an access method when communicating with a plurality of communication devices in a communication network using the same communication line or the same wireless channel. A sense method is used.

  In this method, it is confirmed whether or not another communication apparatus is transmitting before transmission (carrier sense), and transmission is started only when the other is not transmitting.

  In the carrier sense method, the reception strength is detected. If the reception strength is equal to or higher than a threshold value, the carrier is present, that is, it is determined that another communication apparatus is transmitting.

  In this way, the threshold value in the transmission waiting state is called a defer threshold value, and the threshold value for determining whether or not to start the reception operation may be simply expressed as a carrier threshold value.

  In the following, the threshold for determining transmission start is simply expressed as a threshold.

  If a plurality of other communication devices are in a transmission waiting state while a specific communication device is transmitting, the plurality of communication devices may start transmission at the same time and collide when transmission of the communication device is completed. In order to avoid this, a CA (Collision Avoidance) method has been proposed.

  When transmission data is generated in the communication device, a transmission waiting time CW (Contention Window) is generated with a random number, and transmission is started after the CW period elapses without a carrier. Since the CW is different for each communication device depending on the random number, it is possible to probabilistically prevent a plurality of communication devices from starting transmission simultaneously after completion of other transmissions. These are described in Patent Document 1, for example. Setting the threshold is important, and it is said that high sensitivity and low power consumption can be realized by using two levels of threshold.

  Further, in Patent Document 2, it is possible to prevent transmission from being excessively suppressed by dynamically changing the threshold value from the reception intensity when detected as a reception signal.

  Further, Patent Document 3 also describes that even when a received signal is detected, the threshold value is not changed if it is other than the same communication group (cell).

Japanese Patent Laid-Open No. 11-163897 JP 2004-007504 A JP 2004-207921 A

  The series of patent documents described above assumes that only wireless LAN signals of the same standard are received as received signals. When noise larger than a threshold is received, transmission is suppressed during that period. There is a problem.

  In addition, when the threshold value is dynamically changed, the reception strength from the newly connected communication device may be small, and in this case, there is a problem that reception processing cannot be started and reception is not possible.

  It is an object of the present invention to reduce the influence of the misjudgment period when a plurality of communication apparatuses have different reception strengths, and in the method of performing carrier sensing based on the reception strengths and threshold values, when it is determined that there is a carrier and noise is detected, transmission is performed. An object of the present invention is to provide an access method capable of reducing the waiting time.

  The communication apparatus which is the subject of the present invention modulates data and transmits it. The transmission signal is composed of a signal also called a synchronization signal or preamble signal indicating the head of the signal, followed by a header and a data signal.

  If the threshold value is set correctly, it is determined that the carrier is present when the synchronization signal arrives, and the synchronization signal is detected by the synchronization detection circuit at the end of the synchronization signal because the length of the synchronization signal is fixed. By simultaneously operating the threshold determination and the synchronization detection process, it is possible to avoid missing a received signal smaller than the threshold.

  If noise with a reception intensity greater than the threshold is received, it is erroneously determined that there is a carrier, but the elapsed time from immediately after determination that there is a carrier is measured, and if synchronization is not detected after the length of the synchronization signal has elapsed Judge as noise.

  Then, by subtracting the elapsed time from the CW time generated by the random number performed in the transmission waiting state, an increase in the transmission waiting time due to erroneous determination can be suppressed.

  Although it is possible to start transmission in a state where noise is received in this way, if the transmission power and noise are compared and the noise is large, the reception side cannot receive.

  Therefore, transmission is not started when the noise intensity is a certain value or more. In this way, the signal-to-noise ratio (SN) on the transmission side can be kept above a certain value.

  The reception strength at the time of detecting synchronization is compared with a set threshold value, and if the threshold value is larger than the reception strength, the threshold value is changed to a smaller value. In this way, an optimum threshold value can be set for different reception strengths depending on the installation status of the communication apparatus, and erroneous carrier determination can be eliminated.

  As described above, the communication device of the present invention is such that a plurality of communication devices are controlled to be transmitted by the CSMA / CA method using a communication line or a wireless communication channel as a communication medium, and the received signal strength is compared with a threshold value. The carrier determination process and the process of detecting the synchronization signal transmitted at the head of the communication signal are simultaneously performed, and the time from the determination that the carrier is present to the synchronization determination is measured.

  The communication apparatus of the present invention includes a carrier determination processing unit that determines a carrier by comparing a received signal strength and a threshold value, a detection processing unit that detects a synchronization signal transmitted at the head of the communication signal, and a carrier determination process. And a measurement processing unit that measures each of the elapsed time after determination that the carrier is present and the elapsed time after determination that the carrier is absent, and synchronization is detected by the detection processing unit within a certain time after the determination that the carrier is present If the synchronization is not determined, the elapsed time after determining that there is a carrier is subtracted from the transmission waiting time generated by a random number in the CSMA / CA method as the elapsed time when there is no carrier. To do.

  Then, before the detection is detected by the detection processing unit within a predetermined time after the determination that the carrier is present, the elapsed time with the carrier is calculated as CSMA when the determination value changes from the presence of the carrier to the absence of the carrier. It is preferable to subtract from the transmission waiting time generated by random numbers using the / CA method.

  The communication device of the present invention is a device in which a plurality of communication devices are controlled to be transmitted by the CSMA / CA method using a communication line or a wireless communication channel as a communication medium, and the received signal strength is compared with a threshold value to compare carriers. A carrier determination processing unit for determining, a detection processing unit for detecting a synchronization signal transmitted at the head of the communication signal, and an update for comparing the received intensity at the time when the synchronization signal is detected and the threshold value to update the threshold value A processing unit, and a measurement processing unit that measures each of the elapsed time after determination that the carrier is determined to be present by the carrier determination processing unit and the elapsed time after determination that the carrier is not present, and within a certain time after the determination that the carrier is present The detection processing unit determines that synchronization is detected, and when synchronization is not determined, the elapsed time after the determination that the carrier is present is determined as the elapsed time when there is no carrier in the CSMA / CA system. Characterized by subtracting from the transmission waiting time generated by the number.

  As described above, according to the present invention, since synchronization detection and threshold determination are simultaneously performed, carrier sense can be performed without missing a received signal smaller than the threshold.

  Furthermore, when a noise signal exceeding the threshold value is received, the erroneous determination period due to noise is subtracted from the CW time generated by random numbers to avoid collision, so that the transmission waiting time does not increase due to noise. .

The function block diagram of the communication apparatus which is an Example of this invention. The block diagram of the wired communication network using the communication apparatus of this invention. The time waveform figure of each process part which is an Example of this invention. The flowchart of the carrier determination part which is an Example of this invention. The flowchart of the transmission timing control part of the conventional CSMA / CA. The flowchart of the transmission timing control part of CSMA / CA of this invention. The function block diagram of the radio | wireless communication apparatus of this invention. The block diagram of the radio | wireless communication network using the radio | wireless communication apparatus of this invention. The figure which showed the relationship of the signal strength in this invention. The flowchart of the transmission timing control part of this invention.

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

  FIG. 1 is a functional configuration diagram of a communication apparatus 1 according to an embodiment of the present invention.

  FIG. 2 shows a communication network composed of a plurality of line devices 1a to 1e connected via a communication line 2. Each communication device 1 is connected to a control information device 11 (11a to 11e) that transmits and receives information. ing. Reference numeral 12 denotes a noise source.

  FIG. 3 shows the time waveform of each part for explaining the embodiment of the present invention.

  FIG. 4 is a flowchart of the carrier determination unit (carrier determination processing unit) 7 according to the embodiment of the present invention.

  1 includes a coupling circuit 3 connected to a communication line 2, a receiving circuit 4 that receives a reception signal from the coupling circuit 3, and a synchronization that detects the presence or absence of a synchronization signal at the head of the communication signal. A receiving operation is performed by a detection unit (detection processing unit) 5 and a demodulating circuit 6 that demodulates the received signal into digital data after detecting synchronization.

  When transmission data is input from the outside to the modulation circuit 9 in the communication device 1, a signal is transmitted to the communication line 2 via the transmission circuit 10 and the coupling circuit 3.

  The transmission timing control unit 8 controls the transmission timing to the communication line 2, and here, the CSMA / CA method which is one of the access methods is executed.

  The operation will be described below.

  When transmission data is input to the modulation circuit 9 from the outside, transmission control is started by the transmission timing control unit 8, a random number is generated within a specified range, and the random value CW is multiplied by a certain time width ST (slot time). Transmission starts after a certain period of time.

  Since CW is determined at random, even if transmission data is simultaneously input in the plurality of communication apparatuses 1a to 1e shown in FIG. 2, the probability of simultaneous transmission can be reduced, so that data collision can be avoided.

  The transmission timing control unit 8 measures the duration when the carrier determination unit (carrier determination processing unit) 7 determines that there is no carrier, and subtracts CW every time ST time elapses, and the value becomes zero. Send data at the moment.

  Since the carrier determination unit 7 compares the reception strength with the threshold value and determines that there is a carrier when the reception strength is large, setting of the threshold value is important.

  FIG. 3 shows a time waveform of the reception intensity in the communication device 1a. The signal of the communication device 1c having a short communication distance is large, and the strength of the communication device 1e having a long communication distance is naturally reduced.

  If it is determined that there is no carrier even though another communication apparatus is transmitting, a transmission is started and a collision occurs. Therefore, the threshold value is usually set to a value larger than the noise intensity generated inside the receiving circuit 4.

  However, if noise is mixed from the outside and the threshold value is exceeded and it is erroneously determined that there is a carrier, transmission cannot be started and there is a possibility that a device waiting time may occur.

  In the conventional communication device shown in the patent document, the reception operation is started after the carrier determination unit determines that there is a carrier for the purpose of power saving. Therefore, the synchronization detection operation is not started unless it is determined that there is a carrier.

  In the present invention, the carrier determination unit 7 and the synchronization detection unit 5 are always operated simultaneously. Even when a reception signal smaller than the threshold is received, the carrier determination unit 7 determines that there is no carrier, but the synchronization detection unit 5 Since it operates, it can detect synchronization and demodulate and receive the received signal.

  The threshold value set by the carrier determination unit 7 is automatically changed instead of a constant value as shown in FIG. In FIG. 4, the threshold value in the initial state is set to a relatively large initial value as compared with the internal noise of the receiving circuit, and the operation is started. Then, when synchronization is detected by the synchronization detector 5, the received intensity is compared with a threshold value. If the received intensity is low, the received intensity is set as a new threshold value.

  In this way, the threshold value is updated with the reception intensity at the time of synchronization detection, and therefore an optimum threshold value can be obtained.

  FIG. 3 shows the time change of the threshold value. When the synchronization signal 13 transmitted from the communication device 1c arrives, the reception strength at the communication device 1a increases, and the reception strength becomes greater than the threshold value and the carrier. It is determined that there is a carrier.

  Synchronization is detected at the end of the synchronization signal 13, but since the reception intensity is higher than the threshold 16, the threshold is not changed at this point.

  Next, when transmitted from the communication device 1e, the reception strength is smaller than the threshold 16 at the time when the leading synchronization signal 13 is received, and it is not determined that there is a carrier. Synchronization is detected at the end of the synchronization signal 13, and at this point, a comparison is made with the threshold value, and the received signal is small, so that it is changed to a new threshold value.

  As described above, since the threshold value is updated based on the reception strength at the time of synchronization detection, even when there is a large difference in the reception strength from each communication device, the optimum threshold value can be set, and carrier determination is performed reliably. be able to.

  Further, as described in the case of transmission from the communication device 1e having a reception strength smaller than the threshold value, the synchronization detection unit 5 operates simultaneously with the carrier determination unit 7, so that synchronization detection is possible and reception strength is large. It can be received even in a changing communication situation.

  In the embodiment of the present invention described above, the threshold value and the reception intensity are compared, and the smaller one is set as a new threshold value. The reception strength may fluctuate. If the threshold value is large, it may be determined that there is no carrier and transmission may be started. From this viewpoint, the threshold value should be small.

  Therefore, the threshold value and the value obtained by multiplying the reception intensity by a coefficient smaller than 1 are compared, and the smaller value may be changed to a new threshold value. For example, if the coefficient is 1/4, it can be determined that there is a carrier even when the reception intensity from the same communication apparatus fluctuates and decreases to 1/4. In this way, if the coefficient is determined in consideration of the variation of the reception strength, reliable carrier determination is possible.

  First, a conventional transmission timing control method will be described with reference to FIG.

  When received data is input to the communication device, a random number is generated within a certain range to determine CW. A case where random numbers are generated in the range of 0 to 15 and CW = 5 will be described below.

  The presence / absence of the carrier is determined using the determination value of the carrier determination unit. When there is no carrier, the duration is measured by a timer, and when the slot time ST has elapsed, CW is subtracted by 1 and set to 4.

  When the above processing is repeated and CW = 0, transmission of transmission data is started from the communication device. Such a conventional control method has the following problems.

  In FIG. 3, when the noise source 12 is mixed in the communication line 2 and the intensity thereof is larger than the threshold value 16, it is determined that the carrier determination is present. In the flowchart shown in FIG. 5, the timer for determining the elapse of the ST time does not operate during this period, so that the CW subtraction is not performed and the transmission start time is delayed by the length of the period erroneously determined as having a carrier due to noise.

  The present invention solves this problem, and the embodiment will be described with reference to FIG.

  In a communication apparatus that modulates and transmits data, the transmission signal is composed of a fixed-length synchronization signal indicating the head, a header signal, and a data signal as described above.

  Therefore, if the threshold is set to a normal value, it is determined that the carrier is present when the leading synchronization signal is received, and synchronization is detected at the end of the synchronization signal after the carrier is determined to be present. In the case of noise, synchronization is not detected even if the length of the synchronization signal elapses after it is determined that there is a carrier.

  The present invention discriminates noise based on the presence or absence of synchronization detection after determining the presence of a carrier.

  FIG. 6 is a process flowchart of the transmission timing control unit 8.

  First, CW is determined by random numbers as in the conventional method.

  Next, the count value C for counting the duration time after determining that there is a carrier is set to an initial value 0. The process after determining that there is no carrier is the same as the process described with reference to FIG. 5, and the transmission time is started when CW = 0 when the elapsed time when there is no carrier is measured.

  The following processing is different from the conventional one.

  The time from when it is determined that there is a carrier to when synchronization detection is detected is measured in ST time units, and the value is stored in C. If it is a received signal, synchronization is detected after the time of the length of the synchronization signal has elapsed after determining that there is a carrier. By comparing the elapsed time obtained by multiplying C by the ST time and Ts with the time interval as Ts, it is possible to determine whether the signal after determining that the carrier is present is a received signal or noise.

  That is, if synchronization is not detected even after the Ts time has elapsed, the signal is determined to be noise. If it is determined that the noise is present, the subtraction of CW subtraction can be avoided by subtracting the period C during which the carrier is erroneously determined from CW.

  On the other hand, if synchronization is detected before Ts elapses, the process returns to the conventional processing flow where C = 0 and no CW subtraction is performed until no carrier is present.

  As described above, according to the present invention, even if noise larger than the threshold is received and erroneously determined that there is a carrier, noise is determined based on the presence or absence of synchronization detection, the time of the erroneous determination period is measured, and this is calculated from CW. Since a subtraction function is provided, an increase in transmission waiting time due to malfunction can be suppressed.

  In the above-described embodiments of the present invention, the case where the length of noise exceeding the threshold is longer than Ts has been described. When the duration of noise is shorter than Ts, it is sufficient to provide means for measuring the period from the change with carrier to the change without carrier and subtracting the time from CW. In this way, it is possible to suppress a decrease in apparatus waiting time due to carrier misjudgment due to noise shorter than that of a pulsed synchronization signal.

  Next, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 9 shows the relationship between the transmission strength and the signal strength of the minimum reception sensitivity. The reception intensity greater than the SN (required SN) 22 required for reception of the internal noise 21 of the communication device is the minimum reception sensitivity 23.

  Since reception is possible up to this reception strength, the level may be set equal to the carrier sense threshold if no external noise occurs. In order to avoid malfunction due to noise larger than the threshold value, it is determined from the actually received reception intensity as described above.

  The present invention in the case where noise larger than the threshold value is received has been described. However, when transmission is started after determining noise, the SN decreases due to noise and cannot be received.

  As illustrated in FIG. 9, a transmission required SN 25 that is a ratio of the transmission level 26 to the noise allowable for the transmission signal is set.

  The transmission required SN 25 may have the same value as the reception required SN 22, but since the transmission signal may be attenuated in the communication path and external noise may be mixed, the transmission required SN 25 is larger than the reception side. Designed to.

  Although transmission signal distortion is suppressed so as to satisfy the transmission required SN, the transmission required SN cannot be achieved if noise occurs on the transmission side. In the present invention described above, even when the noise is larger than the threshold value, it is determined that there is no carrier, and the transmission waiting time is subtracted.

  However, even when there is a large amount of noise and the required transmission SN cannot be ensured, transmission is started in a state where noise is generated. In order to avoid this, a value obtained by subtracting the transmission required SN from the transmission level for securing the transmission required SN may be used as a second threshold for the transmission waiting time.

  The flowchart will be described with reference to FIG.

  FIG. 10 is a process flowchart of the transmission timing control unit 8 as in FIG.

  First, CW is determined by random numbers as in the conventional method.

  Next, a count value C for counting the duration time after determining that there is a carrier is set to an initial value 0. The process after determining that there is no carrier is the same as the process described with reference to FIG. 5, and the transmission time is started when CW = 0 when the elapsed time when there is no carrier is measured.

  The difference from FIG. 6 is that it is determined whether or not the reception intensity is greater than the noise threshold (second threshold) after determining that there is a carrier. Since transmission is impossible if it is larger, transmission is waited until the received signal decreases. If it is smaller, the same processing flow as in FIG. 6 is performed.

  Noise is determined depending on whether or not synchronization is determined within a certain period of time immediately after determining that there is a carrier. If it is determined that the noise is present, the CW subtraction can be stopped by subtracting the period during which the carrier is erroneously determined as being present from CW.

  As described above, since whether or not CW subtraction can be performed is determined depending on the magnitude of noise intensity, it is possible to avoid excessive transmission suppression due to noise and to reduce the probability that SN due to noise is reduced and communication failure occurs.

  In the above-described embodiment, the second threshold value is determined from the transmission level and the transmission required SN. However, the threshold value may be dynamically varied. The intensity of noise radiated from the same noise source is attenuated in the communication path or the like.

  Therefore, noise intensities received by a plurality of communication devices from the same noise source are not equal. Signal attenuation between communication devices can be measured from the reception level if the transmission level is known.

  By notifying each other of the noise reception strength at each communication device from this, it is possible to estimate what the noise strength received in the device waiting state will be at the destination, so the threshold of noise strength can be determined by the communication partner. It is also possible to change.

  An embodiment using a wireless communication channel as a communication medium will be described with reference to FIGS.

  In FIG. 7, the basic configuration is the same as that shown in FIG. However, the coupling circuit 3 in FIG. 1 is a transmission / reception switching circuit in FIG.

  FIG. 8 shows the relationship between the radio communication master station and the radio communication slave station. The wireless communication master station 19 and the wireless communication slave station 20a (... 20n) perform transmission / reception by wireless communication.

  The present invention can be used in any communication apparatus that employs the CSMA / CA method.

DESCRIPTION OF SYMBOLS 1 Communication apparatus 2 Communication line 3 Coupling circuit 4 Reception circuit 5 Synchronization detection part 6 Demodulation circuit 7 Carrier determination part 8 Transmission timing control part 9 Modulation circuit 10 Transmission circuit 11 Control information apparatus 12 Noise source 13 Synchronization signal 14 Header signal 15 Data signal 16 Threshold 17 Antenna 18 Transmission / Reception Switching Circuit 19 Radio Communication Master Station 20 Radio Communication Slave Station

Claims (5)

In a communication device in which a plurality of communication devices are controlled to be transmitted by the CSMA / CA method using a communication line or a wireless communication channel as a communication medium,
A process for determining the carrier by comparing the received signal strength and the threshold value and a process for detecting the synchronization signal transmitted at the head of the communication signal are performed simultaneously.
A communication apparatus that measures the time from the determination that there is a carrier to the determination of synchronization. In a communication device in which a plurality of communication devices are controlled to be transmitted by the CSMA / CA method using a communication line or a wireless communication channel as a communication medium,
A carrier determination processing unit that determines a carrier by comparing the received signal strength with a threshold value, a detection processing unit that detects a synchronization signal transmitted at the head of a communication signal, and a process after the carrier determination processing unit determines that a carrier is present A measurement processing unit that measures each of the time and the elapsed time after the determination that there is no carrier,
After determining that the carrier is present, it is determined that synchronization is detected by the detection processing unit within a predetermined time. When synchronization is not determined, the elapsed time after determination that the carrier is present is set as the elapsed time when the carrier is not present. A communication apparatus that subtracts from a transmission waiting time generated by random numbers in a CA method. In claim 2,
If the carrier determination processing unit changes the determination value from the presence of the carrier to the absence of the carrier before the detection processing unit detects synchronization within a certain time after the determination that the carrier is present, the elapsed time with the carrier is expressed as CSMA / CA. A communication apparatus characterized by subtracting from a transmission waiting time generated by a random number in a method. In a communication device in which a plurality of communication devices are controlled to be transmitted by the CSMA / CA method using a communication line or a wireless communication channel as a communication medium,
A carrier determination processing unit that determines a carrier by comparing the received signal strength with a threshold value, a detection processing unit that detects a synchronization signal transmitted at the head of the communication signal, and a reception strength and threshold value at the time when the synchronization signal is detected And an update processing unit that updates the threshold value, and a measurement processing unit that measures the elapsed time after determination that the carrier is present and the absence of carrier and the elapsed time after determination by the carrier determination processing unit, Provided,
It is determined that synchronization is detected by the detection processing unit within a certain time after determining that the carrier is present. If synchronization is not determined, the elapsed time after the determination that the carrier is present is set as the elapsed time when there is no carrier. A communication apparatus that subtracts from a transmission waiting time generated by a random number using the / CA method. In claim 4,
When the determination value is changed from the presence of the carrier to the absence of the carrier before the detection is detected by the detection processing unit within a predetermined time after the determination that the carrier is present, the elapsed time with the carrier is determined by the CSAM / CA method. Subtracting from the transmission waiting time generated by random numbers in the above.

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