JP2013201509A - Signal detector and signal detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal detector and a signal detection method which detects a frame duration without demodulating a general signal including signals from a wide variety of different systems.SOLUTION: Before a preamble detection unit 101 carries out preamble detection, a threshold control unit 103 sets a first threshold value obtained by adding a first level margin value to average power of an input signal outputted from an average power calculation unit 102. After the preamble detection unit 101 carries out the preamble detection, the threshold control unit 103, when the average power of the input signal outputted from the average power calculation unit 102 is less than the first threshold value, sets a second threshold value obtained by subtracting a second level margin value from the average power. A power detection unit 104, when signal power continues to be less than the second threshold value for a prescribed determination time, determines the termination of a frame duration.

Description

  The present invention relates to a signal detection apparatus and a signal detection method for detecting a signal of another system.

  In recent years, a plurality of wireless communication standards have been developed or studied in millimeter wave wireless communication using the 60 GHz band. As main wireless LAN (Local Area Network) / wireless PAN (Personal Area Network) standards that do not require a license, for example, WiGig (Wireless Gigabit), IEEE802.15.3c, Wireless HD (High Definition), ECMA- There are 387. In addition, the IEEE 802.11ad standard is being developed.

  Further, even within each standard, a plurality of radio systems (for example, a single carrier system and an OFDM (Orthogonal Frequency Division Multiplexing) system) according to the target application coexist.

  A system corresponding to each of a plurality of wireless communication standards coexists, and a plurality of wireless systems coexist in each system. When millimeter-wave wireless communication becomes widespread, it is assumed that there are more situations in which a plurality of different wireless systems are used in close proximity. Therefore, it is required that a plurality of systems can communicate at the same time in the same space by using different frequency channels for each system.

  However, since frequency channels that can be used in the 60 GHz band are assumed to be 3 to 4 channels, when millimeter-wave wireless communication becomes widespread, different systems may use the same frequency channel. . For this reason, there is a concern that interference between systems occurs and the communication performance in each system is degraded.

  In order to avoid interference, it is first necessary to detect an interference signal from another system with respect to the target system. Conventionally, as a signal detection method disclosed in Patent Document 1, for example, in a wireless LAN system, carrier sense by electric power (hereinafter simply referred to as “carrier sense”) has been widely used. Carrier sense is a method of detecting a signal by detecting power.

  In each of a plurality of wireless communication standards related to the millimeter wave wireless communication described above, a signal pattern of a periodic signal used for a preamble portion is determined. By detecting a preamble using signal correlation, signal detection with higher detection sensitivity than carrier sense is possible.

  For signal detection of the own system, a method of detecting a preamble based on a cross-correlation between a known signal pattern included in the preamble and a received signal is used. On the other hand, in order to detect an interference signal from another system, it is necessary to evaluate all the cross-correlations with signal patterns of a plurality of wireless communication standards by the receiving side apparatus, so the method based on cross-correlation is not necessarily suitable.

  However, the period of the signal pattern used is common among some wireless communication standards, and the number of variations of the period of the periodic signal used for the preamble portion is relatively small compared to the number of variations of the signal pattern. Therefore, instead of the cross-correlation method, by providing an autocorrelation detector for the main period in the receiving apparatus, the receiving apparatus can widely detect interference signals from a wide variety of different systems.

  FIG. 1 is a diagram for explaining an autocorrelation detector disclosed in Patent Document 1. In FIG. FIG. 1A is a diagram showing a configuration of the autocorrelation detector 10 in Patent Document 1. As shown in FIG. FIG. 1B is a diagram conceptually showing processing in the autocorrelation detector. In FIG.1 (b), the 1st period part of a periodic signal is represented by S1, and the 2nd period part is represented by S2.

  As shown in FIG. 1B, the autocorrelation detector performs a correlation operation between the first signal that is the received signal and the second signal obtained by delaying the first signal by the delay device 11. The S1 portion and S2 portion of the first signal, and the S1 portion and S2 portion of the second signal are objects of correlation calculation processing. However, since the second signal is given a delay of one period of the periodic signal, when calculating the correlation between the first signal and the second signal, the S2 part of the first signal is actually The correlation with the S1 portion of the two signals is calculated. Specifically, in the correlation calculation, the first signal and the delayed second signal are multiplied by the multiplier 12, and the multiplication result obtained by the multiplier 12 is integrated by the integrator 13 over a predetermined period. Is done. Thereby, a correlation value is obtained.

  On the other hand, since the processing object of the correlation calculation is the S1 part and S2 part of the first signal and the S1 part and S2 part of the second signal, the observation period of the power used for normalization also corresponds to both S1 and S2. It becomes. That is, the correlation value is normalized by the normalization unit 15 based on the average value of the power during the power observation period by the power detection unit 17, and the presence or absence of a signal is determined by the comparator 16 based on the normalized correlation value.

  Further, the virtual carrier sense method disclosed in Non-Patent Document 1 is generally used. In the virtual carrier sense method, for example, in order to detect the signal of the own system in a wireless LAN, the frame length information is inserted into the frame header of the signal and transmitted, and the receiver extracts the frame length information from the signal. Determine the frame duration. Even if the reliability of carrier sense based on power is insufficient, the duration of a frame can be detected with high reliability by preamble detection and virtual carrier sense.

JP 2004-221940 A

IEEE Std 802.11-2007

  Here, in the carrier sense multiple access (CSMA) method in which a plurality of transmission signals do not collide, it is necessary to detect the duration of the frame. It is necessary to detect the duration of the frame.

  However, the autocorrelation detector disclosed in Patent Document 1 described above can detect the beginning of the frame, but it is difficult to detect the end of the frame. In other words, since the duration of the frame is unknown, it is difficult to establish CSMA.

  Also, in order to use the virtual carrier sense disclosed in Non-Patent Document 1, it is necessary for the receiver to demodulate the received signal and decode the frame length information. Here, in order to obtain frame length information from signals of a wide variety of different systems, it is necessary to demodulate the signals of all target different systems and decode the data. Applying the carrier sense method is not realistic.

  An object of the present invention is to provide a signal detection apparatus and a signal detection method for detecting a frame duration without demodulating a general signal including signals of a wide variety of different systems.

  The signal detection apparatus according to the present invention includes a preamble detection unit that detects a preamble portion arranged at the head of a frame of a received signal, a power detection unit that detects power of the received signal exceeding a variable threshold, and a detection of the preamble portion. And a threshold value control means for controlling the variable threshold value, wherein the power detection means has a predetermined power for the received signal with respect to the variable threshold value set when the preamble portion is detected. In this case, a configuration is adopted in which it is determined that the duration of the frame has ended.

  The signal detection method of the present invention includes a preamble detection step for detecting a preamble portion arranged at the head of a received signal frame, a power detection step for detecting power of the received signal exceeding a variable threshold, and detection of the preamble portion. And a threshold value control step for controlling the variable threshold value. In the power detection step, power of the received signal is predetermined with respect to the variable threshold value set when the preamble portion is detected. It is determined that the duration of the frame has ended when the time is less than the determination time.

  According to the present invention, it is possible to detect the frame duration without demodulating a general signal including signals of various different systems.

FIG. 5 is a diagram for explaining an autocorrelation detector disclosed in Patent Document 1. Diagram for explaining general autocorrelation method The block diagram which shows the structure of the signal detection apparatus which concerns on one embodiment of this invention The figure which uses for description of the signal detection operation | movement of the signal detection apparatus shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, carrier sense will be described.

  In carrier sense, the power of a received signal is measured, and if the measured power value exceeds a predetermined threshold, it is recognized that the signal has been detected. Carrier sense has a feature that a signal can be detected regardless of the type of system. On the other hand, depending on the power, there is a case where noise and a signal cannot be distinguished.

  For this reason, carrier sense has the following relationship. If the predetermined threshold is set low to improve the detection sensitivity, erroneous detection that erroneously detects noise as a signal is likely to occur. Conversely, if the predetermined threshold is set high to prevent erroneous detection, Sensitivity deteriorates. In other words, there is a trade-off between improving detection sensitivity and preventing false detection.

  By the way, in recent wireless communication, since the transmission speed is increasing, multi-level modulation is often used. In communications using multilevel modulation, data errors are likely to occur even with weak interference. In order to effectively avoid the interference, it is necessary to accurately detect a weak level of interference.

  For this reason, in the carrier sense having the trade-off relationship described above, it is highly likely that it is difficult to satisfy the level of interference detection sensitivity required when receiving a signal modulated by multilevel modulation.

  Therefore, as a signal detection method with better signal detection sensitivity than carrier sense, there is a technique that uses correlation between signals. Techniques using correlation are roughly divided into the following two. One is a cross-correlation method for detecting a detection target signal based on a correlation value between a preamble portion included in the received signal and a known pattern signal candidate used for the preamble portion, and the other is a received signal. This is an autocorrelation method for detecting a detection target signal based on a correlation value between preamble portions of a first signal and a second signal that are copied from the first signal.

  In the preamble portion, a periodic signal in which a specific signal pattern is repeated is often used. In the autocorrelation method, the periodicity of the periodic signal is used for signal detection. The signal detection sensitivity of the autocorrelation method is generally lower than that of cross-correlation detection, but higher than that of carrier sense. The signal detection sensitivity of the autocorrelation method is higher than that of carrier sense because noise and a signal can be distinguished by the periodicity of the periodic signal.

  Also, in the autocorrelation method, unlike the cross-correlation method, the receiving side does not need to know the specific signal pattern described above. Therefore, the receiving apparatus can be realized with a simple configuration. Further, in the autocorrelation method, it is only necessary to detect the periodicity of the waveform, so that it is not necessary to perform reception signal processing in accordance with the symbol rate of the interference signal. The autocorrelation method has an advantage that it can be easily applied to signal detection in different systems having different symbol rates or modulation methods.

  FIG. 2 is a diagram for explaining a general autocorrelation method. FIG. 2A shows the basic configuration of the autocorrelation detector 20, and FIG. 2B is a diagram conceptually showing the autocorrelation process.

  In the autocorrelation detector 20 shown in FIG. 2 (a), the second signal is delayed by a delay device 21 for a predetermined time out of the first signal and the second signal to which the received signal is distributed. The predetermined time corresponds to the period of the periodic signal used for the preamble portion of the detection target signal.

  The first signal and the delayed second signal are multiplied by the multiplier 22. In the autocorrelation detector 20 in FIG. 2A, a simple multiplier is provided, but a complex multiplier may be used. This is because a complex baseband signal is treated as a received signal and multiplied by a complex conjugate.

  The multiplication result obtained in the multiplier 22 is integrated over a predetermined period in the integrator 23 to obtain a correlation value.

  The absolute value of the obtained correlation value is calculated by the absolute value calculation unit 24, the absolute value of the calculated correlation value is compared with a predetermined threshold value, and a signal corresponding to the comparison result is output.

  Here, the correlation value obtained from the complex baseband signal is a complex number. However, in an ideal state where the period of the periodic signal used in the preamble portion included in the received signal and the delay time given to the second signal in the delay unit 21 are completely the same, the obtained correlation value is a positive real number. become.

  On the other hand, for example, when phase rotation occurs due to an error factor of the clock deviation, the obtained correlation value may not necessarily be a positive real number. Here, the correlation value obtained in the integrator 23 is not directly used for determination, but the absolute value of the correlation value is used for determination. However, when it is guaranteed that the error factor is sufficiently small, the correlation component substantially matches the real number component, and the imaginary number component is caused by noise, for example. Instead of using the absolute value of the correlation value for the determination, a real component of the correlation value may be used for the determination.

  That is, the absolute value of the correlation value or the real component of the correlation value is input to the comparator 25 and compared with a predetermined threshold value. When the input value is larger than the predetermined threshold value, it is determined that the signal is detected by the comparator. Is done.

  In the autocorrelation detector, in order to reduce erroneous detection as much as possible and detect weak signals with high sensitivity, it is necessary to appropriately set a threshold value. Note that erroneous detection means that noise is not detected as a detection target signal, but an original detection target signal.

(One embodiment)
In the embodiment of the present invention, it is assumed that a plurality of communication systems corresponding to a plurality of millimeter wave wireless communication standards are mixed. A transmission device (for example, an access point) of each communication system arranges and transmits a periodic signal set in each communication system in a preamble portion. A signal detection device according to an embodiment of the present invention is mounted on a receiving device, for example, a terminal device, that communicates in any of the plurality of communication systems described above.

  The signal detection device detects a preamble signal from a plurality of communication systems (hereinafter referred to as “other systems”) other than the communication system (hereinafter referred to as “own system”) with which the mounted receiving device communicates. To do. In the following description, it is assumed that the signal detection device detects a plurality of preamble signals from other systems, but the preamble signal to be detected may be included in the preamble signal to be detected.

  FIG. 3 is a block diagram showing a configuration of the signal detection apparatus 100 according to one embodiment of the present invention. The signal detection apparatus 100 receives a reception signal (that is, a baseband signal) obtained after a radio reception signal received via an antenna in the reception apparatus is subjected to radio reception processing (for example, down-conversion, analog-digital conversion). As input. Hereinafter, the configuration of the signal detection apparatus 100 will be described with reference to FIG.

  The preamble detection unit 101 detects the preamble at the beginning of the frame, and outputs a preamble detection signal to the threshold control unit 103 and the determination unit 105. The use of the autocorrelation detector shown in FIG. 2 as the preamble detection unit 101 is preferable because it is suitable for signal detection in a heterogeneous system. May be used.

  The average power calculation unit 102 calculates the average power of the input signal for the most recent predetermined time, and outputs the calculated average power to the threshold control unit 103. The average time is set to a time sufficient to smooth a short time fluctuation. As the average time is increased, for example, malfunction due to instantaneous fluctuations in noise can be reduced, and precise threshold setting is possible. And CSMA operation will be hindered. It is preferable to set it to several to several tens of times the reciprocal of the bandwidth of the input signal. The average power calculation operation may obtain an accurate average value over a predetermined time, but may be a smoothing operation using a low-pass filter, for example.

  The threshold control unit 103 sets a threshold based on the average power output from the average power calculation unit 102. Specifically, before the preamble detection signal is input, the threshold value control unit 103 sets a value obtained by adding a predetermined level margin (first level margin value) to the average power as the first threshold value. Prevent detection. This is an operation that emphasizes the reduction of false detection. Note that the first threshold may be infinite and the detection operation may be substantially invalidated.

  Further, the threshold control unit 103 receives a preamble detection signal, and when the average power of the input preamble detection signal is lower than the first threshold, the threshold control unit 103 has a predetermined level margin (first power) with respect to the average power (preamble unit power). A value obtained by subtracting (2 level margin value) is set as the second threshold value. This is an operation that places importance on detection sensitivity. In addition, by using two threshold values, it is possible to achieve both improvement in detection sensitivity and reduction in false detection.

  Moreover, the threshold value control part 103 will return to the 1st threshold value before a preamble detection signal input, if the power detection part 104 notifies that signal power will fall below a 2nd threshold value over predetermined | prescribed determination time. The method of returning from the second threshold value to the first threshold value may be instantaneously changed or may be gradually changed stepwise or smoothly over a predetermined time. By gradually changing the threshold value, it is possible to prevent frame detection from being ended erroneously due to instantaneous fluctuations in the signal, and stable frame detection can be performed.

  Further, the threshold control unit 103 includes a timer that counts a predetermined timeout time. When the signal power does not fall from the preamble detection timing over the timeout time, the first threshold value before the preamble detection signal is input is restored. Thereby, for example, it is possible to prevent the false detection from continuing for a long time due to the fluctuation of the background noise level. The timeout time is preferably set to the maximum frame length that is normally used for the signal to be detected.

  The power detection unit 104 compares the power of the input signal with a threshold controlled by the threshold control unit 103, and outputs a power detection signal to the determination unit 105 when the power is greater than the threshold. In addition, when the power of the input signal falls below the second threshold for a predetermined determination time, the power detection unit 104 notifies the threshold control unit 103 to that effect. Here, the fact that the signal power falls below the second threshold for a predetermined determination time means that the frame duration has ended, so that the frame duration can be detected.

  The determination unit 105 outputs a logical sum of the preamble detection signal output from the preamble detection unit 101 and the power detection signal output from the power detection unit 104 as a detection determination signal. That is, if either one or both of the preamble and the power is detected, it is determined that the signal is detected. This operation is effective in the following cases.

  The threshold control unit 103 needs time from detection of the preamble to calculation of an appropriate threshold. This is because time is required for the average operation or calculation for accurately measuring the power of the preamble portion. Therefore, the rise of the power detection signal is delayed from the preamble detection timing. This delay time is not negligible. For example, when the CSMA operation is disturbed, a signal is generated by the preamble detection signal regardless of the power detection signal in which a delay occurs by using the logical sum of the power detection signal and the preamble detection signal. Detection can be determined.

  Note that the determination unit 105 may include a timeout process similar to the timeout time of the threshold control unit 103. That is, the determination unit 105 may forcibly invalidate the detection determination signal after a predetermined time has elapsed from the preamble detection timing.

  Further, the determination unit 105 may forcibly invalidate the detection determination signal before preamble detection, after the falling edge of the power detection signal, and after the timeout time elapses. This is an operation equivalent to setting the first level margin to infinity in the threshold control unit 103.

  Next, the signal detection operation of the signal detection apparatus 100 described above will be described with reference to FIG. Before the detection of the preamble, a first threshold value obtained by adding the first level margin value to the average power is set. For this reason, even if noise occurs, since the power of the noise is less than the first threshold value, signal detection is not performed and erroneous detection can be prevented.

  Subsequently, when the preamble is detected and the average power of the preamble is lower than the first threshold, the second threshold obtained by subtracting the second level margin value from the average power (preamble portion power) is set. Sensitivity can be improved.

  When the signal power falls below the second threshold over a predetermined determination time, it is determined that the duration of the frame has ended, and the second threshold is changed to the first threshold.

  According to the present embodiment, the first threshold value obtained by adding the first level margin value to the average power of the input signal is set before the preamble detection, and the average power is lower than the first threshold after the preamble detection. By setting a second threshold value obtained by subtracting the second level margin value from the average power and determining that the duration of the frame has ended when the signal power falls below the second threshold value for a predetermined determination time, Without demodulating general signals including signals from a wide variety of different systems, it is possible to improve the detection sensitivity and reduce false detection, and to detect the frame duration.

  Although the present embodiment has been described on the assumption that a preamble detection unit that detects the preamble at the beginning of the frame is provided, other characteristic signals existing near the beginning of the frame are detected instead of the preamble detection unit. A feature signal detection unit may be used. As the feature signal, for example, a unique word for frame capture, a synchronization signal, or a frame header can be used.

  Also, although cases have been described with the above embodiment as examples where the present invention is configured by hardware, the present invention can be realized by software in cooperation with hardware.

  Each functional block used in the description of the present embodiment is typically realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of each functional block. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI, or a reconfigurable processor in which connection and setting of circuit cells inside the LSI can be reconfigured may be used.

  Furthermore, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using another technology. Biotechnology can be applied.

  The signal detection device and the signal detection method according to the present invention can be applied to a reception device that communicates with any one of a plurality of communication systems, for example, a terminal device.

101 Preamble detection unit 102 Average power calculation unit 103 Threshold control unit 104 Power detection unit 105 Determination unit

Claims (9)

Preamble detecting means for detecting a preamble portion arranged at the head of the frame of the received signal;
Power detection means for detecting the power of the received signal exceeding a variable threshold;
Threshold control means for controlling the variable threshold based on detection of the preamble portion;
Comprising
The power detection means determines that the duration of the frame has ended when the power of the received signal falls below a predetermined determination time with respect to the variable threshold set when the preamble portion is detected. To
Signal detection device.   The signal detection apparatus according to claim 1, wherein the preamble part is a periodic signal.   The signal detection apparatus according to claim 1, wherein the preamble detection unit detects the preamble part using autocorrelation.   The signal detection apparatus according to claim 1, further comprising: a determination unit configured to use a logical sum of the received signal having power exceeding the variable threshold and the detected preamble part as a detection determination signal.   The signal detection device according to claim 4, wherein the determination unit invalidates the detection determination signal after a predetermined time has elapsed from the detection timing of the preamble part.   The threshold control means sets the variable threshold to the first threshold before the preamble part is detected, and detects the preamble part, and the average power of the received signal is lower than the first threshold The signal detection device according to claim 1, wherein the variable threshold is set to a second threshold.   The threshold control means sets the variable threshold to the second threshold, and when the average power of the received signal falls below the second threshold for a predetermined determination time, the first threshold before detecting the preamble portion. The signal detection device according to claim 6, wherein the signal detection device is returned to the threshold value.   The signal detection device according to claim 7, wherein the threshold value control unit gradually changes the second threshold value to the first threshold value. A preamble detection step of detecting a preamble portion arranged at the beginning of the frame of the received signal;
A power detection step of detecting power of the received signal exceeding a variable threshold;
A threshold control step for controlling the variable threshold based on detection of the preamble portion;
Comprising
In the power detection step, when the power of the received signal falls below a predetermined determination time with respect to the variable threshold set when the preamble portion is detected, it is determined that the duration of the frame has ended. To
Signal detection method.

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