JP6306480B2 - Detection device, control method, and program - Google Patents

Description

  The present invention relates to a signal detection technique.

  In mobile communication, communication is usually performed by transmitting and receiving radio signals between a base station and a mobile terminal using a predetermined frequency band. Therefore, communication is possible when the mobile terminal can receive the radio wave transmitted by the base station and the base station can receive the radio wave transmitted by the mobile terminal. Here, radio waves are attenuated by the propagation distance and shielding objects, and considering that there is a physical or legal limit in the transmission power of signals from base stations and mobile terminals, the radiated signals can be received normally. There may be a geographical area where the received signal power drops to an inadequate power level. Similarly, there may be geographical areas where the radiated power is not normally received at the counterpart device.

  In conventional mobile communication using a frequency band having a relatively low center frequency, many base stations are installed so that such a geographical area becomes as narrow as possible. However, in recent years when demand for high-speed communication is increasing, it is necessary to use a frequency band with a high center frequency, and due to the attenuation characteristics and straightness of the radio waves, there are areas where surface coverage is difficult. Yes.

  However, for example, in a region where radio waves from the base station do not reach, even if the mobile terminal transmits radio waves, it does not reach the base station, that is, the transmission signal does not interfere with the base station. Similarly, in a region where radio waves from other mobile terminals do not reach, it is considered that the other mobile terminals do not interfere. In such a region, it can be considered that the frequency band and time resources that radio waves do not reach are not used (that is, “free”). Therefore, a mobile terminal existing in such a region can directly transmit and receive signals between different mobile terminals using at least one of a frequency band and a time resource used for communication with the base station. It is thought that you can.

  In this way, direct communication between mobile terminals is performed using at least one of frequency resources and time resources that are vacant in some areas so as not to interfere with the base station and other mobile terminals. Thus, the frequency band can be effectively used.

  When performing direct terminal-to-terminal communication using at least one of a free frequency resource and a time resource, it is first necessary to determine whether a signal is transmitted and received in another communication, that is, to detect a signal. At this time, for example, when a large number of mobile terminals perform inter-terminal communication at various places, interference accumulates and increases. Therefore, a sufficiently low power signal (for example, a signal with a power lower than a noise level) Can also affect communications. Therefore, it is important that such interference with low power can be detected. In response to such a problem, Non-Patent Document 1 and Non-Patent Document 2 detect weak signals by signal detection using cyclic autocorrelation function (CAF), which is a characteristic of periodic stationarity. The technology is disclosed.

W. A. Gardner, “Cyclostationarity in Communications and Signal Processing”, IEEE Press, New York, USA, 1993. M.M. Oner and F.M. Jondral, “Air interface recognition for software and radiology system exploration cy- posal system symptoms of the air interface for software radio systems.” 3, pp. 1947-951, September 2004

  Signal detection should be done, for example, while using free frequency and time resources. It should also be possible to determine that communication between terminals is being performed in the vicinity even when the power of the signal from the priority system is very large. However, the techniques of Non-Patent Document 1 and Non-Patent Document 2 described above may fail in detection when a plurality of signals are mixed. In particular, if the power of the first signal is significantly lower than the power of the second signal or vice versa, detection of the low power signal may fail. Therefore, for example, when communication is started with a system that should be prioritized after communication is started with a free frequency resource and time resource, the power of the signal of the priority system is shifted to a state where the resource is not free. Is low and the detection of the signal may fail. Further, for example, when the power of the signal of the priority system is large, it may not be possible to determine whether there is a signal for communication between neighboring terminals. As described above, even when the techniques described in Non-Patent Document 1 and Non-Patent Document 2 are used, the signal detection success rate can be improved under the condition that a plurality of signals are received simultaneously with greatly different powers. It remained as an issue.

  The present invention has been made in view of such a background, and an object of the present invention is to improve a signal detection success rate under a condition in which a plurality of signals are received simultaneously with greatly different powers.

In order to achieve the above object, a detection apparatus according to the present invention demodulates the first signal based on the receiving means for receiving a radio signal including a first signal and a second signal, and the radio signal. A demodulating means, a removing means for generating a replica of the first signal based on a result of demodulation of the first signal and removing it from the radio signal; and a signal from which the replica has been removed, a detecting means for performing detection processing of the second signal, have a, the detection means of the signal in which the replica is removed, the Fourier transform of the correlation function of the signal obtained by delaying the signal and the signal A certain period autocorrelation signal is calculated, and the detection process is performed depending on whether or not a peak of the period autocorrelation signal appears at a predetermined amount of the delay and a predetermined frequency of the correlation function. And

  ADVANTAGE OF THE INVENTION According to this invention, the detection success rate of a signal can be improved on the conditions that a several signal is received simultaneously with the electric power which differs greatly.

The figure which shows the conceptual diagram of a radio | wireless communications system. The block diagram which shows the hardware structural example of a signal detection apparatus. The block diagram which shows the function structural example of a signal detection apparatus.

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

(System configuration)
FIG. 1 shows a conceptual diagram of a wireless communication network according to the present embodiment. In this wireless communication network, as an example, in the wireless communication network 100 in which the base station 101 and the wireless communication terminal 102 (hereinafter simply referred to as “terminal”) communicate, the terminal 151 and the terminal 152 use the same frequency band. Communicate at the same time. At this time, communication between the base station 101 and the terminal 102 is given priority over communication between the terminal 151 and the terminal 152, and communication between the terminal 151 and the terminal 152 is performed between the base station 101 and the terminal 152. It is assumed that interference with the communication 102 should not be caused more than necessary.

  In this wireless communication system, for example, the terminal 151 and the terminal 152 transmit a second signal between the terminal 151 and the terminal 152 when the first signal transmitted from the base station 101 or the terminal 102 is not detected. Communication is possible by transmitting and receiving. For example, the terminal 151 and the terminal 152 perform signal detection by calculating a cyclic automation function (CAF, periodic autocorrelation signal) for the received signal. Then, when the signal is not detected or only detected at a sufficiently low level, the signal is transmitted to the partner terminal or the signal is received from the partner terminal.

のようになる。ここで、αはサイクリック周波数であり、τはラグパラメータである。ＣＡＦは、自己相関関数のフーリエ変換に相当し、信号の波形の周期性に応じて、様々な特徴が出現する（非特許文献２参照）。ここで、ＯＦＤＭ信号に着目すると、ＯＦＤＭ信号では、時間長がＴ_UのＯＦＤＭシンボルのうち、例えばそのシンボルの末尾の時間長Ｔ_CP分の波形がシンボルの先頭にサイクリックプリフィックス（ＣＰ）として付加される。したがって、ＯＦＤＭ信号ｘ(ｔ)についてのｘ(ｔ)ｘ(ｔ−τ)においては、τ＝Ｔ_Uにおいて、Ｔ_U＋Ｔ_CPの周期でピークが出現する。したがって、τ＝Ｔ_U及びα＝ｎ／（Ｔ_U＋Ｔ_CP）（ただし、ｎは整数）において、ＣＡＦはピークを有することとなる。 Here, the calculation formula of CAF is:

become that way. Where α is the cyclic frequency and τ is the lag parameter. CAF corresponds to the Fourier transform of the autocorrelation function, and various features appear according to the periodicity of the signal waveform (see Non-Patent Document 2). Here, focusing on the OFDM signal, in the OFDM signal, for example, a waveform corresponding to the time length T _CP at the end of the symbol is added as a cyclic prefix (CP) at the head of the symbol among the OFDM symbols having the time length T _U. Is done. Therefore, in x (t) x (t−τ) for the OFDM signal x (t), a peak appears at a period of T _U + T _CP at τ = T _U. Therefore, CAF has a peak at τ = T _U and α = n / (T _U + T _CP ) (where n is an integer).

  That is, in the OFDM signal, a CAF peak appears at a position corresponding to the symbol length including the CP and the symbol length excluding the CP. Therefore, even if communication systems using a plurality of OFDM signals are mixed, if the symbol length including / excluding the CP of the OFDM signal used in each system is different, it depends on the CAF peak position. Any system signaling can be determined.

  For signals other than OFDM, the CAF peak appearance position varies depending on the symbol rate or the like, so that signal detection by CAF can be performed. In addition, signal detection using CAF can detect a signal having a level smaller than the noise level according to the observation length.

  However, as described above, in an environment where a plurality of signals are received at the same time, particularly in an environment where a large signal and a small signal are mixed, signal detection fails even when CAF is used. There is a case. That is, for example, when the terminal 151 and the terminal 152 are communicating, the first signal transmitted from the base station 101 or the terminal 102 is much larger than the second signal transmitted and received between the terminal 151 and the terminal 152 or vice versa. In this case, signal detection by CAF may fail.

  Therefore, in the present embodiment, in the signal detection device that calculates the CAF, a signal with low power is detected after removing a signal with high power from the received radio signal by an interference canceller. This solves the problem that a low-power signal cannot be detected because it is buried in a high-power signal.

  Such a signal detection device may be provided in the terminal 151 and the terminal 152. For example, a management device (not shown) that manages the frequency usage status of the entire system includes such a signal detection device. It may be. For example, the signal detection device provided in the management device receives radio signals at a plurality of geographically separated positions, and performs communication using the second signal based on the detection results of the received plurality of radio signals. Determine the geographic area where the Moreover, it is determined based on a signal detection result whether there exists a possibility that communication by a 2nd signal may interfere with communication by a 1st signal. Thereafter, the management device having the signal detection device notifies the communication device requesting communication using the second signal of permission / rejection of the start / continuation of communication according to, for example, the position. As a result, the non-priority wireless communication device can perform communication by reusing the same frequency band while suppressing the interference with the priority wireless communication network below a predetermined value.

  First, when the signal detection apparatus of the present embodiment receives a radio signal, the signal detection apparatus demodulates a signal having a high power (main signal) based on the radio signal. Here, when the power of the main signal is sufficiently large compared to the other signals, the main signal and other signals are subjected to demodulation processing on the radio signal including the main signal and the main signal with a sufficiently low error rate. The signal can be demodulated. Thereafter, the signal detection device removes the main signal component from the radio signal based on the demodulation result, and performs signal detection on the signal after the removal.

(Configuration of signal detection equipment)
FIG. 2 shows a hardware configuration example of the signal detection device. As illustrated in FIG. 2, the signal detection device includes, for example, a CPU 201, a ROM 202, a RAM 203, an external storage device 204, and a communication device 205. In the signal detection device, control is performed such that the CPU 201 executes a program for realizing each function of the signal detection device shown below, which is recorded in any of the ROM 202, the RAM 203, and the external storage device 204, for example. Then, the signal detection device uses the communication device 205 to collect information such as signal reception, or notifies the management device of the determination result. In FIG. 2, the signal detection apparatus has one communication apparatus 205, but may have a plurality of communication apparatuses.

  Note that the signal detection apparatus may include dedicated hardware that executes each function described below, or may execute a part of the hardware with a computer and execute the other part with a computer that operates the program. Good. Further, all the following functions may be executed by a computer and a program.

  FIG. 3 is a block diagram illustrating a functional configuration of the signal detection device. The signal detection device has a function of demodulating the main signal and a function of detecting other signals as functions. The demodulation function of the main signal includes, for example, a demodulation unit 301, an error correction decoding unit 302, an error correction coding unit 303, and a channel multiplication unit 304. Other signal detection functions are based on the delay unit 305 and subtractor 306 for subtracting the replica of the main signal output from the channel multiplier 304 from the received signal, and the signal from which the replica of the main signal has been removed. A detection unit 307 for detecting a signal is included.

  The demodulator 301 demodulates the main signal using the received radio signal itself. That is, even when the radio signal includes other signals as interference, it is treated as noise and the main signal is demodulated. Here, the demodulation includes, for example, channel estimation, and obtains data symbols by, for example, hard decision. The obtained data symbol is input to error correction decoding section 302, and the channel estimation value is input to channel multiplication section 304.

  Error correction decoding section 302 performs error correction decoding on the input data symbol, and inputs the resulting data to error correction encoding section 303. The error correction encoding unit 303 re-encodes the data after error correction decoding with an error correction code, and inputs the re-encoded data to the channel multiplication unit 304.

  The channel multiplication unit 304 generates a replica of the main signal component in the received radio signal. Specifically, the channel multiplication unit 304 outputs, as a replica of the main signal, data obtained by multiplying the data re-encoded by the error correction encoding unit 303 by the estimated value of the transmission path (channel) of the main signal. . Note that an IFFT (Fast Inverse Fourier Transformer) for converting the signal output from the error correction coding unit 303 into, for example, an OFDM signal format may be arranged before the channel multiplication unit 304. Further, the channel multiplication unit 304 may be omitted depending on circumstances. Note that the channel estimation value used by the channel multiplication unit 304 may use the result estimated by the demodulation unit 301, or detect the correlation between the output of the error correction coding unit 303 or the above-mentioned IFFT and the received signal. By doing so, it may be estimated again. In this case, a correlator may be provided separately.

  The replica of the main signal is subtracted from the radio signal including the main signal at the timing corresponding to the replica in the subtractor 306. Note that the delay unit 305 delays the received radio signal and adjusts the timing so that the output timing of the replica matches the timing of the radio signal.

  The detection unit 307 detects a signal other than the main signal based on the signal obtained by subtracting the replica of the main signal from the reception signal by the delay unit 305. This detection is performed based on the cyclic autocorrelation signal (CAF) as described above. That is, the detection unit 307 calculates CAF, and determines whether or not a peak appears at a predetermined lag parameter τ and cyclic frequency α with respect to a signal to be detected. For this determination, for example, any method such as a hypothesis testing method such as χ (chi) square test (see Non-Patent Document 2), a detection method based on a peak size, or the like may be used.

  Note that the sampling frequency may be adjusted for this determination. That is, actual signal processing is performed by applying digital processing to the sampled signal, but depending on the sampling frequency, it may not be possible to calculate the CAF for a predetermined lag parameter τ. For this reason, the sampling frequency (sampling rate) may be adjusted according to the signal to be detected. For example, when the sampling frequency suitable for detection of the first signal and the sampling frequency suitable for detection of the second signal are different, the least common multiple of each sampling frequency may be set as the sampling frequency that is actually used. . In this case, for example, when processing corresponding to the first signal is performed, processing is performed on the sample corresponding to the first sampling frequency, and when processing corresponding to the second signal is performed, the second processing is performed. Processing is performed on samples corresponding to a sampling frequency of 2. For example, the removal of the first signal is performed by generating a replica signal for the sample corresponding to the second sampling frequency from the replica for the sample corresponding to the first sampling frequency by using linear interpolation or the like. It can be broken.

  In the signal detection device described above, the main signal is not detected, but the main signal may be detected. For example, first, signal detection is performed on the received signal with respect to the lag parameter τ and the cyclic frequency α where CAF peaks are expected to appear for some or all of the signals that may be received. May be. As a result, when no signal other than the main signal is detected, the main signal may be removed, and signal detection may be performed on the signal after the removal. By doing in this way, signal detection is performed in order from the one with larger reception power. That is, since the target to be removed first is not specified, signal detection can be performed for any received signal including a plurality of signals. In this case, when a plurality of signals are received with the same level of power, the plurality of signals can be detected simultaneously. Therefore, for example, when only two systems exist, the signals of the two systems can be detected at the same time by performing signal detection once. Disappear.

  As described above, in the present embodiment, when signal detection based on CAF is performed on a received signal including a signal with high power and a signal with low power, the signal with high power is demodulated and removed. And after removing the main signal with large electric power, the detection process regarding the signal with small electric power is performed. As a result, it is possible to prevent a signal having low power from being buried in a signal having high power and failing in detection, and to improve detection performance.

Claims (7)

Receiving means for receiving a radio signal including the first signal and the second signal;
Demodulation means for demodulating the first signal based on the radio signal;
Removing means for generating a replica of the first signal based on the result of demodulation of the first signal and removing it from the radio signal;
Detection means for performing detection processing of the second signal based on the signal from which the replica has been removed;
I have a,
The detection means calculates a periodic autocorrelation signal that is a Fourier transform of a correlation function between the signal and a signal obtained by delaying the signal with respect to the signal from which the replica has been removed, and the peak of the periodic autocorrelation signal is Performing the detection process depending on whether or not a certain amount of the delay and a predetermined frequency of the correlation function have appeared.
A detection device characterized by that. The detection means detects the first signal and the second signal based on the radio signal before the detection process based on the signal from which the replica has been removed,
When the detection means detects both the first signal and the second signal based on the radio signal, the detection means does not perform the detection process of the second signal based on the signal from which the replica has been removed.
The detection apparatus according to claim 1. If the detection means does not perform the detection process of the second signal based on the signal from which the replica has been removed, the demodulation means does not demodulate the first signal, and the removal means generates the replica And does not remove the replica from the radio signal,
The detection apparatus according to claim 2. For each of the first signal and the second signal, the sampling frequency of the radio signal is adjusted based on the delay amount and the predetermined frequency at which the peak of the periodic autocorrelation signal should appear Further comprising adjusting means for
The detection apparatus according to any one of claims 1 to 3, wherein The first signal is a signal having higher power than the second signal.
Detection device according to claim 1 in any one of 4, characterized in that. A method for controlling a detection apparatus having a receiving means for receiving a radio signal including a first signal and a second signal,
A demodulating step for demodulating the first signal based on the radio signal;
A removing step of generating a replica of the first signal based on a result of demodulation of the first signal and removing the replica from the radio signal;
A detection step in which the detection means performs the detection process of the second signal based on the signal from which the replica has been removed;
I have a,
In the detection step, a periodic autocorrelation signal that is a Fourier transform of a correlation function between the signal and a signal obtained by delaying the signal with respect to the signal from which the replica has been removed is calculated, and the peak of the periodic autocorrelation signal is Performing the detection process depending on whether or not a certain amount of the delay and a predetermined frequency of the correlation function have appeared.
A control method characterized by that. In a computer provided in a detection apparatus having a receiving means for receiving a wireless signal including a first signal and a second signal,
A demodulation step of demodulating the first signal based on the radio signal;
A removing step of generating a replica of the first signal based on a result of demodulation of the first signal and removing it from the radio signal;
A detection step of performing detection processing of the second signal based on the signal from which the replica has been removed;
A program for executing,
In the detection step, a periodic autocorrelation signal that is a Fourier transform of a correlation function between the signal and a signal obtained by delaying the signal with respect to the signal from which the replica has been removed is calculated, and the peak of the periodic autocorrelation signal is Performing the detection process depending on whether or not a certain amount of the delay and a predetermined frequency of the correlation function have appeared.
A program characterized by that .

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