CN101136655B - Authorized User Signal Detection Method Based on Spatial Diversity - Google Patents

Abstract

The detection method of authorized user signals based on spatial diversity includes five processes. Each sensing terminal in the sensing sub-area conducts independent periodic sampling of the authorized signal, and then performs multi-scale wavelet transformation on the sampled signal sequence, uses the decision device at each scale to judge the transformation result, and finally uses the phase adder to detect the appearance of the authorized signal independent judgment. Utilizing the diversity of the spatial distribution of the sensing terminals, the access point of the sensing sub-area collects the judgment results of each sensing terminal and executes the decision-making process, wherein the decision-making process is completed by the phase extractor. The access point broadcasts the detection result. If it detects that an authorized user starts to use the frequency band, each sensing user will give up the use right of the frequency band. If it detects that no authorized user uses the frequency band, the sensing user can continue to use the frequency band.

Description

Authorized User Signal Detection Method Based on Spatial Diversity

technical field

The invention utilizes the diversity of the spatial distribution of the cognitive wireless terminals, and the technology that each terminal can detect sudden changes based on wavelet analysis is applied to the detection of authorized user signals in the wireless wireless network.

Background technique

Cognitive radio is a wireless communication concept and technology that has emerged in recent years. It can sense all spectrum usage opportunities in the current communication environment. In other words, by reorganizing the framework of the wireless network system, the cognitive wireless network has the ability to intelligently identify and change spectrum use opportunities. This feature of the cognitive wireless network can reset the reorganization of its networking, and can optimize the use of the perceived spectrum opportunities according to the network architecture, wireless resources, communication settings, etc. These kinds of network collaboration are inseparable. There are various signs that the cognitive wireless network will become a new development in the future with extremely high spectrum utilization efficiency. Cognitive radio theoretically allows multi-dimensional frequency band multiplexing in time, frequency and space, which will greatly reduce the constraints on the development of wireless technology due to frequency band and bandwidth limitations, unlike the previous allocation of specific frequencies to specific purposes. with large differences.

Perceived users have lower spectrum access priority than authorized users. In order not to cause harmful interference to licensed users, sensing users need to be able to independently detect the presence of idle spectrum and licensed users. This requires sensing users to be able to continuously listen to the spectrum in real time to improve the reliability of detection. not to cause harmful interference to authorized users. A reliable detection probability of 99.9% is required. Early detection methods used energy detection method and cycle stationary process feature detection, etc., but the detection performance will decrease with the weakening of received signal strength caused by multipath and shadow fading, and the detection ability itself has certain limitations, so in order to realize Reliable detection requires the exploration of new methods. The current simulation and analysis show that the above-mentioned requirements of reliable detection probability can be achieved by adopting the method of cooperative diversity. Cooperative interception allows multiple sensing users to exchange interception information with each other, which can significantly improve spectrum interception and detection capabilities. Therefore, it is necessary to develop a distributed method with high detection performance.

Contents of the invention

Technical problem: The purpose of the present invention is to provide a method for detecting authorized user signals in a cognitive wireless network, which can meet the detection requirements and can be used to detect weak authorized user signals.

Technical solution: The present invention is a method for detecting authorized user signals based on spatial diversity, which includes three processes: receiving signal sequence processing process, collecting and executing decision-making process and broadcasting detection result process.

The authorization signal detection method based on spatial diversity of the present invention combines distributed detection with centralized decision-making. Firstly, each sensing terminal in the sensing sub-area performs distributed sampling on the authorization signal, and then independently processes the sampled signal, and finally The access point collects the processing results of each sensing terminal and executes a decision to determine whether the authorization signal occurs. The method includes the following five processes and is performed in the order described:

1) Periodic sampling process: each sensing terminal in the sensing sub-area independently periodically samples the authorization signal,

2) Wavelet transform processing process: Each sensing terminal uses wavelet transformer to perform multi-scale wavelet transform on the sampling sequence, and sets different threshold values at each scale to judge the results after wavelet transform, and the judgment at each scale The output result of the device enters the phase AND, and outputs the processing result,

3) Collect and execute the decision-making process: the access point of the sensing sub-area collects the processing results of each sensing terminal and inputs them to the phase processor, and executes the final decision to judge whether the authorization signal appears,

4) The process of broadcasting the detection result: the access point broadcasts the detection result in the sensing sub-area to notify each sensing terminal whether the authorization signal appears,

5) Executing the detection result process: the sensing terminal receives the detection result of the access point and performs corresponding actions; if it detects that an authorized user appears, it starts to use the frequency band, and each sensing user will give up the right to use the frequency band. Authorized users use this frequency band, and perceived users will continue to use this frequency band.

The wavelet transform processing process includes that each sensing terminal in the sensing sub-area performs distributed sampling on the authorized signal, and then performs multi-scale wavelet transform, and uses the decision device at each scale to judge the transformation result, and finally each sensing terminal The phase AND device of the terminal performs AND on the judgment results of each scale, and independently judges whether the authorized signal appears or not.

Collecting and executing the decision-making process includes using the diversity of the spatial distribution of the sensing terminals, and the access point of the sensing sub-area collects the judgment results of each sensing terminal and executes the decision-making process, wherein the decision-making process is completed by the phase extractor.

In the process of broadcasting detection results, the access point broadcasts the decision result in the sensing sub-area. If it detects that authorized users start using this frequency band, each sensing user will give up the right to use the frequency band. If it detects that no authorized user uses this frequency band, the sensing Users will continue to be able to use this frequency band.

Each sensing terminal sets a different threshold value at each scale to judge the result of wavelet transformation, and the output results of the decision device at each scale enter the phase AND device for judgment. In order to reduce the influence of noise, a A smaller threshold value is used on each scale, and those modulus values greater than the threshold value are retained.

Beneficial effects: the present invention proposes a detection method for authorized user signals in a wireless cognitive network. The advantage is that it utilizes the diversity of spatial distribution of sensing terminals, reduces the influence of multipath and fading, and improves the performance of detection. Moreover, a multi-scale wavelet transform detection method is used in each terminal, which can be used to detect weaker authorized user signals and meet the detection performance requirements.

Description of drawings

FIG. 1 is a schematic diagram of a mutation form of an authorized user signal.

Fig. 2 is a schematic diagram of the relationship between local maximum points and signal mutation points of local convolution.

Fig. 3 is a schematic diagram of a quadratic spline scaling function.

Fig. 4 is a schematic diagram of a quadratic spline wavelet function.

Fig. 5 is a schematic diagram of the variation of the quadratic spline wavelet transform modulus of the authorized signal with the scale.

Fig. 6 is a block diagram of a sensing terminal signal detector.

Fig. 7 is a schematic diagram of a distributed sensing solution. Among them, Figure 7(a) is the detection, collection and decision process; Figure 7(b) is the broadcast process.

Fig. 8 is a block diagram of an authorized user signal detector based on spatial diversity.

Detailed ways

The authorization signal detection method based on spatial diversity in the present invention combines distributed detection with centralized decision-making. First, each sensing terminal in the sensing sub-area performs distributed sampling on the authorization signal, and then independently processes the sampled signal. Finally, the The access point collects the processing results of each sensing terminal and executes a decision to determine whether the authorization signal occurs. The method includes the following five processes and is performed in the order described:

1) Periodic sampling process: each sensing terminal in the sensing sub-area independently periodically samples the authorization signal,

2) Wavelet transform processing process: Each sensing terminal uses wavelet transformer to perform multi-scale wavelet transform on the sampling sequence, and sets different threshold values at each scale to judge the results after wavelet transform, and the judgment at each scale The output result of the device enters the phase AND, and outputs the processing result,

3) Collect and execute the decision-making process: the access point of the sensing sub-area collects the processing results of each sensing terminal and inputs them to the phase processor, and executes the final decision to judge whether the authorization signal appears,

4) The process of broadcasting the detection result: the access point broadcasts the detection result in the sensing sub-area to notify each sensing terminal whether the authorization signal appears,

5) Executing the detection result process: the sensing terminal receives the detection result of the access point and performs corresponding actions; if it detects that an authorized user appears, it starts to use the frequency band, and each sensing user will give up the right to use the frequency band. Authorized users use this frequency band, and perceived users will continue to use this frequency band.

The mutation of the authorized user signal can be manifested in two forms: one is from existence to non-existence, and the other is from non-existence to existence. The performance of signal mutation has locality, and the authorized user signal and mutation point can be regarded as local odd symmetry about the mutation center point. If a wavelet function is used at the sensing terminal (the wavelet function may be in the form of local odd symmetry or local even symmetry) to convolve the authorized signal, and observe the convolution result in a local range near the center point of the mutation, It can be seen that the convolution result can express the mutation characteristics of the mutation signal. Moreover, in order to reduce the influence of noise, a small threshold value can be used on each scale, and those modulus values larger than the threshold value can be reserved. Because noise interference will interfere with the exact location of the retrieval, the retrieval points when comparing multiple scales can resist interference. Therefore, only when the extremum values of the wavelet transform moduli in multiple scales are greater than the threshold value, can the signal mutation be accurately judged.

Due to the weakening of the received signal strength caused by multipath and shadow fading, if a single sensing terminal is used to judge the presence or absence of authorized users, it will cause missed judgment or misjudgment. According to the diversity of spatial distribution of mobile terminals, a detection method based on spatial diversity is proposed, that is, all terminals in the sensing sub-area participate in the detection of authorized signals, and this method can overcome multipath and shadow fading. Each sensing terminal detects authorized users, and the access point collects each detection result and executes a decision-making process.

The access point broadcasts the decision result. If it detects that the authorized user starts to use the frequency band, each sensing user will give up the use right of the frequency band. If it detects that no authorized user uses the frequency band, the sensing user will continue to use the frequency band.

In conjunction with the accompanying drawings, the scheme design of the present invention is further specifically analyzed and described.

(1) Wavelet analysis is used to detect authorized user signals

In order to prevent the sensing users from causing harmful interference to the authorized users, the sensing users need to be able to independently detect the occurrence of idle spectrum and authorized users. Assuming that there are p (p=1, 2, ..., K) sensing terminals in a sensing system, and each terminal performs periodic sampling detection on the authorized user signal, use r _p1 , r _p2 , ..., r _pN to indicate that the pth terminal is in N sampling sequences at different times, the detection problem of authorized user signals can be expressed by the following assumptions:

$\left\{\begin{array}{c}{h}_0:r_p={\mathrm{no}}_p\\ h_1:r_p=A_p{S}_i+{\mathrm{no}}_p\end{array}\right.$ p=1,2,...,K; i=1,2,...,N

H ₀ indicates that there is no authorized user signal, and H ₁ indicates that there is an authorized user signal. Among them, n _pi represents the sampling noise of the p-th sensing terminal at time i, S _i represents the normalized value of the authorized user signal at time i, and the random variable A _p is a non-negative real number, which reflects that the authorized user signal at the p-th Attenuation effects on the channel. However, due to the slow decay, it is generally considered that the amplitude of the signal is constant in the observation interval, so it has nothing to do with the sampling time i.

The mutation of the authorized user signal can be expressed in two forms: one is from existence to non-existence, and the other is from non-existence to existence. This mutation process can be shown in Figure 1. The performance of signal mutation is localized. As shown in Figure 1, authorized user signal and mutation point can be regarded as local odd symmetry about the mutation center point. If a wavelet function is used (the wavelet function may be in the form of local odd symmetry, it may also be is a form of local even symmetry) respectively convolve the two local mutation signals shown in Figure 1, and observe the convolution results in a local range near the mutation center point, the following rules are found:

local odd * local odd = local even

local even * local odd = local odd

The local signal and convolution effect are shown in Figure 2.

It can be seen from Figure 2 that the convolution result can represent the mutation characteristics of the mutation signal shown in Figure 1. Since the inner product of wavelet transform is also a form of convolution, the local symmetry and bandpass of wavelet function enable wavelet function to represent the local mutation characteristics of sudden signal as shown in Figure 1. And in order to reduce the impact of noise and attenuation, multi-scale wavelet transform is used to make comprehensive observation and judgment on multiple scales. The scaling function used is a quadratic spline, that is, (as shown in Figure 3) and the quadratic spline wavelet function, namely ψ(t)

(as shown in FIG. 4 ), wavelet transform is performed on the authorized user signal. Assuming that the signal to be detected is r(t), the variation of the modulus extremum value of the wavelet transform obtained after the above wavelet transform with the scale is shown in Figure 5.

In order to reduce the influence of noise, a small threshold value ε can be used on each scale to retain those modulus values greater than ε, and only the wavelet transform modulus extreme values at multiple scales are greater than the threshold value, in order to accurately determine the signal mutation. Because noise interference will interfere with the exact location of the retrieval, the retrieval points when comparing multiple scales can resist interference. Assuming that |w _j r _p | is used to represent the modulus maximum point of the wavelet transform coefficient retrieved on the jth scale, if |w _j r _p |>ε, it means that there is a sudden change in the authorized signal, and a high level "1" is output , otherwise, "0". Then the output signal of the discriminator at each scale enters the phase AND, if the output signal T _p of the phase AND is high level "1", it means that there is a sudden change in the signal detected at each scale, and it can be judged for an authorization signal to appear. This process can be represented by the block diagram shown in Figure 6.

(2) Distributed detection method based on spatial diversity

Due to the weakening of the received signal strength caused by multipath and shadow fading, using a sensing terminal to judge the presence or absence of authorized users will cause missed or misjudged. According to the spatial diversity of mobile terminal distribution, a detection method based on spatial diversity is proposed. Through the detection method of spatial diversity, the detection performance of the system can be greatly improved. Figure 7 is an application scenario of the system. In this scenario, all terminals within the range of the access point perform spectrum detection. This method can overcome multipath and shadow fading. In (a), each sensing user detects the authorized user, and the access point collects each detection result and executes a decision-making process; in (b), the access point broadcasts the detection result, and if it detects that the authorized user starts to use the Each sensing user will give up the right to use the frequency band. If no authorized user is detected to use the frequency band, the sensing user will continue to use the frequency band. This detection process can be shown in Figure 8.

Claims (3)

1. one kind based on the multifarious authorization signal detection method in space, it is characterized in that Distributed Detection combines with centralized decision, at first authorization user signal is sampled by each perception terminal of perception subregion, then sampled signal is carried out independent process, at last collect the result of each perception terminal by access point and carry out decision-making and judge whether authorization user signal occurs, this method comprises following 5 processes and is undertaken by described order:

1) periodic sampling process: each perception terminal of perception subregion carries out periodic sampling independently to authorization user signal,

2) wavelet transform process process: each perception terminal utilizes wavelet transformer that sample sequence is carried out multi-scale wavelet transformation, and different threshold values is set under each yardstick comes the result behind the wavelet transformation is adjudicated, the output result of the decision device under each yardstick enter with device with, and output result

3) collect and carry out decision process: the access point of perception subregion to the result of each perception terminal collect and be input to device with, carry out at last to make a strategic decision to judge whether authorization user signal occurs,

4) broadcasting testing result process: whether access point is broadcasted testing result and is occurred to notify each perception terminal authorization user signal in the perception subregion,

5) carry out the testing result process: perception terminal receives the testing result of access point and carries out corresponding action, if detecting the signal of authorized user occurs, each perception terminal will be abdicated the right to use of the shared frequency band of this signal, do not have authorization user signal if detect, perception terminal can continue to use this frequency band.

2. as claimed in claim 1 based on the multifarious authorization signal detection method in space, it is characterized in that collecting and carrying out decision process and comprise the diversity of utilizing the perception terminal spatial distribution, decision process is collected and carried out to the access point of perception subregion to the court verdict of each perception terminal, wherein, decision process is by finishing with device.

3. as claimed in claim 1 based on the multifarious authorization signal detection method in space, it is characterized in that each perception terminal is provided with different threshold values and comes the result behind the wavelet transformation is adjudicated under each yardstick, the output result of the decision device under each yardstick enter with device with adjudicate, in order to reduce The noise, employing with some less threshold values, keeps those mould values greater than threshold value on each yardstick.

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