CN101867425B

CN101867425B - Available subcarrier detection and synchronization method for discontinuous OFDM dynamic spectrum access

Info

Publication number: CN101867425B
Application number: CN201010219158A
Authority: CN
Inventors: 丁杰; 屈代明; 江涛
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2010-07-08
Filing date: 2010-07-08
Publication date: 2012-10-10
Anticipated expiration: 2030-07-08
Also published as: CN101867425A

Abstract

The invention discloses an available subcarrier detection and synchronization method for discontinuous OFDM dynamic spectrum access. The method comprises the following steps of: (1) transmitting data frames, wherein each initial data frame consists of a training symbol and a synchronizing symbol which are connected with each other in turn; (2) receiving the data frames; (3) detecting the posterior probability of available subcarriers; and (4) acquiring a synchronization word, namely obtaining the available positions of the subcarriers according to the hard decision of the posterior probability, receiving data from the decided subcarriers and performing demodulation, de-interleaving and error correction decoding to acquire a transmitted synchronization word. The method belongs to an in-band signaling solution, saves spectrum resource, reduces the processing time delay of a system and has good synchronization performance in the presence of an interference signal brought by a user.

Description

Available Subcarrier Detection and Synchronization Method for Discontinuous OFDM Dynamic Spectrum Access

技术领域 technical field

本发明属于无线通信技术领域，涉及采用正交频分复用信号（OFDM）的动态频谱接入方法，具体地说是一种接收端在未知频谱同步相关信息情况下进行的可用子载波检测方法，频谱同步是指接收端能够确定发送端可用的OFDM子载波数量和位置。The invention belongs to the technical field of wireless communication, and relates to a dynamic spectrum access method using an Orthogonal Frequency Division Multiplexing (OFDM) signal, in particular to a method for detecting available subcarriers performed by a receiving end under the condition of unknown spectrum synchronization related information , Spectrum synchronization means that the receiving end can determine the number and position of OFDM subcarriers available at the sending end.

背景技术 Background technique

随着通信需求的不断发展和可供通信的频谱资源变得日益稀少，基于认知无线电的动态频谱接入技术是一种有前途的解决方案，因为它能够以一种机会主义的方式复用和分享频谱资源。也就是说当授权用户不使用某段频谱时，非授权用户被允许识别和使用该段瞬时频谱。With the continuous development of communication needs and the spectrum resources available for communication become increasingly scarce, dynamic spectrum access technology based on cognitive radio is a promising solution because it can be reused in an opportunistic manner and share spectrum resources. That is to say, when licensed users do not use a certain spectrum, unlicensed users are allowed to identify and use the instantaneous spectrum.

对于宽带非授权用户来说，OFDM是一种很好的信号结构，因为利用OFDM能够有效地在非连续的频带上传输通信信号。为了避免对正在工作的授权用户形成干扰，非授权用户可以只使用部分OFDM的子载波传输信号，这些被使用的子载波可以是不连续的。For broadband unlicensed users, OFDM is a good signal structure, because OFDM can effectively transmit communication signals on discontinuous frequency bands. In order to avoid interference to licensed users who are working, unlicensed users may only use part of OFDM subcarriers to transmit signals, and these used subcarriers may be discontinuous.

在动态变化的频谱环境中，非授权用户的发送方会根据授权用户对频谱的使用情况随时改变其使用的子载波个数和位置。对于非授权用户的接收方而言，一个关键的问题是保持和发送方同步，即接收方要了解发送方采用了哪些子载波。如果接收方采用的子载波个数和位置与发送方的不同，显然将造成严重的误码率和误包率恶化。我们将上述的同步问题称为频谱同步问题。频谱同步问题是非连续OFDM动态频谱接入系统的一个关键问题，目前，相关的研究和技术还相当少。与本发明相关的现有技术有：In a dynamically changing spectrum environment, the sender of an unlicensed user will change the number and location of the subcarriers used by the licensed user at any time according to the usage of the spectrum by the licensed user. For the receiver of the unauthorized user, a key issue is to maintain synchronization with the sender, that is, the receiver needs to know which subcarriers are used by the sender. If the number and position of sub-carriers used by the receiver are different from those of the sender, it will obviously cause severe deterioration of the bit error rate and packet error rate. We refer to the above synchronization problem as the spectrum synchronization problem. Spectrum synchronization is a key issue in the discontinuous OFDM dynamic spectrum access system. At present, the relevant research and technology are still quite few. The prior art relevant to the present invention has:

部分带宽模式（FBW Mode）检测和同步方法，见Y.W.Jae,G.K.Hyun,H.K.Yun,S.Iickho,and S.S.Myung,“Fractional BandwidthMode Detection and Synchronization for OFDM-Based Cognitive RadioSystems,”in Proc.IEEE Vehicular Technology Conference,May 2008,pp.1599-1603。部分带宽模式同步方法是通过将接收信息与数种可能的部分带宽模式进行匹配来实现的。系统事先定义好21种部分带宽模式，每种模式使用的子载波个数和位置是固定的。发送方只能用其中一种部分带宽模式发送信号。接收方通过检测接收信号中的部分带宽模式实现频谱同步。Fractional Bandwidth Mode (FBW Mode) detection and synchronization method, see Y.W.Jae, G.K.Hyun, H.K.Yun, S.Iickho, and S.S.Myung, "Fractional BandwidthMode Detection and Synchronization for OFDM-Based Cognitive RadioSystems," in Proc.IEEE Vehicular Technology Conference, May 2008, pp. 1599-1603. Partial bandwidth pattern synchronization methods are implemented by matching received information with several possible partial bandwidth patterns. The system defines 21 partial bandwidth modes in advance, and the number and position of subcarriers used in each mode are fixed. The sender can only send signals in one of the partial bandwidth modes. The receiver achieves spectrum synchronization by detecting partial bandwidth patterns in the received signal.

部分带宽模式检测和同步方法的系统模型如图1所示。发送方通过频谱感知（Sensing）确定一个最合适的部分带宽模式（FBW Mode），并使用该模式中规定的子载波发送信号。接收方通过检测接收信号中的部分带宽模式实现频谱同步。The system model of the partial bandwidth mode detection and synchronization method is shown in Fig. 1. The sender determines a most suitable partial bandwidth mode (FBW Mode) through spectrum sensing (Sensing), and uses the subcarriers specified in this mode to send signals. The receiver achieves spectrum synchronization by detecting partial bandwidth patterns in the received signal.

上述方案的缺点是系统能定义的部分带宽模式数量十分有限，因为部分带宽模式多，会影响检测的正确率。上述论文中仅能提供21种模式，这21模式甚至不能支持非连续的频谱情况。在部分带宽模式数量有限的情况下，系统无法针对频谱环境的动态变化，作出精确细致的调整，从而导致系统的频谱利用效率不能得到充分提高。The disadvantage of the above scheme is that the number of partial bandwidth modes that can be defined by the system is very limited, because there are too many partial bandwidth modes, which will affect the accuracy of detection. Only 21 modes can be provided in the above paper, and these 21 modes cannot even support discontinuous spectrum conditions. When the number of some bandwidth modes is limited, the system cannot make precise and detailed adjustments to the dynamic changes of the spectrum environment, resulting in that the spectrum utilization efficiency of the system cannot be fully improved.

发明内容 Contents of the invention

本发明的目的是提供一种用于在未知频谱同步信息情况下用于非连续OFDM动态频谱接入的可用子载波检测同步方法，该方法可以有效检测出可用子载波的位置，在大干扰的条件下得到理想的同步信息。The object of the present invention is to provide a method for detecting and synchronizing available subcarriers for non-continuous OFDM dynamic spectrum access under the condition of unknown spectrum synchronization information. Ideal synchronous information is obtained under the condition.

用于非连续OFDM动态频谱接入的可用子载波检测同步方法，包括以下步骤：A method for detecting and synchronizing available subcarriers for discontinuous OFDM dynamic spectrum access, comprising the following steps:

（1）发送方发射数据帧，数据帧由训练符号和同步符号依次前后相连组成，同步符号携带了可用子载波的位置信息；(1) The sender transmits a data frame, which is composed of training symbols and synchronization symbols connected one after another, and the synchronization symbols carry the position information of the available subcarriers;

（2）接收方接收数据帧；(2) The receiver receives the data frame;

（3）接收方计算第k个子载波为可用子载波的概率P，若P大于等于预定门限值，表示可用，否则不可用；其中，(3) The receiver calculates the probability P that the kth subcarrier is an available subcarrier. If P is greater than or equal to the predetermined threshold value, it means that it is available, otherwise it is not available; among them,

$P P = = \frac{ex ex {{p p {Λ Λ}_{k k}}}}{11 + + ex ex {{{Λp Λp}_{k k}}}},,$

$Λ_{k} = \ln \frac{P (T_{k} = 1)}{P (T_{k} = 0)} + \ln \frac{σ_{I}^{2}}{σ_{n}^{2}} + \frac{{| Q_{k} |}^{2}}{2 σ_{I}^{2}} - \frac{{| Q_{k} - {\hat{H}}_{k} P_{k}^{'} |}^{2}}{2 σ_{n}^{2}}$ 或者 $Λ_{k} = \ln \frac{P (T_{k} = 1)}{P (T_{k} = 0)} + \ln \frac{σ_{I}^{2}}{σ_{no}^{2}} + \frac{{| Q_{k} |}^{2}}{2 σ_{I}^{2}} - \frac{{| Q_{k} - {\hat{h}}_{k} P_{k}^{'} |}^{2}}{2 σ_{no}^{2}}$ or

${Λ Λ}_{k k} = = ln ln \frac{P P (({T T}_{k k} = = 11))}{P P (({T T}_{k k} = = 00))} + + {Σ Σ}_{m m = = k k - - J J / / 22}^{k k + + J J / / 22} {{ln ln \frac{{σ σ}_{I I}^{22}}{{σ σ}_{n no}^{22}} + + \frac{{| | {Q Q}_{m m} | |}^{22}}{22 {σ σ}_{I I}^{22}} - - \frac{{| | {Q Q}_{m m} - - {\overset{^^}{H h}}_{m m} {P P}_{m m}^{' '} | |}^{22}}{22 {σ σ}_{n no}^{22}}}}$

其中k＝1,2,…,N，N表示子载波的总数，T_k表示第k个子载波的状态，P(T_k＝1)和P(T_k＝0)分别表示第k个子载波可用和不可用的概率，

为主用户干扰信号每一维信号的方差，为噪声信号每一维信号的方差，Q_k为接收方从第k个子载波上接收到的数据帧的训练符号，表示接收方对第k个子载波的信道估计值，表示在频谱连续的情况下第k个子载波上的训练符号，J为邻接子载波的个数；Where k=1,2,...,N, N represents the total number of subcarriers, T _k represents the state of the kth subcarrier, P(T _k =1) and P(T _k =0) respectively represent the availability of the kth subcarrier and unavailable probability,

The variance of each dimension signal of the main user interference signal, is the variance of each dimension of the noise signal, Q _k is the training symbol of the data frame received by the receiver from the kth subcarrier, Indicates the receiver's channel estimate for the kth subcarrier, Represents the training symbol on the kth subcarrier in the case of continuous spectrum, J is the number of adjacent subcarriers;

（4）接收方从步骤（3）中得到的可用子载波上解调数据，获知同步符号信息。(4) The receiver demodulates data from the available subcarriers obtained in step (3), and obtains the synchronization symbol information.

本发明的技术效果体现在：本发明通过发送端发送数据帧给接收端，数据帧包括一个训练符号和一个同步符号，同步符号由同步字经过卷积编码、调制和重复编码形成。接收端使用接收到的训练符号计算出每个子载波被发送端利用的后验概率，针对这些后验概率，设置一个适当的门限，将那些大于门限的后验概率所对应的子载波判定为可用子载波，进而进行同步符号数据的检测。本发明实时有效，接收端检测迅速精确，在主用户带来干扰的情况下，可以达到理想的同步性能。该训练符号位于同步符号之前。The technical effect of the present invention is reflected in: the present invention sends a data frame to the receiving end through the sending end, the data frame includes a training symbol and a synchronization symbol, and the synchronization symbol is formed by convolution coding, modulation and repetition coding of the synchronization word. The receiving end uses the received training symbols to calculate the posterior probability of each subcarrier being used by the transmitting end, and sets an appropriate threshold for these posterior probabilities, and determines the subcarriers corresponding to those posterior probabilities greater than the threshold as available Subcarriers, and then detect the synchronization symbol data. The invention is effective in real time, the receiving end detects quickly and accurately, and can achieve ideal synchronization performance under the condition that the main user brings interference. The training symbol precedes the synchronization symbol.

本发明属于带内信令解决方案，节省了频谱资源，减少了系统的处理时延，保证了子载波检测的实时性。The invention belongs to an in-band signaling solution, saves frequency spectrum resources, reduces system processing time delay, and ensures real-time performance of subcarrier detection.

附图说明 Description of drawings

图1是本发明方法流程示意图；Fig. 1 is a schematic flow sheet of the method of the present invention;

图2为本发明非连续OFDM子带划分示意图；Fig. 2 is a schematic diagram of discontinuous OFDM subband division in the present invention;

图3是本发明同步符号生成步骤流程框图；Fig. 3 is a block flow diagram of synchronization symbol generation steps of the present invention;

图4是本发明数据帧结构和接收机处理过程示意图。Fig. 4 is a schematic diagram of the data frame structure and the receiver processing procedure of the present invention.

具体实施方式 Detailed ways

本发明提供的实施例，如图1所示，具体包括以下步骤：The embodiment provided by the present invention, as shown in Figure 1, specifically includes the following steps:

（1）发射帧(1) Transmit frame

一帧由训练符号和同步符号依次前后相连组成，进行逆快速傅立叶变换，并串转换，加循环前缀后发射出去。A frame is composed of training symbols and synchronization symbols successively connected one after the other, undergoing inverse fast Fourier transform, parallel-to-serial conversion, adding a cyclic prefix and then transmitting.

（1.1）训练符号(1.1) Training symbols

首先定义子载波状态矢量T＝[T₀,T₁,…,T_N]，其中T_k表示第k个子载波的状态，k＝1,2,…,N，N表示子载波的总数。如果该子载波可用，T_k＝1，否则T_k＝0。在频谱不连续的情况下，发送的训练符号在频域上用矢量P＝[P₀,P₁,…,P_N]表示，其中P_k是一个复数，表示训练符号在第k个子载波上的幅度和相位，First, the subcarrier state vector T=[T ₀ , T ₁ ,...,T _N ] is defined, where T _k represents the state of the kth subcarrier, k=1, 2,..., N, and N represents the total number of subcarriers. If the subcarrier is available, T _k =1, otherwise T _k =0. In the case of discontinuous spectrum, the transmitted training symbols are represented by a vector P=[P ₀ , P ₁ ,…,P _N ] in the frequency domain, where P _k is a complex number, indicating that the training symbols are on the kth subcarrier amplitude and phase,

其中P′_k(k＝0,1,2,…,N)是矢量P′＝[P′₀,P′₁,…,P′_N]中的元素，P′表示在频谱连续的情况下系统使用的训练符号。Among them, P′ _k (k=0,1,2,…,N) is the element in the vector P′=[P′ ₀ ,P′ ₁ ,…,P′ _N ], and P′ means that in the case of continuous spectrum The training symbols used by the system.

（1.2）同步符号(1.2) Synchronization symbols

图2所示，同步符号在频域上用矢量C＝[C₁,…,C_k,…,C_N]表示，其中C_k表示同步符号在第k个子载波上的幅度和相位，As shown in Figure 2, the synchronization symbol is represented by a vector C=[C ₁ ,...,C _k ,...,C _N ] in the frequency domain, where C _k represents the amplitude and phase of the synchronization symbol on the kth subcarrier,

${C C}_{k k} = = {C C}_{k k}^{' '} \cdot \cdot {T T}_{k k}$

其中

是矢量中的元素，C′由同步字调制符号S重复M倍得到，即in

is a vector The elements in , C′ are obtained by repeating the synchronization word modulation symbol S M times, that is

${C C}_{k k}^{' '} = = {S S}_{n no};; n no = = k k mod mod ((N N / / M m))$

其中k mod(N/M)表示k对(N/M)取余，N和M满足整除关系，即(N/M)为一正整数。S_n是矢量S＝[S₁,…,S_n,…,S_(N/M)]中的元素，其中n表示矢量S中元素的序号，n＝1,2,…,(N/M)。S由同步字B经过纠错编码器编码，交织器交织，M阶调制（如PSK或QAM调制）得到，其中同步字B表示可用子载波的位置。本发明中用同步字表示可用子载波位置，下面举例一种同步字获取的方法，但本发明并不局限于这种方法，也可以采用其它的方式获取同步字。Where k mod (N/M) means that k is the remainder of (N/M), and N and M satisfy the divisibility relationship, that is, (N/M) is a positive integer. S _n is the element in the vector S=[S ₁ ,...,S _n ,...,S _(N/M) ], where n represents the sequence number of the element in the vector S, n=1,2,...,(N/M ). S is obtained by synchronizing word B through an error correction encoder, interleaving, and M-order modulation (such as PSK or QAM modulation), where the synchronizing word B indicates the position of an available subcarrier. In the present invention, the synchronization word is used to indicate the position of the available sub-carriers. The following is an example of a method for obtaining the synchronization word, but the present invention is not limited to this method, and other methods can also be used to obtain the synchronization word.

规定非连续频谱OFDM动态频谱接入系统使用V个子载波进行通信，V的取值范围为[1,N]；如图3所示，假设V个非连续的可用子载波能够分成各自连续的F段，称为F个子带；用每个子带的开始子载波序号和结束子载波序号表示这些子带的位置；第q个子带的开始子载波序号k_qs的二进制数表示为(k_qs)2；结束子载波序号k_qe的二进制数表示为(k_qe)2，其中1≤q≤F,(k_qs)2和(k_qe)2各用个比特表示，

表示对log₂N向上取整；则B＝[(k_1s)2,(k_1e)2,…,(k_qs)2,(k_qe)2,…(k_Qs)2,(k_Qe)2]，B中共有个比特。It is stipulated that the non-continuous spectrum OFDM dynamic spectrum access system uses V subcarriers for communication, and the value range of V is [1, N]; as shown in Figure 3, it is assumed that V non-continuous available subcarriers can be divided into respective continuous F segment, called F sub-bands; the position of these sub-bands is represented by the start sub-carrier number and the end sub-carrier number of each sub-band; the binary number of the start sub-carrier number k _qs of the qth sub-band is expressed as (k _qs )2 ; The binary number of the end subcarrier number k _qe is expressed as (k _qe )2, where 1≤q≤F, (k _qs )2 and (k _qe )2 are respectively used bits represent,

Indicates that log ₂ N is rounded up; then B=[(k _1s )2,(k _1e )2,...,(k _qs )2,(k _qe )2,...(k _Qs )2,(k _Qe ) 2], B has a total of bits.

（2）接收帧(2) Receive frame

接收到的数据进行移除循环前缀，串并转换，快速傅立叶变换处理，得到受信道干扰产生失真的帧。The received data is processed by removing the cyclic prefix, serial-to-parallel conversion, and fast Fourier transform to obtain a frame distorted by channel interference.

（3）可用子载波后验概率的检测(3) Detection of available subcarrier posterior probability

图4给出了接收端对接收数据的处理流程，通过接收到的训练符号首先进行子载波后验概率的检测。Fig. 4 shows the processing flow of the received data at the receiving end, and the detection of the subcarrier posterior probability is first performed through the received training symbols.

非连续频谱OFDM动态频谱接入系统的接收端根据接收到的训练符号进行可用子载波后验概率P(T_k＝1|Q_k)的检测。接收到的第k个子载波上的训练符号为The receiving end of the non-continuous spectrum OFDM dynamic spectrum access system detects the available subcarrier posterior probability P(T _k =1|Q _k ) according to the received training symbols. The received training symbol on the kth subcarrier is

其中Q_k、P_k、H_k分别表示第k个子载波上接收到的训练符号、发送的训练符号、信道响应，I_k表示第k个子载波上的来自主用户的干扰（专利中我们假设主用户带来的复干扰信号的每一维都服从均值为0方差为

的正态分布），W_k表示第k个子载波上的复高斯白噪声，其每一维信号都服从均值为0方差为

的正态分布。Among them, Q _k , P _k , and H _k respectively represent the received training symbols on the kth subcarrier, the transmitted training symbols, and the channel response, and I _k represents the interference from the primary user on the kth subcarrier (in the patent, we assume that the primary user Each dimension of the complex interference signal brought by the user has a mean value of 0 and a variance of

normal distribution), W _k represents the complex white Gaussian noise on the kth subcarrier, and each dimension of the signal obeys the mean value of 0 and the variance is

normal distribution of .

根据接收到的信号Q_k，我们可以得到关于T_k的后验概率P(T_k＝1|Q_k)，其中，According to the received signal Q _k , we can get the posterior probability P(T _k =1|Q _k ) about T _k , where,

$P P (({T T}_{k k} = = 11 | | {Q Q}_{k k})) = = \frac{P P (({T T}_{k k} = = 11 | | {Q Q}_{k k}))}{P P (({T T}_{k k} = = 11 | | {Q Q}_{k k})) + + P P (({T T}_{k k} = = 00 | | {Q Q}_{k k}))}$

$= = \frac{exp exp {{{Λ Λ}_{k k}}}}{11 + + exp exp {{{Λ Λ}_{k k}}}} - - - - - - ((11))$

其中，

exp{ }为指数函数。in,

exp{ } is an exponential function.

根据贝叶斯公式，我们可以得到According to Bayesian formula, we can get

${Λ Λ}_{k k} = = \frac{ρ ρ (({Q Q}_{k k} | | {T T}_{k k} = = 11)) P P (({T T}_{k k} = = 11))}{ρ ρ (({Q Q}_{k k} | | {T T}_{k k} = = 00)) P P (({T T}_{k k} = = 00))}$

其中P(T_k＝1)和P(T_k＝0)是关于子载波可用和不可用的先验概率。Wherein P(T _k =1) and P(T _k =0) are prior probabilities about subcarrier availability and unavailability.

ρ(Q_k|T_k＝1)和ρ(Q_k|T_k＝0)都是关于Q_k的条件概率密度函数，这些条件概率密度函数可以有如下表达形式：Both ρ(Q _k |T _k ＝1) and ρ(Q _k |T _k ＝0) are conditional probability density functions about Q _k , and these conditional probability density functions can have the following expressions:

$ρ ρ (({Q Q}_{k k} | | {T T}_{k k} = = 11)) = = \frac{11}{22 {πσ πσ}_{n no}^{22}} exp exp {{- - \frac{{| | {Q Q}_{k k} - - {\overset{^^}{H h}}_{k k} {P P}_{k k}^{' '} | |}^{22}}{22 {σ σ}_{n no}^{22}}}},,$

$ρ ρ (({Q Q}_{k k} | | {T T}_{k k} = = 00)) = = \frac{11}{{22 πσ πσ}_{I I}^{22}} exp exp {{- - \frac{{| | {Q Q}_{k k} | |}^{22}}{22 {σ σ}_{I I}^{22}}}}$

其中

表示第k个子载波上的信道估计值，in

Indicates the channel estimate on the kth subcarrier,

${\overset{^^}{H h}}_{k k} = = {Σ Σ}_{m m = = k k - - (({N N}_{a a} - - 11)) / / 22}^{k k + + (({N N}_{a a} - - 11)) / / 22} \frac{{Q Q}_{m m}}{{N N}_{a a} {P P}_{m m}^{' '}}$

其中N_a决定了参与信道估计计算的子载波个数，N_a∈[7,15]。Among them, N _a determines the number of subcarriers participating in the channel estimation calculation, N _a ∈ [7,15].

通过上面的推导，我们就可以得到Λ_k的表达式：Through the above derivation, we can get the expression of Λ _k :

${Λ Λ}_{k k} = = ln ln \frac{P P (({T T}_{k k} = = 11))}{P P (({T T}_{k k} = = 00))} + + ln ln \frac{{σ σ}_{I I}^{22}}{{σ σ}_{n no}^{22}} + + \frac{{| | {Q Q}_{k k} | |}^{22}}{22 {σ σ}_{I I}^{22}} - - \frac{{| | {Q Q}_{k k} - - {\overset{^^}{H h}}_{k k} {P P}_{k k}^{' '} | |}^{22}}{22 {σ σ}_{n no}^{22}}$

将Λ_k的表达式代入到（1）式中，我们就可以得到后验概率P(T_k＝1|Q_k)的表达式。但是，由于噪声和干扰的随机性，单独的利用一个采样点Q_k的信息得到的后验概率P(T_k＝1|Q_k)是不准确的，因此，我们利用相邻子载波具有相同状态的特性来改善检测的性能，我们定义P(T_k＝1|Q_k)来代替P(T_k＝1|Q_k)来计算后验概率，其中Q_k＝[Q_k-J/2,…Q_k,…Q_k+J/2]。J为邻接子载波的个数（J∈[9,17]）。Substituting the expression of Λ _k into the formula (1), we can get the expression of the posterior probability P(T _k =1|Q _k ). However, due to the randomness of noise and interference, the posterior probability P(T _k =1|Q _k ) obtained by using the information of a sampling point Q _k alone is inaccurate. Therefore, we use adjacent subcarriers with the same To improve the detection performance, we define P(T _k ＝1|Q _k ) to replace P(T _k ＝1|Q _k ) to calculate the posterior probability, where Q _k ＝[Q _kJ/2 ,… Q _k ,...Q _k+J/2 ]. J is the number of adjacent subcarriers (J∈[9,17]).

类似于上面的推导，我们可以得到Similar to the derivation above, we can get

$P P (({T T}_{k k} = = 11 | | {Q Q}_{k k})) = = \frac{exp exp {{{Λ Λ}_{k k}^{' '}}}}{11 + + exp exp {{{Λ Λ}_{k k}^{' '}}}}$

其中in

${Λ Λ}_{k k}^{' '} = = \frac{ρ ρ (({Q Q}_{k k} | | {T T}_{k k} = = 11)) P P (({T T}_{k k} = = 11))}{ρ ρ (({Q Q}_{k k} | | {T T}_{k k} = = 00)) P P (({T T}_{k k} = = 00))}$

$= = ln ln \frac{P P (({T T}_{k k} = = 11))}{P P (({T T}_{k k} = = 00))} + + {Σ Σ}_{m m = = k k - - J J / / 22}^{k k + + J J / / 22} {{ln ln \frac{{σ σ}_{I I}^{22}}{{σ σ}_{n no}^{22}} + + \frac{{{| | Q Q}_{m m} | |}^{22}}{22 {σ σ}_{I I}^{22}} - - \frac{{| | {Q Q}_{m m} - - {\overset{^^}{H h}}_{m m} {P P}_{m m}^{' '} | |}^{22}}{22 {σ σ}_{n no}^{22}}}}$

给定一个适当的判决门限TH_APP，其中TH_APP是根据接收方预知子载波可用数目来确定的。可用子载波的判决可以根据P(T_k＝1|Q_k)来得到：An appropriate decision threshold TH _APP is given, wherein TH _APP is determined according to the available number of subcarriers predicted by the receiver. The judgment of available subcarriers can be obtained according to P(T _k =1|Q _k ):

其中R_k表示接收端第k个子载波的状态，R_k＝1指接收端判定第k个子载波为可用子载波，R_k＝0指接收端判定第k个子载波为不可用子载波。Where R _k represents the status of the kth subcarrier at the receiving end, R _k =1 means that the receiving end determines that the kth subcarrier is an available subcarrier, and R _k =0 means that the receiving end determines that the kth subcarrier is an unusable subcarrier.

（4）同步符号接收(4) Synchronous symbol reception

经过判决门限的删选后，可用子载波被检测出来，接收方可知道发送方使用了哪些子载波，并只从这些使用了的子载波上解调数据，然后进行解交织，纠错解码得到发射的同步信息。After the deletion of the decision threshold, the available subcarriers are detected, and the receiver can know which subcarriers are used by the sender, and only demodulates data from these used subcarriers, and then performs deinterleaving and error correction decoding to obtain Synchronization information transmitted.

以上所述，仅为本发明较佳的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应该以权利要求的保护范围为准。The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims

1. The available subcarrier detection synchronization method for discontinuous OFDM dynamic spectrum access, comprising the following steps:

(1) The sender transmits a data frame, which is composed of training symbols and synchronization symbols connected one after another, and the synchronization symbols carry the position information of the available subcarriers;

(2) The receiver receives the data frame;

(3) The receiver calculates the probability P that the kth subcarrier is an available subcarrier. If P is greater than or equal to the predetermined threshold value, it means that it is available, otherwise it is not available; among them,

or

Where k=1,2,...,N, N represents the total number of subcarriers, T _k represents the state of the kth subcarrier, P(T _k =1) and P(T _k =0) respectively represent the availability of the kth subcarrier and unavailable probability,

The variance of each dimension signal of the main user interference signal,

is the variance of each dimension of the noise signal, Q _k is the training symbol of the data frame received by the receiver from the kth subcarrier,

Indicates the receiver's channel estimate for the kth subcarrier,

Represents the training symbol on the kth subcarrier in the case of continuous spectrum, J is the number of adjacent subcarriers;

(4) The receiver demodulates data from the available subcarriers obtained in step (3), and obtains the synchronization symbol information.

2. The spectrum synchronization method according to claim 1, wherein the synchronization symbol is expressed as B=[(k _1s )2,(k _1e )2,...,(k _qs )2,(k _qe ) 2,...(k _Qs )2,(k _Qe )2], the non-continuous available subcarriers are divided into consecutive F subbands, and the binary number of the starting subcarrier number k _qs of the qth subband is expressed as (k _qs )2, the binary number of the end subcarrier number k _qe is expressed as (k _qe )2, where 1≤q≤F, (k _qs )2 and (k _qe )2 are respectively used

bits represent,

Indicates that log ₂ N is rounded up.