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

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

Be used for the available subcarrier detection and synchronization method that discontinuous OFDM dynamic spectrum inserts

Technical field

The invention belongs to wireless communication technology field; Relate to the dynamic spectrum access method that adopts orthogonal frequency-division multiplex singal (OFDM); The available subcarrier detection method that specifically a kind of receiving terminal carries out under unknown frequency spectrum synchronization related information situation, frequency spectrum are meant that synchronously receiving terminal can confirm OFDM number of subcarriers and position that transmitting terminal can be used.

Background technology

Along with the continuous development of communication requirement becomes increasingly scarce with the frequency spectrum resource that can supply communicate by letter; Dynamic spectrum access technology based on cognitive radio is a kind of promising solution because it can with a kind of opportunistic mode multiplexing with share frequency spectrum resource.That is to say that when authorized user does not use certain section frequency spectrum unauthorized user is allowed to identification and uses this section instantaneous spectrum.

For the broadband unauthorized user, OFDM is a kind of good signal structure, because utilize OFDM transmit communications signals on discrete frequency band effectively.Disturb for fear of the authorized user of working is formed, unauthorized user can only use the subcarrier transmission signals of part of O FDM, and these subcarriers that are used can be discontinuous.

In the spectrum environment of dynamic change, the transmit leg of unauthorized user can change the subcarrier number and the position of its use at any time according to authorized user to the operating position of frequency spectrum.For the recipient of unauthorized user, the problem of a key be keep and transmit leg synchronous, promptly the recipient will understand transmit leg and adopted which subcarrier.If the subcarrier number that the recipient adopts and position are different with transmit leg, obviously will cause the deterioration of the serious error rate and Packet Error Ratio.We are called the frequency spectrum stationary problem with above-mentioned stationary problem.The frequency spectrum stationary problem is a key issue of discontinuous OFDM dynamic spectrum connecting system, and at present, relevant research and technology are also quite few.The prior art relevant with the present invention has:

Part bandwidth mode (FBW Mode) detects and method for synchronous, sees Y.W.Jae, G.K.Hyun; H.K.Yun, S.Iickho, and S.S.Myung; " Fractional Bandwidth Mode Detection and Synchronization for OFDM-Based Cognitive Radio Systems; " In Proc.IEEE Vehicular Technology Conference, May 2008, pp.1599-1603.Part bandwidth mode method for synchronous is to mate and realize through receiving information and several possible part bandwidth mode.21 kinds of part bandwidth mode of system's predefined, the subcarrier number and the position of every kind of pattern use are fixed.Transmit leg can only use wherein a kind of part bandwidth mode to send signal.The recipient realizes that through detecting the part bandwidth mode that receives in the signal frequency spectrum is synchronous.

The system model of detection of part bandwidth mode and method for synchronous is as shown in Figure 1.Transmit leg is confirmed an only part bandwidth mode (FBW Mode) through frequency spectrum perception (Sensing), and uses the subcarrier of stipulating in this pattern to send signal.The recipient realizes that through detecting the part bandwidth mode that receives in the signal frequency spectrum is synchronous.

The shortcoming of such scheme is that system's part bandwidth mode quantity that can define is very limited, because the part bandwidth mode is many, can influence the accuracy of detection.21 kinds of patterns only can be provided, this 21 pattern even can not support discrete frequency spectrum situation in the above-mentioned paper.Under a limited number of situation of part bandwidth mode, system can't make accurately careful adjustment, thereby cause the spectrum utilization efficiency of system fully not improved to the dynamic change of spectrum environment.

Summary of the invention

The purpose of this invention is to provide a kind of available subcarrier detection and synchronization method that discontinuous OFDM dynamic spectrum inserts that is used under unknown frequency spectrum synchronizing information situation, being used for; This method can effectively detect the position of available subcarrier, under the condition of large disturbance, obtains desirable synchronizing information.

Be used for the available subcarrier detection and synchronization method that discontinuous OFDM dynamic spectrum inserts, may further comprise the steps:

(1) transmit leg transmit data frames, Frame is connected to form front and back by training symbol and synchronizing symbol successively, and synchronizing symbol has carried the positional information of available subcarrier;

(2) recipient's receiving data frames;

(3) recipient calculates the probability P that the k number of sub-carrier is an available subcarrier, and is available if P more than or equal to predetermined threshold, representes, otherwise unavailable; Wherein,

$P=\frac{\mathrm{ex}\left\{p{\mathrm{\Λ}}_k\right\}}{1+\mathrm{ex}\left\{{\mathrm{\Λp}}_k\right\}},$

${\mathrm{\Λ}}_k=\mathrm{Ln}\frac{P(T_k=1)}{P(T_k=0)}+\mathrm{Ln}\frac{{\mathrm{\σ}}_I^2}{{\mathrm{\σ}}_n^2}+\frac{{\left|Q_k\right|}^2}{2{\mathrm{\σ}}_I^2}-\frac{{|Q_k-{\hat{H}}_k{P}_k^{\′}|}^2}{2{\mathrm{\σ}}_n^2}$ Perhaps

${\mathrm{\Λ}}_k=\ln \frac{P(T_k=1)}{P(T_k=0)}+\underset{m=k-J/2}{\overset{k+J/2}{\mathrm{\Σ}}}\{\ln \frac{{\mathrm{\σ}}_I^2}{{\mathrm{\σ}}_n^2}+\frac{{\left|Q_m\right|}^2}{2{\mathrm{\σ}}_I^2}-\frac{{|Q_m-{\hat{H}}_m{P}_m^{\′}|}^2}{2{\mathrm{\σ}}_n^2}\}$

K=1 wherein, 2 ..., N, N represent the sum of subcarrier, T _kThe state of representing the k number of sub-carrier, P (T _k=1) and P (T _k=0) represent that respectively the k number of sub-carrier can use and disabled probability,

Be the variance of main each dimensional signal of user's interference signal, Be the variance of each dimensional signal of noise signal, Q _kThe training symbol of the Frame that receives from the k number of sub-carrier for the recipient, Represent the channel estimation value of recipient to the k number of sub-carrier, Be illustrated in the training symbol on the k number of sub-carrier under the continuous situation of frequency spectrum, J is the number of contiguous subcarrier;

(4) demodulating data on the available subcarrier that from step (3), obtains of recipient is known synchronizing symbol information.

Technique effect of the present invention is embodied in: the present invention sends Frame through transmitting terminal and gives receiving terminal, and Frame comprises a training symbol and a synchronizing symbol, and synchronizing symbol is formed through convolutional encoding, modulation and repeated encoding by synchronization character.Receiving terminal uses the training symbol that receives to calculate each subcarrier and is sent out the posterior probability that end utilizes; To these posterior probability; A suitable thresholding is set; The pairing subcarrier of those posterior probability greater than thresholding is judged to be available subcarrier, and then carries out the detection of synchronizing symbol data.The present invention is effective in real time, and receiving terminal detects rapidly accurately, brings main user under the situation of interference, can reach desirable net synchronization capability.This training symbol is positioned at before the synchronizing symbol.

The invention belongs to the in-band signalling solution, saved frequency spectrum resource, reduced the processing delay of system, guaranteed the real-time that subcarrier detects.

Description of drawings

Fig. 1 is the inventive method schematic flow sheet;

Fig. 2 is a discontinuous OFDM sub-band division sketch map of the present invention;

Fig. 3 is that synchronizing symbol of the present invention generates the steps flow chart block diagram;

Fig. 4 is data frame structure of the present invention and receiver processing procedure sketch map.

Embodiment

Embodiment provided by the invention, as shown in Figure 1, specifically may further comprise the steps:

(1) frame emission

One frame is connected to form before and after successively by training symbol and synchronizing symbol, carries out contrary FFT, and the string conversion, launches after adding Cyclic Prefix.

(1.1) training symbol

At first define subcarrier state vector T=[T ₀, T ₁..., T _N], T wherein _kThe state of representing the k number of sub-carrier, k=1,2 ..., N, N represent the sum of subcarrier.If this subcarrier can be used, T _k=1, otherwise T _k=0.Under the discontinuous situation of frequency spectrum, the training symbol of transmission on frequency domain with vector P=[P ₀, P ₁..., P _N] expression, wherein P _kBe a plural number, amplitude and the phase place of expression training symbol on the k number of sub-carrier,

P ' wherein _k(k=0,1,2 ..., N) be vector P '=[P ' ₀, P ' ₁..., P ' _N] in element, P ' is illustrated in the training symbol that system under the continuous situation of frequency spectrum uses.

(1.2) synchronizing symbol

Shown in Figure 2, synchronizing symbol on frequency domain with vector C=[C ₁..., C _k..., C _N] expression, wherein C _kAmplitude and the phase place of expression synchronizing symbol on the k number of sub-carrier,

$C_k=C_k^{\′}\·T_k$

Wherein

is the element in the vector ; C ' repeats M by synchronization character modulation symbol S and doubly obtains, promptly

$C_k^{\′}=S_n;n=k\mathrm{mod}(N/M)$

Wherein k mod (N/M) expression k gets surplusly to (N/M), and N and M are satisfied divides exactly relation, and promptly (N/M) is a positive integer.S _nBe vector S=[S ₁..., S _n..., S _(N/M)] in element, wherein n representes the sequence number of element in the vector S, n=1,2 ..., (N/M).Through the error correcting encoder coding, interleaver interweaves S by synchronization character B, and M contrast system (like PSK or QAM modulation) obtains, and wherein synchronization character B representes the position of available subcarrier.Represent the available subcarrier position with synchronization character among the present invention, the method that a kind of synchronization character of giving an example below obtains, but the present invention is not limited to this method, also can adopt other mode to obtain synchronization character.

Stipulate that discontinuous frequency spectrum OFDM dynamic spectrum connecting system uses the V number of sub-carrier to communicate, the span of V is [1, N]; As shown in Figure 3, suppose that V discrete available subcarrier can be divided into continuous separately F section, is called F subband; Use the beginning subcarrier sequence number of each subband and finish the position that the subcarrier sequence number is represented these subbands; The beginning subcarrier sequence number k of q subband _QsBinary number representation be (k _Qs) 2; Finish subcarrier sequence number k _QeBinary number representation be (k _Qe) 2,1≤q≤F wherein, (k _Qs) 2 with (k _Qe) 2 each usefulness Individual bit representes,

Expression is to log ₂N rounds up; B=[(k then _1s) 2, (k _1e) 2 ..., (k _Qs) 2, (k _Qe) 2 ... (k _Qs) 2, (k _Qe) 2], total among the B Individual bit.

(2) received frame

The data that receive remove Cyclic Prefix, string and conversion, and FFT is handled, and obtains receiving channel disturbance to produce the frame of distortion.

(3) detection of available subcarrier posterior probability

Fig. 4 has provided receiving terminal to receiving the handling process of data, at first carries out the detection of subcarrier posterior probability through the training symbol that receives.

The receiving terminal of discontinuous frequency spectrum OFDM dynamic spectrum connecting system carries out available subcarrier posterior probability P (T according to the training symbol that receives _k=1|Q _k) detection.Training symbol on the k number of sub-carrier that receives does

Q wherein _k, P _k, H _kRepresent the training symbol, the training symbol of transmission, the channel response that receive on the k number of sub-carrier, I respectively _kRepresent that (it is that 0 variance does that each dimension that we suppose multiple interference signal that main user brings in the patent is all obeyed average for the next autonomous user's on the k number of sub-carrier interference

Normal distribution), W _kRepresent the white complex gaussian noise on the k number of sub-carrier, it is that 0 variance does that its each dimensional signal is all obeyed average

Normal distribution.

According to the signal Q that receives _k, we can obtain about T _kPosterior probability P (T _k=1|Q _k), wherein,

$P(T_k=1|Q_k)=\frac{P(T_k=1|Q_k)}{P(T_k=1|Q_k)+P(T_k=0|Q_k)}$

$=\frac{\exp \left\{{\mathrm{\Λ}}_k\right\}}{1+\exp \left\{{\mathrm{\Λ}}_k\right\}}---\left(1\right)$

Wherein,

exp{ } be exponential function.

According to Bayesian formula, we can obtain

${\mathrm{\Λ}}_k=\frac{\mathrm{\ρ}\left(Q_k\right|T_k=1)P(T_k=1)}{\mathrm{\ρ}\left(Q_k\right|T_k=0)P(T_k=0)}$

P (T wherein _k=1) and P (T _k=0) be to use and disabled prior probability about subcarrier.

ρ (Q _k| T _k=1) and ρ (Q _k| T _k=0) all be about Q _kConditional probability density function, these conditional probability density functions can have following expression-form:

$\mathrm{\ρ}\left(Q_k\right|T_k=1)=\frac{1}{2{\mathrm{\π\σ}}_n^2}\exp \{-\frac{{|Q_k-{\hat{H}}_k{P}_k^{\′}|}^2}{2{\mathrm{\σ}}_n^2}\},$

$\mathrm{\ρ}\left(Q_k\right|T_k=0)=\frac{1}{{2\mathrm{\π\σ}}_I^2}\exp \{-\frac{{\left|Q_k\right|}^2}{2{\mathrm{\σ}}_I^2}\}$

Wherein

representes the channel estimation value on the k number of sub-carrier

${\hat{H}}_k=\underset{m=k-(N_a-1)/2}{\overset{k+(N_a-1)/2}{\mathrm{\Σ}}}\frac{Q_m}{N_a{P}_m^{\′}}$

N wherein _aDetermined to participate in the subcarrier number of channel estimation calculation, N _a∈ [7,15].

Through top derivation, we just can obtain Λ _kExpression formula:

${\mathrm{\Λ}}_k=\ln \frac{P(T_k=1)}{P(T_k=0)}+\ln \frac{{\mathrm{\σ}}_I^2}{{\mathrm{\σ}}_n^2}+\frac{{\left|Q_k\right|}^2}{2{\mathrm{\σ}}_I^2}-\frac{{|Q_k-{\hat{H}}_k{P}_k^{\′}|}^2}{2{\mathrm{\σ}}_n^2}$

With Λ _kExpression formula be updated in (1) formula, we just can obtain posterior probability P (T _k=1|Q _k) expression formula.But, because the randomness of noise and interference, independent utilize a sampled point Q _kThe posterior probability P (T that obtains of information _k=1|Q _k) be inaccurate, therefore, the characteristic that we utilize adjacent sub-carrier to have equal state is improved the performance of detection, and we define P (T _k=1|Q _k) replace P (T _k=1|Q _k) calculate posterior probability, wherein Q _k=[Q _K-J/2... Q _k... Q _K+J/2].J is the number (J ∈ [9,17]) of contiguous subcarrier.

Be similar to top derivation, we can obtain

$P(T_k=1|Q_k)=\frac{\exp \left\{{\mathrm{\Λ}}_k^{\′}\right\}}{1+\exp \left\{{\mathrm{\Λ}}_k^{\′}\right\}}$

Wherein

${\mathrm{\Λ}}_k^{\′}=\frac{\mathrm{\ρ}\left(Q_k\right|T_k=1)P(T_k=1)}{\mathrm{\ρ}\left(Q_k\right|T_k=0)P(T_k=0)}$

$=\ln \frac{P(T_k=1)}{P(T_k=0)}+\underset{m=k-J/2}{\overset{k+J/2}{\mathrm{\Σ}}}\{\ln \frac{{\mathrm{\σ}}_I^2}{{\mathrm{\σ}}_n^2}+\frac{{{|Q}_m|}^2}{2{\mathrm{\σ}}_I^2}-\frac{{|Q_m-{\hat{H}}_m{P}_m^{\′}|}^2}{2{\mathrm{\σ}}_n^2}\}$

A given suitable decision threshold TH _APP, TH wherein _APPConfirm according to recipient's Akebia Fruit carrier wave useful number.The judgement of available subcarrier can be according to P (T _k=1|Q _k) obtain:

R wherein _kThe state of expression receiving terminal k number of sub-carrier, R _k=1 finger receiving terminal judges that the k number of sub-carrier is an available subcarrier, R _k=0 finger receiving terminal judges that the k number of sub-carrier is unavailable subcarrier.

(4) synchronizing symbol receives

Through decision threshold delete choosing after, available subcarrier is detected, the recipient knows which subcarrier transmit leg has used, and demodulating data from these subcarriers that used only, carries out deinterleaving then, the synchronizing information that error correction decoding obtains launching.

The above; Be merely the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, any technical staff who is familiar with the present technique field is in the technical scope that the present invention discloses; The variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (2)

1. be used for the available subcarrier detection and synchronization method that discontinuous OFDM dynamic spectrum inserts, may further comprise the steps:

(1) transmit leg transmit data frames, Frame is connected to form front and back by training symbol and synchronizing symbol successively, and synchronizing symbol has carried the positional information of available subcarrier;

(2) recipient's receiving data frames;

(3) recipient calculates the probability P that the k number of sub-carrier is an available subcarrier, and is available if P more than or equal to predetermined threshold, representes, otherwise unavailable; Wherein,

perhaps

K=1 wherein, 2 ..., N, N represent the sum of subcarrier, T _kThe state of representing the k number of sub-carrier, P (T _k=1) and P (T _k=0) represent that respectively the k number of sub-carrier can use and disabled probability,

Be the variance of main each dimensional signal of user's interference signal,

Be the variance of each dimensional signal of noise signal, Q _kThe training symbol of the Frame that receives from the k number of sub-carrier for the recipient,

Represent the channel estimation value of recipient to the k number of sub-carrier,

Be illustrated in the training symbol on the k number of sub-carrier under the continuous situation of frequency spectrum, J is the number of contiguous subcarrier;

(4) demodulating data on the available subcarrier that from step (3), obtains of recipient is known synchronizing symbol information.

2. frequency spectrum method for synchronous according to claim 1 is characterized in that said synchronizing symbol is expressed as B=[(k _1s) 2, (k _1e) 2 ..., (k _Qs) 2, (k _Qe) 2 ... (k _Qs) 2, (k _Qe) 2], discrete available subcarrier is divided into a continuous separately F subband, the beginning subcarrier sequence number k of q subband _QsBinary number representation be (k _Qs) 2, finish subcarrier sequence number k _QeBinary number representation be (k _Qe) 2,1≤q≤F wherein, (k _Qs) 2 with (k _Qe) 2 each usefulness

Individual bit representes,

Expression is to log ₂N rounds up.

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