CN101562590A - OFDM signal intelligent receiving system and receiving method - Google Patents

Abstract

The invention discloses an OFDM signal intelligent receiving system and a receiving method, aiming mainly at solving problem of existing intelligent receiving technique in identifying OFDM signals and high-order square QAM signals. The receiving process of the method comprises the steps as follows: (1) captured signals are pre-treated and down-conversed, thereby obtaining baseband signal; (2) bandwidth of the baseband signal is estimated; (3) the baseband signal is sampled at frequency that is 4 times as high as the signal bandwidth; (4) characteristic vectors are extracted from the sampled signals by multilayer wavelet decomposition and the vectors are compared with theoretic value to identify OFDM signals; (5) when OFDM signals are verified, parameters such as symbol length and circular prefix length of the OFDM signals are estimated, thereby realizing symbol synchronization; and the OFDM signals are then identified and demodulated by subcarrier demodulation. The OFDM signal intelligent receiving system and the receiving method of the invention can effectively identify OFDM signals and estimate parameters of the OFDM signals, so as to be used in intelligent receiving of OFDM signals in multi-system environment.

Description

Ofdm signal intelligence receiving system and method for reseptance

Technical field

The invention belongs to communication technical field, be specifically related to the ofdm signal method of reseptance.Be used under the situation of unknown communication system ofdm signal is discerned and parameter Estimation.

Background technology

In recent years, along with the development of digital communication technology and Digital Signal Processing, various communication patterns were more and more, and the environment of radio communication is complicated day by day.The active situation that in many application, all needs the monitor communication signal, the character of differentiation signal, even the content of intercepted signal, communication control processor should have more and more stronger parameter recognition ability, and this all be unable to do without the intelligent reception technique of signal of communication.

In May, 1992, the Joseph Mitola of MILTRE company has clearly proposed the notion of software radio first.Promptly construct one and have opening, standardization, modular general hardware platform, with various functions, finish with software as working frequency range, modulation type, data format, encryption mode, communication protocol etc., and make wideband A/D and the as close as possible antenna of D/A converter, have high degree of flexibility to develop, an open new generation of wireless communication system.Generally be to be support, realize the various functions of radio station by software programming with a standardization and a modular hardware platform with versatility.Software radio is emphasized opening and comprehensive programmability of architecture, by the renewal change hardware configuration structure of software, realizes different functions.

The multi-carrier modulation technology that with the orthogonal frequency division multiplex OFDM is representative is widely used in Modern Communication System, for example based on the wlan system of 802.11a/g, digital video broadcasting DVB_T system with based on WMAN system of 802.16 etc.Receiver is single-carrier signal and multi-carrier signal with signal distinguishing at first for the identification communication pattern, and estimated signal parameter then is according to signal parameter identification communication pattern.If the communication pattern based on OFDM is unknown, receiver need be discerned the parameter of ofdm system, to realize purposes such as follow-up monitoring, demodulation.

The intelligence of signal receives and comprises signal capture, carrier estimation, baud rate estimation, signal identification and parameter Estimation etc.Document does not have the specific implementation flow process to the research of OFDM intelligence reception technique at present, can't realize the intelligence of ofdm signal is received.

For the signal baud rate estimation unit in the signal intelligent receiving system.Existing baud rate method of estimation can be divided into based on the time domain baud rate of signal cycle smooth performance to be estimated and estimates based on the frequency domain baud rate of signal FFT conversion, is primarily aimed at single-carrier signal and carries out the baud rate estimation.In the intelligence of signal received, in the time of need carrying out the estimation of signal baud rate, the type of signal was priori the unknown.If what receive is ofdm signal, existing baud rate algorithm for estimating will be invalid.

Signal identification for OFDM and single carrier in the signal intelligent reception.W.Akmouche is at document " Detection of multicarrier modulations using 4th-order cumulants " in proposed to utilize the signal recognition method of 4 rank cumulants OFDM and single carrier under additive white Gaussian noise (AWGN) channel first.Bin Wang, Lindong Ge is at document " Blind Identification of OFDM Signal in RayleighChannels " in will utilize Higher Order Cumulants that the method that OFDM carries out signal identification is generalized to rayleigh fading channel, and obtained good recognition effect.But utilize Higher Order Cumulants that OFDM is discerned, can't distinguish the square QAM signal of high-order in ofdm signal and the single carrier.

Summary of the invention

The objective of the invention is to solve deficiency of the prior art, a kind of OFDM intelligence receiving system and method for reseptance thereof are proposed, with reception and the parameter Estimation of realization, and distinguish ofdm signal and the single-carrier signal that comprises the square QAM signal of high-order to ofdm signal.

The technical scheme that realizes the object of the invention is to carry out baud rate in conjunction with wavelet decomposition, reconstruct and Fourier transform to estimate, utilizes the multilayer wavelet decomposition to carry out ofdm signal identification.Its system comprises:

The signal capture unit is used for signal is caught reception;

Pretreatment unit is used for carrying out to the received signal filtering, amplification and A/D conversion preliminary treatment;

Carrier estimation, down-converter unit are used for obtaining baseband signal S (n) to carrying out estimating carrier frequencies and down-conversion through pretreated signal;

The bandwidth estimation unit is used for the bandwidth estimation of carrying out to baseband signal S (n), and estimated result W is passed to follow-up sampling unit, OFDM parameter estimation unit and ofdm signal demodulating unit;

Sampling unit is used for baseband signal S (n) is sampled, and obtains 4 times of over-sampling baseband signal S ' (n)

The ofdm signal recognition unit, being used for (n) differentiating received signal according to 4 times of over-sampling baseband signal S ' is ofdm signal or single-carrier signal;

The ofdm signal parameter estimation unit, being used for differentiating received signal is under the situation of ofdm signal, according to baseband signal S (n) and estimated signals bandwidth W, estimating OFDM subcarrier number N, circulating prefix-length N _G, symbol original position side-play amount θ, obtain ofdm signal S after the sign synchronization according to θ " (n), and with the OFDM subcarrier number N, the circulating prefix-length N that estimate _GPass to follow-up ofdm signal demodulating unit;

The ofdm signal demodulating unit, being used for differentiating received signal is under the situation of ofdm signal, according to the OFDM subcarrier number N, the circulating prefix-length N that estimate _G" (n) carry out subcarrier modulation modes identification and demodulation with signal bandwidth W, to the ofdm signal S after the sign synchronization.

Ofdm signal intelligence method of reseptance of the present invention comprises the steps:

(1) catches the interior signal of monitoring frequency range, and the signal of catching is carried out filtering, amplification and A/D conversion preliminary treatment;

(2) pretreated received signal is carried out carrier estimation and down-converted, obtain baseband signal S (n);

(3) baseband signal S (n) is obtained base-band signal spectrum by Fourier transform, use Haar wavelet decomposition and wavelet reconstruction, details component in the elimination base-band signal spectrum obtains the step change type base-band signal spectrum, uses statistical method to judge the position, edge of this signal spectrum, obtains signal bandwidth W;

(4) baseband signal S (n) is carried out over-sampling by 4 times of estimated signal bandwidth W, obtain 4 times of over-sampling baseband signal S ' (n);

(5) S ' (n) is extracted characteristic vector by the multilayer wavelet decomposition, calculate the Euclidean distance of this characteristic vector and ofdm signal characteristic vector theoretical value, this distance is compared with thresholding, when distance during less than thresholding, the differentiation received signal is an ofdm signal, when distance during greater than thresholding, the differentiation received signal is a single-carrier signal;

(6) be under the situation of ofdm signal in judgment signal, according to baseband signal S (n) and estimated signals bandwidth W, estimating OFDM subcarrier number N, circulating prefix-length N _GWith symbol original position side-play amount θ, obtain OFDM baseband signal S after the sign synchronization " (n), and with the sample value speed of estimated signals bandwidth W as ofdm signal according to the estimated result of θ;

(7) be under the situation of ofdm signal in judgment signal, according to the OFDM subcarrier number N, the circulating prefix-length N that estimate _G, the OFDM baseband signal S after sample value speed W and the sign synchronization " (n), carries out subcarrier-modulated identification and demodulation to the OFDM baseband signal.

The present invention compared with prior art has the following advantages:

1, the present invention by the estimated signal bandwidth, can carry out the baud rate estimation in conjunction with Fourier transform and Haar wavelet decomposition to single-carrier signal and ofdm signal.

2, the present invention is owing to adopt the multilayer wavelet decomposition to carry out ofdm signal identification, overcome the shortcoming that Higher Order Cumulants can't be distinguished ofdm signal and the square QAM signal of high-order;

3, method of reseptance of the present invention does not need prior information, and the intelligence that can be used for ofdm signal receives.

Description of drawings

Fig. 1 is a system block diagram of the present invention;

Fig. 2 is a method of reseptance flow chart of the present invention;

Fig. 3 is the signal bandwidth estimator flow chart in the method for reseptance of the present invention;

Fig. 4 is the ofdm signal recognin flow chart in the method for reseptance of the present invention.

Embodiment

With reference to Fig. 1, ofdm signal intelligence receiving system of the present invention comprises: signal capture unit, Signal Pretreatment unit, carrier estimation and down-converter unit, signal bandwidth estimation unit, sampling unit, ofdm signal recognition unit, OFDM parameter estimation unit and ofdm signal demodulating unit.The signal capture unit detects the signal energy of monitoring in the frequency range, when signal energy during greater than certain thresholding, signal is caught reception, and received signal is sent into the Signal Pretreatment unit.The Signal Pretreatment unit carries out filtering, amplification and A/D conversion preliminary treatment to the signal that the signal capture unit receives, and will send into carrier estimation, down-converter unit through pretreated signal.Carrier estimation, down-converter unit obtain baseband signal S (n), and S (n) are sent into the signal bandwidth estimation unit carrying out estimating carrier frequencies and down-conversion through pretreated signal.The signal bandwidth estimation unit obtains estimated result W to the bandwidth estimation of carrying out of baseband signal S (n), and baseband signal S (n) and estimated signals bandwidth W are passed to follow-up sampling unit, OFDM parameter estimation unit and ofdm signal demodulating unit.Sampling unit is sampled to baseband signal S (n), and sample frequency is 4 times of estimated signals bandwidth W, and the baseband signal S ' that obtains 4 times of over-samplings (n) and (n) passes to the ofdm signal recognition unit with S '.The ofdm signal recognition unit according to the baseband signal S ' of 4 times of over-samplings (n), whether judgment signal S ' is ofdm signal (n), and court verdict and baseband signal S (n) are passed to ofdm signal synchronously and parameter estimation unit.It is under the situation of ofdm signal that the ofdm signal parameter estimation unit is differentiated received signal at the ofdm signal recognition unit, according to the bandwidth W of baseband signal S (n) and estimation, estimating OFDM subcarrier number N, circulating prefix-length N _GWith symbol original position side-play amount θ, obtain ofdm signal S after the sign synchronization according to θ " (n), and with signal S " (n) and the OFDM subcarrier number N, the circulating prefix-length N that estimate _GPass to follow-up ofdm signal demodulating unit.It is under the situation of ofdm signal that the ofdm signal demodulating unit is differentiated received signal at the ofdm signal recognition unit, according to OFDM subcarrier number N, the circulating prefix-length N of ofdm signal parameter estimation unit estimation _G" (n) carry out subcarrier modulation modes identification and demodulation with signal bandwidth estimation unit estimated signals bandwidth W, to the ofdm signal S after the sign synchronization.

With reference to Fig. 2, ofdm signal intelligence method of reseptance of the present invention comprises the steps:

Step 1 is carried out preliminary treatment to the signal of catching.

The signal energy of monitoring in the frequency range detected, when signal energy surpasses certain thresholding, signal caught reception, and carry out filtering to the received signal, amplification and A/D conversion preliminary treatment.

Step 2 is carried out carrier estimation and down-converted to pretreated received signal, obtains baseband signal S (n).

Step 3, the signal bandwidth W of estimation baseband signal S (n).

With reference to Fig. 3, the step of the signal bandwidth W of estimation baseband signal S (n) is as follows:

(3a) the baseband signal S (n) that receives is divided into groups, it is divided into M group, be further divided into N group in every group;

(3b) (j in the group of 1≤i≤M) (carry out Fourier transform and obtain base-band signal spectrum S by the group's baseband signal of 1≤j≤N) to i _{I, j}(f);

(3c) to base-band signal spectrum S _{I, j}(f) carry out n (n 〉=1) layer Haar wavelet decomposition, obtain the coefficient of wavelet decomposition vector T.

(3d) the approximate component in the retention coefficient vector T is constant, and the details component is put 0, with the details component in the elimination base-band signal spectrum, obtains being used for the coefficient vector T ' of wavelet reconstruction.

(3e) signal spectrum is carried out the Haar wavelet reconstruction, obtain the step change type base-band signal spectrum after the reconstruct according to described coefficient vector T '.In step (3c) with (3d), if wavelet decomposition number of plies n is low excessively, it is level and smooth inadequately that high frequency coefficient is put 0 signal spectrum that carries out behind the wavelet reconstruction, being difficult to carry out the edge detects, if wavelet decomposition number of plies n is too high, it is very low that high frequency coefficient is put 0 resolution of carrying out behind the wavelet reconstruction, has higher resolution simultaneously by choosing the high frequency details that the suitable decomposition number of plies can eliminate in the frequency spectrum, and this example is selected wavelet decomposition number of plies n=6.

(3f) N the step change type base-band signal spectrum S ' that i group signal is obtained _{I, j}(f) (1≤j≤N) carry out statistical average obtains the frequency spectrum S ' after the statistical average _i(f), this frequency spectrum S ' _i(f) position that consecutive value differs maximum in is the steepest change location;

(3g) search described S ' _i(f) two steepest change locations are as the position, frequency spectrum edge of i group signal;

(3h) position, frequency spectrum edge of statistics M group signal, with the bandwidth between two the highest positions of statistic as estimated signals bandwidth W.

Step 4 is sampled to baseband signal S (n).

, as sample frequency baseband signal S (n) is sampled with 4 times of signal bandwidth W, the baseband signal S ' that obtains 4 times of over-samplings (n).

Step 5, whether the baseband signal S ' that differentiates 4 times of over-samplings is ofdm signal (n).

With reference to Fig. 4, whether the baseband signal S ' that differentiates 4 times of over-samplings is that the step of ofdm signal is as follows (n):

(5a) the baseband signal S ' of 4 times of over-samplings (n) is used multilayer wavelet decomposition structural classification characteristic vector:

$x=C\·\frac{1}{{\mathrm{ap}}_2}[{\mathrm{ap}}_3,{\mathrm{ap}}_4,{\mathrm{ap}}_5,{\mathrm{de}}_3,{\mathrm{de}}_4,{\mathrm{de}}_5]$

Wherein, C is the parameter that the amplitude of characteristic vector value is adjusted, and this example is selected C=100,

Ap _iThe approximate portion of energy of representation signal i layer wavelet decomposition is defined as follows:

${\mathrm{ap}}_i={\left|\right|a_i\left|\right|}_2^2=\underset{n}{\mathrm{\Σ}}{a}_{i,n}^2,$ I=1 ..., M, a _iRepresent the approximate part number vector of i layer wavelet decomposition, a _{I, n}The approximate part coefficient of expression i layer wavelet decomposition;

De _iThe detail section energy of representation signal i layer wavelet decomposition is defined as follows:

${\mathrm{de}}_i={\left|\right|d_i\left|\right|}_2^2=\underset{n}{\mathrm{\Σ}}{d}_{i,n}^2,$ I=1 ..., M, d _iRepresent the detail section coefficient vector of i layer wavelet decomposition, d _{I, n}The detail section coefficient of expression i layer wavelet decomposition;

Because the energy of ofdm signal is evenly distributed in frequency band, the theoretical value of its characteristic vector x is $M=C\×[\frac{1}{2},\frac{1}{4},\frac{1}{8},\frac{1}{2},\frac{1}{4},\frac{1}{8}];$

(5b) the Euclidean distance D of calculated characteristics vector x and ofdm signal characteristic vector theoretical value M:

$D=\underset{l=1}{\overset{6}{\mathrm{\Σ}}}{(x_l-m_l)}^2$

X wherein _lBe characteristic vector x l dimension value, m _lBe characteristic vector M l dimension value;

(5c) to the single-carrier signal training sample set by step (5a) extract characteristic vector, calculated characteristics vector and theoretical value M Euclidean distance D _SC, and statistics D _SCProbability distribution p (D _SC); To the ofdm signal training sample set by step (5a) extract characteristic vector, calculated characteristics vector and theoretical value M Euclidean distance D _OFDM, and statistics D _OFDMProbability distribution p (D _OFDM), according to p (D _SC) and p (D _OFDM) set decision threshold according to the Maximum Likelihood Detection criterion, this thresholding also can be set according to experience, and thresholding is set at 33 in this example.

(5d) relatively,, differentiate and be ofdm signal,, differentiate and be single-carrier signal as D during greater than decision threshold as D during less than decision threshold with D and decision threshold.

Step 6 under received signal is differentiated situation for ofdm signal, is carried out parameter Estimation to baseband signal S (n).

Under received signal is differentiated situation for ofdm signal, the parameter Estimation of baseband signal S (n) is comprised OFDM subcarrier number N, circulating prefix-length N _GWith symbol original position side-play amount θ, its step is as follows:

(6a) symbol of ofdm signal has circulating prefix structure, and Cyclic Prefix is duplicating of valid data end, so there is correlation between them.If calculate to receive the auto-correlation of data, when Cyclic Prefix and its copy source are carried out related operation, obtain peak value.So can use a kind of auto-correlation algorithm of variable correlation length to carry out valid data length estimates:

$R_S\left(\mathrm{\Δ}\right)=\left|E\right[S\left(n\right)S^{*}(n+\mathrm{\Δ})\left]\right|=\left\{\begin{array}{cc}{\mathrm{\σ}}_S^2+{\mathrm{\σ}}_w^2& \mathrm{\Δ}=0\\ {\mathrm{\σ}}_S^2& \mathrm{\Δ}=N_D;n\∈\mathrm{\Ω}\\ 0& \mathrm{otherwise}\end{array}\right.$

Wherein auto-correlation, Δ representative data position offset, E[ are asked in R () representative] represent and ask mathematic expectaion, S (n) represents base band time domain signal, σ _SAnd σ _wDifference representation signal energy and noise energy.N _DThe ofdm signal data field length that representative is represented with sampling number, the set of Ω representation signal sampled point.

To N _DEstimation can remember work:

${\hat{N}}_D=\underset{\mathrm{\Δ}}{\arg \max }\left\{\right|R_S\left(\mathrm{\Δ}\right)\left|\right\},\mathrm{\Δ}>0$

Estimated result

It is the ofdm signal valid data section length of representing with sampling number; The subcarrier number $\hat{N}=\frac{{\hat{N}}_D}{f_s/W},$ Wherein W is step 3 an estimated signals bandwidth, f _sFor carrying out the sample frequency of A/D conversion in the step 1;

(6b) in the real system ofdm signal subcarrier number generally in S set={ 2 ⁿ| n is a positive integer } interior value, with step (6a) results estimated

Be modified to ${\hat{N}}^{\′}=\underset{m\∈S}{\arg \min }|\hat{N}-m|,$

Be modified to ${\hat{N}}_D^{\′}={\hat{N}}^{\′}\×(f_s/W);$

(6c), need estimate symbol original position side-play amount to finish the OFDM sign synchronization for the ofdm signal that receives is carried out demodulation.The circulating prefix-length of ofdm signal is optionally in some system, need estimate the circulating prefix-length of ofdm signal.The present invention uses a kind of maximal possibility estimation algorithm to circulating prefix-length N _Gθ estimates that likelihood function is as follows with symbol original position side-play amount:

$\mathrm{\Λ}(S;N_D,N_G,\mathrm{\θ})=\log (\underset{n\∈\mathrm{\Ω}}{\mathrm{\Π}}p\left(S\right[n],S[n+N_D\left]\right)\·\underset{n\∉\mathrm{\Ω}\∪{\mathrm{\Ω}}^{\′}}{\mathrm{\Π}}p\left(S\right[n\left]\right))$

$=\log \left(\underset{n\∈\mathrm{\Ω}}{\mathrm{\Π}}\frac{p\left(S\right[n\left]\right),S[n+N_D]}{p\left(S\right[n\left]\right),p\left(S\right[n+N_D\left]\right)}\underset{n}{\mathrm{\Π}}p\left(S\right[n\left]\right)\right)$

In the formula, S represents the baseband signal vector, S[ ] to represent baseband signal, set omega be the data acquisition system in Cyclic Prefix district in the ofdm signal, set omega ' for being copied to the valid data set in Cyclic Prefix district in the ofdm signal.Suppose that S has the associating Gaussian Profile, as follows to the final result that likelihood function is simplified:

In the formula, S represents the baseband signal vector, S[ ] represent baseband signal,

Representative rounds downwards, and complex conjugate is got in the * representative.

According to revised estimated result in likelihood function of simplifying and the step (6b)

Circulating prefix-length N _GUndertaken by following formula with the estimation of symbol original position side-play amount θ:

$({\hat{N}}_G,\widehat{\mathrm{\θ}})=\underset{N_G,\mathrm{\θ}}{\arg \max }\left\{\widehat{\mathrm{\Λ}}(S;{\hat{N}}_D^{\′},N_G,\mathrm{\θ})\right\}$

In the formula, S represents the baseband signal vector, S[ ] represent baseband signal,

Representative rounds downwards, and complex conjugate is got in the * representative.

Usually, circulating prefix-length N _GBe N _DSome multiple.For example, in 802.16 systems, available length is N _D1/4,1/8,1/16,1/32.Therefore, in the following formula

Value can be limited to

1/2,1/4,1/8,1/16,1/32 these multiple scopes in.Obtain OFDM baseband signal S after the sign synchronization according to the estimated result of θ " (n).

Step 7 is under received signal is differentiated situation for ofdm signal, to the ofdm signal S after the sign synchronization " (n) carries out subcarrier-modulated identification and demodulation.

The sample frequency f of baseband signal S (n) _sBe known, with the sample value speed of step 3 estimated signals bandwidth W, according to OFDM subcarrier number N, the circulating prefix-length N of step 6 estimation as ofdm signal _G, the ofdm signal S after the sign synchronization " (n) is carried out Fourier transform and obtains sub-carrier modulation data.Higher Order Cumulants structural feature vector according to sub-carrier modulation data is discerned subcarrier modulation modes, according to the subcarrier modulation modes of discerning modulating data is carried out demodulation.

Identification step to the ofdm signal subcarrier modulation modes is as follows:

(7a) this example ofdm signal subcarrier modulation modes { is selected among BPSK, QPSK, the 16QAM}, the OFDM sub-carrier modulation data is carried out energy normalized, obtain signal x (n) in set;

(7b) to the OFDM sub-carrier signal x (n) after the energy normalized, according to following formula structural feature vector F _r:

$F_r=\left[\right|\frac{\mathrm{Mean}\left(x\right)}{\sqrt[4]{\left|C_{x,42}\right|}}|,|\frac{C_{x,40}}{C_{x,42}}|,|\frac{C_{x,41}}{C_{x,42}}\left|\right]$

If M _Pq=E[x (n) ^P-q(x (n) ^*) ^q], E[ ] represent and ask mathematic expectaion, in the following formula:

Mean () representative is averaged;

$C_{x,40}=M_{40}-{3M}_{20}^2$

C _x，41＝M ₄₁-3M ₂₁M ₂₀

$C_{x,42}=M_{42}-{\left|M_{20}\right|}^2-{2M}_{21}^2;$

(7c) the characteristic vector F of the OFDM sub-carrier modulation data that step (7b) is obtained _rAdjudicate according to following formula:

${\hat{M}}_k=\underset{k=\mathrm{1,2,3}}{\arg \min }\left(\right|F_r-F_{M_k}\left|\right)$

M in the formula _kThe modulation system of representation signal, M ₁, M ₂, M ₃Represent BPSK respectively, QPSK, three kinds of modulation systems of 16QAM,

Representing modulation system is M _kSignal characteristic of correspondence Vector Theory value,

Represent the estimated signals modulation system, M ₁, M ₂, M ₃Three kinds of modulation system characteristic of correspondence Vector Theory values such as following table 1:

Table 1 M ₁, M ₂, M ₃Three kinds of modulation system characteristic of correspondence Vector Theory values

Advantage of the present invention can illustrate by following simulation performance:

1. to the emulation of the described bandwidth estimation method of step 3

(1a) simulated conditions and content

The signal type that emulation is adopted: OFDM, BPSK, QPSK, 16QAM, 64QAM, wherein ofdm signal subcarrier number is 64, circulating prefix-length is 16, and it is that pulse-shaping is carried out in 0.5 raised cosine roll off filtering that single-carrier signal is used rolloff-factor, and signal is 8 times of over-sampling baseband signals.

Method estimated signal bandwidth W according to step 3 description.For single-carrier signal, W equals the signal baud rate, and for ofdm signal, W equals signal sample speed.Under AWGN and multipath channel, use and estimate accuracy rate measurement estimated performance.

(1b) simulation result

Under the awgn channel and under the multipath channel, estimate accuracy simulation result such as table 2 and table 3.

Signal bandwidth is estimated accuracy rate under table 2 awgn channel

Signal bandwidth is estimated accuracy rate under table 3 multipath channel

By the simulation result of table 2 and table 3 as seen, for ofdm signal, under awgn channel and multipath channel, signal to noise ratio during greater than 0dB the estimation to signal sample speed have very high accuracy rate.For single-carrier signal, under awgn channel, the accuracy rate that signal to noise ratio is estimated baud rate during greater than 4dB is more than 93%; Under multipath channel, the accuracy rate that signal to noise ratio is estimated baud rate during greater than 8dB is more than 91%.

2. to the described ofdm signal recognition methods of step 5 emulation

(2a) simulated conditions and content

The signal type that emulation is adopted: OFDM, BPSK, QPSK, square 16QAM, square 64QAM.Wherein, ofdm signal subcarrier number is 64, and circulating prefix-length is 16, and it is that pulse-shaping is carried out in 0.5 raised cosine roll off filtering that single-carrier signal is used rolloff-factor, and signal is 4 times of over-sampling baseband signals.

According to the described method of step 5, use the multilayer wavelet decomposition to extract signal characteristic vector.Get C=100, then the theoretical value of ofdm signal characteristic vector is M=[50,25,12.5,50,25,12.5].Received signal characteristic vector and ofdm signal characteristic vector theoretical value are compared compute euclidian distances D.D and decision threshold R are compared, when D＜R, be judged to ofdm signal, when D＞R, be judged to single-carrier signal.Regulate thresholding R, obtain best recognition effect.To the ofdm signal court verdict is that ofdm signal is considered as once correctly adjudicating, and is that non-ofdm signals is considered as once correctly adjudicating to the single-carrier signal court verdict.

(2b) simulation result

The recognition correct rate simulation result that under awgn channel and multipath channel, obtains such as following table 4 and table 5:

Ofdm signal recognition correct rate under table 4 awgn channel

Ofdm signal recognition correct rate under table 5 multipath channel

According to the simulation result of table 4 and table 5 as seen, under awgn channel, when signal to noise ratio was higher than 0dB, correct recognition rata was more than 94%; Under multipath channel, when signal to noise ratio when 4dB is above, correct identification probability is more than 96%.

Claims (6)

1. ofdm signal intelligence receiving system comprises:

The signal capture unit is used for signal is caught reception;

Pretreatment unit is used for carrying out to the received signal filtering, amplification and A/D conversion preliminary treatment;

Carrier estimation, down-converter unit are used for obtaining baseband signal S (n) to carrying out estimating carrier frequencies and down-conversion through pretreated signal;

The signal bandwidth estimation unit is used for the bandwidth estimation of carrying out to baseband signal S (n), and estimated result W is passed to follow-up sampling unit and OFDM parameter estimation unit;

Sampling unit is used for baseband signal S (n) is sampled, and the signal S ' after obtaining sampling (n);

The ofdm signal recognition unit, being used for (n) differentiating received signal according to the signal S ' after the sampling is ofdm signal or single-carrier signal;

The ofdm signal parameter estimation unit, being used for differentiating received signal is under the situation of ofdm signal, according to the bandwidth W of baseband signal S (n) and estimation, estimating OFDM subcarrier number N, circulating prefix-length N _GWith symbol original position side-play amount θ, obtain ofdm signal S after the sign synchronization " (n), and with the OFDM subcarrier number N, the circulating prefix-length N that estimate according to θ _GPass to follow-up ofdm signal demodulating unit;

The ofdm signal demodulating unit, being used for differentiating received signal is under the situation of ofdm signal, according to the OFDM subcarrier number N, the circulating prefix-length N that estimate _G" (n) carry out subcarrier modulation modes identification and demodulation with signal bandwidth W, to the ofdm signal S after the sign synchronization.

2. intelligent receiving system according to claim 1, wherein the sample frequency that adopts of sampling unit is 4 times of estimated bandwidth W.

3. an ofdm signal intelligence method of reseptance comprises the steps:

(1) catches the interior signal of monitoring frequency range, and the signal of catching is carried out filtering, amplification and A/D conversion preliminary treatment;

(2) pretreated received signal is carried out carrier estimation and down-converted, obtain baseband signal S (n);

(3) baseband signal S (n) is obtained base-band signal spectrum by Fourier transform, use Haar wavelet decomposition and wavelet reconstruction, details component in the elimination base-band signal spectrum obtains the step change type base-band signal spectrum, uses statistical method to judge the position, edge of this signal spectrum, obtains signal bandwidth W;

(4) baseband signal S (n) is carried out over-sampling by 4 times of estimated signal bandwidth W, obtain 4 times of over-sampling baseband signal S ' (n);

(5) signal S ' (n) is extracted characteristic vector by the multilayer wavelet decomposition, calculate the Euclidean distance of this characteristic vector and ofdm signal characteristic vector theoretical value, this distance is compared with thresholding, when distance during less than thresholding, the differentiation received signal is an ofdm signal, when distance during greater than thresholding, the differentiation received signal is a single-carrier signal;

(6) be under the situation of ofdm signal in judgment signal, according to baseband signal S (n) and estimated signals bandwidth W, estimating OFDM subcarrier number N, circulating prefix-length N _GWith symbol original position side-play amount θ, obtain OFDM baseband signal S after the sign synchronization " (n), and with the sample value speed of estimated signals bandwidth W as ofdm signal according to the estimated result of θ;

(7) be under the situation of ofdm signal in judgment signal, according to the OFDM subcarrier number N, the circulating prefix-length N that estimate _G, the OFDM baseband signal S after sample value speed W and the sign synchronization " (n), carries out subcarrier-modulated identification and demodulation to the OFDM baseband signal.

4. intelligent method of reseptance according to claim 3, wherein step (3) described use Haar wavelet decomposition and wavelet reconstruction, the details component in the elimination base-band signal spectrum obtains the base-band signal spectrum of step change type, carries out as follows:

(4a) base-band signal spectrum is carried out n (n 〉=1) layer Haar wavelet decomposition, obtain the coefficient of wavelet decomposition vector T;

(4b) the approximate component in the retention coefficient vector T is constant, and the details component is put 0, with the details component in the elimination base-band signal spectrum, obtains being used for the coefficient vector T ' of wavelet reconstruction;

(4c) signal spectrum is carried out the Haar wavelet reconstruction, obtain the step change type signal spectrum after the reconstruct according to described coefficient vector T '.

5. intelligent method of reseptance according to claim 3, wherein the described use statistical method of step (3) is judged the position, edge of this signal spectrum, carries out as follows:

(5a) the baseband signal data that receive are divided into groups, it is divided into M group, be further divided into N group in every group;

(5b) (j in the group of i≤M) (carry out Fourier transform and obtain signal spectrum S by the group's baseband signal of j≤N) to i _{I, j}(f);

(5c) to signal spectrum S _{I, j}(f) use Haar wavelet decomposition and wavelet reconstruction, elimination details component obtains step change type base-band signal spectrum S ' _{I, j}(f);

(5d) N the step change type base-band signal spectrum S ' that i group signal is obtained _{I, j}(f) (1≤j≤N) carry out statistical average obtains the frequency spectrum S ' after the statistical average _i(f), this frequency spectrum S ' _i(f) position that consecutive value differs maximum in is the steepest change location;

(5e) search described S ' _i(f) two steepest change locations are as the position, frequency spectrum edge of i group signal;

(5f) position, frequency spectrum edge of statistics M group signal, with the bandwidth between two the highest positions of statistic as estimated signals bandwidth W.

6. intelligent method of reseptance according to claim 3, wherein step (5) is described (n) extracts characteristic vector by the multilayer wavelet decomposition to S ', carries out as follows:

(6a) the baseband signal S ' of 4 times of over-samplings (n) is adopted multilayer wavelet decomposition structural classification characteristic vector:

$x=C\·\frac{1}{{\mathrm{ap}}_2}[{\mathrm{ap}}_3,{\mathrm{ap}}_4,{\mathrm{ap}}_5,{\mathrm{de}}_3,{\mathrm{de}}_4,{\mathrm{de}}_5]$

Wherein, C is the parameter that the amplitude of characteristic vector value is adjusted,

Ap _iThe approximate portion of energy of representation signal i layer wavelet decomposition is defined as follows:

${\mathrm{ap}}_i={\left|\right|a_i\left|\right|}_2^2=\underset{n}{\mathrm{\Σ}}{a}_{i,n}^2,$ I=1 ..., M, a _iRepresent the approximate part coefficient vector of i layer wavelet decomposition, a _{I, n}The approximate part coefficient of expression i layer wavelet decomposition;

De _iThe detail section energy of representation signal i layer wavelet decomposition is defined as follows:

${\mathrm{de}}_i={\left|\right|d_i\left|\right|}_2^2=\underset{n}{\mathrm{\Σ}}{d}_{i,n}^2,$ I=1 ..., M, d _iRepresent the detail section coefficient vector of i layer wavelet decomposition, d _{I, n}The detail section coefficient of expression i layer wavelet decomposition;

(6b) the Euclidean distance D of calculated characteristics vector x and ofdm signal characteristic vector theoretical value M:

$D=\underset{l=1}{\overset{6}{\mathrm{\Σ}}}{(x_l-m_l)}^2$

X wherein _lBe characteristic vector x l dimension value, m _lBe characteristic vector M l dimension value;

(6c) relatively,, differentiate and be ofdm signal,, differentiate and be single-carrier signal as D during greater than thresholding as D during less than thresholding with D and thresholding.

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