CN102316062A - Algorithm for synchronizing carrier wave based on prior probability assistance - Google Patents

Abstract

The invention discloses an algorithm for synchronizing a carrier wave based on prior probability assistance, which belongs to the technical field of wireless communication, and particularly relates to the synchronization of the carrier wave under residual frequency deviation in an environment with a low signal-to-noise ratio. By using the algorithm, the following purposes the phase error information of each symbol is calculated by using a prior probability assisted algorithm, so that the algorithm can realize the synchronization under conditions of the low signal-to-noise ratio and the residual frequency deviation, the performance of the system is improved, and a good compromise is made between calculation complexity and the performance of the system are achieved.

Description

Based on prior probability subcarrier synchronized algorithm

Technical field

The invention belongs to wireless communication technology field, particularly under the low signal-to-noise ratio environment, the carrier synchronization of residual frequency departure.

Background technology

Under the low signal-to-noise ratio condition, Turbo code and LDPC code system are very strict to the synchronous requirement of carrier frequency and phase place, even exist little frequency deviation and skew also can make the mis-behave of system.Therefore data must adopt proper technique to make it can be accurately synchronous before getting into decoder.Yet under utmost point low signal-to-noise ratio environment, accurate carrier synchronization is a very problem of difficulty, such as, adopt the BPSK modulation, the code check of Turbo code encoder is 1/6, when SNR＜-during 7.8dB, wireless receiving function seldom realizes synchronously.

Summary of the invention

The present invention proposes a kind ofly, adopt this algorithm to can be implemented in the carrier synchronization under the residual frequency deviation based on prior probability subcarrier synchronized algorithm, and systematic function can be more near the performance of decoder.

Innovation part of the present invention is: adopt the maximum likelihood estimation approach to estimate the carrier information of each symbol, then control information is input to filter, obtain skew information to be estimated afterwards.

The present invention improves the carrier phase algorithm for estimating on the basis of prior probability subcarrier synchronized algorithm, has proposed based on the prior probability subcarrier synchronized algorithm of symbol one by one.

1, system configuration

As shown in Figure 1 based on prior probability subcarrier synchronized algorithm, [r _i] _kI symbol of the k frame data that expression receives, [y _i] _kI symbol of the k frame data of supination separated in expression.Receiving terminal is with metadata cache; The external information of decoder output is used for the auxiliary iteration carrier phase error of sign indicating number and estimates that loop filter converts phase error signal to control signal, the output of this control signal control digital controlled oscillator; Obtain phase error to be estimated, then to r _iCarry out phase compensation and obtain y _i, phase error estimation and phase error is next time carried out in last demodulation and decoding again.

2, based on prior probability subcarrier synchronized algorithm

2.1 based on the brief introduction of prior probability subcarrier synchronized algorithm

Focus on the estimation of carrier phase error based on prior probability subcarrier synchronized algorithm master.The phase error estimation and phase error expression formula that the present invention adopts can be write as:

${\widetilde{\mathrm{\φ}}}_{\mathrm{ML}}=\frac{{\mathrm{\ω}}_1{\mathrm{\θ}}_1+2{\mathrm{\ω}}_2{\mathrm{\θ}}_2}{{\mathrm{\ω}}_1+4{\mathrm{\ω}}_2}$

Wherein, ω _kBe the amplitude of k subharmonic, θ _kBe the phase place of k subharmonic, ω _kAnd θ _kCan obtain by following formula.

${\mathrm{\ω}}_1\cos \left({\mathrm{\θ}}_1\right)=a_1^i\cos \left({\mathrm{\φ}}_i\right)$

${\mathrm{\ω}}_1\sin \left({\mathrm{\θ}}_1\right)=a_1^i\sin \left({\mathrm{\φ}}_i\right)$

${\mathrm{\ω}}_2\cos \left({\mathrm{\θ}}_2\right)=a_2^i\cos \left(2{\mathrm{\φ}}_i\right)$

${\mathrm{\ω}}_2\sin \left({\mathrm{\θ}}_2\right)=a_2^i\sin \left(2{\mathrm{\φ}}_i\right)$

Wherein, φ _iBe [r _i] _kPhase place,

Be the nth harmonic of i symbol, be defined as:

$a_n^i=\frac{1}{\mathrm{\π}}\underset{-\mathrm{\π}}{\overset{\mathrm{\π}}{\∫}}{\mathrm{\Λ}}_{L,\mathrm{BPSK}}^i\left(\mathrm{\φ}\right)\cos \left(\mathrm{n\φ}\right)\mathrm{d\φ}$

For the Turbo system, be not have prior information utilizable in the first time before the iteration, but can replace with the symbol probability of transmission, use P _i(m) expression utilizes these probable values that likelihood function is averaged, like this can be in the hope of the log-likelihood function (LLF) of i symbol, and for BPSK, the log-likelihood function of i symbol can be write as,

${\mathrm{\Λ}}_{L,\mathrm{BPSK}}^i\left(\mathrm{\φ}\right)=\log \{\mathrm{sech}\left(\frac{L\left(i\right)}{2}\right)\·\cosh [\frac{L\left(i\right)}{2}+\frac{A_i\cos (\mathrm{\φ}-{\mathrm{\φ}}_i)}{{\mathrm{\σ}}^2}\left]\right\}$

The loop filter expression formula can be write as,

$\mathrm{\θ}\left(i\right)=\mathrm{\θ}(i-1)+\mathrm{\γ}{\widetilde{\mathrm{\φ}}}_{\mathrm{ML}}\left(i\right)$

Wherein, γ is the coefficient of loop filter.

2.2 based on prior probability subcarrier synchronized algorithm step

Be based on the synchronized algorithm of symbol one by one based on prior probability sign indicating number subcarrier synchronized algorithm, concrete workflow is following:

The first step: parameter initialization; It is M that maximum iteration time is set, and

[y _i] _k＝[r _i] _kexp(-jθ(0))

Second step: the control information of calculating i symbol of k frame

The 3rd step: obtain

through wave filter

The 4th step: compensate of frequency deviation [y _i] _k=[r _i] _kExp (j θ (i)).

The 5th step: BPSK demodulation.

The 6th step: Turbo decoding.

The 7th step: return step 2 and carry out next iteration.

Description of drawings

Fig. 1 is based on prior probability subcarrier synchronized algorithm block diagram.

Claims (2)

1. based on the auxiliary Carrier Synchronization Algorithm of prior probability; Receiving terminal is with metadata cache; The external information of decoder output is used for the auxiliary iteration carrier phase error of sign indicating number and estimates that loop filter converts phase error signal to control signal, the output of this control signal control digital controlled oscillator; Obtain phase error to be estimated, then to r _iCarry out phase compensation and obtain y _i, phase error estimation and phase error is next time carried out in last demodulation and decoding again.

2. said based on the auxiliary Carrier Synchronization Algorithm of prior probability according to claim 1, comprise following step:

Be based on the synchronized algorithm of symbol one by one based on prior probability sign indicating number subcarrier synchronized algorithm, concrete workflow is following:

The first step: parameter initialization, it is M that maximum iteration time is set, and θ (0)=0,

[y _i] _k＝[r _i] _kexp(-jθ(0))

Second step: the control information

of calculating i symbol of k frame

The 3rd step: obtain

through wave filter

The 4th step: compensate of frequency deviation [y _i] _k=[r _i] _kExp (j θ (i)).

The 5th step: BPSK demodulation.

The 6th step: Turbo decoding.

The 7th step: return step 2 and carry out next iteration.

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