CN102013955A - Method suitable for hardware realization for assisting soft decision decoding by using channel state information - Google Patents

Abstract

The invention relates to a method suitable for hardware realization for assisting soft decision decoding by using channel state information. The method comprises the following steps of: acquiring estimated value of a chance failure rate (CFR); calculating amplitude of the CFR estimated value, taking the average value of the CFR amplitudes corresponding to subcarriers in the same encoding block as a normalized factor and dividing the amplitude by the normalized factor of the encoding block to acquire the channel state information (CSI); multiplying log-likelihood ratio obtained by demapping the subcarriers by the CSI corresponding to the log-likelihood ratio to obtain the log-likelihood ratio with channel reliability information; and inputting into a soft decision decoder so as to obtain information bit transmitted by a transmitting end. In the method, a CSI-assisted soft decision decoder is utilized and the average value of the CFR amplitudes in the same encoding block is used as the normalized factor, so the decoding correctness of the soft decision decoder is improved; meanwhile, the hardware expenditure is saved and the hardware realization is facilitated.

Description

Be fit to the hard-wired method of utilizing the auxiliary Soft decision decoding of channel condition information

Technical field

The present invention relates to OFDM in the communication technology (OFDM) technical field, refer in particular to a kind of orthogonal FDM communication system that is used for and utilize channel condition information (Channel State Information, CSI) auxiliary Soft decision decoding, the method for raising channel decoder reliability of decode.

Background technology;

Orthogonal frequency division multiplexi belongs to multi-carrier modulation, high-speed data-flow is passed through string and conversion, make the data symbol persistence length on each subcarrier increase relatively, thereby reduce the intersymbol interference that temporal dispersion that wireless channel multidiameter delay expansion produced brings effectively, reduced complexity balanced in the receiver.It is divided into many mutually orthogonal and overlapping subchannels with the channel of assignment simultaneously, compares with the Frequency Division Multiplexing system of routine, and ofdm system can maximally utilise frequency spectrum resource.Carry out narrowband modulation and transmission on each subchannel, signal bandwidth is less than the correlation bandwidth of channel, and the frequency selective fading of channel is converted into flat fading.

Just because of above-mentioned advantage, OFDM is widely used in digital audio broadcasting (DAB), digital video broadcasting (DVB) and the various modern communications agreement by people as a kind of digital transmission mode efficiently.

Fig. 1 is the structured flowchart of typical OFDM baseband system.At transmitting terminal, channel encoder is divided into some encoding blocks with the binary data of importing and carries out forward error correction (Forward error correction, FEC) chnnel coding, binary data behind the coding is through interleaver, again by modulation just with binary data map to the planisphere of correspondence.Modulation system can adopt biphase phase shift keying (Binary phase shift keying, BPSK), quaternary PSK (quadrature phase shift keying, QPSK) and quadrature amplitude modulation (quadrature amplitude modulation, QAM) etc.The carrier data that obtains after the modulation carry out after through string and conversion leaf inverse transformation in the N point discrete Fourier (inverse discrete Fourier transform, IDFT).

At receiving terminal, the discrete Fourier transform device is converted to frequency-region signal with the ofdm signal of time domain.Because the influence of wireless channel h (t) and noise v (t), the frequency-region signal that receives have very big-difference with the frequency-region signal that sends.Therefore the channel information that the frequency-region signal that receives need utilize channel estimating to go out carries out equilibrium, to obtain the frequency-region signal of transmitting terminal.Again the signal after the equilibrium is sent into demodulation, deinterleaver, channel decoder, thereby recover the binary data information of transmitting terminal transmission.

Signal is after receiving terminal process channel equalization, what obtain is the estimated value of constellation point, to become the bit information that to decipher to these estimated values, also need constellation point is separated mapping, in addition, because Soft decision decoding improves a lot than the performance of Hard decision decoding, so will utilize the result of channel estimating to carry out the extraction of channel condition information.

In the Soft decision decoding system, the extracting mode of soft bit information is very important to the performance of whole system.Soft bit information has embodied channel condition information CSI.CSI has reflected on this subcarrier the reliability that transmits data, and (Signal to Noise Ratio SNR) is directly proportional with the instantaneous signal-to-noise ratio of this subcarrier.When data-modulated is to multicarrier, different carrier waves will have different signal to noise ratios, and the data that transmit on than the high s/n ratio subcarrier are more reliable than the data that transmit at the low signal-to-noise ratio subcarrier.

Therefore, need to propose a kind of method of reseptance that utilizes the auxiliary soft decision decoder of CSI, to improve the decoding accuracy of Soft decision decoding, this method need consider that minimizing takies hardware resource and hard-wired feasibility simultaneously.

Summary of the invention

It is simple and be convenient to hard-wired a kind of hard-wired method of utilizing the auxiliary Soft decision decoding of channel condition information that is fit to that the object of the invention provides computational methods.

Technical solution of the present invention is:

A kind of suitable hard-wired method of utilizing the auxiliary Soft decision decoding of channel condition information comprises the steps:

A. utilize the channel estimating or the blind Channel Estimation of pilot signal, obtain the estimated value of CFR: $\hat{h}={[{\hat{h}}_0,{\hat{h}}_1,...,{\hat{h}}_{N-1}]}^T;$

B. calculate the amplitude of the CFR estimated value of corresponding each subcarrier k

K=0,1..., N-1 gets the CFR amplitude of subcarrier correspondence in the same encoding block

K=0,1..., the average of N-1 is as normalization factor α, and the amplitude of the CFR estimated value of each subcarrier k obtains CSI divided by the normalization factor α of place encoding block;

C. subcarrier multiply by its corresponding CSI by separating the log-likelihood ratio (Log-Likelihood Ratios) that obtains of mapping, obtains having the log-likelihood ratio of channel reliability information;

D. the log-likelihood ratio that has channel reliability information is sent to soft decision decoder, so obtain that transmitting terminal sends information bit.

Advantage of the present invention:

The CFR amplitude average of the same data transmission block of available technology adopting is as normalization factor, need store the pairing channel amplitude of a large amount of carrier waves during realization, need be when hardware is realized than large memories spare, the present invention utilizes CSI to assist soft decision decoder, consider the realizability and the economize on hardware resource of hardware simultaneously, utilize the interior CFR amplitude average of same encoding block as normalization factor, not only improved the decoding correctness of soft decision decoder, simultaneously also save hardware spending, be convenient to hardware and realize.For example, have 240 encoding blocks at most in a data transmission block in the Wimax system, minimum have 1 encoding block.

Utilize the interior CFR amplitude average of same encoding block as normalization factor, because the unit of the each decoding of soft decision decoder is an encoding block, than the CFR amplitude average that adopts same data block as normalization factor, more can represent the degree of reliability of carrier transmission, improve the decoding correctness of soft decision decoder.

Description of drawings

Fig. 1 is the structured flowchart of OFDM baseband system;

Fig. 2 is the structured flowchart that the present invention utilizes the receiving system of the auxiliary Soft decision decoding of CSI;

Fig. 3 is the planisphere of 16-QAM correspondence;

Embodiment

Utilize the method for reseptance of the auxiliary soft decision decoder of CSI and the enforcement of device to be described to the present invention in conjunction with the accompanying drawings with the lower part, further illustrate purpose of the present invention, specific structural features and advantage.

The principle of the invention: the present invention utilizes the CSI of reflection channel reliability to revise separating the LLR value that obtains after the mapping, carry current subcarrier channel information of living in the feasible LLR value that newly obtains, consider hardware realization expense simultaneously, the average of utilizing the CFR amplitude in the same encoding block is as normalization factor.

Fig. 2 is the structured flowchart that the present invention utilizes the receiving system of the auxiliary soft decision decoder of CSI.This receiving system comprises channel estimator, and it utilizes pilot signal or training signal to carry out the CFR estimated value that channel estimating obtains all subcarriers on the whole running time-frequency resource

Channel estimator can adopt LS to estimate, also can adopt MMSE to estimate.

Channel status weighted factor computing unit calculates the amplitude of the CFR estimated value on each subcarrier

Get average with encoding block CFR amplitude as normalization factor α, suc as formula (1):

$\mathrm{\α}=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{\left|{\hat{h}}_k\right|}^2---\left(1\right)$

In the formula, N represents the carrier wave number that corresponding transmitting terminal encoder code block is comprised.

The CSI value obtains suc as formula (2):

${\mathrm{CSI}}_k=\frac{{\left|{\hat{h}}_k\right|}^2}{\mathrm{\α}}---\left(2\right)$

Output signal obtains the signal through channel compensation through behind the channel equalizer, and formula is as follows:

$z_k=\frac{y_k}{{\hat{h}}_k}---\left(3\right)$

K=0 wherein, 1 ..., N-1.

With the signal z that obtains behind the channel compensation _kBe sent in the demodulator, the present invention is the example explanation that makes an explanation with 16-QAM.Fig. 3 is the planisphere of 16-QAM correspondence, and at the ofdm system transmitting terminal, the binary number of input modulator is four bit b according to this ₃b ₂b ₁b ₀Be one group, be converted to the point on the 16-QAM planisphere shown in Figure 3, be expressed as plural form (I+jQ).b ₃b ₂The in-phase component I of decision modulation signal, b ₁b ₀The quadrature component of decision modulation signal.Demodulator is to b ₃b ₂b ₁b ₀Carry out soft-decision, can not lose some for the decoder Useful Information.Utilize formula (4) can obtain the LLR of corresponding four bits of each subcarrier.

$\mathrm{LLR}\left(b_i\right)=\log \frac{p[b_i=1|z_k]}{p[b_i=0|z_k]}---\left(4\right)$

The CSI value of utilizing the subcarrier correspondence is weighted operation to the LLR signal of the subcarrier that formula (4) obtains, suc as formula (5):

$\hat{L}\mathrm{LR}\left(b_i\right)=\mathrm{LLR}\left(b_i\right)\×{\mathrm{CSI}}_k---\left(5\right)$

In the formula, suppose the noise power approximately equal of each subcarrier, the CSI estimated value is the CFR amplitude of subcarrier k, can characterize the signal to noise ratio snr of subcarrier k position.

The LLR information of CSI weighting is sent in the soft decision decoder, can obtains the bit information that transmitting terminal will transmit.

Claims (1)

1. one kind is fit to the hard-wired method of utilizing the auxiliary Soft decision decoding of channel condition information, and it is characterized in that: it comprises the steps:

A. utilize the channel estimating or the blind Channel Estimation of pilot signal, obtain the estimated value of CFR: $\hat{h}={[{\hat{h}}_0,{\hat{h}}_1,...,{\hat{h}}_{N-1}]}^T;$

B. calculate the amplitude of the CFR estimated value of corresponding each subcarrier k

K=0,1..., N-1 gets the CFR amplitude of subcarrier correspondence in the same encoding block

K=0,1..., the average of N-1 is as normalization factor α, and the amplitude of the CFR estimated value of each subcarrier k obtains CSI divided by the normalization factor α of place encoding block;

C. subcarrier multiply by its corresponding CSI by separating the log-likelihood ratio (Log-Likelihood Ratios) that obtains of mapping, obtains having the log-likelihood ratio of channel reliability information;

D. the log-likelihood ratio that has channel reliability information is sent to soft decision decoder, so obtain that transmitting terminal sends information bit.

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