CN103346860B - A kind of decoding unit of wireless transmitting system and interpretation method thereof - Google Patents

Abstract

Present invention is disclosed a kind of decoding unit and interpretation method thereof of wireless transmitting system, it mainly contains Hamming distance computing module, Gabi selection (ACS) module, survivor path memory module, and minimum value selects module and backtracking module.The present invention be directed to a set of convolutional encoding of high-definition video wireless transmission system and the design implementation of Viterbi decoding of being adapted to of the key issue independent developments such as the real-time of encoding and decoding, reliability and hardware resource use, this decoding unit and interpretation method are applicable to multiple fields of modern communications, the field application such as such as multi-carrier wireless communication, portable mobile wireless video communication, hand-hold type transmission terminal and efficient RF communication, reliably, effectively solve the difficult problem that source code produces error code correction after dissemination channel of making an uproar.<!--1-->

Description

A kind of decoding unit of wireless transmitting system and interpretation method thereof

Technical field

The present invention relates to the code translator and the method that utilize Coded Orthogonal Frequency Division Multiplexing (COFDM) to carry out correcting in the high-definition video wireless transmission system of data processing technique error code, it is adapted to convolutional encoding and the Viterbi decoding of high-definition video wireless transmission system.

Background technology

In recent years, along with GPRS, CDMA, 3G(TD-SCDMA, WCDMA, CDMA2000), the rise of the cordless communication network such as OFDM, wireless video transmission system is with its maneuverability, visual pattern, the advantage such as easy to operate, be widely used in the every field such as army individual-soldier operation, public security remote monitoring evidence obtaining, TV programme relay, the monitoring of mine oilfield safety, the environmental monitoring of underground garage supermarket, cell environment monitoring, and become that people realize at a distance, a kind of important means of on-site supervision on a large scale.COFDM technology is high with its transmission rate, antijamming capability strong, and this makes at " in high-speed motion " and " non-depending under gating condition " realizes high-quality realtime graphic and transfer of data becomes possibility.

In radio communication encoding and decoding technique, channel coding/decoding technology based on convolutional encoding gains great popularity because of advantages such as its code efficiency is high, good in anti-interference performance, therefore convolutional encoding and decoding technique are paid close attention to widely, are one of domestic and international experts and scholars' study hotspots.But in wireless communication procedure, noise jamming in channel can cause certain error rate of receiving terminal, this will affect the accuracy of Wireless Data Transmission, in the algorithm realization process of particularly convolutional encoding and Viterbi decoding, source code produces code symbols by encoder, after noisy channel is propagated, error code phenomenon occurs, thus can decoding error be caused, this problem annoyings designer at present always.

Summary of the invention

Technical problem to be solved by this invention realizes that a kind of decoding efficiency is higher when the constraint length of code is less, and the faster structure of speed is relatively simply easy to the Convolutional Decoder Assembly realized.

To achieve these goals, the technical solution used in the present invention is: a kind of decoding unit of wireless transmitting system, Hamming distance between the coding that Hamming distance computing module is possible under calculating input data and current encoder state, and the Hamming distance signal calculated is delivered to ACS module and path memory module, accumulation distance signal is delivered to minimum value and selects module by ACS module, and compared by it and show that distance path less in distance signal is delivered to path backtracking module as survivor path value, described path backtracking module survivor path value is delivered to path memory module and stores, the Hamming distance signal simultaneously inputted according to survivor path value and path memory module outwards exports and draws decode results.

A kind of interpretation method of wireless transmitting system:

Step 1, Received signal strength;

The length of step 2, status switch corresponding to path and receiving sequence calculating path branch;

Step 3, accumulated path branch obtain length and be path;

Step 4, compare that to obtain the shortest path length of any instant be survivor path;

Input symbols corresponding to step 5, survivor path is just decode results.

Further, source code V _kby encoder X _k, produce code symbols, be designated as Y _k, after noisy channel is propagated, Received signal strength is Z _k;

The length of path branches in described step 2:

$\mathrm{\&lambda;}\left({\mathrm{\&xi;}}_k\right)\stackrel{\mathrm{\&Delta;}}{=}-\ln P\left(X_{k+1}\right|X_k)-\ln P\left(Z_k\right|{\mathrm{\&xi;}}_k)$

Wherein, ξ _krepresent from X _kto X _k+1state transitions

In described step 3, path is-lnP (X, Z),

Wherein X for the status switch corresponding to this path, Z is receiving sequence,

$P(X,Z)=P\left(X\right)P\left(Z\right|X)=\underset{k=0}{\overset{K-1}{\mathrm{\&Pi;}}}P\left(X_{k+1}\right|X_k)\underset{k=0}{\overset{K-1}{\mathrm{\&Pi;}}}P\left(Z_k\right|X_{k+1},X_k)$

Then $-\ln P(X,Z)=\underset{k=0}{\overset{K-1}{\mathrm{\&Sigma;}}}\mathrm{\&lambda;}\left({\mathrm{\&xi;}}_k\right)$ 。

The present invention be directed to a set of convolutional encoding of high-definition video wireless transmission system and the design implementation of Viterbi decoding of being adapted to of the key issue independent developments such as the real-time of encoding and decoding, reliability and hardware resource use, this decoding unit and interpretation method are applicable to multiple fields of modern communications, the field application such as such as multi-carrier wireless communication, portable mobile wireless video communication, hand-hold type transmission terminal and efficient RF communication, reliably, effectively solve the difficult problem that source code produces error code correction after dissemination channel of making an uproar.

Accompanying drawing explanation

Mark in the content expressed every width accompanying drawing in specification of the present invention below and figure is briefly described:

Fig. 1 is Viterbi decoding algorithm schematic diagram;

Fig. 2 Viterbi decoding unit realizes block diagram;

Fig. 3 Hamming distance computing module theory diagram;

Fig. 4 ACS module principle block diagram;

Fig. 5 path backtracking module principle block diagram

Fig. 6 is Viterbi decoding simulation result figure.

Embodiment

The present invention is the Viterbi decoding technique of the high-definition video wireless transmission system based on COFDM; COFDM(CodeOrthogonalFrequencyDivisionMultiplexing) i.e. Coded Orthogonal Frequency Division Multiplexing (COFDM), it is a kind of novel data processing technique, by means of its high availability of frequency spectrum, high transmission rate and strong anti-multipath jamming ability, arouse widespread concern in wireless image transmission field; The decoding algorithm of a kind of convolution code of Viterbi decoding, its very strong error correcting capability, have application in many systems, this wherein just includes wireless video transmission system.This achievement is devoted to a decoding difficult problem for the convolution code solving ofdm system, is one of core key technology of the high-resolution video transfer system based on COFDM, is applicable to the setup and apply of the high-resolution video transfer system based on COFDM.

Source code V _kby encoder X _k, produce code symbols, be designated as Y _k, after noisy channel is propagated, Received signal strength is Z _k.The work that Viterbi decoding unit and interpretation method thereof are done is exactly utilize decoding algorithm, from Z _kjudge V _k, recover information source information.

If the shift register in convolution coder has N position, so X _kstate will have 2 ⁿkind.Whenever a source code enters encoder, the state of shift register changes once, and exports a corresponding encoded radio unique with this state.Viterbi decoding selects most possible one in the path of all possible State Transferring of mark, and the source code corresponding to this paths is exactly decode results.

According to above-mentioned principle, receiving Z _kafter, first, the length of the status switch corresponding to path and receiving sequence calculating path branch, the length of path branches is: $\mathrm{\&lambda;}\left({\mathrm{\&xi;}}_k\right)\stackrel{\mathrm{\&Delta;}}{=}-\ln P\left(X_{k+1}\right|X_k)-\ln P\left(Z_k\right|{\mathrm{\&xi;}}_k)$

Wherein, ξ _krepresent from X _kto X _k+1state transitions;

Definition path be-lnP (X, Z), wherein X for the status switch corresponding to this path, Z is receiving sequence,

$P(X,Z)=P\left(X\right)P\left(Z\right|X)=\underset{k=0}{\overset{K-1}{\mathrm{\&Pi;}}}P\left(X_{k+1}\right|X_k)\underset{k=0}{\overset{K-1}{\mathrm{\&Pi;}}}P\left(Z_k\right|X_{k+1},X_k)$

Then overall path can be expressed as $-\ln P(X,Z)=\underset{k=0}{\overset{K-1}{\mathrm{\&Sigma;}}}\mathrm{\&lambda;}\left({\mathrm{\&xi;}}_k\right)$ ，

Namely path branches length and.Therefore, the shortest path of any instant is exactly each individual path length and minimum path, is called survivor path.And for each moment k, in grid chart, all have 2 ⁿbar survivor path, every paths arrives the state X in a k+1 moment _k

The input symbols corresponding to survivor path relatively obtaining any instant is just decode results.

With (2,1,2) convolution code for example, as shown in Figure 1, S ₀-S ₃represent 4 kinds of possible states of encoder for convolution codes, from time point 0T to 7T, each state Dou Youliangge branch, points to by the source code V newly entering encoder _kthe state that (0 or 1) brings changes, and such as current state is S ₀if, input V _k=0, then subsequent time state is still S ₀, output encoder Y _k=00.Otherwise if be input as 1, state changes over S ₁, output encoder Y _kthe output encoder of individual path and the coding received compare by=11., just obtain Hamming distance, are assigned to this section of individual path as path.The digitized representation Hamming distance on side, path in Fig. 1, numeral in circle arrive the shortest path of this state length and, suppose the coded sequence Z={00 received, 01,10,00,00,00,00}, the Hamming distance calculating each moment successively with arrive this state shortest path and, selects a shortest paths in the 7T moment, the input symbols corresponding to this path is just decode results.

According to above-mentioned algorithm principle, utilize programmable logic device FPGA to build hardware implementation block diagram as shown in Figure 2, the decoding unit of wireless transmitting system primarily of Hamming distance computing module, Gabi selection (ACS) module, survivor path memory module, minimum value selects module and backtracking module to form.

Accompanying drawing is coordinated to be described below with regard to modules and function thereof below:

As shown in Figure 3, the Hamming distance between the coding that Hamming distance computing module primary responsibility is possible under calculating input data and current encoder state.Under a coder state, there is the coding output that two kinds are possible, so when input data are 2, corresponding 4 Hamming distances.These 4 Hamming distances give ACS module, and each ACS example selects two corresponding distances according to the coder state of process, and these two distances obtain according to the state diagram of encoder.

As shown in Figure 4, ACS module primary responsibility calculates the previous moment accumulation distance of current encoder state and the Hamming distance sum of current this state of arrival, produce new accumulation distance, and two arrival path accumulation distance of each state are compared, select the path of less distance as survivor path, preserve this distance as next moment summation, the reference range compared simultaneously.

Path memory module primary responsibility deposits the survivor path value that ACS module produces, and path backtracking module survivor path value, and the Hamming distance signal of path memory module input is simultaneously to path backtracking module.

Minimum value selects module primary responsibility when decoding time reaches decoding depth, compares, select a minimum paths to all survivor paths.

Path backtracking module primary responsibility, according to the final state of minimal path and survivor path value corresponding to each moment, determines the back tracking point of previous stage, until all backtracking is complete, gives fullpath and survival value for change.First module is selected to obtain final state by minimum value, the highest order of each state is exactly survival value, the state that 6 are exactly previous moment is reformulated for low five with the survivor path value of previous moment, the like can obtain all survival values, survival value sequence is exactly the inverted sequence sequence of coding sequence.As shown in Figure 5, the state in K+1 moment is 000000, and highest order is 0, then the survival value in K+1 moment is 0, low five of the state in K+1 moment be the survivor path value in 00000, K moment is 1, and six of composition is 000001, then the state in K moment is 000001, and highest order is 1, and survival value is 1.

The simulation result of Viterbi decoding as shown in Figure 6, is input as (11,10,00,10,01,10,10,10,10,10,11,10,01,00,11,00,10,10,11,00 ...) decode results is (1,0,1,1,0,1,0,0,1,1,1,1,1,1,1,0,0,1,1,1 ...) consistent with standard results, show the feasibility of this Viterbi decoding.

Claims (1)

1. the decoding unit of a wireless transmitting system, the decoding unit of wireless transmitting system is by Hamming distance computing module, ACS module, path memory module, minimum value selects module and path backtracking module composition, it is characterized in that: the Hamming distance between the coding that Hamming distance computing module is possible under calculating input data and current encoder state, and the Hamming distance signal calculated is delivered to ACS module and path memory module, accumulation distance signal is delivered to minimum value and selects module by ACS module, and compared by it and show that distance path less in distance signal is delivered to path backtracking module as survivor path value, described path backtracking module survivor path value is delivered to path memory module and stores, the Hamming distance signal simultaneously inputted according to survivor path value and path memory module outwards exports and draws decode results,

Interpretation method based on the decoding unit of wireless transmitting system:

Step 1, Received signal strength;

The length of step 2, status switch corresponding to path and receiving sequence calculating path branch;

Step 3, accumulated path branch obtain length and be path;

Step 4, compare that to obtain the shortest path length of any instant be survivor path;

Input symbols corresponding to step 5, survivor path is just decode results;

Source code V _kby encoder X _k, produce code symbols, be designated as Y _k, after noisy channel is propagated, Received signal strength is Z _k.The work that Viterbi decoding unit and interpretation method thereof are done is exactly utilize decoding algorithm, from Z _kjudge V _k, recover information source information;

Receiving Z _kafter, first, the length of the status switch corresponding to path and receiving sequence calculating path branch, the length of path branches is:

$\mathrm{\&lambda;}\left({\mathrm{\&xi;}}_k\right)\stackrel{\mathrm{\&Delta;}}{=}-\ln P\left(X_{k+1}\right|X_k)-\ln P\left(Z_k\right|{\mathrm{\&xi;}}_k)$

Wherein, ξ _krepresent from X _kto X _k+1state transitions;

Definition path be-lnP (X, Z), wherein X for the status switch corresponding to this path, Z is receiving sequence,

$P(X,Z)=P\left(X\right)P\left(Z\right|X)=\underset{k=0}{\overset{K-1}{\&Pi;}}P\left(X_{k+1}\right|X_k)\underset{k=0}{\overset{K-1}{\&Pi;}}P\left(Z_k\right|X_{k+1},X_k)$

Then overall path can be expressed as $-\ln P(X,Z)=\underset{k=0}{\overset{K-1}{\&Sigma;}}\mathrm{\&lambda;}\left({\mathrm{\&xi;}}_k\right).$