CN101267214A - De-spreading technology of approximation to shannon limit of code-variable spreading spectrum communication system based on BP decoding - Google Patents

Abstract

The present invention discloses a variable bit spectrum spreading method and a corresponding novel dispreading method based on BP iteration interpretation method. An expanding signal module is composed of s linear feedback shift registers and a nonlinear composite function generator. The information bit passes through s linear feedback shift registers and one nonlinear composite function generator. An output sequence with high linear complexity is outputted. Different information bits will obtain different result output sequence. The random unpredictable property of the information sequence leads to that the result output sequence is provided with unpredictable property, and therefore the new system has higher security and privacy. The dispreading module is expressed through a bidirectional chart of a given nonlinear combination sequence. The bidirectional chart is optimized and the information data is decoded with a BP iteration method. The new system has better capability as the new system takes the interrelation between the information bits into consideration.

Description

Based on the change sign indicating number spread spectrum communication system of BP decoding decoding technology near the shannon limit

Technical field

The invention belongs to electronic technology field, as radio communication, mobile communication, radar, electronic countermeasures etc., the mobile radio system that particularly adopts the sequence spread spectrum technology to communicate.

Background technology

Modern Communication System requirement communication distance is far away, message capacity is big, transmission quality good.That spread spectrum technic has is secret, information hiding and advantage such as anti-interference, thereby has broad application prospects.Along with developing rapidly of spread spectrum, make it in communication, transfer of data, information privacy, the location, aspects such as range finding and multiple access technology demonstrate extremely strong vitality, and have obtained extensive use.Traditional spread spectrum communication system adopts pseudo random sequence (PN sign indicating number) as spreading code, and sequence in the communication process in case produce just immobilizes, and is replicated easily, scouts, synchronously, thereby bring potential safety hazard for the confidentiality of Content of Communication.

Own coding spread spectrum (self_encoded spread spectrum, SESS) communication system does not need traditional pseudo random sequence, but the information sequence self of employing completely random is as frequency expansion sequence, and the frequency expansion sequence that transmits each symbol is all inequality, also can't predict in advance to obtain, so just can effectively solve fixed code directly expand in the stationarity of frequency expansion sequence.Compare with the directly-enlarging system of conventional fixed sign indicating number type, the self-interference characteristic of own coding spread spectrum system makes its performance severe exacerbation under low signal-to-noise ratio.The present invention proposes to use the driving of information sequence as frequency expansion sequence, different information sequences produces different frequency expansion sequences, the present invention simultaneously also proposes corresponding new despreading scheme based on the BP interative encode method, obtain thus than the more superior performance of traditional straight expansion, make new method have and become the characteristics that the sign indicating number spread spectrum improves communication security that the advantage of communication performance good under the low signal-to-noise ratio condition is arranged again.

Summary of the invention

The purpose of this invention is to provide and a kind ofly become yard spectrum spreading method and new despreading method based on the BP interative encode method is provided accordingly, the change sign indicating number spread-spectrum signal of forming according to the inventive method sends and receiver has low system complexity, higher communication security, good characteristics such as error rate of system performance.

A kind of change sign indicating number spread spectrum communication principle as shown in Figure 1.Fig. 2 is for becoming sign indicating number information spread spectrum principles, the spread signal module is made up of s linear feedback shift register and a nonlinear combination Function generator, information bit then by a nonlinear combination function, is exported the output sequence of high linear complexity through s linear feedback shift register.

A kind of despreading method that becomes yard spread spectrum communications signals provided by the invention as shown in Figure 3.Despreading method provided by the invention comprises following step:

Step 1 provides the two-dimensional plot of nonlinear combined sequences and expresses;

Step 2 is carried out two-dimensional plot optimization: the ring 4 in the cancellation two-dimensional plot of 1. trying one's best; 2. cancellation too the rule structure, shown in Figure 4 is that generator polynomial is f (x)=1+x+x ¹⁵The graph expression of linear feedback shift register, adopt and between each check-node, insert 1 to 2 point brokenly and change this too graph structure of rule, as shown in Figure 5.

Step 3 repeatedly exchanges by the information of information bit and check bit on two-dimensional plot, as shown in Figure 6, carries out the despreading of BP iteration, obtains information vector estimated value u '.Following formula is definite again in the t+1 time information exchange of information bit and check bit among Fig. 6:

$R_{i,j}^0(t+1)=\frac{1}{2}(1+\underset{j^{\′}\∈N\left(i\right)\backslash j}{\mathrm{\Π}}(1-2Q_{j^{\′},i}^1\left(t\right))),t=0,1,...---\left(1\right)$

$R_{i,j}^1(t+1)=1-R_{i,j}^0(t+1)$

The t+1 time information exchange of check bit and information bit following formula again determined:

$Q_{j,i}^0(t+1)=k_{j,i}(1-P_j)\underset{k\∈M\left(j\right)\backslash i}{\mathrm{\Π}}{R}_{i,j}^0(t+1)---\left(2\right)$

$Q_{j,i}^1(t+1)=k_{j,i}{P}_j\underset{k\∈M\left(j\right)\backslash i}{\mathrm{\Π}}{R}_{i,j}^1(t+1)$

K wherein _{J, i}Be for guaranteeing $Q_{j,i}^0(t+1)+Q_{j,i}^1(t+1)=1,$ P _jBe that j bit is 1 probability in the code word that obtains by channel characteristics.

The change sign indicating number spread-spectrum signal transmission of forming according to the inventive method and receiver send with existing other Direct Sequence Spread Spectrum Signal and compare with receiver system, and following advantage is arranged:

Because information is at random, different information sequences produces different extended bit sequences, under the prerequisite of unpredictable information sequence in advance, the extended bit sequence also is unpredictable, compare with traditional Direct Sequence Spread Spectrum Signal system, what we obtained is to become the sign indicating number spread-spectrum signal to have higher fail safe;

Because traditional Direct Sequence Spread Spectrum Signal system expands each information bit respectively, do not consider the relation between the information bit, and our new system is when expansion and despreading information bit, all considered the correlation between the information bit, use the BP iterative manner to find the solution information bit simultaneously, there is more performance in therefore new system.

Accompanying drawing and description of drawings

Fig. 1 is the system model that becomes sign indicating number spread spectrum communication principle

Wherein, the 1st, information data expansion module, the 2nd, the local carrier module of transmitter, the 3rd, the modulation module of transmitter, the 4th, radio frequency processing module, the 5th, information data despreading module, the 6th, demodulation module.

Fig. 2 becomes sign indicating number information data Extended Principle Diagram

Wherein, dotted line module 1 is the information data expansion module, total s linear feedback shift register, and s desirable 1,2,3 ..., f is a nonlinear combination function, u needs the information transmitted data, and z is the data bit after the expansion, and b is the sequence of z modulation back in Channel Transmission.

Fig. 3 is the despreading method model that becomes the sign indicating number spread spectrum communications signals

Wherein, dotted line module 5 is information data despreading modules, and b ' is the bit sequence that receives from channel, and z ' is the receiving sequence after b ' demodulation, and u ' is the estimated value of information data u.

Fig. 4 is that generator polynomial is f (x)=1+x+x ¹⁵The two-dimensional plot model of linear feedback shift register

Fig. 5 is to the two-dimensional plot shown in the diagram, inserts 1 to 2 point brokenly and change this too schematic diagram of the graph structure of rule between each check-node

Fig. 6 is that the information by information bit and check bit repeatedly exchanges on two-dimensional plot, realizes the schematic diagram of despreading.

Wherein, Q _{J, i} ^a(t+1) be the information that information node is passed to check-node, a is taken as 0 and 1 respectively in binary system, Q _{J, i} ^a(t+1) calculate by formula (2); R _{I, j} ^a(t+1) be the information that check-node is passed to information node, same, a is taken as 0 and 1 respectively in binary system, R _{I, j} ^a(t+1) calculate by formula (1).

Claims (4)

1. one kind becomes sign indicating number information spectrum spreading method, the spread signal module is made up of s linear feedback shift register and a nonlinear combination Function generator, information bit then by a nonlinear combination function, is exported the output sequence of high linear complexity through s linear feedback shift register.After it is characterized in that adopting change sign indicating number spread spectrum, different information bits obtains different spread signals.

2. a kind of change sign indicating number information spectrum spreading method according to claim 1 provides a kind of despreading method that becomes yard spread spectrum communications signals of this method, comprises following step:

Step 1 provides the two-dimensional plot of nonlinear combined sequences described in the claim 1 and expresses;

Step 2 is carried out two-dimensional plot optimization: the ring 4 in the cancellation two-dimensional plot of 1. trying one's best; 2. the cancellation structure of rule too adopts and to insert 1 to 2 point brokenly change this too graph structure of rule between each check-node.

Step 3 repeatedly exchanges by the information of information bit and check bit on two-dimensional plot, carries out the despreading of BP iteration, obtains information vector estimated value u '.

3. a kind of despreading method that becomes yard spread spectrum communications signals according to claim 2 is characterized in that utilizing the two-dimensional plot of nonlinear combined sequences.

4. a kind of despreading method that becomes yard spread spectrum communications signals according to claim 2, it is characterized in that adopting the information of information bit and check bit repeatedly to exchange, carry out the despreading of BP iteration, the t+1 time information exchange of middle information bit and check bit following formula again determined:

$R_{i,j}^0(t+1)=\frac{1}{2}(1+\underset{j^{\′}\∈N\left(i\right)\backslash j}{\mathrm{\Π}}(1-2Q_{j^{\′},i}^1\left(t\right))),t=\mathrm{0,1},\·\·\·$

$R_{i,j}^1(t+1)=1-R_{i,j}^0(t+1)$

The t+1 time information exchange of check bit and information bit following formula again determined:

$Q_{j,i}^0(t+1)=k_{j,i}(t-P_j)\underset{k\∈M\left(j\right)\backslash i}{\mathrm{\Π}}{R}_{i,j}^0(t+1)$

$Q_{j,i}^1(t+1)=k_{j,i}{P}_j\underset{k\∈M\left(j\right)\backslash i}{\mathrm{\Π}}{R}_{i,j}^1(t+1)$

K wherein _{J, i}Be for guaranteeing $Q_{j,i}^0(t+1)+Q_{j,i}^1(t+1)=1,$ P _jBe that j bit is 1 probability in the code word that obtains by channel characteristics.

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