Direct sequence spread spectrum signal spread spectrum code estimation method based on MLDC and bit-by-bit judgment

Abstract

The invention discloses a direct sequence spread spectrum signal spread spectrum code estimation method based on MLDC and bit-by-bit judgment. The problem that in the prior art, the calculation complexity and the estimation performance under the low signal-to-noise ratio condition cannot be considered at the same time is solved. The method comprises the steps of establishing a direct spread signalmathematical model, performing bit-by-bit judgment on a randomly generated to-be-judged sequence by utilizing an inner product sum function constructed based on MLDC, and then repeatedly performing bit-by-bit judgment to obtain a final spread spectrum code estimation sequence. The inner product sum function directly represents the likelihood degree of the to-be-judged sequence and the spreading code, the to-be-judged sequence is divided into a front part and a rear part by adopting a bit-by-bit judgment method to be judged respectively, and estimation of the spreading code is obtained throughsplicing. According to the method, estimation of the direct spread signal spread spectrum code in non-cooperative spread spectrum communication is completed, the estimation performance under the condition of a low signal-to-noise ratio is good, and the calculation complexity is low. The method can be directly applied to a non-cooperative spread spectrum communication system, and can also be applied to corresponding software radio and other systems.

Description

technical field [0001] The invention belongs to the technical field of signal processing, mainly relates to non-cooperative communication signal processing technology, specifically a method for estimating spreading codes of direct spread signals based on maximum likelihood decoding criterion (MLDC) and bit-by-bit judgment, mainly used for direct spread Extraction estimation of signal spreading code. Background technique [0002] Direct Sequence Spread Spectrum (DSSS) signals have low transmit power spectral density, strong anti-intercept and strong anti-interference characteristics, and can suppress multipath effects, so they are widely used in contemporary civil communications, military countermeasures, detection and navigation, GPS positioning, etc. in a field. The reconnaissance and deciphering of direct spread signals is one of the hotspots and difficulties in the field of communication countermeasures, especially in non-cooperative communications, if the correct spread...

AI Technical Summary

Problems solved by technology

[0006] (1) Establish the mathematical model of the baseband direct spread signal in segmented form: for the short code direct spread signal intercepted in the non-cooperative spread spectrum communication, in the chip width T c , information code cycle T d , spreading code length L, spreading period T s and asynchronous time τ parameter information have been determined, and the noise interference is equivalent to additive white Gaussian noise, the DS signal is calculated according to 1 / T c The frequency is sampled to obtain a discrete form of baseband synchronous short code direct spread signal In the formula, n represents the nth symbol of the baseband synchronous short code direct spread signal in discrete form, A represents the signal amplitude, d represents an independent and equal probability bipolar information code, k represents the kth information symbol, and N represents the information The number of symbols, c represents the spreading code, v represents the additive Gaussian white noise, and r(n) is segmented according to the window length of the spreading code length, and there are N segmented windows to obtain the segmented baseband Direct spread signal r=[r (1) ,r (2) ,...,r (N) ], set up the mathematical model of the baseband direct spread signal in segmented form;

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