Direct sequence spread spectrum method for continuous phase modulation

Abstract

The invention provides a direct sequence spread spectrum and despread demodulation method which is mainly applied to the continuous phase modulation in the field of wireless spread spectrum communication. The method comprises the steps of: at a transmitting end, firstly designing a group of spread spectrum sequence, mapping transmitting bits 0 and 1 into two groups of constant envelope baseband complex signals wit continuous changing phases and identical head and end phases, and during modulation, selecting one of the two baseband complex signals to serve as a modulation signal according to transmission information for transmission; at a signal receiving end, accumulating signals corresponding to all chips to the baseband complex signal corresponding to anyone chip in the sequence according to a spread spectrum rule of the spread spectrum sequence to complete the despread treatment of a spread spectrum signal; and comparing phase change directions at the initial position and the end position of the despread complex signal, and judging the transmission information carried by the spread spectrum sequence according to the increase and decrease of the phase change directions, thereby realizing signal demodulation. According to the invention, the continuous phase characteristic and the constant envelope characteristic of the signal are maintained in the direct sequence spread spectrum, and the estimation of carriers and initial phases under low signal to noise ratio are avoided by adopting incoherent despread and demodulation.

Description

technical field [0001] The invention relates to a direct sequence spread spectrum and despread demodulation method of continuous phase modulation, which is mainly used in the field of wireless spread spectrum communication. Background technique [0002] In recent years, direct sequence spread spectrum communication has attracted widespread attention. In many applications, it is hoped that the power spectral density of the spread spectrum signal is good, such as fast high-frequency roll-off, low out-of-band radiation characteristics, and the system is less affected by nonlinearity, so the direct sequence spread spectrum technology with constant envelope is not only used in communication , Navigation and measurement systems have been increasingly widely valued and applied, and they have also developed rapidly in civil mobile communications and positioning systems. Spread spectrum systems need to expand the spectrum of the transmitted signal many times before radiating it out....

AI Technical Summary

Problems solved by technology

Since BPSK modulation is used in direct sequence spread spectrum communication systems, both the modulation technology at the transmitting end and the despreading technology at the receiving end are quite mature, so traditional direct sequence spread spectrum communication systems mostly use BPSK modulation or QPSK modulation. The disadvantage is that the spectrum utilization rate is low, the signal amplitude fluctuates greatly, and a broadband linear power amplifier is required, and it is difficult for the transmitter to achieve high-power effective radiation

Because in the direct sequence spread spectrum communication system, the spread spectrum signal in the receiving section generally works under the condition of negative signal-to-noise ratio, the carrier recovery and phase estimation under negative signal-to-noise ratio, especially the Doppler frequency and initial phase are difficult to be accurate It is estimated that more pilot signals need to be sent and more complex processing methods are used, which increases the amount of system computation and reduces communication efficiency

Images