Algorithm for non-orthogonal code shift keying and code index modulation

Abstract

To deal with the problem that the bit error rate(BER) performance degradation of orthogonal code shift keying(CSK) and the insufficiency that the non-orthogonal-code index modulation (N-CIM) cannot make full use of the autocorrelation of spread spectrum codes, an algorithm of the non-orthogonal-CSK-code index modulation (N-CSK-CIM) is proposed. The information bits of the transmitter are divided into modulation bits and spread spectrum code mapping bits; Modulation bits are used for symbol modulation, and mapping bits are mapped into spread spectrum code index and code phase index. Firstly, the symbol is modulated according to the modulation bits. Then, the same original spread spectrum code is selected by using the spread spectrum code index mapped by the mapping bits, and the new spread spectrum code is generated by code shift keying according to the code phase index. The real part and imaginary part of the modulated symbol are spread spectrum with this new spread spectrum code respectively. Simulation results show that the BER performance of N-CSK-CIM algorithm is better than that of N-CIM algorithm and orthogonal CSK algorithm in additive white Gaussian noise (AWGN) channel and Rayleigh fading channel with the same signal to noise ratio.