Generalized Code Index Modulation Technique for High-Data-Rate Communication Systems

In this paper, we propose a generalized code index modulation (CIM) technique for direct-sequence spread spectrum (DSSS) communication. In particular, at the transmitter, the bit stream is divided into blocks in which each block is divided into two subblocks: mapped and modulated subblocks. Thereafter, the bits within the mapped subblock are used to select one of the predefined spreading codes, which is then used to spread the modulated bits of the second subblock. In this design, using the spreading code index as an information-bearing unit increases the overall spectral efficiency of this system. At the receiver side, the spreading code index is first estimated, thus resulting in a direct estimation of mapped subblock bits. Consequently, the corresponding spreading code to this estimated index is used to despread the modulated symbol of the modulated subblock. Subsequently, mathematical expressions for bit error rate (BER), symbol error rate (SER), throughput, energy efficiency, and the system complexity are derived to analyze the system performance. Finally, simulation results show that the proposed modulation scheme can achieve a higher data rate than the conventional DSSS system, with lower energy consumption and complexity.