Separate FEC coding for parallel combinatorial spread spectrum communication systems

Abstract

We propose a forward error correction (FEC) coding scheme for partial-code-parallel multicode direct sequence spread spectrum (DS/SS) systems referred to as parallel combinatorial spread spectrum (PC/SS) systems. Information data are conveyed in two ways: the combination of orthogonal codes and the polarity or phase of their transmitting orthogonal code. It is known that FEC coding is an essential factor in the SS systems, especially in the CDMA environment. Straightforward FEC coding shows significant performance improvements. However, it could reduce the data transmission rate of PC/SS systems. From the viewpoint of error rate performance in the PC/SS systems, estimation of a combination of orthogonal codes dominates the total symbol and bit error rate performance. In this paper, FEC coding is separately applied to the combination data of orthogonal codes and the phase data of their transmitting orthogonal code, and less redundant FEC code is used. Therefore, the total information rate exceeds that offered by the conventional FEC coding. Simulation results show that the error rate performance of the PC/SS systems equipped with the separate FEC coding is lower than it is when conventional FEC coding is applied to the PC/SS system, in spite of having higher overall coding rate.