The REAL Approach to Generate Orthogonal Complementary Codes for Next Generation CDMA Systems

Abstract

This paper introduces a new approach to generate the orthogonal complementary (OC) codes suitable for new generation CDMA applications, characterized by isotropic multiple access interference (MAI) free and multipath interference (MI) free properties. The code design methodology proposed in this paper is named as “Real Environment Adaptation Linearization” (REAL) approach and it takes into account major impairing factors existing in real applications, such as MAI, MI, asynchronous transmissions and random signs in consecutive symbols. A CDMA system using the generated codes can ensure a truly interference-free operation. Two important facts will be revealed by the analysis given in this paper. First, implementation of an interference-free CDMA will never be possible unless using complementary code sets, such as the OC code sets. In other words, all traditional spreading codes working on an one-code-per-user basis are not useful for implementation of an MAI-free and MI-free CDMA system. Second, to enable the interference-free CDMA operation, the flock size of the OC codes should be made equal to the set size of the codes, implying that a OC code set can support as many users as the flock size of the code set. A systematic search has been carried out to generate the super-set of various OC codes with the help of carefully selected seed codes belonging to distinct sub-sets. This paper will also propose an implementation scheme based on multi-carrier CDMA architecture and its performance is compared by simulations with the ones using traditional spreading codes.