Code-Hopping Multiple Access Based on Orthogonal Complementary Codes

Code-hopping multiple access (CHMA) is a newly emerging multiple-access technique with the potential to offer high capacity. Unfortunately, orthogonality among user signals in existing CHMA schemes can be preserved only in synchronous channels under an assumption that neither multipath interference (MI) nor multiple-access interference (MAI) exists. Exploiting their ideal orthogonality, we apply orthogonal complementary codes to CHMA systems to overcome problems with existing CHMA schemes. In particular, we will show that the application of orthogonal complementary codes can significantly improve the performance of a CHMA system due to its unique collision-resistant capability. To deal with destructive collisions among spreading codes in CHMA systems, convolutional coding is employed in complementary-coded CHMA systems. The properties and bit error rate (BER) performance of the proposed system are analyzed for both uplink and downlink applications, where the system may simultaneously suffer MI and MAI. Simulation results show that the complementary-coded CHMA with channel coding can provide much higher capacity than complementary-coded code-division multiple access (CDMA) systems in varying operational scenarios.