Cyclically Orthogonal Sequences And Their Applications In Cellular Communication Systems

A class of sequences with cyclic orthogonality (CO) is proposed to overcome themultiple access interference (MAI) in the cellular communication systems. This thesispresents two simple construction approaches to the cyclically orthogonal sequences anddescribes the application of the CO sequences to TDMA systems, CDMA systems andmulti-carrier CDMA systems, respectively. Finally, the simulation results are given.In TDMA systems, a randomization operation can be implemented at thetransmitter via a convolution with a CO sequence, while a de-randomization at thereceiver, leading to a randomized TDMA transmission scheme called R-TDMA. InR-TDMA, we can achieve elimination of intra-cell interference and the mitigation ofinter-cell interference simultaneously in multi-path channels. Simulation results showthat in high SNR region, R-TDMA will be much better to TDMA due to the mitigationof cross-cell interference in R-TDMA.Based on the CO sequences, a class of binary zero correlation zone (ZCZ) codescan be constructed easily with a flexible length of ZCZ. Such ZCZ codes can provide ahigher user capacity than conventional binary ZCZ codes. We proceed to consider theapplication of the new ZCZ codes to quasi-synchronous CDMA systems as spreadingcodes, as long as the synchronization error were controlled within the length of ZCZ,MAI-free transmission can be realized.As the constructed ZCZ sequence set is orthogonal, the ZCZ codes can be resistantto multi-path interference by adding cyclic prefix. It can also be employed tomulti-carrier CDMA systems with offsets in frequency to achieve orthogonaltransmission. Different receiver combing strategies such as MRC, EGC, ORC andMMSEC are analyzed and discussed.