Combined CDMA-SDMA Performance Analysis and Code Assignment Algorithm

This paper present a novel performance enhancement for combined code division multiple access (CDMA) and space division multiple access (SDMA) scheme using SDMA grouping on top of code and spatial signatures. This paper is divided into two parts. In the first part, the system performance of combined CDMA-SDMA scheme is evaluated under Additive White Gaussian Noise (AWGN) channel for a single sectored cell. A fixed number of available codes L kept in a central pool can be utilized by K users, where, K>L. The same code can be assigned to a group of users according to their angle of arrival (which is known as SDMA group). Here, the analytical model of bit error rate (BER) for any arbitrary number of users has been derived and evaluated. In the second part of this paper, a simple code assignment algorithm is proposed to assign a already used code to a new user by which, the orthogonality between users can be maximized. The results show that the system capacity is noticeably improved with the combined system compared to the pure CDMA system. Further enhancement can be obtained when SDMA grouping is considered with orthogonal code assignment to users those belongs to different SDMA groups. Finally, the code assignment algorithm shows that high number of users can be accommodated by a fixed small number of codes.