Comparative study of joint-detection techniques for TD-CDMA based mobile radio systems

Third-generation mobile radio systems use time division-code division multi ple access (TD-CDMA) in their time division duplex (TDD) mode. Due to the t ime division multiple access (TDMA) component of TD-CDMA, joint (or multi-u ser) detection techniques can be implemented with a reasonable complexity. Therefore, joint detection will already be implemented in the first phase o f the system deployment to eliminate the intracell interference. In a TD-CD MA mobile radio system, joint-detection is performed by solving a least squ ares problem, where the system matrix has a block-Sylvester structure. In t his paper, we present and compare several techniques that reduce the comput ational complexity of the joint detection task even further by exploiting t his block-Sylvester structure and by incorporating different approximations . These techniques are based on the Cholesky factorization, the Levinson al gorithm, the Schur algorithm, and on Fourier techniques, respectively. The focus of this paper Is on Fourier techniques since they have the smallest c omputational complexity and achieve the same performance as the joint detec tion algorithm that does not use any approximations. Similar to the well-kn own implementation of fast convolutions, the resulting Fourier-based joint detection scheme also uses a sequence of fast Fourier transforms (FFTs) and overlapping. It is well suited for the implementation on parallel hardware architectures.