Binary-code-allocation scheme in DS-CDMA systems

In this paper, we consider a simple binary-transmitter adaptation in direct-sequence code-division multiple-access systems. We propose a binary-code-allocation scheme for reducing the multiple-access interference (MAI). In this scheme, a user is given an orthogonal binary sequence set. By choosing a better sequence from the sequence set, the user can maximize his/her signal to interference ratio. We examine the scheme analytically by both exact analysis and approximation in equal-power synchronous cases. Theoretically, it is found that the scheme can significantly reduce the MAI. It only involves a few bits of feedback information for the transmitter to adjust the sequences. The scheme can also be modified for multiuser adaptation in asynchronous channels. In a multiuser adaptation, simulations show that the users would have a significantly improved performance against the MAI, and the system throughput can also be increased. It is shown that this binary-code-allocation scheme is a simple, widely applicable, and robust binary-sequence-adaptation scheme.