Coordinated pre-coding for the forward-link in DS-CDMA

In the forward-link in a system employing DS-CDMA, it is possible to some extent monitor how the users are interfering with one another since all spreading sequences are known. Two algorithms making use of this knowledge and computing the amplitude for the transmitted signal in each chip interval, in order to decrease the average error probability, are given. Numerical results show that the maximum number of users simultaneously accessing the channel for a given error probability can be increased by employing any of these algorithms. In particular, the results for the more complex one are seen to be good also when the number of users exceeds the number of spreading chips per coded symbol, implying that more users can be supported using this algorithm than would be the case if the users were using orthogonal spreading sequences, even if the voice activity is not accounted for. Also, both algorithms are shown to be robust in the sense that they work properly for such different channel conditions as the AWGN channel and the flat Rayleigh fading channel