Dynamic Code Allocation for Constructive Interference Exploitation in DS-CDMA Systems

In this paper a new dynamic code distribution technique is presented. This method chooses the optimal code-to-user allocation for transmission between different combinations of the available signature waveforms according to the data to be transmitted at every symbol period by the base station (BS) at the downlink of a cellular code division multiple access (CDMA) system. The selection is done with the aim to minimise the destructive and maximize constructive interference between users. This effectively spreads the signal constellation and enhances the signal to interference-plus-noise ratio (SINR) at the receiver with no additional power-per-user investment. However, the trade-off to this is some extra side information. Theoretical analysis and simulations presented suggest that this method can provide a bit error rate reduction of an order of a magnitude when combined with multiuser detection.