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Optimal transmission scheme for the distributed antenna in CDMA systems

Tong, F. and Glover, I.A. and Pennock, S. and Shepherd, P. (2004) Optimal transmission scheme for the distributed antenna in CDMA systems. In: 5th IEE Internatinal Conference on 3G Mobile Communication Technologies, 2004-10-08 - 2004-10-20.

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Abstract

Distributed antenna diversity employs separately installed, but cooperating, antennas within a single base-station; it has been proved that the uplink capacity (per cell) in terms of maximum achievable SIR (signal-to-interference ratio) is linear with the number of deployed antenna units. While in the downlink, because of the multiple-to-one propagation topology, equal power (transmission power at each antenna) allocation (providing equal SIR) in the base-station results in fixed SIR at the mobile terminal, irrespective of the number of base-station antennas used. A transmission scheme, using optimal power allocation and SIR-balanced power control, is proposed to increase the SIR by exploiting multiple base-station antennas. The downlink diversity (called antenna-multipath diversity) transfers the antenna diversity to multipath diversity by utilizing the spread-spectrum signal property. If optimal, rather than equal, power allocation is employed with antenna-multipath diversity, the SDMA advantage can be exploited. The optimisation result shows that, for a particular user, transmitting a signal from one antenna, instead of all base-station antennas, gives better SIR performance. The SIR CDF has been examined by simulation to verify this scheme. Compared to sending from all antennas, the result shows, that for 8 users, this scheme yields improved SIR by 3 dB with 5 antennas. The SIR advantage increases with increasing numbers of antennas and decreases, however, with increasing numbers of users in the cell.