Spatial-Multiplexed Soft Handoff

We present a new soft handoff scheme in forward link code division multiple access cellular systems, wherein each base station participating in soft handoff sends only a subset of the main data stream (called sub-stream) and the mobile receiver reassembles the sub-streams and restores the main data stream. This approach can reduce the data transmission rate per base station by a factor of the number of participating base stations at the cost of sacrificing the spatial (macro) diversity that is available in conventional soft handoff system. The key to the proposed technique is to increase the signal distance or the processing gain rather than to obtain additional diversity from multiple base stations on top of multi-path diversity that provides diminishing gain. Power gain and the resulting coverage extension over conventional soft handoff system is analyzed as a function of the number of participating base stations and relative signal strengths from different base stations.