Location aided wireless communications

The availability of location information of mobile terminals, relays, femto cells and primary units provides opportunities to greatly enhance the operation of wireless communication systems. We provide an overview of some of the possibilities, starting with physical layer considerations for a single link. However, most of the opportunities concern resource allocation aspects. Especially for multi-user systems, for which recent information theory progress has shown that an optimized handling may lead to significant system capacity increase. But the optimization of multi-user systems requires very precise Channel State Information at the Transmitter (CSIT). The problem is compounded when taking furthermore user selection into account. CSIT is typically obtained by feedback (FB), which leads to transmission overhead. Channel reciprocity based TDD systems only represent a limited alternative in multi-cell settings, or for user selection. For single-cell multi-user communications, we argue for a revival of SDMA (Spatial Division Multiple Access). We then consider the multi-cell problem, and cognitive radio. Some (but not all) of the location aided techniques require substantial databases, which have come into vogue in the context of flexible spectrum access. Location aided techniques may furthermore exploit location prediction through mobility trajectory information. This would allow slow fading (and even connectivity) predictibility, something that is difficult to achieve without location information. Of course, proposals for location aided techniques need to be weighted against classical approaches (CSIT learning) in order to assess their definitive value.