Signal enhancement in a near-field MIMO environment through adaptivity on transmit

Many methods have been developed and are continuing to evolve in recent years, to enhance reception of signals in a multi-input multi-output (MIMO) environment [1,2]. For mobile communication, the development of a methodology that mitigates the deleterious effects of multipath fading, near-field scatterers (buildings, trees, platforms), etc. is necessary for improved reception. To achieve such enhancements, the authors believe that transmit/receive configurations with spatial diversity are required as shown in Figure 1. Unfortunately, the small footprint of a mobile receiver precludes spatial diversity. In contrast, spatial diversity on transmit is obtainable at a base station, if that station has multiple antennas and the signals being fed to each one of the transmitting antennas corresponding to a particular receiver are weighted. So this paper addresses the of what can be done in terms of adaptivity on transmit so as to enhance the field strength of the signal at a pre-specified receiver while simultaneously minimizing the reception signal strength at the remaining receivers. In this way, the transmitted signals would be received essentially at the designated receiver while it would be canceled at the other locations. By providing spatial diversity on transmit it is possible to mitigate the effects of multipath fading, as the directed energy from the transmitted antennas, would combine vectorially at the selected receiving antenna element either to produce a maximum or a minimum.