14.7 Summary

Traditional wireless technologies are not very well suited to meet the demanding requirements of providing very high throughputs with the ubiquity, mobility, and portability characteristics of cellular systems. Given the scarcity and exorbitant cost of radio spectrum, such throughputs dictate the need for extremely high bandwidth efficiencies, which cannot be achieved with classical schemes in systems that are inherently self-interfering. Consequently, increased processing across the spatial dimension appears as the only means of enabling the types of throughputs that are needed for ubiquitous wireless Internet and exciting multimedia services. Whereas the most natural way of utilizing the space dimension may be to deploy additional base stations in order to allow for more frequent spectral reuse with smaller cells, economical and environmental considerations require that performance be enhanced on a per-base-station basis; that, in turn, calls for the use of multiantenna technology. While the deployment of base station antenna arrays is becoming universal, it is really the simultaneous deployment of base station and terminal arrays that unleashes vast increases in throughput by opening up multiple signaling dimensions.

Throughout the chapter, we have quantified the benefits of using such multiantenna technology, in the context of emerging mobile data systems, as a function of the number of available antennas. Although absolute throughput levels are very sensitive to the specifics of the propagation environment, the improvement factors are not. Hence, it is the relative improvement rather than the absolute numbers themselves that is relevant.