Random access in millimeter-wave beamforming cellular networks: issues and approaches

With the formidable growth of various booming wireless communication services that require ever increasing data throughputs, the conventional microwave band below 10 GHz, which is currently used by almost all mobile communication systems, is going to reach its saturation point within just a few years. Therefore, the attention of radio system designers has been pushed toward ever higher segments of the frequency spectrum in a quest for increased capacity. In this article we investigate the feasibility, advantages, and challenges of future wireless communications over the Eband frequencies. We start with a brief review of the history of the E-band spectrum and its light licensing policy as well as benefits/challenges. Then we introduce the propagation characteristics of E-band signals, based on which some potential fixed and mobile applications at the E-band are investigated. In particular, we analyze the achievability of a nontrivial multiplexing gain in fixed point-to-point E-band links, and propose an E-band mobile broadband (EMB) system as a candidate for the next generation mobile communication networks. The channelization and frame structure of the EMB system are discussed in detail.

Introduction

In recent years, mobile data traffic has been dramatically increased and is expected to continue its growth. To cope with the growing demand on mobile traffic, a radio access technology needs to be enhanced by improving spectral efficiency, increasing frequency bandwidth, or increasing cell density. However, the spectral efficiency of point-to-point communication is close to theoretical limit. Cell densification has difficulty handling a large amount of intercell interference since cells may be deployed in an unplanned manner, and the signaling for interference management is limited by non-ideal backhaul links of networks. Taking the aforementioned challenges into account, a straightforward way to deal with the traffic demand is to increase bandwidth for communications. In this sense, the millimeter- wave (mmWave) band is recently being considered as one of promising bands for cellular networks [1] since abundant contiguous frequency resources are available, while the frequency bands under 5 GHz are very fragmented and crowded.