Practical Physical Layer Design of Large-Scale Antenna System Backhaul for Small Cells
05 June 2013
Small cell wireless networks can provide many advantages over traditional macro cell wireless networks, such as better spectral efficiency and energy efficiency, and higher and more even throughput within the coverage area. A successful small cell network deployment strategy, however, must include cost effective backhaul provisioning. Compared to optical fiber backhauls, wireless backhauls are usually less expensive and can potentially provide more flexibility on where a small cell can be installed. We investigate the possibility of using a Large-Scale Antenna System (LSAS) as the wireless backhaul for small cell wireless networks. A successful deployment of an LSAS backhaul system can provide several key advantages such as easy scalability, no line-of-sight requirement, simple low-power single-antenna backhaul terminals for small cells, and operation in unlicensed spectrum with no backward compatibility and standards compliance issues. We propose a general approach to the physical layer design of LSAS backhaul systems in which we dimension the required number of LSAS service antennas, and set the forward and reverse link power requirements for achieving the stipulated backhaul forward/reverse link throughputs. Our approach incorporates forward and reverse link power control so that throughputs among served small cells are equalized. We analyze the performance of two types of spatial multiplexing: conjugate beamforming and zero-forcing on the forward link, and matched filtering and zero-forcing on the reverse link. We find that, within the 650 MHz white space, either 64 or 128 service antennas can provide a sustained 30 Mbps forward link and 10 Mbps reverse link backhaul capacity per small cell for 95% of small cells with the very modest radiated power that is permitted. Conjugate beamforming/matched-filtering is very competitive with respect to zero-forcing, and is in fact preferable because it permits a decentralized array architecture.
