Performance Comparison of Cellular Systems with Co-located Base-station (BS) Antennas and Distributed BS Antennas

　

The next-generation cellular networks are expected to provide high data rates to support the massive mobile applications. Toward this end, there has been a growing interest in implementing large antenna arrays at BSs (popularly known as "Massive MIMO"). It is well-known that for a point-to-point MIMO system with M transmit and N receive antennas, the capacity grows linearly with min(M,N) in a rich-scattering environment.With a large number of colocated antennas at both the BS and the user sides, nevertheless, the capacity may be severely reduced due to strong antenna correlation.

If the BS antennas are grouped into geographically distributed clusters and connected to a central processor by fiber or coaxial cable, in contrast, signals from distributed BS antennas to each user are subject to independent and different levels of large-scale fading, thanks to which potential capacity gains over the co-located counterpart can be expected. In the meanwhile, the implementation cost of distributed BS antennas also becomes significantly higher than that of the co-located ones, especially when the number of distributed BS antenna clusters is large. It is, therefore, of great practical importance to compare the rate performance of cellular networks under different BS antenna layouts to see if the increased cost is justified.

Such a comparative framework was proposed in [Dai'11], where substantial uplink sum capacity gains are shown to be achieved by the distributed BS antenna layout thanks to 1) reduced minimum access distance of each user, and 2) enhanced channel fluctuations which provide a significant boost to the sum capacity when the channel state information is available at both the transmitter and receiver sides. For the downlink, the rate performance closely depends on the precoding schemes. It was shown in [Wang-Dai'15] that although a higher average rate can be always achieved by the distributed BS antenna layout, the gains are much more prominent when an orthogonal precoding scheme such as zero-forcing beamforming (ZFBF) is adopted. The analysis was further extended to the cellular networks for uplink [Dai'14] and downlink [Liu-Dai'14].

		Uplink	Downlink
Single-user		[Dai'11]	[Liu-Dai'14]
Multi-user	Single-cell	[Dai'11]	[Wang-Dai'15]
	Multi-cell	[Dai'14]	[Liu-Dai'14]