Empirical Evaluation of the Received Power Gain when Remote Radio Heads are Used to Enhance the Coverage Area in Urban Environments

We present empirical results on the achievable cellular system throughput gains stemming from the use of remote radio heads (RRH) in an urban environment. Our work is based on simultaneous path-loss measurements of the base station (BS) and RRH links to outdoor street-level users. We calculated the increase in received power, when a RRH is added to improve the coverage achieved by a BS. We consider diverse settings for the RRH and diverse expected coverage areas for the mobile station (MS), evaluating the effect of RRH height and position with respect to the intended users. We also compare the power gains that would be obtained in practice from combining schemes such as selection combining (SC) and maximum ratio combining (MRC). We conclude that under practical conditions, the benefits of using RRHs will depend very strongly on the existence of line-of-sight links between the RRH and the intended users. For RRHs placed at low heights, below the clutter, only users in a "street-canyon" position with respect to the RRH will obtain a significant benefit. Our data also shows that the gains in signal-to-noise ratio achieved when using MRC are only marginally better than those of the much simpler SC.