Empirical gains achievable with low altitude remote radio heads in wireless urban links

We present empirical results on the achievable gains stemming from the use of wireless remote radio heads (RRH) in a typical urban environment. Our work is based on simultaneous path-loss measurements of the base station and RRH links to outdoor street level users. We statistically characterize the increase in received power, when a RRH is added to improve the coverage achieved by a base station. We consider diverse expected coverage areas for the mobile terminal, evaluating the effect of RRH position with respect to the intended users. We also compare the power gains that would be obtained in practice from combining the signals from the base with those of the RRH, using schemes such as selection combining and maximum ratio combining. 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 maximum ratio combining are only marginally better than those of the much simpler selection combining.