Benefits of variation of large scale fading across large antenna arrays

Massive Multiple-Input Multiple-Output (MIMO) antenna arrays are being studied for 5G due to their ability to focus energy towards desired receiver, reducing interference to other users, giving rise to higher spectral and energy efficiencies. Conventional analysis assumes that the large scale fading component of the channel model is constant across the entire Massive MIMO antenna array. However, when the number of Massive MIMO antennas is divided among remote antenna sites, each site experiences independent small and large scale fading. Massive MIMO channel measurements show that large scale fading is not constant but varies across a large antenna array. In this paper, a closed-form expression for the downlink received signal-to-interference ratio (SIR) is derived to evaluate cell spectral efficiency, assuming that large scale fading varies across a large antenna array. Higher cell spectral efficiency results for a downlink multi-user MIMO system is obtained for the new channel model compared with the conventional channel model.