Coherence Time of Wireless Channels with Large Antenna Arrays

In this work, energy coherence time, which is defined to be the coherence time of the channel quality information (CQI), is studied as a function of the number of antennas in a receiver with a large antenna array. It is found that, as a function of the number of receiver antennas, the energy coherence time can be much larger than the inverse of the Doppler frequency associated with the propagation environment. Numerical studies with representative values for cellular systems indicate that the net reduction in the frequency of adapting to changes in channel quality can be orders of magnitude higher with practical large antenna arrays.