  A study of channel hardening in a large-scale antenna system has been carried
out by means of indoor channel measurements over four frequency bands, namely
1.472 GHz, 2.6 GHz, 3.82 GHz and 4.16 GHz. NTNU's Reconfigurable Radio Network
Platform has been used to record the channel estimates for 40 single user
non-line of sight radio links to a 64 element wide-band antenna array. By
examining the rms delay spread and the ratio of the normalized subcarrier to
average SISO link power of the radio channel received by a single user after
combination, the hardening of this equivalent channel is analyzed for various
numbers of nodes. The channel hardening merits show consistent behaviour
throughout the frequency bands. By combining 16 antennas the rms delay spread
of the equivalent channel is reduced from above 100 ns to below 35 ns with
significantly reduced variation in the channel power.
