Achievable Rates and Training Overheads for a Measured LOS Massive MIMO Channel

This letter presents achievable uplink sum-rate predictions for a measured line-of-sight (LOS) massive multiple-input multiple-output (MMIMO) scenario and illustrates the tradeoff between spatial multiplexing performance and channel de-coherence rate for an increasing number of base station (BS) antennas. In addition, an orthogonal frequency division multiplexing (OFDM) case study is formed which considers the 90% coherence time to evaluate the impact of MMIMO channel training overheads in high-speed LOS scenarios. It is shown that while 25% of the achievable zero-forcing sum-rate is lost when the resounding interval is increased by a factor of 4, the OFDM training overheads for a 100-antenna MMIMO BS using a long-term evolution-like physical layer could be as low as 2% for a terminal speed of 90 m/s.