Downlink User Capacity of Massive MIMO Under Pilot Contamination

摘要: Pilot contamination has been regarded as a main limiting factor of time division duplexing (TDD) massive multiple-input-multiple-output (Massive MIMO) systems, it will make the signal-to-interference-plus-noise ratio (SINR) saturated. However, how pilot limit user capacity downlink Massive MIMO, i.e., maximum number users whose SINR targets can be achieved, not addressed. This paper provides an explicit expression MIMO in pilot-contaminated regime where is larger than sequence length. characterizes region within which set requirements jointly satisfied. The size this fundamentally limited by Furthermore, scheme for achieving capacity, uplink training sequences and power allocation, identified. Specifically, generalized Welch bound equality are exploited shown that allocated to each should proportional its target. With capacity-achieving scheme, requirement satisfied energy-efficient transmission achieved large-antenna-size (LAS) regime. comparison with two non-capacity-achieving schemes highlights superiority our proposed terms higher capacity. practical scenario finite antennas, actual antenna required achieve significant percentage asymptotic performance analytically quantified.