Single-User Beamforming in Large-Scale MISO Systems with Per-Antenna Constant-Envelope Constraints: The Doughnut Channel

摘要

Large antenna arrays at the base station (BS) has recently been shown toachieve remarkable intra-cell interference suppression at low complexity.However, building large arrays in practice, would require the use ofpower-efficient RF amplifiers, which generally have poor linearitycharacteristics and hence would require the use of input signals with a verysmall peak-to-average power ratio (PAPR). In this paper, we consider thesingle-user Multiple-Input Single-Output (MISO) downlink channel for the casewhere the BS antennas are constrained to transmit signals having constantenvelope (CE). We show that, with per-antenna CE transmission the effectivechannel seen by the receiver is a SISO AWGN channel with its input constrainedto lie in a doughnut-shaped region. For single-path direct-line-of-sight (DLOS)and general i.i.d. fading channels, analysis of the effective doughnut channelshows that under a per-antenna CE input constraint, i) compared to anaverage-only total transmit power constrained MISO channel, the extra totaltransmit power required to achieve a desired information rate is small andbounded, ii) with N base station antennas an O(N) array power gain isachievable, and iii) for a desired information rate, using power-efficientamplifiers with CE inputs would require significantly less total transmit powerwhen compared to using highly linear (power-inefficient) amplifiers with highPAPR inputs.