Per-Antenna Constant Envelope Precoding for Large Multi-User MIMO Systems

Abstract

Abstract-We consider the multi-user MIMO broadcast channel with M single-antenna users and N transmit antennas under the constraint that each antenna emits signals having constant envelope (CE). The motivation for this is that CE signals facilitate the use of power-efficient RF power amplifiers. Analytical and numerical results show that, under certain mild conditions on the channel gains, for a fixed M , an array gain is achievable even under the stringent per-antenna CE constraint. Essentially, for a fixed M , at sufficiently large N the total transmitted power can be reduced with increasing N while maintaining a fixed information rate to each user. Simulations for the i.i.d. Rayleigh fading channel show that the total transmit power can be reduced linearly with increasing N (i.e., an O(N ) array gain). We also propose a precoding scheme which finds near-optimal CE signals to be transmitted, and has O(M N ) complexity. Also, in terms of the total transmit power required to achieve a fixed desired information sum-rate, despite the stringent per-antenna CE constraint, the proposed CE precoding scheme performs close to the sum-capacity achieving scheme for an average-only total transmit power constrained channel.

A low-complex peak-to-average power reduction scheme for OFDM based massive MIMO systems

“…Ideally it would be desirable to have a low Peak-to-Average Ratio (PAR), which would both reduce the hardware cost of the PA and, more importantly, improve its power efficiency. Adhering to these characteristics of the PA, an extreme approach is multi-user pre-coding schemes with constant envelope [5], where the resulting PAR is 0 dB. This strict restriction on PAR may not be optimal in practice 1 and cannot co-exist with well established Orthogonal FrequencyDivision Multiplexing (OFDM) techniques for handling frequency selective channels.…”

On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems

“…For this reason, single-carrier or single-carrier-like mo dulation schemes like DFT-precoded OFDM are often used when there are stringent requirements on power efficiency of the RF amplifiers. Single-carrier signals have a much lower peak-toaverage ratio and can be shaped to have constant envelope even in multiuser MIMO systems [6].…”

Survey of Large-Scale MIMO Systems

“…Similarly, diverse non-linear detectors, such as the MMSE based Soft Interference Cancellation (MMSE-SIC) scheme [62], the Block-Iterative Generalized Decision Feedback Equalizer (BI-GDFE) [63], Tabu Search (TS) [64] and the Maximum Posterior Probability (MAP) algorithm are also evaluated in terms of the Bit Error Ratio (BER) versus complexity [12]. Moreover, the so-called per-antenna Constant Envelope Precoding (CEP) technique implemented with the aid of a sub-optimal algorithm is also invoked for the DL of LS-MIMO systems in an attempt to improve the efficiency of their Power Amplifiers (PAs) [65]. It is stated in [65] that an eNB relying on CEP needs about 4 dB lower transmit power than a conventional technique having a high Peak to Average Power Ratio (PAPR), which is an explicit benefit of using an efficient PA.…”

“…Moreover, the so-called per-antenna Constant Envelope Precoding (CEP) technique implemented with the aid of a sub-optimal algorithm is also invoked for the DL of LS-MIMO systems in an attempt to improve the efficiency of their Power Amplifiers (PAs) [65]. It is stated in [65] that an eNB relying on CEP needs about 4 dB lower transmit power than a conventional technique having a high Peak to Average Power Ratio (PAPR), which is an explicit benefit of using an efficient PA.…”