An Efficient Manifold Algorithm for Constructive Interference Based Constant Envelope Precoding

Fan Liu,Christos Masouros,Pierluigi Vito Amadori,Huafei Sun

doi:10.1109/lsp.2017.2748230

Fan Liu, Christos Masouros + Show 2 more

Open Access

https://doi.org/10.1109/lsp.2017.2748230

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Abstract

In this letter, we propose a novel manifold-based algorithm to solve the constant envelope (CE) precoding problem with interference exploitation. For a given power budget, we design the precoded symbols subject to the CE constraints, such that the constructive effect of the multi-user interference (MUI) is maximized. While the objective for the original problem is non-differentiable on the complex plane, we consider the smooth approximation of its real representation, and map it onto a Riemannian manifold. By using the Riemmanian conjugate gradient (RCG) algorithm, a local minimizer can be efficiently found for the problem. The complexity of the algorithm is analytically derived in terms of floating-points operations (flops) per iteration. Numerical results show that the proposed algorithm outperforms the conventional methods on both symbol error rate and computational complexity.

Highlights

A S ONE of the most promising approaches in 5G technology, massive multi-input multi-output communication systems are expected to provide significant benefits over conventional MIMO systems by employing much larger antenna arrays [1], [2]
By noting the fact that MUI is known to the base station (BS), and can be utilized as a source of useful power, the previous work [11] considers a novel constant envelope precoding (CEP) approach with the concept of constructive interference (CI) [12]–[16], which obtains a significant performance improvement compared to interference reduction (IR) approaches
We set u = 1, ∀m, which is a common assumption in related literature for the reason that the optimal u is difficult to determine for IR methods [5], [6] whereas arbitrary u can be accepted by CI methods [11]

Summary

INTRODUCTION

A S ONE of the most promising approaches in 5G technology, massive multi-input multi-output (mMIMO) communication systems are expected to provide significant benefits over conventional MIMO systems by employing much larger antenna arrays [1], [2]. By noting the fact that MUI is known to the base station (BS), and can be utilized as a source of useful power, the previous work [11] considers a novel CEP approach with the concept of constructive interference (CI) [12]–[16], which obtains a significant performance improvement compared to IR approaches. Both of the above-mentioned methods demand large amount of computations inevitably. Unlike the relaxed convex problem in [11], the proposed algorithm is guaranteed to yield precoded symbols with exactly constant envelopes, and has better performance than the methods of [11] in terms of both symbol error rate (SER) and complexity

SYSTEM MODEL

PROBLEMS FORMULATION

PROPOSED ALGORITHM BASED ON OBLIQUE MANIFOLD

NUMERICAL RESULTS

CONCLUSION