Practical Interference Exploitation Precoding without Symbol-by-Symbol Optimization: A Block-Level Approach

TL;DR

This paper introduces a block-level constructive interference precoding method for MU-MISO systems that reduces computational complexity by optimizing a single precoding matrix per block instead of per symbol, improving performance.

Contribution

It presents a novel block-level precoding approach that simplifies CI optimization by deriving a closed-form solution and formulating it as a quadratic programming problem.

Findings

Achieves better performance than symbol-level precoding.

Reduces computational costs significantly.

Validates the approach with numerical results.

Abstract

In this paper, we propose a constructive interference (CI)-based block-level precoding (CI-BLP) approach for the downlink of a multi-user multiple-input single-output (MU-MISO) communication system. Contrary to existing CI precoding approaches which have to be designed on a symbol-by-symbol level, here a constant precoding matrix is applied to a block of symbol slots within a channel coherence interval, thus significantly reducing the computational costs over traditional CI-based symbol-level precoding (CI-SLP) as the CI-BLP optimization problem only needs to be solved once per block. For both PSK and QAM modulation, we formulate an optimization problem to maximize the minimum CI effect over the block subject to a block- rather than symbol-level power budget. We mathematically derive the optimal precoding matrix for CI-BLP as a function of the Lagrange multipliers in closed form. By formulating the dual problem, the original CI-BLP optimization problem is further shown to be equivalent to a quadratic programming (QP) optimization. Numerical results validate our derivations, and show that the proposed CI-BLP scheme achieves improved performance over the traditional CI-SLP method, thanks to the relaxed power constraint over the considered block of symbol slots.