Interference is traditionally viewed as a performance limiting factor in wireless communication systems, which is to be minimized or mitigated. Nevertheless, a recent line of work has shown that by manipulating the interfering signals such that they add up constructively at the receiver side, known interference can be made beneficial and further improve the system performance in a variety of wireless scenarios, achieved by symbol-level precoding (SLP). This paper aims to provide a tutorial on interference exploitation techniques from the perspective of precoding design in a multi-antenna wireless communication system, by beginning with the classification of constructive interference (CI) and destructive interference (DI). The definition for CI is presented and the corresponding mathematical characterization is formulated for popular modulation types, based on which optimization-based precoding techniques are discussed. In addition, the extension of CI precoding to other application scenarios as well as for hardware efficiency is also described. Proof-of-concept testbeds are demonstrated for the potential practical implementation of CI precoding, and finally a list of open problems and practical challenges are presented to inspire and motivate further research directions in this area.

In this paper we demonstrate end-to-end precoded multiuser multiple-input singleoutput communications over a live GEO satellite link. Precoded communications enable full frequency reuse schemes in satellite communications to achieve broader service availability and higher spectrum efficiency than with the conventional four-color and two-color reuse approaches. In this scope, we develop a novel over-the-air test-bed for end-to-end precoding validations. We were able to demonstrate precoded communications over an actual geostationary orbit multi-beam satellite using the DVB-S2X standard-compliant state-of-the-art gateway and user terminals. The developed system is capable of fully end-to-end real-time communications over a satellite link and demonstrates novel channel measurements and channel compensation techniques for differential frequency and phase tracking. It is shown, that by successfully canceling inter-user interference in the actual satellite link, the precoding improves the received SINR and increases the total system goodput in aggressive full frequency reuse scenarios.

In this paper, we demonstrate an FPGA-accelerated design of the computationally efficient symbol-level precoding (SLP) for high-throughput communication systems. The SLP technique recalculates the optimal beam-forming vectors by solving a non-negative least squares problem per every set of transmitted symbols. It exploits the advantages of constructive inter-user interference to minimize the total transmitted power and increase service availability. The benefits of using SLP come with a substantially increased computational load at the gateway. The FPGA design enables the SLP technique to perform in real-time operation mode and provide a high symbol throughput for the multiple receive terminals. We define the SLP technique in a closed-form algorithmic expression and translate it to hardware description language (HDL) and build an optimized HDL core for an FPGA. We evaluate the FPGA resource occupation, which is required for the high throughput multiple-input-multiple-output (MIMO) systems with sizeable dimensions. We describe the algorithmic code, the I/O ports mapping, and the functional behavior of the HDL core. We deploy the IP core to an actual FPGA unit and benchmark the energy efficiency performance of the SLP. The synthetic tests demonstrate a fair energy efficiency improvement of the proposed closed-form algorithm compared to the best results obtained through the MATLAB numerical simulations. INDEX TERMS Convex programming, field programmable gate arrays, hardware resources, multicast communication, MIMO, optimization, precoding, power minimization, interference, wireless channels.

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