Constructive Interference Precoding for Reliable Non-Orthogonal IoT Signaling

Efficient signal waveform design is paving the way to next generation Internet of Things (NG-IoT) communications. Non-orthogonal spectrally efficient frequency division multiplexing (SEFDM) waveform brings bandwidth saving advantages but at the cost of complex signal processing in IoT devices. Power efficiency is the main concern in IoT applications since IoT devices have limited battery life and cannot easily recharge after deployment. Therefore, signal processing in each IoT device should be as simple as possible. Precoding is applied as the strategy at transmitters to pre-cancel the self-created inter carrier interference (ICI) caused by the non-orthogonal sub-carrier packing, and to facilitate low-complexity IoT receivers. However, the typical zero forcing (ZF) precoding results in performance degradation due to the ill-conditioned precoding matrix. To achieve reliable communications using SEFDM signals, a robust constructive interference (CI) precoding method is employed, which constructively converts interference power to useful signal power. Thus, signal-to-noise ratio (SNR) is effectively improved leading to better performance than ZF precoding. This work initially studies the performance of precoding methods in simulation. Furthermore, the CI precoding is practically tested over-the-air on a multi-user multiple input multiple output (MIMO)-SEFDM software defined radio NG-IoT platform.