Beamforming in MISO Systems: Empirical Results and EVM-Based Analysis

We show that efficient implementation of codebook-based beamforming Multiple Input Single Output (MISO) systems with good performance is feasible in the presence of channel-induced imperfections (due to imperfect channel estimate and feedback delay) and implementation-induced imperfections (due to real-world radio hardware effects). To present our results, we adopt a mixed approach of analytical, simulation, and experimental evaluation. Our analytical and simulation results take into account channel-induced imperfections but do not take into account implementation-induced imperfections (which are difficult to model in a tractable way). Thus, we complement these results with experimental results that do take into account both channel and implementation-induced imperfections. This mixed approach provides a more complete picture of expected performance. As part of our study we develop a framework for Average Error Vector Magnitude Squared (AEVMS)-based analysis of beamforming MISO systems which facilitates comparison of analytical, simulation, and experimental results on the same scale. In addition, AEVMS allows fair comparison of experimental results obtained from different wireless testbeds. We derive novel expressions for the AEVMS of beamforming MISO systems and show how the AEVMS relates to important system characteristics like the diversity gain, coding gain, and error floor.