Random phase modulation in load modulated arrays

Abstract

Load modulated arrays (LMAs) are gaining research attention as an attractive transmitter architecture for multiple-input multiple-output (MIMO) systems. A key advantage of LMAs is that they eliminate the need for RF chains at the transmitter (consisting of DACs, mixers, filters) and use only one central power amplifier for any number of antenna elements. The algorithmic complexity of the construction of high spectral efficiency load modulation (LM) signal sets for large arrays that attempts to maximize the angular separation between load impedance vectors is high. In this paper, we propose high spectral efficiency LM signal sets for large arrays. In particular, we propose random phase modulation (RPM) for LMAs, where randomly chosen phase vectors constitute the LM signal set. The LM signal sets generated using RPM are shown to achieve performance close to within a fraction of a dB compared to the performance achieved by algorithmically constructed LM signal sets, particularly when the signal set size and signal dimension are large. Further, we propose the use of random phase precoding (RPP) and precoder index modulation (PIM) in LMAs, which is shown to achieve a performance improvement of about 7–8 dB at 104 bit error rate.