Load modulated massive MIMO

We propose a new hardware architecture for cost-and size-effective implementation of massive MIMO transmitters based on load modulation that is fully compatible with standard receiver architectures. With load modulation, a massive MIMO transmitter can be driven by a single power amplifier operating at constant envelope. The various data streams are modulated onto the antennas elements by varying the complex impedances of the various antenna circuits at symbol rate. The law of large numbers ensures that the common power source is matched to the parallel concatenation of the various antenna circuits, if the number of antenna elements is very large. For 100 antenna elements that are supposed to transmit Gaussian-like signals, e.g. due to OFDM modulation and/or precoding, the crest factor is only 1.2 dB at a clipping probability of 0.1%. In that case, load modulation reduces the average consumed power and the amplifier peak power by 49% and 79%, respectively, as compared to classical distributed amplifiers with voltage modulation. Furthermore, one class F amplifier can be used to replace 100 class A/B amplifiers. Mutual antenna coupling need not be addressed by a physical matching network, but can be mitigated dynamically by digital signal processing in baseband without additional hardware. This allows for closer antenna spacing as in architectures with distributed amplifiers.