In this work, we study the achievable rate and the energy efficiency ofAnalog, Hybrid and Digital Combining (AC, HC and DC) for millimeter wave (mmW)receivers. We take into account the power consumption of all receivercomponents, not just Analog-to-Digital Converters (ADC), determine somepractical limitations of beamforming in each architecture, and developperformance analysis charts that enable comparison of different receiverssimultaneously in terms of two metrics, namely, Spectral Efficiency (SE) andEnergy Efficiency (EE). We present a multi-objective utility optimizationinterpretation to find the best SE-EE weighted trade-off among AC, DC and HCschemes. We consider an Additive Quantization Noise Model (AQNM) to evaluatethe achievable rates with low resolution ADCs. Our analysis shows that AC isonly advantageous if the channel rank is strictly one, the link has very lowSNR, or there is a very stringent low power constraint at the receiver.Otherwise, we show that the usual claim that DC requires the highest power isnot universally valid. Rather, either DC or HC alternatively result in thebetter SE vs EE trade-off depending strongly on the considered powerconsumption characteristic values for each component of the mmW receiver.
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