Uplink Interference Analysis With RF Switching for Lens–Based Millimeter–Wave Systems

In this paper, we take a fundamental look at the interference characteristics of a lens–based millimeter–wave multiuser multiple–input multiple–output system. We consider a hybrid architecture, implemented via a bank of radio–frequency (RF) switches which perform beam selection followed by low–complexity uplink maximum–ratio combining at baseband. Considering a Rotman lens antenna array in line–of–sight propagation, we derive tight analytical expressions for the average (expected) interference power of an arbitrary user terminal, with and without the presence of RF switching. Our mathematical expressions show that without RF switching, the Rotman lens losses its benefits and collapses to a conventional uniform linear array. Numerical results demonstrate that the expected interference power of a given terminal decreases significantly with RF switching, due to the beam selection process separating multiple uplink direction–of–arrivals (DoAs). This is in contrast to the case when there is no RF switching, which relaxes the beam selection constraints and thus allows very similar DoAs. Overall, the results in this paper emphasize the necessity of RF switching in order to obtain superior performance with a Rotman lens array, over conventional phased arrays.