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Next generation wireless networks aim at providing substantial improvementsin spectral efficiency (SE) and energy efficiency (EE). Massive MIMO has beenproved to be a viable technology to achieve these goals by spatiallymultiplexing several users using many base station (BS) antennas. A potentiallimitation of Massive MIMO in multicell systems is pilot contamination, whicharises in the channel estimation process from the interference caused byreusing pilots in neighboring cells. A standard method to reduce pilotcontamination, known as regular pilot (RP), is to adjust the length of pilotsequences while transmitting data and pilot symbols disjointly. An alternativemethod, called superimposed pilot (SP), sends a superposition of pilot and datasymbols. This allows to use longer pilots which, in turn, reduces pilotcontamination. We consider the uplink of a multicell Massive MIMO network usingmaximum ratio combining detection and compare RP and SP in terms of SE and EE.To this end, we derive rigorous closed-form achievable rates with SP under apractical random BS deployment. We prove that the reduction of pilotcontamination with SP is outweighed by the additional coherent and non-coherentinterference. Numerical results show that when both methods are optimized, RPachieves comparable SE and EE to SP in practical scenarios.

Spectral and Energy Efficiency of Superimposed Pilots in Uplink Massive MIMO