Energy efficiency comparison of massive MIMO and small cell network

In this paper, we compare the average energy efficiency (EE) of massive MIMO system and small cell network (SCN) under the conditions of identical user density, antenna density and data rate requirements, where the uplink and downlink training overhead as well as multi-cell power control are taken into account. Our analysis shows that the average transmit power of SCN decreases faster than massive MIMO as the antenna density increases. Moreover, massive MIMO achieves a higher average EE than SCN if its power consumption except the power for transmitting data is very low or the data rate requirement is very high. Considering that in SCN with large number of base stations (BSs) the opportunity for turning some BSs into idle mode is higher, massive MIMO exhibits higher EE only if its circuit power of each active antenna is lower than that for each antenna at an idle small BS. If antenna idling is allowed for massive MIMO, massive MIMO will be more energy efficient than SCN when the former has smaller circuit power for each idling antenna.