Comparison of CoMP and MISO for energy efficiency in HetNets

Energy efficiency has become one of the key performance indicators for 5G wireless networks. Coordinated multipoint (CoMP) transmission/reception and multiinput single-output (MISO) are two technologies which can achieve higher energy efficiency in heterogeneous networks (HetNets) compared to conventional single-input single-out (SISO) systems. CoMP improves energy efficiency by joint transmission among cooperative base stations (BSs) while MISO achieves this by maximal ratio transmission (MRT) beamforming. In this paper, we use a stochastic geometry approach to analyze and compare the energy efficiency of CoMP and MISO in HetNets. First we derive an exact theoretical expression for the network coverage probability of MISO which is validated by Monte Carlo simulations. Then energy efficiency of a two-tier HetNet with CoMP and MISO is analyzed respectively and compared. Numerical results show that the energy efficiency of MISO rises with increasing number of antennas. The achievable energy efficiency of both CoMP and MISO is related closely to the density ratio between Pico BS (PBS) and Macro BS (MBS). When the density ratio is lower than a critical value, MISO is more energy efficient than CoMP; while CoMP outperforms MISO when the density ratio goes beyond the critical value. The exact critical value varies with the number of the antennas used in MISO.