The effects of antenna array size and back lobe level on self-interference and transmitted powers for 4G beamforming multicell systems with in-band full duplex relays

This paper considers a 4G multicell system where base-stations and relays employ typical or large size antenna arrays with beamforming capabilities, as well as in-band full duplex relays. The achieved signal to interference ratio (SIR) gain in excess of the maximum required for such systems can be exploited either for reducing the major problem of full duplex self-interference, or for reducing the backhaul and access link powers. The presented analysis and the produced results indicate that using 'small' antenna arrays with 8 elements can lower the requirement of full duplex self-interference cancellation by up to 50/70dB if the back lobe of the produced radiation pattern is kept to -20/-30dB. The same scenario with a large antenna array of 1024 elements gives 90/110dB reduction, respectively. On the other hand, both the backhaul and access transmitted powers can be reduced by ~30dB and ~25dB with 1024 elements, while if the back lobe level is -20dB then the backhaul power reduction increases to ~55dB. No further reduction can be achieved via lower back lobe levels.