A Systematic Beam Broadening Method for Large Phased Arrays

Hybrid beamforming architecture is a key enabler for implementing Massive Multiple-Input Multiple-Output (mMIMO) solutions in next generation wireless communication systems. With such an approach, precoder and combiner designs not only depend on digital weights but also on modulus constraint analog weights controlled by phase shifters. This becomes a critical issue since the calculation of weights becomes a nonconvex problem that needs extensive search or complex iterative methods. In particular, beam broadening capability is of key interest for mMIMO systems to find a trade-off between the array gain and the beamwidth. Indeed, a high gain narrow beam is not always beneficial as far as mobility scenarios or control channel transmissions are concerned. In this paper, a non-iterative phase-only beam broadening method is proposed, relying on a quadratic phase excitation pattern applied to linear and planar arrays. We establish the key laws driving the beamwidth and steering angle adaption. We show that our technique can be applied systematically and is especially well-suited for large antenna arrays.