  The potential of using millimeter-wave (mmWave) to encounter the current
bandwidth shortage has motivated packing more antenna elements in the same
physical size which permits the advent of massive
multiple-input-multiple-output (MIMO) for mmWave communication. However, with
increasing number of antenna elements, the ability of allocating a single
RF-chain per antenna becomes infeasible and unaffordable. As a cost-effective
alternative, the design of hybrid precoding has been considered where the
limited-scattering signals are captured by a high-dimensional RF precoder
realized by an analog phase-shifter network followed by a low-dimensional
digital precoder at baseband. In this paper, the max-min fair problem is
considered to design a low-complexity hybrid precoder for multi-group
multicasting systems in mmWave channels. The problem is non-trivial due to two
main reasons: the original max-min problem for multi-group multicasting for a
fully-digital precoder is non-convex, and the analog precoder places constant
modules constraint which restricts the feasible set of the precoders in the
design problem. Therefore, we consider a low complexity hybrid precoder design
to tackle and benefit from the mmWave channel structure. Each analog beamformer
was designed to maximize the minimum matching component for users within a
given group. Once obtained, the digital precoder was attained by solving the
max-min problem of the equivalent channel.
