  As the spectrum is becoming more scarce due to exponential demand of
formidable data quantities, the new millimiterwave (mmW) band is considered as
an enabling player of 5G communications to provide multi-gigabits wireless
acccess. MmW communications exhibit high attenuation and blockage,
directionality due to massive beamforming, deafness, low-interference, and may
need micro waves networks for coordination and fallback support. The current
mmW standardizations are challenged by the overwhelming complexity given by
such heterogeneous communication systems and mmW band characteristics. This
demands new substantial protocol developments at all layers. In this paper, the
medium access control issues for mmW communications are reviewed. It is
discussed that while existing standards address some of these issues for
personal and local area networks, little has been done for cellular networks.
It is argued that the medium access control layer should be equipped with
adaptation mechanisms that are aware of the special mmW characteristics.
Recommendations for mmW medium access control design in 5G are provided. It is
concluded that the design of efficient access control techniques for mmW is in
its infancy and much work still has to be done.
