  The mmWave communication system is operating at a regime with high number of
antennas and very limited number of RF analog chains. Large number of antennas
are used to extend the communication range for recovering the high path loss
while fewer RF analog chains are designed to reduce transmit and processing
power and hardware complexity. In this regime, typical MIMO algorithms are not
applicable.
  Before any communication starts, devices are needed to align their beam
pointing angles towards each other. An efficient searching protocol to obtain
the best beam angle pair is therefore needed. It is called BeamForming (BF)
training protocol.
  This paper presents a new BF training technique called beam coding. Each beam
angle is assigned unique signature code. By coding multiple beam angles and
steering at their angles simultaneously in a training packet, the best beam
angle pair can be obtained in a few packets. The proposed BF training technique
not only shows the robustness in non-line-of-sight environment, but also
provides very flat power variations within a packet in contrast to the IEEE
802.11ad standard whose scheme may lead to large dynamic range of signals due
to beam angles varying across a training packet.
