Codebook-Based Beamforming Protocols for 5G Millimeter Wave Communications

This chapter focuses on the beamforming mechanism and protocols that enables fast link setup in 5G Millimeter (mm) Wave directional links. In general, there are two kinds of beamforming: adaptive beamforming and switched beamforming. There are three kinds of beamforming architectures, namely, analog beamforming, digital beamforming, and the hybrid beamforming. Beamsearching in the switched beamforming only depends on the measured signal quality of each predefined beams. Transmitter and receiver devices exchange their training packet to measure the channel quality for each beam candidate. Switched beamforming requires predefined codebook so that the beam candidates can be generated directly from the codebook. Codebook is defined specifically in IEEE 802.15.3c, but there is no specific codebook defined in IEEE 802.11ad. N-phase beamforming is similar to IEEE 802.15.3c. However, this beamforming is designed to accommodate the availability of higher phase shift resolution. Digital Fourier Transmorm (DFT)-based beamforming gives more flexible beams where each beam can reach the same maximum gain.