Coverage in Millimeter-Wave Networks with SNR-Dependent Beam Alignment Errors

Narrow beamwidth and inaccurate angle-of-arrival (AoA) estimation make perfect beam alignment difficult in millimeter-wave (mm-wave) systems. The extent of beam misalignment depends on the uplink received signal-to-noise ratio (SNR) at a single antenna element of the array. Using stochastic geometry, this paper analyzes and quantifies the loss in downlink SNR coverage probability due to beam misalignment. The standard deviation of the beam alignment error is obtained through the Cramér-Rao lower bound (CRLB) of AoA estimation. The analytical results are verified through Monte-Carlo simulations and it is shown that the beam alignment errors affect the system coverage significantly when the downlink SNR threshold (with array gain) is less than 5 dB. It is also illustrated that increasing the number of antennas alone cannot counter the effects of beam alignment errors.