Effect of Wideband Beam Squint on Codebook Design in Phased-Array Wireless Systems

摘要

Analog beamforming with phased arrays is a promising technique for 5Gwireless communication at millimeter wave frequencies. Using a discretecodebook consisting of multiple analog beams, each beam focuses on a certainrange of angles of arrival or departure and corresponds to a set of fixed phaseshifts across frequency due to practical hardware considerations. However, forsufficiently large bandwidth, the gain provided by the phased array is actuallyfrequency dependent, which is an effect called beam squint, and this effectoccurs even if the radiation pattern of the antenna elements is frequencyindependent. This paper examines the nature of beam squint for a uniform lineararray (ULA) and analyzes its impact on codebook design as a function of thenumber of antennas and system bandwidth normalized by the carrier frequency.The criterion for codebook design is to guarantee that each beam's minimum gainfor a range of angles and for all frequencies in the wideband system exceeds atarget threshold, for example 3 dB below the array's maximum gain. Analysis andnumerical examples suggest that a denser codebook is required to compensate forbeam squint. For example, 54% more beams are needed compared to a codebookdesign that ignores beam squint for a ULA with 32 antennas operating at acarrier frequency of 73 GHz and bandwidth of 2.5 GHz. Furthermore, beam squintwith this design criterion limits the bandwidth or the number of antennas ofthe array if the other one is fixed.