Beam Squinting Compensation: An NCR-Assisted Scenario

Millimeter wave (MmWave) and sub-THz communications, foreseen for sixth generation (6G), suffer from high propagation losses which affect the network coverage. Another challenge raised by the adoption of high frequency bands is the use of large bandwidths. In order to deal with this last challenge, a common configuration is to divide a large frequency band into multiple smaller subbands. In this context, we consider a mobile network where signaling related to measurements used for radio resource management is transmitted in one subband centered at frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f_{c}$</tex-math></inline-formula> and data transmission is performed at a different frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f_{c} + \Delta f$</tex-math></inline-formula> based on the measurements taken at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f_{c}$</tex-math></inline-formula>. Here, a challenge is that the array radiation pattern can be frequency dependent and, therefore, lead to beam misalignment, called beam squinting. Thus, in this work, we characterize beam squinting in the context of subband operation and propose a solution where the beam patterns to be employed at a given subband can be adjusted/compensated to mitigate beam squinting. For performance evaluation, we present a case study where our compensation method is employed in a network-controlled repeaters (NCRs)-assisted scenario. NCR, which have been standardized in third generation partnership project Release 18, are considered as cost-efficient solutions for coverage extension in the context of millimeter wave (mmWave). Specifically, NCRs are radio frequency repeaters with beamforming capability controlled by the network through side control information. Our results show that, without compensation, the perceived signal to interference-plus-noise ratio (SINR) and so the throughput can be substantially decreased due to beam squinting. However, with our proposed compensation method, the system is able to support NCR subband signaling operation with similar performance as if signaling and data were transmitted at the same frequency.