InFocus: A spatial coding technique to mitigate misfocus in near field LoS beamforming

TL;DR

InFocus is a novel spatial coding technique that uses frequency modulated waveforms to mitigate misfocus and beam squint effects in wideband phased array systems, enhancing data rates in near and far field communications.

Contribution

The paper introduces InFocus, a low complexity spatial coding method that constructs beams suited for wideband phased arrays, addressing misfocus and beam squint issues.

Findings

InFocus improves beam focus across wide bandwidths.

Simulation shows higher data rates with InFocus compared to existing methods.

Effective in both near field and far field systems.

Abstract

Phased arrays, commonly used in IEEE 802.11ad and 5G radios, are capable of focusing radio frequency signals in a specific direction or a spatial region. Beamforming achieves such directional or spatial concentration of signals and enables phased array-based radios to achieve high data rates. Designing beams for millimeter wave and terahertz communication using massive phased arrays, however, is challenging due to hardware constraints and the wide bandwidth in these systems. For example, beams which are optimal at the center frequency may perform poor in wideband communication systems where the radio frequencies differ substantially from the center frequency. The poor performance in such systems is due to differences in the optimal beamformers corresponding to distinct radio frequencies within the wide bandwidth. Such a mismatch leads to a misfocus effect in near field systems and the beam squint effect in far field systems. In this paper, we investigate the misfocus effect and propose InFocus, a low complexity technique to construct beams that are well suited for massive wideband phased arrays. The beams are constructed using a carefully designed frequency modulated waveform in the spatial dimension. For the special case of beamforming along the boresight of an array, this waveform is analogous to the frequency modulated continuous wave (FMCW) chirp signal in radar. InFocus mitigates beam misfocus and beam squint when applied to near field and far field systems. Simulation results indicate that InFocus enables massive wideband phased array-based radios to achieve higher data rates than comparable beamforming solutions.