Spacetime Frequency-Multiplexed Digital-RF Array Receivers with Reduced ADC Count

Wireless systems operating at mm-wave frequencies require dense antenna arrays to achieve directional gain for overcoming high path loss. Digital mm-wave arrays retain spatial degrees of freedom, but require a dedicated analog to data converter (ADC) per spatial channel, leading to undesirably high receiver complexity, large ADC count, and power consumption. This brief exploits directional sparsity to reduce the number of receivers and ADCs with minimal loss in performance. A multidimensional (MD) linear transformation using transmission lines and a K~:~1 combiner is used to reduce the number of ADCs by a factor K. Simulations verify that the proposed method can lead to better than 50% ADC complexity reductions (for K\ge 2) for linear arrays and more than 75% ADC complexity reduction (for K\ge 4) for rectangular arrays when sparsity conditions are met. Unlike in analog-digital hybrid beamforming, where a phased-array combines K channels to a single ADC, the proposed method does not lead to loss of spatial degrees of freedom.