Direction of arrival (DoA) estimation of high-resolution beams is critical for cell search and maintaining communication in millimeter wave (mmWave) cellular systems. All-digital solutions for DoA estimation, though desirable for their flexibility and performance, are impractical because of their use of high-speed, power hungry Analog-Digital Converters (ADCs) at each antenna element. In this paper we take a novel approach to formulate a fully digital DoA estimation solution. Our method utilizes mmWave propagation characteristics to properly design a pilot signal that enables the reduction of the ADC speed and the number of antenna by a significant amount while achieving a desired performance goal. Our proposed method applies subspace-based methods like MUSIC on the heavily subsampled received signals, and performs the DoA estimation on a small subset of the dominant multi-paths in the channel one at a time, thus maintaining the integrity of the DoA estimation algorithm while significantly reducing computational complexity.
Energy efficient array processing is critical to implement feasible solutions for directional communication in a mmWave channel. MmWave channels are highly susceptible to blockage and require frequent angle of arrival (AoA) estimation. An AoA estimation solutions with a fully digital architecture offers a low latency, high performance and flexible solution suitable for the stringent requirements of 5G. However, the large number of high speed converters in a digital receiver are the dominant power consuming elements. Alternative analog or hybrid architectures use fewer high speed converters, but require sweeping measurements to estimate AoAs over the angular space, and thus adds latency to the estimation process. In this paper, we present a variable rate sub-Nyquist decoupling solution that leverages pilot design. The pilot's subsequence properties allow decoupling the source waveforms at fractions of the Nyquist rate. We leverage this concept to scale power consumption by the converters. We preprocess the received signals at the antenna array with the variable rate sub-Nyquist decoupling algorithm and use a few well known digital estimators for AoA estimation including DEML, KR-MUSIC based two level nested array and coprime filter bank. In addition to scalable power consumption, our research indicates some other benefits of the decoupling, including reduced complexity algorithm implementation and improved performance estimation for the non maximum likelihood estimators.
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