IEEE Int. Conf. on Communications, May 2019, Shanghai, China.

A Hybrid Beamforming Receiver with Two-Stage Analog Combining and Low-Resolution ADCs

Jinseok Choi (1), Gilwon Lee (2), and Brian L. Evans (1)

(1) Department of Electrical and Computer Engineering, Wireless Networking and Communications Group, The University of Texas at Austin, Austin, TX 78712 USA -

(2) Intel Corporation, Santa Clara, CA 95054 USA

Paper Draft - Presentation Slides - Software Release

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In this paper, we propose a two-stage analog combining architecture for millimeter wave (mmWave) communications with hybrid analog/digital beamforming and low-resolution analog-to-digital converters (ADCs). We first derive a two-stage combining solution by solving an mutual information (MI) maximization problem without a constant modulus constraint on analog combiners. With the derived solution, the proposed receiver architecture splits the analog combining into a channel gain aggregation stage followed by a spreading stage to maximize the MI by effectively managing quantization error. We show that the derived two-stage combiner achieves the optimal scaling law with respect to the number of radio frequency (RF) chains and maximizes the MI for homogeneous singular values of a MIMO channel. Then, we develop a two-stage analog combining algorithm to implement the derived solution under a constant modulus constraint for mmWave channels. Simulation results validate the algorithm performance in terms of MI.

Questions & Answers

Q1) Is the two-stage analog combiner channel-dependent?
A1) Yes. But only the first analog combiner is channel-dependent and the second analog combiner is independent to the channel. Thus, the first analog combiner needs to be re-tuned as the channel changes and the second analog combiner can be implemented with fixed phase shifters.

Q2) How often does the first analog combiner need to be re-tuned?
A2) The ideal case would be tuning the first analog combiner at the duration of the channel coherence time. But we can also tune the analog combiner at the duration of the coherence time of slowly-varying channel characteristics such as angle-of-arrivals.

Q3) So, can the first analog combiner be tuned for the angle-of-arrivals?
A3) Yes. Since there are few channel paths for millimeter wave channels, tuning the analog combiner to the major angle-of-arrivals would still provide reasonable performance.

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Last Updated 07/27/19.