###### Abstract  
This paper proposes an effective strongest angles of arrival (AoAs) estimation algorithm for a hybrid millimeter wave (mmWave) communication system with 1-bit analog-to-digital/digital-to-analog converters (A/Ds) equipped at transceivers. The proposed algorithm aims to reduce the required number of estimation overheads, while maintaining the root mean square error (RMSE) of strongest AoA estimates at the base station. We obtain the quantization thresholds of A/Ds for different signal-to-noise ratios (SNRs) and numbers of antennas via numerical simulations, based on which, the strongest AoAs can be estimated with a small amount of overheads. The proposed algorithm is compared with conventional schemes including 1-bit FFT and 1-bit exhaustive search, as well as 1-bit Cramer-Rao lower bound. Simulation results verify the effectiveness of our proposed algorithm in terms of reducing estimation overheads while maintaining reasonable estimation performance in low SNRs. hybrid; millimeter wave; 1-bit A/Ds +
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To further reduce the power consumption and hardware complexity of mmWave communication systems, one natural solution is to combine the hybrid architecture with low-resolution A/Ds [12; 21]. For the hybrid architecture with low-resolution A/Ds, one of the most critical problems is to identify the dominant multipath components of the channel, i.e., estimating the strongest angles of arrival (AoAs) [22], where conventional mmWave channel estimation algorithms are not applicable. In the literature, one popular approach to estimate the strongest AoAs of mmWave channels is to use spatial-scanning based beam search [23; 24; 25]. To reduce the overhead of beam search and ensure high AoA estimation accuracy, various algorithms have been proposed [26; 27; 28]. However, compared to scenarios that utilizing low-resolution A/Ds, these algorithms, e.g., [26; 27; 28], assuming high-resolution A/Ds at transceivers will lead to a significant higher energy consumption. For mmWave channel estimation with low-resolution A/Ds, the related works are relatively limited [29; 30] due to its challenging nature. The existing solutions in [29; 30] mainly work in moderate to signal-to-noise ratio (SNR) scenarios, while low SNR scenarios are common especially in outdoor mmWave communications, due to the high propagation loss of mmWave signals. To address the channel estimation problem at low SNRs with 1-bit A/Ds, we first propose a channel estimation algorithm for hybrid architecture with 1-bit A/Ds equipped at transceivers. The proposed algorithm exploits Wald-type confidence interval and detection probability to design a new reward function to reduce the estimation overheads while maintaining the root mean square error (RMSE) performance of the estimation of strongest AoA components. In addition, we obtain the semi-analytical relationship between the receive SNR, the designed practical quantization thresholds, and the average estimation overheads. Also, we compare our proposed algorithm with conventional benchmarks, e.g., the 1-bit FFT algorithm and the approximated Cramer-Rao lower bound (CRLB) for hybrid architecture equipped with 1-bit A/Ds. Numerical results show that the proposed algorithm can obtain a reasonable AoA estimation performance and reduce the estimation overhead at the same time, especially in low SNR regimes.