Multi-User Precoding and Channel Estimation for Hybrid Millimeter Wave Systems

Abstract

In this paper, we develop a low-complexity channel estimation for hybrid millimeter wave (mmWave) systems, where the number of radio frequency (RF) chains is much less than the number of antennas equipped at each transceiver. The proposed mmWave channel estimation algorithm first exploits multiple frequency tones to estimate the strongest angle-of-arrivals (AoAs) at both base station (BS) and user sides for the design of analog beamforming matrices. Then all the users transmit orthogonal pilot symbols to the BS along the directions of the estimated strongest AoAs in order to estimate the channel. The estimated channel will be adopted to design the digital zero-forcing (ZF) precoder at the BS for the multi-user downlink transmission. The proposed channel estimation algorithm is applicable to both nonsparse and sparse mmWave channel environments. Furthermore, we derive a tight achievable rate upper bound of the digital ZF precoding with the proposed channel estimation algorithm scheme. Our analytical and simulation results show that the proposed scheme obtains a considerable achievable rate of fully digital systems, where the number of RF chains equipped at each transceiver is equal to the number of antennas. Besides, by taking into account the effect of various types of errors, i.e., random phase errors, transceiver analog beamforming errors, and equivalent channel estimation errors, we derive a closedform approximation for the achievable rate of the considered scheme. We illustrate the robustness of the proposed channel estimation and multi-user downlink precoding scheme against the system imperfection.

Sparse Channel Estimation and Hybrid Precoding Using Deep Learning for Millimeter Wave Massive MIMO

“…Note that the CENN is trained to predict the beamspace channel amplitude, where the training process of the CENN is independent of J. The proposed DLCS channel estimation scheme is compared with the existing OMP [5] and DGMP [4] channel estimation schemes, while the proposed DLQP hybrid precoder design method is compared with the existing QALS [14] hybrid precoder design method. We also compare the DLQP method with the Exhaustion hybrid precoder design method, i.e., we generate the analog precoding matrix F R for 30, 000 times, where each entry of F R is randomly drawn from the set {e j2πn/Q , n = 1, 2, .…”

“…, Q}. The hybrid precoder design schemes based on beamsteering codebooks design the analog precoder vector as the steering vector of the LOS channel path [12]- [14]. However, such schemes require that Q ≥ N A to obtain high beamforming gain, which will have unsatisfactory performance when Q < N A .…”

“…To obtain the input of the THPNNĥ u , we obtain the real measured r u from practical mmWave channel environments. We compute c u based on (14), which is then fed to the offline-trained CENN for the DLCS channel estimation to getĝ u . We obtain the estimated channel vectorĥ u based on the channel reconstruction in (18).…”

“…To consider the hardware constraint of the limited phase shifter resolution, beam allocation for multiple users was considered [13], where the arXiv:2002.06380v1 [eess.SP] 15 Feb 2020 discrete fourier transformation (DFT) codebook was adopted for analog precoding and the phase shifter resolution must be proportional to the number of antennas. To remove the constraint that the phase shifter resolution was related to the number of antennas, a quantized angle linear search (QALS) precoding scheme was proposed [14], where the angular domain was quantized according to the limited resolution of phase shifters and a linear search method was used to obtain the optimal analog beamforming vectors aligning with the dominant channel paths. However, these hybrid precoding schemes design the analog precoder using the steering vectors of quantized angles, which is heavily constrained by the resolution of phase shifters.…”

Millimeter Wave Communications for Future Mobile Networks

“…[179] proposes a single-user multi-beam transmission scheme in the beamspace, and the corresponding multi-beam selection, cooperative beam tracking, multi-beam power allocation, and synchronization are investigated. [180] develops a low-complexity channel estimation for hybrid mmWave MIMO systems, and investigates the achievable sum-rate of zero forcing with the estimated channel under the consideration of system imperfection. [181] investigates the hybrid precoding for wideband mmWave MIMO, and proposes a unified heuristic design for two different hybrid precoding architectures, i.e., the fully-connected and the partially-connected architectures, to maximize the overall spectral efficiency.…”