High-Mobility OFDM Downlink Transmission with Partly Calibrated Subarray-Based Massive Uniform Linear Array

IEEE Trans. Wireless Commun.

et al. 2019

Self Cite

In this paper, we apply angle-domain Doppler compensation for high-mobility wideband massive multi-input multioutput (MIMO) uplink transmission. The time-varying multipath channel is considered between high-speed terminal and static base station (BS), where multiple Doppler frequency offsets (DFOs) are associated with distinct angle of departures (AoDs). With the aid of the large-scale uniform linear array (ULA) at the transmitter, we design a beamforming network to generate multiple parallel beamforming branches, each transmitting signal pointing to one particular angle. Then, the transmitted signal in each branch will experience only one dominant DFO when passing over the time-varying channel, which can be easily compensated before transmission starts. We theoretically analyze the Doppler spread of the equivalent uplink channel after angledomain Doppler compensation, which takes into account both the mainlobe and sidelobes of the transmit beam in each branch. It is seen that the channel time-variation can be effectively suppressed if the number of transmit antennas is sufficiently large. Interestingly, the asymptotic scaling law of channel variation is obtained, which shows that the Doppler spread is proportional to the maximum DFO and decreases approximately as 1/ √ M (M is the number of transmit antennas) when M is sufficiently large. Numerical results are provided to corroborate the proposed scheme.

Section: B Signal Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High-Mobility Wideband Massive MIMO Communications: Doppler Compensation, Analysis and Scaling Laws

Wei

IEEE Trans. Wireless Commun.

et al. 2019

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“…By combining (47), (48) and (49), a 0 12 ≈ 1 π π 0 π 0 ηα T A b α * sinθdθdθ p can be simplified as (22). Similarly, a 0 11 = ∂g 0…”

Section: Discussionmentioning

confidence: 98%

“…Section VII draws the conclusion of this paper. Part of this paper has appeared in a conference paper [22].…”

Section: Introductionmentioning

confidence: 99%

Angle-Domain Approach for Parameter Estimation in High-Mobility OFDM With Fully/Partly Calibrated Massive ULA

IEEE Trans. Wireless Commun.

Gao

et al. 2019

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In this paper, we consider a downlink orthogonal frequency division multiplexing (OFDM) system from a base station to a high-speed train (HST) equipped with fully/partly calibrated massive uniform linear antenna-array (ULA) in wireless environments with abundant scatterers. Multiple Doppler frequency offsets (DFOs) stemming from intensive propagation paths together with transceiver oscillator frequency offset (OFO) result in a fast time-varying frequency-selective channel. We develop an angle domain carrier frequency offset (CFO, general designation for DFO and OFO) estimation approach.A high-resolution beamforming network is designed to separate different DFOs into a set of parallel branches in angle domain such that each branch is mainly affected by a single dominant DFO. Then, a joint estimation algorithm for both maximum DFO and OFO is developed for fully calibrated ULA.Next, its estimation mean square error (MSE) performance is analyzed under inter-subarray mismatches.To mitigate the detrimental effects of inter-subarray mismatches, we introduce a calibration-oriented beamforming parameter (COBP) and develop the corresponding modified joint estimation algorithm for partly calibrated ULA. Moreover, the Cramér-Rao lower bound of CFO estimation is derived. Both theoretical and numerical results are provided to corroborate the proposed method. Index TermsHigh-mobility OFDM, massive MIMO, partly calibrated antenna array, multiple carrier frequency offsets (CFOs), angle-domain approach, calibration-oriented beamforming parameter (COBP).

“…After estimating and compensating the Doppler shift in each branch, the resultant channel turns to be quasi time-invariant and can be estimated with conventional channel estimation approaches. The array imperfection is further taken into account in [21], [22], and the multi-Doppler shift separation via array beamforming can be done after array calibration. Unlike [20]- [22] addressing the downlink Doppler shifts, [23] and [24] focus on the uplink from the HSR to the base station (BS), where the Doppler shifts are related to AoDs instead of AoAs.…”

Section: Introductionmentioning

confidence: 99%

Beamforming Network Optimization for Reducing Channel Time Variation in High-Mobility Massive MIMO

Gao

et al. 2019

IEEE Trans. Commun.

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Communications in high-mobility environments have caught a lot of attentions recently. In this paper, fast time-varying channels for massive multiple-input multiple-output (MIMO) systems are addressed. We derive the exact channel power spectrum density (PSD) for the uplink from a high-speed railway (HSR) to a base station (BS) and propose to further reduce the channel time variation via beamforming network optimization. A large-scale uniform linear array (ULA) is equipped at the HSR to separate multiple Doppler shifts in angle domain through high-resolution transmit beamforming. Each branch comprises a dominant Doppler shift, which can be compensated to suppress the channel time variation, and we derive the channel PSD and the Doppler spread to assess the residual channel time variation. Interestingly, the channel PSD can be exactly expressed as the product of a pattern function and a beam-distortion function. The former reflects the impact of array aperture and is the converted radiation pattern of ULA, while the latter depends on the configuration of beamforming directions. Inspired by the PSD analysis, we introduce a common configurable amplitudes and phases (CCAP) parameter to optimize the beamforming network, by partly removing the constant modulus quantized phase constraints of matched filter (MF) beamformers. In this way, the residual Doppler shifts can be ulteriorly suppressed, further reducing the residual channel time variation. The optimal CCAP parameter minimizing the Doppler spread is derived in a closed form. Numerical results are provided to corroborate both the channel PSD analysis and the superiority of beamforming network optimization technique.Index Terms-High-mobility communication, time-varying channel, power spectrum density (PSD), Doppler spread, angledomain massive MIMO, beamforming network optimization.