Abstract
The channel state information (CSI) obtained from channel estimation will be outdated quickly in the millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems employing time-division duplex (TDD) setting, which results in significant performance degradation for the precoding and coherent signal detection. In order to overcome the CSI delay problem, this article proposes a novel downlink transmission scheme for the mmWave massive MIMO systems. In the proposed scheme, the base station (BS) estimates the channel coefficients by using the uplink pilots, and calibrates the CSI by employing an enhanced predictor which exploits the channel sparsity in both the angle and the time domains, followed by the interpolation to obtain the channel coefficients at the data rate. Then the signal radiated from the BS array is precoded by using the predicted channel coefficients so that the propagated signal can be added coherently and detected at the terminal. Simulation results show that the proposed scheme can overcome the CSI delay problem effectively, and improve the signal detection performance. We show that for system with 125 Hz Doppler frequency shift and 0.96 ms time slot, the uncoded bit error rate (BER) is improved from $2.4 \times 10^{-2}$ to $2.5 \times 10^{-3}$ by using our proposed method when the noise power ratio (SNR) is 10 dB.
Highlights
The millimeter wave communication is regarded as one of the most potential solutions for the exponentially expanding wireless data traffic in the future, due to the wide usable spectrum in the mmWave band
We develop a novel framework for the mmWave massive multiple-input multiple-output (MIMO) downlink transmission, which consists of the uplink pilot transmission and channel estimation, the angle-time domain (Ag-TD) channel prediction, channel interpolation, massive MIMO precoding and coherent signal detection
There are K = 256 orthogonal frequency division multiplexing (OFDM) subcarriers, and the cyclic prefic (CP) length is Lcp = K /4, which is larger than the maximum channel delay. 200 slots are simulated: the first 100 slots are used for computing prediction coefficients, while the second 100 for performance evaluation
Summary
The millimeter wave (mmWave) communication is regarded as one of the most potential solutions for the exponentially expanding wireless data traffic in the future, due to the wide usable spectrum in the mmWave band. In TDD systems, for downlink transmission, CSI can only be obtained by estimating uplink channel, resulting in unavoidable outdated problem [10], which will seriously degrade the performance of precoding and coherent signal detection. We develop a novel framework for the mmWave massive MIMO downlink transmission, which consists of the uplink pilot transmission and channel estimation, the angle-time domain (Ag-TD) channel prediction, channel interpolation, massive MIMO precoding and coherent signal detection. Unlike the prior investigations, our proposed framework does not assume that the wireless channel remains timeinvariant during channel estimation, channel prediction, or data transmission, which means that the mmWave massive MIMO channel will change sample-by-sample, resulting in highly challenging channel acquisition strategies. With a limited coherence time in mmWave massive MIMO systems, the estimated channel coefficients in the uplink could not be directly used for precoding and detection. PROPOSED FRAMEWORK FOR DOWNLINK TRANSMISSION AND COHERENT SIGNAL DETECTION we detail the main blocks (shown in Fig. 3) of general framework for downlink transmission and signal detection in mmWave massive MIMO systems
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