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1. A Markovian Model-Driven Deep Learning Framework for Massive MIMO CSI Feedback

   Zhenyu Liu, Mason del ( January 2021 , IEEE transactions on wireless communications)

   null (Ed.)

   Channel state information (CSI) plays a vital role in scheduling and capacity-approaching transmission optimization of massive MIMO communication systems. In frequency division duplex (FDD) MIMO systems, forward link CSI reconstruction at transmitter relies on CSI feedback from receiving nodes and must carefully weigh the tradeoff between reconstruction accuracy and feedback bandwidth. Recent application of recurrent neural networks (RNN) has demonstrated promising results of massive MIMO CSI feedback compression. However, the cost of computation and memory associated with RNN deep learning remains high. In this work, we exploit channel temporal coherence to improve learning accuracy and feedback efficiency. Leveraging a Markovian model, we develop a deep convolutional neural network (CNN)-based framework called MarkovNet to efficiently encode CSI feedback to improve accuracy and efficiency. We explore important physical insights including spherical normalization of input data and deep learning network optimizations in feedback compression. We demonstrate that MarkovNet provides a substantial performance improvement and computational complexity reduction over the RNN-based work.We demonstrate MarkovNet’s performance under different MIMO configurations and for a range of feedback intervals and rates. CSI recovery with MarkovNet outperforms RNN-based CSI estimation with only a fraction of computational cost. 

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2. LSTM vs Plot-based CNN for EEG Emotion Detection Tasks

   https://doi.org/10.1109/CHASE52844.2021.00026  

   Kelnhofer, Jared ; Blaisdell, Marcus ; Ghandi, Mona ( December 2021 , 2021 IEEE/ACM Conference on Connected Health: Applications, Systems and Engineering Technologies (CHASE))

   Emotion detection using machine learning and data gathered from an electroencephalogram (EEG) holds the potential for architecture and creating smart adaptive spaces which can respond to the user's current emotional state detected from the Neurophysiological data in real-time. This technology can help people with mental and physical disabilities to have a greater role in shaping their environment and live more independent lives. In this paper, two different machine learning approaches, the Long Short Term memory network, (LSTM) and Convolutional Neural Network (CNN) are compared in order to assess their potential to satisfy this goal of emotion detection. The LSTM network was trained on eight-channel time-series data which had undergone a Fast Fourier Transform, and the CNN was trained on the un-transformed data in the form of a unique plot-image based approach. 

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3. Robust Deep Learning-based Indoor mmWave Channel Prediction Under Concept Drift

   https://doi.org/10.1109/VTC2023-Fall60731.2023.10333513  

   Hasan, Eslam ; Mahalal, Elmahedi ; Ismail, Muhammad ; Wu, Zi-Yang ; Fouda, Mostafa M ; Koketsu_Rodrigues, Tiago ; Kato, Nei ( October 2023 , IEEE)

   The mmWave WiGig frequency band can support high throughput and low latency emerging applications. In this context, accurate prediction of channel gain enables seamless connectivity with user mobility via proactive handover and beamforming. Machine learning techniques have been widely adopted in literature for mmWave channel prediction. However, the existing techniques assume that the indoor mmWave channel follows a stationary stochastic process. This paper demonstrates that indoor WiGig mmWave channels are non-stationary where the channel’s cumulative distribution function (CDF) changes with the user’s spatio-temporal mobility. Specifically, we show significant differences in the empirical CDF of the channel gain based on the user’s mobility stage, namely, room entering, wandering, and exiting. Thus, the dynamic WiGig mmWave indoor channel suffers from concept drift that impedes the generalization ability of deep learning-based channel prediction models. Our results demonstrate that a state-of-the-art deep learning channel prediction model based on a hybrid convolutional neural network (CNN) long-short-term memory (LSTM) recurrent neural network suffers from a deterioration in the prediction accuracy by 11–68% depending on the user’s mobility stage and the model’s training. To mitigate the negative effect of concept drift and improve the generalization ability of the channel prediction model, we develop a robust deep learning model based on an ensemble strategy. Our results show that the weight average ensemble-based model maintains a stable prediction that keeps the performance deterioration below 4%. 

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4. Channel Feedback Based on AoD-Adaptive Subspace Codebook in FDD Massive MIMO Systems

   https://doi.org/10.1109/TCOMM.2018.2849755  

   Shen, Wenqian ; Dai, Linglong ; Shim, Byonghyo ; Wang, Zhaocheng ; Heath, Robert W. ( January 2018 , IEEE Transactions on Communications)

   Channel feedback is essential in frequency division duplexing (FDD) massive multiple-input multiple-output (MIMO) systems. Unfortunately, prior work on multiuser MIMO has shown that the feedback overhead scales linearly with the number of base station (BS) antennas, which is large in massive MIMO systems. To reduce the feedback overhead, we propose an angle-of-departure (AoD) adaptive subspace codebook for channel feedback in FDD massive MIMO systems. Our key insight is to leverage the observation that path AoDs vary more slowly than the path gains. Within the angle coherence time, by utilizing the constant AoD information, the proposed AoDadaptive subspace codebook is able to quantize the channel vector in a more accurate way. From the performance analysis, we show that the feedback overhead of the proposed codebook only scales linearly with a small number of dominant (path) AoDs instead of the large number of BS antennas. Moreover, we compare the proposed quantized feedback technique using the AoD-adaptive subspace codebook with a comparable analog feedback method. Extensive simulations show that the proposed AoD-adaptive subspace codebook achieves good channel feedback quality, while requiring low overhead. 

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5. Scalable user selection in FDD massive MIMO

   https://doi.org/10.1186/s13638-021-02073-4  

   Zhang, Xing ; Sabharwal, Ashutosh ( December 2021 , EURASIP Journal on Wireless Communications and Networking)

   User subset selection requires full downlink channel state information to realize effective multi-user beamforming in frequency-division duplexing (FDD) massive multi-input multi-output (MIMO) systems. However, the channel estimation overhead scales with the number of users in FDD systems. In this paper, we propose a novel propagation domain-based user selection scheme, labeled aszero-measurement selection, for FDD massive MIMO systems with the aim of reducing the channel estimation overhead that scales with the number of users. The key idea is to infer downlink user channel norm and inter-user channel correlation from uplink channel in the propagation domain. In zero-measurement selection, the base-station performs downlink user selection before any downlink channel estimation. As a result, the downlink channel estimation overhead for both user selection and beamforming is independent of the total number of users. Then, we evaluate zero-measurement selection with both measured and simulated channels. The results show that zero-measurement selection achieves up to 92.5% weighted sum rate of genie-aided user selection on the average and scales well with both the number of base-station antennas and the number of users. We also employ simulated channels for further performance validation, and the numerical results yield similar observations as the experimental findings.

    

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