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1. Pilot Symbol Aided Channel Estimation for OCDM Transmissions

   https://doi.org/10.1109/LCOMM.2021.3124627  

   Omar, Muhammad Shahmeer; Ma, Xiaoli (November 2021, IEEE Communications Letters)

   Pilot-aided channel estimation allows the receiver to acquire channel state information (CSI) for each multicarrier block by multiplexing data and pilot symbols in the same block, as long as they can be decoupled. This work proposes several frequency-domain pilot multiplexing techniques to enable independent channel estimation and detection at the receiver for orthogonal chirp division multiplexing (OCDM) transmissions in frequency-selective channels. Analysis shows that each of the proposed schemes is able to achieve the mean squared error (MSE) lower bound for channel estimation and has greater spectral efficiency than the existing schemes for OCDM and chirp spread orthogonal frequency division multiplexing (OFDM). 

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2. Semi-Blind Post-Equalizer SINR Estimation and Dual CSI Feedback for Radar-Cellular Coexistence

   https://doi.org/10.1109/TVT.2020.3001911  

   Rao, Raghunandan M; Marojevic, Vuk; Reed, Jeffrey (June 2020, IEEE Transactions on Vehicular Technology)

   Current cellular systems use pilot-aided statistical channel state information (S-CSI) estimation and limited feedback schemes to aid in link adaptation and scheduling decisions. However, in the presence of pulsed radar signals, pilot-aided S-CSI is inaccurate since interference statistics on pilot and nonpilot resources can be different. Moreover, the channel will be bimodal as a result of the periodic interference. In this paper, we propose a max-min heuristic to estimate the post-equalizer SINR in the case of non-pilot pulsed radar interference, and characterize its distribution as a function of noise variance and interference power. We observe that the proposed heuristic incurs low computational complexity, and is robust beyond a certain SINR threshold for different modulation schemes, especially for QPSK. This enables us to develop a comprehensive semi-blind framework to estimate the wideband SINR metric that is commonly used for S-CSI quantization in 3GPP Long-Term Evolution (LTE) and New Radio (NR) networks. Finally, we propose dual CSI feedback for practical radar-cellular spectrum sharing, to enable accurate CSI acquisition in the bimodal channel. We demonstrate significant improvements in throughput, block error rate and retransmission-induced latency for LTE-Advanced Pro when compared to conventional pilot-aided S-CSI estimation and limited feedback schemes. 

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3. Motion Estimation And Filtered Prediction For Dynamic Point Cloud Attribute Compression

   https://doi.org/10.1109/PCS56426.2022.10018071  

   Hong, Haoran; Pavez, Eduardo; Ortega, Antonio; Watanabe, Ryosuke; Nonaka, Keisuke (December 2022, Proc. of Picture Coding Symposium, PCS 2022)

   In point cloud compression, exploiting temporal redundancy for inter predictive coding is challenging because of the irregular geometry. This paper proposes an efficient block-based inter-coding scheme for color attribute compression. The scheme includes integer-precision motion estimation and an adaptive graph based in-loop filtering scheme for improved attribute prediction. The proposed block-based motion estimation scheme consists of an initial motion search that exploits geometric and color attributes, followed by a motion refinement that only minimizes color prediction error. To further improve color prediction, we propose a vertex-domain low-pass graph filtering scheme that can adaptively remove noise from predictors computed from motion estimation with different accuracy. Our experiments demonstrate significant coding gain over state-of-the-art coding methods. 

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4. Keyed Polar Coding for Physical-Layer Security without Channel State Information

   https://doi.org/10.1109/ICC42927.2021.9500357  

   Pinto, Thyago M.; Vilela, Joao P.; Gomes, Marco A.; Harrison, Willie K. (June 2021, International Conference on Communications)

   Polar codes have been shown to provide an effective mechanism for achieving physical-layer security over various wiretap channels. A majority of these schemes require channel state information (CSI) at the encoder for both intended receivers and eavesdroppers. In this paper, we consider a polar coding scheme for secrecy over a Gaussian wiretap channel when no CSI is available. We show that the availability of a shared keystream between friendly parties allows polar codes to be used for both secure and reliable communications, even when the eavesdropper knows a large fraction of the keystream. The scheme relies on a predetermined strategy for partitioning the bits to be encoded into a set of frozen bits and a set of information bits. The frozen bits are filled with bits from the keystream, and we evaluate the security gap when the cyclic redundancy check-aided successive cancellation list decoder is used at both receivers in the wiretap channel model. 

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5. FASURA: A Scheme for Quasi-Static Fading Unsourced Random Access Channels

   https://doi.org/10.1109/TCOMM.2023.3296593  

   Gkagkos, Michail; Narayanan, Krishna R.; Chamberland, Jean-Francois; Georghiades, Costas N. (July 2023, IEEE Transactions on Communications)

   Liva, Gianluigi (Ed.)

   Unsourced random access emerged as a novel wireless paradigm enabling massive device connectivity on the uplink. We consider quasi-static Rayleigh fading wherein the access point has multiple receive antennas and every mobile device a single transmit antenna. The objective is to construct a coding scheme that minimizes the energy-per-bit subject to a maximum probability of error given a fixed message length and a prescribed number of channel uses. Every message is partitioned into two parts: the first determines pilot values and spreading sequences; the remaining bits are encoded using a polar code. The transmitted signal contains two distinct sections. The first features pilots and the second is composed of spread modulated symbols. The receiver has three modules: an energy detector, tasked with recovering the set of active pilot sequences; a bank of Minimum Mean Square Error (MMSE) estimators acting on measurements at the receiver; and a polar list-decoder, which seeks to retrieve the coded information bits. A successive cancellation step is applied to subtract recovered codewords, before the residual signal is fed back to the decoder. Empirical evidence suggests that an appropriate combination of these ideas can outperform state-of-the-art coding techniques when the number of active users exceeds one hundred. 

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