More Like this

1. Block Soft Decision Feedback Turbo Equalization for Orthogonal Signal-Division Multiplexing Underwater Acoustic Communications

   Xiangzhao Qin, Fengzhong Qu ( September 2019 , MTS/IEEE Oceans)

   Orthogonal signal-division multiplexing (OSDM) is one of the generalized modulation schemes that bring the gap between orthogonal frequency division multiplexing (OFDM) and single carrier frequency domain equalization (SC-FDE). By performing encoding upon subvectors of each interleaved block, it enjoys a flexible resource management with low peakto- average power ratio (PAPR). Meanwhile, the OSDM induces the intervector interference (IVI) inherently, which requires a more powerful equalizer. By deriving the input and output system model, this paper proposes a time domain soft decision feedback equalizer (SDFE) on per vector equalization with successful soft interference cancellation (SSIC). In addition, this paper takes the whole OSDM block to perform the channel encoding rather than on each vector of the OSDM. Simulation and experimental results demonstrate that the proposed SDFE with SSIC structure outperforms the conventional minimum mean square error (MMSE) equalizer and the block encoding (BE) scheme outperforms the vector encoding (VE) scheme, because theoretically the longer the encoded bit stream is, the more stable and more confident the maximum a posteriori probability (MAP) decoder will be. 

   more » « less
2. Bayesian Iterative Channel Estimation and Turbo Equalization for Multiple-Input–Multiple-Output Underwater Acoustic Communications

   https://doi.org/10.1109/JOE.2019.2956299  

   Qin, Xiangzhao ; Qu, Fengzhong ; Zheng, Yahong Rosa ( July 2020 , IEEE Journal of Oceanic Engineering)

   This article investigates a robust receiver scheme for a single carrier, multiple-input–multiple-output (MIMO) underwater acoustic (UWA) communications, which uses the sparse Bayesian learning algorithm for iterative channel estimation embedded in Turbo equalization (TEQ). We derive a block-wise sparse Bayesian learning framework modeling the spatial correlation of the MIMO UWA channels, where a more robust expectation–maximization algorithm is proposed for updating the joint estimates of channel impulse response, residual noise, and channel covariance matrix. By exploiting the spatially correlated sparsity of MIMO UWA channels and the second-order a priori channel statistics from the training sequence, the proposed Bayesian channel estimator enjoys not only relatively low complexity but also more stable control of the hyperparameters that determine the channel sparsity and recovery accuracy. Moreover, this article proposes a low complexity space-time soft decision feedback equalizer (ST-SDFE) with successive soft interference cancellation. Evaluated by the undersea 2008 Surface Processes and Acoustic Communications Experiment, the improved sparse Bayesian learning channel estimation algorithm outperforms the conventional Bayesian algorithms in terms of the robustness and complexity, while enjoying better estimation accuracy than the orthogonal matching pursuit and the improved proportionate normalized least mean squares algorithms. We have also verified that the proposed ST-SDFE TEQ significantly outperforms the low-complexity minimum mean square error TEQ in terms of the bit error rate and error propagation. 

   more » « less
3. The Effects of Narrowband Interference on OCDM

   https://doi.org/10.1109/SPAWC48557.2020.9154217  

   Omar, Muhammad Shahmeer ; Ma, Xiaoli ( May 2020 , 2020 IEEE 21st International Workshop on Signal Processing Advances in Wireless Communications (SPAWC))

   null (Ed.)

   Abstract: Orthogonal chirp division multiplexing (OCDM) is a fairly new multi-carrier modulation scheme that has been proposed for optical fiber communications. It spreads data over an entire band using a set of linear chirps that are mutually orthogonal thus achieving the maximum spectral efficiency. This paper analyzes the performance of OCDM in wireless multi-path channels with narrow band interference (NBI) and in doing so shows that linear minimum mean squared error (MMSE) equalization exhibits an interesting signal-to-noise ratio (SNR) dependent degradation in error performance caused by interference amplification at high SNR. Furthermore, it employs a variant of the MMSE equalizer when the interference energy is known to prevent interference amplification and improve the error performance. 

   more » « less
4. Cross Evaluation of Multiple Access Schemes Using Post-Experimental Field Data for Underwater Acoustic Communications

   Xiangzhao Qin, Y. Rosa ( September 2019 , MTS/IEEE Oceans Conf)

   This paper proposes a post-experimental field data reuse method to test the single carrier modulation (SCM) and orthogonal frequency division multiplexing (OFDM) signals interchangeably for multiple access underwater acoustic (UWA) communications. We call this approach the cross evaluation that transforms a set of SCM or OFDM post-experimental field data to their corresponding OFDM or SCM scheme under test (SUT) via linear matrix operation such as fast Fourier transform (FFT) and its inverse (IFFT). At the receiver side, we derived a general framework of turbo equalization (TEQ) that alters the two physical layer schemes but keeps the passband transmitted and received data unchanged. Inherently, some efficient techniques such as pre-cursor and post-cursor interference cancellation (IC), and overlap adding (OLA) operations enhance the equivalence of input and output (I/O) system model between the SCM and OFDM. The proposed approach will bring the gap between the SCM and OFDM, and evaluate the two physical layer schemes under similar or tougher test conditions. The experimental results of the undersea 2008 Surface Processes and Acoustic Communications Experiment (SPACE08) have verified the feasibility of the cross evaluation approach in terms of the BER benchmark. 

   more » « less
5. 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). 

   more » « less