Omar Hazim Salim

Channel, Phase Noise, and Frequency Offset in OFDM Systems: Joint Estimation, Data Detection, and Hybrid Cramér-Rao Lower Bound

Oscillator phase noise (PHN) and carrier frequency offset (CFO) can adversely impact the performance of orthogonal frequency division multiplexing (OFDM) systems, since they can result in inter carrier interference and rotation of the signal constellation. In this paper, we propose an expectation conditional maximization (ECM) based algorithm for joint estimation of channel, PHN, and CFO in OFDM systems. We present the signal model for the estimation problem and derive the hybrid Cramér-Rao lower bound (HCRB) for the joint estimation problem. Next, we propose an iterative receiver based on an extended Kalman filter for joint data detection and PHN tracking. Numerical results show that, compared to existing algorithms, the performance of the proposed ECM-based estimator is closer to the derived HCRB and outperforms the existing estimation algorithms at moderate-to-high signal-to-noise ratio (SNR). In addition, the combined estimation algorithm and iterative receiver are more computationally efficient than existing algorithms and result in improved average uncoded and coded bit error rate (BER) performance.

An efficient unequal error protection scheme for 3-D video transmission

In this paper, we propose a new unequal error protection (UEP) scheme, called video packet partitioning for three-dimensional (3-D) video transmission. We also propose a new 3-D video transceiver structure that adopts various UEP schemes based on the packet partitioning. The proposed schemes are applied for the modern 3-D video techniques, i.e., multiview video coding (MVC) and color plus depth (VpD). The schemes for MVC and VpD are tested over cooperative multiinput multi-output-orthogonal division multiplexing (MIMOOFDM) systems. For channel adaptation, we propose switching operations between the proposed schemes to achieve a trade-off between the system complexity and performance. Experimental results show that the proposed schemes significantly achieve high video quality at different signal-to-noise ratios (SNRs) in the wireless channel with the lowest possible bandwidth and system complexity compared to the direct transmission schemes.

A novel unequal error protection scheme for 3-D video transmission over cooperative MIMO-OFDM systems

Currently, there has been intensive research to drive three-dimensional (3-D) video technology over mobile devices. Most recently, multi-input multi-output (MIMO) with orthogonal frequency division multiplexing (OFDM) and cooperative diversity have been major candidates for the fourth-generation mobile TV systems. This article presents a novel unequal error protection (UEP) scheme for 3-D video transmission over cooperative MIMO-OFDM systems. Several 3-D video coding techniques are investigated to find the best method for 3-D video transmission over the error-prone wireless channels. View plus depth (VpD) has been found the best technique over other techniques such as simulcast coding (SC) and mixed-resolution stereo coding (MRSC) in terms of the performance. Various UEP schemes are proposed to protect the VpD signals with different importance levels. Seven video transmission schemes for VpD are proposed depending on partitioning the video packets or sending them directly with different levels of protection. An adaptive technique based on a classified group of pictures (GoP) packets according to their protection priority is adopted in the proposed UEP schemes. The adaptive method depends on dividing GoP to many packet groups (PG’s). Each PG is classified to high-priority (HP) and low-priority (LP) packets. This classification depends on the current signal-to-noise ratio (SNR) in the wireless channels. A concatenating form of the rate-variable low-density parity-check (LDPC) codes and the MIMO system based on diversity of space-time block codes (STBC) is employed for protecting the prioritized video packets unequally with different channel code rates. For channel adaptation, the switching operations between the proposed schemes are employed to achieve a tradeoff between complexity and performance of the proposed system. Finally, three protocols for 3-D video transmission are proposed to achieve high video quality at different SNRs with the lowest possible bandwidth.

Prioritized 3-D Video Transmission over Cooperative MIMO-OFDM Systems

Multi-input multi-output (MIMO) systems with orthogonal frequency division multiplexing (OFDM), cooperative communication and three-dimensional (3-D) video coding are state-of-the-art techniques. The combination between cooperative and MIMO systems is crucial to provide high data rates with high quality of 3-D video services. By taking their advantages, this paper presents 3-D video transmission over cooperative MIMO-OFDM systems. Unequal error protection schemes are proposed to protect the 3-D video signal with different important levels. This is achieved by partitioning the compressed 3-D video sequences based on packets partitioning or sending the 3-D video signal with different levels of protection. A concatenating form of the rate-variable low-density parity-check (LDPC) codes and MIMO system based on diversity space-time block code (STBC) is employed, where the sum-product algorithm (SPA) is utilized for LDPC. For channel adaptation, a switching operation between UEP schemes is proposed to achieve a trade-off between performance of the 3-D video system and changes in the wireless channel. Simulation results demonstrate the effectiveness of proposed schemes.

Joint channel, phase noise, and carrier frequency offset estimation in cooperative OFDM systems

Cooperative communication systems employ cooperation among nodes in a wireless network to increase data throughput and robustness to signal fading. However, such advantages are only possible if there exist perfect synchronization among all nodes. Impairments like channel multipath, time varying phase noise (PHN) and carrier frequency offset (CFO) result in the loss of synchronization and diversity performance of cooperative communication systems. Joint estimation of these multiple impairments is necessary in order to correctly decode the received signal in cooperative systems. In this paper, we propose an iterative pilot-aided algorithm based on expectation conditional maximization (ECM) for joint estimation of multipath channels, Wiener PHNs, and CFOs in amplify-and-forward (AF) based cooperative orthogonal frequency division multiplexing (OFDM) system. Numerical results show that the proposed estimator achieves mean square error performance close to the derived hybrid Cramer-Rao lower bound (HCRB) for different PHN variances.

Phase noise and carrier frequency offset in OFDM systems: Joint estimation and hybrid Cramér-Rao lower bound

In this paper, a new iterative pilot-aided algorithm based on expectation conditional maximization (ECM) for joint estimation of Wiener phase noise (PHN) and carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) systems is proposed. Next, a new expression for the hybrid Cramér-Rao lower bound (HCRB) for joint estimation of PHN and CFO in OFDM systems is derived. Numerical results show that the proposed estimator outperforms existing algorithms in terms of mean square error while performing close to the derived HCRB at moderate PHN variances. Moreover, the proposed estimator is found to be computationally more efficient than existing algorithms since it jointly estimates PHN and CFO in a few iterations.

Multi-Relay Communications in the Presence of Phase Noise and Carrier Frequency Offsets

Impairments such as time varying phase noise (PHN) and carrier frequency offset (CFO) result in loss of synchronization and poor performance of multi-relay communication systems. Joint estimation of these impairments is necessary in order to correctly decode the received signal at the destination. In this paper, we address spectrally efficient multi-relay transmission scenarios where all the relays simultaneously communicate with the destination. We propose an iterative pilot-aided algorithm based on the expectation conditional maximization for joint estimation of multipath channels, Wiener PHNs, and CFOs in decode-and-forward-based multi-relay orthogonal frequency division multiplexing systems. Next, a new expression of the hybrid Cramér–Rao lower bound (HCRB) for the multi-parameter estimation problem is derived. Finally, an iterative receiver based on an extended Kalman filter for joint data detection and PHN tracking is employed. Numerical results show that the proposed estimator outperforms existing algorithms and its mean square error performance is close to the derived HCRB at different signal-to-noise ratios for different PHN variances. In addition, the combined estimation algorithm and the iterative receiver can significantly improve average bit-error rate (BER) performance compared with existing algorithms. In addition, the BER performance of the proposed system is close to the ideal case of perfect channel impulse responses, PHNs, and CFOs estimation.

Cross-layer optimization for 3-D video transmission over cooperative relay systems

The rate budget constraint and the available instantaneous signal-to-noise ratio of the best relay selection in cooperative systems can dramatically impact the system performance and complexity of video applications, since they determine the video distortion. By taking into account these constrained factors, we first outline the signal model and formulate the system optimization problem. Next, we propose a new approach to cross-layer optimization for 3-D video transmission over cooperative relay systems. We propose procedures for estimation of the end-to-end instantaneous signal-to-noise ratio using an estimate of the available instantaneous signal-to-noise ratios between the source-destination, and source-relay-destination before starting to send the video signal to the best relay and destination. A novel approach using Lagrange multipliers is developed to solve the optimum bit allocation problem. Based on the rate budget constraint and the estimated the end-to-end instantaneous signal-to-noise ratio, the proposed joint source-channel coding (JSCC) algorithm simultaneously assigns source code rates for the application layer, the number of high and low priority packets for the network layer, and channel code rates for the physical layer based on criteria that maximize the quality of video, whilst minimizing the complexity of the system. Finally, we investigate the impact of the estimated the end-to-end instantaneous signal-to-noise ratio on the video system performance and complexity. Experimental results show that the proposed JSCC algorithm outperforms existing algorithms in terms of peak signal-to-noise ratio. Moreover, the proposed JSCC algorithm is found to be computationally more efficient since it can minimize the overall video distortion in a few iterations. HighlightsA novel optimization algorithm using Lagrange multiplier is proposed to solve the optimum problem.We investigate the impacts of relay selection on the video system performance.Estimation procedures of the total SNR are proposed to control the source and destination nodes.We investigate the impacts of total instantaneous SNR estimation on the video system performance.The performance of video system is very sensitive to the accuracy of the total SNR estimation.

Adaptive allocation of variable length codes for video transmission over OFDM system

This paper proposes a sub-channel partitioning based on adaptive allocation of Variable Length Codes (VLCs) with Unequal Error Protection (UEP) scheme for Orthogonal Frequency Division Multiplexing (OFDM) system. In this scheme, video data is partitioned into high-priority (HP) and low-priority (LP) coefficients according to the importance of the data, then it is allocated to sub-channels for transmission over OFDM system. A proposed technique is applied by interleaving the Resynchronization Markers between VLCs to isolate the propagation of error over video stream and completed by another technique to improve the performance of the video decoder decision at lower values of Signal to Interference Noise Ratio (SINR).