Equalization of a dynamic channel with forward error correction using an adaptive precoder

With the exponential growth of video traffic over wireless networked and embedded devices, mechanisms are needed to predict and control perceptual video quality to meet the quality of experience (QoE) requirements in an energy-efficient way. This paper proposes an energy-efficient QoE support framework for wireless video communications. It consists of two components: 1) a perceptual video quality model that allows the prediction of video quality in real-time and with low complexity, and 2) an application layer energy-efficient and content-aware forward error correction (FEC) scheme for preventing quality degradation caused by network packet losses. The perceptual video quality model characterizes factors related to video content as well as distortion caused by compression and transmission. Prediction of perceptual quality is achieved through a decision tree using a set of observable features from the compressed bitstream and the network. The proposed model can achieve prediction accuracy of 88.9% and 90.5% on two distinct testing sets. Based on the proposed quality model, a novel FEC scheme is introduced to protect video packets from losses during transmission. Given a user-defined perceptual quality requirement, the FEC scheme adjusts the level of protection for different components in a video stream to minimize network overhead. Simulation results show that the proposed FEC scheme can enhance the perceptual quality of videos. Compared to conventional FEC methods for video communications, the proposed FEC scheme can reduce network overhead by 41% on average.

In this chapter, we describe different forward error correction (FEC) schemes currently in use or suitable for use in optical communication systems. We start with the description of standard block codes. The state-of-the-art in optical communication systems standardized by the ITU employ concatenated Bose–Chaudhuri–Hocquenghem (BCH)/RS codes [1, 2]. The RS(255,239), in particular, has been used in a broad range of long-haul communication systems [1, 2], and it is commonly considered as the first-generation of FEC [3, 4]. The elementary FEC schemes (BCH, RS, or convolutional codes) may be combined to design more powerful FEC schemes, e.g., RS(255,239) + RS(255,233). Several classes of concatenation codes are listed in ITU-T G975.1. Different concatenation schemes, such as the concatenation of two RS codes or the concatenation of RS and convolutional codes, are commonly considered as second generation of FEC [3, 4].

This paper shows an important enhancement of TCP behavior over the IEEE 802.11b Wireless Local Area Network (WLAN) if a combination of a Forward Error Correction (FEC) scheme and a Snoop agent is added to the idle Repeat reQuest (RQ) mechanism inherently used by such technology. The FEC scheme has been improved with some smart cross-layer optimizations, and its operation adapts to the channel conditions. Besides, the aim of the Snoop agent is to back up the FEC, overcoming the deficiencies of its adaptation, which are mainly due to the high variability of the channel inside a typical office environment. A complete experimental approach has been followed, and exhaustive measurement campaigns have been carried out over a real platform to derive a large number of performance parameters. Both methods have been implemented as modules belonging to a generic layer-two Performance Enhancing Proxy (PEP).

It is well-known that Vectored Digital Subscriber Line (DSL) transmission promises significant theoretical data-rate increases for DSL technology; however, Vectored DSL requires full knowledge of the channel. The effectiveness of Vectored DSL transmission in a practical setting, where channel knowledge is subject to error, has yet to be determined. This paper proposes a Generalized Regression Neural Network (GRNN)-based approach to DSL channel estimation by interpolating between a subset of measured or estimated data-points. Furthermore, closed-form expressions for the effect of channel estimation error on he achievable Vectored DSL data-rate are derived, using a Zero-Forcing (ZF) interference canceller for upstream transmission and a Diagonalizing Pre-coder (DP) for downstream transmission. Finally, simulation results are provided to demonstrate the performance loss associated with channel estimation error for Vectored DSL transmission, based on the ANN approach and a linear regression approach.

Cell rate moderation of VBR video under an FEC environment in ATM networks

This paper presents an effective packet loss recovery scheme for Internet Protocol (IP) based peer-to-pear (P2P) networks that deliver multimedia streaming contents. The proposed scheme consists of two key components, a packet forward error correction (FEC) scheme and a uniquely decodable coding (UDC) scheme. The FEC scheme is devised to recover network packet loss over the transport layer to improve link transmission reliability at the user-ends of the P2P networks. The UDC scheme is employed to allow multiple sources to transmit data streams simultaneously in such a way that the combined data streams can be separated uniquely without ambiguity at the user-ends. This simultaneous multiple sources data transmission increases the throughput at the user-ends. Theoretical analysis and computer simulations show that the proposed scheme can achieve the commonly acceptable of 10^{-6} end-to-end packet loss rate for input packet loss rate of up to 10%with a reasonably small bandwidth expansion factor, while maintains a high throughput at the user-ends.

The unequal error protection (UEP) has shown promising results for transmitting video over error-prone wireless channels. In this paper, we investigate the cross-layer design of forward error correction (FEC) schemes by using the UEP Raptor codes at the application layer (AL) and UEP rate compatible punctured convolutional (RCPC) codes at physical layer (PHY) for prioritized video packets. The video packets are prioritized based on their contribution to the received video quality. A genetic algorithm (GA)-based optimization algorithm is proposed to find the optimal parameters for both Raptor and RCPC codes, to minimize the video distortion and maximize the peak signal-to-noise-ratio for the given video bit rates and channel constraints (i.e., SNR and available bandwidth). We evaluate the performance of four combinations of the UEP schemes for H.264/AVC encoded video sequences over the AWGN and Rayleigh fading channels and show the superiority of the optimized cross-layer UEP FEC scheme. For Rayleigh fading channel, the proposed cross-layer optimization uses two different time-scales at AL and PHY which allows PHY to adapt faster to the changing channel quality.

This paper considers equalization of the slow fading channel for a serial data transmission application. Linear and decision-feedback adaptive equalization techniques are contrasted. The error propagation effect in decision-feedback equalizers is analyzed by a Markov process model. The error probability magnification is computed for both fixed and fading channels and for both binary and quaternary phase-shift-keying (PSK) transmission. The results show that the error propagation effect is small and in regions of practical error probabilities the decision-feedback equalizer is superior to its linear counterpart. Parameters of a practical decisionfeedback equalizer are estimated and a performance evaluation is performed. The implicit diversity gain is shown to be significant and the intersymbol interference penalty is found to be less than 1 dB. Because the intersymbol interference penalty is small, more complex nonlinear processors such as the Viterbi algorithm cannot be recommended for this application. Time jitter effects for the equalizer are included in a calculation of average error probability.

The author presents a proposal for solving the problem of reduced performance of coded modulation due to colored channel noise by whitening the noise with an added noise predictor in the decision-feedback equalizer (DFE). This also has the benefit of increasing the nominal SNR. The resulting equalizer has a structure encompassing as a special case the noise-predictive DFE proposed earlier by others. Several numerical examples are provided to illustrate the digital subscriber line transmission performance with the new noise-predictive DFE. It is shown that the added noise predictor improves the transmission performance in two ways: first, it decorrelates the noise, and second, it decreases the noise power by its prediction gain.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In this work, we innovatively equalize optical intensity-modulated and directly detected (IMDD) four-level pulse amplitude modulation (PAM-4) signals using a complex-valued decision feedback equalizer (CDFE). Through mapping adjacent symbols of PAM-4 signals onto the complex domain, the influence of strongest inter-symbol interference (ISI) can be alleviated during the decision process in a decision feedback equalizer (DFE), effectively combating burst-error propagation when signals are noisy. Moreover, signal-adaptive manipulations of DFE parameters in both the time and the amplitude domain are performed by using an ultra-stable timing recovery and level-adaptive decision. Performance evaluations are made on vertical cavity surface emitting laser (VCSEL) modulated and multimode fiber (MMF) transmitted 100-Gbit/s optical PAM-4 signals. Based on experimental results of the short-reach optical communication, the proposed DFE outperforms the traditional DFE with a 0.5-dB system power budget gain at the 7% overhead (OH) forward error correction (FEC) bit error rate (BER) threshold.

In this paper, a receiver driven overlap Forward Error Correction (FEC) scheme, which offers unequal importance protection of video layers, is proposed to protect H.264/SVC video over the Internet. A mathematical model is provided to calculate video quality in terms of subjective Video Quality Metric (VQM). With the provided mathematical model, the video server prepares for receivers a lookup table, which lists all optimal combinations of video and FEC layers under various available downlink bandwidth and packet drop rates. By table lookup, a receiver can determine an optimal combination of video and FEC layers to subscribe to maximize the subjective video quality based on its available downlink bandwidth and packet drop rates.

This paper investigates how Scalable Video Coding (SVC) can benefit from different Forward Error Correction (FEC) and transmission schemes in mobile broadcast systems. Simulation are performed in DVB-H (Digital Video Broadcasting - Handheld) systems. In DVB-H, a differentiation in robustness for the different SVC layers can be achieved at the link layer using intra-burst MPE-FEC (multi-Protocol Encapsulation FEC). The paper evaluates the gain that can be achieved with the MPE-FEC using equal (EEP) and unequal error protection (UEP), and the performance improvements of an SVC layer-aware FEC (LA-FEC) approach that can be implemented in DVB-H either at the link layer with MPE-iFEC (inter-burst MPE-FEC) or at the application layer with AL-FEC. LA-FEC improves the SVC base layer robustness generating parity information across existing dependencies within the SVC video coding structure. Laboratory measurement results using a TU6 channel model show that the performance of an SVC service in DVB-H can be significantly increased by a proper link layer FEC scheme. It is shown that using SVC in combination with LA-FEC and a proper transmission scheduling does not only give a better performance in terms of PSNR and amount of video outages compared to a single layer service at the same service bit rate, but also gives an additional lower quality layer which can be used for applications like conditional access.

Interpolated decision feedback equalization for long intersymbol interference channels

This thesis summarizes research on the design and implementation of the unequal error protection (UEP) mechanism for the RaptorQ forward error correction (FEC) scheme. As part of this research, existing UEP mechanisms for various fountain codes were evaluated. Two new UEP methods were proposed for the RaptorQ coding scheme, and these methods were designed with the assumption that all of the symbols in a source block have the same priority. The first method, known as priority based overhead number (PBON), was based on the priority encoding transmission model, wherein the error-correction capability was altered by making the number of overhead symbols proportional to the priority of the information symbols. This method was extended to the RaptorQ codes with some changes and evaluated for failure probability and performance. The second method, known as priority based precode ratio (PBPR), was designed by changing the precode properties of the RaptorQ codes. The ratio of precode symbols to Luby-Transform symbols in the RaptorQ codes was changed to achieve different error correction capabilities for each priority group. The scheme with the higher number of precode symbols provided superior error-correction capabilities compared to those with fewer precode symbols. Both methods were empirically verified through simulation in the C++ programming language. The results demonstrated that the higher-importance class depicted a better error-correction capability than the lower-importance class.

In the end-to-end voice communication networks, the packet losses caused by network congestion and wireless channel errors reduce the efficiency of the forward error correction (FEC) scheme. Especially for mobile VoIP, network congestion and wireless channel status changed very fast. This paper presents an adaptive FEC that can adaptive adjust and predict the FEC block according to the network status.