FEC Code Research Articles

Adaptive-Truncated-HARQ-Aided Layered Video Streaming Relying on Interlayer FEC Coding

Interlayer forward error correction (IL-FEC) coding constitutes an effective unequal error protection (UEP) scheme conceived for transmitting layered video over wireless channels. In contrast to traditional UEP schemes, it operates by embedding extra information concerning the base layer (BL) into the enhancement layers (ELs) without requiring extra transmission resources. The received EL packets assist in the decoding of the BL to reduce the distortion of the reconstructed video. The optimum scheduling of the IL-FEC coded layered video streaming in a truncated hybrid automatic repeat request (THARQ)-aided system is an open problem. Hence, in this paper, we conceive an adaptive THARQ (ATHARQ) algorithm for finding the most appropriate scheduling of the IL-FEC coded layered video packets for the sake of minimizing the video distortion under the constraint of a given total number of transmission time slots (TSs). Furthermore, we develop a method of online coding-rate optimization algorithm for our IL-ATHARQ transmission scheme to find the best FEC code rate distribution among the video layers that results in the lowest possible video distortion. When using a recursive systematic convolutional (RSC) code, our simulation results show that the proposed rate-optimized (RO) IL-ATHARQ system outperforms the traditional THARQ transmission scheme by about 5.3 dB of $E_{b}/N_{0}$ at a peak signal-to-noise ratio (PSNR) of 38.5 dB. Viewing the improvements in terms of the video quality, 2.5 dB of PSNR improvement is attained at an $E_{b}/N_{0}$ of 15 dB.

Error Rate Performance of OFDM Transceiver on Software-defined Radio

2 Abstract: This work is focused on an efficient model of OFDM transceiver with the help of software-defined radio (SDR) system with reconfigurable architecture for wireless communications. SDR possesses revolutionary developments such as algorithm implementation of digital communication and increased computing capabilities. In the paper, OFDM system design and implementation with novel technology development is the primary focus to be studied. Different modulation techniques of OFDM system and other related concepts like PAPR also taken into consideration in order to design the OFDM System. FEC coding is performed by suggesting Convolutional coders. In this paper, bit error rate and symbol error rates performance are analyzed by varying bits per symbol, window size and modulation scheme. Results proved that BER values are improved as modulation scheme size (M) is increased. Moreover, IEEE 802.11a standards are implemented. BPSK modulation with Radix-2 FFT, OFDM transceiver design is implemented using commercial Amitec SDR04 and configured by GNU radio companion in the laboratory environment.

Turbo equalization for single-carrier underwater acoustic communications

Recent research in underwater acoustic communications has taken advantage of MIMO technologies to achieve reliable communication with 10–100 times increase of data rate in comparison to traditional systems. The powerful turbo equalization and FEC coding techniques enable both single-carrier modulation and OFDM systems to combat triply selective UWA channels. This article reviews the time-domain and frequency-domain turbo equalizer schemes for MIMO SCM systems. Low-complexity techniques are presented with both turbo linear equalizers and turbo soft decision feedback equalizers in both the time and frequency domains. Although results are shown specifically for UWA channels, these turbo equalizer techniques are also suitable for terrestrial RF communication systems.

Network throughput analysis of IEEE 802.15.4 enabled wireless sensor networks with FEC coding under external interference

IEEE 802.15.4 enabled wireless sensor networks are often impacted by the coexistence of different sources of external interference sharing the ISM band. Such external interference may significantly deteriorate achievable wireless sensor network throughputs due to uncontrollable collisions of interference transmissions with IEEE 802.15.4 packets. Forward error correction may be considered as a mechanism to alleviate the resiliency of IEEE 802.15.4 packets against partial collisions due to interference. In this paper, theoretical analysis of network throughput of IEEE 802.15.4 enabled wireless sensor networks under external interference with deployment of FEC will be presented. The throughput performance of IEEE 802.15.4 network under FEC deployment is governed by the percentage of collided bits within IEEE 802.15.4 coded payloads that the FEC code can withstand. The analysis in this paper considers convolutional codes as FEC candidate codes for IEEE 802.15.4 networks and proceeds to theoretically derive collision percentage thresholds that convolutional codes may tolerate under Viterbi decoding. Numerical results indicate that an optimal FEC coding rate exists for a given IEEE 802.15.4 and external interference configuration. The optimal coding rate introduces enough resiliency for the IEEE 802.15.4 transmissions to withstand external interference. Any additional redundancy bits for more robust codes would render unneeded protection that unnecessarily reduces the goodput of IEEE 802.15.4 networks.

FPGA implementation of concatenated non-binary QC-LDPC codes for high-speed optical transport.

In this paper, we propose a soft-decision-based FEC scheme that is the concatenation of a non-binary LDPC code and hard-decision FEC code. The proposed NB-LDPC + RS with overhead of 27.06% provides a superior NCG of 11.9dB at a post-FEC BER of 10-15. As a result, the proposed NB-LDPC codes represent the strong FEC candidate of soft-decision FEC for beyond 100Gb/s optical transmission systems.

Let MultiBand-OFDM Modified By Wavelet

This paper throws light on elevating the performance of MB-OFDM by diverse techniques. The initiative was that the wavelet transform altered the place of FFT and IFFT. The use of the wavelet transform can be ascribed to the fact that it counteracts various types of interference. Implementation of various modulation techniques refines the performance. The order of the wavelet transforms used should remain conducive to establish it as an efficient system for high data rates. As an outcome of noise the output of the channel is erroneous. Hence error control codes are utilized which aims at the removal of error from the transmitted bits. Further to achieve diversity space time block codes are concatenated with FEC codes. Keywords: Fast Fourier Transform (FFT), Multiband OFDM, Neural Network, Space Time Block Code (STBC), Ultra Wide Band, Wavelet Transform

Transmission of 16-QAM OFDM Signal with Secure Strategy Technique in DD-OOFDM Systems

The physical layer of optical access network is vulnerable to various attacks. As the dramatic increase of users and network capacity, the issue of physical-layer security becomes more and more important. This paper proposes a physical-enhanced secure strategy for DD-OOFDM system by employing frequency domain chaos scrambling. The FEC coding can also improve the system performance and will not influence the encrypt process. A 2.5Gb/s 16QAM LDPC-OFDM data with Logistic mapped chaos scrambling are successfully transmitted over 40km SSMF. The results show that security sequences protect the system from attacker and keep a good performance for legal receiver.

Layered Wireless Video Relying on Minimum-Distortion Inter-Layer FEC Coding

Layered video coding is capable of progressively refining the reconstructed video quality with the aid of multiple layers of unequal importance. When the base layer (BL) is corrupted or lost due to channel impairments, the enhancement layers (ELs) must be discarded by the video decoder, regardless whether they are perfectly decoded or not, which implies that the transmission power assigned to the ELs is wasted. To circumvent this problem, we proposed a bit-level inter-layer forward error correction (IL-FEC) scheme for layered video transmission in our previous work, which implanted the systematic bits of the BL into the systematic bits of the ELs using exclusive-OR operations (XOR). This allowed the receiver to exploit the implanted bits of the ELs for assisting the BL's decoding and hence improved the overall system performance of our IL-FEC aided layered video scheme. In this treatise, we find the specific FEC coding rates in a real-time on-line fashion for the sake optimizing the overall system performance. The proposed procedure is widely applicable to diverse wireless transceivers and FEC codecs. Our simulation results show that the proposed optimized IL-FEC system outperforms the traditional optimal UEP by about 1.9 dB of Eb/N0 at a peak signal-to-noise ratio (PSNR) of 38 dB. Viewing the improvements in terms of the video quality, 3.3 dB of PSNR improvement is attained at an Eb/N0 of 10 dB, when employing a recursive systematic convolutional (RSC) code.

FPGA Implementation of Viterbi Algorithm for Decoding of Convolution Codes

Abstract: Convolutional code is a coding scheme used in communication systems including deep space communications and wireless communications. It provides an alternative approach to block codes for transmission over a noisy channel. The block codes can be applied only for the block of data. The Convolutional coding has an advantage over the block codes in that it can be applied to a continuous data stream as well as to blocks of data. Viterbi decoder employed in digital wireless communication plays a rife role in the overall power consumption of trellis coded modulation decoder. Power reduction in Viterbi decoder could be achieved by reducing the number of states. A pre-computation architecture with T-algorithm was implemented for this purpose, and when we compare this result with full Trellis Viterbi decoder, this approach significantly reduces power consumption without degrading decoding speed. Convolutional encoding with viterbi decoding is a powerful FEC technique that is particularly suited to a channel in which the transmitted signal is corrupted mainly by Additive White Gaussian Noise (AWGN). It operates on data stream and has memory that uses previous bits to encode. The Viterbi Algorithm (VA) is proposed, used for decoding a bit stream that has been encoded using FEC code. The Convolutional encoder adds redundancy to a continuous stream of input data by using a linear shift register. A pre-computation architecture with Viterbi algorithm is implemented for this purpose, Viterbi (Convolutional) encoder and Viterbi decoder are designed and implemented using FPGA technology, which are the essential blocks in digital communication systems. It is particularly suited to a channel in which the transmitted signal is corrupted mainly by AWGN. The Viterbi decoder of Constraint length 7 and code rate 1⁄2 is considered. The design is implemented using verilog on Xilinx Spartan 3E and advanced Spartan 6 board and the results and Comparisons are presented.

Analysis of the Convergence Process by EXIT Charts for Parallel Implementations of Turbo Decoders

Iterative process is a general principle in decoding powerful FEC codes such as turbo codes. However, the mutual information exchange during the iterative process is not easy to analyze and to describe. A useful technique to help the designer is the EXtrinsic Information Transfer (EXIT) chart. Unfortunately, this method cannot be directly applied to the decoding convergence analysis if parallel processing has to be exploited for the design of turbo decoders. In this letter, an extension of the EXIT charts method is proposed in order to take into account the constraints introduced by parallel implementations. The corresponding analysis associated with Monte-Carlo simulations gives additional understanding of the convergence process for the design of parallel architectures dedicated to turbo decoding.

Analysis and Design of Noncoherent Ultra-wideband Transceiver with FEC Coding for u-Home Networks

Analysis and Design of Noncoherent Ultra-wideband Transceiver with FEC Coding for u-Home Networks

PHY modulation/rate control for fountain codes in 802.11a/g WLANs

In this paper we consider the joint performance of fountain codes and 802.11a/g PHY modulation/coding. We consider optimality both in terms of maximizing goodput and minimizing energy, and results are presented for both theoretical and experimental channel models. In contrast to studies in cellular networks, we find that in 802.11a/g WLANs the cross-layer approach of a higher-layer fountain coding with a PHY layer modulation and FEC coding can yield very limited gains, and the PHY modulation/rate that optimizes the uncoded multicast performance is also close to that for fountain-coded multicast traffic over a wide-range of network conditions. This is potentially an important observation as it indicates that in 802.11a/g WLANs cross-layer design for multicast rate control would bring few benefits and PHY layer rate control can be carried out without regard to the use of fountain coding at higher layers.

Coded QAM Backscatter Modulation for RFID

Radio Frequency Identification (RFID) systems, presently standardized under EPC Global Class-1 Gen-2, have attracted increasing interest as the next-generation technology for tagged object identification. One of the important objectives of this work is to highlight the fact that the performance of the backscatter uplink (determined by constellation choice and forward error correction) is coupled to the downlink via the power harvesting functionality. The concept of normalized power loss per bit is introduced for such RFID communication systems to capture the consequent trade-offs, that form the crux of the results. We explore the use of higher dimensional (4-QAM) modulation schemes in future RFID systems (beyond current binary modulation in Class-1 Gen 2) as a means to improve uplink bit rate. However, this results in significantly increased normalized power loss vis-a-vis 2-PSK, suggesting a role for FEC coding. New coded modulation schemes - based on unequal error protection - are proposed that provides additional degrees of freedom (via choice of code parameters) to trade-off spectral efficiency with normalized power loss. This is explored and quantified, resulting in design recommendations.

Robust Network FEC-Embedded Video Transmission Over Error-Prone Wireless Channels

Most wireless networks incline to include FEC code (Forward error correction) to recover the corrupted packets without retransmission. The sequential packets transmitted over wireless channel are likely to be infected with various errors like noise or deep fading. In this paper, therefore, a frame-level FEC is added across packets at the application layer to define two analytical packet loss models. At the network layer level, Gilbert Elliot Model (GEM) and Extended Gilbert Model (EGM) are considered to characterize the MPEG-4 packets loss over the bursty error-prone wireless channels. The resultant video quality in terms of playable frame rate (PFR) is estimated at the client end when using the underlying TCP-Friendly protocol. Numerical results point out that the EGM-FEC model introduces a robust measure in estimating the perceived video quality in particular at higher packet loss rate and lower effect of packet correlation. Moreover, it is also found that the GEM-FEC model outperforms EGM-FEC but when ignoring the effect of packet correlation.

Proposal for Robust and Adaptive Forward Error Correction for real-time Audio-Video streaming solutions

In this paper, we present a robust and adaptive forward error correction technique for high end Audio-Video Streaming solutions. This solution targets all kinds of network loss conditions and can be used in any embedded platforms. This technique uses optimum solution for packet loss recovery that involves switching between adaptive FEC based packet loss recovery and retransmission management. Whenever network loss increases the permissible limit of adaptive FEC loss recovery, then it switches to re-transmission of media. Adaptive FEC based packet loss recovery works on best of adaptive matrix size selection, loss recovery method selection (on-the-fly or store and compute) and FEC codec selection (Parity 1D, 2D, Raptor, Read Solomon and Hamming etc.) This technique also incorporates support for embedded systems which do not have much computation power. For such embedded systems, the adaptive FEC recovery technique switches to fixed matrix of having store and save approach for single and burst packet loss recovery. This technique provides inter-operability w.r.t FEC codec selection which also takes care of embedded system capability. Keywords - Adaptive FEC, Adaptive matrix size, FEC coding (Parity 1D, 2D, Raptor, read-soloman, hamming etc.), , FEC SDP negotiation, packet loss calculation techniques

H-ARQ Techniques for Wireless Systems with Punctured Non-Binary LDPC as FEC Code

H-ARQ Techniques for Wireless Systems with Punctured Non-Binary LDPC as FEC Code

Performance response of wireless channels for quantitatively different loss and arrival statistics

In this paper we propose a cross-layer performance evaluation framework for wireless channels and subsequently explore the performance response at the FEC and ARQ enabled data-link layer in terms of frame losses and delays for different first- and second-order error and arrival statistics. For a wireless channel model to be appropriate for various FEC capabilities without the need for extensive measurements of the frame error process for each particular FEC code, the error process of the wireless channel is modeled at the physical layer. We assume weak stationary property for bit error observations and model them using a hidden Markov model. The associated parameters matching algorithm allows us to explicitly capture bit error rate and lag-1 autocorrelation of the bit error process. To explore the performance response of the wireless channel at the data-link layer, a cross-layer extension of the bit error model to the data-link layer is then developed. The performance of applications is evaluated using the queuing-theoretic approach that allows both arrival and error processes to be autocorrelated and still retains analytical tractability. The proposed methodology allows us to obtain estimators of frame loss and delay probabilities in the presence of FEC and ARQ procedures at the data-link layer eliminating the need for time-consuming simulations and extensive measurements of wireless channel characteristics for different error correction capabilities of the data-link layer. It is analytical in nature, efficient for small and moderate frame sizes and suitable for performance control purposes where fixed size frames are used at the data-link layer. Particularly, it provides a way to choose the required correction capability of the FEC code resulting in best possible performance at the data-link layer. Numerical results indicate that first- and second-order bit error and frame arrival statistics significantly affect performance parameters provided by a wireless channel and should be taken into account when choosing an appropriate correction capability of the FEC code for given wireless channel conditions.

Robust video broadcasting over 802.11a/g in time-correlated fading channels

In order to deliver video streams efficiently over WiFi to many thousands of consumer handheld devices, broadcast protocols must be employed. In this mode of operation the received video quality can deteriorate rapidly as a result of high application layer packet loss which occurs because MAC frame retransmission cannot be used. In this paper we develop a robust video delivery solution for broadcast transmission over 802.11a/g. Using a cross-layer WiFi simulator in combination with an accurate time-correlated fading channel, the received video quality is evaluated for broadcast H.264 video sequences. Application layer cross-packet forward error correction is then used together with error concealment at the video client. Furthermore, the application of an external packet interleaver is considered. Combining a block size of two hundred packets (which introduces a 4.8 second delay) and an application layer FEC code rate of 0.75 our results demonstrate that video can be successfully broadcast over WiFi to many thousands of handheld terminals at large-scale spectator events.

A Model-Based Approach to Evaluation of the Efficacy of FEC Coding in Combating Network Packet Losses

We propose a model-based analytic approach for evaluating the overall efficacy of FEC coding combined with interleaving in combating packet losses in IP networks. In particular, by modeling the network path in terms of a single bottleneck node, described as a G/M/1/K queue, we develop a recursive procedure for the exact evaluation of the packet-loss statistics for general arrival processes, based on the framework originally introduced by Cidon et al., 1993. To include the effects of interleaving, we incorporate a discrete-time Markov chain (DTMC) into our analytic framework. We study both single-session and multiple-session scenarios, and provide a simple algorithm for the more complicated multiple-session scenario. We show that the unified approach provides an integrated framework for exploring the tradeoffs between the key coding parameters; specifically, interleaving depths, channel coding rates and block lengths. The approach facilitates the selection of optimal coding strategies for different multimedia applications with various user quality-of-service (QoS) requirements and system constraints. We also provide an information-theoretic bound on the performance achievable with FEC coding in IP networks.

Joint Source and Channel Coding for 3-D Scene Databases Using Vector Quantization and Embedded Parity Objects

Three-dimensional graphic scenes contain various mesh objects in one geometric space where different objects have potentially unequal importance regarding display. This paper proposes an object-oriented system for efficiently coding and streaming 3-D scene databases in lossy and rate-constrained environments. Vector quantization (VQ) is exploited to code 3-D scene databases into multiresolution hierarchies. For the best distortion-rate performance, adaptive quantization precisions are allocated to different objects and different layers of each object based on a weighted distortion model. Upon transmission, scalably coded objects are delivered in respective packet sequences to preserve their manipulation independency. For packet loss resilience, a plurality of FEC codes are generated as "parity objects" parallel to graphic objects, which protect the graphic objects concurrently and also preferentially in regard to their unequal decoding importance. A rate-distortion optimization framework is then developed, which performs rate allocation between graphic objects and parity objects and generates the parity data properly. We show that, by treating graphic objects jointly and preferentially in source and channel coding while preserving their independencies in transport, the proposed system reduces the receiving distortion of the 3-D database significantly compared to conventional methods.