A Staggered FEC System for Seamless Handoff in Wireless LANs: Implementation Experience and Experimental Study

We report the design, implementation and evaluation of Merged Hybrid ARQ with staggered FEC (MHARQ) system for video multicast over wireless LANs. MHARQ combines the advantages of receiver-driven staggered FEC and hybrid ARQ schemes to compensate the large dynamic range of WLAN channels and to achieve high reliability, scalability and wireless bandwidth efficiency for video multicast. The FEC packets generated by a cross-packet FEC code are divided into multiple streams according to the pre-configured overhead and are transmitted in different multiple IP multicast groups. Certain FEC streams are delayed from the original video stream. The receivers dynamically join/leave the FEC multicast groups based on the channel conditions. For efficient utilization of WLAN bandwidth, FEC data for a multicast group would not be transmitted by the APs in wireless networks if no receiver joins this group. The time shift between the video stream and the FEC streams introduces temporal diversity and compensates for the client join delay and handoff interruption. In addition, when delayed FEC packets are not enough to recover the lost packets, the receivers can send a hybrid ARQ request to the video server. We design a channel estimation algorithm for a receiver to dynamically determine the delayed FEC multicast groups to join and/or send ARQ NACK to request for retransmission. Using the ORBIT radio grid testbed, we have investigated the performance of the proposed MHARQ system with various numbers of users per AP and different number of APs per video server. It is demonstrated via real system implementation on ORBIT that MHARQ improves wireless bandwidth efficiency and scalability for reliable video multicast, compared with existing reliable multicast schemes.

This paper presents a high-performance BCH-LDPC concatenated forward error correction (FEC) system under the DVB-S2 standard, with hardware implementation on FPGA. For the BCH encoder, a four-bit parallel circular shift register architecture was designed and implemented based on theoretical derivation, ensuring full compatibility with all generator polynomials specified in the standard. Furthermore, an enhanced FiBM (Further-optimized Inverse-free Berlekamp–Massey) algorithm, derived from the RiBM (Reformulated Inverse-Free BM) algorithm, was adopted for error locator polynomial computation. By optimizing the iterative structure, the proposed algorithm effectively reduces the critical path delay, thereby supporting high-speed decoding. For the LDPC decoder, a pipelined architecture based on the layered Min-Sum algorithm was developed. By systematically analyzing the structural properties of the DVB-S2 parity-check matrix, the layer scheduling and pipeline optimization strategy for check nodes were redesigned, which substantially reduces pipeline stalls and decoding latency. Experimental results demonstrate that the proposed FPGA implementation significantly improves system throughput.

This paper presents a constructive discussion and inclusive review on advancements in the coded modulation free-space optical (FSO) communication system and corresponding techniques. These techniques mainly include channel model, forward error correction (FEC) and modulation schemes. Firstly, a complete view of FSO system is presented which contains the description, the current research situation along with the advantages over the traditional radio frequency (RF) wireless communication and fiber optical communications. Then, the channel model, FEC, modulation schemes and complete system of coded modulation FSO are analyzed successively. At last, the review work of coded modulation FSO system is summarized and further improvements are prospected.

Traditional Forward Error Correction (FEC) mechanisms can be divided into Packet level FEC (PFEC) mechanisms and Byte level FEC (BFEC) mechanisms. The PFEC mechanism of recovering from errors in a source packet requires an entire FEC redundant packet even though the error involves a few bit errors. The recovery capability of the BFEC mechanism is only half of the FEC redundancy. Accordingly, an adaptive Sub-Packet FEC (SPFEC) mechanism is proposed in this paper to improve the quality of video streaming data over wireless networks, simultaneously enhancing the recovery performance and reducing the end-to-end delay jitter. The SPFEC mechanism divides a packet into n sub-packets by means of the concept of a virtual packet. The SPFEC mechanism uses a checksum in each sub-packet to identify the position of the error sub-packet. Simulation experiments show the adaptive SPFEC mechanism achieves high recovery performance and low end-to-end delay jitter. The SPFEC mechanism outperforms traditional FEC mechanism in terms of packet loss rate and video Peak Signal-to-Noise Ratio (PSNR). SPFEC offers an alternative for improved efficiency video streaming that will be of interest to the designers of the next generation environments.

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).

Peer-2-Peer (P2P) technologies are rapidly advancing and have already proven successful in the form of various bandwidth demanding applications such as file-transfer and video streaming. The major advantage of the P2P technologies is its built-in scalability feature, relative to traditional client- server architecture. Therefore, keeping in view the large number of users involved in live video-streaming, P2P technology can be considered as a valuable tool aiming to broadcast live-video contents to a large number of users over the internet. Although, there is lot of research going on in analyzing the performance of P2P video streaming in heterogeneous networking scenarios, but to the best of our knowledge no work is done in analyzing the impact of Forward Error Correction (FEC) on the performance of P2P live-video streaming. In this paper we analyze the performance and characteristics of P2P live-video streaming on end-user quality of experience while employing FEC on the coded video packets. Additionally, in-order to carry out the performance analysis with reference to non-error protected benchmarker system; we utilized a realistic realtime French distributed Grid facility known as Grid'5000. More specifically, the performance of the system is evaluated while considering various realistic P2P video streaming constraints, such as limited playout delay, limited upload bandwidth and video rates. We concluded that the FEC will result in noticeable performance improvement in a scenario where each peer is connected with limited number of other peers that have the required contents for download. In such a situation the portion of the stream corrupted due to channel errors may not be recovered with the help of other accessible peers. However, if each peer has more connected peers with various alternative options to download the corrupted contents, then the employment of FEC may not have very noticeable advantage on the performance of the P2P video streaming system.

The preference improvement resulting from modifications to the original ARQ scheme proposed by E.J. Weldon (1982) for use in systems with finite-receiver buffers was analyzed in a previous paper. A modification involving the use of parity retransmission is studied. One drawback of using forward error correcting (FEC) codes is that the parity bits result in a degradation in efficiency under good channel conditions: the maximum throughput is limited to the FEC code rate. Two type II ARQ schemes which overcome this problem are studied. Lower bounds on the throughputs of the two schemes are obtained. The throughput of the type II ARQ scheme is no longer limited by one-half the rate of the FEC code used. Under good channel conditions, the throughput with the type II ARQ scheme is equivalent to not using FEC; as the channel degrades, it approaches the throughput with a rate one-half FEC code.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

There are two kinds of technique used for error control: FEC (forward error correction) and ARQ (automatic repeat request). Combining these two schemes, which is called HARQ (hybrid ARQ), makes it possible to increase the channel throughput. The error of the channel quality estimate that is used to select the MCS (modulation coding scheme) in type I HARQ can be a serious problem in scenarios when the mobile station moves at high speeds. Furthermore, in a system dominated by packet services, the interference level may be bursty, and thus it is difficult to predict the interference level. Therefore, the type II HARQ scheme is a more robust solution compared with type I HARQ. In order to improve channel throughput while at the same time satisfying quality of service (QoS) under various channel conditions, an efficient hybrid ARQ type II scheme is proposed. The optimum redundancy size for every transmission is calculated to maximize the throughput using QoS parameters, the performance of LDPC code and channel conditions. The proposed scheme, together with such benefits as QoS support, provides a way of achieving higher throughput in wireless communication systems.

In order to realize lower power consumption multi-Gbps communications terminals in 60 GHz, this paper proposes a single carrier with FEC (Forward error correction) communications system together with a beam tracking and switching receiver antenna. In the proposed system, communications path will be switched from the LOS (line of sight) path to one of the best S/N path when the LOS path is interrupted by a moving object such as human body and continue the communications. The advantage of the proposed system is to have smaller delay spread that will make no necessity of OFDM (Orthogonal Frequency Division Multiplexing) as a tool to mitigate huge delay spread which is commonly observed in WLAN (Wireless LAN) systems. To validate the proposed system, this paper took the channel models created by IEEE802.15.3c std. in that TX and RX antennas are facing each other and reflected waves are received from all directions (360 degrees) at the RX antenna. The difference created on top of the TG3c channel model is to track and switch the RX antenna to the best S/N reflected wave when the system lost the LOS path. In this way, much smaller delay spread is expected in the proposed system which will lead to no necessity of OFDM signal transmission. The computer simulation results show bit error rate performances of the proposed system has very little degradation by applying strong FEC of “convolutional encoding and Viterbi decoding”, leading to potential necessity of equalizer for further bit error rate improvement but no necessity of OFDM signal transmission. Thus, the proposed system is good for multi-Gbps transmission over low power consumption portable terminals in 60 GHz.

In this paper, we discuss the effect of wireless link characteristics and mobility in wireless access broadband networks, and how major differences between wireline and wireless transmission links introduce a new networking paradigm with difficult and interesting challenges. We show that these differences have a direct impact on the packet-level quality-of-service defined by the packet loss, delay and jitter statistics. Moreover, we examine a number of alternatives such as forward error correction, antenna diversity and retransmission schemes to combat the time varying nature and high bit error rate of the wireless link, as well as how much and in what way these schemes can improve the packet-level quality-of-service. We also show that routing, call admission control, and capacity allocation functions of wireless access broadband networks need to take mobility into account. These functions can be invoked in a reactive manner at every hand-off event, or they can be invoked in a pro-active manner at the call setup time instead of being invoked at every hand-off event. In addition, we discuss the trade-offs between these two call control schemes, and show that each of these schemes is associated with a major cost. To find a balance between the cost of these two call control schemes, we use a connection tree as a basis for routing, call admission control, and resource allocation in wireless access broadband networks.

Recently, an efficient error performance scheme named as labeling diversity has been proposed in the literature for wireless local area network (WLAN). This paper proposes labeling diversity for 8-phase shift keying (8-PSK) modulation named as boosted space-time scheme. A pair of labeling map is opted for this scheme by maximizing the utility function in asymptotic coding gain under the supposition of error-free feedback. Furthermore, labeling diversity is employed with the space-time forward error correction (FEC) codes like convolution and turbo codes for point to point communication scenarios. Since non-line of sight (NLOS) point to point communication scenario is assumed therefore Rayleigh distributed channel model is selected which remains constant for single space-time block code (STBC). The STBC used in boosted space-time scheme is non-orthogonal therefore maximum likelihood (ML) soft de-mapper is employed at the receiver. The convergence of iterative decoding between soft de-mapper and decoder is analyzed by the extrinsic information transfer (EXIT) chart. The validity of the convergence of iterative decoding is also verified by Monte Carlo simulation. It is evident from the simulation results that bit error rate (BER) performance of boosted space-time scheme is superior to the conventional spacetime scheme under identical conditions. Moreover, the boosted space-time scheme with convolution code performs better for low signal-to-noise ratio (SNR) regime in comparison to boosted space-time scheme with turbo code. However, for high SNR regime, turbo coding scheme outperforms the convolution scheme. In addition, turbo coding scheme provides better BER performance to the convolution scheme under non-iterative decoding.

Path and server diversities have been used to guarantee reliable video streaming communication over wireless networks. In this paper, server diversity over mobile wireless ad hoc networks (MANETs) is implemented. Particularly, multipoint-to-point transmission together with multiple description coding (MDC) and forward error correction (FEC) technique is used to enhance the quality of service of video streaming over the wireless lossy networks. Additionally, the dynamic source routing (DSR) protocol is used to discover maximally disjoint routes for each sender and to distribute the workload evenly within the MANETs for video streaming applications. NS-2 Simulation study demonstrates the feasibility of the proposed mechanism and it shows that the approach achieves better quality of video streaming, in terms of the playable frame rate, reliability and real-time performance on the receiving side.

Forward error correction (FEC) techniques are essential for optical core and optical access networks. In optical core networks, the emphasis is on high coding gains and extremely low output bit error rates, while allowing decoder realizations to operate at a throughput of 100 Gb/s and above. Optical access networks operate at 10 Gb/s or above and require low-complexity FEC codes with low power consumption. Coherent optical transmission with higher order modulation formats will become mandatory to achieve the high spectral efficiencies required in next-generation core networks. In this paper, we provide an overview of these requirements and techniques, and highlight how coding and modulation can be best combined in optical core networks. We also present guidelines for modulation and low-complexity FEC system design for optical access networks.

Compared with unicast, video multicast over 802.11 WLANs should handle varying channel conditions of multiple users and user topology changes as well as scalability to achieve good quality for all users in the serving area. This paper analyzes error control strategies available in different layers of the network stack, including modulation and channel coding in physical layer, cross-packet Forward Error Correction (FEC), packet size optimization and scalable video coding in application layer. By combining and adapting these schemes jointly, an adaptive cross layer optimization algorithm is proposed for scalable video multicast over 802.11 WLANs. Based on a variety of criteria, improvement in overall video quality for all the targeted users can be achieved.

This paper investigates the transmission of H.264 /AVC video in the 3GPP Multimedia Broadcast/Multicast Streaming service (MBMS). Application-layer forward error correction (FEC) codes are used to combat transmission errors in the radio access network. In this FEC protection scheme, the media RTP stream is organized into source blocks spanning many RTP packets, over which FEC repair packets are generated. This paper proposes a novel method for unequal error protection that is applicable in MBMS. The method reduces the expected tune-in delay when a new user joins into a broadcast. It is based on four steps. First, temporally scalable H.264 /AVC streams are coded including reference and non-reference pictures or sub-sequences. Second, the constituent pictures of a group of pictures (GOP) are grouped according to their temporal scalability layer. Third, the interleaved packetization mode of RFC3984 is used to transmit the groups in ascending order of relevance for decoding. As an example, the non-reference pictures of a GOP are sent earlier than the reference pictures of the GOP. Fourth, each group is considered a source block for FEC coding and the strength of the FEC is selected according to its importance. Simulations show that the proposed method improves the quality of the received video stream and decreases the expected tune-in delay.