Performance of ATM networks under hybrid ARQ/FEC error controlscheme

In ATM networks, fixed-length cells are transmitted. A cell may be discarded during the transmission due to buffer overflow or detection of errors. Cell discarding seriously degrades transmission quality. This paper analyzes a hybrid automatic repeat request/forward error control (ARQ/FEC) cell-loss recovery scheme that is applied to virtual circuits (VCs) of ATM networks. FEC is performed based on a simple single-parity code, while a Go-Back-N ARQ is employed on top of that. Both throughput efficiency and reliability analysis of the hybrid scheme are presented. In the process we investigate the interactive effects of the network parameters (number of transit nodes, traffic intensity, ARQ packet length, …) on the performance. The analysis provides a method for optimizing the FEC code size for a given network specification     

突发信道下无线ATM的前向差错控制方案

在无线ATM网络中，无线信道的高误码率和突发特性要求对无线ATM信元进行较强的误码保护。本文提出了一种有效的前向差错控制（FEC）方案，对信元头采用较强的FEC，对信息域采用较弱的FEC，并针对信道特性和采用的前向差错控制编码的特点进行元头信元内交织，文中对无线ATM信元在突发信道下的信元丢失率和信元信息错误率进行了分析，仿真结果表明该方案在降低信元信息错误率的同时有效地降低了信元丢失率。     

Cell discard and TDMA synchronization using FEC in wireless ATMsystems

The asynchronous transfer mode (ATM) employs header-error control (HEC) to protect the ATM cell header from bit error and/or avoid the misforwarding of ATM cells. However, wireless ATM systems require a more powerful forward-error correction (FEC) scheme to offer acceptable bit-error rate (BER) performance. This paper proposes the utilization of FEC, which makes it possible to discard ATM cells more reliably. Time-division multiple-access (TDMA) is very suitable for wireless ATM systems. In the TDMA scheme, synchronization is very important. This paper also proposes to combine FEC with unique word (UW) detection for improving TDMA synchronization characteristics     

Sliding‐window forward error correction using Reed‐Solomon code and unequal error protection for real‐time streaming video

Forward error correction (FEC) techniques are widely used to recover packet losses over unreliable networks in real‐time video streaming applications. Traditional frame‐level FEC encodes 1 video frame in each FEC coding window. By contrast, in the expanding‐window FEC scheme, high‐priority frames are included in the FEC processing of the following frames, so as to construct a larger coding window. In general, expanding‐window FEC improves the recovery performance of FEC, because the high‐priority frame can be protected by multiple windows and the use of a larger coding window increases the efficiency. However, the larger window size also increases the complexity of the coding and the memory space requirements. Consequently, expanding‐window FEC is limited in terms of practical applications. Sliding‐window FEC adopts a fixed window size in order to approximate the performance of the expanding‐window FEC method, but with a reduced complexity. Previous studies on sliding‐window FEC have generally adopted an equal error protection (EEP) mechanism to simplify the analysis. This paper considers the more practical case of an unequal error protection (UEP) strategy. An analytical model is derived for estimating the playable frame rate (PFR) of the proposed sliding‐window FEC scheme with a Reed‐Solomon erasure code for real‐time non‐scalable streaming applications. The analytical model is used to determine the optimal FEC configuration which maximizes the PFR value under given transmission rate constraints. The simulation results show that the proposed sliding‐window scheme achieves almost the same performance as the expanding‐window scheme, but with a significantly lower computational complexity.     

Turbo乘积码在卫星ATM系统中的应用

Turbo乘积码(TPC)是一种性能优异的前向纠错编码技术.卫星ATM技术代表了卫星通信网络的研究方向.研究了TPC在卫星ATM系统中的应用方案.首先,分析了卫星信道对ATM信元传输带来的影响;然后对TPC的编、解码的方法进行了简要介绍,并阐述了TPC的优越性能;最后,提出了一种卫星ATM网络中应用TPC的解决方案,并通过仿真得到了该方案的性能曲线.仿真结果证明,TPC的应用能够大幅降低卫星信道的误码率,使ATM信元能够正确传输.     

A novel adaptive hybrid ARQ scheme for wireless ATM networks

This paper describes the design and performance of a novel adaptive hybrid ARQ scheme using concatenated FEC codes for error control over wireless ATM networks. The wireless links are characterized by higher, time‐varying error rates and burstier error patterns in comparison with the fiber‐based links for which ATM was designed. The purpose of the hybrid ARQ scheme is to provide a capability to dynamically support reliable ATM‐based transport over wireless channels by using a combination of our ARQ scheme (called SDLP) and the concatenated FEC scheme. The key ideas in the proposed hybrid ARQ scheme are to adapt the code rate to the channel conditions using incremental redundancy and to increase the starting code rate as much as possible with the concatenated FEC, maximizing the throughput efficiency. The numerical results show that our proposed scheme outperforms other ARQ schemes for all SNR values. This revised version was published online in July 2006 with corrections to the Cover Date.     

A modified topology achieved in OFDM/SAC-OCDMA-based multi-diagonal code for enhancing spectral efficiency

In this paper, a modified topology-based orthogonal frequency division multiplexing–spectral amplitude coding in optical code division multiple access (OFDM–SAC-OCDMA) has been introduced. Such analysis aims to explain the effect of spectral efficiency with respect to multi-diagonal (MD) code. The new proposed technique introduces a fusion system between the two-code keying scheme and the forward error correction (FEC). The introduced analysis has targeted the effect of signal-to-noise ratio, bit error rate, and spectral efficiency with the presence of beat noise, phase incoherent intensity noise, and thermal noise. Numerical simulations have been utilized and tested in order to illustrate the validation of the (MD) code method to eliminate dominant noise. The calculation results show the following; the SNR and BER for MD under the presence of the previous discussed signal degradation is equal 161 and 1.2?×?10^?10, respectively, according to a predefined number of users 150 comparing with some existing codes such as: modified frequency hopping code, Hadamard (HD) code, modified quadratic congruence code. The proposed unipolar encoding with direct detection technique-based OFDM/SAC-OCDMA scheme achieves an enhancement in the performance of SE over the unipolar encoding with direct detection technique-based SAC-OCDMA technique by 3.455 dB. The proposed two keying scheme-based OFDM/SAC-OCDMA introduces an enhancement in the performance of the SE over the unipolar encoding with direct detection technique-based OFDM/SAC-OCDMA technique by 2.8859 dB. FEC has been applied in order to increase the spectral efficiency for different BERs, which the numerical results show that FEC provides 1.7457 dB. Finally, the total enhancement for SE was about 8.0866 dB.

     

A new cell loss recovery method using forward error correction in ATM networks

A new method using an FEC technique is proposed to enhance the ability of consecutive cell loss compensation due to buffer overflow in ATM networks. This article summarizes different applications of cell loss recovery, and presents the design of a new coding scheme and the coding/decoding algorithm. © 1998 John Wiley & Sons, Ltd.     

An adaptive FEC scheme for data traffic in wireless ATM networks

A new adaptive forward-error-correction scheme (AFEC) is introduced at the link layer for TCP/IP data traffic in wireless ATM networks. The fading and interference in wireless links cause high and variable error rates, as well as bursty errors. The purpose of the AFEC scheme is to provide a dynamic error-control mechanism by using Reed-Solomon coding to protect the ATM cell payload, as well as the payload type indicator/cell loss priority fields in the ATM cell header. In order to enhance the error tolerance in cell framing and correct delivery, the AFEC scheme functions within a new concept called LANET framing and addressing protection mechanisms. The AFEC scheme has been validated using a simulation testbed of a low-speed wireless ATM network     

A spread slotted CDMA/ALOHA system with hybrid ARQ for satellitemultiple access

We propose and investigate a new type of satellite multiple access protocol that combines the characteristics of the spread slotted (SS)-ALOHA protocol, code division multiple access (CDMA), and the hybrid automatic repeat request (ARQ) error controlling and retransmission scheme, in order to increase the throughput by reducing the number of retransmissions and to keep the bit error rate (BER) of the satellite link low when the channel experiences heavy traffic. The main feature of our proposed system is the utilization of two different fields in the analysis of the satellite multiple access problem. Since the hub now possesses the forward error correction (FEC) capability to correct errors that appear after the CDMA despreading of the packets, the satellite does not need to ask so often for the retransmission of erroneous packets and will ask for retransmission only when the FEC error correcting capability is exceeded. This paper also presents the adaptive optimization of the balance between the CDMA processing gain and FEC coding gain in order to obtain a better throughput for the SS-CDMA/ALOHA with hybrid ARQ protocol for satellite multiple access. The optimization is made with the constraint of keeping the bandwidth of the transmitted packets constant during all times. According to this, the effective throughput of the protocol (information bits over total transmitted bits ratio) is improved by adaptively changing the CDMA and FEC codes used in the transmission. This adaptive optimization is done by observing the channel status or load and increasing or decreasing both coding schemes' gains. Computer simulations show the performance of the proposed multiple access scheme     

Performance of transmitted reference pulse cluster ultra‐wideband systems with forward error correction

Recently, an improved transmitted reference (TR) signaling scheme, referred to as transmitted reference pulse cluster (TRPC), was proposed for low‐rate ultra‐wideband (UWB) communications. Compared with conventional TR, TRPC has a more compact and uniform spacing for the reference and data pulses and therefore addresses the implementation problems posed by the long delay line requirement, as well as provides better bit error rate (BER) performance. In this paper, a TRPC‐UWB system, which includes practical forward error correction (FEC) coding such as that specified in the IEEE 802.15.4a standard, as well as more powerful convolutional codes, is developed. A performance analysis, which highlights the importance of selecting appropriate FEC codes, is presented. Results show that with a suitable FEC code, the TRPC‐UWB system is a promising candidate for low‐rate wireless personal area networks. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficient adaptive forward error control schemes for Ka-band satellite systems

Adaptive fade margin is required to counter the severe but varying rain attenuation in K_a-band satellite communications. In a search for a suitable rain countermeasure, the effectiveness of adaptive forward error control (AFEC) schemes is studied. Two AFEC schemes using convolution codes and concatenated codes are proposed and their performances analysed. The schemes can provide progressively adaptive fade margins of 10-1 and 10-4 dB, respectively, in excess of the system's fixed fade margin. To improve the efficient use of shared resources of the system, an AFEC scheme using double coding is introduced and its performance analysed. In this scheme a single codec is used repeatedly, resulting in reduced hardware cost and increased use. By using convolutional code and Golay code the above scheme can provide adaptive fade margins of 10°8 dB and 8°1 dB, respectively. Although concatenated codes have slightly better performance than double codes, the hardware implementation and decoding complexity of the latter are significantly less. Implementation complexity of AFEC resource sharing in the light of code complexity, time frame expansion, link condition monitoring and signalling is discussed in detail.     

Fast turbo codes with space‐time block codes in fast fading channels

In this paper, space‐time block coding has been used in conjunction with Turbo codes to provide good diversity and coding gains. A new method of dividing turbo encoder and decoder into several parallel encoding and decoding blocks is considered. These blocks work simultaneously and yield a faster coding scheme in comparison to classical Turbo codes. The system concatenates fast Turbo coding as an outer code with Alamouti's G2 space‐time block coding scheme as an inner code, achieving benefits associated with both techniques including acceptable diversity and coding gain as well as short coding delay. In this paper, fast fading Rayleigh and Rician channels are considered for discussion. For Rayleigh fading channels, a fixed frame size and channel memory length of 5000 and 10, respectively, the coding gain is 7.5 dB and bit error rate (BER) of 10^?4 is achieved at 7 dB. For the same frame size and channel memory length, Rician fading channel yields the same BER at about 4.5 dB. Copyright © 2013 John Wiley & Sons, Ltd.     

ATM‐based multimedia communication via NGSO‐satellites

Future broadband satellite networks for multimedia will be seamlessly integrated into terrestrial broadband networks which often use asynchronous transfer mode (ATM) and recently also the less complex multi protocol label switching (MPLS) technique as transmission and switching protocol. In light of this, future broadband satellite networks may adopt the ATM transmission scheme and implement ATM or ATM‐like switches on board the satellites. However, as compared to communication in fixed networks, satellite communication is characterized by special constraints (e.g. signal delay, channel quality, dynamic network topology) that require novel ATM‐based communication technology for satellite systems. This paper presents results from the ATM‐Sat project that aims to complete this technically challenging and important R&D task in the cooperation between DLR, Fraunhofer Gesellschaft and Tesat‐Spacecom. In brief the following aspects have been addressed in the ATM‐Sat project:

• development of the concept and communication technology for a multimedia satellite system with,
  • non‐geostationary orbit (NGSO) satellites;
  • inter satellite links (ISLs);
  • on‐board ATM switching;
  • fixed and mobile terminals;
• verification of the developed communication technology with a demonstrator.

In particular the ATM‐Sat R&D tasks cover the system and protocol architecture, on‐board processing, ISL routing, up/downlink and on board ATM resource management (including medium access control), error control, IP over satellite‐ATM, and active intelligent antennas. Copyright © 2005 John Wiley & Sons, Ltd.     

采用自适应FEC的卫星ATM网络的有效带宽估计

该文针对采用自适应FEC(AFEC)的卫星ATM网络,研究了两种用于接纳控制的有效带宽估计方法,由于AFEC码率的动态特性使业务实际的传输速率具有不固定性,因此估计有效带宽时要考虑AFEC的影响,作者首先针对一般卫星时变信道和多码率AFEC情况下的卫星ATM,应用流体近似方法分析了有效带宽的计算,然而该方法要求的条件及计算复杂度均比较高,应用中有局限性。以此方法为基础,作者又提出了采用修正因子的估计方法,数值结果表明采用修正因子的有效带宽估计方法比较简单可靠,适用面较广。     

Adaptive predistortion of COFDM signals for a mobile satellite channel

In this paper, we consider the optimization of the performance of QPSK and 16‐QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non‐linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non‐linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non‐linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10^?3 when compared to QPSK COFDM without the predistortion scheme and 16‐QAM COFDM provides a gain of 0.5 dB output back‐off and 1.2 dB signal to noise ratio at a BER of 3×10^?5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10^?4 for QPSK and 16‐QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Interleaved coding and sequential transmission scheme for packet‐level forward error correction over burst loss channels

Burst packet loss is a common problem over wired and wireless networks and leads to a significant reduction in the performance of packet‐level forward error correction (FEC) schemes used to recover packet losses during transmission. Traditional FEC interleaving methods adopt the sequential coding‐interleaved transmission (SCIT) process to encode the FEC packets sequentially and reorder the packet transmission sequence. Consequently, the burst loss effect can be mitigated at the expense of an increased end‐to‐end delay. Alternatively, the reversed interleaving scheme, namely, interleaved coding‐sequential transmission (ICST), performs FEC coding in an interleaved manner and transmits the packets sequentially based on their generation order in the application. In this study, the analytical FEC model is constructed to evaluate the performance of the SCIT and ICST schemes. From the analysis results, it can be observed that the interleaving delay of ICST FEC is reduced by transmitting the source packets immediately as they arrive from the application. Accordingly, an Enhanced ICST scheme is further proposed to trade the saved interleaving time for a greater interleaving capacity, and the corresponding packet loss rate can be minimized under a given delay constraint. The simulation results show that the Enhanced ICST scheme achieves a lower packet loss rate and a higher peak signal‐to‐noise‐ratio than the traditional SCIT and ICST schemes for video streaming applications.     

A Bandwidth Efficient Turbo Coding Scheme for VDSL Systems

The current forward error correction (FEC) scheme for very high bit-rate digital subscriber line (VDSL) systems in the ANSI standard employs a 16-state four-dimensional (4D) Wei code as the inner code and the Reed-Solomon (RS) code as the outer code. The major drawback of this scheme is that further improvement cannot be achieved without a substantial increase in the complexity and power penalty. Also, a VDSL system employing the 4D Wei-RS scheme operates far below the channel capacity. In 1993, powerful turbo codes were introduced whose performance closely approaches the Shannon limit. In this paper, we propose a bandwidth and power efficient turbo coding scheme for VDSL modems in order to obtain high data rates, extended loop reach and increased transmission robustness. We also propose a pipelined decoding scheme to reduce the latency at the receiver end. The objective of the proposed scheme is to provide a higher coding gain than that given by the 4D Wei-RS scheme, resulting in an improved performance of the VDSL modems in terms of bit rate, loop length and transmitting power. The scheme is investigated for various values of transmitting power, signaling frequencies and numbers of crosstalkers for a targeted bit error rate of 10⁻⁵ and is implemented in a system with a quadrature amplitude modulation in which a mixed set partitioning mapping is employed to reduce the decoding complexity. The effects of code complexity, interleaver length, the number of decoding iterations and the level of modulation on the performance of VDSL modems are explored. Simulation results are presented and compared to those of the 4D Wei-RS scheme. The results show that the choice of turbo codes not only provides a significant coding gain over the standard FEC scheme but also efficiently maximizes the loop length and bit rate at a very low transmitting power in the presence of dominant far-end crosstalk and intersymbol interference. In order to compare the hardware complexity, we synthesize the proposed and 4D Wei-RS schemes using SYNOPSYS with the target technology of Xilinx 4020e-3. The Xilinx field programmable gate array statistics of the proposed scheme is compared with that of the 4D Wei-RS scheme.     

A novel methodology for robust VBR video transmission in an ATM system

A dynamic FEC (DFEC) scheme for VBR video in ATM networks is proposed. The scheme combines the design of source encoder, error control, and the network. In the design, we will develop a methodology to vary FEC redundancy dynamically. The methodology considers the fluctuations in video source and network utilisation to adjust the FEC redundancy levels. We demonstrate the effectiveness of the proposed scheme by examining its performance with three existing schemes in terms of loss rates, throughput, and quality degradation. Copyright © 2002 John Wiley & Sons, Ltd.