A New Transport Protocol for Broadcasting/Multicasting MPEG-2 Video Over Wireless ATM Access Networks

Because of the telecommunications de-regulation act and progress in wireless technologies, we will see the co-existence of heterogeneous broadband access infrastructures in the broadband video service industry in the near future. In this paper, we addressed the error control issue when transmitting MPEG-2 video streams over wireless access networks for broadband video broadcast or multicast services. An end-to-end transport protocol based on ATM and wireless ATM technologies is proposed. For video services, the underlying transport network should be transparent and quality should be maintained uniformly over all the segments whether wireline or wireless links. For network resources to be used efficiently, error control should be applied locally on the wireless segments so as to avoid the excessive overhead over the reliable wireline portions. Because a broadband video broadcast or multicast service is a one-to-multiple point service, FEC is the most prevalent error control mechanism. Due to the important role of MPEG-2 control information in the decoding process, priority MPEG-2 control information has to be differentiated from MPEG-2 data information, and excess error protection has to be allocated to it in order to achieve satisfactory QoS. Therefore, a header redundancy FEC (HRFEC) scheme for error control is applied at the local distribution centers before the MPEG-2 encoded video streams are transmitted over the wireless channels. HRFEC is an FEC-based selective protection scheme, which allocates extra error protection to important control information. Simulation results show that the quality of the reconstructed video sequence is vastly improved by using HRFEC, when the channel condition is poor.     

无线视频传输容错算法研究新进展

视频信号经过压缩编码后通过Rayleigh衰减无线信道传输，容易受到突发性错误的影响，造成视频传输质量下降。容错(error resilience)是保证无线视频传输质量的重要措施。本文首先对几种无线信道模型进行了概括与比较，然后总结了各种容错算法的优缺点和最新研究进展情况。重点讨论了在传输层实施的前向纠错编码(FEC)和反馈差错控制，在编码器端根据不同的信道传输特性所采用的容错算法，包括帧内刷新、长期限存储、分层编码和多描述编码。本文还通过一种传输方案对容错策略的组合实施情况进行了分析。最后探讨了无线视频传输容错算法的发展趋势和挑战，提出了几个值得重视的发展方向。     

An efficient protocol architecture for error-resilient MPEG-2 videocommunications over ATM networks

MPEG-2 video communications over ATM networks is one of the most active research areas in the field of computer communications. In the transmission process of a variable bit rate video signal over an ATM network, cells are inevitably exposed to delays, errors and losses due to the statistical multiplexing used in these networks. These phenomena affect the quality of the video signal and without adequate measures to control the propagation of the impairments the quality of the service may fall below acceptable levels. In this paper, we study the impact of cell losses on the quality of a MPEG-2 video sequence encoded in a variable bit rate mode. We introduce a set of control mechanisms at different levels of the protocol architecture to be used in MPEG-2-based video communications systems using ATM networks as their underlying transmission mechanism. Our results (using different video sequences) show the effectiveness to improve the video quality by using a structured set of control mechanisms to overcome for the loss of cells carrying VBR MPEG-2 video streams. We argue that in order to be able to create video systems able to cope with cell losses encountered in computer communications systems, a structured set of error-resilient protocol mechanisms is needed     

Loss-resilient ATM protocol architecture for MPEG-2 videocommunications

MPEG-2 video communications over ATM networks is one of the most active research areas in the field of computer communications. In the transmission process of a variable bit rate video signal over an ATM network, cells are inevitably exposed to delays, errors, and losses due to the statistical multiplexing used in these networks. These phenomena affect the quality of the video signal, and without adequate measures to control the propagation of the impairments, the quality of the service may fall below acceptable levels. In this paper, we study the impact of cell losses on the quality of an MPEG-2 video sequence encoded in a variable bit rate mode. We introduce a set of control mechanisms at different levels of the protocol architecture to be used in MPEG-2-based video communications systems using ATM networks as their underlying transmission mechanism. Our results (using different video sequences) show the effectiveness to improve the video quality by using a structured set of control mechanisms to overcome for the loss of cells carrying VBR MPEG-2 video streams. We argue that in order to be able to create video systems able to cope with cell losses encountered in computer communications systems, a structured set of error-resilient protocol mechanisms is needed     

Broadcast/multicast MPEG-2 video over broadband fixed wirelessaccess networks

With the emergence of broadband fixed wireless access networks, there is an increasing interest in providing broadband video services over outdoor wireless networks. We investigate some fundamental issues related to the broadcasting or multicasting of CBR MPEG-2 videos over fixed wireless channels in B-FWANs using FEC strategies. In B-FWANs, high-frequency wireless channels are used and a direct or indirect LOS propagation path is usually required between a transmitter and a receiver. The wireless channel is modeled by a K factor Rician fading model instead of a Rayleigh fading model. The unique characteristics of the physical channel require special consideration at the system design level. In order to evaluate the overall system performance properly, a set of parameters for objective video quality assessment is introduced and used in our simulation studies, including a definition of the objective grade point value, the number of reconstructed frames, and the conventional peak signal-to-noise ratio value. The feasibility of cell interleaving is also addressed. MPEG-2 control information (i.e., the control blocks) plays a critical role in the decoding process and can influence the reconstructed video quality dramatically; special consideration and excess protection should be given to this information. The concept of a new FEC strategy, header redundancy FEC, is introduced to address this issue. In HRFEC, selected important (high-priority) MPEG-2 control blocks (such as sequence header, sequence extensions, and picture header and corresponding extensions) are replicated before transmission, and duplicate copies are transmitted over the wireless link. Our results indicate that HRFEC is a simple, flexible, and effective error control strategy for broadcasting or multicasting MPEG-2 videos over error-prone and time-varying wireless channels     

Improved rate control for MPEG-4 video transport over wireless channel

Video streaming over wireless channel is challenging due to a number of factors such as limited bandwidth and loss sensitivity. In this paper, we develop a novel rate control algorithm for MPEG-4 video coding. Unlike traditional rate control schemes, we jointly consider the encoding complexity variation and buffer variation as well as human visual properties to optimize the rate control efficiency. We also analyze the sensitivity of a macroblock (MB) as a result of bit errors and calculate its error sensitivity metric. This metric is used in unequal error protection of the MB. Simulation results show that proposed approach can improve the decoded picture quality in wireless video coding and transmission.     

Control mechanisms to improve the robustness of mpeg-2 based communications over ATM networks

Audio-visual and other multimedia services are seen as an important source of traffic for ATM networks. Due to the statistical multiplexing schemes used by ATM networks, cells are exposed to delays, jitters and losses. These phenomena affect the quality of the service provided to the video-based applications. In this paper, we introduce a set of control mechanisms at different levels of the protocol architecture. These mechanisms have been particularly tailored to better support MPEG-2-based video communications applications using ATM networks as their underlying transmission mechanism. We show that the use of errorconcealment mechanisms prove more effective when supplemented by a structured set of protocol mechanisms. We study the impact of cell losses on the quality of MPEG-2 video sequences and provide an evaluation of the quality of the decoded video as perceived by the end user. Our results demonstrate the effectiveness of the proposed protocol architecture in improving the quality of service provided to the video application.     

Error prevention and concealment for scalable video coding with dual-priority transmission

In this work, we present an efficient error resilient system against ATM cell loss using a hybrid error concealment and error propagation prevention (ECP) technique with dual-priority transmission scheme (DPTS). DPTS performs traffic policing to form dual-priority cells in ATM connections and manages to make most cell losses occur in a low priority layer. However, cell loss may still occur in the high priority layer if the bandwidth is not reserved enough for the usually variable bitrate video traffic. Therefore, the ECP technique can still be utilized to reduce the error damage and limit the impact of cell loss to the erroneous slices. Simulation results of two-layer MPEG-2 coding over DPTS in ATM networks demonstrate that ECP with feedback over DPTS can effectively isolate errors and reduce the damage to yield a satisfactory performance, even when the cell-loss rate is as high as 8%.     

A wireless ATM MAC protocol with combined hybrid ARQ and adaptive scheduling with analysis

A combined hybrid automatic repeat request (ARQ) error control and adaptive scheduling scheme is proposed for time-division multiple access/time-division duplex medium access control (MAC) protocols in wireless asynchronous transfer mode (ATM) networks. Specifically, with the aid of proper channel modeling, the performance of various error-control schemes is evaluated. Accordingly, type-II hybrid ARQ is chosen as the error recovery scheme to combat fading effects, while adaptive fair-queueing is designed to achieve a fair and efficient resource allocation in wireless channels. In particular, the weight of a connection used in the fair-queueing algorithm dynamically adapts in terms of varying channel conditions and the types of services. Various simulations are conducted in typical indoor wireless ATM networks. It is shown that the proposed scheme can achieve a high throughput and transfer reliability with minimized delay and cell loss rate when compared with the conventional MAC layer control.     

Packet-by-Packet Adaptive Scheme for Video Coding and Transmission Over Wireless IP Networks Using Rate-Compatible Punctured Turbo (RCPT) Codes

In this paper, we consider real-time video coding and transmission over packet-switched wireless IP networks, such as WLAN, using RCPT codes and joint source-channel coding (JSCC) with concentration on a packet-by-packet adaptive scheme. We present a systematic design methodology to enable the applicability of JSCC techniques. The performance of H.263+ video coding and transmission over wireless channel modeled as slow Rician fading channels using this approach is studied. Results indicate that a packet-by-packet adaptive RCPT-JSCC approach is of significant advantage for real-time video applications and leads to more acceptable video delivery quality over interference-limited and time-varying wireless networks.     

Power control and capacity analysis for a packetized indoormultimedia DS-CDMA network

This paper proposes a packetized indoor wireless system using direct-sequence code-division multiple-access (DS-CDMA) protocol. The indoor radio environment is characterized by slow Rayleigh fading with or without lognormal shadowing. The system supports multimedia services with various transmission rates and quality of service (QoS) requirements and allows for seamless interfacing to asynchronous transfer mode (ATM) broadband networks. All packets are transmitted with forward error correction (FEC) using convolutional code for voice packets and Bose-Chaudhuri-Hocquenghem (BCH) code for data packets with an automatic retransmission request (ARQ) protocol and for video packets without ARQ. A queueing model is used for servicing data transmission requests. A power control algorithm is proposed for the system, which combines closed-loop power control with channel estimation to give the best performance. The cell capacity of each traffic type and various multimedia traffic configurations in both single-cell and multiple-cell networks are evaluated theoretically under the assumption of perfect power control. The effect of power control imperfection on the capacity using the proposed power control algorithm is investigated by computer simulation     

Robust Packet Video Transport Over Wireless Fading Channels Using a Joint Source-channel Coding Approach

In this paper, we address the problem of robust video transmission over wireless networks. Specifically, we consider packet video transmission over wireless IP networks based on the RTP/UDP/IP protocol stack. Digital video delivered over wireless networks is expected to suffer quality degradation from both packet loss and bit errors in the payload. In this paper, both packet loss and bit errors in the payload are considered and the performance of a joint source-channel coding (JSCC) approach employing forward error-correction (FEC) coding schemes for H.263 +  video transmission is studied. Results indicate that with an appropriate JSCC approach, FEC-based error-control techniques can significantly improve the packetization efficiency for a given end-to-end quality requirement and lead to more acceptable video delivery quality over time-varying wireless networks. Another important observation is that with a JSCC approach the fading effects of wireless links upon end-to-end video quality are substantially decreased compared to a system without using channel coding, resulting in attractive robust performance characteristics.

Layered Wyner–Ziv Video Coding

Following recent theoretical works on successive Wyner-Ziv coding (WZC), we propose a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantization, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding with side information at the decoder). Our main novelty is to use the base layer of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the decoder side information and perform layered WZC for quality enhancement. Similar to FGS coding, there is no performance difference between layered and monolithic WZC when the enhancement bitstream is generated in our proposed coder. Using an H.26L coded version as the base layer, experiments indicate that WZC gives slightly worse performance than FGS coding when the channel (for both the base and enhancement layers) is noiseless. However, when the channel is noisy, extensive simulations of video transmission over wireless networks conforming to the CDMA2000 1X standard show that H.26L base layer coding plus Wyner-Ziv enhancement layer coding are more robust against channel errors than H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding is a promising new technique for video streaming over wireless networks     

Layered Wyner-Ziv video coding.

Following recent theoretical works on successive Wyner-Ziv coding (WZC), we propose a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantization, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding with side information at the decoder). Our main novelty is to use the base layer of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the decoder side information and perform layered WZC for quality enhancement. Similar to FGS coding, there is no performance difference between layered and monolithic WZC when the enhancement bitstream is generated in our proposed coder. Using an H.26L coded version as the base layer, experiments indicate that WZC gives slightly worse performance than FGS coding when the channel (for both the base and enhancement layers) is noiseless. However, when the channel is noisy, extensive simulations of video transmission over wireless networks conforming to the CDMA2000 1X standard show that H.26L base layer coding plus Wyner-Ziv enhancement layer coding are more robust against channel errors than H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding is a promising new technique for video streaming over wireless networks.     

Adaptive rate controlled,robust video communication over packet wireless networks

Video transmission over wireless packet networks is gaining importance due to the concept of universal personal communication. Further, it is considered an important step towards wireless multimedia. The challenge however is to achieve good video quality over mobile channels, where typically the channel conditions vary due to signal fading. Hence this paper investigates adaptive rate controlled video transmission for robust video communication under packet wireless environment. A combination of mobile and an ATM backbone network is assumed in this work. An error resilient design for the video coder, as proposed in Rajugopal et al. (1996) is employed here. This video coder comprises wavelet transform (WT), multi-resolution motion estimation (MRME) and a robust design for zero tree quantization. Two configurations, one employing MRME and the other using 1D-WT for temporal analysis, are considered for the video coder. Adaptive dynamic rate control is required to adapt the video communication to the channel conditions. It provides more channel protection when the channel is severe and improves the source rate and hence the performance when the conditions are favorable. An algorithm for dynamic rate control under varying channel conditions is proposed in this paper. It is evaluated under narrowband and broadband channel conditions. From the results, it is concluded that the dynamic rate control is very effective in optimizing the quality under varying mobile channel conditions. It was observed that the dynamic rate control provides at least an acceptable video quality under severe channel conditions and a good video quality when the channel conditions are favorable. This revised version was published online in July 2006 with corrections to the Cover Date.     

OFDM-based turbo-coded hierarchical and non-hierarchicalterrestrial mobile digital video broadcasting

The feasibility of terrestrial digital video broadcast (DVB) to mobile receivers is studied and turbo coded performance enhancements are proposed. Initially, the MPEG-2 codec is subjected to a rigorous bit error sensitivity investigation, in order to assist in designing various error protection schemes for wireless DVB transmission. The turbo codec is shown to provide signal-to-noise ratio (SNR) performance advantages in excess of 5-6 dB over conventional convolutional coding both in terms of bit error rate and video quality. Our experiments suggested that-despite our expectations-multi-class data partitioning did not result in error resilience improvements, since a high proportion of relatively sensitive video bits had to be relegated to the lower integrity subchannel, when invoking a powerful low-rate channel codec in the high-integrity protection class. Nonetheless, DVB transmission to mobile receivers is feasible, when using turbo-coded OFDM transceivers at realistic power-budget requirements under the investigated highly dispersive fading channel conditions. It is interesting to note furthermore that the 5-6 dB SNR improvement due to turbo coding allows us to invoke for example the double-throughput 16-level quadrature amplitude modulation (16-QAM) mode instead of the standard convolutional-coded 4-QAM mode. This facilitates doubling the bit rate and hence improving the video quality     

Error resilient video transmission over ATM networks

In the transmission process of a variable bit rate video signal over an ATM network, cells are inevitably exposed to delays and losses due to the statistical multiplexing used in these networks. These phenomena affect the quality of the video signal, and without adequate measures to control the propagation of impairments, the quality of service may fall below acceptable levels. We introduce a set of control mechanisms at different levels of the protocol architecture to support MPEG-2 based video communications systems using ATM networks as their underlying transmission mechanism. We argue that in order to be able to create video systems able to cope with cell losses encountered in computer communications systems, a structured set of protocol mechanisms is required. Our results show the effectiveness of the proposed set of mechanisms in improving the robustness of the video delivery system