Error concealment for robust arithmetic decoding in mobile radio environments

This paper contains our proposal for a new decoding algorithm for an iterative decoded V-BLAST system. The proposed algorithm is based on maximum a posteriori (MAP) decision criterion. In a V-BLAST system concatenated with channel coding, the extrinsic information from the soft output channel decoder can be utilized as a priori probability, making it possible to apply MAP decision criteria to the V-BLAST decoding process. The MAP decision criterion is applied to the V-BLAST ordering and slicing procedure, resulting in a considerable gain in bit error performance. As the iteration rate increases, the proposed system exhibits performance similar to that of systems with ideal sliced.

Video compression plays an important role in video signal processing, transmission and storage. Since the available bandwidth for transmission is very limited, Multimedia Applications such as video conferencing, video on demand, video telephony and remote sensing are not possible without compression. A lot of video compression techniques have been developed and the video signal transmission has followed at data rates below 64kbps. Wavelet transform based motion compensated video codec performs better compression in order to meet the rate and distortion constraint in video transmission for the available bandwidth than the block based techniques, which are followed in standard video transmissions such as H.261 and H.263. But the efficiency of those technique's depends on the way in which it estimates and compensates the object motions in the video sequence. Wavelet based embedded image coder is quite attractive in modern multimedia applications. Wavelet transform, bit plane coding and other techniques make embedded image coder practical and also provide efficient compression. In this paper, we have proposed a novel video coding using swarm intelligence in dual tree complex wavelet transform for video coding. The 3-D DDWT is an attractive video representation because it isolates motion along different directions in separate subbands. However, it is an over-complete transform with redundancy, which is going to be eliminated by choosing optimal subbands with the help of PSO. The proposed video codec does not require motion compensation and provides better performance than the 3D SPIHT (Embedded type)codec, both objectively and subjectively, and the coder allows full scalability in spatial, temporal and quality dimensions.

This work addresses the problem of error concealment in video transmission systems over noisy channels employing Bregman divergences along with regularization. Error concealment intends to improve the effects of disturbances at the reception due to bit-errors or cell loss in packet networks. Bregman regularization gives accurate answers after just some iterations with fast convergence, better accuracy and stability. This technique has an adaptive nature: the regularization functional is updated according to Bregman functions that change from iteration to iteration according to the nature of the neighborhood under study at iteration n. Numerical experiments show that high-quality regularization parameter estimates can be obtained. The convergence is sped up while turning the regularization parameter estimation less empiric, and more automatic.KeywordsInverse problemsoptical flowBregman divergencesexponential distributionserror concealmentcomputer visionregularization

New robust decoding scheme-aware channel condition for video streaming transmission

It is well known that the performance of TCP deteriorates in a mobile wireless environment. This is due to the fact that although the majority of packet losses are results of transmission errors over the wireless links, TCP senders still take packet loss as an indication of congestion, and adjust their congestion windows according to the additive increase and multiplicative decrease (AIMD) algorithm. As a result, the throughput attained by TCP connections in the wireless environment is much less than it should be. The key problem that leads to the performance degradation is that TCP senders are unable to distinguish whether packet loss is a result of congestion in the wireline network or transmission errors on the wireless links.In this paper, we propose a light‐weight approach, called syndrome, to improving TCP performance in mobile wireless environments. In syndrome, the BS simply counts, for each TCP connection, the number of packets that it relays to the destination host so far, and attaches this number in the TCP header. Based on the combination of the TCP sequence number and the BS‐attached number and a solid theoretical base, the destination host will be able to tell where (on the wireline or wireless networks) packet loss (if any) occurs, and notify TCP senders (via explicit loss notification, ELN) to take appropriate actions. If packet loss is a result of transmission errors on the wireless link, the sender does not have to reduce its congestion window.Syndrome is grounded on a rigorous, analytic foundation, does not require the base station to buffer packets or keep an enormous amount of states, and can be easily incorporated into the current protocol stack as a software patch. Through simulation studies in ns‐2 (UCB, LBNL, VINT network simulator, http://www‐mash.cs.berkeley.edu/ns/), we also show that syndrome significantly improves the TCP performance in wireless environments and the performance gain is comparable to the heavy‐weight SNOOP approach (either with local retransmission or with ELN) that requires the base station to buffer, in the worst case, a window worth of packets or states. Copyright © 2001 John Wiley & Sons, Ltd.

Video quality suffers significant degradation when transmitted over error-prone channel, due to packet loss, errors caused by fading in wireless channel and due to the video codec prediction mechanisms. The H.264/AVC standard suggests some new error-resilient features to enable reliable transmission of compressed video signal over lossy packet networks. Two of those new features are the Redundant Slices and the Flexible Macro-Block Ordering (FMO). In this paper we propose a new error-resilient scheme which merges the H.264/AVC FMO feature with a new technique for dynamic allocation of redundant slices depending on the wireless channel fading parameters. We suggest using a unique smart dynamic redundant slices allocation scheme which considers the dynamic wireless channel parameters rather than using the classical standard static allocation. The proposed redundant slice allocation algorithm is based on both Average Fade Duration (AFD), and Level Cross Rate (LCR) channel's characteristics. Moreover, we propose a new Explicit Spiral-Interleaved (ESI) flexible macroblocks ordering technique, which outperforms all other FMO types. The new ESI ordering results in effective error scattering which maximize the number of correctly received macroblocks located around corrupted macroblocks, leading to better error concealment. The proposed scheme greatly improves video transmission quality over lossy wireless transmission channels. Simulations results for wireless channel characterized by Rayleigh fading indicate that the proposed method improves the standard static allocation of redundant slices in terms of PSNR by about 2.5dB. Performance evaluations show that our approach is especially suited for applications such as video conferencing and mobile TV, where typically a specific main important Region of Interest should be more carefully protected

Access authentication is very important for deploying mobile IPv6 networks. In this paper, we design a two-level hierarchical identity-based signature scheme, based on which we propose a new hierarchical authentication scheme for mobile IPv6 networks. Our solution adopts multi-level network access identifier (NAI) as public key, which simplifies key management in wireless mobile environment. The handover procedure integrating authentication is also cut down by our hierarchical solution. And our solution accomplishes mutual authentication between terminal and network. We propose the handover latency analytical model to evaluate handover latency. The results show that our solution is more efficient than others, especially when a terminal is far away from its home domain and moves frequently. Security analysis shows that the proposed scheme is sufficient for privacy and unforgeability. An extended version for access authentication in multi-hierarchical mobile IPv6 networks is discussed.

Capturing or acquiring video data from advanced gadgets, like cell phone cameras, smart phones, camcorders, etc., is very recent and up growing trend. With the advancement of the video camera as the integrated part of these multimedia devices generates necessity for video stabilization. Digital video stabilization or video frame alignment techniques are used to improve quality of input video by removing the undesired camera motions jitters; undesirable jiggles etc. Many video stabilization techniques are developed till now but only fast and low computational complexity approaches can be applied on the embedded devices. The paper presents the review of fast block matching local motion vector estimation and alignment algorithm. Effectiveness of the algorithm is shown by quantitative evaluation. The proposed work will also help to boost the performance of various error concealment, error resilience and video quality improvement techniques in H.264/HEVC video codec.

H.263 based video codec for real-time visual communications over wireless radio networks

Fixed length entropy codes (FLC) have been employed as an alternative to the usual variable length codes (VLC) in video codecs. The effect of a transmission error in an FLC coded stream does not propagate beyond the corrupted codeword because of its fixed parsing structure. This paper presents a new decoding algorithm for FLC compressed video streams that fully exploits the error resilience properties of FLC codes combined with spatial synchronization points. While maintaining the compression efficiency of VLC coded video streams, the proposed solution is a novel idea to combat the consequences of transmission errors and it is totally compatible with more traditional solutions such as error concealment and forward error correcting codes.

In this paper we proposed a robust video decoding scheme using early resynchronization, error detection (ED) and error concealment (EC). Many video coding standards such as H.263+ and MPEG-2 make the compressed video signals more vulnerable to channel errors because of error propagation due to using variables length coding (VLC). Channel errors cannot only result in false decoding of current bits but also make the decoder lose synchronization. The data between the errors and next resynchronization marker (RM) will be discarded even if they are not corrupted by channel errors. Early resynchronization can retrieve unaffected data between the errors and next RM, which can greatly reduce error propagation due to using VLC. We combined early resynchronization with deliberately designed ED and EC technologies and tested three early resynchronization schemes in our simulation. It has been found that the third scheme can give the best tradeoff between the final reconstructed image quality and searching times.

Recent advances in mobile wireless networks allow handheld devices, such as smart phones, pocket PCs, to connect to the Internet and use the distributed applications conveniently. And the model of software as a service enables the handheld devices to use the applications which previously run on PCs or servers. However, the mobile wireless environment is dynamic and resource-limited. It needs an efficient service supporting mechanism to keep continuous services for those devices. In this paper, we presented a dynamic service management framework for web services in mobile wireless networks. It adopts the architecture style of Representation State Transfer (REST) and supports the dynamic service discovery and adaptive service invocation. It is suitable for dynamic services access through the handheld devices. The case study illustrated that our framework can support the service subscribers to get sustaining and dynamic services.

Caching frequently accessed data objects at the local buffer of a mobile user (MU) has been found to be very effective in improving information availability in mobile wireless environments. Several mechanisms have been proposed in the literature to address the challenging problem of cache consistency in cellular wireless networks. However, these mechanisms are limited to single cell systems. In this paper, we develop a novel Dynamic Scalable Asynchronous Cache Consistency Scheme (DSACCS) that can adaptively maintain mobile data objects globally or locally depending on the minimum consistency maintenance cost in multi-cell systems. The cost function is derived by taking into account each data object's update frequency, MUs' access pattern and roaming frequency, number of cells and number of MUs in the system. Extensive simulation studies demonstrate that DSACCS outperforms three existing cache strategies extended to multi-cell environments. The three cache consistency strategies are homogeneous invalidation reports (IRs), inhomogeneous IR without roaming check, and inhomogeneous IR with roaming check. Finally, an improvisation of DSACCS, called DSACCS-G, is proposed for grouping cells in order to facilitate effective cache consistency maintenance in multi-cell systems.

An alternative form of stereoscopic video is the combination of 2-D video from an ordinary 2-D video camera and depth information from a laser range or depth camera. When this type of 3-D video is compressed and transmitted over error prone channels, the associated packet loss leads to poor visual quality. Therefore, a depth image-based error concealment for 3-D video transmission is proposed, which utilizes a strong correlations between 2-D video and its corresponding depth map. The depth information provides an indication of object boundaries to assist the concealment process. This spatial object based error concealment involves concealment decision process and frequency extrapolation.

We propose a method to prevent the degradation of decoded MPEG pictures caused by video transmission over error-prone networks. In this paper, we focus on the error concealment that is processed at the decoder without using any backchannels. Though there have been various approaches to this problem, they generally focus on minimizing the degradation measured frame by frame. Although this frame-level approach is effective in evaluating individual frame quality, in the sense of human perception, the most noticeable feature is the spatio-temporal discontinuity of the image feature in the decoded video image. We propose a novel error concealment algorithm comprising the combination of i) A spatio-temporal error recovery function with low processing cost, ii) A MB-based image fidelity tracking scheme, and iii) An adaptive post-filter using the fidelity information. It is demonstrated by experimental results that the proposed algorithm can significantly reduce the subjective degradation of corrupted MPEG video quality with about 30% of additional decoding processing power.