Catherine Lamy-Bergot

Cross-layer architecture for scalable video transmission in wireless network

Multimedia applications such as video conference, digital video broadcasting (DVB), and streaming video and audio have been gaining popularity during last years and the trend has been to allocate these services more and more also on mobile users. The demand of quality of service (QoS) for multimedia raises huge challenges on the network design, not only concerning the physical bandwidth but also the protocol design and services. One of the goals for system design is to provide efficient solutions for adaptive multimedia transmission over different access networks in all-IP environment. The joint source and channel coding (JSCC/D) approach has already given promising results in optimizing multimedia transmission. However, in practice, arranging the required control mechanism and delivering the required side information through network and protocol stack have caused problems and quite often the impact of network has been neglected in studies. In this paper we propose efficient cross-layer communication methods and protocol architecture in order to transmit the control information and to optimize the multimedia transmission over wireless and wired IP networks. We also apply this architecture to the more specific case of streaming of scalable video streams. Scalable video coding has been an active research topic recently and it offers simple and flexible solutions for video transmission over heterogeneous networks to heterogeneous terminals. In addition it provides easy adaptation to varying transmission conditions. In this paper we illustrate how scalable video transmission can be improved with efficient use of the proposed cross-layer design, adaptation mechanisms and control information.

JPEG 2000 backward compatible error protection with Reed-Solomon codes

In this paper, a backward compatible header error protection mechanism is described. It consists of the addition of a dedicated marker segment to a JPEG 2000 codestream, that will contain the error correction data generated by a block error correction code (e.g. a Reed Solomon code). This mechanism allows leaving the original data intact, hence providing backward compatibility with the already standardised JPEG 2000. Neither side information from higher level, nor extra signalling encapsulation is needed, as the required information is directly embedded in the codestream and also protected. Finally, it is shown how this mechanism can be used for perform unequal error protection of the whole JPEG 2000 stream.

Analysis and optimization of irregular LDPC codes for joint source-channel decoding

In this paper, we present a characterization, through its convergence analysis, and an optimisation of a joint source-channel receiver composed of a LDPC decoder and a Soft Input Soft Output (SISO) source decoder. Under Gaussian approximation, assuming the knowledge of the extrinsic mutual information transfer function (EXIT chart) of the source decoder, we derive the Mutual Information evolution equations, that semianalytically describe the convergence of the iterative system behavior and, to complete the study, the stability condition at the convergence fixed point is derived for the joint receiver. From this analysis, a general optimisation method of the irregularity of the LDPC codes is proposed, which can be reduced to a linear programming optimisation problem. Simulation results show improved performance when compared to an AWGN optimized LDPC code.

Unequal Error Protection for H.263+ bitstreams over a wireless IP network

This paper presents an original solution to efficiently transmit video bitstreams over an IP networked wireless channel via an unequal rate allocation protection scheme. The originality of this scheme is that it proposes a sensitivity estimation not only for the video stream itself as classically done, but also for the network headers used over the IP wireless network, here considered in their compressed version. Based on this sensitivity measure, the protection allocation algorithm is able to propose an efficient unequal rate allocation scheme using rate compatible punctured codes. Numerical results obtained in the case of H.263+ bitstreams transmitted over an error prone wireless compressed RTP/UDP/IP network show that taking into account both video and headers sensitivity allows this unequal error protection (UEP) scheme to provide PSNR improvements of about 5 dB when compared to equal error protection (EEP) scheme with a low additional complexity

OMNeT++-Based cross-layer simulator for content transmission over wireless ad hoc networks

Flexbility and deployment simplicity are among the numerous advantages of wireless links when compared to standard wired communications. However, challenges do remain high for wireless communications, in particular due to the wireless medium inherent unreliability, and to the desired flexibility, which entails complex protocol procedures. In that context simulation is an important tool to understand and design the protocols that manage the wireless networks. This paper introduces a new simulation framework based on the OMNeT++ simulator whose goal is to enable the study of data and multimedia content transmission over hybrid wired/wireless ad hoc networks, as well as the design of innovative radio access schemes. To achieve this goal, the complete protocol stack from the application to the physical layer is simulated, and the real bits and bytes of the messages transferred on the radio channel are exchanged. To ensure that this framework is reusable and extensible in future studies and projects, a modular software and protocol architecture has been defined. Although still in progress, our work has already provided some valuable results concerning cross layer HARQ/MAC protocol performance and video transmission over the wireless channel, as illustrated by results examples.

Complaint Selective encryption for H.264/AVC video streams

This paper presents a novel selective encryption scheme that allows for secure transmission of video streams such as H.264/AVC ones, while keeping complete backward compatibility with the corresponding video standard. This compatibility allows consequently any standard compliant decoder to decode the ciphered stream without specific provision in terms of resynchronization procedure, albeit incorrectly from the visual point of view. The bits to be encrypted are chosen with respect to the video standard, the full compatibility being achieved by encrypting bits for which the impact of each of the encrypted configurations gives a non-desynchronized and fully standard compliant bitstream. Numerical results obtained with this partial ciphering algorithm in the context of H.264/AVC show that PSNR degradations of about 25 to 30 dB are obtained when the ciphering key is unknown

Temporal scalability through adaptive M-band filter banks for robust H.264/MPEG-4 AVC video coding

This paper presents different structures that use adaptive-band hierarchical filter banks for temporal scalability. Open-loop and closed-loop configurations are introduced and illustrated using existing video codecs. In particular, it is shown that the H.264/MPEG-4 AVC codec allows us to introduce scalability by frame shuffling operations, thus keeping backward compatibility with the standard. The large set of shuffling patterns introduced here can be exploited to adapt the encoding process to the video content features, as well as to the user equipment and transmission channel characteristics. Furthermore, simulation results show that this scalability is obtained with no degradation in terms of subjective and objective quality in error-free environments, while in error-prone channels the scalable versions provide increased robustness.

Modelling H.264/AVC sensivitity for error protection in wireless transmissions

A simple method is proposed to optimise the protection levels on the different parts of an H.264/AVC bitstream for transmission over an error-prone channel. This method relies on a semi-analytical model of the video stream sensitivity, that allows to predict the resulting distortion depending on the channel errors viewed by the video decoder. Valid for a frame, a partition or a group of pictures (GOP) by taking into account the dependencies existing between partitions and frames, the model allows to set the adapted protection for each partition or frame to minimise the overall sequence distortion for a given erroneous context by joint source channel optimisation of the compression and protection mechanisms. The method is then applied to determine the best trade-off of channel and source coding rates for a given operating point or protection rate, with equal or unequal error protection

A simple Multiple Description Coding scheme for improved peer-to-peer video distribution over mobile links

This paper presents an adaptation of peer-to-peer diffusion strategies of video over mobile links based on the use of multiple description coding. The system architecture, including the used overlay algorithm (the unstructured GIA algorithm) and video coding with multiple description coding (MDC), are presented as well as their interest in this context. Simulation results illustrate the approach, showing the interest of using MDC vs. a single description coding solution. The proposed simulation framework involves an H.264/AVC video codec with two descriptions and a simple adaptation of the overlay algorithm.

Data supervision for adaptively transcoded video surveillance over wireless links

This paper describes a solution for on-the-fly adapting the parameters of a video surveillance streams to system varying conditions, both in terms of data to be transmitted (number of streams to be sent) and of transmission conditions (quality of the available wireless link). This solution has been inserted in the system architecture of the EUREKA CELTIC BOSS project for enhancing the security of passengers inside commuter trains. The dynamic adaptation solution proposed allows to offer better Quality of Service (QoS) for critical streams, as well as enhanced robustness to channel conditions variations. Simulation results as well as integration of this feature in the BOSS project demonstrator are presented to illustrate the gains this approach can offer.