Most multimedia source signals are capable of tolerating lossy, rather than lossless delivery to the human eye, ear and other human sensors. The corresponding lossy and preferably low-delay multimedia source codecs however exhibit unequal error sensitivity, which is not the case for Shannon's ideal entropy codec. This paper proposes a jointly optimised turbo transceiver design capable of providing unequal error protection for MPEG-4 coding aided wireless video telephony. The transceiver investigated consists of space-time trellis coding (STTC) invoked for the sake of mitigating the effects of fading, in addition to bandwidth efficient trellis coded modulation or bit-interleaved coded modulation, combined with a multi-level coding scheme employing either two different-rate non-systematic convolutional codes (NSCs) or two recursive systematic convolutional codes for yielding a twin-class unequal-protection. A single-class protection based benchmark scheme combining STTC and NSC is used for comparison with the unequal-protection scheme advocated. The video performance of the various schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the proposed scheme requires about 2.8 dBs lower transmit power than the benchmark scheme in the context of the MPEG-4 videophone transceiver at a similar decoding complexity. Motivation and backgroundTrellis coded modulation (TCM) [1, 2] constitutes a bandwidth-efficient joint channel coding and modulation scheme, which was originally designed for transmission over additive white Gaussian noise (AWGN) channels. By contrast, bit-interleaved coded modulation (BICM) [3] employing parallel bit-based interleavers was designed for communicating over uncorrelated Rayleigh fading channels. Therefore, TCM outperforms BICM, when communicating over AWGN channels since TCM exhibits a higher Euclidean distance. By contrast, the opposite is true, when communicating over uncorrelated Rayleigh fading channels, since BICM exhibits a higher Hamming distance. Spacetime trellis coding (STTC) schemes [4,5], which employ multiple transmit and receive antennas are capable of providing both spatial diversity gain and coding gain. Note that when the spatial diversity order is sufficiently high, the channel's Rayleigh fading envelope is transformed to a Gaussian-like near-constant envelope. Hence, the benefits of a TCM scheme designed for AWGN channels will be efficiently exploited, when TCM is concatenated with STTC in comparison to BICM [6].Multi-level coding (MLC) schemes [7] have been widely designed for providing unequal error protection capabilities [8]. In this paper, we design a twin-class unequal protection MLC scheme by employing two different code-rate maximal minimum distance non-systematic convolutional codes (NSCs) [9] or recursive systematic convolutional codes (RSCs) [1, 2] as the constituent codes. More specifically, a stronger NSC/RSC is used for protecting the more sensitive video bits, while a weaker NSC/RSC is employed for prot...

-A jointly optimised turbo transceiver capable of providing unequal error protection is proposed for MPEG-4 aided wireless video telephony. The transceiver advocated consists of Space-Time Trellis Coding (STTC), Trellis Coded Modulation (TCM) and two different-rate Non-Systematic Convolutional codes (NSCs). A benchmarker scheme combining STTC and NSC is used for comparison with the proposed scheme. The video performance of the both schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the proposed scheme requires about two dBs lower transmit power than the benchmarker scheme in the context of the MPEG-4 videophone transceiver, when aiming for an effective throughput of 2 bits/symbol at a similar decoding complexity. MOTIVATION AND BACKGROUNDThe MPEG-4 standard [1, 2] offers a standardised framework for a whole range of multimedia applications. Examples include tele-shopping, interactive TV, internet games, or mobile video communication. MPEG-4 integrates different types of multimedia services by the introduction of a so-called objectbased approach for the description and coding of multimedia contents. The key functionalities of MPEG-4 include independent coding of objects in a video frame, the ability to interactively embed these video objects into a scene shown on the screen, the transmission of 3D scene descriptions, quality versus bitrate based temporal and spatial scalability and improved error resilience [3].As the MPEG-4 standard targets a broader range of different applications and bitrates than the previously defined hybrid video coding standards such as MPEG-1, 2 or H.263, it employs a higher variety of different algorithms and coding modes. In the MPEG-4 coding algorithm a scene consists of one or more audio-visual objects potentially generated from multiple sources.The MPEG-4 algorithm employed for encoding natural video scenes is the classic block-based hybrid coding scheme [4],The financial support of both the EPSRC, Swindon UK and the EU under the auspices of the Phoenix project is gratefully acknowledged. which is known from the well-established MPEG-1, 2 or H.263 codecs. However, these codecs were further developed in order to allow the encoding of arbitrarily shaped video objects. For employment in error-prone environments, error resilient encoding features were introduced by several parts of the MPEG-4 standards. This renders the MPEG-4 coding standard particularly suitable for wireless video telephony.In this study the MPEG-4 video codec was incorporated in a sophisticated unequal-protection turbo transceiver using joint coding and modulation as inner coding, twin-class convolutional outer coding as well as space time coding based spatial diversity. Specifically, Trellis Coded Modulation (TCM) [5,6] constitutes a bandwidth-efficient joint channel coding and modulation scheme, which was originally designed for transmission over Additive White Gaussian Noise (AWGN) channels. In an effort to mitigate the effects of Rayleigh fading channels ...

-A Turbo-detection aided serially concatenated inner Trellis Coded Modulation (TCM) scheme is combined with four different outer codes, namely with a Reversible Variable Length Code (RVLC), a Non-Systematic Convolutional (NSC) code a Recursive Systematic Convolutional (RSC) code or a Low Density Parity Check (LDPC) code. These four outer constituent codes are comparatively studied in the context of an MPEG4 videophone transceiver. These serially concatenated schemes are also compared to a stand-alone LDPC coded MPEG4 videophone system at the same effective overall coding rate. The performance of the proposed schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the serially concatenated TCM-NSC scheme was the most attractive one in terms of coding gain and decoding complexity among all the schemes considered in the context of the MPEG4 videophone transceiver. By contrast, the serially concatenated TCM-RSC scheme was found to attain the highest iteration gain among the schemes considered. MOTIVATION AND BACKGROUNDThe MPEG-4 standard [1, 2] offers a standardised framework for a whole range of multimedia applications. Examples include teleshopping, interactive TV, internet games, or mobile video communication. MPEG-4 integrates different types of multimedia data and services by the introduction of a so-called object-based approach for the description and coding of multimedia contents. The key functionalities of MPEG-4 include independent coding of objects in a video frame, the ability to interactively embed these video objects into a scene shown on the screen, the transmission of 3D scene descriptions, quality versus bitrate based temporal and spatial scalability and improved error resilience [3].As the MPEG-4 standard targets a broader range of different applications and bitrates than the previously defined hybrid video coding standards such as MPEG-1, 2 or H.263, it employs a higher variety of different algorithms and coding modes. In the MPEG-4 coding algorithm a scene consists of one or more audio-visual objects potentially generated from multiple sources. A specific manifestation of a so-called video object layer is referred to as a video object plane (VOP) [2]. The individual VOPs delivered to an MPEG-4 decoder are allowed to have arbitrary shapes. The individual VOPs of an object may be transmitted separately from each other.In MPEG-4 video coding, the algorithm employed for encoding natural video scenes is based on the classic block-based hybrid coding scheme [4], which is known from the well-established MPEG-1, 2 or H.263 codecs. However, these codecs were further developed in order to allow the encoding of arbitrarily shaped video objects. ForThe financial support of both the EPSRC, Swindon UK and the EU under the auspices of the Phoenix project is gratefully acknowledged. employment in error-prone environments, error resilient features were introduced by several parts of the MPEG-4 standards. This renders the MPEG-4 coding standard particularly sui...

Claude Shannon's pioneering work quantified the performance limits of communications systems operating over classic wireline Gaussian channels. However, his source and channel coding theorems were derived for a range of idealistic conditions, which may not hold in low-delay, interactive wireless multimedia communications. Firstly, Shannon's ideal lossless source encoder, namely the entropy encoder may have an excessive codeword length, hence exhibiting a high delay and a high error sensitivity. However, in practice most multimedia source signals are capable of tolerating lossy, rather than lossless delivery to the human eye, ear and other human sensors. The corresponding lossy and preferably low-delay multimedia source codecs however exhibit unequal error sensitivity, which is not the case for Shannon's ideal entropy codec. There are further numerous differences between the Shannonian lessons originally outlined for Gaussian channels and their ramifications for routinely encountered dispersive wireless channels, where typically bursty, rather than random errors are encountered. This paper elaborates on these intriguiging lessons in the context of a few turbo-transceiver design examples, using a jointly optimised turbo transceiver capable of providing unequal error protection in the context of MPEG-4 aided wireless video telephony. The transceiver investigated consists of Space-Time Trellis Coding (STTC) invoked for the sake of mitigating the effects of fading, Trellis Coded Modulation (TCM) or Bit-Interleaved Coded Modulation (BICM) as well as two different-rate Non-Systematic Convolutional codes (NSCs) or Recursive Systematic Convolutional codes (RSCs). A single-class protection based benchmarker scheme combining STTC and NSC is used for comparison with the unequal-protection scheme advocated. The video performance of the various schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the achievable performance of the proposed scheme is within 0.99 dB of the corresponding capacity of the Rayleigh fading channel.

http://www-mobile.ec.soton.ac.uk A bstract-A Burst-by-Burst Adaptive Coded Modulation-Aided Joint Detection-Based CDMA (ACM-JD-CDMA) scheme is proposed for wireless video telephony and characterise its performance when communicating over the UTRA wideband vehicular fading channels. The coded modulation schemes invoked in our Axed modulation mode based systems are Trellis Coded Modulation (TCM), Turbo TCM (TTCM), Bit-Interleaved Coded Modulation (BICM) and Iterative-Decoding assisted BICM (BICM-ID). When comparing the four schemes at a given complexity, TTCM was found t o be the best scheme and the performance of the TTCM-assisted ACM-JD-CDMA system was evaluated using a practical modem mode switching regime.