Turbo-detected unequal protection MPEG-4 wireless video telephony using trellis coded modulation and space-time trellis coding

Abstract

-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 ...

Turbo-detected unequal protection audio and speech transceivers using serially concantenated convolutional codes, trellis coded modulation and space-time trellis coding

“…This relatively modest advantage of the twin-class protected transceiver was a consequence of having a rather limited turbo-interleaver length. In the longer interleaver of the videohphone system of [1,10] an approximately 2 dB E b /N0 gain was achieved. For a longer-delay non-realtime audio streaming scheme a simliar performance would be achieved to that of [10].…”

“…STTC may be efficiently employed in an effort to mitigate the effects of Rayleigh fading channels and render them Gaussian-like for the sake of supporting the operation of a TCM code. Recently, a sophisticated unequal-protection turbo transceiver using twin-class convolutional outer coding, as well as joint coding and modulation as inner coding combined with STTC-based spatial diversity scheme was designed for MPEG-4 video telephony in [1,10]. Specifically, maximal minimum distance Non-Systematic Convolutional codes (NSCs) [11, p. 331] having two different code-rates were used as outer encoders for providing unequal MPEG-4 video protection.…”

“…Good video quality was attained at a low SNR and medium complexity by the proposed transceiver. By contrast, in this paper, we study the achievable performance of the AMR-WB and the MPEG-4 TwinVQ speech and audio codecs in conjunction with the sophisticated unequal-protection turbo transceiver of [1,10]. and y k denote the vector of the audio/speech source symbol, the estimate of the audio/speech source symbol, the class-i audio/speech bits, the estimates of the class-i audio/speech bits, the encoded bits of class-i NSC encoders, the TCM coded symbols, the STTC coded symbols for transmitter j and the received symbols at receiver k, respectively.…”

“…Furthermore, Ψ and Ψ −1 denote LLR-to-symbol probability and symbol probability-to-LLR conversion, while Ω and Ω −1 denote the parallel-to-serial and serial-to-parallel converter, respectively. The notation m denotes the number of information bits per TCM coded symbol [10] c IEE, 2004, Ng, Chung and Hanzo.…”

“…The iterative turbo-detection scheme shown in Figure 4 enables an efficient information exchange between the STTC, TCM and NSCs constituent codes for the sake of achieving spatial diversity gain, coding gain, unequal error protection and a near-channelcapacity performance. The information exchange mechanism between each constituent decoders is detailed in [10].…”