Link Adaptation for Framed Multimedia Data Transmission over a DS-CDMA Communication System
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Link Adaptation for Framed Multimedia Data Transmission over a DS-CDMA Communication System Charly Poulliat ETIS Laboratory (UMR 8051), ENSEA/University of Cergy-Pontoise/CNRS, 6 Avenue du Ponceau, 95014 Cergy-Pontoise Cedex, France Email: [email protected]
Inbar Fijalkow ETIS Laboratory (UMR 8051), ENSEA/University of Cergy-Pontoise/CNRS, 6 Avenue du Ponceau, 95014 Cergy-Pontoise Cedex, France Email: [email protected]
David Declercq ETIS Laboratory (UMR 8051), ENSEA/University of Cergy-Pontoise/CNRS, 6 Avenue du Ponceau, 95014 Cergy-Pontoise Cedex, France Email: [email protected] Received 31 July 2003; Revised 17 May 2004 In the context of frame-based multimedia wireless transmission, a link adaptation strategy is proposed, assuming that the source decoder may accept some remaining errors at the output of the channel decoder. Based on a target mean bit error rate for erroneous frames, a minimum bit-energy-to-equivalent-noise ratio is chosen. Under this constraint, a new link adaptation criterion is proposed: the maximization of the minimum user’s information rate through dynamic spreading gain and power control, allowing to guarantee a transmission for each and every user. An analytical solution to this constrained optimization problem is proposed and its performance is studied in a Rayleigh-fading environment. Keywords and phrases: resource allocation management, link adaptation, rate and power adaptation, multirate DS-CDMA.
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INTRODUCTION
The framework of the paper is the transmission of multimedia data through a wireless multiuser communication system such as the direct-sequence code-division multiple access (DS-CDMA). The main feature of the transmitted data is that we consider a packet-mode transmission system. On one hand, the source coder and decoder are communicating with compressed data packets, and on the other hand, DSCDMA communication systems such as the Universal Mobile Telecommunication System (UMTS) are framed-based communication systems [1, 2]. Therefore, we can assume that the source-formatted data packets containing the compressed bitstream are sent over one or several frames at the physical layer. Moreover, the source decoder can offer some advanced features, such as robust decoding and rate adaptaThis is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
tion capability [3]. Robust source decoding can be performed using for example an embedded forward-error correction (FEC) and synchronization techniques to mitigate the effect of remaining errors after channel decoding [3]. The source decoder can also tolerate some erroneous packets; however, the bit error rate (BER) within an erroneous packet should be lower than a critical value. The rate adaptation capability [3] allows the source decoder to adapt its rate during the transmission, depending on the available rate in the wired link and/or the possible rate on the wireless link to ensure
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