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The video performance benefits of burst-by-burst adaptive modulation are studied, employing a higher-order modulation scheme when the channel is favorable, in order to increase the system's bits per symbol capacity and conversely, invoking a more robust lower order modulation scheme when the channel exhibits inferior channel quality. It is shown that due to the proposed adaptive modem mode switching regime, a seamless video-quality versus channel quality relationship can be established, resulting in error-free video quality right across the operating channel signal-to-noise ratio (SNR) range. The main advantage of the proposed burst-by-burst adaptive transceiver technique is that irrespective of the prevailing channel conditions, the transceiver achieves always the best possible source-signal representation quality-such as video, speech, or audio quality-by automatically adjusting the achievable bitrate and the associated multimedia source-signal representation quality in order to match the channel quality experienced. This is achieved on a near-instantaneous basis under given propagation conditions in order to cater for the effects of path loss, fast-fading, slow-fading, dispersion, co-channel interference, etc. Furthermore, when the mobile is roaming in a hostile outdoors or even hilly terrain-propagation environment, typically low-order low-rate modem modes are invoked, while in benign indoor environments, predominantly the high-rate high source-signal representation quality modes are employed.

Abstract-Adaptive modulation is applied in conjunction with a decision-feedback equalizer (DFE) in order to mitigate the effects of the slowly varying wide-band multipath Rayleigh fading channel in a noise-limited environment. An upper-bound mean bit-error rate and bits per symbol performance is introduced for this scheme by utilizing the pseudo signal-to-noise ratio at the output of the DFE in order to switch the modulation schemes on a burst-by-burst basis.

In this contribution the performance of adaptive modulationapplied in conjunction with Turbo Equalization (TE)is characterized in a noise limited environment over a slowly varying wideband multi-path Rayleigh fading channel. The iterative structure of the turbo equalizer was also exploited in order to invoke an iterative Least Mean Square (LMS) channel estimator. Finally, the throughput performance of the adaptive modulation scheme was compared to that of its constituent modulation modes, where a gain of 1.5dB to 1.7dB was recorded.

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Abstract-Decision feedback equalizer (DFE)-aided turbocoded wideband adaptive quadrature amplitude modulation (AQAM) is proposed, which is capable of combating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo-coding rates capable of maintaining the target bit-error rate while aiming for achieving a highly effective bits per symbol throughput. As a design alternative, we also employ multiple-input/multiple-output DFE-aided space-time trellis codes, which benefit from transmit diversity and hence reduce the temporal channel quality fluctuations. The performance of both systems is characterized and compared when communicating over the COST 207 typical urban wideband fading channel. It was found that the turbo-coded AQAM scheme outperforms the two-transmitter space-time trellis coded system employing two receivers; although, its performance is inferior to the space-time trellis coded arrangement employing three receivers.