Time-Variant Bitrate Turbo-Coded Near-Instantaneously Adaptive OFDM-Based Interactive Videophony

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Description/Abstract

A range of Adaptive Orthogonal Frequency Division Multiplex (AOFDM) video systems are proposed for interactive communications over wireless channels. The proposed constant target bitrate subband adaptive OFDM (CTBR-AOFDM) modems can provide a lower BER, than a corresponding conventional OFDM modem. The slightly more complex switched or Time-Variant Target Bit Rate (TVTBR) AOFDM modems can provide a balanced video quality performance, across a wider range of channel SNRs, maintaining the best video performance. Upon invoking the technique advocated - irrespective ofthechannel conditions experienced - the transceiver achieves always the best possible video quality by automatically adjusting the achievable bitrate and the associated video 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 eects of pathloss, fast-fading, slow-fading, dispersion, etc. Furthermore, when the mobile is roaming in a hostile outdoor 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.