Subband-adaptive turbo-coded OFDM-based interactive video telephony

A range of adaptive orthogonal frequency division multiplex (AOFDM) video systems are proposed for interactive communications over wireless channels. The proposed constant target bit-rate subband-adaptive OFDM modems can provide a lower bit error rate than a corresponding conventional OFDM modem. The slightly more complex switched or time-variant target bit rate AOFDM modems can provide a balanced video quality performance, across a wider range of channel signal-to-noise ratios, maintaining the best video performance. Upon invoking the technique advocated, irrespective of the channel conditions experienced, the transceiver achieves always the best possible video quality by automatically adjusting the achievable bit rate 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 effects of path-loss, 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.