Scalable Video Transmission over DS-CDMA Wireless Systems
We consider the transmission of video over wireless direct-sequence code-division multiple access (DS-CDMA) channels. A layered (scalable) video source codec is used. The layers may be time-multiplexed and transmitted over a single CDMA channel or each layer can be transmitted over a different CDMA channel. For the latter case, spreading codes of different length are allowed for each CDMA channel (multirate CDMA). Thus, a different number of chips per bit can be used for the transmission of each scalable layer. For a given fixed energy value per chip and chip rate, the selection of a spreading code length affects the transmitted energy per bit and bit rate for each scalable layer. An MPEG-4 source encoder is used to provide a two-layer signal-to-noise-ratio (SNR) scalable bitstream. Each of the two layers is channel-coded using rate-compatible punctured convolutional (RCPC) codes. Then, the data are interleaved, spread, carrier-modulated and transmitted over the wireless channel. A multipath Rayleigh fading channel model is assumed. At the other end, the signal is collected by an antenna array front. After carrier demodulation, multiple-access-interference (MAI) suppressing despreading is performed using adaptive space-time auxiliary-vector (AV) filters. The choice of the AV space-time receiver is dictated by realistic channel fading rates that limit the data record available for receiver adaptation and redesign. Indeed, short-data-record AV filter estimators have been shown to exhibit superior bit-error-rate performance in comparison with least-mean-squares (LMS), recursive-least-squares (RLS), sample-matrix-inversion (SMI), or ``multistage nested Wiener'' adaptive filter implementations. Our experimental results demonstrate the effectiveness of such a multirate DS-CDMA system for wireless video transmission.