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.