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This paper investigates the application of multi-code SS-CDMA
techniquesto three-dimensional stereoscopic video transmission
over wireless ATM networks. 3D visual communications, made
through the use of stereoscopic images, are able toachieve total
display realism. Such services allow users to share the virtual
reality (VR)world without any geographical restrictions. In
order to create a 3D system with two images (left and right)
that should be transmitted over a bandlimited mobile
channelsimultaneously, a cost-effective MPEG-based wavelet
multiresolution coding with an joint motion- and disparity-
compensation is developed to reduce a large amount of
information contained in the images in order to the meet the low
transmission rate limitationof mobile channels. However, the
rapidly variable bit rate (VBR) characteristics of the MPEG-
based 3D videos seems a weakness to the transmission of such
videos via a constantbit-rate (CBR) mobile channel.The ATM
technique is especially wellsuited for variable bit rate (VBR)
MPEG-based 3D video because of its ability to allocate bandwidth
on demand to these services.However, since the mobile radio has
a limited channel capacity,the overall capacity of the
traditional ATM-based SS-CDMA system may not be sufficientto
accommodate the MPEG-based 3D video services requested bythe
multiple mobile users simultaneously.To tackle this difficulty,
a multi-code CDMA technique is proposed to provide VBR MPEG-
based 3D video services by varying the number of spreading codes
assigned to the 3D video in order to meet its dynamic throughput
requirement. Meanwhile, these extra spreading codes would
alsocreate the interference to the other videos and degrade
their picture quality. Hence, a cost-effectivespreading code
assignment mechanism has then been proposed to dynamically
assignappropriate number of codes to each video for achieving
both the maximum resource utilizationand the best picture
quality for multiple video services via the mobile radio
channel. However, both the fading and interference on SS-CDMA
radio channels tend to cause significanttransmission error and
MPEG-based 3D video bit streams are very vulnerable to these
errors. Powerfulforward error correction(FEC) codes are
therefore necessary to protect the video dataso that it can be
successfully transmitted at acceptable signal power levels. Two
separate FEC code schemes are applied to the header and payload
of a ATM cell containing 3D video data,respectively. The ATM
cell header is protected by a relatively powerful FEC code to
ensure correctdelivery and low cell loss rate (CLR).On the other
hand, the ATM cell payload is encoded for varying degrees of
error protection accordingto the priority of the payload data in
MPEG2 videos. An adaptive FEC code combining scheme is
proposedto provide the good protection for payload data with the
maximizationof its code rate in order to minimize the extra
bandwidth for FEC overhead.Simulation results would show that
our FEC code combining scheme is able to ensurethe average
number of ATM cell losses in each typical 3D picture frame bein
the order of O(1).
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