| Abstract | MPEG-2 video communication over wireless challilels has been rece1vmg a lot of
attention recently. MPEG-2 video is, however, extremely sensitive, due to the compression
techniques it employs, to transmission errors. One single bit error may dramatically degrade
the quality of the reconstructed video. Forward error correction (FEC) may be used to protect
the transmitted video sequence. The sensitivity of different bits in the sequence, to
transmission errors, however, varies from bit to bit. Unequal error protection (UEP) is
therefore more beneficial than equal error protection (EEP). Furthermore, frequency-selective
wireless challilels exhibit different fading levels over a period. The error correction
assignments should also vary adaptively with the transmission conditions.
In this thesis, the effects of bit errors at different positions in the video sequence were
investigated. Results of the investigation show that the degree of importance of the bits in each
slice varies from bit to bit. The bits at the begilliling of each slice are far more important than
those bits at the far end of the slice. Therefore, the bits in each slice should be provided with
different error control levels in order to improve video quality while minimizing the overhead
due to FEC.
A new UEP scheme was proposed, based on the above investigation results, which can
improve the video quality of MPEG-2 video, transmitted over frequency selective RC1 yleigh
fading challilels, without bandwidth expansion. In this scheme, not only header and control
info1mation is provided with higher error control level, but also the video data in each slice is
unequally protected. Here, an MPEG-2 video sequence is first split into different layers
according to their importance. In each layer, the header and control information is separated
and protected by higher error protection level. The video data in each slice is also unequally
protected according to the position of the data in the slice. Rate-compatible punctur ~d
convolutional codes, obtained by puncturing a (3,1,6) convolutional code, are used to provide
UEP for the video sequence.
The simulation results (using different video sequences) show remarkable improvement in
both objective (up to 4 dB improvement in peak signal to noise ratio was observed) and
subjective video quality compared to the video quality that was transmitted under the EEP
scheme. Furthermore, the proposed scheme yields the same, or even slightly less, amount of
overhead, due to FEC, compared to the EEP scheme. It was further noted that if the challilel
state information is available at the transmitter, different error correction assignments could be
applied adaptively with the challilel state information, which may give better results. It can,
based on the above results, be concluded that the proposed scheme is a robust scheme to
transmit MPEG-2 video over wireless challilels under a bandwidth constraint. |