We have developed a H.263 based videophone system that works over mobile channels. The system was designed by modifying a software implementation of a H.263 video codec that was developed by Telenor Research. This source code is no longer available from Telenor, however an improved version in available from Univ. British Columbia: Image Processing GroupMaintainers of current version of telenor H.263 software, with H.263+ extensions.
The system uses multiple modulation schemes and uses packet dropping to reduce delay when the channel quality is poor. Here are some of the results obtained by the system in a simulated mobile radio environment.
Here are some of the H.263 sequences as they were received from the
mobile channel simulator. They have been recoded into MPEG format to
make them viewable.
The original video sequence of Miss America @ 30 frames/s
Effect of Packet Dropping
These results show the quality of the decoded video over gaussian (AWGN) channels using 4 QAM modulation. The video can be downloaded and viewed in two formats MPEG, and H.263. This can be done by click the relevant movie icon in the tables below. The MPEG sequences were generated by recoding the decoded H.263, and the quality is therefore not as good as the pure H.263. The H.263 sequences were produced using a software codec from Telenor Research. This source code is no longer available from Telenor, however an improved version in available from Univ. British Columbia: Image Processing GroupMaintainers of current version of telenor H.263 software, with H.263+ extensions.
The Telenor H.263 decoder version 1.5 is required to view the H.263 sequences, the source code can no longer be downloaded from Telenor Research. A Microsoft Windoze version is also available check their Web Site for details. Note however the windoze version probably won't work since it may use a latest version of the decoder. A compiled LINUX binary is available, see below. A MPEG player is available from Berkeley university however this also only compiles for UNIX, but DOS/Windoze versions are available.
The H.263 files are smaller than the MPEG ones, and so are faster to download. The mime-type our server uses for them is video/x-h263. To get your H.263 viewer to work within netscape compile the QCIF version and put the following line in your ~/.mailcap file.
video/x-h263; /usr/local/bin/tmndecode-QCIF -o4 -f10 -q %s
|Very poor channel||5.26||52|
This is a graph of image quality, PSNR(dB) versus frame number for these sequences with packet dropping. (click on graph for full size version).
As the channel degrades and improves the modulation scheme used can be changed to keep down the error rate of the decoded video. Higher order modulation schemes are used when the channels are good, so as to increase the quality of the decoded video. The decoded video sequences below show the image quality for each of the modulation schemes used. To download and view the decoded videos click on the relevant movie icon in the table below. Information on viewers for these videos can be found above.
|4-QAM (AWGN) Error-Free|
|16-QAM (AWGN) Error-Free|
|64-QAM (AWGN) Error-Free|
This is the graph of image quality, PSNR(dB) versus channel SNR(dB) for all the modulation scheme over gaussian and rayleigh channels. (click on graph for full size version).