The original video sequence of Miss America
We have developed a H.261 based videophone system that works over mobile channels, rather than ISDN lines as H.261 was designed for. 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.261 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
These results show the quality of the decoded video over gaussian (AWGN) channels using 16 QAM modulation. Click on the description in the table for the decoded video sequence.
| Description | SNR(dB) | Packets Dropped(%) |
|---|---|---|
| Very poor channel | 11 | 60 |
| Poor channel | 11.5 | 31 |
| Standard channel | 12 | 10 |
| Good channel | 13 | 1 |
| Error-free channel | n/a | 0 |
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.
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).
