| Summary: | 碩士 === 國立中央大學 === 資訊工程研究所 === 95 === With the advance of wireless network technologies, wireless multimedia applications can be
widely used in the near future. The video transmission over wireless networks is an important and
inevitable trend by providing handheld devices with the telecommunication technique. However,
the wireless networks are not trustworthy and reliable. The video multi-media over the wireless
network service will be filled with challenges. The forward error correction (FEC) usually
reduces the errors of the wireless networks with high bit error rate (BER). The FEC sends out
redundant data packets to recover the data errors. If we want to correct data during the wireless
networks with higher BER, we need to send more redundant information. If the BER of wireless
networks is high, the low-strength error correction coding does not offer notable improvement.
On the other hand, the high-strength of error correction coding in low BER would waste network
bandwidth. It is reasonable that using dynamic FEC adapts the variety of BER. For raising the
power of forward error correction for video delivery over wireless networks, we present an
adaptive forward error correction (AFEC) mechanism.
In our AFEC mechanism, if the sender receives feedback information, it will decide whether
the forward error correction transmission should be used or not. The AFEC would adjust the
additional length (redundancy) of data according to the BER of wireless networks. The sender
would not stop transferring data for waiting the feedback information. The result of the
experiments reveals that the AFEC mechanism can improve the quality of video delivery over
bad situations. The experiment comparison result shows that the image quality of AFEC
obviously better than the image quality without FEC method. When PER is 0.2, The PSNR of
AFEC mechanism is higher without FEC mechanism more than 10 db. The result shows that the
image quality of AFEC mechanism almost the same with fixed FEC mechanism. However, AFEC
mechanism cost less redundant packets obviously. When PER is 0.005, the AFEC mechanism
only increase 6% redundancies. In the same situation, Fixed FEC mechanism still increase 100%
redundancies. The AFEC provides a new method for transferring online video. We also suggest a
mean frame corruption rate which estimates a video error rate. The user can set the optimal
threshold value for AFEC according to different video quality level.
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