| Author | Gajaweera, Ruwan Naminda |
| Call Number | AIT Thesis no.TC-00-09 |
| Subject(s) | Video compression
|
| Note | A thesis submitted in partial fulfillment of the requirement for the degree of Master of
Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. TC-00-09 |
| Abstract | The proposed third generation (3G) mobile systems offer an extended data rates up
to 384 kbps for wide area coverage and 2 Mbps for local coverage. The emerging low-bitrate
video compression techniques, such as ISO MPEG-4 and ITU-T H.263 can produce
acceptable quality video at bit rates even less than 64 kbps. However, direct adaptation of
these video compression techniques over hostile mobile channels are limited by random
and burst errors due to multipath fading. Further, compressed video signals are extremely
vulnerable against such transmission errors mainly due to extensive use of variable length
coding and predictive coding techniques. A single error may ruin the synchronization and
result an undecodable bit stream.
Among various techniques for error control, automatic repeat request scheme
(ARQ) is one method to achieve better quality video. However, retransmission of corrupted
data frames introduce additional delay, which might be unacceptable for real-time
applications. In contrast to ARQ schemes, unequal error protection schemes are attractive
since perceptually important bits exist in compressed video.
In this work, unequal error protection (UEP) scheme is considered. The compressed
video bit stream is split into two separate partitions, considering the perceptually
significance of bits present and are provided with different degrees of protection for each.
In our work, all header information up to macro block header and first one or two
variable length codes containing low frequency discrete cosine transformed coefficients of
each block are partitioned in to a better protected partition and the rest of the variable
length codes are placed in a less protected partition. Therefore, even if there is an
uncorrectable error in the second partition, the first partition contains adequate information
to reconstruct the picture with acceptable video quality. The selected partitioning scheme is
applied to the ITU-T H.263 coding standard.
Two channel coding schemes; punctured convolutional codes with hard/soft Viterbi
decoding and turbo codes with iterative decoding have been used in conjunction with the
partitioning scheme to provide UEP. The former coding method found to be attractive for
UEP with a simple decoder structure and the latter could be a possible channel coding
scheme for third generation mobile systems.
The performance of the proposed scheme is evaluated over an A WGN channel and
a channel closely matched with W-CDMA down link parameters via simulation.
Comparison of performance is done with an equal error protection scheme and an existing
unequal error protection scheme. In our evaluation method frame by frame peak signal to
noise ratio (PSNR) and a subjective visual assessment are taken to evaluate the system
performance.
The proposed scheme showed a moderate improvement in PSNR over an A WGN
channel and significant improvement in PSNR over W-CDMA channel compared to equal
error protection scheme and a selected reference scheme at an operating point, where BER
is around 10-5. |
| Year | 2000 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-00-09 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Rajatheva, R.M.A.P ; |
| Examination Committee(s) | Ahmed, Kazi M.;Kimmo Makelainen; |
| Scholarship Donor(s) | Government of Finland; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2000 |