This thesis investigates four FEC (forward error correction) coding schemes for their suitability
for a broadcast system where there is one energy-rich transmitter and many energy-constrained
receivers with a variety of channel conditions. The four coding schemes are: repetition codes (the
baseline scheme); Reed-Solomon (RS) codes; Luby-Transform (LT) codes; and a type of RS and
LT concatenated codes. The schemes were tested in terms of their ability to achieve both high
average data reception success probability and short data reception time at the receivers (due to
limited energy). The code rate (Rc) is fixed to either 1/2 or 1/3. Two statistical channel models were
employed: the memoryless channel and the Gilbert-Elliott channel. The investigation considered
only the data-link layer behaviour of the schemes. During the course of the investigation, an
improvement to the original LT encoding process was made, the name LTAM (LT codes with
Added Memory) was given to this improved coding method. LTAM codes reduce the overhead
needed for decoding short-length messages. The improvement can be seen for decoding up to
10000 number of user packets. The maximum overhead reduction is as much as 10% over the
original LT codes.
The LT-type codes were found to have the property that can both achieve high success data
reception performance and flexible switch off time for the receivers. They are also adaptable to
different channel characteristics. Therefore it is a prototype of the ideal coding scheme that this
project is looking for. This scheme was then further developed by applying an RS code as an
inner code to further improve the success probability of packet reception. The results show that
LT&RS code has a significant improvement in the channel error tolerance over that of the LT
codes without an RS code applied. The trade-off is slightly more reception time needed and more
decoding complexity. This LT&RS code is then determined to be the best scheme that fulfils the
aim in the context of this project which is to find a coding scheme that both has a high overall data
reception probability and short overall data reception time.
Comparing the LT&RS code with the baseline repetition code, the improvement is in three
aspects. Firstly, the LT&RS code can keep full success rate over channels have approximately
two orders of magnitude more errors than the repetition code. This is for the two channel models
and two code rates tested. Secondly, the LT&RS code shows an exceptionally good performance
under burst error channels. It is able to maintain more than 70% success rate under the long
burst error channels where both the repetition code and the RS code have almost zero success
probability. Thirdly, while the success rates are improved, the data reception time, measured in
terms of number of packets needed to be received at the receiver, of the LT&RS codes can reach a
maximum of 58% reduction for Rc = 1=2 and 158% reduction for Rc = 1=3 compared with both
the repetition code and the RS code at the worst channel error rate that the LT&RS code maintains
almost 100% success probability.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/7902 |
| Date | January 2013 |
| Creators | Wang, Xiaohan Sasha |
| Publisher | University of Canterbury. Computer Science and Software Engineering |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Xiaohan Sasha Wang, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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