| Author | Peiris, Beminihennadige Janath |
| Call Number | AIT Thesis no.TC-00-03 |
| Subject(s) | Wireless communication systems
|
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of
Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. TC-00-03 |
| Abstract | Orthogonal Frequency Division Multiplexing (OFDM) has received considerable
attention due to its robustness against multipath fading and impulsive noise. It has been
adopted as a standard for Digital Audio Broadcasting (DAB) and Asymmetric Digital
Subscriber Line (ASDL). Despite its promises, it has been shown that OFDM is very sensitive
to inaccurate frequency references, which may be caused by Doppler effect or transmitter,
receiver oscillator instabilities. This thesis investigates the effect of frequency offset in
OFDM.
A new technique is proposed for carrier frequency offset estimation using redundancy
due to symbol repetition in self intercarrier interference (ICI) cancellation for OFDM based
systems. An Estimator derived is based on maximum likelihood estimation algorithm makes it
possible to estimate the frequency offset up to subcarrier separation. A rough estimator for
frequency offset has also been derived with lower computational complexity. The estimated
frequency offset value is used to compensate the frequency offset at the front end of the
receiver. Subsequently this value is fed to the self ICI cancellation decoder for elimination of
the residual frequency offset which is not compensated at the receiver front end.
To compare the performance improvement of the proposed scheme, simulations have
been carried out for Additive White Gaussian Noise (A WGN) channel and mutipath fading
channel. It is shown that for higher frequency offset values, the proposed scheme gives a
better performance. The self ICI cancellation scheme doubles the bandwidth requirement due
to symbol repetition. A high-rate coding scheme is required for self ICI cancellation based
OFDM systems to avoid further reduction of bandwidth efficiency with the proposed offset
correction scheme. The application of trellis coded modulation (TCM) is discussed. It is
shown the proposed scheme gives better performance with application of TCM coding
compared to the uncoded scheme. It is further shown that the performance of the self ICI
cancellation scheme, with the application of TCM scheme, is lower than that of uncoded self
ICI cancellation scheme, at higher values of frequency offset.
In addition to previous studies, the frequency domain correlative coding is also used to
reduce the effect of frequency offset. The simulation results for A WGN channel and multipath
fading channel are given. It is shown that the system performance increases with the
application of correlative coding without sacrificing the bandwidth. |
| Year | 2000 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-00-03 |
| 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.;Makelainen, kimmo ; |
| Scholarship Donor(s) | Government of Finland; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2000 |