| Author | Chanyut Phrukkumwong |
| Call Number | AIT Thesis no. TC-96-9 |
| Subject(s) | Cellular radio
|
| 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 |
| Abstract | Mobile radio communications channel, in addition to multipath propagation,
usually exhibits time-variant characteristic due to Doppler shift phenomenon when mobile
station is in relative motion with base station. As a result of continuously varying channel
impulse response, it is essential that the receiver be adaptive. That is, there must be an
adaptive functional block in the receiver. This functional block, called channel estimator,
operates together with Maximum Likelihood Sequence Estimator (MLSE, which makes
use of Viterbi algorithm), the optimum demodulator for various digital modulation
techniques. It approximates the constantly changing channel tap coefficients symbol-bysymbol by utilizing the knowledge of an (estimated) transmitted symbol and a received
symbol. In TDMA systems whose data burst length is unvarying, the knowledge of a
transmitted symbol is precisely known at the receiver in a specific part of the burst (called
training period), and estimated by MLSE at the rest of the burst (called tracking mode).
In a short-burst system like the European GSM system, it is possible that we
estimate the channel impulse response only in training period and then fix the estimate
throughout the entire data burst. However, the error between the estimated and real
channel tap coefficients can be very large and unacceptable in case of high channel time
variation. (This error could be decreased by simply including estimation in tracking mode.)
This occurs only at very high Doppler frequency. But in a long-burst system like North
American IS-54 system, this condition of highly time-variant channel could present at
much lower Doppler frequency.
Conventional channel estimation algorithms commonly used in practice are least
mean square (LMS) algorithm and more computationally complex and faster converging
exponential-windowed recursive least squares (EW-RLS) algorithm. A number of
innovative channel estimation algorithms have been introduced by several authors in order
to cope with the problem of fast time-varying channel. In this study, Suboptimal Kalman
Estimation (SKE) algorithm (NEWSON AND MULGREW, 1994) has been
investigated. And it has been found that EW-RLS algorithm still offers more reliable
estimation results than SKE algorithm. |
| Year | 1996 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Makelainen, Kimmo |
| Examination Committee(s) | Ahmed, Kazi Mohiuddin;Zhang, Jian-Guo |
| Scholarship Donor(s) | Aeronautical Radio of Thailand Ltd.
(AEROTHAI) |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1996 |