| Author | Chatterjee, Sujoy |
| Call Number | AIT Thesis no.TC-03-07 |
| Subject(s) | Code division multiple access
|
| 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-03-07 |
| Abstract | Adaptive modulation is proposed by many researchers for future generation
wireless networks based on multi-carrier transmission technologies. In adaptive
modulation, the modulation format of the signal is dynamically changed depending upon
the channel scenario. Thus, one of the most important aspects of adaptive modulation
based systems is reliable channel estimation. Channel estimation may be of two types:
pilot signal based and blind. Pilot based estimation may be computationally simpler, but
the practical implementation complexity of the overall system is high. On the other hand,
blind estimation methods are computationally complex, but as these are independent of
the transmitter, the overall system complexity is lower. Moreover, the full available
bandwidth can be utilized for information transmission.
This thesis is mainly aimed at investigating some blind mechanisms at the receiver
of adaptive modulation based coded OFDM-CDMA systems in Rayleigh fading channels,
for enhancement of the systems both in terms of practical implementation and data
throughput capacity. In this respect, blind techniques to estimate the channel impulse
response and modulation scheme are investigated and their effect on the BER
performance of the systems are analyzed.
A subspace based algorithm is used to estimate the channel impulse response
blindly. This estimate is then used to coherently demodulate the OFDM-CDMA signals
and adaptively switch the modulation schemes for varying channel condition. Simulation
results show that the systems based on blind channel estimation show degradation in
terms of the BER performance. This degradation is due to the errors occurring in the
estimation process because of the high computational complexity of the estimation
algorithm. However, the advantages of blind channel estimation far outweigh this
degradation.
An algorithm to estimate the modulation scheme at the receiver is also proposed.
Results show error free estimation of modulation scheme for a maximum 7 number of
active users in the system at a channel condition of 20 dB. |
| Year | 2003 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-03-07 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Ahmed, Kazi M. ; |
| Examination Committee(s) | Erke, Tapio J. ;Teerapat Sanguankotchakorn; |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2003 |