Performance evaluation of LMDS with OFDM in different channel models | |
| Author | Laizu, Zebunnessa |
| Call Number | AIT Thesis no.TC-02-15 |
| Subject(s) | Wireless communication systems Broadband 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-02-15 |
| Abstract | Local Multipoint Distribution System (LMDS) is currently a promising technology in broadband fixed wireless communications. Cellular structure, high data rates, and flexibility make it perfect for multimedia, digital television, and interactive services. The modem design of LMDS must be matched to the channel characteristics, as the channel behavior is very much different from those of lower frequency wireless communications systems. From various measurements all over the world, it has been seen that, one of the main channel impairments of LMDS in addition to inevitable additive white Gaussian noise (A WGN) is, intersymbol interference (ISI) introduced by multipath propagation. Typical power delay profile reveals the presence of ISI, which can cause severe performance degradation if left un-addressed. To combat ISI in wideband channels Orthogonal Frequency Division Multiplexing (OFDM) is a suitable technique. OFDM is an efficient multicarrier modulation scheme used to avoid ISI due to multipath propagation in radio communications. Since each OFDM sub-carriers occupies a very narrow spectrum, one tap equalizer is usually used for each sub-carrier to correct channel distortion. The tap co-efficient is calculated based on channel state information. In this thesis, the use of OFDM for LMDS is proposed and performance has been investigated over different measured channels. Simulations have been carried out to compare the bit error rate (BER) performance of LMDS with OFDM and without OFDM along with forward error correction coding (FEC). In this thesis concatenated Reed Solomon outer coding and convolutional inner coding are used with block interleaving. Simulations have been carried out for AWGN, Rician, Static multipath channels and Time varying multipath channels for the proposed system and compared with the existing system. The results show that OFDM based LMDS gives BER of I 0-5 at about 20 dB SNR for most of the multipath models, whereas the system without OFDM gives BER of 10-3 for the number of transmitted bits 107. So, a BER improvement of 10-2 is achieved by the proposed system for same condition of propagation. For more number of bits it will give better result. |
| Year | 2002 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-02-15 |
| 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 ;Teerapat Sanguankotchakorn; |
| Scholarship Donor(s) | Government of Norway; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2002 |