الفهرس 
ABSTRACTOnly 14 pages are availabe for public view
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Abstract
Orthogonal frequency division multiplexing (OFOM) provides an effective and low complexity means of eliminating intersymbol interference for transmission over frequency selective fading channels. This technique has received a lot of interest in mobile communication research as the radio channel is usually frequency selective and time variant. In OFDM system, modulation may be coherent or differential. Channel state information (CSI) is required for the OFOM receiver to perform coherent detection or diversity combining, if multiple transmit and receive antennas are deployed. In practice, CSI can be
reliably estimated at the receiver by transmitting pilots along with data symbols. Pilot symbol assisted channel estimation is especially attractive for wireless links, where the channel is time-varying. When using differential modulation there is no need for a channel estimate but its performance is inferior to coherent system.In this thesis, various efficient pilot based channel estimation schemes for OFOM systems and compared. The channel estimation can be performed by either inserting pilot tones into all subcarriers of OFDM symbols with a specific period or inserting pilot
tones into each OFOM symbol. In this present study, two major types of pilot arrangement such as block-type and comb-type pilot have been focused employing Least Square Error (LSE) and Minimum Mean Square Error (MMSE) channel estimators. Block type pilot sub- carriers is especially suitable for slow-fading radio channels whereas comb type pilots provide better resistance to fast fading channels. Also, comb type pilot arrangement is sensitive to frequency selectivity when comparing to block type arrangement. The channel
estimation algorithm based on comb type pilots is divided into pilot signal estimation and channel interpolation. The pilot signal estimation is based on LSE and MMSE criteria, together with channel interpolation using linear interpolation and spline cubic interpolation. The bit error rate (BER) performances of OF OM system for both block type and comb type pilot subcarriers are presented in the thesis.Orthogonal frequency division multiplexing (OFOM) can be combined with transmitter and receiver diversity communication systems. Maximal ratio combining (MRC) and space-time block coding (STBC) can be used in conjunction with receiver and transmitter diversity in order to improve the communication system performance through reducing its bit error rate.