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One of the most promising approaches to 3G is to combine a Wideband Code Division Multiple Access (WCDMA) air interface with the fixed network of Global System for Mobile communications (GSM).
OFDM was found to have total immunity to multipath delay spread provided the reflection time is less than the guard period used in the OFDM signal.
In fact, multipath signals lead to a strengthening of the received signal, improving the performance.
This low cell capacity of CDMA was attributed to the use of non-orthogonal codes used in the reverse transmission link, leading to a high level of inter-user interference.
The only main weak point that was found with using OFDM, was that it is very sensitive to frequency, and phase errors between the transmitter and receiver.
This thesis investigates the effectiveness of Orthogonal Frequency Division Multiplexing (OFDM) as a modulation technique for wireless radio applications.
The main aim was to assess the suitability of OFDM as a modulation technique for a fixed wireless phone system for rural areas of Australia.
The main sources of these errors are frequency stability problems; phase noise of the transmitter; and any frequency offset errors between the transmitter and receiver.
This problem can be mostly overcome by synchronizing the clocks between the transmitter and receiver, by designing the system appropriately, or by reducing the number of carriers used. Keith Kikkert for the endless hours of help, suggestions, ideas and advise during the development of this thesis. Greg Allen for his advise, focus, and pep talks to keep me on track.
In a typical system a delay spread of up to 100 msec could be tolerated, corresponding to multipath reflections of 30 km.
The only problem caused by multipath is frequency selective fading, which can result in carriers being heavily attenuated due to destructive interference at the receiver.