Single frequency broadcasting networks
Abstract: An Orthogonal Frequency Division Multiplexing (OFDM) schemeallows all transmitters in a radio network to transmitidentical signals in the same frequency block, forming a socalled Single Frequency Network (SFN). By avoiding frequencyreuse, substantial improvements in bandwidth utilisation arepossible. The simultaneous transmission creates severeartificial multipath propagation. Thisself-inteiferenceproblem makes it necessary toestablish new planning techniques and performance measures.Based on an analysis of the receiver performance a method toperform coverage calculations is proposed. The receiveranalysis shows that the method that is extensively used intoday's SFN planning is only valid for a special OFDM signalconstellation.One key issue in SFN planning is to find simple andefficient network design rules. Different network architecturesfor both wide area and local SFNs are studied in the thesiswhere we show that the coverage properties depend on manydifferent parameters, e.g. the OFDM constellation, transmitterpower and antenna height. From the obtained results, severaldesign rules are proposed. The most important design parameteris the density of the transmitters which will determine thedegree of diversity. For both wide area and local networks,higher density yields better coverage. We also show that it ispossible to reduce the interference among local networks byincreasing the number of transmitters per local area. Theselection of transrmitter antenna heights is shown to be anon-trivial task for local SFNs mainly due to theseff-interference.Pulse shaping of the transmitted OFDM signal is shown togive significant reductions in self-interference. It is herebypossible to achieve the same coverage with a reduced amount oftransmitters. The system also becomes less sensitive to timeand frequency synchronisation errors.Lastly, we show that an exact network planning of thetransmitters location is not always necessary. For wide areanetworks, quite large displacement from the regular spacing canbe made without any significant losses in coverage. For localarea networks, it is however important to have a set of thetransmitters positioned close to the border.Keywords:digital broadcasting systems, single frequencynetworks, network planning, multicarrier systems, OFDMmodulation, propagation.
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