Local Coverage Probability Estimation in Single Frequency Networks

Abstract

In OFDM based Single Frequency Networks (SFNs) such as Digital Audio Broadcasting (DAB) and Digital Video Broadcasting (DVB), the mobile receiver is provided by the same signal from several synchronous transmitters at the same carrier frequency. This transmitter diversity structure makes SFNs very efficient in fading channels with an excellent spectrum saving, and very good power utilization over the service area. However, depending on the position of the mobile within the service area, these signals arrive with different delays causing possible echoes at the receiver. These echoes contribute to both the useful and the interfering parts of the signal. As the average received power in radio channels is a stochastic process, such contribution creates correlation between the different components of the Signal-to-Interference Ratio (SIR). In broadcasting practice, correlation was not taken into account when estimating the distribution of the SIR and the local coverage probability. This paper considers the effect of correlation on the estimation of the SIR and the coverage probability in OFDM based SFNs. Analyses are provided to show that in some situations the estimation error can be considerable when neglecting this correlation. To obtain a better estimation, the correlation coefficient between the total useful and total interfering parts of the received signal is first evaluated and then used as a correction factor in estimating the mean and standard deviation of the SIR. The obtained results show that such method can significantly reduce the estimation error of local coverage probability without increasing the computation complexity.