Reception of OFDM signals with an array antenna in a SFN environment

In the OFDM SFN (single frequency network) system, where the received signal from the main broadcast station is rebroadcast at the relay station, the area where the delay spread of the received signal is longer than the guard interval length increases as compared to the SFN system where the signals are transmitted at the same time both from the main station and from the relay station. If the channel delay spread is longer than the guard interval length, inter-symbol interference (ISI) and inter-carrier interference (ICI) are generated at the receiver and the bit error rate (BER) characteristics are much degraded. Therefore, the service area of the OFDM SFN system where the signal is re-broadcast at the relay station is narrower that that of the OFDM system where the signals are broadcast at the same time from both stations. In order to improve this problem, an SFN system that rebroadcasts the received signal from the main station after adding an appropriate delay is proposed. We propose an array antenna receiver using a maximum ratio combining technique for the SFN system, where additive delay is inserted to the signal at the relay station. By theoretical analyses and computer simulations, better BER characteristics than the conventional system are confirmed.