A Single Frequency Network (SFN) is a broadcast network where multiple transmitters simultaneously send the same signal over the same frequency. This method is particularly beneficial for broadcasting technologies like T-DAB (terrestrial digital radio) and DVB-T (terrestrial digital television), and can also be applied to wireless local networks.

The core of an SFN’s functionality lies in its use of Coded Orthogonal Frequency Division Multiplexing (COFDM). COFDM excels in handling signals that arrive with their own echoes, a phenomenon known as multipath reception. To combat this, SFNs employ a ‘guard interval’—a break between data transmissions—which helps in distinguishing between the original signal and its echoes. This technique, while reducing the transmission capacity, is crucial for the network’s resilience against multipath effects.

In an SFN, overlapping transmitters on the same frequency create a larger coverage area. In these overlapping zones, the weaker signal is treated as an echo. However, for this system to work efficiently, the echoes must arrive within the guard interval, and the transmitters need to be perfectly synchronized. The larger the distance between transmitters, the longer the guard interval required to accommodate the time delay between signals.

Despite its advantages in extending coverage, SFNs have certain limitations: the guard interval diminishes the network’s capacity, there’s no flexibility for local programming variations, and there’s a necessity for precise synchronization among transmitting stations.