Editing Orthogonal frequency-division multiplexing (section)

=== Space diversity ===
In OFDM-based wide-area broadcasting, receivers can benefit from receiving signals from several spatially dispersed transmitters simultaneously, since transmitters will only destructively interfere with each other on a limited number of subcarriers, whereas in general they will actually reinforce coverage over a wide area. This is very beneficial in many countries, as it permits the operation of national [[single-frequency network]]s (SFN), where many transmitters send the same signal simultaneously over the same channel frequency. SFNs use the available spectrum more effectively than conventional multi-frequency broadcast networks ([[Multi-frequency network|MFN]]), where program content is replicated on different carrier frequencies. SFNs also result in a [[diversity gain]] in receivers situated midway between the transmitters. The coverage area is increased and the outage probability decreased in comparison to an MFN, due to increased received signal strength averaged over all subcarriers.

Although the guard interval only contains redundant data, which means that it reduces the capacity, some OFDM-based systems, such as some of the broadcasting systems, deliberately use a long guard interval in order to allow the transmitters to be spaced farther apart in an SFN, and longer guard intervals allow larger SFN cell-sizes. A rule of thumb for the maximum distance between transmitters in an SFN is equal to the distance a signal travels during the guard interval — for instance, a guard interval of 200 microseconds would allow transmitters to be spaced 60&nbsp;km apart.

A ''single frequency network'' is a form of transmitter [[macrodiversity]]. The concept can be further used in ''[[dynamic single-frequency networks]]'' (DSFN), where the SFN grouping is changed from timeslot to timeslot.

OFDM may be combined with other forms of [[space diversity]], for example [[Phased array|antenna arrays]] and [[MIMO]] channels. This is done in the [[IEEE 802.11]] [[Wireless LAN]] standards.