An accurate assessment of channel conditions represents a first step in any interference mitigation strategy. This channel assessment is generally performed at the receiver and used by the transmitter in order to make an informed decision about the channel state. In some cases, the channel assessment is also performed at the transmitter's side. This is common in most carrier sense multiple access systems, where devices have to “listen” to the medium before transmission. In this case, the transmitter and the receiver devices are assumed to be closely located and therefore have the same channel conditions. However, it is not uncommon for the receiver side to be experiencing different channel conditions from the transmitter. This situation is also known as the hidden node problem and conversely the exposed node problem in carrier sense multiple access sytems. Therefore, to optimize communication it is critical that each transmitter and receiver pair maintains the state of the channel as seen by the receiver.

Given this need to assess the channel conditions per transmitter and receiver pair, there are two basic channel estimation strategies. Channel estimation can be based on either explicit or implicit methods. Explicit methods include bit error rate calculation, packet loss, or frame error rate measurements performed on each receiver. The measurements are then conveyed to the transmitter device at regular time intervals. Alternatively, implicit methods do not require the transmitter and receiver devices to exchange information about the state of the channel.