Multiuser wireless channel models

Multiuser wireless channel models usually depict simple scenarios where more than one user is present in the wireless network, and possible interactions between them capture features of the wireless medium that are not available in a point to point channel. Those models given one reason for the usefulness of results in Multiterminal information theory.

Motivation
Due to the broadcast and superposition features of the wireless medium, it is possible for communication to occur between a single transmitter and multiple receivers, or multiple transmitters and a single receiver, simultaneously, with respect to order. Furthermore, undesired interfering signals can be present at receivers in a general wireless network. The above phenomena give rise to Broadcast, Multiple-access, and Interference channels models.

One wireless channel can be different from another, due to both distance based attenuation and fading. For this reason, it might be useful for transmitters to cooperate or relay each other’s messages. The relay channel model studies the latter possibility in a simple scenario. Various models for cooperative communications also exist in the literature.

An obvious treatment of multiuser wireless communication considers each existing point to point channel in the network separately, thus, making use of the already devised schemes for point to point communication. However, the implementation of these schemes requires orthogonal resource allocation, for example activating only one user in each channel use, in a multiple-user interference channel. This is proven to be strictly suboptimal in a multitude of scenarios. Examples to schemes that activate many users sharing the same wireless medium at the same time include, but are not limited to, superposition coding and interference alignment. For this very reason, analyzing multiuser wireless channel models is beneficial and introduces insights that are not acquired through the point to point channel model.