Editing Communication channel (section)

==Multi-terminal channels, with application to cellular systems==
{{Confusing section|date=March 2010}}
{{See also|Network topology}}
In networks, as opposed to [[point-to-point (network topology)|point-to-point]] communication, the communication media can be shared between multiple communication endpoints (terminals). Depending on the type of communication, different terminals can cooperate or interfere with each other. In general, any complex multi-terminal network can be considered as a combination of simplified multi-terminal channels. The following channels are the principal multi-terminal channels first introduced in the field of information theory{{Citation needed|date=March 2010}}:
* A [[point-to-multipoint communication|point-to-multipoint channel]], also known as broadcasting medium (not to be confused with broadcasting channel): In this channel, a single sender transmits multiple messages to different destination nodes. All wireless channels except directional links can be considered as broadcasting media, but may not always provide broadcasting service. The [[downlink]] of a cellular system can be considered as a point-to-multipoint channel, if only one cell is considered and inter-cell co-channel interference is neglected. However, the communication service of a phone call is [[unicast]]ing.
* [[Multiple access]] channel: In this channel, multiple senders transmit multiple possible different messages over a shared physical medium to one or several destination nodes. This requires a [[channel access]] scheme, including a [[media access control]] (MAC) protocol combined with a [[multiplexing]] scheme. This channel model has applications in the [[uplink]] of cellular networks.
* [[Relay channel]]: In this channel, one or several intermediate nodes (called relay, [[repeater]] or [[gap filler]] nodes) cooperate with a sender to send the message to an ultimate destination node.
* [[Interference channel]]: In this channel, two different senders transmit their data to different destination nodes. Hence, the different senders can have a possible crosstalk or co-channel interference on the signal of each other. The inter-cell interference in cellular wireless communications is an example of an interference channel. In [[Spread spectrum|spread-spectrum systems]] like 3G, interference also occurs inside the cell if non-orthogonal codes are used.
* A unicast channel is a channel that provides a unicast service, i.e. that sends data addressed to one specific user. An established phone call is an example.
* A [[broadcast]] channel is a channel that provides a broadcasting service, i.e. that sends data addressed to all users in the network. Cellular network examples are the [[paging]] service as well as the [[Multimedia Broadcast Multicast Service]].
* A [[multicast]] channel is a channel where data is addressed to a group of subscribing users. LTE examples are the physical multicast channel (PMCH) and multicast broadcast single frequency network (MBSFN).