Communication channel

A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for information transfer of, for example, a digital bit stream, from one or several senders to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.

Communicating an information signal across distance requires some form of pathway or medium. These pathways, called communication channels, use two types of media: Transmission line-based telecommunications cable (e.g. twisted-pair, coaxial, and fiber-optic cable) and broadcast (e.g. microwave, satellite, radio, and infrared).

In information theory, a channel refers to a theoretical channel model with certain error characteristics. In this more general view, a storage device is also a communication channel, which can be sent to (written) and received from (reading) and allows communication of an information signal across time.

(BSC), a discrete memoryless channel with a certain bit error probability

Binary symmetric channel

(BAC), similar to BSC but the probability of a flip from 0 to 1 and vice-versa is unequal

Binary asymmetric channel

Binary channel model, a channel with memory

bursty bit error

(BEC), a discrete channel with a certain bit error detection (erasure) probability

Binary erasure channel

where packets are lost with a certain packet loss probability or packet error rate

Packet erasure channel

(AVC), where the behavior and state of the channel can change randomly

Arbitrarily varying channel

(discrete) or analog (continuous) channel

Digital

for example a fiber-optic cable

Transmission medium

Multiplexed channel

Computer network

virtual channel

duplex communication or half-duplex communication channel

Simplex communication

Return channel

or downlink (upstream or downstream channel)

Uplink

unicast channel or multicast channel

Broadcast channel

in Hertz

Spectral bandwidth

in baud, symbols/s

Symbol rate

in bit/s measures: gross bit rate (signalling rate), net bit rate (information rate), channel capacity, and maximum throughput

Digital bandwidth

Channel utilization

Spectral efficiency

in decibel measures: signal-to-interference ratio, E_b/N₀

Signal-to-noise ratio

(BER), packet error rate (PER)

Bit error rate

in seconds: propagation time, transmission time, round-trip delay, end-to-end delay

Latency

Packet delay variation

Eye pattern

These are examples of commonly used channel capacity and performance measures:

A , 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 unicasting.

point-to-multipoint channel

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.

Multiple access

: 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.

Relay 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 systems like 3G, interference also occurs inside the cell if non-orthogonal codes are used.

Interference channel

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 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.

broadcast

A 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).

multicast

In networks, as opposed to 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: