In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium

Transmission medium

A transmission medium is a material substance that can propagate energy waves...

 such as a wire, or to a logical connection over a multiplexed

Multiplexing

The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...

 medium such as a radio channel. A channel is used to convey

Information transfer

In telecommunications, information transfer is the process of moving messages containing user information from a source to a sink.Note: The information transfer rate may or may not be equal to the transmission modulation rate.-See also:...

 an information

Information

Information in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...

 signal, for example a digital bit stream, from one or several sender

Sender

A sender was a circuit in a 20th century electromechanical telephone exchange which sent telephone numbers and other information to another exchange. In some American exchange designs, for example 1XB switch the same term was also used to refer to the circuit that received this information...

s (or transmitters) to one or several receivers

Receiver (Information Theory)

The receiver in information theory is the receiving end of a communication channel. It receives decoded messages/information from the sender, who first encoded them. Sometimes the receiver is modeled so as to include the decoder. Real-world receivers like radio receivers or telephones can not be...

. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz

HZ

Hz is the International Standard symbol for Hertz, the unit of frequencyHZ may also stand for:* Habitable zone, the distance from a star where a planet can maintain Earth-like life* Hamilton Zoo, in New Zealand...

 or its data rate

Data signaling rate

In telecommunication, data signaling rate , also known as gross bit rate, is the aggregate rate at which data pass a point in the transmission path of a data transmission system.Notes:#The DSR is usually expressed in bits per second....

 in bits per second

Bit rate

In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

In information theory

Information theory

Information theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...

, a channel refers to a theoretical channel model with certain error characteristics. In this more general view, a storage device

Storage device

Storage device may refer to:*Box, or any of a variety of containers or receptacles*Data storage device, a device for recording information, which could range from handwriting to video or acoustic recording, or to electromagnetic energy modulating magnetic tape and optical discs* Object storage...

 is also a kind of channel, which can be sent to (written) and received from (read).

Examples

A channel can take many forms. Examples of communications channels include:

1. A connection between initiating and terminating nodes of a circuit
   Telecommunication circuit
   A telecommunication circuit is any line, conductor, or other conduit by which information is transmitted.A dedicated circuit, private circuit, or leased line is a line that is dedicated to only one use...
   
   .
2. A single path provided by a transmission medium
   Transmission medium
   A transmission medium is a material substance that can propagate energy waves...
   
    via either
   • physical separation, such as by multipair cable
     Cable
     A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...
     
      or
   • electrical separation, such as by frequency-division
     Frequency-division multiplexing
     Frequency-division multiplexing is a form of signal multiplexing which involves assigning non-overlapping frequency ranges to different signals or to each "user" of a medium.- Telephone :...
     
      or time-division
     Time-division multiplexing
     Time-division multiplexing is a type of digital multiplexing in which two or more bit streams or signals are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent...
     
      multiplexing
     Multiplexing
     The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
     
     .
3. A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths.
   • A storage
     Data storage device
     thumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....
     
      which can communicate a message over time as well as space
   • The portion of a storage medium, such as a track
     Track (disk drive)
     A disk drive track is a circular path on the surface of a disk or diskette on which information is magnetically recorded and from which recorded information is read....
     
      or band, that is accessible to a given reading or writing station or head.
   • A buffer from which messages can be 'put' and 'got'. See Actor model and process calculi
     Actor model and process calculi
     In computer science, the Actor model and process calculi are two closely related approaches to the modelling of concurrent digital computation...
     
      for discussion on the use of channels.
4. In a communications system
   Communications system
   In telecommunication, a communications system is a collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment usually capable of interconnection and interoperation to form an integrated whole...
   
   , the physical or logical link that connects a data
   Data
   The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
   
    source to a data sink.
5. A specific radio frequency
   Radio frequency
   Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
   
   , pair or band of frequencies, usually named with a letter, number, or codeword, and often allocated by international agreement.
   Examples:
   • Marine VHF radio
     Marine VHF radio
     Marine VHF radio is installed on all large ships and most seagoing small craft. It is used for a wide variety of purposes, including summoning rescue services and communicating with harbours, locks, bridges and marinas, and operates in the VHF frequency range, between 156 to 174 MHz...
     
      uses some 88 channels in the VHF band for two-way FM voice communication. Channel 16, for example, is 156.800 MHz. In the US, seven additional channels, WX1 - WX7, are allocated for weather broadcasts.
   • Television channels such as North American TV Channel 2 = 55.25 MHz, Channel 13 = 211.25 MHz. Each channel is 6 MHz wide. Besides these "physical channels", television also has "virtual channel
     Virtual channel
     In telecommunications, a logical channel number , also known as virtual channel, is a channel designation which differs from that of the actual radio channel on which the signal travels....
     
     s".
   • Wi-Fi
     Wi-Fi
     Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
     
      consists of unlicensed channels 1-13 from 2412 MHz to 2484 MHz in 5 MHz steps.
   • The radio channel between an amateur radio repeater
     Amateur radio repeater
     An amateur radio repeater is an electronic device that receives a weak or low-level amateur radio signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation...
     
      and a ham uses two bands often 600 kHz (0.6 MHz) apart. For example, a repeater that transmits on 146.94 MHz typically listens for a ham transmitting on 146.34 MHz.
6. A room in the Internet Relay Chat
   Internet Relay Chat
   Internet Relay Chat is a protocol for real-time Internet text messaging or synchronous conferencing. It is mainly designed for group communication in discussion forums, called channels, but also allows one-to-one communication via private message as well as chat and data transfer, including file...
   
    (IRC) network, in which participants can communicate with each other.

All of these communications channels share the property that they transfer information. The information is carried through the channel by a signal.

Channel models

A channel can be modelled physically by trying to calculate the physical processes which modify the transmitted signal. For example in wireless communications the channel can be modelled by calculating the reflection off every object in the environment. A sequence of random numbers might also be added in to simulate external interference and/or electronic noise in the receiver.

Statistically a communication channel is usually modelled as a triple consisting of an input alphabet, an output alphabet, and for each pair (i, o) of input and output elements a transition probability p(i, o). Semantically, the transition probability is the probability that the symbol

Symbol

A symbol is something which represents an idea, a physical entity or a process but is distinct from it. The purpose of a symbol is to communicate meaning. For example, a red octagon may be a symbol for "STOP". On a map, a picture of a tent might represent a campsite. Numerals are symbols for...

 o is received given that i was transmitted over the channel.

Statistical and physical modelling can be combined. For example in wireless communications the channel is often modelled by a random attenuation (known as fading

Fading

In wireless communications, fading is deviation of the attenuation that a carrier-modulated telecommunication signal experiences over certain propagation media. The fading may vary with time, geographical position and/or radio frequency, and is often modelled as a random process. A fading channel...

) of the transmitted signal, followed by additive noise. The attenuation term is a simplification of the underlying physical processes and captures the change in signal power over the course of the transmission. The noise in the model captures external interference and/or electronic noise in the receiver. If the attenuation term is complex it also describes the relative time a signal takes to get through the channel. The statistics of the random attenuation are decided by previous measurements or physical simulations.

Channel models may be continuous channel models in that there is no limit to how precisely their values may be defined.

Communication channels are also studied in a discrete-alphabet setting. This corresponds to abstracting a real world communication system in which the analog->digital and digital->analog blocks are out of the control of the designer. The mathematical model consists of a transition probability that specifies an output distribution for each possible sequence of channel inputs. In information theory

Information theory

Information theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...

, it is common to start with memoryless channels in which the output probability distribution only depends on the current channel input.

A channel model may either be digital (quantified, e.g. binary) or analog.

Digital channel models

In a digital channel model, the transmitted message is modelled as a digital signal

Digital signal

A digital signal is a physical signal that is a representation of a sequence of discrete values , for example of an arbitrary bit stream, or of a digitized analog signal...

 at a certain protocol layer. Underlying protocol layers, such as the physical layer transmission technique, is replaced by a simplified model. The model may reflect channel performance measures such as bit rate

Bit rate

In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

, bit errors, latency

Latency

Latency or latent may refer to:*Latency period , the time between exposure to a pathogen, chemical or radiation, and when symptoms first become apparent...

/delay

Network delay

Network delay is an important design and performance characteristic of a computer network or telecommunications network. The delay of a network specifies how long it takes for a bit of data to travel across the network from one node or endpoint to another. It is typically measured in multiples or...

, delay jitter, etc. Examples of digital channel models are:

• Binary symmetric channel
  Binary symmetric channel
  A binary symmetric channel is a common communications channel model used in coding theory and information theory. In this model, a transmitter wishes to send a bit , and the receiver receives a bit. It is assumed that the bit is usually transmitted correctly, but that it will be "flipped" with a...
  
   (BSC), a discrete memoryless channel with a certain bit error probability
• Binary bursty bit error
  Error burst
  In telecommunication, a burst error or error burst is a contiguous sequence of symbols, received over a data transmission channel, such that the first and last symbols are in error and there exists no contiguous subsequence of m correctly received symbols within the error burst.The integer...
  
   channel model, a channel "with memory"
• Binary erasure channel
  Binary erasure channel
  A binary erasure channel is a common communications channel model used in coding theory and information theory. In this model, a transmitter sends a bit , and the receiver either receives the bit or it receives a message that the bit was not received...
  
   (BEC), a discrete channel with a certain bit error detection (erasure) probability
• Packet erasure channel
  Packet erasure channel
  The packet erasure channel is a communication channel model where sequential packets are either received or lost . This channel model is closely related to the binary erasure channel....
  
  , where packets are lost with a certain packet loss
  Packet loss
  Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is distinguished as one of the three main error types encountered in digital communications; the other two being bit error and spurious packets caused due to noise.-...
  
   probability or packet error rate
• Arbitrarily varying channel
  Arbitrarily varying channel
  An arbitrarily varying channel is a communication channel model used in coding theory, and was first introduced by Blackwell, Breiman, and Thomasian. This particular channel has unknown parameters that can change over time and these changes may not have a uniform pattern during the transmission...
  
   (AVC), where the behavior and state of the channel can change randomly

Analog channel models

In an analog channel model, the transmitted message is modelled as an analog signal

Analog signal

An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...

. The model can be a linear or non-linear, time-continuous

Continuous signal

A continuous signal or a continuous-time signal is a varying quantity whose domain, which is often time, is a continuum . That is, the function's domain is an uncountable set. The function itself need not be continuous...

 or time-discrete

Discrete signal

A discrete signal or discrete-time signal is a time series consisting of a sequence of qualities...

 (sampled), memoryless

Memorylessness

In probability and statistics, memorylessness is a property of certain probability distributions: the exponential distributions of non-negative real numbers and the geometric distributions of non-negative integers....

 or dynamic (resulting in burst errors), time-invariant or time-variant

Time-variant system

A time-variant system is a system that is not time invariant . Roughly speaking, characteristics of its output depend explicitly upon time.- Overview :...

 (also resulting in burst errors), baseband

Baseband

In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...

, passband

Passband

A passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.A bandpass filtered signal , is known as a bandpass signal, as opposed to a baseband signal....

 (RF signal model), real-valued or complex-valued signal model. The model may reflect the following channel impairments:

• Noise
  Electronic noise
  Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
  
   model, for example
  • Additive white Gaussian noise
    Additive white Gaussian noise
    Additive white Gaussian noise is a channel model in which the only impairment to communication is a linear addition of wideband or white noise with a constant spectral density and a Gaussian distribution of amplitude. The model does not account for fading, frequency selectivity, interference,...
    
     (AWGN) channel, a linear continuous memoryless model
  • Phase noise
    Phase noise
    Phase noise is the frequency domain representation of rapid, short-term, random fluctuations in the phase of a waveform, caused by time domain instabilities...
    
     model
• Interference
  Interference (communication)
  In communications and electronics, especially in telecommunications, interference is anything which alters, modifies, or disrupts a signal as it travels along a channel between a source and a receiver. The term typically refers to the addition of unwanted signals to a useful signal...
  
   model, for example cross-talk (co-channel interference
  Co-channel interference
  Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency. There can be several causes of co-channel radio interference; four examples are listed here....
  
  ) and intersymbol interference
  Intersymbol interference
  In telecommunication, intersymbol interference is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable...
  
   (ISI)
• Distortion
  Distortion
  A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
  
   model, for example a non-linear channel model causing intermodulation distortion (IMD)
• Frequency response
  Frequency response
  Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
  
   model, including attenuation
  Attenuation
  In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
  
   and phase-shift
• Group delay
  Group delay
  Group delay is a measure of the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a device under test, and is a function of frequency for each component...
  
   model
• Modelling of underlying physical layer
  Physical layer
  The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
  
   transmission
  Transmission (telecommunications)
  Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
  
   techniques, for example a complex-valued equivalent baseband model of modulation
  Modulation
  In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
  
   and frequency response
  Frequency response
  Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
  
  
• Radio frequency propagation model, for example
  • Log-distance path loss model
  • Fading
    Fading
    In wireless communications, fading is deviation of the attenuation that a carrier-modulated telecommunication signal experiences over certain propagation media. The fading may vary with time, geographical position and/or radio frequency, and is often modelled as a random process. A fading channel...
    
     model, for example Rayleigh fading
    Rayleigh fading
    Rayleigh fading is a statistical model for the effect of a propagation environment on a radio signal, such as that used by wireless devices.Rayleigh fading models assume that the magnitude of a signal that has passed through such a transmission medium will vary randomly, or fade, according to a...
    
    , Ricean fading, log-normal shadow fading and frequency selective (dispersive) fading
  • Doppler shift model, which combined with fading results in a time-variant system
    Time-variant system
    A time-variant system is a system that is not time invariant . Roughly speaking, characteristics of its output depend explicitly upon time.- Overview :...
    
    
  • Ray tracing
    Ray tracing (physics)
    In physics, ray tracing is a method for calculating the path of waves or particles through a system with regions of varying propagation velocity, absorption characteristics, and reflecting surfaces. Under these circumstances, wavefronts may bend, change direction, or reflect off surfaces,...
    
     models, which attempt to model the signal propagation and distortions for specified transmitter-receiver geometries, terrain types, and antennas
  • Mobility model
    Mobility model
    Mobility models represent the movement of mobile users, and how their location, velocity and acceleration change over time. Such models are frequently used for simulation purposes when new communication or navigation techniques are investigated...
    
    s, which also causes a time-variant system
    Time-variant system
    A time-variant system is a system that is not time invariant . Roughly speaking, characteristics of its output depend explicitly upon time.- Overview :...
    
    

Types of communications channels

• Digital
  Digital signal
  A digital signal is a physical signal that is a representation of a sequence of discrete values , for example of an arbitrary bit stream, or of a digitized analog signal...
  
   (discrete
  Discrete signal
  A discrete signal or discrete-time signal is a time series consisting of a sequence of qualities...
  
  ) or analog
  Analog signal
  An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
  
   (continuous
  Continuous signal
  A continuous signal or a continuous-time signal is a varying quantity whose domain, which is often time, is a continuum . That is, the function's domain is an uncountable set. The function itself need not be continuous...
  
  ) channel
• Baseband
  Baseband
  In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
  
   and passband
  Passband
  A passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.A bandpass filtered signal , is known as a bandpass signal, as opposed to a baseband signal....
  
   channel
• Transmission medium
  Transmission medium
  A transmission medium is a material substance that can propagate energy waves...
  
  , for example a fibre channel
  Fibre Channel
  Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
  
  
• Multiplexed channel
  Multiplexing
  The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
  
  
• Computer network virtual channel
• Simplex communication
  Simplex communication
  Simplex communication refers to communication that occurs in one direction only. Two definitions have arisen over time: a common definition, which is used in ANSI standard and elsewhere, and an ITU-T definition...
  
  , duplex communication or half duplex communication channel
• Return channel
  Return channel
  In communications systems that use star topologies, the return channel is the transmission link from a user terminal to the central hub....
  
  
• Uplink
  Uplink
  A telecommunications link is generally one of several types of information transmission paths such as those provided by communication satellites to connect two points on earth.-Uplink:...
  
   or downlink (upstream
  Upstream (networking)
  In computer networking, upstream refers to the direction in which data can be transferred from the client to the server . This differs greatly from downstream not only in theory and usage, but also in that upstream speeds are usually at a premium...
  
   or downstream
  Downstream
  -Science:* In geography, away from the source of a stream or river* In meteorology, away from the source of an air parcel or mass, along the normal direction of water or air flow* Downstream , in computer or telecommunications networks...
  
   channel)
• Broadcast channel
  Channel (broadcasting)
  In broadcasting, a channel is a range of frequencies assigned by a government for the operation of a particular radio station, television station or television channel. In common usage, the term also may be used to refer to the station operating on a particular frequency.-See also:*Broadcast...
  
  , unicast channel or multicast channel

Multi-terminal channels, with application to cellular systems

See also network topology

Network topology

Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....

In networks, as opposed to point-to-point

Point-to-point

Point-to-point or point to point may refer to:Computing* Point-to-point construction, an electronics assembly technique* Point-to-point * Point-to-Point Protocol , part of the Internet protocol suite...

 communication, the communication media is shared between multiple nodes (terminals). Depending on the type of communication, different terminals can cooperate or interfere on 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 which was first introduced in the field of information theory:

• A 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 radio 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.
• 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
  Media Access Control
  The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...
  
   (MAC) protocol combiend with a multiplexing
  Multiplexing
  The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
  
   scheme. This channel model has applications in the uplink
  Uplink
  A telecommunications link is generally one of several types of information transmission paths such as those provided by communication satellites to connect two points on earth.-Uplink:...
  
   of the cellular networks.
• Relay channel
  Relay channel
  In information theory, a relay channel is a probability model of the communication between a sender and a receiver aided by one or more intermediate relay nodes...
  
  : In this channel, one or several intermediate nodes (called relay, repeater
  Repeater
  A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
  
   or gap filler
  Gap filler
  Platform gap fillers on the metro systems like the New York City Subway or on train stations in Hong Kong are movable platform extensions at stations where the curvature of the platform creates a significant gap between the platform and subway car door...
  
   nodes) cooperate with a sender to send the message to an ultimate destination node. Relay nodes are considered as a possible add-on in the upcoming cellular standards like 3GPP Long Term Evolution
  3GPP Long Term Evolution
  3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques...
  
   (LTE).
• Interference channel: In this channel, two different senders transmit their data to different destination nodes. Hence, the different senders can have a possible cross-talk or co-channel interference on the signal of each other. The inter-cell interference in the cellular wireless communications is an example of the interference channel. In spread spectrum systems like 3G, interference also occur inside the cell if non-orthogonal codes are used.
• A unicasting channel is a channel that provides a unicasting service, i.e. that sends data addressed to one specific user. An established phone call is an example.
• A broadcast
  Broadcast
  Broadcast or Broadcasting may refer to:* Broadcasting, the transmission of audio and video signals* Broadcast, an individual television program or radio program* Broadcast , an English electronic music band...
  
  ing 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
  Paging
  In computer operating systems, paging is one of the memory-management schemes by which a computer can store and retrieve data from secondary storage for use in main memory. In the paging memory-management scheme, the operating system retrieves data from secondary storage in same-size blocks called...
  
   service as well as the Multimedia Broadcast Multicast Service
  Multimedia Broadcast Multicast Service
  Multimedia Broadcast Multicast Services is a point-to-multipoint interface specification for existing and upcoming 3GPP cellular networks, which is designed to provide efficient delivery of broadcast and multicast services, both within a cell as well as within the core network...
  
  .
• A multicasting channel is a channel where data is addressed to a group of subscribing users. LTE examples are the Physical Multicast Channel (PMCH) and MBSFN (Multicast Broadcast Single Frequency Network).

From the above 4 basic multi-terminal channels, multiple access channel is the only one whose capacity region is known. Even for the special case of the Gaussian scenario, the capacity region of the other 3 channels except the broadcast channel is unknown in general.