M.Tech ECEDepartment of Electronics

What is a Communication channel….?

• The Communication channel provides the connection between the transmitter and the receiver.

• The physical channel may be a pair of wires that carry the electrical signal, or an optical fiber that carries the information on a modulated light beam, or an underwater ocean channel in which the information is transmitted acoustically, or free space over which the information bearing signal is radiated by use of an antenna.

CommunicationChannel

Transmitter Receiver

Communication Model

COMMUNICATION CHANNELS

Wired

Wireless

Acoustic Channels

Storage Channels

Twisted Pair CableCoaxial Cable

Optical fiber Cable

Terrestrial Microwave

Satellite Communication

Magnetic Tapes

Under water channels

Magnetic Disks

Twisted pair cable :

Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of cancelling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighbouring pairs.

For a Shielded twisted pair :

Cost per node: moderateMedia and Connector size : medium to largeMaximum cable length : 100m

Coaxial Cable :

• Coaxial cable, or coax is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an insulating outer sheath or jacket.

• Used for both analog and Digital.

• Effectively used at Higher Data rate and higher band width.

• For Digital signals requires repeater every 1km

Optical Fiber Cable:

• A technology that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves.

• Optical fibers typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fiber to act as a waveguide

• Fibers that support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those that only support a single mode are called single-mode fibers (SMF). 

• When light traveling in an optically dense medium hits a boundary at a steep angle the light is completely reflected. This is called total internal reflection. This effect is used in optical fibers to confine light in the core.

Terrestrial microwave:• Terrestrial microwave communication employs Earth-based

transmitters and receivers. The frequencies used are in the low-gigahertz range, which limits all communications to line-of-sight.

• You probably have seen the terrestrial microwave equipment in the form of telephone relay towers, which are placed every few miles to relay the telephone signals across the country

Satellite Communication:

• A communication satellite is a radio relay station in orbit above the earth.

• It receives, amplifies and redirects analog and digital signals carried on a specific radio frequency

• These are having different uplink and downlink frequencies and speed is about 1Gbps

Under Water Acoustic Channels:

• Underwater acoustic communication is a technique of sending and receiving message below water. 

• There are several ways of employing such communication but the most common is using hydrophones.

• Under water communication is difficult due to factors like multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges.

• In underwater communication there are low data rates compared to terrestrial communication, since underwater communication uses acoustic waves instead of electromagnetic waves.

Magnetic tapes :• Magnetic tape is a medium for magnetic recording, made of a

thin magnetisable coating on a long, narrow strip of plastic film. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders. A device that stores computer data on magnetic tape is a tape drive .

Magnetic Disks :• Magnetic storage (or magnetic recording) is the storage

of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetisable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads