Wired and wireless communication channels


Communication Channels

In telecoIn telecommunications and computer networking, a communication channel or 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. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) 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 data from one location to another requires some form of pathway or medium. These pathways, called communication channels, use two types of media: cable (twisted-pair wire, cable, and fiber-optic cable) and broadcast (microwave, satellite, radio, and infrared). Cable or wire line media use physical wires of cables to transmit data and information. Twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass.

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 kind of channel, which can be sent to (written) and received from (read).mmunications and computer networking, a communication channel or channel, refers either to a physicaltransmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) to one or several receivers. A channel has a certain capacity for transmitting information, often measured by itsbandwidth in Hz or its data rate in bits per second.

Communicating data from one location to another requires some form of pathway or medium. These pathways, called communication channels, use two types of media: cable (twisted-pair wire, cable, and fiber-optic cable) and broadcast (microwave, satellite, radio, and infrared). Cable or wire line media use physical wires of cables to transmit data and information. Twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass.

In inforIn telecommunications and computer networking, a communication channel or 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. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) 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 data from one location to another requires some form of pathway or medium. These pathways, called communication channels, use two types of media: cable (twisted-pair wire, cable, and fiber-optic cable) and broadcast (microwave, satellite, radio, and infrared). Cable or wire line media use physical wires of cables to transmit data and information. Twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass.

In informaIn telecommunications and computer networking, a communication channel or 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. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) 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 data from one location to another requires some form of pathway or medium. These pathways, called communication channels, use two types of media: cable (twisted-pair wire, cable, and fiber-optic cable) and broadcast (microwave, satellite, radio, and infrared). Cable or wire line media use physical wires of cables to transmit data and information. Twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass.

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 kind of channel, which can be sent to (written) and received from (read).tion theory, a channel refers to a theoretical channel model with certain error characteristics. In this more general view, a storage device is also a kind of channel, which can be sent to (written) and received from (read).mation theory, a channel refers to a theoretical channel model with certain error characteristics. In this more general view, a storage device is also a kind of channel, which can be sent to (written) and received from (read).

Types of communication channels

A physical medium is an inherent part of a communications system – Wires (copper, optical fibers) , wireless radio spectra „ Communications systems include electronic or optical devices that are part of the transmission path followed by a signal – Equalizers, amplifiers, signal conditioners (regenerators) – Medium determines only part of channels behavior. The other part is determined how transmitter and receiver are connected to the medium and what is transmitted in the channel – Therefore, by telecommunication channel we refer to the combined end-to-end physical medium and attached devices „ Often the concept “filter” models a channel. This is due to the fact that all telecommunication channels can be always modeled as filters. Their parameters can be – deterministic – random – time variable – linear/non-linear

Wired channels

1. Twisted pair 

Comes in two flavors: Shielded (STP) / Unshielded (UTP) „ 

Twisting reduces interference, and crosstalk (antenna-behavior) „ 

Applications 

– Connects data and especially PSTN local loop analog links (Intrabuilding telephone from wiring closet to desktop ) 

– In old installations, loading coils added to improve quality in 3 kHz band, resulting more attenuation at higher frequencies (ADSL ) 

– STP used especially in high-speed transmission as in token ringnetworks structure STP-cable UTP-cable •larger attenuation •higher rates •more expensive •more sensitive to interference •easy to install and work with •example: 10BaseT Ethernet 14 Twisted pair - UTP categories in LANs „ 

Category 1: mainly used to carry voice (telephone wiring prior to 1980). Not certified to carry data of any type. „ 

Category 2: used to carry data at rates up to 4 Mbps. Popular in older Token-passing ring LANs using 4 Mbps specs (IEEE 802.5). Rated bandwidth BW = 1 MHz. „ 

Category 3: known as voice grade. Used primarily in older Ethernet 10base-T* LANs (IEEE 802.3). Certified to carry 10 Mbps data. BW= 16 MHz. 3-4 twists/feet. „ 

Category 4: primarily used for token-based or 10 Base-T. BW = 20 MHz. „ Category 5: most popular Ethernet cabling category. Capable of carrying data at rates up to 100 Mbps (Fast Ethernet, IEEE 802.3u) and used for 100 base-T and 10 base-T networks. Rated BW = 100 MHz. 3-4 twists/inch. *100 m / CAT 3 

2. Coaxial Cables

„ Mechanics

 – Cylindrical braided outer conductor surrounds insulated inner wire conductor

Properties 

– Well shielded structure -> immunity to external noise – High bandwidth, up to Ghzrange (distance/model)

Applications

 – CATV (Cable TV networks) – Ethernet LANs – Earlier a backbone of PSTN

Wireless Channels

1. Terrestrial Microwave-

The terrestrial microwave transmission typically uses Uses the radio frequency spectrum 2 to 40 GHz. The transmitter is a parabolic dish (shaped like a bowl) and is mounted as high as possible to get the best frequency and transmission. Both private networks and common carriers can use terrestrial microwaves. An unblocked line of sight must be available between the source and the receiver. Seeing as the Earth is a curved sphere, the stations (otherwise known as repeaters) must be spaced 30 miles apart.

Terrestrial microwaves are used for both radio (voice) and television transmission. It can also be used for closed-circuit television (commonly known as CCTV) but short point-to-point connections between buildings or a data link between Local Area Connections (LANs) will be needed for the transmission to work.

There are several advantages of terrestrial microwave transmission. It can cover a wide bandwidth and has multi-channel transmissions. It can be used for both long-haul or high capacity short-haul transmissions. Also, it requires fewer amplifiers and repeaters, making it efficient and of good quality.

The disadvantages of terrestrial microwave transmission is that it can be expensive to adhere to the 30-mile line of sight requirement. The towers and repeaters can be fairly costly and there is a risk of interference from aeroplanes, birds and rain. Lastly, the frequency bands must be regulated. This means employing extra staff and can be costly seeing as there are a large number of terrestrial microwave transmitters in the world!

2.Satellite Microwave-

Only one repeater in the link 

Covers 1/3 of earths surface. 

Provides high quality communication. 

 Insensitive to fading. 

 Large areas could be covered if the height of the microwave repeater could be increased by putting it on board an artificial earth satellite. 

 In 1965 INTELSAT launched first communication Satellite named “EARLY BIRD” The satellite was having the capacity of 240 voice circuit . 

The Satellite had the life of one and a half years. 

 Rapid advances in launch vehicles & developments in reliable microwave devices,have made satellite communication systems quite affordable and common. 

The present generation satellites carry a no of radio channels called communication Transponders and have the expected life span of 10 to 12 years. 

 ADVANTAGES OF SATELLITE COMMUNICATIONS 

(i)Large Coverage Almost one-third of the earth with the exception of polar regions, is visible from Geo stationary orbit.

 (ii) High Quality Satellite links can be designed for high quality performance. It is free from Ionospheric disturbances and multi-path effects.

 (iii) High Reliability Reliability is high since only one repeater is involved in the communication link. 27 

iv) Speed of Installation Installation of earth terminals can be achieved in a short time as compared to laying of cables or installation of radio relay links. (

v) Mobile, Short-term or Emergency Communication With air-liftable or road transportable terminals, short-term or emergency communication can be provided quickly Reliable long distance land mobile, maritime mobile and Aeronautical mobile services are feasible only by means of satellite. 

(vi) Broadcast Nature of Transmissions Ideally suited for point to multi-point transmission or broadcasting over large areas. Application of satellites for TV broadcasting,and teleconferencing, facsimile data and news dissemination is therefore, increasing rapidly.

Conclusion-

- Communication channel is essential for communication system. The transmission characteristics are important in selecting channel because they directly affect the communication quality.

- Different types of communication channels have different transmission characteristics and costs, they are used in different applications.