Communication channel presentation

Communication Channels

and their features

Communication Channel• In 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

Communication ChannelsWired• Two-Wire Open Line• Coaxial Cable• Twisted Pair Line• Fiber OpticsWireless• Microwave Communication• Radio• Satellite

Features of Two-Wire Open Line• Insulated Wire and open to free space• Signal is applied to one wire and other one is for ground

reference• it is used for connecting modem to computerBandwidth and capacity supported by two-wire open

line:• Bandwidth of two-wire open line is dependent on the

material of wire and cross sectional area of wire.• If we know the bandwidth of this wire than capacity can be

calculated by using Shannon formula or Nyquist formula

Drawbacks:• It is highly effected by Electromagnetic Radiations

Features of Coaxial Cable• Coaxial cable, or coax, has an

inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield.

Bandwidth and capacity supported by Coaxial cable:

• Both 10BASE2 and 10BASE5 coaxial Ethernet cables support transfer speeds of up to 10 Megabits per second.

• For the purposes of transmitting analog or digital channels - is that it has a capacity of at least 900 MHZ. That would equate to 150 analog channels, or to 150 to 600 digital channels.

A: outer plastic sheathB: woven copper shieldC: inner dielectric insulatorD: copper core

Types of Coaxial CableCommon types of coaxial cable include RG-6, RG-8, RG-58, and RG-59. RG-6 is one of the most common, found in household and business applications such as cable television connections. RG-59 is considered to be the predecessor to RG-6. RG-8 cable is used mainly for radio transmissions such as CB radio while RG-58 is found in Ethernet network applications.

Features of Twisted Pair Cable

• Pairs of wires twisted together

• It is the most common medium used for communication over a large distance

• It is used for internet and television connections

• Extensively being used in LAN Connections

Bandwidth and capacity supported by twisted pair cable:

• UTP cable is widely used in 100 Mbps and 1 Gbps networks. In order to guarantee the performance of the cable, standards have been created such as CAT 5e and CAT 6. A 'Cat 5e' UTP cable is sufficient for bandwidths up to 1 Gbps for reasonable run lengths. For networks needing to run up to 10 Gbps then a Cat 6 cable should be used. Of course, this is more expensive so cable selection should be based on what bandwidth is actually required.

Types of Twisted Pair CableShielded Twisted Pair Cable• Covered with a foil shield to reduce

electromagnetic interference• Better in performance than UTP cable

but more expensive than UTP cable

Unshielded twisted Pair Cable• Does Not Include any extra sheilding

around the wire pairs• Used for ordinary phone lines and

local area networks• Less Expensive and easy to work• Support shorter distance

Features of Optical Fiber

• Optical fiber consists of a core and a

cladding layer, selected for total internal

reflection due to the difference in the

refractive index between the two. In

practical fibers, the cladding is usually

coated with a layer of acrylate polymer or

polyimide. This coating protects the fiber

from damage but does not contribute to its

optical waveguide properties.

• An optical fiber is a thin (2 to 125µm),

flexible medium capable of guiding an

optical ray.

Bandwidth–distance product of fiber optics:• Because the effect of dispersion increases with

the length of the fiber, a fiber transmission system is often characterized by its bandwidth–distance product, usually expressed in units of MHz·km. This value is a product of bandwidth and distance because there is a tradeoff between the bandwidth of the signal and the distance it can be carried. For example, a common multi-mode fiber with bandwidth–distance product of 500 MHz·km could carry a 500 MHz signal for 1 km or a 1000 MHz signal for 0.5 km.

Features of Microwave Communication Media• Microwave radio transmission is commonly used

in point-to-point communication systems on the surface of the Earth, in satellite communications, and in deep space radio communications. Other parts of the microwave radio band are used for radars, radio navigation systems, sensor systems, and radio astronomy.

Uses of Microwave CommunicationWireless transmission of information• One-way (e.g. television broadcasting)

and two-way telecommunication using communications satellite

• Terrestrial microwave radio broadcasting relay links in telecommunications networks including e.g. backbone or backhaul carriers in cellular networks linking BTS-BSC and BSC-MSC.

Wireless transmission of power• Proposed systems e.g. for connecting

solar power collecting satellites to terrestrial power grids

Relay towers on Frazier Mountain, Southern California

Bandwidth support:

• Microwave transmission refers to the technology of transmitting information or energy by the use of radio waves whose wavelengths are conveniently measured in small numbers of centimeter; these are called microwaves. This part of the radio spectrum ranges across frequencies of roughly 1 GHz to 30 GHz. These correspond to wavelengths from 30 centimeters down to 1.0 cm.

Features of Radio Communication• Radio is the transmission of signals through free space by

electromagnetic waves with frequencies significantly below visible light, in the radio frequency range, from about 3 kHz to 300 GHz. These waves are called radio waves. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space.

• Information, such as sound, is carried by systematically changing (modulating) some property of the radiated waves, such as their amplitude, frequency, phase, or pulse width. When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form.

How Radio Communication Works

Features of Satellite Communication

• In satellite communication, signal transferring between the sender and receiver is done with the help of satellite. In this process, the signal which is basically a beam of modulated microwaves is sent towards the satellite. Then the satellite amplifies the signal and sent it back to the receiver’s antenna present on the earth’s surface. So, all the signal transferring is happening in space. Thus this type of communication is known as space communication.

• Two satellites which are commonly used in satellite communication are Active and passive satellites.

Satellite Communication Block Diagram

How to Measure bandwidth and channel capacity of a particular channel

• Bandwidth of particular channel depends on the conducting material and cross sectional area of the medium used for transmission.

• In electrical engineering, computer science and information theory, channel capacity is the tightest upper bound on the amount of information that can be reliably transmitted over a communications channel.

Measuring Channel Capacity by Shannon Capacity Formula• An application of the channel capacity concept to

an additive white Gaussian noise (AWGN) channel with B Hz bandwidth and signal-to-noise ratio S/N is the Shannon–Hartley theorem:

• C is measured in bits per second• W is Bandwidth of Channel• SNR is Signal to Noise Ratio

SNR = 10 log10(S/N)Higher SNR leads to better channel capacity

Nyquist Formulation:• if the rate of signal transmission is 2B, then a signal with

frequencies no greater than B is sufficient to carry the signal rate.• Given bandwidth B, highest signal rate is 2B.

• Why is there such a limitation?• due to intersymbol interference, such as is produced by delay

distortion.

• Given binary signal (two voltage levels), the maximum data rate supported by B Hz is 2B bps.• One signal represents one bit

Nyquist Criterion for finding channel capacity• Signals with more than two levels can be used, i.e., each signal

element can represent more than one bit.• E.g., if a signal has 4 different levels, then a signal can be used to

represents two bits: 00, 01, 10, 11• With multilevel signalling, the Nyquist formula becomes: • C = 2B log2M• M is the number of discrete signal levels, B is the given bandwidth, C is

the channel capacity in bps.• How large can M be?• The receiver must distinguish one of M possible signal elements. • Noise and other impairments on the transmission line will limit the practical

value of M.

• Nyquist’s formula indicates that, if all other things are equal, doubling the bandwidth doubles the data rate.

Example:

We assumeF1=0Hz and F2=20 kHz

soB= F2-F1=20000 Hz

By Nyquist formula:C = 2*20000* log2 (16)

C = 2*20000* log10 (16) / log10 (2)

C = 160 000 bps

How particular channel capacity is affected in term of data rate in the presence of noise and in particular in presence of extreme noise?

• Noise Effects Leading to :1. Higher the data rate of the signal, the greater the

effective BW it requires.2. The greater the BW of the tx system, the higher is the

data rate that can be transmitted over the system.3. With the introduction of levels what we are trying to do

is to increase the number of information pieces that travel in one signaling element.

4. For a given BW, the data rate can be increased by increasing the number of signal elements. However this places an additional burden on the receiver since now it has to discern many possible amplitude values.

5. The channel capacity is the maximum rate at which data can be transmitted over a gives communication path and with presence of noise the channel capacity is highly affected in term of data rate and the data rate capacity may decrease in channel in presence of noise.

6. With noise the ability of the receiver to recognize many levels becomes low

According to Shannon:• Faster data rate shortens each bit, so burst of noise

affects more bits• The key parameter is the SNR: Signal-to-Noise Ratio,

which is the ratio of the power in a signal to the power contained in the noise• C = B log2(1+SNR) in bps - maximum data rate

• The wider the bandwidth, the more noise is admitted to the system. Thus, as B increases, SNR decreases. • Lower S/N leads to higher bit error rates thus reducing the

effective data rate.• Noise targets multilevel signalling more• Now according to SNR, if our noise is greater in a channel

corresponds to low SNR which leads to weak signal.

Thank you