• 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
• 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
• Two-Wire Open Line
• Coaxial Cable
• Twisted Pair Line
• Fiber Optics
• Microwave Communication
• Insulated Wire and open to free space
• Signal is applied to one wire and other one is for ground
• it is used for connecting modem to computer
Bandwidth 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
• It is highly effected by Electromagnetic Radiations
• Coaxial cable, or coax, has an
inner conductor surrounded by a
flexible, tubular insulating layer,
surrounded by a tubular conducting
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
A: outer plastic sheath
B: woven copper shield
C: inner dielectric insulator
D: copper core
Common 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.
• Pairs of wires twisted together
• It is the most common medium
used for communication over a
• It is used for internet and
• Extensively being used in LAN
• 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
Shielded Twisted Pair Cable
• Covered with a foil shield to reduce
• Better in performance than UTP
cable but more expensive than UTP
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
• 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
• An optical fiber is a thin (2 to 125µm),
flexible medium capable of guiding an
• 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
• 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.
Wireless transmission of information
• One-way (e.g. television
broadcasting) and two-way
• Terrestrial microwave radio
broadcasting relay links in
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
• 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
• 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.
• 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.
• 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.
• 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
• 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
• if the rate of signal transmission is 2B, then a signal with
frequencies no greater than B is sufficient to carry the signal
• 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
• 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.
F1=0Hz and F2=20 kHz
B= F2-F1=20000 Hz
By Nyquist formula:
C = 2*20000* log2 (16)
C = 2*20000* log10 (16) / log10 (2)
C = 160 000 bps
• Noise Effects Leading to :
1. Higher the data rate of the signal, the greater the effective BW it
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
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
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
• Faster data rate shortens each bit, so burst of noise affects more
• 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.