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COMP 421 /CMPET 401. COMMUNICATIONS and NETWORKING CLASS 5 (4B). TRANSMISSION MEDIA. Overview. Guided - wire Unguided - wireless Characteristics and quality determined by medium and signal For guided, the medium is more important

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COMP 421 /CMPET 401


CLASS 5 (4B)



  • Guided - wire

  • Unguided - wireless

  • Characteristics and quality determined by medium and signal

  • For guided, the medium is more important

  • For unguided, the bandwidth produced by the antenna is more important

  • Key concerns are data rate and distance

Design Factors

  • Bandwidth

    • Higher bandwidth gives higher data rate

  • Transmission impairments

    • Attenuation

  • Interference

  • Number of receivers

    • Major factor in guided media

    • More receivers (multi-point) introduce more attenuation

Electromagnetic Spectrum

Guided Transmission Media

  • The transmission capacity depends on the distance and on whether the medium is point-to-point or multi-point

    MediumFreq Typical Typical Repeater

    Range Atten. Delay Spacing

  • Twisted Pair 0 - 3.5KHz 0.2dB/km 50us/km 2km

  • Twisted Pair0 - 1.0MHz 3.0dB/km 5 us/km 2km

  • Coaxial cable0 - 500MHz 7.0dB/km 4 us/km 1-9km

  • Optical fiber

    • Multi-mode180-370THz 0.5dB/km 5 us/km 2km

    • Single Mode180-370THz 0.2dB/km 5 us/km 40km

Twisted Pair

  • Consists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs

  • Often used at customer facilities and also over distances to carry voice as well as data communications

  • Low frequency transmission medium

Twisted Pair - Applications

  • Most common medium

  • Telephone network

    • Between house and local exchange (subscriber loop)

  • Within buildings

    • To private branch exchange (PBX)

  • For local area networks (LAN)

    • 10Mbps or 100Mbps

Twisted Pair - Pros and Cons

  • Cheap

  • Easy to work with

  • Low data rate

  • Short range

Twisted Pair - Transmission Characteristics

  • Analog

    • Amplifiers every 5km to 6km

  • Digital

    • Use either analog or digital signals

    • repeater every 2km or 3km

  • Limited distance

  • Limited bandwidth (1MHz)

  • Limited data rate (100MHz) using different modulation & signaling techniques

  • Susceptible to interference and noise

Unshielded and Shielded TP

  • Unshielded Twisted Pair (UTP)

    • Ordinary telephone wire

    • Cheapest

    • Easiest to install

    • Suffers from external electromagnetic interference (EM)

  • Shielded Twisted Pair (STP)

    • the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference

    • More expensive

    • Harder to handle (thick, heavy)

UTP Categories

  • Cat 3

    • up to 16MHz

    • Voice grade found in most offices

    • Twist length of 7.5 cm to 10 cm

  • Cat 4 (least common)

    • up to 20 MHz

  • Cat 5

    • up to 100MHz

    • Commonly pre-installed in new office buildings

    • Twist length 0.6 cm to 0.85 cm

Category 5E and 6

Today, cables and related components are available in more grade categories than the industry standards specify. You can choose from Cat 5, Cat 5e, Cat 5e+, Cat 6 and yes, even Cat 6+. While there is plenty of hype and confusion surrounding these implied categories

Cat 6 more than doubles the bandwidth of Cat 5e, from 100 MHz to 250 MHz, supporting future emerging applications

Improved EMC performance to reject outside noise from TVs, wireless, and other adjacent applications.

Full backwards compatibility to support all legacy applications

Simpler and less costly installations, due to reduction in electronics needed for echo and NEXT (Near End Cross Talk) cancellation.

CAT 6 Features

Equations for CAT 6 Parameters

Attenuation (dB) = 1.991*sqrt(f) + 0.01785*f + 0.21/sqrt(f)

pr-pr NEXT (dB) = -20log( 10^( -0.05(74.3-15log(f)) ) + 2*10^( -0.05(94.0-20log(f)) ) )

PSNEXT (dB) = -20log( 10^( -0.05(72.3-15log(f)) ) + 2*10^( -0.05(90.0-20log(f)) ) )

pr-pr FEXT (dB) = -20log( 10^( -0.05(67.8-20log(f)) ) + 4*10^( -0.05(83.1-20log(f)) ) )

PSFEXT (dB) = -20log( 10^( -0.05(72.3-20log(f)) ) + 4*10^( -0.05(90.0-20log(f)) ) )

Return loss (dB) = 19 at 1-20 MHz; 19-10*log(f/20) at 20-250 MHz

Phase Delay (ns) = 546 + 34/sqrt(f)

Delay skew (ns) = 50

pr-pr PS pr-pr PS return phase delay

freq atten NEXT NEXT ELFEXT ELFEXT loss delay skew

(MHz) (dB) (dB) (dB) (dB) (dB) (dB) (ns) (ns)

100 21.7 39.9 37.1 23.2 20.2 12.0 549.4 50.0

250 36.0 33.1 30.2 17.2 14.2 8.0 548.2 50.0

The RJ 45 Connector

To identify the RJ-45 cable type, hold the two ends of the cable next to each

other so you can see the colored wires inside the ends

·Straight-through — the colored wires are in the same sequence at both ends of the cable.

Crossover — the first (far left) colored wire at one end of the cable is the third colored wire at the other end of the cable

8-Wire Jack(10BaseT Data Connections)

8-Wire Jacks(USOC RJ31X Through RJ37X)

6-Wire Jack(USOC - RJ14W)

Understanding USOC & RJ

8-Wire Jack(IBM Token Ring Connections)

8-Wire Jacks(USOC RJ41 Through RJ48)Also TIA 568B(TIA 568A Swaps Pairs 2 & 3)

6-Wire Jack Modified Jack(DEC MMJ)

Understanding USOC & RJ

Twisted Pair Advantages

  • Inexpensive and readily available

  • Flexible and light weight

  • Easy to work with and install

Twisted Pair Disadvantages

  • Susceptibility to interference and noise

  • Attenuation problem

    • For analog, repeaters needed every 5-6km

    • For digital, repeaters needed every 2-3km

  • Relatively low bandwidth


PER Specification TSB-36 for UTP cable connections for LEVEL 5:

- A terminal jack can be 90M (295ft) from the wiring closet.

- A device can be 10M from a terminal jack at the users location.

- There can be up to 6M of cross-connect patch cords in the wire closet

- Termination of cables must obey the following:

- Twists of actual pairs must be maintained to half-inch of termination.

- Cable sheath should be stripped only as far as necessary to terminate.

- Cables bundles should not nopt tightly bound or cinched

- Cable bundles should not be placed under stress or tension

- Cable bend radii should not be less than 8 times the cable diameter

Coaxial Cable

Coaxial Cable Applications

  • Most versatile medium

  • Television distribution

    • Aerial to TV

    • Cable TV

  • Long distance telephone transmission

    • Can carry 10,000 voice calls simultaneously

    • Being replaced by fiber optic

  • Short distance computer systems links

  • Local area networks

Coaxial Cable - Transmission Characteristics

  • Analog

    • Amplifiers every few km

    • Closer if higher frequency

    • Up to 500MHz

  • Digital

    • Repeater every 1km

    • Closer for higher data rates


The outer shield protects the inner conductor from outside electrical signals. The distance between the outer conductor (shield) and inner conductor plus the type of material used for insulating the inner conductor determine the cable properties or impedance. Typical impedances for coaxial cables are 75 ohms for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet. The excellent control of the impedance characteristics of the cable allow higher data rates to be transferred than with twisted pair cable.

Coax Advantages

  • Higher bandwidth

    • 400 to 600Mhz

    • up to 10,800 voice conversations

  • Can be tapped easily (pros and cons)

  • Much less susceptible to interference than twisted pair

Coax Disadvantages

  • High attenuation rate makes it expensive over long distance

  • Bulky



CMCommunication wires & cables

CL2Class 2 remote control, signaling, & power-limited cables

CL3Class 3 remote control, signaling, & power-limited cables

FPLPower limited fire protective signaling cables

MPMulti-purpose cables

PLTCPower limited tray cable

xxRIndicates a RISER cable

xxP Indicates a PLENUM cable

Plenum is highest grade. Order is : MPP -> CMP -> CL3P -> CL2P; FPLP -> CL3P & 2P

Riser is next higher grade. Order is : MPR -> CMR -> CL3R -> CL2R; FPLR -> CL3R & CL2R

General Purpose is next. Order is : MP -> CM -> CL3 -> CL2 : FPL or PLTC -> CL3 & CL2

Residential is lowest. The order is : CMX -> CL3X -> CL2X



1Level 1 cable is for basic comm & power limited circuits. VOICE GRADE ONLY.

2Level 2 cable is similar to IBM Type 3 cable for 2 to 25 twisted pair cable. 1MHz max.

8db/1000ft attenuation @ 1MHz; 4db/1000ft @ 256KHz. DIGITAL DATA GRADE

3Level 3 cable is Unshielded Twisted Pair (typical telephone wire). 16MHz max frequency.

7.8db/1000ft attenuation @ 1MHz; 4db/1000ft @ 256KHz. 10Mpbs ENET/ 4Mpbs TR

4Level 4 cable is Low Loss Premises Telecommunication cable, shielded/unshielded, 20Mhz max

6.5db/1000ft attenuation @ 1MHz; 31db/1000ft @ 20MHz for 24AWG wire

4.5db/1000ft atten @ 1MHz; 24db/1000ft @ 20MHz for 22AWG wire. 16Mbps TR.

5Level 5 cable is DATA GRADE up to 100Mbit


1Dual pair STP 22AWG solid, non-plenum data cable, used for long runs in walls of buildings

1PDual pair STP 22AWG, plenum data cable

2Dual pair STP 22AWG data, 4 pair UTP 24AWG solid, telephone(voice) non-plenum cable

2P Dual pair STP 22AWG data, 4 pair 22AWG telephone plenum cable

3Multi-pair (usually 4) UTP 22 or 24 AWG solid data & voice cable for runs in walls

5Two 100/140 micrometer optical fiber in a single sheath

6Dual pair 26AWG non-plenum patch panel data cable, used for patch panels. Attn=1.5xType1

8One flat STP of 26AWG stranded wire for under carpet

9Dual pair STP 26AWG solid non-plenum data cable, Low grade dual pair. Attn=1.5xType1

9PDual pair STP 26AWG plenum data cable

9RDual pair STP 26AWG riser data cable

Based on general description of cable per IBM definitions

Optical Fiber

Optical Fiber - Benefits

  • Greater capacity

    • Data rates of hundreds of Gbps

  • Smaller size & weight

  • Lower attenuation

  • Electromagnetic isolation

  • Greater repeater spacing

    • 10s of km at least


Optical Fiber - Applications

  • Long-haul trunks

  • Metropolitan trunks

  • Rural exchange trunks

  • Subscriber loops

  • LANs

Optical Fiber - Transmission Characteristics

  • Act as wave guide for 1014 to 1015 Hz

    • Portions of infrared and visible spectrum

  • Light Emitting Diode (LED)

    • Cheaper

    • Wider operating temp range

    • Last longer

  • Injection Laser Diode (ILD)

    • More efficient

    • Greater data rate

  • Wavelength Division Multiplexing

Fiber Optic Types

  • Multimode step-index fiber

    • the reflective walls of the fiber move the light pulses to the receiver

  • Multimode graded-index fiber

    • acts to refract the light toward the center of the fiber by variations in the density

  • Single mode fiber

    • the light is guided down the center of an extremely narrow core

Optical Fiber

Optical fiber

Optical fiber consists of thin glass fibers that can carry information at frequencies in the visible light spectrum and beyond. The typical optical fiber consists of a very narrow strand of glass called the core. Around the core is a concentric layer of glass called the cladding. A typical core diameter is 62.5 microns (1 micron = 10-6 meters). Typically Cladding has a diameter of 125 microns. Coating the cladding is a protective coating consisting of plastic, it is called the Jacket.

Refraction in Fiber

An important characteristic of fiber optics is refraction. Refraction is the characteristic of a material to either pass or reflect light. When light passes through a medium, it "bends" as it passes from one medium to the other. An example of this is when we look into a pond of water.

Angle of Incidence

If the angle of incidence is small, the light rays are reflected and do not pass into the water. If the angle of incident is great, light passes through the media but is bent or refracted.

Optical fibers work on the principle that the core refracts the light and the cladding reflects the light. The core refracts the light and guides the light along its path. The cladding reflects any light back into the core and stops light from escaping through it - it bounds the medium!

Optical Fiber Transmission Modes

Step Index

Step index has a large core, so the light rays tend to bounce around inside the core, reflecting off the cladding. This causes some rays to take a longer or shorter path through the core. Some take the direct path with hardly any reflections while others bounce back and forth taking a longer path. The result is that the light rays arrive at the receiver at different times. The signal becomes longer than the original signal. LED light sources are used. Typical Core: 62.5 microns.

Step Index Mode

Graded Index

Graded index has a gradual change in the core's refractive index. This causes the light rays to be gradually bent back into the core path. This is represented by a curved reflective path in the attached drawing. The result is a better receive signal than with step index. LED light sources are used. Typical Core: 62.5 microns.

Graded Index Mode

Single Mode

Single mode has separate distinct refractive indexes for the cladding and core. The light ray passes through the core with relatively few reflections off the cladding. Single mode is used for a single source of light (one color) operation. It requires a laser and the core is very small: 9 microns.

Single Mode

Comparison of Optical Fibers

Loose Tube Fiber




A Fiber Connector

Fiber Connectors


Avg. Splice Loss (dB)Fusion Splicing 0.10 dBRotary Mechanical* 0.20 dBMechanical Splice 0.20 dB

Splicing Technologies

Splicing technologies may be

divided into two basic categories:

fusion and mechanical.

Mechanical methods may include

products that use mechanical

means to align two cleaved fibers

or products that require polishing

of the fiber ends.

Return Loss

Return loss is the measure of the

level of signal reflected by the

splice back to the source. Return

loss of 40 dB or better is needed

to assure proper performance for

analog video transmission over



DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. In effect, one fiber is transformed into multiple virtual fibers. So, if you were to multiplex eight OC -48 signals into one fiber, you would increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s. Currently, because of DWDM, single fibers have been able to transmit data at speeds up to 400Gb/s. And, as vendors add more channels to each fiber, terabit capacity is on its way.

A key advantage to DWDM is that it's protocol and bit-rate independent. DWDM-based networks can transmit data in IP, SONET/SDH, Ethernet, and handle bit-rates between 100 Mb/s and 2.5 Gb/s. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel.

Fiber Optic Advantages

  • Greater capacity (bandwidth of up to 2 Gbps)

  • Greater distance—can run fiber as far as several kilometers.

  • Smaller size and lighter weight

  • Lower attenuation - The light signals meet little resistance, so data can travel farther.

  • Immunity to environmental interference

  • Highly secure due to tap difficulty and lack of signal radiation

Fiber Optic Disadvantages

  • Expensive over short distance

  • Requires highly skilled installers

  • Adding additional nodes is difficult

Testing and certifying fiber optic cable.It's easy to certify fiber optic cable because of its immunity to electrical interference. You only need to check a few measurements:

Attenuation (or decibel loss)—Measured in dB/km, this is the decrease of signal strength as it travels through the fiber optic cable.

Return loss—This is the amount of light reflected from the far end of the cable back to the source. The lower the number, the better. For example, a reading of -60 dB is better than -20 dB.

Graded refractive index—Measures how much light is sent down the fiber. This is commonly measured at wavelengths of 850 and 1300 nm. Compared to other operating frequencies, these two ranges yield the lowest intrinsic power loss. (NOTE: This is valid for multimode fiber only.)

Propagation delay—This is the time it takes for a signal to travel from one point to another over a transmission channel.

Time-domain reflectometry (TDR)—Transmits high-frequency pulses so you can examine the reflections along the cable and isolate faults.

Fiber Testing

Fiber Design Considerations

  • Maximum 150 to 160 kilometers between repeaters

    • Determined by loss budget

  • Typical installation 60 to 80 kilometer between repeaters

    • 0.25 dB loss per kilometer for fiber

  • Lasers

    • Transmitters have output from 0 to +10 dBm

    • Receivers have -30 dBm average receiver sensitivity

  • Repeater amplifiers consume 100 watts per fiber

  • Under 2.5 Gigabits/sec per fiber pair is no longer state of art

Wireless Transmission

  • Unguided media

  • Transmission and reception via antenna

  • Two techniques are used:

  • Directional

    • Focused beam

    • Careful alignment required

  • Omnidirectional

    • Signal spreads in all directions

    • Can be received by many antennas


  • 2GHz to 40GHz

    • Microwave

    • Highly directional

    • Point to point

    • Satellite

  • 30MHz to 1GHz

    • Omnidirectional

    • Broadcast radio

  • 3 x 1011 to 2 x 1014

    • Infrared

    • Local

Wireless Examples

  • Terrestrial microwave transmission

  • Satellite transmission

  • Broadcast radio

  • Infrared

Troposcatter Antenna Configuration

Terrestrial Microwave

  • Uses the radio frequency spectrum, commonly from 2 to 40 Ghz

  • Transmitter is a parabolic dish, mounted as high as possible

  • Used by common carriers as well as by private networks

  • Requires unobstructed line of sight between source and receiver

  • Curvature of the earth requires stations (called repeaters) to be ~30 miles apart

Microwave Transmission Applications

  • Long-haul telecommunications service for both voice and television transmission

  • Short point-to-point links between buildings for closed-circuit TV or a data link between LANs

Microwave Transmission Advantages

  • No cabling needed between sites

  • Wide bandwidth

  • Multi-channel transmissions

Microwave Transmission Disadvantages

  • Line of sight requirement

  • Expensive towers and repeaters

  • Subject to interference such as passing airplanes and rain

LOS Radio

Fresnel Zones

So, in a nutshell, to visualize what happens to radio waves when they encounter an obstacle, we have to develop a picture of the wavefront after the obstacle as a function of the wavefront just before it (as opposed to simply tracing rays from the distant source). Now we're in a position to talk about Fresnel zones. A Fresnel zone is a simpler concept once you have some understanding of diffraction: it is the volume of space enclosed by an ellipsoid which has the two antennas at the ends of a radio link at its foci. The surface of the ellipsoid is defined by the path ACB, which exceeds the length of the direct path AB by some fixed amount. This amount is n  /2, where n is a positive integer. For the first Fresnel zone, n = 1 and the path length differs by  /2 (i.e., a 180 phase reversal with respect to the direct path). For most practical purposes, only the first Fresnel zone need be considered.

Fresnel Zone

The two-dimensional representation of a Fresnel zone is

In order to quantify diffraction losses, they are usually expressed in terms of a dimensionless parameter , given by:

where d is the difference in lengths of the straight-line path between the endpoints of the link and the path which just touches the tip of the diffracting object (see Fig. 7, where  d = d1 + d2 - d). By convention,   is positive when the direct path is blocked (i.e., the obstacle has positive height), and negative when the direct path has some clearance ("negative height").


“Knife edge" diffraction means that the top of the obstacle is small in terms of wavelengths. This is sometimes a reasonable approximation of an object in the real world, but more often than not, the obstacle will be rounded (such as a hilltop) or have a large flat surface (like the top of a building), or otherwise depart from the knife edge assumption. In such cases, the path loss for the grazing case can be considerably more than 6 dB - in fact, 20 dB would be a better estimate in many cases. So, Fresnel zone clearance can be pretty important on real-world paths. And, again, keep in mind that the Fresnel zone is three-dimensional, so clearance must also be maintained from the sides of buildings, etc. if path loss is to be minimized. Another point to consider is the effect on Fresnel zone clearance of changes in atmospheric refraction, as discussed in the last section. We may have adequate clearance on a longer path under normal conditions (i.e., 4/3 earth radius)

Ground Reflections

One common source of reflections is the ground. It tends to be more of a factor on paths in rural areas; in urban settings, the ground reflection path will often be blocked by the clutter of buildings, trees, etc. In paths over relatively smooth ground or bodies of water, however, ground reflections can be a major determinant of path loss. For any radio link, it is worthwhile to look at the path profile and see if the ground reflection has the potential to be significant. It should also be kept in mind that the reflection point is not at the midpoint of the path unless the antennas are at the same height and the ground is not sloped in the reflection region - just the remember the old maxim from optics that the angle of incidence equals the angle of reflection

Other Sources of Reflections

On long links, reflections from objects near the line of the direct path will almost always cause increased path loss - in essence, you have a permanent "flat fade" over a very wide bandwidth. Reflections from objects which are well off to the side of the direct path are a different story, however. This is a frequent occurrence in urban areas, where the sides of buildings can cause strong reflections. In such cases, the angle of incidence may be much larger than zero, unlike the ground reflection case. This means that horizontal and vertical polarization may behave quite differently When the reflecting surface is vertical, like the side of a building, a signal which is transmitted with horizontal polarization effectively has vertical polarization as far as the reflection is concerned. Therefore, horizontal polarization will generally result in weaker reflections and less multipath than vertical polarization in these cases.

Effects of Rain, Snow and Fog

The loss of LOS paths may sometimes be affected by weather conditions (other than the refraction effects which have already been mentioned). Rain and fog (clouds) become a significant source of attenuation only when we get well into the microwave region. Attenuation from fog only becomes noticeable (i.e., attenuation of the order of 1 dB or more) above about 30 GHz. Snow is in this category as well. Rain attenuation becomes significant at around 10 GHz, where a heavy rainfall may cause additional path loss of the order of 1 dB/km.

Attenuation from Trees and Forests

Trees can be a significant source of path loss, and there are a number of variables involved, such as the specific type of tree, whether it is wet or dry, and in the case of deciduous trees, whether the leaves are present or not. Isolated trees are not usually a major problem, but a dense forest is another story. The attenuation depends on the distance the signal must penetrate through the forest, and it increases with frequency. According to a CCIR report [10], the attenuation is of the order of 0.05 dB/m at 200 MHz, 0.1 dB/m at 500 MHz, 0.2 dB/m at 1 GHz, 0.3 dB/m at 2 GHz and 0.4 dB/m at 3 GHz. At lower frequencies, the attenuation is somewhat lower for horizontal polarization than for vertical, but the difference disappears above about 1 GHz. This adds up to a lot of excess path loss if your signal must penetrate several hundred meters of forest! Fortunately, there is also significant propagation by diffraction over the treetops, especially if you can get your antennas up near treetop level or keep them a good distance from the edge of the forest, so all is not lost if you live near a forest

Link Analysis

Some PDH to SDH Comparisons

  • PDH

  • (Plesiochronous Digital Hierarchy)

  • Asynchronous

    • Bit Interleaving - Requires Complete Demux of Data Stream to Extract a Single Channel

    • Relatively Low Bandwidths

    • 1960’s Technology

    • Limited Network Management

  • SDH

  • SDH (Synchronous Digital Hierarchy)

    • Synchronous

    • Byte Interleaving (Requires Much Demux to Extract a Single Channel

    • Relatively High Bandwidths

    • 1980’s - 1990’s Technology

    • Robust Network Management

SDH Features

  • Modern and Digital

  • Equipment Availability for 15 Years Expected

  • SDH Allows Drop and Insert Without Complete Demultiplexing

  • SDH Allows Multiplexing of Tributaries That Have Different Bit Rates

  • SDH Overhead Is Structured to Provide Access at Section, Line

  • and Path Layers Allows Enhanced Maintenance, Control,

  • Performance and Administration at Each Laye

  • Digital Radio limits the dependence on Trans Atlas routing


Communications satellites are radio relays

in the sky. They receive signals transmitted

from earth-based antennas, amplify the

signals, and return the signals to earth. Satellites

are extremely useful because they can

handle large amounts of different types of traffic,

they offer almost worldwide coverage, and

they can be installed independently and relatively



Satellite systems, which consist of special-

case beyond-LOS equipment, consist of

three parts: the space segment, which includes

the satellite; a ground segment comprising

simple to complex communications terminal

equipment; and a control segment that performs

satellite station-keeping chores and directs

allocation of satellite bandwidth between users.


Satellite systems use different frequencies

for transmitting and receiving information.

A ground terminal transmits the signal on the

uplink frequency; the satellite retransmits the

signal on the downlink frequency to the ground

receiver terminal. A transponder device within a satellite receives the incoming signal, amplifies

it, changes the signal frequency, and retransmits

it to the receiving terminal. Satellite

uplink and downlink frequencies are usually

referred to in pairs, like 6/4 GHz with the first

number the uplink frequency and the second

number the downlink frequency.


Most commercial satellites have more

than one transponder, with bandwidth differing

among various designs. Contemporary C-band

commercial satellites have as many as 34 transponders

each. Each transponder can relay

one color television channel with program sound,

1200 voice channels, or a data rate of up to 50

Mbps. The number of channels a satellite can

provide is related to the available bandwidth

and how it is used. This number may be increased

by improving the efficiency of the transponder

or increasing its power. However, because

more power requires more weight, the

number of channels is related to the satellite’s

size and weight.


  • Amicrowave relay station in space

  • Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency

  • Geostationary satellites

    • remain above the equator at a height of 22,300 miles (geosynchronous orbit)

    • travel around the earth in exactly the time the earth takes to rotate

Satellite Transmission Links

  • Earth stations communicate by sending signals to the satellite on an uplink

  • The satellite then repeats those signals on a downlink

  • The broadcast nature of the downlink makes it attractive for services such as the distribution of television programming

Satellite Transmission Process



Signal Delayed

0.25ms each way



22,300 miles

uplink station

downlink station

Satellite Transmission Applications

  • Television distribution

    • a network provides programming from a central location using direct broadcast satellites (DBS)

  • Long-distance telephone transmission

    • high-usage international trunks

  • Private business networks

Principal Satellite Transmission Bands

  • C band: 4(downlink) - 6(uplink) GHz

    • the first to be designated

  • Ku band: 12(downlink) -14(uplink) GHz

    • rain interference is the major problem

  • Ka band: 19(downlink) - 29(uplink) GHz

    • equipment needed to use the band is still very expensive

Communications Satellite Frequency Bands

Satellite Lettered Bands

Classes of Satellites

The technical/operational performance characteristics that are to be used in

conjunction with the possible services are:

1. Standard T-2

Earth Stations having a nominal G/T of 37 dB/K and operating in the 11/14 GHz frequency bands via the EUTELSAT II satellite system for international public telephony and high quality television transmissions or international public telephony only. (Note: The T1 standard applied to TDMA transmissions on EUTELSAT-I has been replaced by the T2 standard)

2. Standard V-1

Earth Stations having a nominal G/T between 26 dB/K and 30.5 dB/K (depending upon location) and

operating in the 11/14 GHz frequency bands via the EUTELSAT II satellite system for international

high quality television transmissions only.

3. Standard S-1

Earth Stations having a nominal G/T of 30 dB/K and operating in the 12/14 GHz frequency bands via the EUTELSAT I/II satellite system for international SMS services (SMS Open Network).


Generally, commercial systems operate

within different parts of the UHF and SHF bands

than do military systems. The accompanying

chart shows the relation of frequency bands

with letter frequency designators used in the

telecommunications industry. L-, C-, and Kuband

systems are currently available for lease;

all can provide communications services to most

of the world. Wide geographic coverage by Cband

is more prevalent than that by Ku-band

because Ku-band satellites tend to use very

narrow beam antennas to support high population

density regional locations. L-band, which is

associated with small terminals and mobile applications,

is used by INMARSAT and is available


Satellite Communication Access and Topology

  • Multi-Channel Per Carrier

  • Time Division Multiplex

  • Demand Assigned Multiple Access (DAMA) Technology

    • Provides Better Utilization of Bandwidth

    • Adaptable to Traffic Needs of a Mission

  • Topology Can Be a Star or Mesh Depending on Mission

  • Requirements

    • Controlled From Command Center

    • Secondary Sites Are Slaves to Command Center

Multiple Access Control Techniques for Satellite Communications


FDMA (Frequency Division Multiple

Access): A static multiple access technique

where transponder bandwidth is subdivided into

smaller frequency bands, or sub-channels, in which

each subchannel is assigned to a specific user.

TDMA (Time Division Multiple Access):

A static multiple access technique where

the transponder bandwidth is assigned to each

user during a specific time slot in a cyclic time



CDMA (Code Division Multiple Access):

A dynamic multiple access technique,

also known as spread spectrum, where total

transponder bandwidth employs a separate and

distinct code for each user to access a traffic

channel at any instant of time in sharing the

overall bandwidth with other users.

Polling (Roll Call and Round Robin):

A dynamic multiple access technique where

total transponder bandwidth is made available

to a user for the duration of time the user

requires. Upon transmission completion, channel

access is passed to the next user on the

polling list in a cyclic manner.

DAMA (Demand Assigned Multiple Access):

A family of dynamic multiple access

techniques where each user reserves channel

space based upon individual need.

Communications Architecture Considerations

  • Single Channel per Carrier (SCPC)

    • Dedicated point to point communications

  • Demand Assign Multiple Access (DAMA) And Time Division Multiple Access (TDMA)

    • Support multiple users on a as needed basis

    • Very bandwidth efficient


Contention: A family of dynamic multiple

access techniques where users compete

with each other for channel space by transmitting

when required. If separate transmissions

collide, the corrupted transmissions are re-attempted

after a random delay.

Each of the multiple access channel

control techniques has advantages and disadvantages.

The selection of a multiple access

technique depends upon network application,

traffic generation profiles for each network subscriber,

and user tolerance to traffic throughput


Summary of Techniques

Currently, FDMA and TDMA techniques

are static and do not adapt readily to changing

traffic loads. Polling techniques are not suitable

for networks with exceptionally large numbers

of users due to the time needed to cycle through

the polling list. CDMA has an inherent electronic

countermeasure resistance, but is expensive

to implement. DAMA is most efficient

for networks of users with varying traffic loads,

but the automated reservation (control) system

technology is complex.

Antenna Diameter Vs. G/T

The signal level on any contour line is

derived from the satellite’s EIRP at that location,

with values of EIRP measured in decibels

referenced to one watt of power or dBw. The

higher the EIRP value, the better the signal

quality. For example, the EIRP level of a satellite

signal could range from 18 dBw at beam

edge to 21 dBw at beam center. The G/T gain-to-

noise temperature ratio of the ground station

determines the quality of the received signal.

Satellite Terminal Parameters

Satellite Communication

To achieve successful satellite communications,

several technical considerations must

be satisfied. Considerations include the

geolocation of the terminal with respect to the

satellite beam coverage or “footprint” on the

earth’s surface, the frequency band, the signal

bandwidth, the antenna transmit gain expressed

as its Effective Isotropic Radiated Power (EIRP),

the size of the antenna dish, and the antenna

receive performance “figure of merit,” expressed

as G/T (the ratio of antenna receive gain to

system noise temperature in decibels per degrees

Kelvin, or dB/K).

Technical Constraints

Basic technical constraints affect system

performance and dependability of satellite

communications. Antenna size and polarization

influence system performance in terms of

radio receiver sensitivity G/T and transmitter

output power EIRP. Besides these physical

characteristics, other factors such as atmospheric

“noise” and temperature play significant



The EIRP of an earth terminal is a key

parameter in determining system performance.

The EIRP required depends on the communications

traffic that the earth terminal needs to

support. The recently introduced micro earth

terminals and very small aperture terminals

(VSAT) with low ElRPs are not able to support

the communications traffic volume that a large

earth terminal with a high EIRP can support.

There is a trade-off in a communications link

between the transmit EIRP and the receive G/T

required to support a given data rate. There is

also a trade-off in available power versus bandwidth

allocated by the satellite resource manager,

as well as between transmitter power and

antenna gain.

Satellites and Noise

Noise is the principal enemy of a

satellite receiver because it affects the receiver’s

ability to accurately separate the downlink radio

signal from ever-present random electrical energy.

Noise can be natural cosmic background

static, can come from heat generated by the

antenna’s own amplifier, or can originate from

other electronic parts of the receiver. Noise is

also caused by the sun’s RF energy falling on

the antenna. Fortunately, this phenomenon is

relatively short-lived, amounting to several minutes

a day and occurring seasonally in the fall

and spring, when, during the solar equinoxes,

the sun’s transit contributes to these disturbances.

Sun spots and solar flares can also

affect receiver performance at any time.


C-Band Medium EIRP Coverage

Current Area Beam Coverage - Arabsat II

Ku-Band EIRP Coverage

C-Band High EIRP Coverage



Link Budget

Determines the dish

size, output power,

frequency, and other

physical radio parameters













  • Resources Determine

  • Interfaces Type

  • Interface Quantity

  • Bit Rates

  • Satellite Interface

  • Combines lines

  • Compresses Data

  • Buffers Transmission

Terminal Equipment

Physical Transmission

& Reception of

Combined Data

Link Budget & Timing

  • The first step to a design/cost is a Link Budget

  • The Link Budget will provide design requirements for:

    • Operating Band

    • Antenna size

    • Transmitter power

    • Satellite availability

  • All these will help define the system Cost

  • There is a 252 ms delay in the receipt of data over a

  • satellite link

Satellite Data Sheet



---------------------------------- ----------------------------------

*Availability (%): 99.900 *Satellite INTELSAT 705

*Required Eb/No (dB): 5.50 Satellite West Long : 18.0

*Bit Error Rate : E-08 *Transponder SPOT-SPOT

*Modulation Type : QPSK !Usable Trnspndr BW (MHz): 72.00

*Info. Rate (Kbps): 256.00 !SFD @ 0 dB/K (dBW/M^2): -97.10

*FEC Rate : 0.69 *Transponder Atten (dB): 12.0

*Spread Spectrum Factor : 1.00

*Modem Step Size (kHz): 1.00


---------------------------------- ----------------------------------

North Lat: 41.3 West Long: 39.0 North Lat: 51.0 West Long: 23.0

Frequency (GHz): 14.20 Frequency (GHz): 11.20

*Satellite G/T (dB/K): 4.20 *Satellite EIRP (dBW): 42.10

*Antenna Diameter (m): 2.4 *Antenna Diameter (m): 3.8

Antenna Gain (dBi): 49.40 Antenna Gain (dBi): 51.80

Antenna Elevation (Deg): 37.69 Antenna Elevation (Deg): 31.42

Carrier EIRP (dBW): 43.72 *LNA Noise Temp (K): 65.00

*Power Control (dB): 0.00 *Loss betw.LNA & Ant.(dB): 0.06

*Output Circuit Loss (dB): 0.00 System Noise Temp. (K): 107.94

Path Loss (dB): 207.11 Station G/T (dB/K): 31.47

Other Losses (dB): 0.70 Path Loss (dB): 205.16

(other loss = atm,pol,ant point) Other Losses (dB): 0.60

Satellite Data Sheet



C/Io Adj Sat U (dB-Hz): 71.92 #C/Io Intermod (dB-Hz): 75.41

C/Io Adj Sat D (dB-Hz): 78.52 C/No Thermal Up (dB-Hz): 68.71

C/Io Crosspol (dB-Hz): 80.28 C/No Thermal Dn (dB-Hz): 69.62

C/Io Adj Channel (dB-Hz): 79.42 C/Io Total (dB-Hz): 68.79

C/Io Adj Trans (dB-Hz): 83.67 C/No Therm Total (dB-Hz): 66.13

C/Io Microwave (dB-Hz): N/A C/No Total (dB-Hz): 64.25



Overall Link Margin (dB): 4.67 *Rain Model : CRANE

Uplink Availability (%): 99.912

Rain Margin (dB): 4.67 *Uplink Rain Zone : D2

Dnlink Availability (%): 99.988

Rain Margin (dB): 4.47 *Dnlink Rain Zone : C

G/T Degradation (dB): 4.36


---------------------------------- ----------------------------------

*Number of Carriers : MULTIPLE *Number of Carriers : 1.0

*Total OPBO (dB): 3.50 *Total HPA OPBO : 0.00

Total IPBO (dB): 7.00 HPA Power/Carrier (dBm): 24.32

Carrier OPBO (dB): 26.78 Required HPA Size (dBW): -5.68

Carrier IPBO (dB): 30.29 Required HPA Size (W): 0.27

FCC Req: 1) Uplink Flange Density (dBW/4kHz): -22.34 File: I705DBE

(@46.0) 2) Downlink EIRP Density (dBW/4kHz): 2.56

Transponder BW Used Per Carrier (x1.35) (%): 0.35 # = deltas used

Transponder Power Used Per Carrier (%): 0.47 ! = modif. default

Transponder Bandwidth Allocation (MHz): 0.251 * = user's input

Satellite as a Cost Effective Solution

  • Advances in Satellite Hardware has:

    • Lowered Hardware Cost

    • Decreased Large Hub Station Requirements

    • Systems Available in Transportable Configurations

    • Lease Minimal of Space Segment;

      • Full Period

      • Occasional Use

Satellite Advantages

  • Can reach a large geographical area

  • High bandwidth

  • Cheaper over long distances

Satellite Disadvantages

  • High initial cost

  • Susceptible to noise and interference

  • Propagation delay





freq 128.1MHz










118.1 TMA



121.5 TMA


150NM AT 15,000ft

213NM AT 30,000ft


Freq.= 126 MHz








freq 128.8MHz





AT 15,000'

HF Radio Systems










  • Compact Rooftop RLPA

  • Frequency range 2 to 30 MHz

  • Radius of rotation 8.7 m

  • Gain

    • 7dBi @ 6.2 MHz

    • 12dBi @ 30 MHz

  • Range of rotation ± (n x 360°)

  • Efficiency

    • 6.2-3090-98

    • 5.4-6.250-90

    • 4.4-5.425-50

    • 2.0-4.45-25

HF Whip Antenna Patterns

Radiation Pattern between Sites

A Complete HF System

Broadcast Radio

  • Omnidirectional

  • FM radio

  • UHF and VHF television

  • Requires line of sight

  • Suffers from multipath interference

    • Reflections


  • Achieved using transceivers that modulate noncoherent infrared light

  • Requires line of sight (or reflection)

  • Blocked by walls

    • e.g. TV remote control, Infrared port

Protocol Layers

A Laser Infrared Unit

System Block Diagram

System Range

Beam Width


100 x 100mm


100 x 100mm


150 x 150mm


150 x 150mm


200 x 200mm



This lens provides a beam divergence of 0.5 degrees, giving a large beam footprint. This is to avoid problems of loss of signal due to building movement, atmospheric distortions, ease of installation and long-term reliability. A coarse optical filter is placed in front of the lenses to reduce the effect of sunlight on the APD.

The size of the transmit aperture provides a wide area of emission to avoid safety and scintillation problems.

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