telecom

Question 1

what are the transmission mode

Answer 1

1. Broadcasting which involves the use of a single powerful transmitter and
   numerous receivers that are relatively inexpensive to build; example: radio and
   television.
2. Point-to-point communication in which the communication process takes place
   over a link between a single transmitter and receiver. In this case, there is usually a
   bidirectional flow of information signals which requires the use of a transmitter
   and a receiver at each end of the link; example: telephone and a link between an
   earth station and a robot navigation the surface of another planet.

Question 2

what are the transmission moes

Answer 2

1. Simplex: information is sent in one direction. Examples are Radio or TV
   broadcasting.
2. Half duplex: information is sent and received on the same channel but not at the
   same time. Examples are: Walky Talky, Bluetooth data transfer between two
   laptops, etc…
3. Full duplex: information is sent and received at the same time over two separate
   channels. The telephone is an example of full duplex communication.

Question 3

why do we use digital communications

Answer 3

easy to regenerate distorted signals
easier and more efficient to multiplex several signals
can combine difference signal types

Question 4

what are the transmission
mediums

Answer 4

guided:
twisted pair, coaxial cable, fiber optic
UTP cable, stp cablecable
unguided
radio waves, microwaves

Question 5

what is the difference between coaxial and STP

Answer 5

STP uses a foil shield while while coaxial uses a plastic insulation

Question 6

what are the components of a fiber optic cable

Answer 6

jacket
strengening material
buffer
cladding
core

Question 7

what are the types of fiber optic cables

Answer 7

single mode
used for long distances
4-5 times more expensive than multimode
core has a smaller radius
uses a lazer as a light source
handling or manufacturing is much harder
less degradation of signals
can carry singals at much greater speed
multimode

Question 8

what is a PSTN

Answer 8

the public switched telephone network is an overall telecom network consisting of local networks interconnected by one or more long distance networks

Question 9

what are the satellite services

Answer 9

fixed satellite services (FSS)
broadcast satellite services (BSS)
Mobile satellite service (MSS)
Inter Satellite service (ISS)

Question 10

what is a molniya orbit

Answer 10

highly or extremely eliptical orbit

Question 11

what are the 3 segments of a GPS system

Answer 11

Space segment (ss)
control segment (CS)
User segment (US)

Question 12

what are the 3 entities of a control segment

Answer 12

Master control system
monitor stations
ground antennas

Question 13

what do antenna noise
temperature Td depend on?

Answer 13

loss between the antenna and receiver input
sky noise from the galaxy, sun and moon
absorption by amospheric gases and precipitation
radiation from the earth into the backlobes of the antenna
interference from man made radio sources

Question 14

how do you get rid of antenna noise

Answer 14

by placing a metallic rim around the edge of the parabolic dish

Question 15

what are the atmospheric effects on microwaves

Answer 15

absorption
refraction
diffraction

Question 16

what is a microwave link

Answer 16

A (terrestrial) microwave link uses a beam of radio waves in the
microwave frequency range to transmit information between two fixed
locations on the earth.

Question 17

what is frequency reuse

Answer 17

in the context of polarization, same frequency channels can be reused by passing one horizontal and one vertical signal through it

Question 18

what are the two types of towers and when is each one used

Answer 18

self supporting : relatively short towers
guyed towers: for relatively long towers or when there is no space at the base

Question 19

what is refraction

Answer 19

refraction is the bending of the radio waves due to changes in the atmosphere (temperature/density/altitude)

Question 20

describe the condition with respect to n1, n2, and k

Answer 20

if n1 > n2 => Good Condition
if n2 > n1 => Bad condition
if K < 0 => Good Condition
if 1 < k < 0 => Bad Condition
if k > 0 => Good conidtion
if k -> inf => Good condition

Question 21

what is ducting

Answer 21

atmospheric refraction sometimes traps microwave beams in a waveguide called ducting

Question 22

what are the components of a setellite

Answer 22

command antenna
broadcast antenna
radio transmitters and receivers
rocket fuel
rocket thrusters
main rocket
camera
solar panels

Question 23

what is a FSS

Answer 23

a fixed satellite station supports telecommunication services between antennas (satellite and ground station)

Question 24

what is a BSS

Answer 24

a broadcast satellite station uses a high powered beam to transmit radio or television services right to the end user (Simplex)

Question 25

what is a MSS

Answer 25

a mobile satellite service provides telecommunication services but move rather than remain stationary

Question 26

what is a ISS

Answer 26

inter satellite service is used in low or medium orbit to interconnect multiple high orbit satellites constellations

Question 27

what are the two types of communicating satellites

Answer 27

passive: frequency repeating (RF) repeater satellite (Bent pipe)
active: processing satellite (used for digital) demodulates the uplink signal, provides error correction and retransmits the signal back to earth

Question 28

what are the 4 advantages and disadvantages of LEO

Answer 28

advantages
less transmission path loss
less transmission delay
lightweight, compact and low cost antennas
people can go up, and down in a short time

disadvantages
large number of satellites to create a global contellation network
mode difficult controls, complex billing and authentication’
cannot constantly point the antenna at an area because the space craft is constantly moving
large earth gravity on them, 7 year total lifetime

Question 29

what are the 1/3 advantages and disadvantages of MEO

Answer 29

advantages:
provides global coverage with less transmission times and delay then LEO

disadvantage
more satellites than a GEO
system must be deployed and operated in full as a complete network unlike a GEO which can be its own network
de-orbiting requires a great amount of thruster fuel

Question 30

what are the 2 advantages and disadvantages of GEO

Answer 30

advantage
relatively easy to maintain in orbit for about 15-20 years
raised out of orbit at end of life hence spending less fuel

disadvantage
for mobile, it requires high beam power and aperture radius for reliability
each satellite is bigger more complex and expensive to manufacture

Question 31

what is the altitude and period of a gps satellite

Answer 31

20200km above surface with a period of 12 hours

Question 32

what are the components of a GPS user segment

Answer 32

an antenna tuned to the frequency used by the satellite
a receiver processor
highly stable clock

Question 33

what is the total path lost from base station to a satellite a sum of?

Answer 33

free space loss
atmospheric absorption
ionospheric absorption
rainfall loss

Question 34

what is transmission

Answer 34

the transfer of a signal, message or any other information from one location to another

Question 35

what is the difference between analog systems and digital systems

Answer 35

analog systems convert analog messages to signals while digital convert bits into signal

Question 36

what is modulation

Answer 36

is the process of impinging useful information onto the carrier. it involves varying some parameters of the carrier wave according to the message wave

Question 37

what are the components of a coaxial cable

Answer 37

jacket
braided copper shield
plastic insulator
copper conductor