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T324: Keeping ahead
in
Information and Communication Technologies
Abbreviations – Definitions - Calclutions
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First : Abbreviations:IET
: Institution of Engineering and Technology
BCS
: British Computer Society
ACM
: Association for Computing Machinery
IEEE
: Institute of Electrical and Electronics Engineers
EM
: Electromagnetic
BW
: Bandwidth
ISDN
: Integrated Services Digital Network
ISM
: Industrial, Scientific or Medical Band (License exempt)
DSL
: Digital Subscriber Line
ADSL
: Asymmetric Digital Subscriber Line
3G
: Third Generation
PAN
: Personal Area Network
LAN
: Local Area Network
MAN
: Metropolitan Area Network
WAN
: Wide Area Network
Wi-Fi
: Wireless Fidelity
WiMAX
: World Interoperability for Microwave Access
LED
: Light-Emitting Diode
FHSS
: First is frequency-hopping spread spectrum
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DSSS
: Direct Sequence Spread Spectrum
UWB
: Ultra Wideband
MIMO
: Multiple Input-Multiple Output (or sometimes
Multiple In-Multiple Out).
UWB
: Ultra Wideband
OFDM
: Orthogonal Frequency-Division Multiplexing
CDMA
: Code Division Multiple Access
DRM
: Digital Radio Mondiale
AM
: Amplitude Modulation
ASK
: Amplitude Shift Keying
OOK
: On-Off Keying
FM
: Frequency Modulation
FSK
: Frequency Shift Keying
PM
: Phase Modulation
PSK
: Phase Shift Keying
DPSK
: Differential Phase Shift Keying
QPSK
: Quadrature Phase Shift Keying
BPSK
: Binary Phase Shift Keying
QAM
: Quadrature Amplitude modulation
CPFSK
: Continuous-Phase Frequency Shift Keying
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Ofcom
: Office of Communications
FCC
: Federal Communications Commission
MSK
: Minimum Shift Keying
DRM
: Digital Radio Mondiale
EMC
: ElectroMagnetic Compatibility
ERP
: Effective Radiated Power
DAA
: Detect and Avoid
CEPT
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DoD
: Department of Defense
DARPA
: Defense Advanced Research Projects Agency
CSMA/CD
: Carrier Sense Multiple Access with Collision Detection
PPP
: Point-to-Point Protocol
IP
: Internet Protocol
TCP
: Transmission Control Protocol
UDP
: User Datagram Protocol
FTP
: File Transfer Protocol
SMTP
: Simple Mail Transfer Protocol
HTTP
: Hypertext Transfer Protocol
SNMP
: Simple Network Management Protocol
NNTP
: Network News Transfer Protocol
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DHCP
: Dynamic Host Configuration Protocol
DNS
: Domain Name Service
OSI
: Open Systems Interconnection
MAC
: Medium Access Control
PHY
: Physical
SDU
: Service Data Unit
PCI
: Protocol Control Information
PDU
: Protocol Data Unit
CRC
: Cyclic Redundancy Check
CSMA/CA
: Carrier Sense Multiple Access with Collision Avoidance
RTS
: Request To Send
CTS
: Clear To Send
SSID
: System Set Identifier
WEP
: Wired-Equivalent Privacy
XOR
: Exclusive-OR
PRNG
: Pseudo-Random Number Generator
EAP
: Extensible Authentication Protocol
ISP
: Internet Service Provider
RADIUS
: Remote Authentication Dial-In User Service
RSN
: Robust Security Network
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TKIP
: Temporary Key Integrity Protocol
WPA
: Wi-Fi Protected Access
WPA-PSK
: Wi-Fi Protected Access - Pre-Shared Key
AES
; Advanced Encryption Standard
IPsec
: Internet Protocol Security
VPN
: Virtual Private Network
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T324 – Summary for Final Exam
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Second : Definitions:-
‘wireless’ and ‘radio’ are often synonymous.
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term ‘electromagnetic’ is used because all these waves involve the physics of
electricity and magnetism.
1 Hz (hertz) = 1 cycle per second.
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Spectrum: A graph showing the frequencies present in a signal.
Periodic: the term applied to signals that repeat themselves at regular intervals.
Period: the period of a periodic signal is the time it takes for the signal to repeat itself.
The period is equal to the duration of one cycle, it is the reciprocal of the frequency.
Radio waves are electromagnetic waves with wavelengths above 1 mm.
The Radio Spectrum: All electromagnetic waves at frequencies less than 300 GHz.
The region above 1 GHz (or beginning at 3 GHz), which includes the EHF, SHF and
part of the UHF bands, is also commonly called the microwave spectrum.
Unlicensed bands are a bit of a free-for-all, in which finding an unused channel
cannot be guaranteed.
The use of licensed bands involves paying a fee for the legal right to use certain
frequencies, and these are controlled much more closely.
The inverse square law of radio propagation: the received power decreases with
1/d2.
Isotropic: in free space when there is no other matter nearby to affect propagation
between the transmitter and receiver. Also assume that the transmitting and receiving
antennas transmit or receive equally in all directions.
A decibel is a way to express a ratio of powers, such as
Isotropic: in free space when there is no other matter nearby to affect propagation
between the transmitter and receiver. Also assume that the transmitting and receiving
antennas transmit or receive equally in all directions.
Line of sight (LoS) limited for two main factors: Curvature of the earth, Obstacles.
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Two ways in which radio waves propagate in the VLF—HF bands that dominate their
use. These are sky waves and surface waves.
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Sky waves are only dominant at night.
Transmitting Antenna: Radio waves are produced by an oscillating electric current
in the transmitting antenna.
Receiving Antenna: Radio waves then go on to generate a small electric current in
the receiving antenna.
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Half-wavelength (or
) Dipole Antenna
A fundamental form of antenna is called a dipole.
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Omnidirectional Antennas: A vertical rod will radiate (or receive) equally as well
in all horizontal directions around it. This is termed an omni-directional radiation
pattern (is not isotropic - i.e. it does not radiate equally in all three dimensions).
Directional Antennas: The dish antenna used for microwave or satellite
communications. For transmission, a dipole at the focus of the dish radiates energy,
and the dish reflects like a curved mirror to direct most of this energy along a narrow
beam, rather like a spotlight forming a narrow beam of light. For reception the dish
reflects the incoming radiation to a focus at the dipole.
Types of antennas: rods, dish, combs, grids, plates, loops, coils, helices and so on.
A familiar example is the rooftop TV antenna, called a Yagi antenna. planar (flat)
antennas for portable devices.
Polarisation - Polarization: The direction of the electric field vector (which is not
the same as the direction of light propagation!) is called the polarization direction.
Propagation: how radio waves get from point A to point B. The events occurring in
the transmission path between two stations that affect the communications between
the stations.
Propagation Delay: is the time taken for a signal to travel from its source to its
destination. Propagation delay depends on a number of factors, including:
o The distance the signal has to travel.
o The signal's speed.
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Bandwidth (BW): the difference between the highest and the lowest frequencies
present in a signal or the maximum range of frequency that can be transmitted by a
system. Bandwidth spread over a range of radio frequencies is called the bandwidth.
(Bandwidth = higher frequency - lower frequency)
Spread Spectrum: a class of modulation techniques that spreads a signal’s power
over a wider band of frequencies than is necessary for the information being
transmitted.
Baud: a unit of signaling speed.
Baud Rate : Number of symbols transmitted per second.
Data Rate:
Symbol:
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Digital Radio Mondiale (DRM): DRM was originally intended for use on the long,
medium and short wave bands as a replacement for conventional analogue amplitude
modulation.
Repeater: it operates at OSI layer 1 and transmits data bits over a physical medium.
A repeater makes a copy of any packet received on one of its ports and sends it out
on all other ports.
Bridge: it operates at OSI layer 2 and is commonly used to connect similar LAN
segments.
A bridge filters frames by reading the destination address in the frame. The bridge
will only forward a frame onto a connected collision domain if the frame is
addressed to a computer on the opposite side of the bridge.
Switch: it operates at OSI layer 2 or layer 3 and is used to interconnect multiple
similar or dissimilar LANs.
Router: it operates at OSI layer 3. A router is used to interconnect individual
networks whose sizes vary from very small to very large. Routers may be categorized
into backbone router (or core router), border router and access router depending on
their role in the network.
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Each LAN connects to the WAN via a router.
A router is a switching device very similar to a bridge.
It operates at the network layer of the OSI model, and makes routing decisions based upon
the address information supplied by the packets it receives.
For example, a router is able to terminate the Ethernet protocol, extract the data and
address information (if necessary) and re-package the data in a format suitable for
transmission across the WAN.
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Gateways: Routers are also used to interface between a LAN and a WAN. When
carrying out this function the routers are sometimes called gateways, reflecting their
role of extending the reach of a user beyond the boundary of a LAN.
In practice the terminology for connecting devices (repeaters, bridges, routers,
gateways), is not always consistent, as the combination of functions which can be
carried out by a given device may depend on the manufacturer.
What is a DOI name, and why is it claimed to be superior to a URL for identifying a
digital resource?
DOI stand for digital object identifier.
It is a unique identifier of a document (or other piece of intellectual property) and is
claimed to be superior to a URL as it is persistent- that is, unlike a URL it should
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Modulation: is a way of getting an electromagnetic wave to carry data (varying
amplitude, frequency or phase, or a combination of these).
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never change. Another way of expressing this is that a DOI identifies a document
directly and not, like a URL, simply where it is located
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Briefly describe the basic principles of CSMA, TDMA and FDMA.
CSMA,TDMA and FDMA are all techniques for allowing a number of users to share
bandwidth. In CSMA the transmitter “listens before it transmits”. If it detects another
transmitter using the channel, the transmitter waits before transmitting. In TDMA
each user is allocated a particular time slot or time slots and the various users “take
turns”. In FDMA each user is allocated its own frequency band within the total
spectral resource.
Explain what is meant by the terms ’listening mechanisms’ and ‘binary
exponential backoff’ in CSMA. Describe briefly the options recommended for
these when using CSMA for sensor networks.
By “listening mechanism” is meant the specific way in which a transmitter detects the
presence of another user before transmitting. Simply listening at regular intervals
could mean a user never gained access if another user was transmitting at the same
regular intervals. So if a transmission is detected, a common approach is to wait for a
random length of time before trying again. If a transmission is still detected, the wait
period or “backoff” is changed again. A common approach is to choose increasing
backoff times (within a range that doubles for consecutive attempts) until the channel
is free. This is known as (increasing) exponential backoff. The specific options
recommended here (from reference [9] in the paper) are fixed window with random
backoff or exponentially decreasing (rather than increasing) backoff.
What is the rationale claimed for the hybrid scheme? How is the choice made between
TDMA and FDMA?
The hybrid scheme described is designed for a monitoring system that has strict data
latency (delay) requirements. A TDMA approach minimizes the time of transmitting,
but the time needed for synchronization can outweigh this advantage. In a pure FDMA
scheme each node has limited bandwidth and thus restricted data rate. In the hybrid
scheme power consumption is modeled, and the TDMA-FDMA balance determined
so as to minimize power consumption. It turns out that this balance depends on
whether the receiver or transmitter consumes more power. If the transmitter consumes
more power, a greater TDMA element is favored; the opposite if the receiver
consumes greater power.
Briefly discuss in your own words at least 6 recurring themes in poorly performing
projects destined for failure.
The recurring themes in poorly performing projects are(any 6 from B3,P1,Sec3):
1 deficiencies in the apparent organisational structure of the project, resulting in an
inability to measure performance, exercise sufficient control or carry out effective
decision making.
2 inadequate design.
3 deficiencies in the performance of one or more subsystems – for example, a
performance-measuring subsystem may not have performed its task adequately.
4 lack of an effective means of communication between the various subsystems.
5 lack of clarity of purpose.
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6 not enough consideration given to the influence of the environment, and insufficient
resources to cope with those environmental disturbances that were foreseen.
7 an imbalance between the resources applied to the basic conduct of the project and
those allocated to the related monitoring and control processes.
Using a mobile telephone network as an example, explain what is meant by a ‘sociotechnical system’.
Ref: B3, page9 (but answer of students should be in their own words)
Nowadays, almost every large-scale project involves people interacting with
technology. With large-scale projects, one way to think about ‘the whole’ is as a
socio-technical system.
The term socio-technical system was coined by researchers at the Tavistock Institute
in London during the 1950s and 1960s. People at the Tavistock Institute were
interested in the design of work, and saw that work systems comprised:
1. Social (or human),
2. organisational and
3. technical elements.
All three had to be configured together if the whole was to be successful. Why?
There are many reasons why you might want to take a socio-technical systems
approach. For example, you might use it to study:
1. the organisation of work, or
2. the use of resources or
3. why systems fail and so on.
Mobile telephone network (MTN): MTNs are large-scale projects which
comprise all 3 elements of a socio-technical system such as social (or human),
organization and technical elements.The social elements consists of the users as
well as the service providers i.e. the people running the network, the
organizational elements are concerned with the management and the physical
structures of the organization running the network, and the technical elements
comprise the type of technology (TDMA, CDMA, 3G, 4G etc) used by the
system.
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Explain in your own words the following terms in the way that they were used in
T324 Block 3:
(i) Social Capacity; (ii) Capacity and Capability.
Ref1: B3, page 122 (but answer of students should be in their own words)
Social capital:
Social capital is a rather subtle concept. According to one definition: Social capital
consists of the stock of active connections among people: the trust, mutual
understanding, and shared values and behaviors that bind the members of human
networks and communities and make cooperative action possible.
(http://www.infed.org/biblio/social_capital.htm, accessed 29 January 2007)
Ref2: http://abs.sagepub.com/cgi/content/abstract/52/6/846:
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Social capacity is people's ability to work together to organize public relationships,
rather than give responsibility for those relationships wholly to state actors or the flux
of market exchange.
Ref3: Evaluating Capacity Building and Participatory Development in Community
Timber Operations of the Petén, Guatemala by Lisa H. Patel, MESc 2005 “The UNDP
defines capacity-building as “the process by which individuals, groups, organizations,
institutions, and societies increase their abilities to (1) perform core functions, solve
problems, and define and achieve objectives and (2) understand and deal with their
development needs in a broad context and in a sustainable manner” (1997). Capacity
itself can be divided into three realms: physical, human, and social.
Physical capacity describes equipment and capital, human capacity refers to the
education and skill set of individuals, while social capacity, the most difficult of the
three to assess, describes the nature of interactions between individuals in a
community through networks or institutions.”
Answer (ii):
Ref1: page120 (but answer of students should be in their own words)
Capacities and capabilities Some writers make fine distinctions between ‘capacity’
and ‘capability’, but for our purposes we can think of both terms meaning the skills
and abilities that enable knowledge to be put to work, or assets to be exploited
effectively.
Ref2:B3, page 117(but answer of students should be in their own words)
Capacity and capability A combined technological and social issue is that of access in
the sense of capacity and capability to use the technology. For computers and the
internet, there is the technical issue of computer literacy, but there is also the
opportunity cost of investing in such literacy. Another capacity and capability issue
concerns literacy in English, the ‘language’ of the internet. At a deeper level people
need the capacity and capability to communicate in the particular ways that email and
computer conferencing demand. They also need the capacity and capability to sift,
make sense of, edit, judge and so on the information they receive via the internet. This
has led many people to argue that the digital divide is but one manifestation of a wider
divide that they call the knowledge divide. It is also why the benefits of mobile
phones are so lauded by many commentators (as in the Economist article in Section
3.4) in both the North and the South. Mobile phones have few literacy demands (either
technical or in use of language), they can easily be absorbed into everyday life and
they can be used as a simple substitute for human face-to-face interaction.
With reference to the article by Baskaran et. al, briefly describe how ICTs can be used
for wider socio-economic development in developing countries.
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With reference to the article by Bishop et. al, briefly discuss how Grameen Phone is
enabling women to become micro-entrepreneurs?
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With reference to the article by Overa et. al, briefly discuss in your own words at least
2 areas in which traders have benefitted by adopting the ICTs.
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With reference to the article by Overa et. al, List at least 5 developmental benefits and
the role of ICTs in each.
Developmental benefit
Role of ICTs
Synchronization of supply and demand Speedy transmission of information
about supply and demand of products
Coordination of multi-local activities
ICTs enable greater communication to
coordinate multi-local activities in
commodity
chains
that
are
geographically extensive.
Availability as comparative advantage
ICTs (esp. cell phones) make traders
more accessible to customers thus
leading to greater customer satisfaction.
Safer money transactions
ICTs (including cell phones) enable
trust building between traders and banks
thus
leading
to
safer
money
transactions.
Improved services
Entrepreneurial utilization of ICTs
enable coordination of business much
more efficiently thus leading to
improved services.
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T324 – Summary for Final Exam
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T324 – Summary for Final Exam
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Two basic types of wireless local area network: ad hoc and infrastructure networks.
Layered models and how they apply to WLAN networks: Horizontal and Vertical
communications.
TCP/IP Layers:
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OSI vs TCP/IP:
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Two main aspects of network access control: 1. Sending data over a specific
physical link. This is called the physical layer, which in the IEEE 802 standards
includes wired and wireless media. 2. Providing a range of services to higher layers
that control the way data is sent over a transmission channel. This is called the
medium access control (MAC) sublayer.
A cyclic redundancy check (CRC) is a common technique employed to detect
transmission errors.
A block of data from an upper layer is called a service data unit (SDU).
A block of data formed by a layer and then sent to its peer layer is called a protocol
data unit (PDU).
Data added to the service data unit is called protocol control information (PCI).
There are two complementary approaches in Wi-Fi networks: 1. carrier sense
multiple access with collision avoidance (CSMA/CA) (distributed coordination
function); 2. Contention-free periods (point coordination function).
The start of each contention-free period is indicated by the transmission of a
management frame, called a beacon frame, by the central station.
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The end of a contention-free period is indicated by a special management frame,
labelled CF end frame.
The services provided by the IEEE MAC sublayer are limited to metropolitan and
local area networks, and a wireless local area network typically operates within
distances of less than about 100 m.
Three levels of networks: the independent basic service set, the extended service
set and the internetwork.
MAC Address: The addresses provided by the MAC sublayer are sufficient to
identify the stations. An address contains 6 bytes (48 bits) in a Wi-Fi network. The
IEEE assigns ranges of the rst 3 bytes of an address to manufacturers of the
network interface cards and manufacturers use the remaining 3 bytes to identify
each individual interface they produce (also known as hardware addresses and
Ethernet addresses).
IP address: is split into a network address portion and a host address portion.
There are two versions of the internet protocol in current use: version 4 and version
6. In terms of addressing, the main difference between the two versions is that
version 4 has 32-bit addresses and version 6 has 128-bit addresses.
A mobile station has two IP addresses; The IP address that does not change is called
the home address, and the one that does is called the care-of address.
IP tunnels are created simply by encapsulating an IP packet in another IP packet.
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Activities that threaten users’ network security are called attacks.
So a man-in-the middle attack can include elements of fabrication, interception,
interruption and modification.
Types of encryption: There are two basic types of encryption: symmetric (secret key)
and asymmetric (public key).
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Third : Mathmitical Formulas:-
Symbol Rate = Bit Rate / Number of bits per Symbol
Bandwidth = higher frequency - lower frequency
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Shannon’s equation:
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o C is the theoretical maximum channel capacity, measured in bits per second.
o It is the maximum rate at which data can be transmitted error free.
o W is the bandwidth of the data, in hertz. S/N is the signal-to-noise ratio,
expressed as a ratio of powers.
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Fourth : Calclutions:Question (a):
Assuming free space propagation and an isotropic antenna, a
receiver receives 10 µ watt power at a distance of 10 meters. How much power will the
receiver receive at a distance of 20 meters and 5 meters? Write all steps of your work.
Answer: (a)
At 20 m: 20 m is double 10 m.
Therefore the received power will be reduced by
10 µ W ·1/4 = 2.5 µW.
So the received power is 2.5 µW.
At 5 m: 5 m is 0.5 times 10 m.
Therefore the received power will be:
10 µ W ·1/.25 = 40 µW.
So the received power is 40 µW.
= 1/4.
Question (b):
Assuming free space propagation, what would be an adequate length of a dipole antenna for
a cellular system operating at 900 MHz. Write all steps of your work.
Answer (b):
“Typically a dipole antenna is formed by two quarter wavelength conductors or
elements placed back to back for a total length of
Now c=f
, therefore in this case
And hence
Question (c):
Consider a wireless network operating at 5 Mbit/s. Let the frame size used by the network be
1000 bytes. Considering that the initialization vector is 12 bits long, find out how long will it
take for the initialization vector value to be repeated if it is incremented by one for each
frame transmitted? Write all steps of your work.
Answer (c):
With 12 bits, the number of different initialisation vector values is
, which is the number of frames that are transmitted
before a value is repeated.
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The maximum rate of transmitting frames is given by:
data rate/frame size =
frames/s.
The time taken to repeat a value is given by:
4096/625=6.5536 sec.
Question (e):
For a single ‘channel’ from base station to receiving device, how many bits per second are
sent?
Answer (e):
For a single chip stream , the rate is (3.84x
)/16=0.24Mbit/s.
For 2 streams (I and Q), the coded bit rate is 2x.24=0.48Mbit/s.
Question (f):
For a coding ratio of 0.5, what is the user data rate in (a) (that is the data rate after Error
correction)?
Answer (f):
The coding rate is 0.5, so the useful data rate is 0.5x0.48Mbit/s=0.24Mbit/s.
Question (g):
To get the advertised user data rate, how many codes would need to be allocated to a user?
Hence discuss the feasibility of all users simultaneously getting the advertised downlink user
data rate.
Answer (g):
Answer (f) showed that the user data rate for a channel is 0.24Mbit/s. The advertised
data rate is 3.6Mbit/s. Hence the number of codes to achieve this rate is 3.6Mbit/s
0.24Mbit/s=15.
The maximum number of codes available in a cell is 15. It is not possible for more
than one user to have all 15 codes simultaneously. Hence the advertised data rate
cannot be had by more than one user.
(i)
For a SNR of 3:1, what is the theoretical maximum user data rate achievable
with the amount of spectrum used in HSDPA?
From fig 58 of Block1 Part2, a SNR of 3:1 gives a value of
(1+S/N)=2.
Hence for a BW of 5MHz (used in HSDPA) the theoretical maximum user data
rate is 2x5Mbit/s=10Mbit/s.
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(iii)
(iv)
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The theoretical maximum user data rate of HSDPA could be increased by
transmitting a more powerful signal and thereby improving the SNR. What
SNR would be required to give a theoretical maximum user data rate of 40
Mbit/s?
Shannon’s equation becomes:
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From fig 58, S/N=250:1.
Mobile WiMAX has been proposed as a alternative technology for mobile
broadband. It can use various widths of spectrum, but the largest allowed width
is 20 MHz. With the widest allocation of spectrum, what would be the
theoretical maximum user data rate of WiMAX for a SNR of 3:1?
For a bandwidth of 20MHz, which is 4 times the bandwidth used in (i), and
with the same SNR 3:1 as used in (i), the maximum data rate is 4 times that of
(i) i.e. 40Mbit/s.
From the answers to (i), (ii) and (iii), comment on the relative effectiveness of
increasing bandwidth or SNR as ways of increasing the theoretical maximum
user data rate in this case.
Answers (ii) and (iii) show alternate methods of achieving a 4 fold increase in
maximum data rate relative to that in (i). In (ii) this required an 83 fold
improvement in SNR from 3:1 to 250:1. In (iii) it required only a 4 fold
increase of BW. Increasing the BW is more effective.
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Question (a):
Consider a wireless sensor network (WSN). If the SNR of a signal received by a sensor in
the WSN 100m from a transmitter is 20dB, then what will it be 200m, assuming propagation
can be modeled as:
(i) An inverse square power law?
(ii)An inverse third power law?
(iii)
An inverse fourth power law?
In each case assume that the noise power is identical at the two locations, and explain
your reasoning. Write all steps of your work.
Answer:
(a)
(i) For the inverse square law, with constant noise, the S/N will be reduced by a factor of 4
for doubling the distance.
That is, by 6 dB to 20 – 6=14 dB.
(ii) For inverse cube by a factor of 8 or 9 dB to 11 dB.
(iii) For inverse fourth power by a factor of 16 or 12 dB to 8 dB.
Question (b): from (a)
(i) What is the wavelength of 6 GHz signal, assuming free space propagation?
(ii)What is the frequency of a 15 cm wavelength signal, again assuming free space
propagation?
In each case write all steps of your work.
Answer:
(b)
(i) The relevant formula is c = f , so = c/f,
So in this case = 5cm.
(ii) A 15 cm wavelength (3 x 5 cm) will therefore have a frequency of
substitute again in the formula).
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= 2 GHz (or
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