Accredited by NBA, New Delhi: Ifet College of Engineering Gangarampalayam, Villupuram - 605108
Accredited by NBA, New Delhi: Ifet College of Engineering Gangarampalayam, Villupuram - 605108
Accredited by NBA, New Delhi: Ifet College of Engineering Gangarampalayam, Villupuram - 605108
(b) Explain the applications of wireless network and mobile communications. (12m)
Draw Fig 1.1 Page 24 and Fig 2.2 Page 25
Although many applications can benefit from wireless networks and mobile communications,
particular application environments seem to be predestined for their use. Some of them are;
• Vehicles – DAB, UMTS, GPS, GSM, TETRA, and so on.
• Emergencies
• Business
• Replacement of wired networks
• Infotainment and more
• Location dependent services
• Mobile and wireless devices
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2. Describe the History or overview of wireless communication with its figure.
Brief History of Wireless Communications: ( For Fig Refer Fig 1.3 Page 14)
(i) The Birth of Telecommunications: The Telegraph [wikipedia]
pre-1600s - 1833
(ii) From Telegraph to ``The Birth of Radio'', 1867-1896
1867 -1896
(iii) ``The Birth of Radio''
1897 -1898
(iv) Transoceanic Communication
1901-1909
(v) Voice over Radio
1914 -1940
(vi) Birth of Mobile Telephony
1946 -1976
(vii) Cellular Mobile Telephony
1979 1994 and Mobile Communications''
(viii) Wireless Local Area Networks
1990 -2009
(ix) Wireless Local Area Networks
1995 - 2008
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a. Describe about the frequencies for Radio Transmission. (8m)
Radio transmission can take place using many different frequency bands. Each frequency
band exhibits certain advantages and disadvantages. Figure 2.1 gives a rough overview of the
frequency spectrum that can be used for data transmission.
λ = c/f,
where c ≅ 3·108 m/s (the speed of light in vacuum) and f the frequency. For traditional wired
networks, frequencies of up to several hundred kHz are used for distances up to some km with
twisted pair copper wires, while frequencies of several hundred MHz are used with coaxial cable
Radio transmission starts at several kHz, the very low frequency (VLF) range. These are
very long waves. Waves in the low frequency (LF) range are used by submarines, because they can
penetrate water and can follow the earth’s surface. The medium frequency (MF) and high
frequency (HF) ranges are typical for transmission of hundreds of radio stations either as
amplitude modulation (AM) between 520 kHz and 1605.5 kHz, as short wave (SW) between 5.9
MHz and 26.1 MHz, or as frequency modulation (FM) between 87.5 MHz and 108 MHz.
Conventional analog TV is transmitted in ranges of 174–230 MHz and 470–790 MHz using
the very high frequency (VHF) and ultra high frequency (UHF) bands. Super high frequencies
(SHF) are typically used for directed microwave links (approx. 2–40 GHz) and fixed satellite
services in the C-band (4 and 6 GHz), Ku-band (11 and 14 GHz), or Ka-band (19 and 29 GHz).
Some systems are planned in the extremely high frequency (EHF) range which comes close to
infra red. Next step is Infra red (IR) transmission is used for directed links, e.g., to connect
different buildings via laser links.
4. What are the main problems of signal propagation? Why do radio waves not
always follow a straight line? Why is reflection both useful and harmful?
Like wired networks, wireless communication networks also have senders and receivers of
signals. However, in connection with signal propagation, these two networks exhibit considerable
differences. In wireless networks, the signal has no wire to determine the direction of propagation,
whereas signals in wired networks only travel along the wire (which can be twisted pair copper
wires, a coax cable, but also a fiber etc.). 3 Situations / reasons Transmission range, Detection
range & Interference range The different problems are : Path Loss of Radio signals, Additional
Signal propagation effects and Multi-path Propagation
5. Why, typically, is digital modulation not enough for radio transmission? What are
the general goals of digital modulation? What are typical schemes?
Cosine function: g(t) = At cos(2π ftt + φt) This function has three parameters: amplitude At,
frequency ft, and phase φt which may be varied in accordance with data or another modulating
signal. For digital modulation, which is the main topic in this section, digital data (0 and 1) is
translated into an analog signal (baseband signal). Digital modulation is required if digital data
has to be transmitted over a medium that only allows for analog transmission.
The three basic methods for this translation are amplitude shift keying (ASK), frequency shift
keying (FSK), and phase shift keying (PSK). Apart from the translation of digital data into analog
signals, wireless transmission requires an additional modulation, an analog modulation that shifts
the center frequency of the baseband signal generated by the digital modulation up to the radio
carrier.
There are several reasons why this baseband signal cannot be directly transmitted in a
wireless system: ● Antennas, ● Frequency division multiplexing ● Medium characteristics
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As for digital modulation, three different basic schemes are known for analog modulation:
amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).
6. What are the main benefits of a spread spectrum system? How can spreading
achieved?
As the name implies, spread spectrum techniques involve spreading the bandwidth
needed to transmit data – which does not make sense at first sight. Spreading the bandwidth has
several advantages. The main advantage is the resistance to narrowband interference. Figure
shows an idealized narrowband signal from a sender of user data The power level of the spread
signal can be much lower than that of the original narrowband signal without losing data.
Spreading the spectrum can be achieved in two different ways: Direct sequence spread spectrum
(DSSS) systems take a user bit stream and perform an (XOR) with a so-called chipping sequence
and For frequency hopping spread spectrum (FHSS) systems.
Explain the below terms & Compare DSSS and FHSS
In DSSS: Chips - Spreading factors – Integrator – Correlator – Decision Unit – Rake Receiver
In FHSS: Hopping sequence – dwell times – slow & fast hopping
7. What are the main reasons for using cellular systems? How SDM typically
realized and combined with FDM? How does DCA influence the frequencies
available in other cells?
Cellular systems for mobile communications implement SDM. Each transmitter, typically called
a base station, covers a certain area, a cell. Cell radii can vary from tens of meters in
buildings, and hundreds of meters in cities, up to tens of kilometers in the countryside. The shape of
cells is never perfect circles or hexagons as shown in Figure 2.41.
List the advantages and disadvantages of cellular systems.
8. (a) What is the main physical reason for the failure of MAC schemes? (4m)
Several medium access control (MAC) algorithms which are specifically adapted to the
wireless domain. Medium access control comprises all mechanisms that regulate user access to a
medium using SDM, TDM, FDM, or CDM. MAC is thus similar to traffic regulations in the
highway/multiplexing example.
The fact that several vehicles use the same street crossing in TDM, for example, requires rules
to avoid collisions; one mechanism to enforce these rules is traffic lights. MAC belongs to layer 2,
the data link control layer (DLC).
Layer 2 is subdivided into the logical link control (LLC), layer 2b, and the MAC, layer 2a
(Halsall, 1996). The task of DLC is to establish a reliable point to point or point to multi-point
connection between different devices over a wired or wireless medium.
Compared to FDMA, time division multiple access (TDMA) offers a much more flexible
scheme, which comprises all technologies that allocate certain time slots for communication, i.e.,
controlling TDM.
3.4.1 Fixed TDM - time division duplex (TDD).
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3.4.2 Classical Aloha - ALOHANET for.
3.4.3 Slotted Aloha
3.4.4 Carrier sense multiple access -carrier sense multiple access (CSMA): non-
persistent CSMA, & p-persistent CSMA - (CSMA/CA- elimination yield – non-preemptive
multiple access (EY-NMPA) used in the HIPERLAN 1 specification.
3.4.5 Demand assigned multiple accesses: One basic scheme is demand assigned multiple
access (DAMA) also called reservation Aloha, a scheme typical for satellite systems.
3.4.6 PRMA packet reservation multiple access: An example for an implicit reservation
scheme is packet reservation multiple access (PRMA)
3.4.7 Reservation TDMA - An even more fixed pattern that still allows some random access
is exhibited by reservation TDMA .
3.4.8 Multiple access with collision avoidance - request to send (RTS) & clear to send
(CTS).
3.4.9 Polling 3.4.10 Inhibit sense multiple access - digital sense multiple access (DSMA).
9. (a) Explain the term interferences in the space, time, frequency and code domain.(6m)
(b) Compare SDMA, TDMA, FDMA and CDMA mechanisms. (10m)
10. Define CDMA. Explain its function with one theoretical example.
Code division multiple access (CDMA) systems use exactly these codes to separate different
users in code space and to enable access to a shared medium without interference. The orthogonal
in code space has the same meaning as in standard space (i.e., the three dimensional space). Now let
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us translate this into code space and explain what we mean by a good autocorrelation. The Barker
code (+1, –1, +1, +1, –1, +1, +1, +1, –1, –1, –1), for example, has a good autocorrelation, i.e., the
inner product with itself is large, the result is 11. This code is used for ISDN and IEEE 802.11
1. Name the main elements of the GSM system architecture and describe their
functions with neat sketches.
A GSM system consists of three subsystems, the radio sub system (RSS), the network and
switching subsystem (NSS), and the operation subsystem (OSS). Each subsystem will be discussed
in more detail in the following sections. Generally, a GSM customer only notices a very small
fraction of the whole network – the mobile stations (MS) and some antenna masts of the base
transceiver stations (BTS). Figure 4.4 Functional architecture of a GSM system
GSM: Pg no: 96 – 122. The main elements are:
• Mobile services System architecture Radio interface
• Protocols Localization and calling Handover
• Security New data services
Table 4.1 Tasks of the BTS and BSC within a BSS
(b) What are the advantages of specifying not only the Radio Interface but also
all internal interfaces of the GSM System? (10m)
The most interesting interface in a GSM system is Um, the radio interface, as it comprises
many mechanisms presented in chapters 2 and 3 for multiplexing and media access. GSM
implements SDMA using cells with BTS and assigns an MS to a BTS.
To avoid frequency selective fading, GSM specifies an optional slow frequency
hopping mechanism. Logical Channels and Frame hierarchy: 2 basic sub groups – TCH:
-HR, FR, EFR & TCH/F14.4 & CCH: BCCH-CCCH (PCH, RACH, AGCH) – DCCH
(SDCCH, SACCH & FACCH) Draw Figures 4.5 & 4.6
6. (a) Name basic applications for satellite communication and describe the trends.
Draw a typical satellite system for global mobile communication. (8m)
Traditionally, satellites have been used in the following areas:
● Weather forecasting ● Radio and TV broadcast satellites
● Military satellites ● Satellites for navigation
In the context of mobile communication, the capabilities of satellites to transmit data is of particular
interest.
● Global telephone backbones ● Connections for remote or developing areas
● Global mobile communication Draw Figure 5.1
(b) Describe the 2 simple laws of satellites circulate in orbits around the earth. Draw all the
three kinds of circulation diagrams. (8m)
Satellites orbit around the earth. Depending on the application, these orbits can be circular
or elliptical. Satellites in circular orbits always keep the same distance to the earth’s surface
following a simple law: ● The attractive force Fg of the earth due to gravity equals m·g·(R/r)2.
● The centrifugal force Fc trying to pull the satellite away equals m·r·ω2.
Where, Draw figures 5.2 to 5.4
● m is the mass of the satellite;
● R is the radius of earth with R = 6,370 km;
● r is the distance of the satellite to the centre of the earth;
● g is the acceleration of gravity with g = 9.81 m/s2; and
● ω is the angular velocity with ω = 2·π·f, f is the frequency of the rotation.
To keep the satellite in a stable circular orbit, the following equation must hold:
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● Fg = Fc, i.e., both forces must be equal. Looking at this equation the first thing to notice is that
the mass m of a satellite is irrelevant (it appears on both sides of the equation).
● Solving the equation for the distance r of the satellite to the center of the earth results in the
following equation: The distance r = (g·R2/(2·π·f)2)1/3
Tell about 4 types of orbits namely GO, MEO, LEO AND HEO
7. (a) What characteristics do the different types of orbits have? Show its satellite
communication diagram. What are their pros and cons? (10m)
Tell about 4 types of orbits namely GO, MEO, LEO AND HEO in detail.
Draw figures 5.2 to 5.4
(b) Explain Routing, Localization and Handover concepts in Satellite systems. (6m)
Tell about satellite communication after say about Routing: ISL – 2 Uplinks and
Downlinks, Localization (HLR, VLR and SUMR) and Handover : (intra, inter, gateway and
intersystem)
8. (a) List out the four examples of satellite networks in table format. (6m)
Draw Table 5.1 Page 198
(b) Give an overview of Broadcast transmission with its scope and figure. (6m)
Symmetrical communication systems offer the same transmission capabilities in both
communication directions, i.e., the channel characteristics from A to B are the same as from B to A
(e.g., bandwidth, delay, costs). Examples of symmetrical communication services are the plain old
telephone service (POTS) or GSM, if end-to-end communication is considered.
Asymmetrical communication systems are unidirectional broadcast systems where
typically a high bandwidth data stream exists from one sender to many receivers. Draw Fig 6.1
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● Event information table (EIT): EIT contains status information about the current
transmission and some additional information for set-top boxes.
● Time and date table (TDT): Finally, TDT contains update information for set-top boxes.
Draw Figures 6.7 to 6.10
(a) List the pros and cons of WLAN with brief explanation. (8m)
Write short notes about each pros and cons.
Some advantages of WLANs are:
● Flexibility ● Planning ● Design
● Robustness ● Cost
But WLANs also have several disadvantages:
● Quality of service ● Proprietary solutions ● Restrictions
● Safety and security
Many different, and sometimes competing, design goals have to be taken into account for
WLANs to ensure their commercial success:
● Global operation ● Low power ● Easy to use
● License-free operation ● Robust transmission technology
● Simplified spontaneous cooperation ● Protection of investment
● Safety and security ● Transparency for applications
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System architecture: Several nodes, called stations (STAi), are connected to access points
(AP). Basic service set (BSSi) - Distribution system extended service set (ESS) - distribution
system services
Protocol architecture :The IEEE 802.11 standard only covers the physical layer PHY and
medium access layer MAC like the other 802.x LANs do. The physical layer is subdivided into the
physical layer convergence protocol (PLCP) and the physical medium dependent sublayer
PMD. Draw Figures 7.3 to 7.6
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HIPERLAN stands for high performance local area network.) - BRAN (broadband radio
access networks) and wireless ATM activities. However, the standardization efforts had a lot of
impact on QoS supporting wireless broadband networks such as HiperLAN2.
1. Historical: HIPERLAN 1: Elimination-yield non-preemptive priority multiple access
(EY-NPMA): Prioritization - Contention –Transmission ( synchronized channel condition-
access in channel-free condition’) -hidden elimination condition The contention phase is further
subdivided into: Prioritization phase , Elimination phase, Yield phase & Transmission phase.
Quality of service support and other specialties: (HMQoS-parameters - MSDU lifetime -
residual MSDU lifetime - Power conservation is achieved by setting up certain - encryption
and decryption - normalized residual HMPDU lifetime (NRL)
2. WATM: Wireless ATM, Working Group:The following more general extensions of
the ATM system also need to be considered for a mobile ATM: Location management -
Handover Network management - radio access layer (RAL) - Radio resource control, and so
on - Generic reference model -Handover of multiple connections - Location management-
Transparency of mobility - Security - Efficiency and scalability – Identification-● Inter-
working and standards- Mobile quality of service: ● Wired QoS ● Wireless QoS ● Handover
-Access scenarios: MT (mobile terminal) - WT (wireless terminal) WMT (wireless mobile
terminal, etc.,
6. Compare IEEE 802.11, HIPER LAN and Bluetooth with regard to their ad hoc
capabilities. Where is the focus of these technologies?
Refer answers for question 3, 4 & 5
10. (a) What are the advantages and problems of forwarding mechanisms in ad hoc
networks regarding security, power saving and network stability. (10m)
Refer answers from book page nos. 225 to 227
(b) Describe about Cellular IP and HAWALL and HM in IPv6 mobility. (10m)
Cellular IP: (Valko, 1999), (Campbell, 2000) provides local handovers without renewed
registration by instaling a single cellular IP gateway (CIPGW) for each domain, which acts to the
outside world as a foreign agent (see Figure 8.14).
Advantage
● Manageability: Cellular IP is mostly self-configuring, and integration of the CIPGW into a
firewall would facilitate administration of mobility-related functionality. This is, however, not
explicitly specified in (Campbell, 2000).
Disadvantages
● Efficiency: Additional network load is induced by forwarding packets on
multiple paths. ● Transparency: Changes to MNs are required. ● Security: Routing tables are
changed based on messages sent by mobile nodes.
HAWAII (Handoff-Aware Wireless Access Internet Infrastructure): tries to keep micro-
mobility support as transparent as possible for both home agents and mobile nodes (which have to
support route optimization to the new base station as to a foreign agent
Advantages: ● Security: Challenge-response extensions are mandatory ● Transparency:
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HAWAII is mostly transparent to mobile nodes.
Disadvantages
● Security: There are no provisions regarding the setup of IPSec tunnels.
● Implementation: No private address support is possible because of collocated COAs
3. (a) What is the basic purpose of DHCP? Name its entities. How can DHCP
be used for mobility and support of mobile IP? (6m)
The dynamic host configuration protocol (DHCP, RFC 2131, Drohms, 1997) is mainly
used to simplifiy the installation and maintenance of networked computers. If a new
computer is connected to a network -DHCPDISCOVER Figs. 8.17 & 8.18
(b) Describe about Mobile ad-hoc networks with its Routing concepts. (10m)
These networks should be mobile and use wireless communications. Examples for the
use of such mobile, wireless, multi-hop ad-hoc networks, which are only called ad-hoc
networks here for simplicity, are: ● Instant infrastructure ● Disaster relief ‘
● Remote areas ● Effectiveness. ● Fig 8.19
6. What are the difference between AODV and the standard distance
algorithm? Why are extensions needed?
AODV-DSDV now adds two things to the distance vector algorithm:
● Sequence numbers: Each routing advertisement comes with a sequence number. Within ad-hoc
networks, advertisements may propagate along many paths.
● Damping: Transient changes in topology that are of short duration should not destabilize the
routing mechanisms. Advertisements containing changes in the topology currently stored are
therefore not disseminated further.
3. (a) Compare the different types of transmission errors that can occur in wireless
and wired networks. What additional role does mobility play? (8m)
Tell about the Implications on Mobility Pg 354 (9.1.4)
(b) What is the reaction of standard TCP in case of packet loss? In what situation
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does the reaction make sense and why is it quite often problematic in the case of WN
and mobility? (8m)
Tell about Based on these characteristics, (Inamura, 2002) suggests the following configuration
parameters to adapt TCP to wireless environments: Large windows, Limited transmit, Large
MTU, SACK, ECN, Timestamp and No header compression.
4. (a) What are the influences of encryption on the proposed schemes? Consider for
example IP security that can encrypt the payload i.e., the TCP packet. (10m)
Draw Table 9.1 from page 385 & Figure 9.4
(b) How and why does the I-TCP isolate problems on the wireless link? What are
the main drawbacks of this solution? (6m)
Indirect TCP: Two competing insights led to the development of indirect TCP (I-TCP) b
One is that TCP performs poorly together with wireless links; the other is that TCP within the fixed
network cannot be changed. I-TCP segments a TCP connection into a fixed part and a wireless part.
Figures 9.1 & 9.2 List its advantages & disadvantages
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Tell about - Bandwidth and delay, Caching and POSTing.
(c) What are approaches that might help wireless access? (5m)
Tell about the Approaches: Image scaling, Content transformation, content extraction /
semantic compression, special languages and protocols. Draw Figures 10.4 to 10.8
8. Explain about Wireless transport layer security and Wireless transaction protocol.
If requested by an application, a security service, the wireless transport layer
security (WTLS), can be integrated into the WAP architecture on top of WDP as specified in
(WAP Forum, 2000c). Draw Figures 10.12 to 10.19
The first step is to initiate the session with the SEC-Create primitive. Parameters are
source address (SA), source port (SP) of the originator, destination address (DA), destination
port (DP) of the peer. A key exchange suite (KES), ECC, a cipher suite (CS) and a compression
method (CM) The peer answers with parameters for the sequence number mode (SNM), - KR -
the session identifier (SID - key exchange suite (KES’), cipher suite (CS’), compression
method (CM’). The peer also issues a SEC-Exchange primitive from client certificate (CC) from
the originator. Explain WTP Classes namely Class 0, Class 1 and Class 2.
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resume, and session management class 2. Draw Figures 10.20 to 10.27 There are so many
keywords read all from Page 425 to 431.
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