Mobile computing
B.TECH VIIth semester
Paper Code : ETEC-407
Prepared by: Pradeep Gulati
Q1. Differentiate between signal and data.
Ans. The term ‘data’ represents message or information where the signal is the representation of
the
data, and it is also termed as information bearing signal.
Q2. What is a periodic signal?
Ans. In a signal if a particular signal pattern repeats over a time period systematically it is a periodic
signal.
Q3. What is a “Aperiodic” signal?
Ans. In a signal if the same signal pattern does not repeat itself over a time period it is known as
‘Aperiodic’ signal.
Q4. Give an example for periodic and aperiodic signals.
Ans. a. periodic signal  x (t + T) = x(t).
where - ∞ < t < + ∞
b. Aperiodic signal  x (t + T) ≠ x(t).
Q5. Define wavelength.
Ans.The wavelength of a signal represents its distance or range it takes for one cycle. It is denoted as ‘λ’.
Wavelength λ = c/f
Q6. What is a bandwidth?
Ans. Bandwidth is the range of frequencies and represented as BW = f2 – f1, where f1 – f2 are the first and
last frequencies of the signal graph.
Q7. Define attenuation.
Ans. It is nothing but reduction in signal strength mainly at higher frequency ranges, and at receiving end
this attenuated signal has reduced voltage levels.
Q8. Draw the diagram of multiplexing.
Ans.
Input
M
U
X
D
E
One link
M
U
X
Prepared by: Pradeep Gulati
Outputs
Q9. What is the principle used in multiplexers?
Ans. The principle used in multiplexer is ‘many to one’ concept. Many inputs are combined as one link
or one output from a MUX unit where a DEMUX unit at the receiver reproduces the same many
units at the end entity.
Q10. What are the important multiplexing schemes?
Ans.
Multiplexing
Frequency Division
Time Division
Multiplexing (FDM)
Multiplexing (TDM)
Code Division
Multiplexing (CDM)
Q11. What are the multiple access schemes?
Ans. a) FDMA
b) TDMA
c) CDMA
Q12. What is personal communication?
Ans The vision for the emerging mobile and personal communication services and system is to enable
communication with a person, at any time, at any place, and in any form. Besides providing
unlimited reach ability and accessibility, this vision for personal communication is also underlines
the increasing need for users of communication services to be able to manage their individual
calls, and services according to their real time needs.
Q13. What are the different kinds of mobility?
Ans. Terminal mobility: Terminal mobility systems are characterized by their ability to locate and
identify mobile terminals as it moves, and to allow the mobile terminal to access
telecommunication services from any location-even while it is in motion. Terminal mobility is
associated with wireless access and requires that the user carry a wireless terminal and be with in a
radio coverage area.
Personal mobility: personal mobility on the other hand , relies on a dynamic association between
the terminal and the user, so that the call delivery and billing can be based on a personal identity
assigned to a user. Personal mobility systems are therefore characterize by their ability to identify
end users as they move, and allow end users to originate and receive calls, and to access subscribed
telecommunication services on any terminal, in any location.
Service portability: it refers to the capability of a network to provide subscribed services at the
terminal or location designated by the user. The exact services the user can invoke at the designated
terminal, of course, depend on the capability of the terminal and the network serving the terminal.
Prepared by: Pradeep Gulati
Q14 . Define guard band.
Ans. It is unused (dummy) frequency inserted with actual spectrum to reduce adjacent channel
interference to enhance accuracy.
Q15. What are the types of spread spectrum and differentiate them?
Ans.
a) FHSS - Frequency Hopping Spread Spectrum
b) DSSS – Direct Sequence Spread Spectrum..
DSSS
FHSS
Each bit in transmission can be
Signal is transmitted in random series at
represented as multiple bits.
fixed time intervals. Synchronization
between transmitter and receiver is a
must.
Q16. Define a cell.
Ans. The smallest geographical area covered by wireless communication is said to be a cell.
Q17. What are the shapes related to a cell?
Ans. In early days three shapes namely.
a. Circle
b. Square
c. Hexagon
were suggested for a cell. But coverage of signal was very accurate with hexagonal shaped cells
and in later stage it was taken as standard.
Q18. Define BTS.
Ans. BTS is the base transceiver station available in each cellular region.
Q19. What is a MSC? What are the functions of MSC in network and switching subsystem?
Ans. It is mobile switching center and it enables connectivity between BTS and PSTN.
(i) It is like a normal switching node for PSTN fixed telephone and for cellular subscribers of the
same network.
(ii) It is possible to have functions like registration, location updating, and authentication, call routing
etc.
Prepared by: Pradeep Gulati
Q20.What is known as ‘handoff' ?
Ans. Handoff is a principle used to continue the call established in mobile communication. When the
subscriber is towards the cell boundary the signal strength reduces by which the BTS of that cell hand
over the call to the next BTS of another cell where the subscriber enters.
Q21. What are the types of handoff?
Ans. a) Hard hand off.
b) Soft handoff.
Q22. What is mobility management?
Ans. Mobility management is one of the major functions of a GSM or a UMTS network that allows
mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing
calls, SMS and other mobile phone services to be delivered to them.
Q 23.What is frequency reuse in cellular systems?
Ans. The key characteristic of a cellular network is the ability to re-use frequencies to increase both
coverage and capacity. As described above, adjacent cells must utilize different frequencies, however
there is no problem with two cells sufficiently far apart operating on the same frequency. The elements
that determine frequency reuse are the reuse distance and the reuse factor.
The reuse distance, D is calculated as
where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius in the ranges
(1 km to 30 km). The boundaries of the cells can also overlap between adjacent cells and large cells can
be divided into smaller cells.
The frequency reuse factor is the rate at which the same frequency can be used in the network. It is
1/K (or K according to some books) where K is the number of cells which cannot use the same
frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12
(or 3, 4, 7, 9 and 12 depending on notation).
In case of N sector antennas on the same base station site, each with different direction, the base
station site can serve N different sectors. N is typically 3.
A reuse pattern of N/K denotes a further division in frequency among N sector antennas per site. Some
current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4
(GSM).
If the total available bandwidth is B, each cell can only utilize a number of frequency channels
corresponding to a bandwidth of B/K, and each sector can use a bandwidth of B/NK.
Prepared by: Pradeep Gulati
Cells with the same number have the same set of frequencies. Here, because the number of available
frequencies is 7, so the frequency reuse factor is 1/7. That is each cell is using 1/7 of available cellular
channels.
Q 24. What is cluster?
Ans. A cluster is a group of cells. No channels are reused with in a cluster. Figure shows 7-cell cluster.
Prepared by: Pradeep Gulati
Q25. List all the services provided by GSM.
a) Tele services.
b) Bearer services.
c) Supplementary services.
Q26. What are the services provided by supplementary services?
Ans. · User identification
· Call redirection
· Call forwarding
· Closed user groups
· Multiparty Communication
Q27. What are the different managements under GSM protocol architecture?
Ans. (i) Mobility management
(ii) Connection management
(iii) Radio resource management
(iv) Message transfer
Q28. What is a TCH/H GSM channel?
Ans. It is half rate traffic channel that supports traffic channels with half-rate speech coding. It can use up to
16 slots in one frame with a data rate of 11.4 kbps/sec.
Q29. What are the common control channels?
Ans.The common control channels (CCCH) are used for call establishment and they are basically one way
channels.
Q30. What are types of CCCH ?
Ans. (i) Random access channel (RCH) (ii) Paging channel (PCH)
(iii) Access grant channel (AGCH)
Q31. What is a RCH?
Ans. For establishing a call RCH (Random access channel) is used by mobile station to access the base
station involved.
Q32. What is DCCH? What are the types of DCCH?
Ans. It is duplicated control channels known as two way channels and it is useful for signaling and control
operations for individual subscribers.
DCCH types:
(i) Stand alone dedicated control channel (SDCCH)
(ii) The slow associated control channel (SACCH)
(iii) The fast associated control channel (FACCH)
Q33. What are the four types of handover available in GSM?
Ans. (i) Intra cell Handover
(ii) Inter cell Intra BSC Handover
(iii) Inter BSC Intra MSC handover
(iv)Inter MSC Handover
Prepared by: Pradeep Gulati
Q34. What are subsystems in GSM system?
Ans. · Radio subsystem(RSS)
· Network & Switching subsystem(NSS)
· Operation subsystem(OSS)
Q35.What are the information in SIM?
Ans. · card type, serial no, list of subscribed services
· Personal Identity Number(PIN)
· Pin Unlocking Key(PUK)
· An Authentication Key(KI)
Q36. What is meant by GPRS?
Ans. The General Packet Radio Service provides packet mode transfer for applications
that exhibit traffic patterns such as frequent transmission of small volumes.
Q37. What is the function of an AuC?
Ans.The authentication center (AuC) maintains copy of secret key that is stored in each and every subscribers
SIM card. It is used to protect user’s database.
Q38. What are the three types of switching methods?
Ans. a. Circuit switching
b. Message switching
c. Packet switching
Q39. What is QoS in GPRS.
Ans. In GPRS the users can specify the QoS profile where the profile determines
important things like reliability class, delay class and service precedence.
Q40. What is the use of SS7?
Ans. (a) In network subsystem the SS7 (signaling system number 7) is used for signaling between different
functional entities.
(b) SS7 is used for SMS, roaming prepaid network functions.
(c) SS7 is also used for trunk signaling.
Q41. What are the parameters considered for defining QoS in GPRS technology?
Ans. (i) Service precedence
(ii) Delay
(iii) Throughput
(iv) Reliability
Prepared by: Pradeep Gulati
Q42. A certain city has an area of 1300 square miles and is covered by a cellular system using a seven
cell reuse pattern. Each cell has a radius of 4 miles and the city has 40 MHz spectrum with a full
duplex channel bandwidth of 60KHz. Find:
(i)The number of cells in the service area.
(ii) The number of channels per cell.
(iii) Total number of subscribers that can be served.
Ans.
(i) Radius of a cell = 4 miles
Area covered by cell = 50 square miles.
For 7 cell reuse pattern
Area covered by cluster = 7*50 = 350 square miles.
So, no. of cells required to cover 1300 square miles is 28.
(ii)No. of channels per cell = total no. of channels/no. of cells in a cluster
Available frequency = 40MHz
Channel bandwidth = 60 KHz
No. of channels available = 40 MHz/60KHz = 666 channels
No. of channels per cell = 666/7= 95 channels per cell.
(iii)total number of subscriber that can be served =666*4 = 2664 subscribers.
Q43. If a total of 33 MHz of bandwidth is allocated to a particular cellular system which uses
two 25 KHz Simplex channels to provide full Duplex voice. Compute the number of
channels available per cell if the system uses:
(i)
4 cell reuse (ii) 7 cell reuse
Ans. Available bandwidth = 33 MHz
Channel bandwidth = 25 KHz
Total no. of channels available = 1320 simplex channels.
(i)
(ii)
For 4 cell reuse
No. of channels per cell = 1320/4 = 330 channels
For 7 cell reuse
No. of channels per cell = 1320/7 = 188 channels
Q44. What are the functions of MSC in network and switching subsystem?
Ans. (i) It is like a normal switching node for PSTN fixed telephone and for cellular subscribers
of the same network.
(ii)It is possible to have functions like registration, location updating, and authentication, call
routing etc.
Q45. State the requirements of mobile IP.
Ans. i. Compatibility
ii. Transparency
iv Security
iii. Scalability and efficiency
Prepared by: Pradeep Gulati
Q46. What is COA? How is it assigned?
Ans. Care-or address (COA): The COA defines the current location of the MN from an IP point of
view.
There are two different possibilities for the location of the COA:
 Foreign agent COA
 Co-located COA
Q47. How does a MN identify that it has moved?
Ans. Mobile IP describes two methods: agent advertisement and agent solicitation, which are in fact
router discovery methods plus extensions.
Q48. What are the contents of mobility binding?
Ans. Mobility binding containing the mobile node’s home IP address and the current COA.
Additionally, the mobility binding contains the lifetime of the registration which is negotiated
during the registration process.
Q49. Define encapsulation. List the types of encapsulation.
Ans. Encapsulation is the mechanism of taking a packet consisting of packet header and data and
putting it into the data part of new packet. The reverse operation, taking a packet out of the
data part of another packet, is called decapsulation.
 IP-in-IP encapsulation
 Minimal encapsulation
 Generic routing encapsulation
Q50. State any 4 features of IPv6.
Ans.




No special mechanisms as add-ons are needed for securing mobile IP registration. Every
IPv6 node masters address auto configuration – the mechanisms for acquiring a COA are
already built in.
Neighbor discovery as a mechanism mandatory for every node is also included in the
specification; special foreign agents are no longer needed to advertise services.
Combining the features of auto configuration and neighbor discovery means that every
mobile node is able to crate or obtain a topologically correct address for the current point of
attachment.
Every IPv6 node can send binding updates to another node, so the MN can send its current
COA directly to the CN and HA.
Q51. State the layers in WAP architecture.
Ans.
 Transport layer
 Security layer
 Transaction layer
 Session layer
 Application layer
Prepared by: Pradeep Gulati
Q52. What are the different security levels offered by WTLS?
Ans. (i) Privacy
(ii) data integrity
(iii) authentication
Q53. How is reliability achieved in WTP?
Ans. (i) duplicate removed
(ii) retransmission
(iii) acknowledgements
(iv) unique transaction identifier.
Q54. What are the functions of WSP?
Ans.
(i) session management
(iii)content encoding
(ii) Capability negotiation
Q55. List any 4 basic features of WML.
Ans.
(i) Text and images representation.
(ii) User interaction
(ii) Navigation
(iv) Context management.
Q56. List any 4 capabilities of WML script.
Ans.
(i) Validity check of user input
(ii) Access to device facilities
(iii) Local user interaction
(iv) Extension to the device software.
Q57. What are the benefits of IMT-2000 over 2G systems?
Ans.
(i) Circuit and packet bearer capability up to 144 kbps.
(ii) User authentication and ciphering.
(iii) Multimedia services.
(iv) Emergency and priority calls.
Q58. Compare MEO and LEO satellite types.
Ans.
Characteristics
MEO
Satellite lifetime
10 to 15 years
Altitude range
10,000 to 20.000 km
Round - trip delay
40 to 80 msec
LEO
4 to 8 years
500 to 2000 km
5 to 10 msec
Q59. What is a GEO?
Ans. The communication satellite (GEO) orbits in geo stationary orbit which is at 36000 km above
earth's surface. The satellite revolves with same speed as that of the earth (1 Rev / day) that
revolves around sun.
Prepared by: Pradeep Gulati
Q60. What are examples of global mobile satellite system?
Ans.
(i) Iridium
(ii) Teledesic
(iii) Global star
Q61. Give three specifications of Global star and Iridium systems.
Ans.
Characteristic
System type
Data speed
Launched year
Q62.
Ans.
Global star
LEO
7.2 kbps
1999
Iridium
LEO
2.4 kbps
1998
What are the advantages of Iridium satellite system?
(i) Inter-satellite links are possible.
(ii) Number of satellites possible is 66 and 6 numbers of satellites can be maintained as
spares.
(iii) The terminal types can be of dual mode, mobile or handheld.
Q63. Give few advantages of GEO satellites.
Ans.
(i) They have large footprints and provide large coverage.
(ii)Used for communication related applications.
Q64. What is the demerit of GEO satellite?
Ans.
Their round trip time delay is long due to high altitudes, and it results in qua1ity degradation.
Q65. What are the advantages of LEO satellites?
Ans.
(i) LEO satellites provide higher global coverage.
(ii) High spectrum utilization.
(iii)The propagation delay is lower (say  5 to 10 msec).
Q66. What are the demerits of LEO system?
Ans.
(i) The network architecture is complex. (ii) Satellite movement is rapid and analysis is
tough.
(iii) Routing mechanism is difficult.
(iv) Long period of deployment.
Prepared by: Pradeep Gulati
Q67. What is IEEE 802.11? Explain 802.ii family.
Ans. IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN)
computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and
maintained by the IEEE LAN/MAN Standards Committee (IEEE 802).
IEEE 802.11 Family
802.11
protocol
Freq.
(GHz)
Bandwidth
(MHz)
Data rate per stream
(Mbit/s)
Allowable
MIMO
streams
1
-----
2.4
20
1,2
a
5
20
6,9,12,18,24,36,48,54 1
OFDM
b
2.4
20
5.5,11
DSSS
g
2.4
20
6,9,12,18,24,36,48,54 1
OFDM,DSSS
n
2.4/5
20/40
7.2, 14.4, 21.7, 28.9,
43.3, 57.8, 65, 72.2/
15, 30, 45, 60, 90,
120, 135, 150
OFDM
1
4
Modulation
DSSS,FHSS
Q68. What is WLL? Draw the WLL setup diagram.
Ans. WLL is a system that connects subscribers to the local telephone station wirelessly.
It is based on:
– Cellular
– Satellite (specific and adjunct)
– Microcellular
Its Other names:
– Radio In The Loop (RITL)
– Fixed-Radio Access (FRA).
Prepared by: Pradeep Gulati
A general WLL Setup
Q69. State the modes possible when the slave is in connection state in Bluetooth.
Ans. (i) Active
(ii) Sniff
(iii) Hold
(iv) Park
Q70. What are elements available under link security of Bluetooth technology?
Ans. (i) Authentication
(ii) Key management
(iii) Encryption
Q71. What is a LMP? List three security services under LMP.
Ans. It is “link manager specification” that is responsible for radio link between the master and slave
in Bluetooth. This protocol also involves message exchanges in the form of LMP-PDU’s.
a) Authentication b) Change link key c) Encryption
Q72. What is Bluetooth? List few functions of Bluetooth.
Prepared by: Pradeep Gulati
Ans. It is a low power short range wireless standard and it can operate in situations where several
users are involved. At the maximum eight different devices can communicate in a network
using this standard.
(i) It can make call from a headset (wireless) to a mobile phone which is at a distant place.
(ii) It can trigger MP3 players on some other machines to download audio signals like music
in wireless environment.
(iv) It mainly eliminates cables in many user applications.
Q73. Differentiate piconet and scatternet in Bluetooth technology.
Ans.
(i) Piconet – It is a basic network supported by Bluetooth standard where one master and
seven slaves (total eight devices) can interact.
(ii) Scatternet – A device in one piconet either a master or slave can interact with other device
that is overlapping of one piconet on other piconet is possible and termed as a “Scatternet”.
Q74. What is an ‘IrDA’ standard?
Ans. ‘IrDA’ is a standard that is specified by Infrared Data Association formed in the year 1993. It
was developed mainly to enhanced point-to-point or point-to-multipoint communication. It is
dependant on line of sight (LOS) operation.
The infrared rays can be used wherever LOS is preferred and useful for this indoor consumer
applications.
Q75. What are the specifications of ‘IrDA’?
Ans. The IrDA standard 1.0 supports the data rate up to 115.2 kb/sec. for the range up to 1m and
next version ‘IrDA 1.1” developed later supports data transfers up to 35 times faster when
compared to “IrDA 1.0”.
Q76. What are the new specifications supported by current Bluetooth?
Ans. The short range Bluetooth technology is improved for meeting the distance of 100m in open air
and 30 m within building infrastructures for it’s operation. It works with data rate of 1 Kbps.
Q77. What re the two kinds of profiles in Bluetooth 1.1 version?
Ans. The two main profile classification is nine application profiles and four system profile and as a
whole thirteen profiles are supported by Bluetooth 1.1 version.
Q78. What are the system profiles used in Bluetooth 1.1 version?
Ans. The system profiles are generic object exchange, object push, file transfer and synchronization
profiles.
Prepared by: Pradeep Gulati