This document contains the answer key for a continuous assessment test on mobile communication and IoT for Kongu Engineering College. It includes 14 multiple choice and descriptive questions covering topics like radio frequency ranges, signal representation tools, antenna types, cellular network technologies and standards, Bluetooth networking, and the IEEE 802.11 protocol architecture.

1. KONGU ENGINEERING COLLEGE, PERUNDURAI 638 060
CONTINUOUS ASSESSMENT TEST 1
18CST63 - Mobile Communication and IoT
Answer Key
1. Identify the radio frequency range used by RADAR systems.
30 – 300 GHz (2mark)
2. List the representation of signals and its tools (2 mark)
 Time domain - Oscilloscope
 Frequency domain – Spectrum Analyzer
 Phase domain - Oscilloscope
3. Write the type of antenna used by the following devices (4*0.5 = 2 mark)
a. Laptop – Omnidirectional antenna
b. Smart phone – Smart antenna
c. Satellite – Multi element antennal array
d. Direct to Home – Directional antenna
4. Give the maximum data rate of GSM and GPRS systems (2*1 = 2 mark)
 GSM – 9.6 Kpbs
 GPRS – 150 to 170 Kpbs
5. 5
.
Differentiate IMEI and IMSI in GSM network (2*1 = 2 mark)
 International Mobile Equipment Identity (IMEI) – unique code to identify GSM
device
 International Mobile Subscriber Identity (IMSI) – unique code to identify mobile
subscriber in the network globally.
6. What is use of white list, gray list and black list in Equipment Identity Register? ( 2 mark)
 list of valid IMEIs (white list)
 list of malfunctioning devices (gray list)
 list of illegal devices (black list)
 To prevent the theft of mobile device
7. Apply the suitable link that must be established for the given usecases (2*1 = 2 mark)
a. Communication between Earth Observation Satellite (EOS)-3 and EOS-4 – Inter
Satellite Link (ISL)
b. Communication between EOS-3 to Base station of ISRO – Gateway Link (GWL)
8. Give the operating frequency of Bluetooth and define piconet. (2*1 = 2 mark)
 Frequency - 2.4 GHz ISM band
 A piconet is a collection of Bluetooth devices which are synchronized to the same
hopping sequence
9. Identify the cellular generation of the following technologies (4*0.5 = 2 mark)
a. EDGE – 3G
b. GPRS – 2.5 G

2. 2
c. GSM – 2G
d. LTE – 4G
10. Define Internet of Things. (2 mark)
A dynamic global network infrastructure with self-configuring capabilities based on
standard and interoperable communication protocols where physical and virtual things have
identities, physical attributes and virtual personalities and use intelligent interfaces, and
are seamlessly integrated into the information network, often communicate data associated
with users and their environments
11. Assume there is a theft of the mobile phone and the user requests the service
provider to trace the location of the device. Provide a suitable architecture with the
essential subsystems of the GSM network to satisfy the user request. Also sketch the
flow of the signalling information in the proposed architecture.
GSM Subsystems
1. Radio Subsystem (RSS)
2. Network and Switching Subsystem (NSS)
3. Operation Subsystem (OSS)
5 mark
2 mark

3. 3
OSS Entities
 Operation and Maintenance Center (OMC)
 Authentication Center (AuC)
 Equipment Identity Register (EIR)
Authentication Center (AuC)
o To protect user identity and data transmission
o Contains algorithm for authentication
o Keys for encryption and generate values for user authentication in HLR
o AuC present in special protected part of HLR
Equipment Identity Register (EIR)
o EIR – database of all IMEIs
o with valid SIM, anyone could use the stolen MS
o The EIR has a blacklist of stolen (or locked) devices
o In theory an MS is useless as soon as the owner has reported a theft.
Unfortunately, the blacklists of different providers are not usually
synchronized and the illegal use of a device in another operator’s network is
possible
o The EIR also contains a list of valid IMEIs (white list), and a list of
malfunctioning devices (gray list).
2 mark
1 mark
12. Sketch IEEE 802.11 protocol architecture and explain physical and MAC layers
1. Infrastructure based network
2. Adhoc based network
Infrastructure based network
 Communication takes place only between the wireless node and the access point,
but not directly between the wireless nodes
 Access point – control medium access, bridge to other wireless or wired networks
 Several wireless networks – form one logical wireless network- access point
together with fixed network in between can connect several wireless networks –
form larger network – more radio coverage
Adhoc network
2 mark
3 mark

4. 4
 Do not need infrastructure
 Each node can communicate directly with other nodes
 No access point – no medium access control
 Nodes within ad-hoc network – communicate only – if they can reach each
other physically – within each other’s radio coverage
IEEE 802.11 – covers the physical layer PHY and medium access layer MAC
PHY – divided into
• Physical Layer Convergence Protocol (PLCP)
• Physical Medium Dependent (PMD)
 MAC – medium access, fragmentation of user data, encryption
 PLCP – provides carrier sense signal – Clear Channel Assessment (CCA) –
provides PHY Service Access Point (SAP)
 PMD – modulation and encoding / decoding of signals
MAC Management
 association and re-association of a station to access point
 roaming between different access points
 controls authentication, encryption, synchronization
 Power management
3 mark
2 mark
13. Consider DFWMAC – DCF with RTS / CTS extension with DIFS time of 10 ms and
SIFS time of 2 ms. In order to reduce error rate, fragmentation mode is applied.
 Assume three stations A, B and C are in the scenario, in which B can reach
both A and C, whereas A and C are not reachable to each other.
 The transmission medium allows packet size of 1500 Bytes
 The data to be transmitted is 2500 Bytes
 Each Byte will take transmission time of 0.01 ms
 RTS, CTS and ACK packet will take 3 ms in timeline
 Station A sends data to B
Calculate the time period (ms) for the given scenarios
a. How long will the data transmission take place? – 57 ms
b. What is the duration of NAV (frag1)? – 22 ms
c. Give the total number of SIFS packet used in the entire transmission - 5
d. At what time the first fragment reaches the receiver? – 35 ms
When does the station A receives the acknowledgement for frag2? – 57 ms
5 * 1 = 5
mark

5. 5
e.
5 mark
14. Explain the networking of the Bluetooth devices and associated state transitions
Bluetooth operates in the 2.4 GHz ISM band
• Bluetooth operates on 79 channels in the 2.4 GHz band with 1 MHz
carrier spacing
• Each device performs frequency hopping with 1,600 hops/s in a pseudo
random fashion
• Bluetooth applies FHSS for interference mitigation
• A piconet is a collection of Bluetooth devices which are synchronized to
the same hopping sequence
• One device in the piconet can act as master (M), all other devices
connected to the master must act as slaves (S)
• The master determines the hopping pattern in the piconet and the slaves
have to synchronize to this pattern
• Each piconet has a unique hopping pattern. If a device wants to
participate it has to synchronize to this
2 mark

6. 6
Two additional types of device
 Parked devices (P)
 Stand-by (SB)
• Parked devices - can not actively participate in the piconet (i.e., they do
not have a connection), but are known and can be reactivated within
some milliseconds
• Stand-by devices - do not participate in the piconet
• Each piconet has exactly one master and up to seven simultaneous slaves
• More than 200 devices can be parked. The reason for the upper limit of
eight active devices, is the 3-bit address used in Bluetooth
• If a parked device wants to communicate and there are already seven
active slaves, one slave has to switch to park mode to allow the parked
device to switch to active mode
Formation of Piconet
• All active devices have to use the same hopping sequence they must be
synchronized
• Master sends its clock and device ID
• All Bluetooth devices have the same networking capabilities, i.e., they
can be master or slave - there is no distinction between terminals and
base stations, any two or more devices can form a piconet
• The unit establishing the piconet automatically becomes the master, all
other devices will be slaves
• The hopping pattern is determined by the device ID, a 48-bit worldwide
unique identifier
• The phase in the hopping pattern is determined by the master’s clock
• After adjusting the internal clock according to the master a device may
participate in the piconet
• All active devices are assigned a 3-bit active member address (AMA)
• All parked devices use an 8-bit parked member address (PMA)
• Devices in stand-by do not need an address
States of Bluetooth devices
3 mark
2 mark
3 mark