EC2043 – Wireless Networks

Dhanalakshmi College of Engineering EC2043 – Wireless Networks


VIII - Semester
Two Marks Questions and Answers
UNIT – I
PART –A
1. Find out the capacity of a single IS-95 cell that uses QPSK modulation and convolutional
coding 3 db < Sr < 9 db, and bandwidth of the channel is 1.25 MHz
(Nov/Dec2012) ,(May /June 2013)

Solution: No. Of Users M =

M

W is the bandwidth of the channel
R is the Transmission rate
Given Data:
W=
For QPSK Modulation R = 9600bps

M= = 16 Users to M = = 65 Users


2. Determine the transfer time of a 20 kB file with a mobile data network with the transmission
rate of 10 Kbps. (MAY/June 2012)
Solution: For a data rate of around 10 kbps, it would take 20(KB) × 8(B/b) / 10 kbps = 16
seconds to transfer for such a file.

3. Determine the capacity of GSM for k = 3. ( Nov/ Dec2012)
Solution: For GSM system Carrier bandwidth Wc = 200 kHz
Number of users per carrier Nu = 8
Frequency reuse factor K=3
Bandwidth W =1.25MHz
Capacity M=

M=
M = 16.7 users per cell.

Prepared by A.Devasena Asso.Prof., S.Esther GandhiMathi Asso.Prof., Page 1

,Dhanalakshmi College of Engineering EC2043 – Wireless Networks


4. Compute the maximum throughput of a pure ALOHA networking with a large number of
users and transmission rate of 1 Mbps? ( May /June 2013)

For a large number of mobile terminals each using a transmission rate of 1 Mbps to access a
BS using ALOHA protocol, the maximum rate that successfully passes through to the BS is 180
kbps.


5. Differentiate Wired Network from Wireless Network ( Nov/Dec 2009)
Sl.No Wired Networks Wireless Networks
1. Provides Reliable Transmission Provides Unreliable Transmission
2. Guided links provides transmission from Air interface provides transmission from
one fixed terminal to another terminal. one terminal to another.
3. It offers higher bandwidth It offers medium and lower bandwidth
4. It does not support mobility It supports mobility

6. What is meant by Handoff?
Handoff basically involves change of radio resources from one cell to other adjacent cells
without interrupting the call or alerting the user when the mobile unit moves from one cell to
another

7. What is meant by hard handoff?
Hard handoff, also known as “Break before make”,is characterized by releasing current
radio resources from the prior base station before acquiring the resources from the next base
station.

8. What is meant by soft handoff?
Soft handoff, also known as “Make before Break ” is a process that the Mobile Station
communicates simultaneously with the prior base station as well as the new base station for short
duration of time before deciding to communicate its traffic through one of them.

9. List the parameters that influence the handoff.
The parameters that influence the handoff are
(i) The radio link.
(ii) Network management.
(iii) Service issues.




Prepared by A.Devasena Asso.Prof., S.Esther GandhiMathi Asso.Prof., Page 2

, Dhanalakshmi College of Engineering EC2043 – Wireless Networks


10. What are the two types of protocols used to handle multiple access issues?
The two types of protocol that are used to handle multiple access issues are
(i) Contention based protocols
(ii) Conflict free (collision free) protocols.

11. How contention based protocols are classified?
The contention based protocols can be classified into two groups according to the ways
collisions are resolved. They are
(i) Random access protocols
(ii) Collision resolution protocols

12. List the types of Random Access protocols and Collision Resolution protocols.
The types of random access protocols are
(i) ALOHA type protocol
(ii) Carrier Sense Multiple Access (CSMA) type protocol
(iii) Busy tone multiple Access (BTMA) type protocol.
(iv) Idle Signal Multiple Access (ISMA) type protocol
The types of Collision resolution access protocols are
(i) TREE type protocol
(ii) Window type protocol.
13. What are the different types of conflict free protocols?
The different types of conflict free protocols are
(i) Frequency Division Multiple Access (FDMA)
(ii)Time Division Multiple Access (TDMA)
(iii)Code Division Multiple Access (CDMA)

14. List the classifications of the services of wireless security system.
The classifications of the services of wireless security system are
(i) Confidentiality
(ii) Nonrepudiation
(iii) Authentication
(iv) Availability.

15. List the services wireless system security
The services of wireless system security are
(i) Confidentiality
(ii)Nonrepudiation

Prepared by A.Devasena Asso.Prof., S.Esther GandhiMathi Asso.Prof., Page 3