CS547 Wireless Networking and Security Exam 1 Questio.docx

1. CS547 Wireless Networking and Security
Exam 1
Question 1:
Simplify the following expression (10 pts):
cos (2πft + π/2) + sin(2πft – π)
Question 2:
Support the fact that, in a transmission system using radio
frequencies, increasing the
transmission frequency by a factor of 3 incurs a penalty (loss)
of approximately 9.5 dB (10 pts).
Question 3:
How much bandwidth does a communication channel need to
achieve a capacity of 40 Mbps
with a Signal-to-Noise ratio of 255? (Note: 1 Mbps is 1,000,000
bps) (10 pts)
Question 4:
Given the following parameters:
N = number of hops between two end systems
L = message length in bits (e.g., length of the original message,
before being divided in
several packets)
B = data rate in bps, on all links
P = fixed packet size in bits
H = overhead (header) in bits per packet
D = propagation delay per hop in second

2. The number of packets (Np) required to send the original
message of length L (in bits) can be
computed as:
���� = �
��
�� − ��
�
The total end-to-end time delay for packet switching is
calculated using the formula:
T = Np * (P/B) + (N-1) * (P/B) + N * D
Let us assume that L/(P-H) is an integer. What value of P, as a
function of N, L, and H would
minimize the end-to-end time delay? (10 pts)
Question 5:
A Virtual Channel Identifier (VCI), in the header of an ATM
cell, is used for routing to and from the end
user. Explain why a VCI is needed together with the Virtual
Path Identifier (VPI). (10 pts)
Question 6:
Is there a need for a network layer in a broadcast network?
Justify your answer. (10 pts)

3. Question 7:
Describe the significance of the following IPv4 header fields
(10 pts):
(a) Time to live (b) Protocol
Question 8:
The transmit power of a station is 57.67 dBm (10 pts).
(a) How much power in KW is this equivalent to?
(b) Using an antenna with 1 GHz carrier frequency, what will be
the received power in dB at
a free space distance of 0.5 km?
Question 9:
Research Problem: Describe in detail the various diversity
techniques in wireless
communication systems (10 pts).
Question 10:
Research Problem: What is carrier-to-noise ratio (CNR)?
Describe why, in general, raising radio
frequency (RF) levels improves the carrier-to-noise ratio (10
pts).