Budget and Commercial law

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

The number of packets (Np) required to send the original message of length L (in bits) can be
computed as:

𝑁𝑁𝑝𝑝 = �
𝐿𝐿

𝑃𝑃 − 𝐻𝐻
�

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)

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).