CS547 Wireless Networking and Security
Simplify the following expression (10 pts):
cos (2πft + π/2) + sin(2πft – π)
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).
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)
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
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
𝑁𝑁𝑝𝑝 = �
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)
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)
Is there a need for a network layer in a broadcast network? Justify your answer. (10 pts)
Describe the significance of the following IPv4 header fields (10 pts):
(a) Time to live (b) Protocol
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?
Research Problem: Describe in detail the various diversity techniques in wireless
communication systems (10 pts).
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).
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