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).