936 Words Sep 12th, 2012 4 Pages
Q1 Ten users empoly ALOHA to transmit 1000 bit packets of data. The data rate is 100 Mb/s. The data to be transmitted a distance d=10,000 Km. Assume NAK messages contain 100 bits and that is the event of a collision the average waiting time pair to retransmission is 50 µs.
a) Calculate delay as a function of ρ.
b) Plot D vs ρ.

Q2 500 users employ TDMA to transmit 1000 bit packets of data. The channel bandwidth is 100 MHz and QPSK is employed.
a) What is the max is the maximum allowable bit rate in the channel?
b) What is the packet rate?
c) What is the frame time – the time taken to transmit the packet from each user?

Q3
a) Plot the throughput for CSMA as given by eq 16.4.35 as a function of TD/ TP for ρ = 0.25.
b) At what
Calculate the normalized total traffic on the channel.

Q8 A group of slotted ALOHA station generate a total of 120 requests/sec, including both transmissions and retransmissions. Each request is for 12.5 ms duration slot.
a) What is the normalized total traffic of the channel?
b) What is the probability of a successful transmission at the first attempt?
c) What is the probability of exactly two collisions before a successful transmission?

Q9 What is the maximum data rate at which a user can send data in a CSMA/CD network? Given the channel is a coaxial cable with velocity of transmission 200 m/sec. The length of the cable is 5km and packet size is 10 µs.

Q10 Normalized throughput ρ is a measure of channel utilization. It can be found by forming the ratio of successful transmitted message traffic is in bits per sec to the total message traffic including rejected messages in bits/sec. Calculate the normalized throughput of a channel that has a maximum data rate of fb=50 kbits/sec and operates with k=5 ground stations, each station transmits at average rate λ=2 packets/sec. The system format provides b=1350 bits/packet. Which of two ALOHA slotted ALOHA is suitable for this system?

Q11 The bit rate of a CDMA cellular system is 9.6 Kb/s and the chipping rate is 1.788 Mb/s . How many simultaneous users can be accommodated with in the cell with BER=10-2 threshold performance is accepted for voice quality mobile

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