The University of Tennessee, Knoxville

Department of Electrical and Computer Engineering

ECE 553: Computer Networks Spring 2007

Project #3: Media Access Control in a Wireless Network

Overview

The goal of this project assignment is to obtain insight into the performance attributes of media access control (MAC) protocols in wireless networks. The assignment emphasizes the role of link layer services in computer networks. Each student is required to submit one printed project report. The deadline for submitting the project report is March 22, 2007 - there will be no extensions to this deadline.

Network Topology

Assume the following wireless network topology:

There are 16 wireless users (nodes) in the network. Each node can communicates with the rest of the nodes over the shared wireless media. Time is slotted into fixed intervals. All transmissions are synchronized to a global (time slotted) clock. Assume that each node has a frame to transmit at any given time slot, whereby a frame duration is precisely one time slot.

Simulation Environment

You are required to write Matlab code that simulates the behavior of the wireless network described above. Each simulation run should consist of a sufficient number of iterations so as to obtain steady-state results; you will need to observe the simulation data and determine the sufficient time required for obtaining credible (steady-state) results. The Matlab codes should address to the following two MAC protocols:

1.  Slotted ALOHA

Each user attempts to transmit in accordance with the slotted ALOHA MAC protocol (see lecture notes).

  1. Execute the simulation for different values of 0<p<1 and plot the throughput results. Determine which p value yields the highest throughput (throughput is measured as the percentage of time during which successful transmissions occur). Discuss your results.
  2. For each value of p, what is the average waiting time experienced by a frame waiting for transmission? (Note: the waiting time is measured from the first transmission attempt until the successful attempt). Plot a histogram of the waiting times for several values of p and discuss your results.

2. Modified Slotted CSMA

Next assume the following simplistic CSMA scheme: Transmission attempts initially occur with probability 0.7. Linear backoff is employed by the transmitters in cases of collision such that if collision is detected each transmitter selects a random value, kÎ{0,1,….,m} (where m is the number of consecutive unsuccessful transmission attempts), and waits k time slots before reattempting to transmit. Let the maximal value from which k is randomly drawn be 64.

  1. Establish the throughput of the scheme.
  2. Determine the percentage of time that the channel is idle (no transmissions occur).
  3. What is the average waiting time experienced by a frame waiting for transmission?

Note: propagation delay between the users is assumed to be negligible.

Grading Policy

The project report comprises 100% of the grade for this project, so effort should be made to prepare a clear and coherent submission. The following is a suggested outline for the report along with its grading policy:

·  (5) Cover page and Abstract

·  (10) Introduction and Background

·  (50) Design (suggested outline)

o  Design objectives

o  Design challenges

o  Technical approach (preferably including a flow chart)

§  A description of the system designed including Matlab implementation considerations.

§  Detailed explanation of the Matlab source code/s written for the project.

o  Explanation of simulation results as indicated above. Try to provide intuitive justification for the results obtained.

·  (5) Summary

o  What have you learned from this project? What have you achieved?

·  (30) Appendix A: Matlab Source code listings (this item is judged based on the combination of your design and implementation).

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