Homework/Project Assignment 1

H1: Answer the following questions (keep your answers brief):

What is ISI and when does it occur (you can describe it with an example if you prefer)?
What do the terms uplink and downlink mean?
What does wavelength mean (you can describe it mathematically, but explain each term) and name two differences of long waves and short waves.

H2: Assume all stations can hear all other stations. One station wants to transmit and senses the carrier idle. Why can a collision still occur after the start of the transmission?

H3: Name three advantages of CDMA.

H4: A cellular system has 30MHz allocated for uplink communication and 30MHz allocated for downlink communication. The bandwidth of a simplex-channel is 150kHz. The system uses FDMA/TDMA/FDD multiple access and duplexing method and uses 4 time-slots per frame. There are 75kHz guard bands at the beginning and end of each of the 30MHz bands. Assume the hexagon model for cells and a frequency reuse factor of 3. What is the maximum number of users that can talk simultaneously in the example network?

H5: A bit stream 0011001011101001 will be transmitted using MSK modulation (assume the first bit is numbered as 1, i.e., it is an odd bit). Assume MSK uses two different carrier signals: s1(t) = sin (2 π f1 t) and s2(t) = sin (2 π f2 t + π), where f2=2*f1. Draw the signal pattern that we will see on the air while transmitting the 16 bits shown above using MSK modulation. Assume the following transmission rules:

if even-bit = 0 and odd-bit = 0 then use -f2
if even-bit = 1 and odd-bit = 0 then use -f1
if even-bit = 0 and odd-bit = 1 then use f1
if even-bit = 1 and odd-bit = 1 then use f2

Show your steps in reaching your answer.

P1: In the DARTS Lab, you will find a number of Crossbow Stargate devices, the ones on the bottom four shelves in the lab are available for this project. Each team will need at least two of these devices. Use either a third wireless device (e.g., your laptop) or one of the desktops in the lab (using the serial connection) to program these devices. If you use a third wireless device, you must set the device's ESSID to "impresario" (the ESSID used by the Stargates). Write a simple client-server program that allows the client (executed on your first Stargate) to request data (any data) from the server (executed on the second Stargate) using the ad-hoc communication between these two devices. The same program should serve as client and server and implement both UDP and TCP protocols (i.e., the function and protocol used are determined by the command line parameters). The client program should accept the server's port number and IP address as input parameters. Put your final code and a README document (describing your solution, how to use your program, problems encountered, unresolved issues, etc.) into the AFS dropbox. You will also have to meet briefly with the TA to demonstrate your code (details announced later).

P2: Go into the directory /etc/pcmcia on the Stargate and explore the files network.opts and wireless.opts. These are files that are essential to setting up the wireless connection. List and explain the entries for IPADDR, NETWORK, BROADCAST, GATEWAY, ESSID, MODE, and CHANNEL.

P3: How would you modify wireless.opts to switch the device into "managed mode" for ND's nomad network?

Submission

Note: tutorials about certain components of this and future projects can be found at: http://snoopy.cse.nd.edu/dokuwiki/doku.php?id=tutorials. The due date for the homework components is 9/16 (in class) and the due date for the project components is 9/18 (before class). Late submissions will not be accepted!