Advanced Modems
To transmit symbols, such as letters of the alphabet, RU computer modems use two frequencies (1600 and 1800 Hz) and several amplitude levels. A transmission is sent for a period of time T (known as the transmission or baud interval) and equals the sum of two amplitude-weighted carriers.
We send successive symbols by choosing an appropriate frequency and amplitude combination, and sending them one after another.
a) What is the smallest transmission interval that makes sense to use with the frequencies given above? In other words, what should T be so that an integer number of cycles of the carrier occurs?
b) Sketch (using Matlab) the signal that modem produces over several transmission intervals. Make sure you axes are labeled.
c) Using your signal transmission interval, how many amplitude levels are needed to transmit ASCII characters at a data rate of 3,200 bits/s? Assume use of the extended (8-bit) ASCII code.