Digital Data Transmission by Baseband Pulse Amplitude Modulation(PAM)

Aim of the Experiment

In this experiment, you will learn the basics concepts of digital communications like pulse shaping filters, Nyquist criterion, eye diagram, inter-symbol interference and clock recovery. You will learn digital data transmission using baseband pulse amplitude modulation.

Before you start with the experiment, it is necessary that you have an understanding (at some level) of the following concepts:

• Baseband PAM
• Nyquist criterion
• Inter-symbol Interference (ISI)
• Pulse shaping (raised cosine baseband filtering)
• Eye diagrams
• Interpolation filter bank
• Symbol clock recovery

Equipment to be checked out

• Two BNC - BNC Jack cables
• Two BNC - stereo pin (DSP) cables

Downloads

Recitation Slides for Lab 5 by Mr. Akshaya Srivatsa: Part 1

Lab #5 Handout explaining milestones for the lab. Updated Oct. 23, 2011.

TI C6748DSP files for lab #5 as a single zip file (7-zip free zip program). Updated Oct. 23, 2011.

Overview Slides by Prof. Steven Tretter, University of Maryland (from Jan. 2008 lab manual)

PAM class notes by Dr. Guanghan Xu

Pulse shaping impulse response and filter bank coefficients:

• Raised cosine: rascosx64.exe (64-bit x86 program) - rascos.exe (32-bit x86 program) - rascos_1.m and h_impulse.m (Matlab files)
• Square root raised cosine: sqracosx64.exe (64-bit x86 program) - sqracos.exe (32-bit x86 program)

OLD: LabVIEW Virtual Instrument for test and measurement of results on the C6713 DSK

Lab Report

• Do everything in Section 11.6 using Matlab [including 11.6.4]. Discuss how the roll-off factor "alpha" affects the eye diagrams, theoretical error plots, etc.
  (Hint: there is a function named "eyediagram". Your entire Matlab program will likely be only a few (~5) lines.)
  • Consider using the "PAM" function from the Johnson and Sethares book.
  • Don't worry about gray-coding and you may use the built-in random number generator
  • Consider using the "rcosflt" and "eyediagram" functions in Matlab.
• For above, please put all error probabily plots in the same graph. (This will allow you to accurately compare them).
• How could pulse shaping be implemented using only a single "filter" (not a bank of filters). Practically, why would this be undesirable?
• In the clock recovery system, discuss the need for a Prefiltering. For a symbol rate of 2 kHz, what would be the output if the prefilter attenuated all frequencies greater than 900 Hz? Would it be possible to recover the transmitter's symbol frequency (using the same squaring operation and post-filters as in the lab)? If not, give a short reason why.

Oscilloscope Notes

• For best viewing of the eye-diagram, Press /DISPLAY->VECTORS->OFF
  
• Trigger settings can be set by pressing "SOURCE" [Right-hand-side]

Coding Guidelines

• The rascos.exe and sqrascos.exe programs provide the filter coefficients as a 2D array [directly usable for the interpolation filter bank]. This is intended to help you. Recommend main program loop over this array to do the convolutions. The QAM lab will involve a similar filter with 16 sub-filters.
• You wrote functions for the previous labs [FIR/IIR filtering, scrambler, etc.].

LabVIEW Implementation: (not for fall 2011)

A lab5.vi contains a skeleton for the LabVIEW implementation. You will need to set the "Sample Rate" constant and connect the "Format Eye Diagram" and "Display Eye Diagram" VIs. The part that converts an array to a waveform has already been provided.

Assignment

Submitting this assignment is optional, but doing it would be useful with your QUIZ preparations

Assignment

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