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
• C6748 DSP Experimenter's Kit

Reading Assignment

• Real-Time Digital Signal Processing from MATLAB to C with the TMS320C6x DSPs (Jan. 2012) by Thad B. Welch, Cameron H. G. Wright and Michael G. Morrow
  • Chapter 16
  • Chapter 17
• Software Receiver Design by C. Richard Johnson, Jr., William A. Sethares and Andrew Klein
  • Sections 2.6-2.16
  • Sections 9.1-9.4
  • Sections 10.1-10.4
  • Sections 11.1-11.6
• Course reader
  • Lecture 7: Interpolation and Pulse Shaping
  • Lecture 12: Channel Impairments
  • Lecture 13: Digital Pulse Amplitude Modulation
  • Lecture 14: Matched Filtering

Downloads

Recitation slides part 1 and part 2 by Mr. Chao Jia and Ms. Debarati Kundu, The University of Texas at Austin

Instructions part 1 and part 2 by Mr. Chao Jia and Ms. Debarati Kundu, The University of Texas at Austin

LabVIEW transmitter demonstration by Dr. Zukang Shen to show how labs 1-6 fit together

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)

Lab Report

• 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: (only for labs prior to 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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