Lec 26: Probability of Error for PAM

Lec 26: Probability of Error for PAM

🎙 Prof. Ribhu 👥 226K 📅 July 31, 2026 ⏱ 36 min 👁 21 📄 lecture 🧭 2026-08-02
Available in: English (current) Français

Keywords

PAMsymbol error probabilityQ-functiondecision regionsAWGN

Summary

This lecture, part of the NPTEL course ‘Analog and Digital Communications II’, focuses on deriving the probability of error for Pulse Amplitude Modulation (PAM). The instructor begins by reviewing binary antipodal signaling and the maximum likelihood receiver, which selects the nearest symbol. He then extends the analysis to M-ary PAM, defining the constellation points and decision thresholds. The lecture distinguishes between boundary and interior points, deriving the error probability for each. Using the Q-function and the minimum distance between constellation points, he obtains a general formula for M-PAM symbol error probability. He also shows that for binary PAM, the formula reduces to the known result involving the energy per bit. The lecture concludes by previewing future topics: PSK, QAM, and the union bound. The presentation is mathematically rigorous, with clear explanations of the decision regions and the role of AWGN. The instructor emphasizes the symmetry of the Gaussian distribution and the use of the Q-function for tail probabilities. The content is suitable for students with a background in digital communications and probability.

172 words

Critical Evaluation

The lecture provides a thorough and rigorous derivation of the symbol error probability for M-ary PAM, a fundamental topic in digital communications. The instructor, Prof. Ribhu, demonstrates a deep understanding of the subject, systematically building from the binary case to the general M-ary case. The mathematical steps are clear and logical, with careful attention to the decision regions and the use of the Q-function. The distinction between boundary and interior points is well-explained, and the final formula is correctly derived. The lecture also correctly shows that the binary PAM result is a special case of the general formula, reinforcing the theoretical consistency. The presentation is well-structured, with a natural flow from review to new material. However, there are a few minor issues: the notation is sometimes inconsistent (e.g., using ’tn’ instead of ’d_min’), and the instructor occasionally makes verbal slips, but these do not detract from the overall clarity. The lecture does not cite external sources, but this is typical for a course lecture, and the content is standard textbook material. The derivation is accurate and aligns with established literature. The lecture is suitable for advanced undergraduate or graduate students, but it assumes prior knowledge of probability and basic communication theory. Overall, this is a high-quality educational resource that effectively explains a complex topic.

214 words

Title / Content Match

The title accurately reflects the content, which focuses on deriving the probability of error for Pulse Amplitude Modulation (PAM).

Quality & Reliability

8/10

The lecture is a formal academic presentation by a professor from IIT Guwahati, part of an NPTEL course. The derivation of symbol error probability for M-PAM is rigorous, following standard communication theory. The instructor clearly explains the decision regions, uses the Q-function, and relates results to binary PAM. The mathematical steps are logical and consistent with established literature. However, the lecture is a video with no citations or references to external sources, and the derivation is presented in a conversational style with some minor notational inconsistencies (e.g., using 'tn' instead of 'd_min'). Overall, the content is reliable and accurate for an educational context.

Key Moments

Cited Sources

Concurring Sources

  • Digital Communications by John G. Proakis — Standard textbook that covers the same derivation of symbol error probability for PAM.
  • Principles of Digital Communication by Robert G. Gallager — Another authoritative textbook with similar content.

Contribution & Novelties

The lecture provides a clear and systematic derivation of the symbol error probability for M-ary PAM, which is a fundamental result in digital communications. It builds on the binary case and generalizes to M-ary, highlighting the role of the minimum distance and the Q-function. The lecture also emphasizes the distinction between boundary and interior points, which is crucial for understanding the error probability. This derivation is standard but presented in an accessible manner for students.

Pour aller plus loin :

  • Q-function — The Q-function is used to express the tail probabilities of the Gaussian distribution, central to the error probability calculations.
  • Pulse-amplitude modulation — Wikipedia article on PAM, providing background and context.
  • Additive white Gaussian noise — The noise model assumed in the derivation, essential for understanding the error probability.

130 words

Radar Profile

The radar profile shows high scores across all dimensions, indicating a well-balanced and reliable lecture. The quantity and quality of information are strong, with a high technical level appropriate for the topic. The overall reliability is high, reflecting the academic rigor of the NPTEL course.

Reliability 8/10