Understanding Modulation Techniques in Mobile Communications-2 — Lesson 6

This lesson covers the fundamentals of modulation techniques used in mobile communications. It begins with a recap of linear digital modulation techniques and then delves into M-ary Quadrature Amplitude Modulation (QAM). The lesson further explores Pseudo Noise (PN) sequences and spread spectrum techniques, including Direct Sequence Spread Spectrum (DS-SS) and Frequency Hopped Spread Spectrum (FH-SS). It also evaluates the performance of these spread spectrum systems and discusses their advantages and disadvantages. For instance, the lesson explains how spread spectrum techniques are resistant to jamming and provide immunity to distortion due to multipath propagation.

Video Highlights

01:12 - Introduction to the lecture on modulation techniques for mobile communications
02:12 - Discussion on the advantages and disadvantages of spread spectrum systems
03:53 - Introduction to pseudo noise sequences and their role in spread spectrum techniques
15:37 - Overview of the block diagram of the transmitter for the case of direct sequence spread spectrum
17:34 - Explanation of the receiver for the frequency hopped spread spectrum technique
33:15 - Discussion on the performance of direct sequence spread spectrum technique
39:47 - Analysis of the performance of frequency hopping spread spectrum technique
43:00 - Discussion on the advantages and disadvantages of spread spectrum techniques

Key Takeaways

- M-ary Quadrature Amplitude Modulation (QAM) is a hybrid modulation technique that uses both amplitude and phase variations to encode data.
- Pseudo Noise (PN) sequences are binary sequences with an autocorrelation that resembles a random binary sequence.
- Direct Sequence Spread Spectrum (DS-SS) and Frequency Hopped Spread Spectrum (FH-SS) are two basic types of spread spectrum modulation techniques.
- Spread spectrum techniques are inherently difficult to intercept, resistant to jamming, and provide immunity to distortion due to multipath propagation.
- The 'near-far' problem is a significant challenge in direct sequence spread spectrum, where a user closer to the base station may dominate the received signal energy.