Wireless Communication Lecture Series: Introduction to Multiple Access Techniques

Overview

• The lecture introduces multiple access techniques in wireless communication.
• Example used: Sharing of a measurement scale by multiple persons.

Problem Statement

• Scenario: Two persons can easily share a two-scale measurement, but complications arise when additional persons want access.
• Wireless Analogy: In cellular systems, a base station has limited frequency bands to serve multiple mobile stations.

Need for Multiple Access Techniques

• To effectively share limited resources among multiple users.
• Duplexing: Necessary for simultaneous transmission and reception of information.

Types of Multiple Access Techniques

1. Frequency Domain Access

   • Frequency Division Duplexing (FDD):
     • Requires two simplex channels:
       • Forward Link: Signal from base station to mobile station (downlink).
       • Reverse Link: Signal from mobile station to base station (uplink).
     • Uses separate frequencies (F1 for uplink, F2 for downlink).
     • Requires a duplexer to allow simultaneous bidirectional transmission.
     • Frequency separation must be managed to avoid interference.

2. Time Domain Access

   • Time Division Duplexing (TDD):
     • Uses the same frequency for both uplink and downlink.
     • Allocates time slots for each user to transmit and receive.
     • Does not require a duplexer because it operates on a single frequency.
     • Synchronization between transmitter and receiver is crucial to avoid overlapping time slots.

Summary of FDD and TDD

• FDD:
  • Requires duplexer, supports full duplex communication, suitable for long-distance transmission.
  • Needs careful frequency separation to prevent interference.
• TDD:
  • No duplexer needed, not full duplex (uses time slots), potential for signal delay with long distances.

Future Topics

• Next lecture will cover three multiple access methods:
  • Frequency Division Multiple Access (FDMA)
  • Time Division Multiple Access (TDMA)
  • Code Division Multiple Access (CDMA)

Conclusion

• Thank you for watching the video.