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Differentiate between FDMA, TDMA, and CDMA.

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Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA) are three different multiple access techniques used in communication systems to allow multiple users to share the available bandwidth. Each technique employs a different strategy to allocate resources and enable simultaneous communication among multiple users. Let's delve into the technical details of each:

1. Frequency Division Multiple Access (FDMA):

Principle:
FDMA divides the frequency spectrum into multiple non-overlapping channels. Each channel is assigned to a specific user, and users communicate on their allocated frequency bands simultaneously without interfering with each other.

Key Concepts:

  • Frequency bands are allocated based on the number of users and their communication needs.
  • Each user is assigned a unique frequency band for the duration of their communication.

Advantages:

  • Simple implementation.
  • Well-suited for analog communication systems.

Disadvantages:

  • Inefficient use of bandwidth when users have varying data rate requirements.
  • Limited scalability.

2. Time Division Multiple Access (TDMA):

Principle:
TDMA divides the time duration of a communication channel into discrete time slots. Users take turns transmitting and receiving data during their assigned time slots, and the cycle repeats.

Key Concepts:

  • Users share the same frequency band but transmit in different time slots.
  • Time slots are carefully synchronized to avoid collisions.

Advantages:

  • Efficient use of bandwidth.
  • Suitable for systems with variable data rate requirements.

Disadvantages:

  • Synchronization challenges.
  • Limited scalability due to the fixed number of time slots.

3. Code Division Multiple Access (CDMA):

Principle:
CDMA allows multiple users to share the same frequency band simultaneously by assigning unique codes to each user. The signals are spread over a wide frequency band, and each user's data is distinguished by its unique code.

Key Concepts:

  • Users share the entire bandwidth at the same time.
  • Signals are encoded and decoded using specific codes to distinguish users.

Advantages:

  • High capacity and scalability.
  • Resistance to interference and noise.

Disadvantages:

  • Complex implementation.
  • Inherent near-far problem (users at different distances may experience different signal strengths).

Summary:

  • FDMA: Divides frequency spectrum into non-overlapping channels.
  • TDMA: Divides time into time slots for users to transmit sequentially.
  • CDMA: Users share the same frequency band simultaneously, distinguished by unique codes.