Code Division Multiple Access (CDMA) is a digital cellular technology and method of multiple access where several transmitters can send information simultaneously over a single communication channel. This is achieved using spread-spectrum technology where each phone conversation is encoded using a unique sequence of numbers.

Here’s an overview of CDMA:

How CDMA Works:

  1. Unique Code Assignment: Every voice call or data transmission is assigned a unique code.
  2. Signal Spreading: The unique code is used to spread the user’s voice data over a wide frequency spectrum.
  3. Simultaneous Transmission: Multiple users can transmit over the same frequency spectrum without mutual interference since each has a unique code.
  4. Decoding at the Receiver: At the receiving end, the spread spectrum signal is decoded using the same unique code to extract the original data.

Key Features:

  1. Soft Handoff: Unlike hard handoffs in other technologies, CDMA uses a method called “soft handoff” that allows a mobile device to maintain communication with multiple cell towers simultaneously. This results in smoother transitions between cells.
  2. Frequency Reuse: CDMA allows for frequency reuse, meaning that the same frequencies can be used for different conversations as long as they’re encoded with different codes.

Advantages:

  1. Spectral Efficiency: Allows many users to share the same frequency band simultaneously.
  2. Resistance to Multipath Interference: Due to its spread-spectrum nature, CDMA is resistant to multipath interference.
  3. Privacy: Each conversation is encoded with a unique code, making it difficult to intercept or eavesdrop.

Disadvantages:

  1. Near-Far Problem: If a CDMA user near a cell tower transmits with the same power as a user far away from a cell tower, the closer user’s signal might interfere with the signal of the user further away. This is addressed with power control techniques.
  2. Complexity: The encoding and decoding process requires sophisticated electronics, which might increase the cost of CDMA devices.

Applications:

  1. 2G, 3G Cellular Systems: CDMA was the foundation for several mobile standards, notably the 3G standard CDMA2000.
  2. Wireless Broadband: Evolutions of CDMA technology, like W-CDMA and EV-DO, provide broadband speeds for mobile internet.

Variants:

  1. W-CDMA (Wideband CDMA): Used in 3G UMTS networks.
  2. CDMA2000: An evolution of original CDMA and a competitor to W-CDMA.

In conclusion, CDMA is a cellular technology that uses unique codes to allow multiple users to share the same frequencies without interfering with each other. It has been a foundational technology for many wireless communication standards, especially in 2G and 3G networks.