What is the difference between GSM and CDMA?

GSM (Global System for Mobile Communications) and CDMA (Code Division Multiple Access) are two different technologies used in mobile communication networks. They represent different approaches to how voice and data are transmitted over the airwaves. Here's a technical comparison of GSM and CDMA:

  1. Multiple Access Method:
    • GSM: Uses Time Division Multiple Access (TDMA). In GSM, the frequency band is divided into time slots, and each conversation is assigned a specific time slot in a repeating pattern.
    • CDMA: Uses Code Division Multiple Access. In CDMA, all users share the same frequency band simultaneously. Each conversation is assigned a unique code, and the signals are transmitted together but can be separated at the receiving end using their respective codes.
  2. Frequency Band:
    • GSM: Operates in the 900 MHz and 1800 MHz frequency bands in most parts of the world. In North America, it also uses the 1900 MHz band.
    • CDMA: Operates in the 800 MHz and 1900 MHz frequency bands.
  3. SIM Cards:
    • GSM: Uses SIM (Subscriber Identity Module) cards to identify and authenticate subscribers. The SIM card contains user information, contacts, and subscriber-related data.
    • CDMA: Does not use SIM cards traditionally. Subscriber information is usually stored on the device or in the carrier's database.
  4. Roaming:
    • GSM: Generally has better international roaming capabilities. Due to the widespread use of GSM globally, it's easier for users to travel between countries and use their GSM phones.
    • CDMA: Roaming capabilities are more limited, especially internationally.
  5. Handset Compatibility:
    • GSM: More widely adopted worldwide. GSM handsets are generally more interchangeable between carriers and countries.
    • CDMA: Limited interoperability between carriers and regions. CDMA handsets are often carrier-specific.
  6. Voice and Data Transmission:
    • GSM: Separates voice and data channels, allowing for simultaneous voice and data usage (though 2G GSM is primarily for voice).
    • CDMA: Uses a spread spectrum technique, allowing for both voice and data to be transmitted simultaneously on the same frequency band.
  7. Call Quality and Capacity:
    • GSM: Known for its clear voice quality and efficient use of network resources. However, the number of simultaneous connections in a cell is limited by the number of available time slots.
    • CDMA: Known for better call quality and increased capacity due to the use of spread spectrum technology.
  8. Network Architecture:
    • GSM: Uses a network architecture based on a combination of circuit-switched and packet-switched networks (e.g., GSM for voice and GPRS/EDGE for data).
    • CDMA: Can support both circuit-switched and packet-switched data services.