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US-TDMA IS-136, one of the 2nd generation systems mainly in USA

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US-TDMA (United States - Time Division Multiple Access) is a 2nd generation cellular communication system that was predominantly used in the United States during the late 1990s and early 2000s. It was based on the IS-136 standard, which was developed by the Telecommunications Industry Association (TIA) to provide digital voice and data services using Time Division Multiple Access (TDMA) technology.

Background:

The US-TDMA system, based on the IS-136 standard, was introduced as an evolution from the earlier analog cellular systems (AMPS) and was deployed as a digital alternative to improve spectrum efficiency and offer better voice quality. US-TDMA competed with another 2nd generation system, CDMA (Code Division Multiple Access), in the United States during the early stages of digital cellular deployment.

Key Features of US-TDMA (IS-136):

  1. Time Division Multiple Access (TDMA): US-TDMA is a TDMA-based system, where each 30 kHz carrier frequency is divided into multiple time slots, with each time slot assigned to different users. TDMA enables multiple users to share the same frequency channel by transmitting in their designated time slots, thereby increasing spectrum efficiency.
  2. Digital Voice Compression: US-TDMA uses digital voice compression algorithms, such as Enhanced Variable Rate Codec (EVRC), to convert analog voice signals into digital data. This compression allows more voice calls to be transmitted over the same bandwidth compared to analog systems.
  3. Full-Duplex Communication: US-TDMA supports full-duplex communication, allowing users to simultaneously transmit and receive voice and data over the same channel.
  4. Dual-Mode Operation: US-TDMA devices were designed to support dual-mode operation, allowing them to operate in both digital (IS-136) and analog (AMPS) modes. This feature was useful during the transition from analog to digital networks.
  5. Data Services: While US-TDMA primarily focused on voice services, it also provided basic data services with a maximum data rate of up to 14.4 kbps. However, the data capabilities of US-TDMA were limited compared to other 2nd generation systems like CDMA and GSM.
  6. Frequency Band: US-TDMA operated in the 800 MHz and 1900 MHz frequency bands, offering both cellular and PCS (Personal Communications Service) bands.

Comparison with Other 2nd Generation Systems:

During the 2nd generation era, various cellular technologies competed in the global market. Some key differences between US-TDMA (IS-136) and other popular 2nd generation systems were:

  1. CDMA (IS-95): CDMA, based on the IS-95 standard, used spread spectrum technology instead of TDMA. CDMA provided better call quality in challenging environments and offered higher data rates compared to US-TDMA.
  2. GSM: GSM (Global System for Mobile Communications) was the dominant 2nd generation technology worldwide. It also used TDMA, but in a different time slot configuration compared to US-TDMA. GSM gained popularity due to its global standardization, strong data capabilities (up to 9.6 kbps), and widespread international roaming support.

Transition to 3rd Generation (3G) Systems:

As the demand for higher data rates and advanced services increased, 2nd generation systems like US-TDMA, CDMA, and GSM paved the way for the adoption of 3rd generation (3G) technologies, such as UMTS (Universal Mobile Telecommunications System) and CDMA2000. These 3G systems provided faster data speeds, improved voice quality, and better support for multimedia applications.

Conclusion:

US-TDMA (IS-136) was a 2nd generation cellular communication system used mainly in the United States. It was based on Time Division Multiple Access (TDMA) technology and aimed to provide digital voice and basic data services. While US-TDMA played a role in the early stages of digital cellular deployment, it was eventually superseded by more advanced 3rd generation (3G) technologies that offered higher data rates and greater capabilities.