2nd Generation wireless network:
- After few years of 1st generation network 2G wireless network was introduced in 1992, is the 2nd generation of mobile technology and this network was the first to utilise digital encryption on conversations.
- 2G wireless networks was the first to offer internet services and SMS text messaging,
- The 2nd generation cellular systems given more characteristics in comparison to the 1st generation system.
- The 1st generation cellular systems were based on analog transmissions on FDMA/FDD and analog FM The 2nd generation (2G) cellular systems use digital modulation formats including the TDMA/FDD and the CDMA/FDD multiple access techniques.
- The 2nd generation standards include three TDMA standard and one CDMA standard. And they are as follows:
1. Global System Mobile (GSM)
2.Interim Standard 136 (IS-136)
3.Pacific Digital Cellular (PDC)
4. Interim standard 95 CDMA (IS-96)
- In the three TDMA standards, the spectral band is subdivided into many time slots. These time slots form TDMA frames.
- Every subscriber will be assigned time slots in which transmission can occur. The cellular traffic congestion is minimized by this technology. The TDMA standards use half duplex methods. Other features of the TDMA are:
i) Operates at faster data rates.
ii) Utilizes the spectrum efficiently.
iii) Provides good synchronisation.
iv).It has guard intervals for better operation.
- In the CDMA standard (IS-95) every subscriber is assigned an n-bit code and assures a high degree of security than other access methods.
- The transmission of several users is differentiated by a code word that has been assigned to every subscriber.
- Thus, TDMA and CDMA in 2G standards provide less design complexity, more security, faster speeds of transmission and high reliability than the 1G systems.
- A simple comparison with respect to growth of number of mobile users as the technology moves from 1G to 2G in 2001
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