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Evolution from 1G to 2.5G (TDMA)

Short answer

1G (AMPS) used analog FDMA. 2G TDMA systems like GSM (8 slots per 200 kHz carrier) and IS-136 (3 slots per 30 kHz) provided digital voice and SMS. 2.5G evolved with GPRS packet data (up to ~171 kbps) and EDGE (up to 384 kbps) for always-on internet.

Discuss the evolution from 1G to 2G, 2.5G in the case of cellular network based on TDMA.

The TDMA path of cellular evolution started from analog FDMA systems and led to GSM and IS-136, which were then upgraded for packet data.

1G (analog FDMA)

  • AMPS (USA), TACS (UK), NMT; analog FM voice on 30/25 kHz channels, one user per channel, circuit switched, no security, voice only.

2G (digital TDMA)

  • GSM (Europe): 200 kHz carriers, each divided into 8 time slots (8 users per carrier), GMSK modulation, 9.6 kbps data, SMS, SIM, encryption.
  • IS-136 (USDC/D-AMPS) (USA): keeps 30 kHz AMPS channels but puts 3 users per channel using π/4-DQPSK; backward compatible with AMPS.
  • PDC (Japan): TDMA, 25 kHz.

2.5G (data upgrades on TDMA)

  • HSCSD (High Speed Circuit Switched Data): one user gets up to 4 consecutive time slots; up to 57.6 kbps; circuit switched.
  • GPRS (General Packet Radio Service): packet-switched, users share slots, up to 8 slots per user, up to ~171.2 kbps; adds SGSN and GGSN to the core; always-on internet.
  • EDGE (Enhanced Data rates for GSM Evolution): 8-PSK modulation and adaptive coding on GSM carriers; up to ~384 kbps; also used by IS-136 operators to join the GSM path.
AMPS ──→ IS-136 ───────┐
                       ├──→ EDGE ──→ 3G W-CDMA
TACS/NMT → GSM → HSCSD → GPRS ─┘
  1G        2G       2.5G

✓ Answer checked by Claude Opus 5.5 (high effort)

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