- 2074 Bhadra · 5 marks
Short note: Specifications of GSM
Short answer
GSM-900 uses uplink 890-915 MHz, downlink 935-960 MHz, 200 kHz carrier spacing, 8 slots, 270.833 kbps, GMSK BT=0.3, RPE-LTP 13 kbps speech, 4.615 ms frames and 35 km max cell radius. Security uses SIM and A3/A5/A8 algorithms.
Write a short note on specifications of GSM.
GSM (Global System for Mobile communications) is the 2G digital cellular standard developed by ETSI. Its main specifications:
| Parameter | Specification |
|---|---|
| Frequency band (GSM-900) | Uplink 890–915 MHz, downlink 935–960 MHz |
| Other bands | DCS-1800 (1710–1785 / 1805–1880 MHz), PCS-1900 |
| Duplex distance | 45 MHz (GSM-900) |
| Carrier spacing | 200 kHz |
| Number of carriers | 124 (GSM-900) |
| Multiple access | FDMA/TDMA, FDD |
| Time slots per carrier | 8 (16 with half rate) |
| Channel data rate | 270.833 kbps |
| Modulation | GMSK, BT = 0.3 |
| Frame duration | 4.615 ms (slot 576.9 µs) |
| Speech coder | RPE-LTP, 13 kbps (full rate) |
| Gross TCH rate | 22.8 kbps after coding |
| Channel coding | Rate 1/2 convolutional + CRC, interleaving over 8 bursts |
| Equalization | Adaptive, 26-bit training sequence |
| Frequency hopping | Slow, 217 hops/s |
| Max cell radius | 35 km (timing advance limit) |
| Data services | 9.6 kbps CSD; GPRS/EDGE in 2.5G |
| Security | SIM, A3 (authentication), A5 (ciphering), A8 (key) |
| Mobile power | 0.8–8 W (GSM-900 classes) |
Other features: SIM-based subscriber identity and roaming, SMS, mobile-assisted hard handoff, discontinuous transmission (DTX) with voice activity detection, and power control.
✓ Answer checked by Claude Opus 5.5 (high effort)