- 2078 Chaitra · 3+2 marks
FDMA vs TDMA; T1 and E1 hierarchy
Short answer
FDMA gives each user a unique frequency band continuously; TDMA shares one band via time slots with burst transmission and strict synchronisation. T1 hierarchy: 24 ch → 1.544 Mbps (DS1), multiplexes to DS2 (6.312 Mbps), DS3 (44.736), DS4 (274 Mbps). E1: 30 ch → 2.048 Mbps, then E2 (8.448), E3 (34.368), E4 (139.264), E5 (564.992).
Differentiate between FDMA and TDMA. Draw T1 and E1 telephone hierarchy.
FDMA vs TDMA
FDMA (frequency division multiple access) gives each user its own carrier frequency band for the whole call. TDMA (time division multiple access) gives all users the same band, and each user transmits in bursts during its own time slot.
| Point | FDMA | TDMA |
|---|---|---|
| Resource shared | Frequency band | Time slot |
| Transmission | Continuous | Burst (bursty) |
| Synchronisation | Not needed | Strict time sync needed |
| Guard | Guard bands | Guard times |
| Equipment | Separate RF filters and oscillators per user | One carrier shared, digital processing |
| Intermodulation | Problem in non-linear amplifiers (e.g. satellite TWT) | Less, since only one carrier at a time |
| Example | AMPS (1G), SCPC satellite | GSM (2G), TDMA satellite |
T1 and E1 telephone hierarchy
T1 hierarchy (Bell / North America):
24 voice ch x 64 kb/s
|
[ DS1 / T1 ] 1.544 Mb/s 24 ch
| x4
[ DS2 / T2 ] 6.312 Mb/s 96 ch
| x7
[ DS3 / T3 ] 44.736 Mb/s 672 ch
| x6
[ DS4 / T4 ] 274.176 Mb/s 4032 ch
E1 hierarchy (ITU-T / Europe):
30 voice ch x 64 kb/s (+ 2 overhead slots)
|
[ E1 ] 2.048 Mb/s 30 ch
| x4
[ E2 ] 8.448 Mb/s 120 ch
| x4
[ E3 ] 34.368 Mb/s 480 ch
| x4
[ E4 ] 139.264 Mb/s 1920 ch
| x4
[ E5 ] 564.992 Mb/s 7680 ch
Both systems use 125 µs frames. A T1 frame carries 193 bits, giving 1.544 Mb/s. An E1 frame carries 256 bits, giving 2.048 Mb/s.
✓ Answer checked by Claude Opus 5.5 (high effort)
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