--- title: "FDMA vs TDMA; T1 and E1 hierarchy" subject: "Communication Systems" chapter: 5 key: "semester_6/communication_systems:fdma-tdma-t1-e1" source: https://www.bctengineer.com/q/semester_6/communication_systems/fdma-tdma-t1-e1 site: BCT Engineering --- # FDMA vs TDMA; T1 and E1 hierarchy Communication Systems · Chapter 5: Multiplexing Techniques - Asked in: 2078 Chaitra, 3+2 marks - Video: [E1 T1 Lines Tutorial](https://www.youtube.com/watch?v=-fR9ogZ1SpM) — Techniki Bansal - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/communication_systems/fdma-tdma-t1-e1 - Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-5 ## Question Differentiate between FDMA and TDMA. Draw T1 and E1 telephone 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). ## Answer #### 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): ```text 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): ```text 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How do FDMA and TDMA differ in how users transmit? A. FDMA: continuous on own frequency; TDMA: bursts in own time slot on shared band B. FDMA: bursts; TDMA: continuous C. Both continuous D. FDMA needs strict time sync; TDMA does not Answer: A. FDMA users transmit continuously in separate bands, TDMA users burst in their slot and need strict time sync. (Key point: FDMA vs TDMA) 2. Why is intermodulation a bigger problem in FDMA? A. Many carriers share a non-linear amplifier (e.g. satellite TWT) B. Only one carrier is present at a time C. Guard times are too short D. It uses digital signals Answer: A. Multiple simultaneous carriers in a non-linear amplifier produce intermodulation; TDMA has one carrier at a time. (Key point: Intermodulation) 3. What is the T1 (Bell) hierarchy of multiplication factors? A. x4, x4, x4 B. x4, x7, x6 C. x4, x6, x7 D. x5, x5, x3 Answer: B. DS1 to DS2 x4 (6.312), DS2 to DS3 x7 (44.736), DS3 to DS4 x6 (274.176 Mb/s). (Key point: T1 hierarchy) 4. What are the E-levels' rates in order? A. 2.048, 8.448, 34.368, 139.264, 564.992 Mb/s B. 1.544, 6.312, 44.736, 274.176 Mb/s C. 2.048, 6.312, 34.368, 139.264 Mb/s D. 2.048, 8.448, 44.736, 564.992 Mb/s Answer: A. Each E level multiplies by 4 with extra overhead: E1 2.048, E2 8.448, E3 34.368, E4 139.264, E5 564.992 Mb/s. (Key point: E1 hierarchy) ## Related in Communication Systems - [Short note: T1 and E1 hierarchy](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Ashort-note-t1-e1-hierarchy) — Communication Systems, chapter 5 - [T1 and E1 TDM-PCM hierarchy with frame diagrams](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3At1-e1-frame-diagrams) — Communication Systems, chapter 5 - [Differences between T1 and E1 hierarchy](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3At1-vs-e1) — Communication Systems, chapter 5 - [FDMA; FDM in telephone hierarchy](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Afdma-fdm-telephony-hierarchy) — Communication Systems, chapter 5, asked 2× - [Constellation diagram significance; E1 vs T1](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aconstellation-significance-e1-t1) — Communication Systems, chapter 5 - [DPCM vs delta modulation; E1 hierarchy](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adpcm-vs-dm-e1) — Communication Systems, chapter 4 ## Related in other subjects - [North American T1 vs European E1 hierarchy](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3At1-e1-hierarchy-compare) — Telecommunications, chapter 3, asked 2× - [E1 telephone hierarchy](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Ae1-hierarchy) — Computer Networks and Security, chapter 2 - [FDMA vs TDMA; operation of FHMA](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afdma-tdma-fhma) — Wireless Communication, chapter 7 - [TDMA versus FDMA](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Atdma-vs-fdma) — Wireless Communication, chapter 7