- 2070 Magh · 2+4 marks
Multiple access; FDMA vs CDMA
Short answer
Multiple access enables simultaneous sharing of spectrum among users. FDMA assigns narrow frequency bands per user, demands frequency planning, and has hard capacity. CDMA spreads all users over a wide band with unique codes, providing universal frequency reuse, soft capacity, soft handoff, and inherent security, but requires strict power control.
What is multiple access technique? Compare FDMA with CDMA.
Multiple access technique
Multiple access is the technique by which many users share a common, limited radio spectrum at the same time without causing serious interference to each other. The shared resource is divided in frequency (FDMA), time (TDMA), code (CDMA) or space (SDMA). Narrowband systems (FDMA, TDMA) give each user a small part of the spectrum; wideband systems (CDMA) let every user occupy the whole band. Each is combined with FDD or TDD duplexing.
FDMA vs CDMA
| Point | FDMA | CDMA |
|---|---|---|
| Principle | Each user gets its own frequency band | All users share the band, separated by codes |
| Bandwidth | Narrow per user (30 kHz AMPS) | Wide (1.25 MHz IS-95) |
| Time usage | Continuous on its channel | Continuous, same time as others |
| Frequency reuse | Cluster N = 4–12; planning needed | N = 1; no planning |
| Capacity limit | Hard (fixed channels) | Soft (interference limited) |
| Handoff | Hard handoff | Soft handoff |
| Power control | Not critical | Essential (near-far effect) |
| Multipath | Causes fading | Used by RAKE receiver |
| Guard needs | Guard bands, sharp filters | No guard bands between users |
| Security | Low | High (PN codes) |
| Example | AMPS, NMT | IS-95, WCDMA |
✓ Answer checked by Claude Opus 5.5 (high effort)
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