Side-by-side comparison
| Parameter | CDMA | TDMA |
|---|---|---|
| Resource Divided By | Unique spreading code (Walsh + PN) | Time slot in a frame |
| Guard Mechanism | Code orthogonality — no guard band needed | Guard time between slots |
| Bandwidth per User | Full channel bandwidth (1.25 MHz in IS-95) | Time fraction of carrier (577 µs slot in GSM) |
| Near-Far Problem | Severe — needs power control (±1 dB accuracy in IS-95) | Moderate — guard time helps |
| Frequency Reuse Factor | 1 — same frequency everywhere | 3–7 — frequency reuse planning needed |
| Soft Handoff | Yes — mobile talks to multiple BTSs simultaneously | Hard handoff only |
| Capacity Limit | Interference-limited — soft capacity | Hard — fixed number of slots |
| Standard Example | IS-95 (cdmaOne), CDMA2000, WCDMA (3G) | GSM (2G), IS-136 |
Key differences
FDMA is the most straightforward — each user gets a dedicated frequency slice permanently, so no synchronisation is needed, but spectrum efficiency is lowest because guard bands waste usable bandwidth between channels. TDMA improves on this by sharing a wider carrier among 8 users (GSM) in 577 µs time slots, requiring tight timing synchronisation within ±1 symbol but reusing frequency every 3–7 cells. CDMA uses the entire 1.25 MHz (IS-95) or 5 MHz (WCDMA) simultaneously for all users, eliminating guard bands and enabling a frequency reuse factor of 1 — every cell uses the same frequency. CDMA's soft capacity means adding the 101st user only slightly degrades everyone's SNR rather than blocking the call outright.
When to use CDMA
Use CDMA architecture when maximising spectral efficiency in a cellular network and you can implement fast power control. 3G WCDMA and CDMA2000 networks use it to achieve 3–5× the voice capacity of equivalent GSM deployments.
When to use TDMA
Use TDMA when the infrastructure is based on GSM standards and backward compatibility is required. GSM's TDMA structure on 200 kHz carriers is still the backbone of 2G voice networks operating worldwide.
Recommendation
For exam and interview purposes, choose CDMA for highest spectral efficiency and soft capacity, TDMA for GSM-based digital cellular, and FDMA only when discussing 1G analog systems or as a baseline comparison. Never recommend FDMA for a modern system design.
Exam tip: The GATE examiner tests whether you know that CDMA has a frequency reuse factor of 1 (unlike TDMA/FDMA which need 3–7), and that CDMA capacity is interference-limited rather than slot-limited — state both in any written answer.
Interview tip: A core wireless interviewer at Jio or Ericsson expects you to explain the near-far problem in CDMA and how IS-95 solves it with closed-loop power control accurate to ±1 dB — generic answers about spreading codes alone will not impress.