How does FDMA (Frequency Division Multiple Access) work?

FDMA assigns each user an exclusive frequency band for the entire duration of their connection — users are separated in the frequency domain.

How it works:

• The total available spectrum is divided into non-overlapping frequency bands
• Each user gets one band exclusively — no sharing
• The assignment lasts for the entire duration of the connection (call or data session)

Visualized: On a frequency-vs-time diagram, each user occupies a horizontal stripe (fixed frequency, all time).

Advantages:

• Simple to implement — just filter by frequency
• No synchronization needed between users
• Works well for continuous streams (voice)

Disadvantages:

• Wasteful — if a user is silent (e.g., listening during a call), their frequency band sits idle
• Rigid — can't easily reallocate bandwidth based on demand
• Guard bands needed between channels to prevent interference → wastes spectrum

Used in: 1G (AMPS) used pure FDMA. GSM uses FDMA combined with TDMA — first divide by frequency, then subdivide each frequency into time slots.

Go deeper:

• Frequency-division multiple access (Wikipedia) — guard bands, the filtering requirement, and why 1G relied on pure FDMA.