OFDMA Efficiency Calculator
Compare 802.11ax OFDMA against single-user transmissions: resource units per channel, users per TXOP and the airtime saved.
Inputs
Airtime Saved vs Single-User
63.7%
Resource Units per Channel
9
Users Served per TXOP
9
OFDMA Airtime for the Whole Group
1,132µs
Single-User Airtime for the Whole Group
3,120µs
Step by step
Values used
Channel width = 80 MHz; Resource unit size = 106-tone RU; Clients with data queued = 24 clients; Airtime for one frame at full channel width = 30 µs; Fixed overhead per transmission = 100 µs
OFDMA Efficiency
resource units = data subcarriers ÷ RU size; OFDMA airtime = ceil(clients ÷ RUs) × (fixed overhead + frame airtime ÷ RU's share of the channel).
Airtime Saved vs Single-User
= 63.7
Resource Units per Channel
= 9
Users Served per TXOP
= 9
OFDMA Airtime for the Whole Group
= 1,132 µs
Single-User Airtime for the Whole Group
= 3,120 µs
How it works
OFDMA splits a channel into resource units so several clients are served in one transmission, paying the preamble, contention and acknowledgement overhead once instead of once per client. Each client gets a narrower slice, so its payload takes proportionally longer, and the saving comes entirely from amortising the fixed overhead. OFDMA only pays off for small frames from many clients — the exact profile of voice, telemetry and IoT traffic — and for a handful of large downloads it makes things slightly worse.
Formula
OFDMA Efficiency
resource units = data subcarriers ÷ RU size; OFDMA airtime = ceil(clients ÷ RUs) × (fixed overhead + frame airtime ÷ RU's share of the channel).
- resourceUnits
- Parallel sub-channels available in one transmission
- ruShare
- Fraction of the channel width one RU occupies
Frequently Asked Questions
How is OFDMA Efficiency calculated?
resource units = data subcarriers ÷ RU size; OFDMA airtime = ceil(clients ÷ RUs) × (fixed overhead + frame airtime ÷ RU's share of the channel). OFDMA splits a channel into resource units so several clients are served in one transmission, paying the preamble, contention and acknowledgement overhead once instead of once per client. Each client gets a narrower slice, so its payload takes proportionally longer, and the saving comes entirely from amortising the fixed overhead.
Why does OFDMA Efficiency matter?
OFDMA only pays off for small frames from many clients — the exact profile of voice, telemetry and IoT traffic — and for a handful of large downloads it makes things slightly worse.
What values do I need to enter?
This calculator takes 5 inputs: Channel width, Resource unit size, Clients with data queued, Airtime for one frame at full channel width, Fixed overhead per transmission. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.