Wi-Fi 6E introduces the 6 GHz band and brings the benefits of OFDMA, which improves performance in multi-client environments. But how does this work in practice when using 40 MHz channels and 2×2 spatial stream clients? This blog explores how airtime and throughput are affected when 5, 10, or 15 clients are connected to a 4×4 access point.
Key technologies explained
OFDMA (Orthogonal Frequency Division Multiple Access) allows a Wi-Fi 6/6E access point to divide a channel into smaller units, called Resource Units (RUs), enabling multiple clients to transmit or receive simultaneously.
40 MHz channels in 6 GHz
A 40 MHz channel in the 6 GHz band contains about 996 tones (subcarriers). These can be grouped into different RU sizes:
- 26-tone (~2 MHz)
- 52-tone (~4 MHz)
- 106-tone (~8 MHz)
- 242-tone (~20 MHz)
This makes 40 MHz wide channels suitable for dividing spectrum among multiple clients efficiently.
Scenario overview – 2×2 clients, 4×4 AP
We consider a setup where a Wi-Fi 6E access point with 4 spatial streams (4×4 MU-MIMO) serves multiple 2×2 clients on a 40 MHz channel in the 6 GHz band. All clients are capable of using OFDMA, MU-MIMO, and the highest MCS (MCS 11).
The following scenarios demonstrate how performance scales depending on the number of connected clients.
Scenario 1 – 5 clients connected
- Each client can be assigned a 106-tone or even a 242-tone RU.
- The AP has enough spectrum to serve clients with large RUs.
- Downlink MU-MIMO can serve 2 to 4 clients in parallel.
Estimated PHY rate per client: 243–600 Mbps
Latency: Low
Efficiency: High
Scenario 2 – 10 clients connected
- The AP needs to divide the spectrum more evenly.
- Each client could receive a 52-tone RU, or the AP may alternate 106-tone RUs between groups of clients.
Estimated PHY rate per client: 150–250 Mbps
Latency: Low
Efficiency: High
Scenario 3 – 15 clients connected
- The 40 MHz channel is fully used.
- Each client receives a 26-tone RU (≈2 MHz).
- All clients can be served in a single transmission using OFDMA.
Estimated PHY rate per client: 80–120 Mbps
Latency: Very low
Efficiency: Very high
Does distance affect RU assignment?
Distance does not change how many tones a client receives, but it does affect signal quality (SNR), which determines the MCS index. A lower SNR results in a lower MCS and therefore lower throughput, even if the RU size remains the same.
| Clients | RU per client | Estimated PHY rate | Latency | Efficiency |
|---|---|---|---|---|
| 5 | 106–242 tone | 243–600 Mbps | Low | High |
| 10 | 52–106 tone | 150–250 Mbps | Low | High |
| 15 | 26-tone | 80–120 Mbps | Very low | Very high |
Wi-Fi 6E with OFDMA and 40 MHz channels delivers strong performance, especially in dense client environments. It’s not just about maximizing speed for one device — it’s about efficient spectrum use and low-latency access for many devices at once.
Does OFDMA result in lower throughput than OFDM in some cases?
Yes, in some scenarios, OFDMA delivers lower individual throughput per client than OFDM, but that’s by design. Here’s why:
With OFDMA, the access point divides the channel into smaller chunks called Resource Units (RUs) to serve multiple clients simultaneously. As a result:
- Each client gets less spectrum (e.g. a 26- or 52-tone RU instead of the full channel)
- That means lower PHY rate per client
- But: more clients are served at the same time, reducing wait time and improving overall efficiency
In contrast, with OFDM:
OFDM allows one client to use the entire channel, so:
- You get the maximum PHY rate possible (e.g. 1201 Mbps)
- But all other clients must wait
- Latency increases when many clients compete for airtime
- It becomes inefficient for short packets or high client density
| Technology | Clients Served | Channel Usage | PHY Rate per Client | Efficiency | Latency |
|---|---|---|---|---|---|
| OFDM | 1 at a time | Full channel | High (e.g. 1201 Mbps) | Low | High |
| OFDMA | Multiple | Shared via RUs | Lower (e.g. 80–250 Mbps) | High | Low |
Key takeaway:
With a single connected client, Wi-Fi 6/6E uses OFDM, not OFDMA.
The client receives the full 40 MHz channel, achieving the maximum PHY rate — for example, 1201 Mbps with 2 spatial streams and MCS 11.
Why?
- OFDMA is designed for serving multiple clients simultaneously by dividing the channel.
- Using OFDMA with just one client would unnecessarily limit throughput.
- OFDM ensures peak performance for individual clients when there’s no contention.
In environments with many active clients, OFDMA performs better overall, even if individual speeds are slightly lower. When only one or two clients are active, OFDM may deliver higher speed , and Wi-Fi 6 will automatically use it in those cases.