why does wifi OFDMA degrade performance so badly?

Welcome to the Netgear community, and season's greetings!

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Retired_Member wrote:

I would upload a clear well-composed video illustrating it, but this forum doesn't support it.

so I expect nothing from this thread but unqualified off-topic replies.

don't bother.

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Upload it to whatever favorite cloud platform you prefer, unlisted, create a share link accessible to the public, and publish the link in the community.  

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Retired_Member wrote:

my concern is with two PCs, filesharing to each other, both on the same wifi channel.

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Tell us more about the environment your are testing and demonstrating on.

Peer-to-peer WiFi or infrastructure mode on a single access point? Either way - unless you operate access points operating on multi-band or with multiple radios - each wireless client will operate on the same channel set.

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Retired_Member wrote:

the subject line was just a rhetorical question anyway.

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Fearlessly borrowed from an article by Anisha Teckchandani, Technical Marketing Engineer, ARUBA
published on NETWORKWORLD as What’s the Difference between OFDMA and MU-MIMO in 11ax? :

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Orthogonal Frequency-Division Multiple Access (OFDMA) divides available channel bandwidth into several mutual orthogonal subcarriers or resource units (RUs). Access to multiple users is granted in OFDMA by assigning subsets of these subcarriers to individual users. Downlink OFDMA is one of the complex features of 11ax that allows a single downlink transmission (from AP to clients) to be split by frequency within a channel. Uplink OFDMA is similar to downlink OFDMA but in the reverse direction, i.e. from multiple clients to the AP. Since many clients will try to transmit at the same time, they need to be coordinated. To achieve this coordination, the AP sends trigger frames to the clients to inform them which subcarriers (or RUs) they can use to send data. OFDMA is also used by LTE networks as the means of multiuser transmission.

At first, it may appear as though OFDMA offers no added benefit compared to single-user Orthogonal Frequency Division Multiplexing (OFDM) because the speed of transmit links remains unchanged. So, when half the channel is allocated for frame transmission in OFDMA, it would take twice the time. But, in OFDM, each time a frame transmission has to occur, there is significant overhead caused by medium contention. In OFDMA though, since transmit opportunities are shared by several frames bundled together, medium contention overhead is reduced. Efficient use of the channel, therefore, leads to increased overall efficiency in small-packet applications in dense environments.

2 Technologies, Designed for Different Uses

OFDMA and MU-MIMO are complementary technologies. While OFDMA is ideal for low-bandwidth, small-packet applications such as IoT sensors, MU-MIMO increases capacity and efficiency in high-bandwidth applications like mission-critical voice calls and video streaming.

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Fellow Tim Higgins published two comprehensive tests and comparisons on SmallNetBuilder:

Does OFDMA Really Work? Part 1 

Does OFDMA Really Work? Part 2 

Keep in mind Wi-Fi 5 (802.11ac) defaulted to OFDM, while the newer Wi-Fi 6 (802.11ax), Wi-Fi 6E (802.11ax), and Wi-Fi 7 (802.11be) inherit OFDMA by the standard.

You are using some Netgear hardware?

You seem to have come up with a self diagnosis of whatever your problem might be. It is usually better to start with describing the problem.

Is this it?

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Retired_Member wrote:

my concern is with two PCs, filesharing to each other, both on the same wifi channel.

 

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What is that telling us about your problem? It is too slow? It fails? Something else?