What do OFDMA and MU-MIMO mean for routers? When there are many devices at home, it gets laggy. I turned on these two switches and it worked smoothly

my router is a Xiaomi AX3000T, and the claim of capacity is pretty impressive, but last winter things started to go wrong: the internet speed was normal during the day, but at eight or nine in the evening, the living room TV starts spinning to cast, and my wife's phone needs buffering when watching videos. I didn't add any extra equipment—just those 22 at home—4 phones, 2 computers, a TV box, a camera, a vacuum cleaner, a speaker, plus a bunch of Mijia sensors.

At first, I thought it was a broadband issue. I called number 10000, and they remotely tested and said the line was fine. Suspecting it was freeloading on the internet, I logged into 192.168.1.1 and changed the WiFi password, but it was still lagging. Later, after checking the router's backend, I noticed that in the WiFi advanced settings, there are two switches I usually don't dare to touch: one called OFDMA, the other called MU-MIMO. After researching for a long time, I finally figured out that these two are meant for the 'lag when there are too many devices.'

break down the term: a router can only serve one device at a time

first explain where the problems of old routers lie. WiFi 4 and WiFi 5 routers had an inherent limitation: at the same time, on the same channel, they could only communicate with one device. If all 20 devices at home are connected, the routers can only queue up, each sending a short segment in turn. When there are few devices, you don't feel it; but when there are many, the queue time gets longer—the TV buffers, not because broadband isn't fast enough, but because it "can't queue."

this queuing mechanism has a scientific name called CSMA/CA, which simply means "listen before speaking": before contracting equipment, listen to see if anyone is speaking on the channel; if someone is involved, just wait. When the house has many devices, all is waiting, conflicts are frequent, and efficiency is very low. OFDMA and MU-MIMO address the issue of "queuing" from two different approaches.

OFDMA: Divide one lane into multiple lanes and bring several vehicles at once

OFDMA stands for Orthogonal Frequency Division Multiple Access, which sounds impressive. I'll use a highway as an example. The old method (OFDM) means only one car can drive the entire road at a time, even if that car only carries a parcel box, the whole road still belongs to them. OFDMA divides this road into many small lanes (subcarriers), with one car occupying several lanes and the remaining lanes for others. When routers are sent in one package, you can send a bit of data to each of three or four devices at once, and the queue count is cut off directly.

this feature is especially friendly for small bags. What is a small bag? WeChat chats, smart door lock status updates, background phone heartbeats, speaker replies saying 'received'—these data packets are all very small. In the past, sending a package of several kilometers to a door lock with a router took up a full delivery opportunity. Now, if you gather a truckload, you can deliver everything in one round trip. People with many Mijia devices at home feel OFDMA the most—after I turned it on, during the stuttering period at night, the speaker would call 'I'm here' much faster, and if I stopped calling for ages, there was no response.

note, OFDMA was introduced only in WiFi 6 (802.11ax); WiFi 5 routers do not have it. Moreover, there are uplink and downlink: the router sends to the device called the downlink, and the device returns to the router as the uplink. Many routers only turn on the downlink switch in the background, so you have to find the uplink separately. My AX3000T is called differently in either "WiFi Enhancement" or "Advanced Settings." Some firmware is called "Multi-User Scheduling," and if you can't find it, you just check the manual.

MU-MIMO: Multiple antennas transmit and receive simultaneously, each following its own path

MU-MIMO (Multiple Users Multiple Inputs Multiple Output) addresses a different dimension of problem. Doesn't a router have several antennas? In the old method, these antennas work together to serve only one device; MU-MIMO groups antennas; a 2×2 antenna can simultaneously provide two devices with an independent channel, and 4×4 is even more so without queueing for each other. If OFDMA is about "cutting lanes," then MU-MIMO is about "building more roads."

it does not conflict with OFDMA; it is a superimposed relationship: MU-MIMO handles large data transmission (TV casting, NAS copying, and other continuous large packets), while OFDMA manages small packet consolidation. Only when both are enabled together can the router truly "operate on multiple lines."

MU-MIMO has two details that are easily overlooked. First, there are uplink and downlink. In the WiFi 5 era, MU-MIMO only supported downlink, while WiFi 6 added uplink, so the old router's spec page saying "supports MU-MIMO" might only be halfway. Second, it has requirements for the device. The phone must support the corresponding specifications. If your router is 4×4 and your phone is 2×2, you can only use 2×2. Don't expect double the specs and double the experience.

my test of the switch before and after comparison, the changes are in these places

be honest. My AX3000T has these two switches on by default, but I flashed third-party firmware once before. After flashing back, many advanced settings reset to default. I suspect they lost it at that time. After reopening, I observed for three consecutive nights and said three noticeable changes:

ask if the peak speed has changed—really, no, the speedtest scores are still the same. Because OFDMA and MU-MIMO do not increase bandwidth; instead, they optimize the efficiency of "multi-device queuing." If you're using it alone, you don't feel much when you turn it on; the more devices you have, the greater the benefits. That's why, after a major slimming down of all 62 devices at home, I made another move: slimming down equipment is to reduce burden, turning on these two switches is for efficiency—two different things.

families with many devices, check these three points before you start

First, first confirm that the router starts with WiFi 6. WiFi 5 and earlier devices don't have OFDMA, and even if you want to open them, you don't have any. WiFi 6 routers are now available for around a hundred yuan, much cheaper than when I bought AX3000T three years ago.

Second, the switch position is called differently by brand. Xiaomi's WiFi settings in the Mijia app or in the background of 192.168.31.1; TP-Link is generally called "Multi-user MIMO" and "OFDMA," which are directly listed under the advanced wireless settings; In its 'Wireless Network—Professional Settings' section, ASUS uses Chinese names like 'Clear Beamforming' and 'OFDMA'. If you can't find it, search for "Model + Where is OFDMA"; don't blindly turn on other switches.

Third, a very small number of old devices (including my old camera) disconnect after enabling OFDMA. This is a compatibility issue, not a broken router. In such cases, turn off OFDMA or move such devices to a 2.4G dedicated IoT SSID, and don't squeeze into the same frequency band as your new phone. 2. How to choose a 4G channel—I've written about it before. If the channel is congested, you can refer to the on channel interference WiFi.

Finally, here's the order of decisions: first clear the device list and kick out the zombie devices (see my in my article router with power supply), then confirm that OFDMA and MU-MIMO are enabled, and only then is it time to upgrade. If you have fewer than ten devices at home and use a WiFi 5 router, don't be fooled by spec fanatics—it's really not to the point where you absolutely need to upgrade; For over twenty units, these two features are worth the ticket price. If you want to understand the differences between WiFi 6 and WiFi 7 and MLO in depth, you can refer to my article on the I before upgrading. For signal coverage issues, check Mesh the on networking. Don't confuse queue lag with weak signal—one looks at these two switches, and the other on placement and networking.