What is MIMO?

What is MIMO? (SU and MU MIMO)

What is MIMO? If that’s the the question that brought you here, then you’re absolutely on the right blog.

MIMO (or Multiple-Input Multiple-Output) is a wireless technology that uses multiple antennas (transmitters and receivers) to transfer more data at the same time.

If you’ll allow me, let me give you a bit of background before get right back into the subject matter.

Brief background

Older networks like the 2G and 3G, used a single signal/data transfer stream. This is known as SISO or single input single output.

This means that phones that were strictly 2G or 3G usually had only 1 antenna to receive and send signals to a network tower.

What is SISO?

If you check this post What is a Network Frequency band? you’ll  see that both 4G and 3G use the same network frequencies.

For example, Band 1 for 3G has a frequency of 2100MHz and the code name IMT. The band 1 for 4G also has the 2100MHz frequency and code name IMT as well.

So if 3G and 4G are using the same network frequencies, why is 4G so much faster than 3G?

What is MIMO?

Let’s welcome MIMO into the chat.

Multiple input and multiple output refers to the use of multiple transmitters to send data and multiple receivers to accept these signals.

This means that a cell tower can send (and receive) two or more streams of data instead of just one stream.

What is MIMO?

So instead of using only one stream to send and receive data, multiple streams are used. This makes the network so much faster.

MIMO is a key part of LTE deployment. Without it, LTE wouldn’t have been the big revolution that it is. In fact, the LTE standard is based on MIMO and OFDMA, a topic for a another day.

Phones that were built for 4G were built to either have

  • 2×2 MIMO
  • 3×3 MIMO
  • 4×4 MIMO

The numbers there depicts the number of antennas that a phone has to take advantage of 4G multiple data streams.

The more antennas a device has, the faster it will be.

2×2 phones are faster than SISO (or 1×1) phones. 3×3  phones are faster that 2×2 and SISO phones. 4×4 phones are the fastest of them all.


It helps to improve

  1. Throughout capacity
  2. Network coverage
  3. Reliability
  4. Signal quality

Increasing the number of antennas or connection points improves the amount of signal/data that can be delivered to the end user. This means faster load times and quicker downloads.

It also improves network coverage because if one stream is blocked by any form of interference or obstruction, there are other streams that can be used to deliver signal/data.

With multiple antennas to take advantage of signal, network connectivity will be vastly improved.

A very good example is when you look at the signal readings for 3G. A network signal between -90 to -110dBm on 3G would be almost unusable.

But that same -90 to -110dBm range on 4G can be used to download a 500MB movie in less than 3 minutes.

Why? Easy. Multiple input and multiple output antennas.

So most entry level 4G or LTE phones are usually 2×2 MIMO phones. The Midrangers are usually 3×3 MIMO while the flagships are all 4×4 MIMO.


There are two types:

  1. SU MIMO
  2. MU MIMO

SU MIMO means single user MIMO. This is the type of MIMO that you find on smartphones and low end WiFi routers.

MU MIMO or multiple user MIMO is mostly only found on high end WiFi routers.

Single user MIMO devices like phones or WiFi can talk to several other devices but can only do so one at a time.

For a phone, this usually isn’t a problem as phones mostly connect to one cell tower.

This on the other hand may be a problem for WiFi routers that are connected to too many devices.

Especially when all these devices are using high data applications.

Single user MIMO WiFi routers can connect to several devices but can only talk to them one at a time in a clockwise or anti clockwise manner.

When all the phones connected to the wifi are demanding big chunks of data, this will cause network lag as the router can only cater to 1 device at time before moving on to the next one.

Multiple user MIMO routers on the other hand have no such issues as it can create a separate dedicated stream for each device that it is connected to.

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