# Using MIMO in Amateur Radio?

MIMO, Multiple Input, Multiple Output, is used widely in commercial data transmission. 802.11n and LTE devices use it to increase throughput, link reliability, and channel usage without increasing transmission power or using more bandwidth.

While there are many examples of Amateur Radio enthusiasts building and used phased arrays, I haven't found any examples of MIMO use in the Amateur Radio community.

Are there good reasons MIMO isn't used in Amateur Radio? Are there examples of Amateur Radio enthusiasts building and experimenting with MIMO systems?

It seems that the increasing adoption of SDR and the continued interest in QRP would lead some down this path, but I haven't found any information about it in the Amateur community.

• I think MIMO is a pretty broad collection of techniques, and I'd consider phased arrays a subset of MIMO. Did you have something more specific in mind? I think as it stands this is an interesting question, but a bit too blunt to approach an answer effectively. – Phil Frost - W8II Nov 19 '13 at 22:32

## 3 Answers

There are a few radios that support diversity reception, but only to minimize effects of propagation rotation and multipath, not to increase data rates. This isn't true MIMO. It's more like SISO where the input is whichever one of two antennas has the strongest signal.

Which brings up another point - data. There really isn't that much data being used on ham radio at the moment. D-STAR is around, then Yaesu came out with a digital radio, and a lot of work is being done on things like Codec2 and FreeDV, but in general, it's not all that prolific.

However, MIMO in ham radio will still be reserved to things like HSMM and HamWan that actually have very large bandwidths. With that, the equipment is off-the-shelf. Some of it has MIMO capability, like 802.11N routers modified for use on amateur frequencies - just like you mentioned in your post.

It would be cool to have MIMO on lower bitrate and digital voice, but I don't think the gains would be that great.

I do undergrad research in statistical channel precoding using SDR MIMO transceivers on amateur bands, and man, is it cool...but people don't have $40,000 to spend on a MIMO IQ vector generator/demodulator. I have yet to see a QRP MIMO homebrew rig, but that would be great! Broadband Hamnet http://hsmm-mesh.org/ right now is focused on 802.11G devices, but it could grow to encompass MIMO in the future. I believe that the use of MIMO can bring significant SNR gains for the same amount of data transmitted. Even the much simpler diversity reception could already improve the minimum discernable signal a lot (comparable to a mdeium size power amplifier). Also on HF, MIMO and diversity can bring a lot of link improvement. See my scientific publications (search for 'ResearchGate' and 'Ben Witvliet'), and publications of Erhel and others. There are not many dual channel transmitters, unless you start building something yourself or use experimental equipment such as the USRP1. But for reception there are already a few dual channel receivers, e.g. the high-end FlexRadio, the HPSDR and its commercial version Apache Labs ANAN-200D. The latter is expensive, but with some$4500 much cheaper than the professional lab equipment mentioned above. I use that one for my research.

73, Ben Witvliet, PE5B