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RB | March 1, 2018

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MIMO Antennas Explained

MIMO Antennas Explained Wave 2 of the IEEE 802.11ac Wi-Fi standard has been out for a while now. Wave 2 Wi-Fi can support speeds up to 2.3 Gbps. One of the techniques used to generate the increased speeds of the 802.11ac networks is multi-spacial streams or several streams of the same Wi-Fi signal radiating out from several antennas. The multiple antennas are the most noticeable indicator that an access point is 802.11ac capable, especially in the consumer market.

Multiple-Input Multiple-Output

The technology behind using several antennas is called Multiple-Input Multiple-Output (MIMO). MIMO antennas have two or more antennas in a single physical package and are designed for use in IEEE 802.11n/ac Wi-Fi networks. MIMO makes antennas work smarter by utilizing multiple antennas to combine data streams arriving from different paths and at different times to increase data throughput and range compared to a single antenna using the same radio transmit power. By transmitting multiple data streams at the same time, wireless capacity is increased.

Additionally MIMO antennas improve link reliability and experience less fading than a single antenna system. MIMO antennas use spatial diversity technology, which puts surplus antennas to good use. When there are more antennas than spatial streams, the antennas can add receiver diversity and increase range.

Radio-wave multipath

MIMO technology takes advantage of a natural radio-wave phenomenon called multipath to improve wireless performance. In the past, multipath caused interference and slowed down wireless signals. With this iteration, Wi-Fi takes advantage of multipath. With multipath transmitted information bounces off walls, ceilings, and other objects, reaching the receiving antenna multiple times via different angles and at slightly different times

MIMO technology takes a single data stream and breaks it down into several separate data streams and sends it out over multiple antennas. This technique provides redundancy. The receiving MIMO antenna will “look” at each stream being sent to determine the strongest one to choose.

Legacy wireless devices use Single-Input Single-Output (SISO) technology. These devices cannot take advantage of multipath, and can only send or receive one spatial stream at a time.

802.11ac Wave 2 MIMO

A new version of MIMO has been developed. TechHive reports that Multi-user multiple-input, multiple-output (MU-MIMO) technology, enables AP’s to transmit and receive data from multiple Wi-Fi devices at the same time. Although the devices must also support MU-MIMO to utilize it, they aren’t required to have multiple antennas.

MU-MIMO was introduced with 802.11ac Wave 2. Wave 2 MU-MIMO support is required on both the access point and client device to work. It operates in the downstream direction, access point to the client, and allows an access point to transmit to multiple client devices simultaneously. This means networks with a dense number of users in an area, such as public Wi-Fi hotspots, could be able to handle more Wi-Fi devices.

TechHive warns the biggest caveat of MU-MIMO is it doesn’t directly improve the wireless speeds of uplink connections.

Only a handful meet the criteria today

It’s also important to note that the only way to gain the full benefit of MU-MIMO is when the technology is supported on both the access point and the device that’s connecting to the AP. So in addition to having an 802.11ac adapter onboard, the client must explicitly support MU-MIMO—there are only a handful of adapters that meet that criteria today.

Finally, TechHive says MU-MIMO works best with stationary Wi-Fi devices. If users are walking around while watching a video on a smartphone or tablet, they are not going to get the full benefit of MU-MIMO even if that device supports it. Your router might even limit that connection to using SU-MIMO, so that the connection doesn’t negatively impact stronger MU-MIMO connections.

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The client issue is the main reason 802.11ac Wave 2 will not be widely used in the enterprise. it is a big issue to keep the clients up to date to match the AP version. In fact, Zeus Kerravala at NetworkWorld points out that many of the high-volume manufacturers, such as Apple and Samsung, are skipping 802.11ac Wave 2 and plan to support IEEE 802.11ax in the future.

So skip Wave 2 devices in the enterprise and stick to an 802.11ac Wave 1 AP, and get exactly the same performance as its higher-priced Wave 2 counterpart.

Linksys Introduces Their First 11AC Wave 2 Access Point with MU-MIMO (eteknix.com)

Ralph Bach has been in IT long enough to know better and has blogged from his Bach Seat about IT, careers, and anything else that catches his attention since 2005. You can follow him on LinkedIn, Facebook, and Twitter. Email the Bach Seat here.

Category: wi-fi | Tags: 2018, 802.11ac, 802.11ax, Hertz, IEEE, ISM band, MIMO, MU-MIMO, Wi-Fi, Wireless access point

RB | April 28, 2015

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Wi-Fi Marches On

Kevin Fitchard at GigaOm lays out where Wi-Fi is headed. Now that the second wave of 802.11ac Wi-Fi equipment is hitting the market, new pans are happening. The Wi-Fi Alliance and the Institute of Electrical and Electronics Engineers (IEEE) have begun to look ahead to 802.11ac successor. This time around, the wireless industry is turning its focus away from overall network capacity to real connection speed to the device.

Mr. Fitchard explains that the huge gigabit-plus numbers often attributed to 802.11ac can be a bit misleading. They represent the overall capacity a Wi-Fi network can support. For instance, 1.3 Gbps in today’s most advanced routers, but only in the rarest of circumstances would any single device actually be able to connect at such high rates. The author argues that 802.11ac technologies improvements will be able to pack more high-speed connections into a single router and take advantage of bigger swaths of unlicensed spectrum.

Fair share

However, individual connections are still peaking at just over 300 Mbps. Assuming the broadband connection that can even support those speeds. Typical connection speeds are far slower. With 802.11ax, though, wireless engineers are making sure the individual, not just the network, gets its fair share of attention, said Greg Ennis, VP of Technology for the Wi-Fi Alliance.

Though the IEEE is still in the early stages of developing the 801.11ax specifications (we likely won’t have a ratified standard until at least 2018), it has begun setting priorities for the new technology, the Wi-Fi Alliance’s Ennis said. And at the top of that list is a 4X increase in speed to the device, possibly pushing individual device connections into the gigabit range.

MIMO-OFDA

GigaOm speculates that the IEEE is hoping to do this with a new radio technology called MIMO-OFDA. MIMO, or multiple input-multiple output, uses multiple antennas to send multiple streams of data to the same or different devices, while OFDA is a variant of the orthogonal frequency division multiplexing (OFDM) technologies used in 4G mobile and earlier Wi-Fi standards. The idea is to create a more powerful and efficient radio that can shove more bits into the same transmission. That would create a bigger data pipe to the individual devices, which would, in turn, add up to greater overall network capacity and better Wi-Fi performance even in the sketchiest of conditions, Mr. Ennis said. “The goal here is not just to increase average throughput, but the average throughput users would actually see in the real world, even in the densest environments,” Ennis said.

Chinese equipment maker Huawei (002502) — which is heading up the IEEE 802.11ax working group — is already doing trials of MIMO-OFDA systems and it’s hitting 10.53 Gbps in the lab using Wi-Fi’s traditional 5 GHz band. Whether that means a 10 Gbps to your smartphone or tablet remains to be seen, but it hardly seems relevant given it’s difficult to comprehend what any device could possibly do with a 10 Gbps connection (much less a home broadband connection capable of supporting a high-capacity link).

Faster simultaneous Wi-Fi connections

But if 802.11ax lives up to its promise, the author says it should be able to squeeze a lot more and a lot faster simultaneous connections out of a single router or hotspot, which would mean a far better experience for everyone on a crowded network. Though the IEEE won’t ratify 802.11ax until 2018 or later, we might see the Wi-Fi Alliance certify “draft-ax” devices and equipment beforehand just as we saw “draft-n” and “draft-ac” devices before their respective 802.11 standards were finalized. It all depends on how far the wireless industry has progressed with the underlying technology in the coming years, Ennis said. A range comparison for different Wi-Fi technologies. And long before we see the “ax” suffix stamped onto any gadget or router, other combinations of the Wi-Fi alphabet will make an appearance.

The Alliance will begin certifying the first 802.11ad, or WiGig, devices next year, supporting extremely close range but very high-capacity links between gadgets and peripherals. A bit further down the road is 802.11ah, which will take Wi-Fi to the 900 MHz band where it will provide narrowband but long-range connectivity to the internet of things.