Archive for May, 2014

Beamforming Basics for the Wi-Fi Challenged

Monday, May 12th, 2014

With every new Wi-Fi technology or standard, industry fortune tellers are quick to cast adaptive antenna arrays into an early grave. This gets a little (a lot) technical, but it’s required.

Distinctly different from chip-based beamforming, for which every vendor now claims support, patented smart adaptive antennas are designed to dynamically and continuously create unique directional RF patterns (what we call BeamFlex) proven to deliver the highest throughput for each client device at longer ranges.

This innovation, yet to be duplicated in mass, has stood the test of time and remains hugely valuable in the world of Wi-Fi.

The first attempt at dumping of adaptive antenna arrays into a death spiral happened with 11a/g and its blazing fast 54 Mbps. Yet BeamFlex survived and, in fact, thrived as the RF environment became more noisy and complex.

It happened again with the introduction of the 802. 11n standard that came with the ultra-reliability of MIMO.

And, surprise, surprise, it’s happening again with the destruction (sorta) of the gigabit barrier brought by the new 802.11ac standard. The problem is, to which history now attests, BeamFlex has only proven to add more value, not less, to these technological changes.

At the core of current speculation (that adaptive antenna switching is doomed with 802.11ac) is the notion that transmit beamforming (TxBF) with 11ac replaces the need for Smart Wi-Fi. This is due to the common misconception that smart, adaptive antennas—as proprietary Ruckus BeamFlex technology—and transmit beamforming—as a standards-based technology—are one-in-the-same. This whitepaper details the differences.

Despite some similarities (such as the goal of enhancing signal quality and the use of the word “beam”), the two technologies are fundamentally different. Here’s why:

BeamFlex and TxBF are not Mutually Exclusive.

BeamFlex is truly adaptive antenna technology by which an access point (AP) selects an optimal transmit path out of many possible options. It is fundamentally an antenna technology, combining special hardware and sophisticated software, that sits on top of all radio foundations (in a protocol-agnostic way).

beamflex-transmit-beamforming

TxBF, on the other hand, is a digital signal processing technique that occurs within the transmitting radio, and is heavily protocol dependent). It attempts to send multiple copies of the same data so as to create constructive combinations at the receiving radio. The beauty of this is that BeamFlex (antenna technology) and TxBF (radio technology) can be perfectly wed; and a happy marriage it is. Ruckus can support both of these techniques at the same time to deliver a cumulative benefit to signal quality.

BeamFlex works for all clients.

Because it is an antenna technique—and not a radio technique—BeamFlex works equally well for all clients of all capabilities. This means 802.11a/b/g/n/ac clients all benefit, and there are no special requirements for support. Single-stream, two-, three- and four-stream clients all benefit, and there is no trade-off as the number of streams increases.

No transmit beamforming and Spatial Multiplexing at the Same Time.

Because it is a radio technique, effective TxBF DOES require client support (something a lot of people fail to understand). Consequently, 802.11a/b/g/n clients miss out on the perks. And some 11ac clients do not support TxBF. Looking at the pervasive adoption of 11n, we should not expect all (or even most) clients to support TxBF even by the end of 2016.

TxBF must also trade-off with spatial multiplexing. The same transmitters cannot be used for both. In order to be effective, TxBF systems should have double the number of transmit antennas as spatial streams.

1×1 clients (this means one transmit and one receive radio chain, in Wi-Fi parlance) will be happy with even a 2×2 AP; but for a 2×2 MIMO client to benefit (in any appreciable way) from an AP’s use of TxBF, a 4×4 AP is desired. This also means that a 3×3 client sees miniscule (if any) benefit from an AP that is anything less than 6×6 (yes this means 6 transmitters and 6 receivers, can you even imagine what that looks like?).

BeamFlex does not disrupt the neighbours.

As we use 5 GHz spectrum more heavily, and especially as we expand to support wider channels (80 MHz, not 160) in 11ac, we should expect to see more Wi-Fi protocol contention from APs operating on the same channel (because neighbouring APs are more likely to operate on the same channel since we have fewer non-overlapping channels). As a result, our precious 5 GHz spectrum will soon look more like the 2.4 GHz spectrum.

The value of BeamFlex directional transmissions is paramount to preserving capacity with co-channel neighbours. It does so by transmitting with directional patterns that both maximize data rates (allow clients to get on/off wireless airtime quicker) and also avoid sending RF energy where it is undesired (towards neighbouring APs). This reduces unnecessary contention with neighbouring APs, which drags down capacity.

TxBF is often visualized as a directional steering mechanism, but it works by creating signal peaks in point space (hopefully at the receiver’s antenna), which often creates signal peaks in unintended directions, causing interference where it is undesired.

Multi-User-MIMO is gold for BeamFlex

If you’re focused on 160 MHz channels in Wave2—or other Gigabit hype —you’re focused on a spec-bloated red herring. 160 MHz is for (some) consumer networks. The biggest bang from 802.11ac comes in the second wave of products (that hopefully come by Christmas of next year) and is what’s called multi-user MIMO (MU-MIMO). This is a technique by which the AP can send downlink frames to multiple clients at the same time. And this enhancement will require new hardware (yes, for everyone). It’s a lovely protocol enhancement for boosting capacity, given the plethora of very simple 1×1 mobile devices on networks. But it comes with a big catch: signal isolation.

To multiply the efficiency of spectrum with multi-user transmission, we need to ensure that each station receives its data without receiving other stations’ data at the same time (which would cause interference and make MU-MIMO not work as intended).

It’s this need for signal isolation that makes Wave2 MU-MIMO and BeamFlex a perfect complement.

BeamFlex adds directionality and signal separation (along with a boost to SNR), while the TxBF component of MU-MIMO provides additional separation at the radio level. Higher data rates per station, MU signal separation, maximum spectrum efficiency. Call it, well, the perfect storm.

Is Wi-Fi performance a commodity?

Now that we’ve further bludgeoned home the technical superiority of adaptive smart antenna arrays (BeamFlex), let’s get to the real issue.

People claim that all AP hardware is the same and 11ac commoditizes Wi-Fi performance. There are two key requirements needed for Wi-Fi performance to become a commodity:

  • There must be roughly equal—or at least “optimal”—range, capacity, throughput, optimization simplicity, reliability, and interference mitigation from all equipment suppliers, and
  • The ratio of cost-to-performance needs to be the same for all equipment suppliers.

The Ethernet Example.

If you look at Ethernet, performance commoditization is a given because both of these issues are true.

There is enough performance (Gig Ethernet has been sufficient for its application for many years), and the cost-to-performance of line-rate Gigabit switching is nearly identical across suppliers (hence, trends like NFV are occurring).

But, unequivocally, without the most diminutive doubt, the answer to the question is that Wi-Fi absolutely does not share these characteristics (and perhaps never will).

Is Wi-Fi sufficient as of 11ac, even 11ac with Wave2? Do we currently have sufficient spectrum (or spectrum efficiency) to meet all of our capacity, performance, reliability, app delivery, and network optimization needs? If the answers are no, then it stands to reason that a product supplier that enhances the Wi-Fi experience in light of these technical deficiencies could still differentiate on cost and performance alone (but no one, including Ruckus, is really doing that).

When customers start telling us that Wi-Fi performance is as reliable as it will ever need to be, there’s a surplus of radio spectrum, they have no issues connecting devices to the network and there is ample capacity to keep all users and devices happy, we will be happy to admit that adaptive smart antennas should be put to sleep.

Until then it’s simply better wireless for everyone who wants to cause a Ruckus.

To view the original article by Ruckus Wireless visit the Ruckus Room.

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