The Ruckus Room

802.11ac Boosts Buzz More than Bandwidth

The buzz about 802.11ac is in full swing.  But don’t believe everything you read.

The newest of Wi-Fi innovation,the IEEE 802.11ac (still in draft form) looks like it will start making it into enterprise Wi-Fi products as early 2013 and home products even earlier. It’s already being flaunted as Gigabit Wi-Fi. And for the largest Wi-Fi market (the home) it will be. But will it deliver gigabit speeds for the enterprise? Not a chance.  

Defined for the capacity-rich 5GHz spectrum (495MHz) only, 802.11ac introduces a number of new techniques like advanced modulation and encoding, multi-user MIMO and channel bonding, that theoretically, if you’re talking to a vendor anyway, has the potential to dramatically increase Wi-Fi capacity. 

The question is REALLY?

Make no mistake, 802.11ac is a great innovation.  But like any great innovation, the devil is often in the details.  So here are some details that should help demystify the newest, bestest Wi-Fi technology coming soon.

Here's a quick, technoid tutorial on 802.11ac.

 
Eight Spatial Streams

One of the biggest Wi-Fi innovations came with 802.11n the form of spatial multiplexing using a technical called MIMO (multiple input, multiple output). This lets an access point send multiple spatial streams to one client at a time to increase capacity. 802.11n specified up to four spatial streams.

Now in glorious one-upmanship, 802.11ac will support up to 8 spatial streams. Historically it has taken chip manufacturers about two years to add an additional spatial stream (802.11n is only at three right now). While that will surely improve with 802.11ac, don’t look for it to ever get to eight. However it would be a funny sight to see. Just picture an AP with 12 (8 for 11ac in 5 GHz and 4 for 11n in 2.4GHz) omni-directional antennas sticking out of it. Not a pretty picture.  Even if the antennas are integrated, still ugly.
 

Multi-User MIMO

802.11n gave us MIMO (multiple in, multiple out). MIMO is the use of multiple antennas at both the transmitter and receiver to increase data throughput without additional bandwidth or increased transmit power.  Basically it spreads the same total transmit power over the antennas to achieve more bits per second per hertz of bandwidth with the added benefit of greater reliability due to more antenna diversity. With 802.11n, MIMO could only be used for a single client and any given time. 802.11ac tries to improve on this with what they call “multi-user (MU) MIMO.”

This allows an 802.11ac AP to transmit two (or more depending on number of radio chains) spatial streams to two or more client devices. This has the potential to be a good improvement but is optional.  And it’s expected that the first 802.11ac chips out the door won’t support this. What’s more, there’s is a good chance that MU-MIMO won’t ever be supported due to the radio and MAC complexity required.

256 Quadrature Amplitude Modulation (QAM)

QAM is a way to modulate radio waves to transmit data. 802.11n maxed out at 64QAM so the advent of 256QAM should deliver big improvements in maximum throughput. However, the more complex a modulation scheme, the more difficult it is to achieve. In realistic situations it is highly unlikely that any percentage of client devices would consistently achieve 256QAM. Ouch. 
 

5GHz Only

Due to how 11ac really achieves all this speed (channel bonding) it doesn’t make sense for 11ac support 2.4GHz that only has three (of 11) non-overlapping channels. This is great news! What this means is that devices that want to have 11ac will be 5GHz capable. Right now it is a very low percentage that are capable of 5GHz and that is a real shame. Now they’ll be required to do it.

Channel Bonding

An easy and effective method to increase the speed of any radio communication is to give it more frequency.  Outside the radioheads, this is known as bandwidth. To get more bandwidth, 802.11n introduced us to channel bonding: the ability to take two 20MHz channels and make them work as one – basically a bigger Wi-Fi pipe. This effectively doubled throughput that could be achieved.

Now 802.11ac has mandated the support of 80MHz channels with options to bond 8 channels for a total channel of 160MHz.

Even with 802.11n, channel bonding is a double-edged sword. In North America, the 2.4GHz band has 83.5MHz (3 non-overlapping channels) of total bandwidth while the 5GHz bands have a total of 495MHz. That means that 5GHz can carry almost 6 times the traffic of 2.4GHz plus the added benefit that (for now) the 5GHz band is a much cleaner spectrum. 

But don’t count your bits quite yet. What most people don’t realize is that by enabling channel bonding you are actually reducing your overall capacity (see chart below).

When designing and deploying a Wi-Fi network for high density, more channels are preferred to fewer, larger channels. Increasing the number of devices occupying one channel in a given area makes reduces the efficiency of Wi-Fi.

This is why people like wires. Because each device effectively has its own channel and there are no other devices occupying that channel (the copper or fiber). So we see staggering amounts of throughput.

If Wi-Fi could have 100’s of channels, and each client would get their own, this would be wireless nirvana. But as you can see from that chart, we don’t have that many channels and we sure don’t want to exacerbate the problem by bonding them together if it reduces the overall efficiency of the wireless LAN.

Using 802.11ac in the home is a different story.  Bonding channels all the way to 160MHz is preferred given there are few devices trying to access a single AP.

The enterprise is just the opposite. Here, numerous APs are required to support hundreds or thousands of users. And, as much as is possible, those APs should be on different channels.

Ultimately 802.11ac offers improvements for the Wi-Fi industry primarily because it forces clients to add support for the capacity-rich 5GHz spectrum.  Current enterprise APs already support both bands.

Ironically 802.11ac will prolong the viability of current 802.11n networks. As more and more clients become 5GHz capable, capacity and performance will increase without touching the infrastructure.  This is the best news of all.

Wi-Fi for Cellular Backhaul? Really.

The move to smaller cells to augment existing macro mobile network is widely viewed as a potential panacea to the access radio network congestion problem.  But it also directly creates a new one: backhaul. This has become one of the telecom industry’s hottest debates.

Small cells are low-powered, multi-radio access points (cellular / Wi-Fi / backhaul) that improve indoor and outdoor coverage to increase capacity and offload traffic - as much as 80% during peak times.

While small cells benefit 3G service deployments, today, their importance will only grow as the industry moves towards higher capacity 4G / LTE, especially in urban environments. According to In-Stat’s latest report, Femtocells and Small Cells: Making the Most of Megahertz, small cell shipments will reach $14 billion in 2015.

The problem is, as network operators continue to increase coverage and capacity and look to offload data to relieve traffic pressures, they also increase the stress on their cell site backhaul connectivity. In this small cell world, conventional point-to-point microwave, bonded copper, and fiber-based backhaul solutions can quickly become impractical or uneconomical.

While microwave point-to-point equipment costs have come down in recent years, it generally requires a line-of-sight (LOS) link with the connecting backhaul hub, a condition many small-cell locations will be unable to meet. Sub-6 GHz NLOS solutions using a point-to-multipoint architecture are better suited for dense underlays, but when using licensed spectrum, narrow bandwidth channels put strict limits on backhaul capacity, and most sub-6 GHz spectrum bands are expensive and frequently not available for licensing.

Another choice, fiber, is clearly the preferred backhaul option for mobile operators (if you can get it). But pulling fiber to every small cell location is, well, just not going to happen. It’s simply too expensive, disruptive and time consuming. Consequently, traditional cellular backhaul solutions must now be rethought in the context of moving to smaller cells.

New backhaul options, well suited for dense urban environments and for close-to-the ground equipment (both LOS and NLOS), are required to make small cells viable.

Counterintuitive to most, unlicensed smart Wi-Fi has become a viable and affordable option to solve this problem and looks to play a crucial role in backhauling licensed small cell traffic. Yes, cellular traffic. Here’s why:

Assume a mobile network operator (MNO) deploys an infill underlay radio network of small cells to add access capacity to areas where there is a high density of mobile data users, perhaps in an urban city center such as in London, New York, or Hong Kong.

Today this small cell network would likely be comprised of lower-powered 3G and/or Wi-Fi nodes, or possibly in the future LTE radio nodes. No matter what the access radio technology is used, how does the operator get the data from the access radio node back to the network?

One obvious high performance solution is fiber, assuming that it’s available. The operator may have to lease this fiber from a fixed line carrier which drives up operational costs, but perhaps more significantly there is the very real possibility that the fiber POPs will not exist in specific locations where the MNO needs to place the small cell.

The reality is that small cells only increase network capacity if you place them in close proximity to subscribers trying to access the network. Site acquisition, then, becomes a major determinant in the relative effectiveness of the small cell deployment.

This then poses a very real problem – given the constraints of where operators must place small cells. It is highly unlikely that a fiber POP will exist in all of those locations. And given the cost and time delays of provisioning new fiber runs to each small cell location, an alternative solution is clearly needed.

Microwave radio links are of course a well-understood alternative technology that can be used to at least partially address the problem. But while microwave point-to-point (PtP) links are high performance, reliable workhorses for backhauling data and voice traffic, they have issues.

First and foremost, PtP microwave solutions generally rely on licensed radio bands for transmission. This improves reliability but acquiring more licensed spectrum takes deep pockets filled with lots of cash. Also radio capacity is directly related to how much spectrum is used for the radio transmissions.

This means deploying more capacity on the access radio side exacerbates both the cost and the shortage of spectrum for the backhaul radio network. Add to this the problem that PtP radio links require highly skilled installation to aim or align the radio nodes. In a crowded urban area or near street level, this quickly becomes an onerous task.

Using the Unlicensed Band for Transporting Licensed Band Traffic?

Exactly. Wi-Fi has evolved to become an ideal solution for this small cell backhaul problem – if done properly.

New Wi-Fi technology now combines adaptive directional antennas with smart meshing technology and predictive channel management – all used within the channel-rich 5GHz 802.11n spectrum.

Adaptive antenna arrays deliver more signal and reliable client connectivity at longer ranges by focusing RF energy only where it helps deliver the best throughput across a specified link. As the environment changes, these smart antennas mitigate Wi-Fi and non-Wi-Fi interference, constantly selecting better signal paths that yield the highest data rates and lowest latency at any given time.When used within the 5GHz band, these antenna arrays become ideal for constructing highly resilient, long range, adaptive backhaul connections between Wi-Fi nodes.

Now add to this, predictive channel management that optimizes RF channel selection to maximize network capacity specifically in high-density, noisy public Wi-Fi environments. It does this by measuring actual channel throughput and building a statistical model that allows access points to learn over time what channel will yield the highest capacity. By relying on real-time observed capacity on all 2.4 and 5GHz frequencies, backhaul links can be automatically moved to a better channel with less interference to realize higher data rates and greater reliability.

Finally utilizing smart mesh techniques with adaptive antenna arrays as an alternative to fixed PtP links eliminates much of the complexity associated with aiming and alignment during the installation process. This also results in a much more affordable solution with greater resiliency in crowded urban environments given its intrinsic capabilities to dynamically adjust to changing conditions by choosing alternate paths to the network.

In live field trials with multiple network operators today, this small cell Wi-Fi backhaul approach has proven to deliver reliable, carrier grade transport of 3G mobile data and circuit switched voice traffic along with the prioritized transport of timing signals (eg. IEEE 1588v2/PTP or NTP) necessary for small cell network synchronization.

Wi-Fi backhaul technology is currently being built into small cell nodes housing cellular and Wi-Fi access – within a fairly small footprint. This allows operators to deploy a single box to provide Wi-Fi access, cellular access and backhaul together.

We happen to believe this is a ruckus in the making.

Channel Changing Done Right

Since the inception of Wi-Fi there has been an ongoing debate about how APs should pick the best RF channel to yield the highest capacity for clients. Of the 11 channels available in North America, conventional Wi-Fi wisdom states that only channels 1, 6 and 11 should be used but those could actually be the worst channel choices.

Channel Basics

Think of each channel as a lane on a freeway and each lane has a defined width. Every Wi-Fi channel has a width of 5 MHz. The problem is, a typical Wi-Fi transmission takes up 4 lanes (20 MHz) of traffic. 

This chart shows channels 1, 6 and 11 and their respective frequencies. If you were to have two access points, one on channel 1 and the other on channel 2, they will overlap. Depending on the attenuation (signal loss) between each AP, this can cause some interesting issues. If the APs are in signal range of each other they will actually cause interference. 

The way to combat this channel overlapping problem is to skip channels when deploying Wi-Fi. This is why Wi-Fi deployments typically choose channels 1, 6 and 11. Choosing these channels results in 3 non-overlapping (non-interfering) channels. In a perfectly clean environment where no sources of outside interference can be guaranteed, the chosen 3-channel model is the right way to go. 

But what is the right channel when deploying a WLAN in Manhattan, San Francisco or a noisy hospital or school with sources of interference? Other Wi-Fi systems or sources of interference can dramatically reduce performance of any system. Beyond fancy signal path section technology using adaptive antenna arrays, intelligent channel selection is another important way of dealing with interference and increasing the capacity of Wi-Fi networks.

Every vendor has a different take on how to choose the proper channel. Some with built in spectrum analyzers will scan the spectrum and choose the best channel based on what it sees. On the surface this may seem like a good way to determine the right channel but in practice, it doesn’t work very well. Here’s why.

Let’s say you are on stage about ready to speak. Papers are rustling and there are other people having whispered conversations. If you speak, will people hear you? How well will they hear you? You can’t know if they will hear you just by listening. The only way to find out is to talk and observe the results. 

An AP that just listening will give you information about the noise but doesn’t really know how well it will be able to communicate with the clients. Why? Because the AP doesn’t have the same perspective of the client.

Today's Channel Changing Convention

Almost all of today’s channel optimization approaches use background checking methods to identify a better channel in case of throughput degradation in the current channel.  When conducting background checking, the AP jumps to other channels to passively listen for packet retries, transmission errors and RF interference when they it is idle — not sending or receiving data. 

These approaches provide incomplete information for channel selection, as they are not able to measure realizable channel capacity and are a equivalent to a random guess at which alternative channel might provide better results.  In addition, the process of background checking creates “dead time” when the AP is busy checking other channels and may miss transmission from clients.  Although the dead time is short, it can seriously affect client activities and channel performance when bandwidth demands and utilization are high.

The only thing that really matters when choosing channels is channel capacity. Why not choose the best RF channel with the highest capacity?  A new technology called ChannelFly does just that.

Introducing ChannelFly

ChannelFly is a statistical, adaptive channel selection technique optimized around maximum system throughput.  It relies on real time observed capacity on all channels in both 2.4GHz and 5 GHz frequencies to automatically move clients to a better channel with less interference and higher capacity.

Borrowing patented techniques from our popular BeamFlex technology that automatically selects the best Wi-Fi signal path based on actual acknowledgements from each client, ChannelFly learns the proper channel because it knows, at all times, what the capacity is of the channel.  Our new and unique approach involves assessment across all available channels, based on actual realizable capacity, before making any decisions about changes. 

ChannelFly achieves superior results by utilizing actual channel throughput measurements rather than just listening and guessing. The AP will always be in service for its clients.  ChannelFly learns each channel’s conditions by periodically changing channels across 2.4GHz or 5GHz bands. This can be done with or without active clients.  

Once representative statistical capacity data for each channel is learned, the AP will select the best channel less frequently but continue to monitor channel capacity. If a significant drop in capacity occurs on the current channel, ChannelFly can immediately react by switching to a better channel. Operating with or without client activity enables administrators to allow APs to self-tune before any client devices are connected, therefore greatly improve overall channel performance with minimal network disruption.

With ChannelFly in very congested environments, customers have observed a 25% or more increase in channel capacity. ChannelFly, like adaptive antennas, is another advancement by Ruckus to improve the capacity and reliability of Wi-Fi. Because in the end, people only care about two things: 1) connecting reliably and 2) going fast. And we couldn't agree more.

Let's Get Small

The mayor of London today (Big Borris) worried out loud about the prospects of UK mobile data networks melting over the load of data expected to hit during the Olympics. And he’s right.

This is a HUGE issue making its way across the globe as cellular networks, initially designed for voice traffic, are faced with having to accommodate monstrous volumes of data traffic. 

While macro cellular networks will continue to guarantee wide-area coverage, operators are rushing to find complementary alternatives that help ease the pressure, especially in high-traffic areas.

Wi-Fi offload is widely considered one of the best solutions in areas where 3G/4G subscriber density and usage is high – such as urban areas, and locations like airports or stadiums.

Operators are also exploring additional solutions, such as small cell underlays to address high capacity density, and complement and strengthen their Wi‑Fi and macro deployments.

Mobile operators can further improve network utilization by actively managing the traffic beyond the RAN within the core, using content caching, tiered pricing, and policy enforcement. While these solutions do not increase capacity, they make data transmission more efficient, letting operators to pack more content within the same infrastructure.

Bucking Convention with a Different Type of Decongestant

Convention says to simply increase cellular capacity to boost cell density. This has been effective for awhile, but suffers from diminishing returns for a bunch of reasons as bandwidth demand accelerates. High-traffic areas are, for the most part, in urban centers where deploying and operating equipment is more expensive, and where space can be difficult to obtain.  And as the density of macro cells increases, interference become much more difficult to manage with per-sector throughput declining as a result.

A different approach is needed to deliver an increase in capacity of the magnitude sufficient to deal with out-of-control data traffic. This approach is predicated on lower-power, shorter-range equipment such as Smart Wi-Fi access points or 4G small cells installed closer to subscribers, in dense deployments. By limiting the range, the impact of interference is reduced while capacity density is increased. A single sector in a macro cell may have a comparable capacity to a Wi-Fi access point or a small cell, but it spreads it over a larger area, leading inevitably to lower capacity density.

To address these issues, mobile operators are looking at anything and everything including:

• Upgrading the 3G HSPA network
  where it makes technical and financial sense, but realize that this does not provide the increase in capacity that is required in high-traffic areas,
   
• Building a Wi-Fi underlay network
  for mobile data offload to address the immediate need for additional capacity,  
   
• Purchasing more RF spectrum
  as operators move to macros LTE to establish coverage, promote device adoption, and maintain access for high-mobility users,
   
• Rolling out a small-cell LTE underlay network
  to provide additional capacity where needed, once LTE device adoption takes off. The small-cell LTE network complements the Wi-Fi network (and to a large extent it is expected to cover the same high-traffic areas) and the LTE macro network (mostly deployed for coverage and high-mobility access) to provide an additional capacity boost, and
   
• Using 5GHz Wi-Fi for NLOS backhaul
  as lots of smaller cells make it nearly impossible to run expensive fiber or firxed broaddband connections everywhere.

Small cell deployments are one of the most popular long-term strategies of mobile operators worldwide because they provide the capacity boost needed in the near term, along with the flexibility and compact form factor needed for highly-localized deployments in high-traffic environments.

Download Small-Cell White Paper

Mobile operators no longer see Wi-Fi offload and small cells as competing solutions. They realize both are needed with each playing an important role within a multi-RAT, multi-layercellular network – spanning from macro base stations at one end to residential femto cells at the other.

Once a mobile operator has Wi-Fi offload infrastructure in place, it has done most of the hard work to roll out LTE small cells. Thanks to its early Wi-Fi “land grab”, it has secured a network of permitted Wi-Fi access points and small cell sites, with power, backhaul, and lease agreements, ahead of its competitors without Wi-Fi offload. Access to small cell mounting real estate is crucial to keep installation and operation costs down, and to reduce deployment times.

Not only can Wi-Fi and LTE operate side by side, but they completely complement each other in an integrated deployment strategy, delivering the highest capacity increase afforded by next generation radio technology and spectrum availability, combined with the lowest TCO.

The initial deployment of an IEEE 802.11n Wi-Fi offload solution (if it's Smart) provides mobile operators with an immediate capacity increase, available to most data-centric devices already in the hands of their subscribers. But, equally importantly, the Wi-Fi infrastructure provides the foundation on which mobile operators can realize their longer-term data strategy, by establishing a network of sites that can be shared by Wi-Fi and LTE small cells. Once they decide to roll out LTE small cells, operators can simply add an LTE small module to their Wi-Fi access points – sharing lease costs and backhaul capacity.

This small cell strategy looks to deliver BIG time benefits. 

Nice Wi-Fi login screen

Anal About Antennas

When it comes to Wi-Fi, we spend a lot of time spewing the value of antennas - so much so that we often get stereotyped as an antenna company.  We're not.  We have nearly 30 patents now (with another 50 pending on everything from multicast-to-unicast conversion to dynamic pre-shared keys).

But there's one absolute truth that is undeniable:
wireless LAN controllers do nothing to inherently improve Wi-Fi performance.

Period.  

Yes, they add important capabilities that make integration and management of Wi-Fi much better, but they simply can't make signals stronger. And it's strong signals (and low noise) that increases wireless performance and stability to clients. 

Truth is, the vast majority of wireless LAN companies aren't REALLY wireless companies. They are wireless management or security companies.  Every WLAN supplier today has access to the same Wi-Fi chips from Atheros, Broadcom and Marvell but add little or no value to the actual radio interface beyond the silicon vendors' standard reference design.

So what's the value-add that sets on AP apart from another?  For one thing - you guessed it - better antennas.  

Antenna Primer.

The antenna is where radio waves hit the air for the very first time, shaping the RF energy (or waves) and transmitting them to requesting stations — setting the stage for RF performance. Different antennas connected to the same radio typically result in wildly different performance numbers. It’s important to remember that antennas cannot add power to a wireless signal but can focus the RF energy.

Once an RF signal has left the AP’s antenna there is nothing else the radio can do to make it better (or worse). Once a signal has been sent, it either reaches the client within a certain period of time, or it doesn’t. Clearly, Wi-Fi performance is heavily dependent on radio antenna performance. Up until the radio, it’s pure IP networking. But after the radio, how signals are sent and received has the single, most dramatic effect on the stability and performance of a Wi-Fi network.

Three characteristics create huge differences in performance between one antenna and another — even when connected to the same radio: signal gain, directionality and polarity.

Signal Gain
Gain is a measurement of the degree of direction within an antenna’s radiation pattern. An antenna with a low signal gain transmits with about the same power in all directions. Conversely, a high-gain antenna typically transmits in a particular direction. Signal gain focuses the RF emission and improves signal quality, but it doesn’t add power.

Directionality
Signal gain can also be achieved by changing directionality to an RF signal (i.e., antenna sends more energy in one direction at the expense of another). Even omnidirectional antennas have some small amount of signal gain which is why RF patterns are not a perfect spherical shape. Directional antennas are used when signal is desired in a specific direction. A wireless bridge is a good example of when to use a directional antenna because the receiving end of the bridge is effectively fixed and won’t move. So, instead of wasting precious RF energy transmitting to where the bridge is not located, push all of the RF transmissions in the right direction.

Polarization
Discussed in our previous post, polarization is the orientation of the signal as it leaves the antenna and is important because it describes the orientation in which most signals will be transmitted. Any Wi-Fi device must have an antenna, and that antenna has a polarization. Many Wi-Fi clients use vertically polarized antennas. APs equipped with “rubber ducky” (dipole omnidirectional) style antennas are usually polarized in one direction. A common problem is that orientation can be good for some clients but may not be optimal for others.

Interference
Unwanted RF energy is generally referred to as interference, whether it is from an 802.11 device or not. When the transmission is on the same frequency (channel) as other Wi-Fi devices, this is co-channel interference. Co-channel interference can dramatically degrade Wi-Fi performance.

Access points equipped with dipole, omni antennas have few degrees of freedom, when dealing with interference. Interference causes packet loss, which forces retransmissions, that drives delays for all clients trying to access the medium. Access points unable to manipulate Wi-Fi signals typically lower their physical data (PHY) rate until some level of acceptable transmission is achieved.

To solve these problems, miniaturized antenna arrays that can uniquely direct RF energy (Wi-Fi signals) to each client and automatically "steer" these signals over the fastest paths based on feedback from the client solve most of these issues.

Ideally, omnidirectional coverage is desired but with directional performance coupled with the ability mitigate RF interference This precisely what smart antennas provide.

But don't believe us. Just take a look at the recent WLAN tests performed by Tom's Hardware. This pretty much tells the story. 

A Polarizing Problem

"iEverything" (wireless only) devices that don’t have an Ethernet connection will soon outnumber those that do. Unlike laptops, these devices enable truly mobile network computing.

This is a profound and fundamental shift that changes everything for computer networks - placing a BIG spotlight on the imperative to improve Wi-Fi communications.

We'll say this a couple times: with wireless, good speed is ALL about good signal. While bigger, stronger antennas have a significant impact on better Wi-Fi performance, other things related to antennas matter too. Arguably just as important to bigness is antenna orientation and the polarity of RF signals. 

An antenna provides three things to a radio: gain, direction and polarity. Gain is the amount of increase in energy that an antenna adds to the RF signal. Direction refers to the shape of the transmission, which describes the coverage area. Polarity is the orientation of the electric field (transmission) from the antenna. 

Understanding Polarity

Wave your hand up and down like you do when you put your hand out of the car window. That up and down movement of waves is called vertical polarity (VPOL). The opposite of vertical polarity is horizontal polarity (HPOL) which is like a snake slithering in the desert; waves that move from side to side. For an antenna to transmit waves vertically the antenna will be vertical and if an antenna is horizontal, the polarity is also horizontal. 

Here’s the scary part. Horizontal and vertical signals are so different that they aren’t compatible. If you have a perfectly vertical signal hit a perfectly horizontal antenna, that horizontal antenna doesn’t hear anything. Many times, in indoor environments, signals bounce off walls and things (called multipath by geeks) This can change the polarity of signals.

That said, in a linearly polarized system, a misalignment of polarization of 45 degrees can degrade the signal up to 3dB and if misaligned and 90 degrees the attenuation can be more than 20dB. That just sucks. Don't believe us?  Read some "real world" comments from Joe McBreen, who runs IT for a huge school district, St. Vrain Valley School District, in Colorado.

Which Way is Up?

Until fairly recently most wireless devices didn't move much. Laptops typically sit in one spot with the screen up (the antennas are usually behind the screen). And, until recently, the orientation of cellular phones has also been straight up and down because there were only used for talking, not computing per se.

Today, things couldn't be more different. Devices such as iPhones and iPads are so versatile they are moved around in almost every imaginable position. In the Wi-Fi world this is like someone on your roof moving your old free-to-air VHS antenna around with your picture fading in and out. Basically, every time you change the orientation of the device you are also changing the orientation (read: polarity) of the antenna of that device - and most of today's Wi-Fi APs can't do anything to deal with this.  

The Big Rub

Nearly every (non-Ruckus) Wi-Fi access point sold today utilizes omni-directional, "dipole" antennas that are vertically polarized. These have been accepted and considered “normal” for quite some time and for good reason. Prior to the mobile Internet boom, most devices were also vertically polarized and everything worked fine. But here's the rub. Any time your client device isn’t in the perfect orientation, the signal from the omni-directional AP is diminished which results in range, throughput and reliability all suffering. 

Adapt or Die

Contrary to an omni-directional antenna, adaptive antenna arrays (found in Ruckus APs) are designed with both horizontal and vertical antennas. This is much more difficult to do than it may seem. Some of you have already thought, “Well, I’ll just change the orientation of a few omni antennas and fix that polarity problem!” Unfortunately, that won’t work. It gets pretty complicated but what you would be doing is changing the coverage pattern of those antenna(s) but not others. This would seriously mess up your throughput and range of an 802.11n system. 

Giving It to You Straight (or Sideways)

Anytime a Ruckus AP transmits, it matches the polarity of the receiving device. It can use one or both polarities to ensure that the receiver hears as well as is possible. Conversely, every time a Ruckus AP hears a transmission from a client device we adjust how we will talk to them. It’s like playing Marco Polo in the pool. We know where people are just by listening; we don’t need to see them. 

Just Listen!

Since APs can’t control the orientation of the client antenna, it's important to listen on all polarities. This is done with Polarization Diversity Maximal Ratio Combining (PD-MRC). MRC (click on diagram) is an 802.11n standard way of being able to combine multiple multipath transmissions into one good signal. PD-MRC is a way to do the same thing, except with the ability to combine multiple signals of varying polarities. This allows a Ruckus AP to accurately listen better to a client device, no matter how it is oriented. 

From the onset, Ruckus has been (and continues to be) focused on ways to solve the major problem that plagues Wi-Fi networks: optimizing Wi-Fi signaling. To really improve Wi-Fi performance you need to actually improve how Wi-Fi signals are transmitted and received. This will have (by far) the single biggest impact on Wi-Fi performance. At the end of the day, no matter what Wi-Fi equipment suppliers tell you, the more signal you can deliver to your clients, the faster they will be able to send and receive information. 

Ironically, the vast majority of Wi-Fi vendors focus on how to improve Wi-Fi AFTER clients are connected and doing nothing to really make Wi-Fi better. So are they really Wi-Fi vendors? Hmmmmm.

Simplify. Secure. Roam. Repeat.

Still a sore point for many enterprises, secure roaming for Wi-Fi clients doesn't have to be such as chore.

When the IEEE created the 802.11i amendment for Wi-Fi security it did a great job of providing a framework for Wi-Fi security but a not-so-great job with secure roaming. Within the 802.11i spec, 802.1X is effectively the foundation for this enterprise framework. Excellent for carriers and huge Fortune 500 enterprises with large IT staff, 802.1X is state-of-the-art when it comes to wired/wireless security. But what about the unfortunate 50,000?

Originally developed as a port-based wired authentication protocol, 802.1X was adapted for Wi-Fi use within the 802.11i standard but is notoriously slow for client roaming. Not to worry, Wi-Fi devices are still safe when they roam. Yet with 802.1X, more than likely they won?t do it with any great sense of urgency. Here's why:

The majority of 802.1X systems require a RADIUS server to verify the credentials of the wireless user. The first time this happens is during initial association, which is completely normal. What occurs next is where the problem lies. Without 802.1X security a Wi-Fi client can roam quite quickly; somewhere in the neighborhood of <20 milliseconds - plenty fast for any streaming application like voice and video.

802.11i, however, specifies that a Wi-Fi client re-authenticate to the RADIUS server every time it roams to a new AP. Depending on the speed of your wired network and how fast your RADIUS server can respond, the total time will more than likely exceed appropriate roaming times and cause an interruption to your voice or video service. 

The IEEE responded to this problem with the 802.11r (think R for roaming) amendment. 802.11r specifies methods for fast secure roaming that solves this problem by redefining the security key negotiation protocol. This allows both the negotiation and requests for wireless resources to occur in parallel. The approach is to allow part of the key (the shared secret between the authentication server and client) derived from the server to be cached in the wireless network.

Without 802.11r, when a 802.1X client roams it is treated like a new client and must verify credentials with the RADIUS server. 802.11r fixed that by requiring that the supplicant (client) send a PMKID (pairwise master key identifier) to the Wi-Fi system during roaming. When the Wi-Fi system receives that PMKID, it will go through the normal 4-way handshake (which is responsible for encryption) without the need of contacting the RADIUS server.  So, if you?re going to use WPA2-Enterprise, which requires 802.1X authentication, your client will need some kind of fast roaming mechanism if it is running any sort of delay-sensitive application.  

That's what 802.11r was designed to deliver (here's a good primer on 802.11r).

So what's the problem then? In a word: implementation. Or in another word: complexity.  

Ultimately, there is no real standard for secure roaming that can be used by a majority of client devices. 802.11r and the ever upcoming Wi-Fi Alliance Voice-Enterprise certification offers standardized 802.1X roaming support, but just a few clients claim to support it and even those seem to be hit and miss. Most wireless vendors have fixed the problem on the infrastructure side, but since most of us don?t make the client devices we are at their mercy. So how can you get enterprise-grade security that 802.1X promises without all the hassle?  The answer? Dynamic Pre Shared Keys.

A patented a technique called Dynamic Pre-Shared Keys (DPSK) delivers the best of both worlds: the simplicity of pre-shared keys (without the sharing part) and 802.1X (with out the complexity part). But even more important, we've made it brain dead simple.  

DPSK gives you 802.1X level security that roams perfectly with every client produced since the introduction of WPA. It does this by automatically generating a unique 63-byte passphrase for each client that successfully passes authentication against your Zone Director, RADIUS, LDAP or active directory servers. 

The first time a user connects to the network and is challenged with a username and password.  If they successfully authenticate, the system generates a unique passphrase for that client, binding it to the MAC address of the device.  It then automatically installs that passphrase and the requisite wireless configuration info (eg. SSID, the key itself, etc.) on the client. Current customers successfully deploy DPSK security without EVER touching the end user?s device.  What happens if a user is no longer valid? Set time limits on their key or invalidate their key with one click. 

Oh, and to deploy it on every device in your network you don?t need certificates, a RADIUS server or weeks of training. Give us 15 minutes (if that) and you'll have a secure Wi-Fi network that will roam faster than 802.1X ever has, or maybe ever will.  

802.11u and You and You and You

When an IEEE protocol has its own Facebook page, you KNOW the world has gone crazy.  Or has it?

802.11u is a little-known protocol extension (soon to be standard) that stands to have a BIG impact on the user experience of emerging mobile Wi-Fi networks being built by operators. The key for widespread adoption of 802.11u ultimately rests in the hands of the Wi-Fi Alliance and its industry certification process. 

Requiring changes to both clients as well as infrastructure devices, 802.11u was developed to effectively automate (make simpler) how Wi-Fi devices connect to available Wi-Fi networks. The MAC-layer enhancement assists the advertising and connection to remote services by providing information to clients about the external networks available prior to association. 802.11u enables Wi-Fi hotspots to advertise themselves and devices to connect to them using, for example, SIM-based authentication rather than requiring the end user to select an SSID number. 

From a user perspective, the aim is to improve the experience of a traveling user who turns on a laptop in a hotel many miles from home. Instead of being presented with a long list of largely meaningless SSIDs the user could be presented with a list of networks, the services they provide, and the conditions under which the user could access them including indications that a selected network that is being advertised has valid roaming agreements in place with the user’s home network provider.

Typically, when a Wi-Fi device scans the RF environment it can find tens or even hundreds of Wi-Fi networks. How should it select the right one?  If the client doesn't recognize a given SSID, it doesn't know whether it has the right security credentials to connect, whether it has a service plan that applies, or even whether the Wi-Fi network being advertised provides Internet access at all. So devices don't know whether or not to attempt an association. Meanwhile the battery on the mobile devices is being drained.

With 802.11u clients can selectively scan for the desired network type. Bits are set in probe requests that alert APs to the type of Wi-Fi network the client is looking for.  Conversely, special bits can be set in the AP beaconing mechanism to advertise the different network services available to clients.

With 802.11u running, a Wi-Fi client can request a list of all the mobile operators' names that are allowed to automatically connect to the Wi-Fi hotspot. If your operator's name is on the list, your device will automatically authenticate and offload.  

No doubt 802.11u will be a huge help in delivering a seamless subscriber experience, eliminating the need for users to fiddle with configuring their mobile devices.  And at Ruckus, we're anti-fiddling – so stay tuned.

 

Dealing with Density

Our traffic problems aren’t going to getting any better anytime soon.  

More licensed drivers are taking to the roads than ever before. The logical solution would be to build more and wider roads. But what if we just used the road more efficiently?  Exactly. The same is true with Wi-Fi.

Wi-Fi has speed limits that are set by current technology and the laws of physics. Basically, every Wi-Fi vendor can go the same, maximum speed just like most cars can go the speed limit. So if everyone is limited to the same speed, how can one vendor have an advantage in capacity?

Wi-Fi vendors are constantly asked how many concurrent clients a given AP can handle.  The answer is always the same - about 100 to 150. That's basically not so true. Sure, with enough memory an AP can handle 100+ client associations but that's without any data being sent. So what good is that?

When it comes to high capacity Wi-Fi it really isn't about how many concurrent clients your AP can handle, it's about how effectively a system can manage and optimize the use of the radio spectrum.  That's the real limiting factor when it comes to client density because there's only so much of it.

Spectrum, also known as RF bandwidth, is the amount of frequency allocated for our use. North America has about 83.5 MHz in the 2.4 GHz band (60 MHz of which is actually used) and depending on regulations, around 200 MHz in the 5 GHz band. These are hard limits that cannot be broken by one vendor or another. So we all have the same amount of highway to work with and can’t build any more. 

Without explicit control over Wi-Fi signals, vendors then focus on way that help with client density. Consequently there have been good advancements in traffic management that help foster high capacity Wi-Fi networks.  

Air time fairness, client load balancing and band steering are techniques that are all quite useful in easing the density problem. Add to these techniques adaptive, directional antennas and you have something very special for addressing highly-dense user environments.

You see, the Wi-Fi protocol actually does something that you are used to but maybe not conscious of. The better the signal, the faster you go. And it isn’t just your signal that matters, it is the noise.  

Signal strength means nothing without knowing the surrounding noise. The difference between signal and noise is called SNR (signal to noise ratio). Reduced signal and/or more noise equal slow speeds and sometimes complete lack of connectivity.

Wi-Fi is the same except on a smaller scale. You can move 10 feet farther away from the AP or behind a wall and your connection speed can be reduced significantly. As Wi-Fi protocol encounters errors from lower SNR it automatically reduces its speed to ensure that the communication is heard by the recipient. 

This reduction in speed means that it takes longer to say the same thing. And the longer it takes to send a data packet, the longer it is before another device on that same channel can transmit. This is where the beauty lies.  As you increase signal and reduce noise (both accomplished by adaptive antenna arrays) speeds increase, channel capacity goes up - with fewer APs needed to meet the same high density goals.

Adaptive antenna arrays can deliver up to 7dBi more signal gain than standard omni-directional antennas.  So what does 7dB mean in real life?  Try this, find out the Wi-Fi chipset you have in your favorite Wi-Fi device.  Then, look up its RSSI chart. This chart will tell you the minimum signal level needed to achieve a particular data rate. Especially when taking into account the benefits of 802.11n, you will see over a 50% increase in channel capacity just by increasing your signal strength by 7 dB.  

But supporting high capacity in the real world is more than a not-so-well-crafted BLOG entry. Listen to people who've had this problem already: