Understanding the roots of these wireless connectivity issues is an essential first step toward finding remedies.
Pouring tens of thousands of dollars into a Wi-Fi deployment does not guarantee magically outstanding results. We’ve all experienced office “dead zones,” areas in which connectivity falls suddenly, sometimes even to the point of disconnection. Alternatively, connections that work well one day might plummet the next—or vice versa. Obviously, lack of stable Wi-Fi performance can impair a workforce’s productivity.
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Contention And Interference
In some ways, Wi-Fi clients and access points (APs) operate like walkie-talkies. Each participant must agree to use a common frequency and channel, and only one side can transmit at a time. With only two parties in an open environment, this approach works brilliantly. Unfortunately, such conditions rarely happen.
Run anyWi-Fi network scan and odds are that there will be at least a few detected SSIDs. If any of those networks is using the same channel as yours, then it will be competing with your network traffic. (Mind you, those are just the SSIDs you can see. Some don’t broadcast their SSIDs to keep them more secure, but the traffic is still there.) On a more granular level, the data packets flying between client and access point must “contend” with packets on competing networks.
If one of your packets collides with another network’s packet, your packet will fail to reach its target and have to be resent, which increases latency and slows throughput. Most access points can automatically change channels when confronted with excessive contention, but in today’s age of rampant wireless communications, it can be difficult to find a channel that doesn’t already have a fair bit of competing traffic. This is particularly true on the 2.4-GHz band, where there are only three effective non-overlapping channels (1, 6, and 11).
Similarly, Wi-Fi packets must battle against background RF interference. Cordless phones and microwave ovens are infamous for pouring noise into the 2.4 GHz band, which has the same effect on Wi-Fi packets as those from a competing network.
Most access points will respond to persistent interference by lowering their output power. This reduces the diameter of their effective range, hopefully removing the interference source from being within the AP’s sphere of communication. However, less power means lower transmission speeds, which leaves packets in the air longer...where they can collide with other networks and RF interferers. In reality, you want an AP that boosts power in the face of interference, not shrinks away from it.
Polarity And Spatial Multiplexing
Two or three Wi-Fi antennas are better than one thanks performance issues surrounding polarity and spatial multiplexing.
If you understand how polarized sunglasses or LCD screens work, then you get the principle behind radio signal polarity. Consider a transmitter with a single antenna that points straight up in the air. Radio signals being emitted from this antenna will have a vertical orientation. But if the receiving antenna is oriented horizontally—perpendicular to the transmitter—then only a small amount of the signal will be received. Turn the receiver another 90 degrees and it will likely get excellent reception. A 45-degree misalignment will knock 3 dB from the signal.
Orientation starts to get fuzzy once signals begin bouncing off of objects, such as walls, floors, desktop PCs, and so on. These bounced signals may not retain the same angle of polarity they had when first emitted. Thus it can help to not only emit with multiple antennas (each with a different emission angle) but also to have client devices with multiple antennas. This is one reason why the triple-antenna designs in 802.11n laptops get much better wireless performance than single-antenna 802.11n tablets.
Spatial Multiplexing
Another reason two or three antennas are better than one is because additional antennas allow for the transmission and reception of multiple simultaneous data streams. Consider: Who is more likely to shovel a big pile of dirt into a hole—one guy with a large shovel or three guys with somewhat smaller shovels? The three guys, right? Similarly, two or three sub-streams, each carrying a distinct set of packets, will prove faster than a single stream.
This signal splitting is called spatial multiplexing, and it’s a part of the 802.11n industry standard. Still, just because spatial multiplexing is part of the spec doesn’t mean that all products use it. The 802.11b and 802.11g generations are single-stream, and some newer “N-150” products likewise only use one antenna (and thus one stream).
When you see a Wi-Fi described as 3x3, this refers to the use of three transmit (Tx) and three receive (Rx) radio chains. (A radio can be connected to any number of antennas, creating a single “radio chain.”) Adding a “:2” on the end, as in 3x3:2, means three Tx and Rx chains capable of handling two spatial streams. Today’s “300 Mbps” 802.11n equipment is typically 3x3:2. More recent “450 Mbps” parts are 3x3:3. Be aware, though, that the number of streams is only one element among several in determining overall performance. It’s very possible for a 3x3:2 product to outperform a rival with three streams if other wireless optimization techniques are in play.
How To Improve Wi-Fi Performance
Directional antennas, beamforming and dual-band are all useful tools to enhance and improve the performance of a wireless network.
Directional Antennas
When you need to shout across a field, your voice will carry better if you cup your hands into a tube around your mouth, yes? You’re taking the “signal” of your voice and narrowing its directionality. The same principle helps with radio transmissions. Most access point antennas are omnidirectional, broadcasting equally in 360 degrees to reach all clients equally. That’s good for broad coverage, but it also limits signal strength, reception distance, and throughput performance when compared with the same amount of transmit power (Tx) applied to a directional antenna broadcast.
Directional Wi-Fi antennas are most often seen in outdoor settings, particularly when bridging between two buildings. However, they can also assist with indoor communications, especially in crowded environments where signals may have to bounce off of many objects before reaching their destinations. The trick lies in pinpointing the client’s location and orienting the access point’s directional antenna for maximum reception, much like aligning a satellite dish with a geosynchronous satellite. Of course, most clients don’t stay still.
People move their smartphones, laptops, and tablets around constantly. This necessitates having multiple directional antennas in play and an access point with enough integrated intelligence to monitor changing signal conditions and adapt on the fly. The Ruckus Wireless 7962 (internal antenna array shown here) is one example. The model uses 19 directional antennas and is constantly changing its active configuration in response to changing conditions from all connected clients.
Ruckus Wireless 7962 Antenna Array
Beamforming
One way to overcome some of the limitations of omnidirectional antennas is to use beamforming. If you visualize the signals being emitted by an omnidirectional antenna as waves, much like the concentric waves that emanate from a stone dropped into a still pool, then you know how the waves emitted from two antennas will create overlapping patterns. Within these patterns are directional zones of crests and troughs, with the crests indicating an amplified signal. The directionality of these crest zones can be modified by altering the emission characteristics of the antennas, in effect sending the amplified “beam” wherever it is needed.
Photo by Dr. Schorsch via Wikimedia Commons. Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Most consumer access points lack this sort of beamforming. Some enterprise-grade models support it, and their performance advantage shows what a difference the feature can make. (Note that Ruckus has a unique alternative to beamforming, using pieces of metal mounted alongside its directional antennas to assist in its adaptive antenna arrays. Like beamforming, Ruckus’s approach can physically direct the signal’s path, but, according to Ruckus, its adaptive antennas result in a roughly 9 dBi signal gain compared to chip-based beamforming’s 2 dBi.) In addition to creating a stronger signal from AP to client, beamforming can also reduce noise perceived from undesired sources in other directions. In effect, it is both creating a tube around the mouth and cups behind the ears, thus blocking noise from behind and improving overall connectivity conditions.
Dual-Band
As mentioned earlier, the 2.4 GHz Wi-Fi band is notoriously overcrowded. This problem is compounded by overlap between the 11 possible 2.4 GHz channels, yielding only three non-overlapping options (or just two if you’re using 40 MHz channel bonding). In contrast, the 5 GHz band has eight non-overlapping channels and generally less competing traffic since relatively few client devices support these frequencies.
Savvy Wi-Fi users have known to use 5 GHz for years, especially for video, because less contention means more reliable throughput. All other things being equal, 5 GHz does deliver somewhat less reception range than 2.4 GHz, but the technologies described above can help make amends for any deficiency. Organizations should be leveraging 5 GHz as much as possible to realize the best possible Wi-Fi performance.
Wi-Fi In The Workplace
We’ve quickly run through the most common factors that can thwart Wi-Fi in the workplace and the technologies able to help work around them. Finding access points that support these technologies can be tricky.
“Vendors tend to keep their secret sauce under cover,” says David Callisch, vice president of marketing for Ruckus Wireless. “A lot of sales representatives may not even know the answer if you ask them about how they do beamforming or how their antenna arrays adapt to changing conditions. We do, but that’s another way you can tell the serious partners from the herd. Companies with good technology will give you good answers.”
Start asking questions. Before your next Wi-Fi deployment or upgrade, find out which of the above methods (and others) your prospective purchases support and how they will make sense within your environment.