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.
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.
