The three range-extension technologies I'll be comparing all focus on improving receiver performance vs. boosting transmit power, but take different approaches. I'll try to summarize each approach in simple terms, but less geek-inclined readers may wish to skip this section.
ParkerVision's D2D (Direct2Data) patented technology uses a process dubbed RF Energy Sampling to more efficiently extract digital data from the RF carrier that it rides on. The basic approach is to take large samples - in some cases 1/2 a sine wave per sample - vs. the very small samples taken by conventional RF digital conversion methods. D2D also eliminates the need for RF carrier filtering and the signal loss it may cause. The result is a claimed open-field range of 1500 feet and guaranteed "whole-house" coverage (or your money back!).
NOTE: ParkerVision's WLAN products currently support only 11Mbps 802.11b operation. But a company spokesperson said that faster 802.11g-based D2D products will be hitting the market in Q1 2005.
Atheros XR (eXtended Range) also focuses on enhancing receiver sensitivity - they say down to -105dBm. This is 20dB (100X) better than the 802.11 spec requires and comparable to the receivers in some cell phones. Atheros' white paper says that the secret sauce used by XR is enhancement of its "MAC and PHY technology to support very low signal to noise (SNR) operation". XR also adds transmission rates "equivalent to" 3, 2, 1, 0.5 and 0.25Mbps that its adaptive rate algorithm can use to maximize throughput while maintaining a stable wireless connection.
Tip: Download the XR white paper (PDF) here.
Airgo Networks' True MIMO has the magic "MIMO" (Multiple Input Multiple Output) buzzword to flaunt, but the technology is more than just buzz. MIMO uses multiple transmitters and receivers - each with their own antenna - and a healthy dose of signal processing to improve effective signal-to-noise performance by at least 10dB (10X) and up to 15dB (almost 30X). Another key MIMO advantage is that it actually works better in the high multipath environments encountered in most indoor environments. (Multipath is the phonomenon where signals bouncing off physical obstacles arrive at different times at a receiver.)
Tip: Download a Farpoint group white paper on True MIMO (PDF) here.
Note that all three technologies require that they be present both in access points (or wireless routers) and client adapters in order to produce the promised performance improvements.
While I've concentrated on the range extension aspects of this trio of technologies, there are also speed improvements provided by Atheros and Airgo's chipsets. Atheros' Super G technology uses four techniques to increase throughput beyond the 54Mbps provided by standard 802.11g products:
- Data compression (such as you get when you ZIP a file)
- Fast frames (which groups packets together and cuts down wait time between data frames)
- Packet Bursting (which takes advantage of 11g's higher speed and sends more data in an alloted time slot)
- Dynamic Turbo
The Dynamic Turbo technique (formerly called channel bonding) has been the most controversial because it presses two channels into service to double the effective bandwidth - a non-standard use of spectrum, alleged by competitor Broadcom to cause interference with non-Super G products. I examined the alleged "bad neighbor" affects of channel bonding in the Atheros Super-G NeedToKnow - Part 1 and Part 2 and didn't find the effects as severe as Broadcom claimed.
But Atheros has since taken no chances and incorporated an Adaptive Radio feature into Super G. This feature monitors the entire 802.11g band and automatically increases throughput only when channels are available - something that the original Super G supposedly did in the first place.
At any rate, Airgo's True MIMO avoids the "bad neighbor" rap by maximizing spectral efficiency rather than simply grabbing more spectrum. This means True MIMO devices can transmit more bits per second using the same chunk of frequency than non-MIMO methods. Thus, Airgo's current True MIMO implementation can yield 5.4 bps/Hz (bits per second per Hertz) vs. the 2.7bps/Hz provided by standard 54Mbps 802.11g. Put into consumer-marketing terms, True MIMO's maximum data rate is 108Mbps - the same as touted by Atheros' Super G technology - and requires only a single standard 802.11b/g channel.
Enough with the background, let's take a quick look at the embodiment of these technologies that I put to the test.