802.11a has higher throughput than 802.11b, but is not compatible with 802.11b or 802.11g. It has been the least popular flavour of Wi-Fi, although manufacturers are beginning to include it in products alongside 802.11b and 802.11g.
802.11g is faster than 802.11b and is compatible with it. But, like 802.11b, it is more susceptible than 802.11a to interference from common household appliances, such as cordless phones and microwave ovens, that operate in the 2.4GHz radio band.
MIMO transmits data at the highest rates, but it is not an industry standard. In addition, products based on MIMO generally cost more than devices based on 802.11a, 802.11b and 802.11g.
Can I combine products based on different Wi-Fi standards?
The 802.11g and 802.11b standards are compatible. That means if you have an 802.11b client, such as a notebook, it can connect to an 802.11g access point.
The 802.11n is also expected to be compatible with its Wi-Fi predecessors. MIMO products are already on the market and manufacturers have made it a point to make them compatible with 802.11b and 802.11g-based products.
Products based on 802.11a are not compatible with products based on other Wi-Fi standards.
Compatibility is becoming less of a problem, however, as manufacturers increasingly support all three Wi-Fi standards in their devices.
How do various Wi-Fi standards compare on speed?
The 802.11b standard offers a top data transfer speed of 11mbps under optimal conditions, but it typically achieves about half that rate in the real world.
The 802.11g and 802.11a standards top out at data transfer speeds of 54mbps under optimal conditions. Like 802.11b, they generally perform at half their top speed in real-world installations.
Manufacturers of MIMO products say throughput can reach more than 108mbps. Ultimately, the IEEE is aiming for speeds from 100mbps and higher for the 802.11n standard.
What manufacturers currently sell MIMO gear?
A number of wireless networking chipmakers, such as Airgo and Atheros, are manufacturing their own versions of MIMO parts and several gear companies have been shipping products using those chips. Belkin and Linksys use Airgo's MIMO chips in their MIMO products. Belkin calls it MIMO Pre-N, while Linksys refers to it as SRX Speed and Range eXpansion. Netgear uses two types of MIMO technologies, one from Airgo, which it calls Pre-N, and another from Atheros and Video54, which it calls RangeMax.
Early reviews of these products indicate that the less-expensive RangeMax gear is more complicated to use and can potentially interrupt other, nearby Wi-Fi networks. Pre-N products offer higher throughputs at the outer edges of their range, but they cost more.
Do consumers really need dramatic increases in throughput over wireless networks?
Sharing broadband Internet access represents the top application for Wi-Fi networks in the consumer market. Since broadband connections typically perform well below 802.11b data transfer speeds, increased speeds offered by newer specifications such as 802.11g and MIMO do not yet mean much for consumers.
The question is most relevant for MIMO, which offers substantially higher speeds than any approved Wi-Fi standard. Manufacturers initially played up MIMO's role for multimedia applications, saying consumers would want to watch videos or play music streamed from a central home device. So far, those devices have failed to take off. More recently, device makers have touted MIMO-based products for their increased range.
What is WiMax? Will it replace Wi-Fi?
WiMax, similar to Wi-Fi, is a logo marking interoperability between products using a standard approved by the IEEE -- 802.16-2004. However, unlike Wi-Fi, WiMax makes wireless broadband Internet access directly available and is viewed as an alternative to high-speed cable and digital-subscriber lines. Wi-Fi products create wireless networks allowing those who can connect to the networks to share resources, such as an Internet connection or a printer.
WiMax is essentially radio technology that promises to deliver two-way Internet access at speeds of up to 75mbps at long range. Its backers claim that WiMax can transmit data up to 30 miles between broadcast towers and can blanket areas more than a mile in radius.
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