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How MIMO Works

Standard Wi-Fi wireless hardware uses one antenna to receive and one to transmit data. MIMO uses two or more antennas at each end of a connection to send and receive data, enabling transmitter and receiver to accept signals more efficiently than with a single antenna.

MIMO is one of the major features of the next standard for wireless networking, 802.11n. The ability of MIMO to handle multiple signal paths enables MIMO-based wireless networks to provide greater throughput than standard wireless networks. Although the final features of 802.11n have not yet been determined, MIMO will be a vital component in the drive to push speeds past 100Mbps.

Airgo Networks' True MIMO, a "True Pioneer"

Airgo Networks' True MIMO, which was introduced in late 2004, is supported in the following lines of network products:

  • Linksys Wireless-G with SRX
  • Belkin Pre-N
  • SOHOWare AeroGuard

NETGEAR is also selling True MIMO-based products in some markets, but RangeMax, its MIMO implementation for home wireless networks, is instead based on Video54's BeamFlex smart antenna technology.

True MIMO uses three antennas to transmit and receive multiple data streams. A digital signal processor (DSP) is used to divide transmitted data into multiple data streams, while the receiver uses another DSP to reconstruct the multiple data streams -which can be received either directly from the sender or reflected off objects such as walls, floors, doors, and ceilings- into data packets. Airgo refers to this method of transmitting and receiving data as spatial multiplexing. Airgo's True MIMO is the only one of the three MIMO implementations to divide and reassemble multiple data streams.

According to a variety of third-party tests (see the For Further Research section for links), True MIMO-based routers and clients have much longer range and greater throughput at a given range than standard 802.11g-based network hardware. When compared to other MIMO implementations, True MIMO-based routers and clients continue to have greater range and throughput.

Some tests mixed True MIMO and standard 802.11g-based hardware, and these tests also showed improvements in speed and range compared to end-to-end 802.11g networks. Although the best results are seen when using the True MIMO-based hardware at both ends of the connection, many reviewers were impressed with the ability of True MIMO-based hardware to improve the range of an existing network. For example, you could replace an existing 802.11g router with a True MIMO-based router and improve the range of your existing 802.11g network clients.

Belkin and Linksys Implementations of True MIMO

Belkin refers to its line of True MIMO-based wireless products as "Pre-N." Although wireless network vendors have a long history of rolling out products designed to meet proposed certifications and fixing problems after the fact with firmware upgrades, this name is somewhat misleading. Although MIMO will be part of the 802.11n specification, the details of the 802.11n standard have not yet been established. Consequently, it's not at all certain that any current MIMO solution will be upgradeable to 802.11n. Despite the "Pre-N" name, Belkin does not claim that these products will be upgradeable to the final 802.11n standard.

Although Belkin's Pre-N products are more expensive than its other 802.11g or enhanced 802.11g network products, they are considerably less expensive than Linksys' SRX products. Some reviewers who have experience with both Belkin and Linksys products have seen differences in performance or stability in some situations. See the reviews in the For Further Research section for details.

Belkin's Pre-N router uses three fixed antennas and has a horizontal form factor. Linksys' SRX router has three adjustable antennas and has a vertical form factor.

Other MIMO Implementations

Although True MIMO was the first MIMO technology available for wireless networking, it is no longer alone in the market. There are two other implementations:

  • Video54 BeamFlex
  • Atheros AR5005VL "Vlocity"

Video54's BeamFlex technology is based on a seven-antenna array which steers signals around problems such as physical obstacles, RF interference, or interference from other wireless networks. BeamFlex detects which signal path provides the strongest and most reliable signal, and automatically switches to it. It is able to dynamically change signal paths as needed to handle interference issues. However, unlike True MIMO, BeamFlex uses one radio and one transceiver and sends only one data stream. The first adopter of BeamFlex is NETGEAR, whose RangeMax product line was introduced in March 2005.

Atheros, which previously developed the Super G and Super AG enhanced 802.11g and 802.11g/a chipsets used by D-Link and NETGEAR, has combined Super G's optional channel-bonding high-speed enhancements to 802.11g with two radios and four antennas. The antennas send or receive the same data stream simultaneously. The first adopter of the AR5005VL is D-Link, which uses the chipset in its Super G with MIMO product line.

BeamFlex and AR5005VL have not been on the market as long as True MIMO, and early test results suggest that while they provide improved range and speed at a given range compared to 802.11g, they do not perform as well as True MIMO-based products. However, improvements in software and firmware might improve performance. Check the review sources at the end of this article for additional reviews of products based on these technologies.

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