MIMO—multiple-input multiple-output—promises dramatically improved throughput and range for wireless networks. The technology is compelling for enterprises and worth keeping a close eye on, but the gains that available MIMO-based products can provide arent enough to offset the current lack of an interoperable standard or concern over MIMOs interaction with legacy networks for corporate deployments.
In the strictest sense, MIMO allows for multiple receive-and-transmit antennas in the same device. However, what data is being transmitted by these antennas is up for interpretation.
MIMO-OFDM (MIMO-Orthogonal Frequency Division Multiplexing) technology will be a part of the IEEE 802.11n standard, which is expected to be ratified late next year. The TGn Sync proposal, which gained favor in this months downselect vote, provides for multiple antennas and spatial multiplexing technology, in addition to several other components.
Whats less clear at this time is what role channel width will play in the standard. It is likely that 40MHz channels will be used (as a required or an optional part of the standard) to boost capacity. One of the 802.11n working groups mandates is to maintain backward compatibility with 802.11 a/b/g networks, so n-enabled devices will need to detect legacy traffic and step back to 20MHz to avoid interoperability and interference problems. This could make it difficult to maintain optimal performance.
Enterprise-class wireless makers are forgoing MIMO in the near term, but companies can still accommodate greater bandwidth demands with denser and more intelligent wireless network deployments. As the standard ratification nears, however, and MIMO-aided performance escalates, there will be an increasing need to support the technology.
Indeed, all indications are that MIMO performance will ramp up quickly. Airgo Networks Inc. representatives have already hinted at chip-set revisions in development that provide as much as six times more bandwidth than were currently seeing, promising fantastic performance by the time the standard is ratified.
For now, vendors are releasing products based on proprietary MIMO implementations. eWEEK Labs has seen several consumer-oriented MIMO-based products come to market recently, and their different interpretations of what MIMO really entails can lead to some confusion.
Cisco Systems Inc.s Linksys Wireless-G Broadband Router with SRX (Model WRT54GX) and Belkin Corp.s Wireless Pre-N Router are based on True MIMO technology, Airgos term for MIMO, using multiple antennas and spatial multiplexing to boost performance.
Spatial multiplexing takes advantage of multipath reflection to simultaneously transmit different data streams on the same channel with separate spatial signatures. Receiving antennas collect the streams and recombine them quickly, effectively boosting the transmission rate.
Netgear Inc.s RangeMax Wireless Router leverages another MIMO variant, Video54s BeamFlex, to intelligently transmit multiple identical data streams from some combination of RangeMaxs seven antennas to boost range and eliminate dead spots in coverage. Called beamforming, this transmission approach does not use spatial multiplexing because each data stream is identical. However, it does improve performance over long distances by improving antennae gain, allowing wireless devices to maintain higher throughput modes at greater distance.
D-Link Corp.s Super-G with MIMO Wireless Router leverages an Atheros Communications Inc. chip set and four antennas. The wireless router also uses beamforming without spatial multiplexing. The Super-G feature uses two channels to boost throughput performance. To minimize impact on radio-frequency environments, the device must step back to one channel when other devices are present, minimizing the features impact in a crowded RF area.