Today's Wi-Fi gear has limited range, is highly susceptible to interference from cordless phones and other wireless devices, and is much slower than old-fashioned Ethernet. All this is set to change with the advent of 802.11n. The 802.11n standard is still being ironed out, and the IEEE, or Institute of Electrical and Electronics Engineers, doesn't expect to ratify this developing specification until 2006. However, products based on competing versions of 802.11n's powerful smart-antenna technology, called MIMO, are already available.
MIMO, which stands for Multiple Input Multiple Output, allows a wireless device to make more efficient use of data transmissions in indoor environments. The new 802.11n will include some version of MIMO, and it promises to deliver faster throughput than Ethernet and double the range of today's Wi-Fi gear. We've already reviewed the first round of MIMO-enabled networking devices, including the Belkin Wireless Pre-N Router, Linksys WRT54GX and Netgear WPN824 RangeMax, all of which offer clear performance gains over standard 802.11g gear.
So how does MIMO work?
There's still some debate, mostly vendor infighting, about what actually qualifies as MIMO, but basically this technology uses multiple antennas to maximise throughput in a range of indoor environments. Until recently, indoor environments have a posed a serious challenge for wireless networks. Reflections off of metal furniture or construction materials in offices and homes often lead to what radio engineers call a 'multipath scenario' -- a situation in which multiple transmission paths of the same data in a wireless broadcast begin to interfere with each other, degrading network performance and shrinking the coverage area of your network. Other sources of interference, such as cordless phones, microwave ovens, baby monitors and neighbouring networks, also pose problems for standards-based Wi-Fi gear and leave your network with poor range or even intermittent loss of connectivity. MIMO aims to change all that by using multipath to its advantage. The smart antennas on a MIMO router can hand off reception and transmission dynamically to each other, adjusting for the clearest data path on the fly. This increases both range and throughput at any given distance in an indoor setting, especially in multipath or interference-prone environments.
How does MIMO relate to 802.11n?
Unfortunately, what you currently stand to gain with so-called MIMO gear comes at the cost of poor interoperability across vendors and no guarantee of full forward compatibility with the 802.11n gear of the future. For example, connect a MIMO-enhanced Netgear WPN824 RangeMax router with a Belkin Pre-N PC Card adapter, and you'll lose the performance boosts that each product offers when paired with its vendor-specific counterpart -- the Netgear WG511T PC Card and Belkin Wireless Pre-N router respectively. Because these products are based on proprietary solutions, not a ratified standard, mixing and matching gear across vendors typically results in degraded performance.
Also, when 802.11n becomes a reality, today's Pre-N/MIMO solutions probably won't be fully interoperable with gear based on the ratified spec. For this reason, it's often better to wait on a ratified standard than to start building your network with non-standard gear. Scalability and interoperability problems can come back to haunt you down the road when you start adding newer standard-compliant equipment. Still, today's MIMO-enhanced gear shows us what we can expect from 802.11n Wi-Fi in the not too distant future: fast speeds, long range and strong resistance to interference.
