High-speed Wireless LANs

Wireless LAN technology has existed for a long time now. It's a mature technology that has been deployed by a lot of organizations the world over. The maximum data speed offered by current wireless standards is 54 Mbps with a range of up to 300 m. The proposed 802.11n wireless standard is expected to take the throughput and wireless range far beyond what existing standards offer. The higher throughputs will be made possible using a technique called MIMO (Multi Input Multi Output). While the proposal is presently with IEEE, and will take at least a year to be passed, some vendors have already made products based on 802.1 In, and call them 'pre-n'. Whether these products will get certified or not, one thing is definitely clear from this, that by the time the

standard does get approved, you'll find a lot of conforming products in the market. This shows how much excitement there is in the wireless market due to this standard.

Before we tell you the secrets of the new standard, it's important to understand actual limitations of existing ones. One of the biggest limitation is that they seldom deliver upon their rated throughputs. So 802.llg is sup- posed to deliver 54 Mbps, but most products based on this standard won't give you half that through- put. There are many reasons for this-wireless-opaque obstructions such as walls and metallic objects. RF loss and antenna gain, being the prominent reasons. This kind of throughput speed is mostly sufficient for general purpose networking needs such as Internet access, e-mail and basic file sharing. Another limitation is that as the user moves away from a wireless access point, the throughput reduces. Another problem is that existing wireless technology shares the throughput, so as more users board a wireless access point, the throughput reduces accordingly. So if an organization would like to put its wireless network to more throughput-intensive applications, it's not possible with current standards. For that, organizations have to still rely on their wired network. Whether wireless will replace wired is a different debate, as there are other factors, besides the throughput, that have to be considered.

Here, we'll concentrate on developments on the throughput front, and how the 802.11n standard is poised to deliver much higher throughputs. Let's see how. 

How 802.1 In works 



The 802.1 In standard promises to deliver data speeds of at least 100 Mbps and perhaps beyond 500 Mbps. This is achieved by adding more antennae to the access point, which reduces interference caused due to obstructions. Data speed increases proportionally with the increase in the number of antennae. The
technology that will manage a number of antennae is called MIMO. In MIMO, the high data speed stream that passes as radio waves is split into multiple data streams. Each of these data streams is transmitted on the same channel But through a different transmitter antenna. The receiver antennae recombine the multiple data streams using complex algo-rithms.MIM0 will face reduced interference from obstructions, which will in turn increase its usable range. To provide better security, the 802.1 In will use advanced encryption techniques.

Some background 



A high throughput study group was formed to develop the 802.1 In standards. Two competing subgroups made proposals to the IEEE-TGn Sync (Task Group n Synchronization) and WwiSE (World Wide Spectrum Efficiency). The difference between the two groups lies in the channels in which their products will operate. 80th the groups want to use the 20 MHz channel, but TGn wants to operate in 40 MHz too. TGn contends that WWiSE would need four antennae each (for transmission and reception) if it wants to operate at 40 MHz, to

achieve data speeds more than 300 Mbps. In contrast, TGn proposes to achieve this speed using just two antennae, which means decrease in the cost of user equipment. But a few countries (such as Japan) disallow us- age of 40 MHz for public access wireless needs.

Interoperability issues 



As the proposal is still in the draft stage, vendors developing pren will have their own implementations of the specification. Products from different vendors may not work in tandem because how they choose to implement the proposals could vary at the moment. TheWiFi alliance has noted backward compatibility problems of 802.11gwith 802.11b and wants to prevent this from happening in 802.11n. They have made it clear that unless IEEE passes the proposal, they will not certify any product. The alliance also warns that if pre-n is found in- compatible or un-interoperable with earlier products and standards, product certifications may be cancelled. The first announcement of products came from Belk in as early as December last year, with a line up of pre-n routers and desktop and notebook cards. However, we are yet to see these products in the market. Belkin

claimed that these pre-n products are backward compatible with 802.11b/g. 

Do you really need it? 



A big decision for the organizations will be whether to shift entirely to 802.11 or not. Current wireless networks may be sufficient to meet users' needs, but expanding campuses will desire to have good wireless connectivity. This is where 802.1 1n is expected to take over from b and g.

Sushil Oswal