Pick any two of the following: range, robustness, or throughput
A three-stream access point will have the ability to improve range, robustness, and throughput, but not all three at the same time. Range is nearly a given with a 3x3 antenna array, but throughput and robustness will be competing options. Let's pick each of these apart.
Additional send and receive antennas allow an access point to push data further by providing more potential signals that a distant adapter can hear. Likewise, a distance adapter's faint transmissions can be picked up and reconstructed better with three receive antennas. The WiFi Alliance's technical director, Greg Ennis, said, "In a small company, the configuration of the access points geographically within the site, it's probably more a range issue than a capacity issue."
Broadcom, a leading maker of wireless networking chips, emphasizes range over many other factors. Mike Hurlston, the firm's vice president and general manager for wireless LAN, said, "The advantage that a three or four stream product brings is mostly in the range."
Hurlston said, "The interesting property of a three-stream or a four-stream product is that the third antenna or the third transmit and receive [chain] becomes a way to gather more information as a station moves farther and farther away from the access point."
While "there's a close-in benefit of more speed at a relatively close range," Hurlston said that "the most interesting property to us is a much better sustainable throughput at longer ranges."
For an upgrade over an existing network, this range improvement could mean installing access points less densely, saving money while improving performance. Or, with heavily used networks, existing access points could be upgraded and cover the same area with greater resiliency, while also upgrading bandwidth.
Adding bandwidth is, of course, useful in very busy networks with many simultaneous active users and devices, but even increased bandwidth has more impact than pure speed: any given device could move data faster across a network, which means there's a greater amount of data that the network can carry.
"Keep in mind that the raw data rate that really gives two benefits to an installation," said the WiFi Alliance's Ennis. "One is that it allows for the support of applications that take advantage of that high data rate, like video. But the other is that it increases the capacity of the system as a whole."
Ennis explained when "transmitting at a faster raw data rate, that means that they [wireless network users] are occupying less air time on the channel, which has the effect of increasing the capacity of the whole system."
The flip side of speed is robustness: fewer dead areas in a network in which coverage is poor or unavailable, even as the rest of the network performs well, and a network that performs well even under high load or heavy bandwidth use. Using additional streams to provide redundant data through different spatial paths is what aids that process. This robustness also means that higher data rates will be available closer to an access point where, with a 2x2 two-stream system, rates can fall off to far lower than the maximum possible throughput at just tens of feet.
With chipmaker Atheros's new three-stream chips, said Pen Li, the company's senior product marketing manager, a couple of different technologies "will deliver more than 100 percent improvement in rate over range." Li said that if you were seeing 180 Mbps at 30 feet, that same speed would now be available at 60 feet, instead of half that.
Li noted, "The three spatial stream [approach] itself only gives you the data rate, the throughput boost, at short range."
The combination of consistent coverage, improved throughput, and improved range can reduce costs on the wiring side at least in one aspect: cubicles and office spaces have fewer and fewer Ethernet drops. The move to multi-stream radios might allow near-total elimination of wired connections for end users, except for those users with the heaviest data needs.
"You don't have to wire up the cube: you can be in any conference room or any cube" and have the same benefits from the IT infrastructure, said Sameer Bidichandani, the director of technical marketing for WiFi at chipmaker Marvell. The increased bandwidth means that 10 gigabit Ethernet may be increasingly needed in network closets, however, to maintain performance across the network as end points speed up.
The future's so fast you gotta wear 10 gigabit shades
One improvement may be in the use of wider channels. 802.11n supports 20MHz-wide channels, the same width used for 802.11a, b, and g, as well as 40MHz-wide channels, which simply double the available bandwidth. It's far easier to use 40MHz in 5GHz, because most countries allow several or even a couple dozen 20MHz channels, which can then be bonded into a smaller number of 4 MHz channels. In the US, there are eight channels of 23 available that are widely supported and can be used to make four 40MHz channels.
Some of the current work in 802.11ac is looking at 80MHz channels, which would potentially double again the available bandwidth—or even 160MHz channels.
This would be coupled with more efficient modulation techniques. Improvements in modulation, or the process of encoding bits onto radio waves, had a more than 10 percent jump between 802.11g and 802.11n, accounting for some of the speed improvement. (The rest was through wide channels and multiple spatial streams.)
Another element being looked at is MU-MIMO (multiple user MIMO), which the WiFi Alliance's Ennis explained would allow "simultaneous streams to be transmitted to different users on the same channels."
None of this is etched in stone, given that the proposed ratification for 802.11ac is December 2012.
Availability of hardware based on early drafts of this technology doesn't sound likely to hit the market until 2011, given current roadmaps, making it possible to plan to purchase three-stream 802.11n upgrades without short-term buyer's remorse. It took roughly three years between the first MIMO devices to ship before there were plenty of draft-based 802.11n devices on the market with reasonable interoperability.
Planning the office of tomorrow
Dare I say that the wireless office of tomorrow will look much like the wireless office of today, only better? That was the promise of 802.11n, and it's largely been fulfilled. 802.11n works better in a larger variety of office setups with less fuss to get greater speeds.
The evolution to three-and-more stream 802.11n should fill in the gaps of robustness, performance, and range that remain, giving businesses a chance to have better networks without spending enormously more.
The flexibility of three-stream devices should allow networks to be optimized for raw speed, speed-over-range, or range, without giving up much in the process.
With the next generation of standards already far along in the planning stages, it seems like we're at an inflection point where networks will deliver enough performance in 2010 to meet most needs without breaking budgets.
source
http://arstechnica.com/business/guides/2009/12/wifi-looks-to-1-gigabit-horizon.ars/2
