Cisco's new 11n gear boosts legacy Wi-Fi performance with beamforming

In tests, beamforming boosted throughput by 65% for 11a/g clients and provided coverage in areas that previously had no signal

Cisco is positioning its Aironet 1140 access point, with its beamforming technology to improve Wi-Fi performance, as the best way to shift to 802.11n without sacrificing legacy 11g and 11a clients.

Cisco today unveiled a new 802.11n WLAN access point designed to simplify enterprise deployments, lower costs, and improve performance for existing 11g and 11a wireless clients. New financing, trade-in options and consulting services round out the news.

Watch a slideshow of Cisco's access point.

The new Aironet 1140 access point uses the same mounting hardware as Cisco's existing Aironet 1250 11n products. But it has two important new additions. First, it can deliver full 11n performance, with data encryption active, on an existing 802.3af Power-over-Ethernet infrastructure. Second, Cisco plans to introduce in April 2009 a new feature based on an optional part of the 11n draft standard, called beamforming

With beamforming, the 1140 access point can tailor its transmissions to 11a/g clients, creating a stronger signal and higher throughput. Cisco is citing a test report by Miercom that shows this new beamforming feature, dubbed ClientLink, created an average throughput boost of 65% for 11a/g clients and provided coverage in hard to reach areas that previously had no signal at all.

As part of the announcement, Cisco Capital is launching new programs to help enterprises finance large-scale 11n deployments. New WLAN migration consulting services also are available, and Cisco is offering 15% - 25% trade-in credits for existing WLAN gear, to give enterprises an incentive to swap out 11b/g infrastructures in favor of 11n. (Compare enterprise WLAN products

The new 1140 access point is available now in two versions: a one-radio model for $1,099 and a two-radio model for $1,299. Pricing is the same as for the existing Aironet 1250 11n product.

The 1140 has a 2x3 antenna configuration, for two spatial streams. The antennas now are housed under a trim, sleek new casing (the 1250 antennas were externally mounted, and separately priced). It has one Gigabit Ethernet port, and supports 802.11i, Wi-Fi Protected Access and WPA 2, and 802.1x authentication.

The maximum data rate is 300Mbps for each radio. That rate requires bundling two 20MHz channels into wider 40MHz channels, in keeping with the IEEE 11n draft standard. Each radio can support 11abg and 11n clients and operate in either 2.4 or 5GHz bands. The two-radio model can run both transceivers in 11n mode at the same time, without compromising performance, according to Cisco. (Network World blogger Ken Presti talks with Cisco about the 1140 on our Cisco Subnet podcast.) 

New AP runs on existing PoE gear

Both 1140 models can use existing 802.3af PoE infrastructures, a huge gain for Cisco and its customers. As with most rivals, Cisco's previous 11n access point needed additional power, via additional hardware such as power injectors, to run at full 11n performance, especially with two radios. For the 1140, Cisco engineers sifted through the electronics design to boost efficiency and trim power use wherever possible, according to Chris Kozup, Cisco senior manager, mobility solutions. The new product also cuts power consumption by up to 20% by lowering the 1140's energy use during inactive periods.

With the new hardware is a free update to Cisco's Unified Wireless Network software, currently version 5.2. The update bundles together a group of existing features, now labeled M-Drive, including dynamic frequency selection, optimized roaming, and coverage hole detection.

The new element in the M-Drive bundle is beamforming, which is intended to strengthen the signal between a wireless client and an 11n access point, by means of improving the signal-to-noise (SNR) ratio.

Today, according to Cisco, 11n clients and 11n access points use a technique called explicit transmit beamforming to optimize the signal between them: The signal sent from each antenna is coordinated with the others, to improve the signal at the receiving end. It's able to do this because the 11n receiver feeds signal information back to the transmitter. But legacy 11a/g clients can't participate in that feedback.

Nevertheless, they do get some performance improvement on the uplink to an 11n access point. That's because the access point, typically with three antennas, often uses an algorithm called maximal ratio combining (MRC) to adjust the differing phases and amplitudes of the signal it picks up on each of these antennas, from the sending client. In effect, says Cisco, MRC helps the access point to hear the client better.

Beamforming with ClientLink

With ClientLink, Cisco uses these MRC calculations to let the access point more effectively target its transmission back to the downstream client. It does this via modifications to its Wi-Fi chipset, including new algorithms and digital signal processing implemented in silicon. ClientLink will let the 1140 adjust and optimize the signal it transmits back to an 11g or 11a client. According to Cisco, ClientLink enables the access point to optimize the SNR exactly at the position where the client is placed.

Cisco cites ClientLink testing by Miercom that shows 11a/g clients gaining an average of 65% in throughput. Tests proved that with ClientLink enabled, 802.11a/g clients could experience comparable performance to that of the latest 802.11n client technology, according to the report. Tests proved that with ClientLink enabled, there was an overall extended signal reach through obstacles, improved signal-to-noise ratio, and increased throughput at the outer points of an access point's coverage area. Application transaction times and coverage holes were also reduced.

Toyota Motor Sales, Torrance, Calif., has been testing the two-radio 1140 since last summer, and plans to deploy it company-wide, eventually replacing some 2,900 existing Cisco 802.11abg devices. These are located in the corporate offices, regional sales offices and warehouses, used daily by about 3,000 devices, 80% of them wireless scanners and most of the rest laptops. At the start of January, Toyota switched off support for 11b clients, since most existing clients are now capable of 54Mbps 11g or 11a performance.

Toyota has a few 1250 11n models deployed, but these need power injectors for extra juice, and are festooned with big, external wand antennas, says Erik Parker, senior wireless infrastructure analyst with the company's wireless design and engineering department. The 1140 works fine with the existing Cisco PoE switches and Catalyst 6500 modules, he says.

The improved signal strength with the new 1140 means that Toyota can increase the radius of their WLAN cells (the area around each access point) from 35 to 50 feet. That's pretty significant, Parker says. Initially, the company will have 11n users operating in the 5GHz band, where channels can be combined to give the full 11n performance. We still have a decent amount of cell overlap for capacity reasons, he says. For instance, training rooms that will hold more than 15 people will generally have two cells overlap that area.

Parker's initial, though limited, testing with the 1140 does show some performance gain for the 11g clients, but nothing dramatic so far. Normally, we'd see 2.2Mbps over 11g, he says. We're now seeing a couple of hundred kilobits over that with beamforming.

Performance for 11n clients was remarkable, consistently and easily topping 110Mbps with 40MHz channels. It was a pleasant surprise to see it work [fully] on PoE, and to show my colleague that my throughput on a 40MHz channel is higher than his on a 10/100 Ethernet card, Parker says.

An antenna-based alternative

A different approach to beamforming, sometimes called beam-steering, is used by some vendors, such as Ruckus Wireless.  It's based on an antenna design that uses multiple components, each of which can be turned on separately, to create an array of focused energy patterns, as many as 4,000 for Ruckus access points. Software then analyzes these signal patterns and selects the one that offers the best throughput. The Ruckus access points do this continuously, for each packet with each client, says Bill Kish, Ruckus co-founder and CTO.

Kish says that such active antenna systems are more successful in rejecting radio interference than the conventional omni-directional antennas of rival access points, and there is no upper limit on the gain that can be created. He says the Ruckus products can deliver gain improvements of 5-20 bBi.

A Cisco whitepaper on this distinction stresses the efficiency of chip-level technology, says that active antenna systems are suboptimal when clients are moving, and they suffer from the drawback of being one-way only they improve the downlink but not the uplink performance.

Toyota's Parker likes Cisco's silicon-based approach, precisely because it does leverage continued chip improvements without impacting performance, as well as because it leverages Cisco Compatible Extensions (CCX). CCX is code that runs on client Wi-Fi adapters and integrates them tightly with the Cisco WLAN. With CCX, they have more knowledge of and control over the [Wi-Fi] client, Parker says.

ClientLink will be released in April with the next planned release of the Cisco Unified Wireless Network software for its WLAN controllers and access points.

Learn more about this topic

Cisco targets Aironet 1140 Access Point at easing 802.11n deployment

Why Cisco continues to lead in WLANs

The role of beam-forming in 11n

Ruckus launches enterprise 802.11n mesh

Join the Network World communities on Facebook and LinkedIn to comment on topics that are top of mind.

Copyright © 2009 IDG Communications, Inc.