The majority of enterprise wireless LAN vendors have introduced three-spatial-stream access points (APs) to the market, but they have generally relied on three-antenna, or 3x3 MIMO, designs. A three-stream 802.11n access point can establish a theoretical maximum data rate of 450 Mbps with a three-stream client, but enterprises often struggle to achieve those data rates in real-world settings. For instance, the maximum throughput rate is only available 15 feet from the AP. Cisco claims that by adding a fourth radio to a 4x4 MIMO design, it can double the maximum throughput range to 30 feet.
Cisco uses an algorithm for its 4x4 MIMO wireless LAN access point that determines which spatial stream needs a boost. The algorithm then instructs the fourth antenna to boost the transmission or reception of that stream.
"When the system is transmitting, the three streams are going out of the four antennas, so the fourth antenna is helping out whatever stream needs additional assistance," said Tim Zimmerman, research director at Gartner Inc. "The same thing on the receive side. Most clients are going to have two antennas, and smartphones and iPads only have one antenna transmitting. So, the client might have one antenna transmitting, but the access point has four antennas receiving it."
University of South Florida puts 4x4 MIMO wireless LAN access points into production
Joe Rogers, senior network engineer at the University of South Florida (USF), beta tested the 4x4 MIMO Cisco 3600 access points. He's looking for faster and more robust access points in an environment where he often has 300 students in a single classroom, each connecting with a laptop and a smartphone simultaneously.
"We did speed tests with three spatial stream capable clients, and we were able to push upwards of 200 to 220 Mbps [at a certain distance], whereas with old 802.11n access points we were only getting 140 to 150 Mbps,” he said. ". While there aren't a lot of 3x3 clients out there today, we'd rather be putting in the APs that are supporting the new technology so that as the clients come to our network, we are ready and can do higher throughput."
Rogers now has 30 of the Cisco Aironet 3600 APs in production, with 300 more ready for deployment. The new APs will be distributed across the USF campus, which already has approximately 3,000 access points serving nearly 12,000 concurrent daily users. He said the 4x4 MIMO access points got a trial-by-fire recently when USF hosted a Republican presidential debate.
"We deployed the 3600s in the high-density areas for the debate. In the ballroom, we were estimating 300 to 400 reporters and just general people milling around the area. We also had a watch party in a tent in the center of campus and 1,000 people showed up there, with 300 or 400 concurrent [wireless] users," Rogers said. "I don't know if there were any clients that were three-stream capable, but we didn't have any issues with the existing clients."
4x4 MIMO at Cisco Live London could be old news soon
While Cisco's 4x4 MIMO design in the Aironet 3600 series boosts what enterprises can do with 802.11n wireless LANs, the technology is arriving at a time when the next generation of wireless LAN infrastructure is poised to hit the market.
At the Consumer Electronics Show (CES) this month, several vendors announced or demonstrated gigabit Wi-FI consumer devices based on the draft 802.11ac standard, "which means we'll see early 802.11ac devices later this summer," said Mike Spanbauer, principal analyst with Current Analysis.
No enterprise wireless LAN vendors are talking about gigabit Wi-Fi products yet, but Spanbauer expects them to hit the market by late 2012.
"As these capex investments for access points are usually on a three-year depreciation cycle, with 11ac coming, how much do you want to put into this $1,600 access point [from Cisco]?" Spanbauer said. "Is the incremental improvement worth it?"
Modular design, expanded beamforming capabilities
Cisco also announced that the 3600 APs support beamforming for 802.11n networks. Previously Cisco's access point portfolio only offered beamforming for 802.11a/b/g networks. Beamforming is a signal-steering technology where the individual antennas on an access point use algorithms and data streams from clients to determine the best path to send Wi-Fi signals. Many vendors offer the feature.
"The algorithm can decide how much of the radio is used for beamforming and how much is used for data to support greater data performance across one, two and three spatial streams, said Inbar Lasser-Raab, Cisco's senior director of global marketing for enterprise mobility and routing.
The 4x4 MIMO Aironet 3600 APs also has a modular design. Customers will be able to install modules into the APs for specialized applications. The first module, due out at the end of 2012, is an RF monitoring device with a dedicated radio that can monitor constantly the full spectrum of 2.4 GHz and 5 GHz constantly for RF interference. Cisco's CleanAir spectrum analysis technology on its existing Aironet 3500 wireless LAN access points could offer similar capabilities, but CleanAir relied on access points sniffing the RF spectrum while serving clients. The new RF monitoring module will offload that burden to a dedicated radio.
Let us know what you think about the story; email: Shamus McGillicuddy, News Director