* Hotel discovers the RF nuances of voice
The tony InterContinental Mark Hopkins hotel in San Francisco is ringing in the new year with internal voice-over-Wi-Fi (Vo-Fi) connections that are as clear as a bell.
But mobile voice quality and predictability had been iffy until last month, according to Robert Cantrell, the hotel’s director of IT. That’s when the hotel installed new Wi-Fi access points (AP) with smart antennas, which dynamically direct RF energy toward VoIP-enabled mobile devices.
Before then, coverage was hit or miss throughout the narrow halls in the bowels of the building, where RF-averse pipes, concrete walls and metal doors abound. This area is home to housekeeping, catering, maintenance engineering and other mobile employees who need to be reliably reachable by stationary staff, Cantrell explains.
Walkie-talkies were falling out of favor because they lacked volume control and security, and they weren’t directly accessible by all callers. So the hotel settled on Vocera wearable Vo-Fi badges, which allow hands-free operation by leveraging voice recognition commands.
The hotel was already running a population of Cisco Aironet 1231 stand-alone (“fat”) APs for Internet access in guest rooms and conference rooms. So it deployed more of them in the lower five floors of the building to support intra-staff voice calls.
But issues arose. Vocera badges are small, with tiny batteries, so they transmit at low power levels. They also operate flush against the human body, a source of interference. In an attempt to compensate, the hotel first enhanced the output of each Cisco AP with a 20dB amplifier, connected to a 5dB cone that concentrated energy down the hallways. This guaranteed that the badges would pick up the signal of an AP and could connect to the network.
“But voice recognition depends on the uplink,” points out Cantrell.
Because of the APs’ amplified transmit power, the Vocera badges wound up sticking to a given Cisco AP far beyond a distance where the AP could hear the badges, incurring an intolerable volume of dropped packets and audible jitter. Because Vocera badges only operate in the 2.4GHz range with just three non-overlapping channels, a denser Cisco deployment would only create more interference, Cantrell continues.
What to do?
Cantrell stumbled across Ruckus Wireless WLANs at an industry trade show. He tested the company’s APs, which bundle beam-forming technology directly into their antennas. The “smart antenna” technology steers energy dynamically to “where there is the greatest [client access] demand,” he says.
Cantrell has since installed 38 Ruckus APs. The APs are set to transmit at half power to avoid the stickiness problem.
“We learned that we had taken a brute-force approach to what was a more nuanced problem,” Cantrell explains. Having smart antennas adjust to where the client is works, while zapping power in the downlink direction from the APs didn’t.
The Cisco 1231s remain in the hotel guest rooms, where they continue to do their job of providing Internet access just fine, Cantrell concludes.
