Above the Fray

UWB for wireless microphone clarity and security. 9/19/2011 10:14 AM Eastern

Above the Fray

Sep 19, 2011 2:14 PM, By James Careless

UWB for wireless microphone clarity and security.

Because Fairview Health Services wanted to maintain a flexible space without hard wiring a teleconferencing system in its Heritage Room boardroom, Alpha Video selected Audio-Technica SpectraPulse UWB wireless mic system.

One of the most confidential forms of communication is that between doctor and patient. In addition to secure, that communication must also be clear. As the wireless spectrum grows more crowded, noisy, and potentially insecure, Fairview Health Services in downtown Minneapolis found a unique wireless conferencing solution that also suited their third major concern: preserving the integrity of their historical building.

Fairview Health Services is a network of hospitals and clinics through Minnesota. The company’s headquarters is in an early 20th-century building in downtown Minneapolis, and features an elegant boardroom with a carved stone fireplace and full-length windows. The Heritage Room boardroom needed a new conferencing system; Alpha Video, a systems integrator based in Edina, Minn., set out to bring the boardroom up to 21st-century teleconferencing standards.

“They wanted a very flexible space, where they could move the tables around as needed and yet retain the ability to do teleconferencing with a minimum of setup,” says Brian Mathison, Alpha Video’s integration specialist. “They also wanted the space to be easily upgradable to videoconferencing in the future, which is why we installed a large video matrix switch.”

Because Fairview Health Services wanted to keep its boardroom layout flexible, a wired microphone system was impractical. “The room has many hard surfaces, so installing a hanging ceiling microphone system was out of the question because of the way it would sound,” Mathison says. “I don’t think they wanted it either because of the way it would look.”

Going wireless comes with its own perils. First, growing congestion in the RF spectrum is making it increasingly difficult to provide wireless users with continuous, reliable service that resists interference from outside transmitters. Second, anytime someone transmits over radio waves, they risk unauthorized eavesdropping by outside listeners. Since top Fairview doctors and administrators use the boardroom, maintaining signal security is an absolute must.

It is for these reasons that Alpha Video decided to install Audio-Technica’s SpectraPulse UWB Wireless Microphone System in the boardroom. SpectraPulse gets around the issues of RF congestion by transmitting in the 6-10GHz band. “The transmission signals are precisely timed,” Mathison says. “Because the receiver is synced to the transmitter, it knows the exact transmission structure and timing. This ensures that the audio comes through in a continuous, uninterrupted feed.”

By operating at such a high frequency, the SpectraPulse system reduces its vulnerability to interference from outside fixed-band RF sources. In fact, Audio-Technica claims that by “operating in the sparsely populated 6-10GHz range, SpectraPulse systems are completely out of the range of TV signals and white space devices.”

The system transmits the digital audio using “pulses” that are two nanoseconds long. These pulses are transmitted at the extremely low average power level of 40nW. Since there is no carrier wave and the transmission has such a low power, these short pulses are extremely hard to lock onto. Audio-Technica also offers an optional 128-bit AES encryption package for customers who want top-level protection. This level of encryption has actually won approval from the National Security Agency for transmitting classified information.

But ultimately for Alpha Video, the most fundamental question is functionality. The only way to truly know is to set the system up, which Alpha Video did in the boardroom in October 2010. Specifically, Alpha Video installed 14 Audio-Technica mtu101 boundary microphone/transmitters, small personal microphones with built-in transmitter bases; two aci707 wireless audio control interfaces; one drm141 wireless digital receiver; and two cei007 microphone charging stations.

“The Audio-Technica system works well within the confined space of the boardroom, which is about 40ft. by 25ft.,” Mathison says. “The signals bounce around really well, so the receiver had no problems picking up the microphones’ transmissions. We have been able to walk all around the room with the transmitter units, and had no problems with dropouts.”

Above the Fray

Sep 19, 2011 2:14 PM, By James Careless

UWB for wireless microphone clarity and security.

The audio from the wireless system, plus audio from the speaker’s podium captured using a Shure dual-channel wireless mic system, is fed into a Biamp AudiaFlex CM chassis with CobraNet. The chassis has nine Biamp AEC 2-channel echo cancelling mic input cards, an OP2e 2-channel mic/line output cards, and a TI-2 telephone interface card. This forms the backbone for the teleconferencing system. The boardroom also has a Stewart Audio DA-770-2 two-channel 80W amplifier and eight Tannoy low-profile ceiling speakers.

Video is projected on a Draper 4:3 aspect ratio 92”x69” recessed electric projection screen, which is mounted at one end of the boardroom. The video is delivered via a Hitachi 4000-lumen XGA LCD projector, which is ceiling-mounted. At the podium, there are inputs provided for HDMI video and VGA from a laptop, supplemented by a built-in DVD/VHS player.

The system is controlled using a Creston CP2E control system, which is managed with a Creston 8.4in. Wi-Fi-connected touchpanel—again in keeping with the client’s desire for portability and flexibility. A Creston ceiling-mounted Wi-Fi access point, lectern mounting kit, desktop docking/charging station for the touchpanel, and Crestnet distribution block rounds out the installation. A Crestron iLux integrated lighting system controls the lights.

Alpha Video’s installation inside the boardroom has managed to provide the functionality the client wanted, while maintaining the historic character of the room. “We were fortunate that there was already a drop ceiling installed, which gave us a place to run and conceal the wires,” Mathison says. “Still, we did have to do some custom millwork to create a setting that was in line with the boardroom’s history and decor.”

“It is fair to say that Fairview Health Services were very happy with the job,” Mathison says. “The technology does everything they want it to do. In particular, the SpectraPulse wireless mic system is working as billed. The signals are getting to the receivers reliably, and yet security is not an issue. Neither is RF interference from other sources, which is a great relief.”

Alpha Video’s success with the SpectraPulse system proves that there are technological solutions to RF crowding. This said, SpectraPulse has its limits: “This technology works well where there are walls to bounce the signals back to the receivers,” says Mathison. “For outdoor integrations, the system would require more receivers to cover the area.”

In a perfect world, all microphones would be wired, simply because wire provides a guaranteed, totally secured pathway that wireless cannot match. Still, in those cases when clients insist on being able to move their teleconferencing desks around whenever they choose, a robust, secure wireless solution is a viable option.

Above the Fray

Sep 19, 2011 2:14 PM, By James Careless

UWB for wireless microphone clarity and security.

A Word about UWB

Ultra Wide Band (UWB) is a radio communications technology that can currently transmit data at speeds between 40Mbps to 60Mbps and eventually up to 1Gbps. It is already well known in the computer and video wireless space but relatively unknown for audio; Audio-Technica claims SpectraPulse is the first viable commercial audio product to use the technology. UWB transmits ultra-low power radio signals with very short electrical pulses, often in the picosecond (1/1000th of a nanosecond) range, across all radio frequencies at once. UWB receivers translate these short bursts of noise into data by detecting patterns in the pulse sequence sent by the transmitter. Due to the low power, UWB transmissions are generally only used over short distances. However, the large range of frequencies allows for extraordinarily high bandwidth, resulting in the fast data rate the transmission is capable of.

In early conception dating back to inventor Guglielmo Marconi in the late 1800s, a UWB signal was a spark-gap transmission that was used for long-range communications. These early communications systems were replaced by more efficient, longer pulse duration, narrowband techniques.

Short pulse technology was only revisited nearly 80 years later in the mid 1960s. At this time, as technologies, methods, and materials allowed engineers to work in much higher frequency ranges, UWB began to emerge as a novel form of communications due to its low probability of detection characteristics. The successful use of UWB by the U.S. government and military led to the FCC’s groundbreaking rule making that permitted unlicensed commercial use of the technology for the very first time. They set the definition of an ultra wideband signal as having an instantaneous bandwidth of at least 500MHz (where the spectrum is defined as the 10dB down points from the center of the transmission) or a signal with a greater than 20 percent fractional instantaneous bandwidth. (500MHz is approximately 20 percent of a 2.4GHz center frequency signal. 2.4GHz is a popular wireless frequency with many available parts, and many engineers have experience working at this frequency.)

Audio-Technica SpectraPulse

Audio-Technica SpectraPulse UWB Specifications

  • Frequency range: 6.100GHz–6.600GHz
  • Center frequency: 6.350GHz
  • AD/DA: 16 bits
  • Clock: 24.576MHz
  • Sampling rate: 24kHz
  • Pulse duration: 2 nanoseconds
  • Frame length: 1 ms
  • Time slots per frame: 15
  • UWB rate: 8Mbps
  • Compression: None
  • Companding: None
  • Latency: <3ms
  • Average RF power: 40 nanowatts
  • Sync/Re-acquisition time: <3ms
  • Range: 23 meters (75’)
  • Simultaneous channels: 14
  • Power input: 100-240V AC, 50/60Hz
  • System frequency response: 100-12,000Hz
  • Mains (aci707): 100–240V, 50/60Hz RoHs-compliant power supply

    Read the SpectraPulse whitepaper for more information.

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