The Federal Communications Commission’s (FCC) broadcast television spectrum incentive auction has been a source of consternation and hand-wringing from parties on all sides of the relevant issues. Cellphone companies, television broadcasters, wireless mic manufacturers, and integrators and end users who rely on wireless technology for their systems have all weighed in, and each of these parties has expressed concerns about the impact the auction will have on their businesses.
Case in point: CTIA-The Wireless Association, an industry trade group representing wireless communication sectors, recently commissioned a study in response to the FCC’s position that “there is a lack of real-world testing between white space transmitters and LTE receivers.” The CTIA study was based on analysis by V-COMM Telecommunications Engineering, a provider of integrated network engineering and support services to telecommunications companies. V-COMM was tasked by CTIA with “test[ing] LTE mobile device receivers and simulated interference from unlicensed white space devices and wireless microphones.”
According to CTIA, “The goal of this testing was to determine the appropriate power and emissions limits at which unlicensed white space devices and wireless microphones could operate without causing interference to licensed 600MHz operators. By testing wireless devices that were the closest possible representation of 600MHz receivers, and by simulating the technical parameters of white space devices and wireless microphones based on the [FCC’s] technical parameters for those operations, V-COMM was able to conduct a variety of tests that emulate real world conditions.” V-COMM’s investigation led CTIA to assert that, “without significant modifications to the [FCC’s] technical proposals, unlicensed white space devices and wireless microphones operating in the 600MHz duplex gap will cause harmful interference to LTE devices.” These findings were presented in a February 4, 2015, filing to the FCC.
However, in a subsequent filing to the FCC, Shure rebutted the CTIA study, contending that V-COMM’s findings “relied upon fundamentally unsound and inaccurate assumptions about wireless microphone signal propagation in real-world environments.” In this filing, Shure provided the following points to illustrate the flaws in V-COMM’s research:
- CTIA analysis on LTE receiver sensitivity measurements and in-band blocking does not adhere to the 3rd Generation Partnership Project (3GPP, 3gpp.org) 36.101 standard [which provides internationally recognized and adopted RF characteristics and minimum performance requirements for LTE equipment, including equipment under test conditions], and overestimates the LTE receiver performance by a minimum of 10dB, thereby establishing a false and overly sensitive baseline for wireless microphone OOBE (Out-of-Band Emissions) levels necessary to protect adjacent receivers.
- 700MHz LTE devices have successfully coexisted for years with hundreds of millions of consumer devices that emit spurious emissions in the 700MHz band up to the Part 15.109 Class A and B levels that the FCC established decades ago.
- Typical wireless microphone OOBE are 10dB to 20dB lower than the limits for general consumer devices (FCC Part 15.109 Class A and B levels), and therefore do not present a threat of interference to LTE devices. [CTIA actually argues for an OOBE limit for wireless microphones 40dB lower than the longstanding limit applicable to unlicensed devices under Section 15.109.]
- CTIA analysis on the signal received by an LTE receiver from a wireless microphone is not based on measured data, but rather loose approximations, thereby establishing a false and overly aggressive baseline for the 600MHz duplex gap and guard band buffer spacing required for wireless microphones.
- Measured data on wireless microphone signals received by LTE receivers indicates CTIA underestimates the path loss between a wireless microphone and an LTE device by 10dB to 20dB.
- When path loss between wireless microphones and LTE devices used in the CTIA analysis is measured using appropriate assumptions, the potential for interference to LTE devices vanishes, indicating the 600MHz duplex gap and guard band buffer spacing of 1MHz is more than sufficient to protect LTE devices from wireless microphones.
- Shure’s analysis has been confirmed during real-world operations. For example, during the 2014 Academy Awards in Los Angeles, wireless microphones (authorized under FCC STA) were operated at 1MHz of spectral separation from Verizon 700MHz LTE downlink spectrum in Band 13, causing no interference or interruption in service to the several thousand LTE devices in use within the Dolby Theater.
“We felt it was important to respond to the V-COMM study filed by the CTIA that, while executed properly, was based on some flawed fundamental initial assumptions,” said Mark Brunner, Shure’s FCC liaison. “These initial values led to conclusions that we believe do not reflect real-world interactions between mobile handsets and wireless microphones, which have a lower interference potential than everyday consumer devices. Our response supports the FCC’s proposed post-auction band plan, which we feel should be pursued.”
To view the complete CTIA filing, click here.
To view Shure’s rebuttal, click here.