CableLabs this week submitted a report to the FCC detailing its findings from a Globalstar demonstration of terrestrial low power service (TLPS) at FCC headquarters, saying the tests are inconclusive and urging further technical study.
The FCC invited CableLabs to attend a Globalstar demo at its headquarters in Washington, D.C., last month to measure the potential impact on 2.4 GHz Wi-Fi systems, which are immediately adjacent in frequency.
Globalstar has said the demonstration proves that TLPS can be a good neighbor to Wi-Fi, but CableLabs disputes that. Separately, the Bluetooth Special Interest Group (SIG) also says the demonstrations validate its concerns about interference with Bluetooth devices.
CableLabs cautioned that the demonstration was not a fully complete or representative set of tests. Because of facility and space constraints, the organization was able to complete only an estimated 20 percent of all measurements necessary. "Because of these constraints, the demonstration results do not provide CableLabs or the FCC with an adequate basis for determining that TLPS can operate without undermining existing 2.4 GHz Wi-Fi service," CableLabs said in its filing. "More fulsome testing is therefore required, and CableLabs stands ready to participate and, if needed, to host such testing in a controlled environment."
Globalstar doesn't share that sentiment. "What the FCC's Office of Engineering & Technology previously requested was a 'real world' demonstration of TLPS to show that it was compatible with existing Wi-Fi and Bluetooth operations," Barbee Ponder, general counsel and vice president of regulatory affairs at Globalstar, told FierceWirelessTech in a statement. "We are confident that our demonstration, which was performed before numerous FCC engineers, answered any questions that they had regarding compatibility. No further demonstrations have been requested by the FCC, or are needed."
CableLabs said it conducted TCP throughput and RTP latency and jitter tests in both uplink and downlink directions using a combination of access points (APs) and clients, measuring the impact to Wi-Fi channel 11 as a function of different TLPS interference scenarios. Two separate APs--a Belkin N150 and a Ruckus Wireless R700--were used as channel 11 test subjects. The Belkin uses 2x2 MIMO and 802.11n features, and the Ruckus product is a high-performing enterprise AP with beamforming, adaptive polarization diversity and interference-mitigation features. CableLabs said these devices were used to reflect two respective common locations where Wi-Fi is used: in homes and in businesses.
The intention was to test the potential impact on networks operating in channel 11 using both a common residential access point (the Belkin N150) and a full-featured AP used in an enterprise environment, which was the Ruckus product. Globalstar also provided Ruckus 7982 access points operational in channel 14 that have interference-mitigation techniques, adaptive polarization diversity and transmit-beamforming capabilities.
Several client devices were used, including a Samsung Galaxy S5 smartphone and an Apple MacBook Pro laptop.
CableLabs concluded that its measurements, though constrained in scope and form, show a negative impact on Wi-Fi resulting from channel 14 TLPS, with varying impact depending on the type of Wi-Fi equipment that is used. It also notes that both CableLabs' and Globalstar's measurements are useful only to the extent that they used equipment and deployment scenarios that Globalstar would use if allowed. "If Globalstar would be provided the flexibility to use LTE instead of 802.11 Wi-Fi technology, or the ability to operate outdoors, or otherwise deploy TLPS in a manner not represented in the demonstration, then the utility of the demonstration data is limited," CableLabs said.
In an earlier filing, Globalstar said that TLPS was shown to have no negative impact on existing Wi-Fi operations in other channels. Even when three access points were activated on channel 14 within the confines of the FCC's offices, there was no reduction in data throughput from a fourth access point operating on Wi-Fi channel 11, according to Globalstar, which called CableLabs' TLPS/Wi-Fi demonstration set-up "in no sense representative of a real-world deployment" and said that "any results provided by CableLabs in this proceeding should be entirely discounted."
- see this FCC filing
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