Justifications for possible U.S.-only standard, other details, questioned
The FCC’s Office of Engineering and Technology (OET) appears to have assigned a high priority to the issue of the use of unlicensed spectrum by licensed wireless services. Less than six weeks after the close of an initial comment period on the subject, OET has posed a number of supplemental questions to the LTE-U Forum (the Forum), an organization of proponents on the wireless side (it was formed by Verizon, along with Samsung, Qualcomm, Alcatel-Lucent and Ericsson).
As we reported in May, a battle has been brewing between the wireless and Wi-Fi industries over use of the newly-available or newly-expanded unlicensed spectrum in the 3.5 GHz and 5 GHz bands, respectively. The wireless folks are developing technologies – dubbed LTE-Unlicensed – for those bands. By placing an additional chip in cell phones, wireless carriers using LTE-Unlicensed can use unlicensed frequencies in addition to their licensed frequencies. The goal is to relieve congestion on those licensed frequencies. That approach, however, pushes more traffic onto unlicensed frequencies that Wi-Fi proponents, in particular, were expecting to be able to use. And the fear by some is that LTE-Unlicensed technology (or at least certain versions of it) will cause interference in spectrum the FCC had set aside for Wi-Fi.
The precise standards to be used for LTE-Unlicensed technology are still a work in progress. The FCC has identified four different versions being developed: LTE-U, LAA (short for “Licensed Assisted Access”), LWA (short for “LTE-WLAN Radio Level Integration and Interworking Enhancement”) and MuLTEfire (a Qualcomm product). Some versions incorporate sensing technologies to ensure that a channel is open before being used; others don’t. Wi-Fi proponents, while preferring not to share at all, believe that such “listen before talk” protocols would at least be the better alternative to others which, they claim, would have to potential to drown out Wi-Fi transmissions.
Comments submitted in response to OET’s initial inquiry focused on the characteristics of a “listen before talk” technique called “Carrier Sense Adaptive Transmission” (CSAT) developed by the Forum. But a number of aspects of CSAT remain unclear – so OET is asking for more specifics.
It’s also unclear which flavor of LTE-Unlicensed will ultimately be adopted by U.S. industry. Two different private standards-setting organizations – the Third Generation Partnership Project (3GPP) and the Working Group 802.11 of the Institute of Electrical and Electronics Engineers (IEEE Working Group 802.11) – are currently working on different versions. Ordinarily, the FCC does not involve itself in such standards-setting activities, although Commission staffers routinely attend standards-setting group meetings to informally observe and provide advice. But here, OET’s questions seek technical responses as to how CSAT works and how the data “traffic” is managed. And they also inquire specifically into the underlying rationale for the “strong interest” in implementing, sooner rather than later, an LTE-U system that would be “unique to the United States”.
OET appears to be concerned about possible adoption of a system for domestic use that would be incompatible with other wireless technologies (i.e., Wi-Fi) as well as with devices using standards already adopted in Japan and parts of Europe. If U.S. manufacturers come out with devices using a different standard from the rest of the world, U.S. consumers could lose the economies-of-scale benefits that come with international harmonization, namely less expensive devices and greater selection.
As to the technical details, OET’s interest in understandable. Telecommunications Certification Bodies (TCBs) will be consulting with the FCC Lab when it comes to certifying the underlying equipment, so it will be important for the Lab to have a solid handle on how the gear is supposed to work.
The Forum has 30 days in which to respond to OET’s inquiries.