This week has seen Qualcomm pushing the agenda to put LTE into unlicensed spectrum with a US FCC deal to demonstrate LTE-U with Verizon, and another in Germany with LTE-LAA, working with spectrum owned by Deutsche Telekom. It is hard to find technical details as it is certainly the case that the two implementations are very different given the different stages of development that each technology is at, and the different regulatory environments the demonstrations are in.
The Germany deal through Qualcomm Technologies talks about fair coexistence with WiFi in unlicensed spectrum, a reference to the fact that Listen Before Talk has been implemented in the 3GPP release 13. The particular approach to Listen-Before-Talk uses Clear Channel Assessment Procedures and channel occupancy limits which are required in regions such as Europe and Japan.
LTE-LAA coexistence measures are already embedded in 20 plus pages of very specific algorithmic channel access, in almost 3,000 page of the IEEE standard for WiFi. The 3GPP standard is expected to be complete in the first half of this year, and it is likely to be another 9 months before it is built into chips and 18 further months before it can be put into networks and devices, whereupon it will take perhaps 5 or 6 years until it becomes ubiquitous within those networks. So think 2018 before it comes to the average MNO’s rescue.
The over-the-air trial was completed in November in Nuremberg, Germany after a three-week period of extensive measurements and used LAA test equipment designed and deployed by Qualcomm, and Deutsche Telekom provided the licensed spectrum at the Qualcomm Nuremberg campus.
The team measured LAA’s extended coverage and how much it increased network capacity, and it included seamless handovers with eNB base stations. A variety of radio interference conditions were introduced and the fairness of sharing the spectrum was tested with a different number of interfering nodes. Qualcomm is not saying what it found on that score.
Meanwhile the US FCC has granted Qualcomm special temporary authority to conduct very small scale performance evaluation tests of LTE-U equipment at two Verizon sites in Oklahoma City and Raleigh. LTE-U is WiFi’s biggest concern, as it looked like it would be prepared purely for US regulations, and bypass 3GPP ratification with the result being that it interfered far more with WiFi. Since the WiFi Alliance has begun working with advocates of LTE-U, to develop a test plan for coexistence with WiFi that panic appears to be over. A draft of the plan is expected to be released in early February. Qualcomm and Verizon have also agreed to participate in subsequent laboratory and real world co-existence testing of LTE-U.
Julius Knapp, chief of the FCC’s Office of Engineering & Technology, said that while significant steps remain before LTE-U can be considered for commercial deployment, this development is an encouraging step forward. He added that LTE-U devices will have to be tested and authorized by the FCC Laboratory before they can be marketed in the US.
The current concern over LTE-U in particular, but all use of LTE in unlicensed spectrum, was brought about when the CableLabs principal architect, Jennifer Andreoli-Fang, wrote a blog in the middle of last year worried that the two implementations were not being overseen by anyone with a vested interest in ensuring that WiFi continued to work.
Andreoli-Fang also pointed out that the LTE-U Forum published a set of technical reports and specifications, including a document known as the “coexistence specification” which governs the behavior of LTE-U, but which contained almost no detail. It looks like common sense has prevailed after those early warning shots or because of them.