This week has seen Qualcomm taking strides towards putting LTE into unlicensed spectrum, with a deal to demonstrate LTE-Unlicensed with Verizon in the US, and another in Germany to show off LTE-LAA, working with spectrum owned by Deutsche Telekom.
The former will be the most closely watched because LTE-U is both more controversial and more immediate than LTE-LAA (Licensed Assisted Access). The former is already standardized by the 3GPP and so could be deployed as soon as this year, though only in countries, notably the US, which do not insist on Listen Before Talk (LBT) mechanisms to avoid interference in the 5 GHz band (LBT is not supported in the base implementation of LTE-U, though some vendors are adding it in a non-standard way).
By contrast, LAA does support LAA, so could be deployed almost anywhere in the world if regulators are convinced that it will coexist harmoniously with other 5 GHz technologies, particularly WiFi. But it will not be standardized until this year’s Release 13 and so commercial, standards-based roll-outs are unlikely until 2017 at the earliest. Both LTE-U and LAA require a host network in licensed spectrum, which will handle mobility, subscriber management and so on, but there are also emerging options which could be used standalone in 5 GHz (or potentially other licence-exempt and lightly licensed bands like 3.5 GHz). These include LTE-LWA (LTE WiFi Aggregation) and the Qualcomm-driven MuLTEFire.
Many members of the WiFi community remain unconvinced that LTE will not interfere with their networks, though the motivations for opposing LTE-U and LAA are sometimes confused between technical concerns, and fear of an MNO-controlled technology squeezing the commercial opportunity for WiFi in 5 GHz.
A series of lab tests and conferences have tried to bring the two sides closer together and provide scientific evidence to regulators, particularly the FCC, but the answers remain unclear, so real world trials like Qualcomm’s will be essential to see how LTE really operates in 5 GHz.
There are already some signs of truce. For instance, the WiFi players were concerned that LTE-U would be prepared purely for US regulations, and bypass full 3GPP ratification, with higher risks for interference. 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.
In another step forward, the 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, North Carolina.
“Given the significant concerns raised by many stakeholders regarding harm LTE-U will cause to broadband connections over WiFi, we hope the FCC will closely monitor the Qualcomm and Verizon trial,” said Bill Maguire, executive director of WifiForward’s Save our WiFi campaign.
Qualcomm’s SVP of government affairs responded in a statement, saying: “We are collaborating with the WiFi Alliance to develop a coexistence test plan, and we anticipate using that plan for joint lab and field tests to validate that LTE-U will not have any adverse impact on WiFi. Along with the other proponents of LTE-U, we have a substantial vested interest in WiFi.”
The cellular industry claims that LTE delivers better capacity, coverage and spectral efficiency than WiFi in the same spectrum are yet to be proven, though Walsh is convinced, saying: “LTE is a better neighbor to WiFi than WiFi is to itself. We see LTE as a great opportunity to help improve the overall mobile broadband experience for our customers by providing better coverage and faster download speeds.”
Verizon, AT&T and T-Mobile are all members of the Evolve Coalition, a group set up to advocate LTE-U. Sprint is not a member, but has said that LTE-U is “complementary to our network strategy”. However, a spokesperson told IDG News: “We see no reason to rush forward with LTE-U amid uncertainty and acrimony over basic technical facts. Our technology teams are evaluating both LTE-U and LAA, and while the use of unlicensed spectrum is on Sprint’s long term roadmap, our rich 2.5 GHz spectrum position gives us the highest capacity network today and well into the future.”
Meanwhile, Deutsche Telekom and Qualcomm have released details of an over-the-air trial of LAA technology, conducted in November at the US firm’s campus in Nuremberg, after three weeks of measurement. Deutsche Telekom provided the licensed spectrum for the host network.
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.
LTE-LAA coexistence measures are already embedded in 20-plus pages describing very specific algorithmic channel access, within the 3,000-page documentation of the IEEE 802.11 standard. The equivalent 3GPP standard is expected to be complete in the first half of this year.