Could an MVNO Deliver 3.5 GHz Unlicensed-LTE?

On January 21, 2015, the WSJ reported that Google plans to become a mobile carrier by using T-Mobile and Sprint as wholesale providers. This type of mobile reseller, that does not own licensed spectrum or infrastructure, is known in the industry as an MVNO, or Mobile Virtual Network Operator. The news reports also speculated that Google may be delivering a Wi-Fi focused mobile service similar to Republic Wireless, FreedomPop, or Scratch Wireless.

A lot of regulatory and Radio Access Technology (RAT) planets are aligning in such a way that might just create a hugely disruptive mobile world, if Google actually implements its reported plans. This regulatory-technology alignment includes: 1) new extremely low-cost pico and femtocell RATs; 2) the FCC’s opening up of 150 MHz of 3.5 GHz spectrum with 80 MHz of the band open for unlicensed General Authorized Access (GAA) use in many geographies; and, 3) TD-LTE micro base stations and mobile devices that use 3.5 GHz in Asia. TD-LTE uses 3GPP (3rd Generation Partnership Project) Bands 42 and 43 covering 3.4GHz to 3.8 GHz. The TD-LTE spectrum, thus, can be used for delivering mobile service in the 3500-3650 MHz set aside by the FCC. What these facts equate to that any new carrier, like Google, could offer “unlicensed LTE” on 80 MHz of free, unlicensed, and, basically unused, clear 3.5 GHz spectrum.

What is unlicensed LTE, also known as U-LTE? Well the answer is not as simple as one would think. Qualcomm proposed “LTE-Unlicensed” (not “unlicensed LTE”) as a multi-RAT (I am not making up these acronyms) technology for mobile use in the 5GHz unlicensed WiFi spectrum. LTE-U is also known as “Licensed Assisted Access.” 3GPP is working on Release 13 of LAA to standardize the technology. LAA or LTE-U is not the same as “unlicensed LTE”. With LAA, the available unlicensed spectrum is aggregated in the mobile device with the mobile carrier’s LTE licensed spectrum. The technique is called “Carrier Aggregation” or CA. In the Internet-router world, the term would be called “bonding.”

By combining licensed and unlicensed spectrum paths in the mobile handset, LAA can deliver a serious major increase in bandwidth. With LAA, licensed LTE spectrum is used by a mobile carrier as the initial, primary connection from the cellular base station to the device and the unlicensed 5GHz portion of the connection is the secondary spectrum path – think of it as a redundant path, sort of. A second method of LAA is called the “Supplemental Downlink” or SDL where the unlicensed spectrum is used only for the download direction only to the device, and not uploading as used in LTE Carrier Aggregation. Ericsson has been testing the LAA LTE technology bonding and is reporting peak throughput rates of 450 Mbps by combining 20MHz of licensed spectrum with 40MHz of unlicensed 5GHz spectrum.

The key factor is that LAA/LTE-U does not permit operation in the devices without a licensed LTE connection. One concern regarding LAA is that to operate effectively in 5GHz, LTE will need to cooperate with WiFi standards to avoid interference. Changes in WiFi technology will be needed. This means, for example, getting the WiFi Alliance to agree to changing WiFi standards in 5GHz to play friendly with LAA 5GHz LTE. These WiFi hurdles include technical changes to WiFi routers, WiFi standards, WiFi IEEE changes, country by country regulatory and harmonization changes as countries will have to agree to the changes. WiFi has been the savior for mobile carriers letting users depend on their home WiFi rather than using their carrier’s mobile infrastructure and licensed spectrum. Disrupting WiFi’s ecosystem, therefore, could be difficult for more than technical hurdles. LAA, while promising especially for the ability to deliver almost a half gigabit to a device, is a long road ahead, so it seems.

Unlicensed LTE differs from LTE-U/LAA because unlicensed LTE, unlike LAA, does not require a licensed spectrum connection in order to be operational. With unlicensed LTE, there is no carrier aggregation or supplemental download. With unlicensed LTE, there is the ability to deliver large Mbps throughput without requiring bonding within the device with other spectrum. Such bonding demands new chip-sets, extra battery drain, and most importantly access by the device to a base station cell tower using licensed spectrum in the same micro-geography.

Most significantly, 3.5 GHz is not allocated for WiFi which eliminates the problems that 5 GHz LAA has with WiFi cooperation. Thus, there are not WiFi hurdles to overcome. Unlicensed LTE does not require licensed and unlicensed spectrum to cooperate together. Thus, if the appropriate unlicensed spectrum is made available where there are not issues with WiFi and not need to purchase license spectrum, unlicensed LTE could allow the build-out of a nationwide carrier that does not own spectrum and yet operates like a mobile carrier rather than an MVNO using WiFi off-load.

FCC Chairman Tom Wheeler describes 3.5 GHz as the “Innovation Band.” The FCC recognized that 3.5 GHz is ideal for using the new, and well proven, TV White Space database technology. The 3.5 GHz order calls the database the Spectrum Access System or SAS. SAS databases are located in the cloud and direct base-station broadband radios and their connected devices to available spectrum as authorized by the FCC. The database directed base-stations and devices are “agile” radios that can move from one spectrum slice to another as directed by the FCC real-time inputs to the SAS database or by algorithms in the database system without a loss of connection for the user.

The cloud databases are continuously updated with available spectrum from the FCC or other sources. The databases are able to direct the radio base-stations and connected devices to available spectrum in 100 meter micro-geographies, to raise or lower power levels, or to determine spectrum availability based on antenna height, all in real-time. The FCC 3.5 GHz order recognized that the TV White Space database-agile radio technology would be ideal for 3.5 GHz spectrum sharing and efficiencies where there are incumbent government users, like the Navy, that need the 3.5 GHz in some locations and not others, and at some times but not others. The cloud-directed agile radios can move from one spectrum band to another, on the fly, preventing interference with incumbent users like Navy radar or secondary priority users (PAL) like mobile carriers using 3.5 GHz spectrum for small cells. In all, there will be three sets of 3.5 GHz users: i) Incumbent Access, ii) PAL, or Priority Access Licenses, consisting of 10MHz blocks of spectrum auctioned to mobile carriers, and iii) GAA – General Authorized Access for unlicensed use.

Google is well positioned to be one of the authorized 3.5 GHz spectrum database provider. Google has been a steadfast supporter of making 3.5 GHz available for unlicensed use. The FCC approved Google as a TV White Space database provider for TV spectrum (54-698MHz) broadband radios giving the company years of experience that can be applied to the 3.5 GHz spectrum. Other database providers include Microsoft, iConectiv (Telcordia), and Spectrum Bridge. Google’s successful experience with cloud-directed spectrum sharing will translate well into using the 3.5 GHz three-tiered spectrum for TD-LTE pico and femto mobile base stations. The combination of technologies could deliver true “unlicensed LTE” without the need for the massive capital outlay need for licensed spectrum.

If Google, or another new mobile carrier startup, decides to build a greenfield network of 3.5 GHz TD-LTE macro-cells on towers or rooftops, the need for purchasing billions of dollars of spectrum will not be required. At $2.70 per MHz/POP received in the recent AWS auction, 75MHz of nationwide unlicensed spectrum could cost, in an auction, as much as $170 billion. The difference between the initial capital requirement of billions of dollars for licensed spectrum compared to paying nothing unlicensed, clean spectrum is enormous for a mobile business. Thus, a build-out of infrastructure, especially using small cell infrastructure, would enable financially sustainable mobile carrier business model.

One technical hurdle that will need to be overcome is the potential TD-LTE interference from other users of non-LTE equipment in the same GAA unlicensed spectrum. LTE is known to be sensitive to inference from other devices. While LTE is excellent dealing with interference from its own radios, it does not play well with interference from other non-LTE uses within the spectrum. GAA is unlicensed. Thus, other 3.5 GHz unlicensed providers in the same local micro-geography, which will be the size of census-tracts, could cause a poor experience for the unlicensed LTE mobile user. However, because all users of GAA will be connected to a SAS cloud-database directing the agile radios, the SAS database could become a voluntary traffic cop for unlicensed users, directing the unlicensed LTE carriers and the other 3.5 GHz unlicensed GAA users into different slices of clear, unlicensed spectrum eliminating potential interference. The 3.5 GHz GAA spectrum will be essentially new, unused spectrum, and thus will have characteristics of exclusive, interference-free licensed spectrum. WiFi spectrum use found in 2.4GHZ and 5GHz will not interfere with the new 3.5 GHz U-LTE service. And most importantly because TD-LTE is being used in Asia today, low cost base stations, picocells, and mobile devices are already available now. On April 17, 2015, the FCC adopted rules for 3.5GHz, with comments due in 30 days after publication in the Federal Register.

To deliver mobile service without building towers, Google could simply deploy TD-LTE pico and femto cells to customers, just like Comcast does today with dual-use WiFi modems in customers’ homes and on low level outdoor locations. Google could also locate the TD-LTE pico cells on its new Google fiber that will be deployed in 34 cities, in the same manner that Comcast is deploying WiFi on its aerial cable to deliver XFINITY WiFi.

Google likes to do things its own way, using unique disruptive methods. Google built its own web servers from scratch, built its own open-source Android devices, built its own scraping software, built its own datacenters, and built its own self-driving car. Delivering a mobile service using unlicensed LTE in the 3.5 GHz band with existing TD-LTE equipment could be Google’s answer for a new mobile competitor that is not a mere reseller-MVNO dependent on heavily used WiFi.

The SAS cloud-directed agile radio system, deployed, proven, and tested with TV White Spaces, is opening up new mobile possibilities hardly imagined when the first MVNOs were rolled out 15 years ago. Therefore, the stage is now set for a new generation of mobile carriers not dependent on licensed spectrum.