A Range of Views on LTE in Unlicensed Spectrum


March 30th, 2015

A key theme in this “unlicensed spectrum” series of blog posts has been the potential negative impacts on wireless carriers of lower-cost services built on WiFi connectivity, either in a “WiFi-first” or “WiFi-only” mode.

In this two-part post the focus will shift to potential LTE deployments in unlicensed spectrum by licensed carriers, as they seek to increase network capacity while retaining tighter integration with their existing LTE-based networks than they can achieve with WiFi technology.

The prospect of carriers deploying LTE in unlicensed bands marks a new phase in the history of unlicensed spectrum. In this new phase licensed carriers and their preferred technologies (e.g., LTE) could play a much bigger role in the unlicensed space, potentially disrupting the existing spectrum sharing model embodied in WiFi standards and familiar to users of WiFi technology.

The deployment of LTE in unlicensed bands is referred to by multiple names, including “LTE Advanced in unlicensed spectrum,” “LTE Unlicensed” (LTE-U) and, most recently “Licensed Assisted Access” LTE (LAA). In this post I’ll refer to it as LTE-U, though other names will appear in some excerpts included in the post.

Not surprisingly, there exists a fairly broad range of views on the balance of benefits and harms likely to occur from carrier deployment of LTE-U.  As one might expect, Qualcomm, the wireless tech giant that first proposed the idea in late 2013, is enthusiastic. In a November 20, 2013 blog post, Prakash Sangam, Director, Technical Marketing summarized his company’s perspective:

Consider the length that operators are going to address increasing data traffic with small cells and utilizing all spectrum assets….Wouldn’t it be ideal for them to deploy small cells that support LTE not only in their regular licensed spectrum but also in unlicensed spectrum?…[I]nstead of managing two separate networks for licensed and unlicensed spectrum, and dealing with the complexities of interworking between them, they will have one unified network accomplishing the tightest possible interworking. How cool is that?

Okay, the operators are covered. What about the mere mortals like us, the users? Well, remember all the juggling between LTE and Wi-Fi networks; making sure you are connected, and connected to the right technology to get the best speed; worries about the media not seamlessly moving over between the networks, and tolerating video freezing, breaks, restarts etc.? All of that will be over with LTE Advanced in unlicensed spectrum…Because it’s one network, with an anchor in the highly reliable licensed band, you are always in safe hands. Add to that carrier aggregation, across licensed and unlicensed bands, and you, the user, get higher data rates and an enhanced broadband experience.

This is all good, but one natural question someone might ask (we asked it ourselves) is, “will it affect the Wi-Fi networks out there now?” Well, LTE Advanced in unlicensed spectrum has been carefully designed to protect Wi-Fi, so that both can co-exist harmoniously. So, when an operator switches from Wi-Fi (“carrier Wi-Fi” as it is called in the industry) [to] LTE in unlicensed, not only do LTE Advanced users in the unlicensed spectrum benefit but also, in many cases, the neighboring Wi-Fi users.

Moreover, LTE Advanced in unlicensed can be brought to fruition in countries such as the United States, Korea and China using the existing standards (Rel 10) and, of course, by leveraging the existing LTE core networks.

Given the cable industry’s growing enthusiasm for a WiFi-based wireless strategy (see here and here), it’s not surprising that they are less enthusiastic than Qualcomm about wireless carriers deploying LTE in unlicensed spectrum. In a May 21, 2014 post on the CableLabs blog, Ian MacMillan expressed some of their concerns:

LTE is designed for licensed spectrum where all of the data traffic is managed by a single network operator. So LTE as currently designed won’t play fair with other users in the unlicensed bands. Wi-Fi is designed to be a cooperative network. It works with multiple access points owned by different people or companies all trying to use the same spectrum.

Some regions of the world mandate that unlicensed spectrum technologies must be able to share the spectrum, so LTE can’t be used without modifications in those regions. Unfortunately North America is not one of those regions (nor is China)…

It’s unlikely that LTE-U would actually be deployed by a mobile network operator without some form of fairness-mechanism, because the backlash from consumers and industries would be very undesirable. However, even with a fairness-mechanism, more network technologies would be contending for the same amount of unlicensed spectrum, which could mean your Wi-Fi connection is not as fast or responsive as it could be…

LTE-U has many capabilities that we all could benefit from if they were to be included in Wi-Fi. In fact, there is work underway to add some of these capabilities, but the Wi-Fi we know and love has some basic design principles that may preclude it from being as robust and efficient as LTE if LTE were as ubiquitously deployed. These design principles are the same ones that allow anyone to share the unlicensed spectrum with Wi-Fi.

In a statement in early February of this year, the Wi-Fi Alliance expressed a similarly cautious perspective about carriers deploying LTE in unlicensed spectrum bands:

Wi-Fi Alliance is aware of [standards] work addressing LTE operation in the unlicensed 5 GHz band, known as LAA, as well as early deployments of pre-standard LAA-like systems. There is a risk that LAA, and especially pre-standard systems deployed ahead of coexistence work being done in the industry, will negatively impact billions of Wi-Fi users who rely on 5 GHz today for networking and device connectivity. It is generally agreed in principle that fair sharing is required, but there needs to be further work from all parties to address this risk in practice.

The future value of unlicensed spectrum is dependent upon good stewardship by all technologies that share the resource. The LTE and Wi-Fi communities must work toward a mutually understood fair and effective use of the 5 GHz band and ensure that there are no adverse effects to the installed base and future users of Wi-Fi. Wi-Fi Alliance is planning collaboration with 3GPP, and is eager to work with those planning pre-standard deployments to help them continue to satisfy the expectations of Wi-Fi users.

Wi-Fi Alliance will also continue to support regulators in their attempts to understand this emerging technology and its implications. We plan to work with regulators and industry stakeholders toward an industry-led outcome that avoids heavy regulation and ensures that users are able to benefit from Wi-Fi well into the future.

In a blog post later that same month, EJL Wireless Research analyst Maury Wood expressed skepticism about some of Qualcomm’s claims about the performance and impacts of LTE-U. Noting that WiFi “utilizes a polite “Listen-Before-Talk” (LBT) clear channel assessment (CCA) scheme,” Wood expressed doubts about Qualcomm’s claims that: 1) LTE-U’s coexistence protocol (Carrier Sensing Adaptive Transmission, or CSAT) would make LTE-U “a better neighbor to Wi-Fi than Wi-Fi” and 2) LTE-U would provide greater capacity and improved technical performance relative to WiFi.

Wood ended the post by highlighting what he suggested was his greatest concern:

On the one hand, operators who have spent tens of billions of dollars for licensed spectrum access can be expected to strongly support a new standard that will protect their investment in LTE spectrum and infrastructure. On the other hand, what party represents the public’s interest in ubiquitous Wi-Fi services? If LTE-U is adopted by the 3GPP in Release 13, who will protect consumers if LTE-U has unintended consequences on legacy Wi-Fi services? I am concerned that the operator profit motive could lead to a classic “tragedy of the commons” outcome for Wi-Fi in the future.

On June 19, 2014 in Sophia Antipolis, France, the 3rd Generation Partnership Project (3GPP) held a workshop on issues related to the deployment of LTE in unlicensed spectrum. 3GPP is a collaboration among seven organizations (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC) involved in developing standards for cellular network technologies. According to its web site, “the major focus” of 3GPP is “to make the system backwards and forwards compatible wherever possible, to ensure that the operation of user equipment is uninterrupted.”

The 3GPP web site includes links to nearly 30 (zipped) presentations from the June workshop, which attracted 176 participants. Among the presenting organizations were Alcatel-Lucent, AT&T, Broadcom, CableLabs, China Unicom, Ericsson, Intel, LG, Nokia, Qualcomm, Samsung, Sony, T-Mobile and Verizon.

In a follow-up post I’ll focus on emerging plans of U.S. wireless carriers to deploy LTE in unlicensed spectrum.


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