LTE in Unlicensed Spectrum

April 4, 2016

placeholders-1Licensed spectrum is limited. Demand for mobile data is not. So what should a mobile operator do?

Of course, network densification via small cells should be the first step. And for small cells to have the biggest impact on the network, they must be deployed in locations where there are lots and lots of subscribers – locations such as indoor public venues. Once operators have committed to this path, they need to take the next step of supplementing their licensed spectrum with unlicensed spectrum.

There are two approaches to using LTE in unlicensed spectrum:

  1. Licensed Assisted Access (LAA) – In this approach, unlicensed spectrum is aggregated with licensed spectrum to boost LTE downlink speeds to up to 450 Mbps. LAA is being standardized by 3GPP in Release 13 (R13).
  2. MulteFire – In this approach, unlicensed spectrum alone is used to run LTE. No licensed spectrum is required. This approach is being developed by the MulteFire Alliance.

 

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LTE Licensed Assisted Access (LAA)

LAA is a great way to cost-effectively boost the coverage of LTE small cells. The licensed channel remains the primary carrier. This means that all high-priority traffic, such as voice or video calls, can still go over the licensed band. But when a subscriber wants to stream high-bandwidth video the small cell system can leverage available unlicensed spectrum.

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Notice how the decision of which spectrum to use – licensed or unlicensed – rests with the operator controlled LTE-LAA small cell. If the small cell detects that the Wi-Fi channel is extremely congested and unusable it can continue to service the user over licensed spectrum. The scheduler in the small cell manages the user’s quality of experience (QoE). This is a big difference compared to Wi-Fi. When a subscriber connects to a building’s Wi-Fi network the operator is pushed out of the picture. All traffic now goes over the Wi-Fi network if the unlicensed spectrum is congested.

LTE-LAA requires no changes in the LTE core network (EPC). This is really big. In the past, the only way operators could reliably use unlicensed spectrum in public venues was by building their own Wi-Fi networks (so-called “Carrier Wi-Fi”). However, to do this they required new WLAN gateways, management systems, AAA systems, and even more importantly a new organization (people, yes, lots of them) who understood Wi-Fi and could manage it. As a result, very few mobile operators deployed Carrier Wi-Fi. This is not the case with LAA. In fact, LAA is transparent to the core network, and network engineers who know how to manage an LTE network can manage an LTE-LAA network. It is that simple.

Verizon, one of the most technologically advanced operators in the world, is not waiting for R13 to be standardized to benefit from LAA. It has created a pre-R13 approach called LTE-U with its technology partners. Verizon has announced that it will be doing LTE-U trials this year with Qualcomm, Samsung and SpiderCloud Wireless.

MulteFire

MulteFire makes it possible to deploy LTE in unlicensed spectrum only. It builds upon LAA as standardized in 3GPP R13, by (1) removing the need for a licensed channel as anchor, and (2) using unlicensed spectrum for uplink, in addition to downlink.

MulteFire is good for mobile operators. Many mobile operators are deploying licensed spectrum small cells right now. However, doing so is not always possible. There are tens of thousands of buildings where it makes business sense for operators to share small cell infrastructure with each other. Further, many venues insist on shared wireless systems for space and aesthetics. This is where MulteFire comes in, allowing operators to share small cells, without sharing their licensed spectrum, and leverage neutral host providers.

MulteFire will also allow mobile operators to partner with enterprises to deploy mobile connectivity solutions. Over the years, SpiderCloud has met many enterprises that are willing to purchase affordably priced small cell systems that leverage their existing LAN. However, network departments of mobile operators are rarely eager to let enterprise IT own and operate small cells that may, if improperly used, degrade the macro network. By using unlicensed spectrum MulteFire takes that concern away, and makes it easier for able and willing enterprises to invest in LTE small cells.

MulteFire small cell systems do not require any new core network gateways or authentication systems. They can connect to the core network just like normal LTE small cells. Well designed MulteFire small cell systems will connect to multiple core networks without a hitch. They natively use SIM-based authentication. They will honor QCI markings, and any other policies provided by the core network. They can be monetized like any other LTE service. They will offer the same kind of LTE KPIs that network engineers measure on their LTE network.

SpiderCloud’s role in making LTE in unlicensed a success

Since regulations limit transmit power in unlicensed spectrum, this spectrum is ideal for indoor use. At SpiderCloud we are big believers in the importance of adding capacity indoors – especially in high-density indoor locations. When an operator adds a hundred (yes, 100) sectors of capacity inside a building with a few thousand subscribers, it not only offers a great user experience to these subscribers, but also frees up a massive amount of capacity on the macro network for outdoor users. When it comes to capacity build-out, indoor is a 2-for-1 deal! We build licensed spectrum small cells to do this today, and we are really excited about what is possible with unlicensed spectrum.

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SpiderCloud, and many industry analysts, believe that distributed small cell technology (in contrast to centralized baseband units connected to remote radio heads) is the only viable way to implement any LTE technology that requires co-existence with Wi-Fi, whether it is LTE-U/LAA or MulteFire (supporting document). Each small cell should be able to independently pick the unlicensed channel that it uses, just like Wi-Fi systems do. Further, systems operating in unlicensed spectrum must decide within microseconds if a channel is available, inform other users of their intent to transmit, and then use the channel. Of course, the challenge with using distributed small cells in large high-density venues – where the greatest benefit of MulteFire will be – is small cell coordination. SpiderCloud E-RAN architecture has been solving this problem since 2011, and we look forward to extending the E-RAN architecture to LTE-U/LAA and MulteFire.

SpiderCloud Wireless will be exhibiting at LTE LatAm  6 – 7 April, where Amit Jain will also be a featured speaker. Find out more and view the full agenda: https://latam.lteconference.com/

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