Understanding LTE unlicensed and Coexistence

Azimuth Webinar – December 2015

Product Introduction

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• Although licensed spectrum remains operator’s top priority to deliver advanced services and user experience, use of unlicensed spectrum is becoming an important complement for operators to meet the growing traffic demand

• Use of unlicensed spectrum by LTE is a broad industry topic ▪ How will it improve LTE performance? ▪ How will it coexist with other technologies that use this spectrum? ▪ How will fair sharing of the spectrum be achieved? ▪ What impact will this have on Wi-Fi performance?

Introduction

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• Frequency spectrum is reserved for unlicensed wireless transmission throughout the world ▪ Industrial Scientific Medical bands, ISM (defined by ITU-R) ▪ 5 GHz: U-NII: Unlicensed National Information Infrastructure

• At 5 GHz, > 500 MHz of bandwidth is available ▪ Spectrum allocation varies by country

- All or parts of 5150-5925 MHz - 5150-5350, 5470-5725 MHz designated by WRC - 5725 – 5875 MHz ISM - 5850 -5925 MHz allocated to ITS in some regions

▪ Regulations on Power Levels, Dynamic Frequency Selection

Unlicensed Spectrum

Existing and proposed new FCC rules for 5 GHz unlicensed

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• Use of unlicensed bands requires fair sharing or coexistence with other technologies

• Regulatory bodies create basic rules for use: ▪ Transmit power – limits range

- 100 mW to 1W ▪ Radar avoidance – Dynamic Frequency Selection (DFS)

- Requires listen before talk

• Radio technologies and media access control are developed to insure coexistence of the different technologies

Unlicensed Coexistence

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• 3 major proposals /methods are being considered for LTE use in unlicensed bands 1. LTE-U 2. LTE/LAA 3. LWA

• For all methods, fair coexistence with Wi-Fi is considered paramount

LTE and use of unlicensed 5 GHz

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L T E - U

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• LTE-U forum was created in 2014 to jump start operation of LTE in unlicensed band

• LTE-U forum members ▪ Verizon, Alcatel-Lucent, Ericsson, Qualcomm Technologies, Inc., and

Samsung

• Based on existing 3GPP release 10, 11 and 12 specifications ▪ No new standards needed

- Operate within the framework already defined - Define specifics for this application

▪ Can make use of existing devices (with SW upgrades)

LTE-U

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• Effectively Carrier Aggregation of a Unlicensed carrier with a licensed carrier ▪ Also know as Supplemental Downlink (SDL)

• Unlicensed operation is Downlink only and TDD ▪ All uplink is via the licensed carrier

LTE-U

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• Use of U-NII 1 and 3 only ▪ 5 1 5 0 - 5250, 5725 - 5850 MHz / Bands 252, 255

• U-NII-2 is not used - requires regulatory DFS ▪ 5250 -5725 MHz, bands 253 and 254

• Because LTE-U does not use Listen Before Talk (LBT) mode, use is possible only for: ▪ United States, India, China and S. Korea ▪ Others regions require LBT

LTE-U Bands

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LTE-U Coexistence Find a clear channel – dynamically avoid Wi-Fi

If no clear channel is available, adapt LTE transmission to fair share the channel with Wi-Fi via Carrier Sense Adaptive Transmission (CSAT)

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• CSAT

▪ eNB will transmit LTE-U Discovery Signals (LDS) on a periodic basis such that the UEs can perform necessary SCell measurements

▪ Sense the channel for activity ▪ Adapt the eNB transmission to insure fair sharing ▪ Transmissions with PDSCH, limit transmission time to no longer

than 20 msec bursts

• Transmissions ▪ Using a FDD frame structure (type 1) ▪ Supports LTE Transmission modes TM 2, 3, and 4 only

LTE-U CSAT

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• LDS is transmitted at a fixed time periodicity regardless of any UE configured or activated

• Maximum SCell on state shall not be greater than 20 msec. ▪ Minimum time is 1 msec

CSAT Example

Diagram from LTE-U Forum LTE-U CSAT Procedure TS V1.0

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• LTE-U forum has developed requirements, test and coexistence specifications for LTE-U eNB and UE devices

• The UE and eNB minimum requirements and test specifications are based on existing 3GPP documents ▪ TS 36.101 / TS 36.521-1 for UE ▪ T S 36.104 / TS 36.141 for eNB

• The SDL coexistence specification focuses on coexistence conformance and performance testing ▪ Ensure that LTE-U eNB is following the specifications ▪ Ensure interoperability with Wi-Fi as well as other operators that may be

using the unlicensed spectrum ▪ Validate basic coexistence performance

LTE-U Testing

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Coexistence Test configurations define ▪ Real devices: LTE eNB and UE, Wi-Fi AP and STA ▪ Inter operator configurations ▪ Multiple eNBs and APs ▪ Up to 5 Wi-Fi STA ▪ Using data and VoIP traffic ▪ Minimum power levels

- Above Energy Detect (ED) thresholds ▪ Test cases are defined both open air and conducted

LTE-U Coexistence Testing

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L T E / L A A

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LTE/LAA (3GPP) • Kicked off by 3GPP in Jun. 2014, with established initial priorities: ▪ 5 GHz band ▪ Global solution that can work across regions ▪ Licensed-Assisted Access operation (LAA)

- Aggregation of a primary cell, operating in licensed spectrum to deliver critical information and guaranteed Quality of Service, with a secondary cell, operating in unlicensed spectrum to opportunistically boost data rate

- The secondary cell operating in unlicensed spectrum can be configured either as downlink-only cell or contain both uplink and downlink

▪ Fair coexistence between LTE and Wi-Fi as well as between LTE operators

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• Study item was completed in June 2015 ▪ 3GPP TR 36.889: Study on Licensed-Assisted Access to Unlicensed

Spectrum

• For fair coexistence with Wi-Fi, a Listen Before Talk (LBT) mode is required ▪ All sources submitting simulations showed LBT category 1 can

not operate without impact to Wi-Fi ▪ Majority of sources showed that at least one LBT scheme for LAA that

does not impact Wi-Fi by more than another Wi-Fi network ▪ Details of this work can be found in the technical report

• LBT is also necessary for regulatory reasons - DFS

LTE/LAA

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• 4 categories of LBT were defined: ▪ CAT 1 = no LBT ▪ CAT 2 = LBT without random back off ▪ CAT 3 = LBT with random back off with fixed size contention window ▪ CAT 4 = LBT with random back off with variable size contention window

• CAT 4 LBT is recommended for PDSCH transmission ▪ Contention windows parameters should be configurable to support

coexistence

3GPP LBT

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• 3GPP study considered both Downlink and Uplink operation in the unlicensed band ▪ LBT for UL (can be different from DL)

• Define bands in the frequency range of 5150 -5950 MHz

• Discontinuous transmission – to limit maximum transmission durations

• DRS – Discovery reference signals with a periodicity of 40, 80 or 160 msec. ▪ Signals comprising DRS include PSS, SSS and CRS ▪ LBT considerations of such may vary by region

• Carrier selection – if a large bandwidth is available, select the carriers with low interference

• PHY layer operation with bandwidth < 5 MHz is not considered

Other Key Elements of the LAA Study

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• Work is underway with expectation to complete LAA in June 2016 ▪ Core part done Dec 2015, Performance part June 2016 ▪ Comprised of change requests to TS 36.211, 212 and 213

• To support LAA, New UE devices are required ▪ LBT mode ▪ Dynamic Frequency Selection (DFS)

• Initial support will be downlink ▪ Evolution to bi-directional unlicensed

LTE/LAA

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• Conformance and Performance specifications will be developed as part of the 3GPP work ▪ Updates to TS 36.521-1 and TS 36.141

• Test requirements ▪ Most 3GPP test cases are around compliance with minimal performance

- Insures standards and interoperability ▪ Coexistence testing with other technologies will be required to

insure performance ▪ Equipment manufacturers and operators may have specific tests needs

depending on product and deployment

LTE/LAA Testing

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L W A

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• To avoid a new LTE MAC layer to coexist with Wi-Fi (LBT), LTE could use Wi-Fi MAC and PHY and tunnel LTE

▪ Provides fair use of spectrum with Wi-Fi as it is essentially Wi-Fi at the physical layer

• Make use of a LTE licensed cell similar to LAA and aggregate the Wi-Fi channel

• Makes core easier with a single entry point into EPC

• New devices are not required - only a SW upgrade to devices that support 5 GHz Wi-Fi

• Quickly gaining more support

• Part of the 3GPP work item

LWA: LTE / Wi-Fi Aggregation

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LWA Flow

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Summarizing the LTE Unlicensed Flavors Aspect LTE-U LTE/LAA LWA

Technology Aggregation of licensed primary carrier with unlicensed secondary carrier

Aggregation of licensed primary carrier with unlicensed secondary carrier with LBT, DFS

LTE traffic tunneled through Wi-Fi PHY, MAC

Media Control CSAT, No LBT LBT, DFS Wi-Fi media control Standard/Forum LTE-U Forum,

based on 3GPP Rel. 10 - 12

3GPP (Rel. 13) 3GPP

Device Existing handsets (with S/W upgrade)

New handsets with support for LBT, DFS

Existing handsets (with S/W upgrade)

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• Multitude of real devices ▪ APs, eNBs, STAs, UEs, IoT devices, other interferers, radar

• Run real-world use cases ▪ Traffic, Real world applications and report KPIs of interest

• Dynamic field environments ▪ One to One, One to Many, Many to Many topologies -> P2P, Star,

Mesh configurations A Mesh type architecture - where all elements could see each other

▪ Wide frequency ranges ▪ Wideband – wide channels, frequency agile ▪ MIMO

• Automation of the test bed – channel control, traffic conditions, device configuration and gathering metric

What is Needed for Testing Coexistence?

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• Radically different approach compared to link level testing

• Platform ▪ Star, mesh architecture that scales ▪ Controlled path loss with full rank MIMO ▪ Wideband to support dynamic frequency selection ▪ Low insertion loss and insertion delay

• Enabling software ▪ Software that controls the entire test bed (Devices, AP, traffic,

sniffers/monitors) ▪ Automation is key ▪ Enable creation of tests by end users

So, What is a Viable Approach?

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• Integrated H/W and S/W that provide: ▪ Controllable bi-directional MIMO link ▪ One-to-one, Many-to-many topologies ▪ Complete RF isolation ▪ Automation of test bed components (Devices, APs, Traffic Sources)

• Focused, turnkey solutions/personalities built on Spider for different applications/use cases

Spider!!

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• Fully automated, self-contained solution built on the Spider for testing LTE Unlicensed

▪ Includes test cases developed by the LTE-U Forum (LTE-U Forum SDL Coexistence)

▪ Leverages Azimuth’s platforms and modules developed for LTE and Wi- F i testing ▪ Purpose built, yet provides a flexible and scalable solution

Spider Unlicensed

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Azimuth’s Product Portfolio

Test Executives: • Command and control the entire test bed • Tools to support automation, test case creation

and management

RF Emulation & Control Portfolio • Ability to create and control the RF

environment

Accessories • Facilitate test bed connections

Automated Test solutions • Ability to assess user experience and test

performance & interoperability

Field to lab • Ability to test in the lab under field conditions

2017-10 MG No. AZCHEM-E-L-3-(1.00)