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WiFi-LTE Coexistence in Unlicensed Band 3GPP Workshop on LTE in unlicensed spectrum Nadisanka Rupasinghe Dept. of Electrical and Computer Engineering Florida International University 06/13/2014

3GPP workshop - LTE in unlicensed spectrum

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Page 1: 3GPP workshop - LTE in unlicensed spectrum

WiFi-LTE Coexistence in Unlicensed Band

3GPP Workshop on LTE in unlicensed spectrum

Nadisanka RupasingheDept. of Electrical and Computer Engineering

Florida International University06/13/2014

Page 2: 3GPP workshop - LTE in unlicensed spectrum

Why unlicensed band?

• More spectrum is needed for cellular operators to meet the increasing traffic demand.

• Although licensed spectrum is always preferable for providing better user experience, unlicensed spectrum can be considered as an effective complement.

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Page 3: 3GPP workshop - LTE in unlicensed spectrum

Licensed-assisted access (LAA)

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What is LAA?

A Wireless technology that is operating in unlicensed band in order to improve performance of another (or can be the same) wireless technology operating in licensed band

LTE as LAA is preferred over WiFi• Better traffic offloading• Higher user experience• Tighter interworking with licensed and unlicensed bands (Single RAT)• Better spectrum efficiency compared to WLAN

Page 4: 3GPP workshop - LTE in unlicensed spectrum

LAA with LTE

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Page 5: 3GPP workshop - LTE in unlicensed spectrum

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Which Band is preferred? (1) US1 Europe2 Japan China Korea

5.15GHz-5.25GHz (100MHz)

Indoor/Outdoor(U-NII-1)

Indoor (Band A) Indoor/Satellite Indoor/DFS/TPC Indoor

5.25GHz-5.35GHz (100 MHz)

DFS/TPC (U-NII-2A) ACA/DFS/TPC (Band A) Indoor/DFS/TPC Indoor/DFS/TPC DFS/TPC

5.35GHz-5.470GHz (120 MHz)

(U-NII-2B) under study No under study

under study

5.470GHz-5.650GHz (180

MHz)

DFS/TPC(UNII-2C) ACA/DFS/TPC (Band B) DFS/TPC In consideration DFS/TPC

5.650GHz-5.725GHz (75 MHz)

DFS/TPC/RADAR (UNII-2C)

ACA/DFS/TPC (Band B) DFS/TPC In consideration Bcast Relay Service

5.725GHz-5.825GHz (100MHz)

Yes (UNII-3) DFS/RADAR (Band C) No Licensed (3 operators)

EIRP 10 mW, Center Freq 5.775GHz

(allocated for WDCS)

5.825GHz - 5.850GHz (25MHz)

Yes (UNII-3) DFS/RADAR (Band C) No Yes Under Study

5.850GHz - 5.875GHz (25MHz)

UNII-4 RADAR (Band C) No under study

under study

5.875GHz-5.925GHz (75MHz)

U-NII-4 under study No under study

under study

1 FCC Revision of Part 15 for Operation of Devices in 5GHz, NPRM, April 2014 2 ETSI BRANDFS : Dynamic Frequency SelectionTPC : Transmit power control

Page 6: 3GPP workshop - LTE in unlicensed spectrum

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5 GHz Unlicensed band is highly preferred

Dynamic frequency selection (DFS) and Transmit power control (TPC)To overcome interference to Radar transmission and other technologies

Which Band is preferred? (2)

For Europe :

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Feasibility of DFS in LTE (1)Basically proposed to avoid interfering with Radar. But can use with other technologies?

Page 8: 3GPP workshop - LTE in unlicensed spectrum

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DFS detection threshold

Detection threshold is specified to detect signals from Radars that can be interfered by max EIRP of UE or eNB transmitter. If DL only secondary CC, then only eNB needs to implement DFS

Feasibility of DFS in LTE (2)

Page 9: 3GPP workshop - LTE in unlicensed spectrum

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Proposed Deployment Scenarios(1)

Small Cell LAA Macro Cell

LAA as a means of Carrier Aggregation with Licensed operation & achieving Dual connectivity

Page 10: 3GPP workshop - LTE in unlicensed spectrum

Different types of Interference

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Inter-RAT interference• LBT based on Energy detection approach

Intra-RAT interference (Inter- & Intra- operator)• Coordination between LAAs with ICIC & CoMP• Using Adv. Receivers with assuming sync. EvenBetween LAAs of diff. operators

Page 11: 3GPP workshop - LTE in unlicensed spectrum

Information Exchange between Operators

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Common Database

Information sharing between operators using a common databaseThis will enable intelligent channel selection/allocation for LAA LTE

Page 12: 3GPP workshop - LTE in unlicensed spectrum

What can we do with LAA?

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LAA for Carrier Aggregation/Supplemental DL (SDL)Accompanied by a Licensed Primary Carrier Primary Carrier• FDD or TDD• Control signaling, Mobility, user data

Same RAN for Licensed and Unlicensed access

Secondary Carrier• Best effort user data in DL or both UL & DL

Page 13: 3GPP workshop - LTE in unlicensed spectrum

Coexistence Performance Evaluations (1)

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WiFi 802.11n and LTE coexistence performance evaluation

eNodeB Wi-Fi AP Wi-Fi Client

Locations Fixed

Scenario Modeled in Lab Setup

Distance

• Wi-Fi throughput diminishes as LTE transmission moves closer to Wi-Fi devices

Due to SINR degradation

WiFi ED threshold (-62dBm)Not system level simulations ??

Page 14: 3GPP workshop - LTE in unlicensed spectrum

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Coexistence with Duty Cycle LTE

LTE On LTE OnLTE Off

Duty Cycle Period

Duty Cycle:% of cycle LTE is active

time

Wi-Fi access gaps when LTE is off

WiFi T’put vs LTE Duty cycle and periodWiFi 95th percentile delay vs LTE Duty cycle and period

Page 15: 3GPP workshop - LTE in unlicensed spectrum

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U-LTE (Operator B)

U-LTE (Operator B)

WiFi (Operator A)

WiFi (Operator A)

U-LTE (operator B)U-LTE (operator A)

U-LTE (operator B)

U-LTE (operator A)

Coexistence Performance Evaluations (2)

Page 16: 3GPP workshop - LTE in unlicensed spectrum

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3 carriers available for U-LTE deployment from operator A (U-LTE) and operatorB (WiFi)• Baseline: no carrier selection (co-channel deployment)• Random carrier selection: each U-LTE eNB/WiFi AP selects one unlicensed carrier

randomly• Channel-sensing based Carrier selection : each LTE node selects one

interference-less unlicensed carrier

~x 1.5

~x5

Coexistence Performance Evaluations (3)

Page 17: 3GPP workshop - LTE in unlicensed spectrum

Proposed Coexistence Mechanisms

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Investigating the importance of using WiFi packets and methods in LAA LTE• physical RF sensing and virtual carrier sensing (802.11 NAV func.)• eNB transmitting WiFi like Beacons, so that WiFi STAs/APs can detect/avoid the eNB

Investigating methods for information exchange and Management• Geo location information of WiFi access points and LTE-U eNBs• AP and eNB channel allocation statistics• Interference characteristics based on calculation and measurements

Page 18: 3GPP workshop - LTE in unlicensed spectrum

In-device coexistence of LAA LTE and WiFi

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Dual Operation

• UE receives video over LTE + LTE-U• UE relays the video over WiFi to TV• UE has to coordinate between LTE-U

reception and WiFi transmission (same device).

A TD protocol is required for WiFi Tx and LTE-U Rx co-existence

Page 19: 3GPP workshop - LTE in unlicensed spectrum

Hidden node problem for unmanaged WiFi

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UE1 : Communicating with Home WiFi AP

UE2 : Communicating LTE-U eNB Home WiFi AP signal -> InterfereTo UE2

Remote sensing mechanism for optimized channel selection

Page 20: 3GPP workshop - LTE in unlicensed spectrum

Conclusion

• 5 GHz unlicensed band is identified as the preferred band for LAA operation

• DFS and TPC to coexist with other technologies in unlicensed band - LBT implementation in LTE for medium sensing

• Different deployment scenarios for different requirements

• LAA-LTE to achieve CA/SDL – FDD• LAA-LTE as a separate cell - TDD

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