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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
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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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
LAA with LTE
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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
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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?
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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)
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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
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
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
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
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 ??
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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
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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)
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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)
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
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
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
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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