1. 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

2. 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.
2

3. Licensed-assisted access (LAA)
3
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

4. LAA with LTE
4

5. 5
Which Band is preferred? (1)
US
1
Europe
2
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 BRAN
DFS : Dynamic Frequency Selection
TPC : Transmit power control

6. 6
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 :

7. 7
Feasibility of DFS in LTE (1)
Basically proposed to
avoid interfering with
Radar. But can use with
other technologies?

8. 8
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)

9. 9
Proposed Deployment Scenarios(1)
Small Cell LAA Macro Cell
 LAA as a means of Carrier Aggregation with Licensed operation & achieving Dual connectivity

10. Different types of Interference
10
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. Even
Between LAAs of diff. operators

11. Information Exchange between
Operators
11
Common Database
Information sharing between operators using a common database
This will enable intelligent channel selection/allocation for LAA LTE

12. What can we do with LAA?
12
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

13. Coexistence Performance Evaluations (1)
13
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 ??

14. 14
Coexistence with Duty Cycle LTE
LTE On LTE On
LTE 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

15. 15
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)

16. 16
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)

17. Proposed Coexistence Mechanisms
17
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

18. In-device coexistence of LAA LTE and
WiFi
18
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

19. Hidden node problem for unmanaged
WiFi
19
 UE1 : Communicating with Home
WiFi AP
 UE2 : Communicating LTE-U eNB
 Home WiFi AP signal -> Interfere
To UE2
Remote sensing mechanism for optimized channel selection

20. 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
20