1. 助理教授：吳俊興 助教：吳振宇、王瑞元 國立高雄大學 資訊工程學系
教育部行動寬頻尖端技術人才培育計畫-小細胞基站聯盟中心
示範課程：行動寬頻網路之異質性存取
Week #14 LTE-U and LAA: Licensed-Assisted Access to Unlicensed Spectrum
助理教授：吳俊興
助教：吳振宇、王瑞元
國立高雄大學 資訊工程學系

2. Outline Introduction LTE-U and LAA Regulatory Requirements
Spectrum Considerations
LAA Carrier Aggregation Feasibility Study
Deployment scenarios for LAA
Coexistence
Design targets, functionalities and solutions for LAA

3. Introduction
LTE-U (LTE-Unlicensed), or as it is also known LTE-LAA (LTE-License Assisted Access) utilizes unlicensed spectrum, typically in the 5GHz band to provide additional radio spectrum
First introduced in Rel13
Built upon carrier aggregation capability of LTE-A
No changes are needed to the core network

4. 3GPP LTE-U and LTE-LAA
To evaluate LTE enhancements for a single global solution framework for licensed-assisted access (LAA) to unlicensed spectrum
Approved at 3GPP TSG RAN #65
Complementary access using the unlicensed band would be supported by licensed operation, the quality of which can never be matched by unlicensed operation

5. Three Ways of Deployment
Downlink only
Uplink and downlink
FDD / TDD aggregation
The use of carrier aggregation mixes between FDD and TDD

6. LTE-unlicensed Operation Modes

7. LTE-advanced Aggregation Between FDD and TDD Bands

8. Licensed-Assisted Access (LAA)
LTE in unlicensed spectrum serves as an additional tool to maximize the value for users, while the core of the activity remains anchored to the licensed spectrum
The primary component carrier in licensed spectrum will still be used to carry some (or all) of the control signal (and possibly also data, e.g. retransmissions) of the traffic carried over the carrier in unlicensed spectrum
Unlicensed spectrum is better used as “Licensed-Assisted Access”, considered as a secondary component carrier in a carrier aggregation scenario
The use of unlicensed spectrum also increases the need for more licensed spectrum

9. LAA Spectrum
Define 5 GHz unlicensed LAA band or bands within frequency limits 5150 – 5925 MHz
The PHY layer options considered for LAA have at least the following characteristics
Support for at least 20 MHz system BW option in the 5 GHz band
System bandwidths < 5 MHz are not considered for PHY layer options in LAA
Potential interference sources
IEEE (a, n, ac)
Weather radar

10. 3GPP TR36.889 (R13): Study on Licensed-Assisted Access to Unlicensed Spectrum
Scope
References
Definitions, symbols and abbreviations
Regulatory requirements
Spectrum considerations and LAA carrier aggregation feasibility study
Deployment scenarios for LAA
Design targets, functionalities and solutions for LAA
Coexistence evaluations
Conclusions
Annex A: Evaluation methodology
Annex B: Evaluation results for co-channel coexistence
Annex C: Change history
( )

11. Unlicensed Spectrum Availability in Different Regions LTE

12. Spectrum Considerations in Europe
5 GHz spectrum allocations in Europe
Summary of existing and proposed EU regulations for WAS/RLANs in the 5GHz band

13. Transmit Power and Emission Requirement in Europe

14. DFS Requirements in Europe

15. LBT Requirements in Europe
Parameter
Requirement
Comment
Clear Channel Assessment (CCA) time
Minimum 20μs
Channel Occupancy time
Minimum 1 ms, maximum10 ms
Idle period
Minimum 5% of channel occupancy time
Fixed frame period
Equals to Channel Occupancy time + Idle Period
Short control signaling transmission time
Maximum duty cycle of 5% within an observation period of 50ms
Part of Channel occupancy time
CCA Energy detection threshold
Assuming receive antenna gain G=0dBi:
If EIRP=23dBm at transmitter
Threshold ≤ -73 dBm/MHz
Otherwise (different transmit power levels, PH)
Threshold = -73(dBm/MHz) + 23(dBm) – PH(dBm)
For WAS/RLAN
LBT requirements for Frame-Based-Equipment in Europe
Parameter
Requirement
Comment
Clear Channel Assessment (CCA) time
Minimum 20μs
Also referred to as CCA time slot
N (number of clear idle slots) in extended CCA
N shall be randomly selected in the range 1..q every time, q=4…32
Channel Occupancy time
<= (13/32) × q ms
Idle period
At least the duration of a random factor N multiplied by the CCA time slot.
Short control signaling transmission time
Maximum duty cycle of 5% within an observation period of 50ms
Part of Channel occupancy time
CCA Energy detection threshold
Assuming receive antenna gain G=0dBi:
If EIRP=23dBm at transmitter
Threshold ≤ -73 dBm/MHz
Otherwise (different transmit power levels, PH)
Threshold = -73(dBm/MHz) + 23(dBm) – PH(dBm)
For WAS/RLAN
LBT requirements for Load-Based-Equipment in Europe

16. Spectrum Considerations in Taiwan
In Taiwan the bands MHz, MHz, MHz and MHz are allocated to RLANs
Table and Table summarize the current regulatory requirements for transmit power and DFS in Taiwan [40]. DFS is mandate for MHz
Recently, work for specifying requirements for allowing RLANs in MHz and MHz has started but the detailed regulatory requirements for this has not yet been specified
Additionally specification work for allowing MHz outdoor has started, this assumes that DFS will be performed, but detailed requirements are not yet defined

17. Transmit power requirements for 5GHz band in Taiwan
Frequency Range (GHz) *
and
*For indoor use only
Peak transmit power < min(a, b) (dBm) A 17 24 30 B
4+10logB
11+10logB
17+10logB
B is the 26-dB emission bandwidth in MHz
Peak PSD (dBm/MHz) 4 11
Resolution bandwidth 1 MHz
Assumed Antenna Gain (dBi) 6
6**
Peak power is reduced by G-6 dB for directional antennas with gain > 6 dBi;
** Fixed point to point operation power scaling threshold is 23 dBi
Out of band emission
Frequency Support (GHz)
Outside 5.25 – 5.35
Outside
Outside
EIRP (dBm/MHz)
-27
-17
Transmit Power Control
N/A
TPC to 6 dB below a mean EIRP of 30 dBm. No TPC for mean EIRP < 27 dBm
DFS
Required

18. DFS requirements for 5.470-5.725GHz band in Taiwan

19. Licensed Spectrum Needs for LAA
Unlicensed spectrum is better used as “Licensed-Assisted Access” integrated into LTE
Unlicensed spectrum can never replace the need for more licensed spectrum
Inability to be used in macro cells providing wide-area coverage and
Inability to provide highly robust quality-of-service due to the uncontrolled interference
The use of LTE in unlicensed spectrum can serve as a useful additional tool by operators
The primary component carrier in licensed spectrum will be used to carry some (or all) of the control signal (and possibly also data, e.g. retransmissions) of the traffic carried over the carrier in unlicensed spectrum
The use of unlicensed spectrum also increases the need for more licensed spectrum
Carrier aggregation between a macro cell operating in licensed spectrum and clusters of many small cells (remote radio heads) operating only in large chunks of unlicensed spectrum

20. LAA Carrier Aggregation Feasibility Study
Feasibility of UE operation
Feasibility of BS operation
Band definition for unlicensed operation of LTE in 5GHz spectrum
Band range
Suitable duplex method for unlicensed bands
UE RF devices for 5GHz band

21. Feasibility of UE Operation
For 5GHz spectrum available for WAS/RLAN, regulatory requirements such as allowed transmit output power or TPC requirements need to be taken into account
It is reasonable to assume one single front end filter in UE implementation to cover the entire 5GHz spectrum
This does not preclude consideration of other implementation options in the WI phase
For aggregating carrier in unlicensed 5GHz band for inter-band CA, there exists some UE RF architecture that could be feasible
It is feasible for UEs to operate in the 5GHz unlicensed spectrum
RF requirements should be specified taking into account issues including implementation complexity and performance

22. Feasibility of BS Operation
While BS implementation considerations may be different from those of UE in terms of performance, implementation complexity, and fair access to the unlicensed carriers in the presence of WiFi, there are no major issues reported during the study
It is noted that to enable fair access between LAA BS and WiFi AP/STAs, some LAA BS RF requirements may require further study
In summary, it is feasible for BSs to operate in 5GHz unlicensed spectrum. RF requirements should be specified taking into account issues including implementation complexity and performance

23. Band Definition for Unlicensed Operation of LTE in 5GHz Spectrum
Band range
Define 5 GHz unlicensed LAA band or bands within frequency limits 5150 – 5925 MHz
Suitable duplex method for unlicensed bands
In case of eNB operating DL+UL LAA over the same carrier in unlicensed spectrum, the DL transmission burst(s) and UL transmission burst(s) on LAA can be scheduled in a TDM manner while any instant in time can be part of a DL transmission burst or an UL transmission burst, which is different from existing Frame Structure type 2 (FS2)
Potential duplex methods for LAA operation may consider both DL-only and/or DL+UL transmission
Since the duplex method is tied to frame structure, the duplex method for 5GHz unlicensed band shall be based on the physical layer design on L1 enhancements for LAA
UE RF devices for 5GHz band
It is recommended that radio requirements should be specified such that a single filter implementation for UE across the entire frequency range from 5150 to 5925 MHz is possible

24. LTE in 5 GHz Unlicensed Bands and CA
With increased demand for wireless access
3GPP is becoming interested in the 5GHz National Information Infrastructure (UNII)
bands from GHz, which are mainly used by Wi-Fi networks presently
The wider spectrum in 5 GHz can be utilized by LTE operators to enhance their service in licensed bands

25. LTE-U Common Deployment Scenarios

26. Scenario 1 The licensed small cells (F2) do not exist
Carrier aggregation is implemented with
Licensed macro cell (F1)
Unlicensed small cells (F3)
An ideal backhaul
Can be non-colocated
This scenario uses one macro
The mobility management and improving coverage
Indoor and outdoor environments
(e.g., optical fiber with low latency and high throughput)
保證The mobility management and improving coverage

27. Scenario 2 The licensed macro cell (F1) does not exist
Carrier aggregation without macro cell coverage is implemented with
Licensed small cell (F2)
Unlicensed small cell (F3)
an ideal backhaul and co-location
Proper for indoor services

28. Scenario 3
Both the licensed macro cell and small cell use the same carrier (F1)
Carrier aggregation is implemented with
Licensed small cell (F1)
Unlicensed small cell (F3)
An ideal backhaul and co-location
F1 and F3
Can be connected with an ideal backhaul or a non-ideal backhaul
Both indoor and outdoor environments
(non-ideal) backhaul；即基站間不一定會以光纖相連。

29. Scenario 4
The licensed macro cell and licensed small cell use different carriers (F1) and (F2)
Carrier aggregation is implemented with
Licensed small cell (F2)
Unlicensed small cell (F3)
An ideal backhaul and co-location
F1 and F2
Can be connected with an ideal backhaul or a non-ideal backhaul
Both indoor and outdoor environments

30. LAA Deployment Scenarios (R13 TR36.889)
Scenario 1: CA between licensed macro cell (F1) and unlicensed small cell (F3)
Scenario 2: CA between licensed small cell (F2) and unlicensed small cell (F3) without macro cell coverage
Scenario 3: Licensed macro cell and small cell (F1), with CA between licensed small cell (F1) and unlicensed small cell (F3)
Scenario 4: F1 + F2 + F3 - CA between licensed SC (F2) and unlicensed SC (F3)
- CA between macro cell (F1), licensed SC (F2) and unlicensed SC (F3) if ideal backhaul between macro and small cells

31. Coexistence Scenarios
The coexistence between Wi-Fi and LTE-U
The coexistence between LTE-Us of different operators

32. Case 1: LTE-U vs. Wi-Fi LTE-U and Wi-Fi
use different MAC/PHY designs
are usually operated by different operators
LBT-regulated or LBT-non-regulated
avoid mutual interference if both systems use the same unlicensed carrier
A fair Time Division Multiplexing (TDM) scheme
Leveraged to avoid the interference between LTE-U and Wi-Fi if they use the same unlicensed spectrum
Listen before talk
Because
there are great differences between these
two systems, such as different radio frame
structure and transmission scheduling
(see Section “LTE vs. Wi-Fi”), the
implementation leads to high complexity

33. Case 2: LTE-U vs. LTE-U
LTE-Us from different operators coexist in the same 5 GHz unlicensed spectrum
LBT : reduce the interference and improve the spectrum efficiency
multiple LTE-U nodes simultaneously identify a clear unlicensed spectrum
online auction mechanism

34. Comparison of LTE and Wi-Fi
Comparison between LTE and Wi-Fi in the PHY/MAC layers

35. Design Targets of an LAA System
A single global solution framework allowing compliance with any regional regulatory requirements
A single global solution framework for LAA should be defined to ensure that LAA can be operated according to any regional regulatory requirements
Furthermore, LAA design should provide sufficient configurability to enable efficient operation in different geographical regions
Effective and fair coexistence with Wi-Fi
The LAA design should target fair coexistence with existing Wi-Fi networks to not impact Wi-Fi services more than an additional Wi-Fi network on the same carrier, with respect to throughput and latency
Effective and fair coexistence among LAA networks deployed by different operators
The LAA design should target fair coexistence among LAA networks deployed by different operators so that the LAA networks can achieve comparable performance, with respect to throughput and latency

36. Functionalities Required for an LAA System
Listen-Before-Talk (LBT)
Applying a clear channel assessment (CCA) check before using the channel
Energy detection (at least 20 us) to determine presence or absence of other signals
Discontinuous transmission on a carrier with limited maximum transmission duration
4ms in Japan
Dynamic frequency selection (DFS) for radar avoidance in certain bands/regions
Carrier selection for low interference and good co-existence
Transmit Power Control
Able to reduce the transmit power in a proportion of 3dB or 6dB
RRM measurements including cell identification
Enabling mobility between SCells and robust operation in the unlicensed band
Automatic Gain Control (AGC) setting
Coarse synchronization
Fine frequency/time estimation at least for demodulation
Channel-State Information (CSI) measurement, including channel and interference

37. Listen-Before-Talk (Clear Channel Assessment)
The listen-before-talk (LBT) procedure is defined as a mechanism by which an equipment applies a clear channel assessment (CCA) check before using the channel
The CCA utilizes at least energy detection to determine the presence or absence of other signals on a channel in order to determine if a channel is occupied or clear, respectively
European and Japanese regulations mandate the usage of LBT in the unlicensed bands
Apart from regulatory requirements, carrier sensing via LBT is one way for fair sharing of the unlicensed spectrum and hence it is considered to be a vital feature for fair and friendly operation in the unlicensed spectrum in a single global solution framework

38. PHY Layer Options for LAA
The PHY layer options considered for LAA have at least the following characteristics
Support for at least 20MHz system BW option in the 5GHz band
System bandwidths < 5 MHz are not considered for PHY layer options in LAA

39. Solutions for Operation in Unlicensed Spectrum
Physical layer aspects
Discontinuous transmission on the downlink
RRM measurements and reporting
CSI measurements and reporting
Downlink transmissions
Scheduling and HARQ
Listen-Before-Talk Design
UL transmission
Transmission burst
Higher layer aspects
Random Access (RA)
HARQ operation
DRX
QoS control
RRM measurement and reporting
PCI confusion and PCI collision
In-device coexistence (IDC)
Listen-Before-Talk (LBT)

40. LTE-unlicensed Environment

41. Load-based and Frame-based Operation Principles

42. Short Control Signalling Principle

43. LTE Capacity Compared to the Wi-Fi Capacity in the Office Environment Networks.

44. Example Environment Used in the Simulations

45. Outdoor Small Cell Range at 5 GHz Band

46. Performance per Access Node with Two LTE or Two Wi-Fi Networks on the Same Channel

47. Coexistence Performance Between LTE and Wi-Fi

48. Example Measurement for Lower Part of 5 GHz Band

49. Example Measurement over the Full 5 GHz Band in Europe

50. Example Network Utilization at Lower Part of 5 GHz Band

51. Uplink Link Budget Comparison

52. Downlink Link Budget Comparison

53. Summary
LAA: the operation of LTE in unlicensed spectrum as a secondary cell through carrier aggregation
The use of LTE in unlicensed spectrum can serve as a useful additional tool by operators to maximize the value they can provide to users
The core of the activity of the operators remains anchored to the licensed spectrum
A majority of sources providing evaluation results showed
at least one LBT scheme for LAA that does not impact Wi-Fi more than another Wi-Fi network
The LBT scheme and/or parameters shown by different sources to not impact Wi-Fi more than another Wi-Fi network may be different
When an appropriate channel access scheme is used, it is feasible for LAA to achieve fair coexistence with Wi-Fi, and for LAA to coexist with itself based on the evaluated scenarios
The key parameters of the LBT scheme such as contention windows and defer periods should be configurable within limits to enable fair coexistence with other technologies operating in unlicensed spectrum