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

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

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

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

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

LTE-unlicensed Operation Modes

LTE-advanced Aggregation Between FDD and TDD Bands

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

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 802.11 (a, n, ac) Weather radar

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 http://www.3gpp.org/DynaReport/36889.htm (2015-06)

Unlicensed Spectrum Availability in Different Regions LTE

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

Transmit Power and Emission Requirement in Europe

DFS Requirements in Europe

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

Spectrum Considerations in Taiwan In Taiwan the bands 5250-5350 MHz, 5470-5600 MHz, 5650-5725 MHz and 5725-5850 MHz are allocated to RLANs Table 4.3.5-1 and Table 4.3.5-2 summarize the current regulatory requirements for transmit power and DFS in Taiwan [40]. DFS is mandate for 5470-5725 MHz Recently, work for specifying requirements for allowing RLANs in 5150-5250 MHz and 5600-5650 MHz has started but the detailed regulatory requirements for this has not yet been specified Additionally specification work for allowing 5250-5350 MHz outdoor has started, this assumes that DFS will be performed, but detailed requirements are not yet defined

Transmit power requirements for 5GHz band in Taiwan Frequency Range (GHz)   5.25-5.35 * 5.47-5.60 and 5.65-5.725 5.725-5.825 *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 5.47-5.725 Outside 5.715-5.835 EIRP (dBm/MHz) -27 5.715-5.725 5.825-5.835 -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

DFS requirements for 5.470-5.725GHz band in Taiwan

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

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

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

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

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

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 5.150-5.925 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

LTE-U Common Deployment Scenarios

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

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

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。

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

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

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

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

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

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

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

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

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

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

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)

LTE-unlicensed Environment

Load-based and Frame-based Operation Principles

Short Control Signalling Principle

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

Example Environment Used in the Simulations

Outdoor Small Cell Range at 5 GHz Band

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

Coexistence Performance Between LTE and Wi-Fi

Example Measurement for Lower Part of 5 GHz Band

Example Measurement over the Full 5 GHz Band in Europe

Example Network Utilization at Lower Part of 5 GHz Band

Uplink Link Budget Comparison

Downlink Link Budget Comparison

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