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This paper discusses LTE-LAA, a technology that utilizes unlicensed spectrum for LTE enhancements. It covers regulatory requirements, spectrum considerations, deployment scenarios, coexistence issues, and design solutions. The study is conducted by the National Kaohsiung University and offers valuable insights into integrating licensed and unlicensed spectrum.
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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：行動與無線區網整合 Week #16LAA與LSA 助理教授：吳俊興 助教：吳振宇 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
3GPPLTE-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
Licensed-Assisted Access (LAA) • LTE in unlicensed spectrum serves as an additionaltool 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
3GPPTR36.889 (R13): Study onLicensed-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)
Spectrum Considerations in Europe 5 GHz spectrum allocations in Europe Summary of existing and proposed EU regulations for WAS/RLANs in the 5GHz band
LBTRequirements in Europe LBTrequirements for Frame-Based-Equipment in Europe 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
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
LAACarrier Aggregation Feasibility Study • Feasibility of UEoperation • Feasibility of BS operation • Band definition for unlicensed operation of LTE in 5GHzspectrum • Band range • Suitable duplex method for unlicensed bands • UE RF devices for 5GHz band
Feasibility of UEOperation • 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 5GHzspectrum • 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 5GHzSpectrum • 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+ULLAA 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+ULtransmission • 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 5GHzband • 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 5GHzNational Information Infrastructure (UNII) • bands from 5.150-5.925 GHz, which aremainly used by Wi-Fi networks presently • The wider spectrum in 5 GHz can be utilizedby LTE operators to enhance their service inlicensed bands
Scenario 1 • The licensed small cells(F2) do not exist • Carrieraggregation is implemented with • Licensed macro cell(F1) • Unlicensed small cells (F3) • An ideal backhaul • Can be non-colocated • This scenario usesone macro • The mobilitymanagement and improving coverage • Indoor and outdoorenvironments
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
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 (R13TR36.889) Scenario 2: CA between licensed small cell (F2) and unlicensed small cell (F3) without macro cell coverage Scenario 1: CA between licensed macro cell (F1) and unlicensed small cell (F3) 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 coexistencebetween Wi-Fi and LTE-U • The coexistence between LTE-Us ofdifferent operators
Case 1: LTE-U vs. Wi-Fi • LTE-U and Wi-Fi • use different MAC/PHYdesigns • are usually operated by differentoperators • LBT-regulated orLBT-non-regulated • avoid mutual interference ifboth 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
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 LAASystem • 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) • HARQoperation • DRX • QoScontrol • RRM measurement and reporting • PCI confusion and PCI collision • In-device coexistence (IDC) • Listen-Before-Talk (LBT)
LTE Capacity Compared to the Wi-Fi Capacity in the Office Environment Networks.
Performance per Access Node with Two LTE or Two Wi-Fi Networks on the Same Channel
