Introduction to Heterogeneous Networks in Mobile Communication

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：行動寬頻網路之異質性存取 Week #01Introduction toHeterogeneous Networks (HetNet) 助理教授：吳俊興國立高雄大學資訊工程學系

Outline • Syllabus • 教學目標、課程內容、課程教材 • Next-Generation Mobile Networks • Review the Development of Mobile Networks • Toward 5G: IMT-2020 and LTE-Advanced Pro • HetNet’s Fundamental Technologies • LTE-CA: Carrier Aggregation • ICIC: Inter-Cell Interference Coordination • CoMP: Coordinated Multi Point • HetNet’s Advanced Technologies • LTE-U/LTE-LAA: Licensed Assisted Access • LWA: LTE-WLAN Aggregation • LWIP: LTE WLAN Radio Level Integration with IPsec Tunnel

教學目標 本課程介紹行動寬頻最新的發展技術，探討小細胞基站(Small Cells)如何整合各種無線網路，並支援異質性網路(Heterogeneous Networks)，來做為下一代(5G)行動通訊網路的基礎。重點包括： • LTE通訊協定架構暨異質行動網路 • 小基站技術：ICIC干擾管理與CoMP多點協調 • Licensed與Unlicensed整合存取：LTE-CA與LTE-U/LTE-LAA • LTE與WiFi整合存取：LWA與LWIP

課程內容

課程教材 • 參考書 (eBook) • Joydeep Acharya, Long Gao, and Sudhanshu Gaur,Heterogeneous Networks in LTE-Advanced, John Wiley & Sons, Ltd, 2014 Chapter 1. An Introduction to Heterogeneous Networks Part I. OVERVIEW Chapter 2. Fundamentals of LTE Chapter 3. LTE Signal Structure and Physical Channels Chapter 4. Physical Layer Signal Processing in LTE Part II. INTER-CELL INTERFERENCE COORDINATION Chapter 5. Release 10 Enhanced ICIC Chapter 6. Release 11 Further Enhanced ICIC: Transceiver Processing Chapter 7. Release 11 Further Enhanced ICIC: Remaining Topics Part III. COORDINATED MULTI-POINT TRANSMISSION RECEPTION Chapter 8. Downlink CoMP: Signal Processing Chapter 9. Downlink CoMP: Standardization Impact Part IV. UPCOMING TECHNOLOGIES Chapter 10. Dense Small Cell Deployments Chapter 11. TD-LTE Enhancements for Small Cells Chapter 12. Full Dimension MIMO Chapter 13. Future Trends in Heterogeneous Networks

補充教材 • Books • Chris Johnson,Long Term Evolution in Bullets, 2nd Edition, CreateSpace Publishing, 2012 • Harri Holma, Antti Toskala, Jussi Reunanen,LTE Small Cell Optimization - 3GPP Evolution to Release 13,John Wiley & Sons, Ltd, 2015 • Protocols (Specifications) • 3GPP LTE-Advanced Pro • ITUIMT-2020 • Small Cell Forum, LTE-U Forum, NGMN, 5G Americas, 5G PPP • Platforms • ITRIeNB • Open Air Interface

Mobile Networks from GSM to LTE • GSM: developed to carry real time services, in a circuit switched manner • GPRS: the first step towards an IP based packet switched solution • Using the same air interface and access method, TDMA (Time Division Multiple Access) • UMTS: 3G standard based on GSM • Developing UTRAN and WCDMA • EPS (Evolved Packet System): purely IP based • A flat, all-IP architecture with separation of control plane and user plane traffic • Composed with E-UTRAN/LTE and packet-switched EPC (Evolved Packet Core) Core of 3GPP’s SAE Project (System Architecture Evolution)

Network Structure of UMTS(Universal Mobile Telecommunications System) Mobile Station Access Network Core Network • Emulating a circuit switched connection for real time services and a packet switched connection for datacom services • Incoming datacom services are still relying upon the circuit switched core for paging • An IP address is allocated to the UE when a datacom service is established andreleased when the service is released

EPS (Evolved Packet System) / SAE • EPC (Evolved Packet Core): main component of EPS, includes • MME: key control-node for LTE – UE paging; chooses S-GW for UE during attach and handover • Authenticating the user (by interacting with HSS - Home Subscriber Server) • S-GW: manages and stores UE contexts; routes and forwards user data packets • P-GW: provides connectivity from the UE to external packet data networks • ePDG: secures data transmission with UE connected to EPC over untrusted non-3GPP access • ANDSF: provides information to UE to discover available access networks (either 3GPP or not) PDN (Packet Data Network) Gateway Access Network Discovery and Selection Function Serving Gateway Mobility Management Entity A bearer is from UE to eNodeB to S-GW and finally to P-GW Core Network (CN) Radio Access Network (RAN) EvolvedPacket Data Gateway

Evolved Universal Terrestrial Radio Access(E-UTRA) • e-UTRA is the air interface of 3GPP's Long Term Evolution (LTE) • EUTRN is a radio access network (RAN) which is referred to under the name EUTRANstandard

Protocol Models of CN and RAN • Two main layers • Upper layer: manipulate information specific to LTE • Lower layer: transport information from one point to another • Three types of protocols • (Control plane) signaling protocols • User plane protocols • Transport protocols: transfer data and signaling messages On the air interfaceBy the fixed network

Protocol Stack to Exchange Control Signaling TS 23.401 Stream Control Transmission Protocol

Bearer Implementation (Using GTP) TS 23.401 GTP (GPRS Tunneling Protocol)

Challenges to Operators • Challenges • Increasing data traffic: network capability using traditional macrocell-based deployments is growing at about 30% less than the demand for data • Decreasing profit margins: the profit margins of most operators have also been decreasing globally • The flat rate pricing policies prevent the mobile data revenues of an operator to scale proportionately with the increased usage of mobile broadband data • The cost incurred as a result of setting up more base stations to provide increased capacity and coverage • Rethink methods of operating their networks • Key principle: deliver higher capacity at a reduced cost

Enhancement of Key Capabilitiesfrom IMT-Advanced to IMT-2020 Source: ITU-R M.2083-0 (Sep 2015)

Ways to Increase Capacity • A 1000× increase in capacity is required to support rising demand in 2020* • High capacity can be achieved by • Improving spectral efficiency • Employing more spectrum • Increasing network density • The major gains are expected throughincreasing network density by deployingan overlay network of small cellsover the macro coverage area Related to link level enhancements(but already at near optimal) *Reference: Mallinson, K. (2012) The 2020 vision for LTE. Available at http://www.3gpp.org/2020-vision-for-LTE (accessed November 2013)

Detailed Timeline & Process for IMT-2020 in ITU-R • Working Party 5D, Study Group 5, ITU-R (Radiocommunication) • FGIMT-2020, Focus Group on IMT-2020, SG 13, ITU-T (Telecommunication)

IMT-2020 Vision –A Unified Network Architecture • A Heterogeneous (Licensed) Network with Large and Small Cells (HetNet) • Carrier Aggregation (R8+) →eCA • Intra-band/inter-band contiguous/non-contiguous allocation • Interference Management • Inter-Cell Interference Coordination (ICIC, R8) →eICIC (R10) →feICIC (R11) • Dynamic Coordination between Neighboring Cells • Coordinated Multi Point (CoMP) • Simultaneous Connectivity across Cells • DualNet (TR36.842R12) • A Heterogeneous Network Integrating (Unlicensed) WLAN/WiFi • WLAN inter-working (Trusted/Un-trusted) • WiFi Offload and Link Aggregation (LWIP, LWA) • LTE in the unlicensed spectrum • LTE-U, LAA (R13) / eLAA (DualNetR14)

3GPP Roadmap Phase 1: by Sep 2018/Rel-15 • Address a more urgent subset of commercial needs (Not possible to standardize all in time) • Expected deployments in 2020 Phase 2: by Mar 2020/Rel-16 • Target for IMT2020 submission • Address all identified use-cases & requirements

3GPP5G Requirements TR22.891with 70s different user cases of four groups (SA1 finalized June 2016)

Toward a Heterogeneous Network Finding new macro-sites becomes increasingly difficult and can be expensive • Introduce small cells through the addition of low-power base stations (eNBs, HeNBs or Relay Nodes (RNs)) or Remote Radio Heads (RRH) to existing macro-eNBs • Added to increase capacityin hot spots with high user demand and to fill in areas not covered by the macro network – both outdoors and indoors • They also improve network performance and service quality by offloading from the large macro-cells • The result is a heterogeneous network with large macro-cells in combination with small cells providing increased bitrates per unit area HetNet: a wireless network comprised of different types of base stations and wireless technologies, including macro base stations, small cells, distributed antenna systems (DAS), and even Wi-Fi access points

Deployment Scenarios of Small Cell (TR32.835) • A Heterogeneous Network consists of different types of Base Stations (BSs), supporting cells such as macro, micro and picocells • These types of BSs will be mixed in an operating network • Heterogeneous networks management should consider cells in a heterogeneous network, including small cells • both with and without macro coverage, • both outdoor and indoor small cell deployments and • both sparse and dense small cell deployments F1 and F2 are the carrier frequency for macro layer and local-node layer, respectively

HetNet - A Heterogeneous Networkwith Large and Small Cells Large cell • High-power eNB • Macro-eNB site can be difficult to find Small cell • Low-power base station or RRH (Remote Radio Head) • Off load for large cell • Small site size • Indoor coverage • Hot-spot coverage • Coverage at cell edge of large cell • Coverage in area not covered by the macro-network In heterogeneous networks the cells of different sizes are referred to as macro-, micro-, pico- and femto-cells; listed in order of decreasing base station power

From Macro to Small Cells • Small cells using 3GPP radio access technologies will • Enhance capacity and per-user throughput • Reduce costs and • Uniquely offer tight cooperation with the macro coverage layer • Enhancements for small cells as a key component of R12 • Dual connectivity: Devices maintain simultaneous connections to both macro and small-cell low-power layers to improve cell-edge throughput • Inter-node radio resource aggregation can use radio resources on a common frequency in more than one eNB • Connections can be anchored to a macro cell on one frequency while boosting data-rates via the small cell on a different frequency • Small cell on/off: Energy-efficient load balancing by turning off the low-power nodes when there is no ongoing demand for data transmission • More eNBs increases air interface interference and network power consumption • Making nodes dormant can match available capacity to network traffic loading • 256 QAM: Close proximity of devices to small cells enables use of higher-order modulation • Beneficial in sparse small-cell implementations with low device mobility

HetNet Dual Connectivity • Simultaneous connection to the macro and low-power layer

Inter-Cell Interference Coordination (ICIC) • Originally introduced in R8 for macro-cells • eNBs communicate using ICIC via the X2 interface to mitigate inter-cell interference for UEs at the cell edge • “Load Information” X2AP message • Used by an eNB to inform neighbouringeNBs about • UL interference level per Physical Resource Block (PRB); • UL PRBs that are allocated to cell edge UEs, and hence are sensitive to UL interference; • if DL Tx power is higher or lower than a set threshold value • The receiving eNBs use the received information to optimize scheduling for UEs at cell edges

eICIC to Support Heterogeneous Networks • Enhanced ICIC (eICIC) was introduced in LTE R10 • Better support heterogeneous network deployments • Especially interference control for DL control channels • The major change is the addition of time domain ICIC, realized through use of Almost Blank Subframes (ABS) • Includes only control channels and cell-specific reference signals, no user data • Transmitted with reduced power • eICIC between macro-eNB and eNB in small cells • The macro-eNB will transmit ABS according to a semi-static pattern • During these subframes, UEs at the edge, typically in the Cell Range Expansion (CRE) region of small cells, can receive DL information, both control and user data • The macro-eNB will inform the eNB in the small cell about the ABS pattern

ABS for Cell-edge UEs in Small Cells (eICIC) • Further Enhanced ICIC (feICIC) in R11 • Interference handling by UE through inter-cell interference cancellation for control signals • Enabling even further cell range extension • eICIC and feICIC are especially important when Carrier Aggregation (CA) is not used

CoMP – Coordinated Multi Point • CoMP introduced in LTE R11 • One way to ensure that a UE is using both the best DL and the best UL carrier in a heterogeneous network (used both in DL and UL) • With CoMP • A number of transmission/reception points (i.e. eNBs, RNs or RRHs) can be coordinated to provide service to a UE. For examples, • Data can be transmitted at the same time in the same Physical Resource Blocks (PRB) from more than one transmission point to one UE, or • Data can be received from one transmission point in one subframe and from another transmission point in the next subframe

CoMP in a Heterogeneous Network • CoAP is especially useful in heterogeneous networks • The possibility for a UE in the cell range extension region to utilize the best UL in the small cell and the best DL in the macro-cell • A number of macro-cells and small cells can be involved in data transmission to and from one UE • Requires that • The macro-eNB and the base station in the small cell are synchronized Most likely it will require a combination of macro-eNB with Remote Radio Heads (RRH) in the small cell

Example of CoMP • Using CoMP it is possible for the UE in the grey area to have both the best DL from the macro-eNB and the best UL to the base station, or RRH, serving the small cell

Carrier Aggregation • Carrier aggregation is used in LTE-Advanced in order to increase the bandwidth, and thereby increase the bitrate • The aggregation is based on R8/R9 carriers to keep backward compatibility with R8 and R9 Ues • Carrier aggregation can be used for both FDD and TDD • Each aggregated carrier is referred to as a component carrier, CC • The component carrier can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz and • A maximum of five component carriers can be aggregated • hence the maximum aggregated bandwidth is 100 MHz • In FDD the number of aggregated carriers can be different in DL and UL • However, the number of UL component carriers is always equal to or lower than the number of DL component carriers • The individual component carriers can also be of different bandwidths • For TDD the number of CCs as well as the bandwidths of each CC will normally be the same for DL and UL

Example of Carrier Aggregation (FDD) • The LTE-Advanced UE can be allocated DL and UL resources on the aggregated resource consisting of two or more Component Carriers (CC) • The R8/R9UEs can be allocated resources on any ONE of the CCs • The CCs can be of different bandwidths

LTE in the Unlicensed Spectrum • Twoareasto helpoperatorsoffloadtrafficinthe unlicensedspectrum: • WLANviaLTE/WLANInterworking(viaoffloador aggregation) • LTEover unlicensedspectrum WLAN Offload Faster LTE Licensed MoreCapacity Link Aggregation UnifiedNetwork WLAN FairCoexistence Carrier Aggregation LTE Unlicensed Source: Keysight, March 2016

3GPP Standardization Works • Link Aggregation • LTE-WLAN Aggregation (LWA) • LTE WLAN Radio Level Integration with IPsec Tunnel (LWIP) • Licensed Assisted Access (LAA) • Unlicensed band using carrier aggregation with a licensed LTE cell (3GPP Rel. 12) Jun 2017 Mar 2016 Rel.10 Rel.11 Rel.12 Rel.13 Rel.14 WLAN Offload RANAssisted Interworking RAN Controlled Interworking Offload LTE/WLAN Interworking LWIP LWA Aggregation LTE-U LTEover unlicensed eLAA LAA Source: Keysight, March 2016

LTE-U/LTE-LAA • 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 • Three ways of deployed • 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 • 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

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

LTE-WLAN Aggregation (LWA) (TS36.300/22A) • E-UTRAN supports LWAoperation whereby a UE in RRC_CONNECTED is configured by the eNB to utilize radio resources of LTE and WLAN • WLAN AP/AC only interacts with eNB; no interaction with the Core Network • LWA is controlled by eNB, based on UEmeasurement reporting • When LWA is activated, eNB configures one or more bearers as LWAbearers • Two scenarios are supported depending on the backhaul connection between LTE and WLAN • Collocated LWA scenario for an ideal/internal backhaul • Non-collocated LWA scenario for a non-ideal backhaul • WLAN Termination (WT) terminates the Xw interface for WLAN C-Plane connectivity of eNB and WT for LWA U-Plane connectivity of eNB and WT for LWA

LWA Radio Protocol Architecture • In LWA, the radio protocol architecture that a particular bearer uses depends on the LWA backhaul scenario and how the bearer is set up • Two bearer types exist for LWA: split LWA bearer and switched LWAbearer LWA Radio Protocol Architecture for the Collocated Scenario • LWAallows asingle bearertobeconfiguredto utilize LTEand WLANsimultaneously • Splitandswitched bearersare supported • R13LWAsupports aggregationindownlinkonly,whileuplinktransmissionisalwayson LTE • Packets(PDCPPDUs)belongingtoLWAbearercanbe sent byeNBvia LTEorWLANsimultaneously • LWA uses EtherType0x9E65 allocated by IEEE RAC LWA Radio Protocol Architecture for the Non-Collocated Scenario

MME / S - GW S 1 WLAN I P eNB LWIP-SeGW UE LWIP - LTE/WLAN Radio Level Integration with IPsec Tunnel (LWIP) • UEuses WLANviaIPsec tunnelbetweeneNBand UE • Fasttimetomarket,useoflegacyWLANinfrastructure • WLANis hiddenfromCN • Exceptfor WLANauthentication • LWIPis controlledbyeNB, basedonUEmeasurement reporting • For securityreasons IPsec tunnelisterminatedinLWIP-SeGWin eNB • IPsec tunnelis transparent to WLANinfrastructure • There are nostandardizednetworkinterfaces inLWIP • SingleIPSectunnelperUEforULandDLdata

LWIP Protocol Architecture • IP packets transferred between the UE and LWIP-SeGW are encapsulated using IPsec • Provide security to the packets that traverse WLAN • Uplink and downlink data supported over WLAN • Multiple bearers can be offloaded via IPSec

Bearer over LWIP Tunnel - Protocol Stack • The data bearer refers to the EPS bearer mapped to the Data Radio Bearer (DRB) which is maintained on the LTE side • The DRB configuration on the LTE access corresponding to the data bearer using IPsec resources shall not be released • A single IPSec tunnel is used per UE for all the data bearers that are configured to send and/ or receive data over WLAN • Each data bearer may be configured so that traffic for that bearer can be routed over the IPsec tunnel in either only downlink or both uplink and downlink over WLAN • The RRC_Connection_Reconfiguration message provides the necessary parameters for the UE to initiate the establishment of the IPSec tunnel for the DRB

Summary • Advances of wireless networks: A Unified Heterogeneous Network • Fundamental Technologies • Aggregating more channels: LTE-CA • Interference management: ICIC • Coordinated transmission: CoMP • Advanced Technologies • Aggregating unlicensed bands: LTE-U/LTE-LAA • Link-layer aggregation: LWA • IPsec Tunneling: LWIP

Introduction to Heterogeneous Networks in Mobile Communication

Introduction to Heterogeneous Networks in Mobile Communication

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