18-452/18-750 Wireless Networks And Applications Lecture .

Evolution ofCellular Wireless Systems18-452/18-750Wireless Networks and ApplicationsLecture 19: LTEPeter SteenkisteFall Semester 2018http://www.cs.cmu.edu/ prs/wirelessF18/1Peter A. Steenkiste, CMUWho is WhoUMTS and WCDMA International Telecommunications Union (ITU) agency of the United Nations responsible for: » Assisting in the development and coordination of worldwide standards» Coordinate shared use of the global spectrum» Defined the International Mobile Telecommunications 2000(IMT-2000) project for 3G telecommunicationsPart of a group of 3G standards defined as part ofthe IMT-2000 framework by 3GPP Universal Mobile Telecommunications System(UMTS)» Successor of GSM W-CDMA is the air interface for UMTS Third Generation Partnership Project (3GPP)» A group of telecommunications associations that representlarge markets world-wide» Defined a group of 3G standards as part of the IMT-2000framework in 1999» Originally defined GSM, EDGE, and GPRS» Later defined follow-on releases and also LTE (4G)Peter A. Steenkiste, CMU2Peter A. Steenkiste, CMU» Wide-band CDMA» Originally 144 kbps to 2 Mbps, depending on mobility Basically same architecture as GSM» Many GSM functions were carried over WCDMA» But they changed all the names!3Peter A. Steenkiste, CMUPage 14

Later Releases ImprovedPerformanceReminder: CDMA - DirectSequence Spread Spectrum High Speed Downlink Packet Access (HSDPA):1.8 to 14.4 Mbps downlink» Adaptive modulation and coding, hybrid ARQ, and fast scheduling High Speed Uplink Packet Access (HSUPA):Uplink rates up to 5.76 Mbps High Speed Packet Access Plus (HSPA ):Maximum data rates increased from 21 Mbps upto 336 MbpsThese signals willlook like noiseto the receiver» 64 QAM, 2 2 and 4 4 MIMO, and dual or multi-carrier combinations Eventually led to the definition of LTE5Peter A. Steenkiste, CMUAdvantages of CDMA forCellular systemsMobile Wireless CDMASoft Hand-off Soft Handoff – mobile station temporarilyconnected to more than one base stationsimultaneously Requires that the mobile acquire a new cellbefore it relinquishes the old More complex than hard handoff used inFDMA and TDMA schemes Frequency diversity – frequency-dependenttransmission impairments have less effect onsignal Multipath resistance – chipping codes usedfor CDMA exhibit low cross correlation andlow autocorrelation Privacy – privacy is inherent since spreadspectrum is obtained by use of noise-likesignals Graceful degradation – system only graduallydegrades as more users access the systemPeter A. Steenkiste, CMU6Peter A. Steenkiste, CMU7Peter A. Steenkiste, CMUPage 28

Evolution ofCellular Wireless SystemsOverview MotivationArchitectureResource managementLTE protocolsRadio access network» OFDM refresher LTE advancedSome slides based on material from“Wireless Communication Networks and Systems” 2016 Pearson Higher Education, Inc.9Peter A. Steenkiste, CMU10Peter A. Steenkiste, CMUPurpose, motivation, andapproach to 4GHigh Level Features Defined by ITU directives for International MobileTelecommunications Advanced (IMT-Advanced) All-IP packet switched network. Ultra-mobile broadband access Peak data rates No support for circuit-switched voice» Instead providing Voice over LTE (VoLTE) Replace spread spectrum/CDMA with OFDM» Up to 100 Mbps for high-mobility mobile access» Up to 1 Gbps for low-mobility access Dynamically share and use network resources Smooth handovers across heterogeneous networks» 2G and 3G networks, small cells such as picocells, femtocells, andrelays, and WLANs High quality of service for multimedia applicationsPeter A. Steenkiste, CMU11Peter A. Steenkiste, CMUPage 312

Evolved Packet SystemLTE Architecture evolved NodeB (eNodeB)» Most devices connect into thenetwork through the eNodeBRadio AccessNetwork Overall architecture is called the EvolvedPacket System (EPS) 3GPP standards divide the network into Radio access network (RAN): cell towers andconnectives to mobile devices Core network (CN): management andconnectivity to other networks Each can evolve independently Evolution of the previous3GPP NodeB ( 2G BTS)» Uses OFDM instead of CDMA Has its own controlfunctionality» Dropped the Radio NetworkController (RNC - 2G BSC)» eNodeB supports radioresource control, admissioncontrol, and mobilitymanagement (handover)» Was originally the responsibilityof the RNCCoreNetwork» Driven by different technologies: optimizing spectrumuse versus management and control or traffic13Peter A. Steenkiste, CMUPeter A. Steenkiste, CMUEvolved Packet SystemComponentsDesign Principles of the EPS Long Term Evolution (LTE) is the RAN»»»» Packet-switched transport for traffic belongingto all QoS classesCalled Evolved UMTS Terrestrial Radio Access (E-UTRA)Enhancement of 3GPP’s 3G RANeNodeB is the only logical node in the E-UTRANNo Radio Network Controller (RNC)» Voice, streaming, real-time, non-real-time, background Comprehensive radio resource management» End-to-end QoS, transport for higher layers» Load sharing/balancing» Policy management across different radio accesstechnologies Evolved Packet Core (EPC)» Operator or carrier core network –core of the system Traditionally circuit switched but now entirelypacket switched Integration with existing 3GPP 2G and 3Gnetworks Scalable bandwidth from 1.4 MHz to 20 MHz Carrier aggregation for overall bandwidths upto 100 MHz» Based on IP - Voice supported using voice over IP (VoIP)Peter A. Steenkiste, CMU1415Peter A. Steenkiste, CMUPage 416

Evolved Packet CoreComponentsOverview Mobility Management Entity (MME) » Supports user equipment context, identity, authentication, andauthorization Serving Gateway (SGW)» Receives and sends packets between the eNodeB and the corenetwork Packet Data Network Gateway (PGW)» Connects the EPC with external networks Home Subscriber Server (HSS)» OFDM refresher» Database of user-related and subscriber-related information LTE advanced Interfaces» S1 interface between the E-UTRAN and the EPC– For both control purposes and for user plane data traffic» X2 interface for eNodeBs to interact with each other– Again for both control purposes and for user plane data trafficSome slides based on material from“Wireless Communication Networks and Systems” 2016 Pearson Higher Education, Inc.17Peter A. Steenkiste, CMUMotivationArchitectureResource managementLTE protocolsRadio access network18Peter A. Steenkiste, CMUBearer Management based onQoS Class Identifier (QCI)LTE Resource Management LTE uses bearers for quality of service (QoS)control instead of circuits EPS bearersGuaranteed(minimum)Bit Rate» Between entire path between PGW and UE» Maps to specific QoS parameters such as data rate, delay,and packet error rate Service Data Flows (SDFs) differentiate trafficflowing between applications on a client and aserviceNoGuarantees» SDFs must be mapped to EPS bearers for QoS treatment» SDFs allow traffic types to be given different treatment End-to-end service is not completely controlledby LTEPeter A. Steenkiste, CMU19Peter A. Steenkiste, CMUPage 520

EPC: Inter-cell InterferenceCoordination (ICIC)EPC: Mobility Management Reduces interference when the same frequencyis used in a neighboring cell Goal is universal frequency reuse X2 interface used whenmoving within a RANcoordinated under thesame MemoryManagement Entity (MME) S1 interface used to moveto another MME Hard handovers are used:A UE is connected to onlyone eNodeB at a time» N 1 in “Cellular principles” lecture» Must avoid interference when mobile devices are near eachother at cell edges» Interference randomization, cancellation, coordination, andavoidance are used eNodeBs send indicators» Relative Narrowband Transmit Power, High Interference, andOverload indicators Later releases of LTE have improved interferencecontrol» “Cloud RAN”: use a cloud to manage interference, spectrum21Peter A. Steenkiste, CMUProtocol Layers End-to-EndOverview 22Peter A. Steenkiste, CMUMotivationArchitectureResource managementLTE protocolsRadio access network» OFDM refresher LTE advancedFancy L2 forMobile to cell towerSome slides based on material from“Wireless Communication Networks and Systems” 2016 Pearson Higher Education, Inc.Peter A. Steenkiste, CMU23Peter A. Steenkiste, CMUPage 6Communication inEPC24

Protocol LayersPDCP and RLCProtocol LayersMAC and PHY Medium Access Control(MAC) Packet Data ConvergenceProtocol (PDCP)» Delivers packets from UE toeNodeB» Involves header compression,ciphering, integrity protection,in-sequence delivery,buffering and forwarding ofpackets during handover» Performs H-ARQ: combinesFEC and retransmission(ARQ)» Prioritizes and decides whichUEs and radio bearers willsend or receive data onwhich shared physicalresources» Decides the transmissionformat, i.e., the modulationformat, code rate, MIMO rank,and power level Radio Link Control (RLC)» Segments or concatenatesdata units» Performs ARQ when MAClayer H-ARQ fails– ARQ: Automatic RepeatRequest (retransmission)– H-ARQ: Hybrid ARQ –combines FEC and ARQ Physical layer actuallytransmits the data25Peter A. Steenkiste, CMUOverview LTE Radio Access Network LTE uses OFDM and MIMO OFDM offers benefits similar to those of CDMAMotivationArchitectureResource managementLTE protocolsRadio access network» Good immunity to fading as only a small portion of theenergy for any one link is typically lost due to a fade» Fast power control to keep the noise floor as low as possible Additional advantages»»»»»» OFDM refresher LTE advancedHighly resistant to fading and inter-symbol interferenceLow modulation rates on each of the many sub-carriersSophisticated error correctionScales rates easier than CDMAAllows more advanced antenna technologies, like MIMO Breaks information into pieces and assignseach one to a specific set of sub-carriersSome slides based on material from“Wireless Communication Networks and Systems” 2016 Pearson Higher Education, Inc.Peter A. Steenkiste, CMU26Peter A. Steenkiste, CMU27Peter A. Steenkiste, CMUPage 728

Different Solution forUp and Downlink The downlink uses OFDM with MultipleAccess (OFDMA)» Multiplexes multiple mobiles on the same subcarrier» Improved flexibility in bandwidth management, e.g.,multiple low bandwidth users can share subcarriers» Enables per-user frequency hopping to mitigate effects ofnarrowband fading The uplink uses Single Carrier OFDM (SCOFDM)» OFDM but using a single carrier» Provides better energy and cost efficiency for batteryoperated mobiles» Large number of subcarriers leads to high peak-toaverage Power ratio (PAPR), which is /litweb/pdf/5989-7898EN.pdf29Peter A. Steenkiste, CMUPeter A. Steenkiste, CMULTE Radio Access Network30Spectrum Allocation for FDD and TDD LTE uses both TDD and FDD» Both have been widely deployed Time Division Duplexing (TDD)» Uplink and downlink transmit in the same frequencyband, but alternating in the time domain Frequency Division Duplexing (FDD)» Different frequency bands for uplink and downlink LTE uses two cyclic prefixes (CPs)» Extended CP is for worse environmentsPeter A. Steenkiste, CMU31Peter A. Steenkiste, CMUPage 832