Evolution of Cellular Wireless Systems 18-452/18-750 Wireless Networks and Applications Lecture 19: LTE Peter Steenkiste Fall Semester 2018 http://www.cs.cmu.edu/~prs/wirelessF18/ Peter A. Steenkiste, CMU 1 Peter A. Steenkiste, CMU 2 Who is Who UMTS and WCDMA • International Telecommunications Union (ITU) - agency of the United Nations responsible for: Part of a group of 3G standards defined as part of » Assisting in the development and coordination of world- the IMT-2000 framework by 3GPP wide standards • Universal Mobile Telecommunications System » Coordinate shared use of the global spectrum (UMTS) » Defined the International Mobile Telecommunications 2000 (IMT-2000) project for 3G telecommunications » Successor of GSM • Third Generation Partnership Project (3GPP) • W-CDMA is the air interface for UMTS » A group of telecommunications associations that represent » Wide-band CDMA large markets world-wide » Originally 144 kbps to 2 Mbps, depending on mobility » Defined a group of 3G standards as part of the IMT-2000 framework in 1999 • Basically same architecture as GSM » Originally defined GSM, EDGE, and GPRS » Many GSM functions were carried over WCDMA » Later defined follow-on releases and also LTE (4G) » But they changed all the names! Peter A. Steenkiste, CMU 3 Peter A. Steenkiste, CMU 4 Page 1 Reminder: CDMA - Direct Later Releases Improved Sequence Spread Spectrum Performance • 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 up to 336 Mbps These signals will » 64 QAM, 2×2 and 4×4 MIMO, and dual or multi-carrier combinations look like noise • Eventually led to the definition of LTE to the receiver Peter A. Steenkiste, CMU 5 Peter A. Steenkiste, CMU 6 Advantages of CDMA for Mobile Wireless CDMA Cellular systems Soft Hand-off • Frequency diversity – frequency-dependent • Soft Handoff – mobile station temporarily transmission impairments have less effect on connected to more than one base station signal simultaneously • Multipath resistance – chipping codes used • Requires that the mobile acquire a new cell for CDMA exhibit low cross correlation and before it relinquishes the old low autocorrelation • More complex than hard handoff used in • Privacy – privacy is inherent since spread FDMA and TDMA schemes spectrum is obtained by use of noise-like signals • Graceful degradation – system only gradually degrades as more users access the system Peter A. Steenkiste, CMU 7 Peter A. Steenkiste, CMU 8 Page 2 Evolution of Overview Cellular Wireless Systems • Motivation • Architecture • Resource management • LTE protocols • Radio access network » OFDM refresher • LTE advanced Some slides based on material from “Wireless Communication Networks and Systems” © 2016 Pearson Higher Education, Inc. Peter A. Steenkiste, CMU 9 Peter A. Steenkiste, CMU 10 Purpose, motivation, and High Level Features approach to 4G • Defined by ITU directives for International Mobile • No support for circuit-switched voice Telecommunications Advanced (IMT-Advanced) » Instead providing Voice over LTE (VoLTE) • All-IP packet switched network. • Replace spread spectrum/CDMA with OFDM • Ultra-mobile broadband access • Peak data rates » 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, and relays, and WLANs • High quality of service for multimedia applications Peter A. Steenkiste, CMU 11 Peter A. Steenkiste, CMU 12 Page 3 LTE Architecture Evolved Packet System Radio Access • evolved NodeB (eNodeB) Network » Most devices connect into the • Overall architecture is called the Evolved network through the eNodeB Packet System (EPS) • Evolution of the previous • 3GPP standards divide the network into 3GPP NodeB (~2G BTS) • Radio access network (RAN): cell towers and » Uses OFDM instead of CDMA connectives to mobile devices • Has its own control functionality • Core network (CN): management and » Dropped the Radio Network Core connectivity to other networks Controller (RNC - ~2G BSC) Network » eNodeB supports radio • Each can evolve independently resource control, admission » Driven by different technologies: optimizing spectrum control, and mobility use versus management and control or traffic management (handover) » Was originally the responsibility of the RNC Peter A. Steenkiste, CMU 13 Peter A. Steenkiste, CMU 14 Evolved Packet System Design Principles of the EPS Components • Long Term Evolution (LTE) is the RAN • Packet-switched transport for traffic belonging » Called Evolved UMTS Terrestrial Radio Access (E-UTRA) to all QoS classes » Enhancement of 3GPP’s 3G RAN » Voice, streaming, real-time, non-real-time, background » eNodeB is the only logical node in the E-UTRAN • Comprehensive radio resource management » No Radio Network Controller (RNC) » End-to-end QoS, transport for higher layers • Evolved Packet Core (EPC) » Load sharing/balancing » Operator or carrier core network –core of the system » Policy management across different radio access • Traditionally circuit switched but now entirely technologies packet switched • Integration with existing 3GPP 2G and 3G » Based on IP - Voice supported using voice over IP (VoIP) networks • Scalable bandwidth from 1.4 MHz to 20 MHz • Carrier aggregation for overall bandwidths up to 100 MHz Peter A. Steenkiste, CMU 15 Peter A. Steenkiste, CMU 16 Page 4 Evolved Packet Core Overview Components • Mobility Management Entity (MME) • Motivation » Supports user equipment context, identity, authentication, and authorization • Architecture • Serving Gateway (SGW) » Receives and sends packets between the eNodeB and the core • Resource management network • LTE protocols • Packet Data Network Gateway (PGW) » Connects the EPC with external networks • Radio access network • Home Subscriber Server (HSS) » OFDM refresher » Database of user-related and subscriber-related information • Interfaces • LTE advanced » 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 traffic Some slides based on material from “Wireless Communication Networks and Systems” © 2016 Pearson Higher Education, Inc. Peter A. Steenkiste, CMU 17 Peter A. Steenkiste, CMU 18 Bearer Management based on LTE Resource Management QoS Class Identifier (QCI) • LTE uses bearers for quality of service (QoS) control instead of circuits • EPS bearers Guaranteed » Between entire path between PGW and UE » Maps to specific QoS parameters such as data rate, delay, (minimum) and packet error rate Bit Rate • Service Data Flows (SDFs) differentiate traffic flowing between applications on a client and a service No » SDFs must be mapped to EPS bearers for QoS treatment » SDFs allow traffic types to be given different treatment Guarantees • End-to-end service is not completely controlled by LTE Peter A. Steenkiste, CMU 19 Peter A. Steenkiste, CMU 20 Page 5 EPC: Inter-cell Interference EPC: Mobility Management Coordination (ICIC) • Reduces interference when the same frequency • X2 interface used when is used in a neighboring cell moving within a RAN coordinated under the • Goal is universal frequency reuse same Memory » N = 1 in “Cellular principles” lecture Management Entity (MME) » Must avoid interference when mobile devices are near each other at cell edges • S1 interface used to move » Interference randomization, cancellation, coordination, and to another MME avoidance are used • Hard handovers are used: • eNodeBs send indicators A UE is connected to only » Relative Narrowband Transmit Power, High Interference, and one eNodeB at a time Overload indicators • Later releases of LTE have improved interference control » “Cloud RAN”: use a cloud to manage interference, spectrum Peter A. Steenkiste, CMU 21 Peter A. Steenkiste, CMU 22 Overview Protocol Layers End-to-End • Motivation • Architecture • Resource management • LTE protocols • Radio access network » OFDM refresher • LTE advanced Some slides based on material from Fancy L2 for Communication in “Wireless Communication Networks and Systems” © 2016 Pearson Higher Education, Inc. Mobile to cell tower EPC Peter A. Steenkiste, CMU 23 Peter A. Steenkiste, CMU 24 Page 6 Protocol Layers Protocol Layers PDCP and RLC MAC and PHY • Packet Data Convergence • Medium Access Control Protocol (PDCP) (MAC) » Delivers packets from UE to eNodeB » Performs H-ARQ: combines » Involves header compression, FEC and retransmission ciphering, integrity protection, (ARQ) in-sequence delivery, buffering and forwarding of » Prioritizes and decides which packets during handover UEs and radio bearers will • Radio Link Control (RLC) send or receive data on » Segments or concatenates which shared physical data units resources » Performs ARQ when MAC » Decides the transmission layer H-ARQ fails format, i.e., the modulation – ARQ: Automatic Repeat Request (retransmission) format, code rate, MIMO rank, – H-ARQ: Hybrid ARQ – and power level combines FEC and ARQ • Physical layer actually transmits the data Peter A. Steenkiste, CMU 25 Peter A. Steenkiste, CMU 26 Overview LTE Radio Access Network • Motivation • LTE uses OFDM and MIMO • Architecture • OFDM offers benefits similar