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

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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 to those of CDMA » Good immunity to fading as only a small portion of the • Resource management energy for any one link is typically lost due to a fade • LTE protocols » Fast power control to keep the noise floor as low as possible • Radio access network • Additional advantages » Highly resistant to fading and inter-symbol interference » OFDM refresher » Low modulation rates on each of the many sub-carriers • LTE advanced » Sophisticated error correction » Scales rates easier than CDMA » Allows more advanced antenna technologies, like MIMO Some slides based on material from • Breaks information into pieces and assigns “Wireless Communication Networks and Systems” © 2016 Pearson Higher Education, Inc. each one to a specific set of sub-carriers

Peter A. Steenkiste, CMU 27 Peter A. Steenkiste, CMU 28

Page 7 Different Solution for Up and Downlink

• The downlink uses OFDM with Multiple Access (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 of narrowband fading • The uplink uses Single Carrier OFDM (SC- OFDM) » OFDM but using a single carrier » Provides better energy and cost efficiency for battery- operated mobiles » Large number of subcarriers leads to high peak-to- average Power ratio (PAPR), which is energy-inefficient http://cp.literature.agilent.com/litweb/pdf/5989-7898EN.pdf

Peter A. Steenkiste, CMU 29 Peter A. Steenkiste, CMU 30

LTE Radio Access Network Spectrum 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 frequency band, 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 environments

Peter A. Steenkiste, CMU 31 Peter A. Steenkiste, CMU 32

Page 8 Resource Blocks FDD Frame Structure

• A time-frequency grid is used to illustrate allocation of physical resources • Each column is 6 or 7 OFDM symbols per slot • Each row corresponds to a subcarrier of 15 kHz » Some subcarriers are used for guard bands » 10% of bandwidth is used for guard bands for channel bandwidths of 3 MHz and above

Peter A. Steenkiste, CMU 33 Peter A. Steenkiste, CMU 34

Resource Blocks Overview

• Resource Block • Motivation » 12 subcarriers, 6 or 7 OFDM symbols • Architecture » Results in 72 or 84 resource elements in a resource block • MIMO: 4×4 in LTE, 8×8 in LTE-Advanced • Resource management » Separate resource grids per antenna port • LTE protocols • eNodeB assigns RBs with channel-dependent • Radio access network scheduling » OFDM refresher • Multiuser diversity can be exploited • LTE advanced » To increase bandwidth usage efficiency » Assign resource blocks for UEs with favorable qualities on certain time slots and subcarriers Some slides based on material from » Can also consider fairness, QoS priorities, typical “Wireless Communication Networks and Systems” channel conditions, .. © 2016 Pearson Higher Education, Inc.

Peter A. Steenkiste, CMU 35 Peter A. Steenkiste, CMU 36

Page 9 Comparison LTE-Advanced LTE and LTE-Advanced

• Carrier aggregation – up to 100 MHz • MIMO enhancements to support higher dimensional MIMO – up to 8 x 8 • Relay nodes • Heterogeneous networks involving small cells such as femtocells, picocells, and relays • Cooperative multipoint transmission and enhanced intercell interference coordination • Voice over LTE

Peter A. Steenkiste, CMU 37 Peter A. Steenkiste, CMU 38

Relaying Heterogeneous Networks

• Relay nodes (RNs) • It is increasingly difficult to meet data extend the coverage transmission demands in densely populated area of an eNodeB areas » Receive, demodulate and decode the data • Small cells provide low-powered access nodes from a UE » Operate in licensed or unlicensed spectrum » Apply error correction » Range of 10 m to several hundred meters indoors or outdoors as needed » Best for low speed or stationary users » Transmit a new signal • Macro cells provide typical cellular coverage to the base station » Range of several kilometers • An RN functions as a new base station with » Best for highly mobile users smaller cell radius • RNs can use out-of-band or inband frequencies

Peter A. Steenkiste, CMU 39 Peter A. Steenkiste, CMU 40

Page 10 Heterogeneous Trends Network Examples

• Femtocell • Cloud RAN optimizes spectrum use » Low-power, short-range self-contained » Goal is to reuse frequencies very aggressively base station » Leverage cloud technology to centralize the processing » In residential homes, easily deployed for many cells and use the home’s broadband for backhaul • Standards are complex and rigid and need to » Also in enterprise or metropolitan locations support several generations • Network densification is the » E.g., switch seamlessly from 4G to 3G process of using small cells » Still need to support 2G (legacy phones, voice) » Issues: Handovers, frequency reuse, • Scalability of infrastructure wrt signaling QoS, security traffic is a growing concern • A network of large and small cells is called a heterogeneous » Hardware cannot keep up with changes in usage network (HetNet) • Wide-spread use of custom hardware » Move to commodity, programmable equipment

Peter A. Steenkiste, CMU 41 Peter A. Steenkiste, CMU 42

5G Vision Performance Goals ITU

Faster 4G

Growing application domains

https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.2083-0-201509-I!!PDF-E.pdf

Peter A. Steenkiste, CMU 43 Peter A. Steenkiste, CMU 44

Page 11 5G technology

• Goal is 10+ fold increase in bandwidth over 4G » Combination of more spectrum and more aggressive use of 4G technologies • Very aggressive use of MIMO » Tens to hundred antennas » Very fine grain beamforming and MU-MIMO • More spectrum: use of millimeter bands » Challenging but a lot of spectrum available » Bands between 26 and 60 GHz » Beamforming extends range • Also new lower frequency bands » Low-band and mid-band 5G: 600 MHz to 6 GHz

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