Evolution of Cellular Systems

18-452/18-750 Wireless Networks and Applications Lecture 16: LTE

Peter Steenkiste

Spring Semester 2020 http://www.cs.cmu.edu/~prs/wirelessS20/

Peter A. Steenkiste, CMU 1 Peter A. Steenkiste, CMU 2

GSM Multiple Access Example Additional GSM Features

• Combination of FDMA and TDMA • GSM uses GMSK modulation » More on this later » Gaussian Minimum Shift Keying • 890-915 MHz for uplink » Optimized version of Frequency Shift Keying (FM) • 935-960 MHz for downlink • Slow frequency hopping: successive TDMA frames are sent over a different frequency • Each of those 25 MHz bands is sub divided » Switches every 4.615 msec into 124 single carrier channel of 200 KHz » Spreads out effect of multipath fading » Each with a data rate of 270.833 kbps » Also helps with co-channel interference • In each uplink/downlink band there is a 200 • Delay equalization KHz guard band » Mobile stations sharing a frame can be at different • Each 200 KHz channel carries 8 TDMA distances from the base station channels » Tail bits and guard bits provide margin to avoid overlap

Peter A. Steenkiste, CMU 3 Peter A. Steenkiste, CMU 4

Page 1 Generalized Packet Radio GPRS Architecture Service (GPRS)

 Network Subsystem includes several new entities: • Packet-oriented data transport service  Serving GPRS Support (SGSN): data transfer » Bursty, non-periodic traffic typical for access between Base Station and Network Subsystem • Uses a new architecture for data traffic  Gateway GPRS Support Node: connects to other GPRS » Allows users to open a persistent data connection networks and the packet data network (Internet) » Sending data traffic over a voice connection would add  New interfaces between the various entities too much setup and teardown overhead  Transmission plane • Uses the same frame structure as voice  Data packets are transmitted by a tunnel mechanisms » 21.4 kbps from a 22.8 kbps gross data rate  Control plane » Can combine up to 8 GSM connections  Protocol for tunnel management: create, remove, … – Overall throughputs up to 171.2 kbps  GPRS Tunnel Protocol » Enhanced Data Rates for GSM Evolution (EDGE) further  Radio interface increased rates using a more aggressive PHY  Changes the logical channels and how they are managed Peter A. Steenkiste, CMU 5 Peter A. Steenkiste, CMU 6

GPRS Architecture GPRS Radio Interface

Time Slot Other GPRS … 0123 4 56701234 SGSN networks F1 Gp GGSN F2 Uplink Gp Gn F3 BSC F4 Gf BTS Gr Gs Gi 0123 4 56701234 Gc GGSN PDN Carrier F1 BTS frequency D F2 MT HLR Downlink F3 MSC/VLR F4 Base Station Subsystem SGSN – Serving GPRS Support Node User1 Voice User3 GPRS User5 GPRS GGSN – Gateway GPRS Support Node User2 Voice User4 GPRS

Peter A. Steenkiste, CMU 7 Peter A. Steenkiste, CMU 8

Page 2 Evolution of Who is Who Cellular Wireless Systems

• International Union (ITU) - agency of the United Nations responsible for: » Assisting in the development and coordination of world- wide standards » Coordinate shared use of the global spectrum » Defined the International Mobile Telecommunications 2000 (IMT-2000) project for telecommunications • Third Generation Partnership Project (3GPP) » A group of telecommunications associations that represent large markets world-wide » Defined a group of 3G standards as part of the IMT-2000 framework in 1999 » Originally defined GSM, EDGE, and GPRS » Later defined follow-on releases and also LTE ()

Peter A. Steenkiste, CMU 9 Peter A. Steenkiste, CMU 10

Reminder: CDMA - Direct UMTS and WCDMA Sequence

 Part of a group of 3G standards defined as part of the IMT-2000 framework by 3GPP • Universal Mobile Telecommunications System (UMTS) » Successor of GSM • W-CDMA is the for UMTS » Wide-band CDMA » Originally 144 kbps to 2 Mbps, depending on mobility These signals will • Basically same architecture as GSM look like noise » Many GSM functions were carried over WCDMA to the receiver » But they changed all the names!

Peter A. Steenkiste, CMU 11 Peter A. Steenkiste, CMU 12

Page 3 Later Releases Improved Advantages of CDMA for Performance Cellular systems

• High Speed Downlink Packet Access (HSDPA): • Frequency diversity – frequency-dependent 1.8 to 14.4 Mbps downlink transmission impairments have less effect on » Adaptive modulation and coding, hybrid ARQ, and fast signal • High Speed Uplink Packet Access (HSUPA): • Multipath resistance – chipping codes used Uplink rates up to 5.76 Mbps for CDMA exhibit low cross correlation and low autocorrelation • Plus (HSPA+): Maximum data rates increased from 21 Mbps up • Privacy – privacy is inherent since spread to 336 Mbps spectrum is obtained by use of noise-like signals » 64 QAM, 2×2 and 4×4 MIMO, and dual or multi-carrier combinations • Graceful degradation – system only gradually • Eventually led to the definition of LTE degrades as more users access the system

Peter A. Steenkiste, CMU 13 Peter A. Steenkiste, CMU 14

Mobile Wireless CDMA Evolution of Soft Hand-off Cellular Wireless Systems

• Soft Handoff – mobile station temporarily connected to more than one base station simultaneously • Requires that the mobile acquire a new cell before it relinquishes the old • More complex than hard handoff used in FDMA and TDMA schemes

Peter A. Steenkiste, CMU 15 Peter A. Steenkiste, CMU 16

Page 4 Purpose, motivation, and Overview LTE approach to 4G

• Defined by ITU directives for International Mobile • Motivation Telecommunications Advanced (IMT-Advanced) • Architecture • All-IP packet switched network. • Resource management • Ultra- access • LTE protocols • Peak data rates • Radio access network » Up to 100 Mbps for high-mobility mobile access » OFDM refresher » Up to 1 Gbps for low-mobility access • LTE advanced • Dynamically share and use network resources • Smooth handovers across heterogeneous networks » and 3G networks, small cells such as picocells, , and relays, and WLANs Some slides based on material from “Wireless Communication Networks and Systems” • High quality of service for multimedia applications © 2016 Pearson Higher Education, Inc.

Peter A. Steenkiste, CMU 17 Peter A. Steenkiste, CMU 18

High Level Features LTE Architecture

Radio Access • No support for circuit-switched voice • evolved NodeB (eNodeB) Network » Instead providing Voice over LTE (VoLTE) » Most devices connect into the network through the eNodeB • Replace spread spectrum/CDMA with OFDM • Evolution of the previous 3GPP NodeB (~2G BTS) » Uses OFDM instead of CDMA • Has its own control functionality » Dropped the Core Controller (RNC - ~2G BSC) Network » eNodeB supports , admission control, and (handover) » Was originally the responsibility of the RNC

Peter A. Steenkiste, CMU 19 Peter A. Steenkiste, CMU 20

Page 5 Evolved Packet System Evolved Packet System Components

• Overall architecture is called the Evolved • Long Term Evolution (LTE) is the RAN Packet System (EPS) » Called Evolved UMTS Terrestrial Radio Access (E-UTRA) » Enhancement of 3GPP’s 3G RAN • 3GPP standards divide the network into » eNodeB is the only logical node in the E-UTRAN • Radio access network (RAN): cell towers and » No (RNC) connectives to mobile devices • Evolved Packet Core (EPC) • Core network (CN): management and » Operator or carrier core network –core of the system connectivity to other networks • Traditionally circuit switched but now entirely • Each can evolve independently packet switched » Driven by different technologies: optimizing spectrum » Based on IP - Voice supported using voice over IP (VoIP) use versus management and control or traffic

Peter A. Steenkiste, CMU 21 Peter A. Steenkiste, CMU 22

Evolved Packet Core Design Principles of the EPS Components

• Packet-switched transport for traffic belonging • Mobility Management Entity (MME) to all QoS classes » Supports user equipment context, identity, authentication, and » Voice, streaming, real-time, non-real-time, background authorization • Serving Gateway (SGW) • Comprehensive radio resource management » Receives and sends packets between the eNodeB and the core » End-to-end QoS, transport for higher layers network » Load sharing/balancing • Packet Data Network Gateway (PGW) » Connects the EPC with external networks » Policy management across different radio access technologies • Home Subscriber Server (HSS) » Database of user-related and subscriber-related information • Integration with existing 3GPP 2G and 3G • Interfaces networks » S1 interface between the E-UTRAN and the EPC – For both control purposes and for user plane data traffic • Scalable from 1.4 MHz to 20 MHz » X2 interface for eNodeBs to interact with each other • Carrier aggregation for overall bandwidths up – Again for both control purposes and for user plane data traffic to 100 MHz

Peter A. Steenkiste, CMU 23 Peter A. Steenkiste, CMU 24

Page 6 Overview LTE Resource Management

• Motivation • LTE uses bearers for quality of service (QoS) control instead of circuits • Architecture • EPS bearers • Resource management » Between entire path between PGW and UE » Maps to specific QoS parameters such as data rate, delay, • LTE protocols and packet error rate • Radio access network • Service Data Flows (SDFs) differentiate traffic flowing between applications on a client and a » OFDM refresher service • LTE advanced » 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 controlled by LTE Some slides based on material from “Wireless Communication Networks and Systems” © 2016 Pearson Higher Education, Inc.

Peter A. Steenkiste, CMU 25 Peter A. Steenkiste, CMU 26

Bearer Management based on EPC: Mobility Management QoS Class Identifier (QCI)

• X2 interface used when moving within a RAN Guaranteed coordinated under the (minimum) same Memory Bit Rate Management Entity (MME) • S1 interface used to move to another MME No • Hard handovers are used: Guarantees A UE is connected to only one eNodeB at a time

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

Page 7 EPC: Inter-cell Interference Overview Coordination (ICIC)

• Reduces interference when the same frequency is used in a neighboring cell • Motivation • Goal is universal frequency reuse • Architecture » N = 1 in “Cellular principles” lecture • Resource management » Must avoid interference when mobile devices are near each • LTE protocols other at cell edges » Interference randomization, cancellation, coordination, and • Radio access network avoidance are used » OFDM refresher • eNodeBs send indicators • LTE advanced » Relative Narrowband Transmit Power, High Interference, and Overload indicators • Later releases of LTE have improved interference Some slides based on material from control “Wireless Communication Networks and Systems” » “Cloud RAN”: use a cloud to manage interference, spectrum © 2016 Pearson Higher Education, Inc.

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

Protocol Layers End-to-End Protocol Layers PDCP and RLC

• Packet Data Convergence Protocol (PDCP) » Delivers packets from UE to eNodeB » Involves header compression, ciphering, integrity protection, in-sequence delivery, buffering and forwarding of packets during handover • Radio Link Control (RLC) » Segments or concatenates data units » Performs ARQ when MAC layer H-ARQ fails – ARQ: Automatic Repeat Request (retransmission) – H-ARQ: Hybrid ARQ – Fancy L2 for Communication in combines FEC and ARQ Mobile to cell tower EPC

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

Page 8 Protocol Layers MAC and PHY

• Medium Access Control (MAC) » Performs H-ARQ: combines FEC and retransmission (ARQ) » Prioritizes and decides which UEs and radio bearers will send or receive data on which shared physical resources » Decides the transmission format, i.e., the modulation format, code rate, MIMO rank, and power level • Physical layer actually transmits the data

Peter A. Steenkiste, CMU 33

Page 9