4th Generation Systems and Long Term Evolution (LTE) PDF

Chapter 5 4thGeneration Systems and Long Term Evolution (LTE) 4G Technology High-speed, universally accessible wireless service capability Creating a revolution – Networking at all locations for tablets, smartphones, computers, and devices. – Similar to the revolution caused by Wi-F...

Chapter 5 4thGeneration Systems and Long Term Evolution (LTE) 4G Technology High-speed, universally accessible wireless service capability Creating a revolution – Networking at all locations for tablets, smartphones, computers, and devices. – Similar to the revolution caused by Wi-Fi LTE and LTE-Advanced will be studied here – Goals and requirements, complete system architecture, core network (Evolved Packet System), LTE channel and physical layer – Will first study LTE Release 8, then enhancements from Releases 9-12 Purpose, Motivation, and Approach to 4G (1 of 2) Ultra-mobile broadband access – For a variety of mobile devices International Telecommunication Union (ITU) 4G directives for IMT- Advanced – All-IP packet switched network. – 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, including 2G and 3G networks, small cells such as picocells, femtocells, and relays, and WLANs – High quality of service for multimedia applications Purpose, Motivation, and Approach to 4G (2 of 2) No support for circuit-switched voice – Instead providing Voice over LTE (VoLTE) Replace spread spectrum with OFDM Table 14.1 Wireless Network Generations Technology 1G 2G 2.5G 3G 4G Design began 1970 1980 1985 1990 2000 Implementation 1984 1991 1999 2002 2012 Services Analog voice Digital voice Higher capacity Higher capacity, Completely IP packetized data broadband based Data rate 1.9. kbps 14.4 kbps 384 kbps 2 Mbps 200 Mbps Multiplexing FDMA TDMA, CDMA TDMA, CDMA CDMA OFDMA, SC-FDM A Core network PSTN PSTN PSTN, packet Packet network IP backbone network LTE Architecture (1 of 2) Two candidates for 4G – IEEE 802.16 WiMax ▪ Enhancement of previous fixed wireless standard for mobility – Long Term Evolution ▪ Third Generation Partnership Project (3GPP) ▪ Consortium of Asian, European, and North American telecommunications standards organizations Both are similar in use of OFDM and OFDMA LTE has become the universal standard for 4G – All major carriers in the United States LTE Architecture (2 of 2) Some features started in the 3G era for 3GPP Initial LTE data rates were similar to 3G 3GPP Release 8 – Clean slate approach – Completely new air interface ▪ OFDM, OFDMA, MIMO 3GPP Release 10 – Known as LTE-Advanced – Further enhanced by Releases 11 and 12 Table 14.2 Comparison of Performance Requirements for LTE and LTE-Advanced System Performance System Performance LTE LTE-Advanced Peak rate Downlink 100 Mbps @20 MHz 1 Gbps @100 MHz Peak rate Uplink 50 Mbps @20 MHz 500 Mbps @100 MHz Control plane delay Idle to connected < 100 ms < 50 ms Control plane delay Dormant to active < 50 ms < 10 ms User plane delay User plane delay < 5 ms Lower than LTE Spectral efficiency Downlink 5 bps/Hz @2 × 2 30 bps/Hz @8×8 (peak) Spectral efficiency (peak) Uplink 2.5 bps/Hz @1 × 2 15 bps/Hz @4×4 Mobility Mobility Up to 350 k m /h illio etre our Up to 350–500 k m /h illo etre our LTE Architecture (3 of 3) evolved NodeB (eNodeB) – Most devices connect into the network through the eNodeB Evolution of the previous 3GPP NodeB – Now based on OFDMA instead of CDMA – Has its own control functionality, rather than using the Radio Network Controller (RNC) ▪ eNodeB supports radio resource control, admission control, and mobility management ▪ Originally the responsibility of the RNC Figure 14.2 Overview of the EPC/LTE Architecture Evolved Packet System (1 of 2) Overall architecture is called the Evolved Packet System (EPS) 3GPP standards divide the network into – Radio access network (RAN) – Core network (CN) Each evolve independently. Long Term Evolution (LTE) is the RAN – Called Evolved UMTS Terrestrial Radio Access (E-UTRA) – Enhancement of 3GPP’s 3G RAN ▪ Called the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) – eNodeB is the only logical node in the E-UTRAN – No RNC Evolved Packet System (2 of 2) Evolved Packet Core (EPC) – Operator or carrier core network – It is important to understand the EPC to know the full functionality of the architecture Some of the design principles of the EPS – Clean slate design – Packet-switched transport for traffic belonging to all QoS classes including conversational, streaming, real-time, non-real-time, and background – Radio resource management for the following: end-to-end QoS, transport for higher layers, load sharing/balancing, policy management/enforcement across different radio access technologies – Integration with existing 3GPP 2G and 3G networks – Scalable bandwidth from 1.4 MHz to 20 MHz – Carrier aggregation for overall bandwidths up to 100 MHz Functions of the EPS Network access control, including network selection, authentication, authorization, admission control, policy and charging enforcement, and lawful interception Packet routing and transfer Security, including ciphering, integrity protection, and network interface physical link protection Mobility management to keep track of the current location of the UE Radio resource management to assign, reassign, and release radio resources taking into account single and multi-cell aspects Network management to support operation and maintenance IP networking functions, connections of eNodeBs, E-UTRAN sharing, emergency session support, among others Evolved Packet Core Traditionally circuit switched but now entirely packet switched – Based on IP – Voice supported using voice over IP (VoIP) Core network was first called the System Architecture Evolution (SAE) EPC Components (1 of 2) Mobility Management Entity (MME) – Supports user equipment context, identity, authentication, and authorization Serving Gateway (SGW) – Receives and sends packets between the eNodeB and the core network Packet Data Network Gateway (PGW) – Connects the EPC with external networks EPC Components (2 of 2) Home Subscriber Server (HSS) – Database of user-related and subscriber-related information Interfaces – S1 interface between the E10-U TRAN 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 Non-Access Stratum Protocols For interaction between the EPC and the UE – Not part of the Access Stratum that carries data EPS Mobility Management (EMM) – Manage the mobility of the UE EPS Session Management (ESM) – Activate, authenticate, modify, and de-activate user- plane channels for connections between the UE, SGW, and PGW LTE Resource Management LTE uses bearers for quality of service (QoS) control instead of circuits – QoS is discussed in Chapter 3 EPS bearers – Between PGW and UE – Maps to specific QoS parameters such as data rate, delay, and packet error rate Service Data Flows (SDFs) differentiate traffic flowing between applications on a client and a service – 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 Figure 14.3 LTE QOS Bearers Classes of Bearers Guaranteed Bit Rate (GBR) bearers – Guaranteed a minimum bit rate ▪ And possibly higher bit rates if system resources are available – Useful for voice, interactive video, or real-time gaming Non- GBR (GBR) bearers – Not guaranteed a minimum bit rate – Performance is more dependent on the number of UEs served by the eNodeB and the system load – Useful for e-mail, file transfer, Web browsing, and P2P file sharing. Bearer Management (1 of 3) Each bearer is given a QoS class identifier (QCI) Table 14.3 Standardized QCI Characteristics Resource Type Packet Delay Packet Error QCI Priority Budget Loss Rate Example Services 10 to the negative 1 GBR 2 100 ms 10-2power second Conversational Voice -3 10 to the negative third Conversational Video (live 2 GBR 4 150 ms 10 power streaming) 10 to the negative third 3 GBR 3 50 ms 10-3 power Real-Time Gaming 10 to the negative -6 sixth No-nconversational Video 4 GBR 5 300 ms 10 power (buffered streaming) Bearer Management (2 of 3) Table 14.3 [continued] Resource Packet Delay Packet Error QCI Type Priority Budget Loss Rate Example Services 10 to the negative 6 5 Non-GBR 1 100 ms sixth10 power IMS Signalling Video (buffered treaming) 10 to the negative 6 TCP-based (e.g., www, e- 6 Non-GBR 6 300 ms 10power sixth mail, chat, ftp, p2p file sharing, progressive video, etc.) 10 to the negative 3 Voice, Video (live streaming) 7 Non-GBR 7 100 ms 10power third Interactive Gaming Video (buffered streaming) 10 to the negative TCP-based (e.g., www, e- 8 Non-GBR 8 300 ms sixth power mail, chat, ftp, p2p file sharing, progressive video, etc.) Video (buffered streaming) 10 to the negative 6 T C P-based (e.g., www, e- 9* Non-GBR 9 300 ms 10power sixth mail, chat, ftp, p2p file sharing, progressive video, etc.) * QCI value typicaly used for the default bearer Bearer Management (3 of 3) Each QCI is given standard forwarding treatments – Scheduling policy, admission thresholds, rate-shaping policy, queue management thresholds, and link layer protocol configuration For each bearer the following information is associated – QoS class identifier (QCI) value – Allocation and Retention Priority (ARP): Used to decide if a bearer request should be accepted or rejected Additionally for GBR bearers – Guaranteed Bit Rate (GBR): minimum rate expected from the network – Maximum Bit Rate (MBR): bit rate not to be exceeded from the U E into the bearer EPC Functions (1 of 2) Mobility management – X2 interface used when moving within a RAN coordinated under the same MME – S1 interface used to move to another MME – Hard handovers are used: A UE is connected to only one eNodeB at a time EPC Functions (2 of 2) Inter-cell interference coordination (ICIC) – Reduces interference when the same frequency is used in a neighboring cell – Goal is universal frequency reuse (N = 1 from Chapter 13) ▪ Must avoid interference when UEs are near each other at cell edges ▪ Interference randomization, cancellation, coordination, and avoidance are used – eNodeBs send indicators ▪ Relative Narrowband Transmit Power, High Interference, and Overload indicators – Later releases of LTE have improved interference control LTE Channel Structure and Protocols Hierarchical channel structure between the layers of the protocol stack – Provides efficient support for QoS LTE radio interface is divided – Control Plane – User Plane User plane protocols – Part of the Access Stratum – Transport packets between UE and PGW – PDCP transports packets between UE and eNodeB on the radio interface (Figure 14.4) – GTP sends packets through the other interfaces (Figure 14.5) Figure 14.4 LTE Radio Interface Protocols Protocol Layers (1 of 2) Radio Resource Control (RRC) – Performs control plane functions to control radio resources – Through RRC_IDLE and RRC_CONNECTED connection states 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 Protocol Layers (2 of 2) Radio Link Control (RLC) – Segments or concatenates data units – Performs ARQ when MAC layer H-ARQ fails Medium Access Control (MAC) – Performs H-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 Figure 14.5 User Plane Protocol Stack Figure 14.6 Control Plane Protocol Stack LTE Channel Structure Three types of channels – Channels provide services to the layers above – Logical channels ▪ Provide services from the MAC layer to the RLC ▪ Provide a logical connection for control and traffic – Transport channels ▪ Provide PHY layer services to the MAC layer ▪ Define modulation, coding, and antenna configurations – Physical channels ▪ Define time and frequency resources use to carry information to the upper layers Different types of broadcast, multicast, paging, and shared channels Figure 14.8 Radio Interface Architecture and SAPS Figure 14.9 Mapping of Logical, Transport, and Physical Channels LTE Radio Access Network (1 of 3) LTE uses MIMO and OFDM – OFDMA on the downlink – SC-OFDM on the uplink, which provides better energy and cost efficiency for battery-operated mobiles LTE uses subcarriers 15 kHz apart – Maximum FFT size is 2048 LTE Radio Access Network (2 of 3) – Basic time unit is 1 1 Ts   seconds. 15000  2048  30,720,000 – Downlink and uplink are organized into radio frames ▪ Duration 10 ms., which corresponds to 307200Ts. LTE Radio Access Network (3 of 3) 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) – Normal CP = 144 × Ts = 4.7 μs. – Extended CP = 512 × Ts = 16.7 μs. ▪ For worse environments Figure 14.10 Spectrum Allocation for FDD and TDD FDD Frame Structure Type 1 (1 of 2) Three different time units – The slot equals Tslot = 15360 × Ts = 0.5 ms – Two consecutive slots comprise a subframe of length 1 ms. ▪ Channel dependent scheduling and link adaptation (otherwise known as adaptive modulation and coding) occur on the time scale of a subframe (1000 times/second). – 20 slots (10 subframes) equal a radio frame of 10 ms. ▪ Radio frames schedule distribution of more slowly changing information, such as system information and reference signals. FDD Frame Structure Type 1 (2 of 2) Normal CP allows 7 OFDM symbols per slot Extended CP only allows time for 6 OFDM symbols 1 – Use of extended CP results in a  14.3% reduction in throughput 7 – But provides better compensation for multipath Figure 14.11 FDD Frame Structure, Type 1 FDD Frame Structure Type 2 Radio frame is again 10 ms. Includes special subframes for switching downlink-to- uplink – Downlink Pilot TimeSlot (DwPTS): Ordinary but shorter downlink subframe of 3 to 12 OFDM symbols – Uplink Pilot TimeSlot (UpPTS): Short duration of one or two OFDM symbols for sounding reference signals or random access preambles – Guard Period (GP): Remaining symbols in the special subframe in between to provide time to switch between downlink and uplink Figure 14.12 TDD Frame Structure, Type 2 Resource Blocks (1 of 3) 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 Figure 14.13 LTE Resource Grid Resource Blocks (2 of 3) Resource Block – 12 subcarriers – 6 or 7 OFDM symbols – Results in 72 or 84 resource elements in a resource block (RB) For the uplink, contiguous frequencies must be used for the 12 subcarriers – Called a physical resource block For the downlink, frequencies need not be contiguous – Called a virtual resource block Resource Blocks (3 of 3) MIMO – 4×4 in LTE, 8 × 8 in LTE-Advanced – Separate resource grids per antenna port eNodeB assigns RBs with channel-dependent scheduling Multiuser diversity can be exploited – To increase bandwidth usage efficiency – Assign resource blocks for UEs with favorable qualities on certain time slots and subcarriers – Can also include ▪ Fairness considerations ▪ Understanding of UE locations ▪ Typical channel conditions versus fading ▪ QoS priorities. Physical Transmission (1 of 3) Release 8 supports up to 4 × 4 MIMO The eNodeB uses the Physical Downlink Control Channel (PDCCH) to communicate – Resource block allocations – Timing advances for synchronization 1 Two types of rate convolutional codes 3 QPSK, 16QAM, and 64QAM modulation based on channel conditions Physical Transmission (2 of 3) UE determines a CQI index that will provide the highest throughput while maintaining at most a 10% block error rate Table 14.7 4-Bit CQI Table CQI Index Modulation Code Rate × 1024 Efficiency 0 Out of Range Out of Range Out of Range 1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5 QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 Physical Transmission (3 of 3) Table 14.7 [continued] CQI Index Modulation Code Rate × 1024 Efficiency 8 16QAM 490 1.4766 9 16QAM 616 1.9141 10 64QAM 466 2.4063 11 64QAM 567 2.7305 12 64QAM 666 3.3223 13 64QAM 772 3.9023 14 64QAM 873 4.5234 15 64QAM 948 5.5547 Power-On Procedures 1. Power on the UE 2. Select a network 3. Select a suitable cell 4. Use contention-based random access to contact an eNodeB 5. Establish an RRC connection 6. Attach: Register location with the MME and the network configures control and default EPS bearers. 7. Transmit a packet 8. Mobile can then request improved quality of service. If so, it is given a dedicated bearer LTE-Advanced So far we have studied 3GPP Release 8 – Releases 9-12 have been issued Release 10 meets the ITU 4G guidelines – Took on the name LTE-Advanced Key improvements – Carrier aggregation – MIMO enhancements to support higher dimensional MIMO – Relay nodes – Heterogeneous networks involving small cells such as femtocells, picocells, and relays – Cooperative multipoint transmission and enhanced intercell interference coordination – Voice over LTE Carrier Aggregation Ultimate goal of LTE-Advanced is 100 MHz bandwidth – Combine up to 5 component carriers (CCs) – Each CC can be 1.4, 3, 5, 10, 15, or 20 MHz – Up to 100 MHz Three approaches to combine CCs – Intra-band Contiguous: carriers adjacent to each other – Intra-band noncontiguous: Multiple CCs belonging to the same band are used in a noncontiguous manner – Inter-band noncontiguous: Use different bands Figure 14.14 Carrier Aggregation Enhanced MIMO Expanded to 8 × 8 for 8 parallel layers Or multi-user MIMO can allow up to 4 mobiles to receive signals simultaneously – eNodeB can switch between single user and multi- user every subframe Downlink reference signals to measure channels are key to MIMO functionality – UEs recommend MIMO, precoding, modulation, and coding schemes – Reference signals sent on dynamically assigned subframes and resource blocks Relaying Relay nodes (RNs) extend the coverage area of an eNodeB – Receive, demodulate and decode the data from a UE – Apply error correction as needed – Then transmit a new signal to the base station An RN functions as a new base station with smaller cell radius RNs can use out-of-band or inband frequencies Figure 14.15 Relay Nodes Heterogeneous Networks (1 of 2) It is increasingly difficult to meet data transmission demands in densely populated areas Small cells provide low-powered access nodes – Operate in licensed or unlicensed spectrum – Range of 10 m to several hundred meters indoors or outdoors – Best for low speed or stationary users Macro cells provide typical cellular coverage – Range of several kilometers – Best for highly mobile users Heterogeneous Networks (2 of 2) Femtocell – Low-power, short-range self-contained base station – In residential homes, easily deployed and use the home’s broadband for backhaul – Also in enterprise or metropolitan locations Network densification is the process of using small cells – Issues: Handovers, frequency reuse, QoS, security A network of large and small cells is called a heterogeneous network (HetNet) Figure 14.16 The Role of Femtocells Coordinated Multipoint Transmission and Reception Release 8 provides intercell interference coordination (ICIC) – Small cells create new interference problems – Release 10 provides enhanced ICIC to manage this interference Release 11 implemented Coordinated Multipoint Transmission and Reception (CoMP) – To control scheduling across distributed antennas and cells – Coordinated scheduling/coordinated beamforming (CS/CB) steers antenna beam nulls and mainlobes – Joint processing (JT) transmits data simultaneously from multiple transmission points to the same UE – Dynamic point selection (DPS) transmits from multiple transmission points but only one at a time Other Enhancements in LTE-Advanced (1 of 2) Traffic offload techniques to divert traffic onto non-LTE networks Adjustable capacity and interference coordination Enhancements for machine-type communications Support for dynamic adaptation of TDD configuration so traffic fluctuations can be accommodated Other Enhancements in LTE-Advanced (2 of 2) Release 12 also conducted studies – Enhancements to small cells and heterogeneous networks, higher order modulation like 256-QAM, a new mobile-specific reference signal, dual connectivity (for example, simultaneous connection with a macro cell and a small cell) – Two-dimensional arrays that could create beams on a horizontal plane and also at different elevations for user- specific elevation beamforming into tall buildings. ▪ Would be supported by massive MIMO or full dimension MIMO ▪ Arrays with many more antenna elements than previous deployments. ▪ Possible to still have small physical footprints when using higher frequencies like millimeter waves Voice over LTE The GSM Association is the cellular industry’s main trade association – GSM Association documents provide additional specifications for issues that 3GPP specifications left as implementation options. Defined profiles and services for Voice over LTE (VoLTE) Uses the IP Multimedia Subsystem (IMS) to control delivery of voice over IP streams – IMS is not part of LTE, but a separate network – IMS is mainly concerned with signaling. The GSM Association also specifies services beyond voice, such as video calls, instant messaging, chat, and file transfer in what is known as the Rich Communication Services (RCS).