1 Lecture 13 LTE 2 Long Term Evolution (LTE) Material Related to LTE comes from 3GPP LTE: System Overview, Product Development and Test Challenges, Agilent Technologies Application Note, 2008. IEEE Communications Magazine, February 2009 IEEE Communications Magazine, April 2009 1
3 LTE Long Term Evolution Highlights Different network architecture to support packet based access All IP core network that can interface better with technologies such as WiFi and WiMax Use of OFDMA as the medium access/modulation scheme Flexibility to deploy it in as little spectrum as 1.4 MHz and as much as 20 MHz of spectrum Support for true broadband Expected Downlink Data Rates in LTE FDD Downlink Peak Data Rates Using 64 QAM Antenna Configuration SISO 2 2 MIMO 4 4 MIMO Data Rate (Mbps) 100 172.8 326.4 4 History UMTS migration towards LTE was proposed by 3GPP Release-99 Commercial deployment in 2003 Provided 3.84 Mcps we looked at this Release-5 Deployed in 2006 introduced HSDPA Release-6 Deployed in 2007 introduced HSUPA Release-7 Currently in deployment introduced HSPA+ Also includes study of LTE s system architecture evolution (SAE) 2
5 3GPP Release 8 and beyond Expected Deployment HSPA+ this year LTE in 2010 and beyond New IP Core Network OFDMA Air Interface Support for both FDD and TDD In releases beyond release 8 Multimedia broadcast multicast service (MBMS) IMT-Advanced Considered true 4G 6 LTE Network Architecture Evolved Packet System (EPS) consists of two parts E-UTRAN Evolved UMTS Terrestrial Radio Access Network EPC Evolved Packet Core E-UTRAN Consists of only one kind of node: enode-b Compare with UMTS EPC Fully based on IP consists of elements MME Mobility Management Entity (like SGSN) S-GW & PDN-GW: Serving and Packet Data Network Gateways Home subscriber server (HSS) Voice and real-time applications will make use of the IP Multimedia Subsystem (IMS) 3
7 LTE Network Architecture 8 Functional Changes E-NodeB Does a lot more now! (no RNC or BSC) Selection of MME, RRM functions, Handling Mobility MME Sends pages to e-nodebs Security Idle state mobility S-GW Termination of user plane Switching of user plane (mobility) 4
9 Channel Bandwidths Compare with AMPS, GSM, IS-95, UMTS and WiMax Can vary from 1.4 MHz to 20 MHz Resource Block (RB) 180 khz wide and 0.5ms long 12 subcarriers spaced at 15 khz (24 at 7.5 khz possible later) Data rate limited by User Equipment (UE) categories Channel BW (MHz) 1.4 3.0 5 10 15 20 Resource Blocks 6 15 25 50 75 100 10 Downlink Multiple Access: OFDMA 5
11 Uplink Multiple Access: Single Carrier FDMA 12 Why SC-FDMA Avoid high peak-to-average power ratio (PAPR) in MS 6
13 LTE Physical Signals 14 LTE Physical Channels 7
15 Transport Channels in LTE Compare with Transport Channels In UMTS 16 Mapping from Transport to Physical Channels 8
17 Random Access Uplink transmissions in a cell must be orthogonal They are aligned with frame timing of an e-nodeb When a MS powers up or after a long period of inactivity, this alignment is lost RA Procedure MS sends one of several preambles (shared) with a guard period E-NodeB detects preamble, estimates MS s timing, and responds with a correct timing advance and uplink resource MS sends its identity in this allocated resource + some data E-NodeB echos the MS identity 18 More on RA Procedure RA procedure must be repeated if the echoed identity is not correct Backoff indication from e-nodeb can be used to reduce contention After an inter-enodeb handoff, an RA procedure is imminent Contention free RA procedure is possible Unique preamble is assigned to the MS 9
19 Obtaining Uplink Resources If a MS has data to send, it can send a single scheduling request (SR) bit using The RA Procedure Dedicated SR on the PUCCH In the first allocated resource, the MS sends a buffer status report that has more information about how much data it wants to send E-NodeB allocates resources on a per sub-frame basis (every ms!) Scheduler is responsible for handling QoS 20 Frame Structure (FDD) Referenced to T s which is the shortest time interval in the system Defined as T s = 1/(15000 2048) = 32.552 ns OFDM symbol length = 66.7 μs 10
21 Detailed Downlink Frame Structure (FDD) 22 Miscellaneous - 1 Discontinuous Reception MSs can save battery by checking the paging channel once every DRX cycle Handoff E-NodeB s are connected over an X2 interface They can negotiate whether or not a MS must handoff Hybrid ARQ Similar to HSPA Power control It is specified, but not as crucial as in CDMA systems 11
23 Miscellaneous - 2 Frequency reuse of 1 is possible in the center of the cell Some frequency management is essential at the cell edges 12