LTE – Long Term Evolution Introduction

Outline Evolution and Adoption Features Architecture Radio Interface Overview of Protocols and Channels LTE-Advanced

Evolution TDMA EDGE GSM GPRS WCDMA PDC cdmaOne 2G evolved 2G 3G CDMA2000 1x GPRS HSPA WCDMA PDC LTE LTE-A CDMA2000 1x EV/DO cdmaOne 2G evolved 2G 64–144 kbps 3G 384 kbps - 2 Mbps evolved 3G 4G 9.6 - 14.4 kbps 384 kbps - 100 Mbps >1 Gbps Page 2

LTE Adoption (as of May 2012) Red – countries with LTE service Dark Blue – planned or ongoing deployment Light Blue – LTE system trials (pre-commitment)

Features All IP Network (VoIP for voice) Spectrum Flexibility Can also use other 3GPP technologies for voice Spectrum Flexibility (1.25MHz – 20MHz) TDD/FDD (full-duplex and half-duplex) Multi-antenna transmissions (4 MIMO on downlink, 2 MIMO on uplink) 300 Mbps peak downlink in 20MHz x 4 MIMO x 64 QAM 75 Mbps peak uplink

Features (cont) 100 km macro cells (5 km with optimal performance) Up to 200 active users in a cell OFDM downlink and Single Carrier FDMA (SC-FDMA) uplink HARQ (Hybrid ARQ) Co-existence with existing technologies (calls can be started in LTE and transferred to GSM/GPRS, WCDMA)

Architecture UE – User Equipment eNodeB – evolved NodeB (BS) S-GW – Serving Gateway P-GW – PDN Gateway MME – Mobility Management Entity HSS – Home Subscriber Server PCRF – Policy Rules and Charging Control Function

Elements HSS – Home Subscriber Server – stores subscriber information, roaming capabilities, QoS profiles, current registration; may integrate AUC functionality P-GW – PDN Gateway – allocates UE IP address, QoS enforcement, filters downlink packets in different QoS bearers S-GW – Serving Gateway local mobility anchor as UE switches between eNodeBs, buffers downlink data until paging completes, charging for visiting users MME – Mobile Management Entity controls flow between UE and CN (corresponding node) – handles idle mobility PCRF – Policy Control and Charging Rules Function – charging, policy control, QoS authorization

Standardized QoS Class Identifiers (QCI) GBR – Guaranteed Bit-Rate

Radio Interface Multiple Access Scheme Adaptive Modulation and Coding Downlink uses QPSK, 16QAM and 64QAM Uplink uses QPSK and 16QAM Multiple Access Scheme Downlink uses OFDMA Uplink uses Single Carrier FDMA (SC-FDMA) BLER – Block Error Rate

Generic Frame Structure Allocation of physical resource blocks (PRBs) is handled by a scheduling function at the 3GPP base station (eNodeB) Frame 0 and frame 5 (always downlink)

Resource Blocks 2D – Time x Frequency

Common Physical RB (PRB) Formats Channel Bandwidth (MHz) NRBDL/NRBUL Typical IDFT size Number of Non-Zero Sub-carriers (REs) 1.25 6 128 72 5 25 512 300 10 50 1024 600 15 75 1024 or 2048 900 20 100 2048 1200 PRBs are mapped onto contiguous OFDMA/SC-FDMA symbols in the time-domain (6 or 7) Each PRB is chosen to be equivalent to 12 (15 kHz spacing) sub-carriers of an OFDMA symbol in the frequency-domain Because of a common PRB size over different channel bandwidths, the system scales naturally over different bandwidths UEs determines cell bandwidth during initial acquisition and can be any of above

Example: 300 REs, 25 RBs (5 MHz channel) PRB13 PRB24 “Normal” Cyclic Prefix Mode (7 symbols) PRB23 PRB22 PRB21 PRB20 PRB19 PRB18 PRB17 PRB16 “Extended” Cyclic Prefix Mode (6 symbols) PRB15 PRB14 PRB13 PRB12 NRBDL/NRBUL PRB12 PRB11 PRB10 PRB9 PRB8 PRB7 PRB6 PRB5 PRB4 PRB3 NSCRB PRB2 PRB1 PRB0 PRB11 l=0 l=6 NULsymb /NULsymb

Sub-frame and Frame One frame = 10ms Tslot=500ms 1 2 3 18 19 1 2 3 18 19 One subframe 71.3ms 71.9ms Normal Prefix 4.69ms 5.2ms Frequency Domain View 83ms Extended Prefix Time-domain View 13.9ms

OFDM LTE uses OFDM for the downlink – that is, from the base station to the terminal. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. OFDM uses a large number of narrow sub-carriers for multi-carrier transmission. The basic LTE downlink physical resource can be seen as a time-frequency grid. In the frequency domain, the spacing between the subcarriers, Δf, is 15kHz. In addition, the OFDM symbol duration time is 1/Δf + cyclic prefix. The cyclic prefix is used to maintain orthogonality between the sub-carriers even for a time-dispersive radio channel. One resource element carries QPSK, 16QAM or 64QAM. With 64QAM, each resource element carries six bits. The OFDM symbols are grouped into resource blocks. The resource blocks have a total size of 180kHz in the frequency domain and 0.5ms in the time domain. Each 1ms Transmission Time Interval (TTI) consists of two slots (Tslot). In E-UTRA, downlink modulation schemes QPSK, 16QAM, and 64QAM are available.

SC-FDMA The LTE uplink transmission scheme for FDD and TDD mode is based on SC-FDMA (Single Carrier Frequency Division Multiple Access). This is to compensate for a drawback with normal OFDM, which has a very high Peak to Average Power Ratio (PAPR). High PAPR requires expensive and inefficient power amplifiers with high requirements on linearity, which increases the cost of the terminal and also drains the battery faster. SC-FDMA solves this problem by grouping together the resource blocks in such a way that reduces the need for linearity, and so power consumption, in the power amplifier. A low PAPR also improves coverage and the cell-edge performance. Still, SC-FDMA signal processing has some similarities with OFDMA signal processing, so parameterization of downlink and uplink can be harmonized.

SC-FDMA Localized Mapping and Distributed Mapping

User Plane Protocol Stack PDCP – Packet Data Convergence Protocol RLC – Radio Link Control GTP-U – GPRS Tunneling Protocol – User Plane

Control Plane Protocol Stack NAS – Non-Access Stratum RRC – Radio Resource Control PDCP – Packet Data Convergence Protocol RLC – Radio Link Control STCP – Stream Transport Control Protocol

Layer 2 The service access points between the physical layer and the MAC sublayer provide the transport channels. The service access points between the MAC sublayer and the RLC sublayer provide the logical channels.   Radio bearers are defined on top of PDCP layer. Multiplexing of several logical channels on the same transport channel is possible. There are two levels of re-transmissions for providing reliability, namely, the Hybrid Automatic Repeat request (HARQ) at the MAC layer and outer ARQ at the RLC layer. The outer ARQ is required to handle residual errors that are not corrected by HARQ. A N-process stop-and-wait HARQ is employed that has asynchronous re-transmissions in the DL and synchronous re-transmissions in the UL. Synchronous HARQ means that the re-transmissions of HARQ blocks occur at pre-defined periodic intervals. Hence, no explicit signaling is required to indicate to the receiver the retransmission schedule. Asynchronous HARQ offers the flexibility of scheduling re-transmissions based on air interface conditions. ARQ retransmissions are based on RLC status reports and HARQ/ARQ interaction. The three sublayers are Medium access Control(MAC) Radio Link Control(RLC) Packet Data Convergence Protocol(PDCP) [Source: E-UTRAN Architecture(3GPP TR 25.012 ]

Layer 2 MAC (media access control) protocol handles uplink and downlink scheduling and HARQ signaling. Performs mapping between logical and transport channels. RLC (radio link control) protocol focuses on lossless transmission of data. In-sequence delivery of data. Provides 3 different reliability modes for data transport. They are Acknowledged Mode (AM)-appropriate for non-RT (NRT) services such as file downloads. Unacknowledged Mode (UM)-suitable for transport of Real Time (RT) services because such services are delay sensitive and cannot wait for retransmissions Transparent Mode (TM)-used when the PDU sizes are known a priori such as for broadcasting system information.

Layer 2 PDCP (packet data convergence protocol) handles the header compression and security functions of the radio interface RRC (radio resource control) protocol handles radio bearer setup active mode mobility management Broadcasts of system information, while the NAS protocols deal with idle mode mobility management and service setup

Three Types of Channels in LTE In GMS only logical and physical In LTE: Logical Channels – what type of information is transported Control x 5 Traffic x 2 Transport Channels – how is the information transported Modulation, coding, antenna port Physical Channels – where is the information transported What resource blocks are allocated

LTE Downlink Channels Paging Control Channel Paging Channel Physical Downlink Shared Channel

LTE Uplink Channels CQI report Random Access Channel Physical Uplink Shared Channel Physical Radio Access Channel

LTE Downlink Logical Channels

LTE Downlink Transport Channel

LTE Downlink Transport Channel

LTE Downlink Physical Channels

LTE Downlink Physical Channels

LTE Uplink Logical Channels

LTE Uplink Transport Channel

LTE Uplink Physical Channels

LTE Advanced Features 100MHz Bandwidth supported 1Gbps DL, 500 Mbps UL Carrier Aggregation Relays

Carrier Aggregation

Carrier Aggregation

Enhanced Techniques to Extend Coverage Area and/or Data Rates

LTE vs. LTE-Advanced