4 LTE Adoption (as of May 2012) Red – countries with LTE serviceDark Blue – planned or ongoing deploymentLight Blue – LTE system trials (pre-commitment)
5 Features All IP Network (VoIP for voice) Spectrum Flexibility Can also use other 3GPP technologies for voiceSpectrum 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 QAM75 Mbps peak uplink
6 Features (cont) 100 km macro cells (5 km with optimal performance) Up to 200 active users in a cellOFDM downlink and Single Carrier FDMA (SC-FDMA) uplinkHARQ (Hybrid ARQ)Co-existence with existing technologies (calls can be started in LTE and transferred to GSM/GPRS, WCDMA)
7 Architecture UE – User Equipment eNodeB – evolved NodeB (BS) S-GW – Serving GatewayP-GW – PDN GatewayMME – Mobility Management EntityHSS – Home Subscriber ServerPCRF – Policy Rules and Charging Control Function
8 ElementsHSS – Home Subscriber Server – stores subscriber information, roaming capabilities, QoS profiles, current registration; may integrate AUC functionalityP-GW – PDN Gateway – allocates UE IP address, QoS enforcement, filters downlink packets in different QoS bearersS-GW – Serving Gateway local mobility anchor as UE switches between eNodeBs, buffers downlink data until paging completes, charging for visiting usersMME – Mobile Management Entity controls flow between UE and CN (corresponding node) – handles idle mobilityPCRF – Policy Control and Charging Rules Function – charging, policy control, QoS authorization
9 Standardized QoS Class Identifiers (QCI) GBR – Guaranteed Bit-Rate
10 Radio Interface Multiple Access Scheme Adaptive Modulation and Coding Downlink uses QPSK, 16QAM and 64QAMUplink uses QPSK and 16QAMMultiple Access SchemeDownlink uses OFDMAUplink uses Single Carrier FDMA (SC-FDMA)BLER – Block Error Rate
11 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)
13 Common Physical RB (PRB) Formats Channel Bandwidth (MHz)NRBDL/NRBULTypical IDFT sizeNumber of Non-Zero Sub-carriers (REs)1.256128725255123001050102460015751024 or 20489002010020481200PRBs 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-domainBecause of a common PRB size over different channel bandwidths, the system scales naturally over different bandwidthsUEs determines cell bandwidth during initial acquisition and can be any of above
15 Sub-frame and Frame One frame = 10ms Tslot=500ms 1 2 3 18 19 1231819One subframe71.3ms71.9msNormal Prefix4.69ms5.2msFrequencyDomainView83msExtended PrefixTime-domainView13.9ms
16 OFDMLTE 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.
17 SC-FDMAThe 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.
18 SC-FDMALocalized Mapping and Distributed Mapping
19 User Plane Protocol Stack PDCP – Packet Data Convergence ProtocolRLC – Radio Link ControlGTP-U – GPRS Tunneling Protocol – User Plane
20 Control Plane Protocol Stack NAS – Non-Access StratumRRC – Radio Resource ControlPDCP – Packet Data Convergence ProtocolRLC – Radio Link ControlSTCP – Stream Transport Control Protocol
21 Layer 2The 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 ]
22 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) protocolfocuses on lossless transmission of data.In-sequence delivery of data.Provides 3 different reliability modes for data transport. They areAcknowledged 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 retransmissionsTransparent Mode (TM)-used when the PDU sizes are known a priori such as for broadcasting system information.
23 Layer 2 PDCP (packet data convergence protocol) handles the header compression and security functions of the radio interfaceRRC (radio resource control) protocolhandles radio bearer setupactive mode mobility managementBroadcasts of system information, while the NAS protocols deal with idle mode mobility management and service setup
24 Three Types of Channels in LTE In GMS only logical and physicalIn LTE:Logical Channels – what type of information is transportedControl x 5Traffic x 2Transport Channels – how is the information transportedModulation, coding, antenna portPhysical Channels – where is the information transportedWhat resource blocks are allocated