LTE VS UMTS NETWORK ARCHITECTURE GGSN Evolved Packet Core MME MME S-GW or P-GW S-GW or P-GW SGSN RNC RNC e-NodeB e-NodeB NodeB NodeB NodeB NodeB e-NodeB e-NodeB GGSN : Gateway GPRS Support Node MME : Mobility Management Entity SGSN : Serving GPRS Support Node P-GW : PDN (Packet Data Network) Gateway RNC : Radio Network Controller S-GW : Serving Gateway NodeB : Base Stations eNodeB : envolved NodeB
E-UTRA ARCHITECTURE► According to 3GPP TR 25.912, E- UTRAN is described as follows.► “The evolved UTRAN consists of eNB, providing the evolved UTRAN U- plane and C-plane protocol terminations towards the UE. The eNBs are interconnected with each other by means of the X2 interfaces. It is assumed that there always exist an X2 interface between the eNBs that need to communicate with each other, e.g., for support of handover of UEs in LTE_ACTIVE. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core). The S1 interface supports a many-to-many relation between aGWs and eNBs.”
SYSTEM ARCHITECTURE EVOLUTION (SAE)► System Architecture Evolution (SAE) is the network architecture and designed to simplify the network to other IP based communications network. SAE uses an eNB and Access Gateway (aGW) and removes the RNC and SGSN from the equivalent 3G network architecture, to make a simpler mobile network. This allows the network to be built as an “All-IP” based network architecture. SAE also includes entities to allow full inter-working with other related wireless technology (WCDMA, WiMAX, WLAN, etc.). These entities can specifically manage and permit the non-3GPP technologies to interface directly into the network and be managed from within the same network.
LTE PROTOCOL STACK► C-plane Protocol Stack on Uu (UE/eNB) and S1-C (eNB/MME) ► U-plane Protocol Stack on Uu (UE/eNB) and S1-U (eNB/MME)► C-plane Protocol Stack on X2-C (eNB/eNB) ► U-plane Protocol Stack between eNB/eNB
SUMMARY OF THE 3GPP ORIGINAL LTEREQUIREMENTS► Increased peak data rates : 100Mbps downlink and 50Mbps uplink► Reduction of RAN latency to 10ms► Improved spectrum efficiency ( 2 until 4 times compared with HSPA Release 6)► Cost effective migration from Release 6 Universal Terrestrial Radio Access (UTRA) radio interface and architecture► Improved broadcasting► IP-optimized (focus on services in the packet switched domain)► Scalable bandwidth of 20 MHz, 15 MHz, 10 MHz, 5 MHz, 3 MHz and 1.4 MHz► Support for both paired and unpaired spectrum► Support for inter-working with existing 3G systems and non-3GPPP specified systems
LTE CHARACTERISTIC► LTE introduced in Rel 8 ► Minor improvements in Rel 9 and Rel 10► Significantly increased data throughput ► Downlink target 3-4 times greater than HSDPA Release 6 ► Uplink target 2- 3 times greater than HSUPA Release 6► Increased cell edge bit rates ► Downlink: 70% of the values at 5% of the Cumulative Distribution Function (CDF) ► Uplink: same values at 5% of the Cumulative Distribution Function (CDF)► Significantly reduced latency► High mobility► Cell ranges up to 5 km; with best throughput, spectrum efficiency and mobility. Cell ranges up to 30 km ; Mobility with some degradation in throughput and spectrum efficiency permitted. Cell ranges up to 100 km; Supported; degradations accepted
LTE KEY PARAMETERSFrequency Range UMTS FDD bands and UMTS TDD bandsChannel bandwidth 1 1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHzResource Block = 180kHz 6 Resource 15 Resource 25 Resource 50 Resource 75 Resource 100 Resource Blocks Blocks Blocks Blocks Blocks BlocksModulation Scheme Downlink : QPSK, 16QAM, 64QAM Uplink : QPSK, 16QAM, 64QAMMultiple Access Downlink : OFDMA Uplink : SC-FDMAMIMO Technology Downlink : Wide Choice of MIMO configuration options of transmit diversity, spatial multiplexing, and cyclic delay diversity (max 4 antennas at base stations and handset) Uplink : Multi user collaborative at MIMOPeak Data Rates Downlink : 150 Mbps (UE category 4, 2x2 MIMO, 20MHz) Uplink : 75 Mbps (20MHz)
LTE RADIO INTERFACE► Physical Layer ► OFDMA ► SC-FDMA ► MIMO ► Physical Channel► Layer 2 ► Transport Channel ► Layer 2 Structure ► Logical Channel► RRC Protocol► Convolutional Code► Convolutional Decoder► Interleaver and Deinterleaver► Signal Mapping
PHYSICAL LAYER► Enables exchange of data and control info between eNodeB and UE and transport of data to and from higher layer► Consist of Physical Signal for ► system synchronization, ► cell identification, ► channel estimation► Physical Channel, for ► Transporting control ► Scheduling ► User payload from higher layer► OFDMA in Downlink, SC-FDMA in Uplink► Function performed : Error detection, FEC, MIMO, antenna processing, synchronization► LTE Support FDD and TDD modes operation
DOWNLINK TRANSMISSION SCHEME OFDMA► For transmission scheme in FDD and TDD mode E-UTRA : OFDMA► Available spectrum is devided into multiple carriers, called sub-carriers, which are orthogonal to each other and each sub-carriers independently modulated by a low rate data stream.
UPLINK TRANSMISSION SCHEME SC-FDMA► SC-FDMA is the LTE uplink transmission scheme for TDD and FDD mode, with cyclic prefix► Have a better PAPR (peak to average power ratio) properties compared to an OFDM signal for cost effective design of UE powers amplifier► Compare OFDMA vs SC-FDMA OFDMA : ► Parallel transmission ► Multi carrier structure ► Increase M high PAPR SC-FDMA ► Serial transmission ► Each symbol represented by a wide signal – DFT spreads ► Increase M not affected PAPR
LTE FRAME STRUCTURE Applicable for FDD and Half Duplex FDD Each Radio frame is Tf=307200 x Ts = 10 ms long and consist of 20 slots of length Tslot = 15360 x Ts = 0.5 ms numbered from 0 to 19 (Ts = 1/(15000x2048) s One radio frame, Tframe = 10 ms One subframe, Tsubframe = 1 ms One slot, Tslot 15360 x Ts = 0.5 ms UL f ULFDD DL f DL Subframe #0 #1 #2 #3 #4 #5 #6 #7 #8 #9 Applicable only For TDD Each Radio frame consist of two half frame length Tf=153600 x Ts = 5 ms long each half frame consist of 8 slot of length Tslot = 15360Ts = 0.5 ms Three special field DwPTS, GP, UpPTS in subframe #1 and #6 (special subframe) The subframe 0 and 5 and DwPTS are always reserved for downlink transmission The lengths of DwPTS and UpPTS is given below subject to the total length of DwPTS, GP and UpPTS being equal to 30720 Ts = 1ms Supported configurations of uplink-downlink subframe allocation are specified Special subframe =30720 Ts = 1ms Special subframe ULTDD f UL/DL DL D wP TS GP UpPTS
UPLINK DOWNLINK CONFIGURATION► To meet different requirements on uplink/downlink traffic asymmetries, LTE support seven different uplink/downlink configuration
LTE PHYSICAL CHANNEL DL Channels Full Name Purpose PBCH Physical Broadcast Channel Carries cell specific information PDSCH Physical Downlink Shared Channel Payload PMCH Physical Multicast Channel Carries the MCH transport channel PCFICH Physical Control Format Indicator Channel Defines number of PDCCH OFDMA symbols per sub-frame (1,2 or 3) PDCCH Physical Downlink Control Channel Scheduling ACK/NACK PHICH Physical Hybrid ARQ Indicator Channel Carries HARQ ACK/NACK UL Channels Full Name Purpose PRACH Physical random access channel Call setup PUCCH Physical uplink control channel Scheduling ACK/NACK PUSCH Physical uplink shared channel Payload
PBCH► The coded BCH transport block is mapped to four subframes (subframe #0) within a 40 ms interval 40 ms timing is blindly detected , i.e. there is no explicit signaling indicating 40 ms timing Coded BCH mapped to 4 OFDM symbols within a subframe Each subframe is assumed to be self-decodable , i.e the BCH can be decoded from a single reception, assuming sufficiently good channel conditions.
PDSCH► Detailed on TS36.213, Resource allocation of PDSCH► No compact assignment on Downlink only ► Bitmap approach 1 (group wise bitmap) ► Bitmap approach 2 (bitmap within subset) ► Compact assignment for Downlink and Uplink ► Resource indication value (RIV) corresponding to a starting resource block and a length in terms of contiguously allocated resource blocks
PMCH► Only transmitted in sub-frames allocated for MBSFN transmissions ► Only TDM on sub-frame basis of data transmission► Multiplexing of MBSFN and Non-MBSFN data► No transmit diversity for MBSFN and the transmission shall use antenna port 4► Not to transmitted in subframe 0 and 5 on a carrier supporting a mix of PDSCH and PMCH)
PCFICH► PCFICH carries CCFI► CCFI (Control format indication) : information about the number of OFDM symbols (1,2 or 3) used for transmission of PDCCH in a subframe.► The number of bit : 32 bits► Cell-specific scrambling prior to modulation► Modulation: QPSK► Mapping to resource elements: four groups of fo ur contiguous REs not used for RS in the first OFDM symbol ► Spread over the whole system bandwidth ► Same mapping for 1, 2 and 4 antennas
PDCCH► The physical downlink control channel carries scheduling assignments► A physical control channel is transmitted on an aggregation of one or several control channel elements, where a control channel element (CCE) corresponds to a set of resource elements ► 1PDCCH = 1, 2, 4, 8 CCEs ► 1 CCE = 9 REGs► Multiple PDCCHs can be transmitted in a sub-frame► The PDCCH supports multiple formats► Maximum number of blind decoding for LTE_ACTIVE users is 44 in total
PDCCH cont’Aggregation of CCETree-based aggregation with 1, 2, 4, 8 CCE ► 1-CCE start on any CCE position (i=0,1,2,3,4,...) ► 2-CCE every second location (i=0,2,4,6,...) ► 4-CCE on every fourth (i=0, 4, 8, ...) ► 8-CCE on every eight position (i=0, 8, ...)The number of available CCEs in a cell depends on ► Semi-static: bandwidth, #antenna ports, PHICH conf, ... ► Dynamic: PCFICH value
► Common search space PDCCH cont’ ► Common search space corresponds to CCEs 0-15 (four decoding candidates on level-4, CCEs 0-3, 4-7, 8-11, 12- 15 and two decoding candidates on level-8, CCEs 0-7, 8-15 ► Monitored by all UEs in the cell ► Can be used for any PDCCH signalling (not restricted to ’common’ PDCCH, can be used to resolve ’blocking’) • Format 1C • Format 0/1A/3A ► May overlap with UE-specific search space ► Aggregation levels • 4-CCE and 8-CCE ► Number of blind decodes spent on common search space = 12► UE-specific search space ► 32 blind decoding attempts ► Aggregation levels 1, 2, 4, 8 ► Decoding attempts per payload size (assuming 2 payload sizes per aggregation level) • 6 decoding attempts of 1-CCE aggregation • 6 decoding attempts of 2-CCE aggregation • 2 decoding attempts of 4-CCE aggregation • 2 decoding attempts of 8-CCE aggregation • FFS if the above can be changed with RRC signalling (max 2 configurations in total) ► DCI formats, semi-static configuration of one of the alternatives • 0/1A, 1 (”non-spatial-multiplexing”) • 0/1A, 2 (”spatial multiplexing”) • 0/1A, 1B(“rank-1 precoding”)
PHICHPHICH carries the downlink hybrid-ARQ ACK/NACK• PHICH group– 1 PHICH group = 8 PHICHs (Normal CP)– 1 PHICH group = 4 PHICHs (Extended CP)• Repetition factor is 3PHICH mapping– Time and frequency location of PHICH
Orthogonal sequencePHICH con’t 0 [+1 +1 +1 +1] [+1 +1] 1 [+1 -1 +1 -1] [+1 -1]Orthogonal sequence of SF = 4 for normal CP and SF =2 for extended CP 2 [+1 +1 -1 -1] [+j +j]case 3 [+1 -1 -1 +1] [+j -j]Example of extended CP case (SF = 2) and TX=4 case 4 [+j +j +j +j] -► d0 and d1 represent the SF=2 spread ACK/NAK symbol, red and green are two different PHICH groups 5 [+j -j +j -j] - 6 [+j +j -j -j] - 7 [+j -j -j +j] -
LTE LOGICAL CHANNELLogical Channel are offered by the MAC layerControl Channel for control Plane information ► Broadcast Control Channel (BCCH) ► Paging Control Channel (PCCH) ► Common Control Channel (CCCH) ► Multicast Control Channel (MCCH) ► Dedicated Control Channel (DCCH)Traffic Channel for user plane information ► Dedicated Traffic Channel (DTCH) ► Multicast Traffic Channel (MTCH)
LAYER 2 - LTE TRANSPORT CHANNELPhysical layer transport channel offers information transfer to medium access control (MAC) and carrying originatingfrom higher layersUPLINK► Uplink Shared Channel (UL-SCH) characterized by: ► possibility to use beamforming (likely no impact on specifications) ► support for dynamic link adaptation by varying the transmit power and potentially modulation and coding ► support for HARQ ► support for both dynamic and semi-static resource allocation.► Random Access Channel(s) (RACH) characterized by: ► limited control information ► collision riskDOWNLINK► Broadcast Channel (BCH) characterized by: ► fixed, pre-defined transport format ► requirement to be broadcast in the entire coverage area of the cell.► Multicast Channel (MCH) (from Release 9) characterized by: ► requirement to be broadcast in the entire coverage area of the cell ► support for MBSFN combining of MBMS transmission on multiple cells ► support for semi-static resource allocation e.g., with a time frame of a long cyclic prefix.
LAYER 2 - LTE TRANSPORT CHANNEL CONT’► Downlink Shared Channel (DL-SCH) characterized by: ► support for HARQ ► support for dynamic link adaptation by varying the modulation, coding and transmit power ► possibility to be broadcast in the entire cell ► possibility to use beamforming ► support for both dynamic and semi-static resource allocation ► support for UE discontinuous reception (DRX) to enable UE power saving.► Paging Channel (PCH) characterized by: ► support for UE discontinuous reception (DRX) to enable UE power saving (DRX cycle is indicated by the network to the UE) ► requirement to be broadcast in the entire coverage area of the cell ► mapped to physical resources which can be used dynamically also for traffic/other control channels.
LTE PHYSICAL SIGNAL DL Signal Full Name Purpose P-SCH Primary Synchronization Signal Used for cell search and identification by the UE. Carries part of the cell ID (one of three orthogonal sequences) S-SCH Secondary Synchronization Signal Used for cell search and identification by the UE. Carries the remainder of the cell ID (one of 168 binary sequences) RS Reference signal (pilot) Used for DL channel estimation. Exact sequence derived from cell ID (one of 3 x 168 = 504 pseudo random sequence) UL Channels Full Name Purpose RS Reference signal (Demodulation and Sounding) Used for synchronization to the UE and UL channel estimation
P-SCH & S-SCH► Synchronization signals needed during cell search► The synchronization acquisition and the cell group identifier are obtained from different SCH signals► Transmitted on the 72 center sub-carriers (around DC sub-carrier) within the same predefined slots (twice per 10 ms) on different resource element.REFERENCE SIGNAL (RS)► Three types of downlink reference signals are defined: ► Cell-specific reference signals, associated with non-MBSFN transmission (unicast RS) ► MBSFN reference signals, associated with MBSFN transmission ► UE-specific reference signals (Dedicated RS)► There is one reference signal transmitted per downlink antenna port.► REs used for RS transmission on any of the antenna ports in a slot shall not be used
SYNCHRONIZATION SIGNAL FDD TDD ► DwPTS and Location of PSS and SSS ► P-SCH is always transmitted in the 3rd OFDM symbols of DwPTS (subframe 1 and 6) ► PDDCH in DwPTS (subrfame 1 and 6) may span 1 and 2 OFDM symbols► PSS ► Data is transmitted after the control region as in Using not coherent detection estimate 5 ms timing and physical layer identity other DL subframes Channel estimation information for SSS ► Same cell specific RS patterns as in other DL► SSS subframe, RS in GP are muted Physical layer identity (Cell ID) obtained ► UpPTS Mapped to one of 168 cell ID groups (168 cell groups for 504 cell IDs) ► SRS transmission on UpPTS Radio frame timing (10ms) identification ► Agreement on 1 SRS symbol in UpPTS Max # of hypotheses; 336 hypotheses (2x168 : 2 for half frame, 168 for ID group ► Discuss further whether 2 SRS symbols in UpPTS Can be detect RS structure information from SSS and PSS
LTE INITIAL ACCESS System Cell Search and Power On Information Random Access User Data Tx/Rx Selection Receive Initial access procedureThree step initial access on LTE ► Cell Search (PSC, RRC, RS) ► System Information Receive (PBCH, PCFICH, PDCCH) ► Random Access
DOWNLINK PHYSICAL CHANNEL PROCESS Scrambling Modulation Mapping Mapping onto one or more transmission layer Generation of signals each Layer Mapping antenna port MIMO Related Processing Precoding Resource Element Mapping OFDM signal IDFT operation generator
LTE MIMO CONCEPT –► MIMO is one of spatial diversity technique to transmit different streams of data simultaneously on the same downlink resource blocks and increase data rate and capacity ► Increase data rate data stream belong to one single user ► Increase capacity different user
E-NODEB► According to overview of 3GPP Release 8, the eNB hosts the following functions:► Radio Resource Management ► Radio Admission Control ► Radio Bearer Control ► Dynamic allocation of resources to UEs in both uplink and downlink (scheduling) ► Connection Mobility Control► IP header compression and encryption of user data stream► Scheduling and transmission of paging messages (originated from the MME)► Selection of an MME at UE attachment when no routing to an MME can be determined from the information provided by the UE► Routing of User Plane data towards Serving Gateway► Scheduling and transmission of broadcast information (originated from the MME or O&M)► Measurement and measurement reporting configuration for mobility and scheduling