Rev A30-November Outline UMTS architecture and main features (FDD mode) Discussion of packet performance issues Present concepts for support of packet-switched services UMTS evolution Conclusions

Rev A30-November On the Performance of UMTS Packet Data Services Wolfgang Granzow Ericsson Research Corporate Unit Ericsson Eurolab Deutschland, Nürnberg

Rev A30-November UMTS – enabler for the mobile Internet Mobile Internet: the unification of Cellular Networks and the Internet, enabling use of Internet services when mobile Examples of packet data services –Conventional internet services Web-browsing, electronic mail, file transfer, video/audio streaming, e-commerce,... –Combination with location information and mobility Location based services, navigation

Rev A30-November UMTS network architecture Node B Radio network System (RNS) MSC/GSN MSCMobile Services Switching Center GSNGPRS Support Node Node B RNC Node B RNC Node B RNCRadio Network controller Node BBase Node

Rev A30-November UMTS – Main Features New radio access technology using new spectrum –spectrum allocation around 2 GHz –two radio transmission modes Frequency Division Duplex (FDD): 2  60 MHz Time Division Duplex (TDD): MHz –Wideband Code Division Multiple Access (WCDMA) –Chip rate 3.84 Mcps  Channel bandwidth 4.4 – 5 MHz Built on GSM Core Network technology Support of user data rates 0 – 2 Mbps Multi-call, multimedia capability

Rev A30-November Radio interface architecture (simplified) UTRANUE RLC MAC RLC Signaling Radio Bearers Logical Channels Transport Channels Physical Channels CTRL USER PHY Control channels Traffic channels Common Dedicated Shared RRC PDCP

Rev A30-November UMTS Protocol Architecture (user plane)

Rev A30-November Data flow for packet data (UE side)

Rev A30-November Transmission Format UTRA FDD 1 radio frame (10 ms), 15*2560 chips (3.84 Mcps) Slot iSlot 1Slot 2Slot 15 time frequency 5 MHz Macrocell layers Microcell layer Duplex distance, e.g. 190 MHz Uplink Downlink bit level QPSK (downlink) or dual-channel BPSK (uplink) modulation rates Ksps for spreading factors

Rev A30-November Principal Mobile Station Transceiver Structure Encoding Interleaving Rate matching Multiplexing Spreading & Baseband Modulation A/D D/A Decoding Deterleaving Demux Despreading & Baseband Demodulation Up conversion & Power Amplification Down conversion Duplexer Freq. Synthes. Time Sync. Code generator Physical Layer Processing Transport channels Physical channels Higer layers Power control commands Power setting

Rev A30-November Coding, Interleaving, Rate Matching, Multiplexing Rate Matching (repetition and puncturing) Multi- plexing Intra-frame interleaving CRC attachment Coding Inter-frame interleaving CRC attachment Coding Inter-frame interleaving CRC attachment Coding Inter-frame interleaving TFCI Coding TFCI TFI 1 TFI 2 TFI N TrCh 1 TrCh N TrCh 2 TF: Transport Format TrCh: Transport Channel TFCI: Transport Format Combination Indicator

Rev A30-November Sample-and -hold T symbol T chip Baseband modulation Pulse shaping Spreading code Data Principle of spectral spreading Frequency

Rev A30-November General design objectives for packet services High spectral efficiency, i.e. low E b /N 0 for desired error rate (low overhead, efficient radio link adaptation, diversity,...) Low delay (interaction between TCP and RLC) High throughput (system and users) Simplicity and effectiveness of radio resource management (including QoS management) Efficient usage of channelization codes on the downlink Efficient usage of BTS transmitter power Efficient usage of hardware resources (especially in the Node B) Low terminal power consumption

Rev A30-November Performance measures Link performance (BER/BLER vs. E b /N 0 ) –Advanced coding (turbo) –High degree of diversity (multipath, Rx antenna) –Optional enhancements: interference cancellation, adaptive antennas, Space- Time Transmit Diversity (STTD) target BLER req = 10 % Example: performance of a 144 kbps DCH in vehicular environment (120 km/h) with turbo coding

Rev A30-November Packet data throughput definitions average user throughput = „total amount of served data“ „time to deliver data“ time data volume (e.g. # bytes) data arrival in tx buffer Variable-rate tx on the radio link, slope: R link e.g. retransmissions slope: average link throughput R linktrp inititial setup delay slope: average throughput wrt. single packet („packet bit rate“) average link throughput R linktrp = R link / N transm = R link   (1 – BLER) number of transmissions/block: N transm = 1/(1 – BLER) (average packet bit rate for one user)

Rev A30-November Performance measures System throughput (capacity): –Average throughput of all users in the system –Maximum system throughput is reached when the packet delay can grow unbounded –Capacity definitions: average number of users, or system throughput when user quality drops to an unacceptable level („outage“) –Outage can be defined in terms of a delay and/or throughput threshold that should be met with a certain probability –Capacity defined as system throughput is less sensitive to the traffic load generated per user

Rev A30-November UTRA transport channels categories Common channels –Multiplexed users (user ID in the MAC header) Forward Access Channel (FACH) Random Access Channel (RACH) Common Packet Channel (CPCH) Dedicated channels (DCH) –Assigned to a single user (identified by the spreading code) Shared channels –„Sharing“ of code resource by several users by fast re-assignment scheduling Downlink Shared Channel (DSCH)

Rev A30-November Dedicated Channel (FDD downlink) fixed spreading factor Fast closed-loop power control Macro diversitity potential blocking due to insufficient spreading codes DL DCH Features:

Rev A30-November Dedicated Channel (FDD uplink) 1-rate 10 ms Variable rate 1/2-rate 1/4-rate 0-rate : DPCCH (Pilot+TFCI+FBI+TPC), fixed spreading factor 256 : DPDCH (Data) R = 1R = 1/2R = 0 R = 1/2 variable spreading factor on DPDCH Fast closed-loop power control Macro diversitity UL DCH Features:

Rev A30-November DCH characteristics Lowest delay among all transport channels Large overhead in E b /N 0 at low data duty cycle due to physical control : Example: UL R DPCCH = 15 kbps, independent of R DPDCH ( w = 1) DPCCH overhead [dB] mean modulator data rate [kbits]

Rev A30-November Impact of overhead on capacity (E s /N 0 ) req = 3 dB M = 0.6 (load margin) F = 1.5 (ratio of inter-cell to intra-cell interference) R DPCCH = 15 kbps R data = R DPDCH(UL) =120 kbps Example:

Rev A30-November Random Access Channel (FDD uplink) Timing offset “Access slot” 5120 chips Preamble 4096 chips Message chips (10 ms) or 20 ms Acquisition Indicator (AI) 4096 chips Acquisition Indicator Channel (AICH) - Downlink - Physical Random Access Channel (PRACH) -Uplink - DPDCH DPCCH

Rev A30-November RACH characteristics Slotted-ALOHA type of contention-based channel No power control during message transmission –reasonable initial message power derived via preamble ramping Access delay due to ramping 5 – 50 ms (mean  15 ms) Increased delay in case of message collisions

Rev A30-November RACH throughput performance Example (derived with a specific choice of parameter settings, throughput S and offered load G normalized to 1 message per access slot): max normalized throughput S = 3.3 corresponds to 2475 messages/s (80 user data bits/message, 198 kbps)

Rev A30-November Forward Access Channel (FDD downlink) Several FACHs with different transport format can be multiplexed on the physical layer Mapped to Secondary Common Control Physical Channel (S-CCPCH) No fast power control, no macro diversity (transmitted at broadcast power level, i.e. on average rather high energy per data bit E b spent) Scheduling delay S-CCPCH TTI 2 TTI 3 TTI 1 data of other users data of desired users physical control

Rev A30-November Downlink Shared Channel (DSCH) UL-DPCH DL-DPCH PDSCH 1 PDSCH 2 Data for other users Data for the considered user 10 ms DPCCHs Format indicator (TFCI) on associated DPCH includes assignment of PDSCH spreading code Jointly power controlled with the associated DCH

Rev A30-November DSCH characteristics No macrodiversity –mostly suitable in the inner cell area –then approximately same spectral efficiency as a DCH with the same rate Avoids capacity limitation due to non-availability of codes Scheduling delay –Aimed to be compensated by higher link data rate SF = 1 SF = 2 SF = 4 SF = 8 SF = 16 SF = 32 SF = 64 SF = 128 SF = 256 OVSF codes allocated to PDSCHs (example)

Rev A30-November UE modes and RRC States („activity levels“) –UE continuously monitors FACH on downlink –RACH (and/or CPCH) can be used anytime –location known on cell level –UE listens to PCH in DRX mode –location known on cell level –UE listens to PCH in DRX mode –location known on URA level –DPCH allocated –location known on cell level Dedicated (DCH) or Shared (DSCH) Transport Ch. can be used –UE not registered to the network –Cell broadcast info can be received

Rev A30-November Cell_FACH: DPDCH DPCCH DPDCH DPCCH PRACH AICH TCP acks RLC acks RRC measurement reports kbps average load S-CCPCH TTI 2 TTI 3 TTI 1 data of other users data of desired users physical control Service example: e.g. download, WAP browsing

Rev A30-November Cell_DCH: UL-DPCH DL-DPCH DPCCH DPDCH DPCCH DPDCH DPCCH TTI 1 TTI 2 Service example: ftp or download, Web browsing

Rev A30-November Cell_DCH: UL-DPCH DL-DPCH DPCCH DPDCH DPCCH DPDCH DPCCH DPDCH Service example: ftp or upload

Rev A30-November Cell_DCH: UL-DPCH DL-DPCH PDSCH 1 PDSCH 2 Data for other users Data for the considered user 10 ms DPCCHs Service example: e.g. file download, Web browsing

Rev A30-November Channel Switching Dynamic switching between common and dedicated channels, i.e. common channel RRC states (Cell_FACH and Cell_PCH) and dedicated channel RRC state (Cell_DCH) provides radio link adaptation to different levels of data transmission activity, in order to achieve at low transmission activity following objectives: efficient utilisation of BTS TRX hardware resources dedicated to each cell high utilisation of the downlink channelization codes available in a cell low terminal power consumption reasonable high spectral efficiency and reasonable delay compared to dedicated channel transmissions channel type switching is a special type of intra-cell handover

Rev A30-November Up-switching (Cell_FACH  Cell_DCH)

Rev A30-November Down-switching (Cell_DCH  Cell_FACH  Cell_PCH)

Rev A30-November Throughput illustration for Web page download Downlink Traffic Volume [kbits] 50 kBytes data packet slope: R linktrp = R link (1-BLER) R linkmax = 64 kbps

Rev A30-November System throughput vs. user throughput Note: This example shall just illustrate the principal characteristics of throughput performance which were obtained for some specific assumptions not discussed here; absolute capacity figures depend strongly on the choice of simulation parameters and assumptions. packet bit rate (kbps/cell) Example configuration: 64 kbps DCH, 30 codes available per cell with SF= 32 users per cell

Rev A30-November Summary on packet data performance Results from system-level simulations: –Data on dedicated channels throughput very much dependent on configuration and traffic characteristics, can be very low if only a few channels for very high rate are configured due to code limitation effects –Data on common channels inefficient for large amount of data due to lack of tight power control (especially FACH) –Data on shared channels can reach approx. same system throughput as a configuration with low-rate dedicated channels, at much higher peak data rate per user scheduling policy affects performance („fairness“ reduces system throughput)

Rev A30-November UMTS Evolution (Release 4 and 5) Main future new features (affecting packet services): –All-IP transport in the Radio Access and Core Networks –Enhancements of services and service management –High-speed Downlink Packet Access (HSDPA) Introduces additional downlink channels: –High-Speed Downlink Shared Channel (HS-DSCH) –Shared Control Channels for HS-DSCH

Rev A30-November HS-DSCH characteristics Provision of 8 –10 Mbps peak user data rate by –Fast selection of modulation and coding scheme depending on channel conditions (no fast power control) –Short transmission time interval (2 ms) –Fast hybrid ARQ (incremental redundancy and/or Chase combining) –Fast scheduling –Fast cell selection/handover dedicated channels HS-DSCH shared control channels dedicated channels

Rev A30-November HS-DSCH physical layer processing chain Mapping on Code-Tree Turbo Encoding Puncturing and Repetition Interleaving Modulation Ch. Code #1 Ch. Code #N gain other channels scrambling Adaptation Algorithm QPSK 16QAM (64QAM opt.) Coding Rate: 1/3 - 1 Example: 12 out of 16 codes with SF=16 CRC

Rev A30-November Adaptive Modulation and Coding Modulation and Coding Schemes (Example) 64QAM, R=0.75 (12.96 Mbps) 64QAM, R=0.50 (8.64 Mbps) 16QAM, R=0.63 (7.20 Mbps) 16QAM, R=0.38 (4.32 Mbps) QPSK, R=0.50 (2.88 Mbps) QPSK, R=0.25 (1.44 Mbps) C/I time C/I FER for 12 codes (of 16)

Rev A30-November Scheduling Strategies time C/I Example: Max C/I scheduling served mobile Transmission time interval 3 slots (2 ms)

Rev A30-November Conclusions UMTS provides the presently most advanced cellular radio access technology Mature technology, already proven to work Prepared for future evolution Fine-tuning of parameters in order to optimize end-to-end user and overall system performance still remains a challenging task

Rev A30-November Conclusions (cont.) But... the market success will primarily not depend on technology –Marketing strategy of network operators and service providers –Charging policy and tariffing –Availabilty of handsets in large volumes at low price at UMTS introduction –Early provision of useful and inventive new services –Simplicity to apply the offered services –Readiness of the subscribers to get used to new services Social factors: openess to modern technology (provision of high level of security to resolve all doubts on potential hazards, EMC, confidentiallity)