HSDPA presentation

1. HSDPA presentation 3GPP TSG RAN WG2 Chairman, Nortel Networks 3GPP TSG RAN WG1 Chairman, Nokia HSDPA rapporteur, Motorola

2. Content • Introduction • Overall architecture and principles • Radio interface aspects • Physical layer aspects • Future activities

3. Content • Introduction • Overall architecture and principles • Radio interface aspects • Physical layer aspects • Future activities

4. HSDPA objectives • Increased packet data support • Increase maximum user throughput for downlink packet data (streaming, interactive and background services) • Lower packet delay • Compatibility • Evolutionary philosophy • HSDPA architecture is a straightforward enhancement to the R99 architecture • addition of a repetition entity at the Node B below release 99 MAC layer • All R99 techniques can also be supported in a network supporting HSDPA • Mobiles with HSDPA capability can co-exist with R99 mobiles on the same carrier • Standardisation of all interfaces • Including Iur/Iub interfaces

5. Node B is enhanced to handle: HARQ Retransmissions Modulation/coding selection Packet data scheduling HSDPA operation Data packets RNC Node B ACK/NACK + TPC commands + feedback Data packet + possible retransmissions HSDPA capable UE

6. HSDPA Performance • Study in year 2000 (Release 4) indicated a doubling of capacity compared to Rel'99 • Dependant on assumptions, such as scheduler and cell isolation

7. Content • Introduction • Overall architecture and principles • Radio interface aspects • Physical layer aspects • Future activities

8. Key additions to R99 • Adaptive Modulation • Hybrid ARQ • Scheduling/repetition at Node B • Shorter radio frame

9. Release 99 DSCH architecture SRNC UE Node B DRNC

10. Release 5 HS-DSCH Architecture SRNC UE Node B DRNC

11. HSDPA in UTRAN architecture • HSDPA introduction • Compatible with all transport options (AAL2 and IP) • Minor impact on network architecture • No Impact on RLC • New RRC parameters • No impact on mobility • UTRAN functional hierarchy still valid

12. MAC-HS • New MAC-HS entity in the Node B • Two sub-entities – one for scheduling and one for HARQ • Permits fast, adaptive scheduling to leverage AMC and HARQ techniques, thus enabling higher peak data rates • Includes common scheduling/priority handling function as in R99 MAC-c/sh • Provides HARQ functionality • HARQ round trip optimized to keep soft memory requirements at UE to a minimum • Reduces delay for successful decoding of packet compared to RNC based architecture

13. HS-DSCH Transport Channel • Similar attributes as R99 DSCH, with the following modifications • Shorter fixed TTI value (frame size) of 2 ms • One transport block (data block) per TTI • Fixed length CRC (24 bits) per data block • Dynamic modulation • Rate 1/3 Turbo coding • Effective code rate achieved with rate matching • Dynamic redundancy version

14. Content • Introduction • Overall architecture and principles • Radio interface aspects • Physical layer aspects • Future activities

15. UTRAN MAC Architecture

16. MAC-HS-DSCH – UTRAN side

17. MAC-HS-DSCH – UE side

18. HARQ Protocol Details • Asynchronous DL (retransmission can be scheduled independently of occurrence of first transmission) • Synchronous UL (ACK/NACK timing fixed with respect to downlink transmission) • Multiple parallel HARQ processes per UE • HARQ processes are common to all HS-DSCH • Selection of HS-DSCH by HARQ process at first transmission • Scheduler can abort process at any time • One process can transmit at a time • Multiple priority queues

19. HARQ Protocol cont’d • Out-of-band (i.e. not on HS-DSCH) signaling supports all HARQ functionality in terms of combining, abort etc. • In-band (i.e. on HS-DSCH) signaling provides for priority based release of in-sequence PDUs to upper layers at receiver • In-band signaling provides for re-ordering function at receiver • Timer based mechanism provides for release of out-of-sequence data blocks • Other mechanisms may be added

20. Physical Layer Functionality • Transmission of HS-DSCH transport blocks (MAC-hs PDUs) • DL associated signaling • Scheduling information • HARQ process information • Physical layer information • UL associated signaling • ACK/NACK • Scheduling assistance indicator

21. DL Signalling • Two-step approach • Indication of a HS-DSCH transmission provided on dedicated channel to UE • UE then decodes associated shared control channel • UE finally decodes HS-DSCH • UE monitors up to four shared control channels • Shared control channels provide information on transport format and resources for decoding as well as HARQ information (redundancy version, etc.) • HARQ information and TF information are time-multiplexed to reduce needed processing time

22. DL Physical layer model UTRAN UE

23. UL Physical Channel Model UTRAN UE

24. Hybrid ARQ with HSDPA • Fast Hybrid ARQ (Retransmission controlled at Node B ->) Less round trip delay • Combining of the retransmission and first transmission at UE • Node B terminated ARQ protocol means reasonable terminal memory requirements • Both identical (Chase combining) and non-identical (Incremental redundancy) retransmissions allowed • terminal memory capability definition based on the identical retransmissions -> maximum data rate assumes identical retransmissions, lower rates possible also with non-identical retransmissions (Incremental Redundancy)

25. Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Data Pilot Pilot Pilot Pilot Pilot Pilot Pilot Pilot Pilot Uplink DCH ACK/NACK ACK/NACK after data decoding Data Data Data Data Data Data Data Data Data Pilot Pilot Pilot Pilot Pilot Pilot Pilot Pilot Pilot TFCI TFCI TFCI TFCI TFCI TFCI TFCI TFCI TFCI TPC TPC TPC TPC TPC TPC TPC TPC TPC Demodulation Control Downlink DCH HS-SCCH HS-DSCH 2 ms Note: Timing from data to ACK/NACK under discussion! HSDPA Operation Principle

26. HSDPA Operation • Several users can be code multiplexed together • This allows better granularity than with time multiplexing only and takes terminal capability into account (all terminals are not going to be 10.8 Mcps terminals!) • Node B has information of the transmission power for each terminal (Power control commands from the terminal) + ACK/NACK feedback info in the uplink • The number of codes used for HSDPA can vary dynamically between 1 and 15, terminals expected to have varying code handling capability as in Rel'99/Rel'4.

27. Content • Introduction • Overall architecture and principles • Radio interface aspects • Physical layer aspects • Future activities

28. DL Physical Layer • HS-PDSCH – fixed spreading factor = 16 (all channelization codes with same scrambling code) • HS-DSCH has frame length (TTI) of 2 ms (3 slots) • Note this is valid for FDD only • For TDD slightly different principles are used with TTI definition • HS-SCCH – shared control channel – SF=128 or 256 (under study) • UE can be assigned multiple physical channels based on its capability • Code division multiplexing of UEs within one TTI is allowed • QPSK and 16-QAM allowed

29. DL Channel Timing • Associated dedicated channel carrying allocation indication on one slot • Insertion of an indicator by puncturing the data part (DPDCH) of the physical channel • Shared control channel and Physical shared data channel have a one slot overlap (HS-PDSCH codes to receive + modulation indication in the first timeslot) • Transport Format (time critical) and CRC+HARQ information time multiplexed to reduce needed processing time • HARQ information and TF information are time-multiplexed (The channelisation codes & modulation to be used delivered on the control channel before the data part transmission starts) • Target round trip of 12 ms

30. UE DL operation • Maximum 4 HS-DSCH Shared Control Channels that a single UE is monitoring • Network can configure 1 to 4 to UE (more can be used at cell level) • Good performance assuming reasonable terminal complexity. • With continuous activity terminal is able to listen only one control channel. • The terminal memory requirement shall be derived based on Chase (soft) combining i.e. at max data rate (as given by terminal capability) only Chase combining can be used. • Network partitions UE memory to various HARQ processes

31. UL Physical Layer for UL signaling • New Physical channel SF=256 code multiplexed with current dedicated uplink physical channels • ACK/NACK and Feedback time multiplexed • 1 slot ACK/NACK (or DTX) • synchronous to DL HS-DSCH timing • 2 slots either DTX or explicit feedback • Indication of downlink transmissions compatible with target BLER

32. Unsynchronised timing of UEs: within 1 slot Parameters Associated HI DPCH TTI = 3slots Spreading codes, modulation Shared control channel, split in 2 parts FHARQ parameters, CRC etc... HS-DSCH T DL_control=5slots Physical layer timing

33. Both QPSK (as in Rel'99) and 16QAM are defined All terminals with HSDPA capability shall support also 16QAM. 8PSK & 64QAM were agreed not to be part of HSDPA Rel'5 Modulation Aspects

34. Rel'99 rate 1/3 Turbo coding is used, other effective coding rates e.g. 1/4, are created with rate matching Hybrid ARQ repetitions do not have to be identical in Layer 1, i.e. Incremental Redundancy (IR) can be used Channel coding chain is simplified due: Only one TrCh per TTI Only 1 interleaving step No radio frame segmentation needed No DTX during the TTI Channel coding

35. HSDPA Data Rates (Peak) • Modulation method QPSK, 16QAM and potentially also 64 QAM • Currently 64 QAM not in Release 5 • 10.8 Mbps achievable with 15 codes and 16QAM. • Coding rates 1/4-3/4 (Rel'99 Turbo Encoder + rate matching) • Spreading factor 16 used in above table

36. UE Capability • The following parameters characterize a HSDPA terminal capability: • Maximum number of Transport channel bits per HS-DSCH TTI • Maximum number of soft channel bits over all HARQ processes • Number of channelization codes (or, equivalently, number of channel modulation symbols per TTI) • Minimum inter-TTI interval (to be considered when defining lower capability UE classes) • Allowed combinations to be defined so as to reduce number of cases • QPSK and 16 QAM are mandatory for HSDPA capable terminals

37. Content • Introduction • Overall architecture and principles • Radio interface aspects • Physical layer aspects • Future enhancements

38. Examples of future items • More modulations • MIMO • Multiple simultaneous receptions in terminal • New associated DPCH structure

39. Evolution • HSDPA is part of UTRAN release 5, and will be improved along with the other UTRAN features

40. Back-up slides

41. Adaptive Modulation • Higher order modulation provides higher peak data rates in favorable channel conditions. • Gives the flexibility to match Modulation Coding Scheme to the average channel conditions for each user • Provides coarse data rate selection • Extends the system’s ability to adapt to good channel conditions beyond the use of SF alone. • But: • Is sensitive to measurement error and delay. H-ARQ can enable further adaptation

42. Hybrid-ARQ • Hybrid ARQ combines initial transmission with repetitions in the physical layer to provide higher decoding probability. • It automatically adapts to instantaneous channel conditions by adding redundancy only when needed • Insensitive to measurement error and delay • Allows fine data rate adjustment • Independent of various thresholds when combined with AMC • Enabled by instantiation of Parallel Hybrid ARQ processes • Fast uplink feedback channel

43. Scheduling/repetition at Node B • Scheduling at the Node B lowers the delay for critical channel state information • Needed to exploit Adaptive Modulation and HARQ to their maximum potential • Scheduler can better adapt modulation and coding to match current channel conditions and fading environment • Can exploit multi-user diversity by scheduling users in constructive fades

44. Radio frame size • Shorter “frame size” reduces payload to manageable level • Provides fast feedback mechanism • Lower delay • Best leverages scheduling on constructive fades • Benefits primarily for hybrid ARQ • Enables maximum utilization of excess power for data services (i.e. reduced need for power control margin)

45. Feedback channel in uplink • Fast feedback channel in uplink pairing the HS-DSCH • Fast status for HARQ re-transmission • Channel condition feedback to MAC-hs for scheduling