UbiNetics. WCDMA/HSDPA physical layer design. Jon Burrell

Transcription

1 UbiNetics WCDMA/HSDPA physical layer design Jon Burrell

2 Content Slide 1 of 33 Importance of WCDMA Crash course in WCDMA WCDMA implementation Why HSDPA Crash course in HSDPA HSDPA implementation Terminal physical layer only, downlink bias and selective!

3 Slide 2 of 33 UbiNetics outline 3G 3G(HSDPA/WCDMA/EDGE/GPRS) (HSDPA/WCDMA/EDGE/GPRS)handset handsettechnology technology Infrastructure Vendors ODMs Engineering experience Market requirements 3G Test products 3G Volume Product Technology Camera MMI Look and Feel Mmedia Mgr MMI Logic MMI Rsrce Files Display SyncML WAP Browser WAP 2.0 Stack Operators Java Apps MIDP TCP/IP Stack KVM WCDMA AS IrDA Common NAS GSM/ EGPRS AS USB Connection/Data Routing USIM BlueTooth Early proof, in-field, IOT Early revenue Keypad User I/P MMS Client Serial Audio PIM Funcs. Platform Interfacing Baseband HW BT HW Data I/f Silicon Vendors Cambridge CambridgeUK UKbased, based,founded foundedjanuary January and andnow now staff staff R&D R&Dcentres centresininbangalore, Bangalore,Cambridge, Cambridge,Swindon Swindonand andshenzhen Shenzhen Sales Salesand andcustomer customersupport supportcentres centreshong HongKong, Kong,Tokyo Tokyo

4 WCDMA Importance Slide 3 of Device shipments (m) Tech dev Sept 04 Sept 03 GPRS/EDGE Feature phones WCDMA MM? WCDMA Source: Ovum / DB Underestimated prediction for WCDMA/EGPRS technology? WCDMA (multimode) phone technology will dominate

5 What is WCDMA? Layer 1 perspective Slide 4 of 33 Wideband 5 MHz. (For each of DL and UL) Single frequency all users and all cells DS spread spectrum User and cell separation by spreading code Fast power control Soft handover QPSK Turbo coding Multiple transport channel combinations 384 kbps

6 WCDMA crash course Essentials 1: Diversity gain Slide 5 of 33 Narrow band Cancellation, deep fading Inter-symbol interference Tx Rx Wide band Tx Rx Reduced fading Diversity gain Spread signal with pseudo random sequence at high chip rate Spreading code with good autocorrelation function Receive by synchronous correlation to resolve multipaths and coherently combine - Rake Autocorrelation function fails at < 1chip Transmit Diversity to the rescue Good autocorrelation

7 WCDMA crash course Essentials 2: Spreading Codes Spreading is a combination (multiplication) of two codes: Slide 6 of 33 Orthogonal Variable Spreading Factor (OVSF) Separates users in a cell (in DL) Variable length: defines data rate Perfect cross-correllation. If aligned! Very poor auto-correllation OVSF1: OVSF2: Scrambling codes (SC) 10ms long PN sequence Very good correlation properties Separates and identifies cells in DL (Separate users in the UL) SC1 SC2 SC3 But the codes are not perfect Intra-cell interference through loss of OVSF orthogonality in multipath Inter-cell interference from neighbough cell SCs CDMA systems are interference limited, so...

8 WCDMA crash course Essentials 3: Power control Slide 7 of 33 Very important in the UL because of near far problem Reduces interference in the DL by minimising cell power Fast closed loop power control used in both UL and DL Received SIR determines TPC feedback Fast feedback requirements, ~70us, a considerable challenge for physical layer design

9 WCDMA crash course Essentials 4: 3G vs 2G Slide 8 of 33 WCDMA gains from: Better spectral efficiency of CDMA vs TDMA QPSK, and turbo coding Makes WCDMA ~5x more efficient than GSM 6x cheaper WCDMA: high speed, flexible data services, low cost

10 WCDMA implementation WCDMA RF Design (receiver) Slide 9 of 33 Direct conversion receiver gives competitve design low BOM But must be careful to minimise DC offset Trick is to remove DC component but retain fast settling on gain step UbiNetics has developed an WCDMA RF chip with Renesas

11 WCDMA implementation Multimode SoC Block Diagram Slide 10 of 33

12 WCDMA implementation UbiNetics WCDMA SoC design Slide 11 of 33 Release 99, 384kbit/s class UMTS IP core Low power hardware centric design No DSP required for data centric operation ARM 9 class controller required (926 assumed) Bolt-on HSDPA support MM support designed in Working with 2 major semis

13 WCDMA implementation WCDMA HW/SW Partitioning Slide 12 of 33 Functions implemented in hardware Traffic data path (chip and bit rate) Bandwidth intensive processes (e.g. Psync peak sorting) Low latency processes (e.g. power control) Remaining functions partitioned by Size and complexity Intelligence residing in software (e.g. AGC loop) Power consumption advantage Bus bandwidth

14 WCDMA implementation WCDMA H/W block diagram Slide 13 of 33 WRAPPER INTBUS EXT CLOCK INTBUS CLOCK GEN INT CLKS TEST TEST ACCESS TEST PORTS INTERNAL BUS INTBUS UMTS CORE TEST INTBUS SYSTEM BUS SYSTEM BUS BUS I/F TRAFFIC IQ DATA RADIO I/F RADIO PORTS INTBUS

15 WCDMA rolling-out, however.. Slide 14 of 33 The other 3G standard CDMA2000 had a head start WCDMA will dominate long term, but CDMA2000 has a high rate, ~ 3 Mbps, DL extension 1x EV- DO in operation now Sprint and Verizon in US, KDDI in Japan using it Customers like high speed DoCoMo, Vodafone (Japan) and Cingular/AWE (US), WCDMA operators, are nervous Resultant push for High Speed Downlink Packet Access enhancement to WCDMA

16 What is HSDPA? Slide 15 of 33 Increased packet data support in the DL More efficient use of the available bandwidth Increase maximum user throughput for downlink packet data Increase the peak data rates to 14 Mbps Reduce the latency for packet data Minimise the need for additional control signalling Compatibility with R99 HSDPA is a straightforward enhancement to R99 architecture All R99 techniques can be supported in an HSDPA network R99 and HSDPA mobiles can co-exist on the same frequency Scalable UE Complexity 12 categories of terminal capability Target urban and indoor environments

17 HSDPA crash course Essentials 1: Unused power Slide 16 of 33 Unused power capacity allows greater throughput By: User scheduling by Node B Adaptive modulation and coding (AMC) Hybrid automatic repeat request (HARQ)

18 HSDPA crash course Essentials 2: Scheduling Slide 17 of 33 Channel Quality Mobile 1 Time Channel Quality Comm. Tower Channel Quality Time Exploit Multi-User Diversity Transmit when channel is good Time Mobile 2 Mobile 3 Node B scheduler balances overall throughput and users requirements: Quality of Service (Conversational, Streaming, Interactive, Background) Terminal capabilities And uses Adaptive Modulation and Coding (AMC)..

19 HSDPA crash course Essentials 3: AMC Slide 18 of 33 Instead of adjusting the transmit power, change the coding gain Send more user data and less error protection for good channels Use higher order modulation to increase the data rate use higher FEC coding rates optional 16-QAM modulation Use multiple OVSF codes allocated to a single user Send data over up to 15 codes simultaneously Number of codes depends upon UE capability To schedule and set modulation Node B needs fast Channel Quality Indication (CQI) from terminal...

20 HSDPA crash course Slide 19 of 33 Essentials 4: CQI, and HS channels CPICH 10 ms HS-SCCH 1 HS-SCCH 2 SF 128 (60 Kbps). Sets modulation and coding of HS-PDSCH 1 HS-PDSCH 2 2 slots SF 16 OVSF Up to 15 parallel codes (14 Mbps) Uplink HS- DPCCH 1 (ACK & CQI repeated twice, 20ms CQI feedback) 5 ms 7.5 slots ACK CQI ACK CQI ACK ACK SF CQI bits Uplink HS- DPCCH 2 (4ms CQI feedback) CQI CQI CQI CQI ACK CQI UE measures the SIR of the CPICH and calculates best data rate Aim to receive data with <10% PER Consider UE capability CQI reported to Node B via dedicated UL channel HS-DPCCH

21 HSDPA crash course Slide 20 of 33 Essentials 5: HARQ re-transmission 10 ms 5 ms Hybrid-ARQ scheme complements AMC by allowing for rapid retransmission of erroneous packets Instead of discarding the packet (as in R99), combine multiple transmissions Maximises the chance of successful reception Requires additional buffering in the UE Layer 1 Node B handles re-transmission (RNC for R99) to minimise packet delays

22 HSDPA crash course Slide 21 of 33 Essentials 6: HSDPA vs WCDMA HSDPA cell capacity improvement 2-3 times cell capacity Low latency and fast download Wireless Broadband for user

23 HSDPA implementation HSDPA Implementation Slide 22 of 33 Principal Issues: Need better SNR for higher rates Better RF Equaliser not Rake HARQ buffers HS-MAC

24 HSDPA implementation RF considerations Slide 23 of 33 Distortion must be lower for HSDPA! Direct conversion receiver gives competitive design low BOM But must minimise DC offset even more important with HSDPA Trick is to remove DC component but retain fast settling on gain step UbiNetics has just started an HSDPA RF chip development with Renesas

25 HSDPA implementation Equaliser Slide 24 of 33 Rake receiver combines multiple paths Each path adds noise Multi-Access Interference Worse at low SF OVSF correlation worse Equalisers particularly suited to HSDPA HSDPA targeted at low mobility, high bandwidth users Relatively static channel plenty of time for equaliser to adapt QAM-16 requires good SNR Equaliser measures the channel profile Applies an inverse of the channel to the received data No multi-access interference improved Rx SNR! Increased UE complexity - G-RAKE (?) - Linear filter HS-PDSCH receivers: - LMS-based equaliser Complex calculations to evaluate equaliser tap weights - MMSE based equalisers

26 HSDPA implementation H-ARQ re-transmission Multi-Channel Slide 25 of 33 Node B HS-DSCH UE 1 HS-DPCCH NAK ACK NAK NAK ACK ACK UE 2 HS-DPCCH ACK ACK UE 1 UE 2 Process (1) Process (2) Process (1) Process (2) Process (3) Process (4) More efficient use of channel bandwidth, but More memory in the UE for MAC data (re-ordering) buffering

27 HSDPA implementation H-ARQ Combining Bit rate processing (Turbo) block with soft-decision combiner Slide 26 of 33!"#$ Multiple HARQ buffers Store soft decisions More memory in the UE Chase Combining Incremental Redundancy

28 HSDPA implementation HS-MAC Slide 27 of 33 MAC-D RRC CMAC M A C - C O N F I G MAC-RX MAC-hs Disassembly Disassembly Re-ordering Re-ordering Up. to 8 Interface A 3GPP MAC-hs Functionality Re-ordering queue distribution Interface B HARQ (up to 8 processes) Interface C Associated Uplink signalling (From HS-DPCCH) Associated Downlink signalling (To HS-SCCH) CPHY L1 Control HS-DSCH HSDPA Base_band

29 HSDPA implementation HSDPA receivers Generic HSDPA L1 architecture Slide 28 of 33 Radio data Searcher Channel estimator HS-SCCH detector Constellation type Equaliser Descramble HS-PDSCH Despreading BRP: Turbo, Rate matching MAC-d Noise power SIR estimation CQI generation ACK/NAK Uplink Uplink

30 HSDPA implementation WCDMA Baseband migration Typical block diagram for HSDPA entities Key Slide 29 of 33 UMTS RF New Potential enhancement CDMA modulator RAKE receivers HS-SCCH detector Searcher CQI Equaliser HS-PDSCH despreader Delay estimator Channel estimator Turbo decoder Rel 99 baseband Decryption HARQ Rate match Rate match L1 MAC-hs

31 HSDPA implementation WCDMA Baseband migration Typical HW/FW and SW split options Slide 30 of 33 Entity HW FW SW Channel estimator x Equaliser x x HS-SCCH detector x x HS-PDSCH de-spreader x CQI generator x CPICH SIR calculator x x Uplink HS-PDCCH x BRP & HARQ x x MAC-hs x x x

32 And the Up Link? Slide 31 of 33 That is another story!

33 Slide 32 of 33 Thank you Questions?

34 Rel 5 Capability Classes Slide 33 of 33