Bologna 14 October, 2009

Transcription

1 Bologna 14 October, 2009 Video over wireless: FPGA design and implementation of a pulse- based echo canceler for DVB-T/H Ph.D Student: G.Chiurco Tutor: Prof. O.Andrisano Alma Mater University of Bologna, Italy

2 Scenario description: Problems and goals Single Frequency Network (SFN) constituted by: a. a DVB-T/H broadcasting station b. an on-channel relay station or repeater (OCR) c. many stationary and mobile users Main goal: covering with the DVB-T signal an area not reachable by the DVB-T broadcast station.

3 Target Repeater based on DVB-T pilots Repeater general-purpose : The Pulse-based Echo Canceler

4 Outline Project Flow; FPGA development kit; Scenario description: Problems and Goals; The BB-OCR solution for DVB-T signal; Echo canceller: Basic Scheme and Operations; FPGA Design and Implementation; Workbench Test-Bed; Measurements and Results.

5 Project Flow Project & Analysis Simulation Implementation & Measurements

6 FPGA development kit features FPGA Stratix II Altera Analog I/O: dev. Kit EP2S180F1020C3 Two-channel, 12-bit, 125-million samples per second (MSPS) analog-to digital (A/D); Two-channel, 14-bit, 165-MSPS digital-to-analog (D/A). Digital I/O Connector for the Texas Instruments (TI) Evaluation Module (TI-EVM); Two 40-pin connectors for Analog Devices' A/D converter evaluation boards; Mictor connector for Agilent and Tektronix logic analyzers; RS-232 serial port; 10/100 Ethernet physical layer/media access control; (PHY/MAC) and RJ-45 jack. Memory 32-Mbyte SDR SDRAM 16-Mbyte flash 1-Mbyte SRAM 16-Mbyte compact flash

7 Scenario description: Problems and goals (3) Adopted strategy: DVB-T repeater. (c) x (d) (e) (c) (c) (a) (b) (d) (e) Consequence: The echo canceller the amplifier permits power to increase must be the limited coverage area Reduced service area!

8 Repeaters: classical solutions Antenna Isolation Time Delay Quality of Tx signal Selectivity of Rx signal Mantain Sync. RF OCR IF OCR BB OCR Dec. OCR BB-OCR Direct relay scheme: Low delay techniques, based basically on: ESTIMATION of the loop-back channel; (ADAPTIVE) FILTERING to cancel the echoes;

9 Baseband OCR Filter Filter and LNA HPA Down converter IF A/D - BB Down conv. L.O. RF Up converter IF D/A Up conversion Data Process.

10 Baseband OCR (2) OCR architecture implemented on the FPGA board:

11 Echo canceller basic scheme + - Delay Multi-window indo canceller Estimator & Pulse Generator Controller Channel estimation unit Dynamic tap update Possibility to cancel single and multiple echoes; up to Nw different echo clusters can be cancelled; Echo Canceller Multi-window canceller FIR 1 FIR i FIR Nw Delay line the position of the cancelling windows is automatically determined.

12 Echo canceller basic operations Two operative phases: Start-Up (open-loop) determination of the number and position of the cancelling windows (pulse-based) initial coupling channel (pulse) estimation FIR s set-up Steady-State (closed-loop) effective DVB-T signal repetition (fast) echo tracking (LMS-algorithm) stability and coupling channel monitoring (periodical check of new echoes with the pulse technique)

13 Search and cancelling windows Search window: from 3-6ms to about 60ms (nearly correspondent to reflections from obstacles at 8Km); Cancelling window: about 5ms (for 8MHz BW); Target: suppressing a single echo with power 15dB over the useful DVB-T signal power echo suppression > 40 db

14 FPGA design and implementation The ECHO_CANCELLER entity: ESTIMATOR_iq: implementing the channel pulse estimator, the pulse generator and an additional Least Mean Square (LMS) algorithm working in the steady-state mode; hp ( m 1) h ( m ) [ y ( n ) y ( n )] P P P Q Q n h ( 1) Q m h ( m) [ y ( n) y ( n)] Q P Q Q P n n n SHREG&MUX: implementing the delay which allows to position the cancelling window inside the overall search window; DYN_FIR_MCV: implementing the cancelling FIR filters with dynamically variable coefficients, based on the Multi Cycle Variable (MCV) technology.

15 FPGA design and implementation The ECHO_CANCELLER entity: ESTIMATOR_iq: implementing the channel pulse estimator, the pulse generator and an additional Least Mean Square (LMS) algorithm working in the steady-state mode; SHREG&MUX: implementing the delay which allows to position the cancelling window inside the overall search window; DYN_FIR_MCV: implementing the cancelling FIR filters with dynamically variable coefficients, based on the Multi Cycle Variable (MCV) technology.

16 Workbench Test-bed

17 MER: Modulation Error Ratio The modulation error ratio or MER is a measure used to quantify the performance of a digital radio transmitter or receiver in a communications system using digitalit modulation (such as QAM). A signal sent by anideal transmitter or received by a receiver would have all constellation points precisely at the ideal locations, however various imperfections in the implementation (such as noise, low image rejection ratio, phase noise, carrier suppression, distortion, etc.) or signal path cause the actual constellation points to deviate from the ideal locations. The modulation error ratio is equal to the ratio of the root mean square (RMS) power of the error vector to the power of the reference. It is defined in db as: where P error is the RMS power of the error vector, and P signal is the RMS power of ideal transmitted signal.

18 MER gain with Echo Canceller ON MER vs Eco 50,0 45,0 40,0 R [db] ME 35,0 30,0 25,0 20,0 15,0 10, Eco [db] MER con cancellatore MER no-canc

19 Different MER measurements: MER filtering MER modulator

20 MER vs. Power DVB-T signal Signal Level to the ADC: 10dBm MER vs P_mod[dBm] 60,00 50,0 ] MER [db] 40,00 30,0 Eco = +15dB Eco = +10dB Eco = +5dB Eco = -10dB Eco = -5dB Eco = 0dB 20,0 Eco = +25dB Eco = +20dB 10,0-30,0-25,0-20,0-15,0-10,0-5,0 0,0 P_mod [dbm] MER con cancellatore MER modulatore MER filtraggio

21 Echo Suppression intra-window Attenuations vs. Echo Level Attenuatio on [db] Echo Level [db] A.P. A.min A.P.2 A.min 2

22 Locking time Locking Time for echoes [-10, +25] db 2,499 2,500 2, ,500 1,352 1,516 1,844 t [s] 1,000 0,500 0, Number of Pulse Accumulation

23 Measurements: Echo level = -5dB

24 Measurements: Echo level = +10dB

25 Measurements: Echo level = +20dB

26 Publications

27 Crediti acquisiti nel II anno Scuola di Dottorato Napoli: 40 Scuola di Dottorato Bressanone: 21 Mini corso Heterogeneous Network: 12 TOTALE II ANNO: 73 TOT. I + II ANNO: 113

28 Thank you for your attention!