Bologna – 14 October , 2009
Video over wireless:FPGA design and implementation of a pulse-FPGA design and implementation of a pulsebased echo canceler for DVB-T/H
Ph.D Student: G.ChiurcoTutor: Prof. O.Andrisano
Alma Mater University of Bologna, Italy
Scenario description: Problems and goals
Single Frequency Network (SFN) constituted by:a. a DVB-T/H broadcasting station/ gb. an on-channel relay station or repeater (OCR)c. many stationary and mobile users
Main goal: covering with the DVB-T signal an area notreachable by the DVB-T broadcast station
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
reachable by the DVB-T broadcast station.
Targetg
Repeater based on DVB-T pilots Repeater “general-purpose”: The Pulse-based Echo Canceler
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Outline
Project Flow; FPGA d l t kit 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; FPGA Design and Implementation; Workbench Test-Bed; Measurements and Results.
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Project FlowjProject & Analysis
Simulation Implementation &Measurements
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
FPGA development kit featuresp
FPGA Stratix II Altera d Kit EP2S180F1020C3dev. Kit EP2S180F1020C3
Analog I/O:•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;• 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 Mb t t fl h• 16-Mbyte compact flash
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Scenario description: Problems and goals (3)
Adopted strategy: DVB-T repeater.
(d)(c) x (e)
(c)
( )( ) x(c)
(d)(b)( ) (e)(d)(b)(a)
Consequence: the amplifier power must be limited Reduced service area!
The echo canceller permits to increase the coverage area
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Repeaters: classical solutionsp
Antenna Isolation
TimeDelay
Quality ofTx signal
Selectivityof Rx signal
MantainSync.
RF OCR
IF 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;
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Baseband OCR
Filter
HPAFilterand LNA
HPA
RF
Upconverter
IF
Down converter
L.O.
IF
D/A – Up conversion
IF
A/D - BBDown conv.
IF
Data Process.
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Baseband OCR (2)( ) OCR architecture implemented on the FPGA board:
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Echo canceller basic scheme
Delay+
M lti indo cancelle
Ch l
-
Estimator
Multi-window canceller
Possibility to cancel Channel
estimationunit
Controller
Dynamic tap
update
Estimator & Pulse
Generatorsingle and multiple echoes;
up to Nw different echo
FIR1
clusters can be cancelled;
the position of the lli i d i
FIRi
Del
ay li
ne
Echo
……
cancelling windows isautomatically determined.
FIRNw
Echo Canceller Multi-window
canceller
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Echo canceller basic operationsp
Two operative phases:
Start-Up (open-loop) determination of the number and position of the determination of the number and position of the
cancelling windows (pulse-based) initial coupling channel (pulse) estimation FIR’s set-up FIR s set up
Steady-State (closed-loop) effective DVB T signal repetition effective DVB-T signal repetition (fast) echo tracking (LMS-algorithm) stability and coupling channel monitoring (periodical
check of new echoes with the pulse technique)check of new echoes with the pulse technique)
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Search and cancelling windowsg 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 15dBover the useful DVB-T signal powerover the useful DVB-T signal power
echo suppression > 40 dB
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
FPGA design and implementation The ECHO_CANCELLER entity:
ESTIMATOR_iq:implementing the channel pulse estimator, the pulse generator and an additional Least Mean Squarean additional Least Mean Square (LMS) algorithm working in the steady-state mode;
SHREG&MUX:SHREG&MUX: implementing the delay which allows to position the cancelling window inside the overall search window;
( 1)( ) [ ( ) ( )]
Ph mh m y n y n
DYN_FIR_MCV:implementing the cancelling FIR filters with dynamically variable coefficients based on the Multi
( ) [ ( ) ( )]n nP P P Q Qh m y n y n
( 1)Qh m coefficients, based on the Multi Cycle Variable (MCV) technology.( ) [ ( ) ( )]
n nQ P Q Q Ph m y n y n
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
FPGA design and implementation The ECHO_CANCELLER entity:
ESTIMATOR_iq:implementing the channel pulse estimator, the pulse generator and an additional Least Mean Squarean additional Least Mean Square (LMS) algorithm working in the steady-state mode;
SHREG&MUX: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 Multicoefficients, based on the Multi Cycle Variable (MCV) technology.
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Workbench Test-bed
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
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 communicationst i di it l d l ti ( h QAM) A i l t b id lsystem using digital modulation (such as QAM). A signal sent by an ideal
transmitter or received by a receiver would have all constellation pointsprecisely at the ideal locations, however various imperfections in theimplementation (such as noise, low image rejection ratio, phase noise,implementation (such as noise, low image rejection ratio, phase noise,carrier suppression, distortion, etc.) or signal path cause the actualconstellation points to deviate from the ideal locations.
The modulation error ratio is equal to theratio of the root mean square (RMS) powerof the error vector to the power of thereference. It is defined in dB as:
where Perror is the RMS power of the error vector, and Psignal is the RMS power of ideal transmitted signal.
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
MER gain with Echo Canceller ONg
MER vs Eco
45,0
50,0
30,0
35,0
40,0
R [d
B]
15,0
20,0
25,0ME
10,0-10 -5 0 5 10 15 20 25
Eco [dB]
MER con cancellatore MER no-canc
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Different MER measurements:
MER filtering
MER modulator
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
MER vs. Power DVB-T signalg
Signal Level to the ADC: 10dBmMER vs P_mod[dBm]
60 0
Eco = -10dB40 0
50,0
60,0
]
Eco = +20dBEco = +15dB
Eco = +10dBEco = +5dB Eco = 0dB
Eco = -5dB
30,0
40,0
MER
[dB
]
Eco = +25dB
Eco = +20dB
10,0
20,0
-30,0 -25,0 -20,0 -15,0 -10,0 -5,0 0,0
P_mod [dBm]
MER con cancellatore MER modulatore MER filtraggio
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Echo Suppression intra-windowpp
Attenuations vs. Echo Level
70
75
60
65
70
on [d
B]
45
50
55
Atte
nuat
io
35
40
-10 -5 0 5 10 15 20 25 30
Echo Level [dB]
A.P. A.min A.P.2 A.min 2
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Locking timeg
Locking Time for echoes [-10 +25] dB
2,499
2,500
Locking Time for echoes [ 10, +25] dB
1,3521,516
1,844
1 500
2,000
1,000
1,500
t [s]
0,000
0,500
2048 4096 8192 163842048 4096 8192 16384
Number of Pulse Accumulation
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Measurements:
Echo level = -5dB
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Measurements:
Echo level = +10dB
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Measurements:
Echo level = +20dB
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Publications
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Crediti acquisiti nel II anno
Scuola di Dottorato – Napoli: 40
Scuola di Dottorato Bressanone: 21Scuola di Dottorato – Bressanone: 21
Mini corso Heterogeneous Network: 12
TOTALE II ANNO: 73
TOT. I + II ANNO: 113
Giovanni Chiurco
Alma Mater University of Bologna - WiLab
Th k f Thank you for your attention!attention!
Giovanni Chiurco
Alma Mater University of Bologna - WiLab