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Time, Phase and Frequency Synchronization of Low-Cost DVB...
Transcript of Time, Phase and Frequency Synchronization of Low-Cost DVB...
Xuan Liup. 1
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Time, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel
Coherent Receiver
Xuan Liu
Xuan Liup. 2
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Outline
§ Motivation and Objective§ Theoretical Background§ Multi-Channel Coherent Receiver Model§ Hardware and Software Implementation§ Verification and Measurement§ Conclusion and Outlook
Xuan Liup. 3
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Motivation
Software Defined Radio (SDR)§ Pros
• Less need for dedicated hardware• Fulfill multi-purpose with one module
§ Cons• Most SDR platforms are fairly expensive • Less feasibility for having multiple devices
RTL-SDR (DVB-T Receiver) is currently the cheapest (around 10€) andhas surprisingly good performance in terms of general usability
Xuan Liup. 4
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Objective
§ Theoretical study of RTL-SDR§ Building a four-channel coherent receiver with RTL-SDRs
• Time Synchronization• Frequency Synchronization• Phase Synchronization
§ Measurement and Verification
Xuan Liup. 5
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Outline
§ Motivation and Objective§ Theoretical Background§ Multi-Channel Coherent Receiver Model§ Hardware and Software Implementation§ Verification and Measurement § Conclusion and Outlook
Xuan Liup. 6
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Theoretical BackgroundSoftware Defined Radio
§ Software Defined Radio (SDR) offers a solution to build a flexible and cost-efficient wireless network by software defining some or all of the radio operating functions.
§ SDR Block Diagram
Xuan Liup. 7
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Theoretical BackgroundDVB-T Dongle (RTL-SDR)
§ MCX Female Connector§ USB 2.0§ Tuner Chip R820T § Demodulator Chip RTL2832U
Xuan Liup. 8
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Theoretical BackgroundDVB-T as a SDR
R820T RTL2832UDSP
RF Front End ADC & DSP
I
Q
Xuan Liup. 9
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Outline
§ Motivation and Objective§ Theoretical Background§ Multi-Channel Coherent Receiver Model§ Hardware and Software Implementation§ Verification and Measurement § Conclusion and Outlook
Xuan Liup. 10
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Multi-Channel Coherent Receiver Model
§ Coherent Receiver Requirement• The sample clock must be synchronized among receivers• The starting moment of sampling must be aligned among receivers
§ Applications which require phase synchronous reception• Frequency synchronization• Phase prior knowledge
Xuan Liup. 11
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Multi-Channel Coherent Receiver Model
§ Sample clock and frequency synchronization• Clock jitter and drift • 28.8MHz clock crystal is the single clock source for RTL-SDR• Solution: Sharing a common clock source among RTL-SDRs
Xuan Liup. 12
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Multi-Channel Coherent Receiver Model
§ Fractional-N PLL Residual Frequency Error
• Continuous phase drift between two RTL-SDRs even with shared common clock
• Hidden 17th bit of the fractional-N PLL is set randomly at retune• Frequency mismatch assumes discrete values
Frequency Mismatch
Xuan Liup. 13
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Multi-Channel Coherent Receiver Model
§ Time Synchronization
• USB communication couple of milliseconds
• PLL lock time max. 5ms
• Solution: A wideband noise signal is fed into each RTL-SDR at the beginning of the reception and cross-correlation is calculated
Ø The autocorrelation of white noise is a Dirac delta function
Ø No retune is needed when the antenna reception starts
• Time offset stays constant as long as no samples are lost
Xuan Liup. 14
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Multi-Channel Coherent Receiver Model
§ Phase Synchronization• Random phase offset due to the fractional-N PLL inside the tuner chip
R820T occurs at every retune• Solution: Angle difference between time aligned noise signal of RTL-
SDRs is the phase offset • Phase offset stays constant as long as no retune occurs
Xuan Liup. 15
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Outline
§ Motivation and Objective§ Theoretical Background§ Multi-Channel Coherent Receiver Model§ Hardware and Software Implementation§ Verification and Measurement§ Conclusion and Outlook
Xuan Liup. 16
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software Implementation
RTL-SDR 2
RTL-SDR 3
28.8MHz Clock Source
Demodulator TunerRTL-SDR 4
RTL-SDR 1
I2C CommunicationTimer Circuit
Power Divider
RF Switch 1Antenna 1
Antenna 2
Antenna 3
Antenna 4 RF Switch 4
RF Switch 3
RF Switch 2
Wideband NoiseSource
CTRL
Xuan Liup. 17
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software Implementation
Xuan Liup. 18
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software Implementation
MatlabScript Retune Pause
ReceiveData /
Time delayEstimation
AntennaSignal
Detection
ReceiveData
Phase & Frequency
Offset Estimation
Time, Phase &Frequency
Compensented
RTL Status Idle Retune PLL Locked
I2C Idle Active Idle
CTRL Low High Low
RXSignal
AntennaSignal Calibration Noise Signal Antenna Signal
tt=0
Xuan Liup. 19
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Outline
§ Motivation and Objective§ Theoretical Background§ Multi-Channel Coherent Receiver Model§ Hardware and Software Implementation§ Verification and Measurement § Conclusion and Outlook
Xuan Liup. 20
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement
§ S-parameter with a two port vector network analyzer • Magnitude of S21
Ø PCB functionality verification• Angle of S21
Ø PCB phase correction
Xuan Liup. 21
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement§ RF Switches Set to Noise Reception
Xuan Liup. 22
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement§ RF Switches Set to Antenna Signal Reception
Xuan Liup. 23
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement§ Phase offset added by PCB
Xuan Liup. 24
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement§ Measurement Setup
• PC• 12V power supply• Signal generator• 28.8MHz clock source
Output signal with the same phase
I/Q ModulatedRectangle
Signal
Xuan Liup. 25
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement§ Measurement Results
• Without phase drift compensation
• With phase drift compensation
Xuan Liup. 26
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement§ Measurement Results
Before time, phase and frequencysynchronization
After time, phase and frequencysynchronization
Xuan Liup. 27
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Verification and Measurement§ Measurement Results
Xuan Liup. 28
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Conclusion § A four-channel coherent receiver based on the synchronization of RTL-
SDRs has been realized§ The residual frequency error due to the fractional-N PLL has been
successfully compensated from 250 to 1350MHz§ Synchronization shows quite robust performance at 433MHz as long as
the phase drift is continuous
Further Works§ Cooling and shielding§ Measurement at higher frequencies§ AGC for the reference noise signal§ Application demonstration
Xuan Liup. 29
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Thank You !Any Questions?
Xuan Liup. 30
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
§ Timer § RF Switches§ Clock Distribution§ Noise Source Power Switch
Xuan Liup. 31
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software ImplementationRF Switches
§ ADG918• Absorptive SPDT RF switch
§ SCA-4-132+• 4-way power divider• Phase unbalance
§ Minimum loss pad • Provide broadband 50Ω to 75Ω impedance matching
must be compensated !
Xuan Liup. 32
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software ImplementationTrigger Signal
§ SDAT as trigger signal• I2C communication between tuner chip R820T/EEPROM and
demodulator chip RTL2832U only occurs at the beginning of the RTL-SDR configuration
• I2C communication starts with a falling edge at SDAT while SCLK stays high and finishes with a rising edge at SDAT while SCLK stays high
Xuan Liup. 33
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software ImplementationTimer
§ TLC555• Low power timing circuit• Falling edge-triggered
§ LSF0102• Voltage level translator• Open drain and push pull compatible
Xuan Liup. 34
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software ImplementationSynchronization Algorithm
§ Latency difference between channels inside of the first processing loop
§ Latency decreases inside of the secondprocessing loop until there is no latencydifference among RTL-SDRs
Xuan Liup. 35
Chair ofCommunication Systems
N T STime, Phase and Frequency Synchronization of Low-Cost DVB-T USB Receivers Acting as Software Defined Radios in a Multi-Channel Coherent Receiver
Hardware and Software ImplementationSynchronization Algorithm
§ Determine when the antenna signalreception begins