IOT - Basics from the Expert EASP1 Design Case
UHF RFID Reader Design Prof. Roland Küng, 2016
2004 The “Big Bang” of Internet of Things The Electronic Product Code (EPC)
EPC provides unique* numbering scheme for physical objects EPC is only an ID, the information is stored on the network
96 bit = 1029 different codes - Age of earth is 1017 s - Diameter of universe is 1029 cm - 1019 ID’s available per person in this world - Total capacity of chip manufacturers is 1013 tags/year * Uniqueness by EPC and data behind in EPCIS
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Possible Classification of RFID
RuBee
NFC
Semi-active passive
passive
Inductive LF
WLAN
ZigBee
Semi-passive
Semi-passive
Semi-passive passive
BTLE
active
Inductive RF
RFID
UHF & µWave
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Different Frequencies in Use
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IOT Simple passive UID Tag
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Tag Zoo
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Example of Passive Tag
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IOT Semi-passive Sensors
µC Memory Sensor
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Example of Semi-passive Sensor
Rechargeable Battery
Sensor Part
Passive RFID Antenna kunr
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Passive UHF RFID Link Budget: - Read Tags up to 8m Distance
- Limited by Tag Power Consumption * EPC Class 1 Gen 2 2
Pr =
Pt ⋅ Gt ⋅ Gr ⋅ λ ( 4 π ) 2 ⋅ d2 ⋅ L
-13…-17 dBm - 16 dBm received at tag *
S/N = 35 dB
Path Loss 49 dB @ 8 m + 33 dBm (2 W)
- 71 dBm Gain = 7 dB (0.1 nW)
Path Loss 49 dB @ 8 m -22 dBm (6 μW) backscatter signal
Receiver Noise: -99 dBm (F = 25 dB, B = 100 kHz)
Reality: Additionally orientation losses, system losses, fading, n > 2 ... Additional noise sources, amplitude phase, TX to RX coupling
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RFID EPC Gen2 UHF Reader 10 mm TX antenna power amp modulation switch RX antenna
RADIATING
signal processor
120 mm
synthesizer
I
Q
direct conversion receiver
D A filter
Passive Tag (Etikette) Reader (Lesegerät)
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RFID: 4 Watt EPC Gen2 Reader Software Defined Radio (SDR) Architektur
DSP
FPGA
ADC
DAC
Synthesizer DC-RX
Xscale
TX Amp
Supply Circulator
Ethernet USB RS232
4 Antenna Ports kunr1-12
SDR: UHF RFID Reader RISC Processor
Signal Processing
UHF Frontend
- MAC
- Sample Level on FPGA
- Direct Conversion Receiver
- Reader Protocol
- Symbol Level on DSP
- Carrier Suppression
- Interfaces
- Air Protocol on DSP
- Multi Antenna
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Tag to Reader: Sub Carrier Encoding • ASK or PSK modulation: 5 kbps < data rate < 640 kbps • Baseband-FM0 for single reader per frequency channel saves bandwidth • Miller sub carrier encoding for dense reader environment no reader - tag collisions if massive filtering is used
+ Interrogator commanding
Interrogator listening
FM0
Miller
☺
Filter
Tag response
Frequency
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European Regulatory ETSI
Channel BW = 200 kHz •
4 high power channels allowed within EU, ERP 4 W each
•
Concurrent operation in close proximity of readers on same channel needed kunr1-15
Example: Dock Door Application Reader related risks • Mutual interference among readers: • Co-channel interference • Adjacent channel interferences Multi Carrier and Miller Coding • Organize frequency plan • D = 4 m adjacent interferer distance • D = 9 m co-channel interferer distance Nr. 7 an d 13 assumed to be blocked by interferer kunr1-16
Example: Dock Door Application
Metro Germany Logistic Centre Swiss Post Härkingen
Metro RFID Dock Door Portal
Swiss Post Härkingen
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Filtering UHF RFID Reader (Europe) Interrogator commanding
Interrogator listening
Filter HP
Tag response
-240 kHz ± 80
DC
Filter
LP
Frequency
240 kHz ± 80
EPC Gen2/ Europe: Subcarrier and data rates are extremely variable! kunr1-18
Interfering Power Levels
Interferer has advantage over victim tag because its signal decreases with 1/d2 versus 1/d4 of the passive tag
λ PRx,dBm = PEIRP,dBm + GRx,dBi + 20 ⋅ log 4πD
+30 +20 +10 0 -10 -20 -30
First Spec Assumption: Adj. carrier level = weakest tag level fp = 320 kHz, Ap = 1 dB fs = 600 kHz, As = 62 dB
Feature by Feature Comparison
-40 -50 -60 -70
7th order CH Countermeasure
plus HP 2.O. against DC from own carrier kunr1-19
1st idea: Integrated Active Filter
I-,Q-Filter: N = 6, Butterworth • unfortunately above 1 MHz • Attenuation unsufficient • IM3 too high, as IM is generated mainly by interferers kunr1-20
I-/Q- Basisband Filter 2nd idea: Active RC failed due to GBP (Qmax =11 @ 320 kHz) 3rd idea: LC Filter Design selected • Noise free • No IM I
IN
Q
I
OUT
7. Order LP 320 kHz for FM0, Miller
Q
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Modern Characterization of ADC: Dynamic Range , Spurious • Speed and power constraints: 14 Bit ADC 5 Msps • ENOB 12 dB (Noise level -74 dBFS) • Max input level: -10 dBFS (adj. carriers) • Tag signal dynamic range: 36 dB • Min. S/N for tag: 4 Bit
ADC
-10 dBFS Tag Dynamic Range > 36 dB SFDR
-50 dBFS Min SNR 4 Bit -74 dBFS
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Selected ADC
SNR SFDR
Integrated dual 14-bit ADC Single 3 V supply operation (2.7 V to 3.6 V) SNR = 74 dB (to Nyquist, AD9248-20) SFDR = 86 dBc (to Nyquist, AD9248-20) Low power: 90 mW/channel at 20 MSPS
0
1
2
3
4
Nyquist
Example: fs = 5 Msps, FFT 16k-point no averaging kunr1-23
Modern Characterization of ADC:
Noise Floor
DAC
ADC
SNR
Noise Density [dBc/Hz]: Measured Value - 10 log (BW) Noise für SNR: Noise Density + 10 log(fs/2) Noise Density [dBc/Hz]: FFT Floor – 10 log (fs/M)
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Synthesizer for European and US Regulations PLL: Modulus Divider Phase Detector Charge Pump
VCO 850-950 MHZ
TCXO 20 MHz Loop Filter 3. Ordnung B = 4 kHz kunr1-25
I/Q - Downconversion The MAMXSS0011 uses FET mixer 13 dBm LO, IIP3 20 dBm
Interrogator commanding
Interrogator listening
Mixes User Carrier to DC Filter
Tag response
DC
Frequency
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Further Challenges for Reader
Tag response in Dense Reader Mode is received in channel adjacent to carrier
While transmitting, readers are emitting noise to this adjacent channels where the tag response is received
Noise from several modulated readers sum up and interfere with weak tag responses
Min. distance d between co-channel operated readers must be respected Lit.: ETSI EN 302 208-1 V1.2.1
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UHF Signal Propagation
Material
Orientation
• Test fixture with 73 Gen2 tags, equally spaced in air medium • Target read time: < 1 second
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UHF Signal Propagation Multi-path reflections from metal (reinforcing in floors/ dock levellers and other objects), cause nulls and peaks that get worse with distance from the antenna.
height
Reader
-3 dBm
-14 dBm
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Fading - Problem in Passive RFID
Simple 2-Ray Model
Pr =
4 Pt ⋅ Gt ⋅ Gr ⋅ λ2 ( 4 π ) 2 ⋅ d2
2π ⋅ h t ⋅ hr ⋅ sin2 λ⋅d
RFID: Carrier only Slow Flat Fading Channel
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