Radio Frequency Identification
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
RFID in Nutshell
To Enhance the concept of “bar-codes” for faster identification of assets (goods, people, animals)Ingredients:
– Transition to electronic bar codes with wireless communication capabilities
– Transition form optical to wireless “readers”First Bar code patents – 1930sH. Stockman Paper (1948) – Communication by means of reflected powerFirst RFID Patent - 1973Auto-ID center founded at MIT – 1999
– Standardization effort taken over by EPC Global (Electronic Product Code)
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
RFID Building Blocks
Two Basic Devices:
Reader Tag
RF ModuleBattery Scavenging circuitry (active or passive)
§ E2PROM to store ID§ Control Logic/Collision Arbitration
Mechanism§ (sensors)
§ (processing unit)
RF Module§ Memory
§ Processing Unit§ Control Logic/Collision Arbitration
Mechanism§ Battery or Power Supply
§ Other Interfaces (Ethernet, WiFi)
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
The Tags
Tags can be attached to anything:
– pallets or cases of product– vehicles– company assets or personnel– People or animals– Electronic appliances
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Generic Tag Architecture
ProtocolEngine
Receiver
Memory
Ante
nna
Write Path
D
S
G
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Electronic Product Code
Header - Tag version numberEPC Manager - Manufacturer IDObject class - Manufacturer’s product IDSerial Number - Unit ID
With 96 bit code, 268 million companies can each categorize 16 million different products where each product category contains up to 687 billion individual units
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Usage Models
Handheld Smart Shelves Point of Sale
Conveyor Belt PrintersForkliftDock Door
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
HFLF
RFID: Spectrum Snapshot
10 kHz 100 kHz 1 MHz 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz
123/134 kHz 13.56 MHz
VHF UHF SHF
420/460 MHz
869/928 MHz
2.35/2.45 GHz
5.8/5.9 GHz
24.1 GHz
Magnetic Coupling Electromagnetic Coupling
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
RFID: Physical Communication
Near Field Model (HF) Far Field Model (UHF)
Inductive Coupling (125kHz - 13.56MHz): better at lower frequencies (<10MHz) for
the required antenna dimensions
Electromagnetic coupling868MHz, 2.4GHz, 5GHz: better at higher frequencies for the required
antenna dimensions
RFID Collision Arbitration
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
General Problem: Tag Identification
reader
tag
Interrogation
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Conflicts in the Responses
reader
tag
Multiple Answers: Arbitration Required
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Tag Arbitration Peculiarities
Similar to Classical Access Control but:– Fixed unknown population size– Tags cannot implement complex protocols
• E.g., carrier sense is out – Often reader-driven algorithms
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Tag Arbitration Efficiency
The efficiency is commonly defined as the tag population size, N, over the length of the arbitration period L(N)
⌘ =N
LN
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
The Frame ALOHA
Extension of the ALOHA protocol where nodes are allowed to transmit once every frame
– Frame composed of r slots– Every tag chooses a slot in the frame– If transmission is failed, retry at next frame
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Frame ALOHA: Single Frame
The average throughput is:
Thus, the efficiency is:
Which is maximum for: r=n
0
0,1
0,2
0,3
0,4
0,5
0,6
0 2 4 6 8 10 12 14 16 18 20
n
eff m
ax
⌘ =E[S]
r= n
1
r(1� 1
r)n�1
E[S] = n(1� 1
r)n�1
⌘M (n) = (1� 1
r)n�1
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Frame Aloha: Multiple frames
The FA efficiency depends on the initial tag population (N), the current backlog (n) and the frame size (r).
Current Frame size r is dynamically set to the current backlog n -> Dynamic Frame Aloha
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
The average tag resolution process can be recursively calculated as:
which leads to:
Frame ALOHA: Multiple Frames
⌘ =N
LN
Ln = r +n�1X
i=0
P (S = i)Ln�i
Ln =r +
Pn�1i=1 P (S = i)Ln�i
1� P (S = 0)
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Example
Find out the efficiency in case N=2, and r=2.
L2 = 2 +1X
i=0
P (S = i)L2�i = 2 + P (S = 0)L2 + P (S = 1)L1
L2 =2 + P (S = 1)
1� P (S = 0)= 4
⌘ =2
4= 0.5
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
Problem
Initial population N and backlogs n are not knownTag arbitration is actually composed of two modules:
– Backlog Estimation Module: to provide and estimate of the backlog nest
– Collision Resolution: run Frame Aloha with r= nest
BacklogEstimate
DF-Aloha
Tag Responses
Reader Actions
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
The Binary-Tree
Random Numbers are used to partition the set of colliding tags
5
2
0 2
1 1
3
1 2
1
2
3
5 6
4
7
8 9
1 1
10 11
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
The Binary Tree Implementation
Tags have counters set to 1The reader broadcasts
– Trigger command: sent at the beginning and after successful/empty slots• tags decrease their counter and transmit if counter is 0
– Split commands: sent after collided slots• tags with counter equal to 0 randomly choose a new counter
value in [0,1]• Tags with counter greater than 0 increase their counter
IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca
The Binary Tree
A: 1 1->0 0->0 0->1 1->0 0->1 1->0 ResB: 1 1->0 0->0 0->1 1->0 0->0 Res ResC: 1 1->0 0->1 1->2 2->1 1->2 2->1 1->0 Res
T S S T S T T
ABC
AB
0 AB
B A
C
1
2
3
5 6
4
7
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