RFID Collision 問題探討
2010.12.31 王正誠
/ 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Outline
•
•
•
•
•
RFID 介紹
RFID collision problem 探討
Conclusion
Future work
Reference
2 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
什麼是RFID?
• RFID
– Radio Frequency Identification
– 無線射頻識別
– 利用空間電磁感應或電磁傳播進行通信，以達
到自動識別標識物體的目的
3 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的組成元件
• RFID主要有三個組成元件
1. 電子標籤(Tag)
 RFID詢答器(RFID Transponder)、非接觸ID標籤
(Contactless ID Tag)
2. 感應器(Reader)
 辨識器、讀碼器
3. 天線(Antenna)
4 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的組成元件 – Tag
• 依本身具電源與否區分為三類
1. 主動式RFID
 電池型
 通訊距離可達十公尺
 可自行處理和傳送資料
2. 被動式RFID
 免電池型
 由讀寫器的天線接收電力後才能動作，通訊距離較
短
 不能自行處理和傳送資料
5 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的組成元件 – Tag (cont’d)
3. 半主動式RFID
 電池支援式
 標籤內部數位電路供電
 不能自行發送資料
6 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的組成元件 – Reader
• 感應器(Reader)
– 讀取電子標籤
– 射頻信號，不需要與電子標籤接觸及可讀取資
料
– 感應器會與電腦連接，得到的資料傳送至系統
作辨識或後續處理
7 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的組成元件 – Antenna
• 天線(Antenna)
– 傳遞電子標籤和感應器之間的射頻信號
8 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的優點
1.
2.
3.
4.
5.
6.
7.
儲存資訊量多
非接觸式、穿透性
可辨識數個RFID標籤、標籤可覆寫
使用期限長
體積小、多變的形狀
讀取速度快
安全性高
9 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的缺點
1. 有效距離
– 標籤和讀取裝置的通訊距離
2. 成本價格較高
– RFID的標籤成本較傳統條碼高
3. 易受干擾
– 電磁波無處不在
10 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的應用
• 醫療
– 追蹤傳染性疾病患者、病患辨識、醫療廢棄物
品追蹤
• 零售
– RFID標籤取代條碼標籤，追蹤商品，防缺貨
• 監控保全
– RFID技術與無線區域網路結合，取代傳統巡邏
11 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的運作
• Differentiate between two main forms of
communication.
– Multi-access to a reader
– Broadcast mode
12 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的運作 – Multi-access
• Data from many individual tag to reader
Tag 1
Tag 3
Tag 2
Reader
Tag 4
Tag 5
Tag 6
13 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的運作 – Broadcast
• At beginning of identification, reader
broadcast to tags in its range and tags return
message to reader.
Tag 1
Tag 3
Tag 2
Reader
Tag 4
Tag 5
Tag 6
14 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID的運作 – Broadcast (cont’d)
• Three cases
1. Only one tag to respond reader.
2. At the same time have more tag to respond to
the reader that result collision.
3. After reader’s broadcasting no tag respond.
15 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
RFID Tag & Collision之間關係
• Active tag
– Detect other between tags to avoid collision.
• Passive tags
– Not detect other between tags to avoid collision.
16 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Anti-Collision Algorithm – FSA (1/3)
• FSA (Framed Slotted ALOHA)
– Reader broadcast a frame size to tags, all tags
select a random number(less than frame size).
– Tag have own random number, slot equal to the
number, tag transmit message to reader.
– Tag transmit to reader stagger.
– Avoid collision caused by tag.
1 2 Tags
–Reader
3
4
17 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Anti-Collision Algorithm – FSA (2/3)
• When collision occur, reader skip collision tags
until next cycle, and then reader broadcast
again and collision tags select random number
and transmit again.
• Repeat step until all tags are identified by the
reader.
18 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Anti-Collision Algorithm – FSA (3/3)
• Issue
– Additional memory to save the random number
except the ID of tag.
19 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Anti-Collision Algorithm – Query tree (1/2)
• Reader broadcasts a prefix and queries the
tags. ID of tag is same as prefix, reader
recognize it.
• Query again until completing.
20 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Anti-Collision Algorithm – Query tree (2/2)
• Issue
– Not like ALOHA, need extra memory to save
number of tag.
– Whole identification process check ID with prefix
one by one. ID of tags is similar, identification
process of tag maybe cost long time. But ALOHA
type not impact by ID.
21 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Anti-Collision Algorithm – DFSA (1/2)
• DFSA (Dynamic Framed Slotted ALOHA)
– Estimate through algorithm can estimate
remaining number tags after each round of
identification.
– Frame size change according to result.
22 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Anti-Collision Algorithm – DFSA (2/2)
• Issue
– Frame size is no longer fixed, make whole
identification process more efficient.
23 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (1/8)
• Based on ALOHA.
• Solve collision immediately when collisions occur.
• When collision occur, system restart another
identification process(new cycle and abandon
previous cycle).
– Estimate collision tags and reader broadcast a new
frame size to tags. Tag generate random number again
and transmit message.
• Reduce collision tag to collide again in next round
to make more collisions.
24 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (2/8)
• n : passive tags(have unique ID)
– Reader does not know number of tags but can
estimate.
• Ni : frame size at the beginning
– Reader broadcast frame size Ni to tags, tag
generate a number between 1 and Ni.
• nc : estimate number of collision tag
– Reader use nc to differentiate frame size Nc, tag
generate number between 1 and Nc.
25 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (3/8)
26 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (4/8)
• Referring to [2], range of frame size can be
decided.
• Frame size is close number of tag, efficiency of
identification is better.
27 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (5/8)
• Command “throw_away”
– Execute of proposed
method.
• What reader do when
reader detects collision?
• c : greater than zero, mean
collisions occur
• ad : count value to aim at
collision tags
//Reader:
//broadcast “throw_away”
if (c > 0)
tag_respond =
tag(throw_away);
if (tag_respond > 0)
ad = ad + 1;
tag(ad);
start a new round;
broadcast Nc;
28 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (6/8)
//Tag:
• What tag do when the
//Receive initial parameters
reader broadcasts
from reader
command “throw_away” to
ct = 1;
collision tag?
transmission:
• ct : limit collision tags to
respond to reader
receive frame size;
generate random number;
//must <= frame size
if (ct == ad)
transmit message;
ct = 0;
if (receive “throw_away”)
ct = ct + 1;
goto transmission;
29 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (7/8)
• Worst case
30 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simple & Efficient Anti-Collision Algorithm (8/8)
• Analyze probability of worst case
• Number of tags is between 3 and 32
31 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simulation Results (1/3)
• 10≦n≦300, Ni =16
32 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simulation Results (2/3)
• Ni ={16,64,128}
33 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Simulation Results (3/3)
• 10≦n≦1000, Ni =16
34 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Conclusion
• The method of anti-collision algorithm of RFID
system
– Base on ALOHA protocol.
– Cost fewer slots than DFSA about 54% and
efficiency of whole process is about 35% when
number of tags is increased to 1000.
35 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Future work
• Anti-collision algorithm for RFID
• Position of RFID
36 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Reference
[1] Chuen-Ching Wang, Te-Yuan Wang, Tien-Hao Lien, Rong-Ming Su, "A
Simple and Efficient Anti-collision Algorithm for RFID System," iih-msp,
pp.300-305, 2010 Sixth International Conference on Intelligent
Information Hiding and Multimedia Signal Processing, 2010
[2] Wen-Tzu Chen, Guan-Hung Lin “An Efficient Anti-Collision Method for Tag
Identification in a RFID System,” IEICE Transactions on Communications,
Volume E89-B, no.12, pp.3386-3392, Dec. 2006.
[3] Klaus Finkenzeller, RFID Handbook Fundamentals and Applications in
Contactless Smart Cards and Identification,Second Edition, Wiley, 2003.
[4] 龔哲幀著，「主動式RFID室內定位追蹤演算法與系統設計」，碩
士論文，國立台北科技大學資訊工程研究所，台北，2010。
37 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology
Thank You For Listening
• Q&A
38 / 38
Wireless and Broadband Networks Laboratory ◆ Department of Computer Science and Information Engineering ◆ National Taipei University of Technology