EXAMENSARBETE INOM TEKNIK, GRUNDNIVÅ, 15 HP STOCKHOLM, SVERIGE 2017 Performance comparison of tree- based RFID anti-collision algorithms in large scale environments FREDRIK LILJEDAHL ALEXANDER MANSKE KTH SKOLAN FÖR DATAVETENSKAP OCH KOMMUNIKATION Performance comparison of tree-based RFID anti-collision algorithms in large scale environments FREDRIK LILJEDAHL ALEXANDER MANSKE Bachelor in Computer Science Date: May 30, 2017 Supervisor: Michael Schliephake Examiner: Örjan Ekeberg Swedish title: Prestationsjämförelse av trädbaserade RFID antikollisionsalgoritmer i storskaliga miljöer School of Computer Science and Communication ii Abstract Radio Frequency Identification is taking a larger and larger place in our everyday lives. As the use of RFID and the number of RFID-enabled items increase, the technology is more prone to identification collisions, which leads to difficulties using it. A handful of algorithms to avoid these issues already exist today, but no real comparison regarding their performance in large scale collisions have been done. This report focuses on tree- based algorithms and compares them to one another with the use of an implemented benchmark. A large amount of tests were completed, with a various and diverse size of input data. It was shown that algorithms with a dynamic backtracking structure or fixed loop implementations perform far better than others and are suitable for further develop- ment and implementation in large scale environments. iii Sammanfattning Radio Frequency Identification tar en större och större plats i vår vardag. I takt med att användningen av RFID och antalet RFID-aktiverade produkter ökar, så ökar även risken för att identifikationskollisioner uppstår, vilket leder till komplikationer i användningen av tekniken. En handfull algoritmer för att hantera dessa situationer existerar redan, men ingen riktig jämförelse mellan deras prestationer i storskaliga kollisioner har gjorts. Den- na rapport fokuserar på trädbaserade algoritmer och jämför dem sinsemellan med hjälp av en implementerad testmiljö. En stor mängd tester genomfördes med varierande inda- ta. Det visade sig att algoritmer med dynamisk tillbakahoppande struktur eller de med konstanta slingor presterade mycket bättre än andra och bedömdes därför som passande för vidareutveckling och implementation i storskaliga miljöer. Contents Contents v 1 Introduction 1 1.1 Problem statement . .1 1.2 Scope of study . .2 1.3 Report disposition . .2 1.4 Terminology . .2 2 Background 4 2.1 RFID . .4 2.1.1 Reading . .4 2.1.2 Collision . .5 2.2 Anti-collision algorithms . .5 2.2.1 ALOHA-based algorithms . .5 2.2.2 Tree-based algorithms . .7 2.2.2.1 Binary search algorithm . .8 2.2.2.2 Dynamic binary search algorithm . .9 2.2.2.3 Backtracking binary algorithm . 10 2.2.2.4 Jumping and dynamic algorithm . 11 2.2.2.5 Improved binary search algorithm . 11 3 Method 13 3.1 Metrics . 13 3.2 Test data . 14 3.2.1 Structure . 14 3.2.2 Generating data . 14 3.3 Implementation . 14 3.3.1 Code structure . 14 3.3.2 Experiment execution . 15 4 Results 17 4.1 Benchmarks with a low number of tags . 17 4.2 Benchmarks with a high number of tags . 20 5 Discussion 24 5.1 Result analysis . 24 5.2 Method analysis . 25 5.2.1 Source of errors . 26 v vi CONTENTS 5.3 Future research . 26 6 Conclusion 27 Bibliography 28 A Code 30 B Result data 51 Chapter 1 Introduction As technology is advancing in a rapid speed and having an even greater impact on our lives for each year that passes by, optimizing and simplifying already existing solutions has become a main focus area for the creators and inventors in the industry. The demand for doing everyday things more efficiently and seamlessly is forcing the current solutions to become better, lighter and simpler. Keys and cards no longer have to be inserted or swiped, libraries do not use pen and paper to keep a record of their items and inventory tracking is almost completely autom- atized. All due to the rising technology of RFID (Radio Frequency Identification). As the technology moves forward, having a greater impact on our lives for each day, the number of RFID tags that we carry around or are bundled together and readers out in the public increases. To this day, readers have trouble identifying a tag if there is a collision, which means it is forced to read multiple tags at once. There are existing algo- rithms to handle these types of cases, but an efficient one is yet to be found. Due to the fact that RFID is a constantly rising technology, with a market worth of US$8.89 Billion in 2014 and an estimated US$18.68 Billion in 2026 [1], an efficient and optimized solution to the problem is needed. To be able to integrate RFID in our lives to a greater extent, collision needs to be handled appropriately. This report will investigate already existing algorithms and test weather or not they can be changed and optimized to fulfill the lack of efficiency that exists today. 1.1 Problem statement There are not any perfect anti-collision algorithms in RFID environments in use today, therefore all improvements on existing algorithms are appreciated. This study focuses on tree-based algorithms, which work by polling the collided tags with queries in order to distinguish them from one another. This can be done by various methods and is fur- ther presented in Chapter 2. The main subject of this report will be the Improved binary search algorithm presented by Djeddou and Benssalah, which is using a binary search tree combined with preset loop mechanic to optimize the performance of the handling of the collision. The article presents their algorithm as having better performance than similar tree-based algorithms. In their research study, 16 bit identification numbers were used and the number of simultaneously read tags were ranging from 2 to 100 [2]. Many practical uses of RFID today have numbers exceeding the ones used in their simulations, for example, a harbor 1 2 CHAPTER 1. INTRODUCTION with hundreds of containers with each containing tens of thousands of products with individual tags. • How do well known tree-based anti-collision algorithms perform in large scale en- vironments? • Does Djeddou’s and Benssalah’s binary search algorithm perform better in large scale environments compared to other known anti-collision algorithms? 1.2 Scope of study While there are both passive tag collisions and active tag collisions, this study will only focus on passive tags and approaches on handling their collisions. There is also a type of collision caused when several readers tries to read the same tag called reader colli- sion, but this will not be studied in this report due to the lack of relevance to the prob- lem statement. The metrics used in measuring the performance of algorithms are the number of reader requests and the total amount of bits transmitted between the reader and tags. RFID col- lision simulations will be used as the method of measuring performance as there is no need for real life RFID systems when using reader requests and bit amount as metrics. The algorithms considered in the study are tree-based algorithms. While ALOHA- based algorithms are important in RFID collision protocols it will not be studied because they are dependant on time as a metric, which will not be measured. Cases when tags enter the reader’s vicinity in the middle of a running anti-collision protocol will not be studied. 1.3 Report disposition In the following chapter, chapter 2, the theoretical background is presented. It serves the purpose to educate the reader on relevant technology and it presents previous work and research that has been done in the area. The information in chapter 2 is crucial since it will be referred to throughout the report. Chapter 3 includes the methodology of the experiment, explaining the testing envi- ronment and motivation of the approach. This chapter is meant to be thorough, so that the experiments and results can be recreated and verified by someone else. Chapter 4 includes the results obtained and in chapter 5 they are broken down, an- alyzed and discussed. Finally, a conclusion based on the results and discussion is pre- sented in chapter 6, in relevance to the research question. 1.4 Terminology ALOHA A type of RFID anti-collision algorithm which works by telling each tag in the collision to idle for a randomly selected amount of time. BSA Binary Search Algorithm, a type of RFID anti-collision algorithm. Distinguishes tags by sending queries to the set of tags. CHAPTER 1. INTRODUCTION 3 Collision When multiple tags are being read by a reader during the same time frame and part of their identification number collides. Collision bits The colliding bit positions of the response the reader receives when colli- sions occur. DBSA Dynamic Binary Search Algorithm, a type of RFID anti-collision algorithm similar to the Binary Search Algorithm but sends and receives only fragments of queries. Improved algorithm An unnamed anti-collision algorithm proposed by Khelladi, Djed- dou and Benssalah [2]. Sometimes referred to using the name of the authors and sometimes using the placeholder name Improved algorithm. Manchester coding A technique used in readers to identify whether or not there exists any collision bits. Reader Reads and communicates with tags in its operating range by transmitting radio waves. RFID Radio Frequency Identification. Tag A chip stored with data that can be read by a RFID reader. Tags mentioned in this report are passive, meaning that they do not have any internal or dedicated power- ing source. Instead, they are powered by the radio energy that is transmitted by the reader to be able to send their specific data.