1532 IEEE COMMUNICATIONS LETTERS, VOL. 17, NO. 8, AUGUST 2013

Introducing a Novel “Virtual Communication Channel” intoRFID Ecosystems for IoT

Ivan Farris, Antonio Iera, Senior Member, IEEE, and Silverio C. Spinella

Abstract—Purpose of this paper is to illustrate an innovativemethod to exploit an “RFID virtual channel” in future RFIDecosystems. Specifically, it describes a technique that allowsgroups of RFID readers to use the residual User Memory Bank(UM Bank) of nearby RFID tags to establish a piconet and toexchange data. The implications of such a use are extremelyinteresting in a perspective of future IoT applications designedfor environments with a massive presence of conventional RFIDtags and/or (EPCglobal compliant) sensorized RFID tags.

Index Terms—IoT, RFID ecosystems, RFID technology.

I. INTRODUCTION

THANKS to its strong pervasiveness, the RFID technologywill undoubtedly play a key role in the future Internet of

Things (IoT) [1]. RFID ecosystems implemented in domestic(home automation) or professional environments are becominga reality, having their advantages already been widely assessed[2]. The wide spread of the RFID technology and its growinguse for unconventional [3] applications is currently combinedwith efforts to integrate RFID and Sensors within the same IoTplatforms [4]. This pushed towards the deployment of manydevices, compliant with the EPCglobal standard but imple-menting functions beyond the mere identification (sensorizedTag, sensors with RFID RF interface, Wireless Identificationand Sensing Platform - WISPs [5], etc.). Today, we are in afavorable situation, in which everyday environments are richboth in RFID readers (fixed, embedded in mobile phones,cheap and mobile, etc..) and in objects carrying RFID tagsto be identified in the supply chains. The idea, in a sensevisionary, proposed in this paper starts from the observationthat the RFID tags/sensors available on the market or stillunder study have a data storage capacity well beyond thatrequired for mere identification purposes. This gives a chanceto look at these RFID tags as a new “virtual” communicationchannel already available in many environments but not fullyexploited yet. We propose a method that enables low-costmobile RFID readers in future RFID ecosystems to use theresidual User Memory Bank (UM Bank) of nearby RFID tagsto exchange data without resorting to the use of additionalcommunication technologies. Our paradigm also foresees thespecification of rules to establish piconets (called RFID AreaNetworks, RANs) of devices exchanging data over the virtualRFID channel, similarly to what happens with other technolo-gies (e.g. Bluetooth or Zigbee) for sensor networks. Logically,we have chosen to keep full compatibility with the Electronic

Manuscript received February 22, 2013. The associate editor coordinatingthe review of this letter and approving it for publication was K. Witrisal.

The authors are with the Dept. of DIIES, University “Mediterranea”of Reggio Calabria, Reggio Calabria, 89100, Italy (e-mail: {antonio.iera,silverio.spinella}@unirc.it, ivan.farris.524@studenti.unirc.it).

Digital Object Identifier 10.1109/LCOMM.2013.070913.130392

Product Code (EPC) standard and to be complementary toEPCglobal platforms.

The idea of using the RFID technology to support dataexchanges has already been addressed in the literature. As anexample, the research in [6] demonstrates the feasibility of anRFID tag-to-tag communication system. Differently from ourapproach, in that system tags can talk to each other directly inthe absence of RFID reader as long as an external RF carriersource is available to power them up. In addition, fruitfulpatenting activities have addressed the issue of enabling RFIDreader-to-reader or tag-to-tag direct communication [7]. Thecited studies and patenting activities testify to the great interestin the addressed research topic and confirm that only throughnovel paradigms, like the one we are proposing, it is possibleto implement real RFID ecosystems for IoT scenarios.

In this early paper we will give some ideas on the possiblereference scenarios and applications of our paradigm and pro-pose a way to implement it. Then, we estimate the achievabletheoretical performance in case of a single reader-to-readerconnection and present some measurements of simulated re-alistic performance for small piconets.

II. ENVISAGED APPLICATIONS AND USE CASES

Due to current limitations of RFID technology, only appli-cations that rely on data exchanges at a reduced bit rate fullytake advantage from the proposed paradigm. The interest ina cost-free channel, based on RFID tags largely and freelyavailable in any future environment, will be a strong stimulusto research activities towards optimizing the RFID technologyalso for communication purposes. In Table I a non-exhaustivelist of possible applications of the proposed paradigm, withrelevant reference environments and involved devices, is given.One can notice that it ranges from applications for pre-cise positioning and distributed monitoring and searching, tothose for cooperation and communication among devices. Theparadigm involves both indoor and outdoor scenarios, anddiverse devices including sensors, embedded systems, androbots.

A. The reference scenario

The reference scenario for our proposal is made up of:(i) at least one Master RFID Reader (MR), of a highercomplexity level and equipped with multiple communicationinterfaces; (ii) one or more Client RFID Readers (CRs) ofa very basic complexity level and with an RFID interfaceonly; (iii) a plurality of passive RFID tags (EPCglobal Class1Gen2) enabled to reading and writing operations; (iv) a MasterControl Server (MCS). Specifically, any MR obtains fromthe MCS a univocal 5-bit address, the ID-Master. MCS and

1089-7798/13$31.00 c© 2013 IEEE

FARRIS et al.: INTRODUCING A NOVEL “VIRTUAL COMMUNICATION CHANNEL” INTO RFID ECOSYSTEMS FOR IOT 1533

TABLE IPOSSIBLE APPLICATIONS OF THE PROPOSED PARADIGM

Applications Environments Involved devicesPreciseRFID-basedpositioningand locationtracking

Indoor areas, automatedhomes, museums, expo areas,etc., wherein only RFIDtechnology is available andprecise location required

Low-cost mobile readers (alsoembedded) exchanging datafor cooperative RFID posi-tioning

Short rangecooperationbetweencellulardevices

Generic indoor/outdoor envi-ronments, where cellular de-vices come close and theirowners share same interests(stadium, station, airport, etc.)

Cellular devices exchangingdata (cooperation and controlinformation) at low bit-rateover RFID short links (anal-ogous to Bluetooth)

Distributedmonitoring

Indoor scenarios such ashomes, offices, warehouses;generic outdoor scenarios;Body Area Networks forHealth monitoring; stages ofthe supply chain; etc.

Low-cost miniaturized RFIDreaders distributed in the areaor embedded in objects thatgather data from sensorizedRFID tags, and exchangethem to reach a complexRFID reader connected to theInternet

Distributedsearchengines

Warehouses; museums;libraries; archives; harboryards; etc.

A few fixed multi-technologyRFID readers and manylow cost, mobile, single-technology (RFID) readersin the environment used indistributed searches

Device-to-devicecommunica-tion

Home, factory, and office au-tomation environments, hos-pitals, logistics environments,etc.

Embedded devices with RFIDcapabilities, smart things, in-dustrial machinery, exchang-ing low bit-rate data at a verylow cost to implement collec-tive tasks

Robot controland inter-communication

Indoor or outdoor environ-ments (such as emergency ar-eas, hazard areas, etc.)

Robots in a swarm, exchang-ing: positions, sensed data,and other useful control in-formation in their operationalareas

MR communicate through traditional links, such as WiFi,UMTS, Bluetooth, etc. A NAT (Network Address Translation)protocol is also implemented in the MCS for IP to ID-Masteraddress mapping. The MR creates and coordinates one or moreRANs. A multiplicity of CRs and RFID tags are associatedto each RAN, which is conceptually equivalent to a Bluetoothpiconet. Each Client and each RFID tag can be simultaneouslyassociated to different RANs created by a Master. Master andClients in the same RAN establish a “virtual RFID channel”for data exchange. Figure 1 shows a sketch of the scenario.

III. IMPLEMENTING THE “RFID VIRTUAL CHANNEL”

A first requirement is to define a novel AFI (ApplicationFamily Identifier) and a new Data Format to distinguish thenew method of using tags from the traditional ones (identifiedby pre-existing AFIs and Data Formats). To this aim, wepropose to store the decimal value “24” in the EPC Bank andin the last five bits of the DSFID field (Data Storage FormatIdentifier) of the UM Bank. Besides, a new OID (ObjectIdentifier) is defined and used to store into the UM Bankdata and control information required by the system. Thisincludes a variable number of CPOs (Cluster Packed Objects)plus some additional control fields. The CPO fields includeat least: the identifiers of the source and destination reader(IDRS and IDRD); the RAN identifier (IDRAN); the Masteridentifier (IDM); the addresses of the Clients sequentiallyreleased by the Master for a given RAN (RAL); plus othercontrol fields. The number of CPOs is chosen according tothe available dimension of the UM Bank. Last, a DiscoveryTable is foreseen both into the Master and into each Client to

Fig. 1. The basic reference scenario.

establish and maintain all the available communication paths.Any Discovery Table contains: the Client address, released bythe Master sequentially for a given RAN; the Master identifier;the RAN identifier; the tag identifier derived from the EPCBank memory block; plus some additional control bits. Moredetails on the proposed data structures are available in [8].

A. How to build and maintain a RAN

The method that we propose to enable communicationsthrough an RFID virtual channel foresees three phases: (i)“addressing” phase to manage the reader addresses within aRAN; (ii) “communication” phase during which data packetsare exchanged; (iii) “control” phase to maintain the RAN.

During the addressing phase, the Master initializes the RFIDtags, if required. Besides, Master and Client Discovery Tablesare populated to define for each Master one or more RANsand, for each RAN the data paths (i.e. different RFID tags)to use between any couple of devices. Also, Master andClients read the User Memory Size (UM Size) field of the TagIdentification Bank (TID Bank) memory block to know howmany CPOs can be used. Last, the Master assigns sequentialaddresses to the Clients in a RAN and, accordingly, updatesits Discovery Table.

The communication phase foresees that Master and Clientcheck the “Cluster Map” field of the new data structure tounderstand which CPO are available for reading and writingoperations. For each CPO, a priority level is defined on thebasis of the type of exchanged data. Master and Client proceedto further functional steps finalized to data exchanges (unicastor broadcast communications). During this phase, policies tohandle the readers’ access to the tags used as a virtual channelshall be implemented, as described in the next section.

During the control phase the Discovery Tables are updated.It can be started by either a Master or a Client to check for thepresence of any Master/Client/Tag in a RAN over the time.

IV. HANDLING THE ACCESS TO THE VIRTUAL RFIDCHANNEL

When implementing the proposed communicationparadigm, the RFID readers could mutually interfere(during inventory and access to tags). Although in this initialstage of the research we assume the absence of readersexternal to the considered RAN, still the readers’ coverage

1534 IEEE COMMUNICATIONS LETTERS, VOL. 17, NO. 8, AUGUST 2013

areas partially or totally overlap. This raises two problems:Reader-to-reader interference and Multiple-reader-to-taginterference. The first issue is manifested when two readersoperate at the same frequency. In some extent, it can be facedby the EPCglobal Gen2 dense reader modality [9], whichforesees reader and tag transmissions over separate channels.Multiple-reader-to-tag interference happens when a tag iswithin the coverage areas of more than one reader (this isprecisely the situation that allows to establish a RAN). Thereaders simultaneously transmit and the tag is not able todecode collided signals. Solutions in the literature are notappropriate to our proposal, as these are either centralized[10] (we look for a distributed solution) or distributed[11] but relying on “extra RFID technology” control andsynchronization channels (this contrasts our assumption of apure RFID ecosystem).

We propose to address Reader-To-Reader and Reader-To-Tag interference problems by designing an algorithm of theCSMA family, based on the Listen Before Talk (LBT) [12]and enhanced with a mechanism named EMEB, Echo Mes-sage EPC Bank. According to our LBT-based with EMEBalgorithm, all the readers in the RAN operate over the sameunique radio channel at the same transmission power. Likein the standard LBT, before starting any transmission, eachreader monitors the channel for a random time interval todetect possible ongoing transmissions. If the channel is busy,then the channel sensing activity goes on until the channel isfreed and the reader can implement a further medium accessprocedure. According to the ETSI standard, a reader is allowedto occupy the channel for up to 4s. Following the channelrelease, 100ms must elapse before the same reader can accessthe channel again. This is disadvantageous in the case of aRAN with only two readers; thus, future researches must focuson the optimization of this parameter. In this early stage of theresearch, we assume that, (i) 10ms is an acceptable value forthe condition above and (ii) the hidden terminal problem is notconsidered within a RAN. Obviously, our simple LBT-basedalgorithm will introduce several collisions and useless accessesbecause the readers continuously poll the tags to verify thepresence in their UM of possible messages addressed to them.

To solve these problems, according to EMEB, the Masterwrites signaling information (such as, the decided accesssequence for the Clients) into the tag memory and then readsthis information. This way, the response message from thetag is listened by all the readers in its communication range.This allows the Master to spread the information about theClients’ transmission sequence. In the literature [13] there areexamples of readers that hear and decode response messagesfrom tags interrogated by other readers. This echo-basedmechanism prevents any reader to continuously read the tagUM to look for new messages; it is informed by other readersabout any new information transmitted over the RFID tagvirtual channel. According to the LBT-based with EMEBalgorithm, any Client Reader, after having implemented itsread and write operations, simply cancels its reservation in theEPC Bank, and reads again the EPC Bank. The next scheduledreader thus becomes aware that it is its turn to access thetags. The process is repeated until there are no reservationsin the EPC Bank. The “pure” LBT-based procedure is briefly

activated before any round, to allow new Clients to join theRAN. Anyway, this paper only focuses on static RANs (i.e.no new Clients join the RAN).

To implement the protocol, readers must distinguish sig-naling messages from mere UM reading commands. Thetags used as a communication channel within the RAN areidentified by putting signaling messages into the EPC Bank.This can be done because the EPC Bank of several commercialtags has a dimension considerably greater than 96 bits (i.e. theEPC code length). Signaling messages (a IDRS-IDRD-IDRANtriplet associated to each Client) are, thus, appended to theEPC Code, starting from the 97th bit.

V. PERFORMANCE EVALUATION

By referring to the EPCglobal Gen2 standard, which regu-lates the interaction between interrogator and tags, we com-puted the time interval to successfully transmit a messageunder some ideal assumptions. In our performance assessmentstudies we assume a Bit Error Rate (BER) equal to zeroand the presence of a single tag. This avoids any tag-to-tagcollision problem. In the first part of this section we focuson the scenario in which a Master sends unicast messagesto a single Client through the whole tag UM in conditionsof perfect synchronism. In a subsequent analysis we con-sider a more realistic scenario with a variable number ofClients that access the channel according to the proceduredescribed in the previous sections. The main Gen2 standardparameters [9] are set to the following values: Tari=12.5µs, Reader-to-Tag T rx Rate=54.23 Kbps, Tag-to-ReaderT rx Rate=256 Kbps, DivideRatio=64/3, RTcal=36.875µs, TRcal=83.3 µs, Tag-to-InterrogatorEncoding=FM0,TRext=1, T1=39 µs, T2=39 µs, T3=39 µs, T4=73.75 µs,T5=1500 µs.

Our current objective is just to have an idea on the the-oretical achievable performance levels in terms of Bit Rate[bits/s] and Data Rate [bit/s]. The Bit Rate measures the grossvirtual channel capacity, considering the time required for theoperations of Select, Inventory, and Access and referring toall data exchanged through the User Memory. The Data Rate,instead, takes into account the net channel capacity, withoutconsidering any control information overhead (such as forexample message headers).

The sought performance obviously depends on the qualityof the tags. The write commands are the most energy and timeconsuming. Therefore, the highest impact on the conductedanalysis is given by two parameters: TWrite (i.e. the time a tagtakes to write a 16 bit-word) and MaxWordBlockWrite (i.e.the number of words that the reader is able to write duringa single BlockWrite command). Their values are stronglyrelated to the class of devices available on the market. Inour study (more details on the modeling of the performanceparameters are available in [14]) we focus on three RFIDtag classes: (i) the innovative F-RAM Tag, characterized byTWrite ∼ 0ms and MaxWordBlockWrite=128 [16-bit word], (ii)EEPROM Tag, with TWrite=10ms and MaxWordBlockWrite=4[16-bit word], (iii) Standard Tag, i.e. a virtual tag with themaximum values TWrite=20ms and MaxWordBlockWrite=256[16-bit word] defined by the EPCglobal Gen2 standard.

FARRIS et al.: INTRODUCING A NOVEL “VIRTUAL COMMUNICATION CHANNEL” INTO RFID ECOSYSTEMS FOR IOT 1535

Fig. 2. Bit and data rates vs. UM, 1 master & 1 client; Write command.

Fig. 3. Bit and data rates vs. UM, 1 master & 1 client; BlockWrite command.

Figure 2 shows the theoretical Bit Rate and Data Rate valuesvs. the UM size for a variable TWrite in a scenario with a singleMaster, a single Client, and a single RFID tag, utilizing the“Write Command” method, that is the command that allowsto write a 16 bit-word at a time. Currently, tags with UMcapacity of 1024 bits (corresponding to 8 CPOs per tag) arealready commercially available. Thus, the maximum values ofBit Rate and Data Rate obtained when an F-RAM tag is usedare about 5.2 Kbit/s and 3.1 Kbit/s.

Figure 3 shows the theoretical Bit Rate and Data Rate whenvarying the UM size for a variable MaxWordBlockWrite andfor the same scenario as before. Considering the “BlockWriteCommand” method, the maximum Bit Rate and Data Ratevalues of about 11.8 Kbit/s and 7 Kbit/s are obtained by usingF-RAM tags with UM=1024 bit.

In the following, curves relevant to a performance studyof a piconet with a variable number of Clients and in thepresence of collisions are reported. Figure 4 shows the totalBit Rate and Data Rate values attainable in the RAN byincreasing the UM capacity of the F-RAM tag and the numberof Clients when the “Write Command” method is used. TheMaster distributes the CPOs among the Clients according toa Round Robin scheduling policy. From the figure it emergesthat the rate increases with the UM capacity and decreases asthe number of Clients grows. The performance is compared to

Fig. 4. Bit and data rates vs UM, 1 master & more clients.

ideal cases, labeled “Bit Rate 1 Client Theoretic” and “DataRate 1 Client Theoretic”, corresponding to the maximumattainable throughput and goodput in ideal conditions.

VI. CONCLUSIONS

A new paradigm that relies on the RFID technology toestablish a “virtual channel” for data exchange among devicesis introduced. An initial analysis of the achievable performanceis presented. Still much work is needed to better investigateon all the raised issues. Nonetheless, the assessed performancetestifies to the potentialities of the new paradigm in supportingthe deployment of future RFID ecosystems for the Internet ofThings. Currently, we are implementing a prototype to demon-strate the effectiveness of the proposed solutions through realexperiments.

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