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Hindawi Publishing CorporationInternational Journal o Distributed Sensor NetworksVolume , Article ID ,pageshttp://dx.doi.org/.//

Research ArticleSurvey of the DASH7 Alliance Protocol for 433MHz WirelessSensor Communication

Maarten Weyn, Glenn Ergeerts, Luc Wante, Charles Vercauteren, and Peter Hellinckx

CoSys-Lab, Faculty of Applied Engineering, University of Antwerp, Paardenmarkt , Antwerp, Belgium

Correspondence should be addressed to Maarten Weyn; [email protected]

Received July ; Accepted October

Academic Editor: Jianhua He

Copyright Maarten Weyn et al. Tis is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

MHz is getting more attention or Machine-to-Machine communication. Tis paper presents the DASH Alliance Protocol,an active RFID alliance standard or MHz wireless sensor communication based on the ISO/IEC -. First, the majordifferences o MHz communication compared to more requently used requencies, such as . GHz and / MHz areexplained. Subsequently, the general concepts o DASH Alliance Protocol are described, such as the BLAS networking topologyandthe different OSIlayer implementations, in a top-down method. Basic DASH eatures such as the advertising protocol, ad-hocsynchronization and query based addressing are used to explain the different layers. Finally, the paper introduces a sofware stackimplementation named OSS-, which is an open source implementation o the DASH alliance protocol used or testing, rapidprototyping, and demonstrations.

1. Introduction

Machine-to-Machine (MM) communication can be orga-nized using a wide area network (WAN), such as a mobilenetwork, or a personal or local area network (PAN/LAN).Sensor communication is typically done using a PAN witha backbone connection using a wired or wireless WAN [].According to Beale and Morioka [], the most requentlyused technologies or wireless PAN are Wi-Fi (IEEE .),Zigbee (which is based on IEEE ..), Z-Wave, and

KNX-RF. Te requencies used by these technologies are. GHz, , and MHz. Fadlullah et al. [] also identiyBluetooth, Ultra Wide Band (UWB) and LoWPAN asprominent technologies suitable or MM communication.Besides the aorementioned requencies, MHz is alsogaining relevance in the area o MM communication, asstated by uset-Peiro et al. [].

Niyato et al. [] also identiy an neighborhood areanetwork (NAN) which typically connects different homesusing a so called concentrator to a base station o the WAN.Tey ocus on home energy management. Such applicationconsolidate the search or other low-power RF technologieswhich have a longer range than typical PAN technologies.

Tis paper will introduce such a technology: the Dash Alli-ance protocol.

Te DASH Alliance protocol (DA) [] isan activeRFIDalliance standard or MHz wireless sensor communica-tion based on the ISO/IEC - standard maintained bythe DASH Alliance. ISO/IEC - denes parameters othe active air interace communication at Mhz. DA isbuilt on top o an asynchronous Wireless Sensor Network(WSN) Media Access Control (MAC). In contrast to typ-ical WSN standards such as ZigBee (built on top o IEEE

..), the DASH specication denes a ull unctionalRFID tag. Tis means it does include high level unctionalityoptimized or RFID applications. However, it can also beextended or non-RFID applications. In contradiction tolegacy RFID systems [], DA supports tag-to-tag commu-nication.

DASH uses a BLAS network technology. BLAS isan acronym or Bursty, Light, Asynchronous, Stealth, Tran-sitive. Burstymeans abrupt data transer unlike streamingcontent such as video or audio. Light reers to a limitedpacket size ( bytes). Multiple consecutive packets arehowever supported.Asynchronousis one o the key conceptso DASH. Communication is command-response based


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International Journal o Distributed Sensor Networks

without any periodic synchronization. Stealth reers to theact that DASH does not need any periodic address broad-casting, which means nodes can choose to communicateonly in trusted environments.Transitivereers to the mobiletransitional behavior o devices and/or tags.

Tis paper will rst explain the major differences o

MHz communication compared to more requently usedrequencies in Section . Subsequently, it will describe thegeneral concepts o the DA specication in Section .Finally, it will introduce a sofware stack implementationOSS- inSection .

2. 433 MHz Based Sensor Communication

As stated beore, MHz is not the most widely usedrequency or MM communication, although it has someserious advantages. First o all, it is an unlicensed band whichis almost worldwide applicable; however, it is not harmo-nized. Te band spans rom . to . MHz. Second,due to its requency, it has better propagation characteristicsopposed to higher requencies. Tis is discussed later in thissection. However, there are also some disadvantages. Tewavelength at the center requency . MHz is . cm.Tismeansan /4 antenna hasa length o .cm. Moreover,the bandwidth o the band is only . MHz. Tis limits thedata rate o the communication at this requency. Making MHz ideal or low-power low data rate communication.

Some research has already been done in comparing thepropagation aspects o MHz towards other requencies.

uset-Peiro et al. [] compare the propagation peror-mance o MHz and . GHz and show that MHz hasa better communication range despite the effects o havinga larger Fresnel zone. Tey also show that channel hoppingwill not solve multipath propagation effects since the channelcoherence bandwidth is larger than the whole MHz band.

Isnin [] compares path propagation in multiooredbuilding or , and MHz. Te MHz band hasa higher bandwidth then the MHz band which enablesa higher data rate. Tey show that in a waveguided corridorenvironment with line-o-sight, higher requencies have anadvantage. However, MHz has a better penetration capa-bility. Tis leads to a lower path loss-level or multi-oorpropagation with the number o oor obstruction greaterthen two.Zhang et al. [] state thatit is very complex to modelsmall scale indoor propagation.

As already stated, the regulations o MHz transmis-sions are not harmonized.

In Europe, ESI states or short-range devices (SRD)that the band rom . till . MHz can be used ornonspecic SRD with mW Effective Radiated Power (ERP)when the duty cycle is less than % or when then channelspacing is smaller than kHz or with mW ERP withoutduty cycle limitations [].

In USA, FCC states that the eld strength can onlybe V/m at meter or periodic applications and V/m at meter otherwise [, ]. Tis correspondswith an ERP o. dBm or periodic control applicationsand. dBm otherwise.

: DA devices classes.

Device class ransmits ReceivesComplete

eatureset

Wake-onscancycle

Alwayson

receiver

Blinker

Endpoint

Subcontroller

Gateway

3. DASH7 Alliance Protocol

Tis section will describe the basic concepts o the DASHAlliance protocol (DA).

DA denes our different device classes as shown inable . A device can switch between classes. A blinkerdeviceonly transmits data and does not use a receiver. For this,a blinker, or example, cannot perorm carrier sensing. Asecond class is an endpoint. Tis is a typical low powerdevice which can transmit and receive data. An endpoint alsosupports wake-up events. Tis enables the device to receiverequests and typically transmit a response. A gatewaydeviceis in most cases the device which connects the DA networkto another network. A gateway is obliged to support all DAeatures and is never offline. It always listens unless it istransmitting. A subcontrolleris a ull eatured device as well,but it is not always active. It uses wake on scan cycles, just likethe endpoint devices. Tis will activate the device or shortchannel scanning.

DA describes a ull unctional RFID tag. Every devicesupports one or more o the aorementioned+ device classes.For this a correctly congured tag is ully unctional withoutthe need or specic application code. Although, in mostcases specic application code will be added.

DASH supports two communication models: pull andpush. As in most RFID systems, dialogs between tags andinterrogators are query response based (the pull model), asshown in Figure (a). Tis request response mechanism isdescribed by the DA Query Protocol(DAQP). Data transerinitiated rom the tags to the gateway on the other hand isbased on the push model. Tis is shown inFigure (b). Tisapproach can, or instance, be implemented as an automatedmessage or beacon which is sent on specic time intervals. InDA, this system is calledBeacon Transmit Series.

DASH denes two types o rames: a foreground frameand abackground frame. Te oreground rames are regularmessages which contain data or data requests. Backgroundrames on the other hand are very short broadcast mes-sages. Background rames are or instance used by the DA

Advertising Protocol (DAAdvP) or rapid ad-hoc groupsynchronization. Tis DAAdvP enables a low power wake-up o those tags which are interrogated in the pull model.

Te DA specication involves all OSI layers [] anddescribes the protocol in each o those layers. However, someo the eatures are still under revision or reserved or utureextensions.Figure gives an overview. Te remainder o thissection describes the DA implementation o the application


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RequestResponse

Request

Resp

onse

(a) Pull model (e.g., query protocol)

Data

Da

ta

(b) Push model (e.g., beaconing)

F : Communication models.

layer and how its eatures are supported by the underlyinglayers.

Te DA Query Protocol, the Advertising Protocol andthe beaconing concept will be used as an example to clariythe different layers.

.. DA Application Layer. Te application layer typicallydescribes the interaction between the application sofwareand the communication stack. Te application layer enablesthe sofware application, which is used by the user, to be ableto access communication resources, identiy communicationpartners, and activate certain communication concepts.

In DA, this layer describes the so called ApplicationLayer Protocol(ALP), thele access protocol,the cryptographicauthentication protocol, and access to thesensor subprotocol.Te ALP makes it possible to send specic data, structuredby the application. Tis is in contrast to DA specic dataprotocols which are described in other layers. Te crypto-graphic authentication description is at the time o writingstill under revision, but the underlying layers already supportthe necessary data elds. Te sensor subprotocol is based onISO - [] and species the representation o specicsensor data. Te le system protocol describes the accessmethods (read, write, and execute) to the le system whichis described in the presentation layer.

: File data access template.

File ID Start byte offset Byte accessing Data

byte bytes bytes bytes

: Beacon transmit period list.

Channel ID Command

parametersDAQP call

template Next beacon

byte byte bytes bytes

Accessing a le is based on theFile Data Access Template,shown inable . Te File ID reers to a specic le (seeSection .: presentation layer). Te other two values denethe location in the le to be read rom or written to. Te dataeld is the actual data to be written.

A beacon transmit series uses an automated processin the Data Link Layer. Tis process is enabled, disabledand congured by a conguration le described in thepresentation layer.

.. DA Presentation Layer. Every DA device needs tosupport a number o data elements. DA has three typeso data elements: Indexed Short File Series Blocks (ISFSB),Indexed Short File Blocks (ISFB), and Generic le Blocks(GFB). All o these blocks have their own permission code.Tis code denes the read, write an execute rights o the rootuser, current user and guests. An ISFSB is a collection o ISFBles. ISFB Files are stored as structured, mixed-data strings.ISFB IDs speciy different les. For example, x species

the network conguration, x species device capabilitiesand supported eatures, and x species a time controlledsequence or beaconing,. . .. Te beaconing will be urtherexplained inSection ..

Te data denedby thepresentation layeror beaconing isshown inable . TeChannel IDis the physical layer Chan-nel ID, dened inSection .. Te Command Parametersarebiteld parameters that map to data link layer and DAQPparameters. TeDAQP Call Template denes the le or leseries template which will be used as data. Te Next Beaconis the number o ticks between the beacons. A tick is 210

seconds (. ms) and is the basic time unit used by theDA Protocol.

Te network conguration settings (ISFB le with IDx), determines the active device class (gateway, subcon-troller, endpoint or blinker). It will also dene i the deviceis capable o using Forward Error Correction (FEC), hi-ratechannels, and other eatures which are used by the data linkand physical layer.

.. DA Session Layer. Te session layer species whichevents may trigger session initiation or scheduling. Itdescribes management and prioritization o multiple sched-uled sessions and idle state o the data link layer. Moreover itsupports a power level auto-scaling ramework to optimizebattery usage. Tis technique will adapt the transmission


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OSI layers D7A features

Application File Crypto Sensor

accessaccess ALP

CryptoPresent. ISFB

table

Session Sessioncontrol

Transport CA MNQP

Optional Netw. Lay.Network M2AdvP M2NP MNDP

multihop security

LLC Guarding Background Foreground Broadcast Data link Automated ChannelDLL CSMA frame frame unicast security beacon scanningMAC UID VID

PHY Channel CCA GFSK PN9 FECselection

F : OSI layers with DASH specication.

Request Response Response Response Response

Response completion timeout (Tc)

F : Nonarbitrated wo-Party Dialog Example.

power to nd an optimum between power consumption anda stable wireless connection.In a standard situation the subcontrollers and endpoints

operate afer a wake-on event. Te wake-on events denedby DA are automated channel scanning, automated beacontransmit series (both described in the data link layer), andany application layer relevant events (e.g., sensor event or apassive scanning).

Te session layer creates a random session number orany new initiated session. Tis random number is used inthe DAQP as a dialog ID. Te session layer also keeps tracko a devices network state. Te possible states are associated,scheduled, promiscuous, and unassociated.

A host supporting the DA Advertising protocol in thenetwork layer also has to implement a session stack to enablesession scheduling. Tis session stack keeps track o thedifferent initiated sessions. Ad-hoc sessions have a higherpriority than scheduled sessions (such as beaconing) and arealways added on the top o the stack.

.. DA Transport Layer. Generally, the transport layerprovides end-to-end communication services. In DA, thisis covered by the DA Query Protocol Transport Layer(DAQP). It is responsible or communication structuring,ow- andcongestion control, andaddressing beyond the sub-net ltering. In this section, rst the communication dialogs

o DAQP will be described. Aferwards the commandstructuring and nally collision avoidance.

... DAQP Dialogs. Te transport layer supports twotypes o dialogs: Nonarbitrated Two-Party Dialog(NAP) and

Arbitrated Two-Party Dialog(AP). Te NAP is a one-timedialog between a requester and a responder or responders.Te requester is a single host which sends a single request.Te responders can be any host addressed in the request.Besides the query itsel, the requester sends an addressingmethod, a list o channel IDs which can be used or theresponses and two time parameters (,). Te ResponseCompletion Timeout , denes within which time rame

the responders must complete their responses. Te ResponseGuard Time is a parameter used by the Carrier SensingMultiple Access (CSMA) process o the data link layer, asexplained in Section .. An example o such a dialog isshown inFigure .

In contrast to a NAPdialog,the APdialogis a persistentdialog between requester and responders. AP enables theglobal and local addressing, which is an important eatureo DA. An example is shown inFigure . Te rst requestincludes global and local addressing. Te global addressingnoties a large group o potential responders to stay alertor a query. Te local addressing queries a subgroup o thesepotential responders. All responders have to respond within


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Global +local Local Local

Request 0 Response Response Response Request 1 Response Response Request 2

(Tc)

F : Arbitrated wo-Party Dialog Example.

, aferthe next query with local addressing will be sent.When no new request is sent afer the dialog terminates.Tis method enables a DA interrogator to query a largegroup o tags in a well-structured way. As discussed, in theupper layers an interrogator can send a query with a leread or write command. Tis method is also used to sendan acknowledgment group query. For this, the response o allresponders can be acknowledged using one method insteado sending individual acknowledgments.

... Command Structuring. Te transport layer also denes

the structure o the command-response protocol (the com-mand structure). Te command structure is based on tem-plates. It contains the addressing method, the command codeand command extension.

In a request, the addressing method can be broadcast,unicast, multicastor anycast.In case o broadcast andunicast,the command contains a command extension and commanddata. In case o anycast, the command also includes a globalquery. A global query is a query using global addressing, asdescribed in the previous subsection. In case o multicast,the command contains a global query and local query or alocal query with an acknowledgment template. A response isalways unicast and can contain command data or an error.

Te command code contains a command type. It denesi the command is a response, an error response, a Nonarbi-trated Two-Party Dialog,or anArbitrated Two-Party Dialog.In the latter case, it denes whether it is an initial request,a intermediate request or a nal request. Tese dialogs areexplained in the previous subsection.

Te command code also contains an opcode. It species ithe command wants to announce a le or do an inventory orcollection. An inventory means it will request a list o les. Acollection means it will request the content o some le. Tecommand can also dene a so called application shell whichmeans it encapsulates an applications specic data.

And nally, the command extension denes i CSMA is

used or responses and which type o collision avoidance isused. Tis is explained in the next subsection.

... Collision Avoidance. A third important componento the transport layer is collision avoidance (CA). In casea message is sent rom the transport or higher layer, thetransport layer is responsible or collision avoidance and owcontrol. Te data link layer is responsible or the CSMAprocess as is explained in Section .. Te CSMA-CA processuses thevalue rom a response or rom upper layers andcalculates theCollision Avoidance Timeout PeriodCA:

CA= C responseduration. ()

Background Background Background Foreground

advertising advertising advertising request

ETA 500 ETA 2 ETA 0 Request

F : Example o the use o the DA Advertising Protocol.

Tis is the time within a packet has to be transmitted tomake sure it has been sent beore .

Tree CSMA-CA and ow control models are denedby DA: Adaptive Increase No Division (AIND); Random

Adaptive Increase No Division (RAIND); Random IncreaseGeometric Division(RIGD).AIND and RAIND use a xed slot length which is

approximate the duration o the transmission. In AIND, theCSMA process starts in the beginning o a slot. In RAIND,the CSMA process only starts afer a random delay whichis smaller than CA. In RGID the slot duration decreasesollowing CA0/2

+1 and CSMA only starts, as in RAIND,afer a random delay.

.. DA Network Layer. Te network layer denes the Back-ground Network Protocolwhich is used or the DA Advertis-ing Protocol(DAAdvP) and the Foreground Network Protocol

which is used or queries, responses and beacons.

... Background Network Protocols. Background networkprotocols contain very short background rames (BF). Back-ground rames are described in Section .. Currently, onlythe DA Advertising Protocol is dened as a backgroundnetwork protocol. DAAdvP is used exclusively or rapid,ad-hoc group synchronization. It is a transmission only,broadcast protocol. DAAdvP is used to notiy hosts abouta request which will be send in the uture. Te requesteroods the channel with background rames which contains atime span until when the request will be sent. Te responderhosts receive the background rame while listening ora back-

ground rame during background scanning (as described inSection .), and can go to a sleep state until the request isplanned to be received. Te responder only has to receiveone background rame to know this timing. Tis leads toa very low power consumption optimized method o ad-hoc synchronization.Figure shows an example o such asynchronization train.

... Foreground Network Protocols. wo oreground net-work protocols are denedby DA: theDA Network Protocol(DANP) and the DA Datastream Protocol (DADP). TeDANP is an addressable, routable protocol which is usedor the DA Query Protocol in the transport layer. Te


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: Background rame structure.

Subnet Payload CRC

byte bytes byte

: Foreground rame structure.

Length Headers Payload Footer CRC

byte bytes bytes bytes bytes

DADP is a generic data encapsulation protocol, whichcontains no routing or addressing inormation. It allows ormaximum exibility towards the upper layers. Te DADP is,or example, used by theApplication Layer Protocol.

Te DANP supports network layer security and stan-dard two hop routing. It implements unicast, broadcast, mul-ticast and anycast addressing to support the DAQP Dialogs.

.. DA Data Link Layer. Te data link layer (DLL) o DA,species the data link ltering, addressing, the dialog models,MAC processing, rame construction and the eld deni-tions.

... Data Link Filtering. Incoming rames are ltered bythree processes. Te rst one is a Cyclic Redundancy Check(CRC) validation with a bit CRC eld. Te calculationuses the CCI CRC polynomial. I the CRC validationspasses, subnet matching or link quality assessment can beperormed in an arbitrary order. Te subnet is constructedwith a bit specier and a bit mask. I link qualityassessments is enabled, the link budget should be higher than

a predened link quality threshold. Tis makes urther rameprocessing possible.

... Data Link Addressing. Related to addressing, the datalink layer o the DA protocol species an ISO []compliant Device ID maniesting in a xed Unique ID(UID)and a dynamic network-uniqueVirtual ID(VID).

Te UID is a EUI- (Extended Unique Identier) com-pliant ID []. It contains a or bits OrganizationallyUnique Identier (OUI) assigned by the IEEE RegistrationAuthority based on a or bits serial number. Te VIDis a bit ID which is supplied by the network administratorand should be unique within the network.

Te data link layer only supports unicasting and broad-casting. I a target Device ID is present in the rame, it will beprocessed as a unicast message. Te Device ID o the ramewill be matched with the destination devices ID. Te ramewill only be processed by the upper layers when a matchexists.

... Frame Structure. As already mentioned in the net-work layer, the data link layer has background rames andoreground rames. A background rame is a xed length byte rame, proceeded by a sync word o class (dened inSection .). Te structure o a background rame is showninable .

TC TL

Foreground Foregroundrequest response(s)

Frame detected Request ltered and addressed

TLenabled

F : Overview o the oreground rame dialog model.

A oreground rame has a variable length, up to bytes,proceeded by a sync word o class . Te structure is shown inable . Te length byte is the total number o bytes,includingthe length byte and the byte CRC.

Te headers contain inormation related to optional datalink layer security, address control (source and optionaldestination id), the subnet, and the estimated radiated powero the transmission (X EIRP). Tis value can be used by thereceiving node to estimate the link budget.

... Data Link Dialog Models. Following the same concepto oreground and background rames, two related dialogmodels are dened.

A Background Dialog (not really a dialog) starts when abackground rame starts transmitting and ends as soon as itnishes transmitting.

A Foreground Dialog is a dialog between devices and isused to support the DA Foreground Network Protocols. Anoverview is shown in Figure . Te response contention perioddenes the time rame in which responses can transmit.Telisten perioddenes the time period aferin whichthe requester can send another request.

... MAC Processing. Te data link layer supports an auto-mated scanning method. Using this scan scheduler the datalink layer can scan or background or oreground rames.

In a background scan, the DA device rst checks theenergy level. Only i the level is sufficient does it try to detectthe correct sync word (class or background scanning). Inoreground scanning the device rst searches or a sync wordo class .

Using the automated Channel Scan Series, the data linklayer can ollow a predened sequence o background ororeground scans. Te series is dened by a list o channelIDs (explained in Section .), scan types (background or

oreground), a Scan Detection imeout SD, and a imeuntil next scan eventNSE. Te SDis the duration the scanon a specied channel ID and type will be executed. TeNSEis the time when the next scan event in the list will beexecuted.

Te Beacon Transmit Series is another automated datalink layer process. Tis process sends predened beacons atspecied time intervals and channel IDs.

Te data link layer is also responsible or MAC channelguarding. ANonguarded Channel(NGC) is a channel whichdoes not require CSMA. AGuarded Channel(GC), howeveris a channel which does require CSMA. CSMA is alsoimplemented by the data link layer. In this case CSMA-CA


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: Spectrum ID allocation per channel class.

Channel class Spectrum ID

Base

Normal A C E

Hi-rate D

B Blink C

Spectrum . MHz . MHz

ensures that a transmission is only executed when a channelis unguarded. Afer a transmission a guarding period isspecied in which no transmission can be perormed romanother host.

.. DA Physical Layer. Te physical layer denes the spec-trum utilization and channels, the modulation, the symbol

encoding, and the packet structure.

... DA Spectrum. Te spectrum allocation and channelsare shown in able . Te spectrum ID species whichchannels and channel classes are used. Te Channel ID isthe Spectrum ID which is logically ORed with the encodingoption. Te value is x in the case Forward Error Correc-tion (FEC) is used, otherwise the value is x. Te base andnormal class have a bit rate o . kbs. Te hi-rate andblink class have a bit rate o kbs. Te normal class hasa channel bandwidth o kHz. Te hi-rate and base classhave a channel bandwidth o kHz. Te blink class hasa channel bandwidth o kHz. Gaussian requency shif

keying is used as modulation technique.

... Symbol Encoding. As a last stage beore transmission,a data whitening [] technique based on a -bit psuedo-random generator (PN encoding []) is used to avoid a DCoffset in the transmitted data. For this, a PN decoding stagewill be the rst decoding step at the receiver.

Beore the data whitening step, an optional orward errorcorrection (FEC) can be executed []. For FEC, D usesconvolution encoding with constraint length , ollowedby a bit interleaving executed on bit symbols. Teinterleave/deinterleave process lowers the impact o bursty

errors since it separates adjacent symbols.

... Packet Structure. On the physical layer, the ramestructure o the data link layer is preceded by a preambleand a sync word. A preamble o typically bits on the baseand normal channels and bits on the hi-rate and blinkchannels o alternating and s is used to enable the receiverto calibrate the data rate circuit. Te preamble is ollowed bya sync word. Te sync word can be o class or class anddepends on the use o FEC. Afer the sync word, comes thepacket payload, which is dened by the upper layers. In allcases DA uses the big endian ormat (most signicant byterst).

4. OSS-7

OSS- [] is an ongoing sofware stack implementationo theDASH Alliance Protocol mainly developed by the CoSys-Lab o the University o Antwerp. OSS- is being developedwith its main goal to provide a reerence implementationo the DA specication. Tis means that code clarity andstructure is more important than perormance.

OSS- is implemented in ANSI C to be as compatible aspossible with exas Instruments (I) Code Composer Studio(CCS), gcc and mspgcc.

Te OSI layers, as shown in Figure , are used as structureor the implementation. All the layers are implemented aspluggable layers, which makes it easier to benchmark otherimplementations o a specic layer (e.g., a new proposal or aMAC implementation).

Besides the OSI layers, there are two additional layers:Hardware Abstraction Layer (HAL) and the Frameworklayer. Both layers implement an API which can be calledrom any other layer. Te HAL makes an abstraction ohardware aspects such as I/O, buttons, LEDs, CRC sofwareor hardware implementations, UAR, timers, and the Realime Clock (RC). Currently a HAL implementation isprovided or I MSP, I Stellaris (ARM Cortex-M) andposix hardware. Support or ARM Cortex-M is plannedor the near uture. Te ramework API provides hardwareindependent unctionality like logging andqueueing which isused within the stack but can also be used by the application.

Te PHY layer consists mostly o an abstract interace.Tis Radio Abstraction Layer (RAL) is required to beimplemented by radio chip specic code. Tis plugin systemeffectively allows us to support multiple radio chips. One canswitch between them at compile time. Currently Is CC

(which is system-on-chip composed o a I MSP and anI CC sub Ghz transceiver) and an external CC(with communication through SPI) are supported. Supportor SMicroelectronics SPIRI RF chip will be implementedin the near uture.

Figure gives an overview o the le structure o OSS-.Te different OSI layers are visible. RAL and HAL can beextended to different hardware.

Besides the sofware stack itsel, the OSS- project willalso provide additional PC-based tooling or diagnostics,testing, and conguring tags running the stack.

.. Implementation. Figure shows the devices which areused to implement and test OSS-. Device (1)is a CoSys-Labdesigned3 3 cm CC based tag with PCB antenna. Tisdevice is typically used as an endpoint or blinker poweredwith a CR battery or indoor sensor communication.Device () show a small extension board which is used tointerace with the JAG programmer anda serial connection.Device () is a WizziMote and WizziBoard rom WizziLabpowered by AA batteries. Device () is the exas InstrumentEZ-Chronos- which typically acts as endpoint orblinker. Device () consists o the nodes which are usedin device (1) and device () but altered to be used as asubcontroller. Device () is a Raspberry Pi with an extension


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CC430

STUB RAL

CC1101 Physical layer

fec CC430

phyHAL STUB

Data link layer OSS-7Button, crc, led, . . .

Network layer log

Transport layer Framework Queue

Session layer Timer

Presentation layer

Application layer

F : File structure o OSS-.

(1)

(2)

(3)

(4)

(5)(6)

F : Devices used to implement OSS-.

board and device (1) is altered to be used with an externalantenna. Tis device is used as a gateway in our test settings.As an example, devices (1) and () are used by Stevens

et al. [] to test robot localization using DASH.

5. Summary

Tis paper gave an high-level overview o the DASHAlliance Specication and introduced OSS-, a stack imple-mentation or this specication. DA is built or low-powersensor communication with integrated concepts suchas glob-al and local querying, automated beacon transmits series andautomated channel scanning. DA describes a ull unctional

RFID device.OSS- is embedded stack implementation or DA which

currently supports CC, CC, and ARM Cortex-M. Itis build using a modular structure ollowing the DAs ISOlayering and a separate hardware and radio abstraction layer.OSS- ocuses on transparency and code clarity to be usedas a tool to explain the specications and test new protocoladaptations.

Conflict of Interests

Te authors declare that there is no conict o interestsregarding the publication o this paper.

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