Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+ Olaf Czogalla*, Joachim Schade, Sebastian Naumann *Senior Engineer, Institut f. Automation und Kommunikation Werner-Heisenberg-Str. 1, 39106 Magdeburg, Germany Phone +49 391 990 1442, e-mail:
[email protected]
Abstract In this paper we present a method to transmit spatial-temporal mobility data such as local road closure and incident information in urban road and surface road networks into mobile end devices. Beside road traffic information also e-mobility data such as location and occupancy of battery charging stations are to be transmitted over the transparent data channel of DAB. DAB will replace FM radio in the near future. TPEG standard was introduced by Transport Protocol Expert Group to replace FM based Radio Traffic Message Channel TMC. By mobile devices such as smartphones and tablet computers these short-term information can be received and displayed using a DAB reception interface. Handheld devices are a further alternative to OEM integrated navigation systems and personal GPS navigation systems available as off-the shelf product from after sales market. Relevant road traffic information possess the property to be transmitted unidirectional, e.g. without any backward channel from one transmitter to any number of receivers. This justifies that its distribution over Digital Audio Broadcast (DAB) services is useful and appropriate. The data transmission from one sender to many receivers simultaneously is the most efficient way in terms of costs for equipment and energy. In Europe, the rollout of DAB+ services is presently in full swing. Norway has announced to shut off analog FM radio starting in 2017. Data services such as TPEG road traffic information or slide show data or electronic program guide are transmitted and received according to classic DAB standards [1].
KEYWORDS: Road traffic information, e-Mobility, Digital Audio Broadcast DAB, Transport Protocol Expert Group TPEG
Introduction and state of the art Electric cars and electric buses strongly depend on the availability of charging stations. Particularly electric buses in public transportation have to cover distances longer than the range of their battery for which reason intermediate charging operations are required. Therefore, the schedule of electric buses in public transportation includes predefined charging operations. If electric buses are prevented from reaching their targeted charging station due to an incident, a power failure or a defective charging station, for example, appropriate actions have to be taken by the management center of the public transport company. Compared to conventional buses, it is very important to regard the state of charge of the buses battery when altering the buses schedule. If there is no connection to the GSM network – which is often the case in rural areas in Germany – there is no chance for the bus or the bus driver to contact the management center and vice versa. In contrast, DAB+ messages concerning incidents and limitations with respect to charging stations can be received nearly everywhere as the coverage of DAB has increased remarkably in Germany. Information on functioning and non-functioning or non-reachable charging stations as well as alternative charging stations including technical parameters are very beneficial for electric buses as well as for electric car drivers. Classical real time information on road traffic conditions such as travel times, driving speeds representing the level of service, road constructions, closures and events are communicated primarily using the
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+ Internet Protocol (IP). The increased availability of mobile phones functioning as ubiquitous connected computing devices, facilitates the distribution of mobility information to road traffic users for their individual on-trip information and route choices as well as mode choices. In nearly every major city and metropolitan area in the U.S., Europe and Asia/Pacific such comprehensive traffic information systems have been implemented in recent years. Examples of those platforms that are maintained mostly by public governmental authorities in the U.S. are 511 services that are accessible over various information channels. Likewise, in European and Asia/Pacific countries similar mobility information platforms include public transit information and select opportunities for sharing services to enable even different mode choices to traffic users. In addition to authority maintained traffic information services there have been established various privately based services to promote customer loyalty of car users to car manufacturers. Connected services using IP provide additional traffic information to a closed user group of brand owners. Examples for these services are BMW Real-Time Traffic Information RTTI, Audi Traffic Information over INRIX and TomTom. The service HERE WeGo is provided by Here Global B.V., earlier a division of Nokia/NavTeQ that is owned by a consortium of Audi, BMW and Daimler. The service provides turn-by-turn navigation in offline and online modes enriched by real-time traffic data from various local sources. Google live traffic Google Traffic works by analyzing the GPS-determined locations transmitted to Google by a large number of mobile phone users. By calculating the speed of users along a length of road, Google is able to generate a live traffic map that is displayed by colored road sections representing the level of service and real speeds driven. Waze as a GPS supported navigation system, is an example for a community driven solution for traffic and incident information. Current speeds of motor vehicles using Waze are automatically signalled to its service operator. Its users can submit manually additional traffic information such as road incidents, closures and constructions. As a crowd based solution it comprises also functionalities of a social media service. For use of mobile phones real-time road traffic information is accessible by apps installed under the operation system (Android, iOS, Windows). A mobile GSM connection at least 3G/4G is required for operation of any of the above named traffic information services. Whereas the availability of 3G/4G connections in urban areas is given in most cities, Fig.1 indicates that mobile data communication is still unavailable in greater distances from urban centers on rural surface roads as well as on motorways, depending on network providers (T-Mobile, O2, Vodafone). Instead, for the purpose of data dissemination from one source to many recipients such as traffic information, the broadcast of data using DAB is more efficient, economically and more reliable than using point-to-point data connections of GSM communication. The coverage of DAB in Germany and Europe has been remarkably extended in recent years, which enables a seamless reception of audio and data services in outdoor areas and especially along the motorway system and surface road network where 3G coverage is insufficient. Therefore, traffic data transmission by using DAB data services in connection with TPEG decoded traffic messages is the subsequent step towards advanced on-trip road traffic information. The use of this introduced data transmission technology combined with TPEG coded road traffic information allows not only for a factor 100 faster transmission of information than using RDS, but it is also being used a method of location referencing, that enables to identify any position within urban and rural road networks.
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+
Figure 1
Comparison of mobile 3G coverage (left) with noticeable gaps in less populated areas by complete DAB outdoor and indoor reception coverage in Germany. (Sources: TMobile and digitalradio.de).
Problem statement Short-term lane closures that reduce capacity on roads have a significant impact on traffic flow. Road or lane closures are required to carry out roadworks that are caused by frequent maintenance of street lighting, drainage, and sewer systems, lane markings and more. These closure causes occur in addition to long-term planned construction measures that are publicly announced primarily over internet. Short-term incidents can be transmitted over DAB faster and in a shorter update cycle than over FM radio using Traffic Message Channel (TMC) [2]. Furthermore, in TMC method there are available only a restricted number of location codes which does not allow a precise geographic location reference of random incident events or road closures especially in widely branched urban road networks. These road closure and incident information are collected by local road authorities and were made available over the Mobility Data Marketplace (MDM) [3], a data exchange platform maintained by the German Federal Highway Research Institute (BASt). The data sets are provided to both public and institutional users over the MDM for individual trip planning and on-trip traveller information.
Data collection The source of data is a data pool of roadworks, incidents and road closure information system that was built up in central Germany according to a systems concept to unify collection, processing and use of information on traffic related roadworks and closures. For further information on this system we refer to [6] and [7]. The originally heterogeneously structured data sources were consolidated at the common basis of a standardized road database. Information is acquired at different administrational levels and fed into the unified road closure information system of central Germany, see Fig. 2. Both federal and local administrations act as ITS content providers for road traffic information. Data is collected from the federal level administered road information system for the national motorway network and further supplied to state level and municipal road authorities for the facilitated approval of wide and heavy load transports. For the public end user, among broadcast and variable message sign delivery, a web/app solution was developed. This is accessible over the internet and operated seamlessly by the author’s institution
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+ meanwhile for a medium-term time frame, see [8]. Further, the complete roadworks data set is also provided to the traffic condition forecast model as a required important input. For the delivery to the Mobility Data Marketplace MDM indicated in Fig. 3 the identical roadworks data set is provided as point location and link related data sets including information on traffic impact, duration and recommendations for diversions. Within the domain of Mobility Data Marketplace, the mean for exchange of traffic information is Datex II. Datex II has been developed as a standard for information exchange in Europe and plays a strong role for the implementation of integrated ITS. The flexibility of Datex II allows taking advantage of the inherent data model for the present application and enables to carry out minor adaptations to exchanged data structures. Selected service profiles being defined in Datex II standard as basic elements can be used as provided, such as for example traffic event for traffic condition forecast. The data transfer is organized such that HERE Traffic service is subscribed to the MDM data provided by the pool of traffic data. Using push and pull service mechanisms of DATEX II the subscribed HERE Traffic service obtains the data set from MDM to integrate the information into its service offer. HERE traffic data service comprises all relevant Traffic Message Channel TMC road traffic information on motorways and traffic information on urban roads that are referenced by the German TMC location table as amended from time to time. In addition to that, by the present solution urban traffic information can be referenced by arbitrary positions in the road network using TPEG in connection with WGS-84 and further georeferencing methods.
Figure 2
ITS process architecture of data collection processing and delivery.
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+
Figure 3
Data transfer pathways from data pool to multiple DAB single-frequency networks.
Data processing, transmission and broadcast For the purpose of dissemination over the DAB digital radio channel the data is processed and transferred to a transmitter station. At the transmitter station the data is inserted into a continuous stream of audio and data services that are simultaneously broadcasted over the transmitter network, see Fig. 3. In the present case the spatial-temporal e-mobility data and incident data from the data pool are continuously encoded into TPEG messages respectively data telegrams. The set of TPEG messages contains all relevant road traffic information for the broadcast area and is transferred to the broadcast station using the Internet Protocol. At the broadcast station data services and audio services are combined into a multiplex ensemble named S-ANHALT that is broadcasted over the transmitter station. All transmitter stations of a broadcast area form a single frequency transmitter network. For the present field test it was used a transmitter station operating in band III blocks 11C (220.352 MHz) and 12C (227.360 MHz) that are broadcasting from various transmitter stations within the area of central Germany. In the context of DAB a block is denoted as dedicated frequency range of fixed bandwidth of 1.536 MHz, centred at a so called center frequency. A block can be imagined as a channel to be tuned to receive a certain station. However, in contrast to FM radio one block of digital DAB radio holds an entire ensemble of radio stations (10 up to 20), denoted as audio services as well as additional data services. If the receiver is moving inside the single frequency network such as inside a car, it stays tuned to the initial block. In this event a reception of all audio and data services throughout the geographical area of the broadcast region is guaranteed. The block 5C spans all over Germany to ensure a seamless reception of nation-wide radio station as well as TPEG services. The method of data transmission was developed, implemented and successfully tested to meet the requirements of fast and precise traffic information of an arbitrary number of road users at the same time and priority. Within a definite broadcast area all relevant road closure and incident information are collected and provided such that the data set can be encoded into TPEG messages [5] that are suitable for broadcast as a data service. This data service is an element of a DAB ensemble multiplex. The locations of TPEG encoded data are referenced in the present stage by WGS-84 coordinates. A location reference method that establishes a reference of the given position to an underlying digital road network such as OpenLR is considered and will be engaged in the following stage.
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+
Figure 4
Reception, decoding and visualisation of TPEG coded road traffic data and e-mobility data over transparent data channel of DAB for mobile phones, tablets and off-the-shelf GPS navigators.
Data service reception and decoding For the purpose of DAB data reception, decoding and further processing of broadcasted data it was selected a commercial DAB receiver stick with USB interface. The USB interface connects to the mobile end device that provides computing capability as shown in Fig. 5. The receiver NOXON-DABStick includes a RTL2832 chip set. Other test configurations included tablet PC and desktop PC as an arm-linux cross compiler development platform. With regard to mobile phones a market research revealed that at the time of research there is only one mobile phone including a DAB receiver chipset available from LG named Stylus 2. For the purpose to develop a compact solution the option of using an integrated DAB receiver will be pursued preferably at a further development stage. For reason of availability of hardware and GPL software for DAB receiver it was selected a development option using modular components.
Figure 5
Test configuration of DAB receiver NOXON-DABStick, antenna and mobile phone as computing end device for SDR application and data display.
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+ For the given case we use a Software Defined Radio (SDR) application as a DAB receiver that was developed for execution by the end device be it a mobile phone, a tablet or desktop PC. The signal, being sampled from the DAB receiver stick, contains the synchronous stream of 2 Mbit/s samples of the Ensemble Transport Interface (ETI). The ETI stream is transmitted over the USB interface into the mobile device and by this transferred to the SDR-DAB receiver as illustrated in Fig. 4. The DAB transport stream contains all audio services (i.e. radio stations) and data services such as TPEG, Electronic Program Guide EPG and Journaline text messages as well as image slide shows. DAB audio services are not in focus of our application. Instead, the task of the SDR-DAB receiver is to extract the transparent data stream including binary data, TPEG messages or other data from the received DAB transport stream. During reception of DAB ensemble the parallel extracted continuous TPEG stream is decoded by a separate application into textual messages that are displayed for review be the user. These textual messages are human readable and being further processed for a geographical reference. A supplementary use of the data for specialized navigation applications is envisaged. These enriched data sets are especially useful for example as an additional navigation aid for heavy and wide load overland transports.
Implementation of software defined radio and test results Software Defined DAB receiver In order to enable for a reasonable implementation of the SDR systems concept in frame of the given project goals it was selected an open source library and DAB software project that was made available under a GPL General Public Licence by Katwijk [4]. Subject of this project is the realization of a DAB radio receiver as a pure software solution that obtains the signal from a DAB capable dongle with RTL2832 chip set as already pointed out in the above chapter. By using SDR the analogue hardware is reduced to a minimum and the complete signal processing is realised digitally by software components in the mobile or desktop computing end device. As a first step an implementation of the SDR system was achieved by compilation of the DAB project including control elements for the receiver front-end that are provided by the QT-library as a user interface. In subsequent steps, also command line versions of this project were created in order to increase compactness and portability of the solution. Important elements of the SDR application are software components that perform the signal processing steps of input filtering, Fast Fourier Transformation, time and frequency synchronisation, demodulation of the OFDM (Orthogonal Frequency-Division Multiplexing, the modulation method of digital signal transmission in DAB) symbols to decode the information stream into the Fast Information Channel and Main Service Channel. The fast information channel contains data blocks with information about the organisation of audio and data services within the transmitted ensemble. The main service channel contains itself multiplexed audio and data services in up to 64 sub channels. In Fig. 6 is shown the front end application for control of the implemented SDR receiver. Basic control elements are integrated to enable tuning the DAB receiver to required band and block of reception frequency. Different options can be selected as output sinks to connect sound output devices or dump audio into files. This is enabled both for radio services as well as for data services. Different DAB SDR sticks can be configured to be used as input devices. To select the respective service for decoding its name must be highlighted in the ensemble box.
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+
Figure 6
DAB receiver front end of the SDR application with control elements for selection of band, block and service including graphical display of OFDM symbols (above left).
In Figure 6 is highlighted the local test service “TPEG IFAK Test” as the very data service we provide, containing the TPEG data to be extracted from main service channel. The reception quality is indicated by signal to noise ratio in combination with parameters of DAB reception such as bitrate, blocks per frame, number of carriers, block length etc. The quality of the received OFDM signals can be monitored by the display of the complex in-phase/quadrature signal (I/Q-signal) that represents one dot for each received OFDM symbol (left side of the user interface). Data extraction from DAB stream Data that is transmitted and received in a DAB data service is being extracted as a binary stream from the entire DAB ensemble and handled such that it can be provided to separate decoder application in the mobile device. Figure 7 displays the extracted binary stream of the received TPEG test service in raw binary format before decoding it into textual readable TPEG messages. Some of the textual information can be recognized from an ASCII representation of the binary data. The TPEG message container includes street names and additional message content in form of readable text. For the present application it was selected the TPEG – TEC (Traffic event compact) container format, for encoding and decoding of referring road closure and incident information. Other relevant TPEG message containers have been considered for subsequent use such as RTM Road Traffic Message, PKI Parking Information, TTI Traffic and Travel Information. For a more detailed description on TPEG messages the reader may be referred to [5].
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+
Figure 7
Extracted binary stream of TPEG test service for transmission of short-term road closure and incident information.
TPEG Decoder In the sequence of data processing of the extracted binary TPEG messages follows the TPEG decoder. It receives input from the extracted transparent data channel and decodes automatically any recognized TPEG message. At the current stage its output is written to standard output for further processing or logging. In Fig. 8 the decoded message of the identical road closure information, that is shown in Fig. 7, is displayed as human readable text. For the road traffic user it is most important to know the remaining time frame of the concerned road construction, the closure, respectively the end date of the closure. Further, the cause of the incident is coded as “roadworks” with an indicated short text to explain location and type of construction measure. The location can be referenced either using an underlying road network or using coordinates that are independent from a certain digital road map, by means of WGS-84 coordinates in the form of longitude and latitude. The additional step of creating the location reference depends on the used road map in the mobile device and is intended to be solved by further processing steps in the referring end device.
Figure 8
Decoded TPEG message in human readable format of an urban road closure message located apart from TMC location.
Geographical location referencing In order to enhance the representation of the transmitted traffic information it was developed a geographical location referencing method using WGS-84 coordinates that are contained in each of the TPEG messages. The textual output from the TPEG decoder is re-directed to a parser and converted to the GeoJSON format that is particularly well suited for combination with a geographical mapping display software framework. As mapping display framework it was selected the open-source Leaflet JavaScript library for mobile-friendly interactive maps. In the Leaflet application we used OpenStreetMap (© Contributors) as underlying map layer. The map layer browser display is built upon tiles that can be
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+ preloaded in advance for a defined geographical region in order allow for a complete independence from wireless GSM connectivity, while the DAB reception is constantly maintained and updates of road traffic information are being transmitted in rapid cycles. The implementation was developed for the first step as a desktop application under Linux-Ubuntu that is fully functioning as described above. The programming toolchain utilized for implementation of the SDRDAB receiver enables a cross-platform development and additional implementations under Android and Raspberry Pi. Especially the development for Android based systems will be pursued in the further course of the project. The resulting of interaction of the described components of DAB receiver, TPEG decoder and location referencing to receive, process and display on-trip roadworks information is shown in Figure 9. It is noted that the displayed message in the map refers to the TPEG message that is decoded by the TPEG Decoder (Fig.8) from the extracted binary stream shown in Fig.7. The current geographical extent of decoded TPEG messages spans the central German state of Saxony-Anhalt. The total amount of data processed is not more than 80 kBytes for the entire data set, which is a particularly low amount of data and allows for an efficient data transfer, handling and processing. The low amount of data to be transferred allows for extremely high update cycle rates of less than 5 seconds required for the entire data set which causes nearly no delays for traffic information updates. These beneficial transmission properties allow to achieve a finer granularity in the dissemination of road related information. As a result the quality, integrity and credibility of road traffic information can be enhanced remarkably.
Figure 9
Geo-referenced image of a DAB TPEG messages combined with an open street map display for rendering on a mobile device.
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+ Satellite Navigator Solution using MDM Personal GPS navigators for after-sale retrofitting of car dashboards are widely available. Various models of different brands are on the market featuring different transmission pathways for real-time road traffic information. Basic connectivity is provided in devices that enable WiFi connections for map updates and static navigation information such as general points of interest. For this type of connectivity an available local or mobile WiFi tethering hotspot is required (Example: Becker active.6s EU). Advanced connectivity is provided in navigation devices equipped with built-in SIMcard to 2G/3G/4G wireless GSM data interface for life time use (Example: TomTom GO 5200). Live traffic updates using broadcast technology DAB+ do not require an internet connection (Example Garmin nüvi LMT DAB+) as well as do not cause connection costs. Traffic updates are based on HERE Traffic service. Real-time road traffic data are transmitted in TPEG format with a location references to the internally installed mapping bases of the satnav device (Navteq). Presently, Garmin navigator and HERE service are bundled exclusively for product lifetime at no recurrent costs. Satnav devices from latter manufacturer are the only ones that are equipped with a DAB reception interface according to a market research. In order to take advantage from these off-the shelf products the dissemination of real-time traffic data will include the delivery of this content to commercial service providers as described above. As a consequence the provision of real-time traffic information for the German state of Saxony-Anhalt was also achieved for dissemination over HERE Traffic service that is broadcasted in a nation-wide multiplex for reception in personal navigators, see exemplarily the indication of a roadworks construction including potential delay of travel time, Figure 10. The traffic data is converted into DATEX II format and provided over the German Mobility Data Marketplace [3] to be fed into the information service for DAB transmission.
Figure 10 Mobile personal GPS navigator displays urban roadworks information transmitted over DAB depending on significance for route to destination.
Conclusion and Outlook The described and implemented method to disseminate local road traffic and incident information for urban road and surface road networks includes two alternative transmission pathways to reach end users
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Distribution of spatial-temporal e-mobility data and incident information for mobile devices using TPEG over DAB+ equipped with mobile devices such as smartphones and tablet computers as well as with personal satellite navigators. For the data transmission technology it was DAB selected because of its advantages with respect to efficiency and coverage. Although DAB standard was developed and introduced already decades ago, the use of DAB technology for data transmission from one source to many users is not as prevalent as assumable. Mobile wireless data exchange technologies such as 3G/GSM have advanced into application areas that have been reserved for broadcast technologies for several times. But for the purpose of real-time traffic information and other relevant mobility data the use of Digital Audio Broadcast still be of great advantage in terms of technical effort, rapid data transmission as well as both energy and cost efficiency A good example for such an existing service is the Here Traffic service that is broadcasted in a nation-wide covered DAB+ ensemble of the single-frequency network of band III block 5C. TPEG messages of this service are received directly by personal satnav devices and being displayed at the device. Although, it must be stated, that this service is currently primarily focused on traffic condition on motorways. Its origin of information is the same as used for TMC channel over FM. Traffic information in cities or rural areas is still lacking, because of legal, organisational and technical problems related with existing ITS architectures. By the suggested locally broadcasted services, additional road traffic information is provided for a limited region with no need for a nation-wide dissemination. But this information can be very useful for local traffic users for shorter trips within that region. The continuation of the work in this area will be focused on development of cross-platform implementations for the DAB-SDR application in order to broaden hardware basis and usability of our solution.
Acknowledgement Research contained within this paper benefited from participation in the project “Datapool2TPEG - Data exchange between ifak data pool and DAB broadcast multiplex” commissioned by the Media Institution Saxony-Anhalt. Special credits go to Jan van Katwijk, Pijnacker, The Netherlands for his continuing development and support of the SDR software library under General Public Licence GPL, while making DAB reception of audio and data service with low-cost consumer devices achievable.
References 1.
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2.
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Schade, J; Czogalla, O.: Road construction information platform for cities, counties and motorways in the state of Saxony-Anhalt, http://www.movi.de/sperrinfo/index.html, 2012-2017.
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