The radio spectrum is about to get even busier, as Europe’s Galileo satnav system starts services, at the same time the European Space Agency (ESA) tests novel satellite-based telecommunication services. Supporting these developments from the ground, ESA’s new custom-built Telecommunications and Navigation Testbed Vehicle will measure the resulting signals from all over Europe.
Adapted from a Mercedes Benz Sprinter van, this unique measurement vehicle has been delivered to ESTEC by Austria’s Joanneum Research institute. “This is a dual-purpose vehicle, suitable for both telecommunications and navigation system testing,” explained Simon Johns of ESA’s Radionavigation Systems and Techniques Section.
“For navigation, we have the Galileo constellation coming on stream, as well as the stepping up of ESA’s GNSS Evolution programme — designing what comes next after Galileo’s first generation.”
The four wheel-drive vehicle can host a three-person team, and is crammed with dedicated navigation and telecommunication monitoring equipment.
Testbed vehicle screen.
“One of the main goals driving the design was to have an ‘easy to adapt’ test platform suitable to set up test campaigns for different mobile satellite systems and standards that would require different types of antennas and specific receiver/transmit equipment,” explained Olivier Smeyers of ESA’s Communication-TT&C Systems and Techniques Section.
“On the telecommunications side, there is a continuous effort to enhance current and create new mobile satellite-based broadcast and interactive services via the evolution of current systems or developing new standards,” Smeyers said. “Testing in the field is an essential element for validating and eventually establishing evolved or new standards. The vehicle has built-in multimedia equipment, including storage and control computers, multimedia gateway, passenger LCD screens, cameras and microphones, to serve this purpose.”
The vehicle features include two removable roof plates to mount specialized antennas (one currently hosts the antenna of a Broadband Global Area Network satellite terminal for Internet connectivity and multimedia and data streaming), an 8-meter-high telescopic mast capable of carrying 25 kilograms, a rubidium atomic clock synchronized to GPS time with nanosecond accuracy, a high-end spectrum analyzer and oscilloscope for signal measurements, and mobile temperature sensors to monitor the rack equipment.
A fish-eye video camera incorporating onscreen GPS timing and positioning performs continuous recording of its surroundings — to throw light on high buildings, trees, or other factors that might affect results.
Internal and external generators yield up to 5 kilowatts to keep everything running — sufficient power to supply two typical European households.
“The challenge was to fit in all the equipment and provide the necessary power and air conditioning, while still weighing less than 3.5 tonnes,” said Thomas Prechtl of Joanneum Research. “Exceeding this weight would have meant drivers would have needed a special license, and potentially limited its operations in some European nations.”
Steve Spriggs was cited for holding his smartphone in his hand using it for navigation while driving. California code 23123 reads, “A person shall not drive a motor vehicle while using a wireless telephone unless that telephone is specifically designed and configured to allow hands-free listening and talking, and is used in that manner while driving.” Spriggs fought the ticket, saying the law does not apply to looking at maps.
But a judge of the appellate court said holding a phone to look at a map is distracted driving — the same as sending a text message — and the law applies. “Our review of the statute’s plain language leads us to conclude that the primary evil sought to be avoided is the distraction the driver faces when using his or her hands to operate the phone. That distraction would be present whether the wireless telephone was being used as a telephone, a GPS navigator, a clock or a device for sending and receiving text messages and emails. This case requires us to determine whether using a wireless phone solely for its map application function while driving violates Vehicle Code section 23123. We hold that it does. “
The National Safety Council has noted that there is no research or evidence that indicates voice-activated technologies eliminate or even reduce the distraction to the drivers’ mind.
Furuno Electric Co., Ltd., has announced that new multi-GNSS receiver chips eRideOPUS 6 and eRideOPUS 7 will be available in August. The new receiver chips are multi-GNSS compliant single-chip LSIs, capable of concurrently receiving signals from multiple satellites in GNSS systems and satellite-based augmentation systems, as well as Japan’s Quasi-Zenith Satellite System. Both chips receive signals from GPS and Galileo; the eRideOPUS 7 also receives GLONASS signals.
The ability of concurrently receiving GNSS/GNSS augmentation signals from multiple satellites from different satellite services means that the receivers have more probability of acquiring a greater number of satellites at any single time. Subsequently, position stability as well as accuracy will be greatly improved, minimizing the chance of a position lost. Also, the receiver chips incorporate an enhanced level of noise rejection capability, implementing the anti-jamming function as well as the improvement of multipath mitigation.
Time-to-first-fix capability of the existing eRideOPUS 5 (no more than 1 second when hot started) is retained in these new receiver chips with a combination of A-GPS compatibility and self-ephemeris extraction. Moreover, the position update rate of the new receiver chips is greatly improved, achieving a 10-Hz update (every 0.1 second), which is twice as fast as the capability achieved by eRideOPUS 5.
The new receiver chips are capable of dead-reckoning navigation, using a gyro sensor and vehicle speed pulse signals, a gyro sensor and an acceleration sensor, and wheel tick data taken from a CAN-Bus network, achieving high positioning accuracy even in locations where satellite signal reception is not available, such as inside tunnels.
In May 2013, Furuno is planning to start the delivery of evaluation kits for the receiver chips so that third-party manufacturers can evaluate the feasibility of incorporating the receiver chips into their products, and in August 2013, the new compact GNSS receiver module GN-86/GN-87 as well as
dead-reckoning-capable GV-86/GV-87, using these new receiver chips, will be made available for automotive navigation systems as well as eCall systems.
The Metron2 is a multi-function cellular-connected telemetry device capable of making remote fill-level readings in tanks containing liquids and gases. The device’s integral display allows the unit to be used also as a local gauge and for system set up and testing. An optional pulse-counter board allows the device to take external meter readings.
The Metron2 is wide-area-network connected with the Telit GE864-QUAD V2 cellular module and self powered from an internal battery. The Metron2 can be powered from different sources, including an internal battery or an external 6-24Vdc source. It is often not economically feasible to run power to the site for remote telemetry installation, the companies said, such as the cryogenic gas monitoring segment where it is important that the device be on and available to be polled any time, day or night. For this market, Powelectrics developed a solar-powered system.
The solar-powered telemetry system allows the unit to remain always on and connected to the GSM/GPRS network so the server can make contact at any time with instant reading requests. Equipped with the Metron2, a tanker truck can be dispatched to best matching customer locations according to volume available in the tanker and volume required by customers, efficiently exhausting the tanker’s full supply of product instead of transporting it back to base saving fuel and removing the risk of the returned product contaminating the storage or process facility, the companies said.
Knowing how much product is in the customer’s tanks makes it possible to plan when and which truck should make deliveries. This translates into fewer miles driven to deliver the same amount of product and therefore a significant reduction in costs. There is also a dramatic reduction in CO2 emissions. There are also accompanying operational benefits, including fewer emergency shipments, reduced customer service organization and reduced sales resources. These benefits translate into a balance sheet boasting reduced levels of finished goods and raw materials inventory.
The European Chemical Industry Council (CEFIC) has been encouraging more extensive use of Enterprise Resource Planning (ERP) tools to improve supply chain efficiency. According to the Department for Transport in the UK, by 2015, total traffic on the roads will have grown by over 30 per cent compared to 2000 levels and the CBI has estimated that road congestion currently costs the UK up to £20 billion annually.
Telit’s GE864-QUAD V2 ultra-compact, low-power, quad-band GSM/GPRS 3GPP Release 4 module integrated in Powelectrics’ Metron2 has one of the industry’s broadest certification profiles in its class, making it easily deployable anywhere in the global market, Telit said. Modules in this family are capable of data rates of 48Kbps GPRS Class 10 also supporting 9.6Kpbs Circuit Switch Data (CSD) transfers ensuring connectivity in poor coverage areas. The GE864-QUAD V2 family features one of the market’s most compact Ball Grid Array (BGA) package measuring 30 x 30 x 2.8 mm and an extended operating temperature range of -40°C to +85°C, making it suitable for outdoor-environment mobile applications such as the Metron2.
“The last couple of years have seen a dramatic upturn in demand for our product as users of telemetry become comfortable with the reliability and more aware of the benefits that telemetry brings. We continue to develop our already well proven solutions helping drive down the total cost of ownership and therefore reducing the payback time. Telemetry has never been so affordable,” said David Oakes, sales director, Powelectrics. “We realize the need to be flexible in what we offer. Some customers want a complete solution from us encompassing hardware, hosted software and SIM cards whereas others just want the hardware. It’s also vital that data is delivered where it is needed which often means us providing some form of automated interface into the clients systems, delivering data in a customized format.”
The 2014 Rolls-Royce Wraith coupe is using GPS to make a smooth ride even smoother.
Unveiled at the 2013 Geneva Motor Show, the Wraith is the fastest, most powerful car Rolls-Royce has ever made at $320,000 ($245,000 euros). The Wraith’s eight-speed automatic transmission is linked to a GPS receiver. The car uses satellites to constantly determine what road you’re driving on and in what conditions, then uses the data to anticipate when to shift gears.
For example, it can downshift the moment a hill or curve is approached, which helps with both performance and fuel economy, Rolls said. The nav system also compiles real-time traffic data from cellphones in commercial vehicles and taxis, and uses the data to update the travel route every three minutes.
The debut of Satellite Aided Transmission technology takes the power train to a new level of effortless delivery, the automaker said, allowing the car to “see into the future.”
According to the Rolls, Satellite Aided Transmission uses GPS data and the navigation system to scan the road. It anticipates his next move based on location and current driving style, then automatically chooses the optimum gear on the eight-speed transmission. “Power is delivered effortlessly for you, so you can surge through every corner, round every roundabout and into every slip road smoothly,” Rolls-Royce said.
The high-tech doesn’t stop with GPS. The Wraith has a heads-up display, voice command support and an infotainment system with multi-touch trackpad and 10-inch screen.
Start saving your pennies. The Rolls goes on sale this fall.
A new technology to combat dozing off when driving is being developed by two universities with industry partner Ficosa. The drowsiness alerter, Somnoalert, is a smartphone application that uses inertial sensors and GPS data to detect movements that are characteristic of nodding off at the wheel, such as deviation from the driving lane or sudden corrections. A later prototype also incorporates biomedical sensors to analyze respiration data.
“One of the main causes of car accidents is drowsiness, especially on long highway trips,” explains Santiago. “Most monitoring systems developed in the last few years have been integrated systems that need to be connected to the car’s system. Our device combines our group’s expertise in sensors and biological data analysis with FICOSA’s vehicle know-how, and is completely portable.”
“Accidents related with drowsiness have a very high social and economical impact, that the key automotive industry players are facing as a whole, in order to reduce current accident statistics,” said Alan Montesi, who heads the project for FICOSA.
Huawei, a global information and communications technology (ICT) solutions provider, unveiled a series of products heralding the company’s first foray into telematics solutions at the 2013 Mobile World Congress, being held this week in Barcelona, Spain.
Huawei showcased its vehicle-compatible 3G and LTE communication modules, MU609T and ME909T, its 3G mobile hotspot, DA6810, and its 3G onboard diagnostic (OBD) box, DA3100. Huawei’s products for vehicles provide stable wireless solutions in diverse environments regardless of weather conditions, terrain, or reliability of power supply, providing new development opportunities for the automotive industry, and unsurpassed convenience for car owners.
“Huawei is excited to welcome in an era of smart vehicles with the availability of products that integrate wireless communications and automotive electronic technologies,” said Kevin Liu, vice president, Mobile Broadband Division, Huawei Consumer Business Group. “Huawei’s telematic solutions are designed to enable cars and other transportation vehicles to exist in a seamless wireless mobile environment, so that users are truly able to enjoy the benefits brought about by ICT services.”
The MU609T and ME909T are Huawei’s first 3G and LTE communication modules for vehicles. They are both pin-to-pin compatible, and cater specifically to the working enviroment temperature and power consumption of the automotive industry. The MU609T can support up to 14.4M under the HSPA+ network, and the ME909T can support up to 100Mbps under the LTE network. Both modules are pre-installed with GPS and eCall. In addition, the FOTA remote firmwire upgrade capability makes it possible to integrate new technologies into existing MU609T and ME909T modules. The strengths of MU609T and ME909T have been recognized by leading global car manufacturers, and will be integrated into the wireless communication systems of some of the world’s top vehicles in the near future, the company said.
The DA6810 3G Wi-Fi Box creates 3G Wi-Fi hotspots in mobile environments to provide high-speed internet connectivity on-the-go. Once installed with the HUAWEI DA6810 3G Wi-Fi Box, a vehicle becomes interactive, high-tech and networked, providing owners with a high-speed internet and audio-visual entertainment experience, Huawei said.
The DA3100 is an on-board diagnistics (OBD) data transferring system that enables insurance providers and fleet management companies to retrieve information such as location, vehicle conditions and driver habits. This in-car system transfers information in real time through a 3G network to the telematics service provider (TSP) platforms of various third-party entities. It also enables vehicle owners to activate the car horn, headlights and windows remotely via smartphone apps. The DA3100 is powerful yet easy to install, is not limited by geographical region or vehicles types, and can be activated upon installation, Huawei said.
A new system developed by Universidad Carlos III de Madrid (UC3M) researchers uses sensors to improve the ability of GPS to determine a vehicle’s position compared to use of conventional GPS devices by up to 90 percent.
The prototype can guarantee the position of the vehicle to within 1 or 2 meters in urban settings, the researchers said.
Sensor Fusion. The prototype system incorporates a conventional GPS signal with those of other sensors (accelerometers and gyroscopes) to reduce the margin of error in establishing a location. “We have managed to improve the determination of a vehicle’s position in critical cases by between 50 and 90 percent, depending on the degree of the signals’ degradation and the time that is affecting the degradation on the GPS receiver,” said David Martín, a researcher at the Systems Intelligence Laboratory (LSI – Laboratorio de Sistemas Inteligentes) at UC3M. The system was jointly designed and developed by LSI and the Applied Artificial Intelligence Group (GIAA – Grupo de Inteligencia Aplicada Artificial).
The margin of error of a commercial GPS, such as those that are used in cars, is about 15 meters in an open field, where the receiver has wide visibility from the satellites. However, in an urban setting, the determination of a vehicle’s position can be off by more than 50 meters, due to the signals bouncing off of obstacles like buildings, trees, or narrow streets. In certain cases, such as in tunnels, communication is lost, hindering the GPS applications reaching Intelligent Transport Systems, which require a high level of security.
“Future applications that will benefit from the technology that we are currently working on will include cooperative driving, automatic maneuvers for the safety of pedestrians, autonomous vehicles or cooperative collision warning systems,” the scientists comment.
Integration of GNSS antenna of rover receiver and IMU in a platform over the roof of the vehicle.
The greatest problem presented by a commercial GPS in an urban setting is the loss of all satellite signals. “This occurs continually, but commercial receivers partially solve the problem by making use of the urban maps that attempt to position the vehicle in an approximate point,” Martín said. “These devices can indicate to the driver approximately where he is, but they cannot be used as a source of information in an Intelligent Transport System like those we have cited.”
The basic elements that make up this system are a GPS and a low-cost inertial measurement unit (IMU). The latter device integrates three accelerometers and three gyroscopes to measure changes in velocity and maneuvers performed by the vehicle. Then, everything is connected to a computer that has an application that merges the data and corrects the errors in the geographic coordinates. Enrique Martí of UC3M’s GIAA explains, “This software is based on an architecture that uses context information and a powerful algorithm (an unscented Kalman filter) that eliminates the instantaneous deviations caused by the degradation of the signals received by the GPS receiver or the total or partial loss of the satellites.”
The current prototype can be installed in any type of vehicle. It is already working on board the IVVI (Intelligent Vehicle based on Visual Information, pictured above), a car that has become a platform for research and experimentation for professors and students at the university.
The LSI and UC3M researchers working on this “intelligent car” can capture and interpret all of the information available on the road, and that drivers use. To do this, the team is using optical cameras, infrareds and lasers to detect whether drivers are crossing the lines on the road, or whether there are pedestrians in the vehicle’s path, as well as to adapt the speed to the traffic signals and analyze the driver’s level of sleepiness in real time.
Next Steps. The researchers will analyze the possibility of developing a system that makes use of the sensors that are built into smartphones, because intelligent telephones are equipped with more than ten sensors, such as an accelerometer, a gyroscope, a magnetometer, GPS and cameras, in addition to Wi-Fi, Bluetooth or GSM communications.
“We are now starting to work on the integration of this data fusion system into a mobile telephone,” said Enrique Martí, “so that it can integrate all of the measurements that come from its sensors in order to obtain the same result that we have now, but at an even much lower cost, since it is something that almost everyone can carry around in his pocket.”
Telematics Detroit — scheduled for June 5-6, in Novi, Michigan — is a conference and exhibition focused on the entire telematics ecosystem. In 2012, 1800+ executives attended along with 100+ industry speakers.
Key topics this year include:
The Ultimate End-to-End Telematics Platform: Dispel the “killer app” myth to adopt an approach to connectivity that eschews the next big thing in favor of a holistic suite of connected services that encompasses CRM, HMI and content.
Turn the Car into a Money-Making Machine: Subscription-only models have failed to ignite mass adoption of connected vehicle services. Discover how to create a flexible micro-transactional platform that aligns with the service and payment demands of consumers.
Make Big Data Useful Data: Tackle the proliferation of vehicle generated information to debate the granularity of data collection required to provide OEMs with data sets relevant to optimizing the driving and vehicle ownership experience.
The Telematics Trojan Horse: Debate whether strategic partnerships with the titans of CE, including Apple, Google and Microsoft, will result in diminished OEM influence or translate into the ability to attract tech. loyal consumers and close the automotive innovation gap.
The Infotainment Ecosystem Reinvented: BMW, Ford and GM announce their connected car visions to gain cross-industry buy-in. Analyze whether opening up APIs and SDKs will attract third party developers by creating higher volumes to support a truly auto-centric business case.
Accurate, Reliable, Available, Continuous Positioning for Cooperative Driving
By Scott Stephenson, Xiaolin Meng, Terry Moore, Anthony Baxendale, and Tim Edwards
Adoption of network real-time kinematic GNSS positioning can lead to major improvements in vehicle localization, although implementation must overcome some real-world challenges. This article assesses the extent of GNSS signal outage in a motorway environment. The average total GNSS outage period and the average time to resolve ambiguity for the network RTK solution can help assess complimentary sensors for a ubiquitous positioning system.
Real-time vehicle localization is one of three key enabling technologies for the concepts of vehicle-to-vehicle and vehicle-to-infrastructure (V2V and V2I, collectively termed V2X, see opening graphic), a classification of intelligent transport systems (ITS). The further enabling technologies are ad-hoc dynamic networking of agents, and accurate dynamic local traffic maps. Jointly, these require that positioning be accurate, reliable, available, and continuous.
A natural evolution in road transport, V2X promises to deliver the next major safety breakthrough. The concept moves away from vehicles making individual decisions about road safety, as in advanced driver assistance systems, and towards a cooperative driving approach that shifts the emphasis from collision protection to collision prevention. The U.S. National Highway Traffic Safety Administration estimates that V2X technology can avoid or minimize up to 80 percent of collisions of unimpaired drivers, and that even a small number of deployed vehicles will provide tangible safety benefits.
Network RTK GNSS positioning, like V2X applications, requires a communication system; and by its nature V2X has a positioning solution requirement. Thus it is envisioned that network RTK will play an essential role in the implementation of V2X systems. The consensus between car manufacturers and research organizations is that the future of V2X communication lies with Dedicated Short Range Communication (DSRC) devices, and a large pilot study is currently under way. However, in the short term many V2X applications could be achieved using existing technology, such as cellular communication, offering a legacy solution, and initiating early uptake of V2X applications.
Previous research by the Nottingham Geospatial Institute (NGI) at the University of Nottingham showed that network RTK positioning can provide a high-accuracy positioning solution during real-world trials, but also revealed two areas of concern: the loss of the fixed-integer ambiguity during satellite line-of-sight outages; and the fragility of the data communications service that delivers the real-time correction information. During road tests, a fixed-ambiguity network RTK solution was available for less than 50 percent of the time on United Kingdom (UK) roads.
Network RTK Vehicle Positioning
Figure 1. OS Net reference station network in Britain, owned by Ordnance Survey.
Networks of continuously operating reference stations (CORS) extend across Europe, North America, Australia, and East Asia. Networks vary in size from five or six reference stations for agriculture to systems of hundreds of CORSs providing national or regional service. Figure 1 shows the location of the OS Net CORS run by Ordnance Survey in Great Britain.
Figure 2 shows the main advantage of network RTK as compared to traditional RTK. The individual reference stations on the left suffer from the spatial decorrelation of errors as distance between reference and rover receivers increases. Adequate vehicle positioning would require individually operating reference stations to be placed approximately 20–30 kilometers apart. However, a CORS network can be used to develop a model of differential corrections, as shown at right, from which a rover receiver can interpret RTK correction information and use this during the computation of its position. The geometry of a CORS network allows two adjacent reference stations to be located up to 80–100 kilometers apart without degrading the accuracy, although in practice most systems tend to locate them closer together than this. This is essentially a reduction from 30 reference stations per 10,000km² for conventional RTK, to 5–10 reference stations for network RTK, delivering high-precision services to virtually unlimited users.
Figure 2. The improved navigation performance from RTK (left) to network RTK (right).
It is expected that the CORS networks will become a critical part of a country’s spatial infrastructure, and countries like the UK are leading the way. This makes network RTK one of the most promising positioning technologies for road vehicles and ITS applications.
As shown in previous research, network RTK can deliver a vehicle positioning accuracy of better than 5 centimeters, and in real-world tests this level of accuracy had an availability of 41–45 percent, depending on the environment. It was also found that the correction information was available via the GSM network for more than 80 percent of the time. In these same tests, the total time without any GNSS position solution (network RTK, DGNSS, or stand-alone) was up to 16 percent in a motorway environment. Network RTK was able to provide lane-level positioning accuracy, but the sensitivity of the technique to GNSS signal loss and coverage of the communication network had a significant effect on availability. GNSS outages could be caused simply by passing under a road bridge, and the network RTK solution would be lost, although there would continue to be a DGNSS solution for a short period. Finding effective solutions to these current barriers, which prevent wide adoption of network RTK, is a key enabling step for ITS.
Accuracy Assessment
In much more controlled tests to assess the accuracy of network RTK on a dynamic vehicle, the network RTK GNSS receiver was compared to an inertial navigation system (INS). This test was carried out using the NGI roof laboratory, which houses a 120-meter rail track running an electric locomotive.
Both the network RTK receiver and the INS used the same antenna, fed separately through a signal splitter. The network RTK solution was recorded in real time onto an SD card in NMEA GGA format. The INS data was recorded and post-processed in a tightly coupled solution using a continuously operating dual-frequency GNSS receiver base station located inside the rail track circuit. There were no recorded GNSS outages as there is a clear-sky view from the roof laboratory.
The antenna point was also tracked using a total station, recording observations at 10 Hz stamped with GPS time. Although the accuracy of the tracking mode of the total station is not high enough to assess the accuracy of the network RTK solution (because of time synchronization issues), it ensures that any gross errors in GNSS observations that could affect both the network RTK and INS solutions did not occur.
The results in Table 1 show that the network RTK solution consistently performs to a high accuracy, giving a low standard deviation from the mean in all directions. Listed are three laps of the rail circuit recorded at different times. There are a small number of epochs that encounter large differences of more than 200 millimeters, such as during laps 2 and 3, although these appear to be very short-term anomalies, possibly caused by dynamic GNSS signal multipath or delays and message loss in the communication system.
Table 1. Comparison of the tightly coupled (GPS+IMU) solution with the N-RTK solution.
The worst absolute accuracy is shown during lap 3, although even in this case, with a mean of 21 millimeters and 99 percent of the observations lying within 15 millimeters, this solution still delivers a solution within 36 millimeters of the ground truth. 50 percent of the network RTK observations are within 1 millimeter of the mean difference between the two solutions, showing remarkable consistency and precision.
Challenge: Comm Signal Strength
A fundamental aspect of network RTK is the delivery of reference station data used in the processing of the receiver’s position. Although there are various methods used to deliver this data, the most secure and reliable method involves transmitting raw reference station observations, so that the receiver may perform the calculation of the position with all possible data. This provides the highest integrity. The vulnerability here is not the algorithmic method used to transmit the data, but the communication system, in three ways:
There is no connection between reference and rover receivers.
There is data loss from the connection.
There is an unacceptable delay in the transmission of the data.
Lack of Coverage. The preferable communication system is to use mobile Internet over the GSM/GPRS cell network, which is already well established. The major network operators claim over 99 percent coverage of the population in the UK, but this does not take into account physical and local conditions such as land and building obstructions, atmospheric conditions, and inter-ference from vegetation and other
radio signals.
A 2011 BBC survey in the UK found that when users had a cell-phone data connection it was 3G for 75 percent of the time (2G otherwise), but significant “notspots” include major rail and road networks. An ongoing study by OpenSignalMaps has found that a 3G service is only available 58 percent of the time. A 2011 government report detailed the extent of 2G and 3G services, shown in Figure 3. Areas with poor data communication coverage (below 50 percent) pose a significant problem for network RTK in vehicles.
Figure 3. 2G (left) and 3G (right) coverage by geographic area in the UK: green, >90 percent; yellow, 70–90 percent; blue, 50–70 percent; purple, 25–50 percent; red,
Data Loss. Continuity tests show that when using GSM/GPRS mobile communications to transfer the network RTK corrections, the availability was approximately 88 percent, and the connection could be lost after a few hours of continuous use. This can be caused either by SIM cards that use dynamic IP addresses, creating interruptions when renewing the addresses, or where voice data was prioritized on the network. Other research has shown that a typical mobile Internet connection (a combination of wired public Internet and GPRS) suffers from approximately 20 percent data loss.
Message Delay. A network RTK receiver imposes a transmission time limit on the correction messages that are used to fix the common integer ambiguity (in this case, the Leica GS10 limit is 10 seconds), although messages younger than 60 seconds can be used to give an accurate DGNSS solution. Messages older than 60 seconds result in the receiver only being able to output a standalone position, by which time the accuracy will decay beyond vehicle positioning requirements. Earlier research found the typical mobile Internet connection suffers from an average delay of 0.85 seconds.
Challenge: GNSS Outages
The majority of the transport infrastructure is outside and has a clear view of the sky, particularly away from heavily urbanised areas. However, the receiver gets no warning of impending signal obstruction, so that even momentary obstructions such as an overhead gantry on the motorway can cause significant loss of positioning accuracy, and often causes a receiver to output no solution at all, as shown in Figure 4. Here the vehicle is traveling in a northern direction in lane 1 of the left-hand carriageway and passes underneath a series of bridges at a motorway junction. This causes both GNSS outages and deteriorated positional accuracy, so much so that the vehicle is positioned in the southern carriageway (note that the underlying map image is of unknown accuracy).
Figure 4. The typical effect of overhead obstructions on vehicle GNSS positioning.
GNSS outages can occur in several ways: the obstruction of the GNSS signals can lead to a loss of signal lock; a momentary obstruction or partial obstruction can cause cycle slips to occur (during carrier-phase positioning); if the visible satellites at the rover receiver are not the same as at the reference receiver, then the ambiguity cannot be resolved; there may be intentional or unintentional signal jamming or interference; and if the receiver assessed the integrity or accuracy to be poor then it may not provide a solution.
NGI test vehicle.
Experiment Set-Up
The test vehicle was equipped with a GNSS receiver and antenna, receiving real-time corrections using a GSM/GPRS connection. The signal strength was measured simultaneously using the Android application RF Signal Tracker on an Android-based mobile phone.
The data recorded includes: GNSS raw data, RINEX format; network RTK real time output, NMEA format; GSM signal strength, CSV format. As the experiments were not intended for the analysis of the accuracy of the GNSS receiver, there was no need to utilize the ground truth system onboard the NGI test vehicle.
RF SIGNAL TRACKER. Android application and mobile phone used to record the GSM signal strength (left), and GNSS receiver (right).
Test Environment. Two test scenarios were chosen for the experiments. To assess the GNSS signal outages, the test vehicle was driven along the M1 motorway, a length of approximately 100 kilometers. The M1 is a major road transport artery linking London in the South to Leeds in the North of England, typically with three or four lanes in each direction. This route passes under 214 overhead obstructions (northbound and southbound directions), of known classification (gantry, footbridge, road bridge). This scenario was chosen as the environment is quite rigid, allowing repeatable tests, and it is the area in which future ITS technology is most likely to be adopted first.
To test the variation of GSM signal strength in real-world conditions, a small circuit was chosen close to the Nottingham Geospatial Institute (shown in Figure 5), which incorporates a variety of environments from open sky to bridge underpasses, and dense tree coverage. Using a repeatable path allows the identification of issues that are attributable to problems with the communications link as opposed to other issues (such as hardware problems and GNSS signal outages), and despite the short distance, the loop also provides a wide range of GSM signal strengths. During the experiments to follow, the data was measured during three consecutive laps of the circuit.
Experiment Results
GSM Signal Strength. The variation in color along the NGI test route is an indication of the RSSI (Received Signal Strength Indicator). In this area, the RSSI varies between –50 dBm and –105 dBm, which are the typical maximum and minimum strengths of a cellular network. This is despite the assessment from the network provider that this entire area delivers high-speed Internet and email. Figure 5 also shows the subjective rating and expected performance of the RSSI.
Figure 5. The GSM signal strength around the NGI circuit in Nottingham, with the subjective RSSI ratings.Table 2. The spread of RSSI observations recorded during the trials around the NGI circuit.
Table 2 details the RSSI observations measured during the signal strength trials around the NGI circuit. The range of values shows the typical maximum and minimum RSSI values experienced by a cell-phone user (other than no signal being received). The signal strength is recorded every 5 meters, in order to achieve a good geographic spread across the area (as opposed to biasing the results with observations recorded whilst the vehicle is stationary). The RSSI observations do not correspond to a typical Gaussian distribution, suggesting that there are external influences on the strength of the signal and the handover between one cell tower and the next.
Figure 6 shows an increase in the age of correction (AoC) of the messages following a drop in signal strength (RSSI) to approximately –100 dBm. This is visible from the peaks in the age of correction message to over 8 seconds. The graph shows three laps of the NGI circuit, noticeable by the repeated pattern of signal strength. The increase in the AoC occurs at approximately the same geographic location on each lap — an area in the northwest of the circuit that suffers from weak signal strength, as seen in Figure 5. The received signal strength is the sum of the direct and indirect (or reflected) waves, varying with distance between a series of maximum and minimum values. On a moving vehicle, the RSSI will vary with time as it moves between these maximum and minimum values, and is especially complicated in urban areas where there may be no direct waves at all, and waves are propagated by a series of reflections. A moving receiver also suffers from a Doppler shift in the received signal’s frequency.
Figure 6. The effect of GSM RSSI on the age of correction messages.
During network RTK positioning, the receiver considers messages older than 10 seconds unusable for a fixed network RTK solution, although messages younger than 60 seconds can be used to give an accurate DGNSS solution. This scenario has a brief occasion during the loop in which loss of the network RTK solution is attributable to weak GSM signal strength.
A close inspection of Figure 6 highlights a slight delay between the drop in RSSI to –100 dBm and the increase in the AoC. This delay needs further analysis, but is assumed to relate to the slower update rate of the ionospheric and tropospheric corrections (10 seconds and 60 seconds respectively). There are also periods of increased AoC that are uncorrelated with a drop in RSSI, for which there is no clear explanation, although none of these occasions results in a loss of the fixed ambiguity network RTK solution.
Eighty cell handovers were recorded during the trials, which is higher than average as this area is liable to carry a large volume of cellular traffic (there is a university, a large hospital, and major roads, as well as general housing and business properties). The cell handovers showed an average improvement of +1.2 dBm from just before the handover until just after. The maximum improvement is +22 dBM, although there are occasions when the RSSI gets worse, the biggest fall in received signal strength being –12 dBM. Figure 7 displays the frequency distribution of the change in RSSI during a cell handover. The resolution of the RSSI measurements is 2 dBm.
Figure 7. Frequency histogram of the RSSI change during a cell handover (2 dBm bins).
Cell handovers occur at a range of RSSI, not just low signal strength. This suggests that cell handovers are managed by the network operator in a way that does not disrupt the data connection. There appears to be no correlation between a cell handover and a problem with the correction message delivery.
Although this part of the experiment was not a test of receiver performance, during the NGI circuit trial 63.1 percent of the receiver observations were network RTK fixed, and 33.0 percent of the observations were DGNSS observations. Therefore, 3.9 percent of the possible epochs had no observations, partly due to passing under bridges. The largest GNSS outage during circuit trials was 4.85 seconds. These values show an improvement over previous research, particularly as this is considered a difficult GNSS positioning environment.
GNSS Outages. During the GNSS outages tests, the vehicle traveled at a constant speed of 60 mph, mostly in lane 1 of the motorway. Table 3 shows statistical breakdown of the GNSS outages and the resulting reacquisition of the fixed ambiguity in network RTK positioning.
Table 3. Statistical breakdown of GNSS outages caused by overhead objects.
The longest total GNSS outage caused by an overhead obstruction was 4.65 seconds, when passing under a road bridge. At 60 mph this translates into a distance of almost 130 meters without any GNSS solution, which is much further than the width of the overhead object. Once the GNSS signal is reacquired, there is a short period during which the fixed integer ambiguity is resolved, in order to achieve the centimeter-level accuracy. The longest duration between start of a GNSS outage and reacquisition of the fixed ambiguity for the network RTK solution is 52.10 seconds, or 1,450 meters. Although during this period, a DGNSS solution is available as soon as the satellites are reacquired.
Discussion
Nationwide adoption of cellular Internet services by cell phone users has provided a useful communication system for positioning systems. But network providers do not guarantee the type of communication service demanded by advanced ITS and V2X applications. The quality of service is too easily disrupted by passing into an area with weak signal strength, or when many users congest the bandwidth.
Future generations of cell networks, such as 4G, will significantly increase the available bandwidth and increase download speeds, but there is an unknown increase in the demand on the system from non-critical cell-phone users. The issues in the existing system can be minimized slightly through improvements at the user end, such as using stronger gain antennae or accessing multiple networks with different SIM registrations. The nature of cell networks also leads to a decrease in signal strength occurring prior to the cell handover, which can cause delays in the message delivery, so the management of this process could be improved. Future testing of the GSM network can be carried out at the new innovITS ADVANCE test facility at MIRA in the UK, where the private network can be controlled and manipulated as desired.
An alternative communication method, that has the same wide area coverage of a cell network, is satellite communication. In tests, observation of static positions showed 98 percent of messages were received correctly at a latency of less than 10s. This compares with the High-Speed Download Packet Access (HSDPA) cell network figures of 99.8 percent and 1.2s. When in a kinematic mode, the satellite communications fared less well. Testing three separate satellite communication systems, problems were encountered with reacquisition, long latency, and static initialization. At best, 70 percent of correct messages were received, with a latency of 4.2s, although often over 20s.
Digital Audio Broadcasting (DAB) is capable of being used as a future communication method for network RTK positioning. Compared to traditional VHF and UHF radio communication, it uses the frequency more efficiently and is more robust to degradation.
The design of the GNSS receiver used in testing is aimed at delivering a very reliable and highly accurate solution. It was not intended for use on vehicles and in dynamic environments. The receiver deals well with multipath, rejecting low-strength GNSS signals, allowing the resolution of the integer ambiguity. However, this means that in city environments it may provide fewer solutions than a modern smartphone, albeit with a much higher accuracy when it does. Recent research shows it is possible to increase the speed of ambiguity resolution, and customize integrity controls, making the resolution process close to instantaneous in certain circumstances.
Conclusions
As cellular communications networks evolve in the UK and other countries, the performance of the network RTK receiver also improves. We found that once the RSSI drops to approximately –100dBm, the correction messages suffer from either message loss or message delay that causes the receiver to underperform. The performance of the communication link during a cell tower handover has shown that there is no deterioration in the performance linked to the handover, although cell tower handovers generally occur at the limits of a cell tower’s coverage, and hence at low signal strengths.
The resolution of the fixed integer ambiguity is crucial for the high-accuracy solution available with a network RTK receiver. The resolution is relatively fast, typically within two minutes from a cold start, or fewer than 20 seconds from a hot start. During tests on the M1 motorway, passing under an overhead obstruction caused a maximum total GNSS outage of 4.65 seconds, and a maximum time until the ambiguity was resolved of 52.10 seconds. On average, the GNSS outage was 1.14 seconds with an average re-fix time of 13.13 seconds. Until the ambiguity is resolved, the receiver can continue with a DGNSS solution delivering lane-level accuracy.
Manufacturers
NGI’s inertial nav system is an Applanix POS/RS, which consists of a NovAtel OEM4 dual-frequency GPS receiver combined with a navigation-grade Honeywell consumer IMU. The network RTK position was provided by a Leica GS10 receiver and Leica SmartNet correction service over the Vodafone network. Both receivers used a Leica AS10 antenna.
Scott Stephenson is a Ph.D. student at the Nottingham Geospatial Institute within the University of Nottingham.
Xiaolin Meng is associate professor, theme leader for positioning and navigation technologies, and MSc course director for GNSST and PNT at the Nottingham Geospatial Institute of the University of Nottingham.
Terry Moore is director of the Nottingham Geospatial Institute (NGI) at the University of Nottingham, where he is the professor of satellite navigation and also an associate dean within the Faculty of Engineering.
Anthony Baxendale is head of Advanced Technologies & Research at MIRA Ltd.
Tim Edwards is the lead engineer of the Intelligent Transportation Systems (ITS) research group at MIRA Ltd
u-blox, the Swiss positioning and wireless chip and module company, has received approval for its LISA-U110 UMTS/HSPA wireless module from SK Telecom, Korea’s largest mobile telecom operator with more than 50 percent market share. SK Telecom provides multimedia services and connectivity to 24 million customers throughout South Korea.
The certification allows the LISA modem to be used in a wide range of consumer and M2M applications operating over SK Telecom’s nation-wide 3G network including vehicle infotainment, supply chain management, industrial automation, metering, security, and location-based services.
“We are very pleased that SK Telecom has chosen to work with us on this 3G approval. Our compact and high-speed LISA 3G module is a perfect fit with their strategy to provide converged wireless services supporting entertainment, business and financial applications. Our local support in Korea was a key factor in obtaining this certification” said Samuel Ji, u-blox Country Manager, Korea.
The LISA-U110 is an embedded wireless UMTS/HSPA module delivering high data rates in 3G networks intended for consumer, automotive and industrial applications. For telematics applications, the series provides easy integration with u-blox GPS, GLONASS and QZSS receivers.
LISA modules come in SMT form factor and have a very small footprint, allowing easy mounting on any application board. The LISA form factor enables easy manufacturing, u-blox said, as well as simple migration from u‑blox’ GSM/GPRS modules. Support for A-GPS and u-blox’ CellLocate positioning technology is embedded to facilitate advanced telematics applications including indoor positioning.
Features include compatibility with quad-band GPRS/EDGE, low power (idle mode less than 2 mA) and operating temperature -40 to +85 deg. Celsius. RIL software for Android and Embedded Windows is available free of charge.
LISA modules are manufactured in ISO/TS 16949 certified sites and are fully qualified according to ISO 16750 — Environmental conditions and electrical testing for electrical and electronic equipment for road vehicles to provide high durability and reliability.
Researchers at Israel’s Ben-Gurion University of the Negev (BGU) say reveal that data culled from geosocial networks like the GPS traffic app Waze can help prevent traffic incidents with better deployment of police resources at the most accident prone areas.
“Only now are we beginning to discover the potential in the huge amount of data collected daily,” explains BGU researcher and Ph.D. student Michael Fire. “Studies of this kind, which monitor events such as traffic accidents over time, can help the police identify dangerous sections of roads in real time, or alternatively, locations where few police are needed.”
The paper, “Data Mining Opportunities in Geosocial Networks for Improving Road Safety,” was presented at the IEEE 27th Convention of Electrical and Electronics Engineers in Israel.
Waze records location data and enables users to upload and share comments on any detail, including traffic alerts, accidents or police presence. According to its website, Waze has 30 million worldwide users and describes itself as “a community-based traffic and navigation app whose users share real-time traffic and road info, saving time and gas money.”
Using Waze data and Google Earth, the BGU researchers determined that three-quarters (75 percent) of the locations in Israel with the highest number of accidents were intersections. They then analyzed references to a police presence to determine if the police were present at the spots that had the worst traffic accidents.
“There were numerous instances where the police were manning quieter intersections, while busier intersections went unmonitored,” Fire explains. “According to the data, police response time varied from 20 minutes to 40 minutes in some situations.”
Using Waze, data from May and June 2012 was collected and analyzed on accident reports, police presence, traffic jams, and speed traps. BGU researchers identified 579 different locations in Israel that had at least five reoccurring accidents during this time where 5,156 reported accidents occurred. Police were reported at least 15 times at more than 3,500 locations.
Other researchers involved with the study from BGU’s Department of Information Systems Engineering and BGU’s Telekom Innovation Laboratories include Prof. Yuval Elovici, head of the lab, as well as Dr. Rami Puzis, Prof. Lior Rokach as well as student Dima Kagan.
