WAAS – Wide Area Augmentation System
WAAS was jointly developed by the United States Department of Transportation (DOT) and the Federal Aviation Administration (FAA), beginning in 1995, to provide precision approach capability for aircraft. Without WAAS, ionospheric disturbances, clock drift (timing), and satellite orbit errors create too much error in the GPS signal for aircraft to perform a precision approach.
The navigation payloads broadcast the augmentation messages on a GPS-like signal. The GPS/WAAS receiver processes the WAAS augmentation message as part of estimating position. The GPS-like signal from the navigation transponder can also be used by the receiver as an additional source for calculation of the user’s position.
It’s a system of satellites and ground stations that provide GPS signal corrections, giving you up to five times better position accuracy. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don’t have to purchase additional receiving equipment or pay service fees to utilize WAAS.
The signals from GPS satellites are received across the NAS at many widely-spaced Wide Area Reference Stations (WRS) sites. The WRS locations are precisely surveyed so that any errors in the received GPS signals can be detected.
The GPS information collected by the WRS sites is forwarded to the WAAS Master Station (WMS) via a terrestrial communications network. At the WMS, the WAAS augmentation messages are generated. These messages contain information that allows GPS receivers to remove errors in the GPS signal, allowing for a significant increase in location accuracy and reliability.
The augmentation messages are sent from the WMS to uplink stations to be transmitted to navigation payloads on Geostationary communications satellites.
The navigation payloads broadcast the augmentation messages on a GPS-like signal. The GPS/WAAS receiver processes the WAAS augmentation message as part of estimating position. The GPS-like signal from the navigation transponder can also be used by the receiver as an additional source for calculation of the user’s position.
WAAS also provides indications to GPS/WAAS receivers of where the GPS system is unusable due to system errors or other effects. Further, the WAAS system was designed to the strictest of safety standards – users are notified within six seconds of any issuance of hazardously misleading information that would cause an error in the GPS position estimate.
SA – Selective Availability
Back in the days GPS included a feature called Selective Availability (or SA) that introduced intentional errors of up to a hundred meters into the publicly available navigation signals, making it difficult to use for guiding long range missiles to precise targets. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users.
During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in disabling the Selective Availability. In the 1990s the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own, less accurate, radio navigation systems. The military resisted for most of the 1990s, but SA was eventually turned off in 2000 following an announcement by then US President Bill Clinton, allowing all users to enjoy nearly the same level of access.
TMC – Traffic Message Channel
The Traffic Message Channel (TMC) is a specific application of the FM Radio Data System (RDS) used for broadcasting real-time traffic and weather information. Data messages are received silently and decoded by a TMC-equipped car radio or navigation system, and delivered to the driver in a variety of ways. The most common of these is a TMC-enabled navigation system that can offer dynamic route guidance – alerting the driver of a problem on the planned route and calculating an alternative route to avoid the incident.
Here is how it works: data related to traffic flows, incidents, weather etc. are gathered from traffic monitoring systems, emergency services, motorists’ calls etc., and are collated at a central traffic information centre. They are then passed to the TMC traffic information service provider, who generates TMC messages according to the ALERT-C coding protocol.
Standard TMC user messages provide five basic items of broadcast information:
The service provider sends the coded messages to the appropriate FM radio broadcaster for transmission as an RDS (Radio Data System) signal within normal FM radio transmissions. The TMC data are received by the vehicle radio and antenna, and decoded by a TMC decoder. This reconstructs the original message, using a database of event and location codes, which is presented to the driver as a visual or spoken message.
It takes typically about 30 seconds from the first report of a traffic incident to the traffic information centre until the same information is available in the vehicle.
The user can select the language used to present the traffic information by the TMC receiver, typically a navigation system or car radio. The user can also opt to filter messages, so that only those concerning the immediate route are selected.
The service is free in almost all of Europe but you need pay a subscription fee in the U.S. and the U.K usually around $60 per year.
NMEA (0183 Standard)- National Marine Electronics Association
A standard interface protocol, which is often used for real-time tracking and autopilot systems. Most Garmin products output their data in this format (iQue is an exception) so they can easily talk to external devices.
The data is usually RS-232 compatible and it uses 4800 bps, 8 data bits, no parity and one stop bit ( 8N1 ). NMEA 0183 sentences are all ASCII. Each sentence begins with a dollarsign ($) and ends with a carriage return linefeed. Data is comma delimited. All commas must be included as they act as markers. A sample NMAE 0183 sentence may look like this:
$GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0000*1F
DMB – Digital Multimedia Broadcasting
This is a digital transmission system for sending data, radio and TV to mobile devices such as mobile phones. It can operate via satellite (S-DMB) or terrestrial (T-DMB) transmission. The system can be integrated into many gadgets such as personal media players, cell phones, navigation systems, etc… Currently (2006) Korean gadgets are the only ones with this functionality since they have 7 TV channels, 13 radio stations, and 8 data channels broadcasting through DMB. Other countries are still in trial period. Germany will have DMB up and running for World Cup 2006.
Here is how it works:
1. Satellite:
Lets you receive the mobile broadcast signal for satellite DMB service
2. Broadcast Program Provider:
Offers content to the satellite DMB center
3. Satellite DMB Center
Transmits content information to satellite
4. Gap Filler:
Is broadcasting equipment that is additionally installed to let customers enjoy a smooth broadcasting service in shadow areas such as inside buildings in the downtown area. With this addition, they can enjoy broadcasting content via their cellular phone without hindrance.
5. Terminal
Customers are allowed to watch the information received from the Broadcasting Center, via mobile terminals.
TTFF – Time To First Fix
TTFF, or “Time to First Fix” is the time it takes for a GPS to determine its current position.
When the satellites try to acquire a lock they need to rely on both Almanac and Ephemeris data. Almanac data is course orbital parameters for all satellites in the GPS constellation which isn’t very accurate information but is usually current for up to several months. Then there’s Ephemeris data which is very precise orbital and clock correction for each satellite and is required for precise positioning, eg 3D fix. Each satellite broadcasts only it’s Ephemeris data which has a life span of approx 5 hours per satellite. Each satellite will broadcast the Ephemeris data for a 30 second period, and then re-transmit, so if the GPS receiver loses track of the data part way through the 30 second cycle, you will have to start again at the next 30 second cycle.
There are 4 TTFF start types depending on the amount of Almanac and Ephemeris data that is present in the GPS Receiver and where it thinks it is and the satellites are which can help aid the GPS acquire a lock quicker. These are designated as Factory, Cold, Warm and Hot.
Factory is where the receiver has no knowledge whatsoever of Almanac data in turn to locate the satellites and retrieve Ephemeris data, and for a full Almanac to be downloaded can take approx 12.5 mins, hence most companies suggest a factory start of 15 minutes.
Cold start is usually the slowest TTFF you’ll witness on a regular basis which has some knowledge of Almanac data but no Ephemeris data. Almanac data is not precise, but current for several months. When a cold start is required, the receiver has to download a full set of Ephemeris data which as already mentioned above is broadcast over a 30 second cycle and re-transmitted every 30 seconds.
When starting the receiver in a Warm or Hot mode usually you’ll find that the receiver has some Ephemeris data in the case of a Warm start, and in the case of a Hot start it has nearly a full set of Ephemeris data, which aids in making quicker TTFF’s.
One thing to bear in mind is that although Manufacturers quote their average Cold, Warm and Hot TTFF’s, these will vary. Depending on where you are can dramatically change the quickness of acquiring a satellite lock. To load the Ephemeris data form the satellites, the GPS Receiver requires a full 30 seconds of data reception. If this is interrupted from a tall building, or a branch from a tree, or if the signal you are receiving is being reflected off of a building then all of this can cause a problem in the data reception. If the data isn’t received in full, the Ephemeris data collection has to start again at the next cycle.
TPEG – Transport Protocol Experts Group
This Group developed within the EBU (European Broadcasting Union in Geneva, Switzerland) since 1997 a new ISO/CEN standard for the transmission of traffic and travel information within digital broadcast systems such as DAB, DVB and the Internet.
The coding of TPEG is independent of the bearer system and builds in a certain sense on experience gained with the development of RDS-TMC for FM broadcasting, however without the known limitations of that system and specifically without the need to use location code numbers within the road network. The location coding concept of TPEG is very innovative.
TPEG can support a number of different TTI applications, specifically for all modes of transport (trains, trams, busses, ferryboats, airport arrivals and departures – and not just only road traffic messages).
Many TTI experts consider TPEG as the most innovative technology in Traffic and Travel Information broadcasting that will also support a wide range of receivers, simple ones without a map database and more complex ones as car navigation systems.
A-GPS (Assisted GPS)
Assisted GPS (A-GPS), is a technology that uses an assistance server to cut down the time needed to determine a location using GPS. It is useful in urban areas, when the user is located in “urban canyons”, under heavy tree cover, or even indoors. It is becoming more common and it’s commonly associated with Location Based Services (LBS) over cellular networks.
The development of these services is fuelled, in part, by the U.S. Federal Communications Commission’s E911 mandate requiring the position of a cell phone to be available to emergency call dispatchers.
A-GPS differs from regular GPS by adding another element to the equation, the Assistance Server. In regular GPS networks there are only GPS satellites and GPS receivers. In A-GPS networks, the receiver, being limited in processing power and normally under less than ideal locations for position fixing, communicates with the assistance server that has high processing power and access to a reference network. Since the A-GPS receiver and the Assistance Server share tasks, the process is quicker and more efficient than regular GPS, albeit dependent on cellular coverage.
Assisted GPS describes a system where outside sources, such as an assistance server (Mobile Location Server) via a network, help a GPS receiver perform the tasks required to make range measurements and calculate position solutions. The assistance server has the ability to access information from the reference network and also has computing power far beyond that of the GPS receiver. In such a system, the assistance server communicates with the GPS receiver on the mobile phone on a cellular network. With assistance from the network, the receiver can operate more quickly and efficiently than it would unassisted, because a set of tasks that it would normally handle is shared with the assistance server. The resulting AGPS system boosts performance beyond that of the same receiver in a stand-alone mode.
Ordinarily, a standard GPS device needs to have a clear line-of-sight to at least four GPS satellites before it can calculate its position. In addition, it needs enough processing power to transform the data streams from the satellites into a position. In one mode of A-GPS, the mobile receiver takes a snapshot of the satellite signals and transmits these to a cell tower to relay the data to an assistance server that performs the necessary calculations for a position fix. The server may send the fix back to the mobile receiver or to a 911 dispatcher. Some mobile phones will accept converted data streams to compute a position themselves.
One of the main purposes of A-GPS is to provide municipalities with location-based emergency phone service, such as E911 service. Another is to provide mobile carriers with end-user, location-based services such as a turn-by-turn navigation aid.
DR – dead reckoning
Dead reckoning is a “backup” feature that allows GPS navigation systems to estimate your location in situations where it’s unable to receive healthy signals from GPS satellites. The location calculated by dead reckoning depends on the last known location and usually becomes less accurate the longer you go without GPS reception – say a long long tunnel. This feature is not usually available in entry level models.
The technology varies but dead reckoning usually relies on an accelerometer, 3D gyroscope, and/or your vehicles speed sensor.
Source
SA – Selective Availability
Back in the days GPS included a feature called Selective Availability (or SA) that introduced intentional errors of up to a hundred meters into the publicly available navigation signals, making it difficult to use for guiding long range missiles to precise targets. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users.
During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in disabling the Selective Availability. In the 1990s the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own, less accurate, radio navigation systems. The military resisted for most of the 1990s, but SA was eventually turned off in 2000 following an announcement by then US President Bill Clinton, allowing all users to enjoy nearly the same level of access.
TMC – Traffic Message Channel
The Traffic Message Channel (TMC) is a specific application of the FM Radio Data System (RDS) used for broadcasting real-time traffic and weather information. Data messages are received silently and decoded by a TMC-equipped car radio or navigation system, and delivered to the driver in a variety of ways. The most common of these is a TMC-enabled navigation system that can offer dynamic route guidance – alerting the driver of a problem on the planned route and calculating an alternative route to avoid the incident.
Here is how it works: data related to traffic flows, incidents, weather etc. are gathered from traffic monitoring systems, emergency services, motorists’ calls etc., and are collated at a central traffic information centre. They are then passed to the TMC traffic information service provider, who generates TMC messages according to the ALERT-C coding protocol.Standard TMC user messages provide five basic items of broadcast information:
- Event description, details of the weather situation or traffic problem and its severity
- Location, the area, highway segment or point location affected
- Direction and extent, identifying the adjacent segments or point locations affected, and the direction of traffic affected
- Duration, how long the problem is expected to last
- Diversion advice, whether or not drivers are advised to find an alternative route.
The service provider sends the coded messages to the appropriate FM radio broadcaster for transmission as an RDS (Radio Data System) signal within normal FM radio transmissions. The TMC data are received by the vehicle radio and antenna, and decoded by a TMC decoder. This reconstructs the original message, using a database of event and location codes, which is presented to the driver as a visual or spoken message.
It takes typically about 30 seconds from the first report of a traffic incident to the traffic information centre until the same information is available in the vehicle.
The user can select the language used to present the traffic information by the TMC receiver, typically a navigation system or car radio. The user can also opt to filter messages, so that only those concerning the immediate route are selected.
The service is free in almost all of Europe but you need pay a subscription fee in the U.S. and the U.K usually around $60 per year.
NMEA (0183 Standard)- National Marine Electronics Association
A standard interface protocol, which is often used for real-time tracking and autopilot systems. Most Garmin products output their data in this format (iQue is an exception) so they can easily talk to external devices.
The data is usually RS-232 compatible and it uses 4800 bps, 8 data bits, no parity and one stop bit ( 8N1 ). NMEA 0183 sentences are all ASCII. Each sentence begins with a dollarsign ($) and ends with a carriage return linefeed. Data is comma delimited. All commas must be included as they act as markers. A sample NMAE 0183 sentence may look like this:
$GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0000*1F
DMB – Digital Multimedia Broadcasting
This is a digital transmission system for sending data, radio and TV to mobile devices such as mobile phones. It can operate via satellite (S-DMB) or terrestrial (T-DMB) transmission. The system can be integrated into many gadgets such as personal media players, cell phones, navigation systems, etc… Currently (2006) Korean gadgets are the only ones with this functionality since they have 7 TV channels, 13 radio stations, and 8 data channels broadcasting through DMB. Other countries are still in trial period. Germany will have DMB up and running for World Cup 2006.
1. Satellite:
Lets you receive the mobile broadcast signal for satellite DMB service
2. Broadcast Program Provider:
Offers content to the satellite DMB center
3. Satellite DMB Center
Transmits content information to satellite
4. Gap Filler:
Is broadcasting equipment that is additionally installed to let customers enjoy a smooth broadcasting service in shadow areas such as inside buildings in the downtown area. With this addition, they can enjoy broadcasting content via their cellular phone without hindrance.
5. Terminal
Customers are allowed to watch the information received from the Broadcasting Center, via mobile terminals.
TTFF – Time To First Fix
TTFF, or “Time to First Fix” is the time it takes for a GPS to determine its current position.
When the satellites try to acquire a lock they need to rely on both Almanac and Ephemeris data. Almanac data is course orbital parameters for all satellites in the GPS constellation which isn’t very accurate information but is usually current for up to several months. Then there’s Ephemeris data which is very precise orbital and clock correction for each satellite and is required for precise positioning, eg 3D fix. Each satellite broadcasts only it’s Ephemeris data which has a life span of approx 5 hours per satellite. Each satellite will broadcast the Ephemeris data for a 30 second period, and then re-transmit, so if the GPS receiver loses track of the data part way through the 30 second cycle, you will have to start again at the next 30 second cycle.
There are 4 TTFF start types depending on the amount of Almanac and Ephemeris data that is present in the GPS Receiver and where it thinks it is and the satellites are which can help aid the GPS acquire a lock quicker. These are designated as Factory, Cold, Warm and Hot.
Factory is where the receiver has no knowledge whatsoever of Almanac data in turn to locate the satellites and retrieve Ephemeris data, and for a full Almanac to be downloaded can take approx 12.5 mins, hence most companies suggest a factory start of 15 minutes.
Cold start is usually the slowest TTFF you’ll witness on a regular basis which has some knowledge of Almanac data but no Ephemeris data. Almanac data is not precise, but current for several months. When a cold start is required, the receiver has to download a full set of Ephemeris data which as already mentioned above is broadcast over a 30 second cycle and re-transmitted every 30 seconds.
When starting the receiver in a Warm or Hot mode usually you’ll find that the receiver has some Ephemeris data in the case of a Warm start, and in the case of a Hot start it has nearly a full set of Ephemeris data, which aids in making quicker TTFF’s.
One thing to bear in mind is that although Manufacturers quote their average Cold, Warm and Hot TTFF’s, these will vary. Depending on where you are can dramatically change the quickness of acquiring a satellite lock. To load the Ephemeris data form the satellites, the GPS Receiver requires a full 30 seconds of data reception. If this is interrupted from a tall building, or a branch from a tree, or if the signal you are receiving is being reflected off of a building then all of this can cause a problem in the data reception. If the data isn’t received in full, the Ephemeris data collection has to start again at the next cycle.
TPEG – Transport Protocol Experts Group
This Group developed within the EBU (European Broadcasting Union in Geneva, Switzerland) since 1997 a new ISO/CEN standard for the transmission of traffic and travel information within digital broadcast systems such as DAB, DVB and the Internet.
The coding of TPEG is independent of the bearer system and builds in a certain sense on experience gained with the development of RDS-TMC for FM broadcasting, however without the known limitations of that system and specifically without the need to use location code numbers within the road network. The location coding concept of TPEG is very innovative.
TPEG can support a number of different TTI applications, specifically for all modes of transport (trains, trams, busses, ferryboats, airport arrivals and departures – and not just only road traffic messages).
Many TTI experts consider TPEG as the most innovative technology in Traffic and Travel Information broadcasting that will also support a wide range of receivers, simple ones without a map database and more complex ones as car navigation systems.
A-GPS (Assisted GPS)
The development of these services is fuelled, in part, by the U.S. Federal Communications Commission’s E911 mandate requiring the position of a cell phone to be available to emergency call dispatchers.
A-GPS differs from regular GPS by adding another element to the equation, the Assistance Server. In regular GPS networks there are only GPS satellites and GPS receivers. In A-GPS networks, the receiver, being limited in processing power and normally under less than ideal locations for position fixing, communicates with the assistance server that has high processing power and access to a reference network. Since the A-GPS receiver and the Assistance Server share tasks, the process is quicker and more efficient than regular GPS, albeit dependent on cellular coverage.
Assisted GPS describes a system where outside sources, such as an assistance server (Mobile Location Server) via a network, help a GPS receiver perform the tasks required to make range measurements and calculate position solutions. The assistance server has the ability to access information from the reference network and also has computing power far beyond that of the GPS receiver. In such a system, the assistance server communicates with the GPS receiver on the mobile phone on a cellular network. With assistance from the network, the receiver can operate more quickly and efficiently than it would unassisted, because a set of tasks that it would normally handle is shared with the assistance server. The resulting AGPS system boosts performance beyond that of the same receiver in a stand-alone mode.
Ordinarily, a standard GPS device needs to have a clear line-of-sight to at least four GPS satellites before it can calculate its position. In addition, it needs enough processing power to transform the data streams from the satellites into a position. In one mode of A-GPS, the mobile receiver takes a snapshot of the satellite signals and transmits these to a cell tower to relay the data to an assistance server that performs the necessary calculations for a position fix. The server may send the fix back to the mobile receiver or to a 911 dispatcher. Some mobile phones will accept converted data streams to compute a position themselves.
One of the main purposes of A-GPS is to provide municipalities with location-based emergency phone service, such as E911 service. Another is to provide mobile carriers with end-user, location-based services such as a turn-by-turn navigation aid.
DR – dead reckoning
Dead reckoning is a “backup” feature that allows GPS navigation systems to estimate your location in situations where it’s unable to receive healthy signals from GPS satellites. The location calculated by dead reckoning depends on the last known location and usually becomes less accurate the longer you go without GPS reception – say a long long tunnel. This feature is not usually available in entry level models.
The technology varies but dead reckoning usually relies on an accelerometer, 3D gyroscope, and/or your vehicles speed sensor.
Source
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