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ContinuousWave: Small Boat Electrical
New Global Navigation Satellite System Receiver
|Author||Topic: New Global Navigation Satellite System Receiver|
posted 12-29-2013 06:21 PM ET (US)
Interesting article [which describes a new global navigation satellite system or GNSS receiver that is said to be able to work with five systems].
posted 12-30-2013 02:30 AM ET (US)
I think that article is not well written. It seems to confuse the generic term "spaced based augmentation system" or SBAS with a global navigation satellite system (GNSS) and seems to present SBAS as being the name or acronym of a GNSS. There are so many acronyms around already that it is too confusing when they are used incorrectly; that just makes more confusion!
By my count there are presently in operation the following global navigation satellite systems:
--USA's NAVSTAR GPS
There is a plan for a European consortium to operate a GNSS under the name GALILEO, but at present I believe that system is not at full operational status.
China has a GNSS called BEIDOU or COMPASS which is just beginning to be operational, but I do not think it has global coverage at this time. There are a couple of satellites in orbit, and this affords the chance to test a receiver with those limited signals to check that the receiver design is actually working. But I don't think at this time you could really navigate from those signals on a global (or reliable) basis.
There are several space-based augmentation systems (SBAS) in operation at this time. They are mainly located on geostationary satellites or geosynchronous satellites. This means their signals are only available in a limited portion of the globe, that is, in locations that can see those satellites. The correction data they transmit is also localized to the region in which they operate. This means that these SBAS signals are essentially regional, not global. They are:
--the USA's Federal Aeronautics Administration's space-based augmentation system known as the wide area augmentation system or WAAS, which works in North America;
--Japan's QZSS which works in Asia, but only on or close to the Longitude of Japan; and,
--Europe's EGNOS, intended to augment precision over most of Europe.
WAAS and EGNOS are carried on geostationary satellites. QZSS is carried on satellites in geosynchronous orbit.
For use in North America by boaters, only the SBAS from WAAS is useful. So at the present a boater will be well served with a GNSS chip that can receive GPS and GLONAST positioning satellites, and get enhancement from the SBAS of WAAS.
With the increase in the number of GNSS and SBAS systems available, it is great that chip manufacturers are creating devices that can work with all of them. I think this one might be the first to have BEIDOU on a chip.
posted 12-30-2013 12:18 PM ET (US)
By the way, a space-based augmentation system (SBAS) like WAAS or EGNOS that uses satellites in geostationary orbit is intended primarily for aircraft. At high latitudes the look angle to these satellites from a ground based receiver will be very low, but from an aircraft at altitude the satellites will be much easier to receive. Because in North American we do not do a lot of boating in latitudes North of about 48-degrees, the look angle to the SBAS sources of WAAS are not too bad. You can see the look angles to WAAS satellites from these graphics:
--look angles to PRN 133 at 98W shown in http://continuouswave.com/whaler/reference/images/LookAngles696x708.png
--look angles to PRN 135 and 138 shown in
Much of Europe is at a higher latitude than the USA. For example, although Italy is one of the southern-most countries in Europe, Rome is on about the same latitude as Detroit, Michigan. If you were boating around Stockholm, Sweden, you would be in latitude 60-North. That is like being in Alaska, in terms of latitude. The implication of high latitude is low look angles to geostationary satellites.
posted 01-01-2014 09:12 AM ET (US)
I was just thinking about the logical inconsistency of my comment about SBAS from geostationary satellites and aircraft. I think the real purpose of an SBAS like WAAS from the FAA's point of view is to provide precision position information for making a landing. I guess as the plane's altitude nears the ground, the plane is going to have the same problem with low look angles to those satellites that someone on the ground has. Perhaps when the aircraft is down to 100-feet elevation above the runway they have to rely on visual orientation rather than electronic position location.
posted 01-01-2014 09:13 PM ET (US)
One of the prime reasons for the FAA to become involved in GPS / WAAS is to reduce the costs of the land based VOR / OMNI / ILS systems. And to increase coverage.
The WAAS component allows for accuracy enough to replace a typical ILS system.
One typical avionics package (Garmin), can achieve a lateral accuracy well under 15 feet from runway centerline. To put in in perspective, the ILS system is like flying down a funnel, i.e., the accuracy constantly increases as the aircraft gets closer to the transmitter, located at the end (not the beginning) of the runway.
Regards - Don
posted 01-02-2014 10:28 AM ET (US)
The ILS or Instrument Landing System is quite an interesting application of 1920's technology to the problem of landing an airplane in reduced visibility. It is quite nicely described in
Several years ago I became interested in the ILS system. In a somewhat strange way, the interest was sparked by watching a cinematic feature film about an airplane crash that killed an entire college football team (Marshall University) when an ILS approach failed to produce a safe landing. This lead me to discover the system used for horizontal distance away from the runway, the Marker Beacon system. I looked up the data for the local airport (DTW) and found the latitude and longitude of a Marker Beacon transmitter. I used GOOGLE Earth to locate the position, and then drove over to see the transmitter. I was quite surprised to find the Marker Beacon transmitter was located adjacent to the intersection of two major highways, Telegraph Road and Michigan Avenue on the NW corner, and was sitting in a little cabinet on the roadside that I had driven past for years without noticing. I also found another Marker Beacon transmitter for an adjacent runway located a short distance away in the rear of an empty lot in a residential neighborhood. It was another one of my transmitter hunt field trips, you might say.
posted 01-04-2014 09:50 AM ET (US)
The reasoning behind the marker beacon started to dissipate with the advent of some other technologies. The final nail in the beacon has been GPS.
For years (decades, really) a typical published ILS approach procedure had only height and lateral references on an instrument in the dash. No "distance to" readout.
There were technical workarounds, if additional land based equipment was also located at the airport (or very close by, and positioned to assist).
The way to figure out where you were when flying an ILS approach, was to start a timer or stopwatch when flying over the beacon. There is a little section on the ILS approach paperwork that shows the time it would take, in a no wind condition, based on the approach speed.
Pretty primitive when comparing it to what a GPS unit can do, eh?
posted 01-04-2014 11:02 AM ET (US)
For precision approach to an airport, I think the FAA is planning to use a GNSS augmentation system that is ground based (GBAS) and they call it the local area augmentation system or LAAS. This system will have antennas on the ground sending data to the aircraft to enhance their GNSS position fix. I haven't studied this system very much. I think it was part of the system that was being ruined by truckers carrying GPS-Jammers to prevent their employers from tracking their truck movements, as was discovered at Newark Airport when the system was being tested.
Also, I believe the attraction for having a GNSS receiver that can use other satellite constellations besides the NAVSTAR GPS is most appreciated in urban canyon situations when the view of the sky is limited to a very narrow arc. The more satellites that can be employed in a position fix, the better the chance one of them will be visible in those narrow canyon arcs.
We found that when in Princess Louisa Inlet in British Columbia, due to the narrow sky view from that very steep-sided inlet, we lost our GPS position fix. We could only see a limited view of the sky, constrained by the 4,000-foot high mountains on either side of the inlet. In that situation it would be beneficial to be able to track another 24 or more satellites in other constellations.
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