The Future of GPS

[Capt. Mike Maurice]

I have been experimenting with a late model GPS receiver chip that uses the new L5 frequency. There are now about 30 sats in orbit transmitting this signal. Broadcom and Alystar have chips like this that are targeted at the general market. The Galaxy S20 and some other cell phones now have the chips, but it is not clear that any version of them are available in the US.
The chip I have uses the old L1, L2 frequencies, plus the L5. It takes a special antenna to pick up the L5 signal. I just had it out on the street and the fix was about 8 feet in radius with 22 sats being used. This compares with about 30 feet radius with the GPS chip in the phone.
What is really exciting is that parked and sitting still, the heading is an order of magnitude more stable. It is not as stable inside the house with only 13 sats.

An outfit called oneNav has announced a L5 only receiver and it would appear that L5 is the future. Examination of the specs indicates L5 is far more spoof and jam proof. Has multiple channels for improved accuracy, as noted earlier.

Eventually the chips that support RTCM error corrections available from internet servers will become low enough cost that the boating community will be able to afford them. Such access should be pretty widely available near any harbor along the US coastline.
RTCM will result in GPS errors of less than a foot, maybe inches. This sort of precision is technically available now, but expensive.

[Jim Cate]

RTCM will result in GPS errors of less than a foot, maybe inches. This sort of precision is technically available now, but expensive.

While this is a neat techo feat, it seems more exciting to surveyors than to sailors. The current accuracy for GPS location seems adequate for our sort of navigation.

But then I started out doin' celestial and a small cocked hat was exciting then!

Jim

[requiem]

I am curious as to how it determines heading when sitting still. Very useful though.

Worth keeping in mind though that whilst in the old days the chart would be accurate and the fix fuzzy, in relative terms GPS (even without L5) makes the fix accurate and the chart fuzzy. Or, as NOAA mentioned in one article, "In general, federal hydrographic surveys have used the highest standards, with the most accurate hydrographic survey instrumentation available at the time. On a 1:20,000-scale chart, for example, the survey data was required to be accurate to 15 meters."

[smac999]

Gps accuracy might be inch’s. But the chart Accuracy is not. You’ll still be boating over land in the map in some places...

No need for less then 10’ accuracy on a boat.

[Anders]

Originally Posted by Jim Cate

While this is a neat techo feat, it seems more exciting to surveyors than to sailors. The current accuracy for GPS location seems adequate for our sort of navigation.

But then I started out doin' celestial and a small cocked hat was exciting then!

Jim

Accuracy is good enough for navigation but often not good enough for anchor alarms specially when med mooring in bays.

[Jim Cate]

Originally Posted by Anders

Accuracy is good enough for navigation but often not good enough for anchor alarms specially when med mooring in bays.

Relying upon a GPS anchor alarm when med moored a couple of feet from a quay seems odd to me, but if that is important to you then this is a good advancement.

For my usage, the extant accuracy is more than adequate for an anchor alarm, and as others have noted, it already exceeds the accuracy of most charts for navigation.

Jim

[Benz]

This will become most useful when they re-draw all the charts and line the benchmarks up to the GPS positions they should be in. I have charts currently in print that admit that some islands are as much as two miles from their charted position.

[Anders]

Originally Posted by Jim Cate

Relying upon a GPS anchor alarm when med moored a couple of feet from a quay seems odd to me, but if that is important to you then this is a good advancement.

For my usage, the extant accuracy is more than adequate for an anchor alarm, and as others have noted, it already exceeds the accuracy of most charts for navigation.

Jim

I did say med moored in a bay where we usually are 10 - 20 meters from the rocks.

[goboatingnow]

The big advantage, will be low cost RTK gps will be heading info , the data of the flux gate compass are numbered

[goboatingnow]

Data should be days

[carstenb]

As noted above by others, few, if any, charts have the accuracy that current GPS gives. In the -South Pacific, there are still charts that were made by Cook/Bligh and have never been updated.

Even in the so-called civilized world, most charts were made in the 1800's and were made by rowing a boat while taking soundings, then moving 100 yards (meters) over and rowing another straight line. The cartographers then simply noted that if the water depth were 20 feet on both lines then the water depth between them was also 20 feet (meaning there could be a big nasty rock out there for you to hit).

While some countries are redoing their charts using side-scanning sonar etc - they do the most popular (for commercial shipping) routes first - leisure boating comes a far second.
For anchoring purposes, GPS measuring in inches is far too close for my comfort (but then I am old fashioned)

Gadgets are nice, but sometimes are much too fancy for our use as cruisers

[Scorpius]

Originally Posted by carstenb

As noted above by others, few, if any, charts have the accuracy that current GPS gives. In the -South Pacific, there are still charts that were made by Cook/Bligh and have never been updated.

Even in the so-called civilized world, most charts were made in the 1800's and were made by rowing a boat while taking soundings, then moving 100 yards (meters) over and rowing another straight line. The cartographers then simply noted that if the water depth were 20 feet on both lines then the water depth between them was also 20 feet (meaning there could be a big nasty rock out there for you to hit).

While some countries are redoing their charts using side-scanning sonar etc - they do the most popular (for commercial shipping) routes first - leisure boating comes a far second.
For anchoring purposes, GPS measuring in inches is far too close for my comfort (but then I am old fashioned)

Gadgets are nice, but sometimes are much too fancy for our use as cruisers

Hear, hear!

[ArmyDaveNY]

Originally Posted by Capt. Mike Maurice

Examination of the specs indicates L5 is far more spoof and jam proof.

To me, this seems like the real advantage, or perhaps I should say the important advantage.

What is it about the specs that suggests it will be more spoof and jam proof?

[MicHughV]

I don't get this need for pinpoint GPS accuracy.

Seems like the modernday boater has his/her eyes fixed to some or other screen 24/7 these days instead of looking out towards the horizon, much like walking down any street...every face you'll see will be stuck neck deep into an iphone screen instead of watching where they are going..

It's nuts !!!

It's just like all the latest weather gadgets. I can't tell you how many times I've come across a boater, or more usually, a group of boaters, that will huddle around a plethora of weather gizmo's analyzing each and every cloud, to determine if they should leave the dock. Instead of looking to the skies, they are looking at a 9" screen.

I don't know how the old time navigators made it....maybe they were sailors....real one's !!!

Beam me up Scotty...no intelligent life left here on planet earth anymore...

[continuouswave]

Originally Posted by ArmyDaveNY

What is it about the specs that suggests it will be more spoof and jam proof?

First a bit of background on the radio aspect of GNSS signal reception:

All GNSS receivers are fundamentally RADIO RECEIVERS. The signals they are receiving are very weak signals. The signals are generally so weak that without the special modulation techniques used those signals could not even be detected.

The very low signal strength arises from the fundamental constraints of the satellites:

--the are in very high orbits, so even when directly overhead the path distance is very long, over 10,000-miles; there is considerable path loss;

--the transmitted signal level is limited in power by the nature of the satellites; they get power from solar panels. The actual transmitter power available to transmit the GNSS signal is limited to less than 50-Watts in most cases

The expected signal level for a GNSS user on Earth is -125 dBm. That is an extremely weak signal. The only reason the signal is usable is due to the modulation technique. Demodulation of the signal (when "locked") adds over 40 dB of gain.

The fundamental approach to "jamming" a radio signal from being received is to create an interfering signal of much higher strength. Because the GNSS signals are already very weak, brute force jamming with a stronger signal does not require massive power, as long as the jamming signal source is much closer. Of course, the closer the jamming signal source, the smaller the area that is affected by the jamming.

Some further advantages of the L5 signal compared to L1 signals:

-- L5 signals are transmitted at a lower frequency (1176.45 MHz) than L1 signals (1575.42 MHz); this tends to reduce the path loss by about 2.5 dB;

--L5 signals are transmitted at a high power than L1 signals; this is not an intrinsic advantage of L5; it only accrues if the GNSS system intentionally transmits at higher power, which in GPS it does.

--the modulation scheme used on L5 is more complex than on L1, and this results in a receiver being able to have better weak signal detection (better "sensitivity") to the L5 signals compared to L1 signals. This may improve the ability of the L5 signal to be received in the presence of interference.