How does gps module works

These protocols contain the same information, but communicate using binary instead of ASCII for faster communication.

When communicating with a GPS receiver, most commands need to be terminated by a checksum. In most cases, you need to XOR each of your sentences. Here is a simple XOR online calculator. We've got a page just for you! We'll walk you through the basics of how GPS works, the hardware needed, and project tutorials to get you started. Accuracy - How accurate is GPS?

Overall, to get the best accuracy from your GPS, you must be in clear view of the sky and moving. Each track represents a different type of GPS module. This is when the GPS module isn't moving. Once the module starts moving, the track is relatively accurate, and the GPS can 'guess' your track.

However, notice on the approach to the Urban Canyon , which is in between two tall buildings, the accuracy can suffer. Remember, the GPS signals are being transmitted from satellites that are not necessarily over you head; some can be close to the horizon.

Always keep in mind, GPS works best with a full view of the sky. Antenna - Remember, that little GPS module is receiving signals from satellites about 12, miles away, not only above your head, but anywhere in the sky. For the best performance, you want a clear path between the antenna and most of the sky. Weather, clouds, snow storms, shouldn't affect the signal, but things like trees, buildings, mountains, the roof over your head, will all create unwanted interference and your GPS accuracy will suffer.

The smallest and most common form of antenna is the ceramic patch antenna. This antenna is low profile, inexpensive, and compact, but it has lower reception compared to other types of antennas. This antenna needs to face upwards with a clear view of the sky to get good a good signal, i.

This antenna can take up more room than the ceramic patch, but the shape of the antenna allows for a better signal in any orientation, at the expense of slightly lower gain in any one specific orientation.

Some modules can be used with a SMA antenna attachment. The SMA attachment gives you the ability to mount your antenna in a different location than your main circuit. This can be beneficial if your main system is not in good view of the sky. For example, inside of a building or in a car. The most common is bps for 1Hz receivers but bps is becoming more common. Check the datasheet of the receiver for more information. After the module gets a lock or fix, some modules will shut down the extra blocks of channels to save power.

Chipset - The GPS chipset is responsible for doing everything from performing calculations, to providing the analog circuitry for the antenna, to power control, to the user interface.

The chipset is independent of the antenna type, therefore you can have a range of different antennas for GPS modules with specific chipsets.

Common chipsets are ublox, SiRF, and SkyTraq and all contain very powerful processors that allow for fast acquisitions times and high reliability. The differences between chipsets usually falls on a balance between power consumption, acquisition times, and accessibility of hardware. DGPS receivers have additional antenna that receive signals not only from satellites but directly from ground stations.

DGPS devices usually require two antennas. These are much larger and more expensive than your standard GPS device but can provide centimeter accuracy in position. Gain - The gain is the efficiency of the antenna in any given orientation. This applies to both transmitting antennas and receiving antennas. Lock or Fix - When a GPS receiver has a lock or fix, there are at least 4 satellites in good view and you can get accurate position and time.

The NMEA sentences contain all of the useful data, position, time, etc. Power - GPS modules are not power hogs, but they do need some juice to number crunch the data from the satellites and to obtain a lock. On average, a common GPS module, with a lock, draws around 30mA at 3. Also, keeping the start-up time low, saves power. PPS - Pulse per second. This is an output pin on some GPS modules. Generally, when this pin toggles, once a second, you can synchronize your system clock to the GPS clock.

Start-up Times Hot, Warm, and Cold - Some GPS modules have a super-capacitor or battery backup to save previous satellite data in volatile memory after a power down.

This helps decrease the TTFF on subsequent power-ups. Also, a faster start time translates into less overall power draw. Cold Start - If you power down the module for a long period of time and the backup cap dissipates, the data is lost. On the next power up, the GPS will need to download new almanac and ephemeris data.

Warm Start - Depending on how long your backup power lasts, you can have a warm start, which means some of the almanac and ephemeris data is preserved, but it might take a bit extra time to acquire a lock. Hot Start : A hot start means all of the satellites are up to date and are close to the same positions as they were in the previous power on state.

With a hot start the GPS can immediately lock. Trilateration - The mathematical method used to calculate position using multiple reference points. In order for a GPS receiver to compute accurate position and time, it needs to be in good view of at least 4 satellites in the sky. This is called a GPS lock or fix. We all know how to use triangulation to calculate the distance to an object using two reference points x, y. However, with GPS, we need to determine 4 values, i. TTFF - Time to first fix.

The time it takes, after power-on, to accurately compute your position and time using at least 4 satellites. If you are in a location with a bad view of the sky, the TTFF can be very long. The standard for most devices is 1Hz once per second.

UAVs and other fast vehicles may require increased update rates. The WAAS gives close to 5 meter accuracy on position. We have lots of concrete, metal girders, and a large solar array that wreaks havoc with GPS signals and pretty much all cellular carriers for that matter.

This data gives very precise information about the orbit of each satellite. Your GPS receiver can use the ephemeris data to calculate the location of a satellite to with a metre or two. The ephemeris is updated every 2 hours and is usually valid for 4 hours. If your GPS receiver has been off for a while, it may take up to several minutes to receive the ephemeris data from each satellite, before it can get a fix.

Your GPS will have a screen, like the one on the right, which shows which satellites are in use. The bar graphs show the strength of the satellites that the GPS has acquired. If the bar is hollow, the GPS is still downloading the ephemeris.

The circular plot shows the location of the satellites in the sky - the centre of the circle is overhead. To get a fix, the GPS receiver needs a valid almanac, initial location, time, and ephemeris data. The terms mean different things to different GPS manufacturers. In this state, the GPS receiver does not have a current almanac, ephemeris, initial position or time.

Older GPS units may take up to an hour to search for satellites, download the almanac and ephemeris data and obtain an initial position, though newer GPS units may require much less than this. If the GPS receiver has moved several hundred kilometres, its assumptions about which satellites to use will be incorrect and it will have to search for them.

Most units will let you enter an approximate location to speed the process. Warm start - current almanac, initial position, and time are all valid. Ephemeris data is either invalid or only partially valid. Time-to-first-fix is likely to be 30 seconds to 2 minutes depending on satellite availability and the type of GPS receiver. Hot start - if the receiver has been off for, say, less than an hour time-to-first-fix will likely be seconds.

What does this all mean in practice? If the GPS has been recently used you should get a fix almost immediately. If it hasn't, put the GPS outside with a clear view of the sky and have a cup of tea. If you have a GPS in a vehicle, it's better to wait for the unit to get a fix before driving off.

The receiver does this constantly whenever it's on, which means it is nearly as accurate as the expensive atomic clocks in the satellites. In order for the distance information to be of any use, the receiver also has to know where the satellites actually are. This isn't particularly difficult because the satellites travel in very high and predictable orbits. The GPS receiver simply stores an almanac that tells it where every satellite should be at any given time.

Things like the pull of the moon and the sun do change the satellites' orbits very slightly, but the Department of Defense constantly monitors their exact positions and transmits any adjustments to all GPS receivers as part of the satellites' signals. In the next section, we'll look at errors that may occur and see how the GPS receiver corrects them.

So far, we've learned how a GPS receiver calculates its position on earth based on the information it receives from four located satellites. This system works pretty well, but inaccuracies do pop up. For one thing, this method assumes the radio signals will make their way through the atmosphere at a consistent speed the speed of light.

In fact, the Earth's atmosphere slows the electromagnetic energy down somewhat, particularly as it goes through the ionosphere and troposphere.

The delay varies depending on where you are on Earth, which means it's difficult to accurately factor this into the distance calculations. Problems can also occur when radio signals bounce off large objects, such as skyscrapers , giving a receiver the impression that a satellite is farther away than it actually is.

On top of all that, satellites sometimes just send out bad almanac data, misreporting their own position. The basic idea is to gauge GPS inaccuracy at a stationary receiver station with a known location. Since the DGPS hardware at the station already knows its own position, it can easily calculate its receiver's inaccuracy. The station then broadcasts a radio signal to all DGPS-equipped receivers in the area, providing signal correction information for that area. In general, access to this correction information makes DGPS receivers much more accurate than ordinary receivers.

The most essential function of a GPS receiver is to pick up the transmissions of at least four satellites and combine the information in those transmissions with information in an electronic almanac, all in order to figure out the receiver's position on Earth. Once the receiver makes this calculation, it can tell you the latitude, longitude and altitude or some similar measurement of its current position.

To make the navigation more user-friendly, most receivers plug this raw data into map files stored in memory. You can use maps stored in the receiver's memory, connect the receiver to a computer that can hold more detailed maps in its memory, or simply buy a detailed map of your area and find your way using the receiver's latitude and longitude readouts.

Some receivers let you download detailed maps into memory or supply detailed maps with plug-in map cartridges. A standard GPS receiver will not only place you on a map at any particular location, but will also trace your path across a map as you move. If you leave your receiver on, it can stay in constant communication with GPS satellites to see how your location is changing. With this information and its built-in clock, the receiver can give you several pieces of valuable information:.

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Travel Gadgets. A GPS receiver uses satellites to pinpoint locations.