GPS Accuracy - Antenna and Enhancement

Accuracy of GPS Navigation Equipment

Accuracy or precision became a concern for determining the coordinates of a point / location. This position coordinates will always have 'error factor', better known as the 'accuracy'. For example, the tool shows a point's coordinates to an accuracy of 3 meters, which means that the position could be anywhere within a radius of 3 meters from the coordinates (location) is. The smaller the rate of accuracy (i.e. higher accuracy), then the position of the tool would be more appropriate. Price tool will also increase along with the increase in the level of accuracy that can be achieved. In everyday use, the accuracy is more often influenced by peripheral factors that reduce the strength of the satellite signal. Because satellite signals cannot pass through solid objects well, when using the tools, it's important to consider broad sky can be seen.

Geography against Satellite Signal

Little explanation of the satellite signal to the geography:

When a GPS device is located in a valley, the accuracy rate will much lower than in open landscape. In the meadow or mountain peak, the number of satellites that can be reached by means of a lot more than from a mountain valley. So, do not expect to use the navigation tools in a cave. Since this navigation tool totally dependent on the satellite, the satellite signal is very important. Satellite-based navigation tool cannot work optimally when there is interference with the satellite signal. There are many things that can reduce the signal strength of the satellite:

1. Geographical conditions, as described above. As long as we can still see the sky is wide enough, it is still able to function.
2. Forest. The more dense the forest, the more reduced the acceptable signal.
3. Water. Do not expect to use this tool when diving.
4.  Electronic equipment can emit electromagnetic waves.
5. Buildings. Not only when inside the building, located in between high-rise structures also caused effects like being in the valley.
6. Signals that bounce, for example when you are between tall buildings, can disrupt the navigation calculation tool that can show the navigation tool on the wrong or inaccurate.

 The number of satellites and their signal strength that can be accessed by means of navigation can be seen on the display device. Almost all satellite-based navigation tools to display data on connected satellite equipment, satellite locations, and signal strength.

The GPS Antennas

There are two types of antennas innate navigational tools most frequently encountered, the type and the Quad Helix Patch. Patch types, shapes flattened while the quad helix shaped like a tube. Of course, both have their advantages and disadvantages of each. In practical use,  Many factors that could affect its function. Navigation tool that has a patch antenna, the better the signal reception when the device is held horizontally aligned with the earth. While the device has quad helix antenna, will be better when held upright, the upper part towards the sky. To be sure, check the specifications of antennas navigation tool.

In everyday use, it is often necessary external antenna, for example, in the use of four-wheel vehicles. There are several types of external antennas that can be selected. Keep in mind that not all types of navigation device has a slot for an external antenna.

• Active external antenna active called it comes with Low Noise Amplifier (LNA), a signal amplifier, because the signal will be reduced when crossing the wires. This means that they require a power source to perform its function, which is usually taken from a navigation tool. So the navigation tool battery will run out faster. The advantage, cables can be used longer than the passive type.
• Because passive external antenna is not completed by the signal amplifier, the batteries do not run out quickly. But the cable is not long active type.
• External re-radiating antenna type consists of two parts, the first capture satellite signals, which both emit a signal. Since the signal is emitted, then this type does not require a cable to a navigation tool. Navigation devices will receive the signal as usual. Of course this type require an additional power source, but not from the navigation device used. For the type of navigation device has no slot for an external antenna, this type is a good alternative than having to modify the navigation tool.
• Combo Antenna type is a merger between the antenna for navigation devices and mobile phones. The power source is required for its use.

Keep in mind that the coordinates displayed by means of navigation are the coordinates of the position of an external antenna. Thus, placement of an external antenna is also noteworthy.

GPS Enhance and Improvement

DGPS (Differential Global Positioning System) is a system or a way to improve the GPS, using ground stations, which emit correct location. With this system, when the navigation device receives corrections and put it into the calculations, the accuracy of navigation devices will increase. Therefore, using the land station, the signal cannot cover a large area.

Despite having differences in ways of working, SBAS (Satellite Based Augmentation System) in general can be said that using satellite DGPS. Coverage area is much broader than the use DGPS ground stations. There are several SBAS which is known, the WAAS (Wide Area Augmentation System), EGNOS (European geostationary Navigation Overlay Service), and MSAS (Multi-functional Satellite Augmentation System). Managed by the U.S. WAAS,  EGNOS by the European Union while the Japanese MSAS. All three systems are mutually compatible with each other, meaning the navigation tool that can use one system, will be able to use both systems as well. At this time the only WAAS is fully operational and can be enjoyed by the user navigation tools in the world. However, with a DGPS ground station that works well, it can improve the accuracy exceeds / is equal to the increase that can be achieved by SBAS. 

In general those above mentioned, can be divided into two major parts, namely "Real Time (live)" and "Post-Processing (after the activity is complete)". The purpose of the 'real time' is a navigational tool that uses SBAS or DGPS signals directly during use. While the 'post processing' means that the data collected by the navigation tools in the process of re-using data from the DGPS ground stations. There are many DGPS ground stations around the world that we can use for this, both free and paid versions, we can even use it directly via the internet.

Although DGPS or SBAS can improve accuracy, but on condition the signals emitted contains corrections to the area in which we use navigational tools. If it does not contain the correction data for the region, there will be no increase in accuracy.

GPS (Global positioning System) Overviews

GPS (Global positioning System) is a method of measuring the position of the earth's surface with the help of satellite technology. Early development GPS made by the United States defense agencies USDOD (United stated department of defense) as NAVSTAR GPS (Navigation and Timing Satellite Ranging Global Positioning System) which aims to U.S. military interests.

The first GPS satellite was launched and successfully orbited a satellite block-i gps in 1978. Currently the number of GPS satellites that have orbited satellites are 24 pieces that have been circulating on the earth in 6 orbit and each orbit consists of 4 pieces satellite at 20.200Km altitude above the surface of the earth. Orbital period of each satellite is 11 hours 58 minutes (+ 12 hours) and there are approximately 4 s / d 10 satellites that can be observed from the Earth's surface.

GPS consists of three segments:

• Space segment
• Control system segment (ground)
• User segment

Space segment:
The satellite which consists of 24 satellites that emit 2 Frequency: L1 frequency length is at 1575.42 MHz and L2 at 1227.60 MHz frequency length. L1 carry 2 binary code which is P-code (Precise or private code) and C / A-code (Coarse Acquisition or Clear Access), while L2 only carry P-code only.

Control System Segment:
The facility or station which controls and monitoring the movement of all the 24 satellites. These stations among others were in Ascension Island, Diego Garcia, Hawaii, Colorado Springs, etc.

User Segment:
A GPS handheld or can be called GPS Receiver.

Type GPS Receiver
Types of GPS receiver which are divided by the level of precision / accuracy:

1. Navigation Type: Used for navigation devices or measures that do not require a high level of accuracy. Level of error / error of navigation types ranging from 2 m - tens of meters.
2. Geodetic Type: Receiver is the types which possess high accuracy, usually used for measurements requiring high precision, e.g.  For the control point (reference), military precision Geodetic equipment which are used for differential method and with proper planning and execution.

Type receivers based on the data are classified into:

• Receiver code C / A
• Receiver code C / A + L1 phase
• Receiver code C / A phase + L1 + L2 phase
• Receiver code C / A code C + + phase L1, L2

The received signal in GPS receiver informs:

• Position Satellite
• Distance satellite (C. Δt)
• Time
• satellite health / satellite state
• etc.

Positioning Method
In positioning there be some common methods do the observations:

1. Static, where the GPS receiver is not moving at the time of observation, usually done in a long time.
2. Rapid Static, essentially the same as the old method of observation method Static charge is only about 5 minutes until 20 minutes.
3. Pseudo Kinematic, basically the same as the Rapid static, except the Pseudo static observations performed twice with an interval greater than the first observation.
4. Stop and Go, also called Semi kinematic receiver which momentarily stopped a few minutes at an appointed place and move again towards the next point performance turned on and still catch signal.
5. Kinematic, is where the Receiver continues to move in a state on without stopping.

The observations using GPS Receiver does not always get the data that has been accurate and details,
Since there are several factors that affect the accuracy of a GPS Receiver:

•     Type of receiver used (geodetic, navigation)
•     Type of data taken (pseudo range or carrier phase)
•     Method of determining the position (Differential, Absolute, etc.)
•     Conditions Ionosphere and Troposphere
•     Multipath Effects
•     Accuracy data (ephemeris)
•     Satellite Geometry
•     Data processing techniques

And there are still many factors that can affect the accuracy of one GPS Receiver.

Nowadays GPS has been widely used by people both for private interests, education, and interests of institutions or agencies engaged in the field of Geographic Information, Exploration, etc.