A simple Guide to how GPS works - Part 2 some techie stuff!

Whilst GPS is everywhere and is literally rocket science what are the nuts and bolts of how it works. Mike Forbes at Electric Compass explains more...

In standard GPS navigation, each GPS receiver produces “replicas” of the code transmitted by the various satellites. These replicas represent the code the receiver expects to receive from any given satellite. A satellite is located and verified when a replica of the code matches up with the code received(a process known as code phase tracking). At the beginning of each individual signal is a sort of time stamp.

When the two signals are examined by the receiver (called “correlation”), the time stamps of the two signals are compared and a time difference is ascertained. Given this time difference and the rate of propagation of the signal, the GPS receiver uses the simple formula of Rate times Time equals Distance (R*T=D) to compute the distance to each satellite. Due to the uncertainties introduced by the many variables this distance to each satellite is only an estimate, and is known as the pseudo-range.

Pseudo-Range Navigation
The pseudo-range from each satellite can be seen as a radius of a large sphere, and the location of the GPS receiver is one point on that sphere. When several pseudo-ranges from several satellites are used in conjunction, the position of the receiver is simply the intersection of these spheres at a given time. The position is first determined in what is known as the Earth-Centered, Earth-Fixed (ECEF) coordinate system, which describes the receiver’s position relative to the center of the earth. From this ECEF location the receiver then easily deduces the latitude, longitude, and altitude, which of course describes the receiver’s position on the surface of the earth.In solving for the ECEF position the receiver needs to examine four variables (three dimensions and time), and a minimum of four satellites is required. In the event that only three satellites are available, a two-dimensional fix can be calculated by assuming a certain altitude. The greater the number of satellites visible to the receiver the greater the level of GPS accuracy, as five or more satellites can provide position, time and redundancy.

Types of GPS Errors
GPS accuracy is diluted by errors that can be introduced by a number of sources. GPS errors can be any combination of noise, bias, and blunders.Noise errors combine the electronic noise from the space segment and the noise generated by the user’s device.Bias errors were historically a result of the intentional degradation of GPS accuracy by the DOD known as Selective Availability, but this source of bias error is no longer active.

There are many means of improving the accuracy and precision of Global Positioning System data. The most common method of improving position information is known as Differential GPS, or DGPS. DGPS is predicated on the concept that for two receivers positioned reasonably close to each other, several of the errors will be common to both devices, and can therefore be subtracted from the navigation solution. Errors common to both receivers are known as common mode errors, and do not include multipath errors or errors due to noise in the user segment. Specifically,DGPS requires that one receiver is stationary at a known location, and that it sends corrected signals to a roving station; the roving station then incorporates the new information into the range corrections for each satellite.The best DGPS corrections for the roving station occur when the common-mode errors are most similar, or when the receivers are 100 km or closer to each other.

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5 more things to think about when planning an enterprise mobility deployment

Is your organisation investigating ways to eliminate collecting data on paper for your mobile workforce?

This week we are exploring the top 10 important questions you should ask vendors you are evaluating before you make this decision.

5 More things to think about....

6. Can my customers have automatic reports emailed to them when the mobile worker completes the job at the customer location? Can the management team also receive automatic email reports so they can manage the activity in the field?
Data collected in the field can be automatically embedded in a PDF report, attached to an email and sent immediately, all with no intervention from the Administrator. The PDF can embed signatures, photos or sketches that were collected in the application as well. The business rules can be configured so that the report is automatically emailed out to customers, division managers or anyone who needs to review the data. This feature means that your customers could have an email in their inbox before the mobile worker leaves the site.

7. Do I have the option to lock down the device so my mobile workers can’t inadvertently download viruses, games, etc?
Administrators can completely customize what features the users have access to on their devices. For example, devices can be locked down in Kiosk Mode to prevent users from installing games or applications that IT would then be forced to support. Administrators can also control the menu access, thereby giving access to only those menu items they deem appropriate. Because the platform is integrated with LDAP and Active Directory, these options can be set individually, for groups or for all mobile workers globally.

8. What features are built into the solution for me to remotely manage my mobile workforce?
The Desktop allows Administrators to send alerts and messages to mobile workers in the field. When the mobile worker reads the message an acknowledgement is immediately sent to the Administrator for tracking purposes. Administrators can also monitor the device battery life, memory, device ID and version of software deployed. Built in Google Map tracking also allows managers to report activity monitor and coach users.

9. Do I have to manually upgrade each device if the vendor issues a new release of their software or can this be managed remotely?
The platform has built in remote software updates, which means that customers do not have to purchase a 3rd party application to manage software releases. The platform allows remote software updating for not only our own applications, but any third party applications. Instead of calling the devices in from the field to manually upgrade them, Administrators simply import the new release files into the Desktop. During the next synchronization the updates will be sent to the device, activated, and applied. This means your IT department is free from the countless hours of labor typically required to keep your devices on the latest version of software. And, your mobile workforce avoids downtime while waiting for the updates to be applied. This feature eliminates the administrative costs typically required in a mobile project.

10. What happens if I start synching data and my connection gets dropped? Is there any synchronization management built into the solution?
If the mobile worker’s connectivity is lost in the middle of synchronizing data, the system tracks where it left off and will begin syncing again from the exact same place when connectivity becomes available again. This feature greatly minimizes transmission costs and optimizes user productivity.
Customers can prioritize their sync networks as well as set their sync preferences so the system will begin synching at their preferred times or based on an event within the data collection process. If no network is available at the defined times, the system will keep trying to sync until successful. This process is autonomous with the mobile worker taking no action. And, if the mobile worker is in the middle of collecting data at the time of the scheduled sync, the sync engine runs in the background and does not take over the screen or slow performance.

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The first 5 things to think about when planning an enterprise mobility deployment

Is your organisation investigating ways to eliminate collecting data on paper for your mobile workforce?

This week we are exploring the top 10 important questions you should ask vendors you are evaluating before you make this decision.

1. Does the solution allow me to configure applications with no programming required? Will I need to pay the vendor each time I want to make changes to my applications?

We use the MobileFrame platform where no custom programming is required to create applications custom tailored to your organization's needs. Because business is dynamic, most companies need to make changes to their applications as their business evolves. The solution allows customers to simply open the application in the Task Library, make the changes and deploy them to the field without writing a single line of programming code or paying us for each change.

2. Can I use a variety of hardware in the field? Some of my users want a handheld Windows Mobile device and other users want to use tablets or laptops. What about supporting different hardware manufacturers with different operating systems?
Applications can be deployed to any .NET enabled device such as Windows Mobile, Tablet PC, or Laptops without having to compile code for each device-type or re-compile code when the application changes. The software recognizes what device it is installed on and will automatically call the correct barcode drivers, imagers, etc. Over time many customers purchase additional hardware as their workforce grows.

3. I have data in tables that is constantly changing, such as work order assignments, inventory levels, etc. How do the mobile workers get this new data?

Our Dynamic Enterprise Data feature allows the customer to define how often updated/changed data is sent out to the field. And, business rules can be defined that tell the system to send this new data to everyone assigned to the project or to only those workers who need to see the specific data. For example, if work orders were assigned to a specific technician the system could be set up to automatically send the data only to that technician.

4. How can I integrate the mobile applications with my backend business systems?

The majority of applications deployed today require integration to the customer’s business systems so that mobile workers can access data such as inventory levels, work orders assigned to them, account status, etc.

The Integration Wizard makes this task a very simple process that can be accomplished in minutes instead of the months required by traditional development solutions. It also allows automatic table discovery with point and click integration to any OLEDB or ODBC capable database. Once connected to the external database, the Integration Wizard will create the integration code automatically with no programming required. The wizard even allows the user to schedule how often to retrieve new or changed data in the backend system tables. Once changes are detected, the data is routed to the correct mobile worker with no manual intervention required.

5. How does the solution work if there is no internet connectivity?

Because wireless networks are not always available or reliable, the platform is designed to contain all business logic and data on the handheld device, enabling full functionality both online and offline. When wireless or wired access is available, mobile workers can communicate with the office in real-time. The system can automatically or on command send and receive queued transactions, content and messages via a secure connection. This feature optimizes user productivity while minimizing transmission costs.

Next time 5 more things to think about...

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Mobile VPN secures data transmissions

Authenticating users and securing sensitive data transmissions is critical in today's world. Adequately securing network access and protecting data being transmitted to and from mobile devices is more difficult in wireless environments.

NetMotion's Mobility XE prevents unauthorized users from accessing your network and stops eavesdropping, replay and other network-level attacks. Learn More


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