How has Locata achieved a unique ability to replicate a GPS constellation on the ground?
The core invention that allows Locata Technology to relicate GPS on the ground is a completely new and patented synchronization method called TimeLoc.
The synchronization of transmitters is essential in an autonomous, high accuracy radio-location system. Synchronization is one of the critical requirements for GPS, and hence each GPS satellite contains 3 or 4 atomic clocks, which are in turn synchronized by other atomic clocks in the ground-based Control Segment of the GPS system.
TimeLoc allows LocataLite transceivers to achieve incredibly accurate, nanosecond-level timing. For the first time ever – this is achieved without the use of atomic clocks. There is no other technology in the world that can do this.
How does TimeLoc work?
The complete TimeLoc process is described in detail in the Locata TimeLoc Patent (US Patent #7,616,682). Nevertheless, the following is a brief description:
TimeLoc is the mechanism used to synchronize the radio signals transmitted by LocataLites. The unique LocataLite transceiver design utilizes a receiver within the LocataLite to track both signals from an external LocataLite (let’s call it “A”) as well as the signals from its own internal transmitter broadcasting co-located signals (“B”). This sets up a measurable loop which is described in the Locata patent document and has been named a Time Lock Loop (TLL). By taking pseudorange and carrier phase measurements derived from both external received signal A and internal signal B, LocataLite B is able to move or slew its signals to align with A.
TimeLoc is fundamentally based on aligning the timing (range) of LocataLite signals to correspond to the geometric distances from the receive antenna to both external LocataLite A and LocataLite B’s co-located transmit antennas. The distances are computed from antenna locations derived when the antennas for both LocataLites are installed and surveyed into position. The known antenna positions are broadcast as “a Locata equivalent to the GPS satellite system’s ephemeris” as part of the navigation data broadcast around the LocataNet. To synchronize the co-located signals with external LocataLite A, LocataLite B slews its internal signals until the single difference range between A and B is the geometric range. This internal correction process is accurate to the millimeter level.
Locata’s TimeLoc technology is not affected by traditional synchronization problems such as RF delays in the receiver front-end, or timing delays within the receiver/transmitter hardware or components, because all of these delays are cancelled out as a natural consequence of the differencing process in the TimeLoc method. From a Locata receiver’s perspective, the two transmitters are completely synchronized. Once the ranging signals are synchronized, LocataLite B signals it has TimeLoc, sets its health bit to “healthy”, and “joins” the LocataNet. The TimeLoc method is simple, robust, and works extremely well in real world deployments, allowing synchronization at the nanosecond (or better) level.
There is no other technology in the world that can do this.
Does Locata provide a common clock that all receivers can sync with?
Yes. Locata’s current system design generally designates one of the LocataLite transceivers as a “master clock” and, assuming a standard LocataNet network configuration, all other LocataLites and Locata receivers in that network lock to that time base.
There are topologies in the design of a LocataNet that can be used to overcome line-of-sight obstacles between the master LocataLite and other transceivers in a LocataNet (such as “cascading” TimeLoc from LocataLite A to B to C, etc) but those systems can become complex and are not covered in this FAQ.
In another regularly-used TimeLoc variant, a LocataNet to be “locked to GPS time” (or any other time base reference) if that is a customer requirement. In this way, a LocataNet can distribute UTC time, or any other time reference (e.g. an atomic clock reference) throughout the local network.
What are some applications of Locata technology?
Locata allows any entity – mine, construction site, port, warehouse, airport, strategic asset — and eventually entire cities – to determine for itself the level of positioning it wishes to deploy, under its OWN autonomous LOCAL CONTROL. In other words, in any current application where GPS-style positioning is desired — but GPS is either “unreliable,” inaccurate or unavailable — then Locata may supply a complementary solution.
However, Locata also represents an innovative and previously unattainable solution for many new applications that are out of the reach of GPS-style solutions. The easiest ones to grasp are indoor applications such as automating indoor warehousing. But there are obviously many other applications based around providing highly-reliable and configurable positioning in GPS-occluded areas. It will be fascinating to watch the large number of innovative applications that Locata-style positioning will enable in the future.
How accurate is positioning using a LocataNet?
Locata positioning is capable of centimetre-level accuracy – outdoors and indoors. However, the positioning accuracy of a LocataNet can be designed to meet the specified accuracy requirements of a particular application, e.g. guiding automated forklifts in a warehouse. It is possible to design and build “custom” LocataNets because Locata is an autonomous terrestrial system.
With GPS, “you get what you get”. With Locata, “you get what you need”.
Does Locata positioning require correction or augmentation by other networks?
No. Locata navigation positions are generated by a “carrier-phase single-point solution”. Locata can achieve positioning accuracy without requiring any external augmentation, differential correction or other information input to the Locata receiver.
Survey-grade GPS technology is also able to deliver centimetre-level carrier-phase positioning, but not as a “single-point solution”. To obtain high precision positioning from GPS, surveyors require access to other complex, additional technologies, such as reference receivers that are pre-deployed and surveyed into known positions, differential correction networks and communication data links that transmit corrections to an end-user. These additional systems remove the large errors in the standard (i.e. uncorrected) GPS system position solution. Professional survey-grade GPS receivers cost up to US$10,000, and therefore are not affordable for general consumer use.
Does Locata provide a local or global referenced position?
Any desired “reference frame” can be provided by a LocataNet. If LocataLite transmit antennas are surveyed to be referenced, say, to the global WGS84 standard, then the entire LocataNet will adopt and broadcast that reference base. However, surveyors often have to work within a “local reference” such as a local coordinate frame used in areas like open-cut mines. Setting up a LocataNet to utilize the same coordinate frame is relatively straightforward, which means that position calculations do not require conversion between different data sets.
Does LocataTech provide ranges to each LocataLite, or only a computed position?
Yes, LocataTech provides pseudorange and carrier-phase measurements to each LocataLite in view, just like GPS does for satellites in view.
What is the update rate of the Locata position and/or individual LocataLite ranges?
In our current receivers the position solution is calculated at a 25 Hz rate, but up to 50 Hz has been demonstrated.
Are there Doppler speeds of each LocataLite?
Unlike GPS satellites, LocataLites are designed to be stationary when deployed, so they do not present a Doppler shift (except for any shift generated by user movement, of course). This greatly simplifies the search strategy required to acquire a Locata signal because the frequency shift is inherently much smaller than what is expected from satellite-based signals. Hence, when a Locata receiver acquires just one LocataLite signal, it can almost instantly acquire all the others.
Locata Radio-Positioning Basics
In which frequency band does a LocataNet operate?
LocataNets currently operate in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band. The ISM band is license free worldwide. The 2.4 GHz band is also used by two well-known global technologies – Wi-Fi (802.11) and Bluetooth.
A LocataNet can be configured to operate at other radio frequencies, but initially the ISM band provides a straightforward, license free, continuous frequency spectrum. Using the ISM band also allows the Locata system to co-exist with GPS signals (i.e. LocataNet signals do not jam GPS) and permits a Locata-enabled GPS receiver to simultaneously use GPS and Locata signals.
What is the transmission power of a LocataLite?
The maximum signal power for devices in the ISM band is restricted by international regulation to +8 dBm within a 3 kHz bandwidth and to a maximum of 1 Watt. The generally accepted global guidelines for the ISM band are laid out in the United States’ FCC Part 15B regulations, and Locata devices comply with this ordinance.
What range does a LocataLite transmission cover at this power?
The range of a LocataLite signal is generally in the order of tens of kilometres however, the range is limited mainly by terrain, much the same as mobile phone systems. At this time, Locata does not recommend separation of more than 5 km between LocataLites, except for specialist purposes such as military aircraft applications where higher-powered systems have operated at distances of up to 50 km (30 miles) between LocataLite base stations.
What if more signals are required, or there is a need to extend the range of a LocataNet?
If more signal power is needed for extended coverage, additional LocataLites can be added to a LocataNet. This is the same method used by mobile phone operators that add towers to increase coverage in a specific area. For example, to increase the signals in a local shopping mall, the mobile phone operator adds mobile phone towers near the mall. Additional LocataLites can be added in much the same way, inside or outside a LocataNet coverage area, to provide additional location signals. Locata networks can have as few as four or five LocataLites, e.g. to cover a small indoor area.
Does Locata interfere with Wi-Fi, or vice versa?
The short answer is no; however as with every other radio technology that has to share a frequency band with other users, appropriate intelligence and configuration is required when designing and installing potentially competing networks.
Locata has gone to great lengths to ensure LocataNets can interoperate with Wi-Fi networks without deleterious effects to either network. In fact, LocataNets are currently deployed in open-cut mine environments where the entire area is covered with Wi-Fi signals for data communications. LocataNets have been installed in these environments, and both systems operate effectively in the deployment area.
The Locata system does not interfere with normal 802.11b/g operation. Does it still consume a dedicated channel of the 2.4-Ghz spectrum (more or less than a 5-Mhz channel?)
A LocataNets transmits in the free global ISM band at 2.4 GHz, the same band used by Wi-Fi and Bluetooth. Locata systems currently transmit two simultaneous pseudorandom pulsed signals, one in the lower and one in the upper sections of the ISM band. Locata’s signals do spread over more than a single 5 MHz Wi-Fi “channel.” However, all Locata devices have been designed to work to the FCC regulations for that band. From the outset an important design factor for Locata was to ensure that LocataNets work effectively in areas already using Wi-Fi systems. Our networks have been designed to “play nice” with the myriad Wi-Fi networks that are already deployed in the real-world.
What is the benefit of broadcasting more than one signal from a single LocataLite?
LocataLites transmit four PRN-style signals from each device. The signals are both spatially diverse and frequency diverse. This diversity allows Locata positioning solutions to use multiple signals from “substantially the same source” to view the different effects created by multipath and signal occlusion. The differences seen from these “transmission clusters” provides important information that helps Locata positioning solutions mitigate the real-world degradation effects encountered by terrestrial positioning signals. Obviously, much of this information is proprietary, and subject to protection under Locata’s patent portfolio.
Do you need fingerprinting pre-surveys for Wi-Fi positioning before applying the Locata system?
No. Locata does not have anything to do with Wi-Fi-style positioning promoted by companies like Skyhook or Ekahau. Locata does not need any form of “fingerprinting” or updating of Wi-Fi router databases as is required by these Wi-Fi-based positioning systems.
This question actually illustrates a point of confusion bought about by the fact that Locata transmits at the same frequency as Wi-Fi. A LocataNet is a completely independent and autonomous GPS-style network that “looks just like a satellite constellation”.
Locata chose to transmit in the free Wi-Fi radio band because it guarantees that:
- LocataNets do not interfere, in any way, with GPS;
- LocataNets can be set up anywhere in the world without requiring any licensing or regulatory approval (just as any consumer’s Wi-Fi router can be set up anywhere in the world); and
- Locata technology has been developed from the ground up to integrate into a vast array of professional and consumer devices — most modern communications devices already have Wi-Fi receivers built-in. So we envisage that in the future, with minimum modification, these devices will also be able to use the Locata positioning signal for a position solution.
In summary: Locata transmits in the Wi-Fi band, but it is absolutely not a Wi-Fi positioning technology like Skyhook, et al.
Is a LocataLite a Pseudolite?
No. Many experts, upon hearing that Locata networks “terrestrially replicate GPS”, immediately jump to the incorrect conclusion that Locata technology is based around a device the industry has long known as a pseudolite.
These “pseudo-satellites” were designed in the 1970’s to be just that – satellite stand-ins when the USAF needed to terrestrially test GPS-like signals before there were GPS satellites in the sky.
A pseudolite transmitter outputs a ranging signal, traditionally one of the GPS signals on, or near, the GPS frequencies. However pseudolites do not synchronize to each other, which is a critical requirement for the creation of a radio-positioning system.
A pseudolite has no knowledge of neighboring pseudolites and therefore cannot synchronize to other pseudolites.
Many attempts have been made by countless companies and researchers over the years to synchronize pseudolites through the use of GPS time, cables or atomic clocks. However, in the 40+ years spanning the existence of pseudolite devices, there have been no successful commercial applications. In fact, none of the many different approaches has ever delivered a widely-accepted, real-world operational system, despite the enormous technical effort, time and money put into pseudolite development.
Locata had developed a TimeLoc synchronization technology (see CORE TECHNOLOGY section above) that solves the fundamental problem of deploying a ground-based equivalent of GPS, something that pseudolites clearly have not achieved in the 40+ years they have existed.
A LocataLite is not a pseudolite. A LocataLite is “ a device that generates TimeLoc”.
Importantly, Locata signals are not the same as GPS or any other satellite signals. The Locata system architecture is designed to create a ground-based positioning system which is a true GPS-replica, not a ground-based test capability for a satellite system (which is what pseudolites were originally designed to do). The Locata system was designed from the outset with the goal of working exactly like a satellite system, as observed by the “User Segment” – a LocataNet user sees the Locata system as a “terrestrial GPS constellation”.
Put in classic GPS terms, the LocataNet handles both the Space segment and the Ground segment via the LocataLite transceivers and TimeLoc. A user sees a system that is a one-way ranging system providing pseudorange and carrier-phase measurements from a network of synchronized transmitters. This is exactly the same description used to describe the GPS satellite constellation.
Locata is the only technology in the world that can do this.
Do LocataNets transmit signals that can be deciphered by standard GPS receivers?
LocataLites transmit signals that are proprietary, but which would look very familiar to engineers who have worked in GPS receiver design. A “traditional” GPS receiver cannot, at this time, receive and decode Locata signals but that situation changed in September 2012 when Leica Geosystems launched the world’s first GPS+Locata combined receiver at the MINExpo Conference in Las Vegas in September 2012.
The two main reasons that standard GPS receivers cannot receive a Locate signal are:
- LocataNets do not transmit at the standard L1 GPS frequency (they transmit in the license-free 2.4 GHz frequency common to devices such as Wi-Fi and Bluetooth). Therefore, standard GPS receivers cannot use the Locata signal in the same way they use GPS signals; and
- Standard GPS receiver correlators have not yet been designed to receive Locata signals.
In Q3 2011 Locata released an Interface Control Document (ICD) that clearly describes the Locata signal structure. Locata’s ICD is similar in approach to the legacy GPS ICD or the recently released Galileo receiver documentation.
Locata’s ICD allows GPS or radio receiver designers to incorporate Locata signals in their position solutions in the same way they use satellite-based signals today.
Do you eventually see commercial GPS receivers being able to receive and use Locata signals?
Locata is already regarded by its key technology partners as “another independent positioning constellation” that — locally — is just as important and valid as the satellite-based constellations. Locata signals are very similar to GPS signals and can therefore be incorporated into future GPS-style receivers just as easily as any other constellation and similar to the way GLONASS has been integrated into most professional receivers over the past few years.
As described above, Leica Geosystems has already produced the world’s first GPS+Locata Receiver by integrating Locata receivers with NovAtel receivers in a single enclosure for deployment in its open cut mining application, Jigsaw Positioning System – Powered by Locata (“Jps”). The results reported by the mines since the first Leica LocataNet became operational in mid-2012 have been spectacular, both in terms of efficiency gains and financial return to the owners. A detailed white-paper reporting on the Boddington Mine installation highlighting the results was printed in the September 2012 issue of International Mining Magazine.
In Leica’s revolutionary new JPS receiver, Locata’s positioning data and NovAtel’s GPS positioning data have been integrated at the measurement level in the core algorithm library. That is, the JPS receiver computes a position either using signals received from GPS satellites alone, from LocataLites alone – or critically – by using signals from both the satellite and Locata systems. To the end user this process is totally seamless and transparent.
The world-first JPS receiver heralds a new class of positioning receiver which Locata calls “GPS 2.0”. It’s a technological advance which allows the deep integration into new devices of satellite and terrestrial positioning signals – GPS+Locata – that leverage the strengths of each system to produce a seamless and ubiquitous positioning solution across any area where it is required. GPS everywhere.
This is the future of positioning. And it’s enabled by Locata’s spectacular advance in positioning technology.