Software GPS is another approach
GPS receiver elements
A classic GPS receiver, contrary to software GPS, is built with the following blocks:
- Antenna
- GPS Front-end IC (the analog part)
- GPS Baseband IC (the digital part)
- Application Processor with Memory
- Input/Output
In the front-end IC we find a Low Noise Amplifier, a Frequency Down Converter and an Analog to Digital Converter. In the Baseband IC are situated the correlators, a micro-processor and ROM and RAM memory. Both are application specific integrated circuits(ASICs) and sometimes they are built together into one integrated circuit(IC).
GPS Baseband IC
All the hard work of satellite acquisition and tracking, finding the phase transition of the navigation data, measure the pseudorange, demodulation of the navigation data and the decoding of the ephemeris data to obtain the satellites positions is done in the Baseband IC.
Different uses
A GPS receiver to be used in urban canyons must care for multi path mitigation. A receiver to be used in forests will have to treat for weak signals under the thick foliage. Both problems need to be treated differently in different algorithms. In a GPS receiver for pedestrian use the treatment of all the signals should be different than in a GPS receiver to be used in a Formula I car or a plane.
Most Baseband ICs will be designed to do a bit of all different tasks, but this will always result in compromises. And once the design is ready and mass production has started, there is no way to change anything anymore. The next 100.000 or 1.000.000 Baseband ICs will all be identical.
Software Defined Radio
Software Defined Radio (SDR) is a collection of hardware and software technologies that enable reconfigurable system architectures. SDR provides an efficient and comparatively inexpensive solution to the problem of building multi-mode, multi-band, multi-functional wireless devices that can be enhanced using software upgrades. SDR-enabled devices can be dynamically programmed in software to reconfigure the characteristics of the hardware.
Software receivers
Software GPS receivers, based on SDR, accomplish all digital signal processing using a programmable microprocessor rather than with hardwired discrete components. Modern, and certainly future, handheld devices have fast and powerful CPUs and lots of memory and are perfectly capable of performing the computations for a GPS receiver, thus eliminating the extra microprocessor.
GPS and GLONASS are being upgraded; Galileo is coming
A classic Global Navigation Satellite System (GNSS) receiver will not be able to follow all the changes and needs to be replaced if the user wants to benefit from the extra new signals. A Software GPS Receiver can easily be upgraded by a new piece of software, eventually over the air.
A Software GPS Receiver can adapt itself dynamically
A Software GPS Receiver is perfectly capable to find out in what kind of environment it is operating. If it recognizes an urban canyon, it knows that multi path mitigation is important. If all signals are weak, it knows that it finds itself probably in a forest. Also the speed of travel is an important indication of the kind of use. Once recognized, the program can choose the best algorithm in order to calculate the best final solution.
Do Software GPS receivers exist today (October 2006)?
On September 28, 2005 Royal Philips Electronics announced its "Spot" Software GPS technology that directly utilizes the Intel application processors in notebooks, cellular phones and handheld devices. Philips demonstrated the Spot Software GPS in April 2006.
ALK Technologies, Inc. has integrated the Spot Software GPS solution in its latest product, the CoPilot Navigator 9, available on Dell Inspiron Notebooks in the USA.
Maxim Integrated Products created a new GPS solution based on its GPS front-end receiver IC combined with Royal Philips Electronic' innovative Spot Software GPS. Operating in both autonomous (unassisted) and assisted modes, the software solution can provide fixes every second for applications such as automotive tracking. The algorithm can also be tuned to suit pedestrian or indoor use, enabling an optimized GPS solution for mobile products such as cellular phones, PDAs, digital cameras, MP3 players, laptops, and portable DVD players.
The Philips Spot software is 600Kb of code written in ANSI C, which can be ported to, and run on any standard processor, such as ARM, Intel Xscale or TI-OMAP. The software takes the output of the GPS front-end receiver and locates the satellites. It then downloads the satellite ephemeris and, using a new proprietary technique, performs signal processing to extract the satellites' signals. The result is an efficiently generated position fix.
Other manufacturers
Already in 2004 NAVSYS Corporation has developed a PC/104-based Software
GPS Receiver (SGR) test-bed that integrates multiple
sensors for advanced navigation applications. The
sensors compatible with this system can provide
GPS, wireless, inertial, and image information. This
test-bed provides a low-cost hardware and software
platform that can rapidly adapt to new waveforms
and Software Defined Radio (SDR) applications.
NordNav announced the full commercial release of its NordNav E5000 embedded software receivers for Mobile GPS Positioning at the 3GSM World Congress in Barcelona, Spain on February 13, 2006.
On March 22, 2006 RFMD has announced that its new software-based GPS solution, the GPS RF8110, is sampling to initial customers. The GPS RF8110 is a breakthrough end-to-end solution that enables the integration of high-performance GPS applications in handheld, battery-operated mobile devices. RFMD says that the GPS RF8110 is a highly scalable and flexible solution, allowing it to be optimised for a wide variety of product platforms.
As a software-based solution, it offers scalable performance depending on the required sensitivity, accuracy and end-user application. The solution supports push-to-fix, location based services (LBS) applications as well as automotive and pedestrian navigation in outdoor and low signal strength environments.
For consumer electronic products, SiGe Semiconductor and Nordnav Technologies have announced on September 28, 2006 they've collaborated on a GPS/Galileo receiver.
The companies have combined SiGe's SE4120L radio front-end with Nordnav's E5000 software to offer a receiver system with the high performance, small size and power efficiency that is essential for mobile devices including laptops, portable media players, and cellular phones.
The combination of technologies also provides manufacturers with a flexible architecture that will meet evolving standard requirements. SiGe's SE4120L receiver IC used with Nordnav's GNSS software provides the highest level of GPS performance today, along with a simple software upgrade to Galileo when the Galileo system becomes operational. The 'unique' software/hardware architecture also speeds design, test and verification of new GNSS systems in challenging environments, says the duo.
Conclusion
Software GPS is coming to the consumer market and will bring us more sensitive, more accurate and more flexible navigation solutions.
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