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The SOFT-REC project represents the feasibility study of a prototype of a GPS-EGNOS receiver entirely developed as a software application, running on a PC architecture. Currently, the typical GPS receiver, from the handheld version to the more sophisticated one, uses a dedicated hardware circuit in order to implement all the signal processing algorithms. | The aim of the SOFT-REC project is to completely change this approach, transferring all the ad-hoc hardware processing into a set of software algorithms running on a suitable hardware platform, including a digital front-end that is in charge of digitizing the incoming signal and feeding the software with the data. | |  click for larger image |
 click for larger image | | The SOFT-REC prototype main issue is the software implementation for signal processing and navigation algorithms which are currently carried out by hardware circuits in standard handheld receivers. The figure at left shows the software relevant critical elaboration tasks in the SOFT-REC system. | Here follows a survey of the tasks that the software shall implement : - Signal acquisition: Acquisition is a coarse synchronization process giving estimates of the PRN code offset and the carrier Doppler.
- Signal tracking: Tracking means to track the variations in the carrier Doppler and code offset due to line of sight dynamics between the satellite and the receiver. Another important function of the tracking loops is to demodulate the Navigation data from the incoming signal.
- Bit and frame synchronization: After initial C/A-code acquisition, databit timing is subject to navigation (NAV) bit offset ambiguity. Therefore, it is necessary to develop a technique to determine databit timing and eliminate the NAV-bit offset ambiguity.
- Navigation solution: A Navigation solution is an estimate of the user position and any other required parameters. The typical states in a GPS navigation estimator are three components of position, clock offset and clock drift. In order to compute the position estimate, the Navigation algorithm should have a knowledge of pseudorange to at least four GPS satellites and the position of those satellites.
The main milestones of the project were: - BDR (Baseline Design Review) February 2004: presentation and discussion of System Software Specification Document and System Requirements Document,
- PM (Progress Meeting) May 2004:presentation and discussion of Technical Notes about Signal Processing, Software Requirements Document and Interface Control Document,
- MTR (Mid Term Review) September 2004: delivery of the output of the 'Signal analysis' Work Package and of the 'Development of the receiver software prototype' Work Package and discussion of test procedures and plans,
- FR (Final Review) July 2005: delivery of complete Soft-Rec receiver, an open SPR causing position accuracy degradation, has been closed during August. Now Soft-Rec is fully compliant,
- Program end planned October 2005: final acceptance of deliverables.
CDMA
Code Division Multiple Access (CDMA) is a radically new concept in wireless communications. In CDMA, the users utilize the whole available frequency spectrum all the time (spread-spectrum technique). The core principle of spread spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths much wider than that required for simple point-to-point communication at the same data rate. CDMA receivers separate communication channels by means of a pseudo-random modulation that is applied and removed in the digital domain, not on the basis of frequency. Software Defined Radio
The term 'Software Defined Radio' (SDR) was coined in 1991 to signal the shift from the hardware intensive digital radios of the 1980's to the multi-band, multi-mode, software-based radios planned for the year 2000 and beyond. The main goal in SDR is the design of a flexible system that can transmit and receive signals at virtually any frequency using any protocol, any of which can be reprogrammed almost instantaneously: a sort of 'universal receiver'.
An important aspect of using the software approach is the flexibility. A program can be used to process signals digitalized with various sampling frequencies. New algorithms can easily be developed without changing the design of the hardware; this is especially useful to improve the receiver with new signal processing algorithms. For example, when the GALILEO signal will be standardized, upgrading the receiver in order to be compatible with the new signal specifications will be only matter of changing some of the software modules of the system, and almost no need of hardware substitution will arise. Indeed, the only signal specific hardware present in the system is the digital front-end, and a change in the band of the carrier could imply at most the design of a new antenna and a new RF chain. On the other hand, the general purpose PC architecture will not need any modification, except probably for an increase of the CPU speed, this one needed to confront a possible increase of the sampling rates.
Soft-Rec project has been successfully completed. It has demonstrated the ability to operate in real time a complete GPS SW receiver on a standard commercial PC. In addition EGNOS data receiving and processing has been introduced to augment the GPS accuracy. The number of GPS channels that can be tracked depends only on computational power of the computer and satellites in visibility. The 3 meters accuracy in position determination permits to Soft-Rec to satisfy most of present and future application requirements. Intecs and UNIP have acquired the skill and experience to handle the navigation signals and to use them for position determination. Soft.Rec can be adapted to Galileo signal processing with relative no major complexity. Main Commercial objectives of Soft-Rec are: - Commercial applications, service and network monitoring based on PC or DSPs,
- Real time automotive and mobile applications when computers are available,
- Low cost performance consumer platforms such PDAs and handheld PCs, not real time,
- Space based SW receiver supported by DSPs or FPGA architectures.
Last Update: 11 May 2006
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