I have decided to the architecture of the GPS receiver, which makes it a lot more flexible and powerful:

• The GPS receiver has been replaced with the Universal Software Radio Peripheral (USRP). The USRP is a generic software defined radio (SDR) peripheral board that contains two DACs, two ADCs, an FPGA and a USB interface. Several differnent dautherboards can be connected to the motherboard to interface it with several different radio receivers. I have ordered a broadband receiver that is capable of receiving both GPS, GLONASS (Russinan) and Galileo (European) signals.
  
  
• The USRP does digial down-conversion of the received signal, and the raw data is thereafter transfered to the host computer, which does the majority of the signal processing.
  
  
• The signal processing is performed by the GNU Radio toolbox; a general purpose toolbox for building software radios which runs on all major operating systems.
  

The remaining work is therefore to create the neccessary specific signal processing blocks for the GPS receiver. By running the GNU Radio software on the EFIKA we have a complete open source GSP receiver that is also expandable to use other GNSS systems!

More information can be found here:

• GNU Radio
  
• USRP