Enabling hardware technology for GNSS software radio research

Abstract: Software Defined Radio (SDR), has become an increasingly popular alternative to traditional radio technology. In principle the incoming radio frequency signal is sampled as close to the antenna as possible to minimize noise, distortion and other hardware related effects which degrade the signal quality. Even though this sounds simple the trade-off is that the digital data rate is quite high and a significant amount of processing power is required to perform the same operation as a hardware radio. The biggest challenge for a software radio in a digital satellite navigation system is to replace the parallel hardware in the baseband processor, more commonly known as the correlator chip, with an equivalent software solution that preferably can work in real time. The front-end is usually the same regardless of the approach used in the baseband processor. The use of software radios in Global Navigation Satellite Systems (GNSS) is no exception and many applications can benefit from the unmatched flexibility of a software solution. GNSS receivers are being integrated into many traditional products such as cars and cell phones, where the latter now is beginning to contain sufficient processing power to enable true software radio capabilities. Modern production of cell phones is such that adding more hardware, no matter how inexpensive in itself, has a relatively large cost, therefore adding a software radio which requires a minimum of hardware, is likely to be the more cost-effective solution. However, the underlying hardware, in particular the data bridge for moving raw digital samples from the front-end to the processing element should not be forgotten. Depending on the spectral bandwidth and the dynamic range the data rate of the digital signal from the front-end can vary significantly. Typical transfer rates are on the order of 4-40 MB/s, which is about the same as the transfer rate over USB 2.0 when accessing a mass storage device. The focus of this thesis will be on the underlying technology which enables the use of software radio in the field of GNSS.