Satellite Navigation Evolution The Software GNSS Receiver

fined radio (SDR) techniques represents an evolutionary step in the development of modern global navigation satellite system (GNSS) receivers. Software radios perform all digital signal processing via a programmable microprocessor or digital signal processor (DSP) as opposed to using an application-specific integrated circuit (ASIC). This separates analog signal conditioning in hardware from digital signal processing in software and results in significant advantages. This approach to signal handling is particularly important in the case of GNSS, which in the near future will have a number of additional signals that can be utilized for positioning, navigation, and timing. Users of ASIC-based receivers will have to purchase new hardware components to access these new signals. However, users of software receivers will only need a software upgrade to allow for the inclusion of the new signal processing. Traditional Architectures Today’s commercially available GPS receivers are almost exclusively based on the block diagram depicted in Figure 1. An antenna is connected to a radio frequency (RF) signal conditioning component that performs amplification, filtering, frequency down-conversion, and sampling. How It Works. The digital samples are passed to an ASIC responsible for high-speed digital correlation operations on the ranging code, and accumulation of these results over a range-code period. These accumulations are then passed, at a 1 kHz rate for L1 GPS for example, to a programmable microprocessor responsible for controlling the tracking loops (providing feedback to the circuit controlling carrier frequency/phase and range-code rate) as well as for decoding and processing the navigation data stream to determine position, velocity, and the receiver’s clock offset from GPS Time. This general approach has provided a well-engineered partitioning of the required computations across fixed and programmable logic. However, it limits the flexibility of the receiver architecture for many applications of interest.