  Recently, several global navigation satellite systems (GNSS) emerged
following the transformative technology impact of the first GNSS: US Global
Positioning System (GPS). The power level of GNSS signals as measured at the
earths surface is below the noise floor and is consequently vulnerable against
interference. Spoofers are smart GNSS-like interferers, which mislead the
receivers into generating false position and time information. While many
spoofing mitigation techniques exist, spoofers are continually evolving,
producing a cycle of new spoofing attacks and counter-measures against them.
Thus, upgradability of receivers becomes an important advantage for maintaining
their immunity against spoofing. Software-defined radio (SDR) implementations
of a GPS receiver address such flexibility but are challenged by demanding
computational requirements of both GNSS signal processing and spoofing
mitigation. Therefore, this paper reviews reported SDRs in the context of
instrumentation capabilities for both conventional and spoofing mitigation
modes. This separation is necessitated by significantly increased computational
loads when in spoofing domain. This is demonstrated by a case study budget
analysis.
