Communication Systems Engineering with GNU Radio

10Conclusion

Throughout this book, we have attempted to demonstrate how GNU Radio and its graphical interface, GNU Radio Companion, provide an ideal framework to tackle abstract signal processing concepts and yet reach practical results on real signals recorded by general-purpose software defined radio (SDR) hardware. Starting from such mathematical concepts such as negative frequencies and complex voltages as derived from the analytic signal analysis, intuitively displayed with synthetic signals processed by GNU Radio blocks, we have tackled various digital communication challenges including a quadrature phase shift keying (QPSK) radio modem and decoding a QPSK-based weather satellite signal. However, since SDR provides access to the lowest level of the abstraction layers – hardware – with the raw in-phase/quadrature (IQ) streamed from the analog-to-digital converter, radiofrequency wave analysis such as time of flight (radio detection and ranging [RADAR]) or beamforming/null-steering is possible before any digital processing is started. Indeed, once a spoofing signal has reached the initial digital processing steps, a properly tailored signal will no longer be differentiated from the genuine signal. Physics is much harder to spoof, and a constant phase difference between signals broadcast by satellites distributed over the celestial sphere received by two antennas is the sure signature of a unique spoofing source, inconsistent with the varying phase due to the varying directions ...