Potential interfering signals in software defined radio

Software defined radio (SDR) is often heralded as the future of mobile communications with some aspects expected within the fourth generation of European standards. An SDR suitable for commercial narrow- and broad-band applications will typically cover the frequency spectrum between 400 MHz and 6 GHz. This range encompasses all of the (worldwide) existing and emerging standards alongside likely future developments. In order to facilitate such a radio, in the absence of efficient flexible filters, a super-octave-band front-end is needed. The receiver will be subject to all the signals within this band, both wanted and interfering. It is likely that the stronger interfering signals will cause intermodulation products (IMP) within the nonperfect low noise amplifier (LNA). These IMPs can interfere with a wanted signal and, potentially, make it undetectable. This paper reports the results of a radio trial, indicating the strength, frequency and geographical location of potentially interfering signals around the Bristol area. Results are presented for typical urban, suburban, and rural environments and hotspots. The results presented in this paper give an indication of the practical dynamic range requirements of an SDR receiver operating in the frequency spectrum between 400 MHz and 6 GHz.