An algorithm for minimum bandpass sampling frequency for multiple RF signals in SDR systems

The principal idea behind the design of a software radio is to place the analog-to-digital and digital-to-analog converters as near the antenna as possible, such that most of the radio functionalities can be implemented on a programmable digital signal processor. One way lo achieve this is by direct bandpass sampling of the desired RF signal band to baseband frequency. However, the design of a software radio receiver becomes more complicated when two or more distinct RF signals are to be received. The traditional approach for this case has been to bandpass sample a continuous span of spectrum containing all the desired RF signals. The disadvantage with this approach is that the required sampling rate depends upon the span of spectrum, instead of the information bandwidths of the signals. We present an efficient algorithm to compute the minimum bandpass sampling frequency for direct downconversion of multiple distinct RF signal bands simultaneously. The novelty of this algorithm is that, at each iteration, it not only checks for a valid sampling frequency, but also determines the next possible minimum value of sampling frequency