Bandpass Sampling for Software Radio

The principal idea behind the design of a software radio is to place the analog-to-digital and digital-to-analog converters as near to the antenna as possible, such that most of the radio functionalities can be implemented on a digital signal processor. One way to 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 signals are to be received from multiple distinct RF bands. The traditional approaches for this case have 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. In this paper, we present an efficient algorithm to compute the minimum bandpass sampling frequency for direct downconversion of two 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.