An efficient cascade of half-band filters for software defined radio transmitters

Power consumption is an important issue in the software defined radio transmitter and receiver. In this paper we present a technique that aliases an arbitrary bandwidth signal from base-band to its desired center frequency using a sequence of 1-to-2 up-sampling half-band filters embedded in 4-path polyphase engines with center frequencies aligned with the 4-cardinal directions. By judicious choice of the appropriate filter parameters the proper alias of the 1-to-2 up sampled input signal is passed to the next stage for further up-sampling and alias shifting. The number of stages in the cascade is optimized according to the desired output sampling frequency. An initial frequency offset is applied at the low input sample rate by a complex heterodyne prior to the frequency shifting process provided by the cascade of aliased half-band up-sampling operations. A 1-of-4 selection process guides the input spectrum to extract the spectral alias of the appropriate center frequency path at each stage to place the final alias at the desired frequency location. The paper provides detailed workload analysis that motivate the selection of the proposed structure among the others available. Simulation results are presented at the end for supporting the theoretical results.