RF/IF Conversion Segment Tradeoffs This chapter introduces the system-level design tradeoffs of the RF conversion segment. Software radios require wideband RF/IF conversion, large dynamic range, and programmable analog signal processing parameters. In addition, a high-quality SDR architecture includes specific measures to mitigate the interference readily generated by SDR operation. I. RF CONVERSION ARCHITECTURES The RF conversion segment of the canonical software radio is illustrated in Figure 8-1. The antenna segment may provide a single element for both transmission and reception | Software Radio Architecture Object-Oriented Approaches to Wireless Systems Engineering Joseph Mitola III Copyright @2000 John Wiley Sons Inc. ISBNs 0-471-38492-5 Hardback 0-471-21664-X Electronic 8 RF IF Conversion Segment Tradeoffs This chapter introduces the system-level design tradeoffs of the RF conversion segment. Software radios require wideband RF IF conversion large dynamic range and programmable analog signal processing parameters. In addition a high-quality SDR architecture includes specific measures to mitigate the interference readily generated by SDR operation. I. RF CONVERSION ARCHITECTURES The RF conversion segment of the canonical software radio is illustrated in Figure 8-1. The antenna segment may provide a single element for both transmission and reception. In this case a multicoupler circulator or diplexer protects the receiver from the high-power transmission path. In other cases the transmit and receive antennas may be physically separate and may be separated in frequency. First-generation cellular radio and GSM systems separate downlink and uplink bands by typically 45 MHz to limit interference. The transmission subsystem intersects the RF conversion segment as shown in Figure 8-1. This includes a final stage of up-conversion from an IF bandpass filtering to suppress adjacent channel interference and final power am- Figure 8-1 The canonical model characterizes RF IF segment interfaces. 265 266 RF IF CONVERSION SEGMENT TRADEOFFS plification. First-generation cellular systems did not employ power control to any significant degree. CDMA systems including third-generation 3G W-CDMA require power control on each frame 50 to 100 times per second . SDRs may be implemented with a DAC as the interface between IF up-conversion and the RF segment. Alternatively a high-speed DAC may directly feed the final power amplifier. Power amplifiers have less-than-ideal performance including amplitude ripple and phase distortion. Although these effects may be .
