 of the To augment the processing power of a general purpose modulation being carried. If a quiet channel is selected, all DSP, fixed function DSPs are designed to process very that should be on the output of the channelizer is the noise large amounts of data very fast and efficiently. While from the AFE plus the ADC. Since the NSD has already a general purpose DSP can be infinitely reprogrammed, been established in a prior section, the total noise in the the signal flow within a fixed function DSP must be re- channel can be determined by integrating this over the stricted to a single architecture. Programming is also channel bandwidth. In log math, the equation for receiver limited to configuration registers and memory co- channel noise is very simple: efficients. However, since most radios are based on some form of super-heterodyne architecture, this is not such Nchannel = 10108(kxTxlHz) + Gmin + -NFtotal a limitation due to the high degree of similarity between different designs. Therefore, the fixed function DSPs can 10 log BW 1Hz channel (2.3.11) be designed to represent a very large class of receiver or transmitter designs. These fixed function DSPs are often CHAPTER 2.3 Software defined radio ADC Inputs Cascaded Cascaded Integrator Comb Filter Integrator Coef. (CIC2) Filter (CIC5) SYNC NCO SYNC CIC Serial or SYNC_RCF Parallel Output Cascaded Integrator Cascaded Comb Filter Integrator Coef. (CIC2) Filter (CIC5) External JTAG Interface Sync. Circuit Figure 2.3-12 Fixed function receive signal processor (RSP). implemented either in FPGAs or ASICs. Processors Quite often, the passband must be a matched filter or designed for the receive function are called receive signal otherwise shape the characteristics of the incoming processors (RSPs), as shown in Figure 2.3-12, and spectrum. This is easily accomplished with a digital filter, transmit functions are called transmit signal processors a task that is often difficult with analog channel filters. In (TSPs), as shown in Figure 2.3-13. In general, both TSPs fact,