 since these filters are digital, they can implement and RSPs contain exactly the same elements, only the any filter that can be realized using FIR or IIR techniques. order is reversed. For either device, there are three key This filter is determined by Equation (2.3.12): subfunctions found in these devices. The first function is the frequency translation. In the Sample_Rate/2 analog domain, the frequency is translated with a mixer or Noise Processing = 10 log modulator/demodulator. This function is used to mix two channel inputs together in such a way that the sum and difference (2.3.12) frequencies are generated on the output. In the digital domain, this is represented by a multiplication. If the Following channel filtering, the bandwidth will be rel- function is a mix, then a single "real" multiply is atively small compared to the data rate because of the high performed, but most often, the multiply is a complex oversampling rate in the ADC. Therefore, it is advanta- multiply used to generate quadrature data and thus sep- geous to reduce the data rates. This has several benefits. arate positive and negative frequencies. In an IF sampling First, with the reduced data rate, the computational receiver, a real digital IF is applied to one of the complex burden on the general purpose DSP is reduced. Second, in inputs of the multiply. The other input is the output from CMOS technology, lower data rates result in lower power. a complex numerically controlled oscillator (NCO). The Therefore, following the channel filters, data decimation NCO is tuned to the desired frequency such that the is performed. The decimation must be consistent with the result is a complex signal at DC and at the sum frequency. Nyquist, but significantly reduces the computation by the Following the NCO and complex mixer (de- general purpose DSP that follows the RSP. modulator) is a low-pass filter. This filter serves two In the transmit direction, the data flow is reversed. purposes. The first purpose is to remove the undesired First the data 