Receiver power issues related to matched filter implementation for portable wireless communication terminals

A number of personal communication systems (PCS) call for the use of spread-spectrum techniques for transmitting digital data through multiple-access channels. In these systems, a correlator or matched filter is used within the receiver to despread the encoded waveform before the underlying digital data is recovered. The matched filter may be implemented either before or after the received waveform has undergone analog-to-digital conversion. Since power consumption is a principal concern for portable PCS terminals, it is proper to consider which matched filter implementation-analog or digital-leads to a more power efficient spread-spectrum receiver. These two different implementations are examined, and a methodology is provided for choosing the appropriate circuit-implementing technology using power consumption as the primary metric of comparison, It is shown that neither the analog nor the digital matched filter implementation is universally appropriate. Rather, a surface is mapped out in the multi-dimensional design space where, on one side of this surface, a digital solution is preferable, while on the other side of the surface, an analog circuit is appropriate. Equations are given which delineate the position of this transitional surface in terms of the design space parameters, and example calculations and plots depicting the regions of dominance for the digital and analog matched filters for specific process and system parameters are provided.