IMPLEMENTING A NARROW-BAND MULTIRATE DIGITAL-FILTER FOR A FLEXIBLE MODEM CODEC

Narrowband digital filtering in relation to a flexible modem/codec application is outlined. A brief description of digital filtering structures is given, from which multistage multirate structures are introduced. An example design related to the Uncommitted Radio (UCR) project at the Defence Science and Technology Organisation (DSTO) is completed. A novel way to check the frequency response of a multistage multirate filter design using the Fast Fourier Transform is derived. Finally the implementation is described and quantisation effects discussed. Results are presented highlighting the limitations of the current system.