Abstract: A multi purpose digital signal regenerative processing apparatus (1) has three modulation sub-systems (2, 3 and 4) in parallel. Each sub-system is selectively selectable to enable a plurality of users to access, independently of one another, a sub-band of a frequency band in individually selectable access modes and modulation formats. The first sub-system (1) is operable in TDM format, the second (3) is operable in FDM or OFDM format and the third sub-system (4) is operable in CDM format.

Abstract: Apparatus for and a method of digital signal processing utilises a technique known as sub-band decomposition and reconstruction. A plurality of input channels are provided each of which is mixed with a vernier frequency correction. In a multiplexer implementation, a fast fourier transform (FET) weighted overlap-add demultiplexer is provided for decomposing each input channel into sub-bands. The sub-band outputs are decimated by a factor to the common input sampling rate of a multiplexer, the sub-bands from each channel then being passed into the appropriate ports of an FFT weighted overlap-add multiplexer by a switch matrix. The multiplexer reconstructs the individual channels, interpolates each channel up to the output sampling rate of the FDM signal, mixes each channel up to its assigned carrier frequency in the frequency division multiplexed (FDM) (FDM) and multiplexes the channels. This provides a computationally efficient architecture with the flexibility to accommodate channels of differing bandwidths.