Radio receiver

A method of demodulating a plurality of signals of interest, transmitted by different transmitters and received by an antenna, all occupying the same shared frequency band or bands, and each signal having a separate spreading code applied thereto, and comprising of an upper and lower sideband, the method comprising the steps of:

• a) downconverting each sideband of all the received signals to a nominal baseband frequency, to produce a combined upper sideband signal, and a combined lower sideband signal;
• b) filtering the combined upper sideband signal in a first chip matched filter, and the combined lower sideband signal in a second chip matched filter, wherein the chip matched filters are matched to a chip of the spreading code as it appears following downconversion to the respective upper or lower sideband;
• c) providing the filtered upper and lower sideband signals to each of a plurality of channels, one for each received signal of interest, each of the channels being adapted to process both sidebands separately,
• and wherein each sideband of each channel comprises at least three gates, comprising of at least an Early, a Prompt, and a Late gate;
• and within each gate:
• i) sampling, using a nearest-neighbour sampler, the signal from the chip matched filter, using an Early, Late or Prompt timing reference as appropriate;
• ii) multiplying, using a multiplier, samples from (i) with an appropriate part of a local copy of the spreading code, from a spreading code generator;
• iii) multiplying, using a mixer, the signal within the gate by a feedback loop signal for removal of Doppler frequency or local oscillator offsets present on the sideband, the mixer being driven by a numerically controlled oscillator;
• iv) integrating, using an integrator, a gate signal produced from steps (i-iii);
• wherein a feedback signal derived from a combination of outputs of the Early and Late gates is used to drive a numerically controlled oscillator which in turn controls the timing of the nearest-neighbour sampler, and the feedback loop signals in (iii) are derived from the outputs of the Prompt gates.