| 摘要 |
PCT No. PCT/GB96/00745 Sec. 371 Date Aug. 24, 1999 Sec. 102(e) Date Aug. 24, 1999 PCT Filed Mar. 28, 1996 PCT Pub. No. WO97/37436 PCT Pub. Date Oct. 9, 1997The apparatus receives an input signal via an antenna or cable 2, and the signal is applied to a frequency converter 4. Frequency converter generates complex I Q baseband signals which are applied to a respective correlator comprising a multiplier 6 and an accumulator 12 in respect of the inphase signal and the multiplier 8 and an accumulator 14 in respect of the quadrature phase signal. The output of the correlators are subjected to a modulus squaring function which comprises multipliers 16, 18 and an adder 20. The output of the adder 20 is applied to a store 22, and the inputs and outputs to the store are arranged to be added together in an adder 24, the output of which is compared in a comparator 26. The correlators and store are controlled by a controller 28 which is arranged to control the setting and resetting of the accumulators 12 and 14. For a fixed interval of time a local code generator is held constant, the output of which is applied to an input of the multiplier 6, 8, and at the start of the interval the accumulators 12, 14 are reset to zero and allowed to accumulate. At the end of the period the comparison is performed and thereafter the codes generated are shifted by one chip and the accumulators 12, 14 are set to zero and the output of the adder 20 is clocked into the storage means 22. This process is repeated until such time as the threshold values exceeded as determined by the comparator 26.
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