A noncoherent, soft-decision combining processor for the multiple-hop detection of frequency-hopping signals is developed, based on a generalised likelihood-ratio test argument. Hop rate, hop transition times, and the set of candidate carrier frequencies are assumed to be known throughout. The proposed receiver has a simple structure: it consists of a bank of per-hop envelope detectors, a per-hop 'select-the-maximum' operation, a soft-decision accumulator over hops, and a final threshold comparison. For a large number of observed signal hops, this receiver is analysed on the basis of a Gaussian, central-limit theorem type of argument for the decision statistic. A simple formula that relates the detection probability, the false alarm probability, and the signal-to-noise ratio is derived and found adequate for performance purposes. This line of analysis is well supported by extensive simulation. It is shown analytically that the performance of the soft-decision receiver is better than the noncoherent hard-decision combining receiver, which is typically referred to in the literature as the 'multiple-hop maximum-likelihood receiver'.
