Disclosed is a method of generating a detection signal for detecting energy in a spread-spectrum signal, comprising: de-spreading the spread-spectrum signal by applying a predetermined spreading code to obtain a sequence of de-spread signal symbols (202A-202D); accumulating a number of said signal symbols to obtain a single detection signal. The accumulation includes: obtaining a first and a second subset of said de-spread signal symbols, wherein the symbols of the first subset have values that are known to the receiver or at least known to be the same for all symbols of the first subset, and wherein the symbols of the second subset have unknown values; coherently accumulating the symbols of the first subset to obtain a first partial detection signal (203A, 203B, 203C); non-coherently accumulating the symbols of the second subset to obtain a second partial detection signal (204A, 204B, 204C); and combining the first and second partial detection signals to obtain the single detection signal (208).