Abstract: A method and apparatus for estimating a communication channel impulse response h(t) is disclosed. The method comprises the steps of generating a data sequence di having a constrained portion Cdi associated with at least two codes w0, w1, wherein a correlation Acode(k) of the constrained portion Cdi with one of the codes w0, w1 is characterized by a maximum value at k=0 and less than maximum values at k?0; generating a chip sequence cj having a chip period Tc as the data sequence di spread by a spreading sequence Si of length N; generating com(t)=co(t+mNTc) for m=0, 1, . . . , M by correlating a received signal r(t) with the spreading sequence Si, wherein the received signal r(t) comprises the chip sequence cj applied to the communication channel; and generating an estimated communication channel impulse response ?M(t) as a combination of com(t) and dm for m=0, 1, . . . , M.