Encoding of a message is conducted using codewords selected from a codebook. The selected codewords are used to construct a corresponding plurality of waveforms, which are then weighted and added to form a signal for transmission. At a receiver, channel impulse response is used to determine which codewords from the known codebook have been used, and by which weights from a known constellation of weights the resultant waveforms have been weighted. A message embedded in a received signal can then be detected.