1. An improved code word structure for a laser based tactical engagement simulation training system of a type in which a standard code word structure for the system consists of a plurality of bits of logic level “1” in selected positions in the code word with the remainder of the bits being of logic level “0”, said improved code word structure comprising an FM modulated code word having FM modulated bits of selected frequencies in the same selected positions as are the logic level “1” bits in the standard code word.