A detector device, comprising: a plurality of receivers; a plurality of m transmitters; and a controller that controls the transmitters to transmit respective signals defined at least in part by a sequence of 2N pulses within a period, wherein: N is an integer greater than 2, m is equal to N + 1, a first one of the m transmitters transmits 2N first signal pulses (92, 94, 96, 98) within the period, each of the 2N first signal pulses (92, 94, 96, 98) have a first phase,all others of the m transmitters respectively transmit 2N other signal pulses (100, 102, 104, 106, 108, 110, 112, 114) within the period, each of the 2N first signal pulses (92, 94, 96, 98) is simultaneous with one of the 2N other signal pulses (100, 102, 104, 106, 108, 110, 112, 114) of each of the others of the m transmitters, N of the other signal pulses (104, 106, 110, 112) of each of the others of the m transmitters have a phase shift of 180° relative to the first phase, N of the other signal pulses (100, 102, 108, 114) of each of the others of the m transmitters have the first phase, characterized by the N other signal pulses (104, 106, 110, 112) of each of the others of the m transmitters having the phase shift are immediately adjacent each other in the sequence, positions of the N other signal pulses (104, 106, 110, 112) having the phase shift within the respective sequences of the others of the m transmitters are staggered within the period, and wherein the order in each sequence is a different code such that each of the m transmitters has a unique code. a plurality of receivers; a plurality of m transmitters; and a controller that controls the transmitters to transmit respective signals defined at least in part by a sequence of 2N pulses within a period, wherein: N is an integer greater than 2, m is equal to N + 1, a first one of the m transmitters transmits 2N first signal pulses (92, 94, 96, 98) within the period, each of the 2N first signal pulses (92, 94, 96, 98) have a first phase,all others of the m transmitters respectively transmit 2N other signal pulses (100, 102, 104, 106, 108, 110, 112, 114) within the period, each of the 2N first signal pulses (92, 94, 96, 98) is simultaneous with one of the 2N other signal pulses (100, 102, 104, 106, 108, 110, 112, 114) of each of the others of the m transmitters, N of the other signal pulses (104, 106, 110, 112) of each of the others of the m transmitters have a phase shift of 180° relative to the first phase, N of the other signal pulses (100, 102, 108, 114) of each of the others of the m transmitters have the first phase, characterized by the N other signal pulses (104, 106, 110, 112) of each of the others of the m transmitters having the phase shift are immediately adjacent each other in the sequence, positions of the N other signal pulses (104, 106, 110, 112) having the phase shift within the respective sequences of the others of the m transmitters are staggered within the period, and wherein the order in each sequence is a different code such that each of the m transmitters has a unique code. N is an integer greater than 2, m is equal to N + 1, a first one of the m transmitters transmits 2N first signal pulses (92, 94, 96, 98) within the period, each of the 2N first signal pulses (92, 94, 96, 98) have a first phase,all others of the m transmitters respectively transmit 2N other signal pulses (100, 102, 104, 106, 108, 110, 112, 114) within the period, each of the 2N first signal pulses (92, 94, 96, 98) is simultaneous with one of the 2N other signal pulses (100, 102, 104, 106, 108, 110, 112, 114) of each of the others of the m transmitters, N of the other signal pulses (104, 106, 110, 112) of each of the others of the m transmitters have a phase shift of 180° relative to the first phase, N of the other signal pulses (100, 102, 108, 114) of each of the others of the m transmitters have the first phase, characterized by the N other signal pulses (104, 106, 110, 112) of each of the others of the m transmitters having the phase shift are immediately adjacent each other in the sequence, positions of the N other signal pulses (104, 106, 110, 112) having the phase shift within the respective sequences of the others of the m transmitters are staggered within the period, and wherein the order in each sequence is a different code such that each of the m transmitters has a unique code.