Novel rate-division multiple-access scheme for UWB-radio-based sensor networks

A UWB-IR modulation scheme for asynchronous multiple access discussed most often in the literature is TH-PPM; a variation of this is TH-PSK. These modulation schemes allow different transmitters to be distinguished by means of specific pseudorandom TH sequences. As the receiver must be capable of locking to any one of these dithering sequences, the required (signal and sequence) synchronization process can be complex and lengthy. In this paper, a novel multiple-access scheme for asynchronous UWB-IR is proposed, where the modulation is binary antipodal and has a low duty cycle, while the user signals are distinguishable by choosing user-specific symbol rates. We analyze the probability of pulse collisions and present design rules for the choice of symbol rates that make the collision probability independent of the time asynchronism. These design rules also lead to BERs that are independent of the time asynchronism, as shown by simulation results for a sensor network scenario without transmitter power control. It is further demonstrated that the BER performances of TH-PSK and rate-division multiple-access (RDMA) are very similar.