The multiple access interference is the main reason that limits the UWB system capacity. The flexibility of pulse selection is a prominent property which is different from the conventional communications. In this paper, a new multiple-access scheme: Waveform Division Multiple Access (WDMA) based on the orthogonal wavelet function shapes is presented. In this scheme, the scaling function φ(t) and the wavelet function ψ(t) representing the UWB pulses are equally assigned to different users to realize multiple access. Because of the better orthogonality of φ(t) and ψ(t), the multiuser interference will be suppressed more effectively. The performance analysis and simulation results show that WDMA system can accommodate more users than TH-PPM UWB and DS-BPSK UWB system.
In this paper, a hybrid DS/TH multiple access scheme is proposed for UWB impulse radio system on the basis of TH-PPM theoretical research. This scheme makes use of time hopping for multiple access and BPSK for data modulation. It utilizes the characteristics of PN sequence signal of DS to suppress further the multi-user interference of TH-PPM system. Results of performance analysis show that DS/TH scheme has higher system capacity than TH-PPM scheme.