In this paper, three new ultra wideband (UWB) communication systems with quadrature-phase shift keying (QPSK) impulse modulation are proposed. First, direct-sequence (DS) multiple-access scheme is applied. The second proposed system is based on time-hopping (TH) multiple-access scheme. The last proposed system applies TH multiple-access scheme with QPSK impulse modulation and pulse position modulation (PPM). The conventional UWB communications as TH scheme with PPM modulation and DS scheme with binary-phase shift keying (BPSK) are used to compare. The simulation results show that all proposed UWB communication systems can provide obviously better performances compared with the conventional TH-PPM and DS-BPSK UWB communication systems. The comparisons in aspects of transmission bit rate and the number of users are also investigated.

A Time Hopping Pulse Spacing Modulation (TH-PSM) system, which combines the pulse position modulation system with code shift keying, is proposed. The following performances are analyzed; (1) data transmission rate, (2) error rate in a single-user case, (3) error rate in a multi-user case, and (4) spectral efficiency. Consequently, the data transmission rate of the proposed system is higher than that of the conventional Spread Spectrum Pulse Position Modulation (SS-PPM) system. The proposed system can improve the probability of block error by increasing the number of information bits per spreading code. Moreover, the spectral efficiency of the proposed system is higher than that of the conventional system. The proposed system is more attractive than the conventional SS-PPM system for optical communications, power-line communications, and UWB communications.