We study pulse-based ultra wideband (UWB) communications over multipath channels using asynchronous spread spectrum (SS) multiple access (MA) based on time-hopping (TH) and pulse position modulated (PPM) signals. More specifically, we analyze the signal-to-interference (SIR) degradation in the presence of additive white Gaussian noise (AWGN), multi-user interference (MUI), and dense multipath effects (DME) with line-of-sight (LOS) and non-line-of-sight (NLOS). In particular, we define a degradation margin factor for the combined MUI and multipath effects and also find an expression for the maximum number of simultaneous radio links Nuin terms of the operating SIR, the SS processing gain, and the bit transmission rate Rb. We consider both cases with perfect and imperfect power control.

In this work, we study ultra wideband (UWB) communications over dense multipath channels using frequency shift keying (FSK) data modulation. We take into account the effects of both the antenna system and the multipath channel, and calculate the signal-to-noise ratio (SNR) degradation for different frequency deviations.

We propose a simple model for the bursty operation of digital subscriber line (DSL) modems. Based on this model, we derive a power spectrum density (PSD) for the bursty crosstalk. This analysis suggests that both the duty cycle and the bursty activity rate must be optimized when bursty crosstalk is used to increase the performance of crosstalk-limited systems.

Wireless spread spectrum multiple access (SSMA) using time hopping and block waveform encoded (M-ary) pulse position modulated (PPM) signals is analyzed. For different M-ary PPM signal designs, the multiple-access performance in free-space propagation renditions is analyzed in terms of the number of users supported by the system for a given bit error rate, signal-to-noise ratio, bit transmission rate, and number of signals in the M-ary set. The processing gain and number of simultaneous users are described in terms of system parameters. Tradeoffs between performance and receiver complexity are discussed. Upper bounds on both the maximum number of users and the total combined bit transmission rate are investigated. This analysis is applied to ultrawideband impulse radio modulation. In this modulation, the communications waveforms are practically realized using subnanosecond impulse technology. A numerical example is given that shows that impulse radio modulation is theoretically able to provide multiple-access communications with a combined transmission capacity of hundreds of megabits per second at bit error rates in the range 10/sup -4/ to 10/sup -7/ using receivers of moderate complexity.

The use of time-hopped block waveform encoding PPM signals sets for multiple access communications is studied. The multiple access performance is analyzed in terms of the number of users supported by the system for a given bit error rate and bit transmission rate. The analysis shows that this technique is potentially able to provide multiple-access communications with a combined transmission capacity of over 500 Megabits per second at bit error rates in the range 10/sup -4/ to 10/sup -8/ using receivers of moderate complexity.