A N-ary biorthogonal pulse position shape modulation (BPPSM) for hybrid time hopping/ direct sequence (TH/DS) multiple access ultrawideband (UWB) system is proposed and analyzed in this paper. The characteristic function (CHF) of the multiple access interference (MAI) is derived and, accordingly, the average symbol error rate (SER) of the proposed system can be accurately evaluated. Simulation are carried out to verify the analytical results in additive white Gaussian noise (AWGN) channel and to illustrate the system performance in realistic UWB fading channels. As increasing the number of adopting pulses, the proposed TH/DS Nary BPPSM system can provide better SER performance compared with the TH/DS Nary BPPM scheme. Given the constraints of fixed bit rate and signal bandwidth, the impact of adjusting various system parameters on the system performance is also investigated.

A hybrid time-hopping/direct-sequence (TH/DS) multiple access ultra-wideband (UWB) system combined with N-ary biorthogonal pulse position modulation (BPPM) is proposed and analyzed. Based on the exact characteristic function (CF) technique, we also derive the probability distribution of the multiple access interference (MAI) and the average symbol error rate (SER) of the proposed scheme. Simulation results are provided to verify the analytical frameworks. The tradeoff of the system parameters for the proposed system under the constraints of fixed bit rate and signal bandwidth is also examined.

A time-hopping (TH) multiple access ultrawideband (UWB) system combined with a large modulation level of M-ary pulse position modulation (PPM) is considered and analyzed. Unlike the conventional TH method that the number of the provided TH slots becomes fewer as the adopted modulation level of M-ary PPM is lager and the data rate is fixed, a feasible TH scheme that utilizes the whole frame duration to carry out TH and PPM is proposed in the paper. The advantages of proposed TH system are to use the large modulation level of PPM, reduce the effect of the multiple access interference (MAI) and increase multiple access capability. The characteristic function (CF) of the MAI for proposed sytem is derived to obtain the probability density function of MAI and average symbol error rate. The simulation results of the proposed TH system are provided to verify the analytical results and show the performance improvement over the conventional TH and DS UWB systems.

The performance of multiple access interference (MAI) cancellations for the asynchronous M-ary pulse position modulation (PPM) time hopping (TH) ultra-wideband (UWB) systems are investigated. Parallel interference cancellation (PIC) and successive interference cancellation (SIC) are the most popular interference cancellation schemes. However, both the PIC and SIC have some shortcomings that the PIC suffers an error-propagation effect due to the erroneous MAI cancellation and the SIC imports a long processing delay caused by the large number of user. Therefore, a low-complexity iterative interference cancellation (IIC) scheme is proposed in this paper. The IIC scheme is based on the concept of iteratively cancelling MAI from those users whose symbols have been reliably detected. The performances of these interference cancellation schemes are compared in terms of the symbol error rate (SER) for the asynchronous M-ary PPM TH-UWB systems. The simulation results show the proposed IIC scheme performs better than PIC and SIC detectors in a MAI dominant environment.

The bit-error probability (BEP) is evaluated for a fast frequency-hopping binary frequency-shift-keying (FFH/BFSK) spread-spectrum communication system over Rician fading channels in the presence of worst-case multitone jamming (MTJ) and additive white Gaussian noise (AWGN). A diversity reception scheme of product-combining is applied at the receiver. Two types of MTJ models, namely n=1-band MTJ and independent MTJ, are considered in this letter. To obtain the final decision statistics, the closed-form or a single finite integral expressions of cumulative distribution functions (CDFs) of the ratio of two square-law detectors' outputs per hop are derived. According to the numerical results, it is shown, unlike the known knowledge for the AWGN channel, that independent MTJ is more harmful than n=1-band MTJ for the product-combining receivers (L/spl ges/2) in fading channels.

The bit-error probability (BEP) is evaluated for a fast frequency-hopping/binary frequency-shift keying spread-spectrum communication system over a frequency-nonselective, slowly fading channel with worst-case band multitone jamming and additive white Gaussian noise. A diversity reception technique with ratio-statistic combining is applied at the receiver. Both square-law and envelope detectors are utilized and analyzed. Based on circularly symmetric signal theory, the paper obtains the closed-form expressions of probability density function and cumulative distribution function of the ratio-statistic output. It is shown from the analytical results, and verified by simulation, that the BEP performance of the ratio-statistic receiver is sensitive to the fading effect on the desired signal, but is insensitive to that on the jamming tones. It is also shown that the envelope detector provides better performance than the square-law detector.

A bit error probability (BEP) expression is derived for the fast frequency-hopping binary frequency-shift-keying spread-spectrum communication system with self-normalizing combining receiver over a slowly Rician fading channel under independent multitone jamming (MTJ) and AWGN environment. In our study, the close-form or a single finite integral expression of cumulative distribution function (cdf) of the self-normalized output is derived and exact analysis of BEP performance is obtained. Our analytic results, validated with the aid of simulations, show that independent MTJ is more harmful than the corresponding n=1-band MTJ when diversity is taken into account (L>2).

The capacity of a fast frequency-hopped multiple access (FHMA) system is dictated by two major related design concerns: the hopping pattern and the receiver structure. This paper studies the impact of these two factors. We present a maximum likelihood (ML) diversity combiner for detecting asynchronous FHMA multilevel PSK (MPSK) signals in Rician fading channels and analyze the performance of a close approximation of the ML receiver. We compare systems using random hopping patterns and those using optimal hopping patterns of Einarsson (1980). Performance comparisons between chip-synchronous and chip-asynchronous systems are made as well. We propose and examine the effectiveness of a two-stage multiuser detector, in which the first stage makes an initial decision while the second stage tries to reduce multiple access interference (MAI) and resolve the ambiguity left by the first stage detector. The MAI caused by undesired users is constituted by a cochannel interference (CCI) contribution and an interchannel interference (ICI) contribution. This detector is of modest complexity and is capable of removing most of the CCI and part of the ICI. Two methods for mitigating MAI are also examined.