Browsing by Author "Kobayashi, H."
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Item Open Access Adaptation of two types of processing gains for UWB impulse radio wireless sensor networks(The Institution of Engineering and Technology, 2007) Güvenç, I.; Arslan, H.; Gezici, Sinan; Kobayashi, H.Ultrawideband impulse radio systems offer two kinds of processing gains that can be adapted based on the interference level in the system so that quality of service requirements are fulfilled. An adaptive assignment scheme for two types of multiple-access parameters in cluster-based wireless sensor networks is investigated. A mathematical framework is developed for asynchronous communications using a Gaussian approximation method to model the multiple-access interference in two cases: one with fixed frame duration, where the goal is to increase the average throughput, and the other with fixed symbol duration, where the goal is to increase the network lifetime. Extension of the analysis to multipath channels is carried out, and the validity of the Gaussian approximation is investigated using the Kullback-Leibler distance.Item Open Access The tradeoff between processing gains of an impulse Radio UWB system in the presence of timing jitter(Institute of Electrical and Electronics Engineers, 2007) Gezici, Sinan; Molisch, A. F.; Poor, H.V.; Kobayashi, H.In time hopping impulse radio, Nf pulses of duration Tc are transmitted for each information symbol. This gives rise to two types of processing gains: i) pulse combining gain, which is a factor Nf, and (ii) pulse spreading gain, which is Nc=Tf/Tc, where Tf is the mean interval between two subsequent pulses. This paper investigates the tradeoff between these two types of processing gains in the presence of timing jitter. First, an additive white Gaussian noise (AWGN) channel is considered, and approximate closed-form expressions for bit error probability (BEP) are derived for impulse radio systems with and without pulse-based polarity randomization. Both symbol-synchronous and chip-synchronous scenarios are considered. The effects of multiple-access interference (MAI) and timing jitter on the selection of optimal system parameters are explained through theoretical analysis. Finally, a multipath scenario is considered, and the tradeoff between processing gains of a synchronous impulse radio system with pulse-based polarity randomization is analyzed. The effects of the timing jitter, MAI, and interframe interference (IFI) are investigated. Simulation studies support the theoretical results.Item Open Access Two-step time of arrival estimation for pulse-based ultra-wideband systems(SpringerOpen, 2008) Gezici, Sinan; Sahinoglu Z.; Molisch, A. F.; Kobayashi, H.; Poor, H. V.In cooperative localization systems, wireless nodes need to exchange accurate position-related information such as time-of-arrival (TOA) and angle-of-arrival (AOA), in order to obtain accurate location information. One alternative for providing accurate position-related information is to use ultra-wideband (UWB) signals. The high time resolution of UWB signals presents a potential for very accurate positioning based on TOA estimation. However, it is challenging to realize very accurate positioning systems in practical scenarios, due to both complexity/cost constraints and adverse channel conditions such as multipath propagation. In this paper, a two-step TOA estimation algorithm is proposed for UWB systems in order to provide accurate TOA estimation under practical constraints. In order to speed up the estimation process, the first step estimates a coarse TOA of the received signal based on received signal energy. Then, in the second step, the arrival time of the first signal path is estimated by considering a hypothesis testing approach. The proposed scheme uses low-rate correlation outputs and is able to perform accurate TOA estimation in reasonable time intervals. The simulation results are presented to analyze the performance of the estimator.