Browsing by Subject "Broadband networks"
Now showing 1 - 13 of 13
Results Per Page
Sort Options
Item Open Access Capacity bounds for an ultra-wideband channel model(IEEE, 2004-10) Arıkan, ErdalThere is an ongoing effort by the IEEE 802.15.3a subcommittee to reach a UWB personal area network standard. We estimate the achievable rates for such networks using a channel model specified by the same group. The analysis of this channel model is of interest in light of recent information-theoretic work on multipath fading channels which show that in order to take full advantage of such channels' capacity the transmitted signals have to be "peaky" in a certain sense. The immense bandwidth of the UWB channel also suggests at first that peaky signals should be used. However, unlike the many other wireless systems where the transmitter energy is limited, in the UWB channel only the power spectral density of the transmitted signal is constrained. As a result, the signal power can grow in proportion to the utilized bandwidth and peaky signals are not needed. © 2004 IEEE.Item Open Access Coded-reference ultra-wideband systems(2008-09) Gezici, SinanTransmitted-reference (TR) and frequency-shifted reference (FSR) ultra-wideband (UWB) systems employ pairs of reference and data signals, which are shifted in the time and frequency domains, respectively, to facilitate low-to-medium data rate communications without the need for complex channel estimation and template signal generation. On the other hand, the recently proposed coded-reference (CR) UWB systems provide orthogonalization of the reference and data signals in the code domain, which has advantages in terms of performance and/or implementation complexity. In this paper, CR UWB systems are investigated. First, it is shown that a CR UWB system can be considered as a generalized non-coherent pulse-position modulated system. Then, an optimal receiver according to the Bayes decision rule is derived for CR UWB systems. In addition, the asymptotic optimality properties of the conventional CR UWB receivers are investigated. Finally, simulation results are presented to compare the performance of the optimal and conventional CR UWB receivers. ©2008 IEEE.Item Open Access Distributed interactive video system design and analysis(Institute of Electrical and Electronics Engineers, 1997) Wu, Tsong-Ho; Korpeoglu, I.; Cheng, Bo-ChaoThe interactive video (IV) market has been expected to capture a significant share of the huge potential revenues to be generated by the business and residential markets. The level of revenues generated depends on the completion rate of calls the service provider can support, no matter what the IV system or network condition. Thus, a cost-effective, scalable fault-tolerant IV system is needed to maximize the video call completion rate at an affordable cost. This article describes design methodologies for a scalable, fault-tolerant IV system and an IV system design and analysis research prototype called IVSDNA (IV System Designer and Analyzer). The IVSDNA prototype is designed to help network planners and engineers to evaluate quantitative trade-offs (in terms of network communications costs, video storage costs, and degree of system fault tolerance) between two major IV system architectures (centralized and distributed) with a variety of video distribution methods, replication strategies, and fault-tolerant access protocols.Item Open Access Enhancements to threshold based range estimation for ultra-wideband systems(IEEE, 2014-09) Soğancı, Hamza; Gezici, Sinan; Güldoğan, M. B.Ultra-wideband (UWB) signals have very high time resolution, which makes them a very good candidate for range estimation based wireless positioning. Although the accuracy is the major concern for range estimation, it is also important to have low-complexity algorithms that can be employed in real time. In this study, two low-complexity range estimation algorithms are proposed for UWB signals, which achieve improved performance compared to the state-of-the-art low-complexity ranging algorithms. The proposed algorithms are inspired from two well-known algorithms; 'serial backward search' (SBS) and 'jump back and search forward' (JBSF). Performances of the proposed algorithms are compared with those of the SBS and JBSF algorithms based on real measurements. In addition, theoretical bounds are calculated in order to quantify the statistical performance of the algorithms. © 2014 IEEE.Item Open Access Interference mitigation and awareness for improved reliability(Cambridge University Press, 2011) Arslan, H.; Yarkan S.; Şahin, M. E.; Gezici, SinanWireless systems are commonly affected by interference from various sources. For example, a number of users that operate in the same wireless network can result in multiple-access interference (MAI). In addition, for ultrawideband (UWB) systems, which operate at very low power spectral densities, strong narrowband interference (NBI) can have significant effects on the communications reliability. Therefore, interference mitigation and awareness are crucial in order to realize reliable communications systems. In this chapter, pulse-based UWB systems are considered, and the mitigation of MAI is investigated first. Then, NBI avoidance and cancelation are studied for UWB systems. Finally, interference awareness is discussed for short-rate communications, next-generation wireless networks, and cognitive radios.Mitigation of multiple-access interference (MAI)In an impulse radio ultrawideband (IR-UWB) communications system, pulses with very short durations, commonly less than one nanosecond, are transmitted with a low-duty cycle, and information is carried by the positions or the polarities of pulses [1-5]. Each pulse resides in an interval called frame, and the positions of pulses within frames are determined according to time-hopping (TH) sequences specific to each user. The low-duty cycle structure together with TH sequences provide a multiple-access capability for IR-UWB systems [6].Although IR-UWB systems can theoretically accommodate a large number of users in a multiple-access environment [2, 4], advanced signal processing techniques are necessary in practice in order to mitigate the effects of interfering users on the detection of information symbols efficiently [6]. © Cambridge University Press 2011.Item Open Access Low power UWB transceiver design using dynamic voltage scaling(IEEE, 2007-03) Garg, R.; Chunjie, D.; Jinyun, Z.; Gezici, SinanLow power consumption is a critical issue in many UWB systems. In this paper, we investigate the application of dynamic voltage scaling (DVS) and other low power design techniques to a multiband-OFDM UWB transceiver baseband circuit design in order to reduce average power consumption of the chip. Our results show significant power savings over the conventional approach. © 2007 IEEE.Item Open Access Markov modulated periodic arrival process offered to an ATM multiplexer(Elsevier BV * North-Holland, 1995-04) Akar, N.; Arıkan, E.When a superposition of on/off sources is offered to a deterministic server, we are faced with a particular queueing system, the analysis of which has a significant role in ATM networks. Periodic cell generation during active times is a major feature of these sources. We provide an analytical approach to solve for this queueing system via an approximation to the transient behavior of the nD/D/1 queue. The solution to the queue length distribution is given in terms of a solution to a linear differential equation with variable coefficients. The technique proposed here has close similarities with the fluid flow approximation and is amenable to extension for more complicated queueing systems with such correlated arrival processes. A numerical example for a packetized voice multiplexer is finally given to demonstrate our results.Item Open Access Optimal and suboptimal receivers for code-multiplexed transmitted-reference ultra-wideband systems(Wiley, 2013) Tutay, M. E.; Gezici, SinanIn this study, optimal and suboptimal receivers are investigated for code-multiplexed transmitted-reference (CM-TR) ultra-wideband systems. First, a single-user scenario is considered, and a CM-TR system is modeled as a generalized noncoherent pulse-position modulated system. Based on that model, the optimal receiver that minimizes the bit error probability is derived. Then, it is shown that the conventional CM-TR receiver converges to the optimal receiver under certain conditions and achieves close-to-optimal performance in practical cases. Next, multi-user systems are considered, and the conventional receiver, blinking receiver, and chip discriminator are investigated. Also, the linear minimum mean-squared error (MMSE) receiver is derived for the downlink of a multi-user CM-TR system. In addition, the maximum likelihood receiver is obtained as a performance benchmark. The practicality and the computational complexity of the receivers are discussed, and their performance is evaluated via simulations. The linear MMSE receiver is observed to provide the best trade-off between performance and complexity/practicality.Item Open Access Performance analysis of code-multiplexed transmitted-reference ultra-wideband systems(IEEE, 2011) Tutay, Mehmet Emin; Gezici, Sinan; Poor H.V.In code-multiplexed transmitted-reference (CM-TR) ultra-wideband (UWB) systems, data signals and reference signals are transmitted using two distinct orthogonal codes. In this way, performance improvements and/or implementation advantages are obtained compared to transmitted-reference (TR) and frequency-shifted reference (FSR) ultra-wideband (UWB) systems. In this study, performance of CM-TR systems is investigated, and probability of error expressions are obtained. For the single user case, a closed-form expression for the exact probability of error is derived, whereas a Gaussian approximation, the accuracy of which depends on the number of frames per symbol, is considered for the multiuser case. Also, the maximum likelihood detector is derived, and numerical examples are presented. © 2011 IEEE.Item Open Access Sabit genişbantlı telsiz uygulamalarında ÇGÇÇ-DFBÇ için kanal kestirimi(IEEE, 2006-04) Karakaya, B.; Çırpan, H. A.; Panayırcı, ErdalSystems employing multiple transmit and receive antennas, known as multiple input multiple output (MIMO) systems can be used with OFDM to improve the resistance to channel impairments. Thus the technologies of OFDM and MIMO are equipped in fixed wireless applications with attractive features, including high data rates and robust performance. However, since different signals are transmitted from different antennas simultaneously, the received signal is the superposition of these signals, which implies new challenges for channel estimation. In this paper we propose a time domain MMSE based channel estimation approach for MIMO-OFDM systems. The proposed approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Also the performance of the proposed approach is studied through the evaluation of minimum Bayesian MSE. © 2006 IEEE.Item Open Access Theoretical limits for estimation of vital signal parameters using impulse radio UWB(IEEE, 2007) Gezici, Sinan; Şahinoğlu, Z.In this paper, Cramer-Rao lower bounds (CRLBs) for estimation of vital signal parameters, such as respiration and heart-beat rates, using ultra-wideband (UWB) pulses are derived. In addition, a simple closed-form CRLB expression is obtained for sinusoidal displacement functions under certain conditions. Moreover, a two-step suboptimal solution is proposed, which is based on time-delay estimation via matched filtering followed by least-squares (LS) estimation. It is shown that the proposed solution is asymptotically optimal in the limit of certain system parameters. Simulation studies are performed to evaluate the lower bounds and performance of the proposed solution for realistic system parameters.Item Open Access Ultra-wideband orthogonal pulse shape set design by using Hermite-Gaussian functions(IEEE, 2012) Alp, Yaşar Kemal; Dedeoǧlu, Mehmet; Arıkan, OrhanUltra-Wideband (UWB) communication systems have been developed for short distance, high data rate communications. To avoid interfering with the existing systems in the same environment, very short duration pulses used by these systems should satisfy a predefined spectral mask. Data rate of UWB systems can be increased by using multiple pulse shapes simultaneously. Orthogonality of the simultaneously used pulse shapes simplifies the receiver design. In this work, design of orthogonal pulse shapes which satisfy the spectral mask is modelled as an optimization problem. First, it is converted to a convex optimization problem by constraining the pulse shapes to lie in a subspace spanned by the Hermite-Gaussian (HG) functions. Then the optimal solution is obtained. It is shown that a larger pulse shape set can be designed compared to the existing approaches, and hence, a higher data rate can be achieved. © 2012 IEEE.Item Open Access Ultra-wideband range estimation: Theoretical limits and practical algorithms(IEEE, 2008-09) Güvenç, İ.; Gezici, Sinan; Şahinoğlu, Z.The high time resolution of ultra-wideband (UWB) signals enables wireless devices to perform accurate range estimation. In order to realize UWB systems with accurate ranging capabilities, both theoretical limits on range estimation and practical algorithms that approach those limits should be investigated. This paper provides a survey of various UWB ranging algorithms and discusses their performance and complexity tradeoffs. In addition, theoretical limits on range estimation are discussed in terms of Cramer-Rao and Ziv-Zakai lower bounds. Index Terms- Ultra-wideband (UWB), time-of-arrival (TOA) estimation, ranging, Cramer-Rao lower bound (CRLB), Ziv-Zakai lower bound (ZZLB). ©2008 IEEE.