A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> In a tutorial exposition, the following topics are discussed: definition of a matched filter; where matched filters arise; properties of matched filters; matched-filter synthesis and signal specification; some forms of matched filters. <s> BIB001 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> Basic elements of matched filtering and pulse compression optimum pre-detection processing matched-filter waveform considerations the measurement accuracies of matched-filter radar signals the design of dispersive delay functions ultrasonic delay lines microwave and optical matched-filter techniques. <s> BIB002 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> Two different high-resolution time-delay estimation (HRTDE) methods, a temporal method and a frequency method, specially adapted to large bandwidth duration (BT) product time-resolvent signals, are described. The performance gain of these methods is shown to be about four times better in comparison with the classical time-delay resolution methods. The frequency HRTDE method is applied to real data obtained from an ocean acoustic experiment. Although classic methods cannot distinguish close signal components, the method presented yields estimates of the delay differences and the attenuation associated with each propagation path. > <s> BIB003 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> Preface I. Introduction II. Elements of Hypothesis Testing III. Signal Detection in Discrete Time IV. Elements of Parameter Estimation V. Elements of Signal Estimation VI. Signal Detection in Continuous Time VII. Signal Estimation in Continuous Time References Index <s> BIB004 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> A time-of-arrival (ToA)-based ranging scheme using an ultra-wideband (UWB) radio link is proposed. This ranging scheme implements a search algorithm for the detection of a direct path signal in the presence of dense multipath, utilizing generalized maximum-likelihood (GML) estimation. Models for critical parameters in the algorithm are based on statistical analysis of propagation data and the algorithm is tested on another independent set of propagation measurements. The proposed UWB ranging system uses a correlator and a parallel sampler with a high-speed measurement capability in each transceiver to accomplish two-way ranging between them in the absence of a common clock. <s> BIB005 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> Ultra-wideband (UWB) radio is gaining increasing attention thanks to its attractive features that include low-power low-complexity baseband operation and ample multipath diversity. Realization of its potential, however, faces the challenge of low-complexity high-performance timing acquisition. In this paper, we develop a blind timing acquisition algorithm for frame-level synchronization. Relying on simple integrate-and-dump operations over one symbol duration, our algorithm exploits the rich multipath diversity enabled by UWB transmissions. It outperforms existing blind algorithms and has comparable performance to data-aided ones. Equally attractive is its applicability to UWB links with or without time hopping (TH), over frequency-flat or multipath channels. It is also worth stressing that our "dirty" template based scheme is able to achieve timing synchronization at any desirable resolution and is readily applicable to non-UWB systems, so long as intersymbol interference is absent. <s> BIB006 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> Commercial applications for the location of subscribers of wireless services continue to expand. Consequently, finding the Cramer-Rao lower bound (CRLB), which serves as an optimality criterion for the location estimation problem, is of interest. In this paper, we derive the deterministic CRLBs for the estimation of the specular multipath parameters and the positions of the mobiles in an asynchronous direct sequence code division multiple access (DS-CDMA) system operating over specular multipath fading channels. We assume a multilateral radio location system where the location estimates are obtained from some or all of the estimated signal parameters at different clusters of antennas of arbitrary geometry. Extension for unilateral and composite radio location techniques is also discussed. As an application example, we use numerical simulations to investigate the effects of specular multipath and multiple access interference (MAI) on the positioning accuracy for different radio location techniques. <s> BIB007 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> Highly dispersive nature of ultra-wideband (UWB) channels makes time of arrival (TOA) estimation extremely challenging, where the leading-edge path is not necessarily the strongest path. Since the bandwidth of a received UWB signal is very large, the Nyquist rate sampling becomes impractical, hence motivating lower complexity and yet accurate ranging techniques at feasible sampling rates. In this paper, we consider TOA estimation based on symbol rate samples that are obtained after a square-law device. A normalized threshold selection approach based on the minimum and maximum values of the energy samples is introduced, and optimal values of the thresholds for different signal to noise ratios (SNRs) are investigated via simulations. Also, the effect of window size when searching the leading edge prior to maximum energy block is analyzed. Theoretical closed form expressions are derived for mean absolute TOA estimation error for a fixed threshold case. Performances of different algorithms are then compared via simulations using IEEE 802.15.4a channel models and by choosing appropriate normalized threshold and search-back window parameters. <s> BIB008 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> UWB technology provides an excellent means for wireless positioning due to its high resolution capability in the time domain. Its ability to resolve multipath components makes it possible to obtain accurate location estimates without the need for complex estimation algorithms. In this article, theoretical limits for TOA estimation and TOA-based location estimation for UWB systems have been considered. Due to the complexity of the optimal schemes, suboptimal but practical alternatives have been emphasized. Performance limits for hybrid TOA/SS and TDOA/SS schemes have also been considered. Although the fundamental mechanisms for localization, including AOA-, TOA-, TDOA-, and SS-based methods, apply to all radio air interface, some positioning techniques are favored by UWB-based systems using ultrawide bandwidths. <s> BIB009 </s> A Survey on Wireless Position Estimation <s> Time of Arrival (TOA) <s> A process for drying organic waste, such as sewage sludge, by contacting the organic waste with hot vapors wherein the dried material is plasticized and extruded to form compacted granules having good flow characteristics and suitable for application by commercial fertilizer spreaders. A plasticizer and an extrusion aid are added to the dried material prior to extrusion. <s> BIB010
Similar to the RSS parameter, estimating the flight time of a signal traveling from one node to another, called TOA, provides information related to the distance between those two nodes. Therefore, in the absence of any errors, a TOA estimate provides an uncertainty region in the shape of a circle as shown in Figure 2 . In order to calculate the TOA parameter for a signal traveling between two nodes, the nodes must either have a common clock, or exchange timing information by certain protocols such as a two-way ranging protocol BIB005 ,  ,  . Conventionally, TOA estimation is performed via correlator or matched filter (MF) receivers BIB001 . Consider a scenario in which s(t) is transmitted from a node to another, and the received signal is expressed as where τ represents the TOA and n(t) is white Gaussian noise with zero mean and a spectral density of N 0 /2. Then, the correlator based approach correlates the received signal with a local template s(t−τ ) for various delayŝ τ , and calculates the delay corresponding to the correlation peak. Similarly, the MF approach employs a filter that is matched to the transmitted signal and estimates the instant at which the filter output attains its largest value. Both approaches are optimal in the ML sense for the signal model in  . However, in practical systems, the signal arrives at the receiver via multiple signal paths. In such multipath environments, the conventional schemes become suboptimal as they use the transmitted signal to set their template signals or MF impulse responses BIB010 . In order to obtain accurate TOA estimation in multipath environments, high resolution time delay estimation techniques, such as that described in BIB003 , have been studied for narrowband systems, and first path detection algorithms are proposed for ultra-wideband (UWB) systems BIB005 , BIB008 ,  , BIB006 . In order to observe the main relations between the signal bandwidth and the theoretical limits for TOA estimation, consider the CRLB for the signal model in  , which is given by BIB004 , BIB002  whereτ represents an unbiased TOA estimate, SNR = Eα 2 /N 0 is the SNR, with E denoting the signal energy, and β is the effective signal bandwidth defined by (5). BIB010 Since the effects of the propagation environment, such as the multipath, are not known at the time of TOA estimation, the use of a template signal or a MF impulse response that includes the overall effects of the channel is not usually possible.  Refer to BIB007 and BIB009 for the CRLB for TOA estimation in multipath channels. From (7), it is observed that unlike the RSS estimation, the accuracy of the TOA estimation can be improved by increasing the SNR and/or the effective signal bandwidth. Therefore, for (ultra) wideband systems, TOA estimation can provide very accurate distance information.