Showing papers on "Multipath propagation published in 2005"
TL;DR: In this article, theoretical limits for TOA estimation and TOA-based location estimation for UWB systems have been considered and suboptimal but practical alternatives have been emphasized.
Abstract: 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.
2,065 citations
Book•
20 Sep 2005
TL;DR: In this paper, the authors present a review of the probability of propagation of electromagnetic signals in the presence of electromagnetic fields and their effects on the physical environment, as well as the link budget.
Abstract: Preface. 1. Introduction. 1.1 Frequency Designations. 1.2 Modes of Propagation. 1.3 Why Model Propagation? 1.4 Model Selection and Application. 1.4.1 Model Sources. 1.5 Summary. 2. Electromagnetics and RF Propagation. 2.1 Introduction. 2.2 The Electric Field. 2.3 The Magnetic Field. 2.4 Electromagnetic Waves. 2.5 Wave Polarization. 2.6 Propagation of Electromagnetic Waves at Material Boundaries. 2.7 Propagation Impairment. 2.8 Ground Effects on Circular Polarization. 2.9 Summary. 3. Antenna Fundamentals. 3.1 Introduction. 3.2 Antenna Parameters. 3.3 Antenna Radiation Regions. 3.4 Some Common Antennas. 3.5 Antenna Polarization. 3.6 Antenna Pointing loss. 3.7 Summary. 4. Communication Systems and the Link Budget. 4.1 Introduction. 4.2 Path Loss. 4.3 Noise. 4.4 Interference. 4.5 Detailed Link Budget. 4.6 Summary. 5. Radar Systems. 5.1 Introduction. 5.2 The Radar Range Equation. 5.3 Radar Measurements. 5.4 Clutter. 5.5 Atmospheric Impairments. 5.6 Summary. 6. Atmospheric Effects. 6.1 Introduction. 6.2 Atmospheric Refraction. 6.3 Atmospheric Attenuation. 6.4 Loss From Moisture and Precipitation. 6.5 Summary. 7. Near-Earth Propagation Models. 7.1 Introduction. 7.2 Foliage Models. 7.3 Terrain Modeling. 7.4 Propagation in Built-Up Areas. 7.5 Summary. 8. Fading and Multipath Characterization. 8.1 Introduction. 8.2 Ground-Bounce Multipath. 8.3 Large-Scale or Log-Normal Fading. 8.4 Small-Scale Fading. 8.5 Summary. 9. Indoor Propagation Modeling. 9.1 Introduction. 9.2 Interference. 9.3 The Indoor Environment. 9.4 Summary. 10. Rain Attenuation of Microwave and Millimeter Wave Signals. 10.1 Introduction. 10.2 Link Budget. 10.3 Rain Fades. 10.4 The Link Distance Chart. 10.5 Availability Curves. 10.6 Other Precipitation. 10.7 Cross-Polarization Effects. 10.8 Summary. 11. Satellite Communications. 11.1 Introduction. 11.2 Satellite Orbits. 11.3 Satellite Operating Frequency. 11.4 Satellite Path Free-Space Loss. 11.5 Atmospheric Attenuation. 11.6 Ionospheric Effects. 11.7 Rain Fades. 11.8 Antenna Considerations. 11.10 Summary. 12. RF Safety. 12.1 Introduction. 12.2 Biological Effects of RF Exposure. 12.3 CC Guidelines. 12.4 Antenna Considerations. 12.5 FCC Computations. 12.6 Station Evaluations. 12.7 Summary. Appendix A: Review of Probability for Propagation Modeling. Index.
742 citations
TL;DR: The corresponding link-level simulation results are encouraging, and show that MIMO-OFDM is a promising road to future broadband wireless access.
Abstract: Orthogonal frequency-division multiplexing is a popular method for high-data-rate wireless transmission. OFDM may be combined with multiple antennas at both the access point and mobile terminal to increase diversity gain and/or enhance system capacity on a time-varying multipath fading channel, resulting in a multiple-input multiple-output OFDM system. In this article we give a brief technical overview of MIMO-OFDM system design. We focus on various research topics for the MIMO-OFDM-based air interface, including spatial channel modeling, MIMO-OFDM transceiver design, MIMO-OFDM channel estimation, space-time techniques for MIMO-OFDM, and error correction code. The corresponding link-level simulation results are encouraging, and show that MIMO-OFDM is a promising road to future broadband wireless access.
361 citations
TL;DR: A new secret key generation and agreement scheme that uses the fluctuation of channel characteristics with an electronically steerable parasitic array radiator (ESPAR) antenna and has the ability to generate secret keys from the received signal strength indicator (RSSI) profile with sufficient independence is proposed.
Abstract: We describe a secure communication scheme that uses the random fluctuation of the natural environment of communication channels. Only the transmitter and the receiver share the communication channel characteristics. From reciprocity between a transmitter and a receiver, it is possible for them to share one-time information of their fluctuating channel. This can provide a secret key agreement scheme without key management and key distribution processes. In this paper, we propose a new secret key generation and agreement scheme that uses the fluctuation of channel characteristics with an electronically steerable parasitic array radiator (ESPAR) antenna. This antenna, which has been proposed and prototyped, is a smart antenna designed for consumers. Using the beam-forming technique of the ESPAR antenna, we can increase the fluctuation of the channel characteristics. From experimental results, we conclude that the proposed scheme has the ability to generate secret keys from the received signal strength indicator (RSSI) profile with sufficient independence.
348 citations
Book•
02 Sep 2005
TL;DR: The Basics of Digital Communications and CDMA: General Principles of CDMA and Examples for CDMA Systems.
Abstract: Preface. 1 Basics of Digital Communications. 1.1 Orthogonal Signals and Vectors. 1.2 Baseband and Passband Transmission. 1.3 The AWGN Channel. 1.4 Detection of Signals in Noise. 1.5 Linear Modulation Schemes. 1.6 Bibliographical Notes. 1.7 Problems. 2 Mobile Radio Channels. 2.1 Multipath Propagation. 2.2 Characterization of Fading Channels. 2.3 Channel Simulation. 2.4 Digital Transmission over Fading Channels. 2.5 Bibliographical Notes. 2.6 Problems. 3 Channel Coding. 3.1 General Principles. 3.2 Convolutional Codes. 3.3 Reed-Solomon Codes. 3.4 Bibliographical Notes. 3.5 Problems. 4 OFDM. 4.1 General Principles. 4.2 Implementation and Signal Processing Aspects for OFDM. 4.3 Synchronization and Channel Estimation Aspects for OFDM Systems. 4.4 Interleaving and Channel Diversity for OFDM Systems. 4.5 Modulation and Channel Coding for OFDM Systems. 4.6 OFDM System Examples. 4.7 Bibliographical Notes. 4.8 Problems. 5 CDMA. 5.1 General Principles of CDMA. 5.2 CDMA Transmission Channel Models. 5.3 Receiver Structures for Synchronous Transmission. 5.4 Receiver Structures for MC-CDMA and Asynchronous Wideband CDMA Transmission. 5.5 Examples for CDMA Systems. 5.6 Bibliographical Notes. 5.7 Problems. Bibliography. Index.
320 citations
TL;DR: In this article, the impulsive noise and multipath effects are the main reasons to cause bit errors in power line communications and the guard interval is used to improve the bit error performance of the OFDM system.
Abstract: The impulsive noise and multipath effects are the main reasons to cause bit errors in power line communications. In this paper, the bit error rate (BER) performance of the orthogonal frequency division multiplexing (OFDM) system under the impulsive noise and multipath effects are theoretically analyzed in terms of closed form formulas. Through the analysis, it is shown that OFDM can mitigate the adverse effect of the impulsive noise and only the heavily disturbed impulsive noise will interfere the BER performance of the OFDM system. It is also shown that the adverse effect of multipath is more serious than that of impulsive noise. In this paper, the guard interval is used to improve the BER performance of the OFDM system. As the longer guard interval is inefficient in using the signal power, the optimum guard interval that can achieve the best BER performance is studied.
283 citations
TL;DR: This article provides a comprehensive review of UWB multiple access and modulation schemes, and their comparison with narrowband radios, and explores various suboptimal low-complexity receiving schemes.
Abstract: Ultra-wideband wireless communications techniques have many merits, including an extremely simple radio that inherently leads to low-cost design, large processing gain for robust operations in the presence of narrowband interference, covert operations, and fine time resolution for accurate position sensing. However, there are a number of challenges in UWB receiver design, such as capturing multipath energy, intersymbol interference especially in a non-line-of-sight environment, and the need for high-sampling-rate analog-to-digital converters. In this article, we provide a comprehensive review of UWB multiple access and modulation schemes, and their comparison with narrowband radios. We also outline the issues with UWB signal reception and detection, and explore various suboptimal low-complexity receiving schemes
281 citations
TL;DR: It is shown that the bit-error rate for an uncoded OFDM system with quadrature amplitude modulation (QAM) can be expressed by the sum of a few integrals, whose number depends on the constellation size.
Abstract: We introduce an analytical approach to evaluate the error probability of orthogonal frequency-division-multiplexing (OFDM) systems subject to carrier frequency offset (CFO) in frequency-selective channels, characterized by Rayleigh or Rician fading. By properly exploiting the Gaussian approximation of the intercarrier interference (ICI), we show that the bit-error rate (BER) for an uncoded OFDM system with quadrature amplitude modulation (QAM) can be expressed by the sum of a few integrals, whose number depends on the constellation size. Each integral can be evaluated numerically, or, in Rayleigh fading, by using a series expansion that involves generalized hypergeometric functions. Simulation results illustrate that the theoretical analysis is quite accurate, especially for Rayleigh channels, and also with nonlinear amplifiers.
212 citations
03 Oct 2005
TL;DR: The obtained results show that a significant throughput is attained over noisy wireless optical channels, and an adaptive OFDM system is proposed to increase data throughput.
Abstract: In this paper, the application of orthogonal frequency division multiplexing (OFDM) over an indoor wireless optical channel is investigated Previous studies have demonstrated that it can be characterised as almost stationary but with a severe penalty induced by multipath propagation It is also highly dependent on the spatial distribution of emitters and receivers OFDM systems have been chosen owing to their capability of supporting high data rates without channel equalisation They also mitigate the effect of quality fluctuations of the channel induced when the spatial distribution of emitters and receivers varies We present several results about system performance Finally, an adaptive OFDM system is proposed to increase data throughput The obtained results show that a significant throughput is attained over noisy wireless optical channels
198 citations
TL;DR: A novel synchronization criterion is established that is termed "timing with dirty templates" (TDT), based on which timing algorithms in both data-aided (DA) and nondata- aided modes are developed and test.
Abstract: Ultra-wideband (UWB) technology for indoor wireless communications promises high data rates with low-complexity transceivers. Rapid timing synchronization constitutes a major challenge in realizing these promises. In this paper, we establish a novel synchronization criterion that we term "timing with dirty templates" (TDT), based on which we develop and test timing algorithms in both data-aided (DA) and nondata-aided modes. For the DA mode, we design a training pattern, which turns out to not only speed up synchronization, but also enable timing in a multiuser environment. Based on simple integrate-and-dump operations over the symbol duration, our TDT algorithms remain operational in practical UWB settings. They are also readily applicable to narrowband systems when intersymbol interference is avoided. Simulations confirm performance improvement of TDT relative to existing alternatives in terms of mean square error and bit-error rate.
194 citations
TL;DR: Close-form bit-error probability expressions for spread-spectrum systems are derived by approximating narrowband interferers as independent asynchronous tone interferers by developing a new analytical framework based on perturbation theory to analyze the performance of a Rake receiver in Nakagami-m channels.
Abstract: This paper evaluates the performance of wideband communication systems in the presence of narrowband interference (NBI). In particular, we derive closed-form bit-error probability expressions for spread-spectrum systems by approximating narrowband interferers as independent asynchronous tone interferers. The scenarios considered include additive white Gaussian noise channels, flat-fading channels, and frequency-selective multipath fading channels. For multipath fading channels, we develop a new analytical framework based on perturbation theory to analyze the performance of a Rake receiver in Nakagami-m channels. Simulation results for NBI such as GSM and Bluetooth are in good agreement with our analytical results, showing the approach developed is useful for investigating the coexistence of ultrawide bandwidth systems with existing wireless systems.
TL;DR: In this article, an analytical calculation method is presented, which can be used to determine the multipath components of any point-to-point channel in the indoor power-line environment.
Abstract: The time- and frequency-varying behavior of an indoor power-line network is the result of variable impedance loads connected to its termination points In fact, any signal transmitted through such a communications network is subject to time-varying multipath fading In this paper, an analytical calculation method is presented, which can be used to determine the multipath components of any point-to-point channel in the indoor power-line environment The method calculates all transmission characteristics of the network and, therefore, it can be exploited in the process of designing proper transmission algorithms for optimizing system performance The proposed method is applied to an example network to demonstrate its usefulness in explaining the network's time-dependent behavior and in estimating channel parameters, such as subchannel bandwidth, multipath delay spread, fading conditions, etc
01 May 2005
TL;DR: An input/output linear time-varying model for the wireless channel is derived, and some important physical parameters are defined, and a few statistical models of the channel variation over time and over frequency are introduced.
Abstract: A good understanding of the wireless channel, its key physical parameters and the modeling issues, lays the foundation for the rest of the book. This is the goal of this chapter. A defining characteristic of the mobile wireless channel is the variations of the channel strength over time and over frequency. The variations can be roughly divided into two types (Figure 2.1): Large-scale fading , due to path loss of signal as a function of distance and shadowing by large objects such as buildings and hills. This occurs as the mobile moves through a distance of the order of the cell size, and is typically frequency independent. Small-scale fading , due to the constructive and destructive interference of the multiple signal paths between the transmitter and receiver. This occurs at the spatial scale of the order of the carrier wavelength, and is frequency dependent. We will talk about both types of fading in this chapter, but with more emphasis on the latter. Large-scale fading is more relevant to issues such as cell-site planning. Small-scale multipath fading is more relevant to the design of reliable and efficient communication systems – the focus of this book. We start with the physical modeling of the wireless channel in terms of electromagnetic waves. We then derive an input/output linear time-varying model for the channel, and define some important physical parameters. Finally, we introduce a few statistical models of the channel variation over time and over frequency.
TL;DR: A generic statistical-based ultrawide-band (UWB) indoor channel model which incorporates the clustering of multipath components (MPCs) and a new distribution, namely, a mixture of two Poisson processes, is proposed to model the ray arrival times.
Abstract: A generic statistical-based ultrawide-band (UWB) indoor channel model which incorporates the clustering of multipath components (MPCs) is proposed. The model is derived using measurement data collected in the frequency band of 3-10 GHz in various types of high-rise apartment under different propagation scenarios. The measurement procedure allows the characterization of both the large-scale and the small-scale statistics of the channel. The main objective is to study multipath propagation behavior, particularly the phenomenon of clustered MPCs. The description of clustering observed in the channel uses two classes of parameters which characterize the clustering and the MPCs respectively. All parameters are described by a set of empirical probability density functions derived from the measured data such as the distribution of clusters and MPCs, cluster and MPC arrival statistics and small-scale amplitude fading statistics. A new distribution, namely, a mixture of two Poisson processes, is proposed to model the ray arrival times. This new distribution fits the empirical data better than the single Poisson process proposed in the conventional Saleh-Valenzuela (S-V) model. Analysis results show that the small-scale amplitude fading statistics are best modeled by the Weibull distribution. The Weibull b-shape parameter is lognormally distributed and is found to be invariant across the excess delay. Additionally, the temporal correlation between adjacent path amplitudes is investigated. The amplitude temporal correlation coefficients are found to be relatively small, and thus, can be assumed to be negligible in reality. The proposed model can provide a realistic simulation platform for UWB communication systems.
16 Sep 2005
TL;DR: Simulation results show that the Vision Correlator can remove the effects of a multipath signal on the code and carrier measurements when the delay of the multipATH signal is less than 10m from the line of sight signal, and mitigate their effect to a fraction of a meter (code).
Abstract: This paper provides an overview of the general principles and early performance results of the Vision Correlator. The Vision Correlator is a new method of measuring and processing the synchronization signals of a received PRN code. It is a significantly different process than any of the various correlation methods used in GNSS receivers today. It works by precisely measuring the received Radio Frequency (RF) characteristics in the time domain of the phase transitions of the modulated signal broadcast from the satellite. It is particularly useful in detecting and removing close-in multipath. Simulation results show that the Vision Correlator can remove the effects of a multipath signal on the code and carrier measurements when the delay of the multipath signal is less than 10m from the line of sight signal, and mitigate their effect to a fraction of a meter (code). It also provides a very useful statistic that can be used for Signal Quality Monitoring of the received signal. This statistic can be used to filter data that is unrepairable.
TL;DR: Simulation results show that by using the proposed likelihood function generation scheme for soft-decision Turbo decoding following QRM-MLD in 4-by-4 MIMO multiplexing, the required average received signal energy per bit-to-noise power spectrum density ratio is significantly reduced.
Abstract: This paper proposes likelihood function generation of complexity-reduced Maximum Likelihood Detection with QR Decomposition and M-algorithm (QRM-MLD) suitable for soft-decision Turbo decoding and investigates the throughput performance using QRM-MLD with the proposed likelihood function in multipath Rayleigh fading channels for Orthogonal Frequency and Code Division Multiplexing (OFCDM) multiple-input multiple-output (MIMO) multiplexing Simulation results show that by using the proposed likelihood function generation scheme for soft-decision Turbo decoding following QRM-MLD in 4-by-4 MIMO multiplexing, the required average received signal energy per bit-to-noise power spectrum density ratio (E b /N 0 ) at the average block error rate (BLER) of 10 -2 at a 1-Gbps data rate is significantly reduced compared to that using hard-decision decoding in OFCDM access with 16 QAM modulation, the coding rate of 8/9, and 8-code multiplexing with a spreading factor of 8 assuming a 100-MHz bandwidth Furthermore, we show that by employing QRM-MLD associated with soft-decision Turbo decoding for 4-by-4 MIMO multiplexing, the throughput values of 500 Mbps and 1 Gbps are achieved at the average received E b /N 0 of approximately 45 and 93 dB by QPSK with the coding rate of R= 8/9 and 16QAM with R = 8/9, respectively, for OFCDM access assuming a 100-MHz bandwidth in a twelve-path Rayleigh fading channel
TL;DR: This work investigates the effects of imperfect (and thus partial) channel feedback on the throughput of OFDM systems, and develops rate-power allocation algorithms based on the ergodic and quasi-static models.
Abstract: Power loading algorithms improve the data rates of orthogonal frequency division multiplexing (OFDM) systems. However, they require the transmitter to have perfect channel state information, which is impossible in most wireless systems. We investigate the effects of imperfect (and thus partial) channel feedback on the throughput of OFDM systems. Two channel uncertainty models are studied: 1) the ergodic model, where average rate is the figure of merit and 2) the quasi-static model, where outage rate is relevant. Rate-power allocation algorithms are developed. The throughput achieved by these algorithms and the effects of channel multipath are investigated analytically and with simulations.
TL;DR: This paper derives optimal receiver structures for an ultra-wideband transmitted reference (UWB TR) system in multipath environments, based on the average likelihood ratio test (ALRT) with Rayleigh or lognormal path strength models and demonstrates the equivalence between cross-correlation receivers and one theoretically derived ALRT suboptimal receiver.
Abstract: This paper derives optimal receiver structures for an ultra-wideband transmitted reference (UWB TR) system in multipath environments, based on the average likelihood ratio test (ALRT) with Rayleigh or lognormal path strength models. Several suboptimal receivers are obtained by either applying an approximation to the log-likelihood function without any specific channel statistical models or by approximating two ALRT optimal receiver structures. It is shown that the generalized likelihood ratio test optimal receiver is one of the suboptimal receiver structures in the ALRT sense. Average bit error probabilities of ALRT receivers are evaluated. Results show that ALRT optimal and suboptimal receivers derived from Rayleigh and lognormal models can perform equally well in each other's environments. This paper also investigates ad hoc cross-correlation receivers in detail, and discusses the equivalence between cross-correlation receivers and one theoretically derived ALRT suboptimal receiver. Results show that the noise /spl times/ noise term in a cross-correlation receiver can be modeled quite accurately by a Gaussian random variable when the noise time/spl times/bandwidth product is large, and cross-correlation receivers are suboptimal structures which have worse performance than ALRT receivers.
TL;DR: The architecture and performance of a noncoherent low complexity UWB impulse radio based transceiver designed for low data rate, low cost sensor network applications is presented.
Abstract: With the latest improvements in device size, power consumption, and communications, sensor networks are becoming increasingly more popular. There has also been a great increase in the popularity of commercial applications based on ultrawideband (UWB). Impulse radio (IR) based UWB technology utilizes noise-like signal, has potentially low complexity and low cost, is resistant to severe multipath, and has very good time domain resolution allowing for location and tracking applications. In this paper, the architecture and performance of a noncoherent low complexity UWB impulse radio based transceiver designed for low data rate, low cost sensor network applications is presented. The UWB-IR transmitter is based on a delay locked loop (DLL) and UWB monocycle pulse generator. The UWB-IR receiver utilises a noncoherent, energy detection based approach, which makes it largely independent of the shape of the transmit waveform and robust to multipath channels. The test circuits are designed for 0.35 /spl mu/m SiGe BiCMOS technology. This paper presents system simulations results as well as the performance of key functional blocks of the designed UWB application specific integrated circuit (ASIC) transceiver architecture. The simulated power consumption of UWB-IR transceiver circuits is 136 mW with 100% duty cycle with a 3.3 V power supply.
TL;DR: The performance with AWGN and multipath, the resistance to narrowband interference, as well as the simultaneous detection of multiple FM signals at the same carrier frequency are addressed.
Abstract: This paper presents a novel UWB communications system using double FM: a low-modulation index digital FSK followed by a high-modulation index analog FM to create a constant-envelope UWB signal. FDMA techniques at the subcarrier level are exploited to accommodate multiple users. The system is intended for low (1-10 kbps) and medium (100-1000 kbps) bit rate, and short-range WPAN systems. A wideband delay-line FM demodulator that is not preceded by any limiting amplifier constitutes the key component of the UWBFM receiver. This unusual approach permits multiple users to share the same RF bandwidth. Multipath, however, may limit the useful subcarrier bandwidth to one octave. This paper addresses the performance with AWGN and multipath, the resistance to narrowband interference, as well as the simultaneous detection of multiple FM signals at the same carrier frequency. SPICE and Matlab simulation results illustrate the principles and limitations of this new technology. A hardware demonstrator has been realized and has allowed the confirmation of theory with practical results.
13 Mar 2005
TL;DR: A TDOA location system based on the time difference of arrival (TDOA) method is developed, including several techniques such as access point (APs) synchronization, leading edge timing observations, and averaging with diversity.
Abstract: We propose an IEEE 802.11b wireless LAN location system based on the time difference of arrival (TDOA) method. We confirm that IEEE 802.11b, as part of an indoor location system, is potentially highly accurate because of its broad bandwidth. When a location system is implemented in the IEEE 802.11b system, there are two important considerations; system architecture and required positioning accuracy. The accuracy of an indoor location system is apt to be degraded by multipath fading, which is a complex characteristic of indoor propagation. We developed a TDOA location system based on IEEE 802.11b, including several techniques such as access point (APs) synchronization, leading edge timing observations, and averaging with diversity. We experimentally evaluated the proposed system in a storehouse. The positioning accuracy when using ten APs and 3-branch diversity was 2.4 m at the 67/sup th/ percentile.
TL;DR: A self-coherence anti-jamming scheme is introduced which relies on the unique structure of the coarse/acquisition (C/A) code of theatellite signals to excise interferers that have different temporal structures from that of the satellite signals.
Abstract: This paper considers interference suppression and multipath mitigation in Global Navigation Satellite Systems (GNSSs). In particular, a self-coherence anti-jamming scheme is introduced which relies on the unique structure of the coarse/acquisition (C/A) code of the satellite signals. Because of the repetition of the C/A-code within each navigation symbol, the satellite signals exhibit strong self-coherence between chip-rate samples separated by integer multiples of the spreading gain. The proposed scheme utilizes this inherent self-coherence property to excise interferers that have different temporal structures from that of the satellite signals. Using a multiantenna navigation receiver, the proposed approach obtains the optimal set of beamforming coefficients by maximizing the cross correlation between the output signal and a reference signal, which is generated from the received data. It is demonstrated that the proposed scheme can provide high gains toward all satellites in the field of view, while suppressing strong interferers. By imposing constraints on the beamformer, the proposed method is also capable of mitigating multipath that enters the receiver from or near the horizon. No knowledge of either the transmitted navigation symbols or the satellite positions is required.
12 Dec 2005
TL;DR: This work proposes a distributed N-to-1 multipath discovery protocol which is able to find multiple node-disjoint paths from every sensor node to the base station simultaneously in one route discovery process, and a hybrid multipath data collection scheme which combines end- to-end multipath traffic dispersion and per-hop alternate path salvaging.
Abstract: A typical task in a wireless sensor network is that every sensor node senses its local environment and, upon request, sends the data of interest back to a base station. Based on this many-to-one communication pattern, we first propose a distributed N-to-1 multipath discovery protocol which distinguishes from other multipath routing protocols in that it is able to find multiple node-disjoint paths from every sensor node to the base station simultaneously in one route discovery process. Then we propose a hybrid multipath data collection scheme which combines end-to-end multipath traffic dispersion and per-hop alternate path salvaging. Our simulation results show that the proposed N-to-1 multipath discovery protocol is highly efficient and the hybrid data collection scheme based on it provides a seamlessly more reliable and more secure data collection service in wireless sensor networks
19 Dec 2005
TL;DR: In this article, the effect of antenna heights, radiation patterns, and foliage environments on near-ground radio-wave propagation was investigated in a forest environment, and it was shown that path-loss varies inversely with the square of the receiving antenna height.
Abstract: Near-ground radio-wave propagation is of interest for emerging military applications such as battlefield sensor networks and for wireless communication between dismounted soldiers. Narrowband and wideband channel measurement results at 300 and 1900 MHz are presented for near-ground propagation, characterising the effect of antenna heights, radiation patterns and foliage environments. An additional set of channel measurements was performed to study the effect of rain on near-ground propagation at 1900 MHz in a forest environment. Measured power–delay profiles indicate significant multipath propagation with the multipath components becoming stronger relative to the direct path for decreasing antenna heights. In the LOS measurements, the RMS delay spread decreased with the use of directional antennas and increasing antenna heights, and increased with distance. This effect was not evident in the forest measurements, suggesting a larger angle spread of the multipaths. Measurement results indicate that leaves and wet foliage do not contribute significantly to the scattering of radio waves. Foliage effects are more significant at 1900 MHz than 300 MHz. Results from near-ground sensor measurements demonstrate that path-loss varies inversely with the square of the receiving antenna height, as in the plane-Earth and Egli models.
TL;DR: The presented estimator and the hybrid beamforming outperform the existing techniques of comparable complexity and attains, in many situations, the Crame/spl acute/r-Rao lower bound of the problem at hand.
Abstract: This paper addresses the estimation of the code-phase (pseudorange) and the carrier-phase of the direct signal received from a direct-sequence spread-spectrum satellite transmitter. The signal is received by an antenna array in a scenario with interference and multipath propagation. These two effects are generally the limiting error sources in most high-precision positioning applications. A new estimator of the code- and carrier-phases is derived by using a simplified signal model and the maximum likelihood (ML) principle. The simplified model consists essentially of gathering all signals, except for the direct one, in a component with unknown spatial correlation. The estimator exploits the knowledge of the direction-of-arrival of the direct signal and is much simpler than other estimators derived under more detailed signal models. Moreover, we present an iterative algorithm, that is adequate for a practical implementation and explores an interesting link between the ML estimator and a hybrid beamformer. The mean squared error and bias of the new estimator are computed for a number of scenarios and compared with those of other methods. The presented estimator and the hybrid beamforming outperform the existing techniques of comparable complexity and attains, in many situations, the Crame/spl acute/r-Rao lower bound of the problem at hand.
05 Sep 2005
TL;DR: An algorithm for accurate indoor localization of a sensor in a network of known beacons using an Ultra-Wideband signal and a particle filter estimation technique specifically to capture the non-linearity of transitions in the beacon bias as the sensor moves is described.
Abstract: For most outdoor applications, systems such as GPS provide users with accurate position estimates However, reliable range-based localization using radio signals in indoor or urban environments can be a problem due to multipath fading and line-of-sight (LOS) blockage The measurement bias introduced by these delays causes significant localization error, even when using additional sensors such as an inertial measurement unit (IMU) to perform outlier rejection We describe an algorithm for accurate indoor localization of a sensor in a network of known beacons The sensor measures the range to the beacons using an Ultra-Wideband (UWB) signal and uses statistical inference to infer and correct for the bias due to LOS blockage in the range measurements We show that a particle filter can be used to estimate the joint distribution over both pose and beacon biases We use the particle filter estimation technique specifically to capture the non-linearity of transitions in the beacon bias as the sensor moves Results using real-world and simulated data are presented
TL;DR: Results demonstrate benefits of focusing techniques whose performance is not conditioned on the array size, and are intended as a basis for adaptive system implementation in which channel estimates will replace the actual values.
Abstract: High rate underwater communications have traditionally relied on equalization methods to overcome the intersymbol interference (ISI) caused by multipath propagation. An alternative technique has emerged in the form of time-reversal, which comes at virtually no cost in computational complexity, but sacrifices the data rate and relies on the use of large arrays to reduce ISI. In this paper, spatiotemporal processing for optimal multipath suppression is addressed analytically. A communication link between a single element and an array is considered in several scenarios: uplink and downlink transmission, with and without channel state information and varying implementation complexity. Transmit/receive techniques are designed which simultaneously maximize the data detection signal-to-noise ratio and minimize the residual ISI, while maintaining maximal data rate in a given bandwidth and satisfying a constraint on transmitted energy. The performance of so-obtained focusing techniques is compared to the standard ones on a shallow water channel operating in a 5 kHz bandwidth around a 15 kHz center frequency. Results demonstrate benefits of focusing techniques whose performance is not conditioned on the array size. Optimal configurations are intended as a basis for adaptive system implementation in which channel estimates will replace the actual values.
TL;DR: A cost function with proper weighting factor is introduced to improve the performance of the proposed equalizer and is analyzed and compared with that of other equalizers, indicating significant performance improvement.
Abstract: In orthogonal frequency division multiplexing (OFDM) systems, time-varying multipath fading leads to the loss of subcarrier orthogonality and the occurrence of intercarrier interference (ICI). In this study, an efficient ICI suppression with less noise enhancement for multicarrier equalization is presented by using a parallel canceling scheme via frequency-domain equalization techniques, with the assumption that the channel impulse response (CIR) varies linearly during a block period. In order to avoid performance deterioration due to unreliable initial estimations in the parallel cancellation scheme, a cost function with proper weighting factor is introduced to improve the performance of the proposed equalizer. The proposed equalizer consists of a set of prefilters and a set of ICI cancellation filters, with two stages to perform different functions to achieve minimum mean square error (MMSE) equalization. The prefilters compensate for the multiplicative distortion at the first stage, and the ICI cancellation filters remove the effects of ICI by a parallel cancellation scheme at the second stage. Finally, the performance of the proposed equalizer is analyzed and compared with that of other equalizers, indicating significant performance improvement.
TL;DR: It is demonstrated that the use of TR in wireless communication has a promising potential in mitigating the effect of channel dispersion and especially in reducing the cochannel interference where a margin of 18 dB interference reduction has been obtained.
Abstract: Based on outdoor measurements we study the feasibility of applying the time reversal techniques (TR) in multiple element antenna (MEA) wireless communication systems. It is demonstrated that the use of TR in wireless communication has a promising potential in mitigating the effect of channel dispersion and especially in reducing the cochannel interference where a margin of 18 dB interference reduction has been obtained.
TL;DR: Simulation results for a few cases are shown to demonstrate that the model accurately predicts key properties of the measured channels, such as the distribution of rms delay spread.
Abstract: We present models for the ultrawideband (UWB) channel delay profile in indoor environments, based on the processing of two large sets of measured data. Both measurement sets are for a center frequency of 5 GHz, but the bandwidths are very different-1.25 GHz and 6 GHz. We model both line-of-sight (LOS) and nonline-of-sight (NLOS) paths, and do so for both single-family homes and commercial buildings. Also, we consider both the profile at a receiver point, which we call the multipath intensity profile (MIP), and the locally spatially averaged profile, which we call the power delay profile (PDP). For both cases, we find that the profile for NLOS paths can be modeled as a decaying exponential times a noise-like variation with lognormal statistics and that, for LOS paths, the profile has the same form plus a strong component at the minimum delay. The model consists of statistical descriptions of the parameters of these functions, including the effects of transmit-receive (T--R) distance and of variations from building to building. We show simulation results for a few cases to demonstrate that the model accurately predicts key properties of the measured channels, such as the distribution of rms delay spread.