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Showing papers on "Multipath propagation published in 1998"


Proceedings ArticleDOI
29 Sep 1998
TL;DR: This paper describes a wireless communication architecture known as vertical BLAST (Bell Laboratories Layered Space-Time) or V-BLAST, which has been implemented in real-time in the laboratory and demonstrated spectral efficiencies of 20-40 bps/Hz in an indoor propagation environment at realistic SNRs and error rates.
Abstract: Information theory research has shown that the rich-scattering wireless channel is capable of enormous theoretical capacities if the multipath is properly exploited In this paper, we describe a wireless communication architecture known as vertical BLAST (Bell Laboratories Layered Space-Time) or V-BLAST, which has been implemented in real-time in the laboratory Using our laboratory prototype, we have demonstrated spectral efficiencies of 20-40 bps/Hz in an indoor propagation environment at realistic SNRs and error rates To the best of our knowledge, wireless spectral efficiencies of this magnitude are unprecedented and are furthermore unattainable using traditional techniques

3,925 citations


Journal ArticleDOI
TL;DR: The characteristics of impulse radio using a modulation format that can be supported by currently available impulse signal technology are described and analytical estimates of its multiple- access capability under ideal multiple-access channel conditions are given.
Abstract: Impulse radio, a form of ultra-wide bandwidth (UWB) spread-spectrum signaling, has properties that make it a viable candidate for short-range communications in dense multipath environments. This paper describes the characteristics of impulse radio using a modulation format that can be supported by currently available impulse signal technology and gives analytical estimates of its multiple-access capability under ideal multiple-access channel conditions.

2,377 citations


Journal ArticleDOI
TL;DR: This paper shows that the presence of multipath greatly improves achievable data rate if the appropriate communication structure is employed, and an adaptive-lattice trellis-coding technique is suggested as a method for coding across the space and frequency dimensions that exist in the DMMT channel.
Abstract: Multipath signal propagation has long been viewed as an impairment to reliable communication in wireless channels. This paper shows that the presence of multipath greatly improves achievable data rate if the appropriate communication structure is employed. A compact model is developed for the multiple-input multiple-output (MIMO) dispersive spatially selective wireless communication channel. The multivariate information capacity is analyzed. For high signal-to-noise ratio (SNR) conditions, the MIMO channel can exhibit a capacity slope in bits per decibel of power increase that is proportional to the minimum of the number multipath components, the number of input antennas, or the number of output antennas. This desirable result is contrasted with the lower capacity slope of the well-studied case with multiple antennas at only one side of the radio link. A spatio-temporal vector-coding (STVC) communication structure is suggested as a means for achieving MIMO channel capacity. The complexity of STVC motivates a more practical reduced-complexity discrete matrix multitone (DMMT) space-frequency coding approach. Both of these structures are shown to be asymptotically optimum. An adaptive-lattice trellis-coding technique is suggested as a method for coding across the space and frequency dimensions that exist in the DMMT channel. Experimental examples that support the theoretical results are presented.

1,593 citations


Journal ArticleDOI
01 Dec 1998
TL;DR: Novel algorithms are developed for blind identification, direct, zero-forcing equalization and minimum mean square error (MMSE) equalization by combining channel diversity with temporal (fractional sampling) and/or spatial diversity which becomes available with multiple receivers.
Abstract: The time-varying impulse response of rapidly fading mobile communication channels is expanded over a basis of complex exponentials that arise due to Doppler effects encountered with multipath propagation. Blind methods are reviewed for estimating the bases' parameters and the model orders. Existing second-order methods are critiqued and novel algorithms are developed for blind identification, direct, zero-forcing equalization and minimum mean square error (MMSE) equalization by combining channel diversity with temporal (fractional sampling) and/or spatial diversity which becomes available with multiple receivers. Illustrative simulations are also presented.

629 citations


Journal ArticleDOI
TL;DR: The results show that an ultra-wide bandwidth signal does not suffer multipath fading, and the robustness of the UWB signal in multipath is quantified through cumulative distribution functions of the signal quality in various locations of the building.
Abstract: The results of an ultra-wide bandwidth (UWB) signal propagation experiment, using bandwidth in excess of 1 GHz, performed in a typical modern office building are presented. The robustness of the UWB signal in multipath is quantified through cumulative distribution functions of the signal quality in various locations of the building. The results show that an UWB signal does not suffer multipath fading.

612 citations


Journal ArticleDOI
TL;DR: A quasi-analytical experimental analysis is described in this paper to quantify the tradeoff between energy capture and diversity level in a RAKE receiver using measured received waveforms obtained from ultrawide bandwidth signal propagation experiments.
Abstract: A quasi-analytical experimental analysis is described in this paper to quantify the tradeoff between energy capture and diversity level in a RAKE receiver using measured received waveforms obtained from ultrawide bandwidth signal propagation experiments.

551 citations


Proceedings ArticleDOI
05 Oct 1998
TL;DR: The effect of fading correlations in multi-element antenna (MEA) communication systems is investigated and it is shown that the MEA capacity can be expressed as the sum of the capacities of several subchannels, whose gains are affected by the fading correlation.
Abstract: We investigate the effect of fading correlations in multi-element antenna (MEA) communication systems. The enormous capacity of an MEA system can potentially be reduced by fading correlation. To model the narrowband Rayleigh-fading multipath environment, we propose an abstract model. Using this model, the fading statistics can be determined from the geometrical parameters of the MEA and the multipath environment. This, model allows us to directly observe how the choice of antenna geometry affects capacity. We show that the MEA capacity can be expressed as the sum of the capacities of several subchannels, whose gains are affected by the fading correlation. As the fading correlation becomes higher, the disparity between the gains of these subchannels becomes larger and as a result some of the subchannels do not convey information at any significant rate.

510 citations


Journal ArticleDOI
TL;DR: Two blind carrier offset estimation algorithms are presented by exploiting the intrinsic structure information of OFDM signals to offer the accuracy of super resolution subspace methods, viz., MUSIC and ESPRIT, without involving computationally intensive subspace decompositions.
Abstract: While multipath induced phase rotations can be dealt with by differential encoding in orthogonal frequency division multiplexing (OFDM) communications, the loss of orthogonality due to the carrier offset must be compensated before discrete Fourier transform (DFT)-based demodulation can be performed. In this letter, we present a high-performance/low-complexity blind carrier offset estimation algorithm by exploiting intrinsic structure information of OFDM signals. The algorithm offers the accuracy of a super resolution subspace method, viz. MUSIC, without involving computationally intensive subspace decompositions.

404 citations


Journal ArticleDOI
16 Aug 1998
TL;DR: The capacity and mutual information of a broadband fading channel consisting of a finite number of time-varying paths is investigated and it is shown that if white-like signals are used instead (as is common in spread-spectrum systems), the mutual information is inversely proportional to the number of resolvable paths L/spl tilde/ with energy spread out.
Abstract: We investigate the capacity and mutual information of a broadband fading channel consisting of a finite number of time-varying paths. We show that the capacity of the channel in the wideband limit is the same as that of a wideband Gaussian channel with the same average received power. However, the input signals needed to achieve the capacity must be "peaky" in time or frequency. In particular, we show that if white-like signals are used instead (as is common in spread-spectrum systems), the mutual information is inversely proportional to the number of resolvable paths L/spl tilde/ with energy spread out, and in fact approaches 0 as the number of paths gets large. This is true even when the paths are assumed to be tracked perfectly at the receiver. A critical parameter L/spl tilde//sub crit/ is defined in terms of system parameters to delineate the threshold on L over which such overspreading phenomenon occurs.

402 citations


Journal ArticleDOI
TL;DR: The algorithm uses a two-dimensional ESPRIT-like shift-invariance technique to separate and estimate the phase shifts due to delay and direction of incidence with automatic pairing of the two parameter sets.
Abstract: In a multipath communication scenario, it is often relevant to estimate the directions and relative delays of each multipath ray. We derive a closed-form subspace-based method for the simultaneous estimation of these parameters from an estimated channel impulse response, using knowledge of the transmitted pulse shape function. The algorithm uses a two-dimensional (2-D) ESPRIT-like shift-invariance technique to separate and estimate the phase shifts due to delay and direction of incidence with automatic pairing of the two parameter sets. Improved resolution is obtained by enlarging the data matrix with shifted and conjugated copies of itself.

331 citations


Journal ArticleDOI
TL;DR: It is shown that the performance of the proposed method tends to be close to that of the MMSE receiver at high SNR, whereas the constraint parameters converge to the multipath channel parameters.
Abstract: Constrained optimization of the receiver's output variance has previously been proposed as a relatively simple method for designing blind multiuser detectors for DS-CDMA systems. A single constraint is sufficient for the AWGN case, whereas multiple constraints should be used in a multipath environment. It is shown in this paper that the choice of the constraint parameters in the multipath case can have a significant effect on the system performance. A max/min approach for optimizing the constraint is proposed, resulting in blind solutions with improved performance. It is shown that the performance of the proposed method tends to be close to that of the MMSE receiver at high SNR, whereas the constraint parameters converge to the multipath channel parameters. The proposed method does not require knowledge of the interfering users' codes and timing. Simulation results support those performance claims.

Journal ArticleDOI
TL;DR: A synchronous multiuser system operating in an additive white Gaussian noise channel, with or without multipath fading, is considered and it is shown that both multiple access and intersymbol interference can be eliminated by means of a suitable transmitter precoding scheme.
Abstract: A synchronous multiuser system operating in an additive white Gaussian noise channel, with or without multipath fading, is considered. It is shown that when either a conventional single user receiver or the RAKE receiver is employed, both multiple access and intersymbol interference can be eliminated by means of a suitable transmitter precoding scheme. Transmitter precoding represents a linear transformation of transmitted signals, such that the mean squared errors at all receivers are minimized. Precoding, with both conventional single user receiver and with the RAKE receiver, results in near-far resistant performance and outperforms considerably the respective schemes without precoding. The crucial assumption, in the multipath case, is that the transmitter knows the multipath characteristics of all channels and that channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over the block of precoded bits.

Journal ArticleDOI
01 Oct 1998
TL;DR: Developments in interference suppression using blind adaptive receivers that do not receive knowledge of the signal waveforms and propagation channels of the interference are presented, and that require a minimal amount of information about the desired signal.
Abstract: Direct sequence (DS) code division multiple access (CDMA) is a promising technology for wireless environments with multiple simultaneous transmissions because of several features: asynchronous multiple access, robustness to frequency selective fading, and multipath combining. The capacity of DS-CDMA systems is interference-limited and can therefore be increased by techniques that suppress interference. In this paper, we present developments in interference suppression using blind adaptive receivers that do not receive knowledge of the signal waveforms and propagation channels of the interference, and that require a minimal amount of information about the desired signal. The framework considered generalizes naturally to include additional capabilities such as receive antenna diversity. The most powerful application of the methods described here is for linearly modulated CDMA systems with short spreading waveforms (i.e., spreading waveforms with period equal to the symbol interval), for which they provide substantial performance gains over conventional reception. Implications for future system design due to the restriction of short spreading waveforms and directions for further investigation are discussed.

Journal ArticleDOI
TL;DR: This work investigates certain resolution issues that take the fact that the source is bandlimited into account and exploits a new subspace-based high-resolution method for simultaneous estimation of the angle/delay parameters from multiple estimates of the channel impulse response.
Abstract: In a parametric multipath propagation model, a source is received by an antenna array via a number of rays, each described by an arrival angle, a delay, and a fading parameter. Unlike the fading, the angles and delays are stationary over long time intervals. This fact is exploited in a new subspace-based high-resolution method for simultaneous estimation of the angle/delay parameters from multiple estimates of the channel impulse response. A computationally expensive optimization search can be avoided by using an ESPRIT-like algorithm. Finally, we investigate certain resolution issues that take the fact that the source is bandlimited into account.

Journal ArticleDOI
TL;DR: A spatial and temporal communication theory based on an adaptive antenna array, such as spatial andporal channel modeling, equalization, optimum detection for single-user and multi-user CDMA, precoding in a transmitter, and joint optimization of both transmitter and receiver is introduced.
Abstract: An adaptive antenna array or a smart antenna is named a software antenna because it can form a desired antenna pattern and adaptively control it if an appropriate set of antenna weights is provided and updated in software. It can be a typical tool for realizing a software radio. An adaptive antenna array can be considered an adaptive filter in the space and time domains for radio communications, so communication theory can be generalized from a conventional time domain into both space and time domains. This article introduces a spatial and temporal communication theory based on an adaptive antenna array, such as spatial and temporal channel modeling, equalization, optimum detection for single-user and multi-user CDMA, precoding in a transmitter, and joint optimization of both transmitter and receiver. Such spatial and temporal processing promises significant improvement of performance against multipath fading in mobile radio communications.

Journal ArticleDOI
TL;DR: Numerical results show that the proposed multistage detector, which alleviates the detrimental effects of the near-far problem, can significantly improve the system performance.
Abstract: There has been an increasing interest in the use of code-division multiple access (CDMA) in cellular mobile and wireless personal communications. The choice of such multiaccess technique is attractive because of its potential capacity increases and other technical factors such as privacy and multipath rejection capabilities. However, it is well known that the performance of CDMA can be significantly degraded due to cochannel interference (CI) and the near-far effects. We consider the performance of direct-sequence (DS)-based CDMA over fading channels that are modeled as slowly varying Rayleigh-fading discrete multipath channels. Specifically, we propose and analyze an adaptive multistage interference cancellation strategy for the demodulation of asynchronous DS spread-spectrum multiple-access signals. Numerical results show that the proposed multistage detector, which alleviates the detrimental effects of the near-far problem, can significantly improve the system performance.

Journal ArticleDOI
TL;DR: A framework for statistical modeling of the wideband characteristics of the frequency-selective fading multipath indoor radio channel for geolocation applications and the effects of external walls on estimating the location of the DLOS path are presented.
Abstract: A framework for statistical modeling of the wideband characteristics of the frequency-selective fading multipath indoor radio channel for geolocation applications is presented. Multipath characteristics of the channel are divided into three classes according to availability and the strength of the direct line of sight (DLOS) path with respect to the other paths. Statistics of the error in estimating the time of arrival of the DLOS path in a building is related to the receiver's sensitivity and dynamic range. The effects of external walls on estimating the location of the DLOS path are analyzed.

Journal Article
TL;DR: In this article, it was shown that the vector sum of lognormal rays, such as in a narrow-band signal envelope, may best be approximated as being either Rayleigh, Lognormal or Suzuki distributed depending on the fading channel conditions.
Abstract: Empirical justifications for the lognormal, Rayleigh and Suzuki (1977) probability density functions in multipath fading channels are examined by quantifying the rates of convergence of the central limit theorem (CLT) for the addition and multiplication of random variables. The accuracy of modeling the distribution of rays which experience multiple reflections/diffractions between transmitter and receiver as lognormal is quantified. In addition, it is shown that the vector sum of lognormal rays, such as in a narrow-band signal envelope, may best be approximated as being either Rayleigh, lognormal or Suzuki distributed depending on the fading channel conditions. These conditions are defined statistically.

Patent
14 Sep 1998
TL;DR: In this article, a signal processor calculates a signal signature for each active mobile and compares it with a database of calibrated signal signatures and corresponding locations, and a location whose calibrated signature best matches the measured signature is selected as the most likely location of the mobile transmitter.
Abstract: A method and apparatus for location finding in a CDMA wireless communication system uses multipath signals in order to accurately determine a transmitter—s location. Direct path and multipath signals from a mobile transmitter arrive at an array of p antennas belonging to a cellular network base station. A location finding apparatus connected to the base station contains a multichannel receiver that uses PN sequence information provided by the base station receiver to despread the p signals and to separate each of the p signals into temporally distinct multipath parts. A signal processor calculates a signal signature for each active mobile. The signature is comprises a code correlation function, a set of temporal delays corresponding to the multipath parts and a set of signal subspaces. The signature is then compared to a database of calibrated signal signatures and corresponding locations, and a location whose calibrated signature best matches the measured signature is selected as the most likely location of the mobile transmitter. The location information can be used to increase the performance of a cellular telephone network and/or to provide useful services to cellular telephone customers.

Journal ArticleDOI
TL;DR: Empirical justifications for the lognormal, Rayleigh and Suzuki (1977) probability density functions in multipath fading channels are examined by quantifying the rates of convergence of the central limit theorem (CLT) for the addition and multiplication of random variables.
Abstract: Empirical justifications for the lognormal, Rayleigh and Suzuki (1977) probability density functions in multipath fading channels are examined by quantifying the rates of convergence of the central limit theorem (CLT) for the addition and multiplication of random variables. The accuracy of modeling the distribution of rays which experience multiple reflections/diffractions between transmitter and receiver as lognormal is quantified. In addition, it is shown that the vector sum of lognormal rays, such as in a narrow-band signal envelope, may best be approximated as being either Rayleigh, lognormal or Suzuki distributed depending on the fading channel conditions. These conditions are defined statistically.

Proceedings ArticleDOI
01 Nov 1998
TL;DR: This work addresses the problem of downlink interference rejection in a DS-CDMA system by proposing linear zero-forcing (ZF) and minimum mean-squared-error (MMSE) receivers which equalize for the estimated channel, thus rendering the user signals orthogonal again.
Abstract: We address the problem of downlink interference rejection in a DS-CDMA system. Periodic orthogonal Walsh-Hadamard sequences spread different users' symbols followed by scrambling by a symbol aperiodic base-station specific overlay sequence. This corresponds to the downlink of the European UMTS wideband CDMA proposal. The point to point propagation channel from the cell-site to a certain mobile station is the same for all downlink signals (desired user as well as the interference). The composite channel is shorter than a symbol period for some user signals, while other users can have significant ISI owing to a faster transmission rate. In any case, orthogonality of the underlying Walsh-Hadamard sequences is destroyed by multipath propagation, resulting in multiuser interference if a coherent combiner (the RAKE receiver) is employed. We propose linear zero-forcing (ZF) and minimum mean-squared-error (MMSE) receivers which equalize for the estimated channel, thus rendering the user signals orthogonal again. A simple code matched filter subsequently suffices to cancel the multiple access interference (MAI) from intracell users.

Journal ArticleDOI
TL;DR: Two modifications to the design of wireless infrared links are discussed that can yield significant performance improvements, albeit at the price of increased complexity, and may enable infrared wireless networks to employ space-division multiplexing.
Abstract: We discuss two modifications to the design of wireless infrared links that can yield significant performance improvements, albeit at the price of increased complexity. In line-of-sight and non-line-of-sight links, replacement of a single-element receiver by one employing an imaging light concentrator and a segmented photodetector can reduce received ambient light noise and multipath distortion. For a fixed receiver entrance area, such an imaging receiver can reduce transmit power requirements by as much as about 14 dB, depending on the link design and the number of photodetector segments. Imaging receivers also reduce co-channel interference, and may therefore enable infrared wireless networks to employ space-division multiplexing, wherein several transmitters located in close proximity can transmit simultaneously at the same wavelength. In nondirected non-line-of-sight links, replacement of the diffuse transmitter by one that projects multiple narrow beams can reduce the path loss, further reducing the transmit power requirement by several decibels. We describe the design of an experimental 100 Mb/s infrared wireless link employing a multibeam transmitter and a 37-pixel imaging receiver.

Patent
30 Jan 1998
TL;DR: In this article, the authors present a method and apparatus for verifying the integrity of a smart antenna system by simulating multiple sensors with directional and non-directional components with variables from Doppler, delay and angular spread.
Abstract: The invention is a method and apparatus for verifying the integrity of a smart antenna system. The simulator section replicates multiple sensors with directional and non-directional components with variables from Doppler, delay and angular spread. Hardware/software combinations simulate the line-of-sight signal, reflected signals, and refracted signals that require manipulation by the smart antenna processor to extract the temporal and spatial information of the signals of interest. The channel simulator of the present invention introduces independent variability of the most significant factors involved in the simulation; delay spread, Doppler spread, and angular spread. The simulated signals have variable numbers, amplitude, phase, delay and bearing components for representing a variety of terrain, environmental, equipment and capacity conditions for both indoor and outdoor applications. The simulation accounts for the various scattering and multipath conditions that are encountered in typical rural and urban environments. The output of the smart antenna processor is checked against input parameters to compare, verify and calibrate the smart antenna system, and the working condition of the individual smart antenna is accurately tested. Co-channel interference nulling, multipath mitigation, and geo-location capabilities are verified by the analysis of the processed data as compared to the input simulation data.

Journal ArticleDOI
TL;DR: A linear receiver for direct-sequence spread-spectrum multiple-access communication systems under the aperiodic random sequence model is considered and a simple blind adaptive algorithm is developed in order to reduce the computational complexity.
Abstract: A linear receiver for direct-sequence spread-spectrum multiple-access communication systems under the aperiodic random sequence model is considered. The receiver consists of the conventional matched filter followed by a tapped delay line with the provision of incorporating the use of antenna arrays. It has the ability of suppressing multiple-access interference (MAI) and narrowband interference in some weighted proportions, as well as combining multipath components without explicit estimation of any channel conditions. Under some specific simplified channel models, the receiver reduces to the minimum variance distortionless response beamformer, the RAKE receiver, a notch filter, or an MAI suppressor. The interference rejection capability is made possible through a suitable choice of weights in the tapped delay line. The optimal weights can be obtained by straightforward but computationally complex eigenanalysis. In order to reduce the computational complexity, a simple blind adaptive algorithm is also developed.

Patent
18 Feb 1998
TL;DR: In this article, a location finding apparatus measures an array covariance matrix R of a signal and compares it to a database of signatures comprising calibrated signal subspaces, from these calculations a set of likely locations is then determined.
Abstract: A method and apparatus improves the accuracy of a wireless location finding system based on the use of multipath signal signatures. A location finding apparatus measures an array covariance matrix R of a signal. The covariance matrix is compared to a database of signatures comprising calibrated signal subspaces. The comparison is based on calculating the projection of R onto each calibrated subspace. From these calculations a set of likely locations is then determined.

Proceedings ArticleDOI
07 Jun 1998
TL;DR: The benefits and challenges of using angle diversity in nondirected wireless infrared communications systems are outlined and the design and performance of a prototype angle-diversity infrared communication system are discussed.
Abstract: We outline the benefits and challenges of using angle diversity in nondirected wireless infrared communications systems. Multiple transmitter beams and multiple narrow-field-of-view receivers reduce the path loss, multipath distortion and background noise of the channel, which leads to improved range. The design and performance of a prototype angle-diversity infrared communication system are discussed. The prototype can maintain 70 Mb/s at a BER of 10/sup -9/ over a 4 m range.

Patent
21 Apr 1998
TL;DR: In this article, a Code-Division Multiple Access (CDMA) receiver removes the pilot signal from the received signal, defined by its multipath parameters (amplitudes, phase shift and delays) and its signature sequence.
Abstract: A Code-Division Multiple Access (CDMA) receiver removes the pilot signal from the received signal. The pilot signal is defined by its multipath parameters (amplitudes, phase shift and delays) and its signature sequence. Since this information is known at the user's receiver terminal (i.e., handset), the pilot signals of the interfering multipath components of the baseband received signal are detected and removed prior to demodulation of the desired multipath component. The pilot signal may be cancelled prior to or following the data accumulation stage. The pilot signal cancellation can be switched on and off depending on the detected path signal level.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the diversity performance of three candidate dual-antenna handset configurations: two side-mounted planar-inverted F antennas (PIFAs), a back-mounted PIFA with a top-mounted helix, and a "flip" monopole.
Abstract: In personal wireless communications systems, multipath propagation has a significant effect on system design and performance Signal strength fading caused by destructive interference between multiple replicas of the signal of interest arriving at the receiver over different paths often is the limiting factor in system range/fidelity Antenna diversity is one technique that can be used to help overcome multipath fading This paper presents a description of experiments, data processing, and results used to evaluate the diversity performance of three candidate dual-antenna handset configurations: two side-mounted planar-inverted F antennas (PIFAs), a back-mounted PIFA with a top-mounted helix, a top-mounted PIFA, and a "flip" monopole In particular, the indoor industrial, scientific, and medical (ISM) band (902-928 MHz) propagation channel was of interest These experiments did not include operator proximity effects, and in these tests, the dual-antenna handset remained stationary while the transmitter was moved along predetermined indoor paths The issue of data normalization for extraction of fast fading behavior from measured data is addressed, with results showing its effect on observed correlation presented Also, measured indoor fading distributions are presented and seen to fit the Rician and Rayleigh models well From the diversity results presented, it is seen that the three proposed dual-antenna handsets yield sufficient decorrelation to warrant consideration for use in diversity systems

Journal ArticleDOI
TL;DR: Angle of arrival (AOA) estimation utilizing the MUltiple Signal Identification and Classification (MUSIC) algorithm is investigated for land vehicle location systems and a "virtual" antenna array is used to overcome problems inherent to MUSIC when operating in a highly correlated signal environment.
Abstract: Angle of arrival (AOA) estimation utilizing the MUltiple Signal Identification and Classification (MUSIC) algorithm is investigated for land vehicle location systems. A "virtual" antenna array is used to overcome problems inherent to MUSIC when operating in a highly correlated signal environment. Based on assumptions regarding the multipath radio environment, triangulation is possible by estimating the AOA of the line-of-sight (LOS) component in the received signal. Computer simulations are used to analyze the ability of techniques incorporating MUSIC to achieve this. Since triangulation is achieved using a narrowband signal, no new spectrum is required. Instead, the current cellular telephone bands as well as the existing basestation hardware could be exploited resulting in a cost-efficient and easily implemented system. A further cost reduction may be realized by processing received signal data while travelling along a nonlinear trajectory. In this way, an unambiguous angular spectrum is obtained with one antenna.

Journal ArticleDOI
TL;DR: It is shown that through the use of signal subspace estimation, both the decorrelating filterbank and the linear MMSE filterbank can be obtained blindly, i.e., they can be estimated from the received signal with the prior knowledge of only the signature waveform of the desired user.
Abstract: A blind adaptive technique for signal demodulation in multipath code-division multiple-access (CDMA) communication channels is proposed. This technique is based on signal subspace estimation. The receiver employs a bank of linear filters (decorrelating filters or linear MMSE filters) at the front end to mitigate the multiple-access interference and the multipath interference. A channel estimator is used to estimate the channel state for diversity combining. It is shown that through the use of signal subspace estimation, both the decorrelating filterbank and the linear MMSE filterbank can be obtained blindly, i.e., they can be estimated from the received signal with the prior knowledge of only the signature waveform of the desired user. Two forms of the subspace-based linear filterbanks are developed and their equivalence in terms of the interference suppression capability is established. These subspace-based blind adaptive interference suppression techniques require, at each symbol epoch, the eigenvalues and the eigenvectors of an appropriate signal subspace, which ran be obtained using computationally efficient sequential adaptive eigendecomposition (subspace tracking) algorithms. Moreover, a blind adaptive method for estimating the channel state is developed, which also produces the postcombining decision statistic as a byproduct.