Multipath channel

In this search, an important methodology has been presented for communicated information rectification utilizing advanced channel windowing approach. The modern data communication technologies are ensured with numerous challenges because of their unpredictability and arrangement. Various digital transmission topologies in 4G can't fulfill the requirements in future arrangements, therefore, alternative multicarrier modulation (MCM) becoming the nominated approaches among all other data transmission techniques. Wherein prototype filter configuration is a fundamental system based on which the synthesis and analysis filters are derived. This paper presents a complete review on the ongoing advances of finite impulse response (FIR) filter plan procedures in MCM based correspondence frameworks. Initially, the essential issues are tried, taking into consideration the presentation of available data signal applicants and the FIR filter design concept. At that point the techniques for FIR filter configuration are summed up in subtleties and are center around the accompanying three group’s recurrence testing strategies, windowing based strategies and advancement-based techniques. At last, the exhibitions of different FIR structure strategies are assessed and measured by power spectral density (PSD) and bit error rate (BER), and variable MCM plots as well as their potential prototype filters are examined.

We consider the recovery of a finite stream of Dirac pulses at nonuniform locations, from noisy lowpass-filtered samples. We show that maximum-likelihood estimation of the unknown parameters can be formulated as structured low rank approximation of an appropriate matrix. To solve this difficult, believed NP-hard, problem, we propose a new heuristic iterative algorithm, based on a recently proposed splitting method for convex nonsmooth optimization. Although the algorithm comes, in absence of convexity, with no convergence proof, it converges in practice to a local solution, and even to the global solution of the problem, when the noise level is not too high. It is also fast and easy to implement.

In this paper we analyze and compare the performance of matched filter (MF) and energy detector (ED) time-of-arrival estimators based on thresholding in ultra-wide bandwidth (UWB) dense multipath channels. Closed-form expressions for the estimator bias and mean square error (MSE) are de- rived as a function of signal-to-noise ratio using a unified methodology. A comparison with results based on Monte Carlo simulation confirms the validity of our analytical ap- proach. Our analysis enables us to determine the threshold value that minimizes the MSE, critical parameter for optimal estimator design. It is shown that the estimation accuracy mainly depends on large estimation errors due to peak am- biguities caused by multipath at the output of the MF or ED and on the fading statistics of the first path. The evaluation of the performance loss faced by ED estimators with respect to those based on MF is also carried out. Finally, results based on experimental measurements in an indoor resid...

Impulse Radio Ultra-Wideband, in particular the recent standard IEEE 802.15.4a, is a primary candidate for implementing distance bounding protocols, thanks to its ability to perform accurate indoor ranging. Distance bounding protocols allow two wireless devices to securely estimate the distance between themselves, with the guarantee that the estimate is an upper-bound on the actual distance. These protocols serve as building blocks in security-sensitive applications such as tracking, physical access control, or localization. We investigate the resilience of IEEE 802.15.4a to physicalcommunication-layer attacks that decrease the distance measured by distance bounding protocols, thus violating their security. We consider two attack types: malicious prover (internal) and distance-decreasing relay (external). We show that if the honest devices use energy-detection receivers (popular due to their low cost and complexity), then an adversary can perform highly effective internal and external attacks, decreasing the distance by hundreds of meters. However, by using more sophisticated rake receivers, or by implementing small modifications to IEEE 802.15.4a and employing energy-detection receivers with a simple countermeasure, honest devices can reduce the effectiveness of external distance-decreasing relay attacks to the order of 10m. The same is true for malicious prover attacks, provided that an additional modification to IEEE 802.15.4a is implemented.

I wish I could easily express all the joy I feel for having been part of the Alcatel-Lucent Chair in Flexible Radio, especially of being one of its "founding fathers". Clearly, the ambiance of friendship and hard work cultivated in the "Chair" (as we call it in the intimacy), have taught me that the pursue of high quality work is not incompatible with being playful and fun. In fact it is quite the contrary: strong human bonds foster collective creativity and group work. I hope that this kind of ambiance goes on and becomes one of the trademarks of this wonderful group. I also wish to express my deepest indebtedness to my family for all the affection as well as personal and logistical support. Coming from a family rooted in the academia served as a great inspiration to pursue research and carry out a Ph.d. Last, but definitely not least, one very especial thought goes to my companion Justine, who, with great caring, understanding and support helped me through (various) moments of turbulence. Thank you all -Merci beaucoup -Muito obrigado.

Further developing the idea of a cascade structure for
adaptive linear prediction with independently adapting low-order
stages, we develop a new implementation where the single stages
use the forward-backward linear prediction algorithm. Combining
the advantages of the cascade structure, which is less affected by
the eigenvalue spread and mode coupling, with the reduced misadjustment
of the forward-backward predictor delivers a new structure
with improved performance. This new structure is capable of
faster and more accurate tracking of nonstationary inputs in the
early stage of the adaptation.

This study investigates the application potential of the SAGE (space-alternating generalized expectationmaximization) algorithm to jointly estimate the relative delay, incidence azimuth, Doppler frequency, and complex amplitude of impinging waves in mobile radio environments. The performance, i.e., high-resolution ability, accuracy, and convergence rate of the scheme, is assessed in synthetic and real macro-and pico-cellular channels. The results indicate that the scheme overcomes the resolution limitation inherent to classical techniques like the Fourier or beam-forming methods. In particular, it is shown that waves which exhibit an arbitrarily small difference in azimuth can be easily separated as long as their delays or Doppler frequencies differ by a fraction of the intrinsic resolution of the measurement equipment. Two waves are claimed to be separated when the mean-squared estimation errors (MSEE's) of the estimates of their parameters are close to the corresponding Cramér-Rao lower bounds (CRLB's) derived in a scenario where only a single wave is impinging. The adverb easily means that the MSEE's rapidly approach the CLRB's, i.e., within less than 20 iteration cycles. Convergence of the log-likelihood sequence is achieved after approximately ten iteration cycles when the scheme is applied in real channels. In this use, the estimated dominant waves can be related to a scatterer/reflector in the propagation environment. The investigations demonstrate that the SAGE algorithm is a powerful high-resolution tool that can be successfully applied for parameter extraction from extensive channel measurement data, especially for the purpose of channel modeling.

The wireless communication channel has been found recently to have some interesting properties. In particular, it has been found that the multipath wireless channel can be leveraged for the purpose of key generation. In this paper, we investigate this property and propose an intelligent key generation method based on phase shifting and correction. Further, we discuss improvements of this approach and finally, we test our algorithm on a typical outdoor wireless channel. Our simulation results show that more than 90 bits can be generated from a single channel observation.

In this paper, the theory of linear time-variant systems is applied to multipath channels and, in particular, to ionospheric channels. Some useful formulas in time and frequency domains are given for both deterministic and random linear time-variant systems and multipath channels. The fundamental parameters of a multipath channel are the delay and the gain coefficient of each path, and the number of significant paths. We propose a methodology for estimating path-delays and path-coefficients and its application to the ionospheric channel estimation. Also, if path coefficients are stationary random processes, the power spectral density of the coefficients can be estimated from measured data of real (actual) channels. Finally, exhaustive computer simulations have been realized for testing the algorithms and a sample of the results is provided in the paper; also, estimation results for an actual narrowband HF ionospheric channel are provided, where up to four significant paths (rays) are detected with a Doppler spread lower than 0.2 Hz.

We present chip-level MMSE equalizers for the forward link in CDMA that exploit the underlying channel structure, specifically the fact that the channel impulse response is sparse. The assumption we make is that the channel vector lies in the subspace associated with the pulse shaping filter convolution matrix. We can then project the chiplevel MMSE equalizers onto a much lower dimensional subspace due to the sparseness of the channel. The simulations demonstrate that this low-rank MMSE equalizer converges very quickly to the asymptotic SINR, even where the underlying assumption is not valid.

In downlink communication of a direct-sequence (DS) code-division multiple-access (CDMA) system, each user's short spreading codes are superimposed by base station's common long codes. This situation creates much difficulty in blind signal detection when multipath propagation occurs. However, when spatial/temporal diversity is available at the receiver, it is shown in this paper that subspace technique can be directly applied to estimate the common downlink multipath channel. Then, typical linear receivers, such as zero-forcing (ZF), minimum mean-squareerror (MMSE) and RAKE receivers can be designed to detect the desired signal. Since the data covariance matrix is used but estimated from finite data samples, performance of both channel estimator and receivers gets perturbed. It is thus thoroughly and jointly analyzed by perturbation analysis. Justification of analysis and comparison of different receivers are also made through simulations.

This paper derives equations that describe level-crossing rates and average fade durations for mobile receivers operating in spatially complicated multipath channels. The results are useful for describing fading statistics for wireless systems that operate in realistic propagation channels or employ smart antennas, adaptive arrays, or other technologies that lead to a non-omnidirectional distribution of multipath power in space.

This work studies the three-dimensional (3D) identification performance of UHF RFID systems with commodity hardware. Detailed three-dimensional propagation modeling is developed, with ray-tracing that allows examination of tag-as we" as reader-antenna diversity. It is shown that multipath can enhance identification performance compared to free-space conditions. Furthermore, it is found that tag diversity can enhance identification performance on the order of 10%. Reader antenna diversity becomes beneficial only when special attention is given to controlling the destructive summation of the transmitted fields and simple, general antenna-installation rules are provided. Performance can be further enhanced with the introduction of a phase shifter or appropriate transmission scheduling, and various examples are discussed. Measurements inside a room with a dense three-dimensional grid of passive RFID tags confirmed the results. Fina"y, a method to perform power-measurements with commodity RFID hardware that exploits the sensitivity-during-read threshold of each tag is put forth.

This paper introduces a modified version of the discrete multi-tone transceiver (DMT) to increase the data rate in broadband power-line communications (PLC). Basically, a computational-intelligence technique trained by a second-order optimization method is applied to mitigate the high-power impulse noise, while the DMT copes with the severe intersymbol interference observed in power-line channels. The masking of the impulse noise enhances the signal-to-noise ratio in each DMT subchannel. As a result, a high number of bits can be allotted to each subchannel for a given error probability. The simulation results reveal that the proposed PLC-DMT solution outperforms, in terms of the data rate, traditional PLC-DMT over different environments, especially in the presence of additive high-power impulse noise.

The demand for higher capacity wireless communication networks has motivated research in the techniques of adaptive beamforming using smart antennas. The technique is to radiate narrow beams in a desired direction and to suppress interferences. Antenna array beamforming is a fundamental technique for directional signal transmission and reception[1].The LMS algorithm has been identified as a suitable technique that optimises the SNR of the desired signal in a particular direction. The proposed adaptive beamforming scheme uses an array of antennas to realise maximum reception in a specified direction. This is achieved by adjusting the weights of each of the antennas with changing signal environment. This paper analyses the performance of the LMS adaptive algorithm in terms of the convergence rate of the Mean Square Error (MSE), also the effect of some antenna array elements like the number of elements and the spacing between elements, based on the Direction of Arrival (DOA), but also ...

An advanced decision-directed channel estimation scheme is proposed, which is suitable for employment in a wide range of multi-antenna multi-carrier systems as well as for communications over the entire range of practical channel conditions. In particular, we consider a MIMO-OFDM system operating in a mobile wireless multipath channel, which exhibits frequency-selective Rayleigh fading and is characterized by a time-variant power delay profile. Both the mean square error as well as the bit error rate performances achieved by the proposed system are documented. Specifically, we report a virtually errorfree performance of a rate 1 2 turbo-coded 8x8-QPSK-OFDM system, exhibiting an effective throughput of 8•2• 1 2 =8bits/sec/Hz, while having a pilot overhead of only 10%, at an SNR of 10dB and an OFDM-symbol-normalized Doppler frequency of 0.003, which corresponds to the mobile terminal speed of about 65 km/h.

A scalable Impulse Radio (IR) Ultrawideband (UWB) air interface is proposed for Low Data Rate (LDR) Wireless Personal Area Network (WPAN) applications. Reduced-complexity transmitter and receiver designs are also proposed. The performance of the proposed IR-UWB multiuser system is investigated in PAN propagation environments. Various different receiver detection techniques are compared and it is shown that in the case of a multipath channel, the Windowed Signal Multiplication (WSM) scheme outperforms other potential detectors based on pulse template generation.

In this paper a performance analysis of the turbo MIMO equalizer concept for broadband MIMO channel is presented. The channel modeling in the link-level simulation is based on MIMO measurement in different scenarios. The results reveal the strong relationships between the propagation conditions in terms of the available spatial and temporal multipath diversity, the antenna configurations, and the achievable bit

Symbol timing and carrier frequency synchronization are crucial to OFDM systems. One of the blind synchronization methods is the cyclic prefix (CP) based maximum likelihood (ML) symbol timing and carrier frequency synchronization which correlates the cyclic prefix and the last part of the OFDM symbol. However, the performance of this method is seriously reduced in the time-variant multipath channel. In this paper, we propose a new CP which has two parts. One part is a copy of the head of the last symbol and the other part is a copy of the tail of that symbol. Both parts have the length of half of the CP. As a result of this new CP, the starting time of one OFDM symbol is allowed to fall into its effective period (the absolute value of the symbol timing error should be smaller than CP/2). The performance of OFDM systems is improved significantly with this new CP.

Space-time coding is an effective way to combat Rayleigh fading using multiple transmit antennas. By associating a spreading code with each symbol in the space-time block code, a general model for space-time block codes for both narrowband and wideband systems is obtained, where a narrowband system can be interpreted as a specific case of a wideband Direct-Sequence Code-Division Multiple Access system. For both the uplink and downlink, from the Chernoff bound of the pairwise error probability, the classical space-time coding design metrics (diversity gain and coding gain) are investigated for flat fading and multipath channels. In the uplink, the multiuser coding problem decouples to multiple single user coding problems; in the downlink, a true multiuser coding problem exists. It is found that, for wideband systems, if linearly independent spreading codes are employed at different transmit antennas, full diversity gain is easily guaranteed in contrast to narrowband systems. The exact diversity level of a system is determined. It is shown that good flat fading channel codes retain their good coding gain in a multipath environment when the channel delay spread is relatively small in comparison to the symbol interval. Some optimal minimum metric codes for quasi-static channels found via computer search are presented and their relative performances are compared. The search results show that certain optimal minimum metric codes exhibit significant gains over comparable known orthogonal codes or unitary group codes.

We develop a semi-deterministic semi-stochastic channel model for the multiple-input multiple-output (MIMO) system under the macrocell environment with local-to-mobile and local-to-base scatterers. We show that employing closely-spaced antennas (e.g., phased array) at the base station is capable of achieving diversity via the local-to-base scatterers, which avoids impractical large aperture requirement for the spatial diversity at the base station. We evaluate the system performance in terms of ergodic capacity, average pairwise error probability (PEP), and signal-to-noise ratio (SNR); derive closed-form expressions for lower and upper bounds on the capacity and PEP; and show that the capacity, multiplexing and diversity gains are limited by the number of multipaths around the base station. The base-station array affects the lower bound on the capacity and the upper bound on the error probability through the same metric; thus, optimal design of the base station array based on this metric will optimize the two different information theoretic measures simultaneously. The fading correlation matrix also appears in the two bounds in the same form. To improve the performance of the macrocell MIMO system, we propose using artificial scatterers and discuss optimal design issues. Numerical examples demonstrate the accuracy of our analytical results and tightness of performance bounds.

For a directional (a.k.a. directive) transceiver misaligned towards an omni-directional transceiver, the multipaths' time-of-arrival (TOA) distribution is herein derived in closed form explicitly in terms of the "geometric modeling" parameters. This derivation allows the directional beamwidth to mis-point to any arbitrary azimuth-direction, even if entirely away from the intended omni-directional transceiver.

AbstTact-A coherent receiver with a decision-feedback equalizer (DFE) operating on a Rayleigh fading channel under a suitable adaptive algorithm is considered. In the analysis of a DFE, a common assumption is that the receiver has perfect knowledge of the channel impulse response. However, this is not the case in practice, and for a rapidly fading channel, errors in channel tracking can become significant. We analyze theoretically the impact of these errors on the performance of a multichannel DFE. T h e expressions obtained for the achievable average MPSK bit error probabilities depend on the estimation error covariance. In order to specify this matrix, we focus on a special case when a Kalman filter is used as an optimal channel estimator. In this case, the probability of bit error can b e assessed directly in terms of channel fading model parameters, the most interesting of which is the fading rate. Our results show the penalty imposed by imperfect channel estimation, as well as the fading-induced irreducible error rates. Due to its low computational complexity and nearoptimal performance, the decision-feedback equalizer (DFE), operating under a suitable adaptive algorithm, is used in a variety of time-dispersive fading channels, such as a mobile radio channel, a troposcatter channel, or an underwater acoustic channel. It is well-known that the critical issue for its performance in a rapidly changing channel is the tracking capability of the underlying adaptive algorithm. Although a vast body of literature has been devoted to the performance analysis of the DFE, it seems that none addresses the impact of fading-induced imperfect channel tracking. The goal of this analysis is to determine the performance limitations of a coherent receiver which incorporates a DFE, under the conditions that only the statistical properties of the channel are known to the receiver. The primary factor which causes the degradation of the DFE performance from the matched filter bound is the Paper approved by Jack H. Winters, the Editor for Equalization of the IEEE Communications Society. Manuscript

Space-time block coding has emerged as a promising spatial transmit diversity scheme to reduce the fading effects of multipath channels and to increase system capacity, mainly due to its reduced decoding complexity and that channel state information is not required at the transmitter side. Recently, iterative processing has also attracted vast attention for improving system performance at low complexity cost. In this paper, we propose a new chip space-time block coding structure that employs iterative joint decision feedback equalization and decoding scheme for improving the performance of the downlink of a WCDMA system using long scrambling codes under frequency selective fading channels. Simulation results show that the presented schemes offer significant performance improvement against conventional disjoint receivers.

In this paper, we investigate the performance of the downlink of a wideband code division multiple access system employing space-time block coding in a time-varying multipath channel. Space-time block coding is applied at the chip level to improve the robustness of the system to fading envelope variations. Simulation results show that the presented scheme offers considerable diversity gain even for high mobility users transmitting low data rate, outperforming a system employing symbol level space-time block coding in time-variant channels. I.

The Cramer-Rao lower bound (CRLB) was determined for different ultra-wideband (UWB) signal formats and, in particular, for the two UWB high-data-rate (HDR) signal formats proposed within the IEEE 802.15.3a Task Group, that is, the impulsive direct-sequence UWB (DS-UWB) and the nonimpulsive multiband orthogonal frequency-division multiplexing (MB-OFDM), and an impulsive time hopping (TH) UWB format close to the format for UWB low data rate (LDR) of the forthcoming IEEE 802.15.4a standard. The analysis was carried out for both ideal and multipath channels under power constraints as set by emission masks. Results obtained for HDR formats showed that DS-UWB has better ranging accuracy than does MB-OFDM, thanks to its potentially larger bandwidth and higher frequency of operation. In addition, the degree of multipath strongly affected ranging accuracy, although differently for DS-UWB versus MB-OFDM. When incorporating a correlation receiver structure as well as an Early Late gate synchronizer in the model, ranging performance proved to be related to features of the synchronization sequence. For specific synchronization sequences, in particular, the best ranging accuracy was obtained with MB-OFDM. In the case of LDR, the study analyzed the effect of pulse shape on CRLB. Results showed that a suboptimal choice of the pulse shape reduces the ranging accuracy achievable by TH-UWB signals.