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In this paper, we propose a new clustered structure for a multiway relay network (MWRN) with $G$ clusters, $N$ users per cluster, one intracluster relay per cluster, and a single intercluster relay. The proposed structure allows private information exchange among users within a certain cluster through the corresponding intracluster relay and only public information exchange among users in different clusters through the intercluster relay. In this paper, we quantify the dominating error events in the proposed clustered MWRN and derive the expressions for the probability of these error events. Then, we use these expressions to derive the average bit error rate (BER) of a clustered MWRN. It is shown that clustering in an MWRN improves the error performance by reducing the number of dominating error events and, in effect, reducing error propagation, compared with the nonclustered counterpart. The analysis proves that the average BER of a clustered MWRN is minimized when the number of clusters and the number of users per cluster are chosen to be the closest possible factors of the total number of users, i.e., $L=GN$. Finally, numerical simulation results are provided to verify the validity of the analysis. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of a cognitive hybrid satellite–terrestrial network, where the primary satellite communication network and the secondary terrestrial mobile network coexist, provided that the interference temperature constraint is satisfied. By using the Meijer-G functions, the exact closed-form expression of the outage probability (OP) for the secondary network is first derived. Then, the asymptotic result in a high-signal-to-noise-ratio (SNR) regime is presented to reveal the diversity order and coding gain of the considered system. Finally, computer simulations are carried out to confirm the theoretical results and reveal that a more loose interference constraint or heavier shadowing severity of a satellite interference link leads to a reduced OP, whereas stronger satellite interference power poses a detrimental effect on the outage performance. [ABSTRACT FROM AUTHOR]

In this paper, we consider a noncoherent amplify-and-forward (AF) half-duplex cooperative relay system, where the channel gains are completely unknown at the destination. For such a system, the currently available design of noncoherent unitary space-time block codes for the multiple-input—multiple-output (MIMO) systems cannot be applied because of the signal matrix having a certain triangular structure. In this paper, we propose the design of full-diversity nonunitary and unitary diagonal distributed space-time block codes for the noncoherent AF half-duplex protocol. We prove that both the nonunitary and unitary codes enable the unique identification of the channel and transmitted signals in the noise-free case for any given nonzero received signals, as well as full noncoherent diversity in the noise case for the least square error (LSE) receiver. Computer simulations show that our unitary code obtains about 5-dB signal-to-noise-ratio (SNR) gains at the symbol error rate of 10^-5 over the precoded training scheme and the differential coding scheme. [ABSTRACT FROM PUBLISHER]

Most call admission control (CAC) schemes proposed for dynamic channel allocation (DCA)-based systems simply follow the same philosophy as adopted by fixed channel allocation (FCA)-based systems, i.e., only considering intercell handoffs. Doing so is acceptable for FCA and coordinated DCA systems because an intracell handoff caused by a new channel assignment rarely happens in these cases. However, as discussed in this paper, in a distributed DCA with a measurement-based channel assignment, the intracell handoff may happen frequently and can dominate handoff events because failed intracell handoffs reduce the number of intercell handoffs. In this case, the CAC considering only the intercell handoff cannot work properly for such DCA systems. In this paper, we discuss a novel CAC to consider both intercell and intracell handoffs to guarantee a handoff call dropping probability (CDP) by jointly using the channel carrying approach. We also investigate a measurement-based implementation of this proposal through computer simulations. The results show that the proposed CAC can effectively bound the CDP to a target CDP. [ABSTRACT FROM AUTHOR]

In this paper, the authors develop an analytical model to study the performance of a mobile low earth orbiting (LEO) satellite cellular network. The model assumes that the call duration has a gamma distribution and considers the effect of system parameters such as the number of channels per cell, the number of channels reserved for the handoff, and the cell residence time, on the teletraffic performance of the system. The quality of service (QoS) measures studied in this paper include new call blocking probability, handoff failure probability, premature call-termination probability (CTP), and call dropping probability (CDP). Based on the causal central limit theorem, the authors use a two-parameter gamma distribution to approximate the distribution of the sum of the residence times in the cells. The analytical model presented in this paper may be used with any call-holding-time distribution. The analytical results are validated by a computer simulation. [ABSTRACT FROM AUTHOR]

Recently, ultra wide-band (UWB) wireless communication technology, which provides high data transmission rates and is capable of linearly trading off between throughput and signal-to-noise ratio (SNR), has drawn much attention for short-range wireless networks. To fully exploit its desirable features and to minimize its interference with coexisting other systems requires knowledge of the SNRs at the receivers. In this paper, we propose an algorithm for estimating the pulse energy-to-noise ratio of an UWB signal through utilization of output samples from a correlator in the receiver and evaluate the performance of the proposed algorithm through computer simulation. A notable feature of the proposed algorithm is that it does not affect the effective throughput because the estimation process does not require any additional specific training signals. [ABSTRACT FROM AUTHOR]

A cooperative spectrum-sensing technique in cognitive radio (CR) networks based on the data fusion of various chaotic stochastic resonance (CSR) energy detectors is proposed in this paper. Due to noisy uncertainty in unpredictable wireless communication environments, detection performance of conventional energy detection cannot be guaranteed. By introducing the CSR system with various CSR noise types, and with the data fusion on these CSR-based energy detectors, the detection probability can be improved under the same constant false-alarm rate (CFAR), particularly under low signal-to-noise ratio (SNR) circumstances. Theoretical analyses and computer simulation results verify the effectiveness of the proposed novel cooperative spectrum-sensing approach under serious wireless conditions. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a two-hop wireless sensor network (WSN) with multiple relay nodes where the amplify-and-forward (AF) scheme is employed. We present strategies to design jointly linear receivers and the power-allocation parameters via an alternating optimization approach subject to global, individual, and neighbor-based power constraints. Two design criteria are considered: The first criterion minimizes the mean-square error (MSE), and the second criterion maximizes the sum-rate (SR) of the WSN. We derive constrained minimum mean-square error (MMSE) and constrained maximum sum-rate (MSR) expressions for the linear receivers and the power-allocation parameters that contain the optimal complex amplification coefficients for each relay node. Computer simulations show good performance of our proposed methods in terms of bit error rate (BER) or SR compared with the method with equal power allocation and to a two-stage power-allocation technique. Furthermore, the methods with neighbor-based constraints bring flexibility to balance the performance against the computational complexity and the need for feedback information, which is desirable for WSNs to extend their lifetime. [ABSTRACT FROM PUBLISHER]

The use of multitaper spectrum (MTS) for spectrum sensing in cognitive radio (CR) has been investigated by a number of researchers. Meanwhile, its superior detection performance has been numerically demonstrated. Regardless of their importance, the theoretic performance and thresholds for MTS detectors remain unavailable in the literature. In this paper, we tackle such an issue, ending up with various closed-form analytic formulas for the probabilities of detection and false alarm with different settings including single-sensor and multisensor MTS detectors with perfect or inaccurate noise variance. The validity of theoretical formulas is intensively examined through numerical results and computer simulations. [ABSTRACT FROM PUBLISHER]

Driving simulators are increasingly being used for driver evaluation and/or education. In this paper, we describe the design and the modeling aspects of a 2-degree-of-freedom (2-DOF) low-cost motion platform allowing the rendering of the longitudinal and yaw movements. This prototype will be used to study various configurations of motion rendering and the impact of these variants on controllability and simulator sickness. The whole motion platform is considered as two coupled systems that are linked mechanically. The first system consists of a motorized rail for the longitudinal movement, which is mounted on top of the second system, which is a motorized turret allowing rotation of the platform. We present the platform mechanics and a number of experimental studies that have been carried out to obtain a characterization of the platform capabilities and frequency responses, as well as to assess platform performance in a classical drive operation. First conclusions and directions of future work are presented. [ABSTRACT FROM PUBLISHER]

Multiple-input-multiple-output (MIMO) receivers with direct-conversion radio-frequency (RF) architecture are investigated in this paper. Direct conversion is a low-cost RF design that requires fewer external components in chip implementation. Nevertheless, it introduces extra RF impairments such as I-Q imbalance and dc offset in addition to frequency offset that is commonly encountered in all RF architectures. This paper proposes to do the joint least squares (LS) estimation of frequency, dc offset, I-Q imbalance, and a channel in MIMO receivers to improve performance; frequency-dependent and frequency-independent I-Q imbalances are included. Previously, RF impairments were separately estimated in MIMO receivers, which leads to inferior performance. In particular, a receiver architecture that facilitates the joint estimation of the frequency, the dc offset, the I-Q imbalance, and the channel is proposed. The LS criterion is then applied to obtain the joint estimators, with a special training-sequence design to reduce complexity. Simplified estimators on the frequency and dc offset are also proposed with almost no loss in performance. Finally, the estimators are shown through analysis to be unbiased and approach the Cramér-Rao lower bound (CRLB) for signal-to-noise ratios (SNRs) of interest. The analysis is verified by computer simulations. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive digital signal processing technique that cancels self-image interference due to frequency-independent, in-phase/quadrature-phase (I/Q) mismatch in zero-intermediate frequency (IF) direct-conversion receivers. The proposed technique, which is referred to as the normalized least-mean square adaptive self-image cancellation (NLMS-ASIC) algorithm, is an ASIC technique that controls the filter weight to minimize the power of the filter output signal using an NLMS type of weight-control mechanism. Some closed-form equations are derived for the mean-squared error (MSE), as well as the mean image-rejection ratio (IRR) of the proposed NLMS-ASIC algorithm. In particular, a step-size determination method is explained so that the requirements on the image-rejection performance and convergence time can be satisfied. The advantages of the proposed technique are demonstrated through computer simulations. [ABSTRACT FROM AUTHOR]

This paper applies an intelligent intervehicle device (termed a "bridging damper") to a convoy of in-contact vehicles. The field of application is backup for future automated highways and operation of novel guided systems using vehicle-following control. The vehicle represented in computer simulations is a parallel hybrid electric automobile. Using the Advanced Vehicle SimulatOR (ADVISOR) model, the vehicle representation is tuned to achieve matching of the overall force and power characteristics and the same performance over an urban driving cycle. The model for which a dedicated Matlab Toolbox was constructed is described. Simulation results compare the vehicle-following control on its own with a passive damper and a "quasi-active" damper that is controlled in collaboration with the vehicle's drivetrain. Using transient disturbances in the form of wind gusts and short gradients, power peaks and longitudinal ride quality (Vibration Dose Value) are used to evaluate the performance. [ABSTRACT FROM AUTHOR]

This paper presents a modified decorrelated delay lock loop (MD-DLL) for synchronous direct-sequence code-division multiple-access (DS-CDMA) systems under multiuser environments. The structure of the MD-DLL is similar to that of a traditional delay lock loop (T-DLL), aside from the fact that the despreading signals in T-DLL are replaced by a linear combination of all the users' code sequences with various weightings and timing offsets. The basic principles of MD-DLL are given as follows: 1) to use the decorrelating technique of a multiuser detector to remove the multiple-access interference at the on-time code position instant and 2) to choose a proper timing offset for the code sequences to reduce the weighting imbalance between the two arms of the tracking loop and suppress noise enhancement. The proposed MD-DLL scheme solves the tracking bias problems in a decorrelated delay lock loop under a low-signal-to-noise-ratio (SNR) condition. Computer simulations based on Gold code sequences are used to verify the findings. It is shown that MD-DLL achieves a better and stable S-curve with negligible tracking bias, better rms tracking error and mean-time-to-lose-lock performance under high-SNR conditions, and stronger near-far resistance than T-DLL. [ABSTRACT FROM AUTHOR]

This paper deals with a cross-layer approach for cooperative diversity networks, which use a combination of amplify-and-forward (AF) and decode-and-forward (DF) as a relaying strategy. Based on a well-selected ad hoc configuration, the proposed approach combines the cooperative diversity concept with a simultaneous optimization of physical, network, and multiple access control layers. The considered optimization problem requires an appropriate distribution of three roles among the network nodes, which are the diversity relays (AF concept), the intermediate router (DF and routing), and the destination (scheduling). The proposed role assignment is based on the instantaneous channel conditions between the links and jointly supports performance optimization and a long-term fairness concept. To minimize the required complexity, a partial and quantized channel feedback is also proposed. The proposed cross-layer solution is compared with conventional approaches by computer simulations and theoretical studies, and we show that it achieves an efficient performance-complexity tradeoff. [ABSTRACT FROM AUTHOR]

Mobile positioning has drawn significant attention in recent years. Nonline-of-sight (NLOS) propagation error is the dominant error source in mobile positioning. Most previous research in this area has focused on NLOS identification and mitigation. In this paper, we investigate new positioning algorithms to take advantage of the NLOS propagation paths rather than canceling them. Based on a prior information about the NLOS path, a geometrical approach is proposed to estimate mobile location by using two NLOS paths. On top of this, the least-squares (LS)-based position estimation algorithm is developed to take multiple NLOS paths into account, and its performance in terms of root mean-square error (RMSE) is analyzed. A general LS algorithm considering both LOS and NLOS paths is also derived, and the maximum likelihood-based algorithm is presented to jointly estimate the mobile's and scatterers' positions. The Cramer-Rao lower bound on the RMSE is derived for the benchmark of the performance comparison. The performance of the proposed algorithms is evaluated analytically and is done via computer simulations. Numerical results demonstrate that the derived analytical results closely match the simulated results. [ABSTRACT FROM AUTHOR]

Orthogonal-frequency-division-multiplexing (OFDM) techniques allow the transmission of high data rates over broad-band radio channels subject to multipath fading without the need for powerful channel equalization. However, they are very sensitive to nonlinear effects due to the high peak-to-average power ratio (PAPR) owned by their transmitted signals. This paper proposes an efficient technique for reducing the PAPR of OFDM signals. The proposed technique is data-independent and, thus, does not require new processing and optimization for each transmitted OFDM block. The reduction in PAPR of the OFDM signal is obtained through a proper selection of a precoding scheme that distributes the power of each modulated symbol over the OFDM block. The obtained results show that this precoding scheme is an attractive solution to the PAPR problem of OFDM signals. It is shown, through computer simulations, that the PAPR of precoded OFDM signals approaches that of single-carrier signals. The good improvement in PAPR given by the present technique permits the reduction of the complexity and cost of the transmitter significantly. The precoding schemes also take advantage of the frequency variations of the communication channel and can provide considerable performance gain in fading-multipath channels. [ABSTRACT FROM AUTHOR]

It has been well recognized that significant throughput gains can be leveraged in multiuser wireless communication systems by exploiting multiuser diversity with a smart scheduler. This scheduler collects channel state information (CSI) from all users and allocates the resources to the user(s) experiencing favorable channel conditions. However, for a frequency-division-duplex system with a large number of users, how to efficiently collect the required CSI will be a challenging task, especially when the feedback links are of limited capacity. In this paper, we propose a scheduling algorithm to exploit multiuser diversity with possibly imperfect one-bit channel state feedback. The basic idea is to define a threshold λ and let each user report one-bit information to the scheduler about the comparison between its measured channel fading level and λ. Correspondingly, the scheduler uses these feedback bits to classify all users into two sets and assigns the channel to one user belonging to the set experiencing favorable channel conditions. Several implementation schemes are developed by attacking the optimization of λ under different system configurations, covering both the case when the one-bit feedback is perfect and those when the one-bit feedback is imperfect. Computer simulations show that when the user number is large, say, more than ten users, the proposed scheduling supports significantly larger data rate over the round-robin scheduling, while in comparison with the optimum scheduling with complete CSI, the performance loss is limited if the one-bit feedback is of high reliability. In addition, our studies show that we can effectively enhance the robustness against feedback imperfectness by incorporating the feedback reliability into optimization of λ. [ABSTRACT FROM AUTHOR]

The incorporation of the orthogonal frequency(multiplexing (OFDM) with the space-time or space-frequency coding is a robust and effective method to achieve a transmit-diversity gain and to suppress an intersymbol interference for the broadband wireless transmissions. This paper is concerned with the downlink-performance improvement using multiple transmit antennas for the OFDM systems with a large delay spread. A delay-spread reduction method using space-frequency block coding and statistical prefiltering (SPF) was proposed, which combines signal prealignment and multiple transmit beamformers designed with the statistical knowledge of the downlink channel state information. The proposed method, which is called the SPF-OFDM, transforms a large delay-spread channel into multiple channels, each with small delay spread. Thus, it does not only shorten the effective excess delay but also preserves the path diversity through the use of the space-frequency coding. Computer simulations have evaluated the effectiveness of the proposed scheme, and comparisons have been made with the conventional solutions. [ABSTRACT FROM AUTHOR]

The availability of an accurate and systematic channel simulation technique is critical for the verification of the performance of digital radio transceivers designed for use on wireless channels. Despite the abundant results on channel simulation techniques available in the literature, an accurate technique for simulating Nakagami-m fading signals that have nonuniform phase distributions and any prespecified temporal autocorrelation function is not yet available. Such a technique is reported for the first time in this paper. We develop new cumulative distribution function (cdt) mapping methods to generate complex Nakagami sequences from complex Gaussian sequences, based on the independent transformation of their real and imaginary parts. Additionally, we analyze the relationships between the autocorrelation functions of Rayleigh and Nakagami fading signals to determine the autocorrelation function of Rayleigh input that is required to produce a specified autocorrelation function for the Nakagami output. Then, we implement the mapping algorithm to transform Rayleigh sequences with the so-determined autocorrelation functions into Nakagami sequences with the desired prespecified autocorrelation functions. Simulation results verify that our approaches can lead to the accurate simulation of Nakagami fading signals with prespecified autocorrelation functions and nonuniform phase distributions. [ABSTRACT FROM AUTHOR]

An iterative receiver for a multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system is considered to jointly decode the transmitted bits and estimate the channel state. The receiver consists of a list detector, a turbo decoder, and a channel estimator that is based on the space-alternating generalized expectation-maximization (SAGE) algorithm. This paper proposes a way to improve the convergence of the iterative detection and decoding by using a priori information to also recalculate the candidate list, aside from the log-likelihood ratios (LLRs) of the coded bits. A new list parallel interference cancellation (PlC) detector is derived to approximate an a posteriori probability (APP) algorithm with reduced complexity and minimal losses of performance. Further- more, the organization of spectrally efficient decision-directed (DD) SAGE channel estimation under a constrained number of detector-decoder iterations is optimized by computer simulations, and the SAGE algorithm itself is modified for nonconstant envelope constellations. The list recalculation is shown to improve convergence. It is also shown that the list PlC detector with good initialization outperforms the K-best list sphere detector (LSD) in the case of small list sizes, whereas the complexities of the algorithms are of the same order. Despite the low preamble density and fast-fading channel, the proposed iterative receiver shows robust performance. [ABSTRACT FROM AUTHOR]

This paper presents set-membership (SM) adaptive algorithms based on time-varying error bounds for code-division multiple-access (CDMA) interference suppression. We introduce a modified family of SM adaptive algorithms for parameter estimation with time-varying error bounds. The considered algorithms include modified versions of the SM normalized least mean square (SM-NLMS), the affine projection (SM-AP), and the bounding ellipsoidal adaptive constrained (BEACON) recursive least-square technique. The important issue of error-bound specification is addressed in a new framework that takes into account parameter estimation dependency, multiaccess, and intersymbol interference (ISI) for direct-sequence CDMA (DS-CDMA) communications. An algorithm for tracking and estimating the interference power is proposed and analyzed. This algorithm is then incorporated into the proposed time-varying error bound mechanisms. Computer simulations show that the proposed algorithms are capable of outperforming previously reported techniques with a significantly lower number of parameter updates and a reduced risk of overbounding or underbounding. [ABSTRACT FROM AUTHOR]

The fairness concept has been widely studied in the area of data networks. The most well-known fairness criterion (max-min fairness) gives priority to the minimum-rate session. Kelly questioned its appropriateness in his works on the bandwidth sharing among the end-to-end flows and proposed another fairness criterion preferring short-distance flows to enhance the overall throughput, which is called the proportional fairness (PF). A simple scheduler achieving this objective was introduced in wireless access networks and revealed that it can achieve a good compromise between cell throughput and user fairness. Although it has received much attention for some time, research on its performance mainly depended on computer simulations. In this paper, we analyze the PF scheduler to obtain the cell throughput, which is a primary-performance metric, and extend the result to analyze the capacity of multiple-input-multiple-output systems. We evaluate the effect of various parameters on the throughput of the PF scheduler through the numerical analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a frame synchronization method for an adaptive array antenna (AAA) used in digital mobile communications. The proposed scheme, which is based on the maxi- mum likelihood estimation (MLE), calculates error signals by subtracting a training sequence convolved with an estimated channel impulse response from the AAA outputs and searches for the timing that minimizes the mean squared errors. Because the proposed scheme can effectively exploit delayed paths of the desired signal, it can improve the synchronization performance on frequency- selective fading channels. Computer simulations show that the proposed scheme can operate properly even in interference-rich fading environments and that it can significantly improve the synchronization performance. [ABSTRACT FROM AUTHOR]

We propose and analyze new finger replacement techniques for RAKE reception in the soft handover (SHO) region with multiple base stations. The proposed schemes are basically based on the block comparison among groups of resolvable paths from different base stations and lead to the reduction of complexity while offering commensurate performance in comparison with previously proposed schemes. Relying on the newly derived analytical expressions, we investigate not only the complexity in terms of the average number of required path estimations/comparisons and the SHO overhead but the error performance of the proposed scheme over independent identically distributed (i.i.d.) fading channels as well. We also examine, via computer simulations, the effect of path unbalance/correlation as well as outdated/imperfect channel estimation and show the robustness of our proposed scheme to these practical limitations. [ABSTRACT FROM AUTHOR]

Effects of four urban areas of the city of Rio de Janeiro, Brazil, on the propagation channels of three land mobile satellite systems are analyzed using computer simulation. Initially, a digital elevation model, building databases, and a vegetation model are processed to generate azimuth-elevation maps of three path states (clear, shadowed, and blocked) for a large number of users. The simulation procedure combines the maps with signal models for the three states and a satellite orbit predictor. The probabilities of different path-state mixtures, as well as the cumulative distribution functions of fades in several types of received signals resulting from the application of different mitigation techniques, are presented and discussed. [ABSTRACT FROM AUTHOR]

A full mathematical model is developed to formulate the nonlinear characteristics of an automotive electrohydraulic semiactive damper. This multidisciplinary physical parametric model considers the force equilibrium, flow continuity with flow losses due to the volumetric change and pressure difference, total flow through the valve system under different control modes, and dynamics of the floating piston which are balanced by the pressures of the fluid and gas. Both computer simulation and bench testing of the damper demonstrate that the damper has four levels of damping characteristics: “hard mode”, “hard rebound and medium-soft compression mode”, “medium-hard rebound and soft compression mode” and “soft mode”. The considerable consistency between the simulation and experimental results verifies that the mathematical model accurately captures the physical damping characteristics of the damper. Thus, the developed physical damper model is experimentally validated. The obtained full parametric damper model with mode controls is valuable for accurate and reliable damper development and crucial for the next step in vehicle system dynamics simulation and suspension control system synthesis. [ABSTRACT FROM AUTHOR]

The observation of the passenger compartment using an interior RADAR becomes challenging when a vehicle is in motion. The signal received by the RADAR sensor measures not only the target's motion that we would like to detect, e.g., vital signs, but also a second, unwanted motion induced by exterior effects, e.g., displacement caused by the road, strong wind gusts, or car engine vibrations. Consequently, traditional techniques used to remove white Gaussian noise cannot be applied in this scenario. We propose a theoretical framework to investigate the denoising of a signal received by an interior RADAR using accelerometer measurements and a mechanical model to generate the cancellation signal stemming from the (unwanted) vibrational motion. We explain the denoising technique and show that the fundamental idea behind the cleaning process works well. Our observations are corroborated by a robust mathematical model and verified by simulations. Furthermore, the aforementioned denoising techniques enable us to formulate and solve an optimization problem to find an estimation for the passenger's mass in certain cases. [ABSTRACT FROM AUTHOR]

We consider a wireless cooperative relay system with one source, one relay, and one destination node. The average bit-error probability (BEP) of several coherent or differential relay schemes with binary modulation is derived for Nakagami-m fading channels and verified by computer simulation. Our analytical results provide a set of mathematical tools for the design and analysis of cooperative communication systems in general fading channels. [ABSTRACT FROM AUTHOR]

We propose new models for characterizing the cell residence time in a mobile low-Earth-orbit (LEO) satellite cellular network, which, unlike previous models, can accommodate the effect of the Earth's rotation in the teletraffic analysis. The speed of the satellite is typically much higher than that of the mobile; as such, the duration of a cell residence time is finite. Therefore, we use distributions with finite support to model the cell residence time. In particular, we model the residence time in the first (origination) cell with a right-truncated gamma distribution and the residence time in all the other cells with a generalized beta distribution. These distributions have finite support and are sufficiently flexible to accommodate the effects of different system conditions, including the Earth's rotation. To illustrate the use of the proposed models, we study the performance of a mobile LEO satellite cellular network based on the assumption that the residence time in the first cell follows the right-truncated gamma distribution, the residence times in all the other cells follow the generalized beta distribution, and the call duration is gamma distributed. The goodness of the proposed models is validated by computer simulation. [ABSTRACT FROM AUTHOR]

Channel estimation for single-input multiple-output time-invariant channels is considered using superimposed training. A periodic (nonrandom) training sequence is arithmetically added (superimposed) at low power to the information sequence at the transmitter before modulation and transmission. We extend a recently proposed first-order statistics-based channel estimation approach (IEEE Commun. Lett., vol. 7, p. 413, 2003) to iterative joint channel estimation and data detection using a conditional maximum likelihood approach where the information sequence is exploited to enhance performance instead of being viewed as interference. An approximate performance analysis of the iterative channel estimation method is also presented under certain simplifying assumptions. Illustrative computer simulation examples are presented. [ABSTRACT FROM AUTHOR]

The authors present a chip-level blind frequency domain equalizer (FEQ) for the forward-link channel of a cyclic-prefix code division multiple access system. The FEQ coefficients are obtained without the need of training symbols or knowledge of channel state information. The coefficients are instead acquired by solving a constraint energy minimization problem involving the subspace spanned by the active and passive spreading codewords. They also prove that the random scrambling code sequences is required for the operation of the proposed equalization algorithm. Results from computer simulations are provided to verify the performance of the proposed FEQ. [ABSTRACT FROM AUTHOR]

The performance of turbo codes is examined over the Ricean fading channel with soft-decision differential phase detection (DPD). M-ary continuous phase frequency-shift keying (CPFSK) signaling and puncturing of the coded sequence are considered to achieve bandwidth efficient communication. The effects of the number of phase decision regions, fading conditions, number of states of the constituent codes, and code rate are examined. A bit error rate upper bound is developed, which is useful at low values of bit error probability where computer simulations are lengthy. Significant gains using soft-decision DPD over hard-decision DPD and conventional noncoherent detection are reported. [ABSTRACT FROM AUTHOR]

The rake receiver performance of a direct-sequence code-division multiple-access (DS-CDMA) system can significantly be degraded unless the channel condition is properly estimated. Since the channel condition is time-varying and location-dependent, it is desirable to employ an adaptive channel estimator (ACE) that can properly adjust the bandwidth of the channel estimation filter (CEF) according to the channel condition such as the maximum Doppler frequency. To this end, we propose low-complexity ACE and signal-to-interference power ratio (SIR) estimator for wide-band CDMA downlink systems with and without the use of transmit antenna diversity. The proposed schemes adjust the band- width of the CEF by exploiting the correlation characteristics of the received pilot signal. The analytic design is verified by computer simulation. Simulation results show that the proposed ACE and SIR estimation can significantly improve the link performance for a wide range Of channel condition, particularly when the channel condition is poor. [ABSTRACT FROM AUTHOR]

Proposes a practical normal-mode helical antenna array and a method for the compensation of mutual coupling effect. Computer simulations and discussions; Conclusion.