Ground-penetrating radar (GPR) has been traditionally used for subsurface assessment. In many applications, such as precision agriculture via drone-borne radar, it is critical to use machine learning (ML) techniques to map GPR received signals into soil subsurface moisture and texture. Supervised ML methods need a large number of labeled data for their training process which is expensive and time-consuming to attain through actual field measurements. The gprMax software, which is created based on the finite difference time domain (FDTD) method, has been introduced as a reliable tool to emulate soil media and create synthetic labeled data. Proper selection of gprMax soil medium dimensions is critical to the generation of reliable synthetic data. The selection of large soil medium dimensions for gprMax emulations leads to synthetic data consistent with realistic scenarios. However, larger medium dimensions lead to higher computation complexity. This letter investigates and validates a proper selection of medium dimensions that maintains a tradeoff across the accuracy and computational complexity of creating synthetic data. The results of this study are critical to researchers who adopt gprMax or any FDTD-oriented emulations for soil subsurface assessment. To maintain a tradeoff between accuracy and complexity, the letter confirms that the minimum medium surface dimension should be in the order of 1.5 times the maximum wavelength.

This paper introduces a novel adversarial attack targeting Graph Neural Network (GNN)-based radio resource management in point-to-point networks. Our proposed attack, executed during the test phase, manipulates the system's input by exploiting specific constraints. Formulated as an optimization problem, the attack aims to maximize resource stealing, thereby degrading the quality of communication. We assess the attack's efficacy with respect to the number of users, signal-to-noise ratio, and the adversary's power budget. The results demonstrate that our proposed attack approaches the performance of an established upper-bound adversarial benchmark while maintaining lower complexity, highlighting its effectiveness and potential for real-world applicability.

This paper proposes and analyses a set of novel and optimum multi-streaming techniques for mmWave multi-input multi-output systems. It formulates an optimization problem that enables exploiting available uncorrelated paths between the transmitter (Tx) and the receiver (Rx) to enhance the system throughput. In the proposed approach, antenna arrays at Tx/Rx are modeled as a Bipartite graph. Next, two bi-clustering algorithms are applied to the graph to simultaneously cluster antenna elements at Tx and Rx. In addition, the paper shows how the selection of subchannels and their corresponding subantenna arrays can be reduced to a variant of the graph coloring problem, based on which, two algorithms are proposed to find the optimum subchannels and subantenna arrays. Moreover, the paper defines two new beamforming methods and proves that those methods satisfy constant modulus and total power constraints. The first modified beamforming method uses singular vectors (SVs) of subchannels between Tx/Rx and incorporates the Power Iteration algorithm to decrease singular value decomposition complexity. The second newly proposed beamforming method finds precoders/combiners without using SVs which reduces the computational complexity. Performance evaluations in terms data streaming sum-rate demonstrate that the proposed technique increases the throughput using a low processing complexity.

This paper introduces an effective ranging technique for sensor nodes implanted within human body leveraging a novel merger of high-resolution time-of-arrival (ToA) and direction-of-arrival (DoA) estimations. Human body is an in-homogeneous media (IHM) consisting of frequency dispersive sub-media (body organs) with unknown thicknesses that entail addressing two open problems: 1) high-resolution ToA estimation of a wideband ranging waveform propagated within IHM consisting of multipath and dispersive channels and 2) calculation of straight line range between implanted sensor node and receiver sensor array on human body. In the proposed technique, pre-allocated orthogonal frequency division multiplexing is utilized to construct a ranging waveform leveraging equally spaced and orthogonality properties of its sub-carriers which enable high-performance ToA estimation in frequency domain. The estimated ToA, however, cannot be utilized to calculate the straight line range due to refraction of propagated waveform at sub-media boundaries. Therefore, a merger of ToA and DoA is proposed that exploits multiple measurements at different carrier frequencies to develop a system of linear equations. The straight line range, then, is estimated by solving this system of equations with respect to thicknesses of available sub-media. The exploited approximations are discussed and verified via theoretical evaluations and simulations for human body to prove the feasibility of the proposed technique.

Integrating Kirchhoff approximation (KA) and a ray‐tracing (RT) algorithm, this study develops a new directional three‐dimensional channel model for urban millimetre‐wave small cells. The authors study the path loss, spatial correlation, coverage distance, and coherence length for line‐of‐sight (LOS), obstructed LOS, and non‐LOS (NLOS) scenarios in urban areas. Exploiting physical optics and geometric optics solutions, closed‐form expressions for spatial correlation are derived. It is deduced that LOS availability, frequency, and surface roughness scale highly impact spatial diversity. In addition, using antenna arrays of moderate gain at both sides of the link, even under NLOS conditions, a typical urban cell size of 200 m is achievable.

This paper introduces a novel method to improve the Time of Arrival (ToA) estimation resolution for a fixed available bandwidth in the presence of unknown multipath frequency selective (MPFS) channels. Here, the maximum rising level detector technique is proposed which utilizes oversampling and multiple correlation paths to evaluate with high resolution the path corresponding to the maximum rising level of matched filters output. However, employing such technique demands for transmission of waveform that creates a very high rising level at autocorrelation center. This paper proposes an efficient technique to design proper waveforms (very high rising level at autocorrelation center) via minimization of weighted integrated sidelobe level, exploiting the trust-region algorithm. The performance of the proposed technique is evaluated via simulations of the ToA mean square error, and compared with the state-of-the-art approaches considering the same bandwidth, and Cramer-Rao lower bound as benchmark. Simulations confirm that the ToA resolution is improved as the number of correlation paths increases and verify the feasibility of the proposed technique compared with the available approaches for the MPFS channels.

This paper introduces a novel and effective ranging approach in nonhomogeneous (NH) media consisting of frequency dispersive submedia via time-of-arrival (ToA). Here, the NH environment consists of sublayers with a specific thickness that is estimated throughout the ranging process. First, a novel technique for ToA estimation in the presence of frequency dispersive submedia via orthogonal frequency division multiple access subcarriers is proposed. In the proposed technique, preallocated orthogonal subcarriers are utilized to construct a ranging waveform that enables high-performance ToA estimation in dispersive NH media in the frequency domain. The proposed ToA technique is exploited for multiple ToA measurements at different carrier frequencies, which leads to a system of linear equations that can be solved to compute the thickness of the available submedia and calculate the range. Simulation results for underwater-airborne media and underground channel confirm that the proposed technique offers high-resolution ranging at different signal to noise ratio regimes in the NH media.

In this study, small perturbation method (SPM) and Kirchhoff approximation (KA) are incorporated into ray-tracing (RT) routines to model multiuser multi-input multi-output (MU-MIMO) channels formed on a rough dielectric terrain. The effect of surface roughness and correlation length, solid soil fractions, moisture content, link range, antenna height, polarization, radiation pattern, and carrier frequency are examined on received power, power delay and angular profiles, root mean square (RMS) delay and angular spread, coherence bandwidth, and coherence distance. Quantitative and qualitative analyses reveal that antenna directionality and terrain undulation and textural composition have significant impacts on the received signal power and channel multipath parameters and, hence, the performance of MU-MIMO terrain-based communication systems.

This paper introduces the coarse time-of-arrival (ToA) estimation in wireless sensor networks (WSN) via orthogonal frequency division multiple access (OFDMA). In the proposed technique, each sensor node exploits a set of orthogonal subcarrier as its allocated signature to respond of the ToA estimation requests transmitted by target nodes. The target node utilizes the orthogonality across sub-carriers to detect the transmitted signatures and their corresponding delays. This technique is energy efficient as it avoids multiple transmissions and receptions inherent in traditional neighbor discovery protocols and ToA estimation techniques in WSN. Moreover, in this technique, network initiation process does not require channel information or time synchronization across sensor nodes. ToA estimation error is calculated theoretically and via simulations. Moreover, the impact of available bandwidth on the performance of ToA estimation is investigated. Simulation results confirm the feasibility of the proposed method even at low signal to noise ratio (SNR) regimes and in multi- path and frequency selective (MPFS) channels.

This paper characterizes path loss and spatial correlation for near ground channels in an open indoor and snowy terrain. The study is based on conducting extensive measurements at 2.45 GHz frequency range for Line-of-sight scenarios. The index of reflection of log-distance path-loss is evaluated. The impact of antenna height, and transmitter-receiver distance on pathloss and spatial correlation is investigated.

A versatile near-ground field prediction model is proposed to facilitate accurate WSN simulations. Path loss is split into three segments using the principles of the Fresnel zones. The distances that define the edges of each segment are derived theoretically. The model is validated against experimental data sets obtained in different scenarios. All the propagation features affecting the direct, reflected, and higher order scattered waves are effectively incorporated in the model. Effects of antenna height, frequency of operation, polarization, and terrain electrical and geometrical properties on the connectivity of low-altitude WSNs are studied through Monte Carlo simulations.

This paper describes a new parallel polynomial rooting technique for root-MUSIC suitable for real-time signal processing applications. The proposed method is based on Newton's method adapted as global polynomial rooting technique. Well-defined complex dynamics of root-MUSIC polynomial's Newton map were exploited to prescribe a minimal set of initial points for Newton's method. Proposed set of initial points guarantee that at least one of them would converge to the root closest to the unit circle (that corresponds to the direction of arrival (DOA)). The proposed method was compared with existing general polynomial rooting technique in terms of computational complexity and possibility of parallelization. In addition, the performance of proposed system when incorporated into root-MUSIC was analyzed in terms of computations required to achieve a given accuracy of DOA.

This paper integrates small perturbation method (SPM) with a ray-tracing (RT) algorithm to model a multi-input multi-output (MIMO) channel over a dielectric rough terrain. The effects of surface undulation height, surface correlation length, dielectric soil, transmitter and receiver heights, and interelement spacing of MIMO transceivers are examined on relative received power, intra-user spatial correlation, RMS delay spread, and the coherence bandwidth.

In an emergency situation, cognitive radio nodes can be deployed temporarily to form an ad hoc network for data transmission by exploiting available spectrum. Based on some criteria, cognitive radio nodes can form multiple clusters which are connected to form the network. For emergency cognitive radio networks, the number of clusters is an important metric for the network performance evaluation. Hence, in this study, after a clustering scheme is presented briefly, the number of clusters that deployed cognitive radio nodes can form is analysed. First, the maximal number of clusters that can be formed in the given area is studied based on the strict arrangement of nodes. Second, the average number of clusters formed is analysed as the expected value of the number of clusters formed, for which the probability that M clusters are formed is investigated. Thirdly, the upper bound of network simultaneous transmission capacity is derived based on the result of the average number of clusters formed. Finally, simulations are conducted to verify the analytical results.

This paper investigates channel spatial correlation for promising frequency ranges. The surface roughness of the coverage area and partial line of sight is studied. Closed form solutions for the spatial cross-correlation between two receivers using the principles of Kirchhoff's theory are developed. The effects of roughness average height, transmitter-receiver distance, receiver height on spatial correlation are studied. © 2013 IEEE.

In this paper, we present the error probability expressions for a wideband coherent spatially correlated Multiple Input Multiple Output (MIMO) channel in low signal to noise ratio (SNR) regimes. Prior works have depicted a decrease in performance due to spatial correlation in high SNR regimes. This work proves that in a power limited broadband MIMO system, spatial correlation across the channel fading matrix elements improves the probability of error performance. In other words, spatial correlation impacts the MIMO performance differently in high SNR compared to low SNR (wideband) regimes.

Cognitive radio nodes can form a wireless network automatically based on the “group” concept: In a given area, cognitive radio nodes are assumed to be activated randomly. Activated cognitive radio nodes form multiple “groups”. Each group consists of a leader node, some bridge nodes and regular nodes. Leader node is capable of communicating with any group member node, and bridge nodes connect different groups to form a scalable network. With this concept, incorporating the available spectrum, cognitive radio nodes can form a network without the constraint of common channel availability. This paper first proposes a scheme for the node communication, and then based on this scheme, analyzes the numbers of nodes and channels required to maintain full connectivity of the cognitive radio network formed for emergency situation. Finally, this paper investigates the connectivity of the group-based cognitive radio network with arbitrary topology.

This paper presents an Omnidirectional mobile target-node (TN) localization technique in nonline-of-sight (NLOS) scenarios. Here, a TN cooperates with base-nodes (BNs) with antenna-arrays to allow them to find its position via time-of-arrival (TOA) and direction-of-arrival (DOA) measurements. When line-of-sight (LOS) channel is available, each BN localizes TNs in its coverage area with reasonable accuracy. However, when LOS channel is obstructed, considerable localization error is generated. To avoid NLOS error, a technique is proposed to identify if a TN is in the LOS of multiple BNs or not. The technique enables BNs to determine and localize their shared reflection points, and to localize NLOS TNs. The paper assumes single-bounce-reflection NLOS channel between BNs and TNs. In NLOS scenarios, when three or more reflection points are shared by a TN and multiple sets of BNs, the shared reflection points are localized via DOA fusion, and then the TN is localized via TOA fusion. The equations for NLOS identification, shared reflection points determination and localization and NLOS TN localization are theoretically derived. Simulations are conducted to evaluate the proposed technique in terms of the probability of false alarm and misdetection of NLOS identification and shared reflection points determination, and NLOS TN localization accuracy.

This paper investigates Time-of-Arrival (TOA) estimation performance of a non-contiguous multi-band radio considering the realistic assumption of frequency selective channel across all bands. It is depicted that the resulted TOA performance is comparable to that of utilizing a bandwidth equivalent to the addition of all available frequency bands. A high resolution TOA estimation architecture is proposed that is based on concatenating the estimated channels across sub-bands all sub-bands and applying a TOA estimation method to the whole available spectrum. The Cramer-Rao Bound (CRB) of the TOA estimation for this method is computed. Minimum Mean Square Estimation (MMSE) algorithm is applied to evaluate the performance of the proposed system. Simulations are conducted to study the performance in terms of the variance-of-error.

This paper proposes a non-line-of-sight (NLOS) identification technique that exploits statistics of space-frequency correlation of multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. Here, space correlation refers to the correlation across antenna elements and frequency correlation refers to the correlation across subcarriers. In this technique, the mean value and standard deviation of space-frequency correlation over multiple transmit and receive antenna combinations are used to identify NLOS conditions. The technique requires minimal variation of spatial correlation across different multi-path components. The channel model satisfying this requirement is studied and the performance of the proposed technique is investigated.

A novel super resolution time-of-arrival (TOA) estimation technique applicable to multipath wireless channels is proposed. Here, it is assumed that the line-of-sight signal is available. This technique applies the concept of independent component analysis (ICA) to the received signal in the frequency domain. The proposed ICA algorithm solves an optimisation problem for TOA estimation. The selection of a proper cost function for this optimisation is investigated. The objective is to improve the estimation performance in multipath environments. The proposed technique extracts the TOA estimation iteratively. An optimum initialisation constraint is incorporated to detect the desired (shortest) TOA as the first estimated time delay. This reduces the complexity of the proposed approach. Compared with the traditional super-resolution techniques such as MUSIC, this algorithm represents a lower sensitivity to signal-to-noise ratio (SNR) for positive SNRs, and bandwidth. The proposed method is a good candidate for high-resolution TOA estimation in rich scattering wireless environments. It possesses a low complexity implementation over many high-speed fixed-point platforms such as digital signal processor (DSP) and field programmable gate array (FPGA). The proposed technique has applications in radar, sonar, wireless local positioning systems, and, localisation in mobile ad hoc networks.

This study proposes and investigates the performance of a new non-line-of-sight (NLOS) identification technique for multiple antenna systems that is based on the phase difference across two antenna elements. In order to avoid any confusion in the position location process, NLOS identification techniques should be implemented in the localisation systems. A phase wrapping selection algorithm is proposed to calculate the phase difference variance across two-antenna elements. A theoretical relationship is maintained between the phase difference variance and the Rician K-factor. The proposed K estimator requires an uncorrelated phase across antenna elements. The validity of this assumption is verified via channel modelling simulations. Then, a hypothesis test on the K-factor is formed to identify NLOS situations. The prior distributions of K-factor under line-of-sight (LOS) and NLOS conditions, and the K-factor threshold that are used to distinguish LOS and NLOS situation are derived. The impact of shadowing on the performance of the proposed NLOS identification method is studied. The performance of the proposed phase difference K estimator technique is compared with the envelope-based K estimator.

This study introduces a practical use of maximum noise fraction (MNF) in beamforming antennas that enhances users' uplink performance and capacity in cellular systems. The study introduces a non-overlapping window adaptive MNF technique. In addition, it mathematically analyses the proposed method. Moreover, the performance benefits created via MNF technique in uplink scenarios is also studied. A multi-carrier wideband code division multiple access (MC-WCDMA) system is used as a toy example to represent the benefits created by the proposed technique when it is used as a beamformer. The performance of the proposed technique for uplink MC-WCDMA is mathematically analysed. Simulations are conducted to study the performance and the capacity of the proposed method. The effect of the noise covariance matrix estimation that is vital for the operation of MNF systems on the performance is investigated.

The rapid growth of wireless industry and continuous emergence of new applications increase the demand for wireless spectrum. However, currently the spectrum assigned to different organisations is not utilised efficiently. Particularly, when an infrastructure of a service provider is overloaded and cannot accommodate more users because of the channel scarcity, the infrastructures of other service providers operating in the same area might be in under-loaded status. However, without a proper spectrum sharing scheme, the overloaded infrastructure cannot use the channels licensed to other service providers. This leads to low spectrum utilisation efficiency and higher call blocking rate of service providers. Significant research has been conducted to study sharing channels between cells within one service provider; however, sharing spectrum across different service providers is still under investigation. This paper proposes deploying a network of fixed cognitive radio (CR) nodes to maintain spectrum sharing across multiple service providers operating in the same geographical area. These CR nodes estimate the spectrum utilisation in a given area, and cooperate to provide the spectrum usage information for the overloaded infrastructures of service providers. This work discusses the implementation of the proposed CR-based spectrum sharing technique, and studies the impact of spectrum sharing on the service provider's performance. It is shown that the proposed technique reduces the call blocking rate and improves the spectrum utilisation efficiency. This technique removes the need of sensing spectrum in each user. Thus, it reduces the cost, complexity and battery power consumption of user devices.

Considering an ad hoc cognitive radio network, this paper presents channel assignment methods that can be used by a cognitive radio node to select a channel for communication. The proposed channel assignment methods aim to maximize spectral efficiency, minimize transmit power, or maximize data rate. When a number of available channels are detected, based on the proposed methods, a cognitive radio node can decide a suitable channel to use. These methods are executed distributively in cognitive radio nodes without using central controllers. This reduces the complexity of spectrum sharing in cognitive radio networks.

The original diversity-multiplexing tradeoff work by Zheng and Tse assumes multi-input-multi-output (MIMO) systems with frequency flat, spatially independent, and temporally block fading. Several following works have extended the tradeoff to either frequency selective or spatially correlated channels. However, all of them assume that fadings are temporally block. Compared with block fading assumption, it is more realistic to model Rayleigh temporal fadings as a zero-mean stationary complex Gaussian random process . Correspondingly, its power spectral density (or Doppler spectrum) is a sufficient description of the random process, because the correlation between two arbitrary fadings can be calculated through the Fourier transform of the Doppler spectrum. The main contribution of this paper is to derive the diversity- multiplexing tradeoff in frequency flat single-input-single-output (SISO) channels with arbitrary Doppler spectrum. Moreover, the derivation process itself, which is based on the spike sharpening effect, may be extended to facilitate other more complicated diversity-multiplexing tradeoff works.

This paper presents a scheme for cognitive radio network construction. Incorporating the available spectrum, cognitive radio nodes automatically construct a local area network. The active cognitive radio nodes in an area form groups. Each group consists of a leader node, inter-group nodes and regular nodes. Inter-group nodes connect different groups to construct a network. Furthermore, the group leaders of different groups form virtual groups to facilitate the network management. The proposed scheme can also be used to construct large scale cognitive radio networks. Its applications include temporal network deployment in emergency situations and home appliance network construction.

In this paper, we propose a technique for predicting the traffic pattern of primary users in cognitive radio systems. Cognitive radios enable sharing the frequency bands that are licensed to primary users. By forecasting the traffic pattern of primary users, secondary users can estimate the utilization of frequency bands and select one for radio transmission to reduce the frequency hopping rate (the rate of switching from one frequency band to another) and the interference effects, while maintaining a reasonable blocking rate. In this work, we propose an algorithm for the prediction of call arrival rate which exploits the periodicity of the traffic process. In addition, we present an approach for call holding time estimation. The results are incorporated to evaluate the probability of the availability of a frequency band within a time period. Setting a threshold on this probability maintains a tradeoff between the blocking rate of secondary users, interference effects on primary users and spectrum efficiency. Simulations are conducted to investigate the performance of cognitive radio systems with and without traffic prediction.

Current multi-input-multi-output (MIMO) capacity analysis focuses on the optimization of ergodic capacity, i.e., mean of capacity, if the capacity in random channels is considered as a random variable. In addition to ergodic capacity, outage probability is another important criteria of MIMO systems, as already stated by many researchers. However, it is not easy to optimize outage probability, because it is in fact a function of outage capacity. Different from previous outage analysis, in this work we are particularly interested in the relationship between outage probability and outage capacity, when outage capacity is asymptotically low, which is called asymptotic outage. Analogous to deep fading, the proposed asymptotic outage is the major exponent of error event. Moreover, it is convenient to optimize the proposed asymptotic outage, in contrast to conventional outage analysis. Detailed study is conducted in large size (number of antenna elements goes to infinity) MIMO systems, accompanied with a recently proposed correlated MIMO channel model, virtual channel representation. It is interesting to find that logarithm of asymptotic outage probability scales linearly with respect to logarithm of asymptotic outage capacity. Even more importantly, it is found that asymptotic outage performance degrades (higher outage probability) when channel correlation decreases.

Recent Multi-Input-Multi-Output research demonstrates that real wireless environments exhibit spatially correlated fadings: The independent fading assumption does not hold in all cases. Accordingly, spatially correlated MIMO channel models have attracted much attention. The Kronecker product form (KPF) is the currently most widely used MIMO channel model describing spatial correlations. However, its validity in various environments have not been well examined. In this work, first the correlation structure of the KPF is discussed. It is shown that the KPF exhibits a separable correlation structure. Second, it is claimed that the separable correlation structure corresponds to separable scatterers in physical environment. Using this utility, the KPF is examined with two popular scatterer distributions: two ring models and elliptic models. It is shown that the KPF is feasible for describing two ring models, but not capable of describing elliptic models. Numerical ray-tracing simulations verify the theoretical results.

This paper introduces a semi-distributed cooperative localization technique realized via multi-node time-of-arrival (TOA) and direction-of-arrival (DOA) optimal fusion: Each base-node estimates the position of target-nodes by joint TOA- DOA evaluation, and then, the target-node position estimation error is minimized by TOA-DOA optimal fusion across multiple base-nodes. The performance of the proposed technique is studied and compared to two GPS-based positioning techniques, i.e., GPS-aided TOA fusion and GPS-aided DOA fusion. The circular error probability (CEP) is derived theoretically and verified via simulations. The results confirm the superiority of the proposed localization technique in moderate scale mobile ad- hoc networks (MANETs) compared to the two GPS-based fusion schemes. Thus, while the proposed technique is applicable to MANETs in GPS-denied environments, it is also suitable for GPS available environments. Finally, compared to the centralized scheme, the positioning updating rate of the semi-distributed technique is higher and its power consumption in the reference base node is considerably lower.

Previous multi-input-multi-output (MIMO) designs optimize either reliability (average error probability) or capacity (average data rate, or ergodic capacity). However, a proper MIMO design ought to consider both of them; Just one of them is not sufficient. In this work, we analyze both capacity and error performance of correlated MIMO system, via a recently proposed channel model, virtual channel representation. We derive the error probability in correlated channels, and establish its relationship with experimental capacity results. The results leads to a good hint that there should be a tradeoff between capacity and error performance in MIMO systems.

This paper studies the performance of a traffic-aware dynamic spectrum allocation technique in multi-vendor environments. The study is performed for hybrid Frequency Division Multiple Access (FDMA)/Multi-Carrier Code Division MA (MC-CDMA) systems. FDMA/MC-CDMA supports subcarrier clustering which enhances MC-CDMA potential for dynamic spectrum allocation. A Spectrum Allocation Server (SAS) in the MAC layer controls the process of spectrum allocation. A traffic-aware spectrum sharing algorithm is introduced for the SAS which is called smart spectrum allocation. Smart spectrum allocation highly enhances the spectrum allocation performance in terms of blocking rate, spectral occupancy and revenue.

In this paper, we introduce a novel transmit diversity in which the space diversity in space-time block codes (STBC) is combined with time diversity created by beam pattern scanning (BPS). Via this merger, we achieve high bit-error-rate (BER) performance via time diversity inherent in BPS and space-time codes in STBC. A dynamic time (that is, time-varying) block coding (DTBC) is introduced to compensate the effect of time varying array vectors applied to the array elements in BPS. Hence, we call the scheme BPS dynamic time block coding (BPS/DTBC). We discuss the structure of the BS antenna array and receiver, and generate the BER performance simulations.

In this paper, we introduce a simple merger of beamforming (BF) and maximal ratio combining (MRC) in single-input-multi-output (SIMO) wireless communication systems. It is well known that either BF or MRC in SIMO systems does not perform properly in spatially correlated channels, because the former assumes completely coherent fades over the entire antenna elements while the latter assumes independent fades. Here, we study a merger of BF and SIMO via virtual channel representation (VCR). VCR is used as a consistent description of coherent, correlated and independent channels to derive the proposed algorithm. Specifically, this study is performed for a simple SIMO system which leads to high performance gains in spatially correlated channels. The study can be easily generalized to Multi-Input-Multi-Output (MIMO) systems. This approach replaces the traditional channel codes by complex codes generated via signal-to-noise (SNR) optimization at the receiver.

In this paper, we analyze the perturbation effects on the performance of a novel wireless local position system (WLPS) with applications in homeland security, defense, vehicle collision avoidance, and multi-robot collaboration and coordination. This WLPS has two main components: (1) a dynamic base station (DBS), and (2) a transponder (TRX), mounted at the monitoring and target mobiles, respectively. The DBS detects TRX via unique ID codes assigned to them. This structure leads to a unique wireless structure. In this work, we assume direct-sequence code division multiple access (DS-CDMA) transmission in the uplink (i.e., from TRX to DBS), and antenna array with conventional beamforming (BF) mounted at the DBS. This structure leads to a high probability-of-detection (POD) performance and capacity (in terms of number of TRX) at the DBS receiver. We analyze the effect of perturbations, which lead to antenna weight vector error, reduce the POD performance and the capacity of the WLPS system. Simulation are performed specifically for applications of WLPS systems in vehicle collision avoidance.

A novel application of wireless communication in vehicle early warning is introduced. This application establishes an innovative function for mobile handhelds that is the protection of their holders from accidents with cars. Two main components of this vehicle early warning system are a mobile base station (MBS) deployed in vehicles, and a transceiver installed in mobile handhelds that defines mobile handhelds as active targets. The MBS: (a) communicates with all mobiles located in its proximity; (b) discriminates the mobiles via unique codes assigned to each mobile; and (c) locates and tracks those mobiles. An early warning signal is generated in critical conditions that triggers or controls mechanical systems such as brakes, wheels or airbags. This paper discusses the structure and design problems associated with this system. This scheme highly enhances road and pedestrian safety and defines a new application for wireless systems.

In this paper, two transmit diversity techniques, space-time block coding (STBC) and beam pattern scanning (BPS) (also called beam pattern oscillation) are compared. Beam pattern scanning was recently introduced in the literature, where controlled time varying phase shifts are applied to the antenna array elements mounted at the base station. This creates a small movement in the antenna array pattern directed toward the desired user. In a rich scattering environment, this beam pattern movement creates an artificial time varying channel which generates time diversity exploitable at the receiver. The BPS scheme enhances receiver performance via diversity and network capacity via directionality. In this work, we conduct a comparison between STBC and BPS schemes in terms of their complexity and antenna physical dimension, network capacity (in term of number of users), bit-error-rate (BER) performance, and their relative spectrum efficiency. Network capacity (considering inter-cell-interference effects) and BER performance simulations are generated and compared. We see that BPS achieves a higher network capacity and BER performance with a smaller antenna dimension and complexity (especially for wideband systems) with minimal cost of spectrum efficiency. This identifies BPS technique as a promising scheme for future wireless communications.

In this paper, a novel merger of multicarrier code-division multiple access (MC-CDMA) and smart antenna arrays is introduced. Here, a group of Q carriers in the MC-CDMA system is applied to its own M-element smart antenna array at the base station (BS). The smart antennas are located in close proximity to one another. We generate a transmit diversity gain at the receiver by carefully moving (oscillating) the antenna array's pattern. The pattern oscillation is achieved by applying appropriate time-varying phases to array elements of each smart antenna. The beam pattern oscillation ensures a mainlobe at the position of the intended user and small oscillations in the beam pattern. This beam pattern oscillation leads to a time-varying channel with a controllable coherence time; hence, a transmit diversity benefit, in the form of a time diversity benefit, is available at the receiver. Employing MC-CDMA with the proposed smart antenna at the BS, we achieve: 1) directionality which creates high network capacity via space-division multiple access; 2) a transmit diversity gain which supports high performance at the receiver in the mobile unit; and 3) increased capacity and performance via MC-CDMA's ability to support both CDMA and frequency diversity benefits, respectively.

Applying carefully-selected time-varying phases (delays) to array elements of an adaptive antenna, the beam pattern oscillates in a controlled manner. This creates a time varying channel with a controllable coherence time. With an adaptive antenna at the base station (BS) and a single omnidirectional antenna at the mobile, the controllable coherence time is used by the mobile to exploit time diversity and enhance performance. In this work, assuming an oscillating-beam-pattern antenna array at the BS, the channel is properly modeled and the coherence time is evaluated. A so-called geometric-based stochastic channel model is presented, assuming a circular coverage area, and the channel is simulated in an urban environment. We demonstrate the relationship between coherence time and the antenna array control parameters and show that seven-fold-diversity can be created via small beam pattern oscillation.

In this work, the authors introduce the concept of spectral sharing in multi-system environments by application of MC-CDMA technology. The proposed MC-CDMA system supports spectral sharing via dynamic carrier allocation: the orthogonal carriers that make up a transmit signal are borrowed/shared between multiple systems. The resulting system not only supports increased spectral efficiency, but simulations indicate improved BER performance as well. It is hoped that this exploration will serve as a useful beginning in the emergence of a highly efficient spectral exchange.

We merge a smart antenna array with CI/DS-CDMA, a novel implementation of DS-CDMA where chips have a shape referred to as the CI (carrier interferometry) chip shape and are decomposable into N narrowband frequency components. In the antenna array, by applying suitable time-varying phases to the elements, we create small movement (oscillation) in the antenna array's pattern, while steering the main lobe to the position of the intended user. The oscillating antenna pattern creates a time-varying channel with a controllable coherence time. This, in turn, provides transmit diversity in the form of a time diversity gain at the mobile receiver side. Thus, at the receiver, three stages of combining are available: 1) combining time components of the received signal within symbol duration T/sub S/ (each experiencing a different fade) to enhance performance via time diversity; 2) combining frequency components which make up the CI/DS-CDMA chip to enhance the performance via frequency diversity; 3) combining across chips to eliminate interfering users. Employing CI/DS-CDMA with the proposed smart antenna at the base station, we achieve: 1) very high capacity via the merger of SDMA (directionality of antenna array) and CDMA; 2) very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. We focus on the performance benefits of the proposed system.

Applying proper time-varying phases (delays) to the array elements of an adaptive antenna, its beam pattern is carefully controlled to generate an oscillating beam pattern. This creates a time varying channel with a controllable coherence time. With an adaptive antenna at the base station (BS), the controllable coherence time is used by the mobile station (MS) to exploit time diversity and enhance performance. In this work, using an oscillating beam pattern antenna array in the BS, the channel is properly modeled to evaluate the coherence time in the MS. A so-called geometric-based stochastic channel modeling (GSCM) scheme is presented, which allows us to model this new time-varying channel and to investigate the coherence time. We demonstrate the relationship between coherence time and the antenna array control parameters.

We introduce a novel merger of multi-input single-output (MISO) systems and MC-CDMA (multi-carrier code division multiple access) systems. Here, each group of Q carriers in the N-carrier MC-CDMA system (Q

By applying carefully selected time-varying delays to the array elements of a smart antenna located at the base station (BS), small oscillations are generated in the beam pattern. These oscillations create a time-varying channel demonstrating intra-symbol time variation and characterized by coherence time T/sub C/. At a single-antenna mobile station (MS), the time-varying channel (with coherence time T/sub C/) creates a time diversity which is exploited to enhance the mobile's performance (by introducing oversampling to the mobile receiver). We present a channel model which characterizes the time-varying channel that results from beam pattern oscillation. We then use our channel model to evaluate the coherence time, T/sub C/, at the mobile station (MS). The channel model presented corresponds to the so-called geometric-based stochastic channel model (GSCM), with a semi-elliptic coverage area. This geometric approach allows us to stochastically model the parameters of the time-varying channel impulse response. Simulations based on the GSCM show that 7-fold time diversity can be exploited at the MS (when beam pattern movement is small), which significantly improves the MS receiver probability-of-error performance.

In this paper, a smart antenna array is located at the base station (BS). Time-varying delays are applied to the array elements. These time-varying delays create a small oscillation in the beam pattern, which in turn leads to a time-varying channel. At the single-antenna mobile station (MS), the time-varying nature of the channel is exploited to achieve time diversity benefits. In this work, we present a channel model for the time-varying channel, and use our proposed model to evaluate the coherence time at the MS. A so-called geometric-based stochastic channel model (GSCM), with a semi-elliptic coverage area, is presented. This geometric approach allows us to stochastically model the parameters of the time-varying channel impulse response. Simulations based on the GSCM allow for the characterization of coherence time and its relationship to smart antenna control parameters.

Whenever the channel coherence time is less than the symbol duration, a mobile station (MS) receiver can exploit time diversity to enhance its probability of error performance. One way to ensure a channel coherence time less than the symbol duration is by use of a carefully controlled oscillating-beam antenna array at the base station (BS). Here, beam pattern movement creates small coherence times. In this paper, with an oscillating-beam-pattern antenna array at the BS, the time varying channel is modeled to evaluate the channel coherence time and the available diversity in the MS. Here, a geometric-based stochastic channel model (GSCM) is used, and a circular coverage area is assumed. For a mid-sized city center, coherence times are shown to correspond to 1/7/sup th/ the symbol duration, suggesting a 7-fold time diversity is available at the MS when the BS's antenna array pattern is carefully controlled.