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In this paper, a multiple cluster-based transmission diversity scheme is proposed for asynchronous joint transmissions (JT) in private networks. The use of multiple clusters or small cells is adopted to reduce the transmission distance to users thereby increasing data-rates and reducing latency. To further increase the spectral efficiency and achieve flexible spatial degrees of freedom, we consider that a distributed remote radio unit system (dRRUS) is installed in each of the clusters. A key characteristic of deploying the dRRUS in private networks is the associated multipath-rich and asynchronous delay propagation environment. Therefore, we consider asynchronous multiple signal reception at the remote radio units and propose an intersymbol interference free distributed cyclic delay diversity (dCDD) scheme for JT to achieve the full transmit diversity gain without requiring full channel state information of the private network. The spectral efficiency of the proposed dCDD-based JT is analyzed by deriving a new closed-form expression, and then compared with link-level simulations for non-identically distributed frequency selective fading over the entire network. Due to its distributed structure, the dRRUS relies on backhaul communications between the private network server and cluster master (CM), which is the main backhaul connection, and between the CM to remote radio units, which are the secondary backhaul connections. Thus, it is important for us to investigate the impact of reliability of main and secondary backhaul connections on the system. Our results show that the resulting composite backhaul connections can be accurately modeled by our proposed product of independent Bernoulli processes. [ABSTRACT FROM AUTHOR]

This paper presents a fault detection system for photovoltaic standalone applications based on Gaussian Process Regression (GPR). The installation is a communication repeater from the Confederación Hidrográfica del Ebro (CHE), public institution which manages the hydrographic system of Aragón, Spain. Therefore, fault-tolerance is a mandatory requirement, complex to fulfill since it depends on the meteorology, the state of the batteries and the power demand. To solve it, we propose an online voltage prediction solution where GPR is applied in a real and large dataset of two years to predict the behavior of the installation up to 48 hour. The dataset captures electrical and thermal measures of the lead-acid batteries which sustain the installation. In particular, the crucial aspect to avoid failures is to determine the voltage at the end of the night, so different GPR methods are studied. Firstly, the photovoltaic standalone installation is described, along with the dataset. Then, there is an overview of GPR, emphasizing in the key aspects to deal with real and large datasets. Besides, three online recursive multistep GPR model alternatives are tailored, justifying the selection of the hyperparameters: Regular GPR, Sparse GPR and Multiple Experts (ME) GPR. An exhaustive assessment is performed, validating the results with those obtained by Long Short-Term Memory (LSTM) and Nonlinear Autoregressive Exogenous Model (NARX) networks. A maximum error of 127 mV and 308 mV at the end of the night with Sparse and ME, respectively, corroborates GPR as a promising tool. [ABSTRACT FROM AUTHOR]

The increasing deployment of battery storage applications in both grid storage and electric vehicle fields is generating a vast used battery market. These batteries are typically recycled but could be reused in second-life applications. One of the challenges is to obtain an accurate remaining useful life (RUL) estimation algorithm, which determines whether a battery is suitable for reuse and estimates the number of second-life cycles the battery will last. In this article, the RUL estimation problem is considered. We propose several health indicators (HIs), some of which have not been explored before, along with simple yet effective estimation and classification algorithms. These algorithms include classification techniques such as regularized logistic regression (RLR), and regression techniques such as multivariable linear regression (MLR) and multilayer perceptron (MLP). As a more advanced solution, a multiple expert system combining said techniques is proposed. The performance of the algorithms and features is evaluated on a recent lithium iron phosphate (LFP) data set from Toyota Research Institute. We obtain satisfactory results in the estimation of RUL cycles with errors down to 49 root mean square error (RMSE) cycles for cells that live up to 1200 cycles, and 0.24% mean relative error (MRE) for the prediction of the evolution of capacity. [ABSTRACT FROM AUTHOR]

Screen-camera communications, using a liquid crystal display (LCD) screen and camera image sensors, have been attractive variants of visible light communications (VLC) since any external light-emitting modules and photo detectors are required for recent mobile devices, which are usually equipped with display and camera. A major issue in screen-camera communications is a performance loss in transmission rate due to nonlinear channel impairments with ambient noise. To improve transmission rates, we investigate the impact of nonlinear channel equalization, nonbinary channel coding, probabilistic shaping, and nonlinear precoding for high-order modulation schemes. Experimental evaluations using an LCD screen and camera demonstrate that our proposed scheme achieves 3.8–3.3 times higher transmission rates compared to existing schemes for a communication distance of 60–160 cm. [ABSTRACT FROM AUTHOR]

In this paper, a new transmit diversity scheme is proposed for cooperative pseudo-non-orthogonal multiple access (Pseudo-NOMA) without assuming full channel state information at the transmitter (CSIT). To support two users under the near-far user pairing constraint, a distributed cyclic delay diversity (dCDD) scheme is adapted into NOMA by dividing a set of remote radio heads (RRHs) into two groups for multiple cyclic-prefixed single carrier transmissions. To maximize a far user’s rate and two users’ sum rate over independently but non-identically distributed frequency selective fading channels and under a near-far user pairing constraint, we first derive closed-form expressions for the rates of the two users with full CSIT. Considering that only partial CSIT is available, a new RRH assignment and power allocation scheme is proposed for dCDD-Pseudo-NOMA. For various simulation scenarios, the provided link-level simulations verify that higher rates can be achieved by dCDD-Pseudo-NOMA compared with the traditional orthogonal multiple access with dCDD and dCDD-Conventional-NOMA that uses the superimposed signals. Furthermore, the proposed RRH assignment and power allocation scheme makes dCDD-Pseudo-NOMA achieve almost the same rate as that of ideal dCDD-Pseudo-NOMA which requires full CSIT. [ABSTRACT FROM AUTHOR]

This paper investigates the diversity gain of a distributed cyclic delay diversity (dCDD) scheme for cyclic-prefixed single carrier systems in non-identical fading channels. Non-identical small-scale fading is assumed in the environment, in which non-identical line-of-sight and non-line-of-sight fading coexist. A condition for dCDD resulting in intersymbol interference free reception at the receiver, is extended to this new channel environment. For an overpopulated system setup, a generalized performance analysis, is not available from existing works, is conducted after developing closed-form expressions for the distribution of the signal-to-noise ratio (SNR) realized at the receiver. Since the order statistics are involved in the statistical properties of the SNR, the corresponding spacing statistics are utilized to derive feasible closed-form expressions. The finalized closed-form expressions are shown to provide very reliable outage probability and spectral efficiency of dCDD for underpopulated and overpopulated systems. An asymptotic performance analysis verifies the maximum achievable diversity of the dCDD even in the overpopulated case within the considered channel environment. Link-level simulations are conducted and these verify the maximum achievable diversity gain. [ABSTRACT FROM AUTHOR]

A joint data and interference transmission scheme based on a new distributed asynchronous cyclic delay diversity (dACDD) technique is proposed for cooperative communication systems. Without any perfect channel state information from a legitimate user (LU) and an eavesdropping user (EU), joint remote radio head (RRH) selection for the data and jamming signal transmissions is proposed for dACDD to achieve the maximum diversity gain at the LU, while degrading the receive signal-to-interference-plus-noise ratio at the EU. The proposed dACDD is the extension of distributed cyclic delay diversity, which requires a tight synchronization among the central control unit and RRHs. Thus, processing at each RRH causing no intersymbol interference at the LU is developed. Then, the selection scheme for a data RRH is proposed, which selects a single RRH connected with the channel having the greatest channel magnitude as the data RRH to transmit a desired confidential message and controls the remaining RRHs to transmit an artificial interference sequence to the LU and EU. For the proposed distributed system, the marginal secrecy outage probability and marginal probability of non-zero achievable secrecy rate are analyzed by deriving closed-form expressions, whose correctness is verified via link-level simulations over non-identically distributed frequency selective fading channels. [ABSTRACT FROM AUTHOR]

To monitor the power grid over a wide area, the wide area monitoring systems (WAMSs) has been developed. At each substation, the Global Positioning System (GPS) receiving system resides to provide trusted timing. Thus, it is critical for the WAMS to maintain authentic GPS timing over a wide area. However, GPS timing is susceptible to spoofing due to the unencrypted signal structure and its low signal power. Thus, to obtain trusted GPS timing from spoofing, a new wide-area monitoring algorithm, which comprises distributed belief propagation (BP) and a bidirectional recurrent neural network (RNN), is developed under the framework of artificial intelligence (AI). This joint BP-RNN algorithm authenticates each power substation by evaluating the estimated GPS timing error by its distributed processing capability. Specifically, the bidirectional RNN provides fast timing error estimation under the framework of AI. Simulation results demonstrate a fast detection time over the Kullback-Leibler divergence-based approach, and timing error estimation accuracy over the limit provided by the IEEE C37.118.1-2011 standard. [ABSTRACT FROM AUTHOR]

We consider angular-domain channel estimation in massive MIMO systems using one-bit analog-to-digital converters (ADCs) with various thresholding schemes at the receivers. We first derive the performance bounds for estimating angular-domain channel parameters, including the angles-of-arrival (AoA), angles-of-departure (AoD) and the associated path gains. Specifically, we derive 1) the deterministic Cramér-Rao bound (CRB) when all of the angular-domain channel parameters are treated as deterministic unknowns; 2) the hybrid CRB when some parameters have known prior probability density functions (pdfs) while the rest are assumed to be deterministic unknowns; 3) the Bayesian CRB when all of them have known prior pdfs. We also consider using the maximum likelihood (ML) method for channel estimation and a computationally efficient relaxation based cyclic algorithm (referred to as 1bRELAX) to obtain the ML estimates. When the prior information is available, the maximum a posteriori (MAP) and joint ML-MAP (JML-MAP) estimators are derived. We also use the one-bit Bayesian information criterion (1bBIC) to determine the number of scattering paths. Numerical examples are provided to verify the derived performance bounds with different thresholding schemes and demonstrate the performance of the proposed channel estimation algorithms. [ABSTRACT FROM AUTHOR]

In this paper, a cooperative single carrier system comprising multiple cooperating remote radio heads and spatially distributed interferers is investigated. Due to the random location of the interferers within the communication range, a mixture of line-of-sight (LoS) and non-line-of-sight (nLoS) paths is considered in the channel model. Under a frequency selective fading channel with a mixture of the LoS and nLoS paths, the distributed cyclic delay diversity is employed to achieve the maximum transmit diversity gain without the exact knowledge of the channel state information at the transmitter side. It is shown that the operating signal-to-noise regions are divided into two regions, i.e., noise-limited and interference-limited. In this paper, the main focus is on the interference-limited region, in which diversity gain is not achieved due to performance limits determined by the system and channel parameters. The existence of these limits on the performance metrics, such as the outage probability and ergodic capacity, is derived analytically and then verified by link-level simulations. [ABSTRACT FROM AUTHOR]

Wireless multi-view plus depth (MVD) video streaming enables free viewpoint video playback on wireless devices, where a viewer can freely synthesize any preferred virtual viewpoint from the received MVD frames. Existing schemes of wireless MVD streaming use digital-based compression to achieve better coding efficiency. However, the digital-based schemes have an issue called the cliff effect, where the video quality is a step function in terms of wireless channel quality. In addition, parameter optimization to assign quantization levels and transmission power across MVD frames are cumbersome. To realize high-quality wireless MVD video streaming, we propose a novel graceful video delivery scheme, called FreeCast. FreeCast directly transmits linear-transformed signals based on 5-D discrete cosine transform, without digital quantization and entropy coding operations. In addition, we exploit a fitting function based on a multidimensional Gaussian Markov random field model for overhead reduction to mitigate rate and power loss due to large overhead. The proposed FreeCast achieves graceful video quality with the improvement of wireless channel quality under a low overhead requirement. In addition, the parameter optimization to achieve highest video quality can be simplified by only controlling a transmission power assignment. Performance results with several test MVD video sequences show that FreeCast yields better video quality in band-limited environments by significantly decreasing the amount of overhead. For instance, structural similarity (SSIM) performance of FreeCast is approximately 0.127 higher than the existing graceful video delivery schemes across wireless channel quality, i.e., signal-to-noise ratio, of 0–25 dB at a transmission symbol rate of 37.5 Msymbols/s. [ABSTRACT FROM AUTHOR]

In this paper, a cooperative cyclic-prefixed single carrier (CP-SC) system is studied and a scheme to improve its physical layer security is proposed. In particular, a distributed cyclic delay diversity (dCDD) scheme is employed and a deliberate interfering method is introduced, which degrades the signal-to-interference-plus-noise ratio (SINR) over the channels from a group of remote radio heads (RRHs) to an eavesdropper, while minimizing the signal-to-noise ratio loss over the channels from the RRHs to an intended user. This is obtained by selecting one RRH that acts as an interfering RRH and transmits an interfering artificial noise sequence to the eavesdropper. Through the use of the dCDD scheme, a channel that minimizes the receive SINR at the eavesdropper is selected for the interfering RRH. This choice enhances the secrecy rate of the CP-SC system. The system performance is evaluated by considering the secrecy outage probability and the probability of non-zero achievable secrecy rate, which are formulated in closed-form analytical expressions for the case of identically and non-identically distributed frequency selective fading channels. Based on the proposed analytical framework, the diversity order of the system is studied. Monte Carlo simulations are employed to verify the analytical derivations for numerous system scenarios. [ABSTRACT FROM AUTHOR]

Contiguous/noncontiguous carrier aggregation (CA) is one of the key features from 4G systems, which is expected to be evolved within 5G technologies. Thus, there is a need for the development of flexible, agile, and reconfigurable radio transceivers with a native support for the integration of multiple bands and multiple standards. All-digital radio-frequency (RF) transmitters have demonstrated promising potential to the design of next-generation RF transceivers. However, the simultaneous multiband transmission is still one of the key limitations of current approaches. To address this problem, this paper presents a fully digital and parallel architecture that enables the real-time design of agile and concurrent triple-band transmission. The proposed architecture is suitable for both contiguous and noncontiguous CA scenarios and considerably surpasses the state of the art in terms of frequency agility, maximum spacing between bands, and aggregated bandwidth. To enhance the system performance, an extension to a multilevel architecture based on the analog combination of pulsed waveforms is also demonstrated. Both architectures (two and seven levels) were implemented in a field-programmable gate array. Measurement results in terms of signal-to-noise ratio, error-vector magnitude, and adjacent-channel power ratio are presented and discussed. In Implementation-I, the two-level architecture presents a frequency agility from 0.1 to 2.5 GHz (with a frequency resolution of 4.88 MHz) with an aggregated bandwidth of 56.26 MHz. In Implementation-II, the seven-level design presents a frequency agility from 0.1 to 2 GHz (with a frequency resolution of 3.906 MHz) with an aggregated bandwidth of 112.5 MHz. [ABSTRACT FROM AUTHOR]

This paper investigates the secrecy performance of a finite-sized in-band selective relaying system with $M$ transmitters connected via unreliable backhaul links, $N$ decode-and-forward relays, and $K$ collaborative eavesdroppers. To send the source message to the destination, a transmitter-relay pair that achieves the highest end-to-end signal-to-noise ratio is selected for transmissions, while the $K$ eavesdroppers combine all the received signals from the selected transmitter and relay using maximal ratio combining. The proposed model introduces backhaul reliability and eavesdropping probability parameters to investigate practical constraints on the transmitter-relay cooperation and eavesdropper collaboration, respectively. Closed-form expressions are derived for the secrecy outage probability, probability of non-zero achievable secrecy rate, and ergodic secrecy rate for non-identical frequency-selective fading channels with robust cyclic-prefixed single carrier transmissions. These results show that the asymptotic secrecy outage probability and probability of non-zero achievable secrecy rate are exclusively determined by the number of transmitters $M$ and their corresponding set of backhaul reliability levels. Under unreliable backhaul connections, it is found that the secrecy diversity gain is determined by $M$ , $N$ , and the number of multipath components in the frequency selective fading channels. Link-level simulations are conducted to verify the derived impacts of backhaul reliability and collaborative eavesdropping on the secrecy performance. [ABSTRACT FROM AUTHOR]

This paper presents novel machine-learning-based methods for estimating the state of charge (SoC) of lithium-ion batteries, which use the Gaussian process regression (GPR) framework. The measured battery parameters, such as voltage, current, and temperature, are used as inputs for regular GPR, whereas the SoC estimate at the previous sample is fed back and incorporated into the input vector for recurrent GPR. The proposed methods consist of two parts. In the first part, training is performed wherein the optimal hyperparameters of a chosen kernel function are determined to model data properties. In the second part, online SoC estimation is carried out according to the trained model. One of the practical advantages of a GPR framework is to quantify estimation uncertainty and, hence, to enable reliability assessment of the battery SoC estimate. The performance of the proposed methods is evaluated by using a simulated dataset and two experimental datasets, one with constant and the other with dynamic charge and discharge currents. The simulations and experimental results show the superiority of the proposed methods in comparison to state-of-the-art techniques including a support vector machine, a relevance vector machine, and a neural network. [ABSTRACT FROM PUBLISHER]

Soft video delivery i.e. analog video transmission has been proposed to provide high video quality in unstable wireless channels. However existing analog schemes need to transmit a significant amount of metadata to a receiver for power allocation and decoding operations causing large overhead and quality degradation due to rate and power losses. To reduce the overhead while keeping the video quality high we propose a new analog transmission scheme. Our scheme exploits a Gaussian Markov random field for modeling video sequences to significantly reduce the required amount of metadata which are obtained by fitting into the Lorentzian function. Our scheme achieves not only reduced overhead but also improved video quality by using the fitting function and parameters for metadata. Evaluations using several test video sequences demonstrate that the proposed scheme reduces overhead by 99.7% with \text1.2-dB improvement of video quality (in terms of peak signal-to-noise ratio) compared to the existing analog video transmission scheme. We also investigate the impact of bandwidth limitation showing a significant gain up to \text2.7  dB for narrow-band systems. [ABSTRACT FROM PUBLISHER]

This paper investigates a distributed cyclic delay diversity (CDD) transmission scheme for cyclic-prefixed single carrier systems in non-identically and identically distributed frequency selective fading channels. The distinguishable feature of the proposed scheme lies in providing a transmit diversity gain while reducing the burden of estimating the channel state information, which is a challenging task in distributed and cooperative systems. To effectively use the distributed CDD scheme at the transmitters, two sufficient conditions are derived to eliminate the intersymbol interference at the receiver and leveraged to convert the multi-input single-output channel into a single-input single-output channel. These conditions allow the system to achieve the maximum diversity for frequency selective fading channels at a full rate. To achieve this maximum diversity, a fixed number of CDD transmitters are selected based on the channel conditions, symbol block size, and maximum time dispersion of the channel, and a new two-stage transmission mode is proposed. Based on the distributed CDD and the proposed selection schemes, a new expression for the signal-to-noise ratio at the receiver is obtained with the aid of order statistics, and then closed-form expressions for the outage probability and average symbol error rate (ASER) are derived. As far as the identically distributed frequency selective fading channel model is concerned, the achievable maximum diversity gain is proved, with the aid of asymptotic analysis, to be equal to the product of the total number of transmitters in the system and the number of multipath components. Link-level simulations are also conducted to validate the analytical expressions for outage probability, ASER, and maximum achievable diversity gain. [ABSTRACT FROM PUBLISHER]

Energy harvesting is an emerging technology for enabling green, sustainable, and autonomous wireless networks. In this paper, a large-scale wireless network with energy harvesting transmitters is considered, where a group of transmitters forms a cluster to cooperatively serve a desired receiver amid interference and noise. To characterize the link-level performance, closed-form expressions are derived for the transmission success probability at a receiver in terms of key parameters such as node densities, energy harvesting parameters, channel parameters, and cluster size, for a given cluster geometry. The analysis is further extended to characterize a network-level performance metric, capturing the tradeoff between link quality and the fraction of receivers served. Numerical simulations validate the accuracy of the analytical model. Several useful insights are provided. For example, while more cooperation helps improve the link-level performance, the network-level performance might degrade with the cluster size. Numerical results show that a small cluster size (typically 3 or smaller) optimizes the network-level performance. Furthermore, substantial performance can be extracted with a relatively small energy buffer. Moreover, the utility of having a large energy buffer increases with the energy harvesting rate as well as with the cluster size in sufficiently dense networks. [ABSTRACT FROM PUBLISHER]

This letter introduces a new coupled mixture of polynomial phase signal (PPS) and sinusoidal frequency modulated (FM) signal, motivated by real-world applications, for example, contactless linear encoders. Specifically, the coupling is introduced to express the sinusoidal FM frequency as a function of the PPS-related parameters. Given the coupling mixture, it generalizes two existing models: the pure PPS model and the independent mixture model. Performance bounds of parameter estimation for the coupled mixture model are established in terms of the Cramér–Rao bound (CRB). Unlike the pure PPS case, the derived CRB shows its dependence on the PPS-related and sinusoidal FM-related parameters due to the coupling mixture. On the other hand, the derived CRBs for the PPS-related parameters are lower than their counterparts of the independent mixture model, as the sinusoidal FM frequency provides additional information on the PPS parameters. [ABSTRACT FROM PUBLISHER]

In this paper, a cooperative wireless system with unreliable wireless backhaul connections is investigated. To increase the throughput and maximize the receiver signal-to-noise ratio (SNR), a selection combining (SC) protocol is employed. Cooperative transmitters are connected to the control unit (CU) via independent but unreliable wireless backhaul connections. Simultaneously taking into account the reliability of each backhaul and different fading conditions of Nakagami-$m$ fading channels, the statistical properties of the effective SNR (e-SNR) at the receiver are investigated. Closed-form expressions are derived for several performance metrics, including the outage probability, average spectral efficiency (ASE), and average symbol error rate (ASER). The effects of backhaul reliability on these performance metrics are also investigated. The scaling relationship between the convergence behavior of these performance metrics and the conventional diversity gain is also analytically investigated in the asymptotic high-SNR regime. Monte Carlo simulations are conducted to verify the derived impact of backhaul reliability on the performance. [ABSTRACT FROM PUBLISHER]

In this paper, the secrecy performance of finite-sized cooperative cyclic prefixed single carrier systems with multiple eavesdroppers and unreliable wireless backhaul connections across multiple transmitters is investigated. For nonidentical frequency-selective fading channels between the relay and destination nodes, secrecy performance metrics including the secrecy outage probability, ergodic secrecy rate, and probability of nonzero achievable secrecy rate are derived. Furthermore, the existence of performance limits on the secrecy outage probability and probability of non-zero achievable secrecy rate are verified for various backhaul scenarios. These limits are found to be exclusively determined by the backhaul reliability. For imperfect backhaul connections, it is found that the diversity gain promised by cooperative cyclic prefixed single-carrier systems cannot be achieved in the conventional asymptotic high signal-to-noise ratio region. Link-level simulations are conducted to verify the derived impact of backhaul reliability on the secrecy performance. [ABSTRACT FROM PUBLISHER]

This paper presents a performance analysis of a finite-sized co-operative wireless system, where a group of transmitters with unreliable backhauls serve a desired receiver using noncoherent joint transmission. To facilitate analysis, an analytical expression for the distribution of the spatially averaged signal-to-interference-plus-noise ratio (SA-SINR) is derived in terms of key system and channel parameters. Leveraging the derived expression, the joint impact of node co-operation, backhaul reliability, interference, and communication range is investigated in the considered finite-sized co-operative system. Furthermore, based on the SA-SINR, closed form expressions for the average bit error rate (ABER) and average spectral efficiency (ASE) are derived. Further insights are established by analyzing the asymptotic performance in the high transmission power regime. From analytical derivations for the outage probability, ABER, and ASE and link-level simulations, it is verified that these asymptotic performance metrics are exclusively influenced by unreliable backhauls, so that the conventional diversity gains are not achievable. [ABSTRACT FROM PUBLISHER]

Multi-band orthogonal frequency--division multiplexing (MB-OFDM) ultra-wideband (UWB) technology offers large throughput, low latency and has been adopted in wireless audio/video (AV) network products. The complexity and power consumption, however, are still major hurdles for the technology to be widely adopted. In this paper, we propose a unified synchronizer design targeted for MB-OFDM transceiver that achieves high performance with low implementation complexity. The key component of the proposed synchronizer is a parallel auto-correlator structure in which multiple ACF units are instantiated and their outputs are shared by functional blocks in the synchronizer, including preamble signal detection, time-frequency code identification, symbol timing, carrier frequency offset estimation and frame synchronization. This common structure not only reduces the hardware cost but also minimizes the number of operations in the functional blocks in the synchronizer as the results of a large portion of computation can be shared among different functional blocks. To mitigate the effect of narrowband interference (NBI) on UWB systems, we also propose a low-complexity ACF-based frequency detector to facilitate the design of (adaptive) notch filter in analog/digital domain. The theoretical analysis and simulation show that the performance of the proposed design is close to optimal, while the complexity is significantly reduced compared to existing work. [ABSTRACT FROM AUTHOR]

The IEEE 802.16/WiMAX standard has fully embraced multi-antenna technology and can, thus, deliver robust performance and high transmission rates. Nevertheless, due to its inherent cost concerns, a WiMAX mobile station (MS) should preferably contain fewer radio frequency (RF) chains than antenna elements. This is because the former is often substantially more expensive than the latter. Thus, antenna selection, wherein a subset of antennas is dynamically selected to connect to the limited number of RF chains for transceiving, is a highly appealing performance enhancement technique for multi-antenna WiMAX terminals. In this paper, a novel protocol for antenna selection in space division multiple access (SDMA) transmission is developed for the next-generation IEEE 802.16 mobile stations. Both locally and globally optimal selection rules are considered together with various linear precoding designs at the base station (BS). The proposed protocol can readily accommodate various channel situations (e.g., reciprocal and non-reciprocal channels). As demonstrated by analysis and simulation, the proposed protocol delivers considerable performance improvement over conventional IEEE 802.16 terminals that lack antenna selection capability. Moreover, the proposed protocol leverages the existing signaling method defined in IEEE 802.16, thereby incurring a negligible signaling overhead and requiring only minimal modifications of the standard. To the best of our knowledge, this paper represents the first effort to support antenna selection capability for SDMA transmissions in IEEE 802.16 mobile stations. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Wireless sensor networks are emerging as an important area for communications. They enable a wealth of new applications including surveillance, building control, factory automation, and in-vehicle sensing. The sensor nodes have to operate under severe constraints on energy consumption and form factor, and provide the ability for precise selflocation of the nodes. These requirements can be fulfilled very well by various forms of ultra-wide-band (UWB) transmission technology. We discuss various techniques and tradeoffs in UWB systems and indicate that time-hopping and frequencyhopping impulse radio physical layers combined with simple multiple-access techniques like ALOHA are suitable designs. We also describe the IEEE 802.15.4a standard, an important system that adopts UWB impulse radio to ensure robust data communications and precision ranging. In order to accommodate heterogeneous networks, it uses specific modulation, coding, and ranging waveforms that can be detected well by both coherent and noncoherent receivers. [ABSTRACT FROM AUTHOR]

In this paper, performances of stored-reference, transmitted-reference (TR), and energy-detection (ED)-based time-of-arrival estimation techniques are analyzed for impulse-radio ultra-wideband (IR-UWB) systems at sub-Nyquist sampling rates. First, an additive white Gaussian noise channel is considered to emphasize certain fundamental issues related to these different transceivers. In particular, energy collection characteristics and decision statistics are presented. Probability of accurate peak detection is analyzed for each transceiver, and receiver operating characteristics for the leading edge are derived. Effects of number of pulses per symbol and number of averaging symbols are investigated in detail. Then, realistic multipath channels are addressed, and various maximum-likelihood estimation approaches are investigated. A new estimator that jointly exploits the noise statistics and power delay profile of the channel is proposed, and a Bayesian estimator that (ideally) gives a lower bound is analyzed. Simulation results show that while ED and TR have better energy collection capabilities at low-rate sampling, they suffer from distributing the energy over time. [ABSTRACT FROM PUBLISHER]

In this paper, we develop a general reduced-rate orthogonal frequency division multiplexing (OFDM) transmission scheme for inter-subchannel interference (ICI) self-cancellation over high-mobility fading channels. Via transmit and receive processing, we transform the original OFDM system into an equivalent one with fewer subcarriers. By reducing transmission rate, we are able to design a transmitted signal structure with inherent ICI self-cancellation capability without requiring the instantaneous channel state information. We develop a general structure of transmit and receive processing matrices so that all equivalent subchannels in the transformed OFDM system have the same average signal-to-interference ratio (SIR). For the developed structure, we further optimize the transmit and the receive processing coefficients to maximize the SIR based on channel statistics. Numerical and simulation results demonstrate that the developed reduced-rate OFDM transmission achieves an SIR gain of around 5 dB over the existing ICI self-cancellation schemes and significantly reduces the error floor at the receiver. [ABSTRACT FROM PUBLISHER]

A response to a letter to the editor is presented, about the article "TOA Estimation for IR-UWB Systems With Different Transceiver Types," by I. Guveric, Z. Sahinoglu and P.V. Orlik published in the June 2006 issue.