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The multipeaked correlation functions of binary offset carrier (BOC) modulated signals introduce an ambiguity threat into the code tracking. Several techniques have been proposed to solve this problem, such as a class of two-dimensional (2-D) tracking techniques, in which the spreading code and the subcarrier are tracked separately. In this paper, the key properties of correlation functions and the theoretical tracking performance analysis considering noise and multipath environments of the general 2-D tracking loop are studied. Exact explicit expressions, taking into account the effects of local subcarrier waveform mismatching and the front-end bandlimiting, are provided for the correlation function employed in 2-D tracking. From these expressions, the key characteristics of 2-D correlation functions such as the shape, coupling relation between dimensions, and the effects of bandlimiting can be clearly seen. Moreover, general theoretical methods to predict the performance of the 2-D tracking techniques under the multipath and noise environments are provided. The results obtained in this paper can facilitate investigations in the area of 2-D tracking technique parameter optimization and performance assessment. [ABSTRACT FROM PUBLISHER]

The ever increasing demands for mobile network access have resulted in a significant increase in bandwidth usage. By improving the system spectral efficiency, multi-way relay networks (MWRNs) provide promising approaches to address this challenge. In this paper, we propose a novel linear beamforming design, namely partial zero-forcing (PZF), for MWRNs with a multiple-input-multiple-output relay. Compared to zero-forcing (ZF), PZF relaxes the constraints on the relay beamforming matrix such that only partial user-interference, instead of all, is canceled at the relay. The users eliminate the remaining interferences through self-interference and successive interference cancellation. A sum-rate maximization problem is formulated and solved to exploit the extra degrees-of-freedom resulted from PZF. Simulation results show that the proposed PZF relay beamforming design achieves significantly higher network sum-rates than the existing linear beamforming designs. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the secure relay beamforming problem for simultaneous wireless information and power transfer (SWIPT) in an amplify-and-forward (AF) two-way relay network. We consider scenarios that the eavesdropper's channel state information (CSI) is and is not available. When the eavesdropper's CSI is available, our objective is to maximize the achievable secrecy sum rate under transmit power constraint and energy harvesting constraint. Since the optimization problem is nonconvex, we derive its performance upper bound, which requires 2-D search, where a semidefinite programming is solved in each step. We also propose an upper bound-based rank-one solution by employing the Gaussian randomization method. To reduce computational complexity, we transform the optimization problem into a difference-of-convex programming and propose a sequential parametric convex approximation (SPCA)-based iterative algorithm to find a locally optimal solution. Furthermore, we also propose a zero-forcing (ZF)-based suboptimal solution. Simulation results demonstrate that the upper bound-based rank-one solution archives the performance almost the same as the upper bound that has high computational complexity. The low-complexity SPCA-based locally optimal solution performs close to the upper bound. The ZF-based suboptimal solution has the lowest computational complexity among the proposed solutions. When the eavesdropper's CSI is not available, we propose an artificial noise-aided secure relay beamforming scheme. [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]

Recently, an adaptive intercell interference (ICI) mitigation technique has been proposed for downlink cellular systems as a means to increase throughput with low system complexity. However, in the prior work, the issue of intercell user scheduling has not been considered. In this paper, we study multiple-input–single-output (MISO) downlink cellular systems that jointly design adaptive ICI cancelation (ICIC) and intercell user scheduling assuming that partial channel state information (CSI) is shared among base stations (BSs). Since the optimal solution would require high complexity, we investigate a new low-complexity algorithm that selects the best users and their beamforming strategies in terms of maximizing the weighted sum rate (WSR). To this end, we first develop a simple threshold criterion for each user to decide the preferred beamforming strategy based on the derivation of the expected signal-to-interference-plus-noise ratio (SINR). Then, according to users' feedback about their decisions, a successive user and beamforming selection algorithm is performed at the BSs. From simulation results, we show that, combined with proportional fair scheduling, the proposed scheme provides excellent throughput performance with very low computational complexity and the amount of inter-BS CSI exchange. Furthermore, we discuss an extension of the proposed scheme to limited feedback systems and observe that our algorithm also provides similar advantages over conventional schemes with quantized feedback. [ABSTRACT FROM PUBLISHER]

This paper considers transmission schemes in multiaccess relay networks (MARNs) where J single-antenna sources send independent information to one N-antenna destination through one M-antenna relay. For complexity considerations, we propose a linear framework, where the relay linearly transforms its received signals to generate the forwarded signals without decoding and the destination uses its multiantennas to fully decouple signals from different sources before decoding, by which the decoding complexity is linear in the number of sources. To achieve a high symbol rate, we first propose a scheme called ConcurrentS\rightarrowR\rightarrowD-IC_D in which all sources' information streams are concurrently transmitted in both the source-relay link and the relay-destination link. In this scheme, distributed space-time coding (DSTC) is applied at the relay, which satisfies the linear constraint. DSTC also allows the destination to conduct the zero-forcing interference cancellation (IC) scheme originally proposed for multiantenna systems to fully decouple signals from different sources. Our analysis shows that the symbol rate of ConcurrentS\rightarrowR\rightarrowD-IC_D is 1/2 symbols/source/channel use and the diversity gain of the scheme is upperbounded by M-J+1. To achieve a higher diversity gain, we propose another scheme called ConcurrentR\rightarrowD-IC_D in which the sources time-share the source-relay link. The relay coherently combines the signals on its antennas to maximize the signal-to-noise ratio (SNR) of each source, then concurrently forwards all sources' information. The destination performs zero-forcing IC. It is shown through both analysis and simulation that when N\geq 2J-1, ConcurrentR\rightarrowD-IC_D achieves the same maximum diversity gain as the full TDMA scheme in which information streams from each source are assigned to orthogonal channels in both links, but with a higher symbol rate. [ABSTRACT FROM AUTHOR]

Cooperative transmission among wireless network nodes can be exploited to resolve collisions and thereby enhance the network throughput. Incorporation of multi-beam adaptive array (MBAA) at a base station/access point (destination) receiver has been shown to improve the network performance. In this paper, we propose an efficient cooperative wireless medium access scheme that exploits novel relay selection methods in a network equipped with MBAA at the destination receiver. Unlike existing techniques that require the estimation of angles-of-arrival (AoAs), the proposed scheme uses the spatial correlation among users for simpler but more effective collision detection and resolution. We present two useful relay selection methods based on channel gain and spatial correlation. It is shown that the joint use of an effective relay selection method and an MBAA in a wireless network can significantly improve the uplink throughput. The throughput of the proposed scheme and its upper bound are analytically derived. Numerical and simulation results have demonstrated significant performance enhancement achieved by the proposed cooperative wireless medium access scheme. [ABSTRACT FROM AUTHOR]

In order to assess the compliance of ingested wireless device (IWD) with related international safety guidelines, the studies on the biological effects and the signal intensity of an IWD in two realistic human body models using the finite-difference time-domain (FDTD) method are reported in this paper. Simulation studies are carried out in 21 scenarios where the IWD is placed at seven positions with three orientations, for each of the two human models. Specific absorption rate (SAR), temperature rise, near fields and far fields are analyzed in the 21 scenarios at four selected operation frequencies of 430 and 800 MHz, and 1.2 and 2.4 GHz, respectively. Our study indicates that the radiation intensity outside of the human body decreases with the increase of operation frequency. Furthermore, the radiation characteristics of the IWD are orientation and position dependent. The polarization of electric field outside of the human body is similar to that of the Radio Frequency (RF) source. As far as the compliance of safety is concerned, among all the simulated scenarios the maxima of the averaged-1g and averaged-10g SARs can reach 3.71 W/kg and 1.37 W/kg at the input power of 25 mW, respectively. [ABSTRACT FROM AUTHOR]

Analysis of mutual information is important to wireless transmission over fading channels, and is usually done by assuming perfect channel state information (CSI) available at the receiver. En many practical applications, however, the CSI must be estimated by sending a limited number of pilot symbols and thus, can suffer from considerable inaccuracy. The influence of CSI inaccuracy on achievable mutual information, though analyzed in the past, is not well understood. The difficulty arises from the presence of a product term of signal and channel estimation error in the received signal model, and the lack of appropriate tools to determine its probability density function. This situation forces the adoption of a bounding technique in current literature by treating the product term either as a signal component or as a noise component. In this paper, we take a different methodology by accurately fitting the received signal with the multivariate Pearson's type-7 (MPT-7) distribution. The new results are simple in expression, very accurate as evidenced by simulation, and capable of directly revealing the dependence of the achievable mutual information on a particular channel estimator. [ABSTRACT FROM AUTHOR]

Fault detection of networked control systems (NCS) subject to uncertain time-varying delay is studied in this paper. For the convenience of residual generator design, influence caused by network-induced delay is first transformed into time-varying polytopic uncertainty, which greatly facilitates further manipulation. Then design of the optimal residual generator is formulated as a model matching problem, i.e., to design a residual generator best matching the optimal residual generator of NCS in the delay free case. This procedure is assisted by parameter-dependent Lyapunov function matrix based Bounded Real Lemma, which has been proved to be much better than single constant Lyapunov function matrix based results. This approach not only can be used in conditions that the variation part of the delay is less than one sampling period, but also can be applied to scenarios where the variation part of the delay is larger than one sampling period. Simulation results are also given to illustrate effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A typical multicast network consists of a single tree, in which only a few internal nodes contribute most resources and are involved in performing the multicast functionality. This leads to an uneven and inefficient utilization of network resources. The problem is more pronounced in mobile ad hoc networks (MANET5), where network resources are limited. One solution is to split the multicast content over a number of trees. This provides several paths for the multicast content and would involve more nodes in implementing multicast functionality. Although this approach improves network utilization, overall multicast latency increases. This paper presents a distributed algorithm to construct multiple edge, sharing trees (MESTs) for small group multicast. MESTs balance the resource allocation and delay constraints by choosing to overlap certain edges that have low weight. Simulation results show that MESTs can generate multicast networks that have low delays and fair resource utilization. MESTs are designed to work with any form of multicast in both wired and wireless networks. [ABSTRACT FROM AUTHOR]

In this paper, we consider wireless networks with directional antennas using slotted ALOHA medium access control. The channel model incorporates the effects of propagation loss and shadowing with Rayleigh fading. By deriving the cumulative distribution function of the signal-to-interference-and-noise ratio (SINR) of a certain link in the network, the outage probability of the link is analyzed. In particular, the analysis works for the arbitrary beam patterns of the directional antennas used in the networks. Moreover, we propose a new parameter, i.e., the array interference factor, which can characterize the average performance of an arbitrary beam pattern in random wireless networks. This provides an efficient way for designers to evaluate the system performance under different beam patterns. The network throughput and the transport capacity of a random wireless net- work with directional antennas are also analyzed. It is shown that the network transport capacity is of the same order as the square root of the node density, which conforms with the well-known capacity of wireless networks. The analysis is useful for designers to optimize the system performance of wireless networks with directional antennas. [ABSTRACT FROM AUTHOR]

In this paper, we investigate efficient wireless data access algorithms in mobile hotspots. We introduce a proxy cache (PC) and propose PC-based poll-each-read (P-PER) and PC-based callback (P-CB) data access algorithms to reduce the transmission cost over wireless links in mobile hotspots. An analytical model is developed, and extensive simulations are conducted to demonstrate the performance of P-PER and P-CB. It is shown that P-PER and P-CB can improve cache hit performance and significantly reduce transmission cost. A tradeoff between P-PER and P-CB suggests the need to use a hybrid proxy-based approach to attain optimal performance of wireless data access in mobile hotspots. [ABSTRACT FROM AUTHOR]

In this paper, a blind space-time (ST) multiuser detector, called ST constrained minimum output energy (ST-CMOE) detector, is proposed. It can be viewed as an extension of the CMOE method (Proc. Globecom, p. 379, 1994), and therefore it is immune to near-far effect. It processes the antenna array output jointly in spatial and temporal domain. Simulation results show that the proposed algorithm can outperform the space-CMOE detector proposed by Wang and Poor (IEEE Trans. Signal Process. vol. 47, p. 2356, 1999) which process the received signal in spatial and temporal domain separately. It can also outperform the ST subspace detector proposed by Chkeif et al. (IEEE Trans. Commun. vol. 48, p. 729, 2000), which, although processes the received signal jointly in spatial and temporal domains, suffers from the mismatch problem in the multipath environment. The simulation results also show that the proposed ST-CMOE detector can achieve the same performance as the training-based ST minimum-mean-square-error detector. In order to reduce the computational load and adapt to dynamic multiple-access channels, an adaptive algorithm is presented. The computational load of this adaptive detector is comparable to Hu's method (IEEE Trans. Signal Process. vol. 52, p. 1862, 2004), while it does not require any initial training or channel estimation in the multipath environment. Simulation results show that the proposed adaptive ST-CMOE detector can work well in a dynamic multiple-access channel, where interferences may enter or leave the channel at any time. [ABSTRACT FROM AUTHOR]

A nonlinear adaptive whitening method is proposed for blind deconvolution of MIMO systems by whitening the received signals in both time and space, with a highly nonlinear function of the past output data. The whitened signals are ISI-free and can be viewed as outputs of a memoryless paraunitary mixing system. The convergence of the proposed recursive algorithm is proved. Numerical simulation shows that the whitening method proposed in the paper works well, even if the output signal is corrupted by additive noise. [ABSTRACT FROM AUTHOR]

In a code division multiple access (CDMA) system, signal detection under multipath distortion typically requires estimation of unknown channel parameters first. In such a scenario, performance of receivers highly relies on the accuracy of channel estimates. In this paper, effects of channel estimation errors on the performance of linear CDMA receivers due to finite data samples are studied when channel parameters are estimated blindly by a recently proposed covariance-matching technique. Those receivers include zero-forcing (ZF), direct matrix-inversion (DMI) minimum mean-square-error (MMSE), subspace MMSE, and RAKE receivers. Their output signal-to-interference-plus-noise ratios (SINRs) and bit-error-rates (BERs) are adopted for performance measures. Expressions for performance indicators under such an imperfect condition are derived from a perturbation perspective and verified by simulation examples. [ABSTRACT FROM AUTHOR]