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Multipath fading can degrade the performance of a wireless communication system significantly when the data rate is as high as those systems beyond Long-Term Evolution Advanced (LTE-A). To combat the multipath-fading effects, orthogonal frequency-division multiplexing (OFDM) techniques have been extensively studied and used in existing systems. However, another effective method to combat multipath fading is a code-division multiple access (CDMA) scheme, which has not been extensively investigated for relay network communication systems. This paper considers uplink CDMA relay networks (consisting of multiple sources, multiple relays, and a single destination) and downlinks (consisting of a combined source, multiple relays, and multiple destinations) under multipath fading. The objective of this paper is to propose a unique, simple, and effective method of finding optimum nonbinary pseudo noise (PN) spreading and despreading sequences employing a maximum signal-to-interference-plus-noise ratio (SINR) criterion and channel state information (CSI). This paper also examines the sensitivity of the proposed schemes to 1-bit quantization, mistiming alignment, wideband jamming, and imperfect CSI. Simulation results verify that the proposed method shows much faster convergence in finding optimum PN sequences and better performance than existing schemes under the same environment. [ABSTRACT FROM AUTHOR]

In this correspondence, multiuser relay systems with amplify and forward relaying protocol are considered. To make transmission delays as short as possible, the concept of complex field network coding is applied. The relays transmit for all users simultaneously instead of using conventional relaying transmissions over orthogonal channels such as time-division multiplexing for each user. Three transmission schemes with two or three time-slot delays and symbol rates 1/2, 2/3, and 1 are examined. Based on the derived pairwise error probability expressions, optimal precoders achieving the maximum diversity and best coding gains are designed without changing the original ergodic capacity regions. Simulation results are provided to verify the proposed designs. [ABSTRACT FROM AUTHOR]

A response by Nizar Tayem and Hyuck M. Kwon to a letter to the editor about their article "L-Shape Two-Dimensional Arrival Angle Estimation With Propagator Method" that was published in the previous issue is presented.

This paper proposes to encode pilot bits together with information bits by using a systematic encoder and applying them to an iterative receiver, where channel estimation and decoding are iteratively performed. This paper then shows why and how the encoded pilot bits can give a positive gain over a conventional uncoded pilot system. Specifically, this paper considers an orthogonal frequency-division multiplexing system that is encoded by a low-density parity-check code under a frequency-selective fading channel and shows theoretical analysis as well as simulation results. [ABSTRACT FROM AUTHOR]

We propose a technique that enhances the performance of Torrieri and Bakhru's maximin algorithm in the presence of frequency offsets and modulated interferences, a common scenario in multiple-access environments, where we observed that the Maximin algorithm suffers performance degradation in the aforesaid scenario. To combat modulated interferences and fading effects, we propose to update the step length during every smart antenna weight vector update. We found that our scheme improves the robustness of the maximin algorithm to a greater extent. Simulation results for a frequency-hopping system confirm the validity of the approach and demonstrate improvements in the performance of the maximin algorithm in the presence of frequency offsets and data modulated interferences in a fading channel environment. [ABSTRACT FROM AUTHOR]

Abstract: Recently, Wu et al. proposed a scheme for two-dimensional direction of arrival angle estimation for azimuth and elevation angles, using the propagator method. An advantage of this method over the classical subspace based algorithms, such as ESPRIT and MUSIC, is that it does not apply any eigenvalue decomposition (EVD) to the cross spectral matrix or singular value decomposition (SVD) to the received data. This significantly reduces the computational complexity, compared to the EVD and SVD. However, Wu''s method has some drawbacks, such as pair matching between the azimuth and elevation angle estimations for multiple different sources. Furthermore, Wu''s method has an estimation failure problem in the range of practical mobile elevation angles. The objectives of this paper are two-fold: (1) to overcome these two problems with less arithmetic operation counts than Wu used; and (2) to improve the performance significantly. To achieve these objectives, we propose an antenna array configuration which avoids these problems. Simulation results verify that the proposed scheme can remove these problems and give much better performance. [Copyright &y& Elsevier]

It is known that computational loads of the propagator method (PM) can be significantly smaller, e.g., one or two order, than those of MUSIC and ESPRIT because the PM does not require any eigenvalue decomposition (EVD) of the cross-correlation matrix and singular value decomposition (SVD) of the received data. However, the PM of the parallel shape array has nonnegligible drawbacks such as 1) requirement of pair matching between the 2-D azimuth and elevation angle estimation which is an exhaustive search and 2) estimation failure problems when elevation angles are between 70° and 90°. The purpose of this paper is to show a way to remove these problems in the PM without additional computational loads. This paper will employ one or two L-shape arrays because the parallel shape used in the PM may cause the aforesaid problems. Simulation results verify that the PM with one or two L-shape configurations can remove these problems and improve the performance of the PM significantly, e.g., almost 5 dB hi signal to noise ratio for the parameters used in this paper. [ABSTRACT FROM AUTHOR]

In this paper, we present an algorithm to estimate the direction of the arrival angles (DOAs) from noncoherent one-dimensional (1-D) signal sources such as binary phase shift keying (BPSK) and M-ary amplitude shift keying (MASK) The proposed algorithm can provide a more precise DOA estimation and can detect more signals than we D-known classical subspace.methods MUSIC and ESPRIT for the 1-D signals. The complexity is the same as that of ESPRIT since the proposed algorithm uses the same array geometry and subarray processing that ESPRIT does. The main differences between the proposed algorithm and the ESPRIT algorithm are as follows: 1) the number of overlapping array elements between two subarrays is equal to M in the proposed algorithm, while in ESPRIT the maximum number of overlapping elements is M - 1, where M denotes the total number of array elements, and 2) the proposed algorithm employs the conjugate of rotation matrix (CRM) V while ESPRIT uses 1 with no conjugate for the second subarray geometry. [ABSTRACT FROM AUTHOR]

Presents an analysis of the performance of smart antenna algorithms when used in code-division multiple access wireless communication system. System models used; Conditions of general simulation; Results and discussion.

Presents a complementary filter design for performance measurement of an IS-95 code division multiple access wireless communication system. Discussion on base station transmit-filter and phase-equalizer; Explanation on complementary filter; Examples of windowing functions.

Focuses on the development of a digital communication receiver. Receiver's use of the direct-sequence spread signal at a nonzero intermediate frequency; Effects of the intermediate frequency sampling on pseudonoise code synchronization; Study of bit-error rate degradation.

In this paper, we study an information-theoretic secret sharing problem, where a dealer distributes shares of a secret among a set of participants under the following constraints: (i) authorized sets of users can recover the secret by pooling their shares, and (ii) non-authorized sets of colluding users cannot learn any information about the secret. We assume that the dealer and participants observe the realizations of correlated Gaussian random variables and that the dealer can communicate with participants through a one-way, authenticated, rate-limited, and public channel. Unlike traditional secret sharing protocols, in our setting, no perfectly secure channel is needed between the dealer and the participants. Our main result is a closed-form characterization of the fundamental trade-off between secret rate and public communication rate. [ABSTRACT FROM AUTHOR]

Due to emerging mobile applications and an Internet of Things, data traffic carried by wireless networks has increased dramatically. As a result, maximizing the utilization of the limited network resource is a top priority. To date, there exists a large body of work on the stochastic network utility maximization (NUM) problem. On the one hand, the stochastic NUM problem and its associated solutions have been mainly investigated under the light-tailed (LT) data condition. On the other hand, empirical results show that data delivered by wireless networks is not only large in volume but also highly variable, which can be characterized by heavy-tailed (HT) distributions. Such HT traffic exhibits high burstiness and strong temporal correlations, which are fundamentally different from the behavior of LT traffic. In this paper, first it is shown that the classic stochastic gradient algorithms (SGAs), as effective solutions for stochastic NUM problems, fail to prevent HT traffic flows from aggressively competing with LT flows for limited resources. This leads to unbounded queueing delay for LT flows, which results in network instability. To counter such a challenge, the time-average stochastic gradient routing algorithm is proposed, which prevents competition among HT and LT traffic flows so that utility optimality and network stability can be achieved simultaneously. Moreover, because HT data have unbounded moments, such as mean and variance, it is not feasible to apply the conventional convergence analysis, which assumes the moment boundedness of traffic arrivals. To address this problem, the ordinary differential equation method is adopted to prove that the proposed algorithm still converges even with highly variable HT traffic. Comprehensive simulation results are shown to verify the derived theoretical results. [ABSTRACT FROM AUTHOR]

A response by Jean-Pierre Delmas to a letter to the editor about the article on Conjugate ESPRIT is presented.

It is unrealistic to assume that all nodes in an ad hoc wireless network would be willing to participate in cooperative communication, especially if their desired Quality-of-Service (QoS) is achievable via direct transmission. An incentive-based auction mechanism is presented to induce cooperative behavior in wireless networks with emphasis on users with asymmetrical channel fading conditions. A single-object second-price auction is studied for cooperative partner selection in single-carrier networks. In addition, a multiple-object bundled auction is analyzed for the selection of multiple simultaneous partners in a cooperative orthogonal frequency-division multiplexing (OFDM) setting. For both cases, we characterize equilibrium outage probability performance, seller revenue, and feedback bounds. The auction-based partner selection allows winning bidders to achieve their desired QoS while compensating the seller who assists them. At the local level sellers aim for revenue maximization, while connections are drawn to min-max fairness at the network level. The proposed strategies for partner selection in self-configuring cooperative wireless networks are shown to be robust under conditions of uncertainty in the number of users requesting cooperation, as well as minimal topology and channel link information available to individual users. [ABSTRACT FROM PUBLISHER]

In this paper, we study user selection (US) strategies for a multiple-input–multiple-output (MIMO) cognitive radio (CR) downlink network, where the r-antenna underlay CR secondary users (SUs) coexist with a primary user (PU), and all terminals are equipped with multiple antennas. Two main scenarios are considered: 1) The t-antenna cognitive base station (CBS) has perfect or partial channel state information at the transmitter (CSIT) from the CBS to the PU receiver (RX), and 2) the CBS has absolutely no PU CSIT. For these scenarios, we propose and evaluate multiple SU selection schemes that are applicable to both best-effort PU interference mitigation and hard interference temperature (IT) constraints. The computational complexity of the proposed schemes can be significantly smaller than that of an exhaustive search with negligible performance degradation. For the selection of C SUs out of K, whereas an exhaustive search is on the order of \mathcal{O}(\binom{K}{C}C^4r^3). When t$ and r$ are of the same order, the computational complexity of the proposed scheme can be \binom{K}{C}C^4/K times smaller. Mathematical complexity analysis and numerical simulations are provided to show the advantage of our schemes. [ABSTRACT FROM PUBLISHER]

This paper considers a two-way amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network consisting of two sources (each with multiple antennas) and multiple physically dispersed single-antenna relays. A central station finds the optimum relay amplifying matrices and transmit/receive beamforming vectors explicitly and iteratively under the transmit power constraints at the sources and the relays. The minimum-mean-square-error criterion is used. Numerical results show that the proposed scheme outperforms the existing two-way AF MIMO network schemes proposed by Arti et al. and Wang et al. [ABSTRACT FROM PUBLISHER]

Inter-carrier interference (ICI) and multiuser interference (MUI) occur in an uplink orthogonal frequency division multiple access system if a channel between a mobile user and a base station is rapidly time-varying. To reduce the ICI and MUI, this letter proposes a subcarrier allocation method. The key idea is to allocate a high-speed user's subcarrier near a low-speed user's one. Then, a wide Doppler spread of a high-speed user can be spilled over a low-speed user's subcarrier band with insignificant influence, and the signal-to-interference-plus-noise ratio (SINR) at each high-speed user's subcarrier can be maximized. This can provide a significant performance improvement of multiuser detection in an uplink-OFDMA. [ABSTRACT FROM PUBLISHER]

ABSTRACT The effect of void on characteristics of the laterally diffused metal oxide semiconductor (LDMOS) power amplifier (PA) is analyzed using the thermal and circuit analysis together. Thermal analysis is performed for finding the junction temperature of LDMOS PA as void area changes. Circuit analysis is performed from these results and LDMOS PA libraries. The analysis results show the linearity, gain, and efficiency degradation in the LDMOS PA as a result of the increase in void area. And this simulation methodology can be used for the design of the PA. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:691-694, 2016 [ABSTRACT FROM AUTHOR]

A hexaferrite slant and slot multiple-input multiple-output antenna with miniature antenna elements was simulated, fabricated, and characterized for antenna performance. Measured return loss and isolation were −33.9/−26.6 dB (for antenna 1/antenna 2) and −18.6 dB at 2.45 GHz, respectively. Measured bandwidth was 454/502 MHz at VSWR < 3. Correlation coefficient between antenna elements calculated from experimental S-parameters was less than 0.00085 between 2.4 and 2.5 GHz. Radiation efficiency of the antennas was measured to be 82% at 2.45 GHz. The antennas have two lobes, omnidirectional, and flower patterns for potential mobile device applications. Simulated and measured antenna performance was found to be in good agreement with each other. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:551-554, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27370 [ABSTRACT FROM AUTHOR]

As channel time-variation increases, orthogonality among subcarriers in an orthogonal frequency division multiplexing (OFDM) symbol can be destroyed because of the relatively long symbol period, whereupon intercarrier interference (ICI) appears, and hence an irreducible error floor occurs. It was shown recently that grouping pilot tones into a number of equally spaced clusters can yield better channel estimation against the doubly selective channel than placing each pilot tone in an equally spaced manner. However, a random pilot sequence was used in the literature, and an optimal sequence has not yet been studied. This paper presents how to optimize the clustered pilot sequence. First, this paper (a) proves the existence of an optimum pilot sequence and (b) suggests a guideline for finding an optimum sequence. Second, this paper shows that an optimum sequence is independent of the signal-to-noise ratio and Doppler rate, and the sequence is generally optimum for any channels. Third, this paper verifies through analysis and simulation that the coded-OFDM system with an optimized cluster pilot sequence can yield a smaller mean square channel estimation error and lower bit error rate than the system with an equidistance pilot or a random cluster pilot under a rapidly time-varying channel. [ABSTRACT FROM AUTHOR]

An inter-carrier interference (ICI) occurs in an orthogonal frequency division multiplexing (OFDM) system when a channel is rapidly time-varying. The proposed scheme employs a polynomial cancellation code (PCC) to suppress this ICI, and uses a linear complex field (LCF) code as a transmit-diversity technique to make the transmission rate compatible up to {n_T} / {(n_T+1)}, where n_T is the number of transmit antennas used. The conventional orthogonal code (OC), such as the Alamouti code, with accompanying PCC cannot achieve this rate. Both analysis and simulation results verify that the proposed scheme can achieve higher channel capacity as well as lower bit error rate (BER) than the other schemes in rapidly time-varying channels, even with a linear receiver and inaccurate channel estimation. [ABSTRACT FROM PUBLISHER]

We fabricated 0.029 λ miniaturized Co2Z hexaferrite terrestrial digital multimedia broadcasting (T-DMB) antenna. T-DMB antenna was fabricated by winding 12-turn Cu tape around the Co2Z rectangular block. Antenna was mounted on the ground substrate with connection of coaxial feeding line. Fabricated Co2Z antenna showed 196.2 MHz of center frequency, -6.55 dB of 3-D average gain and 22.13% of radiation efficiency at 195 MHz. Average gain of Co2Z antenna is found to be greater than -17.4 dB in the range of 174-216 MHz. [ABSTRACT FROM AUTHOR]