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In this article, a model is proposed for talkative power (TP) implemented wireless power transfer circuit for constant power load applications that concurrently transmit power and information through a shared channel. The innovative model considers critical factors such as load variations and limited receiver knowledge regarding transmitter component values, which are vital for the seamless operation of TP technology in charging devices with varying loads that are oblivious to the parameters of the transmitter. An efficient transmitter and an optimal receiver are introduced in the framework. The transmitter's design revolves around encoding data into the phase angle between the arm bridges, chosen to optimize energy efficiency. Notably, the model employs a buck‐boost converter whose duty cycle is dynamically adjusted by the controller to accommodate changes in information or transmission phases, ensuring smooth system operation. Maximum likelihood detection methods are rendered impractical at the receiver due to the model's assumptions. To address this challenge, a neural network is implemented as a supervised learning classifier to extract information from the output voltage ripple. The simulations utilize the Speedgoat Real‐Time Target Machine in conjunction with Simulink RealTime highlighting the effectiveness of the efficient transmitter and optimal receiver demonstrating the robustness of the model. [ABSTRACT FROM AUTHOR]

Single‐nitrogen‐vacancy (NV) centers in diamond are highly promising quantum nuclear magnetic resonance (NMR) sensors. However, their exposure to many sources of noise, such as surface impurities, shot noise from avalanche photodiode overlaps, and spin‐state projection errors inherent in quantum systems, limits their usefulness. Often, long measurement durations are required to accumulate sufficient data for NMR signal detection via fast Fourier transform spectrometry. For practical reasons, methods to shorten the necessary accumulation time for NMR signal detection are greatly desired. In this article, an on‐line formulation of maximum likelihood estimation (MLE) signal processing for quantum heterodyne NMR measurements is presented as a step toward this goal. This MLE method reduces the required data accumulation time by orders of magnitude and provides good estimates of target frequency locales in real time. These results are significant to practitioners of NMR detection with single‐NV centers in diamond who require a quick litmus test for potential signals when probing a wide area. [ABSTRACT FROM AUTHOR]

This paper presents the performance evaluation of an amplify‐and‐forward (AF) relay‐assisted multiuser multiple input–multiple output (MU–MIMO) downlink transmission system for correlated fading channels. The overall system performance was improved by incorporating a double‐quadrature spatial modulation (DQSM) scheme. The bit error rate (BER) performance and detection complexity of the AF–MU–MIMO–DQSM system were analyzed and compared with those of a conventional AF–MU–MIMO system under the same conditions and parameters. The results showed that the correlated fading channel severely affected the performance of systems with higher spectral efficiency (SE). Considering an SE of 12 bpcu/user, the AF–MU–MIMO–DQSM system yielded a gain of up to 3 dB in BER performance compared with that of its conventional counterpart for the analyzed cases. In terms of detection complexity, the AF–MU–MIMO–DQSM system showed a reduction of up to 56 % compared with that of the conventional system for the optimal maximum likelihood detection criterion. [ABSTRACT FROM AUTHOR]

Reducing SIC operations and interference while maintaining the same radio resources for users in a cluster is a potential research direction in non‐orthogonal multiple access (NOMA) systems. In order to reach this goal, a streamlined user grouping is proposed for a four‐user cluster in downlink NOMA systems, which is carried out based on the in‐phase and quadrature components of a constellation. In terms of bit error rate performance, the proposed scheme is superior in comparison with the conventional NOMA without user grouping and phase rotation‐based user grouping. This improvement is achieved in light of the three positive points of pulse amplitude modulation, the Gray mapping rule, and the joint maximum‐likelihood detector. [ABSTRACT FROM AUTHOR]

For wireless communications, the multiple‐input multiple‐output (MIMO) system efficiently makes use of the spectrum and enhances the transmission throughput. In this work, the maximum‐likelihood (ML) detection for the MIMO system is studied, and two ML detection algorithms are first considered for the MIMO system, including the sphere decoding (SD) algorithm and an algorithm based on differential metrics (DMs). Each of the two algorithms has its advantages and disadvantages. The two algorithms are first modified such that they are based on the same signal model. Then, a new ML detection algorithm is proposed for the MIMO system based on the hybrid operation of the two modified algorithms on the tree search process, in which both the branch‐and‐bound principle and indicative functions are applied to remove unnecessary searches. The proposed algorithm can attain the ML detection with lower average complexity over low and high ranges of signal‐to‐noise ratio (SNR), as the authors verify by simulations. The proposed ML detection can also generate soft output, and anti‐phase sequences are exploited to further reduce the complexity. [ABSTRACT FROM AUTHOR]

The design of an optimal non‐orthogonal multiple access (NOMA) transmission scheme with finite alphabet inputs for a typical two‐user uplink wireless communication system is investigated in which each terminal is equipped with a single antenna. Each of the two users utilises a four quadrature amplitude modulation (4‐QAM) constellation to transmit information data to a common base station, and the receiver employs a maximum likelihood (ML) detector to jointly estimate both transmitted signals. Assuming the availability of channel state information at both the transmitters and the receiver, it is aimed to design a pair of scalar beamformers for the two users such that the minimum Euclidean distance between elements of the received sum‐constellation is maximised subject to the power constraints on the users. A thorough consideration of all the different conditions results in the derivation of a closed‐form optimal beamformer design. As well, examination of the construction of sum‐constellation resulted from the optimum design directly leads to the unique decoding of the original transmitted signal of each user. To facilitate practical implementation, a fast decoding procedure of the optimum NOMA scheme is further developed. The corresponding theoretic probability of ML detection error is also derived. The theoretical development of an optimum sum‐constellation for the basic 2‐user 4‐QAM system provides a solid platform for the derivation of an optimum sum‐constellation for a K‐user and/or M‐QAM system. Indeed, a simple development of the basic sum‐constellation map facilitates such extensions. Numerical simulations not only demonstrate that the performance of the fast decoder agrees closely with the theoretical analysis, but also verify that it is superior in performance to other existing NOMA designs for the same system under high signal‐to‐noise ratio. [ABSTRACT FROM AUTHOR]

Summary: Non‐orthogonal multiple access (NOMA) is a technique to improve spectral efficiency. Based on the constellation relationship (CR) between the superposition‐coded signal and individual user's signals, in the literature, a simple detection scheme threshold‐based signal detection has been proposed for the two‐user downlink NOMA (DL‐NOMA) system with specific power allocations, not arbitrary power allocation. Furthermore, the average symbol error probability (ASEP) with squared M‐ary quadrature amplitude modulation for two‐user DL‐NOMA systems has also been derived based on this CR. Based on the threshold‐based signal detection for the two‐user DL‐NOMA systems with specific power allocation, in this paper, a generalized threshold‐based signal detection is proposed for all users in the multiuser DL‐NOMA systems with arbitrary power allocation, and then a fast generalized threshold‐based signal detection is further proposed. The generalized ASEP for each individual user in the multiuser DL‐NOMA system is further derived in Rayleigh fading channels. Both theoretical ASEP and simulated symbol error rate results validate the fast generalized threshold‐based signal detection scheme and the generalized ASEP for multiuser DL‐NOMA systems with arbitrary power allocations. [ABSTRACT FROM AUTHOR]

Summary: In the Massive MIMO system, complexity reduction acts as a significant role. This problem is focused in previous method whose foremost objective is to attain the low complexity. The main goal of this algorithm is to process the signal vector with more maximum likelihood cost instead of handling every signals vector, which might lead to more iteration. This is done by introducing different heuristic algorithms which attempts to find the signal vectors with more maximum likelihood values. The algorithms introduced in the existing work are QP detector and the Branch and Bound algorithm. The existing work still poses more complexity by taking more number of iterations for finding the more relative signal vector. These problems are resolved in the proposed system by introducing the novel framework, namely, pruning‐based maximum likelihood detection using low complexity detection algorithms (PRUN‐MLD‐LCDA). In the proposed system, complexity of the system is further reduced by introducing the cross correlation based pruning technique which attempts to find the similar signal, which is similar based on more signal components. The modified branch and bound algorithm is introduced to perform low complexity detection for the different QAM modulation techniques. The overall evaluation of the proposed research work is done in the Matlab simulation environment from which it is proved that the proposed research method leads to provide better result than the existing research methods. [ABSTRACT FROM AUTHOR]

Recently, multiple‐input multiple‐output (MIMO) is studied actively such as a key technology for wireless communications. Space division (SD) multiplexing and spatial modulation (SM) have been proposed as the transmission technique of MIMO systems. In the full maximum likelihood detection (MLD), the QR decomposition with M‐algorithm MLD (QRM‐MLD), and the channel ranking QRM‐MLD (CR‐QRM‐MLD) for the SD‐MIMO, there are the trade‐off between the system performance and the computational complexity. Also, in the SM‐MIMO, the transmission rate is deteriorated due to a small number of transmitted signals. To solve these problems, in this article, we propose the CR‐QRM‐MLD for SD‐SM Hybrid MIMO (SD‐SM‐MIMO) systems. From the computer simulation results, the proposed method shows the reduction of the computational complexity and the good bit error rate performance. [ABSTRACT FROM AUTHOR]

Ochthebiinae, with c. 650 species distributed worldwide, are the second most speciose subfamily of the aquatic beetle family Hydraenidae. They are ecologically the most diverse hydraenid subfamily, with terrestrial species as well as species in almost all types of aquatic habitats, including hypersaline waters. Ochthebiinae include the tribes Ochtheosini (four species in three genera) and Ochthebiini. We provide here the first comprehensive phylogeny of the tribe Ochthebiini, based on 186 species and four subspecies from most genera, subgenera and species groups. We obtained sequence data for a combination of mitochondrial and nuclear gene fragments including the 5′ and 3′ ends of the cytochrome c oxidase subunit 1, the 5′ end of 16S RNA plus the leucine tRNA transfer plus 5′ end of NADH dehydrogenase subunit I, and internal fragments of the large and small ribosomal units. The analyses with maximum likelihood (ML) and Bayesian probabilities consistently recovered a generally well supported phylogeny, with most currently accepted taxa and species groups as monophyletic. We provide a new classification of the tribe based on our phylogenetic results, with six genera: Meropathus Enderlein, Ochthebius Leach, Protochthebius Perkins, Prototympanogaster Perkins, Tympallopatrum Perkins and Tympanogaster Janssens. The genus Ochthebius is here divided into nine subgenera in addition to Ochthebius s.s.: (1) O. (Angiochthebius) Jäch & Ribera; (2) O. (Asiobates) Thomson; (3) O. (Aulacochthebius) Kuwert; (4) O. (Cobalius) Rey; (5) O. (Enicocerus) Stephens; (6) O. (Gymnanthelius) Perkins comb.n.; (7) O. (Gymnochthebius) Orchymont; (8) O. (Hughleechia) Perkins comb.n.; and (9) O. (Micragasma) Sahlberg. Within Ochthebius s.s., 17 species groups are proposed, five of them newly established (3, 9, 11, 13 and 16): (1) andraei; (2) atriceps; (3) corrugatus; (4) foveolatus; (5) kosiensis; (6) lobicollis; (7) marinus; (8) metallescens; (9) nitidipennis; (10) notabilis; (11) peisonis; (12) punctatus; (13) quadricollis; (14) rivalis; (15) strigosus; (16) sumatrensis; and (17) vandykei. We elevated to species rank two subspecies of Ochthebius: O. fallaciosus Ganglbauer stat.n. (former subspecies of O. viridis Peyron) and O. deletus Rey stat.rest. (former subspecies of O. subpictus Wollaston). A phylogeny of Ochthebiini (Coleoptera, Hydraenidae), with c. 200 species and a combination of nuclear and mitochondrial markers.Ochthebiini has two sister lineages: the Australian genera Meropathus, Prototympanogaster, Tympanogaster and Tympallopatrum; and the cosmopolitan genus Ochthebius s.l., plus the genus Protochthebius, of uncertain phylogenetic placement.Ochthebius s.l. is divided into ten subgenera, with Ochthebius s.s., the most speciose, divided in 17 species groups, most of them in good agreement with current taxonomy. [ABSTRACT FROM AUTHOR]

In this study, the authors address the spreading sequence estimation in direct‐sequence spread‐spectrum signals. At first, the maximum‐likelihood (ML) estimator is derived. In order to alleviate the greater computational complexity of the ML estimator, an innovative algorithm based on the ML method is proposed. The authors' proposed algorithm uses an initial estimation with low complexity and low estimation accuracy as a result. In the second step, the estimation accuracy increases using the ML decision rule. They analyse their proposed algorithm and they derive an analytical approximation for the error probability of the proposed suboptimal algorithm. Simulation and analytical results show great performance and acceptable complexity of the proposed method. [ABSTRACT FROM AUTHOR]

This study presents a framework of the unitary space time modulation (USTM) constellation based on antipodal points over Grassmannian manifold. The antipodal constellation enables an intrinsic simplified ML detecting algorithm. The algebraic orthogonal USTM constellation is also an antipodal constellation which, apart from being adaptive to the antipodal simplified ML detector, also has another simplified ML detector based on its self-indexing features, and the latter is simpler because of getting rid of the matrix operation. A searching orthogonal USTM constellation based on the grid search algorithm is obtained under the presented framework and its minimum Frobenius chordal distance and simulation performance are be superior to those of the algebraic orthogonal USTM constellation. [ABSTRACT FROM AUTHOR]

Generalised space shift keying (GSSK) technique proposed for massive multi‐input–multi‐output systems has a higher information transmission rate due to the activation of multiple antennas at the same time, and also has significant advantage in terms of hardware cost. However, the maximum likelihood detector has a very high complexity which makes it computationally intractable for large‐scale GSSK systems. In this Letter, a sparse detector is proposed by exploiting the inherent property of sparsity in GSSK. Different from the existing compressed sensing (CS)‐based detectors, the proposed detector utilises Euclidean distance instead of inner product operation for antenna matching. Moreover, it can remove erroneous antenna indices by backtracking to promote the detection performance. The simulation results show that the proposed scheme outperforms the existing CS‐based detectors while maintaining low complexity. [ABSTRACT FROM AUTHOR]

Generalized spatial modulation (GSM) is a spectral and energy efficient multiple-input multiple-output (MIMO) transmission scheme. It will lead to imperfect detection performance with relatively high computational complexity by directly applying the original QR-decomposition with M algorithm (QRD-M) to the GSM scheme. In this paper an improved QRD-M algorithm is proposed for GSM signal detection, which achieves near-optimal performance but with relatively low complexity. Based on the QRD, the improved algorithm firstly transforms the maximum likelihood (ML) detection of the GSM signals into searching an inverted tree structure. Then, in the searching process of the M branches, the branches corresponding to the illegitimate transmit antenna combinations (TACs) and related to invalid number of active antennas are cut in order to improve the validity of the resultant branches at each level by taking advantage of characteristics of GSM signals. Simulation results show that the improved QRD-M detection algorithm provides similar performance to maximum likelihood (ML) with the reduced computational complexity compared to the original QRD-M algorithm, and the optimal value of parameter M of the improved QRD-M algorithm for detection of the GSM scheme is equal to modulation order plus one. [ABSTRACT FROM AUTHOR]

The US Federal Communications Commission (FCC) has mandated wireless network operators and mobile devices to provide accurate location information for E-911. Requirements for time of arrival (TOA) and time difference of arrival (TDOA) measurements have been specified in 3GPP LTE Rel. 9 to ensure accurate user equipment (UE) positioning even under bad conditions (e.g. with channel quickly varying and SNR being as low as −13 dB). To fulfil these requirements, it is vital to accurately estimate the first signal arriving path. In this work, we first derive - without any approximation - the Cramér-Rao lower bound (CRLB) of the LTE TOA and TDOA measurements based on the different pilots, which is shown to be as low as a few metres for SNR = −13 dB. The achievable performance of the LTE system is compared with the FCC and 3GPP requirements, and the impact of mobile multipath channels on the measurements is analysed. Then, we describe practical low-complexity methods for LTE TOA and TDOA measurements with enhanced first arriving path detection. The maximum likelihood based correlation profile is used as detection metric. After grossly determining the signal region by a moving window, three methods, namely, peak detection, SNR-based threshold and adaptive threshold based on noise floor and metric peak value are employed to estimate the first arriving path. Simulation results show that the proposed adaptive threshold-based method can meet all 3GPP requirements under various realistic mobile channels, and can in some cases achieve a performance close to the CRLB. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In massive multiple‐input multiple‐output (MIMO) systems with hundreds of antennas at the base station (BS) and few users with a single transmitter antenna, linear detectors, such as zero‐forcing (ZF), achieve near‐optimum performance due to the property of asymptotically orthogonal channel matrix. However, how far away is ZF from the optimum performance. To answer this question, in this Letter, closed‐form bit error rate (BER) expressions are derived. These BER expressions are subsequently used to evaluate the performance difference between ZF and the optimum detector, which is a function of the number of antennas at the BS and the number of users. Numerical results verify the tightness of the performance difference. [ABSTRACT FROM AUTHOR]

Quadrature spatial modulation (QSM) is one of the recently emerging transmission schemes to improve the throughput of the multi‐input multi‐output systems. QSM transmits an M‐ary complex symbol whose real and imaginary parts activate an antenna index independently thus provides an extra spatial dimension compared to conventional spatial modulation (SM). A generalised QSM (GQSM) transmission is considered in which a set of M‐ary complex symbols activate multiple antennas to transmit their real and imaginary parts separately, which offers higher throughput in terms of bits per channel use (bpcu) than other SM techniques. A detector is proposed, ordering‐based structured orthogonal matching pursuit for GQSM using compressive sensing (CS), which performs very close to the maximum likelihood detector with significantly lesser complexity. Also, the proposed algorithm performs superior to other CS‐based detectors and offers a better trade‐off between complexity and performance. [ABSTRACT FROM AUTHOR]

This paper presents a low-complexity channel-adaptive reconfigurable 4 x 4 QR-decomposition and M-algorithm-based maximum likelihood detection (QRM-MLD) multiple-input and multiple-output (MIMO) detector. Two novel design approaches for low-power QRM-MLD hardware are proposed in this work. First, an approximate survivor metric (ASM) generation technique is presented to achieve considerable computational complexity reduction with minor BER degradation. A reconfigurable QRM-MLD MIMO detector (where the M-value represents the number of survival branches in a stage) for dynamically adapting to time-varying channels is also proposed in this work. The proposed reconfigurable QRM-MLD MIMO detector is implemented using a Samsung 65 nm CMOS process. The experimental results show that our ASM-based QRM-MLD MIMO detector shows a maximum throughput of 288 Mbps with a normalized power efficiency of 10.18 Mbps/mW in the case of 4 x 4 MIMO with 64-QAM. Under time-varying channel conditions, the proposed reconfigurable MIMO detector also achieves average power savings of up to 35% while maintaining a required BER performance. [ABSTRACT FROM AUTHOR]

Multipath effect is the main factor of deteriorating target detection performance in low grazing angle scenario, which results from reflections on the ground/sea surface. Amplitudes of the received signals fluctuate acutely due to the random phase variations of reflected signals along different paths; thereby the performances of target detection and tracking are heavily influenced. This paper deals with target detection in low grazing angle scenario with orthogonal frequency division multiplexing (OFDM) radar. Realistic physical and statistical effects are incorporated into the multipath propagation model. By taking advantage of multipath propagation that provides spatial diversity of radar system and frequency diversity of OFDM waveform, we derive a detection method based on generalized likelihood ratio test (GLRT). Then, we propose an algorithm to optimally design the transmitted subcarrier weights to improve the detection performance. Simulation results show that the detection performance can be improved due to the multipath effect and adaptive OFDM waveform design. [ABSTRACT FROM AUTHOR]

To achieve more high-speed communication systems, multiple-input multiple-output orthogonal frequency division multiplexing (MIMO/OFDM) is adopted in several standardisations. On the other hand, the conventional MIMO/OFDM requires many pilot signals to estimate the channel state information (CSI). To achieve an accurate CSI with the small number of pilot signals, high time resolution carrier interferometry (HTRCI) for MIMO/OFDM has been proposed. Moreover, QR decomposition with M-algorithm maximum likelihood detection (QRM-MLD) and channel ranking has been proposed to achieve both the reducing complexity and the improving system performance. However, the conventional HTRCI-MIMO/OFDM with the QRM-MLD and channel ranking did not consider the problem of the fast fading channel. In the fast fading environment, many errors are caused in the last part of the packet. To overcome this problem, the decision-direct method has been proposed. However, it requires large complexity because of the iterative processing. Therefore, in this paper, we propose the non-linear prediction method for an HTRCI-MIMO/OFDM with the QRM-MLD and channel ranking. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A generalised transmit–receive joint spatial modulation (GTRSM) scheme is proposed, which amalgamates both transmitter‐ and receiver‐side spatial modulation (SM) schemes. The proposed GTRSM jointly employs the combinations of multiple instead of a single activated transmit and receive antennas and baseband symbols to transmit information. The optimal maximum‐likelihood detector for GTRSM is formulated, and the channel capacity of GTRSM is also analysed. Simulated results demonstrate that the proposed GTRSM behaves good BER performance and can significantly improve the channel capacity compared with conventional SMs. [ABSTRACT FROM AUTHOR]

A novel adaptive beamforming (BF) receiver is proposed for a multiple-input-multiple-output communication system over multipath fading channels. By dividing a large number of receive antennas into many adaptive beamformers (ABFs), the proposed system reduces the array dimension in order to simplify the signal detection process and enjoys the benefit of BF techniques to improve the symbol-error-rate (SER) performance. The effectiveness of the proposed system depends on the number of ABFs and the number of antennas per ABF. The statistical properties of complex Wishart matrices are applied to analyse the SER performance of the proposed system with both maximum-likelihood (ML) detection and zero-forcing detection. Furthermore, the authors have derived an upper bound for SER of the ML detection based on the smallest eigenvalue distribution. Through the authors analysis, it has been shown that the proposed system using ML detection provides comparable SER performance, but with a lower complexity as compared with that of a conventional ML receiver because of reduced array dimensions. [ABSTRACT FROM AUTHOR]

SUMMARY In cognitive radio networks based on orthogonal frequency division multiplexing, the subcarrier mapping-induced cyclostationary signatures are utilized for robust network coordination. However, the effect of network coordination depends on the reliable detection of such cyclostationary signatures. Moreover, doubly selective fading increases the difficulty of reliable detection. In this paper, we first derive an exact covariance matrix to characterize the statistics of the cyclostationary signatures induced by subcarrier mapping. Using the exact covariance matrix rather than its estimation adopted in conventional algorithms, we propose an asymptotically maximum likelihood detection algorithm. The detection performance of the proposed asymptotically maximum likelihood detection algorithm is analyzed and evaluated both in flat fading and doubly selective fading channels. Simulation results show that the proposed algorithm outperforms the conventional low-complexity single-cycle signature detection algorithm in terms of less observation period or smaller mapping set size. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study presents a robust image watermarking method based on geometric modelling. In this method, nine samples of the approximation coefficient of the image blocks are utilised to construct a plane in the three‐dimensional (3D) space. The authors change the dihedral angle formed between the created plane and the x–y plane for data embedding. To preserve the imperceptibility of the watermark, geometrical computations are used to minimise the embedding distortion. Maximum‐likelihood detector is implemented to extract the watermark in the noisy channel at the receiver side. The authors experimentally determine the probability density function of the embedding dihedral angle for Gaussian samples. Owing to embedding in the dihedral angle between two planes, the proposed scheme has high robustness to gain attacks. In addition, by using the low‐frequency components of the image blocks for data embedding, high robustness against noise and compression attacks has been achieved. Experimental results confirm the validity of the theoretical analysis given in this study and show the superiority of the method over similar techniques in this field. The proposed method is also robust to a wide range of attacks, namely Gaussian filtering, median filtering, JPEG compression, Gaussian noise and scaling. [ABSTRACT FROM AUTHOR]

The authors use stochastic resonance (SR) for binary signal detection in the presence of a special type of Gaussian mixture noise. This type of noise naturally exists in signal detection problems in a channel with an interferer, and consequently, the investigations are beneficial for analysing the interferer suppression capability of the linear SR‐based detectors. The authors demonstrate analytically that the region where SR‐based detectors outperform the matched filter (MF) detector coincides with the region where the maximum likelihood (ML) detector outperforms the MF detector. An analytical expression is also obtained for error probability performance of the optimal SR‐based detector and ML detector in an interferer channel. [ABSTRACT FROM AUTHOR]

The paper discusses a sequence detector based on univariate marginal distribution algorithm (UMDA) that jointly estimates the symbols transmitted in a multiple input multiple output (MIMO) communication system. While an optimal maximum likelihood detection using an exhaustive search method is prohibitively complex, it has been shown that sphere decoder (SD) achieves the optimal bit error rate (BER) performance with polynomial time complexity for smaller array sizes. However, the worst-case complexity of SD is exponential in the problem dimensions, this brings in question its practical implementation for larger number of spatial layers and for higher-order signal constellation. The proposed detector shows promising results for this overly difficult and complicated operating environment, confirmed through simulation results. A performance comparison of the UMDA detector with SD is presented for higher-order complex MIMO architectures with limited average transmit power. The proposed detector achieves substantial performance gain for higher-order systems attaining a near optimal BER performance with reduced computational complexity as compared with SD. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Quadrature spatial modulation (QSM) is a recently proposed multiple‐input multiple‐output transmission scheme which improves the spectral efficiency of classical spatial modulation (SM) by increasing the number of information bits transmitted by antenna indices. In QSM, a complex data symbol is decomposed into its real and imaginary components; then, these two components are independently transmitted using the SM principle. A low‐complexity, near‐maximum likelihood (ML) error performance achieving detection scheme is proposed for QSM to reduce the overall computational complexity of the ML detector. First, the proposed detector determines the set of most probable active transmit antennas and the corresponding possible transmission patterns. Then, ML‐based detection is used to determine the transmitted complex data vector by performing a search over these transmission patterns and M‐ary constellation symbols. It has been shown via computer simulations that the proposed detection algorithm exhibits near‐ML bit error rate performance with considerably lower decoding complexity. [ABSTRACT FROM AUTHOR]

Considering the effects of primary user traffic, timing misalignment and multiple arrival and departure issues in a sensing period should be addressed for spectrum sensing in future overlay cognitive radio (CR) networks, such as femtocell networks. To achieve this goal, division of the whole sensing duration into multiple windows is proposed. For each window, a two‐step detection scheme, i.e. coarse and fine detection, is proposed to improve the performance of the conventional energy detector (ED) in the overlay CR scenario. [ABSTRACT FROM AUTHOR]

A novel M‐algorithm‐based detection method called M‐algorithm to maximum likelihood (M–ML) is proposed for spatial modulation. The proposed algorithm has fixed complexity and reduces complexity by using a parallel structure to limit the search space of an optimum decoder. The simulation results show that by carefully choosing proper values of M, the new algorithm can reduce the computational complexity significantly while maintaining a near‐optimum bit error rate performance. [ABSTRACT FROM AUTHOR]

Generalised space shift keying (GSSK) technique proposed for massive multi-input-multi-output systems has a higher information transmission rate due to the activation of multiple antennas at the same time, and also has significant advantage in terms of hardware cost. However, the maximum likelihood detector has a very high complexity which makes it computationally intractable for largescale GSSK systems. In this Letter, a sparse detector is proposed by exploiting the inherent property of sparsity in GSSK. Different from the existing compressed sensing (CS)-based detectors, the proposed detector utilises Euclidean distance instead of inner product operation for antenna matching. Moreover, it can remove erroneous antenna indices by backtracking to promote the detection performance. The simulation results show that the proposed scheme outperforms the existing CS-based detectors while maintaining low complexity. [ABSTRACT FROM AUTHOR]

A generalised transmit-receive joint spatial modulation (GTRSM) scheme is proposed, which amalgamates both transmitter- and receiver-side spatial modulation (SM) schemes. The proposed GTRSM jointly employs the combinations of multiple instead of a single activated transmit and receive antennas and baseband symbols to transmit information. The optimal maximum-likelihood detector for GTRSM is formulated, and the channel capacity of GTRSM is also analysed. Simulated results demonstrate that the proposed GTRSM behaves good BER performance and can significantly improve the channel capacity compared with conventional SMs. [ABSTRACT FROM AUTHOR]

Summary: The Alamouti space‐time block code (STBC) achieves full diversity gain at a rate of 1/2. However, the Alamouti scheme does not provide multiplexing gain. The Silver code offers both diversity and multiplexing gain. It has a minimum normalization determinant of 1/7. The Golden code is another STBC that offers both diversity and multiplexing gain. The Golden code is ranked higher than the Silver code because of its lower minimum normalization determinant of 1/5, however, the golden code suffers from a high detection complexity in the modulation order of M4. The 3/4‐Sezginer code is another STBC, which compromises between the Alamouti scheme and the Golden code in terms of diversity gain and multiplexing gain. The 3/4‐Sezginer code achieves full diversity and half of multiplexing gain. The uncoded space‐time labeling diversity (USTLD) is a recent scheme that improves the error performance when applied to the STBC in multiple‐input multiple‐output (MIMO) systems and will be applied to the 3/4‐Sezginer STBC to improve the error performance in this paper. The theoretical error probability for both the 3/4‐Sezginer STBC and the improved system is formulated using the union bound in this paper. The theoretical error probabilities of both 16‐QAM and 64‐QAM are validated through Monte Carlo simulation. The simulation and theoretical results show that the proposed system with 4 NR can achieve an SNR gain of 1 dB for 16‐QAM and 1.2 dB 64‐QAM at a bit error rate (BER) of 10−6. [ABSTRACT FROM AUTHOR]

Summary: The Golden code has full rate and full diversity. The Golden codeword matrix contains two pairs of super symbols. Based on one pair of super symbols, two modulation schemes, Golden codeword–based M‐ary quadrature amplitude modulation (GC‐MQAM) and component‐interleaved GC‐MQAM (CI‐GC‐MQAM), are proposed for single‐input multiple‐output (SIMO) systems. Since the complexities of the maximum likelihood detection for the proposed GC‐MQAM and CI‐GC‐MQAM are proportional to O(M2) and O(M4), respectively, low complexity detection schemes for the proposed GC‐MQAM and CI‐GC‐MQAM are further proposed. In addition, the theoretical average bit error probabilities (ABEPs) for the proposed GC‐MQAM and CI‐GC‐MQAM are derived. The derived ABEPs are validated through Monte Carlo simulations. Simulation and theoretical results show that the proposed GC‐MQAM can achieve the error performance of signal space diversity. Simulation and theoretical results further show that the proposed CI‐GC‐16QAM, ‐64QAM, and ‐256QAM with three receive antennas can achieve approximately 2.2, 2.0, and 2.1 dB gain at a bit error rate of 4 × 10−6 compared with GC‐16QAM, ‐64QAM, and ‐256QAM, respectively. [ABSTRACT FROM AUTHOR]

A low-complexity method for symbol detection in multiple-input multiple-output communication systems with spatial modulation is proposed. The proposed method finds a solution by performing beam search, where the beam search algorithm is modified to apply an additional branch-and-bound technique in order to reduce the search space. Simulation results show that the proposed method achieves a near-optimal bit error rate, and its complexity is much lower than that of previous methods. [ABSTRACT FROM AUTHOR]

A QR decomposition aided belief propagation (QR‐BP) detector for multiple‐input multiple‐output (MIMO) systems is proposed. Before the iterative message passing process, linear transformation is performed by using the unitary matrix obtained from the QR decomposition of the original MIMO channel matrix. Then, the original MIMO channel matrix is replaced by an upper triangular channel matrix after the linear transformation and the proposed QR‐BP detector operates over the new bipartite graph from the upper triangular channel matrix. Therefore, the number of cycles in the new bipartite graph is significantly decreased when compared with the fully connected bipartite graph from the original MIMO channel matrix. In addition, since the unitary matrix is utilised for the linear transformation, there is no information loss on the likelihoods estimated from noisy observations. Simulation results verify that the proposed QR‐BP detector outperforms existing BP detectors and achieves near‐optimum performance close to the maximum‐likelihood detector in terms of bit error ratio. [ABSTRACT FROM AUTHOR]

Proposed is a simplified branch metric calculation method for the (quasi‐)maximum‐likelihood (ML) detector for square quadrature amplitude modulation (S‐QAM) aided multiple‐input and multiple‐output (MIMO) multiplexing systems while retaining identical performance to the respective one. The key idea of the proposed method is to exploit the geometric property of the S‐QAM constellation, so that the branch metric calculation for all the constellation points can be calculated in an incremental way from any constellation point mainly through addition and bit‐shift, thus significantly reducing the computational complexity of the ML detector. [ABSTRACT FROM AUTHOR]