Partial Channel Research Articles

Linear-Complexity ADMM Updates for Decoding LDPC Codes in Partial Response Channels

This letter investigates the application of alternating direction method of multipliers (ADMM) in decoding low-density parity-check (LDPC) codes over partial response (PR) channels. Unlike the ADMM decoding in memoryless channels, the ADMM decoding in PR channels becomes involved with the correlation among adjacent code symbols. As the update equations for code symbols constitute the most complicated part of the ADMM decoding in PR channels, this letter focuses on their derivation by making use of the iterative fashion of ADMM and incorporating the use of a penalty function. A notable advantage of the proposed ADMM penalized decoding algorithm is that its complexity increases linearly with the memory length of PR channels. Simulation results show that the proposed algorithm can achieve error performance comparable with that of Turbo equalization (TE) in the waterfall region. It can also outperform TE at high signal-to-noise ratios as iteration grows.

On the Optimal CSI Feedback Rate of Downlink MIMO Systems Using Multiple Receive Antennas in Cellular Networks

A downlink cellular network is considered, in which multiple-antenna base stations (BSs) are distributed following a homogeneous Poisson point process. Each BS serves a single user equipped with multiple-receive antennas. The partial channel state information is achieved at the transmitter using a limited feedback. The singular-value-decomposition-based precoding is performed for the downlink spatial multiplexing. In this letter, the optimal number of feedback bits that maximizes the net spectral efficiency is investigated. The net spectral efficiency is defined to measure the net profit achieved by using limited-feedback-based spatial multiplexing. By extending previous studies, the effect of using multiple-receive antennas on the optimal number is investigated. Specifically, the scaling rate of the optimal number is newly obtained for more than one receive antenna.

Resource allocation for secure Gaussian parallel relay channels with finite-length coding and discrete constellations

We investigate the transmission of a secret message from Alice to Bob in the presence of an eavesdropper (Eve) and many of decode-and-forward relay nodes. Each link comprises a set of parallel channels, modeling for example an orthogonal frequency division multiplexing transmission. We consider the impact of efficient implementations, including discrete constellations and finite-length coding, defining an achievable secrecy rate under a constraint on the equivocation rate at Eve. Then, we propose a power and channel allocation algorithm that maximizes the achievable secrecy rate by resorting to two coupled Gale-Shapley algorithms for stable matching problem. We consider the scenarios of both full and partial channel state information at Alice. In the latter case, we only guarantee an outage secrecy rate, i.e., the rate of a message that remains secret with a given probability. Numerical results are provided for Rayleigh fading channels in terms of average outage secrecy rate, showing that practical schemes achieve a performance quite close to that of ideal ones.

Fourth-order direction finding in antenna arrays with partial channel gain/phase calibration

In this paper, we consider the problem of direction finding in partly calibrated uniform linear array (ULA) system with channel gain/phase mismatch, by taking advantage of the high-order statistics (HOS) of the array observations. In particular, we devise a (2M−1)×(2M−1) fourth-order cumulant (FOC) matrix for an M-element ULA and exploit it to estimate the directions-of-arrival (DOAs) with subspace techniques. The proposed FOC direction finding method is computationally attractive without spatial spectrum search and robust against spatially correlated noise. It is also able to achieve better DOA estimation performance than the existing method, as illustrated by numerical simulations.

Buffer-aided relay selection for secure two-hop wireless networks with decode-and-forward relays and a diversity-combining eavesdropper

This paper investigates the buffer-aided relay selection issue for achieving physical layer security (PLS) in two-hop wireless networks with Decode-and-Forward (DF) relays. Available works mainly focus on scenarios with independent-decoding eavesdroppers. However, the more hazardous scenarios with diversity-combining eavesdroppers that combine the signals in two hops to decode the packets are largely ignored. This paper considers a two-hop wireless network with multiple DF relays and one diversity-combining eavesdropper under two cases with perfect and partial eavesdropper channel state information (CSI) respectively. We first propose two secure buffer-aided relay selection schemes to suppress the eavesdropper for both eavesdropper CSI cases respectively. We then derive analytical expressions for the end-to-end (E2E) secure transmission probability (STP) and E2E delay of the network. Finally, we provide extensive simulation and numerical results to validate the correctness of the expressions and also to investigate the E2E STP and E2E delay performances. The results showed that the proposed schemes can achieve better E2E STP performance than the well-known Max-ratio buffer-aided relay selection scheme but at the cost of an increased E2E delay.

Whittle index approach to opportunistic scheduling with partial channel information

Opportunistic scheduling in wireless cellular systems utilizes random channel quality variations in time by favoring the users with good channel conditions. However, the success of such schedulers is heavily depending on the accuracy of the available information on the channel states of users. In this paper, we consider the opportunistic scheduling problem of downlink data traffic with partial channel information, where the target is to minimize the flow-level holding costs. In earlier works, the Whittle index approach has successfully been utilized to develop near-optimal scheduling policies for the corresponding problems, however, typically with exact channel information. Using the same approach, we complement and extend the results found thus far. More specifically said, our novel contributions are (i) proving that the flow-level opportunistic scheduling problem with partial channel information is indexable at least in certain parts of the parameter space; (ii) deriving an explicit formula for the corresponding Whittle index; (iii) proving that, in these parts of the parameter space, the optimal policy for the relaxed optimization problem is of threshold type; and (iv) demonstrating that, in the remaining parts of the parameter space, it is possible that the optimal policy for the relaxed problem is not of threshold type. In addition, we evaluate the performance of the derived Whittle index policies and compare them with some greedy policies by numerical simulations.

Energy-Efficiency Optimization for IoT-Distributed Antenna Systems With SWIPT Over Composite Fading Channels

Due to the requirement of low-power network devices for the proliferation of high data communication, enabling technologies for energy sustainable Internet of Things (IoT) are of great significance. In this article, we investigate the energy-efficiency (EE) optimization of IoT-distributed antenna (DA) system with simultaneous wireless information and power transfer (SWIPT) technique over fading channels, where the IoT device is equipped with power splitter to integrate the energy harvesting and information decoding processes via adjusting the transmit power of each DA port and power splitting (PS) ratio of IoT device. According to the analysis of EE, an optimization problem with the aim of maximizing the system EE is formulated under the constraints of maximum transmit power of each DA port as well as minimum harvested energy. Through analyzing the structure of the objective problem, it is found that the EE optimization problem, which combines transmit power allocation (PA) with PS problem, can be predigested to a PA problem. Then, the amount of valid DA ports and the corresponding PA are achieved by utilizing the Karush–Kuhn–Tucker conditions and Lambert function. Based on this, we propose an optimal resource allocation scheme without iteration to obtain the optimal PA and PS ratio, and the resulting closed-form expressions are provided. Considering that perfect channel state information (CSI) is hard to achieve, we also study the resource allocation scheme based on the imperfect CSI (i.e., statistical CSI with large-scale fading information), two suboptimal schemes are proposed. These two schemes have better robustness and lower complexity than the optimal scheme with perfect CSI because they only need partial channel information, but the performances are worse than the latter, as expected. Computer simulation indicates that proposed schemes are valid and can obtain superior EE performance with lower complexity.

Multi-Stream Opportunistic Network Decoupling: Relay Selection and Interference Management

We study multi-stream transmission in the $K \times N \times K$ channel with interfering relay nodes, consisting of $K$ multi-antenna source--destination (S--D) pairs and $N$ single-antenna half-duplex relay nodes between the S--D pairs. We propose a new achievable scheme operating with partial effective channel gain, termed multi-stream opportunistic network decoupling (MS-OND), which achieves the optimal degrees of freedom (DoF) under a certain relay scaling law. Our protocol is built upon the conventional OND that leads to virtual full-duplex mode with one data stream transmission per S--D pair, generalizing the idea of OND to multi-stream scenarios by leveraging relay selection and interference management. Specifically, two subsets of relay nodes are opportunistically selected using alternate relaying in terms of producing or receiving the minimum total interference level. For interference management, each source node sends $S \,(1 \le S \le M)$ data streams to selected relay nodes with random beamforming for the first hop, while each destination node receives its desired $S$ streams from the selected relay nodes via opportunistic interference alignment for the second hop, where $M$ is the number of antennas at each source or destination node. Our analytical results are validated by numerical evaluation.

A New Lower Bound Based Secure Beamforming in MISO Communication Networks

This letter considers a multiple-input single-output network that consists of a base station, multiple legitimate user equipments, and an eavesdropper. A new expression is developed to lower-bound the achievable rates of the legitimate user equipments. Applying this new lower bound, we optimize the beamforming design at the base station to maximize the system performance in terms of the minimum secrecy rate and the secure energy efficiency. We consider both scenarios with perfect and partial channel state information for the eavesdropper. Iterative algorithms with low computational complexity and fast convergence are proposed to solve these non-convex optimization problems. The validity and convergence are demonstrated by simulation results.

Generalized Degrees of Freedom of the Symmetric Cache-Aided MISO Broadcast Channel With Partial CSIT

We consider the cache-aided MISO broadcast channel (BC) in which a multi-antenna transmitter serves $K$ single-antenna receivers, each equipped with a cache memory. The transmitter has access to partial knowledge of the channel state information. For a symmetric setting, in terms of channel strength levels, partial channel knowledge levels and cache sizes, we characterize the generalized degrees of freedom (GDoF) up to a constant multiplicative factor. The achievability scheme exploits the interplay between spatial multiplexing gains and coded-multicasting gain. On the other hand, a cut-set-based argument in conjunction with a GDoF outer bound for a parallel MISO BC under channel uncertainty is used for the converse. We further show that the characterized order-optimal GDoF is also attained in a decentralized setting, where no coordination is required for content placement in the caches.

A Low Impact Ionization Rate Poly-Si TFT with a Current and Electric Field Split Design

In this study, a novel low impact ionization rate (low-IIR) poly-Si thin film transistor featuring a current and electric field split (CES) structure with bottom field plate (BFP) and partial thicker channel raised source/drain (RSD) designs is proposed and demonstrated. The bottom field plate design can allure the electron and alter the electron current path to evade the high electric field area and therefore reduce the device IIR and suppress the kink effect. A two-dimensional device simulator was applied to describe and compare the current path, electric field magnitude distributions, and IIR of the proposed structure and conventional devices. In addition, the advantages of a partial thicker channel RSD design are present, and the leakage current of CES-thin-film transistor (TFT) can be reduced and the ON/OFF current ratio be improved, owing to a smaller drain electric field.

Characterization of abamectin resistance in Iranian populations of European red mite, Panonychus ulmi Koch (Acari: Tetranychidae)

The European red mite, Panonychus ulmi Koch is one of the most important pests in apple orchards and was introduced to Iran by apple seedlings from Europe. The insecticide/acaricide abamectin for example has been used extensively against P. ulmi and some other pests in apple orchards. To evaluate abamectin resistance in field-collected populations of P. ulmi, 12 populations were collected from commercial apple orchards of East Azarbaijan, West Azarbaijan, and Isfahan provinces. The abamectin toxicity was determined by a leaf disc spray method. The LC50 values of abamectin ranged from 0.11 mg a. i.L−1 to 5.50 mg a. i.L−1. All field populations were resistant to abamectin (RR ranged from 11- to 46-fold) in comparing with PSR-TK, a reference susceptible population for abamectin. The Mahabad population was identified as the most resistant population. The glutamate-gated chloride channels (GluCls) are well-known target site of abamectin in mites and it was demonstrated that amino acid substitutions in GluCls can confer abamectin resistance. The partial channels PuGluCl1, PuGluCl2, and PuGluCl3 were sequenced in Mahabad population, but the previously reported point mutations associated with abamectin resistance in Tetranychus urticae Koch were not found. In contrast, the cytochrome P450 monooxygenase inhibitor piperonyl butoxide (PBO) significantly increased abamectin toxicity in Mahabad (synergistic ratio SR= 64), a moderately resistant population, and Shahin Dej (SR = 2) population. Also, pretreatment of triphenylphosphate (TPP) resulted in reduced LC50 values of abamectin in Shahin Dej (SR = 4.79) and Mahabad (SR = 8.91) populations. The second highest synergism ratio (SR = 22.13) against abamectin was observed in the resistant population of Mahabad with the glutathione S-transferase inhibitor diethylmaleate (DEM). Although quantification of activity of detoxification enzymes with model substrates did not support the role of detoxification enzymes, the synergism assays and the lack of target-site resistance suggested that multiple metabolic mechanisms are involved in abamectin resistance.

Structural effects of divalent calcium cations on the α7 nicotinic acetylcholine receptor: A molecular dynamics simulation study.

The α7 subtype of neuronal nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel protein that is vital to various neurological functions, including modulation of neurotransmitter release. A relatively high concentration of extracellular Ca2+ in the neuronal environment is likely to exert substantial structural and functional influence on nAChRs, which may affect their interactions with agonists and antagonists. In this work, we employed atomistic molecular dynamics (MD) simulations to examine the effects of elevated Ca2+ on the structure and dynamics of α7 nAChR embedded in a model phospholipid bilayer. Our results suggest that the presence of Ca2+ in the α7 nAChR environment results in closure of loop C-in the extracellular ligand-binding domain, a motion normally associated with agonist binding and receptor activation. Elevated Ca2+ also alters the conformation of key regions of the receptor, including the inter-helical loops, pore-lining helices and the "gate" residues, and causes partial channel opening in the absence of an agonist, leading to an attendant reduction in the free energy of Ca2+ permeation through the pore as elucidated by umbrella sampling simulations. Overall, the structural and permeability changes in α7 nAChR suggest that elevated Ca2+ induces a partially activated receptor state that is distinct from both the resting and the agonist-activated states. These results are consistent with the notion that divalent ions can serve as a potentiator of nAChRs, resulting in a higher rate of receptor activation (and subsequent desensitization) in the presence of agonists, with possible implications for diseases involving calcium dysregulation.

Exploiting Array Pattern Synthesis for Physical Layer Security in Millimeter Wave Channels

In this paper, we propose a beamformer design scheme for wireless physical layer security using partial channel state information (CSI) in millimeter wave channels. The partial CSI used in this work is the range of angle-of-departure (AOD). Assuming that the AOD range of each node is available, we design a transmit beamformer using semidefinite programming based on array pattern synthesis. Numerical results are presented to verify the secrecy rates achieved by the proposed scheme.

NOMA-Aided Multicell Downlink Massive MIMO

Novel user clustering and pilot assignment schemes are proposed for non-orthogonal multiple access (NOMA) aided multicell massive multiple-input multiple-output systems. Our proposed designs leverage the spatial covariance matrices of users, and they are applicable to both overloaded and underloaded cases. Users having linearly dependent covariance matrices are grouped into the same cluster, and they are assigned with orthogonal pilots to mitigate intra-cluster pilot contamination. These pilots are shared among the users in different clusters to reduce the training overhead. Then, the inter-cluster pilot contamination can be mitigated by exploiting asymptotically linearly independent covariance matrices of pilot-sharing users located in different clusters. The achievable downlink rates are derived by capturing the detrimental effects of practical transmission impairments and partial channel knowledge. Our analysis reveals that the user rates are not fundamentally limited by the intra/inter-cluster pilot contamination arising from pilot reuse for the underloaded case. We show that the achievable rate of each user increases without bound under zero-forcing precoding as the number of base-station antennas grows large. However, for the overloaded case, the users, which share the same spatial direction and located within a NOMA cluster, will have to share pilots. Thus, the achievable rate gains must be traded-off to enable massive connectivity. Three transmit power control policies are designed to maximize the sum rate, while achieving max-min user-fairness by mitigating the adverse near-far effect.

NCCC: NC-OFDM-based control channel establishment in cognitive radio networks using subcarrier pulses

In cognitive radio networks (CRN), the secondary users need control channels for negotiating communication parameters and exchanging control messages. Previous studies either preselect a dedicated control channel or find a control channel dynamically using channel-hopping (CH) approaches. However, preselected control channels in the licensed spectrum are unrealistic, and the time it takes for CH-based approaches increases drastically when the number of channels increases. NC-OFDM is a promising technology that can access partial channels and aggregate spectrum fragments. However, forming NC-OFDM-based Control Channel (NCCC) is seldom discussed. Therefore, we propose an efficient approach for guaranteed NCCC establishment by utilizing subcarrier pulses. The results show that the time needed for NCCC is lower than that of CH-based approaches. Additionally, the proposed approach can establish NCCC even if there is no common channel in the CRN. NC-OFDM-based control interfaces improve the control channel establishment rate even if the interfaces can only access the spectrum bandwidth that is equal to one channel.

Performance analysis of receive diversity under time-varying and spatially correlated channels using partial CSI

In this paper, a single input multiple output system is considered with L receive antennas and the underlying channels are assumed to be time varying with temporal correlation coefficient a and spatially correlated with correlation coefficient $$\rho $$ . Further, the channel is assumed to be identically distributed using Rayleigh fading channels and characterized by first order autoregressive model. For the detection, we assume partial channel state information (CSI) available at the receiver. The partial CSI is in the form of a known preamble (one symbol) only before beginning of a frame of size N symbols. Further, the preamble is imperfectly known with a variance of error $$\sigma _e^2$$ . For the assumed system, closed form expressions of symbol error rate (SER) are derived for M-PSK and M-QAM constellations under the compound effect of spatially correlated channels, temporally correlated channels and partial CSI at the Receiver. The derived expressions are functions of average SNR per symbol, $$\rho $$ , a, $$\sigma _e^2$$ , N, L and modulation order M. Further, these expressions are reduced for some special cases and compared with prevailing results in literature. The analytical expressions are also validated by comparing them with the corresponding simulation results. The derived expressions are very useful to select N, L and M to overcome the deterioration in SER due to adverse effects of $$\rho $$ , a and $$\sigma _e^2$$ .

Support Vector Machine-Based Transmit Antenna Allocation for Multiuser Communication Systems.

In this paper, a support vector machine (SVM) technique has been applied to an antenna allocation system with multiple antennas in multiuser downlink communications. Here, only the channel magnitude information is available at the transmitter. Thus, a subset of transmit antennas that can reduce multiuser interference is selected based on such partial channel state information to support multiple users. For training, we generate the feature vectors by fully utilizing the characteristics of the interference-limited setup in the multiuser downlink system and determine the corresponding class label by evaluating a key performance indicator, i.e., sum rate in multiuser communications. Using test channels, we evaluate the performance of our antenna allocation system invoking the SVM-based allocation and optimization-based allocation, in terms of sum-rate performance and computational complexity. Rigorous testing allowed for a comparison of a SVM algorithm design between one-vs-one (OVO) and one-vs-all (OVA) strategies and a kernel function: (i) OVA is preferable to OVO since OVA can achieve almost the same sum rate as OVO with significantly reduced computational complexity, (ii) a Gaussian function is a good choice as the kernel function for the SVM, and (iii) the variance (kernel scale) and penalty parameter (box constraint) of an SVM kernel function are determined by 21.56 and 7.67, respectively. Further simulation results revealed that the designed SVM-based approach can remarkably reduce the time complexity compared to a traditional optimization-based approach, at the cost of marginal sum rate degradation. Our proposed framework offers some important insights for intelligently combining machine learning techniques and multiuser wireless communications.

Brain Complex Network Characteristic Analysis of Fatigue during Simulated Driving Based on Electroencephalogram Signals.

Fatigued driving is one of the major causes of traffic accidents. Frequent repetition of driving behavior for a long time may lead to driver fatigue, which is closely related to the central nervous system. In the present work, we designed a fatigue driving simulation experiment and collected the electroencephalogram (EEG) signals. Complex network theory was introduced to study the evolution of brain dynamics under different rhythms of EEG signals during several periods of the simulated driving. The results show that as the fatigue degree deepened, the functional connectivity and the clustering coefficients increased while the average shortest path length decreased for the delta rhythm. In addition, there was a significant increase of the degree centrality in partial channels on the right side of the brain for the delta rhythm. Therefore, it can be concluded that driving fatigue can cause brain complex network characteristics to change significantly for certain brain regions and certain rhythms. This exploration may provide a theoretical basis for further finding objective and effective indicators to evaluate the degree of driving fatigue and to help avoid fatigue driving.

Interchannel mixing in the K-shell photoionization of CH4

Rearrangement of the electron shells accompanying inner-shell photoionization of the CH4 molecule is studied theoretically. For this purpose, the K-shell photoionization cross section σ1s (ω) and the respective photoelectron angular distribution (PAD) parameter βe1s(ω) are computed in different approximations using the single center method. It is obtained that a strong mixing of the partial ionization channels in the vicinity of the 1s ionization threshold, caused by the the non-spherical part of the molecular potential, results in a qualitative difference between the electronic rearrangement effects in molecules, as compared to atoms.