Interference Exploitation Precoding for Multi-level Modulations

In this paper, we investigate the interference exploitation precoding for multi-level modulations in the downlink multi-antenna systems. We mathematically derive the optimal precoding structures based on the Karush-Kuhn-Tucker (KKT) conditions. Furthermore, by formulating the dual problem, the precoding problem for multi-level modulations can be transformed into a pre-scaling operation using quadratic programming (QP) optimization. Compared to the original second-order cone programming (SOCP) formulation, this transformation that finally leads to a QP optimization allows a considerable complexity reduction. Simulation results validate our derivations on the optimal precoding structure, and demonstrate significant performance improvements for interference exploitation precoding over traditional precoding methods for multi-level modulations

Multiuser Scheduler and FDE Design for SC-FDMA MIMO Systems

This paper presents a novel spatial frequency domain packet scheduling and frequency domain equalization (FDE) algorithm for uplink Single Carrier (SC) Frequency Division Multiple Access (FDMA) multiuser MIMO systems. Our analysis model is confined to 3GPP uplink SC-FDMA transmission with Multi-user (MU) Spatial Division Multiplexing (SDM). The results show that the proposed MU-MIMO scheduler in conjunction with the new FDE singificantly increases the maximum achievable rate and improves the bit error rate (BER) performance for the system under consideration

Interference Exploitation 1-Bit Massive MIMO Precoding: A Partial Branch-and-Bound Solution With Near-Optimal Performance

In this paper, we focus on 1-bit precoding approaches for downlink massive multiple-input multiple-output (MIMO) systems, where we exploit the concept of constructive interference (CI). For both PSK and QAM signaling, we firstly formulate the optimization problem that maximizes the CI effect subject to the requirement of the 1-bit transmit signals. We then mathematically prove that, when employing the CI formulation and relaxing the 1-bit constraint, the majority of the transmit signals already satisfy the 1-bit formulation. Building upon this important observation, we propose a 1-bit precoding approach that further improves the performance of the conventional 1-bit CI precoding via a partial branch-and-bound (P-BB) process, where the BB procedure is performed only for the entries that do not comply with the 1-bit requirement. This operation allows a significant complexity reduction compared to the fully-BB (F-BB) process, and enables the BB framework to be applicable to the complex massive MIMO scenarios. We further develop an alternative 1-bit scheme through an ‘Ordered Partial Sequential Update’ (OPSU) process that allows an additional complexity reduction. Numerical results show that both proposed 1-bit precoding methods exhibit a significant signal-to-noise ratio (SNR) gain for the error rate performance, especially for higher-order modulations

Multiplexing More Data Streams in the MU-MISO Downlink by Interference Exploitation Precoding

In this paper, we focus on the constructive interference (CI) precoding for the scenario when the number of streams simultaneously transmitted by the base station (BS) is larger than that of transmit antennas at the BS, and derive the optimal precoding structure by employing the pseudo inverse. We show that the optimal pre-scaling vector in IE precoding is equal to a linear combination of the right singular vectors that correspond to zero singular values of the coefficient matrix. By formulating the dual problem, we further show that the optimal precoding matrix can be expressed as a function of the dual variables in a closed form, and an equivalent quadratic programming (QP) formulation is derived for computational complexity reduction. Numerical results validate our analysis and demonstrate significant performance improvements for interference exploitation precoding in the considered scenario

Signal Detection in MIMO Systems with Hardware Imperfections: Message Passing on Neural Networks

In this paper, we investigate signal detection in multiple-input-multiple-output (MIMO) communication systems with hardware impairments, such as power amplifier nonlinearity and in-phase/quadrature imbalance. To deal with the complex combined effects of hardware imperfections, neural network (NN) techniques, in particular deep neural networks (DNNs), have been studied to directly compensate for the impact of hardware impairments. However, it is difficult to train a DNN with limited pilot signals, hindering its practical applications. In this work, we investigate how to achieve efficient Bayesian signal detection in MIMO systems with hardware imperfections. Characterizing combined hardware imperfections often leads to complicated signal models, making Bayesian signal detection challenging. To address this issue, we first train an NN to "model" the MIMO system with hardware imperfections and then perform Bayesian inference based on the trained NN. Modelling the MIMO system with NN enables the design of NN architectures based on the signal flow of the MIMO system, minimizing the number of NN layers and parameters, which is crucial to achieving efficient training with limited pilot signals. We then represent the trained NN with a factor graph, and design an efficient message passing based Bayesian signal detector, leveraging the unitary approximate message passing (UAMP) algorithm. The implementation of a turbo receiver with the proposed Bayesian detector is also investigated. Extensive simulation results demonstrate that the proposed technique delivers remarkably better performance than state-of-the-art methods

Ispitivanje neurotoksičnosti analoga fentanila kod pacova

This study aimed at evaluating the neurotoxicity of fentanyl analogs: (+/-)-cis-3-carbomethoxy fentanyl (C) and (+/-)-trans-3-carbomethoxy fentanyl (T) in rats. C and Tare less potent (2.4-3.1 and 8.4-12.3 times, respectively) than fentanyl (F) in producing both antinociception and morphine-like neurotoxic effects: loss of pinna reflex, Straub tail, impairment of motor coordination, catalepsy, loss of corneal reflex and loss of righting reflex. All of the effects tested were dose-dependent and they were abolished by pretreatment with naloxone, nonselective antagonist of opioid receptors, indicating that they are mediated via opioid receptors. Further, F, C and T exhibited similar relative potencies in producing all tested effects, indicating that similar receptors are involved in producing antinociceptive and neurotoxic effects, most probably of mu type. By using equiantinociceptive doses, C and T produced significantly shorter duration of both antinociception and neurotoxicity than F No significant differences between therapeutic indices for F, C and T were found, indicating that these compounds are equally safe and tolerable in respect to the neurotoxic effects tested. Neurotoxicity testing presented in this paper may be useful in studying the structure-activity relationship of opioid congeners.Cilj studije bio je da se ispita neurotoksičnost analoga fentanila: (±)-cis-3-karbometoksi fentanila (C) i (±)-trans-3-karbometoksi fentanil (T) kod pacova. C je oko 2,4-3,1, a T oko 8,4-12,3 puta manje potentan od fentanila u izazivanju antinocicepcije i morfinu-sličnih neurotoksičnih efekata u koje spadaju: refleks ušne školjke, Straub-ov rep, poremećaj motorne koordinacije, katalepsija, gubitak kornealnog refleksa i gubitak refleksa uspravljanja. Svi ispitivani efekti su dozno-zavisni i bivaju poništeni ako se u pretretmanu primeni nalokson, neselektivni antagonist opioidnih receptora, što ukazuje da se efekti odigravaju posredstvom opioidnih receptora. Dalje, F, C i T ispoljavaju sličnu relativnu jačinu u izazivanju ispitivanih efekata, što ukazuje da su slični receptori uključeni u mehanizam antinocicepcije i neurotoksičnih efekata, i to su najverovatnije μ receptori. Kad se primenjuju ekviantinociceptivne doze, C i T izazivaju značajno kraće i antinociceptivno i neurotoksično dejstvo od F. Nisu dokazane značajne razlike u terapijskim indeksima između F, C i T, što ukazuje da su ovi lekovi jednako bezbedni i podnošljivi kad su u pitanju ispitivani neurotoksični efekti. Ispitivanje neurotoksičnosti prikazano u ovom radu može biti korisno u proučavanju odnosa između strukture i aktivnosti hemijski srodnih opioida

Can greater muscularity in larger individuals resolve the 3/4 power-law controversy when modelling maximum oxygen uptake?

BACKGROUND: The power function relationship, MR = a.m(b), between metabolic rate (MR) and body mass m has been the source of much controversy amongst biologists for many years. Various studies have reported mass exponents (b) greater than the anticipated 'surface-area' exponent 0.67, often closer to 0.75 originally identified by Kleiber. AIM: The study aimed to provide a biological explanation for these 'inflated' exponents when modelling maximum oxygen uptake (max), based on the observations from this and previous studies that larger individuals develop disproportionately more muscle mass in the arms and legs. RESEARCH DESIGN AND SUBJECTS: A cross-sectional study of 119 professional soccer players from Croatia aged 18-34 was carried out. RESULTS: Here we confirm that the power function relationship between max and body mass of the professional soccer players results in an 'inflated' mass exponent of 0.75 (95% confidence interval from 0.56 to 0.93), but also the larger soccer players have disproportionately greater leg muscle girths. When the analysis was repeated incorporating the calf and thigh muscle girths rather than body mass as predictor variables, the analysis not only explained significantly more of the variance in max, but the sum of the exponents confirmed a surface-area law. CONCLUSIONS: These findings confirm the pitfalls of fitting body-mass power laws and suggest using muscle-girth methodology as a more appropriate way to scale or normalize metabolic variables such as max for individuals of different body sizes

A Tutorial on Interference Exploitation via Symbol-Level Precoding: Overview, State-of-the-Art and Future Directions

IEEE Interference is traditionally viewed as a performance limiting factor in wireless communication systems, which is to be minimized or mitigated. Nevertheless, a recent line of work has shown that by manipulating the interfering signals such that they add up constructively at the receiver side, known interference can be made beneficial and further improve the system performance in a variety of wireless scenarios, achieved by symbol-level precoding (SLP). This paper aims to provide a tutorial on interference exploitation techniques from the perspective of precoding design in a multi-antenna wireless communication system, by beginning with the classification of constructive interference (CI) and destructive interference (DI). The definition for CI is presented and the corresponding mathematical characterization is formulated for popular modulation types, based on which optimization-based precoding techniques are discussed. In addition, the extension of CI precoding to other application scenarios as well as for hardware efficiency is also described. Proof-of-concept testbeds are demonstrated for the potential practical implementation of CI precoding, and finally a list of open problems and practical challenges are presented to inspire and motivate further research directions in this area

Joint Optimization for Cooperative Computing Framework in Double-IRS-Aided MEC Systems

Natural Science Foundation of Sichuan Province under Grant 2022NSFSC0887; Fundamental Research Funds for the Central Universities under Grant 2682021ZTPY117 and 2682022CX020; National Natural Science Foundation of China under Grant 62201137; National Natural Science Foundation of China under Grant 62271419; Australian Research Council Laureate Fellowship grant number FL160100032; Australian Research Council Grant DP190101988 and DP210103410