1-persistent carrier sense multiple access in radio channels withimperfect carrier sensing

A comprehensive analysis of a 1-persistent carrier-sense multi-access (CSMA) system using a radio channel with imperfect carrier sensing is presented and discussed. It is shown that a careful optimization of the channel state detector parameters must be performed in order to get good system performance. If the threshold of the detector is too high, the system will tend to behave like an unslotted ALOHA; if the threshold is too low, the system throughput will be zero. It is also shown that for the larger average packet rate G the system throughput is decreased. This is because for the same probability of correct channel sensing, the probability of incorrect transmissions from the waiting mode is increased     

Crystallographic evidence of Gly‐d,l‐Met oxidation to its sulfoxide in the presence of gold(III): solid solution of the racemic mixture of two diastereoisomers

Crystallographic analysis of a solid solution of two diastereoisomers, i.e. ({(1S,R)‐1‐carboxy‐3‐[(R,S)‐methylsulfinyl]propyl}aminocarbonyl)methanaminium tetrachloridoaurate(III) and ({(1S,R)‐1‐carboxy‐3‐[(S,R)‐methylsulfinyl]propyl}aminocarbonyl)methanaminium tetrachloridoaurate(III), (C₇H₁₅N₂O₄S)[AuCl₄], has shown that in the presence of gold(III), the methionine part of the Gly‐d ,l ‐Met dipeptide is oxidized to sulfoxide, and no coordination to the Au^III cation through the S atom of the sulfoxide is observed. In view of our observation, literature reports that methionine acts as an N,S‐bidentate donor ligand forming stable gold(III) complexes require verification. Moreover, it has been demonstrated that crystallization of the oxidation product leads to a substantial 77:23 excess of both S‐methionine/R‐sulfoxide and R‐methionine/S‐sulfoxide over S‐methionine/S‐sulfoxide and R‐methionine/R‐sulfoxide. The presence of two different diastereoisomers at the same crystallographic site is a source of static disorder at this site.     

Wideband CDMA network sensitivity function

We analyze capacity losses in code division multiple access (CDMA) networks due to imperfections in the operation of the system components. The main result of this work is a systematic mathematical framework for capacity evaluation of CDMA-based networks in fading channels. This should be considered as an alternative tool to extensive simulations being used for these purposes at the moment. The intention is to provide simple approximate relations that simultaneously take into account: multiple access intracell interference (MAI), intercell interference, and near-far effect, including different sources of power control imperfections. In addition to this, the efficiencies of the major receiver components are also included in the analysis. A flexible complex signal format is used which enables us to model at currently interesting proposals for wideband CDMA (W-CDMA) standards. The theory is general, and some examples of practical set of channel and system parameters are used as illustration. Further elaboration of these results, including extensive numerical analysis based on the offered analytical framework, would provide enough background for the understanding of W-CDMA system performance in a realistic environment     

Adaptive self-reconfigurable interference suppression schemes forCDMA

In this paper we present a new approach to interference suppression in code-division multiple-access (CDMA) wireless networks. Depending on the interfering signal, these schemes adaptively change not only their parameters but their structures as well. For the relevant types of the interfering signal, suppression is also possible for the wideband interference occupying the same frequency band as the CDMA signal. Probability of error in these schemes is for several orders of magnitude better than in the existing solutions described in the open literature so far. The main applications are the CDMA overlay type wireless network collocated in the same frequency band with a high bit rate microwave communication system, and the multimedia CDMA network where high bit rate signal due to lower processing gain must use a higher level in order to provide the required quality of transmission     

Modeling of the code acquisition process for RAKE receivers in CDMAwireless networks with multipath and transmitter diversity

We present models for the code acquisition process in RAKE receivers. These models include multipath diversity, multiple transmitter (base station or satellite) diversity, and multiple access interference generated by other users in the network. This results in a different probability of false alarm for each cell of the code delay uncertainty region. The analysis is based on signal flow graph theory. By using these models, we elaborate different strategies for RAKE receiver synchronization and derive exact closed-form results for the average acquisition time. These strategies differ in how they organize initial (first RAKE finger) and postinitial search algorithms. If the channel is known, the initial synchronization may organize a parallel search for all fingers simultaneously by a proper set up of the local correlators' mutual delays. If not, then a serial search of different segments (partitioned among the different fingers) can be organized. In the postinitial search, sequential or random initializations are possible. A set of approximations is also included for practical applications where a quick assessment of the system performance is needed     

Symbol synchronization in digital communication systems usingpartial response CPM signaling

The applicability of standard symbol synchronization schemes in digital communication systems using partial-response CPM (continuous phase modulation) signaling has been analyzed. Using the theory of maximum a posteriori estimation of the unknown parameter in Gaussian noise, a theoretical structure for the optimum symbol synchronizer in a system using partial-response CPM signaling is derived. As the first approximation, a closed-loop configuration, known as the early-late loop, is derived and discussed. Due to signal correlation in adjacent symbol time intervals, even this configuration is impractical for a hardware realization. For these reasons, different approximations of the general maximum-likelihood function, leading to the discrete bit timing loop realizations, are derived and discussed. The influence of the carrier phase synchronization error on these synchronizers is also discussed     

Advanced frequency hopping modulation for spread spectrum WLAN

A wireless LAN standard developed by IEEE committee P802.11 operates in the unlicensed 2.4 GHz ISM band. This band is a very hostile environment due to many unpredictable interference sources, such as microwave ovens, utilizing the same frequency bands. At the same time the allowed signal power density that can be used is limited in order to minimize the interference to other users in the same band. In order to avoid these interference and keep a low signal power density the standard supports both direct sequence (DS) and frequency hopping (FH) modulation for these applications. The new test beds for multimedia wireless (WLANs) also use FH modulation. We analyze the performance of a modification of the FH multiple frequency shift keying (MFSK) system that includes a multitone multiamplitude MFSK signal, designated as amMFSK modulation. In this case, in order to meet the transmitted power density limits imposed in the ISM band, the signal energy is split into m separate tones. This makes the system more vulnerable to noise and fading, but still the overall flow of useful information will be increased. The results demonstrate that under the large range of the signal, channel and interference parameters this system offers better performance     

Identification of SARS-CoV-2 Papain-like Protease (PLpro) Inhibitors Using Combined Computational Approach**

In the current pandemic, finding an effective drug to prevent or treat the infection is the highest priority. A rapid and safe approach to counteract COVID-19 is in silico drug repurposing. The SARS-CoV-2 PLpro promotes viral replication and modulates the host immune system, resulting in inhibition of the host antiviral innate immune response, and therefore is an attractive drug target. In this study, we used a combined in silico virtual screening for candidates for SARS-CoV-2 PLpro protease inhibitors. We used the Informational spectrum method applied for Small Molecules for searching the Drugbank database followed by molecular docking. After in silico screening of drug space, we identified 44 drugs as potential SARS-CoV-2 PLpro inhibitors that we propose for further experimental testing.     

Adaptive Integration Time and Threshold Setting Schemes for Two-Dimensional Code Acquisition

In this paper we propose and study two methods for improving two-dimensionalcode acquisition performance in scenarios with nonuniform spatialdistributions of interference. The schemes exploit the fact that integrationtimes and threshold settings are adaptively set for each angular cellaccording to the level of spatial interference prevailing in that cell. Modelsfor the schemes are first developed. Closed-form mean acquisition times arethen computed to allow performance comparisons. Acquisition performance isanalytically evaluated for different spatial distributions of interference.A system with fixed integration time and a fixed threshold is used as areference. It is found that the adaptive integration time scheme is able tofully compensate for the loss of performance caused by the nonuniformdistribution of interference. Furthermore, the mean acquisition times can bereduced by a factor of as much as two, even in environments characterized bysevere distributions of interference, e.g., a high power peak of interferenceconfined to a given angular direction. The adaptive threshold method alsoperforms better than the reference case but provides moderate performancegains.     

Efficiency of block error-correcting codes

Recently, a novel criterion for digital synchronous communication system efficiency estimation has been defined. Using this criterion in the letter we analyse the efficiency of block error-correcting codes.