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In this paper, we study the secure transmission in multiple access wiretap channels when the instantaneous channel state information (CSI) of the wiretap channels is unknown by the legitimate users. We propose a two-phase jamming-assisted secure transmission scheme based on the randomness and independence of wireless channels. In this scheme, we appropriately design artificial noise in two transmission phases and make sure that the eavesdropper's channel is degraded by the artificial noise but the legitimate user's channel is free of the artificial noise. We analyze the capacity of the legitimate channel after using successive interference cancellation (SIC), and demonstrate that the eavesdropping capacity has an upper bound. Furthermore, we prove that a positive secrecy rate can be achieved and the achievable secrecy rate can be maximized by allocating appropriate power to the private information and the artificial noise. [ABSTRACT FROM AUTHOR]

Communication over the i.i.d. Rayleigh slow-fading MAC is considered, where all terminals are equipped with a single antenna. Further, a communication protocol is considered where all users transmit at (just below) the symmetric capacity (per user) of the channel, a rate which is fed back (dictated) to the users by the base station. Tight bounds are established on the distribution of the rate attained by the protocol. In particular, these bounds characterize the probability that the dominant face of the MAC capacity region contains a symmetric rate point, i.e., that the considered protocol strictly attains the sum capacity of the channel. The analysis provides a non-asymptotic counterpart to the diversity-multiplexing tradeoff of the multiple access channel. We then extend this analysis to general multiple-input multiple-output MAC and finally, a practical scheme based on integer-forcing and space-time precoding is shown to be an effective coding architecture for this communication scenario. [ABSTRACT FROM AUTHOR]

We propose a technique for multiple access communications based on the spatial graph coupling principle. Contrary to the existing approaches that require regularized packet transmission times to create a chain of temporally-coupled packets we present a construction of a self-coupling packet. Each transmitted data packet is encoded and modulated in a way that allows the receiver to perform successful cancellation of the inter-packet interference for the case when the packets are transmitted at random times. We show that the overall system throughput can approach the channel capacity limit. Numerical results demonstrate superior bit-error rates achieved by the self-coupling system compared to the temporal-coupling system. [ABSTRACT FROM AUTHOR]

In an uplink scenario, a base station can extract messages from multiple users through received symbols according to individual channel gains. There is a multiple access scheme relying on channel gains for separating users which is referred to as gain division multiple access (GDMA). Our goal is to provide channel estimation for the GDMA system without using pilot signals. We first employ a clustering technique to obtain estimates of the possible linear combinations of channel gains of users through a set of received symbols. We then devise algorithms to estimate the channel gain for each user and recover the message sent from each user. [ABSTRACT FROM AUTHOR]

In this paper, an impartial simultaneous wireless information and power transfer (SWIPT)-assisted cooperation mechanism is proposed for a non-orthogonal multiple access (NOMA) downlink scenario. The key idea of the proposed impartial user cooperation mechanism (IUCM) is that not only the cell-center user but also the cell-edge user applies the power-splitting architecture and utilizes the harvested energy to forward the other user’s information. Analytical results show that the proposed IUCM outperforms the traditional partial cooperation mechanism in terms of outage probability, diversity order and diversity-multiplexing trade-off (DMT). For comparison, the proposed IUCM is further incorporated into an orthogonal frequency-division multiple access (OFDMA) framework, which is shown to preserve the same diversity order, while has a worse but more flexible DMT performance compared with the IUCM in the NOMA framework. Furthermore, a classic non-linear energy harvesting model is introduced, based on which the outage probability, diversity order and DMT performance of the proposed IUCM and the conventional mechanism are analyzed. Finally, representative numerical results are given to validate our theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, we propose joint sequencing and scheduling optimization for uplink machine-type communication (MTC). We consider multiple energy-constrained MTC devices that transmit data to a base station following the time division multiple access (TDMA) protocol. Conventionally, the energy efficiency performance in TDMA is optimized through multi-user scheduling, i.e., changing the transmission block length allocated to different devices. In such a system, the sequence of devices for transmission, i.e., who transmits first and who transmits second, etc., has not been considered as it does not have any impact on the energy efficiency. In this work, we consider that data compression is performed before transmission and show that the multi-user sequencing is indeed important. We apply three popular energy-minimization system objectives, which differ in terms of the overall system performance and fairness among the devices. We jointly optimize both multi-user sequencing and scheduling along with the compression and transmission rate control. Our results show that multi-user sequence optimization significantly improves the energy efficiency performance of the system. Notably, it makes the TDMA-based multi-user transmissions more likely to be feasible in the lower latency regime, and the performance gain is larger when the delay bound is stringent. [ABSTRACT FROM AUTHOR]

A traditional direct sequence CDMA (DS-CDMA) system works based on spreading codes, which should have good auto-correlation and cross-correlation properties to eliminate multiple access interference (MAI) and multipath interference (MI). However, to find a large number of good spreading codes is extremely difficult, and thus the capacity of a DS-CDMA system is limited strictly by the number of available spreading codes. This work proposes a downlink DS-CDMA design to enable multiple access using only one spreading code, namely identical code cyclic shift (ICCS) code, where in-phase and quadrature channels are used to transmit data and pilot, respectively. In particular, the ICCS code is used at a transmitter to perform DS modulation for user data, which is then sent to the in-phase channel. At the same time, the pilots are sent over the quadrature channel in a time-division multiplex (TDM) mode to construct a correlation matrix of ICCS code. At a receiver, MAI is removed by so-designed pilots plus a matched filter-bank. Simulation results show that the proposed ICCS multiple access (ICCSMA) can achieve a better performance than a traditional DS-CDMA system in a high signal to noise ratio region. ICCSMA serves as a bridge to turn CDMA to NOMA to enable massive connectivity in 5 G and beyond communications. [ABSTRACT FROM AUTHOR]

Summary: This article proposes a potential application of quantum key distribution in multiuser networks. In modern networks, variety of multiple access technologies are used for multiuser access purposes. In this article, we focus on a type of widely used media access control protocol—carrier‐sense multiple access (CSMA) and analyze the use of carrier‐sense multiple access with collision avoidance (CSMA/CA) for the quantum key distribution in the network. The quantum key generation is based on a successful experiment that implemented the quantum key distribution by using the decoy‐state method. The secret key generation rate as the main indicator of the performance is given, including the relationship between it and the number of stations in the network, and the relationship between the key generation rate and the transmission distance under the multiple access condition as well. In addition, a multiple access quantum key distribution with channel detection protocol is also proposed. [ABSTRACT FROM AUTHOR]

We design a Blind Network-Assisted Diversity Multiple Access (BNDMA) method for resolving packet collisions in synchronous packet-switched networks. As opposed to typical BNDMA schemes, the method operates in non-blocking mode. Idle transmitters at the start of a collision resolution interval may join the set of active transmitters and contact the receiver before the end of the interval. A naive queuing analysis of the proposed scheme is exponentially complex in the size of the network. We carry out a computationally efficient analysis of the network throughput and queuing delay. We show that the suggested scheme reduces the queuing delay of the buffered packets at the transmitters without sacrificing the maximum throughput achieved by standard BNDMA. Further insights are derived from the numerical experiments. [ABSTRACT FROM AUTHOR]

Various technologies have been developed for the efficient use of the multiple radio access technologies resource at the radio access network level or other network levels to improve user service quality in mobile communication networks. In long-term evolution, mobile carriers are commercializing radio access network-level traffic aggregation technologies such as licensed-assisted access-long-term evolution, long-term evolution-unlicensed, and long-term evolution-wireless local area network aggregation, which use the multi-accesses of the 3rd Generation Partnership Project and WiFi, and the multipath transmission control protocol–based traffic aggregation technologies at the L3 network level. The standardization of 3rd Generation Partnership Project Release 16, which is scheduled to be completed by 2020, is under progress to support the traffic aggregation technology at the L3 network level through a multi-access 5G network. Multipath transmission control protocol is also considered as a traffic aggregation technology. However, it is difficult to apply the multipath transmission control protocol employment model used in long-term evolution to the 5G network structure as it is due to the change to a common core architecture that accommodates multiple radio access technologies through one common interface. Therefore, this article proposes an optimal 5G system architecture and a multipath transmission control protocol adaptation method to support the access traffic steering function based on multipath transmission control protocol in a 3rd Generation Partnership Project 5G mobile communication network. We have verified the development of the multipath transmission control protocol–based multi-access traffic steering technology by implementing the proposed solution in a commercial server on a testbed based on the 5G system standard of 3rd Generation Partnership Project Release 15. Furthermore, this article defines problems that occur when implementing the multipath transmission control protocol–based multi-access traffic steering system and proposes relevant solutions. Based on the implementation results, it is demonstrated that the proposed multipath transmission control protocol–based multi-access traffic steering system can perform traffic steering in the 3rd Generation Partnership Project 5G network. [ABSTRACT FROM AUTHOR]

In orthogonal frequency-division multiplexing, the total spectral resource is partitioned into multiple orthogonal subcarriers. These subcarriers are assigned to different users for simultaneous transmission in orthogonal frequency-division multiple access (OFDMA). In an unsynchronized OFDMA uplink, each user has a different carrier frequency offset (CFO) relative to the common uplink receiver, which results in the loss of orthogonality, among subcarriers and thereby multiple access interference. Hence, OFDMA is very sensitive to frequency synchronization errors. In this paper, we construct the received signals in frequency domain that would have been received if all users were frequency synchronized. A generalized OFDMA framework for arbitrary subcarrier assignments is proposed. The interference in the generalized OFDMA uplink due to frequency synchronization errors is characterized in a multiuser signal model. Least squares and minimum mean square error criteria are proposed to construct the orthogonal spectral signals from one OFDMA block contaminate with interference that was caused by the CFOs of multiple users. For OFDMA with a large number of subcarriers, a low-complexity implementation of the proposed algorithms is developed based on a banded matrix approximation. Numerical results illustrate that the proposed algorithms improve the system performance significantly and are computationally affordable using the banded system implementation.

This paper extensively reviews and analyses Light Fidelity (LiFi), a new technology that uses light to transmit data as a high-speed wireless connection system from a wide spectrum of domains. An in-depth analysis and classifications of pertinent research areas for LiFi networks are presented in this paper. The various aspects constituting this paper include a detailed literature review, proposed classifications, and statistics, which further is deliberated to encompass applications, system architecture, system components, advantages, and disadvantages. LiFi and other technologies are compared, multi-user access techniques used in LiFi networks are investigated and open issues are addressed in detail. The paper is concluded with a comprehensive taxonomy of literature comparison that has served as the basis of the proposed open issues and research trends.

In orthogonal frequency-division multiple access (OFDMA), closely spaced multiple subcarriers are assigned to different users for parallel signal transmission. An interleaved subcarrier-assignment scheme is preferred because it provides maximum frequency diversity and increases the capacity in frequency-selective fading channels. The subcarriers are overlapping, but orthogonal to each other such that there is no intercarrier interference (ICI). Carrier-frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality and introduces ICI, resulting in multiple-access interference. This paper exploits the inner structure of the signals for CFO estimation in the uplink of interleaved OFDMA systems. A new uplink signal model is presented, and an estimation algorithm based on the signal structure is proposed for estimating the CFOs of all users using only one OFDMA block. Diversity schemes are also presented to improve the estimation performance. Simulation results illustrate the high accuracy and efficiency of the proposed algorithm.

Uplink grant-free schemes have the promise of reducing the latency of a user-equipmentinitiated transmission by avoiding the handshaking procedure for acquiring a dedicated scheduling grant. However, the possibility of successfully delivering a payload within a latency constraint may be severely compromised in case of grant-free operations over shared radio resources. In this paper, we study the performance of two different uplink grant-free schemes over shared resources recently discussed within the fifth generation new radio standardization, namely, a solution based on a stop-and-wait (SAW) protocol and a blind retransmission approach. Performance is evaluated assuming Rayleigh fading channels with a maximum ratio combining (MRC) multi-antenna receiver. Analytical results show the benefits of grant-free transmission with respect to the traditional grant-based approach for a tight latency constraint. A highorder receive diversity is beneficial to leverage the MRC gain and enables the possibility of achieving the 10-5 outage probability target set for ultra-reliable low-latency communication services. The blind retransmission approach is significantly penalized by identification and signaling errors, while a SAW solution with potentially scheduled retransmissions out of the shared bandwidth leads to the lowest outage probability, at least for frequent packet arrivals.

Abstract In this paper, bit error performance evaluation of chaotic sequences is presented. Performance of chaotic sequences is evaluated on multiple access spread spectrum system model for USRP software defined radio. LabVIEW is used to perform numerical simulations and bit error rate analysis. Chaotic sequences of different lengths are generated using one-dimensional, two-dimensional, and three-dimensional maps. It is expected that sequences generated from complex maps will have better multiple access performance. Performance of chaotic sequences is evaluated against orthogonal sequences in multiple access scenario. Using Golay figure of merit and Pearson correlation coefficient, analysis of correlation properties and a comparison is performed on orthogonal and chaotic sequences for correlation properties comparison. The results show that chaotic sequences from two-dimensional maps have lower bit error rate than orthogonal and other chaotic sequences. Comparison of correlation properties shows that sequences with a low figure of merit and low Pearson coefficient have lower bit error rate. Those results can be used to generate chaotic sequences with desired correlation properties.

To leverage rich data distributed at the network edge, a new machine-learning paradigm, called edge learning, has emerged where learning algorithms are deployed at the edge for providing intelligent services to mobile users. While computing speeds are advancing rapidly, the communication latency is becoming the bottleneck of fast edge learning. To address this issue, this work is focused on designing a low-latency multi-access scheme for edge learning. To this end, we consider a popular privacy-preserving framework, federated edge learning (FEEL), where a global AI-model at an edge-server is updated by aggregating (averaging) local models trained at edge devices. It is proposed that the updates simultaneously transmitted by devices over broadband channels should be analog aggregated “over-the-air” by exploiting the waveform-superposition property of a multi-access channel. Such broadband analog aggregation (BAA) results in dramatical communication-latency reduction compared with the conventional orthogonal access (i.e., OFDMA). In this work, the effects of BAA on learning performance are quantified targeting a single-cell random network. First, we derive two tradeoffs between communication-and-learning metrics, which are useful for network planning and optimization. The power control (“truncated channel inversion”) required for BAA results in a tradeoff between the update-reliability [as measured by the receive signal-to-noise ratio (SNR)] and the expected update-truncation ratio. Consider the scheduling of cell-interior devices to constrain path loss. This gives rise to the other tradeoff between the receive SNR and fraction of data exploited in learning. Next, the latency-reduction ratio of the proposed BAA with respect to the traditional OFDMA scheme is proved to scale almost linearly with the device population. Experiments based on a neural network and a real dataset are conducted for corroborating the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, multiple-access techniques are viewed as generalized coding schemes to support both multiuser separation and coding gain. In this sense, the traditional coding schemes, e.g., low-density parity-check (LDPC) code, can be viewed as a special case. Note that still a big difference exists between multiple-access techniques and LDPC codes. In particular, both binary and nonbinary LDPC codes are generated based on finite field theory, whereas multiple-access works based on not necessarily a finite field. This paper presents a mathematical framework, called “multiuser coding,” to unify multiple-access and traditional coding theories. To verify the proposed framework, we propose a uniquely decodable mapping based codebook for futuristic multiple-access communications. A three-dimensional Tanner graph based message passing algorithm is introduced for multiuser detection. Simulation results show that the proposed scheme can support a large number of users with a promising performance. [ABSTRACT FROM AUTHOR]

In this work, we consider a sparse code multiple access uplink system, where $J$ users simultaneously transmit data over $K$ subcarriers, such that $J > K$ , with a constraint on the power transmitted by each user. To jointly optimize the subcarrier assignment and the transmitted power per subcarrier, two new iterative algorithms are proposed, the first one aims to maximize the sum-rate (Max-SR) of the network, while the second aims to maximize the fairness (Max-Min). In both cases, the optimization problem is of the mixed-integer nonlinear programming (MINLP) type, with non-convex objective functions, which are generally not tractable. We prove that both joint allocation problems are NP-hard. To address these issues, we employ a variant of the block successive upper-bound minimization (BSUM) framework, obtaining polynomial-time approximation algorithms to the original problem. Moreover, we evaluate the algorithms’ robustness against outdated channel state information (CSI), present an analysis of the convergence of the algorithms, and a comparison of the sum-rate and Jain’s fairness index of the novel algorithms with three other algorithms proposed in the literature. The Max-SR algorithm outperforms the others in the sum-rate sense, while the Max-Min outperforms them in the fairness sense. [ABSTRACT FROM AUTHOR]

Index Modulation Multiple Access (IMMA) technique is proposed recently as a viable candidate for future wireless networks. The idea is to utilize the available orthogonal resources for multiple users as index constellation symbols and allow users to access all available resources without any need of scheduling algorithm. Yet, IMMA receiver applies brute–force search algorithm and suffers from immense computational complexity. Also, IMMA applies index modulation and allows each user to activate a single orthogonal resource at each transmission time. Hence, this letter aims at enhancing the overall performance of IMMA by allowing each user to activate two of the available orthogonal resources to transmit orthogonal data. As well, a novel low complexity receiver is proposed and shown to significantly reduce the computational complexity without any performance degradation. The new scheme is called Quadrature IMMMA (QIMMA) and shown to have superior performance, in terms of number of users and error probability, as compared to IMMA scheme. Analytical framework to compute the average bit error probability for the proposed QIMMA is derived and substantiated through Monte Carlo simulation results. [ABSTRACT FROM AUTHOR]

This paper proposes a novel uplink multiple access scheme to enhance the overall spectral efficiency of wireless systems. The core idea is to exploit index modulation (IM) concept in orthogonal frequency division multiple access (OFDMA) systems. In the proposed scheme, entitled IM-OFDMA, part of the transmitted bits of each user is conventionally modulated, while the rest of the bits determine the index of the active subcarrier that will be used to communicate the modulated symbol. Unlike OFDMA, IM-OFDMA does not require any scheduling algorithm, which results in data collision between the user's received messages. Yet, it is revealed that IM-OFDMA outperforms OFDMA and state of the art uplink non-orthogonal multiple access (NOMA) over a wide range of system and channel parameters. Besides, it is reported that IM-OFDMA can serve up to 3 times the number of served users in OFDMA system while maintaining similar error performance per user. The average bit error rate of IM-OFDMA scheme is derived in a closed form expression that is substantiated through Monte Carlo simulation results. [ABSTRACT FROM AUTHOR]

To fulfill the increasing demand for high speed Variable Bit Rate (VBR) broadcast services with reliable Quality of Service, Group Orthogonal-Orthogonal Frequency Division Multiple Access (GO-OFDMA) and Variable Spreading Length Multicarrier Code Division Multiple Access transmission schemes are examined over Land Mobile Satellite (LMS) channel. This paper presents the performance analysis of aforementioned multiple access transmission schemes in terms of computation complexity, Peak-to-Average-Power-Ratio (PAPR) and the average Bit Error Rate (BER) performance over L-band LMS channel. Minimum Mean Square Equalizer (MMSE) equalizer is employed at the receiver. Based on the simulation results, GO-OFDMA stems out to be a better variable rate transmission scheme in respect of both PAPR and BER performance for higher data rate users. Further, GO-OFDMA based VBR transmitter and MMSE equalizer are prototyped on commercially available virtex5 xc5vlx110t–1ff1136 Field Programmable Gate Array (FPGA) device. A block-by-block analysis of hardware resource utilization and power dissipation for the VBR GO-OFDMA transmitter is provided. The achieved baud rate for VBR GO-OFDMA transmission scheme on FPGA is 103.874 Msps. Thus, GO-OFDMA transmission scheme could be appropriate for VBR communication over LMS channel. [ABSTRACT FROM AUTHOR]

In this paper, we study the problem of providing heterogeneous quality-of-service (QoS) guarantees for asynchronous grant-free uplink transmissions in multichannel wireless networks. The multiple access channel model is the classical collision channel, where partially overlapped packets during the transmissions are assumed to be completely lost. For such a network model, we propose two asynchronous multichannel transmission schedules (AMTS): 1) the EPC-based AMTS and 2) the DS-based AMTS. The EPC-based AMTS is constructed by time-spreading one-dimensional extended prime code (EPC), and the DS-based AMTS is constructed by using difference sets (DS) and finite projective planes. We show for both scheduling algorithms that the maximum delay between two successive successful transmissions of an active device can be upper bounded by a constant when the channel load does not exceed a designed threshold parameter. Moreover, different devices are allowed to have different throughput (rate) guarantees. By conducting extensive simulations, we also show that the overall throughputs of both scheduling algorithms are almost identical to that of the random access protocol, when the number of active devices exceeds the designed threshold parameter. [ABSTRACT FROM AUTHOR]

A modified uplink sparse code multiple access (SCMA) scheme with receive beamforming is herein proposed. Although a base station equipped with multiple antennas can support many users simultaneously using multi-beams, the complexity of the optimal SCMA system may be too large to be implemented in view of a practical system. Therefore, a two stage SCMA system with receive beamforming is proposed, based on uplink scheduling and three step layer selection. Analysis and simulation results of the proposed scheme showed the advantage of large complexity reduction with little performance degradation. [ABSTRACT FROM AUTHOR]

To improve the system throughput, this paper proposes a network non-orthogonal multiple access (N-NOMA) technique for the uplink coordinated multi-point transmission (CoMP). In the considered scenario, multiple base stations collaborate with each other to serve a single user, referred to as the CoMP user, which is the same as for conventional CoMP. However, unlike conventional CoMP, each base station in N-NOMA opportunistically serves an extra user, referred to as the NOMA user, while serving the CoMP user at the same bandwidth. The CoMP user is typically located far from the base stations, whereas users close to the base stations are scheduled as NOMA users. Hence, the channel conditions of the two kinds of users are very distinctive, which facilitates the implementation of NOMA. Compared to the conventional orthogonal multiple access-based CoMP scheme, where multiple base stations serve a single CoMP user only, the proposed N-NOMA scheme can support larger connectivity by serving the extra NOMA users, and improve the spectral efficiency by avoiding the CoMP user solely occupying the spectrum. A stochastic geometry approach is applied to model the considered N-NOMA scenario as a Poisson cluster process, based on which insightful closed-form or quasi closed-form analytical expressions for outage probabilities and ergodic rates are obtained. Numerical results are presented to show the accuracy of the analytical results and also demonstrate the superior performance of the proposed N-NOMA scheme. [ABSTRACT FROM AUTHOR]

We consider a signaling format where the information to be communicated from a single or multiple transmitters to a receiver is modulated via a superposition of independent data streams. Each data stream is formed by error-correction encoding, constellation mapping, replication and permutation of symbols, and application of signature sequences. The relations between the data bits and modulation symbols transmitted over the channel can be represented by a sparse graph. In the case where the modulated data streams are transmitted with time offsets the receiver observes spatial coupling of the individual graphs into a graph chain enabling efficient demodulation/decoding. We prove that a two-stage demodulation/decoding method, in which iterative demodulation based on symbol estimation and interference cancellation is followed by parallel error-correction decoding, achieves capacity on the additive white Gaussian noise channel asymptotically. We compare the performance of the two-stage receiver to the receiver which utilizes hard-decision decoding feedback between the error-correction decoders and the iterative demodulator and estimate the gap between the achievable spectral efficiency and the channel capacity. [ABSTRACT FROM AUTHOR]

Internet of Things is gaining ground in the next generation of Internet. Random access protocols such as ALOHA and its variants play an important role for the successful implementation of 5G. The framed ALOHA is not suitable for such environment due to the relatively low throughput and no guarantee on delay. In this paper, we propose a Finite Projective Plane based random access scheme, FRAM, for multimedia super real-time traffic in the coming 5G Internet. FRAM allows for high throughput by expanding the selection base such that the collisions among users are most likely to be partial. In FRAM, a user packet is sliced into sections, i.e., packet slicing, and transmitted in the time slots of a frame corresponding to the points of a set of a Finite Projective Plane. The error bits induced in a user packet of partial collisions can be removed by forward error control coding. In the performance evaluation, we compare the throughput, pseudo throughput, and probability of blackout of FRAM with those of the framed ALOHA and SIC based CRDSA. The results show that the proposed FRAM has better pseudo throughput and much lower probability of blackout over both the framed ALOHA and CRDSA depending on threshold of partial collision. [ABSTRACT FROM AUTHOR]

In this paper, we propose an enhanced low-complexity binary physical-layer network coding (PNC) based decoding scheme for random access systems with binary phase-shift keying modulation to improve the system throughput. In the proposed scheme, the linear combinations of collided users’ messages in each time slot are first obtained by exploiting a low-complexity PNC decoding scheme. Based on the decoded linear combinations within a MAC frame, we then propose an enhanced message-level successive interference cancellation algorithm to recover more users’ messages. We propose an analytical framework for the PNC-based decoding scheme and derive a tight approximation of the system throughput for the proposed scheme. Subsequently, the number of repeated transmissions of a message, i.e., the number of replicas transmitted by each user, is optimized to further improve the system throughput and energy efficiency. Interestingly, the optimization results show that the optimal number of replicas for maximizing the energy efficiency is a constant for all offered loads. On the other hand, the optimal number of replicas that maximizes the system throughput decreases as the offered load increases. Numerical results show that the derived analytical results closely match with the simulation results. Furthermore, the proposed scheme achieves a considerable throughput improvement, compared to the CRDSA++ scheme. [ABSTRACT FROM AUTHOR]

This paper centers around solutions for the Internet of Things (IoT) challenges in multi-hop connections and the execution of a physical layer network coding (PNC) model for relay broadcasts. For multi-hop transmission, PNC is contemplated as a vigorous solution for multi-hop packet transaction in the linear network topology. The PNC usage has numerous troubles, almost remarkably Carrier-Frequency Offsets (CFO) and timing synchronization. Within the Multiple Access (MA) phase, the relay has to acquire a signal from 2 sources, tracking the CFOs from 2 transmitters when their signals are applied to one of the principal complications. Focusing on practical and implementation concerns of PNC systems, various challenges have been covered and a Software Defined Radio (SDR); PNC technology established on Universal Software Radio Peripheral (USRP) techniques are proposed and applied. Afterward, big computer simulation and experimental outcomes are depicted to evaluate the operation of the urged algorithms in contrast with presently applied technology. [ABSTRACT FROM AUTHOR]

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Objective: The aim of this study is to evaluate the success and complication rates of percutaneous nephrolithotomy (PNL) with multiple single step access in patients with staghorn kidney stones. Materials and Methods: A total of 118 patients with staghorn kidney stones, who underwent PNL in our clinic between 2008 and 2015, were included in the study. All patients were examined with non-contrast abdominal computed tomography before the operation. Demographic data of patients, operation details, intra- and postoperative complications and additional interventions were evaluated. Results: The mean age of the patients included in the study was 49.6 years. The mean operative time was 139.4 minutes and the mean fluoroscopy time was 126.9 seconds. Postoperative residual stone was detected in 28% of the patients. Postoperative fever was observed in 19 patients (16.2%), and sepsis developed in 3 (2.5%) of them. Additional postoperative procedures were required in 11 patients (9.3%). No patient was lost due to complications. Operation success and complication rates were compatible with the literature. Conclusion: For staghorn stones, PNL with multiple single step dilatation technique can be used as an effective and safe method in adult patients. [ABSTRACT FROM AUTHOR]

In this work, a hybrid multiple access scheme for multi-user underwater wireless optical communication (UWOC) systems is proposed and presented. The scheme combines the respective advantages of orthogonal frequency-division multiple access (OFDMA) and non-orthogonal multiple access (NOMA) scheme to reduce the unfairness among users caused by the unique high-frequency fading characteristics of the underwater optical channel. Multi-verse optimizer (MVO) algorithm is further introduced for solving the nonlinear problem of user power allocation. Experimental results in different water quality environments demonstrate that the hybrid OFDMA/NOMA scheme with MVO effectively improves the communication performance of the established 4-user UWOC system compared to the pure NOMA scheme and the pure OFDMA scheme, and a system sum rate of 3.94 Gbit/s is achieved. • A hybrid OFDMA/NOMA scheme is proposed for UWOC system. • MVO algorithm is introduced for user power allocation. • A sum rate of 3.94 Gbit/s is experimentally achieved in a 4-user UWOC system. [ABSTRACT FROM AUTHOR]

The evolution of the concept of cloud communications has posed a growing emphasis on virtual and abstract environments for the flow of information, structuring it in similitude to a natural cloud. The green symbiotic cloud communications (GSCCs) paradigm created on this concept facilitates the use of multiple communication mediums concomitantly creating a first of its kind communication cloud. This paper specifically corroborates a virtualized transport layer and network ports and an abstracted Internet protocol scheme in defining the GSCC architecture. We further address the issue of formulating a cognitive decision function based on utility theory, which allows users with GSCC enabled devices to intelligently distribute its bandwidth requirement amongst the available communication mediums. Considering the multiple criteria associated with different networks, we formulate an optimization problem to find the solution for this resource allocation problem for single user. We further address the multi-user scenario and formulate and solve the multi-objective optimization problem using goal attainment technique. Results in single and multiple user scenarios, demonstrate that by utilizing multiple mediums as per GSCC paradigm coupled with our proposed decision function improves the functionality of the communication cloud. The proposed architecture is dynamic and evolving, embedding greenness by efficiently utilizing the available resources as and when required. The multiple virtual links equate a linearly increasing relationship with the throughput achieved. Experimental results for both real time and static data through the proposed schematic are documented. The augmented paradigm enhances the quality of service, linearly increases throughput and increases the overall security in communications.

Molecular communications is an emergent field that seeks to develop nanoscale communication devices using design principles gleaned from studies of the topology and dynamic properties of biological signaling networks. To understand how these networks function, we must first characterize the functional building blocks that compose them, and the best candidates for those are the topologically distinct subnetworks, or motifs, that appear in a statistically improbable abundance. In transcriptional networks, one of the most prevalent motifs is the feed-forward loop, a three node motif wherein one top-level protein regulates the expression of a target gene either directly or indirectly through an intermediate regulator protein. Currently, no systematic effort has been made to treat an isolated feed-forward loop as a stand-alone signal amplifying/attenuating device and understand its communication capacity in terms of the diffusion of individual molecules. To address this issue, we derive a theorem that estimates the upper and lower bounds of the channel capacity for a relay channel, which structurally corresponds to a feed-forward loop, by using an additive inverse Gaussian noise channel model of protein-ligand binding. Our results are just a first step towards assessing the performance bounds of simplified biological circuits in order to guide the development and optimization of synthetic, bio-inspired devices that can be used as information processing and forwarding units.

In order to study the problem of how to choose the wireless channel connection system to meet the needs of users in the wireless communication environment,according to the number of users using the Irish call loss,the estimated number of users need to meet the channel should be provided.Followed by the number of channels to establish the rela-tion model between user requirements and system capacity,introducing comprehensive evaluation factors to evaluate FDMA,TDMA and CDMA communication system.Finally a solution was put forward to meet the optimal decision the needs of users.This scheme not only realizes the effective utilization of the channel,and the channel has certain redun-dancy,avoid the system reconstruction caused by future user growth,capital waste,provides a measure of win-win choice for different number of users of the communication system.

In the attempt to respond to market demands, new techniques for wireless communication systems have been proposed to ensure, to all active users that are sharing the same network cell, an increased quality of service, regardless of any environmental factors, such as their position within the cell, time, space, climate, and noise. One example is the nonorthogonal multiple access (NOMA) technique, proposed within the 5G standard, known for supporting a massive connectivity and a more efficient use of radio resources. This paper presents two new sets of complex codes— multiple-user shared-access (MUSA) and extended MUSA (EMUSA), and an algorithm of allocation such that the intercorrelation should be as reduced as possible that can be used in MUSA for 5G NOMA-based technique scheme. Also, it analyzes the possibility of creating complex codes starting from PN (cPN), which is a novel idea proposed in this paper, whose results are promising with respect to the overall system performances. First, a description of the basic principles of MUSA are presented; next, the description of the proposed system will be provided, whose performance will be tested using Monte Carlo MATLAB simulations based on bit error rate (BER) versus signal-to-noise ratio (SNR). The system performances are evaluated in different scenarios and compared with classical code division multiple access (CDMA) having the following system parameters in sight: the number of antennas at the receiver side and the number of active users.

The objective of this paper is to provide a multiuser transmission technique for underwater acoustic communication in the framework of an Autonomous Underwater Vehicle (AUV) fleet. By using a variant of a Hyperbolically Frequency-Modulated (HFM) signal, we describe a new family of transmission techniques called MultiUser Chirp Spread Spectrum (MU-CSS), which allows a very simple matched-filter-based decoding. These techniques are expected to provide good resilience against multiuser interference while keeping good robustness to Underwater Acoustic (UWA) channel impairments like Doppler shift. Their implementation for the UWA scenario is described, and the performance results over a simulated shallow-water UWA channel are analyzed and compared against conventional Code-Division Multiple Access (CDMA) and Time-Division Multiple Access (TDMA) transmission. Finally, the feasibility and robustness of the proposed methods are verified over the underWater AcousTic channEl Replay benchMARK (Watermark), fed by several channel responses from sounding experiments performed in a lake.