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This paper presents the design and bit error rate (BER) analysis of a phase-independent non-orthogonalmultiple access (NOMA) system. The proposed NOMA system can utilize amplitude-coherent detection(ACD) which requires only the channel amplitude for equalization purposes. In what follows, threedifferent designs for realizing the detection of the proposed NOMA are investigated. One is based on themaximum likelihood (ML) principle, while the other two are based on successive interference cancellation(SIC). Closed-form expressions for the BER of all detectors are derived and compared with the BER ofthe coherent ML detector. The obtained results, which are corroborated by simulations, demonstrate that,in most scenarios, the BER is dominated by multiuser interference rather than the absence of the channelphase information. Consequently, the BER using ML and ACD are comparable for various cases ofinterest. The paper also shows that the SIC detector is just an alternative approach to realize the MLdetector, and hence, both detectors provide the same BER performance.

Today, steganographic systems with multiple access are of considerable importance. In such sys-tems, the orthogonal Walsh-Hadamard transform is most often used for multiplexing and divid-ing channels, which leads to the need for efficient coding of the Walsh-Hadamard transform coefficients for the convenience of their subsequent embedding. The purpose of the research is to develop a theoretical basis for efficient coding of the embedded signal in steganographic sys-tems with multiple access with an arbitrary number of users N, based on MC-CDMA technology. This purpose was fulfilled by forming the theoretical basis for constructing effective codes de-signed to encode the embedded signal in steganographic systems with multiple access. The most important results obtained are the proposed and proven relations that determine both the possible values of the Walsh-Hadamard transform coefficients, for a given value of the number of divid-ed channels, and the probability of occurrence of the given values of the Walsh-Hadamard transform coefficients, which allow the construction of effective codes to represent the embed-ded signal. In the case of the number of divided channels N=4, we propose to use a constant amplitude code that provides a smaller value of the average codeword length in comparison with the Huffman code, while the constructed code has correcting capabilities. The significance of the obtained results is determined by the possibility of using the developed theoretical basis when constructing effective codes for encoding the embedded signal in steganographic systems with multiple access at an arbitrary value of the number of divided channels N.

Due to the increasingly complicated communication scenarios and network architectures as well as growing traffic demands for high speed connectivity, dynamic spectrum allocation in fifth generation (5G) networks becomes insufficient to guarantee the satisfaction of main network requirements in terms of spectrum efficiency (SE), scalability, delay, and energy efficiency (EE). Enormous multiple access schemes and cognitive radio (CR) network scenarios come to fulfill these requirements and enhance network functionalities. With multiple access schemes, users are able to transmit their data streams simultaneously under maximum capacity constraints. On the other hand, vacant spectrum holes are exploited in an opportunistic manner via CR and software defined radio. In order to exploit these spectrum holes as well as meeting different network requirements, several multiple access techniques have been presented that have been initiated through the adoption of orthogonal multiple access (OMA) scheme. Additionally, non-orthogonal multiple access (NOMA) and space division multiple access (SDMA) are presented to achieve a promising multiplexing gain as well as to address the inefficient spectrum utilization incurred with OMA schemes. However, such multiplexing gain is limited as it depend on the channel conditions. Accordingly, a generalized multiple access scheme has been presented recently, namely rate splitting multiple access (RSMA), to further enhance the SE. In this paper, we provide a comprehensive study regarding the key multiple access schemes presented for CRNs to further enhance the use of spectral resources, and additionally highlights the key implementation challenges and the enabling techniques addressed to overcome it. We have given a special attention to the enhances provided by RSMA as compared with OMA, SDMA, and NOMA techniques. Finally, some open issues are spotted to shed lights on the need for further studies and future research efforts.

The sharply growing demand for increased transmission capacity and bandwidth in last meter and last mile access networks together with the commercialization of fifth generation (5G) wireless systems has been opening up new opportunities for non-radio frequency (RF)-based wireless technologies. Visible light communications (VLC) technology is a potential candidate for access networking in 5G, which offers a higher spectral efficiency than RF-based Femtocell networks by three orders of magnitude. This paper proposes an all wireless optical bidirectional VLC multiple access scheme for pure VLC network access points in terminals. Centralized coordination is adopted to reduce the system complexity. And reservation of resource is introduced to guarantee collision avoidance during data frame transmission. The proposed multiple access scheme introduces special system parameters to achieve the balance of system throughput and access latency. The feasibility of the proposed scheme is verified by both theoretical analysis and experimental investigation. We show that the proposed scheme is suitable for a bidirectional pure VLC access network and can be used as a supplement in the IEEE 802.11 bb for 5G+bidirectional VLC application scenarios.

Swarm robotics is an approach to collective robotics with which it is easily possible to complete the tasks that are difficult to do with single robot. The wireless multiple access network contributes significantly in wireless mobile swarm robotics for communication and networking, especially in disaster scenarios. Since the unpredictable impacts may fail the sensing robots or nodes, causing the loss of valuable data, a coding scheme called the Growth codes is designed to increase data persistence. In the wireless multiple access network, a key requirement of data collection in disaster scenarios is to maintain a high data intermediate recovery rate. In the later period of the Growth codes, the large amount of redundant data in the network affects the efficiency of data collection. In this paper, we design and analyze techniques to reduce the number of redundant data, and propose a sectional configured data collection strategy based on the Growth codes, called the SCGC protocol. Setting cache nodes around the sink to filter the redundant codewords, the sink can collect data faster, ensuring a high data intermediate recovery rate. We also design an information update strategy and some constraints to control node overhead. Through the simulations, we show that the proportion of redundant codewords can be reduced by 10-15%, while the negative impact of these valid codewords is not considered in the Growth codes. We also show that the SCGC protocol can improve the data recovery efficiency without affecting the stability of the network or shortening the network lifetime.

Medium Access Control (MAC) scheduling in ad hoc networks is a challenging task due to the trade-offs between fairness, delay and throughput. In this work, we propose a distributed link scheduling algorithm based on the Ising Model from statistical mechanics, by associating a novel Hamiltonian measure with the network such that its optimization yields a feasible schedule. This work overcomes the shortcomings of previous Ising Model based algorithms by incorporating queuing and servicing dynamics as well as fairness measures for improving aggregate throughput and network latency. Our simulations show considerable improvement in performance compared to existing benchmarks over a variety of traffic arrival patterns and network topologies.

To keep pace with the current rapid evolution of mobile data requirements, IEEE 802.11 was evolved to provide more desirable performance to fulfill the needs of fifth-generation (5G) and Internet of Things (IoT) networks. It provides two different access contention-based schemes; Distributed Coordination Function (DCF) which not differentiates between different services, and Enhanced Distributed Channel Access (EDCA) which provides differentiation between various services through four priority Access Categories (ACs). The dilemma of the conventional IEEE 802.11 networks is the static assignation of parameters in DCF and EDCA regardless of the number of associated stations and no matter what kind of service is required by each station (i.e., the activity of ACs). Consequently, this led to a significant degradation in the performance of the network, especially in the case of ultra-dense load network. Therefore, in this paper, we introduce a novel algorithm for EDCA considering a dynamic assignation of Arbitration Inter-Frame Space Number (AIFSN) and guidance Contention Window (CW) depending on the number of associated stations and ACs activeness status. Based on the analytical models of EDCA, a game-theoretic method is proposed to make each associated station adapts its transmission probability within the guidance CW. The purpose of guidance CW is a pre-stage to detect the selfish stations which pick up a very low CW to maximize its throughput regardless of the overall network throughput. Simulation results show that the proposed game-based algorithm can obtain higher performance than the standard 802.11 networks in terms of normalized throughput, data dropped during retransmissions limit threshold exceeding, and mean average delay for sensitive delay applications.

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.

In Internet of Things (IoT), a massive amount of sensitive data is generated and transmitted by IoT devices. Security risks represent a major concern in IoT, especially when using innovative techniques such as Non-Orthogonal Multiple Access (NOMA) technique, where users can access other users' data. In fact, in NOMA-based IoT systems, communication is not only threatened by external eavesdroppers, but also by untrusted internal users. Therefore, it is necessary to adopt an encryption technique that guarantees IoT system communications. This paper presents a comparative study of secret key generation, where performance analysis of secure NOMA-enabled IoT network in the presence of untrusted users is detailed using different PLS key generation schemes. 2021 IEEE. Qatar Foundation;Qatar National Research Fund Scopus

For supporting the massive connectivities and better adapting the high dynamical channel states of the cellular Internet of things networks, in this paper we proposed a new grant-free rateless sparse code multiple access (RSCMA) protocol. In the proposed grant-free RSCMA, users switch from the inactive mode to the active mode as soon as they receive data packages, and start to transmit the data without the request-grant process between the base station (BS) and users. In each transmission, the active users firstly choose a certain number of the modulated SCMA symbols according to the pre-assigned access control function (ACF), and then transmit the linearly superimposed SCMA symbols to the BS over the available resource elements. At the BS, owing to the sparsity of RSCMA, message passing algorithm which allows multi-user detection with near-optimal performance can be utilized to decode the messages. The transmission will continue until the user successfully receives an ACK signal sent back from the BS. Theoretical analysis in terms of achievable constellation constrained throughput is provided to show the maximal sum rate of RSCMA and to optimize the ACF design under the trade-off between the complexity and throughput performance. Both theoretical and simulation results show that the RSCMA can achieve higher throughput than the existing rateless multiple access schemes, such as hybrid automatic repeat request SCMA, LT code coded SCMA, and rateless multiple access.

In this paper, wireless feedback control of multiple machines over a beacon-enabled IEEE 802.15.4 network is considered. In the beacon-enabled IEEE 802.15.4 network, beacons periodically structure superframes on the time axis, and each superframe consists of a contention access period (CAP) and a contention free period (CFP). In the CAP, a carrier sense multiple access/collision avoidance (CSMA/CA) is used; in the CFP, a guaranteed time slot (GTS)-based time division multiple access is used. Because of collision and backoff periods of packet transmission, the probability of communication failure in the CAP is greater than that in the CFP; however, the number of available GTSs is limited to seven by the standard. In order to improve the control performance of wireless feedback control, the controller must effectively allocate GTSs to transmit control input and state feedback of controlled machines. We provide a simple but efficient idea that takes both the feedback control mechanism and packet transmission mechanism of the CAP and CFP into consideration to better allocate GTSs. We propose a superior GTS allocation method that fully conforms to the IEEE 802.15.4 standard and show that the proposed method can further improve control performance.

Multiple Subcarrier Multiple Access (MSMA) enables concurrent sensor data streamings from multiple wireless and batteryless sensors using the principle of subcarrier backscatter used extensively in passive RFID. Since the interference cancellation performance of MSMA depends on the Signal to Interference plus Noise Ratio of each subcarrier, the choice of channel allocation scheme is essential. Since the channel allocation is a combinatorial problem, obtaining the true optimal allocation requires a vast amount of examinations which is impracticable in a system where we have tens of sensor RF tags. It is particularly true when we have variable distance and variable bandwidth sensor RF tags. This paper proposes a channel allocation scheme in the variable distance and variable bandwidth MSMA system based on a newly introduced performance index, total contamination power, to prioritize indecision cases. The performance of the proposal is evaluated with existing methods in terms of average communication capacity and system fairness using MATLAB Monte Carlo simulation to reveal its advantage. The accuracy of the simulation is also verified with the result obtained from the brute force method.

Uplink grant-free schemes have the promise of reducing the latency of a user-equipment-initiated 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 high-order 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.

Packet collision is a well-known severe impairment in ALOHA-based networks and, more generally, in any random access network. As a consequence, several methodologies have been considered with the aim of lowering the resulting performance degradation. A novel multiuser detection scheme exploiting channel diversity to separate collided signals is proposed here to enable multiple packet reception capability in random access schemes. The performance of this approach is analytically derived and optimized in terms of network throughput, and compared with that of different alternatives. The overall performance in terms of throughput shows the effectiveness of the proposed scheme in different operating conditions.

This paper proposes a novel multiple access method that enables concurrent sensor data streaming from multiple batteryless, wireless sensor tags. The access method is a pseudo-FDMA scheme based on the subcarrier backscatter communication principle, which is widely employed in passive RFID and radar systems. Concurrency is realized by assigning a dedicated subcarrier to each sensor tag and letting all sensor tags backscatter simultaneously. Because of the nature of the subcarrier, which is produced by constant rate switching of antenna impedance without any channel filter in the sensor tag, the tag-to-reader link always exhibits harmonics. Thus, it is important to reject harmonics when concurrent data streaming is required. This paper proposes a harmonics rejecting receiver to allow simultaneous multiple subcarrier usage. This paper particularly focuses on analog sensor data streaming which minimizes the functional requirements on the sensor tag and frequency bandwidth. The harmonics rejection receiver is realized by carefully handling group delay and phase delay of the subcarrier envelope and the carrier signal to accurately produce replica of the harmonics by introducing Hilbert and inverse Hilbert transformations. A numerical simulator with Simulink and a hardware implementation with USRP and LabVIEW have been developed. Simulations and experiments reveal that even if the CIR before harmonics rejection is 0dB, the proposed receiver recovers the original sensor data with over 0.98 cross-correlation.

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.

The Li-Fi paradigm that aims at implementing indoor communications links in indoor scenarios, paid attention to the downlink so as to grant connectivity and illumination to several users in very small cells, also known as attocells. However, few work has been done to face the problem of uplink since the use of visible light that send signals from floor to ceiling can be harmful for human eye. In this work we consider the performance offered by an infrared uplink access essentially based on TDMA. In particular we assume that the access points are characterized by the presence of multiple photodiodes on the ceiling so as to receive the signals coming from different users and directions. In this regard, we explore also the spatial dimension in order to evaluate how many users can access the network with a reasonable level of reliability and without inducing severe interference.

In this paper, we develop a multi-agent reinforcement learning (MARL) framework to obtain online power control policies for a large energy harvesting (EH) multiple access channel, when only causal information about the EH process and wireless channel is available. In the proposed framework, we model the online power control problem as a discrete-time mean-field game (MFG), and analytically show that the MFG has a unique stationary solution. Next, we leverage the fictitious play property of the mean-field games, and the deep reinforcement learning technique to learn the stationary solution of the game, in a completely distributed fashion. We analytically show that the proposed procedure converges to the unique stationary solution of the MFG. This, in turn, ensures that the optimal policies can be learned in a completely distributed fashion. In order to benchmark the performance of the distributed policies, we also develop a deep neural network (DNN) based centralized as well as distributed online power control schemes. Our simulation results show the efficacy of the proposed power control policies. In particular, the DNN based centralized power control policies provide a very good performance for large EH networks for which the design of optimal policies is intractable using the conventional methods such as Markov decision processes. Further, performance of both the distributed policies is close to the throughput achieved by the centralized policies.

A satellite network&rsquo, s multiple access protocol must be well designed to efficiently occupy channel resources and meet various qualities of service requirements. In this paper, a combined free/demand assignment multiple access protocol based on gray forecast is proposed. In terms of access, the adoption of the gray forecast method allows the user to book the number of timeslots to have more than the existing number of burst of packets. In terms of bandwidth allocation, a user priority allocation method is used to prioritize users with high needs and focus on the allocation of satellite resources. Experimental results show that the proposed protocol can effectively improve the channel utilization of the entire system. Thus, this protocol has some advantages over existing protocols in network throughput and end-to-end delay.

The advances in multiple access techniques has been one of the key drivers in moving from one cellular generation to another. Starting from the first generation, several multiple access techniques have been explored in different generations and various emerging multiplexing/multiple access techniques are being investigated for the next generation of cellular networks. In this context, this paper first provides a detailed review on the existing Space Division Multiple Access (SDMA) related works. Subsequently, it highlights the main features and the drawbacks of various existing and emerging multiplexing/multiple access techniques. Finally, we propose a novel concept of clustered orthogonal signature division multiple access for the next generation of cellular networks. The proposed concept envisions to employ joint antenna coding in order to enhance the orthogonality of SDMA beams with the objective of enhancing the spectral efficiency of future cellular networks.

Toward the era of mobile internet and Internet of Things (IoT), numerous sensors and devices are being introduced and interconnected. To support such amount of data traffic, traditional wireless communication technologies are facing challenges both in terms of increasingly shortage of spectrum resource and massive multiple access. In this paper, cognitive code division multiple access (Cognitive-CDMA) is proposed by combining the concept of cognitive radio with dynamic noncontinuous spectrum bands and code division multiple access. In order to suppress multiple access interference resulting from the non-orthogonality of partial available spectrum bins, carrier frequency offset, and spectrum sensing mismatch, an enhanced receiver design using frequency-domain oversampling (FDO) with linear minimum mean square error (MMSE) is considered in this paper for Cognitive-CDMA systems. By spectrum sensing to mitigate spectral interference in the transceiver and by utilizing FDO in the receiver to project received signal to a higher dimension, the proposed Cognitive-CDMA is able to support robust and massive multiple access for IoT applications. The simulation results show that the cognitive-CDMA with FDO-MMSE receiver outperforms that with conventional per-user MMSE receiver in the presence of multipath fading channels, carrier frequency offset, and spectrum sensing mismatch.

In this paper, we perform a performance comparison of two different solutions for next generation mobile fronthauling, both based on digital signal processing (DSP) channel aggregation options, but in the two variants usually indicated as Time Division Multiplexing Access (TDMA) and Frequency Division Multiplexing Access (FDMA). The two DSP-based options are here compared for the scenarios of 48 (20 MHz) LTE-A, 96 (20 MHz) LTE-A or 24 new radio NR (100 MHz) channels by means of simulation on realistic Intensity Modulation and Direct Detection optical fronthauling link. We report on spectral occupation, DSP complexity and error vector magnitude (EVM) as performance metrics. We show that TDMA option has more compact bandwidth, it does not require pre-emphasis to equalize per channel EVM and gives out a slightly better EVM performance than FDMA when the optical channel shows significant frequency roll-off towards higher channels.

25th Signal Processing and Communications Applications Conference (SIU) -- MAY 15-18, 2017 -- Antalya, TURKEY WOS: 000413813100528 For a two-user cooperative multiple access channel with energy harvesting transmitters, we formulate and solve the achievable departure region maximization problem under finite battery capacities and energy storage losses. Treating delay constrained and delay tolerant cooperation scenarios separately, we investigate the dependence of the optimum transmission power and rate allocation policy on the battery limitations and storage inefficiencies. We obtain and compare the achievable departure regions for delay constrained and tolerant scenarios. Turk Telekom, Arcelik A S, Aselsan, ARGENIT, HAVELSAN, NETAS, Adresgezgini, IEEE Turkey Sect, AVCR Informat Technologies, Cisco, i2i Syst, Integrated Syst & Syst Design, ENOVAS, FiGES Engn, MS Spektral, Istanbul Teknik Univ

Cognitive radio (CR) is currently one of the most promising solutions for designing spectrum-efficient wireless com- munication systems. In this paper, we present a greedy cognitive access policy that handles spectrum sensing with the tools of image processing. By means of the Wigner-Ville transform (WVT), we are able to analyze the time and frequency features of the received interference, and represent them on a time-frequency grid as an image in which brightness reveals the spectrum occupancy. Ac- cording to sensed interference, each secondary user autonomously tries to access the grid following a multiple-division principle, i.e., by properly shaping the signal in the code, time, and frequency domains. In detail, this is realized by processing the WVT to derive the shaping mask (and the matching algorithm) that allows the filling up of the "time spectrum holes." Numerical simulations and a test-bed implementation show how the proposed scheme outper- forms selected state-of-the-art approaches while still presenting an affordable computational cost. Index Terms—Cognitive radio (CR), edge detection (ED), multiple access, Wigner-Ville transform (WVT). I. INTRODUCTION developed here fully embraces the cognitive paradigm and, following (3), is characterized by awareness (through interfer- ence shape detection), the ability to make decisions (shaping is based on the learning/acquisition phases), adaptivity (to con- dition evolutions), reliability (i.e., robustness to impairments), and efficiency (from smart energy consumption). A possible application of this kind of device ranges from medical body area networks (MBANs) or smart grids (not power-lined) to public safety networks. Establishing a connection easily is the common denominator of these networks. In fact, smart grids allow the connection of new devices in an unlicensed band (e.g., electrical vehicles needing to be charged). In the area of public safety, CR was identified in 2008 by both a National Emergency Communications Plan report and the National Broadband Plan (4) as one of the emerging technologies for increasing effi- ciency and effectiveness of spectrum usage. Finally, MBANs need devices able to work in some spectrum bands subject to constraints related to forbidden bands, as specified by different hospitals. In this regard, flexibility and self-configuring ability are two relevant issues. The proposed approach answers those requests.

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Interference may pose a severe limitation to massive wireless multiple access unless the central receiver is endowed with strong multipacket reception capabilities. In that respect, Interference Cancellation (IC) has been extensively studied [1]–[3]. Such systems have been proposed for satellite communications, combining Direct Sequence (DS) Code Division Multiple Access (CDMA) with a SIC receiver [4]–[6] or using multipacket transmission as in Contention Resolution Diversity Slotted ALOHA (CRDSA) [7] [8]. The use of powerful encoders coupled with power imbalance at reception favours IC and has considerably improved the throughput of such random access protocols [4] [9]. In a context characterized by high user activity and spectrum/orbit congestion [10], it is of interest to develop schemes for space assets that optimize the aggregate spectral efficiency of the user population.

Due to copyright restrictions, the access to the full text of this article is only available via subscription. In this paper, we propose a novel protocol for cooperative multiple access in visible light communication (VLC) networks. The proposed protocol exploits the features of enhanced unipolar orthogonal frequency division multiplexing (eU-OFDM) scheme in order to enable user terminals to sequentially access the multi-hop network. The signal-to-noise ratios (SNRs) for user terminals within the network are derived and the individual bit-error-rate (BER) expressions are presented. We evaluate the BER performances of each user in the network through Monte Carlo simulation. The theoretical results validates the simulation results.

Rapid and reliable timing synchronization is a demanding task in the receiver design for ultra-wideband (UWB) communication systems, especially when concurrent multiple access is called for. This paper derives a maximum likelihood based timing synchronization scheme for UWB multiple access. Relying on a set of user-specific training sequences, the novel concept of weighted average template is introduced, leading to a multiple access timing synchronizer that works in the absence of any channel knowledge and is resilient to both multiple access interference and noise. Simulation runs testify the effectiveness of the proposed scheme in terms of mean square timing estimation errors and bit-error-rate detection performance when operating in multiple access and dense multipath scenarios.

In this paper, we propose a new modulation named parallel combinatory/high compaction multi-carrier modulation (PC/HC-MCM) using the techniques of parallel combinatory orthogonal frequency division multiplexing (PC-OFDM) and high compaction multi-carrier modulation (HC-MCM). Two types of PC/HC-MCM systems, which are named as modulated PC/HC-MCM system and (unmodulated) PC/HC-MCM system, can be designed. The modulated PC/HC-MCM system achieves better bit-error rate (BER) performance than that of HC-MCM system with equal bandwidth efficiency (BWE). The PC/HC-MCM system can obtain the better peak-to-average power ratio (PAPR) characteristics by selecting appropriate constellation for each subcarrier. On the other hand, since PC/HC-MCM can divide the PC-OFDM symbol duration into multiple time-slots, the advantages of frequency hopping (FH) can be applied in the PC/HC-MCM system. Therefore, we also combine the PC/HC-MCM and frequency hopping multiple access (FHMA) to propose a novel multiple access (MA) system. It can simultaneously transmit multiple users' data within one symbol duration of PC-OFDM.

Sistem celuler GSM memiliki beberapa kekurangan, yaitu tidak mampu untuk mengintegrasikan layanan video call dan video streaming karena kecepatan data masih rendah. Dengan alasan itu, maka ETSI menentukan migrasi dari GSM ke sistem generasi seluler ketiga yang disebut dengan UMTS (Universal Mobile Telephone System). Adapun spektrum frekuensi UMTS terestrial bekerja pada 1920-1980 MHz, 2110-2170 MHz untuk dipasangkan dari band dan 1900-1920 MHz, 2010-2025 MHz untuk tidak berpasangan dari band Seiring dengan perkembangan teknologi, teknologi telekomunikasi sistem seluler terus berkembang dan menggarap sekarang telah mencapai generasi ketiga yang dikenal dengan nama dari International Mobile Telecommunications-2000 (IMT-2000). Adapun kerangka kerja untuk pengembangan teknologi seluler generasi ketiga (3G) di Eropa adalah Universal Mobile Telephone System (UMTS). UMTS menggunakan disebut oleh TD-CDMA multiple access adalah UTRA TDD (UMTS Terrestrial Radio Access dari Time Division Duplex) dan W-CDMA untuk UTRA FDD DARI (UMTS Terrestrial Radio Access dari Duplex Frekuensi Division Kata kunci : UMTS, multiple access, Sistem Seluler

A general method for the evaluation of the symbol error probability (SER) of ultra wideband (UWB) systems with various kind of modulation schemes (N-PAM, M-PPM, Bi-Orthogonal), in presence of multipath channel, multiuser and strong narrowband interference, is presented. This method is shown to be able to include all the principal multiaccess techniques proposed so far for UWB, time hopping (TH), direct sequence (DS) and optical orthogonal codes (OOC). A comparison between the performance of these multiple access and modulation techniques is given, for both ideal Rake receiver and minimum mean square error (MMSE) equalizer. It is shown that for all the analyzed multiple access schemes, a Rake receiver exhibits a high error floor in presence of narrowband interference (NBI) and that the value of the error floor is influenced by the spectral characteristics of the spreading code. As expected, an MMSE receiver offers better performance, representing a promising candidate for UWB systems. When the multiuser interference is dominant, all multiple access techniques exhibit similar performance under high-load conditions. If the number of users is significantly lower than the spreading factor, then DS outperforms both TH and OOC. Finally 2PPM is shown to offer better performance than the other modulation schemes in presence of multiuser interference; increasing the spreading factor is proposed as a more effective strategy for SER reduction than the use of time diversity.

The effect of full-duplex cooperative relaying in a random access multiuser network is investigated here. First, we model the self-interference incurred due to full-duplex operation, assuming multi-packet reception capabilities for both the relay and the destination node. Traffic at the source nodes is considered saturated and the cooperative relay, which does not have packets of its own, stores a source packet that it receives successfully in its queue when the transmission to the destination has failed. We obtain analytical expressions for key performance metrics at the relay, such as arrival and service rates, stability conditions, and average queue length, as functions of the transmission probabilities, the self interference coefficient, and the links' outage probabilities. Furthermore, we study the impact of the relay node and the self-interference coefficient on the per-user and aggregate throughput, and the average delay per packet. We show that perfect self-interference cancelation plays a crucial role when the SINR threshold is small, since it may result to worse performance in throughput and delay comparing with the half-duplex case. This is because perfect self-interference cancelation can cause an unstable queue at the relay under some conditions., Accepted for publication in the IEEE Transactions on Wireless Communications

A fundamental problem for signal processing in wireless communications is the separation multiple signals/users from their mixture. The problem would be simpler if they are non-overlapping in either time domain or frequency domain. Two signals may be overlapping in both time and frequency, but they still can be easily separated if they are uncorrelated (orthogonal), like in Code Division Multiple Access system (CDMA). It may be interesting to know that two signals may be overlapping in both the frequency and time domain and also are not orthogonal to each other, but they can still be separated if each autocorrelation function at the receiver is separable in the domain of time-lags. In this paper, we will show how the Noise-Loop (NL) modulation, originally thought to produce security at physical layer, can be used to effectively separate uncoordinated/unorthogonal users sharing the same time and frequency band. In order to show the potential of noise-loop multiple access (NLMA) scheme, the theoretical solution is derived as well as numerical semi-analytical simulations. It can be shown that the NLMA is able to distinguish the bit stream of the users. This feature together with the intrinsic security make the NL an interesting scheme for wireless technology.

This paper presents a chirp based ultrasonic positioning system (UPS) using orthogonal chirp waveforms. In the proposed method, multiple transmitters can simultaneously transmit chirp signals, as a result, it can efficiently utilize the entire available frequency spectrum. The fundamental idea behind the proposed multiple access scheme is to utilize the oversampling methodology of orthogonal frequency-division multiplexing (OFDM) modulation and orthogonality of the discrete frequency components of a chirp waveform. In addition, the proposed orthogonal chirp waveforms also have all the advantages of a classical chirp waveform. Firstly, the performance of the waveforms is investigated through correlation analysis and then, in an indoor environment, evaluated through simulations and experiments for ultrasonic (US) positioning. For an operational range of approximately 1000 mm, the positioning root-mean-square-errors (RMSEs) &90% error were 4.54 mm and 6.68 mm respectively.

International audience; —In this paper we study a promising multiple access scheme entitled Channel Division Multiple Access (ChDMA). ChDMA was developed to cope with the particularities of low duty cycle Impulsive Radio Ultra Wideband systems (IR-UWB). The idea is based upon the fact that Channel Impulse Responses (CIR) could be exploited as users signatures. Based on the knowledge of the CIRs at the receiver, transmitted signals can be detected and estimated in a very similar approach as performed by DS-CDMA systems. We present in this contribution initial analysis of the spectral efficiency performance of ChDMA systems. As a matter of fact, ChDMA overcomes the multiple access paradigm of impulsive-radio signaling and provides an efficient and low complex technique to exploit the diversity of UWB communications. For the study, we consider three different receiver structures: optimal receiver, matched filter (MF) and linear minimum mean square error receiver (l-MMSE). As a result, it is shown that under certain conditions ChDMA can even outperform CDMA in terms of Shannon's capacity, providing a real option for future communication systems.

Wireless technology for communication and localization in train applications are widely used. Ultra wide band appears as a very suitable technology for this kind of application, due to its large bandwidth, also to its good resistance to the interference and to multipath. In this paper, a new system dedicated to railway transport, based on UWB technology is presented. The originality of this study is combination of the two main functionalities, localization and communication providing a high data rate. The sensor, in order to detect the position of vehicles, uses a matched digital correlation receiver. To allow a multi user access and to combine the two functionalities, two original multiplexing techniques called SSS2 (Sequential Spreading Spectrum technique) and CPM (Code Position Modulation) are performed, in addition to other parameters like used waveform and orthogonal codes.

The Indian electricity sector, despite having the world's fifth largest installed capacity, suffers from a 12.9% peaking shortage. This shortage could be alleviated, if a large number of deferrable loads, particularly the high powered ones, could be moved from on-peak to off-peak times. However, conventional Demand Side Management (DSM) strategies may not be suitable for India as the local conditions usually favor inexpensive solutions with minimal dependence on the pre-existing infrastructure. In this work, we present a completely autonomous DSM controller called the nPlug(1). nPlug is positioned between the wall socket and deferrable load(s) such as water heaters, washing machines, and electric vehicles. nPlugs combine local sensing and analytics to infer peak periods as well as supply-demand imbalance conditions. They schedule attached appliances in a decentralized manner to alleviate peaks whenever possible without violating the requirements of consumers. nPlugs do not require any manual intervention by the end consumer nor any communication infrastructure nor any enhancements to the appliances or the power grids. Some of nPlug's capabilities are demonstrated using experiments on a combination of synthetic and real data collected from plug-level energy monitors. Our results indicate that nPlug can be an effective and inexpensive technology to address the peaking shortage. This technology could potentially be integrated into millions of future deferrable loads: appliances, electric vehicle (EV) chargers, heat pumps, water heaters, etc.

This paper derives tight ergodic sum-rate capacity scaling limits for cognitive radio secondary networks under five different communication environments (CoE) for two different network types when secondary users' (SUs) transmission powers are optimally allocated. The network types studied are power-interference limited (PIL) networks and interference limited (IL) networks. In PIL networks, SUs' transmissions are limited by both an average total power constraint and a constraint on the average interference that they cause to primary users (PUs). In IL networks, SUs' transmissions are only limited by an average interference constraint. The capacity scaling results in PIL networks are derived for three different CoEs in which secondary transmitter to secondary base station (STSB) channel gains are Rayleigh distributed while secondary transmitter to primary base station (STPB) channel gains are Rayleigh, Rician or Nakagami distributed. It is shown that secondary network capacity scales according to log log(N) in these three CoEs, where N is the number of SUs. In addition to these three CoEs, two more CoEs are also studied for IL networks: Rician or Nakagami distributed STSB channel gains and Rayleigh distributed STPB channel gains. It is shown that the secondary network capacity scales according to log log(N) for all five CoEs in IL networks. This result implies exponential capacity gains in IL networks over PIL networks. The same capacity scaling results are shown to hold even for heterogeneous cognitive radio networks in which different SUs experience statistically different channel conditions. In some cases, our analysis leads to a new notion called effective number of users, which signifies the effective number of users contributing to multiuser diversity in cognitive radio networks. For example, effective number of users is given by K+1/e(K)Nwhen STSB channel gains are Rayleigh distributed and STPB channel gains are Rician distributed with a Rician factor K. Refereed/Peer-reviewed

We propose two new protocols based on physical layer network coding for collision resolution in multiple access networks.When a collision occurs the receiver decodes the sum of the collided packets and after a number of transmissions, equal to or slightly higher than the number of original packets, it can recover all of them. One of the proposed protocols based on fountain codes can resolve collisions by sending out just one acknowledgement (ACK), thus being particulary suited to networks with large round trip delays such as satellite networks. We carry out a comparison of the average delay achieved by the proposed schemes with other access techniques, and show how the performance can be improved with little coordination at the receiver.

Two new schemes are proposed for collision resolution in slotted ALOHA networks based on multi-user physical-layer network coding (MU PHY NC). In the proposed random access schemes, a collision of a generic number of packets can be recovered decoding the XOR of the original messages, such that the signal resulting from the collision is exploited rather than being discarded. Two different schemes that differ in terms of the amount of control information that needs to be transmitted from the access point, are studied.

Some issues concerning the use of a nonuniform backoff on the throughput and the successful packet delay of an 802.11 network are discussed. The transient and steady-state behaviours of the single node and of the whole network are investigated in non-saturated traffic conditions.

International audience; Spatial Aloha is probably the simplest medium access protocol to be used in a large mobile ad hoc network: each station tosses a coin independently of everything else and accesses the channel if it gets heads. In a network where stations are randomly and homogeneously located in the Euclidean plane, there is a way to tune the bias of the coin so as to obtain the best possible compromise between spatial reuse and per transmitter throughput. This paper shows how to address this questions using stochastic geometry and more precisely Poisson shot noise field theory. The theory that is developed is fully computational and leads to new closed form expressions for various kinds of spatial averages (like e.g. outage, throughput or transport). It also allows one to derive general scaling laws that hold for general fading assumptions. We exemplify its flexibility by analyzing a natural variant of Spatial Aloha that we call Opportunistic Aloha and that consists in replacing the coin tossing by an evaluation of the quality of the channel of each station to its receiver and a selection of the stations with good channels (e.g. fading) conditions. We show how to adapt the general machinery to this variant and how to optimize and implement it. We show that when properly tuned, Opportunistic Aloha very significantly outperforms Spatial Aloha, with e.g. a mean throughput per unit area twice higher for Rayleigh fading scenarios with typical parameters.

Recently, a new multiple access (MA) scheme called block-interleaved frequency division multiple access (B-IFDMA) is under consideration as an MA scheme candidate for 4G wireless applications. In this paper, the two variants of B-IFDMA are considered, the joint- DFT B-IFDMA and the added-signal B-IFDMA, and compared in terms of sensitivity to carrier frequency offsets (CFOs) for both uplink and downlink. CFO gives rise to multiuser interference and self-user interference. We derive analytical expressions for the power of these interferences, and we quantify their detrimental effect through the evaluation of the signal-to-interference-plus-noise ratio (SINR) degradation. We point out that both variants of B-IFDMA are not similarly affected by CFO. Hence, joint-DFT B-IFDMA provides a better robustness to multiuser interference than added-signal B-IFDMA, and so is better suited for the uplink. Then we show by means of numerical results that added-signal B-IFDMA is less sensitive to CFO in the downlink.

— This paper proposes a novel cross-layer scheduling scheme for a single-cell orthogonal frequency division multiple access (OFDMA) wireless system with partial channel state information (CSI) at transmitter (CSIT) and heterogeneous user delay requirements. Previous research efforts on OFDMA resource allocation are typically based on the availability of perfect CSI or imperfect CSI but with small error variance. Either case consists to typify a non tangible system as the potential facts of channel feedback delay or large channel estimation errors have not been considered. Thus, to attain a more realistic resolution our cross-layer design determines optimal subcarrier and power allocation policies based on partial CSIT and individual user’s quality of service (QoS) requirements. The simulation results show that the proposed cross-layer scheduler can maximize the system’s throughput and at the same time satisfy heterogeneous delay requirements of various users with significant low power consumption.

This paper proposes a generalized carrier frequency offset (CFO) estimator for the uplink of Orthogonal Frequency Division Multiple Access (OFDMA) wireless systems. Using the maximum likelihood criterion, the estimator estimates CFOs using the phase shift between two observation windows at distance less than the length of OFDMA symbol. The scheme offers the possibility to shorten the OFDMA preamble used in synchronization, and thus reduce overhead in packet-based wireless communications.

Multicarrier multiple access with channel knowledge and prescribed power at the transmitters is shown to maximize the sum-rate for circulant intersymbol-interference (ISI) channels. A low-complexity iterative algorithm is derived for optimal subcarrier allocation to multiple users, while power is loaded per user by specializing an existing iterative algorithm to circulant ISI channels. It is analytically shown that each subcarrier should be allocated to the user having relatively better subcarrier gain and that different users may share certain subcarriers.

Systems with single-carrier techniques show significant limits when high data speed transmission is concerned. In order to increase data speed, meet QoS requirements and maximize system capacity, multiple access techniques with efficient resource allocation are investigated. Systems with multi-carriers and multiple spreading in time, frequency, code or space domain, as well as radio link adaptation technologies, are favoured due to huge capacity, robustness and flexibility. Therefore, future research and design of mobile networks shall focus on multi-carrier hybrid modulation systems with adaptive technology and multiple smart antennas. This paper describes multiple access techniques suitable for mobile communication systems, stresses the importance of resource allocation techniques, briefly touches on present mobile network technology and finally gives an overview of multiple-access techniques for future mobile networks

Reservation random access (RRA) protocols have been proposed for handling speech and data traffic on packet wireless networks. Among them, collision resolution based RRA protocols decouple the speech access procedure from the data access procedure. It is well known that capture improves the performance of random access algorithms. However, due to the decoupling and the limited delay requirements, capture could have negative effects on the performance. It has been shown that reservation protocols do not operate correctly in the presence of co-channel interference. Centralised management techniques, based on retransmissions, represent a suitable method for handling channel errors in microcellular radio networks, characterised by a negligible propagation delay. We present analytical results of performance evaluations for decoupling RRA protocols in a wireless network with capture and errors. The model we use allows one to evaluate the performance of RRA protocols with re-transmissions.

The paper presents a simulation study of reservation random access (RRA) protocols for microcellular systems. The considered protocols are based on collision resolution techniques. Previous analytical evaluations show that these techniques represent a suitable solution for handling mixed traffic, consisting of speech and data, because they allow one to decouple the speech access procedure from the data access one. In the previous analytical works, a single cell scenario has been considered, assuming a radio channel with capture and errors. We present a simulation study that validates the analytical model, and extends the study to cellular scenarios. Different reuse factors are considered. The simulation includes the reservation traffic that affects the performance noticeably. The study presented is restricted to speech users only. The results of the simulation study about in-slot, decoupling RRA protocols in a cellular system with Rayleigh fading and shadowing are included.

We determine the performances of a collision resolution multiple access technique for handling speech and data traffic on a radio network with capture. The proposed access technique decouples the speech access procedure from the data access procedure. It follows that speech access performances do not depend on actual data load. It is well known that capture improves the performances of random access algorithms. However, due to the decoupling and the limited delay requirements, capture could have effect on performances of speech access procedure that depend on the speech model. In the paper we present analytical results of performance evaluations for different capture models. Two speech models are taken into consideration.

We propose a methodology for applying contention resolution multiple access techniques on a slotted and framed radio channel. The proposed techniques are able to handle the access of a mixed class of users, one consisting of a dynamic set of speech users whose information must respect strict delay limitations, the other including a population of users which generate a random traffic. The proposed techniques “decouple” the speech access procedure from the data access procedure. It follows that speech access performances do not depend on actual data load. Random traffic access performances are optimised for the Poisson user model. We also propose a multiple access technique for handling multi-rate traffic. The proposed technique permits to implement prioritised access policies and selective packet discarding. If speech users employ coding schemes that separate information components by significance, this technique can be used to drop less significant information.