Multiple User Access Research Articles

Performance Optimization of Diagonal Identity Matrix and Enhanced Double Weight Codes in Terms of Security for Short Haul Communication

Optical code division multiplexing is getting attention because it is an imminent multiple access technology which can cater ever increasing data traffic as well as multiple user access in optical networks. In this work, a zero cross correlation based diagonal identity matrix code is presented and it is compared with the enhanced double weight code to check the superior code in OCDMA system at data speed of 30 Gbps. Effect of some parameters of OCDMA system which prominently affects the security of the system and these are input power, linewidth and modulator extinction ratio. Optimization using single parameter optimization and multiple parameter optimizations has been done. In order to accomplish the work, optiwave optisystem software is used and extensive literature survey is done, issues encountered are carefully checked and to address the issues, proposed system is presented. Results are evaluated in terms of Q factor, bit error rate (BER) and signal to noise ratio. Novelty of proposed work is the search of optimal parameters of both the codes in terms of enhanced security such that eavesdropping at these optimal parameters will become tedious for unauthorized user.

Optimal Multi-View Video Transmission in OFDMA Systems

In this letter, we study the transmission of a multi-view video (MVV) to multiple users in an Orthogonal Frequency Division Multiple Access (OFDMA) system. To maximally improve transmission efficiency, we exploit both natural multicast opportunities and view synthesis-enabled multicast opportunities. First, we establish a communication model for transmission of a MVV to multiple users in an OFDMA system. Then, we formulate the minimization problem of the average weighted sum energy consumption for view transmission and synthesis with respect to view selection and transmission power and subcarrier allocation. The optimization problem is a challenging mixed discrete-continuous optimization problem with huge numbers of variables and constraints. A low-complexity algorithm is proposed to obtain a suboptimal solution. Finally, numerical results further demonstrate the value of view synthesis-enabled multicast opportunities for MVV transmission in OFDMA systems.

Performance Enhancement of Encoding–Decoding Multidiagonal and Walsh Hadamard Codes for Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA) Utilizing Dispersion Compensated Fiber

Abstract Spectral Amplitude Coding-Optical Codes Division Multiple Access (SAC-OCDMA) is a future multiplexing technique that witnessed a dramatic attraction for eliminating the problems of the internet in optical network field such as multiple-user access and speed’s growth of the files or data traffic. In this research article, the performance of SAC-OCDMA system based on two encoding–decoding multidiagonal (MD) and Walsh Hadamard (WH) codes is enhanced utilizing three different schemes of dispersion compensating fiber (DCF): pre-, post- and symmetrical compensation. The system is simulated using Optisystem version 7.0 and Optigrating version 4.2. The performance of the proposed system is specified in terms of bit error rate (BER), Q-factor and eye diagram. It has been observed that the compensated system based on MD code is performs much better compared to the system based on WH code. On the other hand, the compensated SAC-OCDMA system with symmetrical DCF has the lowest values of BER and largest values of Q-factor, so it is considered the best simulated scheme contrasted with pre- and post-DCF.

Secure Alamouti Multiple Access Channel Transmissions: Multiuser Transmission and Multi-Antenna Eavesdroppers

Using the Alamouti space-time block code in conjunction with artificial noise (AN) is an effective approach to secure multiple access (MAC) transmission in the presence of eavesdroppers. Existing studies on this technique focus on the two-user transmission systems and single-antenna eavesdroppers. This letter proposes a novel approach that generalizes this technique to multiuser transmission schemes and multi-antenna eavesdroppers. Security gains are analyzed, and the minimum number of MAC users that should participate in generating the AN in order to secure their transmissions is characterized analytically.

Filter-less WDM for visible light communications using colored pulse amplitude modulation.

This Letter demonstrates, for the first time, to the best of our knowledge, a new wavelength-division multiplexing (WDM) scheme for visible light communications using multi-level colored pulse amplitude modulation. Unlike traditional WDM, no optical bandpass filters are required, and only a single optical detector is used. We show that, by transmitting n independent sets of weighted on-off keying non-return-to-zero data on separate wavelengths over a line-of-sight transmission path, the resultant additive symbols can be successfully demodulated. Hence, the data rates can be aggregated for a single user or divided into individual colors for multiple user access schemes. The system is empirically tested for M=4 and 8 using an off-the-shelf red, green, and blue (RGB) chip light-emitting diode (LED). We demonstrate that for M=4, using the R and B chips, a bit error rate (BER) of ≤10-6 can be achieved for each wavelength at bit rates up to 10Mbps, limited by the LEDs under test. For M=8 using R, G, and B, a BER of ≤10-6 can be achieved for each wavelength at bit rates up to 5Mbps.

Ergodic Capacity of NOMA-Based Uplink Satellite Networks With Randomly Deployed Users

Allowing multiple users access simultaneously, a power-domain nonorthogonal multiple access (NOMA) scheme can provide enhanced resource utilization efficiency and has been viewed as a promising strategy in the satellite networks, to provide high quality-of-service for large number of users within limited spectrum and time resources. Taking into account the random location information of served users, imperfect channel state information (CSI), and antenna-pointing error, we study the ergodic capacity of a NOMA-based uplink satellite network in this article. Specially, we first develop a general framework for the NOMA-based system by applying standard recommendations, configurations, and channel characteristics. Then, the analytical expression for the achievable ergodic capacity of the considered network is derived. Finally, numerical simulations are provided to attest the validity of theoretical results and show the impact of various key parameters, such as location information, link quality, transmission power, imperfect CSI, and antenna-pointing error, on the considered network.

Efficient Resource Management for Sum Capacity Maximization in 5G NOMA Systems

The modern cellular technologies are expected to provide high data rates and massive connectivity in fifth generation (5G) systems; however, this may be impossible through traditional radio access techniques. Recently, non-orthogonal multiple access (NOMA) has emerged as one of the promising cellular techniques for modern cellular communications with its ability to provide access for multiple users to the network over the same system resources. This paper studies resource management problem for downlink transmission of multiuser NOMA system. Our objective is to optimize both frequency and power resources for sum capacity maximization while taking into account each user minimum capacity requirement. Firstly, the problem of resource management decouples into two subproblems, that is, efficient sub-channel assignment and optimal power allocation, respectively. Secondly, for given power at base station, we design two sub-optimal algorithms for sub-channel assignment based on user channel condition and user minimum capacity requirement, respectively. Lastly, for any given sub-channel assignment, the problem first transforms into standard convex optimization problem and then we employ duality theory. To evaluate our proposed NOMA scheme, the enhanced version of existing NOMA optimization scheme is also presented as a benchmark. Results demonstrate that the proposed NOMA resource management scheme outperforms the benchmark NOMA optimization scheme in terms of sum capacity.

Quadrature Polar On-Off Keying in NOMA

Beyond the perfect successive interference cancellation (SIC) performance, one of two users in non-orthogonal multiple access (NOMA) can be served orthogonally in power-domain with polar on-off keying (POOK), which is recently proposed in [6]. We extend the concept of POOK into 2-dimensional modulation constellations, just as the extension of binary phase shift keying (BPSK) into quadrature phase shift keying (QPSK). The suitable name for this modulation can be quadrature polar on-off keying (QPOOK).

OCDMA System Using Two Code Keying Encryption Introducing a SOA Based CMUX And CDEMUX Over a WDM System

This paper introduces an Optical Code Division multiplexing (OCDMA) system using two code keying encryptions. In this paper proposed OCDMA system is designed using Semiconductor optical amplifiers (SOAs) which has nonlinear character and can implementor different logic functions. SOA based 2 × 1 Codeword Multiplexer (CMUX) is designed to multiplex the user data and a 1 × 2 Codeword DE Multiplexer (CDEMUX) to demodulate the user data. Then a multiple user access is provided using WDM system to design the whole OCDMA system. Transmission distance of 70 km is achieved with acceptable bit error rate and Q factor. Open eye diagram is also verified at the receiving end.

Downlink Non-Orthogonal Multiple Access (NOMA) in Poisson Networks

A network model is considered, where Poisson distributed base stations transmit to N power-domain nonorthogonal multiple access (NOMA) users (TIEs) each that employ successive interference cancellation (SIC) for decoding. We propose three models for the clustering of NOMA TIEs and consider two different ordering techniques for the NOMA TIEs: mean signal power-based and instantaneous signal-to-intercell-interference-and-noise-ratio-based. For each technique, we present a signal-to-interference-and-noise ratio analysis for the coverage of the typical TIE. We plot the rate region for the two-user case and show that neither ordering technique is consistently superior to the other. We propose two efficient algorithms for finding a feasible resource allocation that maximize the cell sum rate R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tot</sub> , for general N, constrained to: 1) a minimum throughput T for each TIE, 2) identical throughput for all TIEs. We show the existence of: 1) an optimum N that maximizes the constrained R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tot</sub> given a set of network parameters and 2) a critical SIC level necessary for NOMA to outperform orthogonal multiple access. The results highlight the importance in choosing the network parameters N, the constraints, and the ordering technique to balance the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tot</sub> and fairness requirements. We also show that interference-aware TIE clustering can significantly improve performance.

Multiple Access MmWave Design for UAV-Aided 5G Communications

Unmanned aerial vehicles (UAVs) have tremendous potential to improve wireless network capacity, but are challenging to operate in ultra-dense networks, mainly due to the strong interference received from the dominated lineof- sight channels of the UAVs. By forming multiple highly directional beams, millimeter-wave (mmWave) communication technology allows concurrent user transmissions via beam-division multiple access (BDMA), and thus has emerged as a promising solution to mitigate interference for the fifth generation (5G) UAV communication. However, due to the limited number of beams generated in practical mmWave communication systems, conventional BDMA cannot meet the ever increasing capacity requirement. A new multiple access technique is intensely desired. In this article, we integrate mmWave communication with UAV-aided 5G ultra-dense networks, and design a novel link-adaptive constellation- division multiple access (CoDMA) technique. We discuss key challenges in efficient multiple access technique design, and then investigate design principles on new multiplexing methods and beamwidth optimization for interference management in UAV-aided dynamic networks. We further apply flexible constellation division in rateless codes, and put forward the system-level design of CoMDA with beamwidth adaptation to unleash the multiplexing gain. Finally, we show that our design can successfully enable multiple-user access within a single beam without causing any intra-beam interference while efficiently mitigating interference from adjacent beams. We also demonstrate that the proposed design is adaptive to the UAV network dynamics, and can greatly improve the system throughput.

Spectrum Resource and Power Allocation With Adaptive Proportional Fair User Pairing for NOMA Systems

In this paper, we investigate the spectrum resource and power allocation problem for the tradeoff between maximizing the sum rate and minimum rate requirements of users in non-orthogonal multiple access (NOMA) system. First, we formulate the NOMA techniques, basic principles, and double-objective optimization (DOO) problem. Then, the non-convexity of the DOO problem is converted into a single-objective optimization (SOO) problem by power discretization method. Global optimal search (GOS) algorithm is applied to solve the user-subchannel matching and power allocation problem. Due to its high complexity and unfairness among users, it is only suitable for determining the upper bound of users throughput performance. Finally, yet importantly, a spectrum resource and power allocation algorithm with adaptive proportional fair (APF) user pairing is proposed to convert the original optimization problem into user pairing, sub-channel, and power allocation. The users paired on the sub-channel are determined by the scheduling priority which is based on the equivalent channel gain. The BS dynamically adjusts the forgetting factor in the APF algorithm based on the variance of all the users' scheduling priorities so as to influence the update of users' scheduling weights. The power allocation stage proposes three power allocation schemes to ensure the users' minimum data rate requirements under the condition that effectively guarantees the correct execution of successive interference cancellation (SIC). The simulation results demonstrate that it can not only approach the throughput performance compared with the global optimal search and the classical water-filling (WF) power allocation using matching theory but also can improve the fairness of the users.

Placement of M-Sequences over the Field &amp;lt;i&amp;gt;Fp&amp;lt;/i&amp;gt; in the Space &amp;lt;i&amp;gt;R&amp;lt;sup&amp;gt;n&amp;lt;/sup&amp;gt;&amp;lt;/i&amp;gt;

Spread spectrum communication systems are widely used today in a variety of applications for different purposes such as access of same radio spectrum by multiple users (multiple access), anti-jamming capability (so that signal transmission cannot be interrupted or blocked by spurious transmission from enemy), interference rejection, secure communications, multi-path protection, etc. Several spreading codes are popular for use in practical spread spectrum systems. one of these important codes is Maximal Sequence (M-sequence) length codes, These are the longest codes that can be generated by a shift register of a specific length, The number of 1-s in the complete sequence and the number of 0-s will differ by one, Further, the auto-correlation of an m-sequence is -1, another interesting property of an M-sequence is that the sequence, when added (modulo-2) with a cyclically shifted version of itself, results in another shifted version of the original sequence. Hence, the M-sequences are also known as, pseudo-noise or PN sequences. Current article study placement M-Sequences over the finite field Fp or Mp-Sequences (where p is a prime number) in the space Rn, these sequences can be generated as a closed set under the addition. These sequences form additive groups with the corresponding null sequence that was generated by the feedback shift registers. Such Mp-Sequences see a great application in the forward links of communication channels. Furthermore, they form coders and decoders that combine the information by p during the connection process with the backward links of these channels. These sequences scrutinize the transmitted information to enable it to reach the receivers in an accurate form. This study has defined eminent surfaces in the vector space ‘R’ having dimensions of ‘n’ as quadratic forms, spheres, and planes that contain these sequences.

Power Allocation to Improve Data-Rate Fairness of Non-orthogonal Multiple Access Users

Power Allocation to Improve Data-Rate Fairness of Non-orthogonal Multiple Access Users

Optimal Multicast of Tiled 360 VR Video in OFDMA Systems

In this letter, we study optimal multicast of tiled 360 virtual reality (VR) video from one server (base station or access point) to multiple users in an orthogonal frequency division multiple access (OFDMA) system. For given video quality, we optimize the subcarrier, transmission power and transmission rate allocation to minimize the total transmission power. For given transmission power budget, we optimize the subcarrier, transmission power and transmission rate allocation to maximize the received video quality. These two optimization problems are non-convex problems. We obtain a globally optimal closed-form solution and a near optimal solution of the two problems, separately, both revealing important design insights for multicast of tiled 360 VR video in OFDMA systems.

Joint task scheduling and uplink/downlink radio resource allocation in PD-NOMA based mobile edge computing networks

Mobile edge computing (MEC) is a new paradigm that brings the computation capabilities closer to the edge of wireless networks. In doing so, the computation tasks of users can be offloaded to the network edge for remote executing. Since both the computing and transmission delays in uplink and downlink of each task offloading operation affect the total task execution delays, it is necessary to utilize the physical layer transmission opportunities in the task allocation algorithms. In this regard, we develop an efficient algorithm to minimize the total execution delay of users in a single-cell power-domain non-orthogonal multiple access (PD-NOMA) based MEC system with multiple users and single MEC server. Hence the computation task of each user can be partitioned into two separated parts, one for offloading to the network edge and another for locally computing. In the considered partial offloading scheme, we jointly obtain subcarrier and transmit power allocation policies for both the uplink and downlink transmissions with task scheduling and computation resource allocation at both the users and the MEC server. Numerical results demonstrate that when the communication and computation resources are jointly optimized at the task allocation algorithms, the network performance is improved nearly 30% compared to the existing joint computation and task allocation approach in which both the downlink and uplink data rates are assumed to be fixed.

Design and Implementation of OFDM System using QPSK &amp; QAM

Abstract In this work, OFDM (orthogonal frequency division multiplexing) is analyzed for different transmission schemes on the basis of BER (Bit Error Rate), transmitting-receiving signal, constellation diagram and the best transmitting scheme is determined for OFDM. OFDM is analogous to Frequency Division Multiple Access (FDMA) in which the multiple user access is achieved by sub-dividing the existing spectrum into various channels, which are then allocated to users. In this paper Mat-lab simulation OFDM is used to see, how the Bit Error Ratio (BER) of a transmission varies when signal to Noise Ratio (S/N) and Multi-Propagation effect are altered to transmit a computer file in binary data from modulated by 16-QAM and QPSK modulation, finally at the end of the transmission, when the receiver receives the data, a comparison of the transmitted and the received messages is done in order to calculate the Bit Error Ratio (BER).

A General Framework for Gathering Data to Quantify Annual Visitation

With the increase in outdoor recreation in the United States following WWII and the focus on multiple use management in the wake of the Multiple Use Sustained Yield Act in 1960, land managers have been under increased pressure to balance multiple objectives and ensure that visitor use impacts at the sites under their purview are kept within acceptable bounds. The Act established that multiple uses had “legitimate interests” on public lands (Adams, 1993, p. 137) and that these uses be managed in a “harmonious and coordinated manner” (Cubbage, 1993, p. 298). However, there is no uniform, universally accepted approach to determining the number of visitors at individual sites, especially in light of the various activities undertaken by the public in protected areas. A unified methodology is needed; one that is applicable across multiple types of properties. We propose a generic multi-phase stratified approach capable of capturing visitation in multiple user activity and access categories. The strata used in this protocol are access location, mode of access, day of the week, and season. Access locations are grouped together in zones for ease of data collection. The approach we propose is readily adaptable to target site-specific assessments and strikes a balance between the need to gather sufficient data and staff person-hour commitment. Data are gathered based on mode of visitor access, definable access points, site-specific trends in visitation, and manager delineated zones at each site under consideration. Initial information is used to develop weekly visitation curves (depictions of the variation in visitation by day of the week) for each manager-defined season at each site and to specific survey locations within each zone mentioned above. Weekly visitation curves are confirmed using a two-week census prior to full data collection, thereby improving statistical accuracy. Additionally, multipliers are created for each mode of visitor access to estimate total visitation during the period under review. Data are summed across all zones within the site and across all seasons to gain a full representation of visitor use for the site being studied. The suggested approach may be easily modified to address variation in spatial and temporal patterns of visitation at multiple sites, as well as variation in modes of visitor access. The use of appropriate sampling techniques allows the employment of statistical estimation, thereby greatly reducing the amount of effort required with a full census for a valid estimate of visitation at a particular site or sites. Subscribe to JPRA

Estimating the number of users in TDMA networks based on redundancy of adaptive channel coding

Blind identification of protocols in wireless communication networks is a critical subject in non-cooperative context. In this paper, a novel method is proposed to estimate the number of active users (NoAU) in wireless time division multiple access (TDMA) networks based on the redundancy of adaptive channel coding. The proposed method, which is based on decision trees and machine learning, can also be used in adaptive coding systems to identify the number of distinct code rates employed by a single transmitter. Simulation results show that the proposed method can estimate the number of codes with accuracy around 99% in noiseless situation. Moreover, for noisy environments, reasonable accuracies compared to naïve methods are obtained.

On the performance of a virtual user pairing scheme to efficiently utilize the spectrum of unpaired users in NOMA

This paper evaluates the performance of a virtual user pairing scheme that efficiently utilizes the spectrum of unpaired users in non-orthogonal multiple access (NOMA), termed as VP-NOMA. The scheme aims at utilizing the frequency bands of those users which remain unpaired due to the non-uniform distribution of users in a cellular area. We consider a case where the cell edge users are more than the cell center users, so that complete one-to-one correspondence does not exist between all cell center and cell edge users to be accommodated/paired using conventional NOMA (C-NOMA) user pairing. Thus, some cell edge users remain unpaired, and are served using conventional multiple access (OMA) schemes. In such scenario, VP-NOMA pairs a single cell center user with two or more clustered (closely located) cell edge users over non-overlapping frequency bands, thus enabling the cell center user to efficiently use the frequency bands of these previously unpaired cell edge users. Performance of VP-NOMA in terms of ergodic sum capacity (ESC), outage probability (OP), and outage sum capacity (OSC), is analyzed through comprehensive mathematical derivations and simulations for a generalized system model. Moreover, the mathematical analysis is validated through close concordance between analytical and simulation results of ESC, OP, and OSC.