scholarly journals Joint Resource Allocation for Multiuser Opportunistic Beamforming Systems with OFDM-NOMA

Entropy ◽  
2021 ◽  
Vol 23 (7) ◽  
pp. 809
Author(s):  
Wen-Bin Sun ◽  
Ming-Liang Tao ◽  
Ling Wang ◽  
Xin Yang ◽  
Rui-Zhe Zhou ◽  
...  
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Multiple Access ◽  
Optimization Problem ◽  
Spectrum Efficiency ◽  
Computation Complexity ◽  
Transmit Power ◽  
Feedback Information ◽  
Joint Resource Allocation ◽  
Multiple Access Schemes ◽  
Opportunistic Beamforming

Opportunistic beamforming (OBF) is an effective technique to improve the spectrum efficiencies (SEs) of multiple-input-multiple-output (MIMO) systems, which can obtain multiuser diversity gains with both low computation complexity and feedback information. To serve multiple users simultaneously, many multiple-access schemes have been researched in OBF. However, for most of the multiple-access schemes, the SEs are not satisfactory. To further improve the SE, this paper proposes a downlink multiuser OBF system, where both orthogonal frequency division multiplexing (OFDM) and non-orthogonal multiple-access (NOMA) methods are applied. The closed-form expressions of the equivalent channels and SE are derived in frequency selective fading channels. Then, an optimization problem is formulated to maximize the SE, although the optimization problem is non-convex and hard to solve. To obtain the solution, we divide the optimization problem into two suboptimal issues, and then a joint iterative algorithm is applied. In the proposed optimization scheme, the subcarrier mapping ϑ, user pairing knc and allocated power Pknc are determined to maximize spectrum efficiency (SE) and reduce bit error ratio (BER). According to numerical results, the proposed method achieves approximately 5 dB gain on both SE and BER, compared to the existing beamforming methods with low feedback information. Moreover, the SE of the proposed method is approximately 2 (bps/Hz) higher than sparse code multiple-access (SCMA), when the number of waiting users and the ratio of transmit power to noise variance are respectively 10 and 20 dB. It is indicated that the proposed scheme can achieve high and low BER with the limited feedback and computation complexity, regardless of the transmit power and the number of waiting users.

scholarly journals Performance Analysis of OFDMA vs. NOMA in Cognitive Radio Network

2021 ◽  
Vol 9 (VI) ◽  
pp. 2483-2488
Author(s):  
E. Alwin Richard
Keyword(s):  
Communication Systems ◽  
Orthogonal Frequency Division Multiplexing ◽  
Multiple Access ◽  
Spectrum Efficiency ◽  
Frequency Division Multiplexing ◽  
Frequency Division ◽  
Time Frequency ◽  
New Class ◽  
Overlapping Data ◽  
Multiple Access Schemes

Recent advancements in communication systems have resulted in a new class of multiple access schemes known as non-orthogonal multiple access (NOMA), the primary goal of which is to increase spectrum efficiency by overlapping data from different users in a single time-frequency resource used by the physical layer. NOMA receivers can resolve interference between data symbols from various users, hence increasing throughput. Initially, the combination of SCMA and orthogonal frequency division multiplexing (OFDM) is addressed, establishing a baseline for the overall SER performance of the multiple access strategy. Furthermore, this work suggests the merging of SCMA with generalised frequency division multiplexing (GFDM).GFDM is an intriguing possibility for future wireless communication systems since it is a very flexible non-orthogonal waveform that can imitate various different waveforms as corner cases. This research suggests two methods for integrating SCMA with GFDM.

scholarly journals NOMA for Multinumerology OFDM Systems

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Ayman T. Abusabah ◽  
Huseyin Arslan
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Multiple Access ◽  
Frequency Division ◽  
Ofdm Systems ◽  
Superposition Coding ◽  
Promising Technique ◽  
Successive Interference Cancelation ◽  
Power Domain ◽  
Multiple Access Schemes ◽  
Spectrally Efficient

Nonorthogonal multiple access (NOMA) is a promising technique which outperforms the traditional multiple access schemes in many aspects. It uses superposition coding (SC) to share the available resources among the users and adopts successive interference cancelation (SIC) for multiuser detection (MUD). Detection is performed in power domain where fairness can be supported through appropriate power allocation. Since power domain NOMA utilizes SC at the transmitter and SIC at the receiver, users cannot achieve equal rates and experience higher interference. In this paper, a novel NOMA scheme is proposed for multinumerology orthogonal frequency division multiplexing system, that is, different subcarrier spacings. The scheme uses the nature of mixed numerology systems to reduce the constraints associated with the MUD operation. This scheme not only enhances the fairness among the users but improves the bit error rate performance as well. Although the proposed scheme is less spectrally efficient than conventional NOMA schemes, it is still more spectrally efficient than orthogonal multiple access schemes.

scholarly journals Sparse code multiple access on the generalized frequency division multiplexing

2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Guilherme P. Aquino ◽  
Luciano L. Mendes
Keyword(s):  
Communication Systems ◽  
Orthogonal Frequency Division Multiplexing ◽  
Multiple Access ◽  
Physical Layer ◽  
Spectrum Efficiency ◽  
Sparse Code ◽  
Frequency Division Multiplexing ◽  
Frequency Division ◽  
Time Frequency ◽  
Performance Loss

Abstract Recent advances in the communication systems culminated in a new class of multiple access schemes, named non-orthogonal multiple access (NOMA), where the main goal is to increase the spectrum efficiency by overlapping data from different users in a single time-frequency resource used by the physical layer. NOMA receivers can resolve the interference among data symbols from different users, increasing the overall system spectrum efficiency without introducing symbol error rate (SER) performance loss, which makes this class of multiple access techniques interesting for future mobile communication systems. This paper analyzes one promising NOMA technique, called sparse code multiple access (SCMA), where C users can share U<C time-frequency resources from the physical layer. Initially, the SCMA and orthogonal frequency division multiplexing (OFDM) integration is considered, defining a benchmark for the overall SER performance for the multiple access technique. Furthermore, this paper proposes the SCMA and generalized frequency division multiplexing (GFDM) integration. Since GFDM is a highly flexible non-orthogonal waveform that can mimic several other waveforms as corner cases, it is an interesting candidate for future wireless communication systems. This paper proposes two approaches for combining SCMA and GFDM. The first one combines a soft equalizer, called block expectation propagation (BEP), and a multi-user detection (MUD) scheme based on the sum-product algorithm (SPA). This approach achieves the best SER performance, but with the significant increment of the complexity at the receiver. In the second approach, BEP is integrated with a simplified MUD, which is an original contribution of this paper, aiming for reducing the receiver’s complexity at the cost of SER performance loss. The solutions proposed in this paper show that SCMA-GFDM can be an interesting solution for future mobile networks.

Peak Average Power Reduction in NOMA by using PTSCT Technique

2020 ◽  
Vol 13 (3) ◽  
pp. 502-507 ◽  
Author(s):  
Arun Kumar ◽  
Manisha Gupta
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Multiple Access ◽  
Average Power ◽  
High Peak Power ◽  
Power Ratio ◽  
Transmission Scheme ◽  
Multiple Access Schemes ◽  
Power Ratio Reduction ◽  
Multiple Access System ◽  
Ratio Reduction

Background: High peak power is one of the several disadvantages which need to be addressed for its effective regularization. It hampers the performance of the system due to the utilization of the orthogonal frequency division multiplexing transmission scheme at the sender of the Non-orthogonal multiple access system. Objective: In this work, a new Partial transmission sequence circular transformation reduction technique is designed for Non-orthogonal multiple access schemes. Methods: Partial transmission sequence is considered to be one of the most efficient techniques to reduce the Peak to average power ratio but it leads to high computational complexity. Additionally, a circular transformation is implemented. In the proposed technique, circular transformation and alternate optimization are used. Results: Simulation results reveal that the Peak to average power ratio performance of the proposed technique is better as compared to the conventional partial transmission sequence. Conclusion: It is observed that the proposed technique achieved 80% Peak to average power ratio reduction and 90 % bit error rate performance as compared to the conventional Partial transmission sequence.

scholarly journals Joint User Scheduling, Relay Selection, and Power Allocation for Multi-Antenna Opportunistic Beamforming Systems

Entropy ◽  
2021 ◽  
Vol 23 (10) ◽  
pp. 1278
Author(s):  
Wen-Bin Sun ◽  
Ming-Liang Tao ◽  
Xin Yang ◽  
Tao Zhang ◽  
Chuang Han ◽  
...  
Keyword(s):  
Communication Systems ◽  
Relay Selection ◽  
Optimization Problem ◽  
Optimal Solution ◽  
Achievable Rate ◽  
User Scheduling ◽  
Feedback Information ◽  
Fifth Generation ◽  
Np Hard Problem ◽  
Opportunistic Beamforming

Opportunistic beamforming (OBF) is a potential technique in the fifth generation (5G) and beyond 5G (B5G) that can boost the performance of communication systems and encourage high user quality of service (QoS) through multi-user selection gain. However, the achievable rate tends to be saturated with the increased number of users, when the number of users is large. To further improve the achievable rate, we proposed a multi-antenna opportunistic beamforming-based relay (MOBR) system, which can achieve both multi-user and multi-relay selection gains. Then, an optimization problem is formulated to maximize the achievable rate. Nevertheless, the optimization problem is a non-deterministic polynomial (NP)-hard problem, and it is difficult to obtain an optimal solution. In order to solve the proposed optimization problem, we divide it into two suboptimal issues and apply a joint iterative algorithm to consider both the suboptimal issues. Our simulation results indicate that the proposed system achieved a higher achievable rate than the conventional OBF systems and outperformed other beamforming schemes with low feedback information.

scholarly journals Under Test Filtered-OFDM And UFMC 5g Waveform Using Cellular Network

2019 ◽  
Vol 54 (5) ◽  
Author(s):  
Ahmed Talaat Hammoodi ◽  
Farooq Sijal Shawqi ◽  
Lukman Audaha ◽  
Abdullah Ali Qasim ◽  
Ammar Ahmed Falih
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Multiple Access ◽  
Average Power ◽  
Cyclic Prefix ◽  
Frequency Division Multiplexing ◽  
Frequency Division ◽  
Wireless Technology ◽  
Spectrum Utilization ◽  
Multiple Access Schemes ◽  
Modulation Methods

In this study, filtered orthogonal frequency division multiplexing (F-OFDM) and universal filtered multicarrier (UFMC) were proposed for complexity reduction in the 5G waveform. Cyclic prefix orthogonal frequency division multiplexing (CP_OFDM) is well suited for 4G; however, the major problem of the 4G modulation methods is their susceptibility to high peak to average power ratio (PAPR). Another problem of OFDM is the issue of sideband leakage. The existing 4G systems mainly depend on the CP_OFDM waveform, which cannot support the host of applications provided by the 5G platform. 5G-generated traffic is likely to exhibit different features and requirements compared to the existing wireless technology. Consequently, investigations have been devoted to other multiple access schemes. The existing limitations of OFDM can be mitigated by using the UFMC technique. To ensure that the demands and requirements of the upcoming 5G cellular networks are satisfied, this study presents an enabler called filtered-OFDM (f-OFDM) for flexible waveform configurations. Contrarily, the assigned bandwidth in the f-OFDM is split into various sub-bands to accommodate different services in each sub-band using the most suited waveform, thereby enhancing the spectrum utilization using a different filter. Additionally, the advantages of F-OFDM and UFMC were portrayed via a wide comparison with the current 5G waveforms.

FrFT Angle Division Multiple Access with Optimal Time-Frequency-Angle Resource Distribution

2014 ◽  
Vol 519-520 ◽  
pp. 1012-1015
Author(s):  
Hui Qi Wang ◽  
Wangyong Lv
Keyword(s):  
Data Streams ◽  
Orthogonal Frequency Division Multiplexing ◽  
Multiple Access ◽  
Fractional Fourier Transform ◽  
Resource Distribution ◽  
Base Station ◽  
Spectrum Efficiency ◽  
Optimal Time ◽  
Time Frequency ◽  
Multiple Data

In this paper, optimal time-frequency-angle (TFA) resource distribution is proposed. It is achieved by fractional Fourier transform (FrFT) angle division multiple access (ADMA), and multiple data streams can be transmitted in the same frequency and time slot. Comparing with conventional time-frequency (TF) resource based orthogonal frequency division multiplexing (OFDM) system, the exponential base at each sub-channel is replaced by a set of chirp bases, which keep mutually approximately orthogonal. Each base station (BS) can support more move stations (MSs) or cell throughput. Simulations show the essential advantages in TFA resource distribution and system spectrum efficiency.

scholarly journals Chunk-Based Energy Efficient Resource Allocation in OFDMA Systems

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Yong Li ◽  
Zhengguang Zheng ◽  
Mingyue Zhao ◽  
Shan Jin ◽  
Zhangqin Huang
Keyword(s):  
Resource Allocation ◽  
Energy Efficient ◽  
Orthogonal Frequency Division Multiplexing ◽  
Optimization Problem ◽  
Low Complexity ◽  
Spectrum Efficiency ◽  
Ofdm Systems ◽  
Efficient Resource ◽  
Energy Efficient Resource Allocation ◽  
Frequency Selective Channels

Energy efficiency (EE) capacity analysis of the chunk-based resource allocation is presented by considering the minimum spectrum efficiency (SE) constraint in downlink multiuser orthogonal frequency division multiplexing (OFDM) systems. Considering the minimum SE requirement, an optimization problem to maximize EE with limited transmit power is formulated over frequency selective channels. Based on this model, a low-complexity energy efficient resource allocation is proposed. The effects of system parameters, such as the average channel gain-to-noise ratio (CNR) and the number of subcarriers per chunk, are evaluated. Numerical results demonstrate the effectiveness of the proposed scheme for balancing the EE and SE.

scholarly journals Optimal UAV's Deployment and Transmit Power Design for Two Users Uplink NOMA Systems

2021 ◽  
Vol 14 ◽  
Author(s):  
Fayong Zhao
Keyword(s):  
Multiple Access ◽  
Optimization Problem ◽  
Transmission Rate ◽  
Initial Study ◽  
Power Constraint ◽  
Transmit Power ◽  
Access Technology ◽  
Aerial Vehicle ◽  
Simulation Results ◽  
Rate Requirement

In order to fully utilize the spectrum resources, this work considers a unmanned aerial vehicle (UAV) uplink communication system based on non-orthogonal multiple access technology (NOMA), in which the UAV receives information from the ground users with a certain flying altitude. As an initial study, we consider a simplified setup with two ground users to draw some insightful results. Explicitly, we first formulate an optimization problem that maximizes the sum throughput subject to each user's transmit power constraint and their corresponding minimum transmission rate requirement. Then, both the optimal transmit power and UAV's deployment location are derived with the aid of employing the Karush-Kuhn-Tucher (KKT) conditions. Simulation results show that the proposed UAV's deployment scheme with the users' power allocation can achieve a higher sum throughput compared with two existing benchmark schemes.

scholarly journals User Clustering and Power Allocation for Energy Efficiency Maximization in Downlink Non-Orthogonal Multiple Access Systems

2021 ◽  
Vol 11 (2) ◽  
pp. 716
Author(s):  
Ruibiao Chen ◽  
Fangxing Shu ◽  
Kai Lei ◽  
Jianping Wang ◽  
Liangjie Zhang
Keyword(s):  
Energy Efficiency ◽  
Power Allocation ◽  
Multiple Access ◽  
Spectrum Efficiency ◽  
Lagrangian Multiplier ◽  
Efficiency Gain ◽  
Optimal Power Allocation ◽  
Optimal Power ◽  
User Clustering ◽  
Cluster Dynamic

Non-orthogonal multiple access (NOMA) has been considered a promising technique for the fifth generation (5G) mobile communication networks because of its high spectrum efficiency. In NOMA, by using successive interference cancellation (SIC) techniques at the receivers, multiple users with different channel gain can be multiplexed together in the same subchannel for concurrent transmission in the same spectrum. The simultaneously multiple transmission achieves high system throughput in NOMA. However, it also leads to more energy consumption, limiting its application in many energy-constrained scenarios. As a result, the enhancement of energy efficiency becomes a critical issue in NOMA systems. This paper focuses on efficient user clustering strategy and power allocation design of downlink NOMA systems. The energy efficiency maximization of downlink NOMA systems is formulated as an NP-hard optimization problem under maximum transmission power, minimum data transmission rate requirement, and SIC requirement. For the approximate solution with much lower complexity, we first exploit a quick suboptimal clustering method to assign each user to a subchannel. Given the user clustering result, the optimal power allocation problem is solved in two steps. By employing the Lagrangian multiplier method with Karush–Kuhn–Tucker optimality conditions, the optimal power allocation is calculated for each subchannel. In addition, then, an inter-cluster dynamic programming model is further developed to achieve the overall maximum energy efficiency. The theoretical analysis and simulations show that the proposed schemes achieve a significant energy efficiency gain compared with existing methods.

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