Outage Performance of Non-Orthogonal Multiple Access Based Unmanned Aerial Vehicles Satellite Networks

With rapid development of unmanned aerial vehicles(UAVs), more and more UAVs access satellite networks for data transmission. To improve the spectral efficiency, non-orthogonal multiple access(NOMA) is adopted to integrate UAVs into the satellite network, where multiple satellites cooperatively serve the UAVs and mobile terminal using the Ku-band and above. Taking into account the rain fading and the fading correlation, the outage performance is first analytically obtained for fixed power allocation and then efficiently calculated by the proposed power allocation algorithm to guarantee the user fairness. Simulation results verify the outage performance analysis and show the performance improvement of the proposed power allocation scheme.

On Uplink Non-Orthogonal Multiple Access for 5G：Opportunities and Challenges

In this paper,the concept of grantfree non-orthogonal multiple access(NOMA) for uplink data transmission is elaborated.NOMA in combination with grant-free can be applied to ultra reliability low latency communication(URLLC),massive machine type communication(m MTC),enhanced mobile broadband(e MBB) small packet and two-step random-access channel(RACH) scenarios.The advantages of grant-free NOMA are low latency and signaling overhead,high access capability and efficient resource utilization.Candidate uplink NOMA schemes are summarized and preliminary comparison among a subset of schemes are presented.Furthermore,design aspects for grant-free NOMA are discussed,with special notes on particular issues such as blind UE identification and transmitter/receiver(Tx/Rx) impairments in realistic deployment.

Non-Orthogonal Multiple Access in Cell-Free Massive MIMO Networks

In this paper, we investigate the downlink performance of cell-free massive multi-input multi-output non-orthogonal multiple access(CF-m MIMO-NOMA) system with conjugate beamforming precoder and compare against the orthogonal multiple access(OMA) counterpart. A novel achievable closed-form spectral efficiency(SE) expression is derived, which characterizes the effects of the channel estimation error, pilot contamination, imperfect successive interference cancellation(SIC) operation, and power optimization technique. Then, motivated by the closedform result, a sum-SE maximization algorithm with the sequential convex approximation(SCA) is proposed, subject to each AP power constraint and SIC power constraint. Numerical experiments indicate that the proposed sum-SE maximization algorithms have a fast converge rate, within about five iterations. In addition, compared with the full power control(FPC) scheme, our algorithms can significantly improve the achievable sum-SE. Moreover, NOMA outperforms OMA in many respects in the presence of the proposed algorithms.

Analysis of Non-Orthogonal Multiple Access for 5G

The major challenge faced by the fifth generation(5G) mobile network is higher spectral efficiency and massive connectivity,i.e.,the target spectrum efficiency is 3 times over 4G,and the target connection density is one million devices per square kilometer.These requirements are difficult to be satisfied with orthogonal multiple access(OMA) schemes.Non-orthogonal multiple access(NOMA) has thus been proposed as a promising candidate to address some of the challenges for 5G.In this paper,a comprehensive survey of different candidate NOMA schemes for 5G is presented,where the usage scenarios of5 G and the application requirements for NOMA are firstly discussed.A general framework of NOMA scheme is established and the features of typical NOMA schemes are analyzed and compared.We focus on the recent progress and challenge of NOMA in standardization of international telecommunication union(ITU),and 3rd generation partnership project(3GPP).In addition,prototype development and future research directions are also provided respectively.

Uplink Grant-Free Pattern Division Multiple Access (GF-PDMA) for 5G Radio Access

Massive machine type communication(m MTC) is one of the key application scenarios for the fifth generation mobile communication(5 G). Grant-free(GF) transmission can reduce the high signaling overhead in m MTC. Non-orthogonal multiple access(NMA) can support more users for m MTC than orthogonal frequency division multiple access(OFDMA). Applying GF transmission in NMA system becomes an active topic recently. The in-depth study on applying GF transmission in pattern division multiple access(PDMA), a competitive candidate scheme of NMA, is investigated in this paper. The definition, latency and allocation of resource and transmission mechanism for GF-PDMA are discussed in detail. The link-level and system-level evaluations are provided to verify the analysis. The analysis and simulation results demonstrate that the proposed GF-PDMA has lower latency than grant based PDMA(GB-PDMA), possesses strong scalability to confront collision and provides almost 2.15 times gain over GF-OFDMA in terms of supporting the number of active users in the system.

Frameworks of Non-Orthogonal Multiple Access Techniques in Cognitive Radio Communication Systems

Recently,the increasing demand of radio spectrum for the next generation communication systems due to the explosive growth of applications appetite for bandwidths has led to the problem of spectrum scarcity.The potential approaches among the proposed solutions to resolve this issue are well explored cognitive radio(CR)technology and recently introduced non-orthogonal multiple access(NOMA)techniques.Both the techniques are employed for efficient spectrum utilization and assure the significant improvement in the spectral efficiency.Further,the significant improvement in spectral efficiency can be achieved by combining both the techniques.Since the CR is well-explored technique as compared to that of the NOMA in the field of communication,therefore it is worth and wise to implement this technique over the CR.In this article,we have presented the frameworks of NOMA implementation over CR as well as the feasibility of proposed frameworks.Further,the differences between proposed CR-NOMA and conventional CR frameworks are discussed.Finally,the potential issues regarding the implementation of CR-NOMA are explored.

Symbol Error Rate Performance Analysis of Non-Orthogonal Multiple Access for Visible Light Communications

Non-orthogonal multiple access(NOMA) is considered as one of promising radio access techniques for visible light communications(VLC) in next-generation wireless communications systems.In order to provide theoretical support for designing VLC-NOMA,we derive its analytic expressions for the symbol error rate(SER).Specifically,NOMA is first incorporated with appropriate VLC to establish a VLC-NOMA framework.Afterwards,mathematical expressions of the SER for the VLC-NOMA are developed.Moreover,numerical results are provided carefully to demonstrate that the proposed VLC-NOMA scheme outperforms than state-of-the-art orthogonal frequency division multiple access(OFDMA) one in terms of SER performance.Finally,relationships between the SER performance and the number of users,power allocation coefficient and semi-angle are well investigated,which can give us a scientific guide to devise the VLC-NOMA system for achieving better SER performance.

A Survey of Downlink Non-Orthogonal Multiple Access for 5G Wireless Communication Networks

Non-orthogonal multiple access （NOMA） has been recognized as a promising multiple access technique for the next generation cel-lular communication networks. In this paper, we first discuss a simple NOMA model with two users served by a single-carrier si-multaneously to illustrate its basic principles. Then, a more general model with multicarrier serving an arbitrary number of users on each subcarrier is also discussed. An overview of existing works on performance analysis, resource allocation, and multiple-in-put multiple-output NOMA are summarized and discussed. Furthermore, we discuss the key features of NOMA and its potential re-search challenges.

Non-Orthogonal Multiple Access Schemes for 5G

Multiple access scheme is one of the key techniques in wireless communication systems. Each generation of wireless communica-tion is featured by a new multiple access scheme from 1G to 4G. In this article we review several non-orthogonal multiple access schemes for 5G. Their principles, advantages and disadvantages are discussed, and followed by a comprehensive comparison of these solutions from the perspective of user overload, receiver type, receiver complexity and so on. We also discuss the applica-tion challenges of non-orthogonal multiple access schemes in 5G.

Resource Allocation Based on User Pairing and Subcarrier Matching for Downlink Non-Orthogonal Multiple Access Networks

The traditional orthogonal multiple access(OMA)is unable to satisfy the needs of large number of smart devices.To increase the transmission rate in the limited spectrum resource,implementation of both non-orthogonal multiple access(NOMA)and successive interference cancelation(SIC)is essential.In this paper,an optimal resource allocation algorithm in NOMA is proposed to maximize the total system rate in a multi-sector multi-subcarrier relay-assisted communication network.Since the original problem is a non-convex problem with mixed integer programming which is non-deterministic polynomial-time(NP)-hard,a three-step solution is proposed to solve the primal problem.Firstly,we determine the optimal power allocation of the outer users by using the approach of monotonic discrimination,and then the optimal user pairing is determined.Secondly,the successive convex approximation(SCA)method is introduced to transform the non-convex problem involving central users into convex one,and the Lagrangian dual method is used to determine the optimal solution.Finally,the standard Hungarian algorithm is utilized to determine the optimal subcarrier matching.The simulation results show that resource allocation algorithm is able to meet the user performance requirements with NOMA,and the total system rate is improved compared to the existing algorithms.

Secure Transmission in Downlink Non-Orthogonal Multiple Access Based on Polar Codes

Non-orthogonal multiple access(NOMA)is deemed to have a superior spectral efficiency and polar codes have became the channel coding scheme for control channel of enhanced mobile broadband(eMBB)in the fifth generation(5G)communication systems.In this paper,NOMA combined with polar codes is used to achieve secure transmission.Both degraded wiretap channel and non-degraded wiretap channel are considered,where an eavesdropper intercepts the communication between base station(BS)and users.For the degraded wiretap channel scenario,a secure polar encoding scheme is proposed in NOMA systems with power allocation to achieve the maximum secrecy capacity.With regard to the nondegraded wiretap channel,a polar encoding scheme with multiple-input-single-output(MISO)system is proposed,where artificial noise is generated at BS to confuse the eavesdropper’s channel via transmit beamforming.The security and the secure rate are employed respectively in order to measure the secrecy performance.We prove that the proposed schemes for each scenario can achieve the secure rate and can transmit the signal securely and reliably.The simulation results show that the eavesdropper hardly decoding the secure signal when the legitimate receiver can decode the signal with very low block error rate(BLER).

Joint Non-Orthogonal Multiple Access (NOMA) & Walsh-Hadamard Transform: Enhancing the Receiver Performance

Non-orthogonal multiple access(NOMA) is a new access method to achieve high performance gains in terms of capacity and throughput, so it is currently under consideration as one of the candidates for fifth generation(5 G) technologies. NOMA utilizes power domain in order to superimpose signals of multiple users in a single transmitted signal. This creates a lot of interference at the receive side. Although the use of successive interference cancellation(SIC) technique reduces the interference, but to further improve the receiver performance, in this paper, we have proposed a joint Walsh-Hadamard transform(WHT) and NOMA approach for achieving better performance gains than the conventional NOMA. WHT is a well-known code used in communication systems and is used as an orthogonal variable spreading factor(OVSF) in communication systems. Application of WHT to NOMA results in low bit error rate(BER) and high throughput performance for both low and high channel gain users. Further, it also reduces peak to average power ratio(PAPR) of the user signal. The results are discussed in terms of comparison between the conventionalNOMA and the proposed technique, which shows that it offers high performance gains in terms of low BER at different SNR levels, reduced PAPR, high user throughput performance and better spectral efficiency.

A genetic algorithm based hybrid non-orthogonal multiple access protocol

Both high-dense wireless connectivity and ultra-huge network capacity are main challenges of next generation broadband networks.As one of its key promising technologies,non-orthogonal multi-ple access(NOMA)scheme can solve those challenges and meet those needs to some extent,in the way that different user equipments(UEs)multiplex on the same resource.Researchers around the world have presented numerous NOMA solutions.Among those,sparse code multiple access(SC-MA)technology is a typical NOMA solution.It supports scheduled access and random access which can be called granted access and grant-free access respectively.But resources allocated to granted UEs and grant-free UEs are strictly separated.In order to improve resource utilization,a hybrid non-orthogonal multiple access scheme is proposed.It allows granted UEs and grant-free UEs sharing the same resource unit in terms of fine-grained integration.On the basis,a resource allocation method is further brought forward based on genetic algorithm.It optimizes resource allocation of all UEs by mapping resource distribution issue to an optimization problem.Comparing throughputs of four meth-ods,simulation results demonstrate the proposed genetic algorithm has better throughput gain.

Exploiting Spectral-Energy Efficiency Tradeoff with Fairness in Non-Orthogonal Multiple Access Systems

The spectral efficiency(SE)and energy efficiency(EE)tradeoff while ensuring rate fairness among users in non-orthogonal multiple access(NOMA)systems is investigated.In order to characterize the SE-EE tradeoff with rate fairness,a multi-objective optimization(MOO)problem is first formulated,where the rate fairness is represented with theα-fair utility function.Then,the MOO problem is converted into a single-objective optimization(SOO)problem by the weighted sum method.To solve the converted non-convex SOO problem,we apply sequential convex programming,which helps to propose a general power allocation algorithm to realize the SE-EE tradeoff with rate fairness.We prove the convergence of the proposed algorithm and the convergent solution satisfies the KKT conditions.Simulation results demonstrate the proposed power allocation algorithm can achieve various levels of rate fairness,and higher fairness results in degraded performance of SE-EE tradeoff.A pivotal conclusion is reached that NOMA systems significantly outperform orthogonal multiple access systems in terms of SE-EE tradeoff with the same level of rate fairness.

Optimal UAV deployment in downlink non-orthogonal multiple access system:a two-user case

This paper investigates a unmanned aerial vehicle(UAV)deployment problem in a non-orthogonal multiple access(NOMA)system,where the UAV is deployed as an aerial mobile base station to transmit data to two ground users.An optimization problem is formulated by deploying the UAV for maximizing the sum rate of the two users.In order to solve the optimization problem,the feasible solution region is first reduced to a line segment between two users.Then,the optimization problem is simplified to a univariate problem,which can be solved by derivation under a certain situation,and the corresponding analytical solution is also provided.Moreover,a generalized algorithm,which considers 2 situations,is proposed to further determine the optimal UAV’s location.Specifically,four cases are discussed in the first situation.Extensive simulations are depicted to demonstrate effectiveness of the proposed algorithm and its superiority over the benchmarks in maximizing the two users’sum rate.

Help from space:grant-free massive access for satellite-based IoT in the 6G era

The Sixth-Generation(6G)standard for wireless communications is expected to realize ubiquitous coverage for massive Internet of Things(IoT)networks by 2030.Satellite-based communications are recognized as a highly promising technical enabler to satisfy IoT service requirements in the 6G era.This study analyzes multiple access technologies,which are essential for the effective deployment of satellite-based IoT.First,we thoroughly investigate the existing research related to massive access,including information-theory considerations as well as Non-Orthogonal Multiple Access(NOMA)and Random Access(RA)technologies.Then,we explore the influence of the satellite transmission environment on multiple access technologies.Based on this study,a Non-orthogonal Massive Grant-Free Access(NoMaGFA)scheme,which reaps the joint benefits of RA and NOMA,is proposed for asynchronous transmissions in satellite-based IoT to achieve improved system throughput and enhance the system robustness under varying traffics.Finally,we identify some important and interesting future developments for satellite-based IoT,including waveform design,transceiver design,resource allocation,and artificial intelligence-enhanced design.

Unified Framework Towards Flexible Multiple Access Schemes for 5G

Non-orthogonal multiple access （NOMA） schemes have achieved great attention recently and been considered as a crucial compo-nent for 5G wireless networks since they can efficiently enhance the spectrum efficiency, support massive connections and poten-tially reduce access latency via grant free access. In this paper, we introduce the candidate NOMA solutions in 5G networks, com-paring the principles, key features, application scenarios, transmitters and receivers, etc. In addition, a unified framework of these multiple access schemes are proposed to improve resource utilization, reduce the cost and support the flexible adaptation of multi-ple access schemes. Further, flexible multiple access schemes in 5G systems are discussed. They can support diverse deployment scenarios and traffic requirements in 5G. Challenges and future research directions are also highlighted to shed some lights for the standardization in 5G.

Uplink Multiple Access Schemes for 5G:A Survey

In non-orthogonal multiple access(NMA) system, signal transmitter and receiver are jointly optimized, so that multiple layers ofdata from more than one user can be simultaneously delivered in the same resource. To meet the 5G requirements on the numberof connections and spectral efficiency, uplink NMA is becoming an important candidate technology and has been extensively stud-ied in 3GPP. A number of uplink NMA schemes from different industrial companies have been proposed in recent 3GPP meet-ings. In terms of their basic technique principles, this paper classifies these NMA schemes into three categories, namely: scram-bling based NMA schemes, interleaving based NMA schemes, and spreading based NMA schemes. Moreover, the key characteris-tics of these schemes are summarized, and the detailed introduction of each scheme is provided according to the comprehensivesurvey of the latest progress in 3GPP 5G standardization work.

On the performance of full-duplex non-orthonogal multiple access with energy harvesting over Nakagami-m fading channels

A cooperative full-duplex(FD)non-orthogonal multiple access(NOMA)network is consid-ered,in which a source communicate with multiple users via multiple energy harvesting(EH)FD relays.Based on this structure,a novel relay selection scheme is proposed over Nakagamim fading channels by considering both the channel state information(CSI)and the energy statuses of relays.A finite Markov chain is adopted to capture the evolution of relay batteries and simplify the performance analysis by making some reasonable assumptions.General closed-form expressions of the outage probability and the ergodic sumrate are derived.All the theoretical results are validated by Monte-Carlo simulations.The impacts of various system parameters,such as the number of relays,the self-interference(SI)at the involved relay and battery size,on the performance are extensively investi-gated.It is shown that the usage of NOMA with FD relaying outperforms the half-duplex(HD)-NO-MA and conventional orthogonal multiple access(OMA)network when the self-interference is not too large.

A Survey: Several Technologies of Non-Orthogonal Transmission for 5G

One key advantage of 4G OFDM system is the relatively simple receiver implementation due to the orthogonal resource allocation.However,from sum-capacity and spectral efficiency points of view,orthogonal systems are never the achieving schemes.With the rapid development of mobile communication systems,a novel concept of non-orthogonal transmission for 5G mobile communications has attracted researches all around the world.In this trend,many new multiple access schemes and waveform modulation technologies were proposed.In this paper,some promising ones of them were discussed which include Non-orthogonal Multiple Access(NOMA),Sparse Code Multiple Access(SCMA),Multi-user Shared Access(MUSA),Pattern Division Multiple Access(PDMA)and some main new waveforms including Filter-bank based Multicarrier(FBMC),Universal Filtered Multi-Carrier(UFMC),Generalized Frequency Division Multiplexing(GFDM).By analyzing and comparing features of these technologies,a research direction of guiding on future 5G multiple access and waveform are given.