Interference Mitigation and Secrecy Ensured for NOMA-Based D2D Communications Under Imperfect CSI

The Non-Orthogonal Multiple Access (NOMA) and the Orthogonal Frequency Division Multiple Access (OFDMA) are promising techniques for next-generation wireless systems. Although much attention in the literature considered these techniques, an effective combination between such systems as hybrid multiple access (HMA) needs more attention. For this reason, this paper devotes to proposing two different scenarios of HMA using multi-user OFDM (MU-OFDM) and power domain (PD) NOMA for downlink transmission to overcome the limitations of both Orthogonal Multiple Access (OMA) and NOMA. Due to the randomness of a wireless channel, different user grouping strategies and dynamic power allocation (DPA) strategies are employed to satisfy users’ requirements. The proposed systems give high flexibility utilizing bitrate allocation and user fairness. System results show superior performance to traditional OMA and NOMA systems. The achieved variety of fairness is helpful for the diversity of applications which is a principal requirement for beyond-fifth-generation (B5G) networks. The next step in this analysis is to enhance the proposed systems’ spectral efficiency (SE) by introducing beamforming for massive Multiple-Input Multiple-Output (MIMO) systems. The bit error rate (BER) result of the proposed system achieves almost the same error floor with a benefit of approximately 10 dB signalto-noise ratio (SNR) when 90 resource blocks (RBs) are used.

Opportunistic non-contiguous OFDMA scheduling framework for future B5G/6G cellular networks

Internet of Things (IoT) technology has become ubiquitous in a multitude of applications and its use is growing. However, the expansion of IoT faces a major difficulty: scalability, that is, very dense deployment of communicating devices is currently limited. In long-range networks, such as LoRa, the downlink is critical because it limits the number of acknowledgements that can be sent, and consequently reliability. It also limits the possibility to update the devices, which could be critical when they are deployed for decades. To overcome those problems, we propose a solution, inspired by Non Orthogonal Multiple Access (NOMA) techniques, to increase by at least one order of magnitude the number of devices that can be addressed. While the approach differentiates the devices by the power allocated to them, it differs from the vast majority of previous works on power domain NOMA because it does not require interference cancellation. Instead, it benefits from the spectrum spreading of the modulation scheme (chirp spread spectrum), where, at the end of the decoding phase, the information carried by a symbol is found in the position of a peak in the Fourier domain. In the vast majority of cases, the information from different users results in different peak positions, not creating any interference. In that sense, we get closer to avoidance schemes such as time or frequency hopping, but without using a code. In this article, we propose a new solution for NOMA in the power domain that does not suffer from the limitations induced by interference cancellation residues. The proposed system, including preamble detection and channel estimation, is presented and evaluated by simulations. We demonstrate that our proposed scheme increases the number of devices by one order of magnitude compared to the current system which allows addressing only one user at a time and maintains full compatibility with the LoRa physical layer standard.

The fifth generation (5G) of wireless communication accompanied by the advancement of mobile internet and the Internet of Things (IoT) will create stormy data traffic. The 5G challenges like higher spectral efficiency, massive connectivity, and low latency are addressed by the Non-Orthogonal Multiple Access (NOMA) in recent years. NOMA is proven to be a promising technique from its capability to accommodate a larger number of users in contrast to the conventional orthogonal multiple access (OMA) schemes. NOMA comprises two distinct techniques such as Power-Domain NOMA and Code-Domain NOMA. The non-orthogonal resource allocation in Power-Domain NOMA is practically realized by the Superposition Coding (SC) at the Base Station (BS) and an advanced Successive Interference Cancellation at the User Equipment (UE). In this manuscript, the basic concepts of NOMA, on comparing its channel gain with OMA are discussed first. Specifically, a comprehensive survey of various SIC techniques applied under perfect and imperfect Channel State Information (CSI) uncertainties are summarized in terms of outage probability, ergodic capacity, and system performance. In addition, the sophisticated SIC techniques, when NOMA is integrated with modern wireless communication technologies such as multiple-input multiple-output (MIMO-NOMA) and Cooperative (C-NOMA) communications are investigated. Furthermore, the challenges to be solved with their corresponding opportunities and future research directions of NOMA are explored.

To meet the 5G requirements on spectral efficiency and connection density, non-orthogonal multiple access (NMA) is becoming an important candidate technology. This paper focuses on power-domain NMA (PNMA) due to the relatively low design complexity and standardization impact. In PNMA, the data of more than one user equipment (UE) are superposed with different transmission power setting at the transmitter, and are separated by utilizing interference cancellation at the receiver. The theoretical performance of PNMA has been shown in some previous research. In this paper, we gives our proposals on PNMA practical system design aspects including base station (BS) scheduling, UE receiver implementation and network signaling, aiming to seek for good trade-off between overall performance and complexity. System-level simulations validate that compared to orthogonal multiple access (OMA), PNMA with our proposed scheduling algorithm can bring 14.16% and 23.88% gain in cell average spectral efficiency (SE) and cell edge SE respectively, as well as improve the number of connected UEs by 55%.

NOMA (Non- orthogonal Multiple Access) is an early candidate for 5G that concentrates on networks capacity expansion. It can be broadly classified into two major categories; Power-Domain NOMA (PD-NOMA) and Code-Domain NOMA (CD-NOMA). This research focuses on PD-NOMA. The significance of PD- NOMA is that concurrent transmission and reception can be accomplished on the same frequency and with this spectral efficiency can be enhanced. The objective of this research is to investigate the impact of error propagation caused due to AWGN (Additive White Gaussian Noise) channel in PD-NOMA 5G system. A 2 × 2 PD-NOMA system is simulated in Matlab version 2019a. In the Uplink, the raw data is BPSK modulated and transmitted to the Base Station (BS). In the downlink, from the BS, User 1 data is transmitted with a power level of 0.25 watts and User 2 with 0.75 watts based on their placement. In the Reception section, Successive Interference Cancellation (SIC) is executed to segregate the data which is further recovered through decoding process. To analyze the performance, AWGN channel is introduced in the proposed simulated system model. The Signal to Noise Ratio is varied from 5 to 25 dB. From the results obtained, it is inferred that, Bit Error Rate experienced by the users varies from 0.1 to 1.

Non-orthogonal multiple access (NOMA) on shared resources has been identified as a promising technology in 5G to improve resource efficiency and support massive access in all kinds of transmission modes. Power domain and code domain NOMA have been extensively studied and evaluated in both literatures and 3GPP standardization, especially for the uplink where large number of users would like to send their messages to the base station. Though different in the transmitter side design, power domain NOMA and code domain NOMA share the same need of the advanced multi-user detection (MUD) design at the receiver side. Various multi-user detection algorithms have been proposed, balancing performance and complexity in different ways, which is important for the implementation of NOMA in practical networks. In this paper, we introduce a unified variational inference (VI) perspective on various universal NOMA MUD algorithms such as belief propagation (BP), expectation propagation (EP), vector EP (VEP), approximate message passing (AMP) and vector AMP (VAMP), demonstrating how they could be derived from and adapted to each other within the VI framework. Moreover, we unveil and prove that conventional elementary signal estimator (ESE) and linear minimum mean square error (LMMSE) receivers are special cases of EP and VEP, respectively, thus bridging the gap between classic linear receivers and message passing based nonlinear receivers. Such a unified perspective would not only help the design and adaptation of NOMA receivers, but also open a door for the systematic design of joint active user detection and multi-user decoding for sporadic grant-free transmission.

Device-to-device (D2D) communication is a promising technology in which the spectrum resources are reused efficiently with cellular mobile users (CMUs) in an underlay of the fifth generation network. Using it, network capacity and spectral efficiency increase but it introduces the cochannel interference. Moreover, massive connectivity has not been fully exploited for efficient spectral efficiency usage in the existing solutions. Therefore, to address the aforementioned challenges, we integrate power domain nonorthogonal multiple access (PD-NOMA) technique with the D2D mobile groups (DMGs) to maximize their sum rate and to maintain the signal-to-interference noise ratio provided by CMUs. We formulate the problem of spectrum reuse as mixed-integer nonlinear programming and then converted it into two subproblems. First, the DMGs are formed between the D2D transmitter and D2D mobile users to reduce the intrauser interference using successive interference cancellation technique. Second, the resource allocation scheme for both the CMUs and DMGs is designed to mitigate the cross and cochannel interference using many-to-many mapping scheme. Also, to fully exploit the potential benefits of DMGs, the group rate selection criterion based resource block reuse algorithm among DMGs is designed. Finally, for power optimization, we use the difference of two convex functions programming approach based on a successive convex approximation low complexity. To simulate the proposed scheme, the 3GPP urban path loss model based on release 15 and RAN1 is used. Numerical results demonstrated that the proposed scheme has superior sum rate as compared to the existing NOMA and orthogonal frequency-division multiple access schemes.

OFDM (Orthogonal Frequency Division Multiplexing) is a well-known multicarrier modulation technique that allows high-rate data transmissions over multipath broadband wireless channels. By usingOFDM, a high-rate data stream is split into a number of lower-rate streams that are simultaneously transmitted on different orthogonal subcarriers. Thus, the broadband channel is decomposed into a set of parallel frequency-flat subchannels; each one corresponding to an OFDM subcarrier. In a single user scenario, if the channel state is known at the transmitter, the system performance can be enhanced by adapting the power and data rates over each subcarrier. For example, the transmitter can allocate more transmit power and higher data rates to the subcarriers with better channels. By doing this, the total throughput can be significantly increased. In a multiuser scenario, different subcarriers can be allocated to different users, which constitutes an orthogonal multiple access method known as OFDMA (Orthogonal Frequency Division Multiple Access). OFDMA is one of the principal multiple access schemes for broadband wireless multiuser systems. It has being proposed for use in several broadband multiuser wireless standards like IEEE 802.20 (MBWA: http://grouper.ieee.org/groups/802/20/), IEEE 802.16 (WiMAX: http://www.ieee802.org/16/, 2011) and 3GPP-LTE (http://www.3gpp.org/). This chapter focuses on the OFDMA broadcast channel (also known as downlink channel), since this is typically where high data rates and reliability is needed in broadband wireless multiuser systems. In OFDMA downlink transmission, each subchannel is assigned to one user at most, allowing simultaneous orthogonal transmission to several users. Once a subchannel is assigned to a user, the transmitter allocates a fraction of the total available power as well as a modulation and coding (data rate). If the channel state is known at the transmitter, the system performance can be significantly enhanced by allocating the available resources (subchannels, transmit power and data rates) intelligently according to the users’ channels. The allocation of these resources determines the quality of service (QoS) provided by the system to each user. Since different users experience different channels, this scheme does not only exploit the frequency diversity of the channel, but also the inherent multiuser diversity of the system. In multiuser transmission schemes, like OFDMA, the information-theoretic system performance is usually characterized by the capacity region. It is defined as the set of rates 6

A bandwidth-efficient adaptation scheme for improved device-to-device (D2D) resource allocation is presented. The scheme aims to improve the bandwidth utilization by exploiting the presence of multiple D2D communication links and the randomness of propagation channels to boost the received signal-to-noise plus interference ratio (SINR) at D2D receivers. It also attempts to allocate a D2D transmitter and a spectral channel, which can guarantee the required quality of service at a D2D receiver while reducing its processing load. It is assumed that D2D receivers use tightly spaced array elements, where multipath diversity is not resolvable. However, they are exploited to steer the radiation pattern and cancel some cochannel interference sources while maximizing the gain in the direction of the desired signal. The statistics of the resulting SINR at the D2D receiver are quantified for generic fading models of the desired signal and remaining interference sources. Moreover, the statistics of pre-combined SINRs on D2D links for various fading models are quantified. Analytical results for selected performance metrics and processing load are provided. The results demonstrate the ability of the proposed scheme to achieve decentralized bandwidth-efficient D2D resource allocation, where its relatively low complexity is explained against its achieved performance.

This paper addresses the statistical analysis of Transceiver Phase Noise (PHN) effect on Orthogonal Frequency Division Multiple Access (OFDMA) Uplink system performance for arbitrary subcarrier mapping. In most of the previous publications Complex Gaussian distribution of Inter Carrier Interference (ICI) was assumed, however in this paper we derive a closed form expression for the signal-to-interference+ noise ratio (SINR) without such restriction and then analyse it as a function of critical system parameters. This improved evaluation stringently specifies the plausible acceptable PHN characteristics for a certain OFDMA Uplink system and explains the serious under specification of Local Oscillator (LO) with Gaussian approximation.

Long Term Evolution (LTE) is one of the standards in 4G cellular technologies which offer different data rates for voice, video conference and other services. The Orthogonal Frequency Division Multiple Access (OFDMA) is a well suited multiple access scheme of LTE for supporting variable bit rate services. OFDMA-based Cellular communication network face serious challenges in providing good Quality of Service (QoS) to the users. In order to provide good QoS, network operators have to make the effective use of their available resources, which leads to effective network design and network planning. Erlang capacity is the dominant parameter used for effective network design and network planning. Co-channel Interference is an important limiting factor for Erlang capacity in OFDMA-based cellular systems. The capacity of a OFDMA cellular network is determined by the amount of CCI it can tolerate. In this paper a new method is proposed for the evaluation of Erlang capacity of a OFDMA system under CCI. The Erlang capacity of OFDMA-based cellular systems under CCI is evaluated and compared for different number of co-channel interferers, various spectral efficiencies, voice activity factors and various data rates.

This paper presents a performance analysis of reuse partitioning (RUP)-based subchannelized orthogonal frequency-division multiple-access (OFDMA) uplink systems in multicell environments. The cochannel interference (CCI) statistic is calculated for OFDMA uplink systems. The derived statistic is then used to analyze the performance of subchannelized OFDMA systems based on RUP. Analysis and simulation results show that the performance of a subchannelized OFDMA system in multicell environments is noticeably dependent on the CCI, and the effect of CCI can be reduced by the RUP scheme. Finally, the results of the analysis yield the optimum RUP area for achieving the maximum system throughput.

Interference analysis and MUI-cancellation in DCO-OFDMA-based IM/DD systems for VLC

By enabling multiple non-orthogonal transmissions, power domain non-orthogonal multiple access (PD-NOMA) potentially increases a system’s spectral efficiency. This technique can become an alternative for future generations of wireless communication networks. The efficiency of this method fundamentally depends on two previous processing steps: an appropriate grouping of users (transmission candidates) as a function of the channel gains and the choice of power levels that will be used to transmit each signal. Thus far, the solutions presented in the literature to address the problems of user clustering and power allocation do not consider the dynamics of communication systems, i.e., the temporal variation in the number of users and the channel conditions. In order to consider these dynamic characteristics in the clustering of users in NOMA systems, this work proposes a new clustering technique based on a modification of the DenStream evolutionary algorithm, chosen for its evolutionary capacity, noise robustness and online processing. We evaluated the performance of the proposed clustering technique considering, for simplicity, the use of an already widely known power allocation strategy called improved fractional strategy power allocation (IFSPA). The results show that the proposed clustering technique can follow the system dynamics, clustering all users and favoring the uniformity of the transmission rate between the clusters. Compared to orthogonal multiple access (OMA) systems, the proposed model’s gain was approximately 10%, obtained on a challenging communication scenario for NOMA systems since the channel model adopted does not favor a large difference in the channel gains between users.