A NOMA-enhanced reconfigurable access scheme with device pairing for M2M networks

This paper aims to address the distinct requirements of machine-to-machine networks, particularly heterogeneity and massive transmissions. To this end, a reconfigurable medium access control (MAC) with the ability to choose a proper access scheme with the optimal configuration for devices based on the network status is proposed. In this scheme, in each frame, a separate time duration is allocated for each of the nonorthogonal multiple access (NOMA)-based, orthogonal multiple access (OMA)-based, and random access-based segments, where the length of each segment can be optimized. To solve this optimization problem, an iterative algorithm consisting of two sub-problems is proposed. The first sub-problem deals with selecting devices for the NOMA/OMA-based transmissions, while the second one optimizes the parameter of the random access scheme. To show the efficacy of the proposed scheme, the results are compared with the reconfigurable scheme which does not support NOMA. The results demonstrate that by using a proper device pairing scheme for the NOMA-based transmissions, the proposed reconfigurable scheme achieves better performance when NOMA is adopted

Energy-efficient non-orthogonal multiple access for wireless communication system

Non-orthogonal multiple access (NOMA) has been recognized as a potential solution for enhancing the throughput of next-generation wireless communications. NOMA is a potential option for 5G networks due to its superiority in providing better spectrum efficiency (SE) compared to orthogonal multiple access (OMA). From the perspective of green communication, energy efficiency (EE) has become a new performance indicator. A systematic literature review is conducted to investigate the available energy efficient approach researchers have employed in NOMA. We identified 19 subcategories related to EE in NOMA out of 108 publications where 92 publications are from the IEEE website. To help the reader comprehend, a summary for each category is explained and elaborated in detail. From the literature review, it had been observed that NOMA can enhance the EE of wireless communication systems. At the end of this survey, future research particularly in machine learning algorithms such as reinforcement learning (RL) and deep reinforcement learning (DRL) for NOMA are also discussed

Full Stack 5G Physical Layer Transceiver Design for NOMA in Mobile Heterogeneous Networks

The Fifth Generation (5G) and Beyond 5G (B5G) wireless networks are emerging with a variety of new capabilities, focusing on Massive Machine-Type Communications (mMTC), enabling new use cases and services. With this massive increment of mMTC along with increasing users, higher network capacity is a must for 5G and B5G. The integration of mMTC with traditional user traffic creates a heterogeneous network landscape. To address this challenge, future network designs must prioritize optimizing spectrum efficiency while meeting diverse service demands. Non-Orthogonal Multiple Access (NOMA) stands out as a promising technology for enhancing both system capacity and operational efficiency in such heterogeneous networks. Due to its non-orthogonal resource allocation, NOMA outperforms Orthogonal Multiple Access (OMA) in spectral efficiency, throughput, and user capacity, while also offering superior scalability and adaptability to network heterogeneity. Despite its promising advantages, large-scale implementation of NOMA in cellular systems remains elusive due to various challenges, making it a focal point of current research in cellular network technology. While there has been considerable progress in implementing NOMA for broadcast and multicast services, notably with Layer Division Multiplexing (LDM) in next-generation digital TV, the challenges of unicast downlink transmission in NOMA remain largely unexplored. Unicast transmission requires a highly tailored network configuration adaptable to individual user requirements and dynamic channel conditions. Clustering users under a single NOMA channel must be both efficient and adaptive to ensure successful transmission, especially for mobile receiver. Besides, the interplay between NOMA and other 5G technologies remains insufficiently explored, in part due to the lack of an established NOMA-5G framework. Specifically, the collective impact of 5G physical layer technologies such as Low-Density Parity Check (LDPC) coding, Multiple-Input Multiple-Output (MIMO) Beamforming, and mmWave transmission on NOMA’s performance has not been comprehensively studied. Furthermore, in NOMA schemes involving more than two multiplexed users, known as Multilayer NOMA (N-NOMA), the system becomes increasingly complex and susceptible to noise. While N-NOMA holds considerable promise for scalability, its performance metrics are not yet fully characterized, due to challenges ranging from resource allocation complexities to transceiver design issues. Additionally, existing analytical models for performance evaluation are developed for orthogonal systems, are not fully applicable for assessing NOMA performance. Developing new models that incorporate the impact of non-orthogonality could provide more accurate performance assessments and offer valuable insights for future NOMA research. Initially this thesis investigates the feasibility of LDM for unicast & multicast downlink transmission scenarios for Internet of Things (IoT)- user pairs. The findings indicate the Core Layer (CL) performance aligns with IoT requirements while Enhance Layer (EL) layer is suitable for users. A specialized Bit Error Rate (BER) expression is formulated to precisely predict CL performance, considering Lower Layer (LL) interference with predefined power ratio. Subsequently, the thesis employs a novel surface mobility model and adaptive power ratio allocation to evaluate LDM pair sustainability under various receiver mobility conditions. Extending the LDM-Orthogonal Frequency Division Multiplexing (OFDM) model, this thesis presents a Third Generation Partnership Project (3GPP)-compliant 5G transceiver incorporating N-NOMA. This design incorporates a strategically-arranged set of NOMA functionalities and undergoes a rigorous performance evaluation. In particular, the transceiver provides a comprehensive assessment of N-NOMA performance, considering various transmission parameters such as LDPC code rate, MIMO order, modulation schemes, and channel specifications. These considerations not only provide new insights into non-orthogonal access technologies but also highlight dependencies on these factors for network configuration and optimization. To further advance this work, a one-shot N-NOMA multiplexing technique is developed and implemented, simplifying multi-layer standard sequential combiners to reduce transmission latency and transceiver complexity. A more accurate analytical BER expression is also formulated that considers the impact of both residual and non-residual Successive Interference Cancellation (SIC) errors across NOMA layers. To build upon these advancements, an adaptive Power Allocation (PA) technique is introduced to optimize NOMA cluster sustainability and throughput. Employing a greedy algorithmic approach, this method uses real-time transmission feedback to dynamically allocate power across NOMA layers. In addition, a new Three Dimensional (3D) mobility model has been developed, consistent with existing 3GPP standards, capturing vehicular and pedestrian movement across urban and rural macro & micro-cell environments. When integrated with the PA technique, this model allows for real-time adjustments in the NOMA power ratio, effectively adapting to fluctuating receiver channel conditions. Collectively, the findings from this research not only indicate significant physical layer performance improvements but also provide new insights into the potential of non-orthogonal access technologies. In the LDM-OFDM setup presented in Chapter 3, the EL layer needs 15 dB more Signal-to-Noise Ratio (SNR) than the CL to achieve the same BER, but allows for higher data rates. When it comes to mobility, IoT movement accounts for about 70% of link terminations in scenarios with similar mobility patterns. The N-NOMA-5G shows significant improvement in low SNR performance compared to existing literature. The 3 layer simulations shows on average a 60% reduction in the SNR requirements to achieve similar BER. The implementation of a one-shot multiplexer has demonstrated a substantial reduction in N-NOMA multiplexing time, particularly with the growing number of NOMA layers, as detailed in Chapter 4. Notably, the simulation outcomes spanning 2 to 10 layers of NOMA multiplexing indicate an remarkable 52% reduction in processing time. This underscores the effectiveness of the one-shot multiplexer in enhancing efficiency, particularly as the complexity of the NOMA setup intensifies. The developed analytical model also shows over 95% similarities with the simulation results. The impact of dynamic PA for both static and mobile receivers demonstrates on average, over 40% improvements in link sustainability time for mobile users and for static users, it achieves optimal PA and fast convergence within just 12 iterations, as detailed in Chapter 5

Energy-driven techniques for massive machine-type communications

In the last few years, a lot of effort has been put into the development of the fifth generation of cellular networks (5G). Given the vast heterogeneity of devices coexisting in these networks, new approaches have been sought to meet all requirements (e.g., data rate, coverage, delay, etc.). Within that framework, massive machine-type communications (mMTC) emerge as a promising candidate to enable many Internet of Things applications. mMTC define a type of systems where large sets of simple and battery-constrained devices transmit short data packets simultaneously. Unlike other 5G use cases, in mMTC, a low cost and power consumption are extensively pursued. Due to these specifications, typical humantype communications (HTC) solutions fail in providing a good service. In this dissertation, we focus on the design of energy-driven techniques for extending the lifetime of mMTC terminals. Both uplink (UL) and downlink (DL) stages are addressed, with special attention to the traffic models and spatial distribution of the devices. More specifically, we analyze a setup where groups of randomly deployed sensors send their (possibly correlated) observations to a collector node using different multiple access schemes. Depending on their activity, information might be transmitted either on a regular or sporadic basis. In that sense, we explore resource allocation, data compression, and device selection strategies to reduce the energy consumption in the UL. To further improve the system performance, we also study medium access control protocols and interference management techniques that take into account the large connectivity in these networks. On the contrary, in the DL, we concentrate on the support of wireless powered networks through different types of energy supply mechanisms, for which proper transmission schemes are derived. Additionally, for a better representation of current 5G deployments, the presence of HTC terminals is also included. Finally, to evaluate our proposals, we present several numerical simulations following standard guidelines. In line with that, we also compare our approaches with state-of-the-art solutions. Overall, results show that the power consumption in the UL can be reduced with still good performance and that the battery lifetimes can be improved thanks to the DL strategies.En els últims anys, s'han dedicat molts esforços al desenvolupament de la cinquena generació de telefonia mòbil (5G). Donada la gran heterogeneïtat de dispositius coexistint en aquestes xarxes, s'han buscat nous mètodes per satisfer tots els requisits (velocitat de dades, cobertura, retard, etc.). En aquest marc, les massive machine-type communications (mMTC) sorgeixen com a candidates prometedores per fer possible moltes aplicacions del Internet of Things. Les mMTC defineixen un tipus de sistemes en els quals grans conjunts de dispositius senzills i amb poca bateria, transmeten simultàniament paquets de dades curts. A diferència d'altres casos d'ús del 5G, en mMTC es persegueix un cost i un consum d'energia baixos. A causa d'aquestes especificacions, les solucions típiques de les human-type communications (HTC) no aconsegueixen proporcionar un bon servei. En aquesta tesi, ens centrem en el disseny de tècniques basades en l'energia per allargar la vida útil dels terminals mMTC. S'aborden tant les etapes del uplink (UL) com les del downlink (DL), amb especial atenció als models de trànsit i a la distribució espacial dels dispositius. Més concretament, analitzem un escenari en el qual grups de sensors desplegats aleatòriament, envien les seves observacions (possiblement correlades) a un node col·lector utilitzant diferents esquemes d'accés múltiple. Depenent de la seva activitat, la informació es pot transmetre de manera regular o esporàdica. En aquest sentit, explorem estratègies d'assignació de recursos, compressió de dades, i selecció de dispositius per reduir el consum d'energia en el UL. Per millorar encara més el rendiment del sistema, també estudiem protocols de control d'accés al medi i tècniques de gestió d'interferències que tinguin en compte la gran connectivitat d'aquestes xarxes. Per contra, en el DL, ens centrem en el suport de les wireless powered networks mitjançant diferents mecanismes de subministrament d'energia, per als quals es deriven esquemes de transmissió adequats. A més, per una millor representació dels desplegaments 5G actuals, també s'inclou la presència de terminals HTC. Finalment, per avaluar les nostres propostes, presentem diverses simulacions numèriques seguint pautes estandarditzades. En aquesta línia, també comparem els nostres enfocaments amb les solucions de l'estat de l'art. En general, els resultats mostren que el consum d'energia en el UL pot reduir-se amb un bon rendiment i que la durada de la bateria pot millorar-se gràcies a les estratègies del DL.En los últimos años, se han dedicado muchos esfuerzos al desarrollo de la quinta generación de telefonía móvil (5G). Dada la gran heterogeneidad de dispositivos coexistiendo en estas redes, se han buscado nuevos métodos para satisfacer todos los requisitos (velocidad de datos, cobertura, retardo, etc.). En este marco, las massive machine-type communications (mMTC) surgen como candidatas prometedoras para hacer posible muchas aplicaciones del Internet of Things. Las mMTC definen un tipo de sistemas en los cuales grandes conjuntos de dispositivos sencillos y con poca batería, transmiten simultáneamente paquetes de datos cortos. A diferencia de otros casos de uso del 5G, en mMTC se persigue un coste y un consumo de energía bajos. A causa de estas especificaciones, las soluciones típicas de las human-type communications (HTC) no consiguen proporcionar un buen servicio. En esta tesis, nos centramos en el diseño de técnicas basadas en la energía para alargar la vida ´útil de los terminales mMTC. Se abordan tanto las etapas del uplink (UL) como las del downlink (DL), con especial atención a los modelos de tráfico y a la distribución espacial de los dispositivos. Más concretamente, analizamos un escenario en el cual grupos de sensores desplegados aleatoriamente, envían sus observaciones (posiblemente correladas) a un nodo colector utilizando diferentes esquemas de acceso múltiple. Dependiendo de su actividad, la información se puede transmitir de manera regular o esporádica. En este sentido, exploramos estrategias de asignación de recursos, compresión de datos, y selección de dispositivos para reducir el consumo de energía en el UL. Para mejorar todavía más el rendimiento del sistema, también estudiamos protocolos de control de acceso al medio y técnicas de gestión de interferencias que tengan en cuenta la gran conectividad de estas redes. Por el contrario, en el DL, nos centramos en el soporte de las wireless powered networks mediante diferentes mecanismos de suministro de energía, para los cuales se derivan esquemas de transmisión adecuados. Además, para una mejor representación de los despliegues 5G actuales, también se incluye la presencia de terminales HTC. Finalmente, para evaluar nuestras propuestas, presentamos varias simulaciones numéricas siguiendo pautas estandarizadas. En esta línea, también comparamos nuestros enfoques con las soluciones del estado del arte. En general, los resultados muestran que el consumo de energía en el UL puede reducirse con un buen rendimiento y que la duración de la batería puede mejorarse gracias a las estrategias del DLPostprint (published version

Age of Information: Can CR-NOMA Help?

The aim of this paper is to exploit cognitive-ratio inspired NOMA (CR-NOMA) transmission to reduce the age of information in wireless networks. In particular, two CR-NOMA transmission protocols are developed by utilizing the key features of different data generation models and applying CR-NOMA as an add-on to a legacy orthogonal multiple access (OMA) based network. The fact that the implementation of CR-NOMA causes little disruption to the legacy OMA network means that the proposed CR-NOMA protocols can be practically implemented in various communication systems which are based on OMA. Closed-form expressions for the AoI achieved by the proposed NOMA protocols are developed to facilitate performance evaluation, and asymptotic studies are carried out to identify two benefits of using NOMA to reduce the AoI in wireless networks. One is that the use of NOMA provides users more opportunities to transmit, which means that the users can update their base station more frequently. The other is that the use of NOMA can reduce access delay, i.e., the users are scheduled to transmit earlier than in the OMA case, which is useful to improve the freshness of the data available in the wireless network

Cellular, Wide-Area, and Non-Terrestrial IoT: A Survey on 5G Advances and the Road Towards 6G

The next wave of wireless technologies is proliferating in connecting things among themselves as well as to humans. In the era of the Internet of things (IoT), billions of sensors, machines, vehicles, drones, and robots will be connected, making the world around us smarter. The IoT will encompass devices that must wirelessly communicate a diverse set of data gathered from the environment for myriad new applications. The ultimate goal is to extract insights from this data and develop solutions that improve quality of life and generate new revenue. Providing large-scale, long-lasting, reliable, and near real-time connectivity is the major challenge in enabling a smart connected world. This paper provides a comprehensive survey on existing and emerging communication solutions for serving IoT applications in the context of cellular, wide-area, as well as non-terrestrial networks. Specifically, wireless technology enhancements for providing IoT access in fifth-generation (5G) and beyond cellular networks, and communication networks over the unlicensed spectrum are presented. Aligned with the main key performance indicators of 5G and beyond 5G networks, we investigate solutions and standards that enable energy efficiency, reliability, low latency, and scalability (connection density) of current and future IoT networks. The solutions include grant-free access and channel coding for short-packet communications, non-orthogonal multiple access, and on-device intelligence. Further, a vision of new paradigm shifts in communication networks in the 2030s is provided, and the integration of the associated new technologies like artificial intelligence, non-terrestrial networks, and new spectra is elaborated. Finally, future research directions toward beyond 5G IoT networks are pointed out.Comment: Submitted for review to IEEE CS&