121 research outputs found
Sub-channel Assignment, Power Allocation and User Scheduling for Non-Orthogonal Multiple Access Networks
In this paper, we study the resource allocation and user scheduling problem
for a downlink nonorthogonal multiple access network where the base station
allocates spectrum and power resources to a set of users. We aim to jointly
optimize the sub-channel assignment and power allocation to maximize the
weighted total sum-rate while taking into account user fairness. We formulate
the sub-channel allocation problem as equivalent to a many-to-many two-sided
user-subchannel matching game in which the set of users and sub-channels are
considered as two sets of players pursuing their own interests. We then propose
a matching algorithm which converges to a two-side exchange stable matching
after a limited number of iterations. A joint solution is thus provided to
solve the sub-channel assignment and power allocation problems iteratively.
Simulation results show that the proposed algorithm greatly outperforms the
orthogonal multiple access scheme and a previous non-orthogonal multiple access
scheme.Comment: Accepted as a regular paper by IEEE Transactions on Wireless
Communication
Evolution of NOMA Toward Next Generation Multiple Access (NGMA) for 6G
Due to the explosive growth in the number of wireless devices and diverse
wireless services, such as virtual/augmented reality and
Internet-of-Everything, next generation wireless networks face unprecedented
challenges caused by heterogeneous data traffic, massive connectivity, and
ultra-high bandwidth efficiency and ultra-low latency requirements. To address
these challenges, advanced multiple access schemes are expected to be
developed, namely next generation multiple access (NGMA), which are capable of
supporting massive numbers of users in a more resource- and
complexity-efficient manner than existing multiple access schemes. As the
research on NGMA is in a very early stage, in this paper, we explore the
evolution of NGMA with a particular focus on non-orthogonal multiple access
(NOMA), i.e., the transition from NOMA to NGMA. In particular, we first review
the fundamental capacity limits of NOMA, elaborate on the new requirements for
NGMA, and discuss several possible candidate techniques. Moreover, given the
high compatibility and flexibility of NOMA, we provide an overview of current
research efforts on multi-antenna techniques for NOMA, promising future
application scenarios of NOMA, and the interplay between NOMA and other
emerging physical layer techniques. Furthermore, we discuss advanced
mathematical tools for facilitating the design of NOMA communication systems,
including conventional optimization approaches and new machine learning
techniques. Next, we propose a unified framework for NGMA based on multiple
antennas and NOMA, where both downlink and uplink transmissions are considered,
thus setting the foundation for this emerging research area. Finally, several
practical implementation challenges for NGMA are highlighted as motivation for
future work.Comment: 34 pages, 10 figures, a survey paper accepted by the IEEE JSAC
special issue on Next Generation Multiple Acces
Downlink MIMO-NOMA with and without CSI: A short survey and comparison
Non-orthogonal multiple access (NOMA) concatenated with multiple-input multiple-output (MIMO) or with massive MIMO, has been under scrutiny for both broadband and machine-type communications (MTC), even though it has not been adopted in the latest 5G standard (3GPP Release 16), being left for beyond 5G. This paper dwells on the problems causing such cautiousness, and surveys different NOMA proposals for the downlink in cell-centered systems. Because acquiring channel state information at the transmitter (CSIT) may be hard, open-loop operation is an option. However, when users clustering is possible, due to some common statistical CSI, closed-loop operation should be exploited. The paper numerically compares these two operating modes. The users are clustered in beams and then successive interference cancellation (SIC) separates the power-domain NOMA (PD-NOMA) signals at the terminals. In the precoded closed-loop system, the Karhunen-Loève channel decomposition is used assuming that users within a cluster share the same slowly changing spatial correlation matrix. For a comparable number of antennas the two options perform similarly, however, while in the open-loop downlink the number of antennas at the BS is limited in practice, this restriction is waived in the precoded systems, with massive MIMO allowing for a larger number of clusters.info:eu-repo/semantics/acceptedVersio
Survey on the state-of-the-art in device-to-device communication: A resource allocation perspective
Device to Device (D2D) communication takes advantage of the proximity between the communicating devices in order to achieve efficient resource utilization, improved throughput and energy efficiency, simultaneous serviceability and reduced latency. One of the main characteristics of D2D communication is reuse of the frequency resource in order to improve spectral efficiency of the system. Nevertheless, frequency reuse introduces significantly high interference levels thus necessitating efficient resource allocation algorithms that can enable simultaneous communication sessions through effective channel and/or power allocation. This survey paper presents a comprehensive investigation of the state-of-the-art resource allocation algorithms in D2D communication underlaying cellular networks. The surveyed algorithms are evaluated based on heterogeneous parameters which constitute the elementary features of a resource allocation algorithm in D2D paradigm. Additionally, in order to familiarize the readers with the basic design of the surveyed resource allocation algorithms, brief description of the mode of operation of each algorithm is presented. The surveyed algorithms are divided into four categories based on their technical doctrine i.e., conventional optimization based, Non-Orthogonal-MultipleAccess (NOMA) based, game theory based and machine learning based techniques. Towards the end, several open challenges are remarked as the future research directions in resource allocation for D2D communication
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