19 research outputs found
Rate-Splitting for Multigroup Multicast Beamforming in Multicarrier Systems
In this paper, we consider multigroup multicast transmissions with different
types of service messages in an overloaded multicarrier system, where the
number of transmitter antennas is insufficient to mitigate all inter-group
interference. We show that employing a rate-splitting based multiuser
beamforming approach enables a simultaneous delivery of the multiple service
messages over the same time-frequency resources in a non-orthogonal fashion.
Such an approach, taking into account transmission power constraints which are
inevitable in practice, outperforms classic beamforming methods as well as
current standardized multicast technologies, in terms of both spectrum
efficiency and the flexibility of radio resource allocation.Comment: SPAWC 2018, 5 Pages, 2 fig
Resource Allocation for Multicarrier Rate-Splitting Multiple Access System
In this article, we investigate the resource allocation problem for the multicarrier rate-splitting multiple access (RSMA) systems. On each subcarrier, messages are non-orthogonal superimposed on the power domain through the one-layer RSMA scheme. A novel three-step resource allocation algorithm is proposed to deal with the non-convex problem of sum rate maximization. In step 1, assuming average power allocation among subcarriers, we obtain the power distribution factors of the users in a single subcarrier by converting this problem into a difference of convex program (DCP), and approximate it by its first-order Taylor expansion. In step 2, we convert the user-subcarrier matching problem into an assignment problem and use the Hungarian algorithm to solve it. In step 3, the optimized power allocation algorithm is used to calculate the power allocation among the subcarriers, and then updates the power vector for each user. Numerical results show that our proposed three-step resource allocation algorithm could achieve comparable sum rate performance to the existing near-optimal solution with much lower computational complexity and outperforms orthogonal multiple access (OMA) scheme
Multicarrier Rate-Splitting Multiple Access: Superiority of OFDM-RSMA over OFDMA and OFDM-NOMA
Rate-splitting multiple access (RSMA) is a multiple access technique
generalizing conventional techniques, such as, space-division multiple access
(SDMA), non-orthogonal multiple access (NOMA), and physical layer
multi-casting, which aims to address multi-user interference (MUI) in
multiple-input multiple-output (MIMO) systems. In this study, we leverage the
interference management capabilities of RSMA to tackle the issue of
inter-carrier interference (ICI) in orthogonal frequency division multiplexing
(OFDM) waveform. We formulate a problem to find the optimal subcarrier and
power allocation for downlink transmission in a two-user system using RSMA and
OFDM and propose a weighted minimum mean-square error (WMMSE)-based algorithm
to obtain a solution. The sum-rate performance of the proposed OFDM-RSMA scheme
is compared with that of conventional orthogonal frequency division multiple
access (OFDMA) and OFDM-NOMA by numerical results. It is shown that the
proposed OFDM-RSMA outperforms OFDM-NOMA and OFDMA under ICI in diverse
propagation channel conditions owing to its flexible structure and robust
interference management capabilities.Comment: Updated version of published paper in IEEE Communications Letters
with correction in optimization problem (17b
A Low-Complexity Design for Rate-Splitting Multiple Access in Overloaded MIMO Networks
Rate-Splitting Multiple Access (RSMA) is a robust multiple access scheme for
multi-antenna wireless networks. In this work, we study the performance of RSMA
in downlink overloaded networks, where the number of transmit antennas is
smaller than the number of users. We provide analysis and closed-form solutions
for optimal power and rate allocations that maximize max-min fairness when
low-complexity precoding schemes are employed. The derived closed-form
solutions are used to propose a low-complexity RSMA system design for precoder
selection and resource allocation for arbitrary number of users and antennas
under perfect Channel State Information at the Transmitter (CSIT). We compare
the performance of the proposed design with benchmark designs based on Space
Division Multiple Access (SDMA) to show that the proposed low-complexity RSMA
design achieves a significantly higher performance gain in overloaded networks
Rate Splitting Multiple Access for Cognitive Radio GEO-LEO Co-Existing Satellite Networks
Low Earth orbit (LEO) satellite communication has drawn particular attention recently due to its high data rate services and low round-trip latency. It is low-cost to launch and can provide global coverage. However, the spectrum scarcity might be one of the critical challenges in the growth of LEO satellites, impacting severe restrictions on the development of ground-space integrated networks. To address this issue, we propose rate splitting multiple access (RSMA) for cognitive radio (CR) enabled nongeostationary orbit (GEO)-LEO coexisting satellite network. In particular, this work aims to maximize the system's sum rate by simultaneously optimizing the power allocation and subcarrier beam assignment of LEO satellite communication while restricting the interference temperature to GEO satellite users. The problem of sum rate maximization is formulated as non-convex and a Global optimal solution is challenging to obtain. Therefore, we first employ the successive convex approximation technique to reduce the complexity and make the problem more tractable. Then for the power allocation, we exploit Karush–Kuhn–Tucker (KKT) condition and adopt an efficient algorithm based on the greedy approach for subcarrier beam assignment. We also propose two suboptimal schemes with fixed power allocation and random subcarrier beam assignment
Energy-Efficient Hybrid Precoding Design for Integrated Multicast-Unicast Millimeter Wave Communications with SWIPT
In this paper, we investigate the energy-efficient hybrid precoding design
for integrated multicast-unicast millimeter wave (mmWave) system, where the
simultaneous wireless information and power transform is considered at
receivers. We adopt two sparse radio frequency chain antenna structures at the
base station (BS), i.e., fully-connected and subarray structures, and design
the codebook-based analog precoding according to the different structures.
Then, we formulate a joint digital multicast, unicast precoding and power
splitting ratio optimization problem to maximize the energy efficiency of the
system, while the maximum transmit power at the BS and minimum harvested energy
at receivers are considered. Due to its difficulty to directly solve the
formulated problem, we equivalently transform the fractional objective function
into a subtractive form one and propose a two-loop iterative algorithm to solve
it. For the outer loop, the classic Bi-section iterative algorithm is applied.
For the inner loop, we transform the formulated problem into a convex one by
successive convex approximation techniques and propose an iterative algorithm
to solve it. Meanwhile, to reduce the complexity of the inner loop, we develop
a zero forcing (ZF) technique-based low complexity iterative algorithm.
Specifically, the ZF technique is applied to cancel the inter-unicast
interference and the first order Taylor approximation is used for the
convexification of the non-convex constraints in the original problem. Finally,
simulation results are provided to compare the performance of the proposed
algorithms under different schemes.Comment: IEEE_TVT, Accep
Robust Beamforming and Rate-Splitting Design for Next Generation Ultra-Reliable and Low-Latency Communications
The next generation ultra-reliable and low-latency communications (xURLLC)
need novel design to provide satisfactory services to the emerging
mission-critical applications. To improve the spectrum efficiency and enhance
the robustness of xURLLC, this paper proposes a robust beamforming and
rate-splitting design in the finite blocklength (FBL) regime for downlink
multi-user multi-antenna xURLLC systems. In the design, adaptive rate-splitting
is introduced to flexibly handle the complex inter-user interference and thus
improve the spectrum efficiency. Taking the imperfection of the channel state
information at the transmitter (CSIT) into consideration, a max-min user rate
problem is formulated to optimize the common and private beamforming vectors
and the rate-splitting vector under the premise of ensuring the requirements of
transmission latency and reliability of all the users. The optimization problem
is intractable due to the non-convexity of the constraint set and the infinite
constraints caused by CSIT uncertainties. To solve it, we convert the infinite
constraints into finite ones by the S-Procedure method and transform the
original problem into a difference of convex (DC) programming. A constrained
concave convex procedure (CCCP) and the Gaussian randomization based iterative
algorithm is proposed to obtain a local minimum. Simulation results confirm the
convergence, robustness and effectiveness of the proposed robust beamforming
and rate-splitting design in the FBL regime. It is also shown that the proposed
robust design achieves considerable performance gain in the worst user rate
compared with existing transmission schemes under various blocklength and block
error rate requirements.Comment: 12 pages, 9 figure
DESIGN AND OPTIMIZATION OF SIMULTANEOUS WIRELESS INFORMATION AND POWER TRANSFER SYSTEMS
The recent trends in the domain of wireless communications indicate severe upcoming challenges, both in terms of infrastructure as well as design of novel techniques. On the other hand, the world population keeps witnessing or hearing about new generations of mobile/wireless technologies within every half to one decade. It is certain the wireless communication systems have enabled the exchange of information without any physical cable(s), however, the dependence of the mobile devices on the power cables still persist. Each passing year unveils several critical challenges related to the increasing capacity and performance needs, power optimization at complex hardware circuitries, mobility of the users, and demand for even better energy efficiency algorithms at the wireless devices. Moreover, an additional issue is raised in the form of continuous battery drainage at these limited-power devices for sufficing their assertive demands. In this regard, optimal performance at any device is heavily constrained by either wired, or an inductive based wireless recharging of the equipment on a continuous basis. This process is very inconvenient and such a problem is foreseen to persist in future, irrespective of the wireless communication method used. Recently, a promising idea for simultaneous wireless radio-frequency (RF) transmission of information and energy came into spotlight during the last decade. This technique does not only guarantee a more flexible recharging alternative, but also ensures its co-existence with any of the existing (RF-based) or alternatively proposed methods of wireless communications, such as visible light communications (VLC) (e.g., Light Fidelity (Li-Fi)), optical communications (e.g., LASER-equipped communication systems), and far-envisioned quantum-based communication systems. In addition, this scheme is expected to cater to the needs of many current and future technologies like wearable devices, sensors used in hazardous areas, 5G and beyond, etc. This Thesis presents a detailed investigation of several interesting scenarios in this direction, specifically concerning design and optimization of such RF-based power transfer systems.
The first chapter of this Thesis provides a detailed overview of the considered topic, which serves as the foundation step. The details include the highlights about its main contributions, discussion about the adopted mathematical (optimization) tools, and further refined minutiae about its organization. Following this, a detailed survey on the wireless power transmission (WPT) techniques is provided, which includes the discussion about historical developments of WPT comprising its present forms, consideration of WPT with wireless communications, and its compatibility with the existing techniques. Moreover, a review on various types of RF energy harvesting (EH) modules is incorporated, along with a brief and general overview on the system modeling, the modeling assumptions, and recent industrial considerations. Furthermore, this Thesis work has been divided into three main research topics, as follows. Firstly, the notion of simultaneous wireless information and power transmission (SWIPT) is investigated in conjunction with the cooperative systems framework consisting of single source, multiple relays and multiple users. In this context, several interesting aspects like relay selection, multi-carrier, and resource allocation are considered, along with problem formulations dealing with either maximization of throughput, maximization of harvested energy, or both. Secondly, this Thesis builds up on the idea of transmit precoder design for wireless multigroup multicasting systems in conjunction with SWIPT. Herein, the advantages of adopting separate multicasting and energy precoder designs are illustrated, where we investigate the benefits of multiple antenna transmitters by exploiting the similarities between broadcasting information and wirelessly transferring power. The proposed design does not only facilitates the SWIPT mechanism, but may also serve as a potential candidate to complement the separate waveform designing mechanism with exclusive RF signals meant for information and power transmissions, respectively. Lastly, a novel mechanism is developed to establish a relationship between the SWIPT and cache-enabled cooperative systems. In this direction, benefits of adopting the SWIPT-caching framework are illustrated, with special emphasis on an enhanced rate-energy (R-E) trade-off in contrast to the traditional SWIPT systems. The common notion in the context of SWIPT revolves around the transmission of information, and storage of power. In this vein, the proposed work investigates the system wherein both information and power can be transmitted and stored. The Thesis finally concludes with insights on the future directions and open research challenges associated with the considered framework