Reinforcement Learning for Link Adaptation and Channel Selection in LEO Satellite Cognitive Communications

in IEEE Communications Letters (2023)

Radio Resource Management Techniques for Multibeam Satellite Systems

in IEEE Communications Letters (2021), 25(8), 2448-2452

Next–generation of satellite communication (SatCom) networks are expected to support extremely high data rates for a seamless integration into future large satellite-terrestrial networks. In view of the ... [more ▼]

Next–generation of satellite communication (SatCom) networks are expected to support extremely high data rates for a seamless integration into future large satellite-terrestrial networks. In view of the coming spectral limitations, the main challenge is to reduce the cost (satellite launch and operation) per bit, which can be achieved by enhancing the spectral efficiencies. In addition, the capability to quickly and flexibly assign radio resources according to the traffic demand distribution has become a must for future multibeam broadband satellite systems. This article presents the radio resource management problems encountered in the design of future broadband SatComs and provides a comprehensive overview of the available techniques to address such challenges. Firstly, we focus on the demand matching formulation of the power and bandwidth assignment. Secondly, we present the scheduling design in practical multibeam satellite systems. Finally, a number of future challenges and the respective open research topics are described. [less ▲]

Resource Allocation for AF Relaying Wireless-Powered Networks with Nonlinear Energy Harvester

in IEEE Communications Letters (2021), 25(1), 1089-7798

This letter considers a relay-based wireless-powered communication network to assist wireless communication between a source and multiple users. In particular, the relay adopts a nonlinear energy model to ... [more ▼]

This letter considers a relay-based wireless-powered communication network to assist wireless communication between a source and multiple users. In particular, the relay adopts a nonlinear energy model to harvest energy from a power beacon and subsequently uses it for information transmission over timedivision multiple access. Aiming at the maximization of end-toend (e2e) sum throughput, we formulate a novel optimization problem that jointly optimizes the power and time fraction for energy and information transmission. For a simple yet efficient solution for the nonconvex problem, we first convert it to a more computationally tractable problem and then develop an iterative algorithm, in which closed-form solutions are obtained at each iteration. The effectiveness of our proposed approach is verified and demonstrated through simulation results. Moreover, the results reveal that the source should transmit with its maximum allowable power budget to obtain the optimal e2e sum throughput. [less ▲]

Symbol-Level Precoding with Constellation Rotation in the Finite Block Length Regime

in IEEE Communications Letters (2021)

This paper tackles the problem of optimizing the parameters of a symbol-level precoder for downlink multiantenna multi-user systems in the finite block length regime. Symbol-level precoding (SLP) is a non ... [more ▼]

This paper tackles the problem of optimizing the parameters of a symbol-level precoder for downlink multiantenna multi-user systems in the finite block length regime. Symbol-level precoding (SLP) is a non-linear technique for multiuser wireless networks, which exploits constructive interference among co-channel links. Current SLP designs, however, implicitly assume asymptotically infinite blocks, since they do not take into account that the design rules for finite and especially short blocks might significantly differ. This paper fills this gap by introducing a novel SLP design based on discrete constellation rotations. The rotations are the added degree of freedom that can be optimized for every block to be transmitted, for instance, to save transmit power. Numerical evaluations of the proposed method indicate substantial power savings, which might be over 99% compared to the traditional SLP, at the expense of a single additional pilot symbol per block for constellation de-rotation. [less ▲]

Precoding for Satellite Communications: Why, How and What next?

in IEEE Communications Letters (2021)

Optimization of Rate Fairness in Multi-Pair Wireless-Powered Relaying System

in IEEE Communications Letters (2020), 24(03), 603-607

This letter considers a multi-pair decode-andforward relay network where a power-splitting (PS) protocol is adopted at the energy-constrained relay to provide simultaneous wireless information and energy ... [more ▼]

This letter considers a multi-pair decode-andforward relay network where a power-splitting (PS) protocol is adopted at the energy-constrained relay to provide simultaneous wireless information and energy harvesting (EH). To achieve higher efficiency of EH, we propose a new PS-based EH architecture at the relay by incorporating an alternating current (AC) computing logic, which is employed to directly use the wirelessly harvestedACenergyforcomputationalblocks.Underanonlinear EHcircuit,ourgoalistomaximizethefairnessofend-to-endrate amonguserpairssubjecttopowerconstraints,resultinginanonconvex problem. We propose an iterative algorithm to achieve a suboptimal and efficient solution to this challenging problem by leveraging the inner approximation framework. Numerical results demonstrate that the proposed algorithm outperforms the traditional direct current computing and other baseline schemes. [less ▲]

Wireless Scheduling for Heterogeneous Services With Mixed Numerology in 5G Wireless Networks

in IEEE Communications Letters (2019)

This letter studies the scheduling problem which determines how time-frequency resources of different numerologies can be allocated to support heterogeneous services in 5G wireless systems. Particularly ... [more ▼]

This letter studies the scheduling problem which determines how time-frequency resources of different numerologies can be allocated to support heterogeneous services in 5G wireless systems. Particularly, this problem aims at scheduling as many users as possible while meeting their required service delay and transmission data. To solve the underlying integer programming (IP) scheduling problem, we first transform it into an equivalent integer linear program (ILP) and then develop two algorithms, namely Resource Partitioning-based Algorithm (RPA) and Iterative Greedy Algorithm (IGA) to acquire efficient resource scheduling solutions. Numerical results show the desirable performance of the proposed algorithms with respect to the optimal solution and their complexity-performance tradeoffs. [less ▲]

Collaborative Distributed Q-Learning for RACH Congestion Minimization in Cellular IoT Networks

in IEEE Communications Letters (2019), 23(4), 600-603

Due to infrequent and massive concurrent access requests from the ever-increasing number of machine-type communication (MTC) devices, the existing contention-based random access (RA) protocols, such as ... [more ▼]

Due to infrequent and massive concurrent access requests from the ever-increasing number of machine-type communication (MTC) devices, the existing contention-based random access (RA) protocols, such as slotted ALOHA, suffer from the severe problem of random access channel (RACH) congestion in emerging cellular IoT networks. To address this issue, we propose a novel collaborative distributed Q-learning mechanism for the resource-constrained MTC devices in order to enable them to find unique RA slots for their transmissions so that the number of possible collisions can be significantly reduced. In contrast to the independent Q-learning scheme, the proposed approach utilizes the congestion level of RA slots as the global cost during the learning process and thus can notably lower the learning time for the low-end MTC devices. Our results show that the proposed learning scheme can significantly minimize the RACH congestion in cellular IoT networks. [less ▲]

An Optimization Approach for an RLL-Constrained LDPC Coded Recording System Using Deliberate Flipping

in IEEE Communications Letters (2018)

For a recording system that has a run-length-limited (RLL) constraint, this approach imposes the hard error by flipping bits before recording. A high error coding rate limits the correcting capability of ... [more ▼]

For a recording system that has a run-length-limited (RLL) constraint, this approach imposes the hard error by flipping bits before recording. A high error coding rate limits the correcting capability of the RLL bit error. Since iterative decoding does not include the estimation technique, it has the potential capability of solving the hard error bits within several 7 iterations compared to an LDPC coded system. In this letter, we implement density evolution and the differential evolution approach to provide a performance evaluation of unequal error protection LDPC code to investigate the optimal LDPC code distribution for an RLL flipped system. [less ▲]

Power Optimization With BLER Constraint for Wireless Fronthauls in C-RAN

in IEEE Communications Letters (2016), 20(3), 602-605

Cloud radio access network (C-RAN) is a novel architecture for future mobile networks to sustain the exponential traffic growth thanks to the exploitation of centralized processing. In C-RAN, one data ... [more ▼]

Cloud radio access network (C-RAN) is a novel architecture for future mobile networks to sustain the exponential traffic growth thanks to the exploitation of centralized processing. In C-RAN, one data processing center or baseband unit (BBU) communicates with users via distributed remote radio heads (RRHs), which are connected to the BBU via high capacity, low latency fronthaul links. In this letter, we study C-RAN with wireless fronthauls due to their flexibility in deployment and management. First, a tight upper bound of the system block error rate (BLER) is derived in closed-form expression via union bound analysis. Based on the derived bound, adaptive transmission schemes are proposed. Particularly, two practical power optimizations based on the BLER and pair-wise error probability (PEP) are proposed to minimize the consumed energy at the RRHs while satisfying the predefined quality of service (QoS) constraint. The premise of the proposed schemes originates from practical scenarios where most applications tolerate a certain QoS, e.g., a nonzero BLER. The effectiveness of the proposed schemes is demonstrated via intensive simulations. [less ▲]