Transmission Scheduling Problem Research Articles

Large-volume LEO satellite imaging data networked transmission scheduling problem: Model and algorithm

With the current miniaturization and cost reduction trend, many small imaging satellites are deployed in low Earth orbit (LEO). Efficient scheduling of transmission links is crucial for handling the large volume of imaging data in the time-varying inter-satellite broadband communication networks. This ensures optimal utilization of inter-satellite link resources and gives rise to a novel problem known as the Large-volume LEO satellite Imaging Data Networked Transmission Scheduling Problem (LLSIDNTSP). This problem requires the integrity of the imaging data received on the ground station. A Specific Time-Evolving Graph (STEG) model is introduced to formulate this problem, while a highly effective Sequential Two-Phased Heuristic Algorithm (STPHA) is proposed to solve it. STPHA determines an optimized Contact Plan (CP) with a Contact-Fast Construction Algorithm (CFCA) in the first phase. With this CP as input, it produces an optimal transmission schedule with Linear Programming in the second phase. The CFCA incorporates a novel heuristic called Mission Residual Volume Factor(MRVF), which guides the selection of a proper inter-satellite and satellite-to-ground link at each construction step. Extensive simulation results demonstrate the effectiveness of the proposed STPHA. In particular, it can achieve the optimal solution for small-sized scenarios with one-hundredth of the computing time used by the exact solver CPLEX. Also, it is consistently better than other heuristic algorithms adapted from the literature for large-sized scenarios. Additional experimental analysis is conducted to showcase the effectiveness of the innovative components of STPHA.

Structure-Enhanced DRL for Optimal Transmission Scheduling

Remote state estimation of large-scale distributed dynamic processes plays an important role in Industry 4.0 applications. In this paper, we focus on the transmission scheduling problem of a remote estimation system. First, we derive some structural properties of the optimal sensor scheduling policy over fading channels. Then, building on these theoretical guidelines, we develop a structure-enhanced deep reinforcement learning (DRL) framework for optimal scheduling of the system to achieve the minimum overall estimation mean-square error (MSE). In particular, we propose a structure-enhanced action selection method, which tends to select actions that obey the policy structure. This explores the action space more effectively and enhances the learning efficiency of DRL agents. Furthermore, we introduce a structure-enhanced loss function to add penalties to actions that do not follow the policy structure. The new loss function guides the DRL to converge to the optimal policy structure quickly. Our numerical experiments illustrate that the proposed structure-enhanced DRL algorithms can save the training time by 50% and reduce the remote estimation MSE by 10% to 25%, when compared to benchmark DRL algorithms. In addition, we show that the derived structural properties exist in a wide range of dynamic scheduling problems that go beyond remote state estimation.

QoS-Aware User Association and Transmission Scheduling for Millimeter-Wave Train-Ground Communications

With the development of wireless communication, people have put forward higher requirements for train-ground communications in the high-speed railway (HSR) scenarios. With the help of mobile relays (MRs) installed on the roof of the train, the application of Millimeter-Wave (mm-wave) communication which has rich spectrum resources to the train-ground communication system can realize high data rate, so as to meet users’ increasing demand for broad-band multimedia access. Also, full-duplex (FD) technology can theoretically double the spectral efficiency. In this paper, we formulate the user association and transmission scheduling problem in the mm-wave train-ground communication system with MR operating in the FD mode as a nonlinear programming problem. In order to maximize the system throughput and the number of users meeting quality of service (QoS) requirements, we propose an algorithm based on coalition game to solve the challenging NP-hard problem, and also prove the convergence and Nash-stable structure of the proposed algorithm. Extensive simulation results demonstrate that the proposed coalition game based algorithm can effectively improve the system throughput and meet the QoS requirements of as many users as possible, so that the communication system has a certain QoS awareness.

Data Placement and Transmission Scheduling for coded multicast in mobile edge networks

Edge caching is a promising strategy to reduce the traffic load in mobile core networks, by caching popular contents at the edge of mobile networks, e.g., base stations (BSs). For the BSs to transmit data to user equipment (UEs), coded multicast can be used to improve the transmission efficiency. Moreover, in future densely deployed networks, the coverage areas of adjacent BSs are overlapped. Therefore, these cache-aided BSs can collaboratively carry out coded multicast to improve the performance of data transmission. In this paper, we consider the Data Placement and Transmission Scheduling (DPTS) problem for cached-aided coded multicast in mobile edge networks. Our objective is to minimize the total cost of data download from the data source to BSs and data transmission from the BSs to UEs. The DPTS problem is proved to be NP-hard and we first propose an Iterative Relaxation Linear Programming (IRLP) algorithm to solve it. Since the complexity of IRLP algorithm is high, we also propose another two low-complexity algorithms to solve the DPTS problem. Performance evaluation by simulation shows that the proposed algorithms can achieve a substantial reduction in total cost of data download and transmission, compared with the existing methods.

Joint Optimization of Relay Selection and Transmission Scheduling for UAV-Aided mmWave Vehicular Networks

To deal with the explosive growth of mobile traffic, millimeter-wave (mmWave) communications with abundant bandwidth resources have been applied to vehicular networks. As mmWave signal is sensitive to blockage, we introduce the unmanned aerial vehicle (UAV)-aided two-way relaying system for vehicular connection enhancement and coverage expansion. How to improve transmission efficiency and to reduce latency time in such a dynamic scenario is a challenging problem. In this paper, we formulate the joint optimization problem of relay selection and transmission scheduling, aiming to reduce transmission time while meeting the throughput requirements. To solve this problem, two schemes are proposed. The first one is the random relay selection with concurrent scheduling (RCS), a low-complexity algorithm implemented in two steps. The second one is the joint relay selection with dynamic scheduling (JRDS), which fully avoids relay contentions and exploits potential concurrent ability, to obtain further performance enhancement over RCS. Through extensive simulations under different environments with various flow numbers and vehicle speeds, we demonstrate that both RCS and JRDS schemes outperform the existing schemes significantly in terms of transmission time and network throughput. We also analyze the impact of threshold selection on achievable performance.

Adaptive Scheduling MAC Protocol in Underwater Acoustic Broadcast Communications for AUV Formation

With the rapid development of autonomous underwater vehicles (AUVs) and the continuous improvement of marine exploration requirements, AUV formation has emerged as a promising technique for performing underwater tasks with greater flexibility, adaptability, and scalability. To achieve AUV formation control, underwater acoustic communication networks (UACNs) are widely used to support information exchange among AUVs. Considering broadcast communications in fully connected mobile UACNs, existing medium access control (MAC) protocols face severe packet collision risk or low reuse efficiency. To improve the timeliness and reliability of the information exchange among AUVs, we develop an efficient scheduling-based adaptive broadcasting MAC (AB-MAC) protocol. The AB-MAC protocol is incompletely centralized, which can be reflected in two aspects. First, to ensure the consistency of the transmission schedule in the network, the AB-MAC protocol selects a control node for each frame to schedule the transmission of all nodes according to the updated network topology. The slot lengths and transmission sequences are changeable in each frame to avoid packet collisions and minimize frame lengths. Second, to further improve the efficiency and robustness of the protocol, all nodes adaptively adjust their transmission time by integrating the information contained in their previously received control packets and ordinary packets. The transmission scheduling problem is formulated as a combinatorial optimization problem, which can be solved by our proposed improved Genetic Algorithm. Numerical results demonstrate that the AB-MAC protocol not only performs well in terms of network throughput and average update interval but also has a high level of robustness even in low-quality underwater acoustic channels.

Latency Aware Transmission Scheduling for Steerable Free Space Optics

Free space optics (FSO) has been demonstrated as a secure and high-speed solution for long distance and line-of-sight wireless communications. Applying FSO as fronthaul/backhaul communications between base stations (BSs) and the gateway can significantly increase the fronthaul/backhaul link capacity. Traditionally, the gateway has to be equipped with multiple FSO transceivers, each of which is used to communicate with a BS by establishing a dedicated FSO. In this paper, we propose to use a steerable FSO system, where the gateway is equipped with a steerable FSO transceiver to communicate with multiple FSO transceivers at different BSs in a time division multiplexing manner. Applying the steerable FSO system can reduce the number of FSO transceivers at the gateway, and thus reduce the capital cost of implementing an FSO based fronthaul/backhaul network. We formulate the transmission scheduling problem in the steerable FSO system to optimize the active time for each FSO link associated with the steerable FSO transceiver such that the overall delay of transmitting a packet from geo-distributed BSs to the steerable FSO transceiver at the gateway is minimized, while the latency requirements of the BSs are met. We propose the laTency aWare transmIssion Scheduling for sTeerable FSO (TWIST) algorithm to efficiently solve the proposed problem.

Multi-channel transmission scheduling with hopping scheme under uncertain channel states

This paper investigates the multi-channel transmission scheduling problem for remote state estimation based on a hopping scheme in cyber-physical systems. The smart sensor sends multiple subpackets over different orthogonal channels to the remote end simultaneously. Owing to the randomness and vulnerability of transmission environments, the uncertain multi-channel states are considered in this paper, which relaxes the assumption of existing deterministic models. The objective is to find an appropriate hopping scheme that minimizes the remote estimation error covariance. First, the multi-channel selection problem is modeled as a multi-arm bandits (MAB) matrix via taking the packet receiving probability as the gain. From the perspective of strategy and channel, two exponential-weight online learning algorithms are designed with the assistance of transmission energy switching policy. Then, based on Bernstein’s inequality for martingales and mini-batching loop, the upper bounds of algorithms’ regret values are analyzed under stochastic and adversarial channel states, respectively. Further, the estimator expression in iterative form and a sufficient condition for the error covariance to be bounded are derived. Finally, an example of unmanned vehicle moving demonstrates all the theoretical results.

The multi-action transmission scheduling problem for remote state estimation under global energy constraint

The multi-action transmission scheduling problem for remote state estimation under global energy constraint

Joint Observation and Transmission Scheduling in Agile Satellite Networks

Compared with traditional observation satellites, agile earth observation satellites are capable of prolonging observation time windows (OTWs) for targets, which significantly alleviates observation conflicts, thereby facilitating imaging data collection. However, it also leads to more uncertainties in determining the start time to image targets within these longer OTWs for an agile satellite network (ASN) to collect imaging data. Furthermore, these collected data are offloaded only within short transmission time windows between data collectors and data sinks, thus resulting in a transmission scheduling problem. Toward this end, this paper investigates joint observation and transmission scheduling in ASNs, aiming at accommodating more imaging data to be collected and offloaded successfully. Specifically, we formulate the studied problem as integer linear programming (ILP) to maximize the weighted sum of scheduled imaging tasks. Then, we explore the hidden structure of this ILP and transform it into a special framework, which can be solved efficiently through semidefinite relaxation (SDR). To reduce computation complexity, we further propose a fast yet efficient algorithm by combining the advantages of the devised SDR method and a genetic algorithm with special population initialization. Finally, simulation results demonstrate that the proposed algorithm can significantly increase the weighted sum of scheduled tasks.

Downlink Transmission Scheduling With Data Sharing

We formulate and analyze a fundamental downlink transmission scheduling problem in a wireless communication system, composed of a base station and a set of users, each requesting a packet to be served within a time window. Some packets are requested by several users and can be served simultaneously due to the broadcast nature of the wireless medium. The base station can choose from a set of transmission strategies, e.g., in terms of combination of data rate and coding scheme, to serve the users. Each request can be served by a subset of transmission strategies. We seek a downlink transmission scheduling algorithm generating maximum aggregated system-wide utility. In this paper, we develop approximation algorithms for the formulated downlink transmission scheduling problem in both offline and online settings. We first establish the NP-hardness of the offline scheduling problem and the approximation hardness and bound of the online scheduling problem in non-preemptive and preemptive-restart models, respectively. We then design approximation algorithms and derive the approximation and competitive ratios of our online and offline scheduling algorithms. Numerical simulations are performed to further evaluate our algorithms in a wide range of network settings.

State-to-Noise-Ratio-Based Transmission Scheduling in Wireless Control Systems for IIoT

In industrial internet-of-things (IIoT), conventional event-triggered control method requires sensors continuously monitoring control states in periodical time. This would consume a huge amount of energy resource, which impedes the application of such conventional methods since the sensors are powered by batteries in most cases. To deal with this issue, this paper proposes a new state-to-noise-ratio (SNR) based transmission scheduling method from wireless communication perspective. Specifically, we first adopt an Additive White Gaussian Noise (AWGN) channel model to represent the event-triggered control model, by which we can convert the original event-triggered control problem into a wireless transmission scheduling problem from the sensor to the controller. Based on that, the mutual information is proposed to measure the value of the control states. More importantly, a new control SNR is defined based on mutual information. Using control SNR as the transmission activating criterion, perfect state observation assumption and sensor’s monitoring with periodical time in traditional event-triggered control are no longer needed. Furthermore, we provide an analytical expression of dynamic SNR thresholds to determine whether the transmission should be activated. Finally, we prove the mean-square stability of our proposed method. Numerical comparisons are provided to demonstrate the effectiveness of our proposed method.

Transmission scheduling for privacy-optimal encryption against eavesdropping attacks on remote state estimation

In remote state estimation systems, the state being estimated may be wiretapped by eavesdropping communications from the sensor to the remote estimator. A straightforward remedy for protecting the state privacy is to encrypt all the sensory data before transmission, which however may not be affordable for an energy-constrained sensor. In this paper, we address the optimal sensor transmission scheduling problem in order to protect the state privacy in an energy-efficient manner. The sensor can choose either to transmit data in plaintext or encrypted text, or to stay in silence without transmitting. We formulate the problem as the one of maximizing the eavesdropper’s estimation error of the system state, while guaranteeing a certain level of the remote estimation performance under a given energy budget for the sensor in the finite time horizon. Then, we transform the problem into an optimal scheduling problem under any fixed transmission times and an energy allocation problem, and propose algorithms to solve each of them. We theoretically prove that, provided that a certain level of remote estimation performance is guaranteed, the optimal sensor schedule is to group instants of encrypted transmissions and silent states as tighter as possible and the optimal energy allocation tends to arrange more energy to transmit encrypted text. Furthermore, we extend our results over finite time horizon to infinite periodic time horizon. We construct a set of monotonic sequences to approximate the estimator’s performance constraint. Then, we design an algorithm to obtain the suboptimal schedule Finally, numerical results are presented to demonstrate the performance of the proposed methods.

Optimization of packet forwarding scheduling in wireless ad-hoc networks: Deployment on a 3D environment

The key aim of a multi-hop wireless network is to increase service efficiency in terms of transmission scheduling, packet transfer volume, and other factors. In a practical deployment of Ad- Hoc wireless network in three-dimensional (3D) environments, we study the optimizing transmission scheduling problem by end-to-end latency minimization using the signal-to-interference-and-noise rate (SINR) mechanism. Two strategies are considered. The former directly deals with end-to-end latency and eliminates the constraint of frame periodicity. The latter combines two cooperative transmission and transmission interference suppression models. The properties of both strategies are analyzed, and mixed-integer programming (MIP) models and solution heuristics are developed. Simulation results are presented to clarify the end-to-end latency performance of strategies, especially in 3D environments.

An improved genetic algorithm for the integrated satellite imaging and data transmission scheduling problem

The study of Integrated Satellite Imaging and Data Transmission Scheduling Problem (ISIDTSP) has assumed increasing importance due to the growing number of satellites observing large quantities of targets and seeking to transmit their images to the ground stations. This paper formulates the ISIDTSP as a mixed integer programming model and develops an improved genetic algorithm. With regard to the individual representation, a novel idea of encoding and decoding is adopted to match the specific request with the corresponding satellite-ground resources, and a conception of conflicting request set is proposed to limit the chromosome length, thereby reducing the algorithmic time complexity. For the trade-off between diversity and convergence, several effective operators are introduced, including the population initialization based on the way of uniform design, the multi-point greedy mutation and the adaptive selection. Evaluations with two test cases demonstrate the efficiency of the proposed algorithm and show its ability to obtain high-quality solutions within an acceptable time period for the large scale optimization instances.

Transmission scheduling for multi-process multi-sensor remote estimation via approximate dynamic programming

In this paper, we consider a remote estimation problem where multiple dynamical systems are observed by smart sensors, which transmit their local estimates to a remote estimator over channels prone to packet losses. Unlike previous works, we allow multiple sensors to transmit simultaneously even though they can cause interference, thanks to the multi-packet reception capability at the remote estimator. In this setting, the remote estimator can decode multiple sensor transmissions (successful packet arrivals) as long as their signal-to-interference-and-noise ratios (SINR) are above a certain threshold. In this setting, we address the problem of optimal sensor transmission scheduling by minimizing a finite horizon discounted expected estimation error covariance cost across all systems at the remote estimator, subject to an average transmission cost. While this problem can be posed as a stochastic control problem, the optimal solution requires solving a Bellman equation for a dynamic programming (DP) problem, the complexity of which scales exponentially with the number of systems being measured and their state dimensions. In this paper, we resort to a novel Least Squares Temporal Difference (LSTD) Approximate Dynamic Programming (ADP) based approach to approximating the value function. More specifically, an off-policy based LSTD approach, named in short Enhanced-Exploration Greedy LSTD (EG-LSTD), is proposed. We discuss the convergence analysis of the EG-LSTD algorithm and its implementation. A Python based program is developed to implement and analyse the different aspects of the proposed method. Simulation examples are presented to support the results of the proposed approach both for the exact DP and ADP cases.

Adaptive Transmission Scheduling in Wireless Networks for Asynchronous Federated Learning

In this paper, we study asynchronous federated learning (FL) in a wireless distributed learning network (WDLN). To allow each edge device to use its local data more efficiently via asynchronous FL, transmission scheduling in the WDLN for asynchronous FL should be carefully determined considering system uncertainties, such as time-varying channel and stochastic data arrivals, and the scarce radio resources in the WDLN. To address this, we propose a metric, called an effectivity score, which represents the amount of learning from asynchronous FL. We then formulate an Asynchronous Learning-aware transmission Scheduling (ALS) problem to maximize the effectivity score and develop three ALS algorithms, called ALSA-PI, BALSA, and BALSA-PO, to solve it. If the statistical information about the uncertainties is known, the problem can be optimally and efficiently solved by ALSA-PI. Even if not, it can be still optimally solved by BALSA that learns the uncertainties based on a Bayesian approach using the state information reported from devices. BALSA-PO suboptimally solves the problem, but it addresses a more restrictive WDLN in practice, where the AP can observe a limited state information compared with the information used in BALSA. We show via simulations that the models trained by our ALS algorithms achieve performances close to that by an ideal benchmark and outperform those by other state-of-the-art baseline scheduling algorithms in terms of model accuracy, training loss, learning speed, and robustness of learning. These results demonstrate that the adaptive scheduling strategy in our ALS algorithms is effective to asynchronous FL.

Multicommodity Flow Modeling for the Data Transmission Scheduling Problem in Navigation Satellite Systems

Introducing InterSatellite Links (ISLs) is a major trend in new-generation Global Navigation Satellite Systems (GNSSs). Data transmission scheduling is a crucial problem in the study of ISL management. The existing research on intersatellite data transmission has not considered the capacities of ISL bandwidth. Thus, the current study is the first to describe the intersatellite data transmission scheduling problem with capacity restrictions in GNSSs. A model conversion strategy is designed to model the aforementioned problem as a length-bounded single-path multicommodity flow problem. An integer programming model is constructed to minimize the maximal sum of flows on each intersatellite edge; this minimization is equivalent to minimizing the maximal occupied ISL bandwidth. An iterated tree search algorithm is proposed to resolve the problem, and two ranking rules are designed to guide the search. Experiments based on the BeiDou satellite constellation are designed, and results demonstrate the effectiveness of the proposed model and algorithm.

Information Cofreshness-Aware Grant Assignment and Transmission Scheduling for Internet of Things

The proliferation of Internet of Things (IoT) applications has prompted the continuous increase of research efforts in recent years. In light of the diversified use cases and service requirements, the information freshness [or Age of Information (AoI)] of IoT data is key for latency-sensitive IoT applications (e.g., industrial automation and intelligent transportation) because stale information may lead to delayed responses and catastrophic outcomes. In addition, various types of IoT applications require the analytics of IoT data collected from their constituent IoT devices. While previous AoI-related works have analyzed or optimized the information freshness of various communication systems, the problem that the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">information cofreshness</i> [or Coage of Information (CoI)] of an IoT application is determined by the maximum AoI of the constituent IoT devices has been rarely investigated. In this article, we address the grant assignment and transmission scheduling (GATS) problem for IoT and formulate it as an integer linear program (ILP) to minimize a weighted sum of CoI. Due to the intractability of the original GATS problem, we transform it to an equivalent problem of the maximization of the number of the eliminated age blocks. Then, we propose the CoI-aware age block elimination (CABEL) algorithm in which information updates are selected progressively according to their coage efficiency (CE) values and prove that the achieved approximation factor depends on the relative service costs and uplink delays. Our simulation results demonstrate that the proposed solution can effectively perform information updates and utilize service budgets, thereby achieving low CoI compared with the existing solutions under various parameter settings.

A message transmission scheduling algorithm based on time-domain interference alignment in UWANs

High propagation delays cause message collisions at intended nodes, which seriously affects network performance. In this paper, we consider the transmission scheduling problem of messages with specified transmission requirements, which is ignored by most MAC protocols of Underwater Acoustic Networks (UWANs). We focus on the actual applications of UWANs and adopt time-domain interference alignment to design a scheduling algorithm (TDIA-MAC). Firstly, we study the nature and the existence conditions of perfect scheduling. Secondly, we analyze the constraints required for feasible transmissions and design the value function to evaluate feasible transmissions. The optimal decision is selected from feasible transmissions by the value function. The algorithm meets the message transmission requirements in practical applications and ensures that multiple nodes can work simultaneously without conflicts. Finally, we simulate the proposed algorithm under two settings of varying offered traffic and the number of nodes. The results show that the TDIA-MAC outperforms the other three algorithms in terms of throughput, successful delivery ratio, and fairness under varying offered traffic and the number of nodes.