Literatura científica selecionada sobre o tema "Downlink semi-persistent scheduling transmission"

In LTE(Long Term Evolution) system, scheduling plays an important role in the process of allocating resource. LTE system puts forward semi-persistent scheduling (SPS) for new applications such as VoIP(Voice on Internet Protocol) and online games. Considering the problem of resource collision in SPS HARQ(Hybrid Automatic Repeat reQuest) process, we explore the relationship between uplink semi-persistent scheduling period and the number of semi-persistent transmissions, and propose two novel solutions. One is choosing specific uplink semi-persistent period for different uplink/downlink (UL/DL) configurations and the number of transmissions. The other is delaying collision processes for the configuration of small uplink period. The analysis proves that the two solutions can reduce the collision probability and improve the stability of LTE system.

Cyber–physical systems (CPS) have been widely employed as wireless control networks. There is a special type of CPS which is developed from the wireless networked control systems (WNCS). They usually include two communication links: Uplink transmission and downlink transmission. Those two links form a closed-loop. When such CPS are deployed for time-sensitive applications such as remote control, the uplink and downlink propagation delay are non-negligible. However, existing studies on CPS/WNCS usually ignore the propagation delay of the uplink and downlink channels. In order to achieve the best balance between uplink and downlink transmissions under such circumstances, we propose a heuristic framework to obtain the optimal scheduling strategy that can minimize the long-term average control cost. We model the optimization problem as a Markov decision process (MDP), and then give the sufficient conditions for the existence of the optimal scheduling strategy. We propose the semi-predictive framework to eliminate the impact of the coupling characteristic between the uplink and downlink data packets. Then we obtain the lookup table-based optimal offline strategy and the neural network-based suboptimal online strategy. Numerical simulation shows that the scheduling strategies obtained by this framework can bring significant performance improvements over the existing strategies.

This article investigates the transmission of downlink control signals for multiple unmanned aerial vehicle (UAV) clusters in collaborative search and rescue operations in mountainous environments. In this scenario, a reconfigurable intelligent surface (RIS) mounted on the UAV is utilized to overcome obstacles between the ground base station (BS) and UAVs. By leveraging the fixed channel of the RIS to the BS, the line-of-sight (LoS) path characteristics of the air-to-air channel, and the position information of the UAV, the RIS forms a directional beam by adjusting the RIS coefficient, which points towards UAVs in the cluster. To ensure low delay in control signaling and UAV state transmission, we adopt semi-persistent scheduling (SPS), which allocates pre-specified periodic intervals to each UAV for the formation of corresponding RIS coefficients. The allocation of time slots is constrained by the transmission intervals required by different UAVs and the number of RISs available. We propose a time slot scheduling scheme for UAVs to reduce inter-cluster interference caused by RIS beams. The time slot allocation problem is formulated as a combinatorial optimization problem. To solve this problem, we first propose an intuitive greedy scheme called local interference minimization (LIM). Building upon the LIM scheme, we propose a rollout-based algorithm called rollout interference minimization (RIM). Through simulation, we compare the LIM and RIM schemes with the benchmark scheduling scheme. The results demonstrate that our proposed scheme significantly reduces interference between UAV clusters while satisfying the conditions of periodic transmission and RIS quantity constraints.

Vehicle-to-Vehicle (V2V) messaging is an indispensable component of connected autonomous vehicle systems.The 3rd Generation Partnership Project (3GPP) is designed to support V2V communication without any infrastructure using sensing-based Semi-Persistent Scheduling (SPS) in order to avoid resource collisions for Cooperative Awareness Messages (CAMs) transmission. However, the legacy system suffers from significant collisions in a traffic congestion environment and resource waste in light traffic conditions. To address these problems, in this paper we propose a novel dynamic resource scheduling algorithm for real-time group broadcasting, inspired by the Lyapunov optimization framework, where the optimization objective is to minimize time-average failure probability subject to queue stability. Through extensive simulations, we show that the proposed scheduling algorithm outperforms the standard in both traffic jams and leisurely road environments.

For cellular-based vehicle-to-everything (C-V2X) communication, vital information about status and intention is periodically broadcasted by each vehicle using the cooperative awareness message (CAM) service. In C-V2X, the task of resource allocation can either be carried out in a centralized manner by the network, termed Mode 3, or by the vehicles themselves in a distributed manner without any core network support, termed Mode 4. Mode 4 scheduling is accomplished by employing sensing-based semi-persistent scheduling (SB-SPS), where the vehicles sense the medium and identify the best time-frequency resource combination for transmission of the CAM. Focusing on Mode 4 in this paper, we present a comprehensive analysis of the impact of variations in the transmit power of the vehicle on the performance of SB-SPS for C-V2X communications in various traffic scenarios through simulations. An adaptive-transmit power control (A-TPC) algorithm is presented to improve the quality of service for various large-scale traffic scenarios, where each vehicle uses real-time channel-sensing information to adjust the transmit power in order to avoid interference with neighbouring vehicles. The results demonstrate that our proposed algorithm outperforms the conventional TPC schemes.

The Third Generation Partnership Project (3GPP) Release 16 defines the sensing-based semi-persistent scheduling (SPS) as the resource allocation scheme for Sidelink Mode 2 in New Radio (NR)-based vehicle-to-everything (V2X) communication. A well-known issue in Mode 2 is the persistent packet collision that results from two or more vehicles repeatedly using the same resource for transmission. It may create serious safety problems when the vehicles are in a situation where only the broadcast safety beacons can assist in driving. To resolve this issue, a solution that relies on the feedback from neighboring vehicles is proposed, through which the vehicles suffering from persistent packet collisions can quickly part and select other resources. Extensive simulations show that the proposed broadcast feedback scheme reduces persistent packet collisions by an order of magnitude compared to SPS, and it is achieved without sacrificing the average packet reception ratio (PRR). Namely, it is the quality aspect (i.e., burstiness) of the packet collisions that the proposed scheme addresses rather than the quantity (i.e., total number of collision losses). By preventing extended packet loss events, the proposed scheme is expected to serve NR V2X better, which requires stringent QoS in terms of the information update delay thereby helping to reduce the chances of vehicle crashes.

AbstractFifth-generation (5G) cellular mobile networks are expected to support mission-critical low latency applications in addition to mobile broadband services, where fourth-generation (4G) cellular networks are unable to support Ultra-Reliable Low Latency Communication (URLLC). However, it might be interesting to understand which latency requirements can be met with both 4G and 5G networks. In this paper, we discuss (1) the components contributing to the latency of cellular networks and (2) evaluate control-plane and user-plane latencies for current-generation narrowband cellular networks and point out the potential improvements to reduce the latency of these networks, (3) present, implement and evaluate latency reduction techniques for latency-critical applications. The two elements we detected, namely the short transmission time interval and the semi-persistent scheduling are very promising as they allow to shorten the delay to processing received information both into the control and data planes. We then analyze the potential of latency reduction techniques for URLLC applications. To this end, we develop these techniques into the long term evolution (LTE) module of ns-3 simulator and then evaluate the performance of the proposed techniques into two different application fields: industrial automation and intelligent transportation systems. Our detailed evaluation results from simulations indicate that LTE can satisfy the low-latency requirements for a large choice of use cases in each field.

L'émergence de nouveaux cas et d’applications tels que la réalité virtuelle/augmentée, l'automatisation industrielle, les véhicules autonomes, etc. en 5G fait définir au Third Generation Partnership Project (3GPP) Ultra-reliable low-latency communications (URLLC) comme un des trois services. Pour soutenir URLLC avec des exigences strictes de la fiabilité et de la latence, 3GPP Release 15 et 16 ont standardisé des fonctionnalités d’URLLC dans le spectre sous licence. Release 17 en cours agrandit des fonctionnalités d’URLLC au spectre sans licence pour cibler des nouveaux cas dans des scénarios industriels. Dans la première partie de cette thèse du Chapitre 2 au Chapitre 4, nous nous concentrons sur URLLC dans le spectre sous licence. La première étude est confrontée au problème de garantir le nombre des répétitions dans des uplink configured-grant (CG) ressources. Ensuite, nous étudions la collision entre une eMBB UL transmission d'un UE et une URLLC UL transmission d'un autre UE sur des CG ressources. Enfin, nous recherchons la DL transmission où le feedback de la DL semi-persistent scheduling transmission est abandonné à cause du conflit entre des DL/UL symboles. Dans la deuxième partie du Chapitre 5 au Chapitre 8, nous nous focalisons sur URLLC dans le spectre sans licence. Dans le spectre sans licence, un appareil demande d'accéder au canal en utilisant load based equipment (LBE) ou frame based equipment (FBE). L’incertitude d’acquérir un canal par LBE ou FBE pourrait empêcher la URLLC transmission d’atteindre l’exigence de la latence. Par conséquent, l'étude de l'impact de LBE ou FBE sur la URLLC transmission et des améliorations de LBE et de FBE sont nécessaires
The advent of new use cases and new applications such as augmented/virtual reality, industrial automation, autonomous vehicles, etc. in 5G has made the Third Generation Partnership Project (3GPP) specify Ultra-reliable low-latency communications (URLLC) as one of the service categories. To support URLLC with the strict requirements of reliability and latency, 3GPP Release 15 and Release 16 have specified the URLLC features in licensed spectrum. The ongoing 3GPP Release 17 extends the URLLC features to unlicensed spectrum to target the new use cases in the industrial scenario. In the first part of the thesis from Chapter 2 to Chapter 4, we focus on the URLLC in licensed spectrum. The first study deals with the problem of ensuring the configured number of uplink (UL) configured-grant (CG) repetitions of a transport block. Secondly, we study the collisions of an eMBB UL transmission of a user equipment (UE) and an URLLC UL transmission of another UE on the CG resources. Thirdly, the focus of this study is the downlink (DL) transmission where the feedback of the DL semi-persistent scheduling transmission is dropped due to the conflict of the DL/UL symbols. In the second part from Chapter 5 to Chapter 8, we focus on URLLC operation in unlicensed spectrum. In unlicensed spectrum, a 5G device is required to access to a channel by using load based equipment (LBE) or frame based equipment (FBE). The uncertainty of obtaining channel access through LBE or FBE can impede the achievement of the URLLC latency requirements. Therefore, the study of impact of LBE and FBE on URLLC transmission and the enhancements of LBE and FBE are needed

碩士
國立中央大學
通訊工程學系
101
Long Term Evolution (LTE) is the key technology to deal with the increasing number of mobile network users. The core network of LTE system is all-IP based. In order to support voice service in LTE systems, VoIP (Voice over Internet Protocol) technology is used. The challenges of supporting VoIP transmission in LTE system are that the VoIP packet is loss sensitive and delay sensitive. The VoIP capacity is limited by control channel numbers. According to the challenges mentioned above, scheduling algorithm is main factor of reducing the delay time and packet loss rate. In this paper we propose a scheduling algorithm which is combining the semi-persistent scheduling algorithm and the dynamic scheduling algorithm. Due to the dynamic character, the scheduling pattern of VoIP user is more fit in with the channel condition. According to the simulation result, the proposed algorithm can effectively reduce the delay time and packet loss rate, while enhancing the VoIP capacity of LTE systems.