Semi-persistent Scheduling Research Articles

Adaptive sensing-based semipersistent scheduling with channel-state-information-aided reselection probability for LTE-V2V

LTE-V2V mode 4 utilizes sensing-based semipersistent scheduling (SB-SPS) to support the vehicle user equipment to autonomously select appropriate radio resources and allow the UE to be retained for several consecutive periods. Then, resource reselect is determined based on the reselection probability P k . For conventional SB-SPS, the value of P k is fixed identically for all vehicles. In this work, we introduce an improved SB-SPS scheme, which aims to adaptively adjust the value of the reselection probability P k based on the channel state information. Through simulations, we concluded that the proposed algorithm outperformed the conventional algorithm and effectively improve the performance of each scenario.

A Multi-Service Adaptive Semi-Persistent LTE Uplink Scheduler for Low Power M2M Devices

The prominence of Machine-to-Machine (M2M) communications in the future wide area communication networks place various challenges to the cellular technologies such as the Long Term Evolution (LTE) standard, owing to the large number of M2M devices generating small bursts of infrequent data packets with a wide range of delay requirements. The channel structure and Quality of Service (QoS) framework of LTE networks fail to support M2M traffic with multiple burst sizes and QoS requirements while a bottleneck often arises from the limited control resources to communicate future uplink resource allocations to the M2M devices. Moreover, many of the M2M devices are battery-powered and require a low-power consuming wide area technology for wide-spread deployments. To alleviate these issues, in this article we propose an adaptive semi-persistent scheduling (SPS) scheme for the LTE uplink which caters for multi-service M2M traffic classes with variable burst sizes and delay tolerances. Instead of adhering to the rigid LTE QoS framework, the proposed algorithm supports variation of uplink allocation sizes based on queued data length yet does not require control signaling to inform those allocations to the respective devices. Both the eNodeB and the M2M devices can determine the precise uplink resource allocation related parameters based on their mutual knowledge, thus omitting the burden of regular control signaling exchanges. Based on a control parameter, the algorithm can offer different capacities and levels of QoS satisfaction to different traffic classes. We also introduce a pre-emptive feature by which the algorithm can prioritize new traffic with low delay tolerance over ongoing delay-tolerant traffic. We also build a model for incorporating the Discontinuous Reception (DRX) mechanism in synchronization with the adaptive SPS transmissions so that the UE power consumption can be significantly lowered, thereby extending their battery lives. The simulation and performance analysis of the proposed scheme shows significant improvement over the traditional LTE scheduler in terms of QoS satisfaction, channel utilization and low power requirements of multi-service M2M traffic.

Intelligent Radio Resource Allocation for Human-Robot Collaboration

The recent surge in human-controlled robotics and haptic devices research is expediting a paradigm shift in today’s communication networks towards human-to-robot (H2R) centric technologies that support Industrial Internet of Things (IIoT) and Industry 5.0. In both IIoT and Industry 5.0, human skills are extended through collaboration with robots that are geographically separated from the human. Depending on the dynamicity of the actual use case, human-to-robot communications necessitate low-latency networking. While Long Term Evolution (LTE) cellular technology has been successful in fulfilling the bandwidth demands of massively-connected sensors and devices of Industry 4.0, it is insufficient to meet the low latency demands of the future Industry 5.0 where dynamic interactions between humans and robots are paramount. In reducing the latency caused by radio resource contention in wireless H2R communications, in this work, we propose a novel approach that exploits an Attention-based Recurrent Neural Network (Att-RNN) to improve the Semi-Persistent Scheduling (SPS) resource allocation scheme adopted by LTE and new radio (NR) standards developed for the fifth generation (5G) mobile networks. We conduct a series of real haptic experiments to collect H2R traffic traces to train, test and evaluate the accuracy of Att-RNN in predicting H2R traffic. Then, with extensive simulations based on the empirical H2R traffic traces, we show that our proposed Att-RNN SPS scheme outperforms classic SPS and other existing resource allocation schemes in terms of reduced latency and improved resource allocation efficiency, thus making Att-RNN SPS a suitable candidate in future Industry 5.0 deployments.

Improving Performance of C-V2X Sidelink by Interference Prediction and Multi-Interval Extension

Cellular Vehicle-to-Everything (C-V2X), as a next-generation V2X communication technique, has attracted much attention recently. Especially, SideLink (SL) of C-V2X in the mode 4 is a promising technique for disseminating various information in a non-line-of-sight area via direct inter-vehicle communication without requiring base stations. In order to better prevent accidents, it is important to improve the reliability and adaptability of SL. However, the Semi-Persistent Scheduling (SPS) method has a limited performance at short distances due to transmission collisions, and cannot well support applications with different transmission intervals. To solve these problems, in this paper, we propose a new packet collision avoidance method, Interference Prediction and Multi-Interval extension (IPMI), for the C-V2X SL mode 4, based on directly predicting the interference vehicles (defined as vehicles in the overlapping communication range of two vehicles using the same resource, and susceptible to packet collisions at reception), without causing extra overhead. Specifically, the proposed method selects for each vehicle a resource that has (i) a minimal number of interference vehicles and (ii) a maximal inter-vehicle distance, to reduce packet collisions. It is further extended to support applications with different transmission intervals. Simulation results confirm that compared with the conventional methods, the proposed method can achieve higher reliability and still have a promising performance even in times of partial deployment.

Space Division Multiple Access for Cellular V2X Communications

Vehicular communication is the backbone of future Intelligent Transportation Systems (ITS). It offers a network-based solution for vehicle safety, cooperative awareness, and traffic management applications. For safety applications, Basic Safety Messages (BSM) containing mobility information is shared by the vehicles in their neighborhood to continuously monitor other nearby vehicles and prepare a local traffic map. BSMs are shared using mode 4 of Cellular V2X (C-V2X) communications in which resources are allocated in an ad hoc manner. However, the strict packet transmission requirements of BSM and hidden node problem causes packet collisions in a vehicular network, thus reducing the reliability of safety applications. Moreover, as vehicles choose the transmission resources in a distributed manner in mode 4 of C-V2X, the packet collision problem is further aggravated. This paper presents a novel solution in the form of a Space Division Multiple Access (SDMA) protocol that intelligently schedules BSM transmissions using vehicle position data to reduce concurrent transmissions from hidden node interferers. The proposed protocol works by dividing road segments into clusters and sub-clusters. Several sub-frames are allocated to a cluster and these sub-frames are reused after a certain distance. Within a cluster, sub-channels are allocated to sub-clusters. We implement the proposed SDMA protocol and evaluate its performance in a highway vehicular network. Simulation results show that the proposed SDMA protocol outperforms standard Sensing-Based Semi Persistent Scheduling (SB-SPS) in terms of safety range and packet delay.

Resolving Persistent Packet Collisions through Broadcast Feedback in Cellular V2X Communication

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.

Latency reduction for narrowband URLLC networks: a performance evaluation

Fifth-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.

An Evasive Scheduling Enhancement Against Packet Dropping Attacks in C-V2X Communication

Third Generation Partnership Project (3GPP) has standardized the Sensing-Based Semi-Persistent Scheduling (SB-SPS) as the radio resource allocation algorithm for Cellular V2X (C-V2X) sidelink communication Mode 4. The algorithm leverages on past resource use pattern and reservation information of neighbor vehicles to reduce the chances of packet collisions. However, the very predictability can be exploited by potential attackers to intentionally cause packet collisions in the predicted transmission locations in the resource plane. In this letter, we demonstrate that such packet dropping attack can cause the victim to become a “ghost vehicle” to neighbors for a long duration. If used in highly safety-critical situations, the attack can push the victim into a situation of higher crash risk, which would be worse off than not having the C-V2X safety communication. Therefore, we propose an enhancement to the SB-SPS algorithm to guard against the attack by randomizing actually used resource locations to a certain degree. We demonstrate the effectiveness of the proposed enhancement through analysis and simulation, and discuss its cost aspect as well.

Cross-Layer Design and Performance Analysis for Ultra-Reliable Factory of the Future Based on 5G Mobile Networks

To provide a new level of reliability, latency, and support a massive number of users and smart objects, a new 5G multi-services air interface needs to be addressed for the factory of the future (FoF). However, there are limitations in providing connectivity to a dynamic machine in a factory due to several strict industrial automation requirements. In particular, the strict wireless communication latency and reliability requirements are the major challenges to enable the Industry 4.0 vision. In this paper, a PHY-MAC layer cross-layer model that combines a semi-persistent scheduling at the medium access control layer and NOMA at the physical layer has been proposed to address the limitations. The work extensively investigates the performance of the factory of the future with various considerations of 5G spectrums (in this case 3.5 GHz and 28 GHz), speeds and frequency diversity. In addition, the packet error rate (PER), outage probability and throughput in MAC are evaluated in terms of network density deployment (sparse, moderate, dense), different kinds of speed; 0 km/h, 3 km/h, 7 km/h and 10 km/h, under two 5G frequency spectrums. Through extensive simulations, the considered 5G system parameters produced better results in terms of reliability, where the results showed that the frequency diversity outperformed non-diversity by 2 dB. In a sparse network, the PER results showed better results compared to the dense network density by 2 dB (MMSE), 8 dB (LS-Linear) and 2 dB (LS-Spline). Besides that, robotics in sparse network density and stationary exhibited the best PER results, which is as low as 10−7. Moreover, the performance of mid-band frequency outperformed the high-band frequency by 1.8dB (MMSE) in dense condition and 1.5 dB (MMSE) in sparse deployment at PER = 10−6. Hence, this study could be a useful insight for the factory of the future services that are utilizing a 5G mid-band spectrum as well as a high-band spectrum.

On Reliability Bound and Improvement of Sensing-Based Semipersistent Scheduling in LTE-V2X

After the sensing-based semipersistent scheduling (SPS) is introduced in the media access control layer of the long-term evolution vehicle-to-everything (LTE-V2X) Mode 4, many tests have been conducted to measure its performance. However, until now, there is still no clear mathematical expression for the reliability of this scheduling. To this end, in this article, we attempt to provide the lower and upper bounds of the reliability and propose a distributed algorithm for improving reliability. First, we give a mathematical description of sensing-based SPS and apply packet pass rate (PPR) to represent its reliability. Then, we analyze the SPS without sensing and present a theoretical expression of the reliability, which is described as a function of channel busy rate (CBR). Second, an iterative approach is applied to analyze the sensing-based SPS, and the mathematical expressions of lower and upper-reliability bounds are derived. Third, based on the existing condition of the upper bound, we propose a reliability improvement solution, which utilizes a distributed algorithm to process added information, such as the counter and the offset for the remaining storage space. Finally, this solution is applied to LTE-V2X, and simulation shows that the proposed scheme can significantly improve the scheduling reliability.

Age of Information Optimized MAC in V2X Sidelink via Piggyback-Based Collaboration

Real-time status update in future vehicular networks is vital to enable control-level cooperative autonomous driving. Cellular Vehicle-to-Everything (C-V2X), as one of the most promising vehicular wireless technologies, adopts a Semi-Persistent Scheduling (SPS) based Medium-Access-Control (MAC) layer protocol for its sidelink communications. Despite the recent and ongoing efforts to optimize SPS, very few work has considered the status update performance of SPS. In this paper, Age of Information (AoI) is first leveraged to evaluate the MAC layer performance of C-V2X sidelink. Critical issues of SPS, i.e., persistent packet collisions and Half-Duplex (HD) effects, are identified to hinder its AoI performance. Therefore, a piggyback-based collaboration method is proposed accordingly, whereby vehicles collaborate to inform each other of potential collisions and collectively afford HD errors, while entailing only a small signaling overhead. Closed-form AoI performance is derived for the proposed scheme, optimal configurations for key parameters are hence calculated, and the convergence property is proved for decentralized implementation. Simulation results show that compared with the standardized SPS and its state-of-the-art enhancement schemes, the proposed scheme shows significantly better performance, not only in terms of AoI, but also of conventional metrics such as transmission reliability.

On Wireless Blind Spots in the C-V2X Sidelink

The third generation partnership project (3GPP) has issued specifications for the autonomous assignment of radio resources by vehicles on the sidelink of the cellular-vehicle-to-everything (C-V2X) technology. It is based on a sensing mechanism for resource selection and a semi-persistent scheduling for resource reservation to periodic safety messages. Imperfect sensing due to hidden terminals and to half-duplex on board transceivers may result in the selection of interfered resources for successive message transmissions. As a consequence of the lost packets, involved vehicles may become blind to the presence of other vehicles in their vicinity even for many seconds, with threats to the road safety. In this paper, we define these events as wireless blind spot s (WBSs) and characterize their probability to occur. We propose an enhancement to the autonomous mode in order to reduce the WBS duration and demonstrate the benefits of the proposal against the legacy mode, both analytically in a simplified scenario and through simulations in a highway environment.

Design and Analysis of a Short-Term Sensing-Based Resource Selection Scheme for C-V2X Networks

The cellular vehicle-to-everything (C-V2X) networks can support direct vehicle-to-vehicle (V2V) communications via sidelink/PC5 interface without cellular infrastructure support. The sensing-based semipersistent scheduling (SPS) scheme is to allow vehicles to autonomously reserve and select radio resources. However, the common sensing nature of the distributed SPS algorithm gives rise to that C-V2X distributed communications can be challenged by the resource selection collisions, especially in aperiodic traffic, which results in low reliability. In this article, we propose a short-term sensing-based resource selection (STS-RS) scheme to reduce packet collisions due to resource contention, where a short-term sensing duration is configured at the beginning of the resource unit right before resource selection, and whether the packet is ultimately transmitted on the selected resource depends on the sensing result. Furthermore, analysis models of the performance for the proposed STS-RS scheme and SPS scheme defined in C-V2X mode 4 are investigated. Finally, simulations and numerical results show that the STS-RS scheme significantly reduces the packet collisions and increases the C-V2X direct communication performance compared to the SPS scheme.

Group-Based Data Transmission Protocol for Small-Sized URLLC Services

This letter presents a group-based data transmission protocol for small-sized ultra-reliable and low latency communication (URLLC) services. For the users within the same group, the semi-persistent scheduling (SPS) and grant-free based scheduling schemes are adopted for their initial transmission and retransmission to reduce signaling overhead consumption, respectively. We further investigate the optimal number of consecutive slots within one group and derive a closed-form optimal configuration to maximize the utilization of retransmission resources. Results show that the proposed protocol can significantly reduce the control signaling while guaranteeing the stringent latency and reliability requirements.

Analysis of Control Overhead Reduction by Semi-Persistent Scheduling

For the efficient use of radio resource, semi-persistent scheduling (SPS) has been adopted to reduce control overhead required for resource allocation. In this letter, for voice over Internet protocol traffic, a lower bound on blocking probability and a closed-form maximum achievable control overhead reduction ratio are derived through a novel Markov chain model. Also, the performance evaluation of SPS under various resource assignment algorithms is provided on the blocking probability and overhead reduction ratio. Analytical expressions are validated through simulations.

Joint Frame Design and Resource Allocation for Ultra-Reliable and Low-Latency Vehicular Networks

The rapid development of the fifth generation mobile communication systems accelerates the implementation of vehicle-to-everything communications. Compared with the other types of vehicular communications, vehicle-to-vehicle (V2V) communications mainly focus on the exchange of driving safety information with neighboring vehicles, which requires ultra-reliable and low-latency communications (URLLCs). However, the frame size is significantly shortened in V2V URLLCs because of the rigorous latency requirements, and thus the overhead is no longer negligible compared with the payload information from the perspective of size. In this paper, we investigate the frame design and resource allocation for an urban V2V URLLC system in which the uplink cellular resources are reused at the underlay mode. Specifically, we first analyze the lower bounds of performance for V2V pairs and cellular users based on the regular pilot scheme and superimposed pilot scheme. Then, we propose a frame design algorithm and a semi-persistent scheduling algorithm to achieve the optimal frame design and resource allocation with the reasonable complexity. Finally, our simulation results show that the proposed frame design and resource allocation scheme can greatly satisfy the URLLC requirements of V2V pairs and guarantee the communication quality of cellular users.

A Comparison of Voice-over-IP Capacity and Performance for Different Scheduling Techniques

To ensure Quality of Service (QoS), different scheduling techniques play a very vital role for Voice over IP (VoIP) traffic. The traffic for VoIP service is constant bit traffic and has low latency, which implies that small VoIP packets are imparted in the typical duration of time. Also, for QoS related to packet delay and packet loss, the Voice over IP packet needs to be anticipated periodically. Dynamic scheduling is used for packet scheduling in the Evolved UTRAN (E-UTRAN) type of radio systems. In present work, we will compare different type of scheduling techniques such as dynamic scheduling, persistent scheduling, and semi-persistent (with SID packets) scheduling used for VoIP packets in Long Term Evolution (LTE). We try to find out the number of users supported for different Control Channels (CC) with and without restrictions. The results show that semi-persistent scheduling is the most efficient scheduling as it helps in better-optimized resource utilization while dynamic scheduling has a large amount of signaling involved which reduces its efficiency. Persistent scheduling technique fails to utilize the resource as compared to semi-persistent scheduling. VoIP capacity related to the number of users is calculated for Semi-persistent Scheduling without any condition on control channels and as a result, we observed some prominent data.

MmWave-NOMA-Based Low-Latency and High-Reliable Communications for Enhancement of V2X Services

The enhanced vehicle-to-everything (eV2X) systems have stricter constraints of latency and reliability than before. To meet the low latency and high reliability (LLHR) demands, the investigation of semi-persistent scheduling (SPS) is of great significance. For the first time, we integrate millimeter wave (mmWave) and non-orthogonal multiple access (NOMA) into SPS strategy. The proposed strategy includes the beam division and user clustering process, the power allocation process, and the vehicular user equipment (VUE) – resource block (RB) matching process. Firstly, the joint-optimization problem in terms of user scheduling indicators and power allocation factors is formulated to minimize the SPS period. This problem is then proved to be non-deterministic polynomial hard (NP-hard) by being reduced into a vertex coloring problem. To solve it with polynomial complexity, we divide it into two subproblems and calculate them by iteration. For one subproblem, the LLHR power control algorithm is proposed to solve the non-convex reliability-optimization problem, which can provide an evaluation indicator for the user scheduling. For the other subproblem, the beam division and VUE clustering algorithm is designed to reduce the complexity of the VUE-RB matching. After that, the matching problem with peer effects is solved by the proposed union-based matching algorithm. The analytical results on stability, convergence and computational complexity are presented, and simulation results show that the proposed SPS strategy outperforms the existing schemes.

Comparison of IEEE 802.11p and LTE-V2X: An Evaluation With Periodic and Aperiodic Messages of Constant and Variable Size

V2X (Vehicle to everything) communications can be currently supported by standards based on IEEE 802.11p (e.g. DSRC or ITS-G5) or LTE-V2X (also known as Cellular V2X or C-V2X) technologies. There has been an intense debate in the community on which technology achieves best performance. However, existing studies do not take into account the variability present in the generation and size of V2X messages. This variability can significantly impact the operation and performance of the Medium Access Control (MAC). This study progresses the state of the art by conducting an in-depth evaluation of both technologies under different message traffic patterns. In particular, we consider aperiodic and periodic messages of constant or variable size based on the standardized ETSI Cooperative Awareness Messages (CAMs). This study considers different scenarios and possible configurations of IEEE 802.11p and LTE-V2X. We demonstrate that IEEE 802.11p can better cope with variations in the size and time interval between messages. We also demonstrate (and characterize) that the LTE-V2X sensing-based semi-persistent scheduling faces certain inefficiencies when transmitting aperiodic messages of variable size. These inefficiencies result in that IEEE 802.11p generally outperforms LTE-V2X when transmitting aperiodic messages of variable size except when the channel load is very low.

Performance Evaluation of NOMA for Sidelink Cellular-V2X Mode 4 in Driver Assistance System With Crash Warning

This article presents the performance characteristics of a potential extension of sidelink cellular-vehicle-to-everything mode 4 (simply called mode 4) with uplink non-orthogonal multiple access (UL-NOMA), named SPS-NOMA, in driver assistance systems with a crash warning. In SPS-NOMA, multiple nodes (e.g., cars or pedestrians with communication equipment) simultaneously broadcast their data frames at a time-frequency resource selected by sensing-based semi-persistent scheduling (sensing-based SPS), the distributed random access protocol of mode 4. The transmitted signals are superposed at the receiver sides, and successive interference canceller (SIC) supports decoding the superposed signal. In SPS-NOMA, sensing-based SPS is expected to enhance the signal-to-interference-plus-noise ratio at each SIC iteration. The effect boosts the performance gains of the SIC in broadcast cases and mitigates the channel congestion. Our computer simulations highlighted that SPS-NOMA improved the performance of the ordinary mode 4 by 38% in the fundamental node distribution model. In conclusion, SPS-NOMA is expected to be the next generation sidelink C-V2X as the extended mode 4.