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Multi-AP Coordination PHY/MAC Management for Industrial Wi-Fi
Recent advancements in wireless local area network (WLAN) technology include IEEE 802.11be and 802.11ay, often known as Wi-Fi 7 and WiGig, respectively. The goal of these developments is to provide Extremely High Throughput (EHT) and low latency to meet the demands of future applications like as 8K videos, augmented and virtual reality, the Internet of Things, telesurgery, and other developing technologies. IEEE 802.11be includes new features such as 320 MHz bandwidth, multi-link operation, Multi-user Multi-Input Multi-Output, orthogonal frequency-division multiple access, and Multiple-Access Point (multi-AP) coordination (MAP-Co) to achieve EHT. With the increase in the number of overlapping APs and inter-AP interference, researchers have focused on studying MAP-Co approaches for coordinated transmission in IEEE 802.11be, making MAP-Co a key feature of future WLANs. Moreover, similar issues may arise in EHF bands WLAN, particularly for standards beyond IEEE 802.11ay. This has prompted researchers to investigate the implementation of MAP-Co over future 802.11ay WLANs. Thus, in this article, we provide a comprehensive review of the state-of-the-art MAP-Co features and their shortcomings concerning emerging WLAN. Finally, we discuss several novel future directions and open challenges for MAP-Co.
The demand for high-data-rate and time-sensitive applications, such as 4k/8k video streaming and real-time augmented reality (AR), virtual reality (VR), and gaming, has increased significantly. Addressing the inefficiency of distributed channel access and the fairness problem between uplink and downlink flows is crucial for the development of wireless local area network (WLAN) technologies. In this study, we propose a novel transmission scheme for IEEE 802.11be networks that addresses the fairness problem and improves the system throughput. Utilizing the concept of multi-AP coordinated OFDMA introduced in the 7th-generation WLAN IEEE 802.11be, the proposed transmission scheme allows an AP to share a granted transmission opportunity (TXOP) with nearby APs. A mathematically analysis of the throughput performance of the proposed schemes was performed using a Markov chain model. The simulation results verify that the scheme effectively improves the downlink fairness and the system throughput. Combined with the advanced multiuser (MU) features of IEEE 802.11ax, such as TUA, MU cascading sequence, and MU EDCA, the proposed scheme not only enhances downlink AP transmission, but also guarantees improved control over the medium. The scheme is carefully designed to be fully compatible with conventional IEEE 802.11 protocols, and is thus potentially universal.
The IEEE 802.11ax pave the way to deliver the high-speed communications in the Wi-Fi network even in the dense areas. In this regard, the most challenging task is to enhance the throughput as IEEE 802.11ax standard promises to provide four times improvement in average throughput per station. Unfortunately, none of the existing protocols could satisfy the demand of the standard yet. The performance of the IEEE 802.11ax protocol largely depends on the efficient and wise scheduling of resource units to the stations. The uplink scheduling is more challenging than the downlink since in the uplink path many stations send data to the access point where the stations must be synchronized for the OFDMA transmissions. This paper innovates an uplink scheduling protocol named Efficient Resource Allocation (ERA) that promises to provide a high-throughput to the Wireless LAN along with the reduction of retransmissions of the packets. The simulations and analyses show that the proposed protocol would be a robust one to satisfy the promises of the latest IEEE 802.11ax standard. To the best of our knowledge, the proposed protocol is the unique one of its kind where the resource units are distributed to the stations according to their available loads.
With the emergence of 4k/8k video, the throughput requirement of video delivery will keep grow to tens of Gbps. Other new high-throughput and low-latency video applications including augmented reality (AR), virtual reality (VR), and online gaming, are also proliferating. Due to the related stringent requirements, supporting these applications over wireless local area network (WLAN) is far beyond the capabilities of the new WLAN standard – IEEE 802.11ax. To meet these emerging demands, the IEEE 802.11 will release a new amendment standard IEEE 802.11be – Extremely High Throughput (EHT), also known as Wireless-Fidelity (Wi-Fi) 7. This article provides the comprehensive survey on the key medium access control (MAC) layer techniques and physical layer (PHY) techniques being discussed in the EHT task group, including the channelization and tone plan, multiple resource units (multi-RU) support, 4096 quadrature amplitude modulation (4096-QAM), preamble designs, multiple link operations (e.g., multi-link aggregation and channel access), multiple input multiple output (MIMO) enhancement, multiple access point (multi-AP) coordination (e.g., multi-AP joint transmission), enhanced link adaptation and retransmission protocols (e.g., hybrid automatic repeat request (HARQ)). This survey covers both the critical technologies being discussed in EHT standard and the related latest progresses from worldwide research. Besides, the potential developments beyond EHT are discussed to provide some possible future research directions for WLAN.
The adoption of real-time wireless technologies within the ever-growing field of networked industrial control systems is continuously gaining popularity. Widespread sensing and actuation devices based on high-throughput wireless standards allow for an increased system mobility and lower configuration and maintenance costs. The IEEE 802.11 standard, especially in its most recent amendments, pushes performance to a very high level, theoretically approaching those of the most common real-time Ethernet networks. Its nondeterministic communication behavior, however, makes 802.11 unsuitable for mission- and safety-critical applications with high-reliability requirements, at least in its standard form. In this paper, we present several major solutions that tackled this issue to achieve real-time and reliability guarantees in wireless networked control systems, capitalizing on the strong efforts devoted to the adoption of IEEE 802.11 physical layer (PHY) technologies. We first provide a deep analysis of the 802.11 protocols in order to propose guidelines toward smart parameter selection at the data-link layer (DLL). In addition, the design of effective rate selection algorithms is considered as a way of increasing both the timeliness and reliability of data delivery. A further systematic solution is represented by real-time (RT)-WiFi, a new time-division multiple-access (TDMA)-based highly configurable DLL protocol that enables high-speed hard real-time data exchange over 802.11 networks. An important goal of this paper is also to provide a thorough comparison among different discussed solutions, in order to put in evidence their advantages and disadvantages, possibly in relation with systems based on different underlying PHYs. We will finally highlight the open challenges and future directions in this active research field.
While celebrating the 21st year since the very first IEEE 802.11 “legacy” 2 Mbit/s wireless Local Area Network standard, the latest Wi-Fi newborn is today reaching the finish line, topping the remarkable speed of 10 Gbit/s. IEEE 802.11ax was launched in May 2014 with the goal of enhancing throughput-per-area in high-density scenarios. The first 802.11ax draft versions, namely D1.0 and D2.0, were released at the end of 2016 and 2017. Focusing on a more mature version D3.0, in this tutorial paper, we help the reader to smoothly enter into the several major 802.11ax breakthroughs, including a brand new OFDMA-based random access approach as well as novel spatial frequency reuse techniques. In addition, this tutorial will highlight selected significant improvements (including PHY enhancements, MU-MIMO extensions, power saving advances, and so on) which make this standard a very significant step forward with respect to its predecessor 802.11ac.
Due to the current structure of digital factory, it is necessary to build the smart factory to upgrade the manufacturing industry. Smart factory adopts the combination of physical technology and cyber technology and deeply integrates previously independent discrete systems making the involved technologies more complex and precise than they are now. In this paper, a hierarchical architecture of the smart factory was proposed firstly, and then the key technologies were analyzed from the aspects of the physical resource layer, the network layer, and the data application layer. In addition, we discussed the major issues and potential solutions to key emerging technologies such as Internet of Things (IoT), big data, and cloud computing, which are embedded in the manufacturing process. Finally, a candy packing line was used to verify the key technologies of smart factory, which showed that the Overall Equipment Effectiveness (OEE) of the equipment is significantly improved.
In order to meet the continuously increasing demands for high throughput in wireless networks, IEEE 802 LAN/MAN Standard Committee is developing IEEE 802.11ax: a new amendment for the Wi-Fi standard. This amendment provides various ways to improve the efficiency of Wi-Fi. The most revolutionary one is OFDMA. Apart from obvious advantages , such as decreasing overhead for short packet transmission at high rates and improving robustness to frequency selective interference, being used for uplink transmission, OFDMA can increase power spectral density and, consequently, user data rates. However, the gain of OFDMA mainly depends on the resource scheduling between users. The peculiarities of OFDMA implementation in Wi-Fi completely change properties of classic schedulers used in other OFDMA systems, e.g. LTE. In the paper, we consider the usage of OFDMA in Wi-Fi for uplink transmission. We study peculiarities of OFDMA in Wi-Fi, adapt classic schedulers to Wi-Fi, explaining why they do not perform well. Finally we develop a novel scheduler, MUTAX, and evaluate its performance with simulation.
Many industrial automation systems rely on time-synchronized (and timely) communication among sensing, computing, and actuating devices. Advances in Ethernet enabled by time-sensitive networking (TSN) standards, being developed by the IEEE 802.1 TSN Task Group, are significantly improving time synchronization as well as worst case latencies. Next-generation industrial systems are expected to leverage advances in distributed time coordinated computing and wireless communications to enable greater levels of automation, efficiency, and flexibility. Significant progress has been made in extending accurate time synchronization over the air (e.g., 802.1AS profile for IEEE 802.11/Wi-Fi). Given the inherently unreliable, varying capacity and latency prone characteristics associated with wireless communications, proving the feasibility of worst case latency performance over the wireless medium is a major research challenge. More specifically, understanding what levels of capacity, reliability, and latency could be guaranteed over wireless links with high reliability are important research questions to guide the development of new radios, protocols, and time coordinated applications. This paper provides an overview of the potential applications, requirements, and unique research challenges to extend TSN capabilities over wireless. The paper also describes advances in wireless technologies (e.g., next-generation 802.11 and 5G standards) toward achieving reliable and accurate time distribution and timeliness capabilities. It also provides a classification of wireless applications and a reference architecture for enabling the integration of wired and wireless TSN capabilities in future industrial automation systems.
Wireless networks are ever more deployed in the industrial control scenario, thanks to the numerous benefits they can bring, especially in terms of costs and flexibility. However, some critical fields of application, such as motion control, power systems automation, or power electronics control, to mention some, have extremely tight requirements in terms of timeliness, reliability, and determinism, which nowadays can only be satisfied by wired communication networks. Indeed, the available industrial wireless solutions are far from offering adequate performance levels, especially in the timing budget, due to the native limitations of their physical (PHY) layers. In this paper, an innovative approach for high-performance industrial wireless networks [wireless high performance (WirelessHP)] is presented, based on a substantial redesign of the lower layers of the industrial wireless protocol stack, with the aim of supporting the requirements of critical industrial control applications. The required levels of timeliness, reliability, and determinism are first derived through a comprehensive survey that looks at real-world application scenarios as well as at the performance of wired networks for industrial control, such as real-time Ethernet networks. The design of a new solution, which is able to satisfy these targets, is then discussed in detail, introducing a low-latency PHY layer that aims at reducing the transmission time of short packets to
$1~\mu \text{s}$
, or even less. The feasibility of the proposed solution is presented through an experimental demonstrator based on software-defined radios, while its performance bounds are computed through theoretical analyses. Finally, future activities in the context of WirelessHP are widely discussed, providing an overview of the directions that will have to be addressed, particularly in the design of the upper layers.
This paper considers the fair scheduling problem for dense wireless networks with access point cooperation and multiple-input-multiple-output (MIMO) links. The problem is to maximize the aggregate throughput subject to a fairness constraint that is general enough to capture many different fairness objectives. We formally specify a non-convex optimization problem that captures all aspects of the problem setting, and we propose two algorithms to approximate its solution. The first algorithm jointly optimizes the selection of user sets, MIMO precoders, and assignment of user sets to time slots. The second algorithm separately optimizes first user sets and MIMO precoders and second assignment of user sets to time slots. The first algorithm guarantees perfect fairness and produces a local optimum or a saddle point for aggregate throughput at a fairly high computational cost. The second algorithm also guarantees perfect fairness and produces optimal aggregate throughput for a given set of (possibly non-optimal) user sets while having lower computational complexity. The second algorithm also has a parameter that allows throughput and fairness to be traded off for situations where maximizing throughput is critical and approximate fairness is acceptable. Analyses are complemented by simulation results, which show that: 1) the first algorithm produces significantly higher aggregate throughput than known approaches with a running time that is practical for scenarios with up to 50 users and 2) the second algorithm produces aggregate throughput that is very close to existing heuristics while having significantly lower running time. IEEE
In this paper we compare the implicit and explicit methods of providing channel state information (CSI) to the transmitter in a multi-user multiple-input-multiple-output (MU-MIMO) system as specified in the draft specification IEEE 802.11ac [1]. The comparison is made on the basis of both overhead requirements and packet-error-rate (PER) performance. We also propose a hybrid feedback scheme that combines the explicit and implicit feedback methods thus benefiting from more frequent calibration without incurring extra overhead.
IEEE 802.11be-Wi-Fi 7: New Challenges and Opportunities
One Channel Information Feedback Method for Multi-AP Coordination
- Y G Liang
- Ming Gan
- Guogang Huang
- Yu Jian
IEEE P802.11 Wireless LANs, TGn Channel Model
- Vinko Erceg
Discussions of Multi-AP JT
- Xiaogang Chen
One Channel Information Feedback Method for Multi-AP Coordination
- Dandan Liang
Considerations on Coordinated OFDMA
- Sungjin Park