Wireless Local Area Network Scenarios Research Articles

Wi-Fi Sensing Based on IEEE 802.11bf

Conventionally, Wi-Fi radio signals are widely used for data transmissions in a wireless local area network (WLAN). Recently, it has been an interesting topic to also apply Wi-Fi radio signals to sense the environment where these signals propagate and identify changes associated with certain activities. This technique is referred to as Wi-Fi sensing, and it has been proven effective in a variety of use cases, such as proximity detection, gesture recognition, target counting, and health monitoring. As a result, the IEEE 802.11 working group has formed a new Task Group, 802.11 bf, to develop a new amendment to define necessary PHY and MAC protocols to support Wi-Fi sensing in all spectrum bands, including sub-7 GHz bands (2.4 GHz, 5 GHz, and 6 GHz band), as well as 60 GHz millimeter-wave band. In this article, our primary goal is to identify and describe the basic elements that have been developed in IEEE 802.11 bf to enable Wi-Fi sensing applications in different WLAN scenarios.

Wi-Fi Sensing Based on IEEE 802.11bf

Conventionally, Wi-Fi radio signals are widely used for data transmissions in a wireless local area network (WLAN). Recently, it has been an interesting topic to also applyWi-Fi radio signals to sense the environment where these signals propagate and identify changes associated with certain activities. This technique is referred to as Wi-Fi sensing and it has been proven effective in a variety of use cases, such as proximity detection, gesture recognition, target counting and health monitoring. As a result, the IEEE 802.11 working group has formed a new Task Group, 802.11bf, to develop a new amendment to define necessary PHY and MAC protocols to supportWi-Fi sensing in all spectrum bands, including sub-7 GHz bands (2.4 GHz, 5 GHz, and 6 GHz band), as well as 60 GHz millimeter wave (mmWave) band. In this paper, our primary goal is to identify and describe the basic elements that have been developed in IEEE 802.11bf to enable Wi-Fi sensing applications in different WLAN scenarios.

Revisiting Acknowledgment Mechanism for Transport Control: Modeling, Analysis, and Implementation

The shared nature of the wireless medium induces contention between data transport and backward signaling, such as acknowledgment. The current way of TCP acknowledgment induces control overhead which is counter-productive for TCP performance especially in wireless local area network (WLAN) scenarios. In this paper, we present a new acknowledgment called TACK (“Tame ACK”), as well as its TCP implementation TCP-TACK. TACK seeks to minimize ACK frequency, which is exactly what is required by transport. TCP-TACK works on top of commodity WLAN, delivering high wireless transport goodput with minimal control overhead in the form of ACKs, without any hardware modification. Evaluation results show that TCP-TACK achieves significant advantages over legacy TCP in WLAN scenarios due to less contention between data packets and ACKs. Specifically, TCP-TACK reduces over 90% of ACKs and also obtains an improvement of up to 28% on goodput. A TACK-based protocol is a good replacement of the legacy TCP to compensate for scenarios where the acknowledgment overhead is non-negligible.

Majority Voting-Based MAC Protocol for Exploiting Link-Layer Diversity in Wireless Networks.

In wireless local area networks (WLANs), the effect of interference signals between neighboring nodes increases as the number of wireless nodes using limited radio frequency resources in a limited space increases, which can significantly degrade the reliability of data transmission. In high-density WLANs, there can be several neighboring access points (APs) that can receive uplink transmission from a station. In conventional medium access control (MAC) protocols, uplink data frames containing errors or transmitted from a non-associated station are discarded at APs. Alternatively, we propose a MAC protocol using redundant wireless links between neighboring APs and the non-associated stations. In the proposed MAC protocol, we consider a centralized WLAN with a control node that performs error corrections of erroneous uplink data frames via a majority voting algorithm-based link-layer diversity scheme using uplink data received from multiple APs to increase the reliability of data transmission. In addition, we propose an adaptive carrier sensing ranging mechanism to improve the uplink network throughput in the proposed centralized WLAN system. Further, we conduct simulation studies and software-defined radio-based experiments to evaluate the performance of the proposed MAC protocol in various WLAN scenarios.

A Spatial Group-Based Multi-User Full-Duplex OFDMA MAC Protocol for the Next-Generation WLAN.

The Wireless Local Area Network (WLAN) has become a dominant piece of technology to carry wireless traffic for Internet of Things (IoT). The next-generation high-density WLAN scenario is very suitable for the development trend of the industrial wireless sensor network. However, in the high-density deployed WLAN scenarios, the access efficiency is low due to severe collisions, and the interference is diffused due to the scattered locations of the parallel access stations (STAs), which results in low area throughput, i.e., low spatial reuse gain. A spatial group-based multi-user full-duplex orthogonal frequency division multiple access (OFDMA) (GFDO) multiple access control (MAC) protocol is proposed. Firstly, the STAs in the network are divided into several spatial groups according to the neighbor channel sensing ability. Secondly, a two-level buffer state report (BSR) information collection mechanism based on P-probability is designed. Initially, intra-group STAs report their BSR information to the group header using low transmission power. After that, group headers report both their BSR information collected from their members and inter-group interference information to the access point (AP). Finally, AP schedules two spatial groups without mutual interference to carry on multi-user full duplex transmission on the subchannels in cascading mode. The closed-form formulas are theoretically derived, including the number of uplink STAs successfully collected by AP, the network throughput and area throughput under saturated traffic. The simulation results show that the theoretical analysis coincide with the simulation results. The system throughput of the GFDO protocol is 16.8% higher than that of EnFD-OMAX protocol.

Concurrent decentralized channel allocation and access point selection using multi-armed bandits in multi BSS WLANs

Enterprise Wireless Local Area Networks (WLANs) consist of multiple Access Points (APs) covering a given area. In these networks, interference is mitigated by allocating different channels to neighboring APs. Besides, stations are allowed to associate to any AP in the network, selecting by default the one from which receive higher power, even if it is not the best option in terms of the network performance.Finding a suitable network configuration able to maximize the performance of enterprise WLANs is a challenging task given the complex dependencies between APs and stations. Recently, in wireless networking, the use of reinforcement learning techniques has emerged as an effective solution to efficiently explore the impact of different network configurations in the system performance, identifying those that provide better performance.In this paper, we study if Multi-Armed Bandits (MABs) are able to offer a feasible solution to the decentralized channel allocation and AP selection problems in Enterprise WLAN scenarios. To do so, we empower APs and stations with agents that, by means of implementing the Thompson sampling algorithm, explore and learn which is the best channel to use, and which is the best AP to associate, respectively. Our evaluation is performed over randomly generated scenarios, which enclose different network topologies and traffic loads. The presented results show that the proposed adaptive framework using MABs outperform the static approach (i.e., using always the initial default configuration, usually random) regardless of the network density and the traffic requirements. Moreover, we show that the use of the proposed framework reduces the performance variability between different scenarios. Also, results show that we achieve the same performance (or better) than static strategies with less APs for the same number of stations. Finally, special attention is placed on how the agents interact. Even if the agents operate in a completely independent manner, their decisions have interrelated effects, as they take actions over the same set of channel resources.

Design and Dosimetric Analysis of an Exposure Facility for Investigating Possible Effects of 2.45 GHz Wi-Fi Signals on Human Sleep.

A new head exposure system for double-blind provocation studies investigating possible effects of 2.45 GHz Wi-Fi exposure on human sleep was developed and dosimetrically analyzed. The exposure system includes six simultaneously radiating directional antennas arranged along a circle (radius 0.6 m) around the test subject's head, and enables a virtually uniform head exposure, i.e. without any preferred direction of incidence, during sleep. The system is fully computer-controlled and applies a real wireless local area network (WLAN) signal representing different transmission patterns as expected in real WLAN scenarios, i.e. phases of "beacon only" as well as phases of different data transmission rates. Sham and verum are applied in a double-blind crossover study design and all relevant exposure data, i.e. forward and reverse power at all six antenna inputs, are continuously recorded for quality control. For a total antenna input power (sum of all antennas) of 220 mW, typical specific absorption rate (SAR) in cortical brain regions is approximately 1-2 mW/kg (mass average SAR over respective brain region), which can be seen as a realistic worst-case exposure level in real WLAN scenarios. Taking into account variations of head positions during the experiments, the resulting exposure of different brain regions may deviate from the given average SAR levels up to 10 dB. Peak spatial 10 g average SAR in all brain and all head tissues is between 1.5-3.5 and 10.4-25 mW/kg, respectively. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

An Antenna System With a Voice-Controlled Personalized Switchable Radiation Coverage

This letter discusses an antenna system that steers its radiation pattern to personalize coverage in a wireless local area network scenario. The change in the pattern occurs either by mechanically rotating or electrically switching the feeding network toward the appropriate antenna structure. The user controls the personalized coverage using an Android-based voice recognition application on a mobile device. Each antenna structure operates at 5.28 GHz with 110 MHz bandwidth and an increased gain around 7.5 dB. The antenna's radiation insures a redistributed sector coverage of two diametrically opposite geographical zones that are 180° apart from each other. A multiple-input–multiple-output (MIMO) implementation is also proposed with a discussion on the various possible coverage zones. The various antenna concepts are measured, and the results validate the predicted data.

Traffic differentiation in dense collision-free WLANs using CSMA/ECA

The ability to perform traffic differentiation is a promising feature of the current Medium Access Control (MAC) in Wireless Local Area Networks (WLANs). The Enhanced Distributed Channel Access (EDCA) protocol for WLANs proposes up to four Access Categories (AC) that can be mapped to different traffic priorities. High priority ACs are allowed to transmit more often than low priority ACs, providing a way of prioritising delay sensitive traffic like voice calls or video streaming. Further, EDCA also considers the intricacies related to the management of multiple queues, virtual collisions and traffic differentiation. Nevertheless, EDCA falls short in efficiency when performing in dense WLAN scenarios. Its collision-prone contention mechanism degrades the overall throughput to the point of starving low priority ACs, and produce priority inversions at high number of contenders.Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is a compatible MAC protocol for WLANs which is also capable of providing traffic differentiation. Contrary to EDCA, CSMA/ECA uses a contention mechanism with a deterministic backoff technique which is capable of constructing collision-free schedules for many nodes with multiple active ACs, extending the network capacity without starving low priority ACs, as experienced in EDCA. This work analyses traffic differentiation with CSMA/ECA by describing the mechanisms used to construct collision-free schedules with multiple queues. Additionally, evaluates the performance under different traffic conditions and a growing number of contenders. Furthermore, it introduces a way to eliminate Virtual Collisions (VC), which also contributes to the throughput degradation in EDCA WLANs. Simulation tests are performed using voice and video packet sources that emulate commonly used codecs. Results show CSMA/ECA outperforming EDCA in different commonly-found scenarios with high number of users, including when both MAC protocols coexist in the same WLAN.

Joint localization of multiple sources from incomplete noisy Euclidean distance matrix in wireless networks

One major challenge of massive wireless networks is to identify the locations of source nodes from partially observed and noisy distance information. This is especially important for wireless sensor networks (WSN) and wireless local area networks (WLAN). In this paper, we propose a unified localization framework of multiple sources from an Euclidean distance matrix (EDM) with noise and outliers both in WSN and WLAN scenarios. We first develop a semidefinite programming (SDP) based low rank matrix completion (LRMC) estimator by using the semidefinite embedding lemma to recover EDM. Based on our recovered EDM, two robust localization estimators, namely, semidefinite relaxation localization (SDRL) and weighted semidefinite relaxation localization (WSDRL), are derived to efficiently relax our non-convex localization problem into a convex one, and yield more accuarate location estimates. As compared with existing techniques, our proposed techniques are more robust to noise and outliers with higher accuracies both in EDM recovery and source localization. Simulations and real data experiments are included to evaluate the performance of the proposed algorithms by comparing them with some existing methods.

Traffic differentiation in dense collision-free WLANs using CSMA/ECA

The ability to perform traffic differentiation is a promising feature of the current Medium Access Control (MAC) in Wireless Local Area Networks (WLANs). The Enhanced Distributed Channel Access (EDCA) protocol for WLANs proposes up to four Access Categories (AC) that can be mapped to different traffic priorities. High priority ACs are allowed to transmit more often than low priority ACs, providing a way of prioritising delay sensitive traffic like voice calls or video streaming. Further, EDCA also considers the intricacies related to the management of multiple queues, virtual collisions and traffic differentiation. Nevertheless, EDCA falls short in efficiency when performing in dense WLAN scenarios. Its collision-prone contention mechanism degrades the overall throughput to the point of starving low priority ACs, and produce priority inversions at high number of contenders. Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is a compatible MAC protocol for WLANs which is also capable of providing traffic differentiation. Contrary to EDCA, CSMA/ECA uses a contention mechanism with a deterministic backoff technique which is capable of constructing collision-free schedules for many nodes with multiple active ACs, extending the network capacity without starving low priority ACs, as experienced in EDCA. This work analyses traffic differentiation with CSMA/ECA by describing the mechanisms used to construct collision-free schedules with multiple queues. Additionally, evaluates the performance under different traffic conditions and a growing number of contenders. (arXiv's abstract field is not large enough for the paper's abstract, please download the paper for the complete abstract.)

Efficient Protocols Design and Performance Analysis for Centralized WLAN

Device-to-device communications have attracted much more attention recently in the realization of smart cities. In this paper, we propose a network coding (NC) scheme based on device-to-device communication for centralized wireless local area network (WLAN). In centralized WLAN scenarios, users’ communication can be implemented through multiple interaction of access points acted as relay nodes, which are similar to direct link session (DLS) protocol in IEEE 802.11 standard and we named the proposed protocol as advanced DLS scheme, where analytical performance results of the proposed two-way communication system using NC, with and without AP selection, are obtained in multi-AP cases, as well as the asymptotic results in high transmitting power. In addition, the performance comparisons of throughput, delay and collision probability of proposed scheme with IEEE 802.11 are provided in simulation, which present the advantages of centralized WLAN. By the analysis, it is found that the proposed advanced DLS scheme can achieve almost exactly the same bit error ratio performance as the optimal selection at all signal to noise ratio ranges. It is also shown that the proposed transmission scheme significantly outperform the current mode in two-way communication Nakagami channels owing to the diversity order and array gains. The proposed scheme only need little frame modification and can be compatible with the current standard. Finally, simulation results validate the theoretical analysis.

Experimental Optimization of Exposure Index and Quality of Service in Wlan Networks.

This paper presents the first real-life optimization of the Exposure Index (EI). A genetic optimization algorithm is developed and applied to three real-life Wireless Local Area Network scenarios in an experimental testbed. The optimization accounts for downlink, uplink and uplink of other users, for realistic duty cycles, and ensures a sufficient Quality of Service to all users. EI reductions up to 97.5% compared to a reference configuration can be achieved in a downlink-only scenario, in combination with an improved Quality of Service. Due to the dominance of uplink exposure and the lack of WiFi power control, no optimizations are possible in scenarios that also consider uplink traffic. However, future deployments that do implement WiFi power control can be successfully optimized, with EI reductions up to 86% compared to a reference configuration and an EI that is 278 times lower than optimized configurations under the absence of power control.

Fair QoS multi-resource allocation for uplink traffic in WLAN

In wireless local area network (WLAN), improving the quality of service (QoS) of users is often at odd with striking fairness among users. In this work, we suggest that in WLAN, multiple types of network resources should be jointly allocated to users to achieve "QoS fairness", which is a new fairness concept targeting at balancing QoS and fairness in WLAN by allocating multiple types of network resources to users. To this end, we first transform user QoS requirements to multi-resource demands and apply the dominant resource fairness scheme to allocate network resources for each user. We prove several salient QoS-based fairness properties based on a model mapping between QoS and resources. We further discuss about more general conditions for diverse mapping models where QoS fairness properties can be satisfied. We find that the QoS fairness properties can be guaranteed as long as the mapping model meets a few practical requirements, indicating the wide applicability of our scheme. To consolidate our multi-resource allocation scheme, we design a practical protocol for WLAN. The simulation results validate that the QoS fairness can be guaranteed in practical WLAN scenario.

Experimental evaluation of interference alignment for broadband WLAN systems

In this paper, we present an experimental study on the performance of spatial interference alignment (IA) in indoor wireless local area network scenarios that use orthogonal frequency division multiplexing (OFDM) according to the physical-layer specifications of the IEEE 802.11a standard. Experiments have been carried out using a wireless network testbed capable of implementing a 3-user MIMO interference channel. We have implemented IA decoding schemes that can be designed according to distinct criteria (e.g., zero-forcing or MaxSINR). The measurement methodology has been validated considering practical issues like the number of OFDM training symbols used for channel estimation or feedback time. In case of asynchronous users, a time-domain IA decoding filter is also compared to its frequency-domain counterpart. We also evaluated the performance of IA from bit error ratio measurement-based results in comparison to different time-division multiple access transmission schemes. The comparison includes single- and multiple-antenna systems transmitting over the dominant mode of the MIMO channel. Our results indicate that spatial IA is suitable for practical indoor scenarios in which wireless channels often exhibit relatively large coherence times.

Channel allocation algorithms for WLANs using distributed optimization

The performance of a wireless local area network (WLAN) depends on the channel assignments among interfering access points (APs). Due to the limited number of non-overlapping channels, severe interference scenarios may arise if no appropriated spectrum planning is employed. In our study we focus on WLANs scenarios where APs may belong to different administrative domains, which is actually a very common situation in dense urban deployments. In such cases the use of centralized algorithms is not feasible and the already proposed distributed methods does not guarantee optimal channel assignment. In this paper, therefore, we formalize the channel allocation as a distributed constraint optimization problem (DCOP) and propose a new distributed channel assignment algorithm named DCAA-O, which can find the optimal solution to the channel assignment problem for a group of APs. A suboptimal strategy denoted DCAA-S is also investigated, which aims at reducing the number of control messages to be exchanged between APs, while still achieving a suboptimal solution which is very close to the optimal one. The simulation results show that the proposed algorithms are able to outperform the best known techniques both in terms of solution quality and number of exchanged messages.

Channel capacity study of polarization reconfigurable slot antenna for indoor MIMO system

This article presents a polarization reconfigurable slot antenna with compact feed.Fed by dual modes of coplanar waveguide, a dual orthogonal linear polarization is excited in the slot and controlled by two PIN diodes. The proposed antenna has been built and its reflection coefficient, radiation pattern, gain were tested. The capacity performance in an indoor wireless local area network scenario was measured by using two proposed antennas as access point in a 2 × 2 multi-input multi-output system. The results show the advantage of polarization reconfigurable antennas in channel capacity, especially at the condition of non-line-of-sight. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1209–1213, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26014

Mobile-Host-Centric Transport Protocol for<newline/>EAST Experiment

Some physics researchers retrieve EAST experiment data using the Transmission Control Protocol (TCP) in a wireless local area network (WLAN). TCP is the most commonly used transport control protocol. It assumes that every packet loss is caused by network congestion and invokes congestion control and avoidance. TCP's blind congestion control results in degraded performance in lossy wireless networks. In a wireless network, mobile hosts have first-hand knowledge of the lossy wireless links; therefore, mobile stations can make better transmission control based on the known status of wireless link. In this paper, we proposed a new mobile-host-centric transport protocol (MCP) that integrates the characteristics of sender-centric and receiver-centric transport control schemes. MCP shifts most control policies to the mobile host side. The general behavior of MCP is similar to the TCP, but by utilizing the local information collecting from the mobile node in WLAN, MCP allows for better congestion control and loss recovery. Specifically, we designed a cross-layer implementation of MCP and ran it on NS-2 network simulator. With valuable Medium Access Control (MAC) layer feedback information, MCP is able to distinguish packet loss caused by wireless random errors from network congestion more clearly and can perform a more accurate congestion control. We did extensive simulations of MCP on various WLAN scenarios, and the results show that the throughput of MCP with cross-layer feedback is higher than that of TCP Reno and Westwood.