Airtime Fairness Research Articles

Enhancing TCP Airtime Fairness through Precise Computation for Upload and Download Flows in WiFi Networks

Airtime fairness has emerged as a key approach to enhancing wireless throughput performance. However, existing research often overlooks the precise calculation of airtime, particularly in relation to TCP acknowledgments. This paper introduces a novel method, implemented on the access point side, for accurately calculating the airtime of TCP and UDP flows. Building on this, we propose a QoS-based scheduling algorithm designed to improve fairness between upload and download traffic. The effectiveness of the algorithm is validated through experiments that accurately measure both throughput and airtime for upload and download traffic.

Dynamic A-MPDU Adaptation Method for Airtime Fairness in Channel Bonding-Ready WLANs

Dynamic A-MPDU Adaptation Method for Airtime Fairness in Channel Bonding-Ready WLANs

Maximizing the stable throughput of heterogeneous nodes under airtime fairness in a CSMA environment

The stability region of non-persistent CSMA is analyzed in a general heterogeneous network, where stations have different mean packet arrival rates, packet transmission times probability distributions and transmission probabilities. The considered model of CSMA captures the behavior of the well known CSMA/CA, at least as far as stability and throughput evaluation are concerned. The analysis is done both with and without collision detection. Given the characterization of the stability region, throughput-optimal transmission probabilities are identified under airtime fairness, establishing asymptotic upper and lower bounds of the maximum achievable stable throughput. The bounds turn out to be insensitive to the probability distribution of packet transmission times. Numerical results highlight that the obtained bounds are tight not only asymptotically, but also for essentially all values of the number of stations. The insight gained leads to the definition of a distributed adaptive algorithm to adjust the transmission probabilities of stations so as to attain the maximum stable throughput.

Efficiency increase in the 802.11 Ac standard performance due to the influence of Airtime Fairness technology

The article considers one of the critical problems of wireless network performance, namely, monopolization of airtime by slow clients.The advantages of wireless Wi-Fi technology are considered. The main versions of Wi-Fi standards are analyzed. It is shown that a wide variety of Wi-Fi standards is aimed at improving network performance indicators, which is expressed in increasing the transmission speed, optimizing the use of frequency bands, increasing the efficiency of Wi-Fi in segments with high subscriber density, as well as in the possibility of multiple streaming of high definition video.The IEEE 802.11ac standard is analyzed. The choice of 802.11 ac technology is based on its availability and flexibility. It is indicated that the main problem point of this standard is the inconvenience of its performance under strong differentiation of client devices, which is reflected in a decrease in network bandwidth as a whole.The network performance using Airtime Fairness technology is analyzed. To solve the problem of monopolization of airtime by slow clients, the cyclic method of dividing airtime into given intervals has been used. The necessary equipment, hardware and initial conditions for the study are indicated. It is shown that the network efficiency is determined by the following productivity indicators: average packet productivity, average bandwidth and wireless channel utilization.It has been explained that with changes in system settings due to activation of Airtime Fairness technology algorithms, there is an increase in packet productivity and average bandwidth, as well as a decrease in the utilization rate of the wireless channel, which proves the presence of positive changes in the wireless network.

Decoupling-Based Channel Access Mechanism for Improving Throughput and Fairness in Dense Multi-Rate WLANs

Legacy IEEE 802.11 Medium Access Control (MAC) adopts the Distributed Coordination Function (DCF) mechanism, which provides the same access opportunity for all contenders. However, in dense multi-rate Wireless Local Area Networks (WLANs), the pure distributed control mechanism will cause high collision rate and performance anomaly, which results in low network utilization and wasting valuable channel resources. In this paper, we present a decoupling MAC mechanism (DMAC) based on the idea of contention/reservation to reduce collision and realize collision free data transmission. In proposed mechanism, the channel access time is partitioned into channel contention process and data transmission process. The proposed algorithm makes full use of the distributed random channel access mechanism and performs a centralized collision-free data transmission. Wherein, we also design an adaptive algorithm to adjust the length of the contention period to improve the channel utilization. Furthermore, we further propose two airtime fairness algorithms Improve-DMAC1 (I-DMAC1) and Improve-DMAC2 (I-DMAC2) for delay sensitive network and high throughput network scenarios, respectively, to solve the performance anomaly in multi-rate WLANs, based on DMAC. We verify the effectiveness of these decoupling algorithms through extensive simulations. Moreover, the simulation results show that the proposed algorithms achieve better performance than the 802.11 standard and other protocols.

A Differentiated Reservation MAC Protocol for Achieving Fairness and Efficiency in Multi-Rate IEEE 802.11 WLANs

This paper focuses on designing a medium access control and channel usage algorithm in multi-rate wireless local area networks for improving the efficiency and fairly sharing channel resources among the contending nodes. Aiming for the problems that the high collision is often caused by binary exponential backoff mechanism in the legacy IEEE 802.11 and the shared channel can be overused by low bitrate nodes, we propose a differentiated reservation (DR) algorithm to reduce the collision among the contending nodes by setting their backoff counter as a deterministic value once accessing successfully to the channel. Furthermore, to eliminate the performance anomaly, some nodes are permitted to send multiple packets in one transmission opportunity according to their feature. Moreover, we present the implementation of the DR algorithm that is readily applied to both the existing 802.11 DCF and 802.11e EDCA networks with minimum modification. In addition, we also investigate the limitation of the DR algorithm and propose a group-based differentiated reservation (GDR) algorithm applied to high dense scenarios. The results of the theoretical analysis and simulation validate that our proposed algorithms (DR and GDR) can obtain high throughput, good airtime fairness, and low collision rate.

A Responsible Airtime Approach for True Time-Based Fairness in Multi-Rate WiFi Networks

Airtime fairness, or time-based fairness, has been well recognized as a method to solve WiFi performance anomalies and provide a balance between fairness and spectrum efficiency in multi-rate wireless networks. However, the definition of airtime is vague and simplistic. In this paper, it is demonstrated that current airtime fair scheduling results in unfairness in reality because overheads are neglected or unfairly counted. We introduce a notion of responsible airtime, which covers not only the data transmission time, but also all overheads, even a TCP ACK segment in TCP traffic. An approach based on responsible airtime can provide true time-based fairness, but responsible airtime is too complicated to directly handle. A practical method is thus introduced for evaluating responsible airtime fairness indirectly via throughput measurement. The key element, throughput fair share, of a node, is based on the baseline property in time-based fairness. For each node, an achieving ratio of actual throughput to the throughput fair share is determined, and a new fairness index considering deficiency as well as equity is applied. To validate the feasibility of responsible airtime fairness, we have developed a simple responsible airtime fair scheduler in access points for download traffic. Extensive simulation experiments are conducted in various network and traffic environments using the ns3 simulator. The results show that true time-based fairness is achievable in practice.

Bidirectional LiFi Attocell Access Point Slicing Scheme

LiFi attocell access networks will be deployed everywhere to support diverse applications and service provisioning to various end-users. The LiFi infrastructure providers will need to offer LiFi access points (APs) resources as a service. This, however, requires a research challenge to be solved to dynamically and effectively allocate resources among service providers (SPs) while guaranteeing performance isolation among them and their respective users. This paper introduces an autonomic resource slicing (virtualization) scheme, which realizes autonomic management and configuration of virtual APs, in a LiFi attocell access network, based on SPs and their users service requirements. The developed scheme comprises of traffic analysis and classification, a local AP controller, downlink and uplink slice resources manager, traffic measurement, and information collection modules. It also contains a hybrid medium access protocol and an extended token bucket fair queueing algorithm to support uplink access virtualization and spectrum slicing. The proposed resource slicing scheme collects and analyzes the traffic statistics of the different applications supported on the slices defined in each LiFi AP and distributes the available resources fairly and proportionally among them. It uses a control algorithm to adjust the minimum contention window of user devices to achieve the target throughput and ensure airtime fairness among SPs and their users. The developed scheme has been extensively evaluated using OMNeT++. The obtained results show various resource slicing capabilities to support differentiated services and performance isolation.

Network utility maximization in uplink multiuser wireless LANs

Multiuser Multiple-Input Multiple-Output (MU-MIMO) enables several simultaneous transmission from the stations toward a multiple antennas access point of a WLAN and thereby boosts the network throughput. However, this throughput enhancement greatly depends on which stations are transmitting concurrently, which in turn necessitates the design of an efficient scheduling algorithm. In this paper, we model uplink MU-MIMO scheduling as a network utility maximization problem that is a non-convex problem due to the wideband channel aware transmission rate function and scheduling constraints. Relying on the zero duality gap, a stochastic learning algorithm is designed to solve the dual of that problem. Determination of stochastic subgradient in the stochastic learning algorithm involves an NP- complete problem, hence imperialist competitive algorithm is exploited to solve this problem. The simulation results substantiate significant throughput improvement and airtime fairness superiority of this scheme compared to the existing ones. The results also show the proposed scheme is not able to guarantee the optimal throughput due to employing imperialist competitive algorithm.

Hypergraph matching for MU-MIMO user grouping in wireless LANs

This paper investigates the user grouping problem of downlink wireless local area networks (WLANs) with multi-user MIMO (MU-MIMO). Particularly, we focus on the problem of whether single user transmit beamforming (SU-TxBF) or MU-MIMO should be utilized, and how many users and which users should be in a multi-user (MU) group. We formulate the problem for maximizing the system throughput subject to the multi-user air time fairness (MU-ATF) criterion. We show that hypergraphs provide a suitable mathematical model and effective tool for finding the optimal or close to optimal solution. We show that the optimal grouping problem can be solved efficiently for the case where only SU-TxBF and 2-user MU groups are allowed in the system. For the general case, where any number of users can be assigned to groups of different sizes, we develop an efficient graph matching algorithm (GMA) based on graph theory principles. We evaluate the proposed algorithm in terms of system throughput using an 802.11ac emulator, which is created using collected channel measurements from an indoor environment and simulated channel samples for outdoor scenarios. We show that our GMA achieves at least 93% of the optimal system throughput in all considered test cases.

Spatial Coordinated Medium Sharing: Optimal Access Control Management in Drive-Thru Internet

Driven by the ever-growing expectation of ubiquitous connectivity and the widespread adoption of IEEE 802.11 networks, it is not only highly demanded but also entirely possible for in-motion vehicles to establish convenient Internet access to roadside WiFi access points (APs) than ever before, which is referred to as Drive-Thru Internet. The performance of Drive-Thru Internet, however, would suffer from the high vehicle mobility, severe channel contentions, and instinct issues of the IEEE 802.11 MAC as it was originally designed for static scenarios. As an effort to address these problems, in this paper, we develop a unified analytical framework to evaluate the performance of Drive-Thru Internet, which can accommodate various vehicular traffic flow states, and to be compatible with IEEE 802.11a/b/g networks with a distributed coordination function (DCF). We first develop the mathematical analysis to evaluate the mean saturated throughput of vehicles and the transmitted data volume of a vehicle per drive-thru. We show that the throughput performance of Drive-Thru Internet can be enhanced by selecting an optimal transmission region within an AP's coverage for the coordinated medium sharing of all vehicles. We then develop a spatial access control management approach accordingly, which ensures the airtime fairness for medium sharing and boosts the throughput performance of Drive-Thru Internet in a practical, efficient, and distributed manner. Simulation results show that our optimal access control management approach can efficiently work in IEEE 802.11b and 802.11g networks. The maximal transmitted data volume per drive-thru can be enhanced by 113.1% and 59.5% for IEEE 802.11b and IEEE 802.11g networks with a DCF, respectively, compared with the normal IEEE 802.11 medium access with a DCF.

Adaptive Two-Level Frame Aggregation for Fairness and Efficiency in IEEE 802.11n Wireless LANs

This paper deals with the problem of performance degradation in wireless local area networks (WLANs) based on IEEE 802.11n. When a wireless channel is shared by heterogeneous stations that have different data rates and packet sizes, each station occupies a different amount of airtime because the basic channel access mechanism of WLAN was originally designed to provide fair chance of channel access, regardless of packet size and data rate. This leads to the degradation of overall network throughput and airtime fairness among stations, which is known as performance anomaly. To resolve this problem, we firstly formulate an optimization problem for a generalized two-level frame aggregation whose objective is to maximize the achievable throughput under the constraint of airtime fairness. Then, we propose a frame size adaptation scheme that controls the number of packets in an aggregated frame. The proposed scheme is fully compatible with the IEEE 802.11 standard and works in a distributed manner, which neither modifies the channel access mechanism nor resorts to a centralized scheduling algorithm. The extensive simulation results confirm that the proposed scheme tightly regulates the airtime usage of each station to be almost the same and significantly improves the overall network throughput compared to other existing schemes.

Hybrid Control of Contention Window and Frame Aggregation for Performance Enhancement in Multirate WLANs

The IEEE 802.11 standard has been evolved to support multiple transmission rates in wireless local area networks (WLANs) to cope with diverse channel conditions and to increase throughput. However, when stations with different transmission rates coexist, the basic channel access mechanism of WLAN, distributed coordination function (DCF), not only fails to assure airtime fairness among competing stations but also decreases overall network throughput, because DCF was designed to provide fair opportunity of channel access, regardless of transmission rate. As an effective solution to this problem, we propose a hybrid control mechanism that integrates contention window control and frame aggregation. The former adjusts the size of contention window and differentiates the channel access opportunity depending on the transmission rates of stations. The latter controls the number of packets in the aggregated frame to tightly assure per-station airtime fairness with the reduced channel access overheads. Moreover, we derive an analytical model to evaluate the performance of the proposed mechanism in terms of throughput and fairness. Along with the analysis results, the extensive simulation results confirm that the proposed mechanism significantly increases the overall throughput by about three times compared to the conventional DCF, while assuring airtime fairness strictly.

Transmission Order Deducing MAC (TOD-MAC) protocol for CSMA/CA wireless networks

The increase in physical (PHY) layer transmission rates in IEEE WLAN does not necessarily give the corresponding increase of MAC layer throughput because of MAC overhead such as PHY headers and contention time. To improve MAC layer efficiency, we propose the Transmission Order Deducing MAC (TOD-MAC) protocol, which controls packet length in such a way that the transmission duration is adjusted to implicitly provide necessary information for a node to determine its transmission order among all the nodes in a network. Each node transmits frames of different duration, and thus the other nodes can determine the time when they can transmit, which has the same effect as announcing the transmission order, without using a control message. Each node transmits a frame in a round robin manner, which minimizes the idle time between two consecutive transmissions without collisions, and significantly improves the MAC efficiency in very high speed CSMA/CA wireless networks. Extensive simulation results indicate that TOD-MAC achieves high throughput performance, short/long-term air-time fairness in multi-rate networks and excellent transient behavior in dynamic environments.

Distributed Multiuser Scheduling for Improving Throughput of Wireless LAN

In wireless LANs, the performance of CSMA/CA might be degraded by several problems: (i) severe collisions in the uplink, (ii) head-of-line problem caused by fading in the downlink, and (iii) serious unfairness between uplink and downlink. In this paper, a distributed multiuser scheduling (DMUS) scheme is proposed to simultaneously address these problems. In DMUS, a node (i) computes its normalized SNR (signal to noise ratio) as the ratio of its instantaneous SNR to its average SNR, and (ii) contends via a contention window (CW) for the channel to initiate its uplink or downlink transmission when its normalized SNR is greater than a threshold. The contribution is threefold: (i) All three problems are solved in a unified framework by applying multiuser diversity in both uplink and downlink. Fresh SNR is exploited for distributed scheduling meanwhile airtime fairness is retained. (ii) SNR threshold and CW are jointly optimized to maximize throughput, taking into account time-variant link quality, collision probability and protocol overhead. (iii) Network performance is theoretically analyzed. Extensive simulations confirm that DMUS greatly improves total throughput under almost all scenarios compared with both the contention-based CSMA/CA scheme and the contention-free PCF scheme.

Running Multiple Instances of the Distributed Coordination Function for Air-Time Fairness in Multi-Rate WLANs

Conventional multi-rate IEEE 802.11 Wireless LANs (WLANs) are associated with the so-called performance anomaly to describe the phenomenon of high bit rate nodes being dragged down by slower nodes. This anomaly is known to be an impediment to obtaining high cumulative throughputs despite the employment of effective link adaptation mechanisms. To cope with the performance anomaly, air-time fairness has been proposed as an alternative to throughput fairness, the latter being a main characteristic of the IEEE 802.11 Distributed Coordination Function (DCF). In this paper, we propose a novel distributed air-time fair MAC (Medium Access Control) without having to change the operation of the conventional DCF. In the proposed MAC, each node in the system runs multiple instances of the conventional DCF back-off algorithm where the number of DCF instances for the nodes can be chosen in a distributed manner. Both analytical and simulation-based results are provided to validate the effectiveness of the proposed air-time fair MAC.

Achieving airtime fairness of delay-sensitive applications in multirate IEEE 802.11 wireless LANs

In multirate IEEE 802.11 wireless LANs, performance anomaly is a well-studied problem. Most existing solutions try to solve this problem by achieving airtime fairness. However, these solutions tend to increase the frame delay of some stations. If these stations run delay-sensitive applications, e.g., VoIP and video conferences, their quality of service would be seriously degraded. In this article we introduce and classify the existing solutions. The frame delay of each type of approach is illustrated by analytical results. We also propose an adaptive approach to solve this delay issue. The proposed approach could accurately model the condition of each station and concurrently adjust multiple MAC parameters. Simulation results validate that the proposed approach not only achieves airtime fairness but also improves frame delay. Therefore, the proposed approach could be applied to improve the quality of service of multimedia applications over WLAN environments.

Achieving Airtime Fairness and Maximum Throughput in IEEE 802.11 under Various Transmission Durations

IEEE 802.11 Wireless LANs (WLANs) support multiple transmission rates. When some stations transmit at low transmission rates, the performance of the high transmission rate stations degrades heavily, and this phenomenon is known as the performance anomaly. As a solution to the performance anomaly, airtime fairness was proposed. However, the distributed coordination function (DCF) of IEEE 802.11 cannot provide airtime fairness to all competing stations because the protocol is designed to ensure fair attempt probability. In this paper, we propose a new medium access control, successful transmission time fair MAC (STF-MAC), which is fair in terms of successful transmission time and also provides the maximum aggregate throughput of a basic service set (BSS) in distributed manner. STF-MAC can be easily applied to solve the uplink/downlink fairness problem in infrastructure mode. Through simulations, we demonstrate that STF-MAC not only remedies the performance anomaly but also maximizes the aggregate throughput under the fairness constraint.

Wireless MediaNets: application-driven next-generation wireless IP networks

Thanks to the explosive creation of multimedia contents, the pervasive adoption of multimedia coding standards and the ubiquitous access of multimedia services, multimedia networking is everywhere in our daily lives. Unfortunately, the existing best effort IP network infrastructure, originally designed with little real-time QoS requirement, has started to suffer from performance degradation on emerging multimedia networking applications. This inadequacy problem is further deepened by the prevalence of last/first-mile wireless networking, such as Wi-Fi, mobile WiMAX, and many wireless sensors and ad-hoc networks. This can be evidenced by more and more fragmentation of application-driven IP-based networks, such as for power grid distribution, networked security surveillance, intelligent transportation communication, and many other sensor networks. To overcome the QoS challenges, the next generation wireless IP networks have to be architected in a top-down manner, i.e., application-driven layered protocol design. More specifically, based on the application media data, compression schemes are applied, the subsequent Network, MAC- and PHY-layered protocols need to be accordingly or jointly enhanced to reach the optimal performance. This is the fundamental concept behind the design of Wireless MediaNets. In this survey paper, I will address the QoS challenges specifically encountered in video over heterogeneous wireless broadband networks and address several application-driven Wireless MediaNet solutions based on effective cross-layer integration of APP and MAC/PHY layers. More specifically, the congestion control for achieving airtime fairness of video streaming to maximize the link adaptation performance of Wi-Fi, the minimum latency event-driven data exchange for distributed wireless ad-hoc sensor networks, and the opportunistic multicast of scalable video live streaming over mobile WiMAX.

Airtime Fair Distributed Cross-Layer Congestion Control for Real-Time Video Over WLAN

We propose a distributed cross-layer congestion control algorithm that provides enhanced quality of service QoS and reliable operation for real-time uplink video over WiFi applications. Such applications are characterized by many wireless devices transmitting video at various PHY rates over a relatively congested channel. Unfortunately, today's off-the-shelf 802.11 equipment can be easily demonstrated to suffer catastrophic failure when subject to these conditions-let alone provide acceptable perceptual quality to the user. We show that in order to remedy these issues, it is preferable to apply airtime fairness with a cross-layer approach. The idea is to use a fast frame-by-frame control loop in the carrier sense multiple access/collision avoidance (CSMA/CA)-based medium access control (MAC) layer while simultaneously exploiting the powerful control loop gain attainable by performing source-rate adaptation in the application layer. We support the proposed algorithm through both simulation and experimentation with various channel and PHY rate scenarios.