High Density Wireless Local Area Networks Research Articles

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.

Dynamic Channel Bonding in Spatially Distributed High-Density WLANs

In this paper, we discuss the effects on throughput and fairness of dynamic channel bonding (DCB) in spatially distributed high-density wireless local area networks (WLANs). First, we present an analytical framework based on continuous-time Markov networks (CTMNs) for depicting the behavior of different DCB policies in spatially distributed scenarios, where nodes are not required to be within the carrier sense range of each other. Then, we assess the performance of DCB in high-density IEEE 802.11ac/ax WLANs by means of simulations. We show that there may be critical interrelations among nodes in the spatial domain–even if they are located outside the carrier sense range of each other–in a chain reaction manner. Results also reveal that, while always selecting the widest available channel normally maximizes the individual long-term throughput, it often generates unfair situations where other WLANs starve. Moreover, we show that there are scenarios where DCB with stochastic channel width selection improves the latter approach both in terms of individual throughput and fairness. It follows that there is not a unique optimal DCB policy for every case. Instead, smarter bandwidth adaptation is required in the challenging scenarios of next-generation WLANs.

Online Primary Channel Selection for Dynamic Channel Bonding in High-Density WLANs

In order to dynamically adapt the transmission bandwidth in wireless local area networks (WLANs), dynamic channel bonding (DCB) was introduced in IEEE 802.11n. It has been extended since then, and it is expected to be a key element in IEEE 802.11ax and future amendments such as IEEE 802.11be. While DCB is proven to be a compelling mechanism by itself, its performance is deeply tied to the primary channel selection, especially in high-density (HD) deployments, where multiple nodes contend for the spectrum. Traditionally, this primary channel selection relied on picking the most free one without any further consideration. In this letter, in contrast, we propose dynamic-wise (DyWi), a light-weight, decentralized, online primary channel selection algorithm for DCB that improves the expected WLAN throughput by considering not only the occupancy of the target primary channel but also the activity of the secondary channels. Even when assuming important delays due to primary channel switching, simulation results show a significant improvement both in terms of average delay and throughput.

To overlap or not to overlap: Enabling channel bonding in high-density WLANs

Wireless local area networks (WLANs) are the most popular kind of wireless Internet connection because of their simplicity of deployment and operation. As a result, the number of devices accessing the Internet through WLANs such as laptops, smartphones, or wearables, is increasing drastically at the same time that applications’ throughput requirements do. To cope with these challenges, channel bonding (CB) techniques are used for enabling higher data rates by transmitting in wider channels, thus increasing spectrum efficiency. However, important issues like higher potential co-channel and adjacent channel interference arise when bonding channels. This may harm the performance of the carrier sense multiple access (CSMA) protocol because of recurrent backoff freezing, while making nodes more sensitive to hidden node effects. In this paper, we address the following point at issue: is it convenient for high-density (HD) WLANs to use wider channels and potentially overlap in the spectrum? First, we highlight key aspects of DCB in toy scenarios through a continuous time Markov network (CTMN) model. Then, by means of extensive simulations covering a wide range of traffic loads and access point (AP) densities, we show that dynamic channel bonding (DCB) – which adapts the channel bandwidth on a per-packet transmission – significantly outperforms traditional single-channel on average. Nevertheless, results also corroborate that DCB is more prone to generate unfair situations where WLANs may starve. Contrary to most of the current thoughts pushing towards non-overlapping channels in HD deployments, we highlight the benefits of allocating channels as wider as possible to WLANs altogether with implementing adaptive access policies to cope with the unfairness situations that may appear.

Network Planning Based on Interference Alignment in Density WLANs

In high-density scenarios, wireless local area networks (WLANs) encounter serious interference. Interference alignment (IA) is an effective manner to control interference and improve system capacity in the interference channel. However, interference channels interact with each other in existing network planning manners and the network throughput cannot be improved significantly through the IA. In order to control interference and improve the network throughput more efficiently, we propose a network planning scheme based on the IA in high-density WLANs. The whole network is divided into a plurality of subregions, and neighbor subregions use different channels. Each subregion is considered as an interference channel, and the IA is utilized to control interference in a single subregion. Meanwhile, inter-subregion interference is controlled by channel allocation. The appropriate size of subregions and the optimal channel allocation will be selected according to the principle of maximizing the degree of freedom (DoF) of the whole network. The DoF describes the number of messages transmitted at the same time, therefore, this manner will make high-density WLANs more competitive by improving the average DoF. In the simulations, the proposed network planning manner is compared to the traditional manner in different scales of the WLANs, and the results show that the proposed manner can improve the average DoF in high-density WLANs.

Channel Assignment Mechanism for Multiple APs Cochannel Deployment in High Density WLANs

In Wireless Local Area Networks (WLANs), cochannel deployment can bound channel access delay and improve network capacity due to mitigating the collision and interference among different Access Points (APs). In this paper, we present a network model and an interference model for multiple APs cochannel deployment and propose a channel assignment mechanism which formulates the channel assignment problem into a time slot allocation problem. Meanwhile, we assign the channel based on the vertex coloring algorithm and make extra polls by utilizing the time slot reservation strategy to improve the channel assignment. Furthermore, we optimize the polling list of APs through classifying the clients to improve the channel utilization. The simulation results show that our proposed algorithm can improve the performance in terms of network throughput, transmission delay, and packet loss rate compared with the DCF (Distributed Coordination Function) and TMCA algorithms.

IEEE 802.11ax: Challenges and Requirements for Future High Efficiency WiFi

The popularity of IEEE 802.11 based wireless local area networks (WLANs) has increased significantly in recent years because of their ability to provide increased mobility, flexibility, and ease of use, with reduced cost of installation and maintenance. This has resulted in massive WLAN deployment in geographically limited environments that encompass multiple overlapping basic service sets (OBSSs). In this article, we introduce IEEE 802.11ax, a new standard being developed by the IEEE 802.11 Working Group, which will enable efficient usage of spectrum along with an enhanced user experience. We expose advanced technological enhancements proposed to improve the efficiency within high density WLAN networks and explore the key challenges to the upcoming amendment.

Queuing Theory Based Co-Channel Interference Analysis Approach for High-Density Wireless Local Area Networks.

Increased co-channel interference (CCI) in wireless local area networks (WLANs) is bringing serious resource constraints to today’s high-density wireless environments. CCI in IEEE 802.11-based networks is inevitable due to the nature of the carrier sensing mechanism however can be reduced by resource optimization approaches. That means the CCI analysis is basic, but also crucial for an efficient resource management. In this article, we present a novel CCI analysis approach based on the queuing theory, which considers the randomness of end users’ behavior and the irregularity and complexity of network traffic in high-density WLANs that adopts the M/M/c queuing model for CCI analysis. Most of the CCIs occur when multiple networks overlap and trigger channel contentions; therefore, we use the ratio of signal-overlapped areas to signal coverage as a probabilistic factor to the queuing model to analyze the CCI impacts in highly overlapped WLANs. With the queuing model, we perform simulations to see how the CCI influences the quality of service (QoS) in high-density WLANs.

QoE based power control scheme for interference mitigation in high-density WLANs

Mobile data traffic is going through an explosive growth recently as mobile smart devices become more and more ubiquitous, causing huge pressure on cellular network. Taking advantage of its low cost and easy-to-deploy feature, wireless local-area networks (WLAN) becomes increasingly popular to offload data streams from cellular network, followed by higher and higher density of its deployment. However, the high density of WLAN will cause more interference, which results in degradation of its performance. Therefore, in order to enhance the performance of the network, we aim to minimize the interference caused by high density of WLAN. In this paper, we propose a novel power control scheme to achieve the above aim. We use the quality of experience (QoE) evaluation to coordinate the power of each access point (AP) and finally realize the optimization of the entire network. According to the simulation results, our scheme improves the performance of the network significantly in many aspects, including throughput and QoE.

Green WLANs: On-Demand WLAN Infrastructures

Enterprise wireless local area networks (WLANs) that consist of a high-density of hundreds to thousands of access points (APs) are being deployed rapidly in corporate offices and university campuses. The primary purpose of these deployments is to satisfy user demands for high bandwidth, mobility, and reliability. However, our recent study of two such WLANs showed that these networks are rarely used at their peak capacity, and the majority of their resources are frequently idle. In this paper, we bring to attention that a large fraction of idle WLAN resources results in significant energy losses. Thousands of WLANs world-wide collectively compound this problem, while raising serious concerns about the energy losses that will occur in the future. In response to this compelling problem, we propose the adoption of resource on-demand (RoD) strategies for WLANs. RoD strategies power on or off WLAN APs dynamically, based on the volume and location of user demand. As a specific solution, we propose SEAR, a practical and elegant RoD strategy for high-density WLANs. We implement SEAR on two wireless networks to show that SEAR is easy to integrate in current WLANs, while it ensures no adverse impact on end-user connectivity and performance. In our experiments, SEAR reduces power consumption to 46%. Using our results we discuss several interesting problems that open future directions of research in RoD WLANs.