Elena Lopez-Aguilera

Effect of adjacent-channel interference in IEEE 802.11 WLANs

Frequency channels are a scarce resource in the ISM bands used by IEEE 802.11 WLANs. Current radio resource management is often limited to a small number of non-overlapping channels, which leaves only three possible channels in the 2.4GHz band used in IEEE 802.11b/g networks. In this paper we study and quantify the effect of adjacent channel interference, which is caused by transmissions in partially overlapping channels. We propose a model that is able to determine under what circumstances the use of adjacent channels is justified. The model can also be used to assist different radio resource management mechanisms (e.g. transmitted power assignments)

An Asymmetric Access Point for Solving the Unfairness Problem in WLANs

In atypical deployment of IEEE 802.11 wireless LANs in the infrastructure mode, an access point acts as abridge between the wireless and the wired parts of the network. Under the current IEEE 802.11 Distributed Coordination Function (DCF) access method, which provides equal channel access probability to all devices in a cell, the access point cannot relay all the frames that it receives on the downlink. This causes significant unfairness between upload and download connections, long delays, and frame losses. This unfairness problem comes from the not-so-complex interaction of transport-layer protocols with the MAC-layer access method. The main problem is that the access point requires more transmission attempt probability than wireless stations for correct operation at the transport layer. In this paper, we propose to solve the unfairness problem in a simple elegant way at the MAC layer. We define the operation of an Asymmetric Access Point that benefits from a sufficient transmission capacity with respect to wireless stations so that the overall performance improves. The proposed method of operation is intrinsically adaptive so that when the access point does not need the increased capacity, it is used by wireless stations. We validate the proposed access method by simulation to compare it with other solutions based on IEEE 802.11e. Unlike many papers in this domain, which only validate MAC-layer modifications through simulation or analytical modeling, we provide measurement data gathered on an experimental prototype that uses wireless cards implementing the proposed method.

Outdoor IEEE 802.11g cellular network performance

Most studies about the performance of IEEE 802.11 are limited to a single cell environment. Nevertheless, the idea of designing an outdoor cellular network based on WLAN IEEE 802.11 is very attractive, due to the several advantages that this technology presents: the low cost of the equipment, its operation in unlicensed spectrum and its higher data rates. In this paper, we study the possibility of designing an outdoor cellular network based on the IEEE 802.11g standard. We present its performance under different load conditions and compare this behavior with the results obtained in an isolated single cell environment, without co-channel interference. Finally, going a step further, this paper explores the IEEE 802.11g cellular network performance for different cluster sizes, as a method to reduce the interference influence on networks performance.

Wireless technology applied to GIS

At present, there is a growing interest in wireless applications, due to the fact that the technology begins to support them at reasonable costs. In this paper, we present the technology currently available for use in wireless environments, focusing on Geographic Information Systems. As an example, we present a newly developed platform for the commercialization of advanced geographical information services for use in portable devices. This platform uses available mobile telephone networks and wireless local area networks, but it is completely scalable to new technologies such as third generation mobile networks. Users access the service using a vector map player that runs on a Personal Digital Assistant with wireless access facilities and a Global Positioning System receiver. Before accessing the information, the player will request authorization from the server and download the requested map from it, if necessary. The platform also includes a system for improving Global Positioning System localization with the Real Time Differential Global Positioning System, which uses short GSM messages as the transmission medium.

Evaluation of dynamic sensitivity control algorithm for IEEE 802.11ax

The explosive growth in the usage of IEEE 802.11 network has resulted in dense deployments in diverse environments. Most recently, the IEEE working group has triggered the IEEE 802.11ax project, which aims to amend the current IEEE 802.11 standard to improve efficiency of dense WLANs. In this paper, we evaluate the Dynamic Sensitivity Control (DSC) Algorithm proposed for IEEE 802.11ax. This algorithm dynamically adjusts the Carrier Sense Threshold (CST) based on the average received signal strength. We show that the aggregate throughput of a dense network utilizing DSC is considerably improved (i.e. up to 20%) when compared with the IEEE 802.11 legacy network.

Enabling always on service discovery: Wifi neighbor awareness networking

There is untapped potential in the WiFi radios embedded in our smartphone and tablet devices. In this article we introduce the WiFi Neighbor Awareness Networking technology being standardized in the WiFi Alliance®, which leverages this potential by allowing handheld devices to continuously discover other interesting services and devices while operating in the background in an energy-efficient way. In addition, we present a thorough performance evaluation based on packet-level simulations that illustrates the performance of WiFi NAN to be expected in realistic scenarios.

IEEE 802.11ah: A Technology to Face the IoT Challenge

Since the conception of the Internet of things (IoT), a large number of promising applications and technologies have been developed, which will change different aspects in our daily life. This paper explores the key characteristics of the forthcoming IEEE 802.11ah specification. This future IEEE 802.11 standard aims to amend the IEEE 802.11 legacy specification to support IoT requirements. We present a thorough evaluation of the foregoing amendment in comparison to the most notable IEEE 802.11 standards. In addition, we expose the capabilities of future IEEE 802.11ah in supporting different IoT applications. Also, we provide a brief overview of the technology contenders that are competing to cover the IoT communications framework. Numerical results are presented showing how the future IEEE 802.11ah specification offers the features required by IoT communications, thus putting forward IEEE 802.11ah as a technology to cater the needs of the Internet of Things paradigm.

Client-driven load balancing through association control in IEEE 802.11 WLANs

The growth of IEEE 802.11 wireless local area networks (WLANs) (Wi-Fi) brings new possibilities of getting connected in public spaces, known as Hot Spots. Current client-access point associations are an interesting research topic because in these scenarios, users tend to be ‘gregarious’ and essentially static. Under IEEE 802.11 standards, association and roaming decisions are made by client devices and most implementations are based on signal strength measurements; i.e. a client station selects the access point (AP) that provides the strongest signal, which leads to an uneven distribution of clients and load between neighbouring APs. As it can be observed in practical scenarios, the default AP-client association scheme followed in IEEE WLANs, produces unfair situations. This work provides means to effectively alleviate this performance issue and also gives details for a feasible implementation. In this paper we analyse how new IEEE 802.11 standards will allow new radio measurements to provide more efficient association decisions. We propose a new load metric that will produce client-driven associations that ensure greater fairness and throughput. Copyright

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.

WLC29-2: Performance of Wireless LAN Access Methods in Multicell Environments

In this paper, we address the issue of evaluating performance of wireless LANs in multicell scenarios. We try to understand the complex behavior of the DCF (distributed coordination function) access method defined in the IEEE 802.11 standard [1] and its modifications proposed for improving performance: slow decrease [2], asymptotically optimal backoff [3], and idle sense [4]. We analyze the influence of overlapping cells and large multicell environments on their performance. Our results show that the IEEE 802.11 DCF and its two modifications (slow decrease and AOB) exhibit important unfairness between stations close to the access point and those near the border of a neighbor cell. Idle Sense performs much better: it provides much better fairness than the IEEE 802.11 DCF and its modifications. It also obtains the highest throughput when stations adapt their bit rate to channel conditions.