IEEE 802.11n MAC frame aggregation mechanisms for next-generation high-throughput WLANs [Medium access control protocols for wireless LANs]

IEEE 802.11n is an ongoing next-generation wireless LAN standard that supports a very highspeed connection with more than 100 Mb/s data throughput measured at the medium access control layer. This article investigates the key MAC enhancements that help 802.11n achieve high throughput and high efficiency. A detailed description is given for various frame aggregation mechanisms proposed in the latest 802.11n draft standard. Our simulation results confirm that A-MSDU, A-MPDU, and a combination of these methods improve extensively the channel efficiency and data throughput. We analyze the performance of each frame aggregation scheme in distinct scenarios, and we conclude that overall, the two-level aggregation is the most efficacious

FastM: Design and Evaluation of a Fast Mobility Mechanism for Wireless Mesh Networks

Although there is a large volume of work in the literature in terms of mobility approaches for Wireless Mesh Networks, usually these approaches introduce high latency in the handover process and do not support realtime services and applications. Moreover, mobility is decoupled from routing, which leads to inefficiency to both mobility and routing approaches with respect to mobility. In this paper we present a new extension to proactive routing protocols using a fast mobility extension, FastM, with the purpose of increasing handover performance in Wireless Mesh Networks. With this new extension, a new concept is created to integrate information between neighbor wireless mesh routers, managing locations of clients associated to wireless mesh routers in a certain neighborhood, and avoiding packet loss during handover. The proposed mobility approach is able to optimize the handover process without imposing any modifications to the current IEE 802.11 MAC protocol and use unmodified clients. Results show the improved efficiency of the proposed scheme: metrics such as disconnection time, throughput, packet loss and control overhead are largely improved when compared to previous approaches. Moreover, these conclusions apply to mobility scenarios, although mobility decreases the performance of the handover approach, as expected

Application of the DQCA protocol to the optimization of wireless communications systems in cellular environments

This final career thesis (Master thesis) is a contribution on the enhancement of wireless communications, specifically WLAN multi-cell systems based on the IEEE 802.11 standard. The objectives were to propose and study different Cross-Layer AP selection mechanisms that include single, dual and multiple metric based criteria using PHY-MAC interactions. These mechanisms are designed in order to improve system efficiency through the increase of the utilization of the available transmission resources. The key idea of these mechanisms is to make use of certain PHY and MAC parameters, other than the traditional RSSI measurements, in order to optimize the association to the best AP, specially focusing on the innovative use of MAC level state metrics. In this regard, of special interest is the inclusion of MAC level AP traffic load estimations within these association decisions. All the proposals are based on the use of a high-performance MAC protocol called DQCA (Distributed Queueing Collision Avoidance), which is specially fitted to include the proposed techniques. Computer simulations have been carried out to evaluate and quantify the benefits of the proposed mechanisms and techniques in representative scenarios. Moreover, a completely new handoff procedure has been designed for the DQCA muti-cell operation. This handoff process allows implementing each of the proposed AP selection mechanisms. Furthermore, the interaction between a Cross-Layer scheduling technique at the MAC level and two proposed AP selection mechanisms has also been studied. The performance of these techniques has also been assessed by means of computer simulations. The analysis of the obtained results show that the proposed mechanisms perform differently under the considered scenarios. However, the main conclusion that can be drawn is that AP selection mechanisms that are based on joint multiple metrics considerations (SNR, AP load, delay, etc.) perform significantly better than those that use only single or dual metric based mechanisms. After the study, we can conclude that the proposed techniques and mechanisms provide significant efficiency enhancements for DQCA-based WLAN multi-cell systems so that all of them may be taken into account in future wireless networks

A Novel IEEE 802.11 Power Save Mechanism for Energy Harvesting Motivated Networks

The spread of wirelessly connected computing sensors and devices and hybrid networks are leading to the emergence of an Internet of Things (IoT), where a myriad of multi-scale sensors and devices are seamlessly blended for ubiquitous computing and communication. However, the communication operations of wireless devices are often limited by the size and lifetime of the batteries because of the portability and mobility. To reduce energy consumption during wireless communication, the IEEE 802.11 standard specifies a power management scheme, called Power Saving Mechanism (PSM), for IEEE 802.11 devices. However, the PSM of IEEE 802.11 was originally designed for battery-supported devices in single-hop Wireless Local Area Networks (WLANs), and it does not consider devices that are equipped with rechargeable batteries and energy harvesting capability. In this thesis, the original PSM is extended by incorporating with intermittent energy harvesting in the IEEE 802.11 Medium Access Control (MAC) layer specification, and a novel energy harvesting aware power saving mechanism, called EH-PSM, is proposed. The basic idea of EH-PSM is to assign a longer contention window to a device in energy harvesting mode than that of a device in normal mode to make the latter access the wireless medium earlier and quicker. In addition, the device in energy harvesting mode stays active as far as it harvests energy and updates the access point of its harvesting mode to enable itself to be ready for receiving and sending packets or overhearing any on-going communication. The proposed scheme is evaluated through extensive simulation experiments using OMNeT++ and its performance is compared with the original PSM. The simulation results indicate that the proposed scheme can not only improve the packet delivery ratio and throughput but also reduce the packet delivery latenc

Channel Scanning and Access Point Selection Mechanisms for 802.11 Handoff: A Survey

While the cellular technology has been evolving continuously in recent years and client handoffs remain unnoticed, the 802.11 networks still impose an enormous latency issue once the client device decides to roam between the Access Point (AP). This latency is caused by many factors reckoning on scanning the channels and searching for APs with better signal strength. Once data from all the nearby APs has been collected, the client picks the most suitable AP and tries to connect with it. The AP verifies if it has enough capability to serve the client. It also ensures that the client has the required parameters and supported rates to match with the AP. The AP then processes this request, generates a new Association ID and sends it back to the client, thereby granting access to connect. Throughout this re-association process, the client fails to receive or send any data frames and experiences a lag between leaving the old and associating with a new AP. Originally, 802.11 authentication frames were designed for Wired Equivalent Privacy protocol, but later it was found to be insecure and thus got depreciated. Keeping these security aspects concerning shared key authentication in mind, few additional drafts were introduced by IEEE that concerned many key exchanges between the devices. IEEE 802.11r was introduced in 2008 that permits wireless clients to perform faster handoff along with additional data security standards. The key exchange method was redefined and also the new security negotiation protocol started serving wireless devices with a better approach. This enables a client to set up the Quality of Service state and security on an alternative AP before making a transition which ends up in minimal connectivity losses. Although this was an excellent step towards minimizing the service disruption and channel scanning, failure to remain connected with consecutive suitable APs within the minimum time continued to be a challenge. Different manufacturers use their custom-built methodology of handling a client handoff and hence the latency costs differ based on the type of handoff scheme deployed on the device. This thesis focuses on the foremost economical researches throughout recent years which targets minimizing the delays involved with channel scanning and AP selection. A wide sort of enhancements, whether it is on a client device or the AP, has been discussed and compared. Some modifications are associated with enhancing channel scan period or using beacons, and probe requests/responses in an efficient manner. Others concentrate on modifying the device hardware configuration and switching between Network Interfaces. Central controllers are a solution to handoff delays that may track the status of each device within the network and guide them to provide the appropriate Quality of Service to the end-users