Evaluations and Enhancements in 802.11n WLANs – Error-Sensitive Adaptive Frame Aggregation

IEEE 802.11n is a developing next-generation standard for wireless local area network (LAN). Seamless multimedia traffic connection will become possible with the 802.11n improvement in the Physical and MAC layer. The new 802.11n frame aggregation technique is particularly important for enhancing MAC layer efficiency under high speed wireless LAN. Although the frame aggregation can increase the efficiency in the MAC layer, it does not provide good performance in high BER channels when using large frame aggregation size. An Optimal Frame Aggregation (OFA) technique for AMSDU frame under different BERs in 802.11n WLANs was proposed. However, the suggested algorithm does not take into account the loss rate and the delay performance requirements for Voice or Video multimedia traffic in various BER channels. The optimal frame size can provide good throughput in the network, but the delay might exceed the Quality of Service (QoS) requirement of Voice traffic or the Frame-Error-Rate (FER) might exceed the maximum loss rate tolerable by the streaming Video traffic. We propose an Error- Sensitive Adaptive Frame Aggregation (ESAFA) scheme which can dynamically set the size of AMSDU frame based on the maximum Frame-Error-Rate (FER) tolerable by a particular multimedia traffic. The simulations show that our adaptive algorithm outperforms the optimal frame algorithm by improving both the delay and the loss rate in the 802.11n WLANs. The measured FER of the Error-Sensitive Adaptive Frame Aggregation scheme can be kept at about the same as the loss rate requirement for Video traffic even under high Bit-Error-Rate (BER) channel. The delay compared to OFA is also decreased by around 50% under different channel conditions. Moreover, the results show that the Error-Sensitive Adaptive Frame Aggregation scheme works particularly well in error-prone wireless networks

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

Experimental Performance Evaluation and Frame Aggregation Enhancement in IEEE 802.11n WLANs

The IEEE 802.11n standard promises to extend today’s most popular WLAN standard by significantly increasing reach, reliability, and throughput. Ratified on September 2009, this standard defines many new physical and medium access control (MAC) layer enhancements. These enhancements aim to provide a data transmission rate of up to 600 Mbps. Since June 2007, 802.11n products are available on the enterprise market based on the draft 2.0. In this paper we investigate the effect of most of the proposed 802.11n MAC and physical layer features on the adhoc networks performance. We have performed several experiments in real conditions. The experimental results demonstrated the effectiveness of 802.11n enhancement. We have also examined the interoperability and fairness of 802.11n. The frame aggregation mechanism of 802.11n MAC layer can improve the efficiency of channel utilization by reducing the protocol overheads. We focused on the effect of frame aggregation on the support of voice and video applications in wireless networks. We also propose a new frame aggregation scheduler that considers specific QoS requirements for multimedia applications. We dynamically adjust the aggregated frame size based on frame's access category defined in 802.11e standard

Advanced Protocols for Peer-to-Peer Data Transmission in Wireless Gigabit Networks

This thesis tackles problems on IEEE 802.11 MAC layer, network layer and application layer, to further push the performance of wireless P2P applications in a holistic way. It contributes to the better understanding and utilization of two major IEEE 802.11 MAC features, frame aggregation and block acknowledgement, to the design and implementation of opportunistic networks on off-the-shelf hardware and proposes a document exchange protocol, including document recommendation. First, this thesis contributes a measurement study of the A-MPDU frame aggregation behavior of IEEE 802.11n in a real-world, multi-hop, indoor mesh testbed. Furthermore, this thesis presents MPDU payload adaptation (MPA) to utilize A-MPDU subframes to increase the overall throughput under bad channel conditions. MPA adapts the size of MAC protocol data units to channel conditions, to increase the throughput and lower the delay in error-prone channels. The results suggest that under erroneous conditions throughput can be maximized by limiting the MPDU size. As second major contribution, this thesis introduces Neighborhood-aware OPPortunistic networking on Smartphones (NOPPoS). NOPPoS creates an opportunistic, pocket-switched network using current generation, off-the-shelf mobile devices. As main novel feature, NOPPoS is highly responsive to node mobility due to periodic, low-energy scans of its environment, using Bluetooth Low Energy advertisements. The last major contribution is the Neighborhood Document Sharing (NDS) protocol. NDS enables users to discover and retrieve arbitrary documents shared by other users in their proximity, i.e. in the communication range of their IEEE 802.11 interface. However, IEEE 802.11 connections are only used on-demand during file transfers and indexing of files in the proximity of the user. Simulations show that NDS interconnects over 90 \% of all devices in communication range. Finally, NDS is extended by the content recommendation system User Preference-based Probability Spreading (UPPS), a graph-based approach. It integrates user-item scoring into a graph-based tag-aware item recommender system. UPPS utilizes novel formulas for affinity and similarity scoring, taking into account user-item preference in the mass diffusion of the recommender system. The presented results show that UPPS is a significant improvement to previous approaches

Advanced Wireless LAN

The past two decades have witnessed starling advances in wireless LAN technologies that were stimulated by its increasing popularity in the home due to ease of installation, and in commercial complexes offering wireless access to their customers. This book presents some of the latest development status of wireless LAN, covering the topics on physical layer, MAC layer, QoS and systems. It provides an opportunity for both practitioners and researchers to explore the problems that arise in the rapidly developed technologies in wireless LAN

Cross-Layer Techniques for Efficient Medium Access in Wi-Fi Networks

IEEE 802.11 (Wi-Fi) wireless networks share the wireless medium using a Carrier Sense Multiple Access (CSMA) Medium Access Control (MAC) protocol. The MAC protocol is a central determiner of Wi-Fi networks’ efficiency–the fraction of the capacity available in the physical layer that Wi-Fi-equipped hosts can use in practice. The MAC protocol’s design is intended to allow senders to share the wireless medium fairly while still allowing high utilisation. This thesis develops techniques that allow Wi-Fi senders to send more data using fewer medium acquisitions, reducing the overhead of idle periods, and thus improving end-to-end goodput. Our techniques address the problems we identify with Wi-Fi’s status quo. Today’s commodity Linux Wi-Fi/IP software stack and Wi-Fi cards waste medium acquisitions as they fail to queue enough packets that would allow for effective sending of multiple frames per wireless medium acquisition. In addition, for bi-directional protocols such as TCP, TCP data and TCP ACKs contend for the wireless channel, wasting medium acquisitions (and thus capacity). Finally, the probing mechanism used for bit-rate adaptation in Wi-Fi networks increases channel acquisition overhead. We describe the design and implementation of Aggregate Aware Queueing (AAQ), a fair queueing discipline, that coordinates scheduling of frame transmission with the aggregation layer in the Wi-Fi stack, allowing more frames per channel acquisition. Furthermore, we describe Hierarchical Acknowledgments (HACK) and Transmission Control Protocol Acknowledgment Optimisation (TAO), techniques that reduce channel acquisitions for TCP flows, further improving goodput. Finally, we design and implement Aggregate Aware Rate Control (AARC), a bit-rate adaptation algorithm that reduces channel acquisition overheads incurred by the probing mechanism common in today’s commodity Wi-Fi systems. We implement our techniques on real Wi-Fi hardware to demonstrate their practicality, and measure their performance on real testbeds, using off-the-shelf commodity Wi-Fi hardware where possible, and software-defined radio hardware for those techniques that require modification of the Wi-Fi implementation unachievable on commodity hardware. The techniques described in this thesis offer up to 2x aggregate goodput improvement compared to the stock Linux Wi-Fi stack