Steve Emeott

Power management for VoIP over IEEE 802.11 WLAN

Power consumption is a critical issue for voice-over-IP (VoIP) over wireless LAN applications, especially when handheld 802.11 voice terminals are used as the end-user device. This paper provides an overview of power save procedures defined in the IEEE 802.11 wireless LAN standard, and proposes a novel power management technique for stations and services that use contention-based channel access, which we call unscheduled power save delivery (UPSD). We further investigate the performance of UPSD in combination with the eDCA mechanism defined in the 802.11e draft standard via an OPNET-based simulator. The results indicate that UPSD permits a lower duty cycle and delivers better VoIP capacity than legacy techniques.

Voice capacity evaluation of IEEE 802.11a with automatic rate selection

This paper analyzes the transmission of voice and isochronous traffic in general over an 802.11a wireless local area network. In particular, we provide a simple analytic technique for estimating the capacity of an 802.11a access point under the contention-based access method when all stations can select an optimal transmission rate using automatic rate selection. Capacity is additionally estimated using a wireless LAN (WLAN) system simulator that models contention-based access in a noise limited channel, in which packet erasures are modeled using quasi-static link simulation techniques. The impact of automatic rate selection on capacity is evaluated. Results from the analytic and simulation based methods of estimating capacity are compared. In addition, impact on voice capacity from data traffic is studied.

A Correctness Proof of a Mesh Security Architecture

The IEEE 802.11s working group is tasked to provide ways of establishing and securing a wireless mesh network. One proposal establishes a Mesh Security Architecture (MSA), with a developed key hierarchy and full protocol definitions. This paper examines the correctness and security of the MSA proposal and its corresponding protocols. We utilize Protocol Composition Logic (PCL) to prove individual protocols secure, as well as their composition. We add to the structure of PCL, generalizing it for peer-to-peer applications. We also discuss two security issues we discovered with original versions of the proposals and our proposed remedies.

Application of MIMO and proportional fair scheduling to CDMA downlink packet data channels

There are many capacity enhancement techniques in wireless networks. Multiple-input-multiple-output (MIMO) antenna systems, channel-state based packet data scheduling algorithms and adaptive modulation and coding are examples of such techniques. In this paper, we provide the simulation results for various transmission schemes (including MIMO) in conjunction with a channel-state-based scheduling algorithm and an adaptive modulation and coding scheme Consequently, we demonstrate the cellular system capacity gain resulting from interaction between these three techniques. Specifically, system-level simulations are presented for the wideband CDMA (WCDMA) downlink shared channel.

A Network-Assisted Association Scheme for 802.11-Based Mesh Networks

Wireless mesh networks provide a flexible yet cost- effective means to expand wireless coverage, but their performance can be limited without carefully managing station-to-AP associations to minimize the total end-to-end resource impact. The received signal strength-based approach that is commonly used by 802.11 devices can lead to inefficient use of network resources in a mesh network. In this paper we propose a network-assisted association scheme for 802.11-based mesh networks that provides guidance without exposing stations to the details of the network. We show via simulation that our approach produces improved performance as compared to the RSS-based approach and conclude that our scheme can yield higher system capacity in 802.11-based wireless mesh networks.

WLC24-6: An Analytical Model of Block Acknowledgement and Selective Retransmission in an 802.11e WLAN Network

The 802.11e amendment to IEEE 802.11 standard defines a block acknowledgement (ACK) mechanism to reduce the overhead required by a station to acknowledge the receipt of multiple frames. This paper presents an analytic model for estimating the overhead required to selectively retransmit data frames when using the block ACK mechanism in a noisy channel. This model is applicable both to the present block ACK mechanism and further refinements that could be proposed in a future standards amendment, such as the 802.11n high throughput task group.

Scheduled Mesh Access Mechanism for an IEEE 802.11 Mesh Network

One of the key issues for an IEEE 802.11-based mesh network is the effectiveness of its distributed listen-before-transmit media access control approach. In this paper we proposed one technique, called scheduled mesh access (SMA), for reducing the impact of interference on a mesh network. The SMA mechanism reserves time on the media for future transmissions, and then accesses the media at reserved times using the 802.11 channel access procedures. We study the ability of mesh network employing SMA to avoid non-mesh interference and schedule around self interference. Results indicate that SMA is more robust to interference than the enhanced distributed channel access (EDCA) function (defined by in the IEEE 802.1 le amendment to the IEEE 802.11 standard), which does not includes a mesh-aware scheduling mechanism.

Impact of scheduled mesh access on the capacity of wireless mesh links

In this paper we evaluate the performance of a dual-radio 802.11-based mesh network in which each mesh node adheres to a transmission schedule negotiated with peers to avoid interfering with one another when transmitting delay sensitive traffic (e.g. conversational voice). A comparison is made between the performance of scheduled access for delay sensitive traffic and the contention-based Enhanced Distributed Channel Access (EDCA) function defined in the IEEE 802.11e amendment. The performance evaluation considers the impact of scheduler design on the performance of the network. The results indicate that scheduled access is more robust to interference than EDCA, and that the choice of scheduling approach can have a significant impact on the data throughput achieved through the mesh at a given voice traffic load.

Optimization of a link adaptation algorithm for voice over wireless LAN applications

Auto rate fallback (ARF) is a link adaptation algorithm that uses layer-2 acknowledgement messages to make decisions to increase or decrease the transmission rate. The algorithm is configured by choosing thresholds to define its behavior. The ARF algorithm is applied to voice-over-IP users in an IEEE 802.11a wireless LAN system, and system simulation is used to determine the optimal ARF configuration. Configuration performance is judged using a unique voice quality metric, which is used to establish a measure of system capacity for a single access point with several voice users. Results indicate that the ARF configuration can significantly impact capacity, and one configuration of ARF provides a capacity within 13% of the available capacity.

Link adaptation evaluation for WLAN using a voice quality metric

Link adaptation, the process of adapting a mobile users link speed as channel conditions change, is investigated for IEEE 802.11a wireless local area networks (WLANs). An ideal algorithm using channel signal-to-noise ratio and a practical algorithm based on acknowledgement message (ACK) reception are discussed, and their performance is compared to cases without link adaptation. The analysis is performed by simulating a combination voice and data WLAN system, and voice call quality is judged using a unique quality metric. The metric contains two scores: a packet loss percentage and an estimate of the number of audible imperfections based on the pattern of packet loss. System capacity estimates result from applying the metric, and are used to compare the link adaptation schemes.