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A virtual WLAN concept for increasing the bandwidth of 802.11 Wireless LANs

IP.com Disclosure Number: IPCOM000010778D
Original Publication Date: 2003-Jan-21
Included in the Prior Art Database: 2003-Jan-21
Document File: 4 page(s) / 105K

Publishing Venue

IBM

Abstract

A virtual WLAN concept is described that allows to increase the throughput of 802.11 Wireless LANs (WLANs). The concept can be implemented in software above the current 802.11 MAC layer and therefore does not require the development of a new 802.11 PHY or MAC layers. It is also operable with the current standard.

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A virtual WLAN concept for increasing the bandwidth of 802.11 Wireless LANs

1 Introduction

There is currently a strong general interest on the specification and development of new WLANs with data rates which are higher than the ones currently supported by 802.11a. This interest is driven by the anticipation of an extensive usage of wireless technologies in future home networks, in which multimedia and entertainment applications require the support for high bandwidth and guaranteed quality of services. Following this trend the IEEE 802.11 Working Group has created a new Study Group called the "High Throughput Study Group (HTSG)" with the purpose "to investigate the feasibility of providing through-puts of at least 2x greater than the existing 802.11 standard." The most obvious way for increasing the throughput of an WLAN is to define a new PHY with higher data rates, see for example [1]. Besides the common disadvantages of a new high rate PHY like interoperability with current WLANs, increase of power consumption, decrease of coverage ranges, cost of developing and implementing a new PHY, etc., this method also leads to the need for developing a new MAC layer. This is due to the PHY-independent overhead imposed by the current 802.11 MAC layer. As shown in [2], with the overhead parameters given by the standard 802.11a, the maximum achievable throughput of an 802.11 WLAN is equal to 75.24 Mbps, even if one can increase the data rate to infinity! This dramatic performance lost, in particular at high data rates, is caused mainly by the fixed "dead" air-times defined in the 802.11 MAC protocol, namely backoff times after every transmission, fixed interframe spacing, and ACK for all data frames. Decreasing these dead air-times may lead to some improvements but has its limit given by the real time decoding process needed in the MAC layer, e.g. immediate acknowledgment for a data frame. New access methods like the Hybrid Coordination Function currently being defined by the IEEE 802.11 Task Group E, in particular when supporting the burst ACK algorithm, may also improve the efficiency, but their implementation cost at high data rates is still unknown. In the next section we will describe a method that allows us to increase the throughput of 802.11 WLANs. The concept can be implemented in software above the current
802.11 MAC layer and therefore does not require the development of a new 802.11 PHY or MAC layers. It is also operable with the current standard.

2 2 Description of the idea

2.1 General overview

The proposed method is based on the multi-link concept which is commonly used in network and transport layers to increase the bandwidth between two communicating devices. Because the bandwidth of a single link cannot be increase at will, one can however combine multiple ones into a single, virtual one with a higher aggregate bandwidth. Applying the multi-link concept to our situation means that we now combine multiple member WLANs into a...