Mecanismo Agregacion Mac 802.11

M E D I U M A C C E S S C O N T R O L P R O T O C O L S F O R W I R E L E S S LAN S

IEEE 802.11N MAC FRAME AGGREGATION MECHANISMS FOR NEXT-GENERATION HIGH-THROUGHPUT WLANS
DIONYSIOS SKORDOULIS AND QIANG NI, BRUNEL UNIVERSITY HSIAO-HWA CHEN, NATIONAL SUN YAT-SEN UNIVERSITY ADRIAN P. STEPHENS, INTEL, UK CHANGWEN LIU, ENTROPIC COMMUNICATIONS ABBAS JAMALIPOUR, UNIVERSITY OF SYDNEY

MSDU MSDUsubframe subframe 21

ABSTRACT
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 aggregationmechanisms 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.

A-MSDU
MPDU MPDUdelimiter delimiter

MPDU MPDU

Pad

MPDU MPDU frame 1 frame 1

MPDU MPDU subframe 2 subframe 2

The authors investigate 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.

INTRODUCTION
Over the last decade, the applications of wirelessand cellular devices have expanded rapidly. The most popular network in the wireless domain is the IEEE 802.11 wireless local area network (WLAN) [1] mainly because of the advantages that its systems possess. Its key characteristics, such as interoperability, mobility, flexibility, and cost-effective deployment, have led to its gaining vast support across enterprises, the public sector, homes,and data service providers. However, the low efficiency of its medium access control (MAC) and physical (PHY) layer protocols restricts its applications to support high data rate multimedia services. Current WLAN systems endure difficulties with the increasing expectations of end users and with volatile bandwidth and delay-boundary demands from new higher data rate services, such as high-definitiontelevi-

sion (HDTV), video teleconferencing, multimedia streaming, voice over IP (VoIP), file transfer, and online gaming. In July 2002, the IEEE 802.11 standard working group established the High-Throughput Study Group (HTSG) with the aim to achieve higher data rate solutions by means of existing PHY and MAC mechanisms [2, 3]. Its first interest was to achieve a MAC data throughput over 100Mb/s using the 802.11a standard. However, the objective proved to be infeasible as the estimated throughput bounds are well below the theoretical maximum link rate because of the existing MAC and PHY overhead [4, 5]. So, in September 2003, the HTSG set off the IEEE 802.11n (“n” represents next-generation) resolution to compose a high-throughput (HT) extension of the current WLAN standard that willincrease transmission rate and reduce compulsory overhead. The main goal of the IEEE 802.11n Task Group (TGn) is to define an amendment that will have maximum data throughput of at least 100 Mb/s, as measured at the MAC data service access point (SAP), and at the same time, to allow coexistence with legacy devices. Some of their recent propositions [6] for the PHY include multiple input multipleoutput (MIMO) antennas with orthogonal frequency division multiplexing (OFDM) and various channel binding schemes. For the MAC, the main developments are the introduction of frame aggregation at the same time as multiple protection schemes have been designed to allow coexistence of “n” with legacy devices. In this article we mainly focus on the MAC frame aggregation methods that TGn has proposed...