IEEE 802.11ac 论文

2011 IEEE 22nd International Symposiile Radio Communications
IEEE 802.11ac: Enhancements for Very High Throughput WLANs
Eng Hwee Ong and Jarkko Kneckt
knowledge, this is one of the first studies to introduce the draft 802.11ac amendment and analyze its potential benefits in terms of MAC performance gains as compared to existing 802.11n devices over various frame aggregation mechanisms. The remainder of this paper is organized as follows. Section II presents an overview of the key mandatory and optional PHY features together with the MAC enhancements of 802.11ac over the existing 802.11n standard. Section III provides the numerical analysis of 802.11ac and 802.11n MAC performances in terms of maximum throughput and MAC efficiency. Section IV validates the numerical analysis with simulation results, and compares the performance analysis between 802.11ac and 802.11n over various frame aggregation mechanisms. Finally, Section V concludes this paper with some directions for future work. II. OVERVIEW OF K EY PHY F EATURES AND MAC E NHANCEMENTS In general, 802.11ac could be seen as a lateral extension of 802.11n in which the two basic notions of multiple input, multiple output (MIMO) and wider channel bandwidth, anchored in 802.11n [5], [6] are enhanced. The basic idea is that the theoretical maximum PHY data rate can be linearly increased by a factor of the number of spatial streams (transmit/receive antennas) or channel bandwidth. In other words, PHY data rate can be doubled (quadrupled) by doubling the number of spatial streams or (and) channel bandwidth. Fig. 1 illustrates the key mandatory and optional PHY features, as well as the MAC enhancements introduced in 802.11ac. Note that the blocks in dashed lines represent the new PHY features and key MAC enhancements of 802.11ac in contrast to 802.11n at the time of writing. A. Mandatory and Optional PHY Features As depicted in Fig. 1, 802.11ac maintains most of the mandatory PHY features of 802.11n such as binary convolutional coding (BCC) for forward error correction, basic MIMO, modulation and coding schemes (MCSs) of 0 to 7, and regular guard interval of 800 ns. The key difference in these mandatory features is the support of 80 MHz channel bandwidth for an approximately twofold increase in data rate as compared to 802.11n where 40 MHz is the largest channel bandwidth. As a result, 802.11ac mandates only a single
Nokia Research Center It¨ amerenkatu 11 – 13, FIN-00180 Helsinki, Finland Email: {eng-hwee.ong, jarkko.kneckt}@
Olli Alanen, Zheng Chang, Toni Huovinen, and Timo Nihtil¨ a
I. I NTRODUCTION In recent years, the continued effort in pursuit of gigabit wireless communications has been most noticeable in the IEEE 802.11 WLAN [1]. For example in 2010, the Wireless Gigabit (WiGig) Alliance, formed by a consortium of industry leaders, has completed the first draft of the WiGig specification [2] that defines a unified architecture to enable tri-band communications over the frequency bands of 2.4, 5, and 60 GHz. The WiGig specification, which aims to achieve multi-gigabit wireless communication in the 60 GHz band, has since been contributed to the new 802.11ad amendment. It is built on the existing 802.11 standard where interoperability with the 2.4 and 5 GHz bands are based on the existing 802.11b/a/g/n and the upcoming 802.11ac standards. In this paper, we focus on gigabit solution in the 5 GHz band where the emerging 802.11ac amendment [3] could provide a maximum PHY data rate of close to 7 Gbps. To be more specific, it promises MAC throughput of more than 500 Mbps for a single user scenario and aggregated MAC throughput of more than 1 Gbps for a multi-user scenario, both utilizing no more than 80 MHz of channel bandwidth. Consequently, 802.11ac is targeted at higher data rate services such as high-definition television, wireless implementation of high-definition multimedia interface (HDMI replacement), and lately the wireless display applications which according to the report in [4] could result in an expected shipment of 50 million wireless video devices in 2015. To the best of the authors’
Magister Solutions Ltd Hannikaisenkatu 41, FIN-40100 Jyv¨ askyl¨ a, Finland Email: {fistname}@magister.fi
Abstract—The IEEE 802.11ac is an emerging very high throughput (VHT) WLAN standard that could achieve PHY data rates of close to 7 Gbps for the 5 GHz band. In this paper, we introduce the key mandatory and optional PHY features, as well as the MAC enhancements of 802.11ac over the existing 802.11n standard in the evolution towards higher data rates. Through numerical analysis and simulations, we compare the MAC performance between 802.11ac and 802.11n over three different frame aggregation mechanisms, viz., aggregate MAC service data unit (A-MSDU), aggregate MAC protocol data unit (A-MPDU), and hybrid A-MSDU/A-MPDU aggregation. Our results indicate that 802.11ac with a configuration of 80MHz and single (two) spatial stream(s) outperforms 802.11n with a configuration of 40 MHz and two spatial streams in terms of maximum throughput by 28% (84%). In addition, we demonstrate that hybrid A-MSDU/AMPDU aggregation yields the best performance for both 802.11n and 802.11ac devices, and its improvement is a function of the maximum A-MSDU size.