IEEE 802.11ac Standard


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This Document is describing the features of new wireless standard 802.11ac

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IEEE 802.11ac Standard

  1. 1. Registration Number: CUPBMTECH-CSSETCST2013-1401 CBS.503 IEEE 802.11ac: Wi-Fi Standard Harsh Kishore Mishra M.Tech. Cyber Security Centre for Computer Science & Technology Abstract - Wi-Fi has become such an amazingly successful technology because it has continuously advanced while remaining backwards compatible. 802.11ac can be considered the next step after 802.11n, along the path running from 11b, to 11a/g, then 11n, and now 802.11ac. 802.11ac has the capability to maintain a higher level of performance at any range, compared with its predecessors and it is likely to be introduced along with related amendments to 802.11 including video-related improvements in 802.11aa (video transport streams) and 802.11ad (very high throughput, short-range at 60 GHz). 802.11ac solves mobile devices problems by significantly improving range and providing 3 times the performance, while preserving the battery life. The goal is to continue the thrust of 802.11n to extend rates and throughput. In short, 802.11ac will have the capability to handle our insatiable demand for robust, high speed connectivity – from a wide range of devices. This paper explains the latest advance in Wi-Fi, i.e. 802.11ac, which provides the next step forward in performance. Keywords—Wi-Fi, 802.11ac, IEEE Standards, Wireless LAN Standard, Wi-Fi Advancements I. INTRODUCTION The First Wi-Fi enabled devices were introduced in 1997. Over the years, Wi-Fi has become ubiquitous on laptop computers, tablets, televisions, video game consoles, and smart phones. Every few years since the 802.11b amendment was ratified, the industry has released successive amendments increasing Wi-Fi data rates and capabilities, but even the latest Wi-Fi systems are able to interoperate with 1999 equipment built to the original standard. Luckily the IEEE 802.11 working group and the Wi-Fi Alliance, the industry bodies standardizing Wi-Fi are already working on 802.11ac, the successor standard to 802.11n and its corresponding interoperability certification program. The IEEE 802.11ac amendment is expected to achieve final IEEE ratification at the end of 2013 [1]. 802.11ac is an improved version of 802.11n offering higher speeds over wider bandwidths. 802.11ac will be backward-compatible with 802.11n networks operating in the 5GHz range and is expected to offer dramatic improvements in Wi-Fi reliability, throughput and range. The increase in speed is achieved by providing wider frequency bands, faster processing, and multiple antennas.802.11ac is worth having when it is available, and especially when the client mix converges to being dominated by 802.11ac devices. II. 802.11ac STANDARD 802.11ac represents the fifth generation of IEEE 802.11 WLAN standards. The IEEE 802.11 standard refers to the PHY rates of 802.11n as high throughput (HT) and those of 802.11ac as very high throughput (VHT) while those prior to 802.11n are non-HT [1]. The important new technologies in 802.11ac should be considered as extensions of the physical layer wireless techniques pioneered in 802.11n, notably using multiple antennas at the transmitter and receiver to exploit multiple input/multiple output (MIMO) for parallel delivery of multiple spatial streams. The 5 GHz channel of 802.11ac is much cleaner with less interference, with 23 non- overlapping channels − 8 times more than what is available in the 2.4 GHz spectrum − which makes it far more suitable for applications such as video streaming and gaming, which are very sensitive to packet loss and delay [4]. It is expected to deliver a data rate connection of at least three times that of 802.11n. Many of the algorithms of 802.11n are being reused but enhanced, with 802.11ac, which should make the technology easy to fold into existing networks [3].
  2. 2. Registration Number: CUPBMTECH-CSSETCST2013-1401 CBS.503 It’s also better equipped to handle the seemingly boundless growth in the number and type of Wi-Fi devices (even many appliances are becoming Wi-Fi equipped), as well as the corresponding traffic that comes with that growth. 802.11ac will significantly enhance the user experience by improving the playback quality to any point throughout the house. III. 802.11ac TECHNOLOGY Among the technologies that 802.11n and 802.11ac have in common [3]: Channel bonding for wider channels and greater throughput Multiple input, multiple output (MIMO) antenna technology to avoid multipath interference problems and improve data throughput Air time fairness to prevent overall network performance from “falling back” to the transmission speed of the slowest device on the network. In other words, just as an 802.11a client joining a 5GHz 802.11n network no longer degrades an 802.11n client’s performance in the 5GHz band, a 5GHz-band 802.11n client is not expected to degrade the performance of an 802.11ac client. This section gives a brief overview of the new features and technologies in 802.11ac [1]. Wider RF channel bandwidths: it is clear that doubling the RF channel bandwidth allows twice the data throughput, representing a significant improvement. The 40-MHz channel of 802.11n is extended to 80- and 160-MHz in 802.11ac. There are practical obstacles to using these wider channels, but now that they are defined, equipment will be developed to use them. The details: • 80-MHz and 160-MHz channel bandwidths are defined • 80 MHz mandatory, 160 MHz optional • 80-MHz channels are two adjacent 40-MHz channels but with tones (sub channels) in the middle filled in. • 160-MHz channels are defined as two 80-MHz channels. The two 80-MHz channels may be contiguous or noncontiguous. More spatial streams: 802.11n defines up to four spatial streams, although there are to date few chips and APs using more than three streams. 802.11ac extends this to eight spatial streams. There will be a number of consequences. A divergence between chips and equipment for APs (with four+ antennas) and clients (typically with < four antennas) will occur due to cost, physical size and power constraints. APs will grow by adding antennas, while clients will become more capable by implementing multiple spatial streams and beam forming features behind a smaller number of antennas. This divergence will create opportunities for multi-user MIMO, where a high-capacity AP can communicate with multiple, lower-throughput clients simultaneously. • Support for up to eight spatial streams (vs. four as in 11n) in both single-user (SU) and multi- user (MU) MIMO • No more than four spatial streams per client in a MU transmission • For each user in an MU transmission, all spatial streams have same MCS • In single-user transmission, all spatial streams have same MCS Beamforming: Another feature that is expected to boost the reliability of the connection at required speed and range is the much improved “beamforming” standard, which provides directional signal transmission and reception. Previous standards can only receive and transmit omnidirectional Figure 1: 802.11ac Beamforming Technology
  3. 3. Registration Number: CUPBMTECH-CSSETCST2013-1401 CBS.503 signals, which are subject to significant levels of interference, due to the fact that the signals are transmitted indiscriminately in every possible direction. With beamforming, there’s an understanding of the relative location of the device, and the signal is correspondingly strengthened in that direction. Multi-user MIMO (MU-MIMO): Thus far, all 802.11 communications has been point-to-point (one- to-one) or broadcast (one-to-all). With 802.11ac, a new feature allows an AP to transmit different streams to several targeted clients simultaneously. This is a good way to make use of the expected surplus of antennas at APs over clients, and it requires beam forming techniques to steer signal maxima over the desired clients while minimizing the interference caused at other clients. For example, if an AP wishes to use MU-MIMO for clients A and B simultaneously, it will beam form the transmission for A so it presents a maximum at A but a minimum at B, and vice versa for the transmission for B. There are some new terms associated with this: • Space Division Multiple Access (SDMA): A term for streams not separated by frequency or time, but instead resolved in space like 802.11n-style MIMO. • Downlink MU-MIMO where the AP transmits simultaneously to multiple receiving devices is an optional mode. Modulation and coding: As semiconductor radios become ever-more accurate, and digital processing ever-more powerful, 802.11ac continues to exploit the limits of modulation and coding techniques, this time with the leap from 64-quadrature amplitude modulation (QAM) to 256-QAM. 256-QAM, rate 3/4 and 5/6 are added as optional modes. For the basic case of one spatial stream in a 20 MHz channel, this extends the previous highest rate of 802.11n from 65 Mbps (long guard interval) to 78 Mbps and 86.7 Mbps respectively, a 20% and 33% improvement. (Note that 802.11ac does not offer every rate option for every MIMO combination). Below is a summary of additional elements and features. • Single sounding and feedback method for beam forming (vs. multiple in 11n). This should enable inter-vendor beam forming to work with 802.11ac devices; the diversity of optional feedback formats in 802.11n resulted in differing implementations and stifled adoption. • MAC modifications (mostly to adapt to above changes) Figure 2 : Single and Multi User MIMO Figure 3 : How 802.11ac accelerated 802.11n
  4. 4. Registration Number: CUPBMTECH-CSSETCST2013-1401 CBS.503 • Coexistence mechanisms for 20-, 40-, 80- and 160-MHz channels, 11ac and 11a/n devices. Extensions of 802.11n techniques to ensure that an 802.11ac device is a good neighbor to older 802.11a/n equipment. • Non-HT duplicate mode duplicates a 20-MHz non-HT (non-802.11n) transmission in four adjacent 20-MHz channels or two sets of four adjacent 20-MHz channels. Sometimes termed quadruplicate and octuplicate mode. IV. ADVANTAGES OF 802.11ac The main advantages of the standard – speed, reliability, and quality. But apart from the “cool factor”, or advancement solely for the sake of advancement, why should a user consider moving to the new standard? What needs can it meet better or more easily than the current standard? The answer is that the new standard has two main advantages for the everyday user – it improves current use cases and paves the way for future use cases. In addition to meeting today’s growing needs such as streaming video, the new standard will also enable a variety of new use cases such as simultaneous HD video streams to multiple receivers, wireless displays, and large file wireless transfers. It’s also better equipped to handle the seemingly boundless growth in the number and type of Wi-Fi devices (even many appliances are becoming Wi-Fi equipped), as well as the corresponding traffic that comes with that growth. In short, 802.11ac will have the capability to handle our insatiable demand for robust, high speed connectivity – from a wide range of devices. 802.11n does include many options with reduced value. 802.11ac takes a very pragmatic approach to them. If a “useless” option is used and affects a third- party device, then typically 802.11ac forbids an 802.11ac device (operating in 802.11ac mode) from using the option. If a “useless” option has not been used in 802.11n products or only affects the devices that activate the option, then the feature is not updated for 802.11ac but is instead “left to die.” Another area of concern that will be addressed by 802.11ac is the Wi-Fi performance for mobile devices like Smartphones and tablets. Dropped connections, poor quality connections, and limited mobility are major areas of frustration for users today. 802.11ac solves these problems by significantly improving range and providing 3 times the performance, while preserving the battery life. Wireless LAN sites will see significant improvements in the number of clients supported by an access point (AP), a better experience for each client, and more available bandwidth for a higher number of parallel video streams. Even when the network is not fully loaded, users see a benefit: their file downloads and email sync happen at low lag gigabit speeds. Also, device battery life is extended, since the device’s Wi-Fi interface can wake up, exchange data with its AP, then revert to dozing that much more quickly [2] . Speed is largely irrelevant if the connection lacks reliability. For example, most users have experienced the irritating video buffering during video playback, which causes frozen or jittery screens. By increasing the bandwidth capacity and improved processing, 802.11ac enables far more bandwidth to be available for consumption by wireless devices, which helps avoid interference, and improves the speed for demanding applications such as hi-definition video streaming. The result is more effective coverage with fewer dead zones. The 3X speed improvement achieved by the new standard means that the 450 Mbps performance from today’s fastest 3 antenna 802.11n device can be achieved by single antenna 802.11ac device – with similar power consumption. This means that a typical tablet with single antenna 802.11n 150Mbps Wi-Fi can now support 450 Mbps with 802.11ac − without any increase in power consumption or decrease in battery life [4]. Table 1: Wireless Performance Comparison Antenna Configuration 802.11n 802.11ac Single Stream 150 Mbps 450 Mbps Dual Stream 300 Mbps 900 Mbps Triple Stream 450 Mbps 1.3 Gbps
  5. 5. Registration Number: CUPBMTECH-CSSETCST2013-1401 CBS.503 Key advantages of 802.11ac over 802.11n [4]: • Gigabit speed wireless with approximately 3 times the performance of 802.11n. • Better performance at any range with fewer dead spots and backward compatibility. • More reliable connections for media streaming with beam-forming. • More Wi-Fi bandwidth on your mobile. • Only utilizes the 5 GHz Band, which is less prone to interference. V. CONCLUSION 802.11ac will be backward-compatible with 802.11n networks operating in the 5GHz range and is expected to offer dramatic improvements in Wi-Fi reliability, throughput and range. There’s a fine balance between accommodating the high density of these devices with enough channels to avoid co channel interference and reaping the aggregate throughput benefits of the greater channel widths of 80MHz and, eventually, 160MHz, which have been specified by 802.11ac standards [3]. 801.11ac is expected to be ratified by IEEE late 2013. The earliest, pre-ratified products are expected late 2012 and will likely ship for the home/consumer market. From there, it’s expected that the rollout of new IEEE 802.11ac devices will take between one and three years. By 2015, according to experts, all new Wi-Fi products coming to market are expected to be based on 802.11ac technology. 802.11ac- enabled products are the culmination of efforts at the IEEE and Wi-Fi Alliance pipelines. IEEE 802.11ac delivered an approved Draft 2.0 amendment in January 2012 and a refined Draft 3.0 in May 2012, with final ratification planned for the end of 2013. In parallel, the Wi-Fi Alliance is expected to take an early IEEE draft, most likely Draft 3.0, and use that as the baseline for an interoperability certification of first-wave products in early 2013. Later, and more in line with the ratification date of 802.11ac (that is, after December 2013), the Wi-Fi Alliance is expected to refresh its 802.11ac certification to include testing of the more advanced 802.11ac features [2]. REFERENCES [1] Aruba Networks, Inc. (2012). 802.11ac In-Depth. Sunnyvale, California, USA. [2] Cisco Systems, Inc. (2012, August). 802.11ac: The Fifth Generation of Wi-Fi. San Jose, CA, USA. [3] Motorola Solutions. (2012, July). What You need to know about 802.11ac. USA. [4] NETGEAR. (2012). Next Generation Gigabit Wi-Fi - 802.11ac. USA.