A Comparison of IEEE 802.11 Standards

Posted on 13. Feb, 2013 by in Papers

The IEEE 802.11 series of standards for wireless local area network (WLAN) electronic communication and are ubiquitous throughout modern society. This paper will discuss the inception, evolution, implementation, and future of the standards from both a technical as well as regulatory point of view.

1. INTRODUCTION
IEEE 802.11 is a series of standards that cover an implementation of WLAN in the 2.4, 3.7, 5, and 60GHz frequency bands. Theses standards were created, and are maintained by, the IEEE Local Area Network/ Metropolitan Area Network committee. There have been 7 variants (past, present, and planned) of 802.11: 1997, b, a, g, n, ac, and ad. The creation of this series of standards stemmed from a need in the late 1980′s for a standard WLAN solution capable of the expansion happening in the technology field at the time. The implementation in its current form came by way of a 1985 FCC ruling which released a series of frequency bands for industry, scientific, and medical (ISM) purposes. The regulatory restrictions on these bands are such that they are for unlicensed use by RF devices. The intended goal of this was to allow for industrial (such as RF heating and microwaves) as well as medical imaging, which cause electromagnetic interference, to be able to operate without disrupting other forms of wireless transmission. Due to the unlicensed nature of these bands (one does not need a license to operate a station) consumer use of WLAN becomes possible. The standards of 802.11 are maintained, from a commercial standpoint, by the Wi-Fi Alliance, a trade association tasked with promoting the Wi-Fi brand as the WLAN solution, certifying products for compliance to the standards, and controlling the trademarks and logo’s related to the brand and its certified products. Due to the nature of the 802.11 standards, the IEEE and the Wi-Fi Alliance, own patents related directly to the communication and modulation itself, and not specifically to how a device interfaces between the LAN network it is connected to and the actual wireless transmissions itself. As such, there have been numerous cases of patent litigation involving Wi-Fi related patents over the years, none of which help foster innovation in the WLAN field. Wi-Fi is the defacto standard for WLAN computer communication and is ubiquitous throughout modern society as almost all portable, or cordless devices, make use of a version of Wi-Fi for connecting to a network and the internet.

The breakdown of the channels in the 2.4GHz frequency band.

The breakdown of the channels in the 2.4GHz frequency band.

2. IEEE 802.11-1997

The first version of the Wi-Fi standard, 802.11-1997,was released in 1997 and uses the 2.4GHz ISM band for communication. The 2.4GHz band offers both the advantages of fast data rates but also allows for better propagation due to it lower carrier frequency (when compared to 5GHz). The 802.11-1997 standard can achieve data rates of 1-2Mb/s and can cover an indoor operational radius of 20-30m. 802.11-1997 uses uses a frequency hopping (two devices communicating are able to switch, on the fly, between which areas of the frequency band they are communicating on), spread spectrum (deliberately widening the frequency domain being used to communicate in an attempt to mitigate the effects of natural interference), implementation of carriers sense multiple access (CSMA) (based on the principle “sense before transmit” and “listen before talk”). Though similar techniques are still used in more recent implementations the exact protocols and modulation techniques in this standard go almost completely unused in the versions of the standard in use today. 802.11-1997 also included the Wired Equivalent Privacy (WEP) algorithm. Though 802.11-1997 was a certified standard there was limited interoperability between products. Due to this 802.11-1997 in not compatible with any of the future standards and was quickly, and thoroughly supplemented by 802.11b which followed in late 1999.

3. IEEE 802.11a
Following soon after 802.11-1997 was 802.11a which was released in September 1999. This standard was designed to utilize the 5GHz ISM band, which increased the maximum possible data rate to 54Mb/s. This speed increase was possible due to the increased carrier frequency as well as a change in modulation. The use of Orthogonal Frequency Division Multiplexing (OFDM), where many transmissions are made simultaneously on small sub-divisions (in this case 52) of the main band, thus allowing for a much higher throughput. These 52 sub-carrier bands were repeated across the available 12/13 (and up to 24 in some countries) channels used by Wi-Fi in the 5GHz range. The use of the 5GHz band though has its advantages and disadvantages. Where 2.4GHz is grossly over-saturated, the 5GHz band is relatively empty of electromagnetic interference, both natural and from other devices, meaning that the signal does not get drowned out by other communication. However, the disadvantage of using a 5GHz carrier frequency is that it is more susceptible to decreased propagation as it is more easily absorbed by walls and other solid objects (due to the loss being equal to the square of the signal frequency). This means that the effective range of 802.11a is similar to versions using 2.4GHz when you factor in the advantages of OFDM in mitigating these losses. The use of a higher frequency also had an impact on the antenna design, which could now be smaller while achieving higher gain. The use of the 5GHz band also caused some regulatory issues in that not all regions supported the band when 802.11a was being released. 802.11a relied mainly on WEP for security up until WPA (which was designed to be compatible with legacy WEP devices) was released in 2003. Due to the difference in frequency between 802.11a and b they are not directly compatible. Due to increased cost and difficulty in the manufacture the devices for 5GHz the release of 802.11a fell behind those using 2.4GHz which was cheaper for consumers at the time. However, 802.11a found great success in the business market as cost was less of a concern when looking to achieve the higher speeds. Though no longer nearly as popular as a stand-alone solution, the use of 5GHz and improved versions of 802.11a (and its use of OFDM) are still used in dual-band devices today.

4. IEEE 802.11b
The IEEE 802.11b standard is the third iteration of the Wi-Fi standard, and laid the foundation for most current versions. The standard returned to the original 2.4GHz ISM band (which was cheaper to make than those using 5GHz) and is capable of up to 11Mb/s peak data rate, though in practice 5.9Mb/s over TCP and 7.1 over UDP is the maximum. This limitation was due to interference issues in the 2.4GHz band, the limitations of the lower frequency of the carrier band than in 802.11a, and the limitations of the use of the legacy CSMA modulation technique. 802.11b also makes use of Direct-sequence Spread Spectrum (DSSS) modulation, and Complementary Code Keying (CCK) in its modulation. Though the range of 802.11b depends on the output power of the transmitter, the operating environment, as well as the sensitivity of the receiver, one can expect to achieve a range of about 35m. There are 14 channels used by Wi-Fi in the 2.4GHz range, each 22MHz wide, and ranging from 2.401GHz – 2.495GHz with channels 1-11 being useable in Canada and the USA, 12-13 in most other countries, and 14 only available in Japan. 802.11b is capable of Adaptive Rate Selection (ARS) where a Network Interface Card (NIC) can scale between 11, 5.5, 2, and 1Mb/s in order to decrease the packet loss rate. Security on 802.11b relied primarily on the WEP security algorithm until the release of WPA in 2003. Though the upgrade to WPA was possible on all devices that shipped with 802.11b and WEP the feasibility of the upgrade meant that many products, released pre-2003, remained WEP-only. The biggest problem with 802.11b, and the reason an attempt was made with 802.11a to fix it, is that the 2.4GHz band has unbelievable interference and user saturation, causing signal loss issues for the majority of devices. The lower cost of components for the 2.4GHz band compared to its 5GHz counterparts caused 802.11b to gain significant popularity. Though there is no compatibility with the original standard, even with the modulation method being the same, 802.11b was the foundation for the 2.4GHz component of both 802.11g and 802.11n, both of which are backwards compatible with 802.11b.

5. IEEE 802.11g
Building on the foundation developed by 802.11b, the IEEE released the 802.11g standard in 2003. 802.11g use the 2.4GHz band as well as the 14 channels from 802.11b. Through the use of OFDM, which was pulled from the 802.11a standard, 802.11g is able to achieve maximum raw data rates of 54Mb/s, or a net throughput of 19Mb/s. 802.11g is fully backwards compatible with 802.11b, and when using ARS or communication with a legacy device at 1Mb/s or slower, OFDM is swapped for CCK (which is required for the legacy communication). This increased speed and backwards compatibility was a win-win for everyone and resulted in an extremely fast adoption rate among consumers and businesses. By mid 2003 most access points and NIC’s were equipped for either dual or triple band use on 802.11a,b,g. Unfortunately the change in modulation techniques didn’t nothing to mitigate the existing interference or saturation issues already a problem with 802.11b (and could only have been exacerbated by high use). In an attempt to avoid as much direct interference as possible, it became commonplace to use the 3 non-overlapping channels in North America (1, 6, 11), and the 4 in the Europe (1, 5, 9, 13), each with 25MHz and 20MHz of separation respectively. With the introduction of WPA as a replacement for WEP as the security standard in 2003, and its subsequent replacement by WPA2 in 2004 the security on 802.11g was significantly improved over most 802.11b devices. WPA brought with it Wi-Fi Protected Setup (allowing for one-touch pairing), the Temporal Key Integrity Protocol (TKIP) which updated the 40-104-bit encryption used in WEP with a 128-bit encryption, greatly reducing the security risks which plagued WEP. The use of Cyclic Redundancy Check (CRC) for message integrity comparison was replaced with a much more secure system called Michael, to verify the integrity of packets. 802.11g was a huge improvement over 802.11b and has become so ubiquitous that it is still in common use over a decade later. With the foundation for modern Wi-Fi set by 802.11g the 7 year wait for the release of 802.11n only helped solidify the position of 802.11g in the marketplace.

6. IEEE 802.11n
In 2009, 7 years after the release of 802.11g the next iteration of the Wi-Fi Standard was released in the form of 802.11n. This new standard stood to improve upon the shortcomings of both 802.11a and 11g by combining their strengths with improvements in modulation and antenna design while utilizing 2.4 and 5GHz. 802.11n is capable of a raw data rate up to 600Mb/s (though practical speed are reduced slightly due to error checking) by making use of 4 40MHz-wide stream channels. 802.11n uses a completely overhauled modulation technique with the inclusion of multiple-input multiple-output (MIMO) and a modernized frame aggregation approach. MIMO uses multiple antenna, and Spatial Division Multiplexing (SDM), to separate the data into different streams, each going to an independent antenna, all contained within the assigned spectral channel. Though SDM significantly increases the throughput by using 4 antenna working simultaneously it also causes the cost of the device to go up as not only are 4 antenna needed but also 4 analog-to-digital converters, one for each antenna. While use of 40MHz-wide channels allows for greater throughput it also increases the possibility of interference with more devices operating in the same band as 40MHz-wide channels are severely restrictive on the possible separation of channels, causing further interference. With the release of WPA2 in 2004 802.11n is fully supportive of the standard as well as WPA-802.1X enterprise network security. With 11g having become so popular the transition to 802.11n was slower that anticipated as people were initially reluctant to upgrade. The release of a draft version 802.11n in 2007 gave early adopters and eager corporations and chance to deploy compatible products early. After nearly 5 years since its release 802.11n has the majority of the market share and is still growing while prices are still coming down. 802.11n was released with the intention of being backwards compatible with not only 11b and 11g but also 11a now that 802.11n supports both 2.4 and 5GHz frequency bands. 802.11n devices can run in mixed mode which, among many features, allows data transmissions to be embedded in a legacy format to support 802.11a, b, g (see Fig. 2). Unfortunately these protections cause large setbacks in the maximum throughput of the device, reducing some of the advantages the new system. The backwards compatibility, and continued reliance on the 2.4GHz band are the biggest weaknesses of 802.11n and were key considerations when creating its successor.

 

Figure 2 shows the breakdown of channels in 802.11n when when working in mixed mode.

Figure 2. The breakdown of channels in 802.11n when when working in mixed mode.

 

7. IEEE 802.11ac

As file sizes and internet connections continue to increase in speed it is only natural that WLAN keeps pace with that trend. In late 2012 IEEE 802.11ac received approval its 4.0 draft form (with planned WLAN working group approval in late 2013). 802.11ac is the 6th iteration of the IEEE 802.11 standard and building on the designs of 11a and 11g, uses the 5GHz band to achieve 500Mb/s per stream with a theoretical max of 1Gb/s using up to 8 MIMO streams, each 160MHz wide. The modulation techniques used are similar to its predecessors in the use of MIMO (in this case for multiple simultaneous user) and SDM (from 11n) and the use of OFDM (from 11n and 11a) are key to the increase in speed. In keeping with the backwards compatibility for 802.11a and 11n, devices are able to scale back the channel width to support 20/40/80/160MHz wide channels (see Fig. 3), which will result in slower speeds. When it comes to wireless security 802.11ac supports the latest WPA2 personal and enterprise protection. Due to 802.11ac only have been certified in December 2012 there are few, if any, products currently available which support it. This will change over time as people naturally upgrade their network or go looking for faster speeds. The biggest threat to a speedy migration to 802.11ac is people getting confused about the support for their legacy hardware. Though it is true that all 802.11a devices will work, only dual-band 802.11n devices will because the single-band models only have support for 2.4GHz, which is not compatible with 11ac. 802.11 has the potential to keep Wi-Fi at the forefront of WLAN technologies but, there is no way to predict its success until the technology starts making its way into more consumer products.

Figure 3 shows the scaling ability of the channels in 802.11ac, from 20MHz to 160MHz.

Figure 3. The scaling ability of the channels in 802.11ac, from 20MHz to 160MHz.

8. IEEE 802.11ad
Advancements in technology are always happening, and Wi-Fi is no exception. The creation of the Wireless Gigabit Alliance (WiGig) was announced May 2009, with the release of the first draft of IEEE 802.11ad happening in December 2009. WiGig will allow for communication at up to 7Gb/s and will operate on the 2.4, 5, and 60GHz bands. The intention is to maintain backwards compatibility with legacy versions, although exact support has not yet been determined. WiGig has plans to support wireless DiplayPort, High-bandwidth Digital Content Protection 2.0, HDMI mapping, and many other high-bandwidth audio/video applications. Though this version is not nearly ready for release it is slated to reach consumers around 2015-2016 by which time gigabit wireless communication should be a necessity.

9. Conclusions
IEEE 802.11 is a series of 7 standards that cover the implementation of WLAN network on the 2.4, 3.7, 5, and 60 GHz bands. Each of these standards (802.11-1997, a, b, g, n, ac, ad) brought something new to the world of WLAN. As the different versions cover a 15 year time-span there is no way to accurately compare them. One could choose to consider the level of innovation and the jump in speeds each introduced relative to their release date, but to what end? This paper does not intend to reach verdict on which of the standards is better because comparing them would be unfair. Instead it is intended to summarize the key aspects of each iteration, and point out flaws in the overall set of standards, their designed, implementation, and conditions out of their control. Of the issues currently plaguing Wi-Fi the use of the 2.4GHz spectrum band is one of the most problematic. Due to the congested nature of both that band, and the surrounding spectrum, communication is made overly complicated compared to the use on other bands. That being said there is no perfect alternative because lower carrier frequencies have an inherent data rate disadvantage while higher frequencies encounter propagation issues. There is no perfect iteration of the Wi-Fi standard, but with each new version improvements are made, adapting and updating with the ever-changing technological climate.

REFERENCES

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