Metropolitan and Regional Wireless Networking: 802.16, 802.20 and 802.22

Justin Thiel [justin@binaryllama.net]

Abstract

Table of Contents

• 1. Introduction
• 2. 802.16: WiMAX and Mobile WiMAX
  • 2.1 802.16a/d: WiMAX
    • 2.1.1 802.16a/d PHY Layer Overview
    • 2.1.2 802.16a/d MAC Layer Overview
  • 2.2 802.16e: Mobile WiMAX
    • 2.2.1 802.16e PHY Layer Overview
    • 2.2.2 802.16e MAC Layer Overview
  • 2.3 WiMAX vs. Mobile WiMAX Comparison
• 3. 802.20: Mobile Broadband Wireless Access (MBWA)
  • 3.1 802.20 PHY Layer Overview
  • 3.2 802.20 MAY Layer Overview
  • 3.3 802.20 vs 2.5/3G Cellular Networks
• 4. 802.22: Wireless Regional Area Networks (WRAN)
  • 4.1 802.22 PHY Layer Overview
  • 4.2 802.22 MAC Layer Overview
• Summary
• References
• List of Acronyms

1. Introduction

More recently, with the arrival of 2.5G cellular technology consumers have begun to realize the power of having Internet access anywhere in the world. For the first time, people are now able to check their e-mail from their car and make "micro" purchases directly from their cellular telephones. Cellular standards, however, are by no means universal and the charges for accessing cellular data services can quickly add up. Some of these costs result from the fact that current cellular services were not designed to transmit packetized data, but the most important factor driving up access costs is the fact that no viable competing services exist [Klerer03].

The IEEE is well aware of these issues and has taken steps to create the 802.16, 802.20 and 802.22 working groups in order to define new wireless standards which can provide the necessary technology to support fully wireless ISP's as well as compete with current and next generation cellular technologies [Goth04, Santhi06]. The IEEE 802.16 working group, formed in 1999, is the most mature of the next generation wireless standard developing bodies and has developed both fixed (802.16a/d) and low-mobility (802.16e) broadband wireless access systems operating in "metropolitan" areas that are approximately 1 to 5 km in size [Nichols04, Fong04]. The IEEE 802.20 working group, formed in 2002, seeks to extend the mobility support provided by 802.16e to provide access at speeds up to 250 km/h across metropolitan-sized areas [Klerer03]. The 802.22 standard, on the other hand, aims to provide broadband access across entire "regions" that are up to 100 km in radius [Chouinard04]. Figure 1 provides a clear picture of where 802.16, 802.20 and 802.22 fit in with the other IEEE wireless networking standards.

Figure 1: Classifications and Ranges of the Various IEEE Wireless Networking Standards

In all of three of these working groups, committee members are working towards developing flexible and open standards for next-generation wireless networking. In doing so, the IEEE hopes that their work becomes the global standards for long-distance wireless networking in much the same way the 802.11 technologies have become the defacto standards for wireless local area networks (WLANs). In the rest of this paper an overview the of 802.16, 802.20 and 802.22 standards will be provided, along with a discussion of the possible markets for these technologies and the type of service end-users should expect to receive.

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2. 802.16: WiMAX and Mobile WiMAX

From 2002 to 2004, the working group focused on developing a fixed-broadband non-line-of-sight (NLOS) standard referred to as 802.16a/d (depending on the implementation used) intended for use by consumers as a replacement for the 802.11b-based Wireless ISP's that first emerged during the same time period. The standard aims to provide wireless access at DSL-like speeds of 1.5 Mbps downstream and 384 Kbps upstream [Goth04]. In terms of marketability, the install base for the technology is expected to be upwards of 20 Million by 2009 [Pipeline05].

Despite the significant market share projected for 802.16a/d-based products, it is 802.16e that has generated the most industry hype of all the WiMAX variants. This standard was recently approved in December 2005 and builds upon the 802.16d standard to provide low-mobility (60 Km/h or less) wireless Internet access that uses a Cellular-like handoff mechanism to extend the range of the system [Santhi06, Fong04]. Although the standard has just recently been approved, a variant of it called "WiBro" is set to be deployed in Korea in the second-half of 2006 [Robinson06]. Figure 2 provides a summary of the markets that 802.16, 802.16a/d and 802.16e hope to service.

Figure 2: Target Markets for the 802.16, 802.16a/d and 802.16e Standards

To ease consumer confusion in regards to the alphabet soup that the 802.16 standard has become, the WiMAX Forum was founded as a non-profit corporation in June of 2001 by various manufacturers of 802.16-supporting hardware to define interoperability standards and to encourage cooperation between competing hardware vendors. Recently, the forum has begun certifying both provider and end-user devices based on the 802.16d standard from vendors such as Wavesat and Aperto Networks [WiMAXForum06a]. Prior to this, a number of "pre-802.16d" devices have been made available but were not widely deployed [Skylight05]. Certified devices based on the 802.16e standard are expected to be available by the end of 2006.

2.1 802.16a/d: WiMAX

2.1.1 802.16a/d PHY Layer Overview

2.1.1.1 802.16a/d Frequency Ranges and Duplexing

The original 802.16 standard operates on licensed bands in the 10 to 66 GHz range over 20, 25 or 28 MHz channel widths and requires LOS between the base station and the user terminal to work properly. The wide channels used by the system allow data rates from 33 up to 134 Mbps to be achieved, but due to the use of high frequency bands the system is limited to a range of 2 to 5 km around the base station [Legg04]. The decision to make use of licensed and somewhat wide frequency bands clearly illustrates the fact that 802.16 is intended for use at the enterprise level where dedicated high speed access is required and the monetary investment needed to obtain a license would put the cost of service far out of the range of most consumers.

In contrast to 802.16, 802.16a/d operates on both licensed and unlicensed bands in the 2 to 11 GHz range over 1.5 to 20 MHz wide channels. The use of unlicensed and lower frequency bands allows for NLOS access and makes it less expensive to both manufacture equipment and to create the infrastructure required to operate a network. This, in turn, lowers the cost of access for end-users and thus makes the service more appealing to the consumer market that it was designed for. As an added bonus, the lower frequencies utilized by the system increases the range of the service to almost 10 km, therefore allowing a single base station to serve a larger area than is possible with 802.16. An aggregate bandwidth of 75 Mbps is supported if a 20 MHz channel width is used, but the actual amount a single user receives is largely dependant on how many users a base station is supporting [Nichols04].

Both 802.16 and 802.16a/d have optional support for a channel bonding feature. This allows service providers to chain multiple channels together in an effort to support more users with a single tower or to provide higher access speeds. Up to five channels can be bonded together to provide an aggregate bandwidth of 350 Mbps (in 802.16a/d), but in order to do so both the provider and user equipment need to support the feature [Nichols04].

2.1.1.2 802.16a/d Transport, Modulation and Coding

In terms of modulation, both 802.16 and 802.16a/d support methods from BPSK up to 64QAM. For encoding purposes, Reed-Solomon coding combined with an inner convolutional code is standard, while a variety of turbo-coding mechanisms can optionally be used to increase connection throughput. Due to the hardware complexity of implementing turbo coding, however, not many 802.16a/d products are expected to make use of it [Ghosh05].

In order to cope with changing airlink conditions such as interference, competing users and user distance from the base station, adaptive modulation and coding techniques are supported. This enables a user to, for instance, switch from higher to lower modulation methods in order to reduce the error rate of packets sent over the connection. The spectral efficiency (coding rate) of the encoding method used can also be manipulated to achieve similar results [Ghosh05].

2.1.1.3 802.16a/d Advanced Transmission Mechanisms

One such feature supported by the 802.16a/d standard is the adaptive antenna system (AAS). AAS requires OFDM or OFDMA transport modes, and utilizes multiple transmitting antennas to divide the subcarriers transmitted into segmented groups that are then each transmitted over a unique antenna. In doing so, the subcarriers can be assigned on a "geographic" basis and better tune the transmitted signal towards the receiving users in order to reduce their susceptibility to interference. Users can, in turn, provide feedback to the base station in order to properly beam-form their signals and fine-tune the connection [Ghosh05].

In addition to supporting AAS, the 802.16a/d standard also allows for the use of Space Time Block Codes (STBC). Like AAS, STBC requires the use of multiple transmission antennas to increase the diversity of the signal and reduce susceptibility to interference. Unlike the beamforming used in AAS, however, STBC uses multiple antennas to send out time shifted copies of the same signal. The receiver then stitches together the shifted signals to form their best estimate of the signal that was actually sent [Ghosh05].

While STBC uses multiple transmitting antennas to increase signal diversity, another supported antenna option known as Spatial Multiplexing (SM) or Multiple-Input/Multiple-Output (MIMO) uses multiple transmitting and receiving antennas to transmit different sub-streams of data and increase throughput. A feedback mechanism similar to the one utilized in AAS is used to fine-tune the transmitted signal. In theory, this method of transmission should increase the data rate of the connection, but in reality due to the reduced resiliency to interference caused by using MIMO, data rates are often lower than those achieved by a STBC-based system. To combat this, STBC and MIMO can be combined into a single system. Doing so, however, can require an inordinate number of both transmitting and receiving antennas to be effective [Ghosh05].

2.1.2 802.16a/d MAC Layer Overview

The MAC layer itself is actually split into two portions: a convergence-specific sublayer and a common-part sublayer. The convergence-specific sublayer is unique to a particular PHY implementation and differs depending on the type of network the end user wishes to connect to (such as Ethernet or ATM). The common-part sublayer, on the other hand, is the same regardless of what type of network the user wishes to transmit across and is responsible for handling functions such as transmission scheduling and QoS support [Ghosh05].

2.1.2.1 802.16a/d Connection Establishment and Framing

Figure 3: Time Division Duplexed WiMAX OFMDA Frame

When a user terminal is first powered-on it scans a set a known frequencies for a supporting BS. When a BS is found, the user attempts to establish a connection. In order to do so, the user watches for frame transmission preambles that are sent prior to each frame. As can be seen in Figure, the preamble is followed by a ranging period used to tune the power usage of a terminal and associate the user terminal with the base station [Kwon05].

In terms of data transmission, downlink frames from the BS to users are simply broadcast to all user terminals within range [Cho05]. Special care is taken when AAS or MIMO is used to ensure that beam-formed data streams are directed at the proper users. Downlink frames are themselves preceded by a DL-MAP (Downlink Map) that specifies which portions of the transmitted frames are for which users. Each user in range of the BS receives this map and then can selectively copy any data in the proceeding frame that is intended for the user [Kwon05].

For uplink transmission from users to the base station, transmission slots are allocated via a small contention period at the start of the uplink frame. Unlike in 802.11, however, once a user is allocated one or more transmission slots they are allowed to keep them without going through contention again the next time they wish to transmit. Transmission slots are granted exclusively by the BS and the ordering of assignment within a uplink frame is sent via a UL-MAP (Uplink Map) message with a format much like that of the DL-MAP used for downlink connections. The UL-MAP is sent prior to the start of the uplink frame to give user terminals the chance to synchronize their connections and prepare for data transmission [Cho05, Kwon05].

In allowing users to reserve uplink transmission slots, the ability to provide guaranteed bandwidth is provided. In effect, this enables a provider to offer a DSL or Cable-like connection over a wireless medium. This is much different than is the case with a 802.11b/g-based network where all transmissions are contention based and the BS only plays a passive role in deciding who is allowed to transmit uplink traffic [Cho05, Goth04].

2.1.2.2 802.16a/d QoS Support

Signaling methods are also provided for requesting rtPS, nrtPS and BE-levels of traffic support but inter-frame support for these transmission classes is not provided. Furthermore, no sort of admission control system is provided for determining which user should be allow to request what levels of service and how large those requests should be allowed to be. As a result, a large portion of the QoS support defined in 802.16a/d is left up to vendors to implement as they choose [Cho05, Ghosh05].

2.1.2.3 802.16a/d Security Features

2.2 802.16e: Mobile WiMAX

2.2.1 802.16e PHY Layer Overview

2.2.1.1 802.16e Frequency Ranges and Duplexing

2.2.1.2 802.16e Transport, Modulation and Coding

In accordance with the 802.16a/d standards on which 802.16e is based, support for adaptive modulation and encoding is also provided. To provide for more flexible encoding an advanced Low Density Parity Check (LDPC) method is provided in addition to the convolutional and turbo coding mechanisms that 802.16a/d define. LDPC is designed to provide higher throughput versus typical turbo codes with a minimum complexity. With LDPC codes in place, it is possible to provide up a 5/6 code rate (6 bits coded for every 5 of actual data) which is somewhat better than the 3/4 code rates previously possible [Classon05, Xu05].

2.2.1.3 802.16e Advanced Transmission Mechanisms

2.2.2 802.16e MAC Layer Overview

2.2.2.1 802.16e Handoff Support

For handoff to work properly, mechanisms for allowing BS-to-BS and BS-to-backhaul (wired network) communications were also added. The BS-to-BS connection links allow for handoff negotiations between cells while the BS-to-backhaul links provide support for roaming user authentication much like in GSM-based cellular networks. By providing a roaming authentication mechanism service providers will be able to provide coast-to-coast support for users of Mobile WiMAX services [Kitroser03].

2.2.2.2 802.16e Power Management

Idle mode operation is entered by a mobile user when the device wishes to become temporarily unavailable to receive downlink traffic. In these cases, the mobile user disassociates itself from all BS's, first alerting them of what it intends to do. While in idle mode, the mobile station needs to periodically check for paging messages sent by the BS to see if new downlink frames have been sent to the device. Idle mode is intended to be used in cases when a mobile user is traversing a location where multiple BS's are present and the user wishes to avoid multiple handoffs and connection negotiation sessions [WiMAXForum06b].

Sleep mode operation, on the other hand, is entered only after the mobile user makes a request to do so to the BS. The BS then responds (if sleep is allowed) with a sleep interval time vector indicating how long the mobile user device is allowed to go into low-power mode and sleep. After the sleep interval expires, the mobile device wakes up and sees if any new frames intended for it have been transmitted. If not the mobile device is allowed to increase it's sleep interval, doubling it each time up to a pre-defined maximum period [Xiao05].

2.2.2.3 802.16e Enhanced QoS Support

2.2.2.4 802.16e Enhanced Security Support

2.2.2.5 802.16e Hybrid ARQ Support

2.3 WiMAX vs. Mobile WiMAX Comparison

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3. 802.20: Mobile Broadband Wireless Access (MBWA)

Figure 4: Example 802.20 Network Architecture

The 802.20 standard is being positioned as an alternative to 2.5 and 3G cellular services by virtue of the fact that both technologies support high-speed handoffs and wireless network access. Once ratified, "green-field" providers could use products based on the standard to create highly mobile wireless data networks. In doing so, the high prices that cellular providers currently charge for access to data networks would likely drop due to the emergence of a competing service. [MBWA05].

The 802.20 working group originally started as a small committee within the 802.16 standards group in March of 2002, prior to when work on the 802.16e standard started [Klerer03]. The committee quickly broke off into it's own working group in December of 2002 due to the fact that 802.16 was focusing on fixed-wireless standards during that time period [Fong04]. Since then, minimal progress towards defining the standard has been made, while the entire 802.16e standard has been defined, designed and ratified [Robinson06]. At this point in time, the standard seems to be in limbo, but the IEEE claims that work is ongoing.

In the following sub-sections, what little information is currently known about the 802.20 PHY and MAC layers will be presented. In reading the descriptions please keep in mind that the standard itself is still in the planning stages and that not so much as a preliminary standard has been published at this point.

3.1 802.20 PHY Layer Overview

3.1.1 802.20 Frequency Ranges and Duplexing

A spectral efficiency of at least 1 bps/hz is targeted in order to provide acceptable data rates. Using 1.25 MHz channels speeds similar to ADSL, with 1 Mbps downstream and 300 Kbps upstream, are expected and should scale accordingly with wider channels. In all cases, up to 100 users/cell should be supported although not all of them may be active at once [Upton05].

3.1.2 802.20 Transport, Modulation and Coding

Modulation and coding in 802.20 is essentially identical to that of 802.16a/d. Modulation rates from BPSK to 64QAM are all supported, along with both convolutional and turbo coding. Both mechanisms are fully adaptable, scaling to support both changing channel conditions and mobility rates. This enables the system to, for instance, provide a faster data connection to walking users than to those moving in automobiles or high-speed trains [Upton05].

3.1.3 802.20 Advanced Transmission Mechanisms

SDMA is forward-link transmission technique used at the BS to signal multiple users via the same time-frequency resources. This method can increase aggregate data rate by grouping transmission recipients together and transmitting signals to "zones" within a cell or cluster. Since directed beams need to be tuned towards their receivers, SDMA requires a feedback channel similar to that used by AAS to operate properly [Tomcik06].

3.2 802.20 MAC Layer Overview

3.2.1 802.20 Connection Establishment and Framing

Transmission and framing mechanisms in 802.20 will also be complicated somewhat if a hybrid OFDMA downlink and CDMA uplink system is implemented. In such a case, users will request transmission resource via the R-ACH over CDMA and then receive feedback from the BS over OFDMA. The OFDMA frame format will remain largely the same as that used in 802.16, with similar UL and DL mapping structures used to indicate when users are allowed to transmit as well as what transmitted data segments are meant for them [Tomcik06].

3.2.2 802.20 Handoff Support

3.2.3 802.20 Power Management

3.2.4 802.20 QoS Support

3.2.5 802.20 Security Features

3.2.6 802.20 Hybrid ARQ Support

3.3 802.20 vs 2.5 and 3G Cellular Networks

As can be seen in the table, the 802.20 standard offers performance similar to that of typical 2.5G and 3G cellular technologies. 802.20, however, has the distinct benefit of being a fully IP-based packetized network standard. As a result, network throughput is enhanced versus a circuit-switched standard, since messages do not have to be transcoded from pre-allocated circuits into packets and back again each time a request is sent or received. Furthermore, 802.20 offers a higher spectral efficiency that any current or near-future cellular standard and thus can do more with less channel bandwidth and support a higher number of users per cell [Klerer03].

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4. 802.22: Wireless Regional Area Networks (WRAN)

Figure 5: Example Deployment of an 802.22 Network

Work on the 802.22 standard first began in November of 2004 just after the FCC passed an important resolution entitled NPRM 04-186. In a nutshell, NPRM 04-186 defines provisions that allow license-exempt devices to operate in the TV-band so long as they can co-exist with existing services such as broadcasters and wireless microphone operators. The frequencies that the TV-Band covers are well known for their excellent signal propagation rates and appear to be ideal for use in a WRAN. As a result, work towards defining standard based around usage of the TV-band has swiftly progressed [Chouinard04, Cordiero05].

At this point in time, the 802.22 standard is steadily moving closer towards being finalized, as competing proposals by a variety of small consortiums inside the working group have begun to merge. Once this work and other various technology tests are completed the standard should be ready for market deployment. The next sub-sections of this paper outline the current proposed MAC and PHY layers with special attention paid to unique incumbent-sensing mechanisms being incorporated into the standard.

4.1 802.22 PHY Layer Overview

4.1.1 Frequency Ranges and Duplexing

Using a 6 MHz channel, an aggregate bandwidth of up to 23 Mbps can be provided. Optionally, 2 or 3 channels, either contiguous or separated, can be bonded together to provide up to 71 Mbps of bandwidth. When channels are bonded, separate sets of OFDMA carriers are used on each channel for a total of 6144 sub-carriers when 3 channels with 2048 sub-carriers each are used. This feature was not included in the original specification, and was added only after a number of committee members raised concerns about whether or not a single channel could meet the needs of an estimated 100 users/cell [Benko06].

In order to share the spectrum with incumbent users, 802.22 devices are also capable of operating over partial channels from 1 to 8 MHz in size. This allows an 802.22 base station to share a channel with incumbent devices such as wireless microphones that only use 1 or 2 MHz of the total bandwidth allocated to a channel. Furthermore, this ability allows 802.22 devices to selectively tune out portions of channels where interference and cross-talk make it impossible to transmit and receive a recognizable radio signal [Benko06].

4.1.2 Transport, Modulation and Coding

In terms of modulation, rates from BPSK up to 64QAM supported with the ability to dynamically adapt the method used as channel conditions change. Coding via convolutional codes is mandatory with optional support for LDPC and turbo coding. Furthermore, a more advanced method of turbo coding known as Shorted Block Turbo Code (SBTC) is expected to be supported as well. SBTC is based on the Turbo Product Code (TPC) used in 802.16 and is said to provide better parity checking mechanisms than the method used in 802.16e [Benko06, Chouinard04].

4.1.3 Advanced Transmission Mechanisms

4.2 802.22 MAC Layer Overview

4.2.1 Connection Establishment and Framing

Data in 802.22 networks is transmitted by an OFDMA frame structure similar to that of 802.16e where the BS controls all downlink traffic and users must request uplink slots before they transmit. Minor additions, however, were made to the 802.16e framing structure to allow for incumbent detection and channel bonding. When channel bonding is used, a "super frame header" is transmitted to indicate to supporting users which channels they should look for and transmit data on (via an enhanced DL/UL map structure). Furthermore, in order to provide support for users that do not support channel bonding a portion of the OFDMA super frame is reserved for such users to alert the BS of their restrictions so that the BS does not attempt to schedule transmissions and upload slots that the user cannot physically receive or make use of [Benko06].

4.2.2 Incumbent Sensing and Detection

Figure 6: Incumbent Operators in Range of an 802.22 Network

In the proposed sensing method, both the BS and user terminals will participate in incumbent detection. This allows sensing tasks to be distributed and gives the BS a better chance of identifying localized broadcasters (such as wireless microphone operators) that only a user would be able to detect. The BS reserves portions of the OFDMA frame to tell users which channels they should monitor for traffic. Users then collect this data and report it back to the BS at pre-specified intervals. Once all sensing information is collected, the BS then creates a revised list of occupied and unoccupied channels based on the results [Benko06].

Depending on the level of accuracy required sensing can either be done via either "fast" or "fine" mechanisms. Fast sensing is performed in-band during the guard interval portions of OFDMA frames. The advantage of fast sensing is that transmission time is not wasted on sensing. This advantage, however, comes at the cost of some accuracy [Benko06].

Fine sensing, on the other hand, is done out-of-band during defined "quiet periods" in which no network traffic is generated. The BS schedules "quiet periods" ahead of time so that all user stations can synchronize their sensing with one another. This method of sensing provides a higher degree of accuracy, but reduces the overall throughput of the network. As a result fine sensing is typically only used in cases when ambiguities in fast sensing arise [Benko06].

If, as a result of sensing, a BS realizes that it is operating on the same channel as an incumbent user it must broadcast a channel hop message to all users in the service area and switch to an unoccupied channel within in a 2 second time period. It should be noted that since television operators do not typically switch broadcasting channels the vast majority of interference will be with less significant devices such as wireless microphones [Benko06].

In rare cases, a situation may arise where a user terminal is powered on and cannot sense the presence of a BS because an incumbent, that the BS cannot see, is transmitting on the same channel as the BS. This issue is referred to as the "Hidden Incumbent Problem" (see Figure 7), and can remedied by having the BS periodically broadcast transmission frames on both it's current designated channel and one or more additional unoccupied channels. When the blocked user picks up the broadcasted signal they can then alert the BS that they are interfering with an incumbent user and that a channel hop is needed [Benko06].

Figure 7: The Hidden Incumbent Problem

4.2.3 Self Co-Existence

To facilitate communication between operators a BS-to-BS communication channel is specified in the 802.22 standard. By use of this mechanism, competing BS's can negotiate with one another to fairly partition the available channels and work to come to a solution that best meets the needs of both operators. Although the exact methodology for conflict resolution has yet to be defined, one current proposal involves the use of replenishable "tokens" and a bidding system by which the operator most willing to "pay" for an available channel is the one that is allowed to transmit on it. Only time will tell, however, if such a system is actually implemented in the standard [Benko06].

4.2.4 QoS Support

4.2.5 Security Features

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Summary

As can be seen in the above table, the standards are largely based on the same technologies and all offer support for features such as adaptive modulation/coding and various enhanced transmission systems. These similarities can largely be attributed to the fact that 802.20 and 802.22 were developed after the 802.16a/d standards. As a result, their developers have been able to learn from the mistakes made in defining that standard, while at the same time integrating the most successful portions into their own implementations.

In terms of marketability, 802.16 is the only of the three standards for which both service-provider and end-user devices are available for purchase. Furthermore, with the recent approval of the semi-mobile 802.16e specification and the backing of the WiMAX Forum, the standard seems destined to garner nearly universal support throughout the industry. This success, however, does not come without a certain amount of controversy, as various developers within the 802.20 working group have criticized those in the 802.16e camp for developing what essentially could be construed as a self-competing standard [Kiernan05]. The argument can be made, however, that the 802.20 developers have had just as much time to work as the 802.16e group yet they have not managed to deliver anything remotely resembling a full-featured standard.

Meanwhile, the 802.22 standard has been developing at a fairly brisk pace. Within 2 years of being founded, the working group has produced a nearly complete specification that addresses the unique incumbent detection problems associated with operating within the Television band. As a result, the standard seems poised to provide a solid alternative to current satellite-based approaches for broadband network access in remote or rural regions.

In short, 802.16, 802.20 and 802.22 are all striving to provide wireless access to users in areas that pre-existing technologies such as 802.11 simply cannot. If all three standards eventually succeed in the marketplace, users will be able to connect to the Internet from locations never before possible. This, in turn, will lead to a more mobile society as a whole and allow consumers living "off-the-grid" to have access to the same types of services as those living in urban or suburban areas.

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18. [WiMAXForum06b] The WiMAX Forum, "Mobile WiMAX - Part I: A Technical Overview and Performance Evaluation," W
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19. [Robinson06] Teri Robinson, "WiMAX to the World," netWorker [Vol.9, No. 4].
    

20. [Cordiero05] Carlos Cordiero, et. al., "IEEE 802.22: The First Worldwide Wireless Standard Based on Cognitive Radios," New Frontiers in Dynamic Spectrum Access Networks (DySPAN 2005).
    

21. [Johnston04a] David Johnston and Jesse Walker, "Overview of IEEE 802.16 Security," IEEE Security and Privacy [Vol. 02, No. 3].
    

22. [Johnston04b] David Johnston, "AES-CCM Encryption and Authentication Mode for 802.16,"
    http://www.ieee802.org/16/tge/contrib/C80216e-04_12.pdf

23. [Pipeline05] "WiMAX Will Succeed As Fixed Broadband, Study Predicts," Mobile Pipeline,
    http://www.informationweek.com/story/showArticle.jhtml?articleID=163701459

24. [DailyWireless05] "Mobile WiMAX: It's Done," DailyWireless,
    http://dailywireless.org/modules.php?name=News&file=article&sid=5004

25. [Classon05] Brian Classon, et. al. "LDPC Coding for OFDMA PHY,"
    http://www.ieee802.org/16/tge/contrib/C80216e-05_135.pdf

26. [Xu05] Robert Xu, et. al. "Rate 5/6 LDPC Coding for OFDMA PHY,"
    http://www.ieee802.org/16/tge/contrib/C80216e-05_311.pdf5

27. [Roh05] Wonil Roh, "Support for Closed-Loop MIMO in H-ARQ MAP IE"
    http://www.ieee802.org/16/tge/contrib/C80216e-05_249r3.pdf

28. [Skylight05] Skylight Research, "Pre WiMAX Solutions Primary Driver for 2004 Revenue,"
    http://www.WiMAXforum.org/news/reports/SLRs_Wireless_Broadband_Analysis_Report_Press_Release_2004_to_2009_TOC.pdf

29. [Kiernan05] Brian Kiernan, "The Sordid Sage of Sixteen,"
    http://www.ieee802.org/16/tge/contrib/C80216e-05_406.pdf

30. [Borisov01] Nikita Borisov, Ian Goldberg and David Wagner, "Security of the WEP Algorithm,"
    http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html

31. [Bruno05] Raffaele Bruno, Marco Conti and Enrico Gregori, "Throughput Analysis of UDP and TCP Flows in IEEE 802.11bWLANs: A Simple Model and its Validation," Proceedings of the 2005 Workshop on Techniques, Methodologies and Tools for Performance Evaluation of Complex Systems (FIRB-PERF 05).

List of Acronyms

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