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Introduction.doc

  1. 1. ACP WGC8 WP11 AERONAUTICAL COMMUNICATIONS PANEL Working Group C - 8th Meeting Munich, Germany 20-24 September 2004 Agenda Item 5: New Technologies Wireless Broadband Solution – 802.16/20 Presented by Jocelyn Descaillot, SITA Prepared by Jocelyn Descaillot, SITA SUMMARY The 802.16 standard - in particular 802.16a and its extention 802.16e - is a wireless metropolitan area network technology that will provide a wireless alternative to cable and DSL (Digital Subscriber Line) for last mile broadband access. The associated technology allows a connection throughput of about 70Mbps in a single RF channel with a coverage of up to 50 km (radius), in the 10-66Ghz and 2-11Ghz bands. The following future evolutions of the 802.16a are in the process of being developped and are recommended to be considered as candidates to meet future mobile Aeronautical Communications requirements, and specifically for Airport based communications:  802.16e, enhancement for mobile vehicles.  802.20 mobile broadband wireless access (i.e. similar to 3G)
  2. 2. 1 Introduction This paper provides back-ground information on existing or in-development broadband wireless tehnologies that are being standardized within IEEE. These technologies are recommended be taken into account in the ICAO process of selecting future candidate for broadband aeronautical communications. Described in http://standards.ieee.org/getieee802/802.16.html, the 802.16a standard is the first generation of Fixed Wireless broadband system with relatively wide range access (up to 50km). The generation that may be of interest to ICAO Working Group C are 802.16e and 802.20 which integrate mobility requirements. 2 802.16 standards 2.1 Brief Overview of WiMAX Forum (www.wimaxforum.org) While the 802.16 standards have been written under IEEE, there has been a move in the industry to create a Forum, namely WiMax, to promote the deployment of broadband wireless access networks by using a global standard and certifying interoperability of products and technologies. Principles: WiMAX is comprised of industry leaders who are committed to the open interoperability of all products used for broadband wireless access. • Support IEEE 802.16 standard • Propose and promote access profiles for their IEEE 802.16 standard • Certify interoperability levels both in network and the cell • Achieve global acceptance • Promote use of broadband wireless access overall Motivation: WiMAX intends to foster a more competitive BWA marketplace by specifying minimum air-interface performance between various vendors' products and certifying products that meet those performance benchmarks. • For network operators this means interoperability between equipment vendors • For equipment vendors this means fewer product variants • For component vendors this means larger series • For end-users this means faster and cheaper access which is more widely available 2.2 WiMAX Forum Objectives Representing a significant step forward in catalyzing the growth and future viability of the global fixed broadband wireless market, leading equipment and component manufacturers have formed the Worldwide Interoperability for Microwave Access (WiMAX) Forum. As a non-profit organization, the objective of WiMAX is to promote wide-scale deployments of point-to-multipoint networks operating between 2 and 66 GHz by leveraging new global consensus standards and certifying the interoperability of various products and technologies from multiple manufacturers. 2
  3. 3. As has been proven many times in the past, true market success of a particular technology can only be realized through a global standard and a concerted effort to ensure the interoperability of multi-vendor products which in turn result in economies of scale and, ultimately, a healthy competitive environment. The recent completion and formal approval of IEEE® Standard 802.16™ ("Air Interface for Fixed Broadband Wireless Access Systems"), which defines the IEEE 802.16 WirelessMANTM air interface, was achieved through successful collaboration of many individuals and companies in the wireless industry. Together, they produced the industry's first broadband wireless access standard to be published by an accredited standards body. As the next step in widespread adoption and use of the WirelessMANTM standard, WiMAX has been created to further define this global specification. Current participants in the Forum can be found at http://www.wimaxforum.org/memberinfo/Current_Members. The Forum's membership is expected to grow substantially as progress is made on drafting conformance specifications, developing compliant products, and proving the interoperability of those products. The focus on WiMAX membership and its work will only intensify with the participation of service providers that are committed to advancing the broadband wireless industry and rollout of broadband, high-frequency networks. 2.3 Benefits of the 802.16 Standard In current commercial deployments, broadband wireless networks deliver more bandwidth than traditional copper cables and exhibit a clear economical advantage over wireline alternatives in the last mile. Historically, many operators worldwide have used broadband wireless technologies, namely point-to-point radios, as a proven, service provider-class method of connecting long-haul networks. And while point-to- point technologies have also been used for access in isolated cases (and with mixed results), point-to-multipoint technologies have long been recognized as the 'holy grail' for service providers because of their ability to provide broadband services over large geographic areas with greater flexibility and improved economies of scale. The industry has suffered from limited deployments, however, due to the high cost and low functionality of early-generation of broadband wireless systems. In addition, a lack of healthy competition caused by various factors has contributed to the industry malaise. And with frequency regulations varying from country to country, equipment manufacturers have used only proprietary air interface technologies. These and other factors have precluded the broadband wireless market from benefiting from the economies of scale that other technologies enjoy from open standards. For service providers - interoperability of next-generation systems, lower-priced systems WiMAX is an open certification forum based on IEEE Standard 802.16. WiMAX also plans to certify that products are compliant with the interoperability requirements set forth by WiMAX. For network operators, this interoperability yields the operator 3
  4. 4. more options, the flexibility of deploying broadband wireless systems from multiple vendors, and the knowledge that all products deployed interoperate seamlessly. Further, the evolution of a service provider's network over time-especially the multivendor network that might result from standards-based products being available- is also a key concern and is solved through WiMAX. For example, one of the building blocks of the IEEE 802.16 standard is the concept of a "variable burst length," a feature adopted to ensure a growth path from ATM networks to IP networks. With WiMAX, service providers can be sure that this type of evolution can occur in their network even when it is made up of products from multiple vendor as certified interoperability will guarantee a known interoperability level between systems. And if required, this level can also be changed over time. 2.3.1 For equipment vendors - less product variants, larger volumes A single global standard provides equipment manufacturers, whether current broadband wireless suppliers or not, new opportunities to develop products that are optimized for volume production -- a task not easily accomplished with frequency and feature tailoring of each product as is done currently. Since each product variant translates into additional costs, if a number of product variants can be reduced significantly, product costs drop. One reason for this reduction is that with fewer product variants comes a decrease in component selection resulting in an increase in the production series of remaining components. For example, with standardization, some of the same expensive radio frequency components can be used in multiple manufacturer's designs. This makes it possible to further increase component-manufacturing series levels while decreasing costs. Another potential result which reduces costs is that some suppliers will decide to concentrate on only some part of the equipment design and then sell that same design to several system providers. 2.4 Challenges As with all telecom access markets, broadband wireless has survived significant challenges over the last five years. Certainly, there has been some significant progress by several service providers in different parts of the world, but the promise of this broadband delivery method can only be fully achieved if many, many service providers achieve deployment success with benefit accruing to operators, systems suppliers and other component manufacturers. Beyond the troubled economics of broadband wireless networks deployment and limitations of systems, the lack of standards is a contributing factor to the industry's slow development. There are numerous challenges and issues facing developers of IEEE 802.16- compliant systems: 2.4.1 Host of Options The IEEE Standard 802.16 is a large and complex document designed to cover the broadband wireless access needs of a variety of different situations. As a comprehensive specification, there are allowances for different physical layers for different frequency bands and country-by-country frequency use restrictions. There are features that allow suppliers to build IP- or ATM-centric systems, depending upon the needs of customers. The specification is also designed to cover applications that 4
  5. 5. address diverse markets -- from very high bandwidth businesses to SOHO and residential users. Because of the wealth of options available, an implementer currently faces a tough decision. Do you build an IEEE 802.16-compliant system implementing every possible feature, even those features you know will never be used in systems for your target customers? Or, do you build a system with only the subset of features you need for your market, risking accusations of non-compliance and lack of interoperability? With regard to adaptating to the Aeronautical Communications, it is recommended to screen through the pletoria of options available and match them against requirements set forth within ICAO. WiMAX is now addressing this issue by drafting "System Profiles" for use in conjunction with IEEE 802.16. The purpose of these system profiles is to specify which features are mandatory or optional for the various MAC or PHY scenarios that are most likely to arise in the deployment of real systems. This allows vendors addressing the same market to build systems for that market that are interoperable, while not requiring the implementation of every feature. It is likely that ICAO would need to work and define a system profile that meet the aeronautical communication requirements. 2.4.2 Lack of Test Specifications Another issue facing IEEE 802.16 developers is that fact that, to this point, no guidelines as to how to test to that specification are provided. Since there is currently no work item in IEEE 802.16 to address the creation of test specifications, for the good of the industry and the full implementation of the standard, a third party group such as WiMAX had a role in generating the specifications and test products against them. Testing and certifying products based on an agreed set of test specifications have the following benefits: • Ensuring that equipment and systems claiming compliance to the standard or a profile have been sufficiently tested to demonstrate that compliance. • Guaranteeing that equipment from multiple vendors has been tested the same way, to the same interpretation of the standard, increasing the interoperability of the equipment. • Enabling independent conformance testing, giving further credibility to the previous two items. This test specification initiative is an area where the ETSI has an official process that has typically been more complete than IEEE. ETSI follows the guidelines of the ISO/IEC 9646 series (ITU-T X.29x series). The Test Suite Structure and Test Purposes (TSS & TP) document and the Abstract Test Suite (ATS) specification, both described in ISO/IEC 9646-2 (ITU-T X.291), suit the purpose particularly well. 2.4.3 No Conformance Statements A final issue facing developers of IEEE 802.16-compliant systems is that having profiles is only part of the interoperability challenge. There must be a standard method of identifying which profiles a device or system complies with and which optional features are implemented so that system integrators can make educated 5
  6. 6. decisions about specific features to provide to customers and to aid in the selection of equipment. The lack of such a method leads to the tendency to build systems that do much more than they need to and the likelihood of accusations that standards to not specify interoperable systems. In contrast, the ETSI process generally addresses this issue by the development of Implementation Conformance Statement (ICS) proforma documents, following the guidance of ISO/IEC 9649-7 (ITU-T X.296). The most common form of ICS is the Protocol ICS or PICS Proforma. For IEEE 802.16 equipment, an ICS Proforma is a perfect means of describing the MAC protocol and PHY features that are required for various system profiles. An ICS proforma is also a necessary tool for vendors to specify their level of compliance and to specify which optional features have been implemented. 2.5 802.16a Technical Description The first version of the 802.16 standard released addressed Line-of-Sight (LOS) environments at high frequency bands operating in the 10-66 GHz range, whereas the recently adopted amendment, the 802.16a standard, is designed for systems operating in bands between 2 GHz and 11 GHz. The significant difference between these two frequency bands lies in the ability to support Non-Line-of-Sight (NLOS) operation in the lower frequencies, something that is not possible in higher bands. Consequently, the 802.16a amendment to the standard opened up the opportunity for major changes to the PHY layer specifications specifically to address the needs of the 2-11 GHz bands. This is achieved through the introduction of three new PHY-layer specifications (a new Single Carrier PHY, a 256 point FFT OFDM PHY, and a 2048 point FFT OFDMA PHY);major changes to the PHY layer specification as compared to the upper frequency, as well as significant MAC-layer enhancements. Although multiple PHYs are specified as in the 802.11 suite of standards, it was determined that the first interoperable test plans and eventual certification will support the 256 point FFT OFDM PHY (which is common between 802.16a and ETSI HiperMAN), with the others to be developed as required. The OFDM signaling format was selected in preference to competing formats such as CDMA due to its ability to support NLOS performance while maintaining a high level of spectral efficiency maximizing the use of available spectrum. In the case of CDMA (prevalent in 2G and 3G standards), the RF bandwidth must be much larger than the data throughput, in order to maintain processing gain adequate to overcome interference. This is clearly impractical for broadband wireless below 11 GHz, since for example, data rates up to 70 Mbps would require RF bandwidths exceeding 200 MHz to deliver comparable processing gains and NLOS performance. Some of the other PHY layer features of 802.16a that are instrumental in giving this technology the power to deliver robust performance in a broad range of channel environments are; flexible channel widths, adaptive burst profiles, forward error correction with concatenated Reed-Solomon and convolutional encoding, optional AAS (advanced antenna systems) to improve range/capacity, DFS (dynamic frequency selection)-which helps in minimizing interference, and STC (space-time coding) to enhance performance in fading environments through spatial diversity. Table 1 gives a high level overview of some of the PHY layer features of the IEEE 802.16a standard. 6
  7. 7. The IEEE 802.16 Air Interface Standard is truly a state-of-the-art specification for fixed broadband wireless access systems employing a point-to-multipoint (PMP) architecture. The initial version was developed with the goal of meeting the requirements of a vast array of deployment scenarios for BWA systems operating between 10 and 66 GHz. As a result, only a subset of the functionality is needed for typical deployments directed at specific markets. An amendment is almost finished to do the same for systems operating between 2 and 11 GHz. Additionally, the IEEE process stops short of providing conformance statements and test specifications. In order to ensure interoperability between vendors competing in the same market, the WiMAX technical working groups were created by the leaders in IEEE 802.16 technology. The working groups address these issues by developing system profiles and by producing PICS proforma, Test Suite Structure and Test Purposes specifications and Abstract Test Suite specifications according to the ISO/IEC 9464 series (equivalent to ITU-T x.290 series) of conformance testing standards. 2.5.1 Overview of IEEE 802.16 Task Group 1 of IEEE 802.16 developed a point-to-multipoint broadband wireless access standard for systems in the frequency range 10-66 GHz. The standard covers both the Media Access Control (MAC) and the physical (PHY) layers. Task groups a and b are jointly producing an amendment to extend the specification to cover both the licensed and unlicensed bands in the 2-11 GHz range. A number of PHY considerations were taken into account for the target environment. At the higher frequencies, line of sight is a must. This requirement eases the effect of multipath, allowing for wide channels, typically greater than 10 MHz in bandwidth. This gives IEEE 802.16 the ability to provide very high capacity links on both the uplink and the downlink. At the lower frequencies, line of sight is not required, giving other tradeoffs. Adaptive burst profiles (modulation and forward error correction (FEC)) are used to further increase the typical capacity of 802.16 systems with respect to older technology. The MAC was designed to accommodate different PHYs for the different environments. The single service provider PHYs are designed to accommodate either Time Division Duplexing (TDD) or Frequency Division Duplexing (FDD) deployments, allowing for both full and half-duplex terminals in the FDD case. The OFDM PHYs are designed for TDD. The MAC was designed specifically for the PMP wireless access environment. It is designed to seamlessly carry any higher layer or transport protocol such as ATM, Ethernet or Internet Protocol (IP), and is designed to easily accommodate future protocols that have not yet been developed. The MAC is designed for the very high bit rates (up to 268 mbps each way) of the truly broadband physical layer, while delivering ATM compatible Quality of Service (QoS) to ATM as well as non-ATM (MPLS, VoIP, etc.) service. The uplink is TDMA with each CPE bursting in an assigned slot using an individually assigned burst profile (modulation/FEC combination). The frame structure allows terminals to be dynamically assigned uplink and downlink burst profiles according to their link conditions. This allows a trade-off between capacity and robustness in real-time, and provides roughly a two times increase in 7
  8. 8. capacity on average when compared to non-adaptive systems, while maintaining appropriate link availability. The 802.16 MAC uses a variable length Protocol Data Unit (PDU) along with a number of other concepts that greatly increase the efficiency of the standard. Multiple MAC PDUs may be concatenated into a single burst to save PHY overhead. Additionally, multiple Service Data Units (SDU) for the same service may be concatenated into a single MAC PDU, saving on MAC header overhead. Fragmentation allows very large SDUs to be sent piece-meal to guarantee the QoS of competing services. And, payload header suppression can be used to reduce the overhead caused by the redundant portions of SDU headers. The MAC uses a self-correcting bandwidth request/grant scheme that eliminates the overhead and delay of acknowledgements, while simultaneously allowing better QoS handling than traditional acknowledged schemes. Terminals have a variety of options available to them for requesting bandwidth depending upon the QoS and traffic parameters of their services. They can be polled individually or in groups. They can steal bandwidth already allocated to make requests for more. They can signal the need to be polled, and they can piggyback requests for bandwidth. As can be seen, by the time authentication, security, capability negotiation and a host of other features are added, the IEEE 802.16 standard becomes almost overwhelming. 2.5.2 The Interoperability Challenge: Plethora of Options From the preceding overview, it is clear that the IEEE 802.16 Air Interface Specification is a very large specification. It was designed to cover the fixed broadband wireless access needs of a variety of different situations. There are allowances for different physical layers for different frequency bands and country-by- country frequency use restrictions. There are features that allow one to build an IP centric system or an ATM centric system depending upon the needs of customers. The specification is designed to cover application to diverse markets from very high bandwidth businesses to SOHO and residential users. Because of the wealth of options available, an implementer currently faces a tough decision. Do you build an IEEE 802.16 compliant system implementing every possible feature, even those features you know will never be used in systems for your target customers? Or, do you build a system with only the subset of features you need for your market, risking accusations of non-compliance and lack of interoperability? The IEEE 802.16 working group started to address this issue by the inclusion of Chapter 12, "System Profiles" in the IEEE 802.16 specification. The purpose of these system profiles is to specify which features are mandatory or optional for the various MAC or PHY scenarios that are most likely to arise in the deployment of real systems. This allows vendors addressing the same market to build systems for that market that are interoperable while not requiring the implementation of absolutely every feature. Unfortunately, this portion of the standard was not completed when the standard was released. Additionally, as new markets and new system scenarios emerge, the industry cannot operate on the schedule required to form a task group under IEEE 802.16 to 8
  9. 9. create new profiles and take it through all the procedural steps required to officially publish an amendment to the standard. New profiles must be created by industry agreement in a more timely fashion, and then rolled back into amendments to the standard at the slower pace endemic to the formal process. There might a need to develop such profile to meet specific Aeronautical Communication requirements. 2.6 10-66 GHz Band Because of the pieces missing in the IEEE process, WiMAX created the 10-66 GHz technical working group. The profiles and test specifications are created by the technical working group, but actual testing is done by an authorized, independent laboratory. For each system profile, functions are separated between mandatory and optional feature classes by the PICS proforma document. There can be differences from one equipment manufacturer to another in implementing optional features, but mandatory features will be same in every vendor's product. Implementation of an optional feature is noted when the vendor fills out the PICS proforma. System Profiles for 10-66 GHz WiMAX currently is defining two MAC system profiles: • Basic ATM system MAC profile • Basic IP system MAC profile Two primary PHY system profiles are also being defined: • 25 MHz wide channel for (typically for U.S. deployments) use in the 10-66 GHz range. • 28 MHz wide channel for (typically European deployments) use in the 10-66 GHz range. The PHY profiles are the same except for their channel width and their symbol rate, which is proportional to their channel width. Each primary PHY profile has two sub- profiles - FDD and TDD. The technical working group will produce the following technical documents: • PICS proforma, per ISO/IEC 9646-7, describing mandatory and optional features for each system profile, enabling developers to state support for features. • TSS & TP document, per ISO/IEC 9646-2, for the system profiles. • ATS specification, per ISO/IEC 9646-2, for the system profiles. In addition, the working group has developed subsections for inclusion is section 12 of the IEEE 802.16 Air Interface Specification for each of the system profiles. These profiles are already being rolled back into 802.16. 2.7 Adding 2-11 GHz Band In early 2003, the IEEE 802.16 standard was expanded with the adoption of the 802.16a amendment, focused on Broadband Wireless Access in the frequencies from 2 to 11GHz. Given the charter of the WiMAX forum, to promote certification and interoperability for Microwave Access around the globe, WiMAX agreed to expand and include the 802.16a standard in terms of addressing testing and conformance issues. 9
  10. 10. The WiMAX 2-11 GHz Technical Working Group (TWG) has the mandate of creating testing and conformance documents as contributions to IEEE and ETSI standards bodies in support of the IEEE 802.16a and ETSI HiperMAN standards. Although WiMAX is actively working on and will produce the actual test documents, an authorized and independent laboratory that has been certified by WiMAX will conduct actual testing. The WiMAX 2-11GHz TWG is currently defining MAC and PHY System Profiles for IEEE 802.16a and HiperMAN standards. The MAC profiles that are being developed include IP based versions for both WirelessMAN (Licensed) and WirelessHUMAN (License-exempt). While the IEEE 802.16a amendment has several physical layer profiles, the WiMAX forum through its 2-11 GHz TWG is focusing on the 256 point FFT OFDM PHY mode as its initial and primary interoperability mode. Various channel rasters covering typical spectrum allocations in both licensed and license exempt bands around the globe have been chosen, all supporting the 256-point FFT OFDM PHY mode of operation. This admendement could clearly cover the use of this technology in the MLS band if required. 3 802.20 (Mobile Broadband Wireless Access - MBWA) On 11 December 2002, the IEEE Standards Board approved the establishment of IEEE 802.20, the Mobile Broadband Wireless Access (MBWA) Working Group. · Mission The mission of IEEE 802.20 is to develop the specification for an efficient packet based air interface that is optimized for the transport of IP based services. The goal is to enable worldwide deployment of affordable, ubiquitous, always-on and interoperable multi-vendor mobile broadband wireless access networks that meet the needs of business and residential end user markets. · MBWA Scope Specification of physical and medium access control layers of an air interface for interoperable mobile broadband wireless access systems, operating in licensed bands below 3.5 GHz, optimized for IP-data transport, with peak data rates per user in excess of 1 Mbps. It supports various vehicular mobility classes up to 250 Km/h in a MAN environment and targets spectral efficiencies, sustained user data rates and numbers of active users that are all significantly higher than achieved by existing mobile systems. The 802.20 version is more adapted to the mobile environment. However, this version of the standard is not mature today and the launch on the market (first installed based) may not happen until late 2007 / early 2008. 4 Conclusion The IEEE conducted a multi-year effort to develop this new standard, culminating in final approval of the 802.16a Air-Interface Specification in January 2003. This 10
  11. 11. standard has since received broad industry support from leading equipment makers. The 802.16a standard delivers carrier-class performance in terms of robustness and QoS and has been designed from the ground up to deliver a suite of services over a scalable, long range, high capacity wireless communications. It is recommended this work to be taken into account by the ICAO Working Group C as a viable technology for Broadband Wiressless aeronautical communications to be used preferrably in the 5 GHz band and Non-Line-Of-Site mode of Operation. The proposed technology and associated set of protocols should be considered as a part of the future communication infrastructure and its development should be monitored for possible adaptation to meet aviation specific requirements. 11

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