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[802SEC] 802 news IEEE 802.16 Backgrounder ++FYI++




Angela Ortiz
Program Manager - Technical Program Development
__________________________
IEEE Standards, 445 Hoes Lane,
Piscataway, NJ  08855-1331 USA
Telephone: 1732-562-3809  ><  Fax: 1732-562-1571
E-m:  a.ortiz@ieee.org   ><   www.standards.ieee.org

FOSTERING TECHNOLOGICAL INNOVATION

--- Forwarded by Angela Ortiz/STDS/STAFF/US/IEEE on 05/14/2002 12:13 PM
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                    k.mccabe@ieee.org                                                                                      
                    Sent by:                     To:     802news@ieee.org                                                  
                    owner-802news@majordom       cc:                                                                       
                    o.ieee.org                   Subject:     802 news IEEE 802.16 Backgrounder                            
                                                                                                                           
                                                                                                                           
                    05/14/2002 11:41 AM                                                                                    
                                                                                                                           
                                                                                                                           


IEEE-SA News
IEEE 802.16 Backgrounder


Contact:  Roger Marks,
          303 497 3037, marks@nist.gov
               or
          Dean Chang,
          408 719 9977, dchang@apertonet.com
               or
          Karen McCabe
          732 562 3824, k.mccabe@ieee.org



Broadband Wireless Access:  An Introduction to the Technology
Behind the IEEE 802.16 WirelessMAN? Standard


     Broadband wireless access (BWA) has become the best way to meet


escalating business demand for rapid Internet connection and integrated


data, voice and video services.  BWA can extend fiber optic networks and


provide more capacity than cable networks or digital subscriber lines


(DSL).  One of the most compelling aspects of BWA technology is that


networks can be created in just weeks by deploying a small number of base


stations on buildings or poles to create high-capacity, point-to-multipoint


(PMP) systems.


     BWA has had limited reach so far, in part because of the unmet need


for a universal standard.  While providing such a standard is important for


developed countries, it is even more important for the undeveloped world


where wired infrastructures are minimal.





The IEEE 802.16 WirelessMAN? Standard


     The Institute of Electrical and Electronics Engineers Standards


Association (IEEE-SA) sought to make BWA more widely available by


developing IEEE Standard 802.16, which specifies the WirelessMAN? Air


Interface for wireless metropolitan area networks.  The standard, which


received final IEEE approval on Dec. 6, 2001 was published on 8 April 2002,


was created in a two-year, open-consensus process by hundreds of engineers


from the world's leading operators and vendors.


     IEEE 802.16 addresses the "first-mile/last-mile" connection in


wireless metropolitan area networks.  It focuses on the efficient use of


bandwidth between 10 and 66 GHz (the 2 to 11 GHz region will be added in


mid 2002) and defines a medium access control (MAC) layer that supports


multiple physical layer specifications customized for the frequency band of


use.


     The 10 to 66 GHz standard supports continuously varying traffic levels


at many licensed frequencies (e.g., 10.5, 25, 26, 31, 38 and 39 GHz) for


two-way communications.  It enables interoperability among devices, so


carriers can use products from multiple vendors.  The draft amendment for


the 2 to 11 GHz region will support both unlicensed and licensed bands.





Telecommunications Choices


     Business-based telecommunications encompasses many options.  Major


businesses often access large-capacity, high-speed fiber optic networks for


broadband, converged services.  Less than five percent of commercial


structures worldwide are served by fiber networks, however, and extending


these networks with cable is costly and time consuming.


     Small businesses and home offices typically use lower-bandwidth wired


networks such as cable modem networks and DSL.  Cable systems are based on


residential cable TV infrastructure, so they are often not competitive in


serving business subscribers.  DSL is a copper-based method that typically


offers 128 kbps to 2 Mbps data services.  It faces many technical hurdles


and is limited in both bandwidth and range.


      DSL, cable and older wireless systems tend to have low upstream


bandwidth.  The same is true of another option, two-way satellite


transmission, which is still early in its life cycle.  While invaluable in


some rural areas, it has limited application in more populous locales due


to limited spectrum availability and high latency (i.e., a short time


between transmitted packets).


     Early BWA networks were costly and problematical and had limited


information capacity per channel. They were also inefficient in the use of


spectrum.  Current BWA systems offer true differentiated broadband services


at minimal cost.  They let thousands of users share capacity for data,


voice and video.  They also are scalable: carriers can expand them as


subscriber demand for bandwidth grows by adding channels or cells.





Quality of Service (QoS) in Broadband Wireless


     BWA networks use air as the transmission medium and so are affected by


temperature, humidity and obstructions such as vegetation or buildings.


This makes them less predictable than networks based on copper or glass.


IEEE Standard 802.16 recognizes this and includes mechanisms to make robust


links for PMP BWA systems with line-of-sight, obstructed line-of-sight, and


non line-of-sight transmission.


     Mechanisms in the WirelessMAN MAC provide for differentiated QoS to


support the different needs of different applications.  For instance, voice


and video require low latency but tolerate some error rate.  By contrast,


generic data applications cannot tolerate error, but latency is not


critical.  The standard accommodates voice, video, and other data


transmissions by using appropriate features in the MAC layer, which is more


efficient than doing so in layers of control overlaid on the MAC.


     Many systems in the past decade have involved fixed modulation.


Higher-order modulation in such systems offers higher data rates but


requires optimal links, while lower orders of modulation are more robust


but support lower data rates.  The new standard supports adaptive


modulation, effectively balancing different data rates and linkage quality.


The modulation method may be adjusted almost instantaneously for optimum


data transfer. Adaptive modulation allows efficient use of bandwidth and a


broader customer base.


     The standard also supports both frequency and time division duplexing


(FDD and TDD).  Frequency division duplexing (FDD), the legacy duplexing


method, has been widely deployed in cellular telephony.  It requires two


channel pairs, one for transmission and one for reception, with some


frequency separation between them to mitigate self-interference.


     TDD is a more efficient method in which data is sent and received in a


single channel.  It is especially valuable for data transmission and


Internet traffic in which the asymmetry can vary greatly over time.  TDD


allows efficient use of spectral resources by continuously adapting the


fractions of time dedicated to uplink and downlink traffic in order to meet


current traffic requirements.


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