The Impact of 802.16 Technology Will Enable 
Ubiquitous Delivery of Broadband Wireless Services

By Dr. Mohammad Shakouri, WiMAX Forum Board Member and VP of Marketing
Assist Vice President, Business Development Alvarion

    Introduction

    The 802.16 standard, amended this January by the Institute of Electrical and Electronics Engineers (IEEE) to cover frequency bands in the range between 2 GHz and 11 GHz (802.16a), specifies a metropolitan area networking protocol that will enable a wireless alternative for cable, DSL and T1 level services for last-mile broadband access, as well as providing backhaul for 802.11/WiFi networks or "Hot Spots."  The new standard 802.16a standard specifies a protocol that provides broadband connectivity without requiring direct line of sight to close the link between subscriber terminals (customer premise equipment) and the base station (or main hub).  The standard will accelerate the introduction of wireless broadband equipment and networks into the marketplace, thereby speeding up city-wide broadband deployment worldwide by enabling service providers to increase system performance and reliability while reducing their equipment costs and investment risks.

    The WiMAX Forum (World Interoperability for Microwave Access) was formed to remove an important barrier to adoption of the standard by assuring demonstrable interoperability between system components developed by OEMs.  As a non-profit organization, WiMAX will develop conformance test plans and select certification labs, and will host interoperability events for IEEE 802.16 equipment vendors.  Members of the forum comprise leading equipment and component vendors, including Airspan Networks, Alvarion, Andrew Corporation, Aperto Networks, Atheros, China Motion Telecom, Compliance Certification Services, Ensemble Communications, Fujitsu, Hughes Network Systems, Intel, News IQ, Nokia, OFDM Forum, Powerwave Technologies, Proxim, REMEC, Redline Communications, RF Integration, SiWave, SiWorks, SR Telecom, Stratex Networks, TowerStream, TurboConcept, Wavesat Wireless, Wi-LAN, and Winova Wireless.

    By defining and conducting interoperability testing and by awarding vendor systems a "WiMAX Certified" label, the forum will model the approach pioneered by the Wi-Fi Alliance to ignite the wireless LAN industry, bringing the same benefits to the wireless broadband last-mile (or metropolitan area network – MAN) market segment.

Figure 1: Wireless Standard Technologies and Networks

    By mid 2004, WiMAX certified products will be generally available to support both licensed and unlicensed bands which are complementary to the bands used by Wi-Fi and do not overlap. WiMAX networks will complement Wi-Fi by providing necessary broadband backhaul (instead of DSL or T1 connections) to these Hot Spots and delivering critical last-mile broadband to homes and businesses. With future enhancements to the specification (in the form of 802.16e) and integration with Wi-Fi components, WiMAX solutions will support portable and mobile services within a metropolitan area such as public safety and transportation.

   Overview of Technology

    Satisfying the growing demand for last-mile wireless access in underserved markets has been a continuing challenge for service providers because of the absence of a truly global standard that will reach underserved business and residential markets in a manner that supports infrastructure build outs comparable to cable, DSL and fiber.  The 802.16a standard systems delivers carrier-class performance (known as 99.999 percent reliability) and has been designed from the ground up to deliver scalable, long-range, high-capacity communications for service providers. The IEEE conducted a multi-year effort to address this gap, culminating in final approval of the 802.16a Air-Interface Specification in January 2003.  This standard has since received broad industry support from leading equipment makers.

    A number of WiMAX members are active in both the IEEE 802.16 standards development and the IEEE 802.11 efforts for Wireless LAN, and envision that these networks will deliver a complete wireless solution for delivering high speed Internet access to businesses, homes and Wi-Fi Hot Spots. 

Figure 2. Ubiquitous Coverage by WiMAX (IEEE 802.16) Wireless Broadband

    The standard's targeted applications include residential broadband access, DSL-level service for SOHO and small businesses, T1 and fiber optic service for enterprise, wireless backhaul for hotspots, cellular tower backhaul service and wireless local loop. The standard was developed to address these conventional fixed services, but development is already underway to specify enhancements to the technology that will provide support for mobile broadband wireless access applications, including nomadic coverage.

    OFDM Overview: Achieving Non Line of Sight

    Orthogonal Frequency Division Multiplexing (OFDM) technology has been around for decades. OFDM has been used successfully used in wire-line access applications such as Digital Subscriber Line (DSL) since 1995, digital broadcasting since 1992, and Wireless Local Area Networks (WLAN) since 2001 where throughput is at a premium and severely impaired channel conditions exists. The essence of OFDM is to break up the transmitted signal into many small signals. For the 256 OFDM example, instead of a signal carrying 70 Mbps of data, there are 256 separate signals, each carrying about 280 Kbps of data. This allows significant protection against multipath interference and deep fades typically encountered in an outdoor propagation environment. 802.16a has optimized 256 OFDM solution for outdoor as 802.11a/g has optimized 64 OFDM for indoor environments.

    Both IEEE 802.16 and ETSI HiperMAN standards share this same 256 OFDM physical layer profile, along with common media access control (MAC) layer system profiles. WiMAX is working in both standards-making bodies to ensure that there is a global standard for Wireless MAN. Initially, WiMAX products in the 2-11 GHz will be based upon the 256 OFDM mode of the 802.16a spec.

    The WiMAX Forum—Interoperability for 802.16 Compliant Systems

    In an effort to bring interoperability to the wireless broadband industry, WiMAX is focused on establishing a unique subset of baseline features grouped in what is referred to as "System Profiles" that all compliant equipment must satisfy.  These profiles will establish a baseline protocol, allowing multiple vendors' equipment to interoperate, and providing system integrators and service providers with the ability to purchase equipment from more than one supplier.

    Profiles can address, for example, the regulatory spectrum constraints faced by operators in different geographies.  For example, a service provider in Europe operating in the 3.5 GHz band, who has been allocated 14 MHz of spectrum, is likely to want equipment that supports 3.5 and/or 7 MHz channel bandwidths and, depending on regulatory requirements, TDD (time-division duplexed) or FDD (frequency-division duplexed) operation.  Similarly, a WISP (Wireless Internet Service Provider) in the U.S. using license-exempt spectrum in the 5.8 GHz UNII band might desire equipment that supports TDD and a 10 MHz bandwidth.

    Ultimately, the WiMAX suite of conformance tests, in conjunction with interoperability events, will enable service providers to choose from multiple vendors offering broadband wireless access equipment conforming to the IEEE 802.16a standard, which is optimized for their unique operating environment.

    Impact of WiMAX on Future Telecom Services, Access

    Key Enhancements Differentiate the IEEE 802.16a Protocol

    1.) QoS.  Since the 802.16a MAC relies on a Grant/Request protocol for capacity assignment, it supports differentiated service levels (e.g., T-1/OC-3 for business and best effort for residential).  The protocol employs TDM data streams on the downlink and TDMA on the uplink, with a centralized scheduler to guarantee efficient and prioritized allocations, which makes it a natural fit for delay-sensitive services like voice and video.  By assuring collision-free data access to the channel, the 16a MAC improves total system throughput and bandwidth efficiency, in comparison with contention-based access techniques like CSMA-CA. The 16a MAC also assures bounded delay on the data (CSMA-CA by contrast, offers no guarantees on delay).  The TDM/TDMA access technique also ensures easier support for multicast and broadcast services.  And since subscriber allocations are predetermined, smart power saving algorithms can be developed to support low-power terminals.

    2.) Scalability.  The standard supports flexible RF channel bandwidths and reuse of these channels (frequency reuse) as a way to increase cell capacity as the network grows. The standard also specifies support for transmit power control and channel quality measurements as additional tools to support cell planning and efficient spectrum use. The standard has been designed to scale up to hundreds or even thousands of users within one RF channel. Operators can re-allocate spectrum through sectorization and cell splitting as the number of subscribers grows. Also, support for multiple channel bandwidths enables equipment makers to provide a means to address the unique spectrum use and allocation regulations faced by operators in diverse international markets.

    3.) Coverage.  The standard is designed for optimal performance in all types of propagation environments, including line of site (LOS), near-LOS and non-LOS environments, and delivers fiber-like performance even in cases where extreme link pathologies have been introduced by signal reflections. As discussed earlier, the robust OFDM modulation scheme yields high spectral efficiency (bits per second per Hertz) over ranges from two to 40 kilometers with up to 70 Mbps in a single radio frequency (RF) channel. Advanced topologies (mesh networks) and antenna techniques (beam-forming, STC, antenna diversity) can be employed to improve coverage even further. These advanced techniques can also be used to increase spectral efficiency, capacity, reuse, and average and peak throughput per RF channel.

    Impact on the Mobile Workforce

    WiMAX solutions will facilitate citywide wireless broadband coverage for fixed residential and portable broadband devices such as PDAs and laptops. For example, a service provider could use an 802.16 standard-compliant CPE (customer premise equipment – the box that resides at customer's premise) in either licensed or unlicensed band to quickly deliver V-DSL speed network connectivity to their customers or connect Wi-Fi hotspots and hot zones. Today, it will take many months for services provider to provision T1 or DSL broadband connection for a new customer.

    With WiMAX, the same service provider can provide a true broadband network delivering broadband services covering neighborhoods and business campuses within days -- at a fraction of the cost. In addition, this service provider could offer on demand, high-speed bandwidth to local events, public locations and schools. Typically, a single WiMAX cell has enough capacity to serve multiple businesses, and hot spots while simultaneously providing hundreds of households with DSL-level broadband connectivity. As mentioned earlier, the latest enhancements to the standard (802.16e) will define a way for WiMAX systems to support nomadic and regional mobile devices with roaming, which is sure to impact business users that are constantly on the go.