Understanding WiMAX™

May 16, 2008

Worldwide Interoperability for Microwave Access (WiMAX) is a wireless digital communication technology, based on the IEEE 802.16 and ETSI HiperMAN wireless metropolitan area network (MAN) standards. It can provide broadband wireless access (BWA) up to 50 km for fixed stations (e.g., desktop PCs), and 5 - 15 km for mobile stations (e.g., notebooks, computers, mobile phones, personal media players, and PDAs).

As compared to a wireless technology like Wi-Fi, WiMAX is more immune to interference, allows more efficient use of bandwidth and is intended to allow higher data rates over longer distances. Because it operates on licensed spectrum, in addition to unlicensed frequencies, WiMAX provides a regulated environment and viable economic model for wireless carriers. These benefits, coupled with the technology's global support (e.g., ongoing worldwide deployments, spectrum allocation and standardization), make it the popular choice for quick and cost-effective delivery of super-fast broadband wireless access to underserved areas around the world.

The Technology

The fixed version of WiMAX, provides non-line-of-sight (NLOS) transmission to stationary devices using the 2-11 GHz frequencies. Higher frequencies require line of sight. Fixed WiMAX™ provides a high throughput broadband connection at speeds up to 75 Mbps over a distance as far as 30 miles. It is based on orthogonal frequency division multiplexing (OFDM), uses multiple pilot tones and supports modulations ranging from BPSK to 64 QAM. WiMAX systems can use variable bandwidths from 1 to 28 MHz with 256 subcarriers (192 data subcarriers) in either licensed or unlicensed spectrum. It can be used for a variety of applications including a "last mile" broadband connection, hotspot and cellular backhaul, and high-speed enterprise connectivity for businesses. The mobile version of WiMAX is an extension for mobile use in the 2-6 GHz band (see the Table). It allows WiMAX technology to be built into notebook computers and other mobile devices.

Table 1. Comparison of 802.16 wireless technologies.

Helping to promote and facilitate deployment of broadband wireless networks based on the IEEE 802.16 standard is the industry-led organization known as the WiMAX Forum®. Formed in 2001, it is working toward this goal by certifying compatibility and interoperability of broadband wireless products. Certification takes place via the WiMAX Forum Certified testing and certification program at any one of five WiMAX Forum designated Certification Laboratories (WFDCLs). These labs include: AT4 Wireless in Spain and the United States, Telecommunications Technology Association in Korea, the China Academy of Telecommunications Research in China, and Advanced Data Technology Corporation in Taiwan.

Market Impact

WiMAX technology is increasingly being embraced by countries worldwide. According to analysts with the Dell'Oro Group, the Mobile WiMAX™ market will grow by a compounded annual growth rate exceeding 50 percent through 2011. As evidence of this growth, both trials and commercial deployments are currently ongoing around the world. In the United States, for example, Sprint recently announced a nationwide build-out. More critically though, the rate of build-out is accelerating (see Figure 1). Recent data from Infonetics suggests that the overall broadband market (4G) could be upwards of $20 billion in 2010 with $5 billion of that total attributable to Mobile WiMAX. That translates to the availability of Mobile WiMAX technology to literally millions of subscribers - over 30 million users by 2010 alone, with most users in Asia and North America.

WiMAX Services are also now being rolled out in Europe, India, Puerto Rico, Russia, South Korea, and the United States, just to name a few. In addition, many operators are either planning similar fixed systems or biding their time while Mobile WiMAX equipment makes its way through the certification process.

Figure 1. This table, courtesy of Infonetics, highlights the growth in WiMAX equipment revenue through 2010. As is evident from this table, Mobile WiMAX equipment sales will quickly overtake Fixed WiMAX products.

Widespread deployment of WiMAX is being driven by its ability to deliver a lower cost, flexible, high-performance solution to "last mile" broadband Internet services. Consider a typical 20-MHz channel bandwidth deployment scenario. A WiMAX product could support downlink data rates of 65 Mbps at close range to 16 Mbps at distances of 9-10 km. That's enough bandwidth and transmission range to deliver high-speed simultaneous access to triple-play applications (e.g., applications that offer voice, data and video services) to literally hundreds of businesses or thousands of residences.

While some analysts have suggested that Fixed WiMAX is destined to become as widely used as digital subscriber line (DSL) and cable modem Internet access technologies, others feel that its true potential lies in its mobility. Mobile WiMAX delivers another choice to existing cellular operators who could use it to supplement their networks in metropolitan areas with full-featured multi-media mobile applications including audio, data and video. New operators might deploy the technology to compete with the cellular networks.

Challenges Ahead

Despite its growing market approval, many factors conspire to make WiMAX system design challenging, including consumers, who today demand greater range, faster data rates and lower price-points. The 802.16 specification itself also poses challenges as it forces engineers to face many different system considerations in terms of RF requirements and architectures. Will the WiMAX system be deployed as Time Division Duplexing (TDD), Frequency Division Duplexing (FDD) or half-duplex FDD? Will it be based on a superheterodyne or direct-conversion RF architecture? Ineffectively addressing any one of these challenges threatens to hamper the proliferation of WiMAX and directly ties into the success of a WiMAX product. Some of the key engineering challenges that now exist include:

Challenge: Orthogonal Frequency Division Multiple Access (OFDMA) Complexity

OFDMA is the digital modulation scheme employed by Mobile WiMAX. It uses OFDM technology in an innovative way to allocate the RF spectrum more effectively to more users. While this provides a very "granular" way to dissect bandwidth and charge for service, the standard and signal structure are extremely complex, creating a number of challenges. To begin with, as the expected and required services from WiMAX networks expand, ever greater demand will be placed on the processors in both the base and mobile stations. Additional processor strain will come from service providers using dynamically allocated subcarriers to allocate spectrum resources. And, while WiMAX's complex signal structure provides network operators with the flexibility they need, its associated cost puts enormous strain on the power amplifier (PA). Another challenge stems from WiMAX's utilization of non-traditional frequency re-use schemes which can create inter-cell interference, especially at the edges of the cell -- just when a critical hand off needs to occur.

Challenge: Multiple-Input Multiple-Output (MIMO) Complexity

MIMO technology uses multiple antennas at both the transmitter and receiver to improve communication performance. Because it allows more bits/hertz to be transmitted in a given bandwidth, the technology improves spectral efficiency which, in turn, allows service providers to flexibly configure communication services and not just peak data rates. While MIMO offers increased signal robustness and capacity improvements, those benefits come at the cost of increased complexity for both the base station and the mobile station, placing large demands on processing power and antenna design.

Challenge: A Tight EVM Requirement

The 802.16 standard specifies that Error Vector Magnitude (EVM) be held to -31 dB, based on a 1% packet error rate. While this error rate, and a stringent receiver noise figure (7 dB maximum), help contribute to WiMAX's longer range, having to meet the EVM target has a number of implications. For example, all system blocks must be more linear and phase noise must be considerably better than in an 802.11 design, impacting the synthesizer and resulting in a longer settling time.

The PA is also impacted by the tight EVM requirement. In WiMAX systems, PAs must deliver more power, be more linear, and be able to handle a high Peak-To-Average Power Ratio (PAPR) - about 10 dB. Consequently, they consume more power and are less efficient. As a result, considerable effort must be made to develop higher efficiency, more linear PAs, especially for mobile applications where power consumption is critical.

Challenge: Receiver Performance

Nearly all WiMAX-enabled devices have two receivers and many are capable of MIMO reception in several frequency bands, commonly 2.3 GHz and 2.5 GHz. This added complexity challenges the designer to find space to adequately separate two receive antennas in the mobile station (MS) and thereby ensure signal recovery. Also, the need to differentiate the multiple data streams from the received signals places increased demands on the processor. WiMAX designs must therefore be thoroughly evaluated to ensure success in the conformance test process, and to verify the device will operate in the electromagnetically harsh and dynamic world in which it will work. Unfortunately, the wide range of wanted and unwanted signals, combined with the many nested feedback loops, make receiver design one of the most difficult challenges in the Mobile WiMAX cellular system. In fact, many consider this task one of the hardest in modern radio design, forcing designers to deal with everything from hardware performance and current consumption to memory and algorithm complexity constraints, while recovering some highly complex MIMO signals suffering from linear and non-linear distortions.

One of the specific challenges designers face results from the 802.16 specification's support of subchannelization. This means that instead of transmitting on all 192 data subcarriers, the base station (BS) can transmit on just a subset for a given user. Using the same amount of power over fewer carriers can result in greater range for the system, but because the subcarriers are spaced more closely together, tighter requirements exist for phase noise and timing jitter. Also, higher-performance synthesizers must be utilized.

Another challenge stems from the fact that WiMAX systems rely on multipath to provide NLOS coverage. The receivers used in the system are especially susceptible to phase noise, timing jitter and frequency mismatch/synchronization. This can create a challenging situation, given the already tight requirement for phase noise and jitter as specified in the standard. Improving the receiver's performance will help by also improving its range and data rate. If receiver performance is not adequately addressed, the range and data rate of the WiMAX system will be adversely impacted, as will the price.

Challenge: Spectral Efficiency/Latency

The overall complexity of Mobile WiMAX, along with its highly dynamic air interface requires a significant amount of optimization and management. Enabling the MS to make some decisions about engaging on the network, for example, can reduce latency and free the base station to manage more of the additional, complex tasks associated with network management. Also, the flexibility to dynamically allocate spectrum comes at the price of tremendous signaling complexity. As a result, the base station must manage the constantly changing data requirements of multiple antennas (for MIMO) and a wide range of mobile stations traveling at potentially high speeds. The signaling must be flexible enough to manage these issues. Further, the designers and service providers must be able to verify the performance of the network under realistic traffic conditions both before and after deployment.

Challenge: Integration with Legacy Systems

WiMAX networks must be able to integrate into existing cellular networks, providing seamless connectivity and user experience. Of course designing this into the network operation, base station and mobile station is a challenge task since WiMAX's modulation scheme is so very different from legacy systems.

Solutions

Now a Principal Member of the WiMAX Forum, Agilent Technologies first came to market with a WiMAX-based solution in November 2004. With its innovative technology, unrivalled expertise and outstanding customer support, it has quickly established itself as a premier test and measurement leader in WiMAX. Bolstered by overwhelming market acceptance, and with its ability to understand the engineering challenges facing its customers in the WiMAX arena, Agilent is continuing to deliver a broad range of solutions to the market.

Agilent today offers the largest breadth of WiMAX design and test solutions spanning the entire lifecycle from R&D, design verification, pre-conformance, conformance, and manufacturing, through network deployment and service assurance -- for Fixed and Mobile WiMAX, WiBro, and including support for Wave 2 and MIMO. These up-to-date, comprehensive solutions provide engineers the reliable, repeatable and consistent results they need to deploy WiMAX devices, networks and services.

• Research and Development
  WiMAX technology continues to evolve. Product development, however, cannot always wait for standards to stabilize. To aide in this process, Agilent delivers a complete, integrated R&D design and test environment including simulation, characterization and evaluation tools. As an example, Agilent's Advanced Design System (ADS) Wireless Design Library for Fixed and Mobile WiMAX, 89601A Series Vector Signal Analysis (VSA) software, PSA Series high-performance Spectrum analyzer and E6651A Mobile WiMAX Test Set offer analysis of component and system performance, thereby streamlining the design of WiMAX designs (see Figure 2).

Figure 2. Agilent's 89601A VSA software offers comprehensive WiMAX modulation analysis for evaluating and troubleshooting fixed and mobile WiMAX signals. It can measure the different WiMAX equipment profiles with bandwidths from 1.25 to 28 MHz, at frequencies from baseband to 11 GHz and beyond, and supports advanced WiMAX features such as sub-channelization.

• Design Verification and Pre-Conformance
  During design verification, engineers must validate that their designs conform to the WiMAX standard. To ensure that base stations and subscriber stations conform to the various regulations established in different countries, both the WiMAX receiver and transmitter must be tested. Here, the ability to generate, detect, demodulate and troubleshoot WiMAX signals is critical. Agilent Signal Studio for 802.16 WiMAX software allows engineers to quickly and easily configure Fixed and Mobile WiMAX-compliant waveforms for both component and receiver design verification and testing. The Agilent ESG vector signal generator helps simplify this process by delivering calibrated WiMAX test signals (see Figure 3). When used in a connected solution with ADS and VSA, designers have a virtual prototyping solution. Agilent's PSA Series high-performance spectrum analyzer aids in this process as well, measuring and monitoring complex WiMAX signals. In addition, the E6651A Mobile WiMAX Test Set, MXA Spectrum Analyzer and WiMAX Design Verification Test System support engineers validating WiMAX designs. Together, these tools offer a compelling solution for designing and testing WiMAX components, subsystems and systems.
  
  

  

  Figure 3. Agilent's ESG vector signal generator incorporates a broad array of capabilities for evaluating the performance of nearly all current and proposed air interface standards such as WiMAX. Together with Signal Studio software it provides pre-configured and user-configurable WiMAX waveforms that developers can use to stimulate their WiMAX components at frequencies to 6 GHz.

  Designers must also be able to test the WiMAX Forum's Wave 2 system profiles -- a task crucial to the successful deployment of Mobile WiMAX products. Support for these profiles in Agilent's VSA, Signal Studio and Mobile WiMAX Test Set solutions enables accurate and cost-effective testing of MIMO and other Wave 2 Profile functionality in Mobile WiMAX products. Agilent's VSA software and Signal Studio support Matrix A and Matrix B signals for downlink, uplink collaborative MIMO and creation of HARQ bursts, and uplink sounding zones. Signal Studio also provides STC/MIMO support, as well as features like uplink sounding to support beamforming and MIMO fading embedded in a waveform. The Mobile WiMAX Test Set features cross-channel metrics and MIMO channel measurements which allow the engineer to characterize transmitted signals either directly from the Tx antenna or after fading.

• Conformance Test
  Conformance test ensures interoperability with other WiMAX equipment and a positive end-user experience for today's consumers. Agilent's range of WiMAX test products incorporate the latest industry-required measurements and are found in the AT4 Wireless MINT RCT System. MINT T2110 covers the transmitter and receiver test cases for base stations and subscriber stations according to the WiMAX CS 103 001 test specification.
  
  Agilent also now offers an IEEE 802.16e 2005 Protocol Conformance Test (PCT) Solution based on the Agilent E6651A Mobile WiMAX Test Set. When equipped with the PCT capability, Agilent's E6651A Mobile WiMAX Test Set allows equipment developers and test houses to run validated protocol test cases to verify that their implementation conforms to WiMAX standards.
  
  The WiMAX Forum's product-certification process is designed to ensure WiMAX-enabled products perform as expected and provide the customer with a reliable communication experience. One portion of this process is the RPT which measures transmit power and receive sensitivity of WiMAX devices (www.wimaxrpt.com). The Agilent E6651A Mobile WiMAX Test Set is used in RPT systems like the AMS-8500 RPT system from ETS-Lindgren. The E6651A's combined RF, protocol and functional test capabilities help engineers make the required RPT measurements and assure customers of the quality of their WiMAX-enabled products.

• Manufacturing
  Engineers developing WiMAX receivers and components require signal-generation and analysis tools to verify compliance with still-evolving WiMAX conformance test requirements. Agilent's N8300A Wireless Networking Test Set provides a complete one-box transmitter and receiver test solution for Mobile and Fixed WiMAX devices and modules to increase manufacturing test throughput (see Figure 4). The MXG Vector Signal Generator, with Signal Studio for WiMAX, provides the standards-based signals needed for the evaluation, while the Agilent MXA Signal Analyzer allows the engineer to analyze the WiMAX signals. Additional products, such as the MXZ-1000 WiMAX Manufacturing Test System, can also aide in this process. Together these solutions provide today's engineers with a complete and fast WiMAX test system for design and production environments.

Figure 4. Agilent Technologies' One-Box Wireless Networking Test Set provides for the testing of high volumes of Mobile WiMAX devices that require a standard-compliant Mobile WiMAX physical layer test tool.

• Network Deployment and Service Assurance
  Critical to the growth of a wireless provider's customer base and revenue is the successful installation, optimization and troubleshooting of its WiMAX network. Having the right test and measurement tools in place to accomplish these goals, therefore, is absolutely essential. As a leading provider of WiMAX design and test solutions, including network deployment and service assurance tools, Agilent is dedicated to helping engineers address the challenges associated with this emerging technology by providing the right solution at the right time. The Agilent E6474A Wireless Network Optimization Platform, for example, allows early verification of network deployments. This enables wireless service providers and network equipment manufacturers to proactively address challenges with wireless voice and data networks through quick and accurate problem identification. Another tool, the J7910A Signaling Analyzer WiMAX Solution, is a high-performance solution for system verification, troubleshooting and RAN optimization. It enables distributed call trace, performance measurements and drill-down problem isolation (see Figure 5).

Figure 5. Agilent's signaling analyzer, the J7910A, WiMAX solution offers a breakthrough in troubleshooting methodology with a high-performance, client server, multi-user architecture, and seamless drill down from statistics and call traces, to messages and decodes.

Conclusion

WiMAX is intended to make point-to-multipoint broadband network access widely available, without the expense and distance limitations associated with wired options. Critical to this emerging technology and the overall success of WiMAX applications is the ability to generate, detect, demodulate, and troubleshoot PHY layer signals. As a leader in WiMAX test and measurement, Agilent Technologies has, and continues to deliver a broad range of solutions for addressing the unique challenges brought about by the Fixed and Mobile WiMAX specifications. Agilent was first to market with R&D-based WiMAX solutions and is an active member of the WiMAX Forum. Agilent's measurement solutions are currently used in WiMAX certification testing.

Agilent's innovative solutions play a critical role in helping to grow the WiMAX market, while its technical expertise enables it to stay ahead of any engineering challenges that may arise. With its ongoing commitment to supporting WiMAX, Agilent will continue to develop and introduce solutions as the market grows and the technology advances.

Agilent in WiMAX
A Principal Member of the WiMAX Forum (www.wimaxforum.org), Agilent Technologies is an active participant in this organization. As a world leader in test and measurement solutions, Agilent continues to be at the forefront of this emerging market, offering WiMAX design and test solutions that span the entire technology lifecycle -- R&D, design verification and pre-conformance, conformance, manufacturing through network deployment, and service assurance. Information about Agilent's WiMAX design and test solutions can be found at www.agilent.com/find/wimax.

About Agilent
Agilent Technologies Inc. (NYSE: A) is the world's premier measurement company and a technology leader in communications, electronics, life sciences and chemical analysis. The company's 19,000 employees serve customers in more than 110 countries. Agilent had net revenue of $5.0 billion in fiscal 2006. Information about Agilent is available on the Web at www.agilent.com.

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"WiMAX," "Fixed WiMAX," "Mobile WiMAX," "WiMAX Forum," the WiMAX Forum logo, "WiMAX Forum Certified," and the WiMAX Forum Certified logo are trademarks of the WiMAX Forum. All other trademarks are the properties of their respective owners.

Contacts:

Janet Smith, Agilent
+1 970 679 5397
janet_smith@agilent.com