WiMAX is a wireless digital communication technology based on IEEE 802.16 and ETSI HiperMAN wireless metropolitan area network (MAN) standards. It can provide up to 50 kilometers of broadband wireless access (BWA) for fixed stations (such as desktop computers) and 5 to 15 kilometers of broadband for mobile stations (such as laptops, mobile phones, personal media players and PDAs) Wireless access.
Compared with Wi-Fi and other wireless technologies, WiMAX has stronger interference resistance, can provide higher bandwidth utilization, and can transmit data at a higher rate over a longer distance. WiMAX can operate on authorized and unlicensed frequencies, so it can provide a standardized environment and a feasible economic model for wireless carriers. These advantages combined with worldwide technical support (such as ongoing deployment, spectrum allocation and standardization) make WiMAX the first choice for quickly and cost-effectively opening ultra-fast broadband wireless access in areas not covered by global services.
technology
The fixed version of WiMAX (IEEE 802.16-2004) can use the 2-11 GHz frequency band to provide non-line-of-sight (NLOS) transmission to fixed equipment. Higher frequencies require coverage within line of sight. Fixed WiMAX can provide high-throughput broadband connections at up to 75 Mbps over a distance of 30 miles. It is based on Orthogonal Frequency Division Multiple Access (OFDM), uses multiple pilot tones, and supports a modulation range from BPSK to 64 QAM. WiMAX systems can use a variety of bandwidths from 1 to 28 MHz in licensed or unlicensed spectrum, including 256 subcarriers (192 data subcarriers). It can be used for various applications such as "last mile" broadband connections, hotspots and cellular backhaul, and high-speed enterprise connections for enterprises.
The mobile version of the standard, IEEE 802.16e-2005, is an extension of 802.16-2004 and is used for mobile applications in the 2-6 GHz frequency band (see table). It can build WiMAX technology into laptops and other mobile devices.
Table 1. Comparison of 802.16 wireless technologies
The WiMAX Forum is the industry ’s leading organization that helps accelerate the deployment of broadband wireless networks based on the IEEE 802.16 standard. The forum was created in 2001 to achieve this goal by verifying the consistency and interoperability of broadband wireless products. It can be certified in any of the three WiMAX Forum designated certification laboratories (WFDCL) through testing and verification procedures certified by the WiMAX Forum. These laboratories include: the AT4 wireless laboratory in Spain, the Korea Telecommunications Technology Association and the China Academy of Telecommunication Research of the Ministry of Information Industry of China.
Market impact
WiMAX technology is more and more widely used in the world. Analysts from the Dell'Oro Group predict that by 2011, the compound annual growth rate of the mobile WiMAX market will exceed 50%. Mobile WiMAX trial operations and commercial deployments in full swing around the world attest to this rapid growth. Countries such as Europe, India, Puerto Rico, Russia, South Korea, and the United States have opened such businesses. In addition, many operators are planning to deploy similar fixed systems or strive to get mobile WiMAX equipment certified. As of June 2006, more than 200 operators plan to deploy WiMAX or have already deployed trial operations or commercial systems (see Figure 1).
Figure 1. This form is provided by TeleGeography and highlights recent deployments, most of which are planned for deployment or trial operation in the Asia Pacific region. As of June 2006, the total number of global networks exceeded 117, of which 14 new networks are planned to be deployed in North America.
WiMAX can provide lower-cost, more flexible, and high-performance solutions for "last mile" broadband Internet services, so it is widely deployed worldwide. Take the typical 20-MHz channel bandwidth deployment as an example. WiMAX products can support a downlink data rate of 65 Mbps at close range and a downlink data rate of 16 Mbps at a distance of 9-10 kilometers. Adequate bandwidth and transmission range can support hundreds of business users or thousands of home users to simultaneously access triple-play applications (such as applications that provide voice, data, and video services) at high speed.
Some analysts believe that fixed WiMAX is destined to be widely used like digital subscriber line (DSL) and cable modulation Internet access technologies, while other analysts believe that its true development potential lies in mobile communications. Mobile WiMAX â„¢ provides another option for current cellular operators. Operators can use it to supplement the network in a metropolitan area network to provide multimedia mobile applications (including audio, data, and video) with complete features. New operators can deploy the technology to compare with cellular networks.
Current challenges
Although it has gained more and more recognition in the market, many unfavorable factors still pose great challenges to WiMAX system design, including users who currently need greater coverage, faster data rates, and lower prices. The 802.16 standard itself also has problems, so that engineers need to consider many different factors in terms of system RF requirements and architecture. Is the WiMAX system deployed on time division duplex (TDD), frequency division duplex (FDD) or half duplex FDD? Is the WiMAX system based on superheterodyne or direct conversion RF architecture? If these challenges cannot be effectively solved Any one of them will hinder the application of WiMAX and directly related to the success of WiMAX products. Other engineering problems now facing include:
Challenge: strict EVM requirements
The 802.16 standard specifies that based on a 1% packet error rate, the error vector amplitude (EVM) is up to -31 dB. Although this bit error rate and strict receiver noise figure (7 dB maximum) help WiMAX achieve greater coverage, there must be many problems with meeting EVM goals. For example, this means that all system modules must have better linear characteristics, and the phase noise must be far superior to the design in 802.11. Accordingly, the harsh phase noise requirements have an impact on the synthesizer and may require a longer settling time.
Harsh EVM requirements also have an impact on power amplifiers (PA). In WiMAX systems, the PA must provide higher power, have better linearity, and be able to handle the peak-to-average power ratio (PAPR)-about 10 dB. But therefore they also consume more power and are less efficient. As a result, we must make considerable efforts to develop more efficient and linear PAs, especially in mobile applications where power consumption is critical.
Challenge: receiver performance
The 802.16 standard supports the use of sub-channels, which means that the base station (BS) can transmit signals to designated users through only part of the data sub-carriers without having to use all 192 data sub-carriers for transmission. Using the same amount of power on fewer carriers can expand the coverage of the system, but because the spacing between subcarriers is smaller, the requirements for phase noise and timing jitter are higher. Similarly, a high-performance synthesizer must be used.
Adding MIMO functionality to the design of mobile WiMAX receivers may make the design more complicated. It is very difficult to find enough space in the mobile station (MS) to isolate the two receiving antennas, but it is essential to ensure signal recovery. The need to distinguish between multiple data streams and received signals places higher demands on the processor.
WiMAX systems rely on multipath to provide non-line-of-sight (NLOS) coverage. The receiver used in the system is particularly susceptible to phase noise, timing jitter, and frequency mismatch / synchronization. Given that the standards have very strict requirements for phase noise and jitter, this may pose severe challenges to the system. Increasing the coverage and data rate to improve the performance of the receiver will effectively solve this problem. If the performance of the receiver is insufficient, the coverage, data rate and price of the WiMAX system will be affected.
solution
Agilent Technologies is now a major member of the WiMAX Forum®. In November 2004, Agilent introduced the first WiMAX-based solution to the market. With its innovative technology, unparalleled professional experience and outstanding customer support capabilities, Agilent quickly established its leading position in the field of WiMAX. Agilent has a high degree of market acceptance, and has a deep understanding of the engineering challenges encountered by customers in the WiMAX field. Agilent will continue to provide a wide range of solutions for the market.
Agilent's measurement solutions for testing fixed WiMAX and mobile WiMAX can cover the entire life cycle of the product, from research and development, design verification and pre-conformance to conformance testing and manufacturing. These latest comprehensive solutions provide engineers with the reliable, repeatable, and consistent results needed to deploy WiMAX equipment, networks, and services.
R & D
Wireless connectivity technology will continue to face a series of developing standards. However, product development cannot always wait for standards to be set before proceeding. To help in this process, Agilent provides a complete integrated R & D design and test environment, including simulation, characterization, and measurement tools. For example, the Agilent Advanced Design System (ADS) wireless design library for fixed WiMAX and mobile WiMAX, 89601A series vector signal analysis (VSA) software, PSA series high-performance spectrum analyzer, and E6651A mobile WiMAX tester, etc And system performance analysis, thus making WiMAX design into a streamlined design (see Figure 2).
Figure 2. The Agilent 89601A VSA software provides comprehensive WiMAX modulation analysis for the evaluation and troubleshooting of fixed WiMAX signals and mobile WiMAX signals. It can measure various performances of WiMAX equipment with a bandwidth of 1.25 to 28 MHz from baseband to 11 GHz and higher, and supports advanced WiMAX features such as sub-channelization.
Design verification and pre-compliance testing
During R & D, engineers must confirm whether their designs comply with WiMAX standards. In addition, in order to ensure that the base station and the user service station comply with various regulations made by different countries, both WiMAX receivers and transmitters must be tested. At this time, the ability to generate, detect, demodulate, and troubleshoot WiMAX signals is critical. Agilent Signal Studio for 802.16 WiMAX software enables engineers to quickly and easily configure waveforms that comply with fixed and mobile WiMAX in design verification and testing of components and receivers. The Agilent ESG vector signal generator helps simplify the above process by providing calibrated WiMAX test signals (see Figure 3). When used in ADS and VSA connection solutions, designers have a virtual prototype solution. Agilent PSA series high-performance spectrum analyzers also help in this process, measuring and monitoring complex WiMAX signals. In addition, the E6651A mobile WiMAX tester, MXA spectrum analyzer, and WiMAX design verification test system can also help engineers verify WiMAX designs. At the same time, these tools also provide powerful solutions for designing and testing WiMAX components, subsystems, and systems.
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