In the communications industry, new technologies are constantly emerging. The 802.16 standard (also commonly referred to as WiMAX) will be the new wave of technology development. Worldwide Microwave Access Interoperability (WiMAX) technology has swiftly swept the industry and attracted widespread attention and rapid adoption among small rural operators, large service original equipment manufacturers (OEMs) and suppliers. The WiMAX standard was originally intended for broadband communication deployments on fixed stations. With the increasing popularity of these applications, WiMAX is evolving toward point-to-multipoint connectivity (ie, for the last mile of wireless broadband access technology), cellular backhaul and high-speed LAN applications for enterprises or universities. Although many of the technologies prior to WiMAX can achieve similar functionality, the main selling point of WiMAX is the interoperability of this unique technology. WiMAX is based on the 802.16 standard so that systems that comply with this standard can ensure interoperability with each other. This gives WiMAX vendors the flexibility to build their own systems with a variety of vendors without worrying about usability issues, fear of incompatibilities in system updates and upgrades, or delays in purchasing. From a vendor's perspective, interoperability allows small companies to enter the market to take a slice. If you can't ensure interoperability, you can only trust the system components provided by large enterprises. The advantage of interoperability is that small companies can also leverage their own Internet Protocol (IP) technology to squeeze into the ranks of vendors to provide various system components, thereby avoiding the risk of service providers dying at one vendor. Can be freely chosen between different vendors. WiMAX uses interoperability standards, but there are still many variables in the system that affect the implementation of RF solutions. Currently, WiMAX is available for the 3.5 and 5.6 GHz bands and the 2.5 GHz band with no license restrictions. In addition, some new 4.9 GHz and 700 MHz bands also use the WiMAX standard. In terms of interoperability and global compatibility, companies are looking to find new and creative ways to achieve performance benefits and their unique capabilities to differentiate themselves from competitors while ensuring compliance with WiMAX standards. The RF chipset for WiMAX radio technology implementation should be flexible enough to meet the requirements of multiple implementations and should have sufficient performance to meet the requirements of the standard specification. The design challenge we face is to ensure that the basic functional requirements are met and that the finer performance parameter architecture requirements are met while still meeting the standard requirements. It is important to ensure that the parameters meet the requirements of the WiMAX specification so that a robust solution that is suitable for manufacturing requirements can be designed. WiMAX transmitter The key performance parameter of the transmitter is its error vector magnitude (EVM) at a given power. EVM represents the integrity of the array (digital constellaTIon) after passing the transmitter. The main cause of transmitter EVM attenuation is the phase noise of the local oscillator (LO) source and the final power amplifier. Since the impact of the power amplifier is very large, it is necessary to discuss the EVM performance of the transmitter at a given output power. The EVM reference is 2.7%. Unlike cellular systems and 802.11 parameters, EVM requirements are much more stringent, and we typically calculate EVM values ​​in decibels to improve accuracy. The standard value of 2.7% is equivalent to -31.4 dB. We determine the performance of the transmitter based on the maximum rated modulation power of the EVM of -31.4 or better. Client Equipment (CPE) The line connecting the outdoor system to the base station is usually unaffected by obstacles and the output power is rated at 20 dBm. Systems deployed in buildings must address severe multipath environmental issues that would otherwise increase the rated power to 24 to 27 dBm. If the base station transmits power from 4W to 20W, then a more stringent power rating is required, depending on the required connection distance and system implementation. Designers must adjust the power amplifier as the primary device when increasing the system's rated power output. Since the power amplifier has a large impact on the EVM, we should use a larger, more robust device to achieve higher output power while meeting the EVM parameter of -31.4 dB. But this is not enough to ensure full compliance with the standard requirements. The relevant standard specifies an absolute parasitic output parameter of -40 dBm. Regardless of the output power, the spurious signal cannot exceed this parameter value. As the power rating increases, if we assume that the input power provided by the baseband processor remains the same, then the gain of the transmitter should be increased accordingly. An increase in transmitter gain will not only affect the desired signal, but will also affect unwanted spurious signals. Since the parasitic output parameter is fixed, the gain increase will result in a lower output parasitic tolerance relative to the parameter, so if the system originally meets the 20 dBm output power standard, it will be difficult to meet 24 dBm due to the gain increase. Or higher output power requirements. To ensure the flexibility of the RF chipset and to meet multiple output power requirements in a variety of situations, we must ensure good EVM performance of approximately -37 dB before the PA and a tolerance of 7 to 10 dB with parasitic output parameters. This allows designers to be more flexible in selecting the appropriate power amplifier for their system needs while ensuring that EVM requirements are met and does not exceed the parasitic output limits. WiMAX receiver The key performance parameter of the receiver is its sensitivity. The specification establishes the minimum bit error rate (BER) of 1E-6, which meets the requirements of the specification. In the case of testing only RF and analog circuitry, it is difficult to make actual BER measurements. We usually convert BER to EVM values. According to the correspondence between the two, the sensitivity of the 64-QAM signal is equivalent to the EVM value of -21.5 dB. In general, to achieve -23.5 dB, we should add a 2 dB tolerance to this parameter.
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January 04, 2023