introduction
With the development and maturity of wireless local area network technology, wireless local area network products have begun to be used more and more in homes, businesses, and public places such as airports and coffee shops to provide people with high-speed wireless Internet access. At present, a considerable number of manufacturers have launched their own wireless LAN products (such as wireless LAN access points, terminals, access controllers, etc.), providing consumers with a large number of choices, but at the same time due to product quality and compatibility The quality of the products varies, and it also brings a lot of problems to consumers' actual use. Therefore, there is an urgent need to further strengthen the quality supervision, inspection and testing of wireless LAN products.
Physical layer testing of wireless LAN products
Wireless LAN product testing mainly includes three aspects, namely physical layer testing, function and performance testing, and interoperability testing between products of different manufacturers. Among them, the physical layer test of wireless LAN products is mainly to detect the radio frequency indicators of wireless LAN terminals and access points, including transmitter indicators and receiver indicators, such as: transmit power, transmitter center frequency tolerance, spectrum mask, occupied bandwidth, Carrier suppression, spurious emission, receiver threshold level, maximum input level, adjacent channel suppression ratio, etc. Common testing tools for physical layer testing are spectrum analyzers, vector signal analyzers, power meters, vector signal generators, and other instruments. Typical test connections are shown in Figures 1 and 2.
Figure 1 Typical test connection diagram of transmitter specifications
Figure 2 Typical test connection diagram of receiver specifications
Wireless LAN product function and performance testing
The functional and performance tests of wireless LAN products are mainly for functional tests such as wireless LAN parameter configuration, authentication, encryption, switching, operation management and maintenance of wireless LAN terminals and access points, as well as the product's uplink / downlink throughput, delay, Performance tests such as stability. Taking the access point test as an example, a typical test connection is shown in Figure 3.
Figure 3 Typical test connection diagram of the access point
Among them, DUT1 and DUT2 are samples of the product to be tested, and the AAA server and certificate server are mainly used to test the authentication and billing functions of the product; the wireless protocol analyzer and protocol analyzer can capture the signal between the product to be tested and the terminal and server During the transmission process, perform protocol consistency analysis; the operation and maintenance platform configures the platform for the parameters of the product to be tested; and the performance tester is mainly used for performance testing of the product to be tested, such as throughput, delay, and stability.
Interoperability testing and certification of wireless LAN products
In addition to physical layer, function, and performance tests, interoperability tests between terminals and access point products of different manufacturers are required, that is, interoperability tests. The reason for this test is mainly due to differences in the understanding of technical standards by different manufacturers, and the use of reserved bits in the standards, so that wireless LAN products that follow the same technical standards will experience reduced performance when interoperating, and even The problem of not being able to communicate with each other has greatly affected the popularity and application of wireless LAN products.
At present, interoperability testing has begun to get more and more attention. The test methods mainly come from the interoperability test standards for wireless LAN products developed by the Wi-Fi Alliance. As a global non-profit industrial organization, the Wi-Fi Alliance has developed interoperability test methods for wireless LAN products and conducted interoperability certification to ensure compatibility between wireless LAN products of different manufacturers, thereby promoting wireless LAN technology. Development and product marketing. At present, the Wi-Fi Alliance's product interoperability certification mainly includes 802.11a, 802.11b, and 802.11g three required items, as well as wireless LAN security WPA2 (Wi-Fi Protected Access 2), wireless LAN multimedia WMM (Wi-Fi MulTI-media), wireless LAN regional standards 802.11d and 802.11 MAC layer / 802.11a physical layer enhanced standard 802.11h and other optional certification projects, and requires all certification tests on the standard Wi-Fi interoperability test platform. among them,
1) The three mandatory items of 802.11a, 802.11b, and 802.11g are the basic test items in Wi-Fi interoperability certification. Only after the corresponding basic item certification has been completed for the wireless LAN product according to its own working mode, can other tests be performed. Optional item certification test. 802.11a, 802.11b, 802.11g pass the test and the products of other manufacturers are under the settings of different wireless LAN parameters (such as: SSID, channel, RTS threshold, segment threshold, security mode, energy saving mode, etc.), still It can establish association, have certain upstream / downstream throughput, and can complete the normal work of functions such as handover, multicast / broadcast, etc., to ensure the interoperability between products of different manufacturers. For some special wireless LAN products (such as mobile phones, printers, and cameras with wireless LAN functions) and other PC-based network card products, the operating system, memory, and functions are different. The Wi-Fi Alliance allows According to its own characteristics, the indicators and functional requirements of standard test methods such as 802.11a, 802.11b, and 802.11g are adjusted to form a special device (ASD: ApplicaTIon Specific Device) test method, and then the product is certified according to this method.
2) WPA2 certification is mainly for wireless LAN products that support WPA2 security mode, testing the ability of different manufacturers' products to establish associations when interconnecting, upstream / downstream throughput, multicast, pre-authentication, PMK cache and other functions, and Compatibility with products that support WPA security mode, etc., to verify the interoperability of WPA2 products.
3) WMM certification is mainly to test the interoperability between products that support wireless local area network quality of service (QoS). In the case of simultaneous transmission of multiple services, the test products can be different according to the priority of the business.
(Respectively, from high to low, audio (VO: Voice), video (VI: Video), best effort (BE: Best Effort), background traffic (BK: Background)), accurate use of QoS parameters such as back-off time to ensure High traffic for high-priority services; and requires testing the interconnection between such products and wireless LAN products that do not have QoS functions to verify the interoperability of products that support QoS functions.
4) 802.11d certification is only carried out on wireless LAN products whose working mode is 802.11a. It is tested that wireless LAN access points can include regional information bits in beacons and paging response frames. Terminal products of other manufacturers can be based on the received region The location information in the information bit configures its own physical layer parameters to meet the operation requirements of the corresponding region.
5) The 802.11h certification includes two parts, power limit information element (Power Constraint Element) test and channel switch announcement information element (Channel Switch Announcement Element) test. The power limit information element test mainly verifies that the wireless LAN access point device can include the power limit information element in the beacon and paging response frame. Terminals of other manufacturers can determine the maximum transmit power allowed by the current channel based on this information; channel switching The declaration information element test verifies that the access point can automatically add a channel switching declaration information element (including the channel number field to which the access point may switch) to the beacon frame after detecting the radar channel on the current operating channel. The terminal can According to the received channel switching declaration information element, the transmission signal on the current channel is stopped to avoid interference with the radar signal.
At present, more than 2,000 wireless LAN products have passed one or more of the above Wi-Fi interoperability certification tests. At the same time, in order to meet the development of wireless LAN technology and the emerging certification needs of new wireless LAN products, the Wi-Fi Alliance is also actively carrying out research and development of new interoperability authentication methods, mainly including: wireless LAN and cellular Web Convergence Product Certification (WCC: Wi-Fi Cellular Convergence), Wi-Fi Voice Product Certification (Voice over Wi-Fi), Wi-Fi-enabled consumer electronics product certification (Consumer Electronics), and Biosafety Specific Absorption Rate SAR , Wireless LAN authentication and encryption, simple configuration method, spectrum and area, wireless LAN high-speed transmission 802.11n, etc. Among them, WCC will begin certification in January 2006. It mainly targets dual-mode products (such as PDAs, smart terminals, etc.) for wireless local area networks and cellular networks with Wi-Fi voice capabilities, using conduction testing and the CTIA Alliance (Cellular TelecommunicaTIons & Internet Association's (OTA: Over the Air) test two methods to verify that the transmission power and reception sensitivity of such devices meet the requirements of the index.
Conclusion
In summary, wireless LAN product testing is composed of three aspects: physical layer testing, function and performance testing, and interoperability testing. Only by further strengthening the research on test methods of wireless LAN products, formulating test standards, and carrying out related testing can we better regulate the market of wireless LAN products, ensure the quality and interconnection of products, and promote the promotion and application of wireless LAN technology.
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