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i. Xác minh và kiểm tra bảo đảm chất lượng: Một khi hệ thống hoàn chỉnh hoạt động đúng, nhưng trước khi phát hành vào sản xuất, bộ phận bảo đảm chất lượng của các nhà cung cấp hệ thống phải đặt các thiết bị thông qua một pin mở rộng | Physical Layer Measurements As it is much simpler to measure frame error ratio FER by using the frame check sequence FCS in each frame to detect a frame error than BER it is more common to substitute FER for BER. BER can be translated to FER by simply multiplying by the number of bits in the frame thus a BER of 1 X 10 5 for a 1000 byte frame corresponds to an FER of 8 . For 802.11b the frame size used is 1024 bytes and the FER level is set to 8 . For 802.11a g the frame size is 1000 bytes and the FER level used is 10 . The actual sensitivity values are highly dependent on the specific receiver used -and in fact on the manufacturing tolerances for the receiver - but typical sensitivity figures range from -76 dBm to as good as -92 dBm for most modulation types. Generally the lower the signal required to reach the FER threshold the better. Dynamic range is measured by finding the maximum input level overload level of the receiver and then simply subtracting the sensitivity. This is basically the blocking dynamic range and corresponds to the receiver maximum input level specification of the 802.11 standard. The measurement process used is similar but instead of increasing the attenuation the attenuation is decreased and the VSG level potentially increased until the received frames start showing bit errors. The same criteria in terms of FER is applied to the maximum input level so that a consistent measurement of dynamic range can be obtained. As with sensitivity the dynamic range is significantly affected by receiver design and manufacturing parameters. Typical maximum input levels for WLAN receivers range from -20 dBm to as high as 0 dBm producing dynamic ranges in the region of 80-90 dB the 802.11 standard requires a maximum input level tolerance of at least -30 dBm for802.11a -20 dBmfor 802.11g and -10 dBm for 802.11b. Rather than the third-order IMD product measurements commonly used for analog receivers at HF and VHF WLAN receivers are characterized in terms of .
