WiMax Power Amplifier Testing Solutions

About WiMAX

WiMax (worldwide interoperability for microwave access, Worldwide Interoperability for Microwave Access) is based on the IEEE 802.16 standard for a wireless transmission technology. Connect users as "last mile" technology, WiMax has been developed to replace, such as DSL and other broadband cable networks, and supports mobile broadband wireless access, it uses OFDM transmission technology for non line of sight (NLOS) connections, providing up to 75 Mbit / s data rate. Which, IEEE 802.16-2004 physical layer is divided into two modes: OFDM and OFDMA (orthogonal frequency division multiplexing). In the OFDM mode, the use of all the carrier (200) in TDD or FDD mode for data transmission; in the OFDMA mode, a significant increase in the number of carrier, and is divided into a number of self-Channel (subchannelization), for each user to specify one or more sub-channels to provide services for multiple users simultaneously. IEEE 802.16e mobile WiMax applications mainly made, the carrier can use the FFT the number of base (128,512, 1024, 2048) significantly changed the standard WIBRO Korea is a special case of 802.16e. With different WLAN, WiMAX signal bandwidth is not fixed, but variable between 1.25MHz and 28MHz.

The main test parameters PA

For the common power amplifier, the main focus on the following test parameters:

(1) power gain, reflecting the amplification of the signal amplifier capacity;

(2) 1dB compression point, reflecting the linearity of the amplifier, ie the capacity of large-signal amplifier;

(3) Maximum output power, in fact, the first two indicators can be used to reflect the actual amplifier the maximum output power. CW signals are used to test, as long as the signal source frequency index excellent, with power capacity can be scanned.

Power amplifiers for WiMAX, in order to fully assess the amplifier performance, are often concerned about the following test parameters.

(4) "sudden" Output power: into the smallest RMS "burst" output power, the average RMS "burst" output power and maximum RMS "burst" output.

(5) frequency error: frequency error can be compared to the spectrum analyzer center frequency of the carrier frequency error to describe. Transceiver frequency error between the various sub-carrier will cause the receiver FFT frequency spectrum relative to the movement, resulting in intercarrier interference (ICI),

(6) symbol clock error: refers to the sampling clock relative to the system clock reference symbol clock and the actual measurement of the difference between symbols. If the symbol clock lower than the reference clock signal will OFDM longer than required, causing sub-carrier spacing; the other hand is caused by subcarrier spacing increases. Both situations produce ICI, the EVM performance of the signal deterioration.

(7) EVM (Error Vector Magnitude): This is one of the most important test parameters to ensure sufficient power amplifier output signal to obtain good quality. EVM results can be for all carriers, data carriers and pilot carriers.

(8) ACPR (Adjacent Channel Power Ratio): ACPR measured means adjacent channel power and the main channel power ratio, reflecting the amplifier distortion of the adjacent channel interference.

(9) Spectrum Flatness: reflect WiMAX subcarrier signal power changes, which measure the average power of each sub-carrier average power for all sub-carrier deviation.

(10) difference spectrum (spectrum difference): the leading part of the emergency measure the power difference between adjacent subcarriers.

(11) spectral mask (spectrum mask): emission spectrum measurement transmitters, "profile" to ensure that not too much outside the main channel of the power transmission.

For the above (5), (8), (9), (10), (11), although the general R & S standard signal source of the multi-carrier continuous wave function can simulate a WiMax signal to be measured, but that often regulator problems and not accurate enough; while for (4), (6), (7) requires a real WiMax signal can be measured, especially EVM. Therefore, a WiMax signal can produce a signal source on the WiMAX Power Amplifier Testing is essential.

R & S WiMAX Power Amplifier Testing Solutions

R & S company is testing WiMAX power amplifier provides a fast and accurate solution. Test setup shown in Figure 2 includes three parts.

WiMax Power Amplifier Testing Solutions

Figure 2 WiMAX Power Amplifier Testing Solutions

(1) Signal source: Use SMU200A and option SMU-K49, or SMJ100A and Option SMJ-K49, can easily generate 802.16 -2004 - OFDM, WiMAX 802.16e OFDMA and WIBRO signal. Which SMU200A addition has excellent RF and baseband performance, but also with a strong decline of analog functions, more suitable for research use.

(2) Spectrum Analyzer: FSQ Series spectrum analyzer and optional R & S FSQ-K92 support the 802.16-2004-OFDM signal analysis; or use the FSQ and FSQ-K93 option supports WiMAX 802.16e OFDMA and WIBRO signal analysis; also choose to FSL Series spectrum analyzer, and FSL-K92 option supports 802.16-2004-OFDM signal analysis.

(3) external PC software DemoMeas_WiMAX: via GPIB or LAN control signal source (SMU200 and SMJ100) and the spectrum analyzer (FSQ and FSL). Shown in Figure 3, users simply select the unknown parameters of the left column, the software can automatically complete the required test set, but also generate test reports.

WiMax Power Amplifier Testing Solutions

Figure 3 DemoMeas-WiMAX software windows

In addition, OFDM, OFDMA and WIBRO three kinds of standards for the test parameters are different, so DemoMeas_WiMAX also provides users the choice of the difference (see Table 1), which includes a range of settings files corresponding to the three standard , the user can choose the uplink (uplink) or downstream (downlink) were measured, and may need to edit the settings file.

In short, as a wireless testing field guide, Rohde & Schwarz test solutions WiMAX power amplifier based on its high performance signal source and spectrum analyzer, fully embodies the advantages of automated testing, with simple, fast and accurate feature greatly improve the efficiency of user testing.

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