WiMax power amplifier Test Solution

WiMAX Overview

World wide (WiMax) is a wireless transmission technology based on the IEEE 802.16 standard. As the "last mile" technology connecting users, WiMax is developed to replace broadband wired networks such as DSL and support mobile broadband wireless access, it uses OFDM transmission technology for NLOS connections, providing a data rate of up to 75 Mbit/s. The IEEE 802.16-2004 physical layer is divided into two modes: OFDM and OFDMA (Orthogonal Frequency Division Multiplexing ). In the OFDM mode, all carriers (200) are used for data transmission in TDD or FDD mode. In the OFDMA mode, the number of carriers increases significantly and is divided into several self-channels (subchannelization ), specify one or more sub-channels for each user and provide services for multiple users at the same time. IEEE 802.16e is mainly proposed for mobile WiMax Applications. The number of carriers varies significantly according to the FFT base (128,512,102 4, 2048). The Korean Standard WIBRO is a special case of 802.16e. Different from WLAN, the bandwidth of WiMAX signals is variable between 1.25MHz and 28 MHz instead of fixed.

Main test parameters of Power Amplifier

For general power amplifiers, focus on the following test parameters:

(1) power gain, reflecting the amplifier's signal amplification capability;

(2) 1 dB compression point, reflecting the linearity of the amplifier, that is, the amplifier's ability to enlarge large signals;

(3) maximum output power. In fact, the first two indicators can reflect the maximum output power available for the amplifier. They are tested using CW signals. As long as the RF indicators of the signal source are excellent, the power scanning capability is sufficient.

For WiMAX power amplifiers, the following test parameters are often used to fully measure the performance of the amplifiers.

(4) "burst" output power: it can be divided into the smallest RMS "burst" output power, the average RMS "burst" output power and the maximum RMS "burst" output power.

(5) frequency error: the frequency error can be described by the carrier frequency error relative to the center frequency of the spectrum instrument. The frequency error between the receiving and sending devices will lead to the movement of the sub-carrier spectrum relative to the receiver's FFT frequency, resulting in inter-carrier interference (ICI), as shown in 1.

Figure 1 inter-Carrier Interference caused by frequency error

(6) symbol clock error: the difference between the reference symbol clock and the actually measured symbol clock relative to the system sampling clock. If the symbol clock is lower than the reference clock, the OFDM signal ratio is longer, resulting in reduced sub-carrier spacing; otherwise, the sub-carrier spacing increases. In both cases, inter-Carrier Interference is generated, and the EVM performance of the signal is deteriorated.

(7) EVM (error vector amplitude): This is one of the most important test parameters to ensure that the amplifier outputs sufficient power while obtaining good signal quality. The EVM results can be for all carriers, data carriers, and pilot carriers.

(8) ACPR (adjacent channel power ratio): ACPR refers to the ratio of the power measured by the adjacent channel to the power of the main channel, reflecting the interference of amplifier distortion on the adjacent channel.

(9) Spectral flat: reflects the power variation of WiMAX subcarriers. It measures the deviation between the average power of each subcarrier and the average power of all subcarriers.

(10) spectrum difference: measure the power difference between adjacent subcarriers In the abrupt lead.

(11) spectrum template (spectrum mask): it measures the "Profile" of the transmitter's emission spectrum to ensure that there is no excessive power emission outside the main channel.

For the aforementioned (5), (8), (9), (10), (11 ), although the multi-carrier continuous wave function of the General R & S standard signal source can simulate A WiMax signal for measurement, this is often difficult to adjust and is not accurate enough; For (4), (6) and (7) require real WiMax signals for measurement, especially EVM. Therefore, a signal source that can generate WiMax signals is essential for WiMAX power amplifier testing.

R & S WiMAX power amplifier Test Solution

R & S provides fast and accurate solutions for WiMAX power amplifier testing. Test Settings 2 are shown in the following section.

Figure 2 WiMAX power amplifier Test Solution

(1) Signal Source: Using SMU200A and option SMU-K49, or SMJ100A and option SMJ-K49, can easily produce 802.16-2004-OFDM, WiMAX 802.16e OFDMA and WIBRO signal. In addition to excellent RF and baseband performances, SMU200A also provides powerful fading simulation functions, making it more suitable for R & D and use.

(2) spectrum analyzer: FSQ series spectrum analyzer and option R & S FSQ-K92 support 802.16-2004-OFDM Signal Analysis; or use FSQ and option FSQ-K93 to support WiMAX 802.16e OFDMA and WIBRO signal analysis; you can also choose the FSL series spectrum analyzer and the option FSL-K92 to support 802.16--OFDM signal analysis.

(3) DemoMeas_WiMAX, an external PC software, controls the signal source (SMU200 and SMJ100) and spectrum analyzer (FSQ and FSL) through a GUI or LAN ). As shown in 3, you only need to select the parameters to be tested in the left column. The software can automatically complete the settings required for the test and generate a test report at the same time.

Figure 3 DemoMeas-WiMAX software window

In addition, the required test parameters are different for the OFDM, OFDMA, and WIBRO standards. Therefore, DemoMeas_WiMAX provides different options for users (see table 1 ), it includes a series of setting files corresponding to these three standards. You can choose to measure the uplink or downlink, and edit these setting files as needed.

In short, as a leader in the wireless testing field, the WiMAX power amplifier testing scheme of Rode & Schwarz based on its excellent signal source and spectrum spectrometer fully reflects the superiority and simplicity of automated testing, quick and accurate features greatly improve the testing efficiency of users.

1. Expert analysis: Several Problems in WiMAX Testing
2. Special topics: wimax technology and trends