Breaking the bottleneck of WiMAX physical layer testing

The development of WiMAX technology has also put forward higher requirements for the receiving and transmitting tests corresponding to the WiMAX physical layer test. R&S provides targeted testing solutions for this.

WiMAX stands for World Interoperability for Microwave Access. It is a wireless metropolitan area network technology ( WMAN ). One base station can provide a maximum downlink data transmission rate of 100Mbps for multiple fixed users within a radius of 3 to 10 kilometers, and a maximum downlink data transmission rate of 15Mbps for multiple mobile users within a radius of 3 kilometers. There are currently two major international standards for WiMAX, namely IEEE802.16-2004 and IEEE802.16e-2005. IEEE802.16-2004 is a revision of 802.16a and 802.16d, mainly used for fixed broadband wireless access, including OFDM and OFDMA technologies; IEEE802.16e-2005 standard is an extension of IEEE802.16-2004 standard, which adds support for mobile broadband data access. Physical layer test In WiMAX technology, OFDM technology is mainly used as the signal transmission method for non-line-of-sight connection (NLOS). As we all know, OFDM signals are composed of some orthogonal carriers, and digital modulation is performed on each carrier. Compared with single-carrier technology with the same data rate, OFDM signals have a longer symbol period, so this technology has strong resistance to multipath fading. In addition, the modulation methods applied on the carrier are BPSK, QPSK, 16QAM and 64QAM, and various modulations are adaptively switched according to the requirements of the transmission rate. Compared with wireless LAN WLan, WiMAX signal bandwidth is not fixed and can vary from 1.25MHz to 28MHz. In IEEE802.16-2004, there are two modes: OFDM and OFDMA. In OFDM mode, there are 200 subcarriers and it can work in TDD or FDD mode; in OFDMA mode, the number of subcarriers is variable, and a carrier group (subchannel) is allocated to each user to transmit the user data, and the number of carriers is greatly increased. IEEE802.16e-2005 supports mobile or roaming broadband data access. Korean standard WiBro is a special 802.16e technology. For WiMAX devices, physical layer testing (RF testing) is a necessary means to ensure that they have good quality and work properly. The test is mainly divided into receiver testing and transmitter testing; in addition, amplifiers and other devices require similar testing processes. According to the needs of WiMAX testing, R&S has launched corresponding WiMAX signal generation and signal analysis equipment, which can perform complete tests on the receiving and transmitting parts to comprehensively evaluate WiMAX devices. Receiver testing R&S's digital signal sources SMU, SMJ, and SMATE can support the generation of various WiMAX signals with the corresponding WiMAX option SMx-K49, including signal frame content configuration, channel coding, etc. With this device, the required WiMAX signals can be generated for receiver testing. WiMAX signal generation In SMU, the generation of IEEE802.16-2004, IEEE802.16e-2005 and WiBro signals can be completed. During the signal generation process, various important parameters of the signal are set according to the test requirements. Such as physical layer mode (OFDM/OFDMA), duplex mode (TDD/FDD), uplink and downlink, frame structure, zone/segment, signal bandwidth, modulation mode, burst type, data length, subchannel, etc. Among them, WiMAX signal generation has the following characteristics: In OFDMA mode, up to 8 zones are supported, each zone can be configured separately, and its type can be set to FUSC, PUSC, AMC2×3 and Sounding. In OFDMA mode, Burst channel coding supports CC and CTC. It supports space-time coding, and MatrixA or MatrixB can be selected. Combined with the design concept of SMU dual channels, it is very convenient to generate two-way signals of transmission diversity after fading. Fading simulation In order to test the performance of WiMAX receivers, especially 802.16e, testing in a fading environment is particularly important. SMU200A has a built-in fading simulator that can simulate the fading environment of a single channel 40-path or a dual channel 20-path. Each path can be set with corresponding parameters, such as loss, delay, moving speed, Doppler frequency shift, etc. At present, SUI (Stanford University Interim) models (SUI1-SUI6) can be used to perform relevant WiMAX fading tests. In the fading simulator of SMU200A, SUI models are predefined and users can call them directly. MIMO MIMO (Multiple Input Multiple Output) technology achieves spatial multiplexing through antenna systems to increase the efficiency of bandwidth utilization. It has been widely used in new high-speed data service systems, such as 802.11n, LTE, WiMAX, etc. Therefore, MIMO is an indispensable part for WiMAX testing. SMU200A has a dual-channel design concept, and each channel can independently generate the required WiMAX signal; in the specific WiMAX signal configuration, it supports the corresponding space-time coding to distinguish the signals of different antennas; in addition, the fading simulator of SMU200A can work in two channels respectively, and the two fading channels can set their correlation. Therefore, SMU200A can fully support the tests for transmit diversity (2×1) and receive diversity (1×2). For 2×2 MIMO or more than 2×2 MIMO, such as beamforming, R&S will launch an implementation based on SMU200A in the near future. Therefore, SMU200A will support comprehensive MIMO tests in WiMAX. Transmitter test R&S's signal analyzer FSQ with the corresponding WiMAX option FSQ-K93 can analyze various types of WiMAX signals, including frequency domain characteristics, time domain characteristics and modulation quality. With this device, complete WiMAX transmitter tests can be performed. In FSQ, the analysis results of WiMAX signals are displayed in a numerical list. The numerical list includes test results of parameters such as EVM, IQ non-ideality, frequency domain and time domain power, symbol clock error, frequency error, CINR, RSSI, Crest Factor and pilot BER. In addition, FSQ also provides graphical results display of many analysis parameters, including: EVM corresponding to symbol and carrier changes, phase frequency error corresponding to Preamble changes, spectrum flatness, group delay, constellation diagram, bit stream, Burst statistics, spectrum emission mask (IEEE, ETSI), adjacent channel power and CCDF, etc.



































In addition, FSQ also has the following features: For 802.16e-2005 OFDMA signals, FSQ supports automatic demodulation, that is, FSQ can automatically analyze the MapBurst information contained in the signal, so that the demodulation analysis results can be automatically obtained without manually configuring the frame content of the analyzed signal. FSQ can automatically load the configuration file of the WiMAX signal from the signal source (such as SMU200A) through LAN, making the analysis process simpler, especially suitable for testing devices such as amplifiers. In addition, R&S will launch a signal analysis solution for MIMO testing in the near future, which even includes phase-coherent multi-channel analysis function. It can be seen that the signal analyzer FSQ can analyze various types of WiMAX signals, so as to make a comprehensive evaluation of the quality of the WiMAX transmitter.