WCDMA base station testing solves key deployment issues

With the opening of the Olympic Games, the third generation mobile communication system is getting closer and closer to our lives. The trial commercial use of China Mobile's TD-SCDMA has finally given us the opportunity to enjoy the various services based on high-speed data transmission brought by 3G in China. I believe that in the near future, the other two technologies (WCDMA and CDMA2000) will also enter our lives, enriching the choice of technology for Chinese people. However, a key factor in determining whether the network is good is the RF performance of its base station equipment . Therefore, how to test it has become a hot topic. For these three technologies of 3G, Rohde & Schwarz can provide comprehensive test solutions. This article mainly introduces the test solution for WCDMA base stations.

Basic principles of base station testing

The WCDMA base station test itself is different from the terminal test. According to the requirements of 3GPP test specification 25.141, all of its test items can be completed without signaling. Compared with GSM base stations, WCDMA base stations adopt code division multiple access technology, so its different code channel configurations (or channel models), especially the number of code channels, will affect the test results, especially the indicators related to modulation. Therefore, specification 25.141 defines a variety of different test models for testing WCDMA base station transmitters, receivers, performance and other indicators.

Transmitter Tests are tests of the downlink signal transmitted by the base station transmitter, including transmission power, modulation quality (such as EVM, etc.), occupied channel bandwidth, spectrum transmission template, adjacent channel leakage ratio, spurious and code domain errors, etc. These tests must be performed under the corresponding test model (Test Mode) defined in 3GPP TS25.141, so as to ensure that the base station meets the specification requirements and make the test results of different base stations from different manufacturers comparable.

Receiver Tests test the receiving performance of the base station receiver under specific conditions; for example, the received mobile phone signal is very strong (dynamic range test), very weak (reference sensitivity test), and the receiving bit error rate under interference conditions (such as adjacent channel selectivity, blocking, intermodulation and spurious tests). This part of the test assumes that the base station does not support receive diversity. If the base station supports receive diversity, its diversity function must be turned off, and then each antenna is tested separately.

Performance tests also test the demodulation performance of the base station receiver. Unlike receiver tests, they test the block error rate of the base station working in the receive diversity state with different fading and Gaussian white noise conditions. Therefore, when performing performance tests, it is necessary to test the base station's receive block error rate (BLER) at different frequencies, different signal-to-noise ratios , and different rates.

Testing solutions

For base station testing, it is very important to test in full accordance with the specifications, because the test results are the basis for measuring whether the base station is qualified; at the same time, we also need other more abundant test functions to meet the needs of R&D and troubleshooting. Therefore, Rohde & Schwarz has launched two sets of RF test solutions, namely FSMU and single-solution base station comprehensive tester CMU300, to meet the needs of different departments of different companies.

1.FSMU test suite

Rohde & Schwarz's FSMU is composed of a vector signal source SMU200A and a vector signal analyzer FSQ. Figure 1 shows the WCDMA base station test connection diagram. The red NodeB in the upper left is a WCDMA base station, which is connected to the test combination FSMU composed of Rohde & Schwarz's SMU and FSQ through an RF line or air interface to test its RF indicators. FSMU not only provides full support for WCDMA's R99, but also can test various HSPA RF indicators. If automatic testing is required, you can use the free software 3G_FSMU_NodeB provided by Rohde & Schwarz to implement program automatic testing; this program integrates various test setting parameters in the 25.141 test specification, so you can easily test according to the specification by clicking a few simple buttons.

2. Single test solution CMU300

The base station integrated tester CMU300 is a single test solution, which integrates the signal source and signal analyzer in one, and has signaling mode and non-signaling mode. We know that in non-signaling mode (using FSMU or CMU300 non-signaling mode), the base station transmitter and receiver can be tested under static conditions. All test items defined in specification 25.141; however, in actual applications, the base station will change its corresponding parameters under normal working conditions, such as transmission power, reallocation of code channel resources, etc., so we need to ensure that the base station takes corresponding actions at the right time. The signaling mode of CMU300 provides us with the possibility of verifying this function, allowing us to establish a signaling connection with the base station, and realize the transmitter, receiver test and performance test of the base station in the signaling mode (data loopback under the signaling connection), realizing a complete simulation of the real usage scenario . In addition, CMU300 is a single instrument with very good cost performance. It covers the main test items in 25.141 and also supports the test of HSDPA technology included in 3GPPTS25.141R5, so it is particularly suitable for R&D and production use.

The above FSMU can not only fully support various RF tests of WCDMA base stations and terminals, but also support base stations and terminals of multiple standards such as GSM, CDMA2000, TD-SCDMA and WiMAX. CMU300 also supports signaling and non-signaling RF tests of GSM base stations.

As demand increases, WCDMA technology is constantly changing and updating to meet people's demand for higher transmission rates. Rohde & Schwarz always keeps up with the development of technology and always supports the latest test specifications in its products. For example, after HSPA, people proposed LTE (Long Term Evolution) to achieve higher transmission rates, and Rohde & Schwarz quickly launched support for LTE on its universal test platform FSMU combination.