3G access WLAN test solution

With the official operation of 3G networks of China's three major operators and the recent opening of mobile WLAN (WAPI), 3G and WLAN technologies will complement each other and their integration will become increasingly close. The high speed of WLAN system can be combined with the high mobility and large coverage of 3G mobile communication technology: in hot spots, WLAN can provide users with cheap and higher bandwidth "nomadic" wireless data services, and in other areas and high-speed mobile areas, 3G technology can provide real "roaming" wireless data services. This kind of integration will make WLAN in 3G terminals as successful as WLAN in PCs. At the same time, 3G terminals have also increased the demand for WLAN research and development, certification and production testing.
2 Basic concepts of WLAN testing
IEEE 802.11 is the IEEE standard for wireless local area networks (WLANs), which includes 802.11a, b, g, and the next-generation wireless LAN standard 802.11n using the latest MIMO and OFDM technologies. Here we mainly introduce the 802.11a/b/g standards.
IEEE 802.11b was released in 1997 as a supplement to IEEE 802.11 in the 2.4~2.4835GHz frequency band. The data rate can reach up to 11Mbit/s. The modulation method uses complementary code keying (CCK). The operation mode is divided into point-to-point mode and basic mode. The data transmission rate can be automatically switched between 11, 5.5, 2, and 1Mbit/s, and is backward compatible.
IEEE 802.11a was released in 1999 as a supplement to IEEE 802.11 in the 5.15~5.825GHz frequency band. Since the 2.4GHz frequency band in which IEEE 802.11b works is public and does not require a license, this frequency band is not only used for industry, education, and medical treatment, but also for microwave ovens and cordless phones, so electromagnetic interference is very serious. Therefore, the IEEE 802.11a standard specifies the 5.15~5.825GHz frequency band, and the 802.11a data rate can reach 54Mbit/s or 72Mbit/s (Turbo), using orthogonal frequency division multiplexing (OFDM) technology and BPSK, QPSK, 16QAM and 64QAM modulation.
IEEE 802.11g was released in 2003, extending the 802.11b standard to a higher transmission rate. It includes the previous 802.11b standard and implements the OFDM transmission technology of the 802.11a standard on the 2.4GHz ISM band. At the physical layer, the structure and modulation format of the data packet are the same as those of 802.11g and 802.11a, except for the transmission frequency. It has a data rate of up to 54Mbit/s on the 2.4GHz frequency band and is backward compatible. The key technologies are DSSS, CCK, PBCC (packet binary convolution) and OFDM technology.
Due to the differences between the three 802.11 standards, the corresponding test parameters and requirements are also different. The specific test items can be roughly divided into the following categories:
WLAN IEEE 802.11a/b/g test method

3 Rohde & Schwarz WLAN test solutions
According to the above 802.11a/b/g specifications, the test of WLAN RF modules can be divided into two parts: transmitter test and receiver test. It should be noted that testing WLAN, especially 802.11n, requires a wide bandwidth measuring instrument. Some of the customers' existing instruments cannot be upgraded to WLAN test functions due to bandwidth limitations. Rohde & Schwarz can provide a variety of test instruments and solutions from R&D, certification to production.
(1) RF and protocol R&D and certification test solutions
RF test solutions such as traditional vector signal sources SMx (such as SMU200A) and vector signal analyzers FSx series (such as FSQ/FSV) or integrated testers CMW500/280. These instruments have very wide bandwidths, so as long as the corresponding WLAN test options are added, they can be tested for various WLAN standards. The measurement option test functions of the signal analyzer mainly include transmission spectrum mask, spectrum flatness, various modulation parameters (EVM, constellation diagram, bit stream, IQ parameters) and CCDF, etc. Regarding the receiver test, in addition to using the signal source in the test mode of the WLAN module, the signaling mode can also be simulated to perform the PER (packet error rate) performance test of the receiver. Regarding the PER test, the application document 1GP56 "802.11 Packet Error Rate Testing" on the Rohde & Schwarz website has a detailed introduction.
Protocol test solutions such as PTW70. PTW70 is a multi-mode protocol tester for IEEE802.11, supporting 802.11a and 802.11g systems, that is, it provides a variety of functions from the RF front end, physical protocol layer and MAC protocol layer to application testing. In terms of 802.11b standard testing, the focus is on interoperability measurements, especially the monitoring mode and analysis functions of 802.11b and 802.11g interoperability tests. PTW70 is an indispensable troubleshooting tool for WLAN system components, including chipsets and the entire system architecture. Relying on its own WLAN software and hardware modules, PTW70 can be used to evaluate the interaction between different system components and test the compatibility between different technologies. In analyzer mode, PTW70 can simulate the WLAN access point or base station of the IEEE802.11 reference model; in detection or monitoring mode, it can record the
data communication and messages within the WLAN cell.
(2) Production test solution, CMW500/280 broadband comprehensive tester
CMW500/280 is a multi-standard wireless comprehensive tester. In addition to supporting various cellular mobile communication standards such as 2G and 3G, it can also support non-cellular communication standards such as WLAN. CMW500/280 is a broadband wireless communication tester that integrates vector signal source and analyzer, providing comprehensive measurement of WLAN terminals. At the same time, the greatly improved test speed will greatly reduce the production test cost. Due to its bandwidth of up to 40MHz, CMW500/280 not only supports 802.11a/b/g, but also supports the latest 802.11n. It has comprehensive test functions, including WLAN transmitter module test, such as transmit power; OFDM, DSSS demodulation, EVM vs Symbol, EVM vs Carrier, EVM vs Chip, IQ constellation diagram and other modulation parameters; and spectrum mask and other measurements, including receiver module test, such as the generation of various WLAN signals on the CMW instrument for FER and RSSI tests.
It is worth mentioning that, thanks to R&S's innovative "Multi-Evaluation" parallel test method (see Figure 1), the test speed of CMW is several times faster than that of previous comprehensive testers. Generally speaking, the transmitter performance we want to test can be divided into three major indicators: power/power time curve, modulation quality, and spectrum. In the past, when using traditional methods to test these three major indicators, the following process was used for these three indicators: data collection → storage → evaluation and analysis. Therefore, in order to measure these three major indicators, data must be collected three times. We know that data collection takes up the most test time because it requires collecting enough samples. If the process can be improved, data can be collected only once and stored, and the analysis of the three major indicators uses the same set of collected data, the time of data collection can be saved at least twice. CMW's "Multi-Evaluation" adopts this innovative method, and its process is: collect data → store → multiple evaluation (Multi-Evaluation). Using this process, data can be collected only once to test all emission indicators. Therefore, the test speed is doubled compared with traditional test methods.

Figure 1 shows the CMW500 "Multi-Evaluation" parallel test interface. This example shows that CMW tests the EVM vs Symbol, EVM vs Carrier and Spectrum indicators of 802.11g at the same time.
In addition, since China allows 3G mobile phones with WAPI to access the network, it is foreseeable that the production test demand for 3G+WLAN mobile phones will increase significantly. Consumers want mobile phones to integrate more and more functions. Therefore, many 3G mobile phones are equipped with Bluetooth, GPS, FM radio, and may even include mobile TV CMMB. A mobile phone integrates so many functions, and the test will naturally increase accordingly. If traditional instruments are used to build such a test, at most, 6 different test instruments are needed: 2G/3G mobile phone comprehensive tester, WLAN comprehensive tester, Bluetooth comprehensive tester, GPS signal source, FM signal source, CMMB signal source. First of all, the
equipment investment needs to increase, and the complexity of the test system will increase greatly, which will bring about an increase in maintenance costs; secondly, due to the increase in the number of communication standards to be tested, the test time will be greatly extended. As a result, the overall production test cost will increase significantly. Therefore, mobile phone manufacturers will face such a difficult problem: when testing mobile phones that support multiple wireless technologies, the testing cost will be greatly increased accordingly. However, consumers cannot accept that multi-standard, multi-functional mobile phones are much more expensive than before.
If CMW500/280 is used, this problem can be solved well. Since CMW500/280 is a multi-standard wireless integrated tester. It can support 2G/3G standards and WLAN, Bluetooth, GPS, FM and CMMB standards. In this way, only one instrument is needed to test multi-standard mobile phones, which reduces equipment investment and greatly simplifies the production test system. Thus, the problems caused by the above equipment investment and complex test system are solved. In addition, CMW adopts the innovative R&S "Multi-Evaluation" parallel test method for each communication standard, and the "Smart Alignment" fast intelligent calibration technology suitable for 2G/3G mobile phone RF calibration can greatly reduce the test time, thereby greatly alleviating the problem of extended test time caused by the increase in communication standards. Therefore, using CMW can increase the communication standards while the test cost does not increase significantly, which is conducive to manufacturers to produce more cost-effective multi-wireless standard mobile phones.
4 Conclusion
The opening of WLAN for 3G terminals and the perfect complementary application of these two technologies will bring more and more 3G terminals supporting WLAN and promote the development of mobile Internet services. However, since consumers do not want 3G+WLAN and other wireless technology mobile phones to be much more expensive than previous mobile phones, mobile phone manufacturers need to optimize the test process and adopt innovative test technology to reduce the test cost of multi-standard mobile phones. Rohde & Schwarz's CMW500/280 complies with this demand. With its innovative design and test concept, CMW can help customers produce more cost-effective mobile phones that support various wireless technologies.