Rohde & Schwarz's TD-SCDMA measurement solution

1. Introduction

In May 2000, the TD-SCDMA technology proposed by my country was approved by the International Telecommunication Union as the third-generation mobile communication international standard. In March 2001, the TD-SCDMA standard was accepted by 3GPP (3rd Generation Mobile Communication Partnership Project), marking that TD-SCDMA has become an important standard and development direction in the future mobile communication field. In January 2006, the Ministry of Information Industry issued 23 communication industry standards such as "Technical Requirements for Wireless Access Network Equipment of 2GHz TD-SCDMA Digital Cellular Mobile Communication Network". It can be seen that TD-SCDMA has passed the initial R&D, design and verification stage in China, and various related standards have gradually been improved, and it has entered the network planning and optimization stage.

Rohde & Schwarz is the largest manufacturer of electronic measuring instruments in Europe and has been active in the fields of test and measurement, information and communication technology. As a leading global manufacturer of test and measurement equipment, R&S is always paying attention to the development of TD-SCDMA and can currently provide a full set of solutions for TD-SCDMA systems from signal generation to signal analysis - signal source and spectrum analyzer. The signal source can generate TD-SCDMA signals with flexible configuration, and the spectrum analyzer can measure and analyze TD-SCDMA signals in the modulation domain, time domain, frequency domain and code domain.

2. Introduction of TD-SCDMA test equipment

Rohde & Schwarz offers a range of instruments to meet different TD-SCDMA test requirements. The following is a brief introduction to the test instruments mentioned in this article (see Figure 1).

Figure 1 Rohde & Schwarz's TD-SCDMA measurement solution SMU200A+FSQ

2.1 Dual-channel vector signal source SMU200A

The dual-channel vector signal source SMU200A integrates two independent signal sources in one unit, which can meet all the requirements encountered in the research and development and production of modern communication systems. Its excellent RF and baseband characteristics are as follows:

(1) It has two completely independent baseband and RF paths: one instrument can generate both useful signals and interference signals.

(2) Built-in fading simulation and AWGN (Additive White Gaussian Noise): It can support various multipath fading and AWGN simulations required by the TD-SCDMA test specifications.

(3) Extremely low SSB phase noise, typically -135dBc/Hz (f=1GHz, 20kHz carrier offset): Extremely low phase noise is required when the interference source frequency is very close to the useful signal.

(4) Excellent ACLR characteristics: Typical ACLR value for 3GPP FDD: +70dB: This is extremely important when testing RF modules, especially amplifier modules.

(5) The level stabilization time and frequency stabilization time are extremely short, making it suitable for automated testing needs.

SMU200A can not only output various continuous waves, analog modulation signals, and digital modulation signals, but also generate various digital standard signals such as GSM, IS-95, WCDMA, TD-SCDMA, cdma2000, WLAN802.11, etc. by selecting different options. The instrument can generate TD-SCDMA signals with the optional arbitrary waveform generator SMU B1O and TD-SCDMA signal generation software SMU-K50 and K51.

2.2 SMJ1OOA single-channel vector signal source

SMJ100A is a single-channel vector signal source based on the SMU platform, which provides analog and digital modulation solutions. This series of instruments takes into account the needs of the third-generation digital mobile communications. The standard high-performance I/Q modulator ensures a small error vector amplitude and high intermodulation suppression. Due to the use of modern digital processor technology, it can generate high-precision, high-data-rate digital modulation signals.

2.3 FSU spectrum analyzer

The FSU spectrum analyzer is the most outstanding spectrum analyzer of R&S. It has a wide dynamic range, which makes it easy to measure and analyze the spectrum of the signal.

(1) TOI>20dBm, typical value is 25dBm, 1dB compression point is 13dBm, displayed average noise level (DANL) is -158dBm (1Hz resolution bandwidth): This is the basic element to ensure the excellent dynamic range of the FSU. When performing spurious and ACLR tests, the dynamic range of the instrument is the most critical.

(2) For 3GPP signals, it has an ACLR of 77dB (typical): High ACLR is required for RF module testing.

(3) The phase noise is typically -160dBc (1Hz) at a deviation of 10MHz from the carrier.

FSU is a universal spectrum analyzer that can perform frequency domain measurements on various common signals. Based on its hardware, it can test various digital standard signals such as GSM, WCDMA, TD-SCDMA, IS-95, cdma2000, BLUETOOTH, WLAN802.11, etc. by configuring different firmware.

2.4 FSP spectrum analyzer

FSP is a mid-range spectrum analyzer with a highly integrated front end, a back end of all-digital signal processing technology, and a dedicated ASIC designed by R&S. These innovative technologies have produced a mid-range spectrum analyzer with high-end features, high reliability, and high compactness. All important functions and interfaces are standard in this spectrum analyzer. It has RMS detectors and CCDF functions for statistical measurements of digital modulation signals, which are not available in other mid-range spectrum analyzers.

2.5 FSQ Signal Analyzer

The FSQ signal analyzer is a spectrum analyzer and vector signal analyzer in one instrument. It not only has the same excellent spectrum analyzer features and functions as the FSU, but also has powerful vector signal analysis functions. It has a standard 28MHz (expandable to 120MHz) demodulation and analysis bandwidth, which makes FSQ widely used in WLAN, WiMAX and 3GPP product development and production. In addition to broadband demodulation capabilities, it also provides the wide dynamic range required for multi-carrier measurement and spurious measurement of BTS.

3. TD-SCDMA R&D test solutions

According to the RF conformance test specifications of 3GPP25.142 (base station) and 34.122 (terminal), wireless transmission and reception in TDD mode define the characteristics of transmitters and receivers and the requirements for system performance. Among them, the base station/terminal of TD-SCDMA LCR is tested according to the requirements of the 1.28Mcps TDD Option of the specification. The above specifications are the criteria often used in R&D testing. At this stage, the test of the device under test is often very strict. In order to eliminate various potential defects. R&D testing has extremely high requirements for the function, dynamic range, accuracy, etc. of the instrument.

R&S provides the R&D test solution of SMU200A+FSQ. SMU200A can have two independent built-in signal sources. One of them is used to generate useful signals, and the other can generate various interference signals defined by the specification. In addition, SMU200A can generate fading simulation and AWGN required by the specification, so that one SMU200A can meet the signal source requirements of the specification. The spectrum analyzer mode of FSQ has the best dynamic range among similar products, which is very important for performing spurious tests and ACLR tests required by the specification. The vector signal analysis mode of FSQ can analyze the signal in the IQ domain, which is convenient for locating and analyzing faults in the R&D stage. SMU200A+FSQ is the most compact and powerful R&D test solution that the industry can provide.

For TD-SCDMA, R&S has launched options for signal generation (K50, K51) and signal analysis (K76, K77). The following is a brief introduction to these two options:

(1) TD-SCDMA signal generation options K50 and K51

K50 software is a firmware built into the SMU200A or SMJ100A instrument, used to generate TD-SCDMA RF signals. Currently, it can support the simultaneous setting of four TD-SCDMA cells to simulate the actual network environment. Each cell can set parameters such as scrambling code, synchronization code, power of downlink pilot time slot, and uplink and downlink switching points. It can also flexibly set parameters such as the type of channel in each time slot, the data rate of the channel, the spread spectrum code of the channel, Midamble offset, and the data source format of each channel (see Figure 2). After the settings are completed, the channel map and code domain distribution map in each time slot can be previewed to verify the correctness of the settings and prevent code domain conflicts.

Figure 2 Configuration of each time slot of TD-SCDMA in SMU-K50

K51 software is used to generate firmware with extended functions such as TD-SCDMA channel coding, which is also built into the instrument. It can simulate PCCPCH and DPCH channels in the actual environment. PCCPCH can be mapped to BCH broadcast channel with channel coding, DPCH can be mapped to various reference measurement channels with channel coding from 12.2kbit/s to 2048kbit/s, and bit and data block errors can be inserted into the data, so as to facilitate BER and BLER tests in receiver and performance tests. K51 also supports the channel coding function of the latest HSDPA reference measurement channel.

(2) TD-SCDMA signal analysis test firmware FS-K76 and FS-K77

Base station test firmware FS-K76 and terminal test firmware FS-K77 are test solutions for TD-SCDMA. They can be installed inside FSQ, FSU or FSP instruments, and can be remotely controlled via GPIB and LAN interfaces. The measurement speed is extremely fast, up to five times per second. It can automatically detect the channel data rate and select the number of time slots of the captured TD-SCDMA signal. Figure 3 shows the measurement results of TD-SCDMA signals in FSQ.

Figure 3. Measurement results of TD-SCDMA signal in FSQ

After installing K76 or K77 inside the instrument, we can use the shortcut keys on the instrument panel to measure the modulation accuracy parameters such as error vector amplitude EVM, frequency error and waveform coefficient in the modulation domain of TD-SCDMA signal, indicators such as adjacent channel power leakage ratio ACLR, spectrum spurious mask, power time diagram in the frequency domain, and parameters such as code domain power and peak code domain error in the code domain. The operation is very convenient, and the measurement results are faster and more accurate.

4. Production solutions

The TD-SCMDA production solution of R&S is a solution that comprehensively considers test items, test speed, reliability, data consistency and cost savings, and is suitable for the testing needs of base stations, mobile stations and a series of network equipment including repeaters. It helps customers quickly establish production lines that meet their requirements.

TD-SCDMA wireless devices are generally divided into two categories, one is handheld terminal devices, and the other is network-side devices. Different types of devices require different test solutions. Handheld terminal devices have large production and complex test items. Not only do they need to consider RF indicators, but they also need to consider different test conditions and assembly conditions of the terminal. The requirements for the complexity of test implementation are very high. Network-side devices have relatively high technical indicators and relatively simple test conditions. They do not need to consider cumbersome test conditions, but require test instruments with first-class test indicators and good data reliability.

4.1 Terminal production solutions

The test requirements of TD-SCMDA handheld terminals are usually divided into two steps: calibration and final test. The former is to perform RF modulation on the terminal's receiver and transmitter. The latter is to test whether the performance indicators of the whole machine meet the specified requirements after the whole machine is assembled. For the RF calibration and final test of the terminal, Rohde & Schwarz recommends FSP+SMJOOA, a high-speed and economical test solution.

When performing terminal calibration tests, SMJ with the K50 option can generate standard signals of different levels and frequencies under multiple rate sets for linear calibration of the terminal's receiver. SMJ has a fast frequency stabilization time and a large amplitude range, and can quickly establish signals in the full frequency band and full level range, which is conducive to improving the accuracy and speed of calibration. The spectrum analyzer FSP with the K77 option can accurately test the terminal's transmission power, frequency error and other parameters, thereby calibrating the terminal's transmitter.

When conducting the final test of the terminal, SMJ, in conjunction with the TD-SCDMA real-time channel coding option K51, can generate a downlink signal with complete channel information and control information, allowing the terminal to synchronize and demodulate the downlink signal and perform receiver sensitivity index tests such as BER and BLER. At the same time, FSP can test the terminal's transmission indicators, such as power, error vector magnitude (EVM), frequency error, and spectrum characteristics, completing the test of the terminal's transmitter indicators.

4.2 Network Equipment Production Solutions

For RF testing of network equipment, R&S recommends SMJ100A+FSU. This configuration has excellent technical indicators and powerful functions, and can meet the stringent testing requirements of base stations or repeaters. The test conditions of network equipment are generally flexible, and manufacturers can modify the equipment status at will, but higher requirements are placed on the test system. For the spectrum analyzer for transmission testing, it is necessary to have powerful demodulation capabilities and dynamic range to meet the needs of the equipment under different conditions. For receiving testing, not only does the signal source need to be able to simulate different working states of the terminal and multiple terminals working at the same time, but it may also need to include broadband Gaussian white noise. These requirements can all be met in SMJ100A+FSU. The technical features of this solution are as follows:

(1) High speed: R&S's TD-SCDMA test solution is based on a vector signal source and spectrum analyzer. All TD-SCDMA signal generation and signal analysis are generated and calculated inside the instrument, most of which use parallel technology and dedicated co-processing data computing technology, with a high processing speed, and will not cause data loss and result display lag or even loss. It is very suitable for the speed requirements of the production line.

(2) Stability: Since everything is built-in and there is no external computer involved, based on the traditional stable and reliable signal source spectrum analyzer, R&S's TD-SCDMA can work extremely stably. In the continuous high-intensity and high-frequency testing of the production line, it can provide customers with continuous stable performance, reduce false detection in production, and improve consistency and output.

(3) Quasi real-time: Because a lot of processing is done in parallel and in the form of co-processing data computing technology inside the instrument, it can provide customers with a flexible way to change parameters without having to wait too long. Different from waveform synthesis or other low-cost implementation methods, R&S always provides customers with efficiency and practicality.

(4) Strong scalability: R&S signal sources and spectrum analyzers can not only be used for TD-SCMDA signal generation and analysis, but can also be extended to other communication standards by simply adding corresponding options. For users, this protects investment, expands scope, and enhances value.

5. Conclusion

Rohde & Schwarz provides complete solutions not only in the field of TD-SCDMA R&D, but also in the field of production, which are applicable to different scopes. R&S's advanced TD-SCDMA analysis and signal generation options provide the best support for customers to directly and quickly enter the TD-SCDMA field.