Composition and Function Analysis of Drive Test System

1 Introduction

The drive test system is an important component of network coverage assessment, network optimization, and network KPI assessment. Different test equipment can be used according to different test tasks. Generally speaking, a typical drive test system consists of drive test software, test mobile phone, network frequency sweeper, GPS receiver, etc., as shown in Figure 1. The drive test software is responsible for the hardware driver and the recording, display, statistics, and analysis of the output results; the test mobile phone is responsible for the recording of signaling and the simple measurement of air interface signals; the GPS is responsible for the longitude and latitude recording and PPS output; the network frequency sweeper is responsible for the high-performance demodulation of the most critical air interface signals during the drive test and the measurement of the spectrum (for interference testing). R&S's TSMX series frequency sweepers fully support GSM, cdma2000 1x/IS95/EV-DO, WCDMA/HSPA, continuous wave testing, and spectrum testing.

Figure 1 Typical drive test system

2 Requirements for each component

Based on the logical function division of the road test system, we can divide the system into two parts: data collection and data display.

(1) Data display requirements: that is, requirements for drive test software, which mainly examine whether the drive test software can stably drive the hardware, whether the system is stable and has a complete exception handling mechanism, whether it has a user-friendly interface and powerful thematic analysis functions.

(2) Data acquisition requirements: This part is the core of the entire drive test system, because the number and accuracy of the display items are entirely dependent on the data provided by the acquisition part, and the effectiveness of the thematic analysis function depends on whether the performance of the acquisition part meets the requirements. Sweep frequency analyzers and mobile phones have their own strengths in applications.

3 Why is a sweeper necessary?

Compared with mobile phones, frequency sweepers have absolute advantages in breadth, depth, speed, and accuracy of air interface signal measurement. Breadth mainly refers to whether the network signal can be measured extensively; depth mainly refers to whether the air interface information can be deeply mined; speed mainly refers to whether the carrier can be measured at high speed to meet the requirements of specific measurement scenarios; accuracy refers to the accuracy and consistency of the measurement data. The following takes TDMA and CDMA systems as examples.

(1) In terms of the breadth of measurement

●First, the frequency scanner is independent of the operator, that is, it does not need to register to the communication network like a mobile phone to perform measurements, so it can measure the networks of different operators at the same time, and can also measure the networks at the national border.

● For the measurement of CDMA & WCDMA standard networks, mobile phones can generally only measure a single carrier frequency, while densely populated cities generally have more than two carriers. If a mobile phone is used for comprehensive measurement, multiple mobile phones are required and the mobile phones must be able to lock the frequency in real time, which is often not feasible in actual engineering. However, a frequency sweeper can complete the measurement of multiple carriers, and excellent frequency sweepers also support parallel measurement of multiple carriers. The frequency sweeper can analyze the load of different carriers by comparing carriers of different frequencies in the same sector, and load sharing is also an important part of network optimization (see Figure 2).

Figure 2 Analysis of the breadth of frequency sweepers in air interface signal measurement

● Even when measuring a single carrier, the behavior of a mobile phone is controlled by the network most of the time, and it can only measure the SCs in the active set and the neighboring set. Moreover, according to the gear principle, this measurement is also non-uniform speed measurement, and the measurement is strictly limited by the search window. However, the sweeper does not have such limitations and can measure all SCs within the threshold. [page]

(2) In terms of measurement depth

●The frequency sweeper can dig deep into the air interface information. It can output the real-time spectrum diagram and even waterfall diagram of the air interface (see Figure 3) to troubleshoot various interferences. By combining omnidirectional and directional antennas, this function can be widely used in interference troubleshooting. Moreover, compared with the solution of using a handheld spectrum analyzer, this measurement can also be combined with geographic information, such as Mapinfo and GPS information.

Figure 3: In-depth analysis of frequency sweeper in air interface signal measurement

● For WCDMA networks, an excellent frequency sweeper can analyze multipaths and provide multipath distribution and statistical results, namely, root mean square delay, so as to understand the propagation characteristics of the wireless channel and perform corresponding network optimization, such as search window optimization. Figure 4 uses actual measurements of cdma2000 1x and EV-DO as an example.

Figure 4: Examples of actual measurements of cdma2000 1x and EV-DO

● Any communication standard has two most important parameters, quality and level. The frequency scanner can analyze the signal at a worse signal quality and lower signal level. For example, a GSM mobile phone needs a C/I of 9dB to measure the signal reliably, while an excellent scanner needs a C/I much lower than this value. The Ec/Io required for normal demodulation of a WCDMA mobile phone is much lower than that of an ordinary mobile phone.

(3) In terms of measurement speed

The measurement speed of the test terminal is strictly limited by the communication standard. For example, the measurement speed of Rxlev and RxQual of GSM mobile phones is reported every 480ms, while the measurement speed of the frequency sweeper is at least 20 times that of GSM mobile phones. The scanning speed of R&S TSMQ reaches 100channel/s. In addition, the measurement speed of the mobile phone will be affected by the behavior of the mobile phone itself, so the frequency sweeper is more suitable for measuring the network in hot spots at high speed.

(4) In terms of measurement accuracy

● Due to differences in production and design between different mobile phones, the measurement results of different mobile phones will have great differences, generally around 3dB. The measurement accuracy of high-end sweep frequency analyzers is generally around 1dB.

●Generally speaking, for unified certification testing, a standard reference measurement device is required, and the performance of the sweep frequency meter in this regard can meet this requirement.

4 Why is it necessary to test the phone

Compared with the frequency sweeper, the mobile phone is irreplaceable in QoS and service testing. The role of the mobile phone in the drive test system is more reflected in the following aspects:

●Data services, such as throughput testing in EDGE, HSPA, and EV-DO.
●Network KPI testing, such as using mobile phones to test call establishment success rate and call drop rate.
●Network performance verification, such as soft handover testing and hard handover testing.
●Voice quality and streaming media quality testing.
●IP layer path verification.
●Layer3 signaling verification.
●In terms of QoS testing and end-to-end testing, the role of mobile phones is very obvious and irreplaceable. [page]

5 Summary

Table 1 shows the strengths of the test mobile phone and the frequency sweeper in different test items. In addition, the stability, portability, durability and power consumption of the measurement system are also important evaluation indicators of the drive test system.

Table 1 Performance of the test phone and the frequency scanner in different test items

6 Introduction to R&S Series TSMX Sweeper

Rohde & Schwarz's TSMX series of sweepers cover various communication standards such as CW, GSM, cdma2000, WCDMA, WiMAX, LTE, etc. The product classification takes into account both the demand for single network measurement and the operators who have measurement requirements for various standards, and even includes the demand for parallel measurement of 2G and 3G networks. In terms of device interface, it not only supports the drive test software Romes of Rohde & Schwarz, but also opens interfaces for third-party drive test software companies to integrate (see Table 2).

Table 2 Introduction to R&S TSMX series sweep analyzers

7 Advantages and features of the R&S series TSMX sweeper

Compared with other sweepers in the industry, the R&S series sweepers have very obvious characteristics and advantages, which can be summarized in terms of performance and application. Performance mainly refers to measurement speed and measurement accuracy; application mainly refers to measurement items and advanced functions developed based on measurement.

(1) Performance

● R&S TSMX series frequency sweepers have continuous frequency bands and can perform spectrum and CW measurements on any frequency band of interest. Therefore, uplink interference of 2G and 3G networks can be measured. If there is a measurement task for a new frequency band, the measurement can be performed directly without upgrading the frequency band.

● R&S's TSMX series of sweepers have the best performance in terms of measurement speed. For example, in GSM, the TSMX sweep speed is 100 channel/s, which is about 70% ahead of the industry. CW test can reach more than 700 points per second, and can fully meet Lee's theorem even in high-speed measurement. In WCDMA, the measurement speed reaches 50ms per measurement point, and 12 carriers can be measured in parallel. Moreover, the measurement speed of the TSMX series sweepers will not be affected by the signal quality of the air interface, and can maintain stable measurement.

●In terms of measurement accuracy, the absolute accuracy of level measurement is 0.5dB.

●TSMQ can complete 2500-way multipath measurement on CDMA and WCDMA, and will not miss any measurement even in the most complex multipath environment, which is about 8 times ahead of the industry level.

●The false detection probability of SC of WCDMA and cdma2000 is the lowest, which is 10-9, while the industry level is generally 10-3.

(2) Application

●R&S's TSMX series of frequency sweepers can distinguish between co-channel and adjacent-channel interference in GSM network measurements when the C/I ratio is poor.

●R&S's TSMX series of frequency scanners can not only demodulate common SIB messages, such as SIB3 and SIB11, but also demodulate all other SIB messages, such as the uplink interference report message in SIB7.

●R&S supports new technologies. The TSMW frequency sweeper launched by R&S can now support WiMAX and LTE (FDD&TDD).

● R&S TSMQ can measure different networks in parallel, such as GSM and WCDMA networks in parallel, which can greatly improve measurement efficiency and save network optimization expenses.

●The device is portable, light and has low power consumption. The TSMX frequency sweeper weighs only 1.5kg and consumes only 8W, so it can be directly powered by a vehicle.

8 Conclusion

After 20 years of experience in drive test systems and extensive application in the networks of world-renowned operators such as Vodafone and T-Mobile, we believe that R&S can bring successful experiences from all over the world to China and build China's 2G and 3G networks into high-quality networks.