Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments


Based on the introduction of the TD-LTE laboratory test conducted by CATR and CMCC, this paper focuses on the simulation of complex channel models. Spirent’s next-generation channel simulator VR5-HD fully considers current and future needs, supports all TD-LTE, and LTE-A tests, simulates a real wireless channel environment, is easy to use, and simple to connect. Support for this test.

TD-LTE multi-antenna test

1.1 MIMO and beamforming

MIMO, that is, multiple input multiple output, has become one of the designated technologies of LTE because it can double the system capacity. On the other hand, TD-LTE has natural uplink and downlink channel symmetry, and can use multiple antennas to achieve beamforming, thereby increasing gain and reducing interference. In fact, in the 3G stage of TDD, TD-SCDMA makes full use of the symmetry of the uplink and downlink channels to realize beamforming. TD-LTE innovatively proposes dual-stream beamforming, that is, MIMO+beamforming technology, which can improve capacity, reduce interference and improve gain at the same time, which is the most significant feature of TD-LTE.

The uplink and downlink channel symmetry is also called channel reciprocity. When testing beamforming, the antenna reciprocity must be satisfied.


TD-LTE base station has two antenna configurations, one is two antennas, namely 2*2MIMO, this configuration only uses MIMO technology and does not use beamforming technology, and is mainly used in indoor and micro-cellular scenarios; the other is 8 antennas, namely 8*2MIMO, this configuration divides 8 antennas into two groups, each group includes 4 antennas, beamforming is used within the group, and MIMO is used to send dual streams between groups. This is dual stream beamforming. The 8-antenna configuration is the main direction in the future, and the main content of our testing.

8 antennas bring a challenge, because the antennas are placed in parallel with a certain interval, which makes the size of the antenna larger and is not easy to use in engineering. Therefore, starting from 3G, the +-45° dual-polarized antenna is used, and the size is reduced by about half, which greatly enhances the practical usability. At the same time, the dual-polarized antenna is beneficial to improve the MIMO capacity because the correlation between the two groups of antennas is naturally reduced.

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 1 Dual-polarized 8-antenna for TD-LTE application

CMCC also requires the use of directional antennas to further improve the efficiency of antenna coverage.

When simulating the wireless channel environment, the polarization and directivity of the antenna must be simulated, otherwise the channel model and output power will be incorrect.

Multi-antenna wireless channel environment simulation

Because of the characteristics of controllability, repeatability, and comparability, laboratory evaluation testing has been paid more and more attention. It has the irreplaceable advantages of actual field testing, and has become an indispensable key step before field verification. Then it becomes a subject to simulate the real wireless environment in the laboratory, that is, how to simulate the wireless channel environment in the laboratory real and fast, so as to construct a complete test environment in the laboratory to verify the network equipment or terminals.

TD-LTE requires 8-channel reciprocal channels, which puts forward higher requirements for system integration; channel models unique to multi-antenna technology require better reliability and authenticity of channel simulators; at the same time, due to the complexity of testing, the cycle is long , I hope it is easy to use, real-time processing, and real-time simulation.

Spirent, as the industry standard for channel simulators in the 1990s, not only provides economical solutions, but the latest generation of highly integrated channel simulators provides the most advanced and easy-to-use solutions. Real-time simulation of all required channel models, built-in power meter, convenient GUI, and simple connections for fast and accurate testing.

Requirements for TD-LTE R&D Technology Test

R&D technology trials include two types of tests. One is the uplink demodulation test, which mainly verifies the demodulation performance of the receiver under the specified channel environment of the base station, requires to obtain the signal-to-noise ratio under different throughputs, and evaluates and compares the performance of the receiver.

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 2 Upstream demodulation test structure diagram – SR5500M

The other type is bidirectional testing, which mainly verifies MIMO, MIMO plus beamforming bidirectional testing in different channel environments, and requires drawing a curve of throughput and signal-to-noise ratio to evaluate and compare the overall performance.

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 3 Bidirectional 8*2 Test Structure Diagram-VR5-HD

From the above test requirements, it can be seen that the channel fading environment simulation plays a crucial role, requiring a realistic channel model, accurate and easy-to-control noise level and output power, and reliable equipment. Simple, easy to operate, and high test efficiency.

2.1 Basic hardware requirements

In the test of uplink demodulation, the test capability of one-way 8 channels is required, and no external equipment or attenuator is required.

In the two-way test, the two-way 8-channel test capability is required, no external equipment or attenuator is required, the phase calibration is convenient, the accuracy is high, and the calibration period is as long as possible.

The input and output should have a real-time power meter, and support real-time pulse mode measurement to meet the requirements of TD-LTE, and observe the power of each port in real time.

The instrument has good reliability, and each port has overload power protection measures, which is not easy to be damaged.

The maintenance and calibration of the instrument should be carried out locally, and the abnormal situation can be quickly dealt with and restored.

Functional requirements

Supports all channel models: Supports the SCME model based on geometric geography and the channel model specified by IMT-A M.2135.

The channel model must be based on the geometric geography method and cannot be approximated by the channel model based on the correlation matrix.

Supports the settings of antenna polarization and antenna directivity.

The power of the instrument is accurate and the signal-to-noise ratio of the output is accurate, which is very important for the evaluation of the test results.

The instrument has a high dynamic range, the signal-to-noise ratio and noise power required by the test need to cover a very wide range, and the dynamic range of the instrument is required to be as large as possible, so as to ensure that the lowest and highest power requirements can be met and the critical point of the device can be found.

Spirent Advanced Channel Simulation Solutions

3.1 Introduction to Spirent

Spirent’s wireless communication test series products can provide the most advanced and accurate test solutions for 2G, 2.5G, 3G, 4G mobile communication systems and WLAN/WiMAX systems. It runs through product research and development, system performance The entire process of testing, quality assurance, production testing, product evaluation, design verification, conformance testing, and network certification. Spirent Wireless Channel Emulator has been an industry standard for 20 years, see the evolution of the following diagram:

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 4 Spirent Wireless Channel Emulator Family

The SR5500/SR5500M is the most widely used channel emulator. SR5500-M provides support for LTE/WIMAX and other technologies for new technologies such as MIMO, SCME/IMT-A M.2135 and other spatial channel models. SR5500M provides a modular and flexible test configuration (a single module provides 2 physical RF channels, 4 internal channels, and 96 paths), which not only meets the needs of multiple test items at the same time, but also can be combined to meet the needs of large-scale testing.

Spirent’s new-generation channel simulator product platform VR5-HD fully considers the testing requirements of B3G and 4G, and has greatly improved its indicators in many aspects. For example, it is easier to use and create scenes (natural two-way connection and GUI design, touch screen and external computer control, etc.), support higher bandwidth (100M), wider frequency band coverage (400M~6G), in one device It supports more channels (up to 8*4MIMO, and also inherits the modular and cascadable design ideas of SR5500M), and supports future LTE-A test requirements (such as carrier aggregation), etc.

Next Generation Platform: VR5-HD

VR5-HD can support MIMO and beamforming testing in various multi-channel configurations. Support all 3GPP conformance test channel models, support channel models based on geometric geography, such as SCME, IMT-A M.2135, etc. And can customize any channel model.

Same as SR5500, VR5-HD is a real-time channel simulator. Real-time channel simulation means that it has super-long random sequences, the most realistic simulation of real scenes, and real-time modification of parameters, which brings great convenience to testing without re-editing, For tedious and error-prone processes such as compilation and modification, you only need to modify and edit parameters in the GUI and press Enter to complete all tests.

The main control software interface of VR5-HD is as shown in the figure below, which can be set:

Receiver and transmitter wiring topology

Two-way connection timing and configuration port for easy connection

All parameters of the multipath environment

Output power and output carrier-to-noise ratio, etc.

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 5 VR5-HD Graphical User Interface

Basic testing capabilities of VR5-HD

For a single VR5-HD, MIMO testing in the following configurations can be supported:

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 6 VR5-HD flexible MIMO configuration

Complete the test with a Spirent meter

Real-time channel simulator, real simulated channel scene; real-time modification of parameters, greatly improving test efficiency; powerful GUI, accurate signal and noise power, reliable test results; simple connection, flexible port configuration, and simple test. The above features make VR5-HD very powerful to support the needs of wireless channel emulation, especially for multi-antenna testing of TD-LTE, up to 16 RF channels, many ports and complex connections, it is necessary to have an easy-to-use connection method , VR5-HD’s unique 8-channel built-in duplexer can complete the bidirectional 8-channel connection without any external device, which is very simple.

3.3.1 Upstream demodulation test

The uplink test needs to use a unidirectional 1*8 environment, support SCME, IMTA channel models, the base station is set to cross polarization, the terminal is set to vertical polarization, and the antenna has directivity.

Under each channel model, different throughputs are obtained by adjusting the signal-to-noise ratio.

It is convenient to traverse the terminal speed, signal-to-noise ratio settings, etc.

SR5500M or VR5 can be used for uplink demodulation test. The following figure is an example of SR5500M:

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 7 Upstream demodulation test connection

The channel model is a real-time SCME or IMTA M.2135 model:

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 8 SCME channel model real-time configuration

3.3.2 Two-way 8*2 test

The two-way test requires a two-way 8*2 environment, supports SCME and IMTA channel models, the base station is set to cross-polarization, the terminal is set to vertical polarization, and the antenna is directional.

The two-way test must ensure the reciprocity of the uplink and downlink channels. Therefore, phase calibration needs to be performed before starting the test. And ensure the accuracy of phase calibration. The interval between phase calibrations should be as long as possible. The calibration accuracy of VR5-HD reaches 5° in the bandwidth of 20M, and the calibration period can reach 1 week. Greatly improve the test efficiency.

The VR5 has a built-in duplexer, which can complete bidirectional testing without adding and then external components:

Spirent Fast and Accurate Solution for Simulating Multiple Antenna Environments

Figure 9 Bidirectional 8*2 connection

Figure 10 Bidirectional 8*2 configuration


TD-LTE has more antennas and must perform both uplink and downlink bidirectional tests because of beamforming, which brings great challenges to the channel simulation in the laboratory. At the same time, TD-LTE needs a brand-new industry-leading channel model based on geometric geography, which brings a new subject to the simulation of the channel simulator.

How to accurately and conveniently complete such high-complexity simulation and testing? Spirent’s excellent engineers gave the answer. Based on the accumulation of up to 20 years, a new generation of channel simulator VR5-HD was launched. Through the introduction of this article, we can understand this test and future requirements and Spirent’s solution.

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