Datang Mobile 5G large-scale multi-antenna test solution

With the official release of the 3GPP 5G standard NSA solution, the development of 5G NR-related commercial products has accelerated, and 2018 will be a key year for 5G standard determination and commercial product development. At present, 5G is in the critical stage of standard determination, and the international standard organization 3GPP will complete the international standard of the first version of 5G SA in June this year. China started the 5G R&D and testing at the beginning of 2016. It has entered the third phase of R&D trials and will promote the 5G system equipment to reach the pre-commercial level.

As one of the key technologies of 5G, large-scale multi-antenna technology achieves greater wireless data traffic and connection reliability by using a very large-scale antenna array (such as hundreds of antennas or more) on a base transceiver station . Compared with traditional single/dual-polarized antennas and 4/8-channel antennas, large-scale antenna technology can improve spectral efficiency and energy utilization efficiency through different dimensions (space, time domain, frequency domain, etc.); 3D shaping and The channel estimation technique can adaptively adjust the phase and power of each antenna element, significantly improve the beam pointing accuracy of the system, concentrate the signal strength on a specific pointing area and a specific user group, and significantly reduce intra-cell interference while enhancing user signals. The neighboring area interference is an excellent technique for improving the SINR of the user signal.

How to evaluate large-scale multi-antenna technology, what kind of test indicators and test methods are used for the design and algorithm of large-scale multi-antenna technology on the protocol; how to measure the overall performance of large-scale antenna systems, and how to control the overall system during mass production Verification; how large-scale antenna systems can be verified in various scenarios in different application deployment scenarios; they are all issues that need to be fully considered from a test perspective. With its accumulation and advantages in 5G technology and testing, Datang Mobile has made more progress in large-scale multi-antenna testing.

Protocol design test

In the 5G NR protocol, different downlink pilots are defined in different transport channels to improve coverage performance, different DMRSs are used for different users, and multiple multi-port CSI-RSs are defined for channel quality measurement and precoding. The calculation of the codebook. The same idea is also applied to the upstream channel, defining different users' DMRS and multi-port SRS for channel quality measurement and precoding codebook calculation. After the number of antennas increases, the coverage of the traffic channel can usually meet the requirements, and the capability of the control channel does not increase with the increase of the number of antennas. Therefore, the coverage of the control channel will become a bottleneck of system performance. In the NR system, a technique of beam scanning enhanced coverage is introduced for the control channel. In large-scale multi-antennas, it is necessary to select the appropriate beam scanning width and frequency for beam management and beam tracking. In different user locations and channel environments, it is necessary to verify which codebooks are used for base station transmission and reception. The transmission of several port pilots can be used to minimize interference between users, with less pilot overhead and spectrum efficiency. In response to the above problems, Datang Mobile proposed a corresponding test strategy.

1. Perform uplink pilot and precoding tests. Through the phase shift system or channel simulation system, the far-end near-point user constructs different inter-user interference and multi-path channel to calculate the SRS transmission scheme and uplink pre-coding version of different ports, and conduct pilot. Overhead, codebook calculation accuracy test.

2. Perform downlink pilot and precoding tests to verify the CSI-RS transmission scheme and the downlink precoding codebook calculation of different ports, and perform downlink measurement pilot overhead and codebook calculation accuracy test.

3. The beam scanning test is performed by using a phase shifting system or a channel simulation system to simulate different positions of the user and different motion directions, horizontal + vertical motion, to confirm that different users receive the beam that the theory should receive, and at the same time perform coverage enhancement gain. test.

Key algorithm performance test

Under the existing integrated system architecture, the research directions of base stations for large-scale multi-antenna systems mainly include: base station antenna architecture design, physical layer signal detection, physical layer channel estimation; MU-MIMO pairing algorithm, user scheduling and resource allocation. Strategy, etc. As the number of antennas increases, the performance of large-scale multi-antennas will tend to be flat. When the antennas tend to be large, the channels tend to be orthogonal. In this case, multi-user multiplexing (MU-MIMO) can be used. The core of MU-MIMO technology is channel estimation and multi-user pairing algorithms. Fast and efficient channel detection and estimation; according to the scenario and application, select the appropriate multi-user pairing algorithm for physical resource scheduling and resource allocation. For the research of these key algorithms, the corresponding verification test is needed.

First, an antenna calibration test is required. In order to achieve accurate beamforming, the phase difference between the RF signal paths must be less than ±5°. Verification of calibration results for all RF channels of large-scale antennas by using phase shifters or channel simulators.

Second, an interference suppression performance test is required. In order to reduce interference between users, the interference between the shaped signals sent to each user should be as small as possible, and the base station needs to perform interference suppression, and perform performance test of interference suppression in different channel positions of different channel scenarios.

Finally, multi-user pairing performance testing is required. By connecting the channel simulator, when different mobile channels have different motion speeds and different users are present at the same time, the appropriate users are selected for pairing, and the multi-user pairing performance test with maximum throughput is performed.

Large-scale antenna system overall performance test

For large-scale antenna systems, the currently widely used method is an active antenna in which a radio frequency unit and a signal radiating unit are integrated. For the frequency range below 6 GHz, the wavelength is relatively large, and the spacing between the RF units is relatively large. It can be tested by the traditional conduction method, but the integration of the active antenna is still required to be integrated. OTA test. For the millimeter wave band in the frequency range greater than 6 GHz, because the wavelength is small, the spacing between the RF units is small, and the RF unit and the radiating element are integrated, and the traditional conduction method can no longer be used for testing. test.

The OTA is used to test the service performance of the system, and the OTA transmission is verified. After the channel simulation, the overall service performance of the system is continuously optimized and tested under the condition that multiple users in different channel scenarios exist simultaneously. verification.

For the production test of large-scale active antennas, the OTA method is also mainly used, including radiation test, beam test and transceiver function test, such as error vector magnitude (EVM) measurement when all transceivers are turned on. Efficient and fast verification of product qualification, saving test time and saving test costs.

Performance testing of different scenarios

The main deployment scenarios for large-scale multi-antenna systems include macro coverage, micro-coverage, and high-level coverage. The macro coverage scene base station has a large coverage area and a large number of users; the micro coverage scene is mainly for hotspot areas, such as large-scale events, concerts, transportation hubs and other areas with high user density, with small coverage area and high user density; The main reason is to provide coverage to high-rise buildings through relatively low-level base stations, and the user presents a 3D distribution, which requires the base station to support vertical coverage and perform 3D shaping. There will also be suburban coverage or other wireless backhaul scenarios.

Verification of different deployment scenarios can be performed directly through the real network in the field. In the laboratory, the main scenarios are to simulate different scenarios by constructing different channel environments. Use the channel simulation system to simulate the different positions and angles of the base station and the user and the propagation parameters, such as whether to select the Uma scene or the Umi scene, whether it is LOS or NLOS propagation, whether the user position is horizontally distributed or horizontally + vertical, etc., and the user distribution density needs to be considered. , speed of movement, etc. Through the construction of different deployment scenarios, the service performance of different scenarios is verified, and the laboratory test coverage for the external application scenario is achieved.