Currently available OTA test systems and measurement techniques are ill-suited for large vehicles and the automotive industry’s growing demand for system performance analyses. To address this, ATC has begun developing a process to evaluate automotive antennas in real-world environments using drive tests. This technique uses existing 4G mobile network infrastructure in real environments to show how good is the user experience of your antenna system. Neither the size of vehicle nor a lack of investment capital hinders the ability to characterize 4G systems using this technique.
Your various types of antennas under test antennas (AUT’s) are evaluated in several mounting positions and simultaneously compared to a reference system. This reference consists of either existing reference antennas or a standalone mobile phone. In these scenarios, an optimal mounting position is determined or the benefit can be estimated of vehicle-mounted antennas compared to a smartphone placed inside a car. .Furthermore, a lot of other of customizable scenarios are possible.A test setup schematic used to optimize a 2×2 MIMO array in LTE environment is shown in Figure 1. For this test, two monopole antennas mounted on the roof of the car act as reference.
For statistical evaluation, the drive test procedure is repeated several times on a number of well-known test routes. Each test route allows the ATC team to analyze different settings, such as frequency of LTE band, network coverage, and carrier aggregation. These different test routes also allow ATC to investigate the AUT’s behavior in worst-case and best-case scenarios. For example, AUT’s tested in a good network coverage environment with the highest data throughput could suffer from link interruptions or low throughput in a bad network environment and vice versa. Under these circumstances, the complexity of analysis increases based on the huge amount of end-user key performance indicators (KPI) present in 4G networks which need to be considered. RSRP relates to the gain of the AUT at the antenna-level and must be analyzed, although its effects are included in some system metrics. For system performance, other KPIs have to be analyzed to get valuable test metrics.
Figure 2 shows throughput as a function of vehicle position on an urban test route in Hamburg, Germany. As expected, the results highlight that throughput constantly varies during drive tests as a result of the multipath and multi-user environment. However, the wide range of measured throughput is quite remarkable. For example, some areas highlighted in red/orange along the test route (<10 Mbit/s) have network coverage with up to 150 Mbit/s maximum data throughput. In contrast, the spot marked with a red ellipse has up to three Carriers in LTE band 3 & 7 available and thereby has a maximum data throughput of 475 Mbit/s. In this urban region ATC measured some samples with up to 130 Mbit/s data throughput, which is very high because data throughput is shared to all attached users.
ATC, in cooperation with Keysight and others, developed the Normalized Antenna Performance Indicator (NAPI) to provide automotive customers with a useful drive test metric. This quality metric has been specially tailored for presenting performance results of a drive test.
The drive test procedure described here offers a simple and cost-effective approach to characterize various OTA metrics using real-world conditions that would be difficult to achieve in an indoor test facility. The results presented herein show that measured throughput can vary drastically from published coverage maps and there is no substitute for this type of empirical measured data. On the other hand, this approach places a great deal of reliance on the network operator to provide stable and consistent performance since this measurement technique relies on deployed base stations.
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