Bridging the Gap between MIMO Lab and Field Test Results
Testing mobile devices involves many phases, including the validation of the devices in the actual field conditions where subscribers will use them. However, field testing in the diverse conditions of terrain, population density, physical location and motion of devices is extremely time-consuming and costly.
As the wireless industry works to introduce 4G LTE and WiMAX products and solutions, field testing will be particularly important. The MIMO technology used to enhance system performance and achieve the high data rates expected will cause product performance to vary substantially depending on the RF environment.
The Azimuth Field-to-Lab solution allows service providers and equipment manufacturers to take real-world channel conditions collected from drive testing, performed in many ecosystems in different sites around the globe, and replay this data in the ACE™ MX MIMO channel emulator in any lab, at any phase of the design and qualification cycle.
Field conditions in laboratory product testing have typically been recreated with channel emulation using industry-approved and standardized channel models. These statistical representations of channel conditions are very useful in characterizing generalized RF environments for testing and certification, but they do not capture the unique and specific conditions experienced by a device as it moves through RF conditions in an actual wireless network. The Azimuth Field-to-Lab solution can augment current test conditions with actual field data collected from locations of interest.
Using the Azimuth Field-to-Lab solution involves three phases:
- Collecting field data
- Conditioning the data for playback
- Playback of the field data on the Azimuth ACE MX MIMO Channel Emulator
To collect field data, the Azimuth Field-to-Lab solution is integrated with industry-standard drive testing software allowing the re-use of data from drive tests. Drive test data is converted into a playback file for a given number of base stations. The data can be filtered, smoothed and filled to ensure realistic playback conditions. The data is played back on the channel emulator. A playback control tool configures the ACE MX MIMO channel emulator and streams the playback conditions to the signal path of the channel emulator between the mobile device (e.g. UE) and the base station (e.g. eNodeB).
ACE MX MIMO Channel Emulator
The flexible, scalable ACE MX wireless channel emulator has been designed for MIMO- and OFDM-based systems, delivering a range of configurations for MIMO and/or SISO system testing. The intuitive and easy-to-use configuration and control interface enables efficient, automated and repeatable testing of 2G, 3G WiMAX, LTE and other 4G infrastructure equipment and devices.
AzMapper software analyzes drive test logs and automatically recreates these channel conditions for playback. First, the field data is filtered to extract the useful and significant data from the mass of collected information. The data is then smoothed to make sure that the behavior of the playback best imitates the time varying nature of the real world. Finally, the data is analyzed for missing segments, which can be filled or closed with interpolated data to ensure continuity. All the parameters of the filtering and mapping are configurable to the user's preferences.
Any components that are removed (filtered out) and interference that is detected in the field data is added back to the environment in the form of AWGN to ensure operating conditions identical to those in the field. In addition, the velocity of the mobile device is added based on either information from the GPS coordinates over time or as a fixed velocity. The application provides advanced visualization views to help the user interpret both the source data and output data before creating the playback file.
The ACE MX MIMO channel emulator, together with the AzPlayer application, supports real-time streaming of playback files for unlimited playback to channels on one or more ACE MX wireless channel emulators. With the easy-to-use play control, the data can be played back, paused, looped and even coupled with other playback files, accurately replicating real-world conditions.
Figure 1 Mobile device testing process with Azimuth solution.
Figure 1 shows the complete process flow and components.
By utilizing measurements of field data and playing them back through a wireless channel emulator, R&D and QA engineers and operators can test device performance against the dynamics of the field before ever deploying products in these environments. Operators can troubleshoot and optimize system performance, introduce field-trial support for qualification of devices in the lab, reproduce known trouble spots in the lab for analysis, provide throughput performance metrics on devices before deployment and allow qualification for specific markets and environments. Semiconductor and device manufacturers are able to characterize expected performance in real-world environments, reproduce and verify field issues, benchmark performance with other devices and optimize algorithms for best performance. Infrastructure manufacturers are able to test interoperability with devices under real-world conditions, benchmark system performance, characterize enhancements or improvements under real conditions and test algorithms such as soft handover in life-like conditions.