Compact Radio Channel Emulator for MIMO Verification
A transition is underway in the wireless communications industry as wireless cellular devices migrate from 3G to 4G technologies such as LTE. For 4G products it is necessary to upgrade existing SISO test systems to MIMO capable test systems. This does not just mean multiplying the test hardware, but updating the test system capability to address the MIMO radio channel characteristics such as spatial correlations, power polarizations and antenna radiation patterns, too. To address this issue EB (Elektrobit) has introduced a new, compact EB Propsim® FS8 radio channel emulator to meet the demanding design and verification challenges of 4G products cost effectively.
The EB Propsim FS8 radio channel emulator is designed for testing MIMO performance scenarios according to 3GPP standard and is also compliant with operator defined performance testing requirements. Operators are often held responsible for the quality of service despite the possible underlying performance issue in the actual device and carry the risk of diminishing revenues due to possible increased operating and support costs caused by poor performance. Leading operators recognize the risk and are demanding thorough acceptance test criteria in order to mitigate the risk of poor performance.
4G MIMO RADIO CHANNEL EMULATION
The EB Propsim FS8 emulates the typical radio channel characteristics like path loss, multipath fading, delay spread, Doppler spread, polarization and spatial parameters such as Angle of Arrival (AoA) and Angular Spreads (AS), which are critical for MIMO product performance. It is designed for LTE testing, supporting carrier bandwidth up to 40 MHz and frequency bands up to 2700 MHz, and features a very compact and highly integrated design.
In order to get reliable results from MIMO product testing, the radio channel emulator has to have excellent RF performance. Error Vector Magnitude (EVM) and internal noise level must be very low to minimize errors impacting the measurement results.
Also, the fading process has to be repeatable in order to have consistent test results across different test rounds. This is very important when benchmarking the performance of different 4G products. The EB Propsim FS8 minimizes these risks by exhibiting excellent RF performance and the use of EB’s patented emulation technology, with excellent channel condition repeatability.
The emulator addresses RF, data, mobility and voice performance evaluation under realistic propagation conditions. In addition, Over-The-Air (OTA) testing in an anechoic chamber is supported, providing the capability to measure realistic mobile terminal performance without using artificial cabling in the test setup. With EB Propsim FS8, the bottlenecks in 4G product performance can be identified early in the product development cycle enabling savings in costly redesign and verification later in the development stages.
4G DEVICE PERFORMANCE
To test the performance of a 4G LTE handset or chipset, developers can measure bit-error rate (BER), block-error rate (BLER), and frame-error rate (FER) as a function of the signal-to-noise ratio. All of these measurements count the number of errors in a predefined amount of data. High error values mean that the device does not adequately mitigate fading effects in the radio channel. Another typical performance measure is the data throughput versus the signal-to-noise-ratio. This is typically measured in megabits per second and defines how much data the system is able to correctly transmit in 1 second.
Performance tests require a communications tester and a radio channel emulator for the device under test (DUT). A communications tester establishes a link to a cellular device by emulating a base station, but featuring only a small subset of functionality of a real base station. For a throughput measurement, the communications tester sends a known data pattern to the DUT. With a direct cable connection from the tester to the device, the test setup can achieve its highest possible throughput. When placed between the tester and the DUT, the EB Propsim FS8 radio channel emulator will distort the signal as it occurs in real wireless communications correspondingly changing the data throughput. Figure 1 shows a typical test setup for a 4G MIMO device.
Typically, the main purpose of testing is to verify a product’s compliance to a standard. Standard channel models are defined by the 3GPP LTE standard. The standard also sets performance limits with a given model, ensuring a certain minimum performance for all 4G LTE devices on the market. Most tests against the standard requirements are simply pass/fail measurements, so they do not measure the performance limits of the device.
COMPATIBILITY with performance test systems
MIMO product performance testing solutions depend on the desired coverage of different layers from RF and protocol levels to network radio resource management. EB Propsim FS8 is designed and verified to be compatible with used key components in the performance test systems from vendors like Rohde & Schwarz, Agilent, Anritsu and Aeroflex. This compatibility, coupled with the ability to cost-effectively replace existing CDMA or GSM/UMTS tests systems to add LTE testing capability, ensures that the investment in the test equipment continues to pay back throughout the product lifecycle.
The emulator brings additional value to 4G product performance test systems with realistic propagation scenarios, provided by cutting edge channel modelling applications. EB’s Virtual Drive Testing (VDT) application with the EB Propsim FS8 enables the verification of challenging propagation scenarios with full repeatability. VDT utilizes the field measurement data from real live networks captured by drive test tools or a channel sounder in order to bring repeatable real-world conditions to laboratory testing. All the elements of the real environment: fast fading, Doppler, signal level variations, interference and antenna parameter effects can be replicated, making it possible to isolate performance issues early in the development and design verification phase.
ACCELERATED DEVELOPMENT CYCLE
Realistic field scenarios in laboratory testing at the early development stages provide immediate feedback and facilitate the improvement of product maturity before field trials and operator acceptance testing, thus accelerating the product development cycles and yielding better product quality and acceptance. EB Propsim FS8 4G performance test capabilities enable quantification of the device performance in the most critical areas. Beyond testing for conformance to industry specifications, the emulator is indispensable in comparing device performance, gathering data for operational and support cost projections, or to identify issues that are not caught by basic conformance testing. Testing with the new radio channel emulator guarantees high quality user experience of devices and hastens the time to market of new wireless 4G products and systems.