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Using Calibration to Optimize Performance in Crucial Measurements
SATIMO has integrated the Anritsu MT8820C One-Box Tester into its OTA measurement systems for LTE measurements (see Figure 1). The combination of SATIMO multi-probe measurement technology with Anritsu LTE measurement solutions enables device developers and manufacturers to perform LTE OTA measurements in both single input, single output (SISO) and multiple-input, multiple-output (MIMO) modes in record times (up to 10 times faster, depending on measurements).
Multiple antenna techniques are a central concept to LTE, and they are used to increase coverage and system capacity (see Table 1). LTE Over-The-Air (OTA) testing can be split into SISO and MIMO testing. The former uses Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS) as figures of merit (FOM), in order to characterize a transmitter and receiver, respectively. This methodology is not suitable for MIMO testing, creating the need for a new testing methodology.
Figure 1 Standard LTE MIMO testing solution with Anritsu One-Box Tester.
The SATIMO StarMIMO is a commercial solution based on the Spatial Fading Emulation (Technique Alessandro Scannavini, et. al. "OTA Throughput Measurement by Using Spatial Fading Emulation Technique," EuCap 2010, Barcelona 2010) in which a spatial-temporal characteristics environment (multipath plus fading) is simulated at the device location.
SATIMO has offered traditional SISO OTA testing with its SG64, 32, 24 series, as well as its compact StarLab, which are suitable for 2G, 2.5G and 3G SISO OTA testing. With the recent interest in LTE OTA testing, SATIMO worked with Anritsu to integrate the MT8820C into its SW package. SATIMO's automated software SAM 2 for OTA measurement (latest software release SAM 2.17.2) is now compatible with Anritsu's MT8820C One-Box Tester, which supports measurement of transmit power and receive throughput for multimode LTE devices when incorporated into the SATIMO system. Additional capabilities provided by the MT8820C include high speed RF calibration; RF parametric tests in either signaling or non-signaling mode; and functional tests, including voice calls, video calls, end-to-end throughput and current consumption.
The integration of the MT8820C enables the SATIMO solution to conduct OTA measurements for two recent protocols: LTE and the TD-SCDMA/HSPA. The MT8820C One-Box Tester also includes additional 2G/3G protocols, such as W-CDMA/HSPA and HSPA Evolved, CDMA2K to 1xEV-DO rel. A, TD-SCDMA and GSM/GPRS/E-GPRS. OTA-tested performances include all declination of TRP and TIS measurements (upper hemisphere, near-horizon, total and effective, intermediate channel).
Figure 2 Throughput as a function of channel model power in two environments-Urban Micro (Umi) and Urban Macro (Uma).
The MT8820C makes the testing of LTE physical layer parameters quick and simple, including the measurement of both TX and RX parameters in accordance with 3GPP test standards. Parameter setups and pass/fail limits for tests defined in 3GPP 36.521-1 are pre-programmed, including automatic setup of uplink and downlink Resource Block (RB) allocations. Further improving test times and efficiency is the Parallel Phone Measurement (PPM) function of the MT8820C, which allows two UEs to be tested simultaneously and independently (see Figure 2).
Testing the performance of LTE MIMO capable devices Over-The-Air is fundamental for manufacturers. MIMO OTA testing is designed for receiver performance testing such as downlink data rate. Manufacturers are designing optimization algorithms into their devices' chipset to improve performances in low signal, high interference and other challenging environments.
With multiple antennas, improvement of performance is made by clustering signal paths in the most effective way. Indeed, even if the chip is working properly – for instance two receiving antennas – the same signal can be received twice. The diversity of the received signals (Rx diversity testing) can be used to improve the sensitivity of the device in challenging conditions. With SATIMO's multi-probe approach, 4-32 probes can be selected to form clusters of direct signals, scatterers and interferers. Using SATIMO's MV-Cal™ technology, calibration of all the emulated channels can be performed almost instantaneously, drastically reducing the measurement time by 15 to 20 percent.
With SATIMO's MIMO testing solution and Anritsu's MT8820C One-Box Tester, measurement of multiple antennas terminals can be performed in a fully RF controlled environment. The MT8820C supports a 2×2 MIMO mode, so it can generate two data streams in downlink mode. The generated signals are then transformed, and mapped to eight dual polarized probes (16 outputs) in the channel emulator in order to emulate specific propagation models at the device location. The emulations of multi-path signal include Cross Polar Ratio (XPR), delay spread, fading profiles and Doppler shift. They are compliant with 3GPP standardized Channel Propagation Models for conformance testing of HSPA and LTE MIMO capable devices.
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