On the Impact of Multi-antenna RF Transceivers' Amplitude and Phase Mismatches on Transmit MRC

Abstract-Multiple input multiple output (MIMO) systems that enable data transfer rates beyond 100Mbps for WLAN applications is under development and will emerge rapidly. While the higher data rates will enable numerous features in modern communication devices, the industry has to face the soaring test cost due to the increased test complexity and test time. Since MIMO systems have multiple RF paths, each path needs to be individually tested. Moreover, mismatch parameters among the multiple paths require synchronized sampling of RF signals, requiring complicated equipment. In this paper, we propose a low cost MIMO test solution that targets the specifications that are fundamental for MIMO operation, such as gain, IIP3, and phase imbalances between the RF paths. Our test methodology measures these parameters with a high accuracy while requiring only one RF frequency synthesizer. Using the proposed test method, RF MIMO systems can be tested using a mixed signal tester and a single fixed frequency RF signal generator. I. INTRODUCTIONIncreased performance expectations in the communications market drive the industry towards implementing cost effective solutions to meet consumer demands. Recently, multiple antenna based communications systems are reported to increase spectral efficiency and to improve the link reliability [1]. While such multiple input multiple output (MIMO) systems are in their infancy, the growing demand for high throughput in communication systems will make them an integral part of future wireless communication systems.The MIMO technology utilizing the orthogonal frequency division multiplexing (OFDM) scheme will be the basis of the future IEEE 802.11n standard [2]. The combination of these two technologies will enable transfer rates over 100M bps which represents a two-fold increase over the current 802.11a/g WLAN standard. However, these improvements lead to various manufacturing challenges, such as increased RF test cost. The increase in the number of RF signal paths with the MIMO technology will increase the RF test overhead considerably. In addition, various specifications, such as the mismatches between the RF branches of the transceiver, will need to be measured to meet the stringent performance requirements of the overall system. These challenges necessitate the allocation of more test resources compared to single input single output (SISO) systems.In this paper, we propose a novel MIMO test technology that enables MIMO RF testing on a lower cost mixed-signal tester by using special configurations on the tester board. We take a

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