The Performance Of Passive And Active Mimo Antenna Research And Test Validation

Multi-Input Multi-Output (MIMO) technology, which employs multiple antennas at both the transmitter and receiver, provides a significant improvement on channel capacity without increasing the system bandwidth or transmit power, and thus is recognized as one of the key techniques in the next generation of cellular communication systems. As the network of the3rd Generation Partnership Project Time Division-Long Term Evaluation (3GPP TD-LTE) that supporting MIMO transmission is being employed in China, corresponding multi-antenna devices will enter the cellular network soon. The MIMO antenna equipped by the mobile device has significant effect on the gain and correlation of the channel matrix between the transmitter and receiver, and thus influences the effectiveness and reliability of MIMO transmission. In order to fully develop the advantage of MIMO transmission, it is necessary to evaluate the MIMO antenna performance at the mobile devices, as well as its effect on the MIMO transmission. This study on one hand will be able to support the MIMO antenna design, and also provide measurement solutions for radiated and receiver performance of multi-antenna devices. The MIMO antenna contains multiple single-antenna elements. Besides the traditional performance metrics of single antenna, there are more factors such as the mutual coupling and isolation among multiple antenna elements that also affect the MIMO antenna performance. Therefore, traditional method developed for single antenna devices is not adequate to evaluate the performance of MIMO antenna. It is necessary to study new methodology for the MIMO antenna performance evaluation.Since the prevalent cellular systems only support downlink MIMO transmission, but do not allow uplink MIMO transmission, we focus on the receiver performance evaluation for multi-antenna devices. As the multi-antenna devices may perform single-stream receiving in traditional cellular networks, first we study the measurement method for total radiated sensitivity (TRS) of multi-antenna devices, which is an important performance metric to evaluate the receiver performance during single stream transmission. Then we study the receiver performance evaluation for passive MIMO antenna, which does not include any radio-frequency circuit. Considering that the body of the mobile device may affect the performance of the antenna, and the signal processing unit of the mobile device also has impact on its receiving performance, we then study the evaluation method for receiver performance of the active MIMO antenna, which evaluate the performance of the whole device including the antennas, radio-frequency circuits and baseband signal processing. Based on the above theoretical work, we establish a multi-probe anechoic chamber test system, which offers the solutions for single-input single-output (SISO) and MIMO Over-the-Air (OTA) test for TD-LTE devices.The main contribution of this thesis includes,First, propose a new TRS measurement approach for multi-antenna devices. We analyze the effect of the combining of multiple received signal streams from MIMO antenna on the received signal-to-noise ratio (SNR). It shows that devices with identical MIMO antenna but different combing algorithms will experience different receiver sensitivities. Therefore, we propose to include the combining process of multi-streams into the measurement scope when evaluating the TRS for multi-antenna devices. Compared to the existing measurement method which tests the TRS of each receiver antenna separately, the proposed approach offers more accurate evaluation on the receiver sensitivity of multi-antenna devices, and reduces the test time consumption by more than50%.Second, propose a performance evaluation method for passive MIMO antenna based on the complex antenna pattern. It employs the measurement results of the antenna pattern to compute the correlation matrix of the MIMO channel with given spatial channel model, and then calculates the channel capacity of the system that employing the antenna-under-test as the receiver antenna, based on the existing work on the MIMO channel capacity. In this way, we are able to evaluate the effect of the MIMO antenna on the end-to-end achievable data rate directly. In addition, we propose a low-complexity method for the MIMO antenna pattern measurement, based on the detecting of the downlink reference signal from the base station. It shows tiny gap between the measurement results of the proposed and existing pattern measurement approaches.Third, propose a3-D channel emulation and measurement method using the2-D multi-probe anechoic chamber for the active MIMO antenna performance evaluation. It is able to measure the receiver performance of multi-antenna devices under given3-D spatial channel model, only using a low-complexity2-D multi-probe anechoic chamber. The measurement and simulation results show that the performance measured in the proposed approach is similar to that measured directly in a3-D channel environment. In addition, we also analyze the principle of the spatial channel emulating inside the2-D multi-probe chamber, and then optimize the number and position of the probes in the system with given spatial channel model. Based on the proposed optimization procedure, we are able to lower down the system complexity by reducing the required number of probes, under the constraint of guaranteeing the accuracy of channel emulating inside the test zone.Finally, establish a multi-probe anechoic chamber test system, which offers the solutions for SISO and MIMO OTA test for TD-LTE devices. We study the key elements of the test system, such as the input-output calibration, channel model validation, the downlink power control, to guarantee the accuracy of the measurement results. We perform SISO and MIMO OTA test using the established system for TD-LTE device samples, and discuss the standardization of the OTA measurement metrics based on the practical measurement results.