Multiple-input Multiple-output Terminals Research Articles

Achieving Wireless Cable Testing for MIMO Terminals Based on Maximum RSRP Measurement

It is essential to perform end-to-end performance testing of multiple-input–multiple-output (MIMO) systems under realistic propagation channel conditions. However, due to the highly integrated and compact radio frequency (RF) system design, the traditional conducted cable testing method is getting more and more problematic. The wireless cable solution, which can achieve the equivalent functionality of the conducted cable testing without actual RF coaxial cables, has attracted huge attention from the industry and standardization for over-the-air (OTA) testing in recent years. However, the state-of-the-art solutions to achieve wireless cable testing necessitate at least reference signal received power (RSRP) reporting per device under test (DUT) antenna port for MIMO capable terminals, which is demanding and might not be accessible for commercial DUTs. In this work, a novel wireless cable solution based only on the maximum RSRP measurement of all DUT antenna ports is proposed, which can significantly alleviate the requirement of DUT RSRP reporting. To achieve the wireless cable testing, a novel calibration procedure is proposed to determine the transfer matrix between the probe antenna ports and the DUT antenna ports based on the DUT maximum reported RSRP measurement. The proposed algorithm is theoretically derived and experimentally validated for a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> MIMO system, where the isolation of above 25 dB is achieved for the measurement setup. The numerical simulation and experimental validation demonstrate the efficiency and robustness of the proposed algorithm.

Throughput Multiplexing Efficiency for High-Order Handset MIMO Antennas

In multipath environments, multiple-input multiple-output (MIMO) terminals typically suffer from non-zero correlations due to limited handset space and power imbalances due to different antenna efficiencies or partial hand blockage. These antenna–channel impairments can lead to significant throughput performance degradation of MIMO terminals. The multiplexing efficiency was proposed to quantitatively assess this performance degradation. Previous work only derived the analytical expression of the throughput-based multiplexing efficiency of two-port MIMO antennas for user equipment (UE). However, the fifth-generation (5G) UE dictates four or more antennas. In this paper, we extend the multiplexing efficiency metric to high-order MIMO UEs. Both correlation-based channel models and geometry-based stochastic channel models were used for validation. Besides dipole antennas, two representative terminal antennas were also employed for simulation verifications in this work.

Dual-Band Antenna Pair With Lumped Filters for 5G MIMO Terminals

This article proposes a novel design of the dual-band antenna pair. Starting from the single-band antenna pair composed of T-shaped monopole and T-shaped slot that are intersected with each other, orthogonal T-monopole and odd-symmetrical slot modes are excited. By adding symmetrical low-pass high-stop filters into the horizontal stub of the T-monopole and high-pass low-stop filters into the gap of the T-slot, an extra mode is introduced for each antenna, producing dual-band operation. Impedance bandwidths and radiation efficiencies of both bands can be adjusted flexibly using the filters. A detailed design guideline is given. The dual-band antenna pair operating at partial N78 (p-N78, 3.4~3.6 GHz) and partial N79 (p-N79, 4.8~4.9 GHz) is with a footprint of 15×6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measured results show that the average efficiencies are both -3.4 dB at p-N78/p-N79 for the odd-symmetrical slot and -2.8 dB/-3.7 dB at p-N78/p-N79 for the T-monopole, isolations are better than -16.8 dB at p-N78 and -11.8 dB at p-N79, and ECCs are lower than 0.1 at p-N78 and 0.2 at p-N79. The proposed dual-band antenna pair exhibits great potential to be applied in the fifth-generation (5G) multiple-input multiple-output (MIMO) terminal.

Highly Isolated Compact Planar Dual-Band Antenna With Polarization/Pattern Diversity Characteristics for MIMO Terminals

A highly isolated two-element dual-band antenna with polarization/pattern diversity is presented in this letter for multiple-input–multiple-output (MIMO) terminals. The MIMO configuration consists of two orthogonally placed identical monopole antenna elements. In both the bands (2.3–2.5 and 5–5.2 GHz), isolation (| S 21| or | S 12|) ≥ 20 dB is achieved by using a simple decoupling structure. Measured impedance bandwidth of 200 and 190 MHz is achieved in the lower and upper bands, respectively. The individual antenna element has a size of 14 mm × 14 mm, and the MIMO configuration of two elements covers an area of 38 mm × 18.2 mm. Polarization diversity between the elements is achieved by placing them orthogonal to each other, whereas pattern diversity is verified through measurement of the envelope correlation coefficient and radiation patterns. The elements exhibit good efficiency and gain in spite of being compact. The measured and simulated results verify that the proposed design performs well in both the bands.

Over-the-Air Testing for Carrier Aggregation Enabled MIMO Terminals Using Radiated Two-Stage Method

Multiple-input multiple-output (MIMO) over-the-air (OTA) testing of wireless devices has become increasingly attractive in radiated performance evaluation. As one of the OTA testing methods, the radiated two-stage (RTS) method achieves flexible channel models with low-system cost. However, the existing MIMO OTA testing using RTS method is valid only for single carrier frequency application. This paper applies the RTS method to multiple carrier frequency applications [carrier aggregation (CA)]. Two setups are presented to discuss system cost and calibration time. To validate the RTS OTA testing for CA, the transfer matrices from the OTA antenna ports to device under test antenna ports in three types of RF shielded enclosure are investigated. The results demonstrate that the applied RTS method for CA works better in anechoic chambers. One calibration matrix might need to be adopted for each component carrier when the frequency separation of component carriers is large.

Design of Closely Packed Pattern Reconfigurable Antenna Array for MIMO Terminals

In this communication, a compact pattern reconfigurable dual-antenna array is designed at 2.65 GHz for multiple-input multiple-output (MIMO) terminal applications, such as laptops. Each antenna is composed of two layers, i.e., the monopole layer and the planar inverted-F antenna (PIFA) layer. By switching the p-i-n diodes on each layer, its radiation patterns can be varied between conical and boresight patterns. Two such identical antennas are placed side by side on a common ground plane for MIMO application, providing altogether four operating modes. The center-to-center separation between the antennas is 0.25 wavelength, to keep the overall array compact. To facilitate an isolation of above 17 dB over all the modes for this compact array, two decoupling techniques based on the decoupling slits and the shielding wall are effectively combined. The envelope correlation coefficients (ECCs) of the far-field patterns in the four modes are below 0.05 in free space, and below 0.1 for most cases in the indoor and outdoor scenarios. The only exception is the monopole-PIFA mode in the outdoor scenario, but the ECC is still below 0.3 for this case. The measured efficiencies of the antennas are between −1.7 (68%) and −0.7 dB (85%) for all the modes. Therefore, good diversity and MIMO performances are expected for the proposed design.

Impact of Antenna Design on MIMO Performance for Compact Terminals With Adaptive Impedance Matching

Using the metrics of channel capacity and multiplexing efficiency, the adaptive impedance matching (AIM) performances of two multiple-input multiple-output (MIMO) terminals with different antenna designs were evaluated and compared. The evaluation was performed in LTE Band 18 Downlink (860–875 MHz) under realistic usage conditions of two measured user handgrips and simulated propagation channels with different angular spreads (ASs). The results provide potential performance gains from AIM based on realistic MIMO terminal prototypes, and the underlying mechanisms by which the gains were achieved, which can serve as antenna and AIM circuit design guidelines. In particular, the evaluation revealed that ideal uncoupled AIM networks can increase the capacity by up to 52% relative to $50\text{-}\Omega$ terminations. However, the observed gains depend heavily on the antenna design, the user scenario, and the channel’s AS. For example, the wideband design in different user cases experienced capacity gain of 4%–9% from AIM in uniform 3-D channels, in contrast to the 1.3%–44% gain seen in a conventional narrowband design. In nonuniform channels with small ASs, the AIM gain for different mean incident angles depends on the absolute mean effective gain (MEG) and the change in correlation due to AIM; in cases where AIM has little impact on correlation, the mean incident angles with high AIM gains were close to those with high MEGs.

Modified PIFA and its array for MIMO terminals

A study on a modified planar inverted-F antenna (PIFA), operating at 5.2 GHz within the IEEE802.11a WLAN frequency band (5.15–5.35 GHz) with a very small ground plane (7 mm×12 mm) and its application to multiple input multiple output (MIMO) systems is presented. While it inherits the attractive features of PIFAs, such as compact size and low profile, the modified antenna exhibits low coupling to the printed circuit board (PCB). A 2-element PIFA array is implemented on a mobile handset PCB and an isolation better than 28 dB is achieved in both simulation and measurement.