Future MIMO Research Articles

Over-the-Air Antenna Array Calibration for mmWave Hybrid Beamforming Systems Based on Monte Carlo Markov Chain Method

The antenna phase calibration is critical for the millimeter wave (mmWave) hybrid beamforming communication system. Especially, with the increasing number of antennas being deployed in future massive MIMO systems, it is unrealistic to calibrate each antenna path in a microwave anechoic chamber. This work proposes a phase calibration based on over-the-air (OTA) scheme for mmWave hybrid beamforming systems, where the calibration process is performed automatically by the online signal transmission. The challenge for the OTA-based phase calibration is the imperfect channel estimation due to the phase error. To solve the challenge, we simplify the channel estimation process by integrating the beam alignment and phase calibration process. Consequently, the phase calibration is formatted to an MMSE-criterion based optimization problem solved by the Monte Carlo Markov Chain (MCMC) with probabilistic conversion improved Gibbs sampling method. Furthermore, an alternating iteration algorithm is developed to calibrate phase deviation for both the transmitter and receiver. We also extend our method to solve the joint amplitude and phase calibration problem. According to the simulation result, the calibration results outperform existing methods when the signal-to-noise ratio is less than 15dB. Besides, the proposed method exhibits a high beamforming gain during the calibration process, which paves the way for future massive device deployment in a practical system.

Temperature stable Sm(Nb1−xVx)O4 (0.0 ≤ x ≤ 0.9) microwave dielectric ceramics with ultra-low dielectric loss for dielectric resonator antenna applications

A temperature-stable Sm(Nb0.8V0.2)O4 (SNV-0.2) microwave dielectric ceramic with ultra-low dielectric loss was fabricated, and an RDRA was designed for 5G mm-wave application for the first time, which is a good candidate for 5G and future millimeter-wave MIMO antenna applications.

A Broadband Circularly Polarized Fabry-Perot Resonant Antenna Using A Single-Layered PRS for 5G MIMO Applications

This paper presents the design and the realization of broadband circularly polarized (CP) Fabry-Perot resonant antenna using a single superstrate for the fifth-generation (5G) wireless multiple-input-multiple-output (MIMO) applications. The antenna consists of a corner cut patch with a diagonal slot and a superstrate. The individual resonances of the corner cut patch and patch with diagonal slot are overlapped to improve the intrinsic narrow impedance and axial ratio (AR) bandwidths of the single-fed patch antennas. A half-wavelength spaced superstrate having a half-wavelength thickness is employed as a partially reflecting surface (PRS) for high gain and wide AR as well as impedance bandwidths. The design procedure and mechanisms of the PRS are discussed in detail through the equivalent circuit and ray tracing analysis. Simulated and measured results show that the proposed antennas have a wide operational bandwidth of 25-33 GHz (27.6%) for |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB with a stable gain achieving a maximum value of 14.1 dBiC and a wide 3-dB AR bandwidth ranging from 26-31.3 GHz (17%). This operational bandwidth of the antenna covers the proposed entire global 5G millimeter wave (mmWave) spectrum (26-29.5 GHz). Moreover, a 2 × 2 MIMO antenna is designed using the proposed antenna in such a way that the polarization diversity of the adjacent radiator is exploited, resulting in high isolation between antenna elements and low-envelope correlation coefficient, which makes it a suitable candidate for future 5G MIMO applications.

Universal Design Approach for Multiport Filtering Power Divider

This paper presents a universal design approach of multiport filtering power divider with the arbitrary power-division ratio, which is applicable for the designs of the single-ended/balanced circuit or hybrid of them. The power allocation in a specified passband is fulfilled by relying on two key factors in building a filter, i.e., coupling coefficient and external $Q$ -factor ( $Q_{\mathrm {e}}$ ). After synthesis for the bandpass response, the total input/output $Q_{\mathrm {e}}$ and the total coupling coefficient at each power dividing level can be determined. Subsequently, according to the desired power-dividing ratio, the coupling coefficient between the two coupled resonators and $Q_{\mathrm {e}}$ of each output can be easily determined. Once the parameters for filtering response are fixed, the power allocation can be determined by $Q_{\mathrm {e}}$ without effect on the filtering response. Thus, the two functions of bandpass and power dividing can be designed independently, which provides tremendous freedom for the overall design with the arbitrary order of filtering and number of output ports. The proposed topology has several advantages, such as flexibility, cost efficiency, and simple design procedure, which would be a good candidate for multiple-path operation in the current and future MIMO systems.

A Novel Architecture to Eliminate Bottlenecks in a Parallel Tiled QRD Algorithm for Future MIMO Systems

QR decomposition (QRD) is one of the performance bottlenecks in a lot of high performance wireless communication algorithms and should have the flexibility property for future multiple-input multiple-output systems. However, the existing QRD architectures only focus on several fixed dimension matrices. The parallel tiled QRD algorithm is a perfect choice to implement QRD for its flexibility and modularity property. The size of the tile is set to 2 $\times$ 2 instead of the traditional 200 $\times$ 200 or more to support flexible antenna configurations in this brief. Using a look-ahead technique and the property of unitary matrix, a novel algorithm based on a modified Gram–Schmidt (MGS) algorithm is proposed for the bottleneck operations (GEQRT and TTQRT) of the parallel tiled QRD algorithm. A corresponding hardware architecture is also designed with the proposed algorithm. The implementation results show that the hardware architecture based on the proposed algorithm achieves a 2.7× reduction in normalized processing latency, compared with the one based on the traditional MGS algorithm.

An Efficient Practical MIMO–OFDM Scheme with Coded Modulation Diversity for Future Wireless Communications

An efficient coded modulation diversity scheme is proposed to improve the performance of multiple-input-multiple-output orthogonal-frequency-division-multiplexing (MIMO---OFDM) systems in frequency-selective time-varying fading channels. By introducing the rotated modulation and space-time-frequency component interleavers, the proposed scheme globally optimizes powerful forward error correction codes, rotated quadrature amplitude modulation, linear precoding MIMO, and OFDM, thus can achieve modulation diversity and space-time-frequency diversities as much as possible. A simple efficient optimal precoder selection criterion is put forward for this scheme. Based on the analysis of average mutual information, optimal rotation angles are given for different modulation and coding schemes, and the superiority of the proposed scheme is proved. Both software simulation and hardware prototype test results also verify that this new scheme can significantly outperform the conventional bit-interleaved coded modulation scheme under the non-ideal channel estimation, which is up to 4.5 dB signal-to-noise-ratio gain. In a word, the proposed scheme is a simple, efficient and robust transmission technique for the future MIMO---OFDM wireless systems.

Design of a CPW-fed slot antenna with small size and ultra-broadband circularly polarized radiation

In this research, a coplanar waveguide (CPW)-fed slot antenna is proposed with a compact size and an ultra-broadband circularly polarized (CP) radiation. The proposed antenna, just with a small size of 40 mm × 40 mm × 1 mm in overall configuration, achieves an ultra-broad CP bandwidth of 68.1% from 3.05 to 6.2 GHz, suitable for both WiMAX (3.3–3.8 GHz) and WLAN (5.15–5.35 GHz/5.725–5.825 GHz) systems. The presented antenna proposes two linked rectangular slots in the ground to obtain CP radiations. The linked slots can also be considered as a square slot with two perturbations in the corners. The perturbations can split the fundamental resonant mode into two near-degenerate modes, leading to CP waves. The adjacent excited CP modes are merged for ultra-wideband CP radiation. With a symmetric series impedance line connected to CPW feedline, broadband input impedance matching from 2.65 to 6.8 GHz can be obtained. The proposed design has been verified by the simulated and measured results. The future MIMO potential of the proposed CP antenna has also been studied.