Multiple-input Multiple-output Performance Research Articles

Dual-Band Eight-Element MIMO Array Using Multi-Slot Decoupling Technique for 5G Terminals

This paper presents a dual-band eight-element multiple-input multiple-output (MIMO) array using a multi-slot decoupling technique for the fifth generation (5G) mobile communication. By employing a compact dual-loop antenna element, the proposed array obtains two broad bandwidths of 12.2% and 15.4% for sub-6GHz operation. To reduce the mutual coupling between antenna elements, a novel dual-band decoupling method is proposed by employing a multi-slot structure. The proposed MIMO array achieves 15.5-dB and 19.0-dB isolations across the two operating bands. Furthermore, three decoupling modes generated by different bent slots can be independently tuned. Zero ground clearance is also realized by the coplanar arrangement of the antenna elements and decoupling structures. The proposed MIMO array was simulated, fabricated, and measured. Experimental results agree well with the simulations, showing that the dual-band MIMO array has good impedance matching, high isolation, and high efficiency. In addition, the envelope correlation coefficient and channel capacity are calculated and analyzed to validate the MIMO performance of the 5G terminal array. Such a dual-band high-isolation eight-element MIMO array with zero ground clearance is a promising candidate for 5G or future mobile applications.

Joint data transmission and dimming control optimization for MIMO–VLC systems with channel-adaptive spatial constellation design

In the field of indoor wireless communications, visible light communications (VLCs) have attracted great attention for synergistically providing both illumination and data transmission. Meanwhile, multiple-input multiple-output (MIMO) technique has been applied in VLC systems to boost data rate by utilizing spatial resources. However, different geometrical locations of transceivers provide distinct optical channels which may effect the performance of the conventional MIMO–VLC techniques severely. In this paper, we propose the channel-adaptive spatial constellation (CASC) design for the MIMO–VLC systems by fully taking advantage of the channel state information (CSI), where the optimal transmitted signal constellation can be constructed via maximizing the minimum Euclidean distance (MED) of the received signal constellation. Meanwhile, the practical lighting constraints are taken into consideration with the non-linearity characteristic of light-emitting diode (LED) and the dimming requirements to maintain a specific indoor illumination level. Finally, simulations results indicate that the proposed CASC design can achieve significant improvement of error performance compared with the conventional MIMO–VLC schemes.

Side-Edge Frame Printed Eight-Port Dual-Band Antenna Array for 5G Smartphone Applications

An eight-port antenna array operating in 3.5 GHz band (3400–3600 MHz) and 5 GHz band (4800–5100 MHz) for fifth-generation multiple-input multiple-output (MIMO) in mobile handsets is presented. To reserve space for 2G/3G/4G antenna configuration, the eight-antenna array formed by two quad-antenna arrays is printed along the two long frames of the smartphone. Each antenna array unit is formed by a folded monopole and a gap-coupled loop branch, and they are disposed on the upper and bottom sides of the system circuit board, respectively. As the gap between each array unit is only 10 mm, a neutralized line is introduced between the two middle antenna units for reducing the mutual coupling. The measured results have exhibited good impedance matching and isolation. To evaluate the MIMO performance, the envelope correlation coefficient, mean effective gain, and ergodic channel capacity are investigated. Furthermore, the hand phantom effects and display panel effects are also given.

Printed millimeter-wave MIMO-based slot antenna arrays for 5G networks

In this work, a broadband millimeter-wave (mm-wave) multiple-input–multiple-output (MIMO) antenna system for upcoming fifth generation (5G) networks is presented. The MIMO antenna system is two ports and realized using two antenna arrays, aligned in opposite directions. Each array consist of three elements in each, as each element is a simple recognized printed wide-slot antenna proximity excited by microstrip line with a widened tuning stub; manipulated for operating in the Ka-band, which includes the 28 and 38 GHz bands, as potential candidates for 5G communications. An electromagnetic band-gap (EBG) reflector is placed behind the antenna structure toward the feeding network to decrease the backward radiation and improve the front-to-back (F/B) ratio. Results show that the proposed MIMO antenna system with EBG reflector provides wideband impedance bandwidth >27 GHz (from 22.5 to >50 GHz) and good radiation characteristics with a total realized gain up to 11.5 and 10.9 dBi at the two frequencies of interest, respectively. The envelope correlation coefficient (ECC) and diversity gain (DG) were evaluated and showed good MIMO performance. These remarkable features with the benefits of design simplicity and easily expansion to large-scale antenna system make the proposed design suitable for mm-wave communications.

Dual-Band Platform-Free PIFA for 5G MIMO Application of Mobile Devices

A dual-band platform-free antenna is proposed for the 5G multiple-input multiple-output (MIMO) application of mobile devices. The antenna is formed by adding a vertical metallic patch to the planar inverted-F antenna (PIFA) and setting another PIFA to feed the antenna by coupling. The vertical patch can effectively suppress the fringe currents on the ground plane, which makes the antenna electromagnetic compatible on different working platforms, e.g., the antenna is not affected by other components inside the real device and vice versa. The coupling feed helps to realize a dual-band operation and reduces the length of antenna to around $\lambda $ /8, which makes the antenna more applicable in smartphones. As a design example, a handset MIMO antenna with eight elements is fabricated and measured. Furthermore, the throughput achieved by the antenna in an indoor environment is tested with an MIMO system developed by the Communication Laboratory of Huawei Corporation. The effect of one hand on the MIMO performance is also studied.

Closed-formed distribution for the SINR of MMSE-detected MIMO systems and performance analysis

In this paper, we investigate the error performance of multiple-input multiple-output (MIMO) wireless communications systems using minimum mean-square error (MMSE) detection. Particularly, a new closed-form statistical distribution for the output signal-to-interference-plus-noise ratio (SINR) of MMSE receiver is derived, for independent Rayleigh fading channels. The expression for the distribution of SINR is shown to be a linear combination of gamma distributions and polynomial of 11+x, where x is the SINR. Base on the derived distribution for the SINR, closed-form and approximated expressions for the symbol error probability (SEP) of quadrature amplitude modulation (QAM) and phase shift keying (PSK) signaling are obtained, respectively. The derived SINR density and SEP are valid for arbitrary number of transmit and receive antennas. Furthermore, a reduced complexity approximation is introduced to obtain the SINR distribution and SEP performance of MMSE-Detected MIMO Systems with a large number of antennas. The provided simulation results confirm the validity of our theoretical analysis for both the SINR and SEP.

Compact circular connected monopole antenna arrays for wideband MIMO applications

In this work, a connected circular monopole antenna array is presented for ultra-compact, wideband, multiple-input multiple-output (MIMO) wireless access point applications. Two configurations of the circular array are considered; one with 4- and another with 8-antenna elements using the same substrate size. The frequency bands covered were from 2.3 to 5.3 GHz (LTE 2.3-3.8 GHz, Bluetooth 2.4 GHz, wireless local area network 2.4, 5.2 GHz and WiMax 2.3 GHz). The obtained measured bandwidth was 3 and 2 GHz for the 4- and 8-element arrays, respectively. The antenna system is fabricated on a commercially available Roger 4350 substrate with epsilon(r) equal to 3.5 and height of 1.52 mm. The radius of the array is 32 mm (the most compact with wideband characteristics). The length of a single element is only 15 mm which is λ/8 at the lowest frequency. The design is planar, low profile and very compact. Good MIMO performance is achieved.

Design of a Low-Profile Antenna for Use with 698-2,700 MHz Femtocell Base Stations [Antenna Applications Corner

A low-profile multiple-input, multiple-output (MIMO) antenna for long-term evolution (LTE) femtocell base stations (BSs) is presented in this article. The antenna element consists of a modified bowtie loaded by three arcs with different lengths that extend the lowest frequency to 698 MHz, a microstrip feeding line, and a planar reflector. It has dimensions of 260 mm t 150 mm t 50 mm and a bandwidth of 698n2,700 MHz. Four of the antenna elements are used to form a four-port MIMO antenna in a novel cross shape. The resulting MIMO antenna has a compact size (480 mm t 480 mm t 50 mm), reasonably low mutual couplings, and extremely low antenna correlations. The MIMO capacity of the proposed antenna is evaluated via numerical simulations, and good MIMO performance is observed.

Robust waveform design for MIMO–OFDM‐based STAP in the presence of target uncertainty

The issue of robust orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) radar waveform design is investigated here with target uncertainty to enhance the worst-case space-time adaptive processing (STAP) detection performance of MIMO–OFDM radar. Based on the max–min method, the robust waveform optimisation problem is constructed under the criterion of maximising the worst-case output SINR, namely, signal–interference–noise ratio, with constraints of constant modulus and target estimation errors to enhance the robustness of STAP's detection performance to target uncertainty. To handle the obtained non-linear and complicated issue, an approach based on diagonal loading (DL) is presented. By employing DL method, the optimisation issue can be relaxed to semidefinite programming one, and thus it can be tackled very efficiently. When compared with uncorrelated signals, the state-of-the-art robust and non-robust waveform design methods for MIMO–STAP, numerical simulations reveal that the developed approach can enhance the robustness of the detection performance of STAP significantly.

Optimizing channel capacity in a MIMO–PSK wireless rayleigh fading channel

Due to the continual advancement of future generation communication systems, channel capacity is considered to be an important parameter for achieving greater signal strength by means of faster data transmission speed. Usually in multiple input multiple output (MIMO) systems, the diversity technique lessens the propagation speed significantly than the channel capacity. Using MIMO in combination with phase shift keying (PSK) modulation jointly known as MIMO–PSK systems, the present paper focuses on a novel distribution method in order to optimize the channel capacity over a Rayleigh fading channel. First, ergodic channel capacity and distribution capacity in terms of outage capacity is simulated for different MIMO–PSK configurations as well as channel conditions. Later, the channel performance of MIMO–PSK for the novel distribution conditions with antenna correlation effect is evaluated and finally the optimal channel capacity is determined.

Equivalence between orbital angular momentum and multiple‐input multiple‐output in uniform circular arrays: Investigation by eigenvalues

AbstractIt had been shown that array weight vectors using uniform circular arrays (UCAs) in multiple‐input multiple‐output (MIMO) can generate helical phase distribution used in orbital angular momentum (OAM) communication system. In this letter, the MIMO channel, or OAM multiplexing characteristic, was investigated by means of eigenvalues. It was also found that the OAM is not effective as the distance between transmitting and receiving antennas increases because the radiation pattern along the direction of propagation is null with helical phase front. It was found that MIMO and/or OAM performance improve in near‐field region. It was also found that the performance improves when radius of UCAs becomes large.

Dual polarized triple‐band dielectric resonator based hybrid MIMO antenna for WLAN/WiMAX applications

AbstractIn this article, a dual polarized triple‐band dielectric resonator based hybrid multiple‐input multiple‐output (MIMO) antenna is presented. The proposed MIMO antenna is designed with the help of two cylindrical dielectric resonators along with two symmetrical modified Y‐shaped microstrip printed lines. Two metallic strips and a slot on the ground plane are used to enhance the isolation. A prototype of the proposed design is fabricated and tested to validate the simulation outcomes. The measured outcomes confirmed that the proposed antenna can be utilized in three different frequency bands such as 2.21–3.13, 3.40–3.92, and 5.30–6.10 GHz with fractional bandwidth of 34.45%, 14.2%, and 14%, respectively. The modified Y‐shaped printed line is used to obtain circular polarization in the upper frequency band with fractional axial ratio (AR) bandwidth of 4.18%. Besides, MIMO performance has also been examined in terms of diversity parameters like envelope correlation coefficient (ECC), mean effective gain (MEG), diversity gain (DG), and channel capacity loss (CCL).

Dual-band multiple-input multiple-output antenna based on half split cylindrical dielectric resonator

In this article, a dual-band half split cylindrical dielectric resonator antenna is proposed for multiple-input multiple-output (MIMO) applications. The dual-band operation is achieved by simultaneously exciting and modes in an aperture coupled fed half split cylindrical dielectric resonator. The topology of four element MIMO antenna is such that it provides both spatial and polarization diversities. Over both the operating bands, the measured port-to-port isolation is better than 20 dB. The proposed antenna exhibits broadside radiation with cross polarization level below dB in both xz- and yz-plane. The peak gain of antenna is 4.88 and 5.32 dBi at lower and upper operating frequency, respectively. The MIMO performance of the proposed antenna is found to be good with ECC0.06. Moreover, the channel capacity of the proposed MIMO is near to uncorrelated case for uniform propagation scenario. The proposed antenna could be suitable for LTE 22/LTE 42 and WLAN applications.

A miniaturized multi-wideband Quasi-Yagi MIMO antenna system

A multi-band directional multiple-input–multiple-output (MIMO) antenna system is presented based on a rectangular loop excited Quasi-Yagi configuration. A 64% reduction in size is obtained using a rectangular meandered element as well as a small ground plane. The proposed two-element MIMO antenna system covers the Telemetry L-band and several LTE/WLAN bands. It has a wide measured bandwidth of 689 MHz (1.897–2.586 GHz) in the desired band centered at 2 GHz, and a measured bandwidth of more than 168 MHz across rest of the bands. The MIMO antenna system has a total size of 45 × 120 × 0.76 mm3, with a single element size of 55 × 60 × 0.76 mm3. The non-desired back-lobe radiation which is obtained using a small ground plane, is significantly reduced by using a novel defected ground structure (DGS) as compared with the complex techniques present in literature. The proposed DGS provides a high measured front-to-back ratio of 14 dB at 2 GHz and 11 dB in other bands. A maximum measured realized gain of 5.8 dBi is obtained in the desired band using a single parasitic director element. The proposed MIMO antenna system has a minimum measured radiation efficiency of 70%, isolation of 12 dB, and envelope correlation coefficient of 0.098 within all bands which ensures very good MIMO performance.

A Two Concentric Slot Loop Based Connected Array MIMO Antenna System for 4G/5G Terminals

In this paper, an integrated design with a multiple-input multiple-output (MIMO) antenna system for fourth generation (4G) and fifth generation (5G) applications is presented. The proposed design contains a two-element slot-based MIMO antenna system for 4G and a connected antenna array (CAA)-based two-element MIMO antenna system for a potential 5G band. Two rectangular loops are etched on the periphery of the ground plane. The top and bottom portions of the thin loops act as the two 4G MIMO antennas, while parts of their sides are acting as 5G arrays. The antenna system is fabricated on a commercially available Roger 4350 substrate with $\epsilon _{r}$ equal to 3.5, while the dimensions of the board are $100\times 60 \times 0.76$ mm3 representing a typical smart phone back plane size. The integrated antenna system covers multibands at 4G with a combined bandwidth of 1.565 GHz (−6 dB BW) in addition to the band between 16.50 and 17.80 GHz for 5G. The design is planar, low profile, simple, and compact in structure making suitable for wireless handheld devices and mobile terminals. The measured gain at 3.46 GHz was at least 2.22 dBi and at 17 GHz was 8 dBi for the 4G and 5G MIMO antenna systems, respectively. The envelope correlation coefficient was also calculated from the measured 3-D patterns and showed good MIMO performance. This is the first integrated 4G/5G MIMO antenna system with below 6 GHz and above 10-GHz covered bands using CAA.

Multipath Clustering and Cluster Tracking for Geometry-Based Stochastic Channel Modeling

This paper presents a clustering and tracking method that exploits the geometry of the scattering points (SPs) obtained from the measurement-based ray tracer. The multipath components (MPCs) were categorized into clusters by applying the KPowerMeans (KPM) framework to those SPs. The clusters were tracked by comparing the cluster-centroid SPs of the adjacent snapshots. The clusters were estimated based on the indoor environment geometry at 11 GHz, and their physical mechanisms were interpreted. The complexity and performance of this method was assessed and compared with that of conventional KPM by comparing the number of floating point operations (FLOPS) and the channel eigenvalues obtained from the reconstructed channel matrices, which were calculated by superposing the MPCs randomly generated from intracluster parameters. The verification of this method showed that most clusters were estimated and tracked according to the physical location of the scatterers in the environment with acceptable error. Moreover, the eigenvalues reconstructed from the proposed method were closer to the measured ones with less number of FLOPS, which indicates both accuracy and complexity improvement. The results also imply that multiple-input multiple-output performance is highly dependent on the radio propagation channel; therefore, it is imperative that clusters in the channel be determined accurately.

A novel very wideband integrated antenna system for 4G and 5G mm‐wave applications

AbstractIn this work, a novel very wideband 4‐element monopole based multiple‐input multiple‐output (MIMO) antenna system with single connected antenna array (CAA) is presented. The CAA is based on a single slot which is etched on the ground plane. A 2 × 1 power divider/combiner is used to excite the slot to act as a CAA. The proposed design covers the 4G bands between 1850 and 3700, and the 28 GHz 5G band. The covered bandwidths are 1462 and 240 MHz from 1843 to 3305 MHz and 3500 to 3740 MHz, respectively, for 4G applications. A bandwidth of 1.22 GHz from 27.5 to 28.72 GHz is obtained for 5G applications. The proposed antenna system is designed on a double layer RO4350B substrate with height of 0.76 mm and dielectric constant of 3.5. The total size of the design is 115 × 65 × 0.76 mm3. It is compact, low profile and suitable for wireless handheld devices. The MIMO performance metrics such as isolation and ECC are evaluated and good agreement between simulations and measurements is achieved.

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.

On the Performance of Spatial Modulation MIMO for Full-Duplex Relay Networks

In this paper, we investigate, for the first time, the performance of a full-duplex (FD) relaying protocol, where a single-RF spatial modulation (SM) multiple-input multiple-output (MIMO) system is employed at the relay node. We refer to this protocol as SM-aided FD relaying (SM-FDR). At the destination, a demodulator that takes advantage of the direct connectivity between the source and destination is developed in order to maximize its performance. Based on this demodulator, we introduce a mathematical framework for computing the average error-probability of SM-FDR in the presence of residual self-interference (SI). Furthermore, we derive mathematical expressions for computing the achievable rate of SM-FDR. With the aid of these achievable rate expressions, we provide an estimate on the quality of SI cancellation required for the suitability of FD transmission. In addition, we develop and evaluate three relay selection policies specifically designed for the SM-FDR protocol. The mathematical analysis is substantiated with the aid of extensive Monte Carlo simulations. Finally, we also assess the performance of SM-FDR against traditional FD relaying protocols.

Wideband multiple‐input–multiple‐output dielectric resonator antenna

A two-element multiple-input–multiple-output (MIMO) dielectric resonator antenna having wideband characteristics is presented. The wideband operation is achieved by using a mushroom shaped dielectric resonator excited by a conformal trapezoidal patch. In order to realise two-element MIMO configuration, two wideband radiators are arranged orthogonally which offers polarisation diversity. The measured bandwidth (VSWR ≤ 2) for Port1 is 61% (5.08–9.50 GHz), whereas for Port2 it is 65% (4.89–9.61 GHz). The isolation between the two ports is better than 20 dB for the desired frequency band. The antenna exhibits broadside radiation with cross polar level below 15 dB. The peak gain of antenna varies from 3.34 to 7.40 dBi at Port1 and from 2.34 to 7.9 dBi at Port2. Moreover, the various MIMO performance metrics including envelope correlation coefficient (ECC), diversity gain, channel capacity loss and total active reflection coefficient are investigated. The ECC is less than 0.01 and capacity loss is under 0.5 bps/Hz throughout the operating bandwidth. The results confirm that the antenna offers effective MIMO/diversity performance. The proposed antenna can be suitable for WLAN and upper ultra wideband frequency band applications.