A Compact Planar Monopole UWB MIMO Antenna for Short-Range Indoor Applications

A compact, four-element planar MIMO (Multiple Input, Multiple Output) antenna that operates in an ultra-wideband is presented for diversity application. The orthogonal position of the unit cells replicates the single antenna thrice, thereby decreasing mutual coupling. A UWB MIMO antenna measuring 35 × 35 × 1.6 mm³ is built using a microstrip line (50 Ω impedance) on an FR4 substrate having a thickness of 1.6 mm. The ground plane and radiator of this antenna are adjusted in several ways to bring it within its operating constraints between the frequencies of 3.1 GHz and 10.6 GHz. This technique makes the antenna small and covers the entire ultra-wideband (UWB) frequency range. The NI USRP was used to test the proposed MIMO antenna to determine its real-time performance. Based on the computed results, we conclude that this proposed antenna has outstanding characteristics in terms of performance and is suitable for wireless ultra-wideband indoor communication and diversity utilization with a small size.

Flexible UWB and MIMO Antennas for Wireless Body Area Network: A Review

In recent years, there has been a surge of interest in the field of wireless communication for designing a monitoring system to observe the activity of the human body remotely. With the use of wireless body area networks (WBAN), chronic health and physical activity may be tracked without interfering with routine lifestyle. This crucial real-time data transmission requires low power, high speed, and broader bandwidth communication. Ultrawideband (UWB) technology has been explored for short-range and high-speed applications to cater to these demands over the last decades. The antenna is a crucial component of the WBAN system, which lowers the overall system's performance. The human body's morphology necessitates a flexible antenna. In this article, we comprehensively survey the relevant flexible materials and their qualities utilized to develop the flexible antenna. Further, we retrospectively investigate the design issues and the strategies employed in designing the flexible UWB antenna, such as incorporating the modified ground layer, including the parasitic elements, coplanar waveguide, metamaterial loading, etc. To improve isolation and channel capacity in WBAN applications, the most recent decoupling structures proven in UWB MIMO technology are presented.

Flexible Antennas for a Sub-6 GHz 5G Band: A Comprehensive Review

The ever-increasing demand and need for high-speed communication have generated intensive research in the field of fifth-generation (5G) technology. Sub-6 GHz 5G mid-band spectrum is the focus of the researchers due to its meritorious ease of deployment in the current scenario with the already existing infrastructure of the 4G-LTE system. The 5G technology finds applications in enormous fields that require high data rates, low latency, and stable radiation patterns. One of the major sectors that benefit from the outbreak of 5G is the field of flexible electronics. Devices that are compact need an antenna to be flexible, lightweight, conformal, and still have excellent performance characteristics. Flexible antennas used in wireless body area networks (WBANs) need to be highly conformal to be bent according to the different curvatures of the human body at different body parts. The specific absorption rate (SAR) must be at a permissible level for such an antenna to be suited for WBAN applications. This paper gives a comprehensive review of the current state of the art flexible antennas in a sub-6 GHz 5G band. Furthermore, this paper gives a key insight into the materials for a flexible antenna, the parameters considered for the design of a flexible antenna for 5G, the challenges for the design, and the implementation of a flexible antenna for 5G.

Sparse Space Shift Keying Modulation with Enhanced Constellation Mapping

For reducing the switching frequency between the radio frequency (RF) chain and transmit antennas, a class of new sparse space shift keying modulation (SSSK) schemes are presented. This new class is proposed to simplify hardware implementation, through carefully designing the spatial constellation mapping pattern. Specifically, different from traditional space shift keying modulation (SSK), the proposed SSSK scheme utilizes more time slots to construct a joint design of time and spatial domain SSK modulation, while maintaining the special structure of single RF chain. Since part of the multi-dimension constellations of SSSK concentrate the energy in less time slots, the RF-switching frequency is effectively reduced due to the sparsity introduced in the time domain. Furthermore, through theoretical analysis, we obtain the closed-form expression of the bit error probability for the SSSK scheme, and demonstrate that slight performance gain can be achieved compared to traditional SSK with reduced implementation cost. Moreover, we integrate transmit antenna selection (TAS) to achieve considerable performance gain. Finally, simulation results confirm the effectiveness of the proposed SSSK scheme compared to its traditional counterpart.

Efficient Transmit Antenna Subset Selection for Multiuser Space-Time Line Code Systems

We consider the problem of the efficient transmit antenna subset (TAS) selection for maximizing the signal-to-interference-plus-noise ratio (SINR) of multiuser space–time line code (MU–STLC) systems. The exhaustive search for optimal TAS selection is impractical since the total number of transmit antennas increases. We propose two efficient TAS selection schemes based on the Woodbury formula. The first is to incrementally select NS active transmit antennas among the available NT transmit antennas. To reduce the complexity of the incremental selection scheme, the Woodbury formula is employed in the optimization process. The second is to perform the decremental strategy in which the Woodbury formula is also applied to develop the low-complexity TAS selection procedure for the MU–STLC systems. Simulation results show that the proposed incremental and decremental TAS selection algorithms offer better alternatives than the existing greedy TAS selection algorithm for the MU–STLC systems. Furthermore, in terms of bit error rate, the proposed minimum mean square error decremental TAS selection algorithm turns out to outperform the existing greedy algorithm with significantly lower computational complexity. Finally, we analyze the detection SINR penalty experienced from TAS selection and the analytical quantity is shown to be well matched with simulation results.

Adaptive Waveform Design for MIMO Radar-Communication Transceiver

The system architecture for an adaptive multiple input multiple output (MIMO) radar-communication transceiver is proposed. A waveform design approach for communication data embedding into MIMO radar pulse using M-ary position phase shift keying (MPPSK) waveforms is introduced. A waveform optimization algorithm for the adaptive system is presented. The algorithm aims to improve the target detection performance by maximizing the relative entropy (RE) between the distributions under existence and absence of the target, and minimizing the mutual information (MI) between the current received signals and the estimated signals in the next time instant. The proposed system adapts its MPPSK modulated inter-pulse duration to suit the time-varying environment. With subsequent iterations of the algorithm, simulation results show an improvement in target impulse response (TIR) estimation and target detection probability. Meanwhile, the system is able to transmit data of several Mbps with low symbol error rates.

Design of Sparse FIR Decision Feedback Equalizers in MIMO Systems Using Hybrid l₁/l₂ Norm Minimization and the OMP Algorithm

In this paper, a novel scheme using hybrid l₁/l₂ norm minimization and the orthogonal matching pursuit (OMP) algorithm is proposed to design the sparse finite impulse response (FIR) decision feedback equalizers (DFE) in multiple input multiple output (MIMO) systems. To reduce the number of nonzero taps for the FIR DFE while ensuring its design accuracy, the problem of designing a sparse FIR DFE is transformed into an l₀ norm minimization problem, and then the proposed scheme is used to obtain the sparse solution. In the proposed scheme, a sequence of minimum weighted l₂ norm problems is solved using the OMP algorithm. The nonzero taps positions can be corrected with the different weights in the diagonal weighting matrix which is computed through the hybrid l₁/l₂ norm minimization. The simulation results verify that the sparse FIR MIMO DFEs designed by the proposed scheme get a significant reduction in the number of nonzero taps with a small performance loss compared to the non-sparse optimum DFE under the minimum mean square error (MMSE) criterion. In addition, the proposed scheme provides better design accuracy than the OMP algorithm with the same sparsity level.

A New Low Complexity Angle of Arrival Algorithm for 1D and 2D Direction Estimation in MIMO Smart Antenna Systems

This paper proposes a new low complexity angle of arrival (AOA) method for signal direction estimation in multi-element smart wireless communication systems. The new method estimates the AOAs of the received signals directly from the received signals with significantly reduced complexity since it does not need to construct the correlation matrix, invert the matrix or apply eigen-decomposition, which are computationally expensive. A mathematical model of the proposed method is illustrated and then verified using extensive computer simulations. Both linear and circular sensors arrays are studied using various numerical examples. The method is systematically compared with other common and recently introduced AOA methods over a wide range of scenarios. The simulated results show that the new method has several advantages in terms of reduced complexity and improved accuracy under the assumptions of correlated signals and limited numbers of snapshots.