Ultra-wideband Multiple-input Multiple-output Systems Research Articles

A compact UWB MIMO antenna augmented with isolation improvement structures in situ with ground stubs and slots

Abstract An orthogonally oriented microstrip-fed bi-element ultra-wideband (UWB) diversity antenna possessing a super-wide bandwidth, high isolation, and band rejection attributes is proposed. The intended diversity antenna uses a 2nd-order Cayley fractal tree-shaped neutralization line among a pair of radiating square monopoles along with additional components like extended ground stubs, hybrid Koch fractal parasitic elements, and an L-shaped defected ground structure to attain high isolation of <−20 dB over 3.1–18 GHz. To nullify the intervention from the existent wireless local area network band, a hybrid Koch–Minkowski slot is carved out from the radiators. A minimal inter-element spacing of 8 mm is attained with the suggested layout measuring 28 mm (L) × 42 mm (W) in extent. The numerical as well as experimental investigations of vital diversity attributes like the envelope correlation coefficient, mean effective gain, total active reflection coefficient, and multiplexing efficiency depict high diversity actualization. The consistency amidst the simulation as well as the empirical results recommends the worthiness of the intended antenna for handy UWB and UWB multiple-input multiple-output systems.

Design and analysis of a compact UWB MIMO antenna incorporating fractal inspired isolation improvement and band rejection structures

This paper numerically proposes and experimentally investigates a compact coplanar waveguide fed two element ultra-wideband (UWB), multiple-input–multiple-output (MIMO) antenna array accompanying peak isolation and triple band notch mechanism. The proposed antenna consists of two identical printed monopole elements along with the incorporation of multiple 2nd order Hilbert defects in the ground structure and proposes to incorporate three different mechanisms to reduce the electromagnetic interference of the UWB antenna with existing narrowband systems. The measured impedance bandwidth for the intended antenna ranges from 2.7 GHz to 11.22 GHz. The incorporation of notch mechanisms provides interference suppression at the C-band (3.7–4.2 GHz), WLAN (5.15–5.825 GHz), and X-band communication (7.9–8.4 GHz). The overall size of the intended UWB MIMO antenna is 30.75 mm × 37.80 mm. Moreover, the diversity parameters of the proposed UWB MIMO antenna are numerically calculated and empirically investigated, these calculations and investigations depicts high diversity performance. It is noteworthy to observe that the spacing between the elements is staggeringly reduced to 2 mm. The concurrence among the diverse numerical and experimental outcomes supports the candidature of the suggested layout for portable UWB as well as UWB MIMO systems.

Path Loss Model and Channel Capacity for UWB–MIMO Channel in Outdoor Environment

A demand for high speed wireless communication system has increased tremendously. Two approaches for fulfilling this demand are to use system with large bandwidth as proposed by ultra-wideband (UWB) systems, or by adopting multiple-input multiple-output (MIMO) antenna systems. This paper presents the path loss model and the capacity of UWB channels in outdoor environment for infostation application. The close in free space and floating intercept path loss models are used to investigate the power decay for the UWB channel. The capacity of the UWB channel is computed based on the measured time-domain data obtained from channel measurement. Comparison between the capacities of UWB single-input single-output (SISO), UWB single-input multiple-output (SIMO), UWB multiple-input single-output (MISO), and UWB–MIMO systems is conducted. The path loss exponent for the MIMO channel is comparable with free space path loss exponent of 2. Result shows an improvement at about 27 bps/Hz in channel capacity for 2 × 2 UWB–MIMO systems when compared to UWB–SISO systems. In addition, we also found that 1 × 2 UWB–SIMO systems achieved higher capacities than 2 × 1 UWB–MISO systems.

Compact UWB MIMO Vivaldi Antenna With Dual Band-Notched Characteristics

A novel ultra-wideband (UWB) multiple-input multiple-output (MIMO) Vivaldi antenna with dual band-notched characteristics is presented and fabricated. The antenna is comprised of an improved ground plane and two microstrip feeding lines with a compact size of $26\times 26$ mm 2 . The evolutionary process of the antenna is given. By etching the T-shaped slot on the ground plane, the port isolation between individual antenna elements can be greatly increased. Meanwhile, by adding two split ring resonator (SRR) of different sizes next to the microstrip feed lines, dual notches can be achieved to filter the interfere of WLAN and X-band communication satellites. The notched mechanism is analyzed from the surface current distributions. The experimental results show that the impedance bandwidth of the designed MIMO antenna is from 2.9 to 11.6 GHz, along with two notched bands covering 5.3-5.8 GHz and 7.85-8.55 GHz, and the mutual coupling is less than -16 dB in the whole working bandwidth. The MIMO antenna has good radiation characteristics, stable gain, and very low envelop correlation coefficient (ECC <;0.02), which is suitable for UWB MIMO system applications. The idea in this paper also has a certain guiding significance for the study of band-notched MIMO Vivaldi antenna.

Compact band-notched UWB antenna for MIMO applications in portable wireless devices

A compact 5.5 GHz band-notched ultra-wideband (UWB) 2-element antenna with high isolation for multiple-input multiple-output (MIMO) portable wireless devices in wireless personal area network (WPAN) application is proposed. The MIMO antenna is designed for 3.1–10.6 GHz range on Neltec substrate with compact dimension of 43 × 20 mm2 and is tested experimentally. For the rejection band at 5.5 GHz, a slot of length 1.0 λ is etched into the radiator. Simple structure, i.e., receded steps at ground are used to improve isolation by 3 dB between two UWB antennas. The simulated and measured results show |S11| ≤ −10 dB and |S21| ≤ −20 dB in most of the frequency range excluding the reject band at 5.5 GHz in UWB range. The measured, simulated and calculated results show that the proposed UWB MIMO antenna is a good candidate for UWB MIMO systems. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1390–1394, 2016

A Compact UWB MIMO Antenna With Reflector to Enhance Isolation

A compact ultrawideband (UWB) multiple-input multiple-output (MIMO) antenna, with high isolation, is proposed for portable UWB MIMO systems. Two coplanar stripline-fed staircase-shaped radiating elements are connected back-to-back. The prototype is designed on a substrate of dielectric constant 4.4 with an overall dimension of 25 mm × 30 mm × 1.6 mm. This antenna configuration with an isolating metal strip placed in between the two radiating elements ensures high isolation in the entire UWB band. The proposed antenna exhibits a good 2:1 VSWR impedance bandwidth covering the entire UWB band (3.1-10.6 GHz) with a high isolation better than 20 dB, peak gain of 5.2 dBi, peak efficiency of 90%, and guaranteed value of envelope correlation coefficient (ECC) ≤0.1641.

Compact Dual Band-Notched UWB MIMO Antenna With High Isolation

A compact dual band-notched ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with high isolation is designed on a FR4 substrate (27 × 30 × 0.8 mm3). To improve the input impedance matching and increase the isolation for the frequencies ≥ 4.0 GHz, the two antenna elements with compact size of 5.5 × 11 mm2 are connected to the two protruded ground parts, respectively. A 1/3 λ rectangular metal strip producing a 1.0 λ loop path with the corresponding antenna element is used to obtain the notched frequency from 5.15 to 5.85 GHz. For the rejected band of 3.30-3.70 GHz, a 1/4 λ open slot is etched into the radiator. Moreover, the two protruded ground parts are connected by a compact metal strip to reduce the mutual coupling for the band of 3.0-4.0 GHz. The simulated and measured results show a bandwidth with |S11| ≤ -10 dB, |S21| ≤ -20 dB and frequency ranged from 3.0 to 11.0 GHz excluding the two rejected bands, is achieved, and all the measured and calculated results show the proposed UWB MIMO antenna is a good candidate for UWB MIMO systems.

A Real Time UWB MIMO System With Programmable Transmit Waveforms: Architecture, Algorithms and Demonstrations

Research on ultra-wideband (UWB) systems with multiple-input multiple-output (MIMO) configuration has gained a great deal of attention recently. In this article we report a real time experimental UWB MIMO system testbed developed at Tennessee Technological University. We present the architecture, unique capabilities, algorithms development, experimental demonstrations, secure communications scheme with measurement based performances evaluation, and potential applications of the system testbed. Two demonstration cases are used to validate the system. In the first demo case we experimentally investigate UWB MIMO enhanced spatial-temporal focusing property in a harsh RF environment with time reversal waveform precoding technique to take advantage of multipath propagation. In the second demo case UWB MIMO spatial division multiple access (SDMA) in a typical office environment is experimentally verified. In particular, as a physical layer security enhancement, a unique location based security-enhanced communications concept is tested with normal office-area propagation channels, and it is proved to be feasible at certain data rates. First-hand experimental results are collected to support UWB MIMO research.

QR Decomposition-Based Antenna Selection for Spatial Multiplexing UWB Systems with Zero-Forcing Detectors Followed by Rake Combiners

This letter presents a criterion for selecting a transmit antenna subset when ZF detectors followed by Rake combiners are employed for spatial multiplexing (SM) ultra-wideband (UWB) multiple input multiple output (MIMO) systems. The presented criterion is based on the largest minimum post-processing signal to interference plus noise ratio of the multiplexed streams, which is obtained on the basis of QR decomposition. Simulation results show that the proposed antenna selection algorithm considerably improves the BER performance of the SM UWB MIMO systems when the number of multipath diversity branches is not so large and thus offers diversity advantages on a log-normal multipath fading channel.

Spatial Multiplexing Receivers in UWB MIMO Systems based on Prerake Combining

In this paper, various ultra-wideband (UWB) spatial multiplxing (SM) multiple input multiple output (MIMO) receivers based on a prerake diversity combining scheme are discussed and their performance is analyzed. Several UWB MIMO detection approaches such as zero forcing (ZF), minimum mean square error (MMSE), ordered successive interference cancellation (OSIC), sorted QR decomposition (SQRD), and maximum likelihood (ML) are considered in order to cope with inter-channel interference. The UWB SM systems based on transmitter-side multipath preprocessing and receiver-side MIMO detection can either boost the transmission data rate or offer significant diversity gain and improved BER performance. The error performance and complexity of linear and nonlinear detection algorithms are comparatively studied on a lognormal multipath fading channel.

An Ordered Successive Interference Cancellation Scheme in UWB MIMO Systems

In this letter, an ordered successive interference cancellation (OSIC) scheme is applied for multiple-input multiple-output (MIMO) detection in ultra- wideband (UWB) communication systems. The error rate expression of an OSIC receiver on a log-normal multipath fading channel is theoretically derived in a closed form solution. Its bit error rate performance is analytically compared with that of a zero forcing receiver in the UWB MIMO detection scheme followed by RAKE combining. Performance of the ZF detector is known to be similar to that of the MMSE receiver at high signal-to-noise ratios (SNRs). This work focuses on the analysis of a ZF related scheme. In this letter, we present the error performance of a ZF scheme with an ordered successive interference cancellation (OSIC) for UWB SM MIMO detection in a log-normal fading channel. We analytically investigate the theoretic bit error rate (BER) performance of the ZF-OSIC architecture followed by RAKE combining, called a ZF-OSIC-RAKE, in an UWB SM MIMO receiver. The diversity order that the ZF-OSIC-RAKE offers for detecting the n-th transmitted data stream is obtained for UWB MIMO systems. It is also seen that the ZF-OSIC-RAKE scheme outperforms the ZF-RAKE.

Spatial-Temporal Combining-Based ZF Detection in Ultra-Wideband Communications

The performance of ultra-wideband (UWB) multiple input multiple output (MIMO) receiver based on the RAKE maximal ratio combiner (MRC) followed by a zero forcing (ZF) detector is analytically examined. For a UWB MIMO system with NT transmit antennas, NR receive antennas, and L resolvable multipath components, the proposed MIMO detection scheme is shown to have the diversity order of LNR-NT+1 and its analytical error rate expression is presented in a log-normal fading channel. We also compare the analytical BERs with the simulated results.

Simple correlated channel model for ultrawideband multiple-input multiple-output systems

A simple correlated channel model for ultrawideband (UWB) multiple-antenna systems is proposed. The authors show that a single numerical value of the spatial correlation coefficient is sufficient to accurately model the performance of UWB spatial multiplexing systems in an indoor environment. The appropriate value of the correlation coefficient is selected by ensuring a close match between the bit error rate results achieved on the proposed correlated channel and those on the measured indoor channel. The authors also experimentally confirm that the performance substantially degrades in the presence of high values of spatial correlation for a range of spatial multiplexing receivers, and quantify the relationship between this degradation and the value of the spatial correlation coefficient. Thus, a route for the development of the existing standards for single-antenna UWB channels to the multiple-antenna regime is provided here.

A New Distance Notion for PPAM Space--Time Trellis Codes for UWB MIMO Communications

We introduce a new distance notion and develop novel design criteria for optimal MN-ary pulse position amplitude modulation (PPAM) space-time trellis codes (STTC) for ultrawideband multiple-input multiple-output systems for slow and fast fading at both low and high SNR. Simulation results of the 2,2-ary PPAM STTC, constructed through set partitioning, confirm significant reduction in bit error rate.