Spatial Diversity Antenna Research Articles

Performance optimization of spatial diversity antenna using hybrid combination for terrestrial optical wireless communication

The coherent laser signals of optical wireless communication suffer dramatic intensity fluctuations due to the atmospheric turbulence effect. A larger receiver aperture could only increase the average laser intensity without adaptive optics. Adaptive optics and wavefront reconstruction are popular in laser wireless transmission systems. Still, the alternative spatial diversity receivers are more convenient and economical to mitigate the irradiance scintillation, in which the antenna array combines multiple signals in digital signal processing or analog laser beams coherent combination. We provide channels correlated spatial diversity models and compare the performances of digital and optical combinations. In addition, reception experiments with a 19-aperture optical combination for horizontal 2 km transmission showed a ten times increase in average optical intensity and decreased scintillation index to 16 %. The large-scale spatial diversity receivers of 64-aperture that adopt hybrid optical and digital combinations are proposed to reduce the complexity of digital processing or cascaded optical combination structure.

A Modified SWB Hexagonal Fractal Spatial Diversity Antenna With High Isolation Using Meander Line Approach

This manuscript introduces a novel miniaturized super wideband (SWB) hexagonal fractal spatial diversity 2-element multiple-input-multiple-output (MIMO) antenna for broadband applications, as a compact wideband antenna is required for military radio and space communication devices. The designed antenna includes two hexagonal ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1^{st}$ </tex-math></inline-formula> modified Koch iteration) Koch fractal radiators with two linear tapered feedlines (TLTF) and a step tapered slotted ground plane (STSGP) that provides the broad impedance characteristic with miniaturized size in the operating band of 1.78-30 GHz. Moreover, the STSGP is also accountable for enabling the isolation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{12/21}$ </tex-math></inline-formula> ) better than 10 dB. To further meet the isolation higher than 22 dB, a meander line is protruded from the ground plane while maintaining a 6 mm edge-to-edge distance between two antenna elements. Typically, the MIMO antenna with high isolation is beneficial for high-speed data transmission. The experimental outcomes represent that the proposed MIMO antenna is with the advantages of reasonably good diversity gain (nearly 10 dB), stable radiation patterns, high peak gain (almost 6.6 dBi), and moderate radiation efficiency (around 85%) across -10 dB impedance bandwidth. The total active reflection coefficient (TARC) and envelop correlation coefficient (ECC) are less than −25 dB and 0.1 respectively. Due to all these attributes, the proposed 2-element MIMO antenna array can be a potential candidate for military radio, spectrum sensing for cognitive radio, and space communication applications.

Optimal receive beamforming in spatial antenna diversity system using evolutionary genetic algorithm

Frequent packet loss and power inadequacy are the major issues in wireless fading networks owing to the deep fading effects and inefficient resource utilization caused by unoriented information forwarding mechanisms. Diversity techniques are potentially employed in wireless communication systems to combat the impact of fading and reinforce the desired service level guarantees for data transmission. In this work, we employ spatial diversity and antenna beamforming methods to significantly improve the signal quality performance of wireless networks and enhance the reliability by decreasing the bit error probability. A constrained optimization problem is formulated for alleviating the net noise power integrated with the adaptive beamforming vector and ameliorated channel state information. For this, the evolutionary genetic algorithm scheme is iteratively implemented for evaluating the optimal solution of the proposed optimization problem. The influence of various selection functions in the application of genetic algorithm is investigated for effective heuristic modeling design and searching through the feasible solution space. Through extensive simulation results, several crucial network parameters characterizing the proficiency of wireless communications including the noise power, signal-to-noise ratio (SNR), bit error rate (BER) are estimated and analyzed for varying number of antennas deployed at the receiver node. Furthermore, the performance of the proposed genetic algorithm based optimization technique is compared with the existing models using the key channel quality metrics of achievable SNR, BER, and model computational complexity. • Spatial diversity and receive beamforming techniques can be jointly implemented. • This optimization model achieves enhanced signal quality and reliability performance. • Evolutionary genetic algorithm solves the problem using intelligent heuristic design. • Disparate selection functions exhibit different iterative complexity for optimization. • Simulation is used to show the improved noise power, SNR, BER with evolving antennas.

RFID over low cost VCSEL‐based MMF links: experimental demonstration and distortion study

Radio-over-fibre (RoF) distributed antenna system (DAS) technology has been investigated for the distribution of ultra-high frequency (UHF) radio frequency identification (RFID) signals. RoF DAS allows for reduced number of readers and centralised placement of readers which facilitates easy system maintenance, but it is important to find a low-cost solution that can achieve comparable performance to a conventional RFID system. In this work, a low-cost vertical-cavity surface-emitting laser (VCSEL)-based multimode fibre (MMF) link has been developed and demonstrated for passive UHF RFID applications. The reported results show almost the same performance when compared with a conventional RFID system. In addition, simple spatial antenna diversity schemes are tested, with improved performance reported in comparison with an RFID-RoF system without diversity. Also, an investigation of RFID over fibre with RoF non-linearity is carried out showing that phase-reversal amplitude shift keying (PR-ASK) RFID modulation allows for higher levels of RF carrier and modulated signal power than the ASK RFID, for low levels of non-linearity.

Dual CP Polarization Diversity and Space Diversity Antennas Enabled by a Compact T-Shaped Feed Structure

A compact T-shaped feed structure (TFS) is reported that enables the realization of two types of diversity antennas: a polarization diversity antenna (PDA) and a spatial diversity antenna (SDA). Both systems have a high potential for mobile wireless communication applications. The TFS includes four ports and two independent coaxial channels with effective isolation between them all. The PDA is a dual CP omnidirectional antenna. Its optimized prototype achieves measured impedance bandwidths of 16.4% and 15.28% in its LHCP and RHCP states, respectively, and realized gains in both between 4.8 and 6.46 dBic. The inner thin coaxial cable (ITCC) of the TFS directly drives its LHCP subsystem, facilitating its improved omnidirectional performance. This ITCC is also used to directly feed the SDA’s low-profile directional planar equiangular spiral antenna and its side port drives its omnidirectional RHCP antenna. Good hemispherical coverage is realized with a measured common impedance bandwidth larger than 14.35% with more than 40-dB isolation between its two ports. The corresponding measured realized gain of the SDA is between 4 and 7.8 dBic. The measured results for both optimized prototypes confirm their simulated performance characteristics.

Weak GPS Signal Acquisition Using Antenna Diversity

GPS signal acquisition is challenging in attenuating and multipath fading environments. Standard methods, such as extending the coherent integration time to achieve more processing gain, are not always feasible for acquiring weak signals using unaided receivers. Spatial antenna diversity is used for indoor applications to mitigate the multipath fading effect in the acquisition process. Equal gain combining of two received signals is considered in a standalone processing strategy. The main novelty of this paper is to investigate improvement in acquisition time by utilizing antenna diversity for indoor scenarios. A detection threshold for which mean acquisition time is minimized is numerically shown to exist. The importance of acquisition time variance is discussed and diversity gain is evaluated. Theoretical analysis is compared with Monte Carlo simulations and real GPS data. Results show that antenna diversity improves detection probability, reduces false alarms and mean and variance of acquisition time in fading environments. Copyright © 2015 Institute of Navigation

A COMPACT BAND-NOTCHED ULTRA-WIDEBAND SPATIAL DIVERSITY ANTENNA

A compact band-notched ultra-wideband (UWB) spatial diversity antenna is presented in this paper. The antenna is fabricated on an FR4 substrate and consists of two tapered microstrip feeding lines and two radiating elements. The wireless local area network (WLAN) for IEEE 802.11a operating in 5.15{5.825GHz band-notched function is achieved by introducing two slits in the radiators as ‚/4 resonators. The simulated and measured results show that the presented antenna has a broadband impedance bandwidth which covers UWB band and also has a band-notched characteristic. Additionally, the antenna has a good transmission coe-cient better than i15dB across the UWB. The radiation patterns, peak gain, and envelope correlation coe-cient are measured and discussed.

Performance of W-CDMA systems with rectangular signalling in OSTBC MIMO generalised Nakagami- m fading channels

The performance of combined temporal multipath diversity with statistically independent branches and spatial antenna diversity with arbitrarily correlated branches is investigated. A downlink wide-band code-division multiple access system employing orthogonal space-time block coding multiple-input-multiple-output communications is considered. The performance is quantified in terms of the average symbol error probability (SEP) of coherent arbitrary rectangular quadrature amplitude modulation in Nakagami-m fading with arbitrary statistics. Through the analysis, new expressions for the average SEP are derived under the generalised system model described above. Specifically, the considerations of the combined path and space diversity model, the arbitrary correlation profile among spatial diversity branches, and the arbitrary statistics of Nakagami-m fading processes are the main aspects that make the system model herein generalised as compared to previous ones. Furthermore, for this generalised system model, the consideration of distinct in-phase and quadrature decision distances as well as modulation orders in the rectangular signalling constellation through the analysis provide additional enhancements on some existing results. Numerical and simulation results are presented to demonstrate the enhanced validity of the analytical development.

Spatial diversity antenna for WLAN application

AbstractThis article presents a novel printed diversity planar monopole antenna integrated on a PCMCIA network card with minimized the mutual coupling for WLAN application at the 5 GHz bands (5150–5350 and 5725–5875 MHz). The proposed diversity antenna is printed on FR‐4 substrate and small size enough to be embedded in the laptop computer. Optimizing the separation distance and antenna parameters with use of two slots on a ground, the good isolation performance (less than −20 dB) between the two printed monopole antennas is achieved. The proposed diversity antenna has an impedance bandwidth of 2360 MHz ranging from 4520 to 6889 MHz (S11 &lt; −10 dB). There is a good agreement between the simulated and measured results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1290–1294, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22414

Performance of DS-CDMA Receivers With MRC in Nakagami-&amp;lt;tex&amp;gt;$m$&amp;lt;/tex&amp;gt;Fading Channels With Arbitrary Fading Parameters

The receivers that combine spatial antenna diversity with temporal multipath diversity are known as two-dimensional (2-D) RAKE receivers. In this paper, we consider the outage probability and the bit error rate performance of a coherent binary phase shift keying 2-D RAKE receiver in the context of an asynchronous direct sequence (DS)-code division multiple access (CDMA) system operating in a Nakagami-m fading channel with real and arbitrary fading parameters. The closed-form expressions derived for the two wireless performance measures are easily evaluated numerically and enable the link designer to examine the effects of system parameters, such as the number of receive antennas, RAKE fingers per antenna, and asynchronous CDMA users in the cell, as well as channel conditions, such as the amount of fading in the combined paths and the multipath intensity profile of the channel on the link performance. In addition, the diversity loss due to correlated fading among the spatially separated RAKE fingers is quantified.

Performance analysis of selection diversity gain for narrow-band and wide-band systems

Usually employed at the receiving end to avoid deep fading, the well-known spatial antenna diversity technique may have different gain properties for the second generation global system for mobile communication (GSM) and the third generation wideband code division multiple access (W-CDMA) system because of the difference in channel bandwidth and receiver architecture. By means of statistical analysis, the diversity gain for these two systems is derived for both line-of-sight (LOS) and non-LOS (NLOS) channels. The theoretical results are verified by numerical simulation and experimental measurement. The GSM system always has better diversity gain (4-10 dB) than the W-CDMA system (1-4 dB) in a typical wireless channel with a K-factor from 0 to 8 dB.

Overview of spatial channel models for antenna array communication systems

Spatial antenna diversity has been important in improving the radio link between wireless users. Historically, microscopic antenna diversity has been used to reduce the fading seen by a radio receiver, whereas macroscopic diversity provides multiple listening posts to ensure that mobile communication links remain intact over a wide geographic area. In later years, the concepts of spatial diversity have been expanded to build foundations for emerging technologies, such as smart (adaptive) antennas and position location systems. Smart antennas hold great promise for increasing the capacity of wireless communications because they radiate and receive energy only in the intended directions, thereby greatly reducing interference. To properly design, analyze, and implement smart antennas and to exploit spatial processing in emerging wireless systems, accurate radio channel models that incorporate spatial characteristics are necessary. In this tutorial, we review the key concepts in spatial channel modeling and present emerging approaches. We also review the research issues in developing and using spatial channel models for adaptive antennas.