Seunghyeon Hwang

A Discussion About Some of the Principles/Practices of Wireless Communication Under a Maxwellian Framework

There has been a plethora of papers dealing with wireless communication that use techniques, which when viewed from the perspective of a Maxwellian framework raise more questions than they answer. By Maxwellian framework we imply not only the relevance of electromagnetics in studying communication systems but also the proper interpretation of an ensemble processing in mathematical physics which was first introduced by Maxwell to study the behavior of an aggregate of molecules rather than the property of individuals. Initially, most of the modern signal processing techniques was developed for scalar acoustic problems. However, with the advent of wireless, these same techniques are being applied to the vector electromagnetics problem, which is fundamentally different in concept with respect to the scalar acoustic problem. The objective is to discuss some of these concerns associated with some of the current modeling methodologies particularly related to propagation modeling and antenna diversity. A goal is to initiate a dialog about the scientific merits of these new applications. One of the points to be made is that an incorrect use of probability theory can often lead to erroneous conclusions that directly contradict the principles of physics. A few examples are presented to initiate this dialog, mainly the applicability of scalar techniques to the vector wireless problem, including a proper interpretation of the Shannon channel capacity theorem. A methodology is also presented to illustrate how a simple multiple-input-multiple-output system can be based on the principles of reciprocity. Integration of the electromagnetic principles in some of the current methodologies of signal processing and communications theory may lead to a better system

Direction of Arrival (DOA) Estimation Using Electrically Small Tuned Dipole Antennas

We present a methodology for the direction of arrival (DOA) estimation using the induced voltages that are measured at the loads connected to electrically small tuned dipole antenna arrays illuminated by the signal of interest (SOI). The matrix pencil method is applied directly to the induced voltages to estimate the DOA of the various signals. Using electrically small tuned antennas can be advantageous as they can be placed in close proximity of each other saving the real estate and, thus, making it possible to deploy phased arrays on small footprints. When dealing with closely spaced tuned electrically small antennas, it is necessary to use a transformation matrix to compensate for the strong mutual coupling that may exist between the antenna elements. The transformation matrix converts the voltages that are induced at the loads corresponding to the feed point of the array operating in the presence of mutual coupling and other near field scatterers to an equivalent set of voltages that will be induced by the same incident wave in an uniform linear virtual array (ULVA) consisting of omnidirectional isotropic point radiators equally spaced and operating in free space. For any given incident field, the open circuit voltage developed across the feed-point of the small dipole will always be less than the open circuit voltage developed across the feed-point of the half-wavelength dipole. The difference is in the voltage developed across the loads connected to the dipoles feed-point. With the small dipole antenna, the voltage developed across the load impedance will be orders of magnitude greater than the voltage developed across the load connected to the half-wavelength dipole, even though the power captured by any conjugately matched antenna is approximately the same irrespective of their lengths. Three different scenarios are presented to illustrate the methodology. First, we consider resonant dipole elements spaced half wavelength apart, electrically small tuned antenna elements spaced half wavelength apart and electrically small tuned antenna elements placed in close proximity of each other to reduce the footprint without affecting the performance of the phased array. In addition, we consider the possibility of DOA estimation using a combination of different type of electrically small antennas both uniformly and nonuniformly spaced. Numerical examples are presented to illustrate the principles of this methodology

Direction of arrival (DOA) estimation using electrically small resonant dipole antennas

In this paper we present a methodology for the direction of arrival (DOA) estimation using the induced voltages that are measured at the feed points of electrically small resonant dipole antenna arrays illuminated by the signal of interest. The matrix pencil method is applied directly to the induced voltages to estimate the DOA of the various signals. Using electrically small resonant antennas can be advantageous if they are spaced half a wavelength apart as it will significantly reduce the mutual coupling between the various antenna elements. However, the electrically small antennas can also be placed in close proximity of each other saving the real estate and thus making it possible to deploy phased arrays on small footprints. For the latter case it may be necessary to use the transformation matrix to compensate for the strong mutual coupling that may exist between the antenna elements. The transformation matrix converts the voltages that are induced at the loads corresponding to the feed point of the array operating in the presence of mutual coupling and other near field scatterers to an equivalent set (ULVA) consisting of omni-directional isotropic point radiators equally spaced and operating in free space. Three different scenarios are presented to illustrate the methodology. First we consider resonant dipole elements spaced half wavelength apart, electrically small resonant antenna elements spaced half wavelength apart and electrically small resonant antenna elements placed in close proximity of each other to reduce the footprint without affecting the performance of the phase array. Numerical examples are presented to illustrate the principle of this methodology.

Signal enhancement in a near-field MIMO environment through adaptivity on transmit

A technique is presented on how to enhance the received signals in a near field multi-input multi-output (MIMO) environment where beam forming is not possible. This is done through the use of adaptivity on transmit. This technique is based on the principle of reciprocity, is independent of the material medium in which it is transmitting, and incorporates near-field environments and multipath. The objective here is to select a set of weights adapted to each receiver to be applied to each transmitting antenna, which is a function of the user location, so that the transmitted signal at the carrier frequency may be directed to a particular receiver location while simultaneously minimizing the received signal strengths at other receiver locations. Numerical simulations have been made to illustrate the novelty of the proposed approach.

Direction of arrival (DOA) estimation using a transformation matrix through singular value decomposition

In this paper we present how we choose the proper number of virtual array elements from the real array for direction of arrival (DOA) estimation using a conformal hemispherical real array and a single snapshot of the data. The number of virtual array is achieved by using singular value decomposition (SVD) of a real array manifold and the concept of the interpolation techniques. Then, the transformation matrix is generated from both the virtual array manifold and the real array manifold. A numerical simulation has been made to illustrate of the proposed approach. We estimate direction of arrival (DOA) of signals using the matrix pencil method.

Signal enhancement through polarization adaptivity on transmit in a near-field MIMO environment

In this paper polarization adaptivity on transmit has been used to enhance the received signals directed to a pre-selected receiver in a near-field multi-input multi-output (MIMO) environment. The objective here is to select a set of weights on the transmitting antennas adapted to each receiver based on the principles of reciprocity. Using the polarization properties, when the number of receiving antennas is greater than the number of transmitting antennas, the transmitted signal may be directed more to a particular receiver location while simultaneously minimizing the reception signal strength at other receivers. A numerical simulation has been made to illustrate the novelty of the proposed approach.

Interpolation technique for direction of arrival (DOA) estimation using a transformation matrix through singular value decomposition

The number of elements in a virtual array is achieved by using singular value decomposition (SVD) of a real array manifold and the concept of interpolation techniques. Then, the transformation matrix is generated from both the virtual array manifold and the real array manifold. Through this interpolation technique, we perform DOA estimation using a conformal hemispherical real array and a single snapshot of the data. A numerical simulation has been made to illustrate of the proposed approach. We can estimate the DOA of signals using the matrix pencil method.