arXiv subjects

Joohwan Chun

Publications and source records attributed to Joohwan Chun.

3 recordsLinked to original sources

arXiv2018

Monopulse beam synthesis using a sparse single-layer of weights

A conventional monopulse radar system uses three beams; sum beam, elevation difference beam and azimuth difference beam, which require different layers of weights to synthesize each beam independently. Since the multi-layer structure increases hardware complexity, many simplified structures based on a single layer of weights have been suggested. In this work, we introduce a new technique for finding disjoint and fully covering sets of weight vectors, each of which constitutes a sparse subarray, forming a single beam. Our algorithm decomposes the original non-convex optimization problem for finding disjoint weight vectors into a sequence of convex problems. We demonstrate the convergence of the algorithm and show that the interleaved array structure is able to meet difficult beam constraints.

eess.SP↗

arXiv2018

Joint Range and Angle Estimation for FMCW MIMO Radar and Its Application

Recently, frequency-modulated continuous wave (FMCW) radars with array antennas are gaining in popularity on a wide variety of commercial applications. A usual approach of the range and angle estimation of a target with an array FMCW radar is to form a range-angle matrix with deramped receive signal, and then apply the two-dimensional fast Fourier transformation (2D-FFT) on the range-angle matrix. However, such frequency estimation approaches give bias error because two frequencies on the range-angle matrix are not independent to each other, unlike the 2D angle estimation with a passive planar antenna array. We propose a new maximum-likelihood based algorithm for the joint range and angle estimation of multiple targets with an array FMCW radar, and show that the proposed algorithm achieves the Cramer-Rao bounds (CRBs) both for the range and angle estimation. The proposed algorithm is also compared with other algorithms for a simultaneous localization and mapping (SLAM) problem.

eess.SP↗

arXiv2010

Signal Space Alignment for an Encryption Message and Successive Network Code Decoding on the MIMO K-way Relay Channel

This paper investigates a network information flow problem for a multiple-input multiple-output (MIMO) Gaussian wireless network with $K$-users and a single intermediate relay having $M$ antennas. In this network, each user intends to convey a multicast message to all other users while receiving $K-1$ independent messages from the other users via an intermediate relay. This network information flow is termed a MIMO Gaussian $K$-way relay channel. For this channel, we show that $\frac{K}{2}$ degrees of freedom is achievable if $M=K-1$. To demonstrate this, we come up with an encoding and decoding strategy inspired from cryptography theory. The proposed encoding and decoding strategy involves a \textit{signal space alignment for an encryption message} for the multiple access phase (MAC) and \textit{zero forcing with successive network code decoding} for the broadcast (BC) phase. The idea of the \emph{signal space alignment for an encryption message} is that all users cooperatively choose the precoding vectors to transmit the message so that the relay can receive a proper encryption message with a special structure, \textit{network code chain structure}. During the BC phase, \emph{zero forcing combined with successive network code decoding} enables all users to decipher the encryption message from the relay despite the fact that they all have different self-information which they use as a key.

cs.IT↗