Junil Choi

In massive multiple-input multiple-output (MIMO) systems, it may not be power efficient to have a pair of high-resolution analog-to-digital converters (ADCs) for each antenna element. In this paper, a near maximum likelihood (nML) detector for uplink multiuser massive MIMO systems is proposed where each antenna is connected to a pair of one-bit ADCs, i.e., one for each real and imaginary component of the baseband signal. The exhaustive search over all the possible transmitted vectors required in

The concept of deploying a large number of antennas at the base station, often called massive multiple-input multiple-output (MIMO), has drawn considerable interest because of its potential ability to revolutionize current wireless communication systems. Most literature on massive MIMO systems assumes time division duplexing (TDD), although frequency division duplexing (FDD) dominates current cellular systems. Due to the large number of transmit antennas at the base station, currently standardiz

Accurate channel state information (CSI) is essential for attaining beamforming gains in single-user (SU) multiple-input multiple-output (MIMO) and multiplexing gains in multi-user (MU) MIMO wireless communication systems. State-of-the-art limited feedback schemes, which rely on pre-defined codebooks for channel quantization, are only appropriate for a small number of transmit antennas and low feedback overhead. In order to scale informed transmitter schemes to emerging massive MIMO systems with

We study a quantized distributed reception scenario in which a transmitter equipped with multiple antennas sends multiple streams via spatial multiplexing to a large number of geographically separated single antenna receive nodes. This approach is applicable to scenarios such as those enabled by the Internet of Things (IoT) which holds much commercial potential and could facilitate distributed multiple-input multiple-output (MIMO) communication in future systems. The receive nodes quantize their

Accurate channel direction information is essential to achieve considerable capacity gains in multiple-input multiple-output (MIMO) wireless communication systems. Limited feedback using a polar-cap differential codebook which utilizes the temporal correlation in multiple-input single-output (MISO) channels is presented in this paper. We first describe the general properties of the polar-cap differential codebook and then explain the design methodology of the size of the polar-cap given the temp

It is of great interest to develop efficient ways to acquire accurate channel state information (CSI) for massive multiple-input-multiple-output (MIMO) systems using frequency division duplexing (FDD). It is theoretically well known that the codebook size (in bits) for CSI quantization should be increased as the number of transmit antennas becomes larger, and 3GPP Long Term Evolution (LTE) and LTE-Advanced codebooks have sizes that scale according to this rule. It is hard to apply the convention

A highly active and stable catalyst La_1.2Sr_0.8Mn_0.4Fe_0.6O_4−α (R.P.LSMF) decorated with <italic>in situ</italic> exsolved Fe nanoparticles was derived from La_0.6Sr_0.4Mn_0.2Fe_0.8O_3−δ (LSMF) by simple annealing and applied to CO₂ electrolysis on solid oxide electrolysis cells (SOECs).

It is critical to understand the properties of spatial correlation matrices in massive multiple-input-multiple-output (MIMO) systems. We derive new bounds on the extreme eigenvalues of a spatial correlation matrix that is characterized by the exponential model in this paper. The new upper bound on the maximum eigenvalue is tighter than the previously known bound. Moreover, numerical studies show that our new lower bound on the maximum eigenvalue is close to the true maximum eigenvalue in most ca

Spatiotemporal control of full freedoms of polarized light emission is crucial in multiplexed optical computing, encryption and communication. Although recent advancements have been made in active emission or passive conversion of polarized light through solution-processed nanomaterials or metasurfaces, these design paths usually encounter limitations, such as small polarization degrees, low light utilization efficiency, limited polarization states, and lack of spatiotemporal control. Here, we a

In this paper, we consider a distributed reception scenario where a transmitter broadcasts a signal to multiple geographically separated receive nodes over fading channels, and each node forwards a few bits representing a processed version of the received signal to a fusion center. The fusion center then tries to decode the transmitted signal based on the forwarded information from the receive nodes and possible channel state information. We show that there is a strong connection between the pro

We developed a bifunctional electrode of Pr0.8Sr1.2(Fe,Ni)0.8Nb0.2O4−δ (R.P.PSFNNb) fashioned with in situ exsolved Ni-Fe alloy nanoparticles (NPs) for electrochemical oxidations of H2, CO, and syngas as well as CO2 electrolysis. The NiFe-R.P.PSFNNb was prepared by in situ phase transition of Pr0.4Sr0.6Fe0.8Ni0.1Nb0.1O3−δ (PSFNNb) along with exsolution of Ni-Fe alloys in a reducing atmosphere, as confirmed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS) characterization. XPS and

The broadcast problem with multiple antennas at the transmitter end and a single antenna at each user is studied in this work. A low-complexity transmitter architecture where linear beamforming is used to convey information to the users, and multi-user interference is treated as noise at the receiver unit of each user is considered. The vector channels that connect the transmitter to the users are assumed to be spatially correlated. The goal of this work is the design of a low-rate limited feedb

Massive multiple-input multiple-output (MIMO) with uniform planar arrays (UPAs), which is often referred to as full-dimension (FD) MIMO, is being strongly considered for future wireless communication standards. FD-MIMO can control transmit and receive beams in both the horizontal and vertical domains and fully exploit the large number of antennas of massive MIMO. It is widely accepted that Kronecker-product codebooks using a discrete Fourier transform (DFT) structure are suitable to quantize the

As driving becomes more automated, vehicles are being equipped with more sensors generating even higher data rates. Radars are used for object detection, visual cameras as virtual mirrors, and LIDARs for generating high resolution depth associated range maps, all to enhance the safety and efficiency of driving. Connected vehicles can use wireless communication to exchange sensor data, allowing them to enlarge their sensing range and improve automated driving functions. Unfortunately, conventiona