Yeonggyu Shim

Design of Millimeter Wave Hybrid Beamforming Systems

Millimeter wave (mmWave) signals experience a significant path-loss in free space. To overcome this weakness, a large number of antennas are needed to obtain a high beamforming gain. Although a large number of antennas can be implemented in small area due to the short wavelength, the digital beamforming techniques cannot be implemented easily due to the high complexity of hardwares. To solve this problem, the hybrid beamforming systems which have smaller number of radio frequency (RF) chains are proposed in the literature. Although the hybrid beamforming systems may achieve the spectral efficiencies of the digital beamforming systems closely, the spectral efficiency cannot be monotonically increase along with the number of data streams due to the limited scattering in mmWave channel. In this paper, we provide a guide for the design of mmWave hybrid beamforming systems. We find the optimal number of streams, and present the spectral efficiency achievable region in which the system guarantees the reliable communications with the lowest cost.

Beamforming Design for Full-Duplex Two-Way Amplify-and-Forward MIMO Relay

We consider the full-duplex (FD) two-way amplify-and-forward relay system with imperfect cancellation of loopback self-interference (SI) and investigate joint design of relay and receive beamforming for minimizing the mean square error (MSE) under a relay transmit power constraint. Due to loopback channel estimation error and limitation of analog-to-digital converter, the loopback SI cannot be completely canceled. Multiple antennas at the relay can help loopback SI suppression, but beamforming is required to balance between the residual SI suppression and the desired signal transmission. Moreover, the relay beamforming matrix should be updated every time slot, because the residual SI in the previous time slot is amplified by the current beamforming matrix and added to the received signals from the two sources in the current time slot. We derive the optimally balanced relay beamforming and receive beamforming matrices in closed form based on minimum MSE, taking into account the propagation of the residual loopback SI from the first to the current time slot. We also propose beamforming design using only the channels of the

A Closed-Form Expression of Optimal Time for Two-Way Relay Using DF MABC Protocol

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Optimal power allocation for two-way decode-and-forward relay networks with equal transmit power at source nodes

latest time slots, not from the first time slot. Based on our numerical results, we also identify when FD is beneficial and propose selection between FD and half-duplex according to signal-to-noise ratio and interference-to-noise ratio.

Design of Downlink Control Channels for Millimeter Wave Mobile Hotspot Network System

In this paper, we propose the optimal time allocation for two-way relay using decode-and-forward (DF) multiple access broadcast (MABC) protocol. We analytically determine the optimal transmit time durations for the first and the second time slots, which maximize the achievable sum rate under a sum time constraint for a given squared magnitude of the channel coefficients and transmit power values. Numerical results show that the achievable sum rate of the optimal time allocation is greater than or equal to that of the equal time allocation.

Adverse Wireless Communication Environment Impacts on AF Wireless Relay Networks

This paper proposes an optimal power allocation method for two-way decode-and-forward (DF) relay networks when transmit power values at source nodes are the same. In this paper we consider the multiple access (MAC) capacity for DF relaying scheme. Using case studies, it analytically determines the optimal power values for the two source nodes and one relay node. The achievable sum rate is maximized under a sum power constraint for given squared magnitude of the channel coefficients. Finally, numerical results show that the achievable sum rate for proposed optimum power allocation is greater than or equal to that for equal power allocation.

AF Wireless Relay Network Analysis under Receiver Power Constraint

Recently, according to the survey, one of the most frequent place to use mobile internet is the moving vehicle, such as bus, subway and train. Therefore, the high speed data rate services for mobile group vehicles moving at high speed are severely required. We design and develop a new system, which can support upto 2.5Gbps data rate services for mobile group vehicles moving at high speed over 400km/h, e.g., KTX (Korea Train Express), TGV (Train a Grande Vitesse) and ICE (InterCity Express), etc. in ETRI (Electronics and Telecommunications Research Institute). In this paper, we propose and design a new structure of the physical layer downlink control channels, and furthermore, we verified the performance of the downlink control channels by computer simulation. Especially, we compared the performance between floating point simulation and fixed point simulation. We verified the performance gap is under 0.5dB. Currently, we develop the test-bed of MHN system and have a target to demonstrate the real time performance of the MHN system on the outdoor environment in 2014. Outdoor demonstration will be done in subway in 1st step. In this paper, we are focusing on the performance of MHN DL control channels, especially on the fixed performance to develop RTL design in test-bed system. We also show the performance of these channels meet the required SNR.

Optimal Amplify-and-Forward Precode and Relay Amplifying Matrices

This paper proposes amplify-and-forward (AF) relay matrices for a one-source-one-destination pair and cooperative distributed N relay nodes under three adverse wireless relay communication environments: (1) broadband noise jamming (BNJ), (2) node geometry (NG), and (3) channel uncertainty (CU). The main objective of this paper is to analytically derive the minimum mean square error (MMSE)-based optimal relay amplifying matrix. Another objective of this paper is to analyze the MMSE cost function, relay power usage, and signal component power of the received signal at the destination using the derived optimal relay amplifying matrix. Finally, the impacts on these three wireless communication environments for the wireless relay networks will be observed by presenting bit error rate (BER) performance.

Optimal time allocation for two-way relay channel using physical-layer network coding

This paper presents both cooperative and noncooperative amplify-and-forward (AF) relay networks consisting of a one-source-one-destination pair and N-relays under receiver power constraint (RPC) at the destination. The optimal AF relay amplifying matrices for the relays by minimizing the mean square error are analytically derived. This paper also shows that the performance of the optimum cooperative relay network is identical to that of the optimum noncooperative network, as long as the same receiver power constraint is applied. The purpose of the RPC is to reduce the interference level for users located in neighboring cells. Finally, using the derived optimal relay amplifying matrices, the achievable rate, the pairwise error probability, and the outage probability are investigated.

Selection of Amplify-and-Forward Mobile Relay under Cascaded Rayleigh Fading

A cooperative amplify-and-forward (AF) wireless relay scheme consisting of M sources, N relays, and L destinations all equipped with a single antenna is studied in this paper. The main objective is to design jointly and iteratively the closed-form of minimum mean square error (MMSE)-based source precode and relay amplifying matrices under a jamming environment with transmit power constraints and aggregate power constraints. With the derived optimal source precode and relay amplifying matrices, the jamming influence on system performance with both transmit and aggregate power constraints is examined numerically by using Monte-Carlo simulations.