Minchae Jung

Joint Mode Selection and Power Allocation Scheme for Power-Efficient Device-to-Device (D2D) Communication

This paper proposes a power-efficient mode selection and power allocation scheme in device-to-device (D2D) communication system as an underlay coexistence with cellular networks. The proposed scheme is performed based on the exhaustive search of all possible mode combinations of the devices which consist of the mode indices for all devices in the system. Specifically, the proposed scheme consists of two steps. First, we calculate the optimal power with respect to the maximum power-efficiency for all possible modes of each device. Since the power-efficiency is not a concave function for the transmission power, we obtain the suboptimal solution by using the concavity of the lower and upper bound for the power-efficiency. The powerefficiencies for all possible modes of each device are obtained by the suboptimal power allocation in the first step. In the second step, we select a mode sequence which has the maximal power-efficiency among all possible mode combinations of the devices based on the obtained power-efficiencies in the first step. Then we can jointly obtain the suboptimal transmission power and the mode maximizing the power-efficiency. The proposed suboptimal scheme for the power allocation and mode selection performs close to the upper bound with respect to the power-efficiency. The simulation results also show that the proposed scheme outperforms the conventional schemes with respect to the power-efficiency and system capacity.

Optimal number of users in zero-forcing based multiuser MIMO systems with large number of antennas

The optimal number of users achieving the maximum sum throughput is analyzed in zero-forcing (ZF) based multiuser multiple-input multiple-output (MIMO) systems with a large number of base station (BS) antennas. By utilizing deterministic ergodic sum rates for the ZF-beamforming (ZF-BF) and ZF-receiver (ZF-R) with a large number of BS antennas [1], [2], we can obtain the ergodic sum throughputs for the ZF-BF and ZF-R for the uplink and downlink frame structures, respectively. Then, we can also formulate and solve the optimization problems maximizing the ergodic sum throughputs with respect to the number of users. This paper shows that the approximate downlink sum throughput for the ZF-BF is a concave function and the approximate uplink sum throughput for the ZF-R is also a concave function in a feasible range with respect to the number of users. The simulation results verify the analyses and show that the derived numbersof users provide the maximum sum throughputs for the ZF-BF as well as ZF-R in multiuser MIMO systems with a large number of BS antennas.

Interference Minimization Approach to Precoding Scheme in MIMO-Based Cognitive Radio Networks

A precoding scheme based on the interference minimization is proposed for an interference-limited communication system such as multiple-input multiple-output (MIMO)-based cognitive (CR) networks. The proposed precoder is to maximize the sum capacity through the minimization of interference power. By selecting a channel with the minimum singular value of the interference channel, the transmitter with the proposed precoder sends the information signals through the channel which produces the minimum interference in the system. Simulation results show that the proposed precoding scheme has the best performance in terms of the sum capacity in a MIMO-based CR network.

Asymptotic Distribution of System Capacity in Multiuser MIMO Systems with Large Number of Antennas

In this paper, an asymptotic distribution for the sum rate capacity is derived in zero-forcing beamforming (ZF-BF) based multiuser MIMO systems with a large number of base station (BS)antennas. By utilizing the characteristics of a large number of antennas and the central limit theorem, we prove that the asymptotic distribution for the sum rate capacity follows Gaussian distribution. Also we derive the mean and variance values for the asymptotic Gaussian distribution. Based on the asymptotic Gaussian distribution, we also obtain the outage probability for the sum rate capacity as a closed form. Simulation results show that the asymptotic Gaussian distribution is well follows the actual sum rate capacity, and the both asymptotic mean and variance value are also very accurate.

Pilot Power Ratio for Uplink Sum-Rate Maximization in Zero-Forcing Based MU-MIMO Systems with Large Number of Antennas

This paper analyzes the pilot power ratio (PPR) in multiuser multiple-input multiple-output (MU-MIMO) systems with a large number of receive antennas (M) at the base station (BS). We consider zero-forcing based MU-MIMO orthogonal frequency division multiplexing (OFDM) systems. Based on the deterministic uplink sum-rate approximation for imperfect channel state information, we can formulate the optimization problems in terms of the PPR to maximize the ergodic uplink sum-rate subject to the per-slot or per-symbol power constraint. Under the per-slot power constraint, the optimal PPR can be obtained in a closed form while under the per-symbol power constraint, we propose an iterative algorithm which generates a suboptimal PPR. Simulation results show that the proposed PPRs perform close to the optimal performance in terms of the sum-rate. Also, it is shown that the proposed PPRs outperform the equal power allocation. In particular, in the ZF-R based MU-MIMO OFDM system with 8 users and M=32 under the per-slot power constraint, the proposed PPR can achieve about 8bps/Hz performance gain compared to the equal power allocation.

Multi-mode precoding scheme based on interference channel in MIMO-based cognitive radio networks

The interference minimization approach to pre-coding is an appropriate scheme to mitigate the interference efficiently while it may cause the capacity loss of the desired channel. On the other hand, the precoding scheme for the maximal capacity of the desired channel improves the capacity of the desired users while it increases the interference power and finally causes the capacity loss of the interfered users. Therefore, we propose a precoding scheme which satisfies these two conflicting goals and manages the interference signal in an interference-limited environment such as a multiple-input multiple-output (MIMO)-based cognitive radio (CR) network. The proposed scheme consists of two steps. The first step nulls out the largest singular value of the interference channel to mitigate the dominant interference signal based on the interference minimization approach. The second step calculates the total system capacity of each mode and selects a mode to maximize the total system capacity. In the second step, each mode consists of the right singular vectors corresponding to the singular values except the largest singular value eliminated in the first step. Simulation results show that the proposed precoding scheme not only efficiently mitigate the interference signal, but also has the best performance in terms of the total system capacity in a MIMO-based CR network.

Statistical Beamforming Based on Effective Channel Gain for Spatially Correlated Massive MIMO Systems

A statistical beamforming (SBF) scheme based on the effective channel gain (ECG) is proposed for spatially correlated massive multiple-input multiple-output systems. The proposed SBF scheme consists of outer and inner precoders. The outer precoder is designed to eliminate multiuser interference based on the correlation matrix of downlink channel. Then, according to the ECG defined as the squared inner product of the dedicated channel and an arbitrary precoding vector, the inner precoder is selected among the eigenvectors of the dedicated channel’s correlation matrix with the maximum ECG. Simulation results show that the proposed SBF scheme outperforms conventional schemes.

System Level Simulation of mmWave Based Mobile Xhaul Networks

To support tens of Giga-bits/second (Gbps) data rate, 5G mobile communication systems consider the integration of backhaul and fronthaul links into Xhaul networks. This paper introduces the system-level simulation for mmWave based mobile Xhaul networks. Network scenarios, hybrid beamforming, with large antenna elements, and link-level models are discussed based on the results of the system-level simulation for the mobile Xhaul network. System-level simulation results show that the mobile Xhau network using a 40 GHz carrier frequency band can support a 20 Gbps data rate.

Optimal power control for wireless power transfer system: A deterministic approach

This paper proposes an optimal power control in wireless power transfer systems with a large number of energy harvesting (EH) devices. Based on the rectenna circuit, we consider a practical non-linear energy harvesting model and derive the practical radio frequency to direct current conversion efficiency. Based on the conversion efficiency, we also analyze the harvesting power and power efficiency with respect to the transmission power. Then we derive the optimal harvesting power and power efficiency by utilizing the characteristics of a large number of EH devices. Simulation results show that the results of deterministic approaches perform close to the Monte Carlo results and the maximum power efficiency can be asymptotically achieved.