Jongrok Park

CoMP-CSB for ICI Nulling with User Selection

The capacity of downlink multiple-input multiple-output (MIMO) cellular networks is significantly limited by inter-cell interference (ICI), particularly at cell boundaries. Recently, two types of coordinated multiple point transmission (CoMP) technologies, joint processing and transmission (JPT) and coordinated scheduling and beamforming (CSB), were proposed. These technologies are intended for the latest cellular communication standard in order to improve the performance of cell-edge users who suffer from significant ICI. In this paper, we propose an ICI cancellation technique based on a user selection algorithm for CoMP-CSB. Under partial channel state information (CSI) and no data sharing condition, each base station (BS) concentrates more on the direction of interference to the adjacent cells users, during the user selection process. Unlike prior concepts for a single-cell environment, in which each BS generates a precoding matrix for selected users to be served, the proposed technique considers the effects of interference to users located in adjacent cells. Although there are obvious trade-offs between ICI mitigation and the number of simultaneous scheduled users in terms of system capacity, the simulation results demonstrate that our proposed algorithm achieves higher sector throughput and is more robust against ICI if the system is limited by interference. Furthermore, through simulation we are able to obtain the preferred option for the coordination distance (R) and the number of degrees of freedom for ICI nulling (ξ).

MIMO Beamforming for QoS Enhancement via Analog, Digital and Hybrid Relaying

Quality-of-service (QoS) of multimedia broadcast/multicast service (MBMS) is the most challenging issue that needs to be addressed for next generation wireless broadcasting. Multiple-input/multiple-output (MIMO) and multihop relay technologies are viable options for improving QoS of MBMS. For stable MBMS, the average throughput of overall cell region must be guaranteed. Nevertheless, severe throughput degradation may occur in the outer region of multicells due to significant interference from neighboring cells or relay stations, thereby limiting the overall performance. This paper describes an effective technique, which combines MIMO and two-hop relay, to guarantee the QoS of edge users. We assume that the channel between the base station (BS) and the fixed relay station (FRS) is line-of-sight (LOS). First, we define a criterion needed to install the FRS. Second, we construct a weight matrix for hybrid relaying having lower complexity than digital relaying. Finally, we propose a user scheduling algorithm which can be adapted to analog relaying (amplify and forward), digital relaying (decode and forward) and hybrid relaying (filter, amplify and forward). The simulation results show that the proposed method can improve both the QoS of edge users and the sum-rate.

Throughput and QoS improvement via fixed relay station cooperated beam-forming

Throughput and quality-of-service (QoS) over multicell environments are two of the most challenging issues that must be addressed when developing next generation wireless network standards. Currently, multiple-input/multiple-output (MIMO), inter-cell coordination and multi-hop relay technologies are viable options for improving channel capacity or coverage extension. Nevertheless, severe QoS degradation occurs in the outer region of multi-cells due to significant interference from neighboring cells or relay stations, thereby limiting overall performance. This paper describes an effective technique, fixed relay station cooperated beam-forming (FCBF), which combines MIMO, multi-hop relay and multi-cell coordination. Simulated testing of FCBF demonstrates an increase of 10% in the average sum-rate and a decrease of 25% in the outage probability compared with conventional techniques. In particular, throughput at the cell boundary is remarkably increased with FCBF compared with traditional beam-forming technologies.

Distributed MIMO Ad-hoc Networks: Link Scheduling, Power Allocation, and Cooperative Beamforming

For next-generation network topologies, the distributed wireless ad-hoc network is one of the most challenging issues because of the inherent node intelligence decision. Nevertheless, due to the randomness of node distribution, it is difficult to achieve high efficiency without signaling to neighboring nodes to coordinate random interference among the nodes, which, in turn, leads to high computational overhead in general. In this paper, we propose a framework of distributed multiple-input- multiple-output (MIMO) ad-hoc networks to improve link capacity while achieving computational simplicity without interworking with other links in a fully distributed manner. To achieve this goal, we align three main resource management algorithms, i.e., the distributed link-scheduling algorithm (DLSA), the distributed power allocation algorithm (DPAA), and the distributed cooperative beamforming algorithm (DCBA). In the simulation results, performance has proven to be promising in terms of the average sum rate, compared with that of other conventional schemes.

M 2 -m 2 Beamforming for Virtual MIMO Broadcasting in Multi-Hop Relay Networks

The emerging demand for multi-hop relay networks requires significant improvement of the end-to-end throughput through the development of a more advanced transmission technology. Research on multiple-input multiple-output (MIMO) has been actively pursued for achieving channel throughput improvements for cellular networks. In a multi-hop ad-hoc network, it is difficult for each sensor node to have multiple transmit antennas, therefore, virtual MIMO has been introduced as an extended version of cellular MIMO. The conventional virtual MIMO scheme requires additional complexity in order to implement the same functionality used for cellular systems. Therefore, we propose a new framework for the broadcast virtual MIMO system (BVMS) by developing an innovative max-min/min-max (M2-m2) beamforming technology optimized for the multi-hop relay network. Compared to the conventional singular value decomposition (SVD)-based or random beamforming technologies, M2-m2 beamforming significantly improves the end-to-end channel throughput up to the optimal bound for the BVMS over a multi-hop relay network.

MIMO Broadcast Channels Based on SINR Feedback using a Non-Orthogonal Beamforming Matrix

The signal to interference plus noise ratio (SINR) feedback has been utilized in random beamforming (RBF) to select users for multiple-input multiple-output (MIMO) systems where a large number of users are required to obtain a multi-user diversity gain. However, if the number of users is not large enough, it may be difficult to obtain the performance gain and be easy to have a performance degradation conversely. To resolve this problem, it is necessary to find orthogonal random beams close to the channel matrix of selected users. In this paper, we present RBF using a non-orthogonal beamforming matrix (RBF NOBM), demonstrating an efficient search of random beams correlated with the channel matrix of selected users over a small number of users. For single user RBF using NOBM (SU-RBF NOBM) with two transmit antennas, the beamforming matrix for user data service is obtained through closed form expressions, and SU-RBF NOBM is then expanded to more than two transmit antennas. We also propose user selection algorithms for SU-RBF NOBM and multi-user RBF using NOBM (MU-RBF NOBM). Via simulation results, we demonstrate that the performances of RBF NOBM represent significant improvements compared to conventional beamforming schemes.

Hierarchical modulation-based cooperation utilizing relay-assistant full-duplex diversity

In this paper, we present a hierarchical modulation-based cooperation (HMC) scheme to overcome capacity degradation due to half-duplex transmissions in conventional cooperative relay systems. In the HMC scheme, two relay terminals are used for both transmit and receive operations, i.e., full-duplex transmission. This scheme reduces the required number of time slots for cooperation. Utilizing this cooperative mechanism, the HMC scheme achieves cooperative diversity at the destination node by combining the signals delivered from the source and relay nodes. In addition, we derive a closed form of the end-to-end bit error rate for the HMC scheme, which is utilized to determine an optimal power ratio for hierarchical signals at the source node. In concurrence with the HMC scheme, we develop the best relay selection scheme for a practical wireless communication networks.

A Target Position Decision Algorithm Based on Analysis of Path Departure for an Autonomous Path Keeping System

To realize a path keeping system (PKS), it is essential to guide autonomous vehicle (AV) to a desired direction while maintaining safety. To maintain a desired driving path, it is necessary for an AV to perceive its surrounding environment by gathering directional information while traveling. Therefore, precise localization of an AV and autonomous guidance are essential technologies for the successful implementation of a PKS. As a type of radio guidance, an AV can use trilateration to identify its location relative to three reference positions by measuring the strength, time, or time difference of the reception of transmitted radio signals. Direction of arrival (DOA) techniques can also be used to estimate the direction of a signal emitted from a transmitter, and this information can be used to set the driving direction of an AV. However, in a practical environment, estimation errors may arise when the AV estimates its location or the direction of signal emitted from a transmitter, and these errors may cause the problem of path departure. To address this problem, we conducted a mathematical analysis to identify potential errors in estimating location and direction. Herein we propose a target position decision algorithm for PKS, which uses trilateration and DOA (PKS-TnD) to drive an AV in a desired direction to avoid path departure. By using this algorithm, an AV calculates its next target position based on the error constraints of trilateration and DOA by means of numerical analysis. Additionally, an energy efficiency problem is also formulated herein and energy use is optimized by using a Lagrangian equation.

Virtual MIMO broadcasting transceiver design for multi-hop relay networks

To improve end-to-end throughput and to reduce signaling overhead in multi-hop relay networks, broadcast virtual multiple-input and multiple-output (MIMO) systems (BVMSs) have been introduced. Conventionally, this research has been done for a limited environment where each node is equipped with a single-antenna and also interference from other networks is not included for the numerical analysis. In this paper, we propose a new virtual MIMO broadcasting transceiver (VMBT) to overcome the limitation of conventional BVMS and to improve end-to-end throughput for BVMS-based multi-hop-relay networks while the signaling overhead effectively reduced. Toward this goal, proposed VMBT is designed based on the following contributions: analysis of the channel ellipse property, convergence proof of the iterative algorithm and utilization of the null and span of channel vectors. The simulation results show that the proposed VMBT achieves the highest end-to-end throughput compared with that of other conventional technologies.

Effective channel control random beamforming for single user MIMO systems

In general, it has been demonstrated that the performance of conventional random beamforming (RBF) approaches that of ideal eigen beamforming when the number of users is large in a cell by exploiting multi-user diversity. However, if the number of users decreases, such as femto or pico cell in the 3GPP Long Term Evolution-Advanced standard, the performance degradation occurs in the RBF scheme due to the lack of multi-user diversity. In this paper, we present a novel precoder based on singular value decomposition (SVD) using feedback of weight values in an RBF environment. For achieving performance improvement in the femto cell environment, we generate a precoding matrix appropriate to user channel by controlling the feedback values with an equivalent feedback quantity. In the simulation results, we verify the outstanding performance of the proposed scheme for a small number of users.