Seung-Ri Jin

Adaptive relay selection for hybrid relay systems

Hybrid relay systems using Amplify-and-Forward protocol (AF) and Decode-and-Forward protocol (DF) together are introduced in cooperative networks. For hybrid systems, we propose adaptive relay selection scheme to maximize the overall received Signal to Noise Ratio (SNR) at the destination. At first two relays are selected among many according to the instantaneous channel conditions. One is a relay to operate as the Amplify-and-Forward protocol and the other is a relay to operate as the Decode-and-Forward protocol. Next the total transmission power is allocated to the source and two selected relays. Simulation results show that the proposed scheme achieves better performance than that of conventional cooperative schemes.

A multi-user beamforming scheme in MIMO downlink channels for multi-cell networks

In this paper, a multi-user beamforming scheme is presented in multi-user multi-input multi-output (MIMO) downlink channels with other cell interference (OCI). The proposed scheme consists of maximizing signal-to-leakage-and-noise ratio (SLNR) and whitening the OCI for power allocation. The conventional scheme which eliminates perfectly intra-cell interference has several problems such as antenna constraints and noise enhancement. The proposed scheme has resolved these problems and could obtain an additional channel gain by the number of antennas. We confirm the increasing of the performance via numerical results.

Linear Precoding Design for Mutual Information Maximization in Generalized Spatial Modulation With Finite Alphabet Inputs

In this letter, we develop a new precoding scheme that improves the performance of mutual information for generalized spatial modulation (GSM). First, the closed-form expression of the mutual information of the GSM with finite alphabet inputs is derived in order to update the precoder with regard to the mutual information. The joint precoding design problem to maximize the mutual information of the GSM is difficult to solve directly since it is a non-convex coupled problem. In order to solve this problem, we transform the GSM system into a virtual multiple-input multiple-output (MIMO) system, and then an extended ellipsoid algorithm is applied. Each precoder of the GSM can be solved using the common precoder of the virtual MIMO. The numerical results demonstrate that the proposed precoding scheme significantly enhances the performance in terms of the mutual information.

Average approach to amplify-and-forward relay networks

In this paper, the analysis of an average received signal-to-noise ratio (SNR) for a cooperative communication network with amplify-and-forward (AF) relays is presented. In AF systems, the overall instantaneous SNR at the receiving end can be expressed as the form of a harmonic mean of perhop SNRs. This means that the received SNR can be analyzed by applying the statistical expectation of the harmonic mean of two exponential random variables, which was derived in a closed-form expression. The proposed result can help examining the performance of AF relay systems by using the average sense approach. The simulation results demonstrate the exact derivation of the expectation of harmonic means. The result also shows that the destination node can obtain larger average received SNR as the number of relay nodes is increased.

Maximum likelihood population estimator of RFID tags with Hadamard footprint

A novel method is proposed that can estimate the tag population in Radio Frequency Identification systems by using a Hadamard code for the sub-preamble of the tag response. We formulate the maximum likelihood estimator for the tag population using a given number of the observed footprints. In simulations, the proposed estimator performs considerably better than the conventional schemes.

Improved timing estimation for OFDM systems using preambles with repetitive patterns

We propose an improved timing estimation method for orthogonal frequency-division multiplexing (OFDM) systems that employ a preamble with time-domain repetitive patterns. The proposed method exploits the unique correlation property of the preamble including its cyclic prefix. Numerical results show that the proposed scheme is robust in fading multipath channels, achieving better performance than the existing methods.

A resource assignment algorithm to enhance outage performance in cooperative systems

An adaptive resource assignment scheme for the multi-user cooperative communication systems with amplify-and-forward (AF) relays is investigated. We consider maximizing system capacity while guaranteeing the QoS (Quality of Service) of each user. A resource assignment is proposed using space-time coding with only source-to-relay channel gain information (CGI). It performs well in allocating relay nodes to the multiple source-destination pairs. The proposed algorithm enhances the system performance without loss of diversity.

An adaptive space-time coding based relay allocation scheme in AF cooperative systems

An adaptive relay allocation scheme for multi-user cooperative communication systems with amplify-and-forward (AF) relays is investigated. We consider maximizing system capacity while guaranteeing the QoS (Quality of Service) of each user. Proposed relay allocation scheme uses space-time coding technique. It performs well in allocating relay nodes to multiple source-destination pairs. The proposed algorithm enhances system performance without loss of diversity.