Nam Yun Lee

This paper proposes a random network model for a device-to-device (D2D) underlaid cellular system using stochastic geometry and develops centralized and distributed power control algorithms. The goal of centralized power control is twofold: ensure that the cellular users have sufficient coverage probability by limiting the interference created by underlaid D2D users, while scheduling as many D2D links as possible. For the distributed power control method, the optimal on-off power control strateg

In this paper, we study a network information flow problem for a multiple-input-multiple-output (MIMO) Gaussian wireless network with three users each equipped with M antennas and a single intermediate relay equipped with N antennas. In this network, each user intends to convey independent messages for two different users via the intermediate relay while receiving two independent messages from the other two users. This is a generalized version of the two-way relay channel for the three-user case

This paper deals with design of a amplify-and- forward (AF) relay beamforming matrix in a two-way relay protocol when a relay node has multiple antennas. Two-way relaying is a promising protocol since it provides enhanced spectral efficiency compared to one-way relaying protocols. In this paper we derive the achievable sum-rate upper bound of AF beamforming scheme and propose the achievable sum-rate maximizing relay beamforming scheme when the destination and the relay node have perfect knowledg

In this paper, we study a new network information flow for a multiple-input multiple-output (MIMO) wireless network system with three users and a single intermediate relay which of each is equipped with multiple antennas. In this system, each user wants to convey independent messages for different two users via the intermediate relay while receiving two independent messages from the other two users by using only two time slots. This network information flow is a generalized version of the two-wa

In this paper, we study a K-cell multiple input single-output interfering broadcast channel (MISO-IFBC) with finite rate feedback. In this channel, we first derive the rate loss due to the quantization error by considering both a coordinated zero-forcing beamforming and random vector quantization method. Using this result, feedback bits allocation methods are proposed to minimize the performance degradation in K-cell MISO-IFBC. Furthermore, we investigate how many feedback bits per user are nece

This paper considers large random wireless networks, where transmit-and-receive node pairs communicate within a certain range while sharing a common spectrum. By modeling the spatial locations of nodes as a Poisson point process, analytical expressions for the ergodic spectral efficiency of a typical node pair are derived as a function of the channel state information available at a receiver (CSIR) in terms of relevant system parameters: the density of communication links, the number of receive

In this paper, a downlink cellular model based on stochastic geometry is put forth in order to analyze the performance of base station (BS) cooperation with dynamic clustering in highly dense BS deployments. Utilizing the proposed model, a closed-form expression for the complementary cumulative distribution function of the instantaneous signal-to-interference ratio (SIR) is derived in terms of relevant system parameters, chiefly the number of cooperating base stations and the path-loss exponent.

A reliable support detection is essential for a greedy algorithm to reconstruct a sparse signal accurately from compressed and noisy measurements. This paper proposes a novel support detection method for greedy algorithms, which is referred to as maximum a posteriori (MAP) support detection. Unlike existing support detection methods that identify support indices with the largest correlation value in magnitude per iteration, the proposed method selects them with the largest likelihood ratios comp

This paper characterizes the degree-of-freedom (DoF) regions for the multiuser vector broadcast channel with periodic channel state information (CSI) feedback. As a part of the characterization, a new transmission method called space-time interference alignment is proposed, which exploits both the current and past CSI jointly. Using the proposed alignment technique, an inner bound of the sum-DoF region is characterized as a function of a normalized CSI feedback frequency, which measures CSI feed

A relay based wireless network system is basically composed of three nodes, two source nodes which are also destination nodes and the relay node which helps reliable communications between two nodes. The amplify-and-forward (AF) relaying scheme is more convenient to implement than the decode-and-forward (DF) relaying scheme which requires a decoding process at the relay node. In this paper, we design an optimal linear precoder and decoder which minimize the sum of mean squared error (SMSE) when

A conventional relay causes a processing delay of at least one symbol duration relative to the direct paths between a source and a destination. This delay caused by using the conventional relay limits the degrees of freedom (DoF) gain in a wireless interference network. In this paper, it is shown that the exploitation of an instantaneous relay (relay-without-delay) improves DoF gain significantly for a two-user wireless network. Specifically, for two different message settings: the interference

Interference management has the potential to improve spectrum efficiency in current and next generation wireless systems ( e.g., 3GPP LTE and IEEE 802.11). Recently, new paradigms for interference management have emerged to tackle interference in a general class of wireless networks: interference shaping and interference exploitation. Interference shaping is a technique that creates a particular linear combination of interference signals when transmitters propagate signals to minimize the aggreg

In this paper, we study degrees of freedom for the K-User multiple-input multiple-output (MIMO)-interference channel (IFC) with constant channel coefficients. In this channel, we investigate how many total number of transmit antennas, M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> + M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> + ¿ + M <sub xmlns:mml="http://www.w3.org/1998/Math/M

This letter investigates a new class of index coding problems. One sender broadcasts packets to multiple users, each desiring a subset, by exploiting prior knowledge of linear combinations of packets. We refer to this class of problems as index coding with coded side-information. Our aim is to characterize the minimum index code length that the sender needs to transmit to simultaneously satisfy all user requests. We show that the optimal binary vector index code length is equal to the minimum ra

In this paper, we consider a two-cell interfering multiple-input multiple-output multiple access channel (MIMO-MAC). We first investigate the multiplexing gain of such channel when users have perfect channel state information at the transmitter (CSIT) by exploiting an interference alignment scheme. In addition, we propose a quantized transmit beamforming vector feedback method for the interference alignment in the limited feedback system. On the basis of the proposed feedback framework, we analy