Hye Joong Kang

Mobile caching policies for device-to-device (D2D) content delivery networking

We consider a mobile content delivery network (mCDN) in which a special form of mobile devices designated as caching servers (caching-server device: CSD) can provide the near-by devices with some popular contents on demand via device-to-device (D2D) communication links. On the assumption that mobile CSDs are randomly distributed by a Poisson point process (PPP), an optimization problem is formulated to determine the probability of storing the individual content in each server in a manner that minimizes the average caching failure rate. Further, we present a low-complexity search algorithm, optimum dual-solution searching algorithm (ODSA), for solving this optimization problem. We identify the important characteristics of the optimal caching policies in the mobile environment that would serve as a useful aid in designing an mCDN.

Mobile device-to-device (D2D) content delivery networking: A design and optimization framework

We consider a mobile content delivery network (mCDN) in which special mobile devices designated as caching servers (caching-server device: CSD) can provide mobile stations with popular contents on demand via device-to-device (D2D) communication links. On the assumption that mobile CSDs are randomly distributed by a Poisson point process (PPP), an optimization problem is formulated to determine the probability of storing the individual content in each server in a manner that minimizes the average caching failure rate. Further, we present a low-complexity search algorithm, optimum dual-solution searching algorithm (ODSA), for solving this optimization problem. We demonstrate that the proposed ODSA takes fewer iterations, on the order of O (log N) searches, for caching N contents in the system to find the optimal solution, as compared to the number of iterations in the conventional subgradient method, with an acceptable accuracy in practice. Furthermore, we identify the important characteristics of the optimal caching policies in the mobile environment that would serve as a useful aid in designing the mCDN.

Dynamic Topology Control for Multi-Hop Relaying in a Cellular TDD-OFDMA System

This paper introduces a notion of divide-by-K reuse strategy, which allows for K orthogonal chunks (subzones) of OFDMA data regions to be fully reused for all relay links throughout each cell in a N-hop relay-enhanced cellular TDD-OFDMA system with K ≤ N. Our objective is to configure a topology of relay stations subject to the divide-by-K reuse strategy, such that the end-to-end routes for relay stations are determined while maximizing the bandwidth efficiency of resource available for relay links. We propose a sub-optimal algorithm for a topology control that reduces co-channel interference while balancing the time-varying traffic load in a dynamical manner. Our system-level simulation results show that the average system throughput can be significantly improved by the proposed algorithm for the divide-by-K reuse strategy, especially with K = 3.

Adaptive yielding scheme for link scheduling in OFDM-based synchronous device-to-device (D2D) communication system

Compared to asynchronous contention-based random access, e.g., carrier sensing multiple access, synchronous and distributed link scheduling for orthogonal frequency-division multiplexing (OFDM) systems is a viable solution to improve system throughput for device-to-device (D2D) ad hoc network. In particular, spatial spectral efficiency can be improved by scheduling as many concurrent D2D links necessary to satisfy individual signal-to-interference ratio (SIR) requirements. In this paper, we propose an adaptive yielding mechanism that can further improve the spatial spectral efficiency by allowing for more concurrent D2D links whenever more interference can be accepted, e.g., when the instantaneous bandwidth efficiency requirement is less than the current link capacity. Even if the system throughput varies with the link density, it is shown that the average system throughput can be significantly improved by the proposed yielding mechanism.

Performance analysis of device-to-device discovery with stochastic geometry in non-homogeneous environment

In this paper, we present the mathematical analysis of discovery performance in device-to-device (D2D) communication system. As opposed to the previous work which deals with outdoor devices only, we consider a non-homogeneous environment in which both indoor and outdoor devices exist with the different intensities and channel characteristics. A stochastic geometry model with various system parameters, including inband emission and channel parameters, has been employed to derive the average number of devices discovered within the given time constraint. It has been found from our analytical results that the in-band emission is a most critical factor that limits the discovery performance, especially in the mixed environment, implying that its performance can be improved significantly by any means of reducing the in-band emission.

Adaptive Yielding Scheme for Link Scheduling in OFDM-Based Synchronous D2D Communication System

As compared to asynchronous contention-based random access, synchronous & distributed link scheduling for OFDM system turns to be a viable solution to improve the system throughput for device-to-device (D2D) communication. In particular, a spatial spectral efficiency can be improved by scheduling the concurrent D2D links as many as the individual signal-to-interference ratio (SIR) requirement is satisfied. In this paper, we propose an adaptive yielding mechanism that can further improve the spatial spectral efficiency by allowing for more concurrent D2D links whenever more interference can be accepted, e.g., when the instantaneous bandwidth efficiency requirement is less than the current link capacity. Even if the system throughput varies with the link density, it has been shown that the average system throughput can be significantly improved by the proposed yielding mechanism.

GAMMA: Genetic Algorithm for Link-Adaptive Joint Path and Capacity Design in Mobile Multi-Hop Relay System

In this paper, we consider a topology control problem that dynamically configures the path and capacity for constructing a multi-hop backbone network under the varying traffic load in TDD–OFDMA system. In order to deal with the co-channel interference among the different relay stations,

Economic Cost Analysis of Relay-Enhanced Cellular Networks

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