Chih-Hsiang Ho

Resource Block Assignment for Interference Avoidance in Femtocell Networks

In this paper, we investigate resource block assignment in femtocell networks. A resource block assignment algorithm is designed to avoid co-channel intercell interference and ensure service quality for femtocell networks with dense and random femto deployments. We first formulate the optimization problem as the integer linear programming (ILP) on resource block assignment. The goal of the optimization formulation is to maximize the overall utilization of resource blocks with quality of service (QoS) constraints. We propose an efficient and simple algorithm termed interference-aware resource block assignment (IARBA). By considering conditions of resource blocks, the proposed approach achieves better resource block efficiency and assignment within QoS requirements. Our analytical and simulation results show that IARBA not only provides interference-free resource block assignment but also outperforms existing schemes in terms of average throughput with comparable complexities.

Increasing Reliability for IEEE 802.16j Mobile Multi-hop Relay Networks Planning

IEEE 802.16 network is a new generation of broadband networks. Recently, relay stations in IEEE 802.16j are proposed to perform as lightweight base station solutions to extend coverage and/or increase throughput. However, the 802.16j networks are tree-based structure which suffers from the single point of failure problem. In this paper, we define the coverage problem to place the base stations (BSs) and relay stations (RSs) at the lowest cost to support desired utilities and constrained by reliability limit. We develop two heuristic algorithms to solve coverage problems. We decide the proposed algorithms whose performance is quite near to the optimal selection by implementing a number of randomly selected graphs.

Optimal Frequency Offsets with Doppler Spreads in Mobile OFDM System

In highly mobile OFDM systems, the carrier frequency offsets (CFO) with Doppler spreads for downlink detection can be considerably large, which degrades the frequency alignment for uplink transmission, particularly in employing directional antennas for inter-carrier interference (ICI) reduction. In prior works, the directional antenna was investigated with appropriate frequency alignment in receivers local oscillator to efficiently reduce ICI in fast time varying OFDM systems. To resolve the optimal frequency offsets problem with Doppler spreads, this paper develops a simple scheme to capture instant Doppler power spectrum density (PSD) through moving directional antennas with arbitrary gain patterns. Thus, the optimal aligning frequency is derived as the center of gravity of the Doppler PSD. Simulations show our approach acquires the highest carrier to interference (C/I) ratio and the lowest bit error rates (BER) compared with other approaches.

A Novel User-Oriented Quality of Service Algorithm for Home Networks

This paper aims to present a novel dynamic quality of service (QoS) algorithm for home networks. The algorithm carries out the QoS management of a service for a user in a home network based on the profile consisting of the past responses of the user for that service. It performs the prediction of the future responses to the service from the profile using the general regression neural network algorithm. The algorithm finds the bandwidth allocation consuming minimum total bandwidth among those predicted to produce desired responses. The minimum bandwidth allocation is then used for the service. The corresponding user responses are used to update the profiles for the subsequent dynamic QoS managements. The algorithm requires no offline training and achieves fast adaptation to the user responses. Both analytical and numerical results reveal that the proposed algorithm provides an effective alternative for user-oriented QoS management in the heterogeneous home networks.

Coverage hole detection in cellular networks with deterministic propagation model

This paper proposes a deterministic propagation model for Coverage Hole Detection (CHD). In the well known 3GPP and the 4G mobile telecommunications technology, the minimization of drive test is an important issue, where CHD is often conducted by the costly drive test. This paper utilizes the radio link failure report mechanism specified in 4G to achieve CHD, which can significantly reduce the costly drive tests. During CHD, radio propagation model is required to reconstruct the radio map of target cell. In general, deterministic propagation model requires precise structural information of the cell, and statistical propagation model assumes the existence of spatial correlation, which may be unavailable due to 1) the absence of spatial correlation information and 2) the high cost in learning the required parameters. This paper targets on the scenario where prior terrain information and spatial correlation are unavailable, which is a more practical assumption in CHD problem.

Outage Users First Cell Outage Compensation Algorithm for Self-Organizing Networks

In cellular communication networks, base stations experience cell outages for various reasons including hardware malfunctions, firmware upgrades, or problems in the network backhaul. During a cell outage, users serviced by a base station disconnect from the network without warning because of a lack of signal coverage. Cell outages affect consumer interests and results in substantial losses for the telecommunications operator. In this study, cell outages in base stations are examined by constructing system models. Wireless interference and base station load were key considerations in the proposed outage users first cell outage compensation (OUF-COC) algorithm. The algorithm restores signal coverage and connections to users in the outage area without affecting users outside of the outage area. Simulations showed that OUF-COC could restore connections for over 90% of outage users. Approximately 50% of these users and 70% of users outside of the outage area experienced data rates of 250Kbps or higher (i.e., a typical data rate for a 3G network). These results indicated that the OUF-COC algorithm could effectively maintain quality of service among regular users while restoring connections to outage users and enhancing their data rates.

Interfered Users Protection Algorithm for Self-Organizing Networks

Small cells are generally used by telecom operators to effectively share the loading of conventional macrocells and backbone networks, because they cost considerably less to deploy and are also capable of improving communication quality and capacity. However, radio frequency spectrum resources are limited and expensive, so using the same frequency band to deploy small cells in densely populated metropolitan environments could lead to overlapping signal coverage between neighboring cells. If a user is situated in such areas, this can result in severe radio signal interference and result in a significant decline in network transmission performance. This study therefore proposes combining cell grouping and base station power adjustment, as well as radio resource allocation algorithms, into an interference mitigation method for small cells. According to simulation results, the proposed Interfered Users Protection (IUP) algorithm produces a significantly higher signal-to-interference-plus-noise ratio (SINR) under varying numbers of base stations deployed, and the effect is stronger under densely deployed base stations with severe interference. Approximately 56% of the interfered users maintained a data rate of 250 Kbps and above. In addition, the average SINR of regular users were not affected; 67% of the regular users were still capable of maintaining this transmission rate. The IUP algorithm is capable of effectively improving interfered users’ signals and transmission capacity, while accounting for the transmission performance of the overall network. 

Quality of Service Management for Home Networks Using Online Service Response Prediction

A novel quality of service (QoS) provisioning algorithm for home networks is presented in this paper. The algorithm carries out the QoS-aware bandwidth allocation using the general regression neural networks (GRNNs). Among all the allocations predicted to receive positive service responses, the algorithm finds the allocation with minimum total bandwidth for the current service. The service response prediction is based on the GRNN with the training set containing the bandwidth allocations and their service responses for past transmissions. The new service responses will then be used to update the training set for the subsequent transmissions. To attain accurate tracking of diversified service requirements, flexible specification of service response levels and QoS levels are provided. Both analytical and numerical studies reveal that the proposed algorithm is able to provide prompt or steady reactions to the service feedback depending on the variations of the source data rates. Because of its simplicity and effectiveness, the proposed algorithm is well suited for dynamic QoS management for heterogeneous home networks.

A Novel QoS Mapping Algorithm for Heterogeneous Home Networks Using General Regression Neural Networks

This paper presents a novel QoS management algorithm for heterogeneous home networks using the general regression network (GRNN). The algorithm first establishes profiles of the responses of users to various usages of different communication links for different services. By the employment of the GRNN, the prediction of the future responses of a service from a user could then be made based on the profiles. Among the bandwidth allocations predicted to receive positive feedback, the algorithm finds the bandwidth allocation consuming minimum total bandwidth in the network. The algorithm requires no offline training and achieves fast adaptation to the responses of users. Both analytical and numerical analyses of the proposed algorithm have been included in the paper to show the effectiveness of the proposed algorithm.