Chih-Cheng Tseng

Cognitive Radio Resource Management for QoS Guarantees in Autonomous Femtocell Networks

Deploying femtocell networks embedded in the Macrocell coverage greatly benefits communication quality in variety manners. However, the lack of schemes to effectively mitigate detractive interference, fully utilize radio resources and provide quality-of-service (QoS) guarantee (in terms of delay) creates challenges to practically facilitate the concept of femtocell. To tackle these challenges to achieve a successful dense femtocell deployment, this paper proposes a cognitve radio resource management (CRRM) scheme which is inspired by the spirit of cognitive radio technology. Instead of the need of a centralized manner, the femtocell with the proposed CRRM can autonomously sense the radio resource usage of the Macrocell so as to mitigate interference. By analytical deriving the effective capacity of the CRRM that specifies the QoS guarantee capability of the system, the optimum sensing period and radio resource allocation are proposed for the CRRM to achieve a fully radio resource utilization while statistically guaranteeing the QoS of the femtocell. Numerical results demonstrate that the proposed CRRM outperforms the randomized scheme (without CRRM) in terms of the radio resource utilization efficiency. Simulation results also support the effectiveness on the delay guarantee performance.

Carrier Sensing Based Multiple Access Protocols for Cognitive Radio Networks

Cognitive radio (CR) dynamically accessing inactive radio spectrum of the primary system (PS) at link level has attracted a lot of research interests. The cognitive radio network (CRN) organized by multiple CRs has been considered as an emerging wireless communication technology. In order to efficiently utilize the radio spectrum, the multiple access schemes of the CRN shall be considered together with physical layer (PHY) transmission schemes. In this paper, we propose a novel class of carrier sense multiple access (CSMA) based MAC protocols for the CRN while the PS is also operating with widely-applied carrier sensing protocols. Different from conventional CR either to transmit packets or not, our protocols with a feasible adaptive PHY transmission scheme allow possible transmission(s) for a CR even when the PS is actively transmitting. We analyze the proposed class of CSMA based MAC protocols and further propose the transmission strategy for each CR to improve the throughput of the CRN. Numerical results show that our proposed scheme improves the throughput of the CRN more than 36% and 100% as compared with the conventional CSMA and conventional CR operations, respectively.

Power efficient topology control in wireless ad hoc networks

In the wireless ad hoc networks, for prolonging the communication duration of the nodes, the transmission power is required to be minimized to conserve the limited battery life. In addition, for the wireless ad hoc networks to be applicable, the networks are required to he connected. Unfortunately, the two requirements are against each other. In this paper, by analyzing the probability of isolated node, we obtain the relationships between transmission range, service area and network connectedness. Furthermore, we propose a generalized (N,B) wireless ad hoc network model to investigate the impact of boundary nodes on the network connectivity, equivalent service area and average node degree.

On The Distance Distributions of The Wireless Ad Hoc Networks

Separation distance between nodes is an important index in characterizing the optimum transmission range, the most probable Euclidean distance between two random selected nodes, the node degree and the network connectivity of wireless ad hoc networks. However, because nodes are randomly deployed, the separation distances between nodes in the wireless ad hoc networks are also random. Thus, in this paper, we present methodologies to analyze three distance-related probability distributions: the distribution of the distance to the k-th nearest neighbor, the distribution of the distance between two random selected nodes and the joint distribution of the distances between nodes and a common reference node

Organizing an optimal cluster-based ad hoc network architecture by the modified Quine-McCluskey algorithm

An optimal cluster-based ad hoc network architecture that requires the minimum number of cluster maintenance overheads not only reduces the waste of the precious bandwidth but also saves the consumption of the limited battery power. Mathematical analyses show that the cluster maintenance overheads can be minimized by minimizing the number of generated clusters and the variance of the number of cluster members. By using the modified Quine-McCluskey (MQM) algorithm, the number of generated clusters and the variance of the number of cluster members of the generated cluster-based network architecture are minimized. Thus, the number of overheads required to maintain the cluster architecture is minimized and the precious bandwidth and the limited battery power are saved.

Delay and Power Consumption in LTE/LTE-A DRX Mechanism With Mixed Short and Long Cycles

Energy consumption is a major concern in todays wireless communications due to the consensus for a greener world. LTE-Advanced (LTE-A) has been standardized for the fourth-generation mobile communications to meet the growing demands for high-speed wireless communications. However, high-speed signal processing on LTE/LTE-A user equipment (UE) causes excessive power consumption. The discontinuous reception (DRX) mechanism is a critical technique for tackling this issue. Delay constraint and power savings are two contradictory performance metrics associated with the DRX mechanism. Using recursive deduction and Markov model, this paper provides an in-depth analysis on the average delay and average power consumption of the DRX mechanism. Two performance metrics, namely, power-saving factor and relative power saving, are devised to assess the power-saving performance of the DRX mechanism. The accuracy of theoretical analysis is validated by computer simulations using the parameters in compliance with LTE specifications. The performance of the DRX mechanism is governed by a set of parameters that interact with one another in an intricate manner. Therefore, the values of key parameters are tested to assess their impacts on the performance of the DRX mechanism. The results shown in this paper give an insight into the operation and further improvement of the DRX mechanism.

Bandwidth Enhancement of Internal Antenna by Using Reactive Loading for Penta-Band Mobile Handset Application

A metal-wire-cutting bended monopole antenna (BMA) fed by mini-coaxial cable jointly with a thin printed ground-line which protrudes from ground-plane to be a balance-feed structure for bandwidth enhancement is proposed. A prototype of the proposed antenna with 40 mm in length, 6 mm in height and 5 mm in width has been fabricated and experimentally investigated. The humans hand effect on impedance bandwidth and radiation characteristics of the proposed antenna is studied. A prototype is designed to cover penta-band: CDMA (824-894 MHz), GSM (880-960 MHz), DCS (1710-1880 MHz), PCS (1850-1990 MHz) and WCDMA (1920-2170 MHz). Experimental results are shown to verify the validity of theoretical work.

A Water-Wave Broadcast Scheme for Emergency Messages in VANET

Vehicular Ad Hoc Network (VANET) is an emerging new technology and a promising platform for the intelligent transportation system. The most important application of VANET is disseminating emergency messages to drivers in case of dangerous events. The effectiveness depends on the design of a broadcast scheme. A simple broadcast scheme encounters many problems such as broadcast storm, connection hole, building shadow, and intersection problems. In this paper, we propose an efficient broadcast scheme that simulates water wave propagation to spread emergency messages. This scheme provides warning services with both space and time constraints. Most existing broadcast schemes provide inadequate strategies for limiting the time period of a warning. We verified the performance of our proposed scheme in a simulated street environment with vehicle movements to show the superiority of this scheme in high broadcast coverage areas.

Energy-Efficient DRX Scheduling for QoS Traffic in LTE Networks

LTE has been touted as a leading-edge mobile communication technology offering high data rate and low latency. However, with a sophisticated physical layer to boost performance, the processing demand on user equipment (UE) is tremendous, which implies that the energy consumption is heavy. To curb undesirable energy waste and extend battery life, a variety of energy-conserving measures have been developed, among which discontinuous reception (DRX) is shown to be useful. This paper introduces the light sleeping mode in order to further improve the performance of DRX for traffic with QoS requirements in LTE networks. The key idea of light sleeping is to turn off the power amplifier but leave the other components in the transceiver on to cut down energy consumption while allowing fast wakeup. Quantitative analysis shows that the proposed method can substantially reduce energy consumption and satisfy the delay requirement of QoS traffic.

A WiFi-Based Weighted Screening Method for Indoor Positioning Systems

Past studies of WiFi-based indoor positioning systems (IPS) have mainly been divided into three types of positioning: proximity, trilateration, and scene analysis. This paper proposes a WiFi-based weighted screening method (WSM) to improve displacement error in trilateration. WSM is designed for part of pedestrian navigation in indoor environment which most likely use smart phone as the WiFi signal detector. Thus the less computational power consuming, irregular deploying position of APs and the irregular RSSI variation are all take into consideration when designing WSM. Experiment results show that this method performs better than conventional matrix method and the error correction algorithm, one trilateration in IPS.