43 research outputs found
Nonsaturated Throughput Analysis of Coexistence of Wi-Fi and Cellular With Listen-Before-Talk in Unlicensed Spectrum
No full textThis paper analyzes the coexistence performance of Wi-Fi and cellular networks conditioned on nonsaturated traffic in the unlicensed spectrum. Under the condition, the time-domain behavior of a cellular small-cell base station (SCBS) with a listen-before-talk (LBT) procedure is modeled as a Markov chain, and it is combined with a Markov chain which describes the time-domain behavior of a Wi-Fi access point. Using the proposed model, this study finds the optimal contention window size of cellular SCBSs in which total throughput of both networks is maximized while satisfying the required throughput of each network, under the given traffic densities of both networks. This will serve as a guideline for cellular operators with respect to performing LBT at cellular SCBSs according to the changes of traffic volumes of both networks over time.
A QoE-aware Joint Resource Allocation Algorithm for Uplink Carrier Aggregation in LTE-Advanced Systems
No full textRadio Resource Management Based on QoE-aware Model for Uplink Multi-Radio Access in Heterogeneous Networks
No full text이종 무선 네트워크에서의 네트워크 다이버시티에 관한 성능 분석
No full text학위논문(박사) - 한국과학기술원 : 전기및전자공학부, 2016.8
,[vii, 85 p. :]In this dissertation, various techniques utilizing network diversity are introduced to analyze the effect of the network diversity on the performance enhancement of heterogeneous networks (HetNets).
First, a vertical handover scheme is proposed to minimize total power consumption required in serving a traffic flow without affecting the constant service rate of each network by using dynamic power control. The proposed scheme uses a Markov decision process (MDP) to capture the system's stochastic behaviors as well as the power consumption during a handover execution.
Second, a traffic offloading method is proposed to minimize the energy consumption of 2-tier HetNets that support 2 classes of packets with different packet delay requirements. Under given base station (BS) densities, the optimal BS association biases that minimize the delay of both packet classes is analyzed. Then, by means of the analysis, the optimal BS densities that minimize network energy consumption are found, while satisfying the delay requirement of both packet classes.
Third, slot-by-slot joint resource allocation algorithms are proposed for uplink multi-homing networks, in which the objective is to maximize uplink network utility. According to difference sub-channel allocation assumptions (i.e., fractional and integer sub-channel allocation), different joint resource allocation algorithms are investigated. Under the assumption of fractional sub-channel allocation, an optimization problem for joint resource allocation is formulated as a convex optimization problem. To achieve an optimal solution of the problem, one adopts Lagrange duality theory and derive an iterative algorithm to achieve the optimal solution. In contrast, under the assumption of integer sub-channel allocation, an optimization problem for joint resource allocation is formulated as a mixed-integer nonlinear programming (MINLP) problem. Thus, a sub-optimal joint resource allocation algorithm is investigated, where the optimization problem is decoupled into three separate sub-problems: initial power allocation, sub-channel allocation for given initial power allocation, and power allocation improvement for given sub-channel allocation.
Fourth, a mathematical model is provided to evaluate the coexistence of Wi-Fi and Listen before talk (LBT)-enabled cellular networks sharing the unlicensed spectrum. Based on the proposed model, the throughput difference between the Wi-Fi access points (APs) and cellular BSs that results from the different medium access mechanisms of the two networks is investigated. In addition, because the two networks must coexist in a friendly manner, their \emph{graceful coexistence} is defined as the condition in which the performance of an individual node under a network scenario with Wi-Fi APs and cellular BSs is not worse than that under a network scenario with only Wi-Fi APs. Using this definition, we first examine whether this graceful coexistence is feasible through adjusting the LBT parameter of the cellular BSs, particularly the contention window (CW) size. Then, the optimal CW size that maximizes the total throughput of the two networks under the graceful coexistence condition is obtained for cases with various physical data rates and numbers of nodes in each network.
Finally, a mathematical framework is proposed based on queuing theory that models the time-domain behaviors of a Wi-Fi AP with the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism and a cellular small BS without the regulatory requirement for LBT in the unlicensed spectrum. Based on the proposed framework, the mean packet delay of Wi-Fi AP and cellular small BS investigated as a coexistence performance metric, according to changes in their packet arrival rates. With help of our analysis, the maximum allowable packet arrival rates of Wi-Fi AP and cellular small BS are identified, under which the required Wi-Fi performance is satisfied without the coexistence mechanisms at the cellular small BS. This will serve as a guideline for the cellular small BS on when it needs to employ the coexistence mechanisms.한국과학기술원 :전기및전자공학부
QoS Provisioning in Underwater Acoustic Sensor Networks with 3-Dimensional Topology
No full textIn this work, we study the issue of providing quality-of-service (QoS) in terms of packet delay and packet error probability in 3-dimensional (3D) underwater acoustic sensor networks (UASNs). It is assumed that each underwater sensor communicates with its corresponding sink node using slotted ALOHA, which is the representative random access-based medium access control (MAC) protocol in UASNs. To measure the QoS metrics, we develop an analytical model, in which each underwater sensor following slotted-ALOHA is modeled as an M/G/1 queue in the MAC layer. Then, we analyze the performance of mean packet delay of each underwater sensor in 3D UASNs. Using the proposed analytical model, we formulate an optimization problem which seeks to find the minimum sink density while guaranteeing the lower bound of an acceptable SINR corresponding to the upper bound of the pre-determined acceptable packet error probability. Numerical results show not only the mean packet delay performance of each underwater sensor following slotted ALOHA but also the optimal sink density for various parameter values.1
Network switching strategy for energy conservation in heterogeneous networks.
No full textIn heterogeneous networks (HetNets), the large-scale deployment of small base stations (BSs) together with traditional macro BSs is an economical and efficient solution that is employed to address the exponential growth in mobile data traffic. In dense HetNets, network switching, i.e., handovers, plays a critical role in connecting a mobile terminal (MT) to the best of all accessible networks. In the existing literature, a handover decision is made using various handover metrics such as the signal-to-noise ratio, data rate, and movement speed. However, there are few studies on handovers that focus on energy efficiency in HetNets. In this paper, we propose a handover strategy that helps to minimize energy consumption at BSs in HetNets without compromising the quality of service (QoS) of each MT. The proposed handover strategy aims to capture the effect of the stochastic behavior of handover parameters and the expected energy consumption due to handover execution when making a handover decision. To identify the validity of the proposed handover strategy, we formulate a handover problem as a constrained Markov decision process (CMDP), by which the effects of the stochastic behaviors of handover parameters and consequential handover energy consumption can be accurately reflected when making a handover decision. In the CMDP, the aim is to minimize the energy consumption to service an MT over the lifetime of its connection, and the constraint is to guarantee the QoS requirements of the MT given in terms of the transmission delay and call-dropping probability. We find an optimal policy for the CMDP using a combination of the Lagrangian method and value iteration. Simulation results verify the validity of the proposed handover strategy
Radio Resource Management Based on QoE-Aware Model for Uplink Multi-Radio Access in Heterogeneous Networks
No full textCoexistence of Wi-Fi and Cellular With Listen-Before-Talk in Unlicensed Spectrum
No full textIn this letter, we analyze the coexistence performance of Wi-Fi and cellular networks with different listen-before-talk (LBT) procedures in the unlicensed spectrum. For this analysis, the behavior of a cellular base station is modeled as a Markov chain that is combined with Bianchi's Markov model depicting the behavior of a Wi-Fi access point. The proposed mathematical framework finds the optimal contention window size of cellular base stations, which maximizes the total throughput of both networks while satisfying the required throughput of each network. Numerical results show the validity of adjustment in the parameter of LBT.</p
