Browsing by Author "Ren, Fang-Ching"

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A utility function-based access selection method for heterogeneous WCDMA and WLAN networks
(2007)
Chen, Yung-Han
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Yang, Nuan-Yu
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Chang, Chung-Ju
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Ren, Fang-Ching
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電信工程研究所
WCDMA/WLAN interworking networks are considered to support high-data-rate multimedia services and high mobility. In this paper, we propose a utility function-based access selection method (UFAS) to determine which cell is most suitable for a mobile node's service request in heterogeneous WCDMA and WLAN networks. The UFAS method contains three parts, cells classification, utility function computation, and target cell determination. This utility function is composed of four evaluation functions, and is designed with a balancing index which can reduce the utility value of a cell if the cell is heavily loaded. Simulation results show that the UFAS method achieves larger system throughput than a policy-enabled (PE) handoff decision method [8]. Moreover, the UFAS method can reduce handoff occurrence rates and strike a balance between system utilization and cell loading while maintaining QoS requirements.
Adaptive radio resource allocation for downlink OFDMA/SDMA systems
(2007)
Tsai, Chun-Fan
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Chang, Chung-Ju
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Ren, Fang-Ching
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Yen, Chih-Ming
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電信工程研究所
The paper proposes an adaptive radio resource allocation (ARRA) algorithm for downlink OFDMA/SDMA systems with goals to achieve quality of service (QoS) satisfied and throughput maximized. The ARRA algorithm considers multiple service classes of multimedia traffic and their diverse QoS requirements. It contains two parts, a dynamic priority adjustment scheme and a priority-based greedy (PBG) algorithm. The dynamic priority adjustment scheme gives high priority to urgent users and dynamically adjust the value frame by frame based on users' QoS requirement and queue occupancy. The PBG algorithm allocates the radio resource iteratively according to a cost value to maximize the system throughput while allocating enough resource to high-priority users. Simulation results show that the ARRA algorithm outperforms the conventional algorithms in terms of system throughput under the satisfaction of QoS requirements.
Adaptive radio resource allocation for downlink OFDMA/SDMA systems with multimedia traffic
(2008-05-01)
Tsai, Chun-Fan
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Chang, Chung-Ju
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Ren, Fang-Ching
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Yen, Chin-Ming
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電信工程研究所
This paper proposes an adaptive radio resource allocation (ARRA) algorithm for downlink OFDMA/SDMA systems with multimedia traffic. Considering multiple service classes and diverse QoS requirements of multimedia traffic, the ARRA algorithm is designed with the goal to maximize spectrum efficiency and to fulfill quality of service (QoS) requirements. It is composed of two parts, a dynamic priority adjustment (DPA) scheme and a priority-based greedy (PBG) scheme. The DPA adopts a type of time-to-expiration to indicate the degree of user's urgency, and dynamically gives high priorities to urgent users. The PBG allocates the radio resource iteratively, based on a cost value, to maximize the system throughput while allocating enough resource to high-priority users. Simulation results show that the ARRA algorithm outperforms conventional algorithms in terms of system throughput and satisfaction extent of QoS requirements; it can sustain users' QoS requirements up till a traffic load of 0.8, while the conventional algorithms cannot guarantee QoS requirements after a traffic load of 0.3.
An Intelligent HARQ Scheme for HSDPA
(2011-05-01)
Huang, Chiao-Yin
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Chung, Wen-Ching
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Chang, Chung-Ju
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Ren, Fang-Ching
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電機工程學系
In this paper, we propose an intelligent hybrid automatic repeat request (iHARQ) scheme for high-speed downlink packet access (HSDPA) systems. The challenge in the hybrid automatic repeat request (HARQ) control problem of HSDPA is how to choose an appropriate modulation and coding scheme (MCS) for initial transmission in the situation wherein the channel quality indication (CQI) has report delay. The iHARQ scheme will determine the suitable MCS to maximize the system throughput and guarantee the block error rate requirement in such an uncertain environment. By modeling the HARQ behavior as a Markov decision process, we adopt fuzzy logics to determine an appropriate MCS for each initial packet transmission. In addition, a Q-learning algorithm is utilized to update the fuzzy rule base, according to well-designed reinforcement signals fed back from the HSDPA system, such that the iHARQ scheme can adapt to the delayed CQI. Simulation results show that, compared with a conventional adaptive threshold selection method, the proposed iHARQ scheme increases the system throughput by up to 75.2%.
Deployment and radio resource reuse in IEEE 802.16j multi-hop relay network in Manhattan-like environment
(2007)
Fu, I-Kang
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Sheen, Wern-Ho
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Ren, Fang-Ching
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電信工程研究所
;
Institute of Communications Engineering
IEEE 802.16j is an amendment to the IEEE 802.16 broadband wireless access standard to enable the operation of multi-hop relay stations (RS). It aims to enhance the coverage, per user throughput and system capacity of IEEE 802.16e. Compared with base station (BS), RS does not need a wire-line backhaul and has much lower hardware complexity. Using RSs can significantly reduce the deployment cost of the system. In this paper, the RS deployment and radio-resource reuse strategies for IFEE 802.16j multi-hop relay (MR) networks are investigated. Simulation results show that the per-user throughput and system capacity of IEEE 802.16j MR network can be substantially improved by the proposed method.
Dynamic Priority Resource Allocation for Uplinks in IEEE 802.16 Wireless Communication Systems
(2009-10-01)
Yen, Chih-Ming
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Chang, Chung-Ju
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Ren, Fang-Ching
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Lai, Jian-Ann
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電信工程研究所
In this paper, a dynamic priority resource-allocation (DPRA) scheme is proposed for uplinks in IEEE 802.16 wireless communication systems. The DPRA scheme dynamically gives priority values to four types of service traffic based on their urgency degrees and allocates system radio resources according to their priority values. It can maximize the system throughput and satisfy differentiated quality-of-service (QoS) requirements. Furthermore, the DPRA scheme performs consistent allocation for packets of users to conform to the uplink frame structure of IEEE 802.16, to fulfill the QoS requirement, and to reduce the computational complexity. Simulation results show that the proposed DPRA scheme performs very close to the optimal method, which is by exhaustive search in system throughput, and it outperforms the conventional efficient and fair scheduling (EFS) algorithm in the performance measures such as system throughput, real-time polling service (rtPS) packet dropping rate, ratio of unsatisfied non-real-time polling service (nrtPS), and average transmission rate of the best effort (BE) service. In addition, the DPRA scheme takes only 1/1000 and 1/10 the computational times of the optimal method and the conventional EFS algorithm, respectively, thus making it more feasible for real applications.
Dynamic Priority-based Resource Allocation for Uplinks in IEEE 802.16 Wireless Communication Systems
(2008)
Chang, Chung-Ju
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Yen, Chih-Ming
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Ren, Fang-Ching
;
Lai, Jian-Ann
;
電信工程研究所
In this paper, a dynamic priority-based resource allocation (DPRA) scheme is proposed for uplinks in IEEE 802.16 wireless communication systems. The goal of the DPRA scheme is to maximize the system throughput while satisfying diverse QoS requirements. Four types of multimedia traffic are considered, where these multimedia traffic are given urgency degrees via dynamic priority values, and the radio resources are allocated according to their priority values. Also the DPRA scheme performs consistent allocation for packets with multimedia traffic in aspects of subchannel, modulation order, and power. Simulation results show that the proposed DPRA scheme outperforms the conventional algorithm in system throughput by an amount of 15%. The rtPS packet dropping rate of DPRA scheme is 70% lower than other schemes and satisfies QoS requirements. Besides, the proposed DPRA scheme can achieve less computational complexity and lower transmission overhead.
Fuzzy Q-Learning-based Hybrid ARQ for High Speed Downlink Packet Access
(2009)
Huang, Chiao-Yin
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Chung, Wen-Ching
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Chang, Chung-Ju
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Ren, Fang-Ching
;
電信工程研究所
In this paper, a fuzzy Q-learning-based hybrid automatic repeat request (FQL-HARQ) scheme is proposed to enhance the system performance of high speed downlink packet access (HSDPA) in universal mobile telecommunications system (UMTS). In the HSDPA system, it is an important issue to choose modulation and coding scheme (MCS) for new data packet when channel quality indicator (CQI) is inaccurate. Hence, the purpose of the FQL-HARQ scheme is to determine a suitable MCS for new data packet so as to maximize the system throughput while guarantee the block error rate (BLER) requirement. In the FQL-HARQ scheme, the fuzzy logic is used to choose a suitable MCS for each new data packet. According to the feedback information from the HSDPA system, the Q-learning algorithm is adopted to update fuzzy rule base. This makes the FQL-HARQ scheme can adapt to the variation of environment. Simulation results show that the proposed scheme can increase the system throughput of up to 70 % compared to the conventional adaptive method in the case with CQI report delay.
GGRA: A Feasible Resource Allocation Scheme by Optimization Technique for IEEE 802.16 Uplink Systems
(2010-01-01)
Chang, Chung-Ju
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Chiu, Yin
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Feng, Kai-Ten
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Ren, Fang-Ching
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電信工程研究所
Generally, optimization techniques for resource allocation of OFDMA systems are infeasible for real-time applications. In this paper, we propose a genetic algorithm with subscriber station (SS) grouping resource allocation (GGRA) scheme for IEEE 802.16 uplink systems. The GGRA scheme firstly designs a rate assignment strategy, applied with a predefined residual lifetime, to allocate resource to each service dynamically. It then aggregates high correlation SSs into the same group, where the SSs will be allocated to different slots so as to avoid mutual user interference. Finally, the GGRA scheme finds an optimal assignment matrix for the system by the genetic algorithm, based on the SS groups to greatly lessen the computation complexity. The GGRA scheme can also maximize system throughput and fulfill QoS requirements. Simulation results show that the proposed GGRA scheme performs better than the EFS algorithm [6] and the MLWDF algorithm [7] in system throughput, voice/video packet drop rate, unsatisfied ratio of HTTP users/packets, and FTP throughput. The computation complexity of the GGRA scheme is also tractable and thus feasible for real-time applications.
GGRA: A Feasible Resource-Allocation Scheme by Optimization Technique for IEEE 802.16 Uplink Systems
(2010-03-01)
Chiu, Yin
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Chang, Chung-Ju
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Feng, Kai-Ten
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Ren, Fang-Ching
;
電機工程學系
Generally, optimization techniques for resource allocation of orthogonal frequency-division multiple-access (OFDMA) systems are infeasible for real-time applications. In this paper, with consideration of grouping for subscriber stations (SSs), a resource-allocation scheme by an optimization technique of a genetic algorithm is proposed for the uplinks of IEEE 802.16 OFDMA systems. The genetic algorithm with SS grouping resource-allocation (GGRA) scheme first designs a rate assignment strategy that is applied with a predefined residual lifetime to dynamically allocate resource to each service. It then aggregates high-correlation SSs into the same group, where the SSs will be allocated to different slots to avoid mutual user interference. Finally, the GGRA scheme finds an optimal assignment matrix for the system by the genetic algorithm based on the SS groups to greatly lessen the computation complexity. The GGRA scheme can also maximize the system throughput and fulfill the quality-of-service (QoS) requirements. Simulation results show that the proposed GGRA scheme performs better than the efficient and fair scheduling (EFS) algorithm and the maximum largest weighted delay first (MLWDF) algorithm in system throughputs, voice/video packet drop rates, unsatisfied ratios of hypertext transfer protocol (HTTP) users/packets, and file transfer protocol (FTP) throughputs. The computation complexity of the GGRA scheme is also tractable and, thus, feasible for real-time applications.
NACK-based Retransmission Schemes for MBMS over Single Frequency Network in LTE
(2011)
Lu, Cheng-Chung
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Chung, Wen-Ching
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Chang, Chung-Ju
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Ren, Fang-Ching
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電機工程學系
In this paper, we propose NACK-based retransmission schemes for multimedia broadcast and multicast service over single frequency network (MBSFN) in LTE systems to enhance goodput and reduce retransmission rate. It is known that more retransmissions in MBSFN will reduce the spectrum efficiency. Hence, to provide a reliable broadcast/multicast service in LTE systems is an important issue. We first group mobile users into three sets according to their SNRs. Each set can report NACK messages on dedicated or shared feedback channel. The retransmission is triggered by pre-defined probability or pre-defined threshold. By applying different retransmission trigger schemes on different feedback channels, we have four kinds of NACK-based retransmission schemes. Simulation results show that, the proposed retransmission schemes can enhance the goodput by up to 28.3% and reduce the retransmission rate by up to 37.8% compared to the conditional HARQ scheme [12].
Q-learning-based hybrid ARQ for high speed downlink packet access in UMTS
(2007)
Chang, Chung-Ju
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Chang, Chia-Yuan
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Ren, Fang-Ching
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電信工程研究所
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Institute of Communications Engineering
In this paper, a Q-learning-based hybrid automatic repeat request (Q-HARQ) scheme is proposed to achieve efficient resource utilization for high speed downlink packet access (HSDPA) in universal mobile telecommunications system (UMTS). The Hybrid ARQ procedure is modeled as a discrete-time Markov decision process (MDP), where the transmission cost is defined in terms of the signal-to-interference-and-noise (SINR) which is based on the desired (quality-of-service) QoS parameters of transport block error rate (BLER) for enhancing spectrum utilization subject to QoS constraint. The Q-learning reinforcement algorithm is employed to accurately estimate the transmission cost to perform the most suitable decision of modulation and coding scheme for the packet initial transmission while the requirement of transport block error rate is guaranteed. Simulation results show that the QoS requirement of block error rate for Q-HARQ is nearly met around a reasonable value indeed. In addition, the system throughput of the Q-HARQ can be improved under the specific QoS constraint of BLER. It is verified finally that the Q-HARQ scheme is feasible in the practical system because of the short processing and convergence time.
QoS-Promoted Dynamic Bandwidth Allocation for Ethernet Passive Optical Networks
(2008)
Tang, Wen-Shiang
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Huang, Chin-Ya
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Chang, Chung-Ju
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Ren, Fang-Ching
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交大名義發表
In this paper, we propose a QOS-promoted dynamic bandwidth allocation (Q-DBA) method to support quality-of-service (QoS) requirement services for Ethernet passive optical networks (EPON). The Q-DBA method classifies the three types of services: voice, video, and data into six priorities. It can not only satisfy QoS requirements of real-time service and but also improve the QoS or non-real-time packets, Simulation results show that the Q-DBA can fulfill the video dropping probability requirement while the conventional dynamic bandwidth allocation with multiple services (DBAM) fails. Also, the Q-DBA can achieve the fairness index of average data delay close to 1 but DBAM's fairness index of average data delay varies greatly.
QoS_GTE: A centralized QoS guaranteed throughput enhancement scheduling scheme for relay-assisted WiMAX networks
(2008)
Chang, Chung-Ju
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Yen, Chih-Ming
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Ren, Fang-Ching
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Chuang, Chia-Hsuan
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電信工程研究所
A centralized QoS guaranteed throughput enhancement (QoS_GTE) scheduling scheme for downlink relay-assisted WiMAX networks is proposed. The QoS_GTE consists of a transmission time based path selection algorithm (TT_PSA), a service order based resource allocation algorithm (SO_RAA), and a transmission concurrency decision algorithm (TCDA). The TT_PSA selects the path with the minimal transmission time for packets, which takes path loss, shadow fading, and interference into consideration. The SO_RAA gives high priority to urgent users and maximizes throughput under QoS satisfaction. The TCDA carries out flexible resource reuse by deciding which relay station (RS) can transmit concurrently using the same frequency and time slots. Simulation results show that the proposed QoS_GTE outperforms the scheme of without relay by an amount of 63% and that of the LMP by an amount of 28%, in the system throughput. The QoS_GTE can also guarantee QoS requirements of real time services by 97%.
RACH Collision Probability for Machine-type Communications
(2012)
Cheng, Ray-Guang
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Wei, Chia-Hung
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Tsao, Shiao-Li
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Ren, Fang-Ching
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資訊工程學系
This paper summarizes the two definitions of the collision probability from the perspective of an MTC device and an RAO were presented in 3GPP TR 37.868. We use the results presented in TR 37.868 to show the inconsistency between the two definitions. It worth to note that the researcher needs to clearly specify the definition they used in presenting the results of their proposed radio access network overload control schemes. This paper further presents an analytical model to derive the collision probability, the success probability, and the idle probability based on the two definitions.
Situation-aware data access manager using fuzzy Q-learning technique for multi-cell WCDMA systems
(2006-09-01)
Chen, Yih-Shen
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Chang, Chung-Ju
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Ren, Fang-Ching
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交大名義發表
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National Chiao Tung University
This paper proposes a novel situation-aware data access manager using fuzzy Q-learning technique (FQ-SDAM) for multi-cell WCDMA systems. The FQ-SDAM contains a fuzzy Q-learning-based residual capacity estimator (FQ-RCE) and a data rate scheduler (DRS). The FQ-RCE can accurately estimate the situation-dependent residual system capacity, and appropriately chooses the received interference powers from the home-cell and adjacent-cell as input linguistic variables, which simplifies the multi-cell environment into a single-cell environment by applying a perceptual coordination mechanism. The DRS can effectively allocate the resource for non-real-time terminals by modifying the exponential rule [10], which considers the effect of interference on adjacent cells. Simulation results show that, compared to the link and interference-based demand assignment (LIDA) scheme proposed in [7], FQ-SDAM can effectively reduce the packet error probability and improve aggregate throughput of the non-real-time services in both the homogeneous and non-homogeneous multi-cell WCDMA environments. Additionally, the modified exponential rule achieves better system performance than the original exponential rule.
TAPS: Traffic-Aware Power Saving Scheme for Clustered Small Cell Base Stations in LTE-A
(2015)
Lin, Kuan-Yu
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Chen, Jen-Yeu
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Ren, Fang-Ching
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Chang, Chung-Ju
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電機工程學系
To meet the soaring demand of high data rate from today\'s applications of mobile Internet, small cells would be widely deployed to achieve higher data rate and better spectral efficiency in 4G and B4G/5G cellular networks. However, when the network traffic load is low, a large number of small-cell base stations could incur a tremendous energy waste. To overcome this pitfall, in this paper, we propose a traffic-aware power saving scheme (TAPS) by which a small-cell base station can adequately switch its operation mode -- namely, normal, sniff and low-duty modes -- according to its traffic load to reduce its power consumption. Simulation results show that TAPS can save a large amount of energy but only slightly hamper system performance compared with the case without power-saving scheme.