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A Q-learning-based multi-rate transmission control scheme for RRC in WCDMA systems
(2002-01-01)
Ren, FC
;
Chang, CJ
;
Chen, YS
;
交大工研院聯合研發中心
;
NCTU/ITRI Joint Research Center
In this paper, a Q-learning-based multi-rate transmission control scheme (Q-MRTC) for radio resource control (RRC) in WCDMA systems is proposed. The RRC problem is modelled as a semi-Markov decision process (SMDP). And we successfully apply a real-time reinforcement learning algorithm, named Q-learning, to accurately estimate the transmission cost for the multi-rate transmission control. For the cost function approximation, we apply the feature extraction method to map the original state space into a more compact set which represents the resultant interference profile. Simulation results show that the Q MRTC can achieve higher system throughput and better users' satisfaction index, by an amount of 87% and 50%, respectively, than the interference-based multi-rate transmission control scheme, while keeping the QoS requirement.
Neural-network connection-admission control for ATM networks
(1997-04-01)
Cheng, RG
;
Chang, CJ
;
電信工程研究所
;
Institute of Communications Engineering
ATM connection-admission control (CAC) using neural networks offers improvement over conventional CAC but creates some difficulties in real operation, such as complicated training processes. This is because ATM traffic characteristics are quite diverse, and quality of service (QoS) and bandwidth requirements vary considerably. A neural-network connection-admission control (NNCAC) method which can overcome these difficulties by preprocessing neural-network input parameters is proposed. The NNCAC method introduces a unified metric for input-traffic parameters by utilising robust analytical results of the equivalent-capacity method. It diminishes the estimation error of the equivalent-capacity method, due to modelling, approximation unpredictable statistical system, by employing the learning capability of a neural network. The method further considers the congestion status parameter and the cell loss probability, which provides insight information about the system. Simulation results revealed that the proposed NNCAC method provided a 20% system-utilisation improvement over Hiramatsu's neural-network CAC scheme and a 10% system-utilisation improvement over based CAC scheme, while maintaining QoS contracts. It was also found that the NNCAC: method provided utilisation comparable with that of the NFCAC scheme but possessed a lower cell loss probability. NNCAC is suitable for designers who are not familiar with fuzzy-logic control schemes or have no ideas about the requisite knowledge of CAC.
Analysis of a general service nonexhaustive polling system using a heuristic combination method and pseudoconservation law
(1996-05-01)
Chang, CJ
;
Hwang, LC
;
電信工程研究所
;
電信研究中心
;
Institute of Communications Engineering
This paper is devoted to the analysis of the mean waiting time for a polling system with general service order sequence and nonexhaustive service discipline. We obtain an expression for the mean waiting time in terms of a so-called residual cycle time and derive a pseudoconservation law (PCL) to help improve the accuracy of estimations of the mean waiting time. By multiplying the estimations of the residual cycle times for all stations by equal and unequal constants, we obtain two separate solutions for the mean waiting time. We furthermore propose a heuristic method that combines these separate mean waiting times into a final solution for the mean waiting time. Numerical examples show that our combination method generates accurate estimations for the mean waiting times in both cyclic and general cases over all traffic loads.
The effect of laser wavelength on the photorefractive characteristics of PMDA-DR19 based photorefractive polymeric materials
(1997-09-01)
Chang, CJ
;
Wang, HC
;
Liao, GY
;
Whang, WT
;
Liu, JM
The photoconductivity and photorefractive characteristics of PMDA-DR19-based photoconducting nonlinear optical polymeric films with different compositions were studied using red and green lasers. Contributions of dopants and the host to the photoconductive and photorefractive properties are systematically discussed. The virgin nonlinear optical material PMDA-DR19 was neither photoconductive nor photorefractive in nature. However, it became photoconductive and photorefractive once the charge transport material was incorporated into the PMDA-DR19/PVB polymer film. Films containing more nonlinear optical chromophore exhibited higher diffraction efficiency. Response speed was further elevated when an additional charge generation material was doped in. Diffraction grating was observed under zero electric field and was confirmed due to a photorefractive effect by the two-beam coupling effect. In addition to composition modification, the laser light source was also an important factor in changing the PR response speed. The photorefractive response speed was tremendously improved when films were written and read by two different laser beams, either red/green lasers or green/red lasers. (C) 1997 Elsevier Science Ltd.
An exact analysis of an asymmetric polling system with mixed service discipline and general service order
(1997-12-01)
Hwang, LC
;
Chang, CJ
;
電信工程研究所
;
電信研究中心
;
Institute of Communications Engineering
This paper derives the exact mean waiting time fur an asymmetric polling system with general service order and mixed service discipline. The mixed sen ice discipline means that the service discipline of each stage (a turn in the service order sequence) for the same station can be gated or exhaustive. The general service order denotes that each station can be polled more than once in a polling cycle. We use the mean age and the mean excess of a cumulative time to obtain the mean waiting times fur stages and stations, where the cumulative time for a stage is defined as the total arrival time period of all customers that are served at one visit of the server to the stage. The accuracy of our analysis is verified by comparisons with previously published results and simulation results. We also use a genetic algorithm (GA) to search for an optimal pattern of service order and service discipline For the asymmetrical polling system. The results of the paper can be applied to the design of computer communication networks with polling schemes. (C) 1997 Elsevier Science B.V.
Design of a power-spectrum-based ATM connection admission controller for multimedia communications
(1998-02-01)
Chang, CJ
;
Lin, CH
;
Guan, DS
;
Cheng, RG
;
電信工程研究所
This paper proposes a power-spectrum-based connection admission controller design in asynchronous transfer mode (ATM) switches for multimedia communications, The controller contains a power-spectrum-indexed table for managing multimedia call requests, where traffic characteristics of call requests are described by the power spectrum, The power spectrum can be obtained from the claimed traffic parameters of peak rate, mean rate, and peak rate duration; the pow er spectrum has been shown to have a dominant effect on system performance, The results show that the proposed power-spectrum-based connection admission control method achieves higher system utilization and lower call-blocking probability than the equivalent-capacity allocation method.
Design of power control mechanisms with PCM realization for the uplink of a DS-CDMA cellular mobile radio system
(1996-08-01)
Chang, CJ
;
Lee, JH
;
Ren, FC
;
電信工程研究所
;
電信研究中心
Power control (PC) is an important issue in a direct sequence-code division multiple access (DS-CDMA) cellular mobile radio system. Higher link performance and greater system capacity cannot be achieved unless an appropriate PC mechanism is employed. In previous research, a delta-modulation (DM) realization of strength-based and SIR-based PC mechanisms for uplink communication has been studied by simulation. In order to obtain higher PC trackability, in this paper we study a pulse-code-modulation (PCM) realization of the above two PC mechanisms for the uplink of a DS-CDMA cellular mobile radio system. The simulation results presented here indicate that PC mechanisms with PCM realization for the uplink can achieve a lower outage probability and thus higher link performance than PC mechanisms with DM realization. We also obtain optimal design parameters such as the stepsize and the control mode for the two PCM PC mechanisms. In addition, we compare the two PCM PC mechanisms in terms of their outage probability and stability and find that the strength-based mechanism has a higher outage probability but greater stability than the SIR-based mechanism.
A variable partition duplex scheme with enlarged reservation duration on packet reservation multiple access protocol
(1999-05-01)
Chang, C
;
Chang, CJ
;
電信工程研究所
;
Institute of Communications Engineering
A variable partition duplex scheme on packet reservation multiple access protocol (VPD-PRMA) is analyzed in this paper. We assume a four-state speech model for a conversational pair and successfully obtain performance measures by approximate Markovian analysis. Analytical results show that they quite fit simulation results; and VPD-PRMA can get higher statistical multiplexing gain than fixed partition duplex (FPD)-PRMA, due to the trunking effect. We further investigate the effect of design parameters of permission probability and enlarged reservation duration on system performance by computer simulation. Simulation results shows that it exists appropriate values for these two design parameters so that the packet dropping probability can be minimized. The adjustment of permission probability can greatly improve the performance of uplink traffic with slight deterioration of the performance of downlink traffic; the provision of enlarged reservation duration scheme can enhance the system performance.
Analysis of buffer requirement for ATM-LSRs with partial VC-merging capability
(2002-06-01)
Lin, PC
;
Chang, CJ
;
電信工程研究所
;
Institute of Communications Engineering
In an Multi-Protocol Label Switching (MPLS) network domain, Asynchronous Transfer Mode-Label Switch Routers (ATM-LSRs) are considered the best candidate for providing the highest forwarding capability. ATM-LSRs implement a VC-merging scheme that allows many IP routes to be mapped into the same VPI/VCI label, hence supporting scalability. The VC-merging requires reassembly buffers to reconstruct an original packet from its segmented but interleaved AAL-5 cells. In this paper, we analyze the performance of an ATM-LSR with partial VC-merging capability and investigate the impact of VC-merging on the requirement of the reassembly and output buffer. The numerical computation complexity of the mathematical analysis can be reduced from O(M-4) to O(M-2), where M is the total number of ON-OFF sources. We also propose a closed-form equation, which approximates the distribution of the output buffer with satisfactory accuracy. Numerical results show that when incoming cells are severely interleaved, the VC-merging needs the reassembly buffer size to be of the same order as the output buffer size, which cannot be ignored.
QoS-guaranteed fuzzy transmission controller for dynamic TDMA protocol in multimedia communication systems
(2002-10-01)
Ren, FC
;
Chang, CJ
;
Cheng, RG
;
電信工程研究所
;
Institute of Communications Engineering
The paper proposes a QoS-guaranteed fuzzy transmission controller (FTC) for the dynamic TDMA protocol in multimedia communication systems. The dynamic TDMA protocol adopts a mini-slot technique for reducing contention cost, and the mini-slots are further partitioned into multiple MAC regions that users can access with their respective quality-of-service (QoS) requirements. The FTC mainly contains a Sugeno self-tuning fuzzy MAC threshold controller and a fuzzy access controller. The former applies a position-gradient-type reasoning method to properly determine the MAC regions; the latter employs max-min inference fuzzy logic to determine the access probabilities of users for enhancing dynamic TDMA efficiency under the QoS constraint. Simulation results show that the dynamic TDMA protocol with FTC can always guarantee the QoS requirement of real-time packet loss probability, regardless of the non-real-time traffic loads. Furthermore, it achieves higher system utilisation and less non-real-time packet delay compared to previously proposed PRMA, IPRMA and FRMA protocols.

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