Browsing by Author "Lo, KR"

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A combined channel assignment mechanism for hierarchical cellular systems
(1998-09-01)
Lo, KR
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Chang, CJ
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Chang, C
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Shung, CB
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電子工程學系及電子研究所
This paper proposes a combined channel assignment (CCA) mechanism for hierarchical cellular systems with overlaying macrocells and overlaid microcells. The proposed CCA mechanism combines overflow, underflow, and reversible schemes, where new or handoff calls having no available channel to use in the overlaid microcell can overflow to use free channels in the overlaying macrocell, handoff calls from a neighboring macrocell can underflow to use free channels in the overlaid microcell, and handoff attempts from a macrocell-only region to an overlaid microcell can be reversed to use free channels in the microcell. We apply the CCA mechanism in two different hierarchical cellular systems of Strip type and Manhattan type and compare the CCA with the overflow channel assignment (OCA) scheme. Simulation results show that the CCA mechanism outperforms the OCA scheme by once in forced termination probability, by several times in new call blocking probability, and by 4.7% in system utilization for a hierarchical cellular system, and the CCA mechanism is more suitable for the Manhattan type than for the Strip type. (C) 1998 Elsevier Science B.V.
A hierarchical cellular system with reneging and dropping for waiting new and handoff calls
(1997)
Chang, C
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Chang, CJ
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Lo, KR
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交大名義發表
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電信工程研究所
In this paper, we analyze a hierarchical cellular system with overflow scheme and finite queues for new and handoff calls. The effect of guard channel scheme and the effects due to reneging of waiting new calls because of the caller's impatience and dropping of queued handoff call as the callers move out of the handoff area are considered. We successfully solve the system by adopting the multi-dimensional Markovian chain and use the transition-probability matrix and the signal-how graph to obtain the average new-call blocking probability, the forced termination probability, and the average waiting time of queued new and handoff calls. We further investigate how the guard channel scheme and buffer provision scheme affect the hierarchical cellular system. The results show that it seems unnecessary to provide guard channel and waiting buffer for microcells in the hierarchical cellular system with over flow mechanism.
A neural fuzzy resource manager for hierarchical cellular systems supporting multimedia services
(2003-09-01)
Lo, KR
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Chang, CJ
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Shung, CB
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交大名義發表
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National Chiao Tung University
Using intelligent techniques to perform radio resource management is an effective method. This paper proposes neural fuzzy control for radio resource management in hierarchical cellular systems supporting multimedia services. A neural fuzzy resource manager (NFRM) is designed, which mainly contains a neural fuzzy channel allocation processor (NFCAP), and NFCAP is in a two-layer architecture: a fuzzy cell selector (FCS) in the first layer and a neural fuzzy call-admission and rate controller (NFCRC) in the second layer. The FCS chooses not only the handoff failure. probabilities and the resource availabilities in both microcell and macrocell but also the mobility of user as input linguistic variables. The NFCRC takes the handoff failure probability and the resource availability of the selected cell as input variables to perform call admission control and rate control for the call. Simulation results show that NFRM can always gruarantee the quality of service (QoS) requirement of handoff failure probability for all traffic loads. Also, NFRM improves the system. utilization by 31.1% while increasing the handoff rate by 2% over the overflow channel allocation (OCA) scheme [3]; it enhances the system utilization by 6.3% and 1.4%, and still reduces the handoff rate by 14.9% and 6.8%, as compared to the combined channel allocation (CCA) scheme [201, [21] and fuzzy channel allocation control (FCAC) scheme [9], respectively, under a predefined QoS constraint.
A QoS-guaranteed fuzzy channel allocation controller for hierarchical cellular systems
(2000-09-01)
Lo, KR
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Chang, CJ
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Chang, C
;
Shung, CB
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電信工程研究所
This paper proposes a fuzzy channel allocation controller (FCAC) for hierarchical cellular systems. The FCAC mainly contains a fuzzy channel allocation processor (FCAP) which is designed to be in a two-layer architecture that consists of a fuzzy admission threshold estimator in the first layer and a fuzzy channel allocator in the second layer. The FCAP chooses the handoff failure probability, defined as quality-of-service (QoS) index, and the resource availability as input linguistic variables for the fuzzy admission threshold estimator, where the Sugeno's position gradient-type reasoning method is applied to adaptively adjust the admission threshold for the fuzzy channel allocator. And the FCAP takes the mobility of user, the channel utilization, and the resource availability as input variables for the fuzzy channel allocator so that the channel allocation is finally determined, further based upon the admission threshold. Simulation results show that FCAC can always guarantee the QoS requirement of handoff failure probability for all traffic loads, Also it improves the system utilization by 31.2% while it increases the handoff rate by 12.9% over the overflow channel allocation (OCA) scheme [7]; it enhances the system utilization by 6% and still reduces the handoff rate by 6.7% as compared to the combined channel allocation (CCA) scheme [10], under a defined QoS constraint.
Analysis of a hierarchical cellular system with reneging and dropping for waiting new and handoff calls
(1999-07-01)
Chang, C
;
Chang, CJ
;
Lo, KR
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電信工程研究所
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Institute of Communications Engineering
In this paper, we analyze a hierarchical cellular system with finite queues for new and handoff calls. Both the effect of the reneging of waiting new calls because of the callers' impatience and the effect of the dropping of queued handoff calls as the callers move out of the handoff area are considered, besides the effect of guard channel scheme. We successfully solve the system by adopting the multidimensional Markovian chain and using the transition-probability matrix and the signal-flow graph to obtain the average new-call blocking probability, the forced termination probability, and the average waiting time of queued new and handoff caps. We further investigate how the design parameters of buffer sizes and guard channel numbers in macrocell and microcells affect the performance of the hierarchical cellular system. The results show that provision of buffering scheme and guard channel scheme can effectively reduce the new-call blocking probability and the forced termination probability in the hierarchical cellular system, and the effectiveness is more significant in the macrocell than in the microcells.