Browsing by Author "Tsai, Hong-Cheng"

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An Analytical Approach to Coexisting Evaluation in Multi-RAT Heterogeneous Networks with Opportunistic CSMA/CA
(2016)
Tsai, Hong-Cheng
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Liu, Chun-Hung
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Wang, Li-Chun
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電機工程學系
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Department of Electrical and Computer Engineering
This paper proposes an analytical approach to modeling and analyzing the coexisting transmission performance in a multi-tier heterogeneous network with multiple radio access technologies (Multi-RATs). The coexistence issue is a special phenomenon uniquely existing in a multi-RAT network and it is rarely studied in prior works on heterogeneous wireless network. To simply characterize the coexisting transmission impacts in a multi-RAT network, in this paper we consider a three-tier heterogeneous network using the RATs of L and U, where RATL is adopted by the access points (APs) in the first two tiers, APs in the third tier only use RAT-U and the APs in the second tier can opportunistically use RAT-U. The opportunistic CSMA/CA protocol is used by the APs contending the RAT-U channel and the channel access probabilities for the RAT-U AP in two different tiers are derived under the proposed user association scheme with random weights. The coexisting coverages of RAT-L and RAT-U are defined and found, respectively. Numerical results show that the proposed modeling and analyzing approach can be well applied to evaluate the coexistence transmission performance while LTE and WiFi APs both access the unlicensed band.
On the Limits of Coexisting Coverage and Capacity in Multi-RAT Heterogeneous Networks
(2017-05-01)
Liu, Chun-Hung
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Tsai, Hong-Cheng
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資訊工程學系
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Department of Computer Science
This paper devises a general modeling and analyzing framework for a heterogeneous wireless network (HetNet) in which several wireless subnetworks coexist and use multiple radio access technologies (multi-RATs). The coexisting coverage and network capacity in such a multi-RAT HetNet are hardly investigated in prior works. To characterize the coexisting interactions in a multi-RAT HetNet, in this paper, we consider a HetNet consisting of K tiers of access points (APs) and two different RATs, RAT-L and RAT-U, are adopted in the HetNet. RAT-L is adopted by the APs in the first K-1 tiers and APs in the Kth tier only use RAT-U. Both noncrossing-RAT and crossing-RAT user association scenarios are considered. In each scenario, the void probability and the channel access probability of the APs in each tier are first found and then the tight lower bounds and their lowest limits on the proposed coexisting coverage and network capacity are derived. We show that multi-RAT networks in general can achieve higher link coverage and capacity by using opportunistic carrier sense multiple access with collision avoidance that avoids/alleviates severe interfering between all coexisting APs. Also, crossing-RAT user association is shown to achieve much higher coexisting coverage and network capacity than noncrossing-RAT user association. Finally, numerical simulations for the LTE-U and WiFi networks coexisting in the HetNet validate our findings.
Traffic Management for Heterogeneous Networks With Opportunistic Unlicensed Spectrum Sharing
(2017-09-01)
Liu, Chun-Hung
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Tsai, Hong-Cheng
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電信工程研究所
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Institute of Communications Engineering
This paper studies how to maximize the per-userbased throughput in an M-tier heterogeneous wireless network (HetNet) by optimally managing traffic flows among the access points (APs) in the HetNet. The APs in the first M - 1 tiers can use the licensed spectrum at the same time whereas they share the unlicensed spectrum with the APs in the Mth tier by the proposed opportunistic CSMA/CA protocol. We characterize the statistical property of the cell load and channel access probability of each AP using a general AP association scheme. For an AP in each tier, the tight bounds on its mean spectrum efficiencies in the licensed and unlicensed spectra are derived in a low-complexity form for general random channel gain and AP association weight models and they can give some insights on how channel gains, AP association weights and void AP probabilities affect the mean spectrum efficiencies. We define the per-user link throughput and per-user network throughput based on the derived the mean spectrum efficiencies and maximize them by proposing the decentralized and centralized traffic management schemes for the APs in the first M - 1 tiers under the constraint that the per-user link throughput of the tier-M APs must be above some minimum required value. Finally, a numerical example of coexisting LTE and Wi-Fi networks is provided to validate our derived results and findings.