• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10A
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• pp.987-996
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• 2008

In this paper, the conventional anti-collision algorithms, such as Channel Monitoring algorithm and Pulse Protocol algorithm are analyzed. To decrease tag identification time, and increase system throughput and efficiency, we propose a new reader anti-collision algorithm, Pulse Protocol-based Hybrid Reader Anti-collision Algorithm, using Slot-occupied Probability under dense reader environment. The proposed algorithm uses Slot-occupied Probability to improve the performance of Pulse Protocol Algorithm. That is, A reader checks Slot-occupied Probability after generating random backoff time. If Slot-occupied Probability is greater than 0, it uses another new random backoff time to avoid reader collision. We also compare the performance of the proposed algorithm with those of Channel Monitoring and Pulse Protocol algorithms in respect of identification time system throughput, and system efficiency. Simulation results show that the proposed algorithm has an increment of 5% of identification time and system throughput as increasing the number of readers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1088-1094
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• 2002

A channel flow with a high Reynolds number but coarse grids is numerically studied to investigate the prediction possibility of its turbulence which is three-dimensional and time-dependent. In the present paper, a Reynolds-Averaged Navier-Stokes (RANS) model, a Large Eddy Simulation (LES) and a Navier-Stokes equation with no model are tested with a new approach of hybrid RANS/LES, which reduces to RANS model in the boundary layers and at separation, and to Smagorinsky-like LES downstream of separation, and then compared with each other. It is found that the simulations of hybrid RANS/LES method sustain turbulence like those of LES and with no model, and the results are stable and fairly accurate. This indicates strongly that gradual improvements could lead to a simple, stable, and accurate approach to predict turbulence phenomena of wall-bounded flow.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.1
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• pp.9-15
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• 1997

In this paper, the performance of a hybrid direct-sequence/slow-frequency-hoped (DS/SFH) spread-spectrum (SS) system with noncoherent DPSK modulation is considered. Th ebit error probability is derived ovef a rayleigh fading channel in the presence of multiple tone jamming. Numerical evaluations are presented for some combinations of system parameters. The performance of a hybrid DS/SFH SS system is shown to be inferior to that of a pure DS SS system at low jamming-to-signal power ratio (JSR). At high JSR, the performance of a pure DS SS system is shown to be the same as the worst case peformance of a hybrid DS/SFH SS system.

• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.213-218
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• 2006

In this paper, we analyzed the performance of orthogonal frequency division multiplexing/ frequency hopping multiple access(OFDM/FHMA) hybrid system that in impulsive interference and broadband wireless communication channel then we applied the turbo code scheme to make satisfied in data and voice transmission service. Also, we compared the bit error rate(BER) performance of turbo coded diversity scheme in the OFDM/FHMA hybrid system. As a result of simulation, proposed OFDM/FHMA hybrid system shows the enhancement of 10 times compared to the general OFDM/FHMA system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.1A
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• pp.91-103
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• 2005

In designing a video-on-demand (VoD) system, the major challenge may be how to reduce the channels concurrently used maintaining the client's waiting time. For this reason, the various architectures which integrate the multicast streams with the unicast streams were suggested in order to improve channel efficiency in recent years. In combining multicast with unicast, the ways to group the unicast channels together are important so that clients can share the multicast transmission channels. This paper proposes a hybrid video-on-demand system which gathers the unicast channels in new ways and shares multicast transmission channels efficiently by using dynamic channel allocation architecture. The numerical results demonstrate that the proposed architecture in some case achieves performance gain of $551{\%}$ compared to existing architecture. This paper presents procedure of channel release and reuse, performance analysis, and simulation results of the dynamic channel allocation architecture.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.2
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• pp.10-21
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• 1998

In this paper, we analyze the anynchrous cellular hybrid DS/FH spread spectrum system with diversity on nonselective Nakagami fading channel. Binary Psk scheme is considered and random spreading code sequences and random hopping patterns are used. We compare the performance of system using hard-limiting correlation receiver with diversity and linear corrleation receiver in Nakagami fading channel. We compute the average bit error probabilities with/without diversity according to spreading code sequence and the number of hop-ping frequencies under the same handwith espansion, and analyze near-far effect. The results show that hard-limiting correlation receiver with diversity gives a good performance over severe fading channel.

• Journal of Internet Computing and Services
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• v.10 no.4
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• pp.213-222
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• 2009

IEEE 802.15.3 HR-WPAN is designed to enable wireless connectivity of high-speed, low-power, low-cost multimedia-capable portable consumer electronic devices. For quality of service, the standard specifies the use of TDMA (Time Division Multiple Access). However, during low contention TDMA gives much lower channel utilization and higher delays than CSMA (Carrier Sensing Multiple Access) because in TDMA, a node can transmit only during its scheduled time slots whereas in CSMA, nodes can transmit at any time as long as there is no contention. By mixing CSMA and TDMA, Hybrid MAC becomes more robust to timing failures, time-varying channel conditions, slot assignment failures and topology changes than a stand-alone TDMA.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.586-591
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• 2015

This study discusses numerically-explored thermal performances of hybrid fin heat sinks (HF HSs) for lightweight thermal management of LED modules under natural convection. A hollow hybrid fin heat sink (HHF HS) and a solid hybrid fin heat sink (SHF HS) are proposed as HF HSs. A 3-D CFD analysis has been carefully conducted to obtain reliable numerical results. The 3-D CFD study investigates the effects of both fin spacing and an internal channel diameter on performances of the HHF HS and the SHF HS. The study results show that the mass-based thermal resistance of the HHF HS is 20~32% smaller compared with the pin fin heat sink (PF HS). The results also show that the mass-based thermal resistance of the HHF HS decreases with the increase of the channel diameter. These results are mainly due to coupled effects of the mass reduction and heat pumping through an internal channel. Considerably superior mass-based thermal performances of the HHF HS to the conventional PF HS suggest the feasible application for the lightweight thermal management of the LED modules under natural convection.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.687-708
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• 2017

The machine-to-machine (M2M) communication is featured by tremendous number of devices, small data transmission, and large uplink to downlink traffic ratio. The massive access requests generated by M2M devices would result in the current medium access control (MAC) protocol in LTE/LTE-A networks suffering from physical random access channel (PRACH) overload, high signaling overhead, and resource underutilization. As such, fairness should be carefully considered when M2M traffic coexists with human-to-human (H2H) traffic. To tackle these problems, we propose an adaptive Slotted ALOHA (S-ALOHA) and time division multiple access (TDMA) hybrid protocol. In particular, the proposed hybrid protocol divides the reserved uplink resource blocks (RBs) in a transmission cycle into the S-ALOHA part for M2M traffic with small-size packets and the TDMA part for H2H traffic with large-size packets. Adaptive resource allocation and access class barring (ACB) are exploited and optimized to maximize the channel utility with fairness constraint. Moreover, an upper performance bound for the proposed hybrid protocol is provided by performing the system equilibrium analysis. Simulation results demonstrate that, compared with pure S-ALOHA and pure TDMA protocol under a target fairness constraint of 0.9, our proposed hybrid protocol can improve the capacity by at least 9.44% when ${\lambda}_1:{\lambda}_2=1:1$and by at least 20.53% when ${\lambda}_1:{\lambda}_2=10:1$, where ${\lambda}_1,{\lambda}_2$ are traffic arrival rates of M2M and H2H traffic, respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.5
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• pp.239-247
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• 2013

In network based on multi-interface, there are needed channel assignment strategy that reduce interference and improve bandwidth efficiency by assigning each interface to available channels in order to utilize effectively multiple wireless interfaces on each node. MCS protocol had been proposed, which improve capacity and throughput of network by using hybrid assignment. MCS uses as the criterion to assign channel the number of node that use the same channel in contention area. but there have an problem that this information exactly does not reflect actually offered channel load. in this paper, we proposes CAMCS protocol to assign channel by that the channel busy degree to indicate the occupancy rate of channel by nodes as well as the number of nodes that use the same channel in inference area is used as criterion for estimation channel load, and conform performance improvement effect by simulation.