• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.4
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• pp.53-63
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• 2008

Reader collision may occur when neighboring RFID readers use the same channel at the same time. Especially when the readers are operated in dense mode, even though many channels are available, because of frequent reader collisions we can not guarantee the performance of RFID readers. Conventional solutions such as FH(Frequency Hopping) or LBT(Listen Before Talk) are not effective in this situation because they can not schedule RFID readers effectively when RFID readers are operated in multi-channel, dense reader mode, In this paper, we propose a new RFID reader anti-collision algorithm which employs LBT, random backoff before channel access, and probabilistic channel hopping at the same time. While LBT and Random backoff before channel access reduces collisions between competing readers, probabilistic channel hopping increases channel utilization by adaptively changing the hopping probability by reflecting the reader density and utilization. Simulation results shows that our algorithm outperforms conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.277-285
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• 2008

We previously proposed an Orthogonal Code Hopping Multiplexing (OCHM) scheme for statistical multiplexing on a synchronous downlink. OCHM enables a large number of users to share a limited number of code channels through statistical multiplexing. We here improve the performance of OCHM by prioritizing encoded symbols according to their importance using both the conventional code division and the previously proposed code hopping multiplexing schemes. Prioritization is useful for channel coding schemes with different levels of importance for encoded symbols such as turbo-codes. Scheme performance is evaluated by simulation in terms of the required Eb/N0 for a 1% block error rate.

• Journal of IKEEE
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• v.16 no.1
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• pp.51-55
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• 2012

In this paper, we propose to employ a ternary sequence as a cyclic code shift keying (CCSK) modulation sequence. And we simulate the performance in a frequency hopping spread spectrum/time division multiple access (FHSS/TDMA) system with CCSK. Wireless channel is modeled as Rayleigh fading channel. From the simulation results, it is demonstrated that the system adopting the ternary sequence as a CCSK sequence has higher performance than that with a random sequence.

• The KIPS Transactions:PartC
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• v.9C no.6
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• pp.857-864
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• 2002

Channel coding is one of the most important things to improve digital communications. In this paper, we analyze the performance of turbo code with block interleaver using hopping algorithm (i. e., non-linear interleaver) for high speed multi-media service. The input and output of conventional block interleaver is achieved by the order of column and row, but hoping algorithm is achieved by hopping the column and row that increase the minimum distance and average distance between the nearest data dually. To verify and compare the performance of an proposed method the computer simulation have been performed using turbo code in gaussian channel environment.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.253-256
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• 2008

In this paper, we analyze the performance of RAKE receiver for impulse radio-ultra wide band (IR-UWB) systems in indoor multipath radio channel. Pulse position modulation-time hopping (PPM-TH) signal is considered. And we also consider three types of RAKE receivers, which are ideal RAKE, selective RAKE, and partial RAKE receivers. The indoor channel is modeled as the modified Saleh and Valenzuela (SV) model which has been proposed as a UWB channel model by the IEEE group, IEEE 802.15.SG3a.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.429-432
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• 2008

In this paper, performance of a double binary turbo coded ultra wide band (UWB) system is analyzed and simulated in an indoor wireless channel. Binary pulse position modulation-time hopping (BPPM-TH) signals are considered. The indoor wireless channel is modeled as a modified Saleh and Valenzuela (SV) channel. The performance is evaluated in terms of bit error probability (BER). From the simulation results, it is seen that double binary turbo coding offers considerable coding gain with reasonable encoding complexity. It is also demonstrated that the performance of the UWB system can be substantially improved by increasing the number of iterations.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.39-42
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• 2008

In this paper, we analyze the performance of ultra wide band (UWB) systems in indoor wireless channel in accordance with the number of pulses per bit at transmit signals and the decision types of receiver. The indoor channel is modeled as the modified Saleh and Valenzuela (SV) model which has been proposed as a UWB channel model by the IEEE group, IEEE 802.15.SG3a. Two types of UWB signals are considered One is the pulse position modulation-time hopping (PPM-TH) signal. And the other is the pulse amplitude modulation-direct sequence (PAM-DS) signal. It is assumed that the receiver is an ideal receiver which can receive all signals of the multipath.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.577-578
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• 2018

In this paper, we evaluate the throughput performance of IEEE 802.15.4 Time Slotted Channel Hopping (TSCH) tree network using Contiki-NG operating system. We build a virtual simulation environment to compare the throughput performance of various IEEE 802.15.4 TSCH networks according to the changes in the number of nodes and the hop counts. The simulation results show that the throughput increases as the number of nodes increase while it decreases as the hop counts increase.

• Journal of Internet Computing and Services
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• v.12 no.4
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• pp.45-50
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• 2011

In this paper, the encoding time delay of FH/TDD(Frequency Hopping/Time Division Duplex) based Motion JPEG image compression CODEC is analyzed for radio video transmissions of multi-camera systems in a vehicle. And, Synchronized connection of minimum channel collision is designed with synchronized shift and access according to channel status for Motion JPEG based FH/TDD multiple access.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.197-200
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• 2001

Recently, Switching time is the principal factor in a design of frerquency synthesizer for Spread-Spectrum Communications. fast switching frequency synthesizer is important to improve the channel efficiency in a Frequency Hopping Spread Spectrum (FH-SS) tranceiver. In this paper, we design the frequency synthesizer with fast switching time as fast as 1${\mu}\textrm{s}$. In frequency synthesizer design, we use the interpolated PLL method inserted memory Look-up table of DDS to reduce switching time, and have result of improved channel efficiency about 20% by applying to FH-SS Transceiver.