• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4C
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• pp.200-206
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• 2005

Adaptive transmission techniques can improve the performance of wireless communication system by adaptively changing the transmission parameter such as modulation, code-rate, and power according to the channel state. For orthogonal frequency division multiplexing (OFDM) system, the adaptive transmission techniques can be applied to each subcarrier unit. In this paper, we consider the adaptive code-rate OFDM system in which optimal code-rate is applied to each subcarrier according to the subchannel state. Performance analysis show that $3\sim6$dB gain of SNR or up to $30\sim50\%$ increase of data rate are achieved in the condition of bit error rate $10^{-6}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.281-289
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• 2007

In this paper, a novel pseudo noise (PN) code acquisition scheme called the phase-shift-network-based differential sequential estimation (PDSE) is proposed, in the presence of data modulation in code division multiple access (CDMA) systems. The PDSE has even less complexity compared with that of the dual correlating sequential estimation (DCSE), and the reduction in complexity becomes more significant as the period of PN code increases. Numerical results demonstrate that the PDSE performs equivalently to the DCSE with less complexity.

• Journal of the Korea Society of Computer and Information
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• v.17 no.8
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• pp.51-60
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• 2012

I propose the 5Gbps/1.25Gbps WDM/TDM hybrid Passive Optical Network(PON) with inverse RZ(Return to Zero) code coded downstream and NRZ(Non Return to Zero) upstream re-modulation and analyze its performance by performing simulation with MATLAB. The results have shown that an optical line termination (OLT) can be connected to 8, 16 optical network unit (ONU)s with the Bit Error Rate(BER) of $10^{-9}$ when the distance between OLT and ONU is 10Km and transmitted optical powers are more than -3.8, -0.9dBm, respectively. The proposed WDM/TDM hybrid PON system can solve the problem of data rate limit in upstream which happened in the conventional TDM PON because the upstream data rate is proportional to ONU and does not require a light source in ONU and its control circuits in OLT, thus can be a useful technology for asymmetric optical subscriber networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11C
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• pp.1102-1110
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• 2007

In this paper, we design the FPGA (Field-Programmable Gate Array) of the CAMB (Constant-Amplitude Multi-code Biorthogonal) modulation, and implement the SoC (System on Chip). The ASIC (Application Specific Integrated Circuit) chip is be implemented through targeting and board test. This 12Mbps modem SoC includes the ARM (Advanced RISC Machine)7TDMI, 64Kbyte SRAM(Static Random Access Memory) and ADC (Analog to Digital Converter)/DAC (Digital to Analog Converter) for flexible applications. Additionally, the modem SoC can support the variable communication interfaces such as the 16-bits PCMCIA (Personal Computer Memory Card International Association), USB (Universal Serial Bus) 1.1, and 16C550 Compatible UART (Universal Asynchronous Receiver/Transmitter).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.9
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• pp.1047-1056
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• 2007

In this paper, we analyze the performance of the encoding and the modulation processes in the downlink and uplink of the EPCglobal Gen-2 system through the analysis and simulation. Furthermore, the synchronization issues on time and frequency domain and the preamble architecture are evaluated. By incorporating the encoding and the modulation technigue in the downlink and uplink, we assess the performance of the EPCglobal Gen-2 system. We also introduce the encoding and backscatter modulation process as well as the BER performance of FM0 code. In addition, the importance and the role of the frequency and time synchronization, such as the preamble and frame synchronization are explained. Through the simulation in the uplink on the detection probability through preamble, we find that the detection probability approaches 1 for 13 dB $E_b/N_0$.

• Journal of Korea Society of Industrial Information Systems
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• v.11 no.4
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• pp.112-120
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• 2006

Multicarrier code division multiple access(MC-CDMA) system that combines multicarrier modulation with CDMA offers robustness to frequency selective fading and can support higher rate data transmission with higher spectral efficiency. A new asynchronous MC-CDMA system to implement multiple data rate communications is proposed in this paper. In a W-CDMA downlink the orthogonal variable spreading factor(OVSF) code is used for variable spreading factor for various multimedia traffic. Proposed system utilizes the OVSF code that generated by generation property for spreading. The proposed MC-CDMA system use different lengths of OVSF code as a spreading code according to their data rate. The groupwise processing is accomplished by code grouping in OVSF code generation tree. For the analysis of average BER performance, numerical method and computer simulation were used. We also compare the system performance with that of a single rate MC-CDMA system used orthogonal code as a spreading code.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.69-75
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• 2010

Advanced T-DMB(Terrestial DMB )system which is a new portable mobile broadcasting system has been developed to increase data rate up to double of conventional T-DMB in same bandwidth while maintaining backward compatibility, using hierarchical modulation method. The Advanced T-DMB system realize high qualification of conventional T-DMB system by adding BPSK signal or QPSK signal as enhanced layer to existing DQPSK signal. The enhanced layer signal should be small enough to maintain backward compatibility and to minimize the coverage loss of existing T-DMB service area. But this causes the enhanced layer signal of Advanced T-DMB susceptible to fading effect in transmission channel. In this paper we applied the duo-binary turbo code which has powerful error correction capability to the enhanced layer signal for compensating channel distortion. And the computer simulation results about the performance of the duo-binary turbo code in Advanced T-DMB system are presented along with analysis comments.

• Journal of Internet Computing and Services
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• v.23 no.3
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• pp.1-12
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• 2022

As the performance of Unmanned Aerial Vehicles (UAVs) are improving and the prices are lowering, it is expected that the use of UAVs will continuously grow in the future. It is important to always maintain control signal and video communication to operate remote UAVs stably, especially in military UAV operations, as unexpected jamming attacks can result in fatal UAV crashes. In this paper, to improve the network reliability and low latency when supporting UAV operations, the anti-jamming performance of Second generation Anti-jam Tactical UHF Radio for NATO (SATURN) networks is analyzed and enhanced by applying Forward Error Correction (FEC) and Minimum Shift Keying (MSK) modulation as well as Hamming code based multiple transmission techniques.

• Journal of IKEEE
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• v.15 no.2
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• pp.171-178
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• 2011

In this paper, a novel pulse repetition interval (PRI) jittering coder based on quasi-random M-sequence codes is proposed for improvement of counter-countermeasure capability in a radar. Each of the proposed jittered 256 PRI codes has a unique code chip combination with 256 code chips, such that any set of three consequent code chips (4 pulses) from any code appears only once among the entire code chip sequences of the codes. This indicates that only 4 of received pulses are enough to determine uniquely the exact timing position of the incoming pulse train (or code chip sequence) required for counter-countermeasure, as well as the identity of the transmitted code. To prove the proposed idea experimentally, the jittered PRI coder is implemented and demonstrated.

• 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.