• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.3
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• pp.235-240
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• 2018

FTN method which transmits signals faster the Nyquist rate is representative method for improving throughput efficiency sacrificed performance due to inter-symbol interference. To compensate performance loss, in this paper, we propose a multiband FTN method which split the coded bits into several bands and transmits signals applying FTN method. As coded bits are being assigned different bands, number of samples per bit of each band is increased, it induced performance improvement by noise averaging effect. In the simulations, compared the performance of single band FTN method and multiband FTN method when the interference rate is 25%. The results of simulation show the performance of proposed method is better than that of single band FTN one by 0.3dB~0.5dB.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.1
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• pp.17-23
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• 2015

In this paper, we propose an efficient joint demodulation and decoding scheme for FTN (Faster than Nyquist) systems. Several previous works have demonstrated that ISI (Inter Symbol Interference) cancellation schemes based on BCJR (Bahl-Cocke-Jelinek-Raviv) algorithm are suitable for FTN systems. Unfortunately, required complexity of the previous ISI cancellation schemes is very high, especially when a multi-level modulation scheme is employed. In this paper, we propose a joint demodulation and decoding scheme for FTN systems with an iteratively decodable channel coding scheme and a multi-level modulation. Compared with the previously proposed schemes, the proposed scheme not only offers reliable performance but also requires relatively low complexity. Also, the proposed scheme can be easily applied to the FTN system with a multi-level modulation with a minor modification.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.392-399
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• 2014

The underwater acoustic communication is characterized by doubly spread channels, which are the delay spread due to multiple paths and the doppler spread due to environmental fluctuations or a moving platform. An equalizer is used to remove the inter-symbol interferences that the delay spread causes, but an equalizer doesn't use an acoustic environment such as a multipath. However, a passive time-reversal mirror is simpler than an equalizer because a matched filter is implemented numerically at the receiver structure along with one-way propagation. In this paper, a passive time-reversal mirror is applied to remove interferences due to a multipath in sea-going experimental data in East Sea in Oct. 2010 and improved communication performance is confirmed. The performance is verified by comparing the signal-to-interference plus noise ratio before/after passive time-reversal mirror. It is also performed independently of the passive time-reversal mirror and adaptive equalizer and the bit error rate is compared to verify the performance of underwater acoustic communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11A
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• pp.1820-1826
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• 2001

In this paper, we present a modeling scheme for the already-installed two-wire home phone lines with arbitrary topologies and show that the inter-symbol interference due to the topology can be removed using an adaptive equalizer. The transmission characteristics of the arbitrary-configured two-wire home phone lines can be analyzed through the ABCD matrices. The simulation result shows that the impedance mismatch due to the branch lines renders nulls in the frequency response or delayed pulses in the impulse response. These nulls or delayed pulses cause inter-symbol interference that inhibits correct signal detection. An adaptive equalizer is shown to be effective in eliminating the interference. Also, the simulation result shows that the equalizer converges in 1.5 ms at a data rate of 1 Msps at signal-to-noise ratios greater than 15 dB. In addition, from the result of relation between E$\_$b//N$\_$and BER(Bit Error Rate), we can see that E$\_$b//N$\_$o/ more than 19 dB is required for the data communication with a BER less than 10$\^$-5/.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.6
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• pp.1193-1199
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• 2015

Studies applying multiple carrier method such as OFDM(Orthogonal Frequency Division Multiplexing) or FMT(Filtered Multi-Tone) to Underwater acoustic communication(UAC) system are actively under way as UAC is utilized in the various fields and the demand of high speed data transmission increases. In the existing OFDM method, the use of virtual carrier, which is inserted not to affect the adjacent channel in the frequency domain, and the cyclic prefix, which is used to reduce the impact of Inter Symbol Interference and Inter Channel Interference, decrease the throughput. In particular, the length of cyclic prefix to be used becomes longer under water since underwater has a rapidly changing channel characteristic, and the data throughput diminishes because it has to allocate more subcarrier on virtual carrier. This study therefore suggests FMT-OFDM system, a combination of OFDM and FMT, for the purpose of enhanced throughput in the underwater channel environment. Besides, in this study, channel is modeled based on data measured in real sea and the performance is analyzed after setting system parameters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6A
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• pp.468-475
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• 2009

In OFDM-based Full Duplex Relays (FDR) with Decode and Forward (DF) scheme, an interference cancellation technique in the frequency domain is more efficient than the one in the time domain. However, an Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) may occur due to the timing mismatch between the feedback interference signal and the desired signal from Base Station (BS) when the feedback interference cancellation and demodulation are performed in the frequency domain. In this paper, the effects of timing mismatch on the synchronous type and asynchronous type of OFDM-based FDR are analyzed for uplink and downlink cases. Then, synchronization procedure and methods for reducing ISI and ICI in OFDM-based FDR with frequency-domain feedback interference canceller are proposed and verified by computer simulation.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.1
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• pp.1-6
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• 2021

In this paper, in order to mitigate ISI(inter-symbol interference) in a diffusion-based molecular communication channel, an ISI Hamming code is proposed in which ISI characteristics are applied to a channel decoding algorithm. In order to prove the bit error rate performance of the proposed channel code, the bit error rate performance of the major channel codes applied to the molecular communication channel with ISI was compared and analyzed through simulation. From the simulation results, it can be seen that the bit error rate performance of the ISI Hamming code is the best when the number of radiated molecules is less than or equal to 1100. In addition, when the number of transmitted molecules is M=1000, the decoding method of the ISI Hamming code proposed in this paper has improved the bit error rate of approximately 5.9×10-5 compared to the Hamming code using only soft values. Compared with the ISI-mitigating channel code, which is effective for removing ISI in the molecular communication channel, the ISI Hamming code proposed in this paper is the most advantageous in a channel environment where the number of transmitted molecules is not big (M<1100). And we can see that the ISI-mitigating channel code is more advantageous when the number of transmitted molecules is large(M>1100).

• Proceedings of the IEEK Conference
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• summer
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• pp.97-102
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• 2004

The very complicated proplem in spatial processing is effects of phading (Multipath and Delay Spread) and co-channel interference (CCI). The phading is one of principal causes, that form inter-symbol interference (ISI). Spatial-Temproral Adaptive Filter (STAF) has been taken as a solution of this problem, because it can suppress both these types of interference. But the performance of STAF exposes some elemental limitations, in which are the slow convergence of adaptive process and computational complexity. The cause of this is that, STAF must treat a large quantity of information in both space and time. The way that master these limitation is a use of Subband Spatial-Temproral Adaptive Filter (SSTAF). SSTAF reduce computational complexity by pruning off samples of signal and thus it lost some information in time. This draw on attennation of output SINR of SSTAF. The article analyse a optimal solution of this problem by introducing SSTAF with nonuniform weighted distribution.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.41-44
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• 2000

In this paper, an improved timing synchronization method for OFDM system is proposed. In multipath fading channels, timing offset estimation algorithm based on simple correlation metric can cause inter-symbol interference (ISI). The proposed algorithm promises accurate timing offset estimation, which can be achieved by simple windowing. The estimation errors in several multipath channels are evaluated in computer simulations.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.81-84
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• 2000

This paper has been studied the design of 16-QAM demodulator used in broadband wireless local loop subscriber station. In B-WLL systems, transmission signal experience the inter symbol interference(ISI) due to multipath, frequency offset of RF/IF local oscillator and phase offset. In this paper, we discuss the effective data recovery algorithm for 16-QAM demodulator to compensate the distorted signal from ISI, frequency offset and phase offset.