• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.28-38
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• 2013

In this paper, we propose a improved turbo equalizer which generates a feedback signal through a simple calculation to improve performance in single carrier system with the LMS(least mean square) algorithm based equalizer and LDPC(low density parity check) codes. LDPC codes can approach the Shannon limit performance closely. However, computational complexity of LDPC codes is greatly increased by increasing the repetition of the LDPC codes and using a long parity check matrix in harsh environments. Turbo equalization based on LDPC code is used for improvement of system performance. In this system, there is a disadvantage of very large amount of computation due to the increase of the repetition number. To less down the amount of this complicated calculation, The proposed improved turbo equalizer adjusts the adoptive equalizer after the soft decision and the LDPC code. Through the simulation results, it's confirmed that performance of improved turbo equalizer is close to the SISO-MMSE(soft input soft output minimum mean square error) turbo equalizer based on LDPC code with the smaller amount of calculation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12C
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• pp.1197-1207
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• 2009

Orthogonal Frequency Division Multiple Access (OFDMA) is widely used as a multiple access technique for next generation mobile communication systems, however, its main drawback is the high peak-to-average ratio (PAPR). Thus for the uplink case where the transmit power is strictly limited due to the battery life of mobile units, single carrier frequency division multiple access (SC-FDMA) with low PAPR is preferred to OFDMA method. In this paper, we propose a method to improve the performance of SC-FDMA using frequency domain MMSE equalization. The proposed improved log-likelihood ratio (LLR) generation method exploits both the diversity characteristic of channels and the reciprocity that is obtained from the received signals. The complexity of the proposed method is analyzed and its performance gain is demonstrated via a set of computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1C
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• pp.102-109
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• 2008

The higher data rate of mobile communications has been required for various multimedia services. In DS-CDMA system, one of the solutions to increase the throughput is to use multicode. However, multipath channel destorys the orthogonality of spreading codes, which causes the intercede interference(ICI). ICI gives severe effect on multicode DS-CDMA for BER performance. Conventionally, multicode DS-CDMA system uses the Rake receiver with turbo code, which cannot overcome error floor caused by ICI. In this paper, we propose frequency domain turbo equalization based on minimum mean squared error(FDTE-MMSE) for multicode DS-CDMA in frequency selective channel and evaluate its BER performance by computer simulation. The simulation results show that FDTE-MMSE gives much better performance in high Eb/N0 than the Rake receiver with turbo code in multipath length L>1.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.6
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• pp.23-28
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• 2009

In this paper, we proposed and analyzed the performance of the adaptive switching equalization for SC-FDMA system. It is well known that SC-FDMA system have a fairly similar structure to OFDMA system. Furthermore, SC-FDMA system has great advantage of low PAPR compare to OFDM system. However, this system often suffers from wireless channel characteristics such as multipath fading and increased channel impulse response and so on. To reduce this channel influence, it strongly requires efficient adaptive equalization. Therefore, the proposed system operated upon two modes namely, ZF mode for slow speed and MMSE mode for high speed. From the simulation results, we can confirm that the proposed scheme has more efficient performance from the system complexity point of view. So we can expect that the proposed system will be applied design of 3GPP LTE uplink.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.138-145
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• 2007

Wireless transmission system using the multipath channel is affected ISI due to the delay spread. So we use a decision feedback equalizer which consist of decision part and feedback filter for remove the ISI effectively. In this paper, we propose a improved adaptive decision feedback equalizer to mitigate ISI effectively. The proposed adaptive decision feedback equalizer is construct by using soft decision device and hierarchical feedback filter based on MMSE sub-optimal equalizer using the LMS algorithm. Soft decision device mitigate the error propagation in feedback filter by incorrectly detected decision symbol and feedback filter which is divided two step independently mitigate the ISI by using a adaptive algorithm. As a result this structure shows better performance than conventional decision feedback equalizer by mitigating the error propagation in filter cause incorrectly detecting symbol. and we get the MSE more rapidly by using larger step-size due to reduce the number of feedback filter tap. In computer simulation, we compare the bit error rate performance of proposed decision feedback equalizer with conventional one on the S-V channel model for UWB system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.830-837
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• 2005

ISI is caused by delay spread in the multipath channel environment. There are two kinds of channel equalizer: Linear and Non-Linear type according to the structures. In this paper, we propose an improved adaptive linear equalizer to mitigate ISI. The proposed adaptive equalizer is constructed by using asymmetrical Dsmvenu filter based on USE sub-optimal receiver. Asymmetrical structure of the transversal filter is realized by moving the main tap position from center to side. If this structure is used, we can divide ISI to precusor and postcusor. As a result the proposed equalizer has a larger extended compensation range than conventional adaptive linear equalizer. In computer simulation, we compare the bit error rate performance of the proposed linear equalizer with the conventional one on the S-V channel which is modeled for WB systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.1034-1041
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• 2007

In this paper, we propose a FD USE (frequency domain minimum mean square error) equalizer algorithm for MBOK DS-UWB (M-ary bi-orthogonal keying direct sequence UWB) systems considered as a PHY proposal for high-speed wireless communication in IEEE 802.15.TG3a. The conventional FD MMSE equalization scheme has a structural limit due to insertion of the cyclic prefix (CP) in all transmit packets, but the proposed scheme is able to equalize the channel effect without CP. In order to overcome channel estimation error by multipath delay, we introduce a moving FFT and a moving average scheme. Compared with conventional FD MMSE equalizer and the traditional TD (time domain) MMSE-RAKE receiver, the proposed FD MMSE equalizer has better BER performance and we demonstrate this result by computer simulation.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2014.06a
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• pp.250-253
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• 2014

방송 서비스를 안정적으로 제공하기 위해서는 가시청시간율을 안정적으로 확보하는 것이 중요하다. 이를 위해서는 수신단에서 ToV SNR 부근에서의 추가적인 margin을 확보하는 기술이 요구된다. 기존 방송 시스템은 안테나를 하나만 사용하는 수신 환경을 가정하고 있으므로, 본 논문에서는 하나의 안테나로부터 수신된 신호를 서로 다른 equalizer 기법 2가지를 동시에 적용하여 마치 2개의 수신 안테나부터 신호를 수신한 효과를 얻었고, 그 출력을 weight combining 하여 최종 SNR 이득을 높이는 기술을 제안하였다. 특히, equalizer 기법은 기존에 성능이 우수하다고 알려져 있는 MMSE-DFE 기술과 최근 큰 주목을 받고 있는 compressed Sensing 기반 sparse-DFE 기술을 동시에 사용하였다. Simulation을 통해서 MMSE-DFE 또는 sparse-DFE를 단독으로 사용하는 것보다 두 기법을 가중치 결합을 통해서 사용함으로써 가시청시간율이 크게 향상되는 것을 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.12
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• pp.864-869
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• 2014

In this paper, we propose an OFDM system with a pre-equalizer which pre-distorting a transmission signal to compensate for the degradation of the system by the intersymbol interference and multi-path fading at the high-speed multimedia communications. We model an OFDM system by using C language, a simulation was performed. As a result, there was a performance of BER is about 7dB at $10^{-3}$, improved to $10^{-4}$ on the MMSE property also $10^{-3}$.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.3
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• pp.1-7
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• 2013

We perform simulation. It is that LED panels is fixed and moving the terminal with PD in order to analyze the performance of visible-light wireless communication system based on MIMO under variety of the interference environment. And, based on the technology MIMO, we analyzed whether the interference caused by external light to give what effect changes in the quality of the communication channel. The distortion due to time delay in channel transmission must be compensated by using the equalizer. Especially, use of equalizer is need absolutely as data rate becomes high speed. Therefore, in this paper, the system VLC, were analyzed BER performance using channel equalization.