• Journal of Broadcast Engineering
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• v.21 no.4
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• pp.552-561
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• 2016

In OFDM system, frequency-domain sub-carriers of a symbol generally consist of data sub-carriers and scattered pilot sub-carriers and in the receiver, channel is estimated through time-axis interpolating pilot sub-carriers of several OFDM symbols. However, time-axis interpolation fails to keep track of rapid channel variation caused by fast moving receiver. Although symbol by symbol channel estimation without time-axis interpolation enables fast estimation, the performance is severely degraded for a long delay spread channel in a single frequency networks (SFNs) because of insufficient pilot sub-carriers. In this paper, a channel estimation scheme for OFDM receiver in a fast mobile SFN channel is proposed. The proposed scheme is applied to DVB-T receiver to improve the Doppler mobile performance in SFN channel.

• Journal of Broadcast Engineering
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• v.10 no.2
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• pp.174-181
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• 2005

In this paper, we proposed new fast scattered pilot synchronization techniques to reduce the burst synchronization time for the DVB-H receiving system with robustness. DVB-H terminals employ a TDM system called 'Time-Slicing' to reduce power consumption. In order to fully exploit the potential power reduction, the synchronization time for the DVB-H receiver must be very short. A typical DVB-T system uses the TPS Synchronization to determine the position of scattered pilots which are used for channel estimation, and it takes 68 OFDM symbol time. In this paper, several new fast scattered pilot synchronization techniques are proposed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9A
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• pp.1265-1275
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• 1999

An adaptive MMSE detector can be used to cancel the MAI in CDMA system. But standard adaptive MMSE detector cannot be used in real mobile environment due to fast fading channel. Furthermore multipath reception make it more difficult to converge to optimum weight values. In this paper we discuss and model the multipath fading environment in Forward-link Synchronous CDMA channels and propose adaptive MMSE RAKE detector structure which can be applied in the mobile station. A proposed adaptive MMSE detector requires estimation of received signal delay and complex channel coefficients such as amplitude and phase variation. These burden can be solved by utilizing the common pilot channel. The pilot channel may have higher power than the traffic channel, which give more exact channel estimation. Moreover RAKE structure gives more accurate and stable result which can be used as reliable reference signal in multipath fading channel environment. With this structure, conventional adaptive algorithm such as LMS or NLMS can be applied in adaptive MMSE detector.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11A
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• pp.1081-1091
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• 2005

Unlike conventional DVB-T transmission with the streaming method, DVB-H system based on the IPDC(IP Data Casting) method uses Time-slicing scheme to achieve the maximization of portability by reducing the power consumption of a receiver. To enhance the power efficiency of the receiver, Time-slicing scheme controls the receiver operation to perform only for corresponding burst in specific time slot. The additional power saving can also be achieved by reducing the required time for synchronization. In this paper, we propose a fast scattered pilot synchronization algorithm, which detects the pilot pattern of currently received OFDM symbol. The proposed scheme is based on the correlation between the adjacent subcarriers of potential scattered pilot position in two consecutively received OFDM symbols. Therefore, it can reduce the time for the scattered pilot synchronization within two symbols as com-pared with the conventional method used for DVB-T. And the proposed algorithm has better performance than the two schemes proposed by Nokia for DVB-H and the method using correlation with reference signal. Extensive com-puter simulation is performed based on ETSI EN300 744 ETSI and performance results show that the proposed algorithm has more efficient and stable operation than the conventional schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.8
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• pp.981-987
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• 2019

In this paper, we propose a new SC-FDE (single carrier frequency domain equalization) structure to cope with narrow band interference signals or jammers and reduce pilot overhead. The conventional SC-FDE structure has a problem that the receiver performance degrades severely due to difficulty in time-domain channel estimation when narrow band jammers exist. In addition, the spectral efficiency is lowered by transmitting pilot at every SC-FDE block to estimate channel response. In order to overcome those problems, the proposed structure is devised to estimate frequency domain channel directly without time domain channel estimation. To reduce the pilot overhead, several data blocks are transmitted between two pilots. The channel estimate of each data block is found through linear interpolation of two channel estimates at two pilots. By performing frequency domain channel equalization using this channel estimate, the distortion by the channel is well compensated when narrow band jammers exist. The performance of the proposed structure is confirmed by computer simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.123-131
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• 2007

This paper developed a FIR-Rake receiver which makes use of a pilot signal broadcast by the TD-SCDMA (division-synchronous code division multiple access) base station to estimate the channel parameters. The FIR-Rake receiver can reduce multipath interference for the mobile stations. The analysis in frequency and discrete domain and computer simulations confirm that the proposed FIR-Rake receiver achieves a better performance under typical multipath fading propagation conditions.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2006.11a
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• pp.191-195
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• 2006

국내와 북미 지역에서 ATSC DTV 방송 서비스가 시작된 이래 수신 성능을 개선하기 위한 계속적인 노력이 경주되어 왔다 [1]-[6]. 본 논문에서는 2005 년 8 월 캐나다 CRC (Communications Research Center) 센터의 테스트 결과를 토대로 최신 ATSC 수신기의 성능을 고찰해 보고자 한다 [4]. CRC 테스트는 수신 감도, 다중 경로 환경에서의 수신 성능, 간섭 신호에 대한 강건성 등 다양한 항목에 걸려 실시되었으며, A/74 권고안에 기술된 난시청 지역의 50 개 신호 샘플에 대한 성능 평가를 포함하고 있다. 테스트에 사용된 ATSC 수신기는 당사에서 개발한 최신 칩 (GEMINI)을 탑재한 것으로 파일럿 (pilot) 신호가 손상된 경우에도 안정적인 동기 획득이 가능하며 현존 수신기 중 가장 넓고 강력한 반사파 (ghost) 제거 성능을 보유하고 있다. CRC 테스트 결과와 국내외 필드테스트 결과는 최신 ATSC 수신기가 A/74 권고안뿐만 아니라 각종 성능 지표에서 이전 수신기에 비해 대폭 개선되었음을 확인시켜 준다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.660-666
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• 2004

Transmitted data may be compensated by using estimated channel values that are obtained with pilot symbols in OFDM-CDMA systems. Generally, a USE (Minimum Mean-Squared Error) estimator using correlations between pilot symbols gives good results, but its structure is so complicated. Starting with a modification of PA (Pilot-Aided) algorithm using pilot symbols and PADD (Pilot-Aided Decision-Directed) algorithm using both pilot and data symbols, a new channel estimation algorithm with more simpler structure is proposed. The performance of this algorithm is evaluated with varying mobile speed in a Ralyleigh multipath fading environment through computer simulations. The simulation results show that the proposed channel estimation algorithm outperforms a conventional PA algorithm.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2006.11a
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• pp.153-156
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• 2006

본 논문에서는 T-DMB 수신기의 채널추정 성능향상을 위한 잡음감소 기법을 제안한다. 일반적으로 T-DMB 수신기에서의 채널추정은 파일럿 신호 추출과 채널계수 추정에 의해 수행된다. 채널추정의 성능은 수신 SNR (Signal to Noise Ratio)과 연관되어 추정된 채널계수에 남아있는 잡음성분에 의해 결정되기 때문에, 잔존하는 잡음성분을 감소시키는 것은 매우 중요하다. 이러한 잡음성분을 감소시키기 위해, M-point 가중이동평균(weighted moving average)을 기반으로 한 잡음제거 기법을 제안한다. 전산 실험에 의하면, 제안된 방법은 등화 후 SER (Symbol Error Rate) 측면에서 기존의 방법에 비해 2-3 dB의 성능 향상을 보인다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.8-15
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• 2006

In this paper, we propose the iterative receiver for LDPC-coded OFDMA systems in uplink environments. Applying the Wiener filtering to pilot symbols, an initial channel estimation can be performed effectively. To reduce the complexity of the Wiener filtering, we approximate Wiener filtering coefficients to pre-determined coefficients according to estimated correlation of channel. After an LDPC decoding process, soft symbol derived by extrinsic information of decoder outputs is used to estimate channel. we also derive the error variance of channel estimation and maximum ratio combined results. Using combined results, the channel correlation is re-estimated. Then the proper Wiener filtering coefficients are chosen according to the re-estimated result of the channel correction. Using a computer simulation, we show that the proposed receiver structure has the better performance than the receiver using only pilot symbols.