• Journal of Broadcast Engineering
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• 제13권5호
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• pp.565-573
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• 2008

This paper proposes noise reduction methods to improve the channel estimation performance in Equalization On-Channel Repeater (E-OCR) for Terrestrial-Digital Multimedia Broadcasting (T-DMB) system. In the E-OCR for T-DMB system, the channel estimation is performed by the pilot signal extraction and the channel coefficient estimation. Since the performance of the channel estimation highly depends on the estimated channel coefficients whose accuracy is associated with the received signal-to-noise ratio (SNR), it is important to reduce noise existing at the estimated channel coefficients. To reduce such noise components, various noise reduction methods of the estimated channel coefficients based on the M -point weighted moving average are proposed. Computer simulations show that the proposed methods improve the estimation performance by more than 2 to 3 dB in terms of the symbol error rate after equalization.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제43권11호
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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.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제43권6호
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• pp.1-8
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• 2006

In the asynchrous OFCDM(Orthogonal Frequency and Code Division Multiplexing) system, a three-step cell search algorithm is performed for the initial synchronization in the following three steps: OFCDM symbol timing, i.e., Fast Fourier Transform(FFT) window timing is estimated employing guard interval (GI) correlation in the first step, then the frame timing and CSSC (Cell Specific Scrambling Code) group is detected by taking the correlation of the CPICH(Common Pilot Channel) based on the property yeilded by shifting the CSSC phase in the frequency domain. Finally, the CSSC phase within the group is identified in the third step. This paper proposes a modification code(PCSSCG:Patial Cell Specific Scrambling Code Group) of the conventional CPICH based cell search algorithm in the second step which offers MS(Mobile Station) complexity reductions with the nearly same performance. The proposed method is to be compared and verified through the computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제24권8A호
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• pp.1163-1168
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• 1999

This paper proposes a wireless positioning method using the CDMA mobile communicaton network. The proposed method is time-based positioning method that uses mobile-station arrival time of forward link signal from base-stations. In this mehtod there are TDOA and TOA methods that use time-difference-of-arrival and time-of-arrival, respectively. Error characteristics and implementation simplicity of the two methods are compared and analyzed each other. As a results, it showed that TDOA has advantage of less sensitivity to the time error compared to TOA but has disadantage of more sensitivity to the spatial error. Also, from architecture of the CDMA system that is time synchronized to only active base-station it is analyzed that adoption of TDOA method is more advantageous than TOA because time difference of signal arrival from the neighbor base-stations against the active base-station can be measured more easily. Therefore, conclusion is made that TDOA is beat suit to the time-based positioning method for the present CDMA mobile communication networkgorithm performs block-by-block coherent decoding with the aid of pilot symbols. It is shown that the complexity of the algorithm grows linearly as a function of sequence length. The performance of the algorithm is shown to better than that of the conventional pilot symbol aided (PSI) algorithm. Simulation results are presented to assess the performance of the algorithm and the results are compared with that of the conventional PSI alforithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제28권12A호
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• pp.1009-1018
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• 2003

A new fading channel estimation technique is proposed for an OFDM based modem In the ITS system. The algorithm is based on the transfer function extraction of the channel using the pilot signals and compensated the channel preceding the equalization. The newly derived algorithm is division-free arithmetic operations allows the faster circuit operation and the smaller circuit size. Proposed techniques compensate firstly the distortion which is generated at fading channels and secondly eliminate inter-symbol interference. All algorithms are suitability estimated and improved for a system implementation using digital circuits. As the results, the circuit size is reduced by 20% of the conventional design and achieved about 10% performance improvement at low SNR under 10dB in case of ITS system adapted 16-QAM mode.

• Journal of Broadcast Engineering
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• 제24권6호
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• pp.1143-1151
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• 2019

In this paper, we propose a wireless transmission scheme that maximizes transmission efficiency per frequency bandwidth in a single carrier modulation scheme. The proposed scheme employs a decision directed channel tracking technique to remove both pilot signal and the guard interval signal between symbols in frames. It performs a raised cosine pulse shaping function with an roll-off factor of 0.05. In addition, 2×2 multiple input and multiple output using two polarized antennas is applied and both equalization and signal separation are performed in the frequency domain. The wireless modem with this technology confirms that the transmission speed of up to 63.3Mbps is achieved under the 5MHz frequency bandwidth

• Journal of the Korea Institute of Information and Communication Engineering
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• 제11권1호
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• pp.139-149
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• 2007

Asynchronous OFCDM(Orthogonal Frequency and Code Division Multiplexing) systems must have a cell search process necessarily unlike synch개nous systems. this process is hewn initial synchronization and a three-step cell search algorithm is performed for the initial synchronization in the following three steps: OFCDM symbol timing, i.e., Fast Fourier Transform(FFT) window timing is estimated employing guard interval (GI) correlation in the first step, then the frame timing and CSSC(Cell Specific Scrambling Code) group is detected by taking the correlation of the CPICH(Common Pilot Channel) based on the property yielded by shifting the CSSC phase in the frequency domain. Finally, the CSSC phase within the group is identified in the third step. This paper proposes a modification group code with two or three block of the conventional CPICH based cell search algorithm in the second step which offers MS(Mobile Station) complexity reductions. however, the effect of the reduction complexity leads to degradation of the performance therefore, look for combination to have the most minimum degradation. the proposed block type group code with suitable combinations is the nearly sane performance as conventional group code and has a complexity reduction that is to be compared and verified through the computer simulation.

• Journal of Broadcast Engineering
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• 제14권3호
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• pp.357-365
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• 2009

In an OFDM system, the sampling frequency offset between the transmitter and receiver is known to cause the inter-channel interference (ICI), resulting in performance degradation. Sampling frequency offset can be generally estimated by correlation of the pilot signal within contiguous OFDM symbol. In this paper, we propose sampling frequency offset estimation schemes using various mixture of consecutive symbols. We conduct a simulation in DVB-T(2K mode) system, which shows that the proposed schemes can improve the performance of sampling frequency offset estimation by decreasing noise effect within consecutive symbols in AWGN channel model.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제4권5호
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• pp.1027-1035
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• 2000

In this paper, we have proposed the optimum technique for wireless ATM (WATM) error control in indoor environment. As the optimum technique, the conventional concatenated FEC only is regarded as the efficient error control method for time-critical ATM traffic in AWGN, and the pilot symbol-added fading compensation with the concatenated FEC is required to optimize the WATM performance in fading environment. Also, the truncated Type- H hybrid ARQ technique will be developed for quality-critical ATM traffic in order to improve its throughput. Therefore, this paper presents the optimization of WATM performance in indoor environment by means of evaluating above techniques using theoretical analysis and simulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제8권6호
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• pp.568-580
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• 1997

In this paper we evaluate the performances of two types of 16-QAM system such as square QAM and star QAM. First we analyze the performances of QAM systems under AWGN(adaptive white Gaussian noise) and afterward analyze the performances under fading environments. The performances of QAM systems in case of using the PSAM(Pilot Symbol Assisted Modulation) are finally evaluated under fading environments. In conclusion, the Square QAM's performance is better than star QAM in AWGN. But the performances of the both QAM systems are very poor under the fading environments. QAM performance using the PSAM system is verified to be improved in that case, and the star QAM's performance is better than square QAM.