• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.682-688
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• 2006

In this paper, a soft-decision method for initial PN code acquisition in pilot-channel aided Direct Sequence Code Division Multiple Access (DS-CDMA) systems is proposed in order to improve the acquisition performance. We apply this technique to the conventional hybrid search algorithm and analyze it in terms of mean code acquisition time. For the analysis, we present mathematical model of proposed algorithm and also perform the simulation under IMT-2000 channel models. Numerical results show that our proposed scheme outperforms the conventional one by 0.2 - 0.4 sec with respect to the mean code acquisition time because the soft decision technique can mitigate the possible decline in search performance caused by the use of a hard-decision technique.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.293-300
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• 2015

Recently, multiuser diversity(MUD) technique is used to improve the performance of OFDM transmission systems. With STBC antenna diversity technique, the performance of OFDM systems can be also improved. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of MUD STBC OFDM systems using pilot symbol, gauged by the bit error rate, is analyzed considering the channel estimation error. Result shows that MUD can improve the required power by a factor of approximately 5 dB for users number 32.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.21-24
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• 2000

In this paper, We introduce effective handoff method from W-COMA system of 3$^{rd}$ generation to 15-95 system of 2$^{nd}$ generation. In case of this handoff, Ms should know long code state using traffic channel, timing information and pilot offset of 26 synchronous system during the compressed mode. So We establish additional common channel in order to obtain handoff information. Common channel transmits same information from all base stations and provides MS with timing information of zero offset. long code state and timing of super frame for sync. channel. Therefore during the compressed mode. MS can obtain information for handoff using common channel..

• Journal of Communications and Networks
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• v.5 no.2
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• pp.167-173
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• 2003

We treat the problem of channel estimation and interference cancellation in multiuser ultra-wide-band (UWB) communication systems over multipath fading channels. The UWB system under consideration employs a random time-hopping impulse radio format. We develop a channel estimation method based on linear weighted algorithm. An iterative channel estimation and interference cancellation scheme is proposed to successively improve the receiver performance. We also consider systems employing multiple transmit and/or receive antennas. For systems with multiple receive antennas, we develop a diversity receiver for the wellseparated antennas. For systems with multiple transmit antennas, we propose to make use of Alamouti’s space-time transmission scheme, and develop the corresponding channel estimation and interference cancellation receiver techniques. Simulation results are provided to demonstrate the performance of various UWB receiver techniques developed in this paper.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10A
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• pp.941-948
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• 2008

In this paper, the effect of unobtainable channel frequency response (CFR) inside virtual subcarreiers on DFT-based channel estimation is derived and introduced numerically because the CFRs cause the leakage to the estimated channel and degrade the estimation performance. In addition, the performance of DFT-based channel estimation is analyzed with respect to the number of virtual subcarriers, pilot spacing and the number of unobtainable CFRs at equi-distance subcarriers inside virtual subcarriers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.1
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• pp.44-53
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• 1999

In this paper, we propose a pilot based time-averaging channel estimation method and analyze error performances for efficient transmission of OFDM(Orthogonal Frequency Division Multiplexing) in multipath fading environment. Frequency domain channel estimations have been used in OFDM systems to compensate signal distortions due to fading on each subcarrier. The frequency domain estimation scheme uses scattered pilot to estimate channel response by simple interpolation. This implies that the estimated channel response includes signal distortions due to the noise. In this paper, we propose time-averaged channel estimation method to remove the distortion by noise. The proposed scheme can effectively remove noise components by taking time-average of the estimated channel response after estimating frequency domain channel. The computer simulations were performed to evaluate the performance of the proposed channel estimator. For the Rician channel, we compared the performance of the proposed method to that of a conventional one using channel estimation by gaussian interpolation when SER(Symbol Error Rate) = $10^{-4}$, and compared to perfect channel estimation case. The proposed method showed differences of 0.07 dB, 0.6 dB compared to perfect channel estimation and improvements of 1.7 dB, 1.9 dB for 16 QAM, 64 QAM respectively compared to conventional method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.2
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• pp.151-160
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• 1997

In this paper, we have carried out the DS/CDMA with a suppressed pilot channel, which is used in receiving coherently with Rake diversity and in synchronizing the chip timing, in the mobile satellite communication. Also, we have investigated the envelope variation of a shadowed Rician fading simulator, and analyzed the error performences of DS/CDMA in the mobile satellite communication. The results showed that the error performance in the Heavy shadowing environment might be degraded more than in the Rayleigh fading environment since the fading envelopes in the former environment are varied randomly compared with those in the latter environment. And the performence of DS/CDMA system could be improved about 10 dB compared with that of narrowband QPSK system. In conclusion, DS/CDMA with a suppressed pilot channel had the best performance in the case of the suppressed pilot channel to transmission power ratio $\beta$=-8 dB, the number of complex delay profiles $N_{profile}$=32, and using these values, the error performance of DS/CDMA in Light shadowing environment was identical to the ideal QPSK error performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.796-804
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• 2010

It is important to use the comb type pilot allocation for the continuous channel and efficient processing. And DFT-spreading OFDM is used a lot to solve high PAPR problem of OFDM system. However, PAPR is increased again when comb type pilot is used to estimate channel characteristics. So, in this paper, we employ a new SLM method to DFT-spreading OFDM system to reduce increased high PAPR. And we suggest an effective method to transmit side information without additional bandwidth. Pilot and side information must be preserved from jamming or intentional interferences since those are very important in DFT spread OFDM system using SLM. So, in this paper, we like to analyze and simulate the performance of DFT spread OFDM system based on SLM against jamming signal. To remedy the vulnerable shortcomings of DFT spread OFDM about jamming or intentional interferences, we employ FH(Frequency Hopping) method and analyze system performance under the several jamming conditions such as MTJ(Multi Tone Jamming) and PBJ(Partial Band Jamming).

• Journal of Advanced Navigation Technology
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• v.12 no.4
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• pp.332-340
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• 2008

In this paper, comparisons of the superimposition schemes for orthogonal frequency division multiplexing (OFDM) system are made. The time domain superimposition of data (TDSD) has a tradeoff between the degree of freedom for data transmission and inter-carrier interference (ICI). While SPPT and APSB experiences the increases of interference as the transmit data rate increases, TDSD can effectively improve spectral efficiency by exploiting preprocessing structures which prevents interference between the signals in the different domain. TDSD which we proposed is compared with the conventional superimposition schemes or OFDM, such as SPPT (the superimposed periodic pilot in the time domain) and APSB (the added pilot semi-blind channel estimation) by simulation. As the result, comparing the conventional OFDM, TDSD can increase the spectral efficiency up to about 20% with the superimposition factor M=16 while SPPT has the similar efficiency. APSB has the worst efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12A
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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.