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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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The Journal of Korean Institute of Communications and Information Sciences
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Volume 24, Issue 12B - Dec 1999
Volume 24, Issue 12A - Dec 1999
Volume 24, Issue 11A - Nov 1999
Volume 24, Issue 10B - Oct 1999
Volume 24, Issue 10A - Oct 1999
Volume 24, Issue 9B - Sep 1999
Volume 24, Issue 9A - Sep 1999
Volume 24, Issue 8B - Aug 1999
Volume 24, Issue 8A - Aug 1999
Volume 24, Issue 7B - Jul 1999
Volume 24, Issue 7A - Jul 1999
Volume 24, Issue 6B - Jun 1999
Volume 24, Issue 6A - Jun 1999
Volume 24, Issue 5B - 00 1999
Volume 24, Issue 5A - 00 1999
Volume 24, Issue 4B - 00 1999
Volume 24, Issue 4A - 00 1999
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Volume 24, Issue 3A - 00 1999
Volume 24, Issue 2B - 00 1999
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Volume 24, Issue 11B - 00 1999
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Compensation for Nonlinear Distortion in OFDM Systems Using a Predistorter Based on the Fixed Point Approah
Kim, Man Je ; Im, Seong Bin ; Sin, Yo An ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 459~459
Recently, there has been much interest in orthogonal frequency division multiplexing (OFDM) for future digital television broadcasting systems. The OFDM systems are based on the transmission of a given set of signals on several orthogonal subcarriers. As compared to single carrier systems, the OFDM systems provide an advantage of being more robust in applications involving channels affected by severe multipath propagation, such as in mobile communication systems. However, in the radio systems it is also important to consider distortion introduced by high power amplifiers (HPA's) such as traveling wave tube amplifier (TWTA) considered in this paper. Since the signal amplitude of the OFDM system is Rayleigh-distributed, the performance of the OFDM system is significantly degraded by the nonlinearity of the HPA in the OFDM transmitter. One way of compensating nonlinear distortions is to exploit a predistorter in the transmitter in front of the HPA. In this paper, we propose a new predistorter design technique for OFDM systems based on the fixed point approach. The predistortion is accomplished by regarding the compensation of the nonlinearity as a fixed point problem, and the predistorted signals can be iteratively determined by the contraction mapping. The proposed predistorter utilizes identical processing units, resulting in implementational simplicity. Computer simulations on an OFDM system under AWGN channels with 16-QAM modulation scheme and modulator/demodulator implemented with 512-point IFFT/FFT, demonstrate that the proposed predistorter achieves significant performance improvement by effectively compensating for nonlinearity introduced by the TWTA.
Diversity Performance in the Return Link of a Wideband DS-CDMA System for LEO Mobile Satellite
Lee, Yeon U ; Jeong, U Yeon ; Kim, Jin Dae ; Gang, Chung Gu ; Cha, Gyun Hyeon ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 468~468
In this paper we investigate the diversity performance of return link for wideband DS-CDMA, which has been considered as one of the promising multiple access options in the future LEO mobile satellite communication systems. Since there are fundamental differences in the channel characteristics between the LEO mobile satellite and terrestrial mobile systems, such as a small delay spread and the varying elevation angles, these factors must be taken into consideration for channel simulation model. In our simulative studies, the concerning channel model is based on the actual measurement data from European Space Agency (ESA), which further provides the specific model parameters to capture both rural and urban area channel characteristics. The main objective of the current study is to evaluate the performance of the different diversity techniques, namely multi-satellite diversity and multi-path diversity schemes, which play an essential role to cope the performance degradation due to the low elevation angle under the different mobile satellite channel environments. It is shown that the different types of diversity techniques can be successfully applied to combat the performance degradation due to the low elevation angle. In particular, the simulation results confirm that the multi-satellite and multipath diversity schemes are useful in the rural and urban areas respectively as the urban area is dominated by the wideband channel characteristics as opposed to the rural area.
Hybrid Serial/Parallel Interference Cancellation Scheme in Multi-Rate DS/CDMA Systems
Kim, Seong Gi ; Park, Sang Gyu ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 478~478
Performance Analysis of Hybride I ARQ Schemes Using BCH code for Wireless ATM QoS Management
Won, Jeong Jae ; Lee, Hyeong U ; Jo, Chung Ho ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 487~487
InRecently studies on wireless ATM has been attracting many researchers who are concerned with provisions of users a simplified access to information. Acquiring information from the network without regard to its location and its form and anytime at user's convenience is the goal of the next generation network. In order to modulation schemes, diversity techniques, dynamic beam forming antennas the are being studied. Also, in order to resolve the problems that seems to be prevalent in the wireless links, new control techniques such as FEC, ARQ, hybrid REC/ARQ have been proposed and being researched. In this paper, as a means to overcome high and bursty nature of bit errors in the logical link control(LLC) of the data link layer, we have presented realistic QoS parameter and proposed DLC frame structure and new error control techniques of Hybrid I ARQ schemes using BCH code. By using these proposed models we have compared and analyzed their performance.
A Study on Differential Detection of Duobinary MSK with Nonredundant multiple error correction
Song, Seok Il ; Han, Yeong Yeol ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 498~498
An analysis of Differential Detection of Duobinary MSK, with nonredundant multiple error correction for power limited, it investigated. Proposed scheme for differential detection of Duobinary MSK with nonredundant multiple error correction utilizes the output that employ the received signal delayed by more than two time slots. The error rate performance of the proposed Differential Detection of Duobinary MSK with nonredundant multiple error correction is studied for Nakagami fading channel and AWGN.
A Fast DS/CDMA Acquisition Technique Based on the SRG State Sample Conveyance
Kim, Byeong Hun ; Lee, Byeong Gi ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 510~510
In this paper, we propose a new acquisition scheme called distributed sample acquisition(DSA) which is applicable to the DS/CDMA system with a long-period PN sequence. The proposed scheme is based on an auxiliary PN sequence called igniter sequence with has relatively short period and the distributed sample scrambling(DSS) technique recently developed for the ATM cell transmission. In the DSA scheme, transmitter generates the igniter sequence and sends the SRG state samples over it. Receiver acquire the long-period PN sequence by applying the DSS comparison-correction technique to the receiver SRG based on the received sample. Since the operation of each step takes very short time, the overall acquisition is done very fast. If compared with the existing serial-serial scheme, the DSA scheme can perform acquisition 100 times faster when the period of the PN sequence is
. Nonetheless, the additional circuit complexity for its implementation is very small, which enables us to implement it easily.
A Study on the Performance Evaluation and Approximate Result for M-ary PAM Signal with Phase Error
Lee, Ho Gyeong ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 519~519
The Performance Analysis of the Successive Interference Canceller with the Pseudo-Decorrelator as the First Stage
Park, Jung Hu ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 525~525
In this paper, the performance of the successive canceller with the Pseudo-Decorrelator as the first stage was analyzed. The Pseuso-Decorrelator adopted in the first stage is designed using the concept of Penrose's generalized inverses. In the successive interference canceller, the multiple access interference caused by other users are estimated with the estimated information bit obtained at the first stage, and substracted them from the received signal. This may increase the detection probability for the desired user. In this case, the performance of receivers depend on the accuracy of the information bit estimated at the first stage. It is possible to increase this accuracy when the Pseudo-Decorrelator is adopted in the first stage. The simulation results show that this assumption is correct. The confidence interval estimation technique was used to verify the simulation results. The simulations have been performed under the situation in which there are the synchronization errors, such as timing and phase errors. The proposed successive interference canceller performs well in both cases.
Performance of a Coded OFDM System for Fixed Code Rate and Bandwidth Expansion
Kim, Yun Hui ; Park, So Ryeong ; Song, Ik Ho ; Kim, Hong Gil ; Kim, Seok Chan ; Lee, Seong Ro ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 532~532
The OFDM is an effective technique for high data rate transmission under multipath fading channels. In this paper, we analyze the influence of interference due to the time variation and delay spread of mobile radio channels on an OFDM system. With the result, we obtain the bit error rate performance of the 16-QAM OFDM system. Then, we investigate the performance of the Reed-Solomon (RS) coded 16-QAM OFDM system when the number of subcarriers varies. In the investigation, we assume that the information transmission rate and total bandwidth expansion (due to coding, guard interval, and several subcarriers) are fixed. Under this condition, it is observed that there are optimum numbers of subcarriers that minimize the symbol error probability for various channel states.
A Study on Call Admission Control Methods for Multiple Traffic Classes in CDMA System
Ryu, Byeong Han ; Park, Yeong Ok ; Kim, Gyeong Su ; Baek, Jang Hyeon ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 538~538
In this paper, we propose the call admission control methods for accommodating the multiple traffic classes in CDMA (code division multiple access) system. For reducing the handoff call dropping probability, a portion of resource is reserved for handoff call request. For the resource reservation method, two kinds of guard channels are considered one is that the reserved resource is used only for handoff call request, and the other is a new call request fractionally uses the reserved resource depending on the amount of available resource. The call request not accepted immediately is buffered during its allowable delay time, and when there exists the available resource, we first handle the handoff call prior to the new call. Further, we take into account two kinds of resource allocation methods a shared resource allocation and a dedicated resource allocation. To evaluate our call control models, we consider two kinds of voice traffic standard voice traffic as normal speed service and premium voice traffic as high speed service. Through simulation results, we derive the amount of resource reserved for handoff call, and evaluate the call blocking and dropping probabilities, and throughput.
A New Soft Handoff Algorithm with the Pilot Signal Thresholds Adjustment according to the Speed of the Mobile Station
Choe, U Yong ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 547~547
As smaller cells are deployed to meet the demands for increased capacity, the number of cell boundary crossings increases. Each handoff requires network resources to direct the calls to a new base station, and the service quality may be degraded with the increased number of handoffs. In this paper, we survey the existing handoff methods for the reduction of the number of unnecessary handoffs and a new soft handoff algorithm will be proposed to change the pilot strength thresholds according to the speeds of the mobile stations.
A Study on Hyperimposed Trellis Coded Modulation
Hong, Seong Gwon ; Gang, Chang Eon ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 555~555
In this work, we discuss a configuration method of hyperimpose trellis coded modulation meaning that hyperimposed convolutional code is applied to a spectrally efficient modulation. We also analyze and compare the performance of the proposed scheme with a conventional TCM scheme in terms of BER, complexity, and confirm the conclusion by the simulation. The analysis show that hyperimposed trellis coded modulation scheme has a gain of about 0.5∼1 dB in the AWGN channel environment, and about 3∼4 dB in the Rayleigh fading channel environment at a BER of 10-5. The application to 8PSK and QPSK of the proposed scheme, 33% and 100% of computational complexity is more needed.
Performance Analysis of Turbo Codes by Error Range Search in Rayleigh Fading Channel
Jang, Jin Su ; Jeon, Ji Ung ; Choe, Seung Bae ; Lee, Mun Ho ; Lee, Han Seop ; Yun, Chan Ui ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 566~566
Turbo codes were introduced in 1993 by Berrou, Glavieux, and Thitimajshima. This concept, based on iterative decoding, soft-in/soft-out decoding, parallel concatenation of two recursive systematic convolutional codes and random interleaving, is amazing by its performance. But in spite of the high performance and some applications, there are still remained problem such as increment of complexity by decoding computation, latency by interleaver and iterative deciding. Intuitionally, convolutional encoding process and it's reverse process (MAP decoding), MAP algorithm depends on the common adjacent bits or received symbols.
A Study on the Comparison of the Power Detection Method for the Tx Power Control in the 2.45GHz ISM Band
Jeong, Myeong Rae ; Lee, Sang Won ; Kim, Hak Seon ; Lee, Yun Hyeon ; Lee, Hyeong Jae ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 576~576
In this paper, we designed the power detector with the capacitor to decrease the estimation error and directional coupler which are used in 2.45GHz ISM band, also compared and analyzed the characteristics of the power sensitivity to estimate the performance of detector, the bandwidth and the printed circuit board size. As the results, their voltage sensitivity is constant from -50dBm to -25dBm which is the input power, but the detector composed by the directional coupler is superior about 3㎷/㎼ than that by the single diode from -25dBm to -10dBm and its bandwidth is wider about 63MHz than the directional coupling power detector with the capacitor. Therefore when the output level of transmitter is below -20dBm, the power detector with the capacitor had better be selected as the detector for the power control to reduce the area because of the similar characteristics, and above -20dBm or in the wide band system, the estimation error can be eliminated by the selection of directional coupler considered the voltage sensitivity for the power detector.
Design of A Tunable Low-pass Active Filter for Communication
Lee, Geun Ho ; Bang, Jun Ho ; Lee, U Chun ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 585~585
In this paper, a integrator as a basic block of the low-voltage(2.5V) active filter for communication system are proposed. The integrator is composed of the CMOS complementary circuit which can extend transconductance of an integrator. Therefore, the unity gain frequency which is determined transconductance is increased about two times larger than that of the conventional continuous-time integrator. And then frequency and gain of the integrator can be controlled with simple tuning circuit. Finally, tunable low-pass active filter is designed with double-poly double-metal CMOS process.
An Efficient Hardware Design of Demodulating Fingers for CDMA Mobile System
Hwang, Sang Yun ; Kim, Jae Seok ;
The Journal of Korean Institute of Communications and Information Sciences, volume 24, issue 4A, 1999, Pages 592~592
This paper presents an efficient hardware architecture of demodulating fingers to demodulate the multi-path propagating signals in CDMA Mobile System. We design a new architecture of demodulating fingers which share the single arithmetic unit to reduce the hardware complexity. This arithmetic unit performs MAC(Multiplication and Accumulation) operations of all demodulating fingers. We design the proposed architecture using VHDL and implement it on Altera FPGA chip. The proposed architecture is suitable for IS-95 based CDMA PCS system. It contains about 23K logic gates when the number of demodulating finger is 3. The hardware complexity of our proposed architecture is decreased by 11% to be compared with the conventional one. Three demodulating fingers for MC-CDMA which demodulate 7 channels contain about 42K logic gates. Our proposed system is shown to be very useful for hardware architecture which uses multiple demodulating fingers, and also for Multi-code CDMA system in which several channels are demodulated simultaneously.