• Journal of Korea Society of Industrial Information Systems
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• v.16 no.4
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• pp.27-35
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• 2011

Multicarrier-Direct Sequence/Code Division Multiple Access(MC-DS/ CDMA) which is a combination of Orthogonal Frequency Division Multiplexing(OFDM) and DS/CDMA has been of significant interest as a means to take such advantages as bandwidth efficiency, high bit rate and robustness against multipath fading. In this paper we study a reduced-complexity multiuser detection aided multirate MC-DS/CDMA with time(T)-domain and frequency(F)-domain spreading. The one- dimensional orthogonal variable spreading factor(1D OVSF) code extracted from 2D OVSF code are used as a spreading code in T/F-domain. The proposed system will use code grouping interference cancellation(CGIC) receiver to reduce Multiuser Interference(MUI). The CGIC receiver uses code grouping by the correlation properties of 1D OVSF code and dose not requires the code information and activity of other user. The multiuser detector with CGIC receiver will be analyzed in Time- and Frequency-domain separately(jointly). The system performance is analytically derived in Additive White Gaussian Noise(AWGN) channel and we also compare the system performance between proposed system and T/F spreaded single(multi) rate multiuser MC-DS/CDMA system. In the computer simulation results, the proposed receiver of demonstrated huge performance improvement over conventional matched filter receiver.

• Journal of Digital Contents Society
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• v.1 no.1
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• pp.39-52
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• 2000

In this paper, we derive the BER performance of an asynchronous DS/CDMA system and analyze the improvement of BER performance through turbo coding and RAKE receiver in multipath Rayleigh fading and impulsive noise environments. As a result, impulsive noise affects the performance of the system more than multipath fading in lower $E_b/N_o$ than a certain threshold. However, in higher $E_b/N_o$, multipath fading are more dominant than impulsive noise. It is found that in lower $E_b/N_o$, turbo code improves the performance of the system against impulsive noise, and in higher $E_b/N_o$, RAKE receiver improves the performance of the system against multipath fading. Therefore, great improvement can be obtained by employing turbo code and RAKE receiver in multipath Rayleigh fading and impulsive noise environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.952-959
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• 2006

In this paper, 2-D RAKE receiver simulator is made which beamforming technique is applied to in WCI)MA uplink basestation, and the performance is compared with that of 1-D RAKE receiver with varying the number of array elements, RAKE fingers and users. To model angular component of received signal and interfering signals due to multiple access, it is assumed that multiple users are located in the arbitrary direction of the same distance far from the basestation within a sector of the cell, and the channel simulator is made by using Geometry Based Single Bounce Elliptical Model(GBSBEM) suggested by Rappaport. BER performance is compared and analyzed with the various choise of the number of array elements, the number of RAKE fingers, the number of users and Eb/No. These results indicate that increasing the number of array elements eliminates efficiently multiple access interfering signals and improves dramatically BER performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.10
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• pp.909-916
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• 2016

The beacon receiver is an equipment which detects and measures the signal strength of transmitting satellite beacon signal. Beacon signals transmitted by satellites are low power continuous wave(CW) signals without any modulation intended for antenna steering to satellite direction and power control purposes on the earth. The beacon signal detection method using a very narrow band analog filter and RSSI(Received Signal Strength Intensity) has been typically used. However, it requires the implementation to track the frequency at the beacon receiver, thus a beacon frequency variation of the satellite due to temperature changes and long-term operation. Therefore, in this paper, the beacon signal detection receiver is designed by using a very narrow band digital filter array for a faster acquisition and SNR(Signal to Noise Ratio) method detection. For this purpose, by calculating the satellite link budget with the rain attenuation between satellite and ground station, and then extracting the received $C/N_o$ of the beacon signal, this work derives the bandwidth and the array number of the configured digital filter that gives the required C/N.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.776-781
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• 2005

In this paper, using received channel information, we analyze performance in MIMO multiuser system in low-to-medium mobile speed by selecting each user's constellations, powers, and transmit antennas. Given a target of symbol error, we determine each user's constellations, powers, selected tranprobability smit antennas such that the required signal-to-noise(SNR) is minimized for MMSE, V-BLAST receiver according to each user's information and channel estimation information. When we do power control with antenna selection technique through uplink channels of MIMO system in low-to-medium mobile speed, we analyze system performance with wireless channel information from Base-Station(BS) to Users. By simulation, it has been shown that the proposed antenna selection scheme for transmitting data offer better performance improvement than all transmit antennas for transmitting data.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.129-132
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• 2001

In this paper a new multiple access scheme, CI/DS-CDMA rising the interference of multiple carriers, is introduced. In this system the chip is made up of N orthogonal carriers equally spaced in frequency, where N corresponds to the number of chips in DS-CDMA. The characteristics of CI/DS-CDMA systems in a typical frequency selective fading channel environment, are analyzed. And it is shown that the frequency diversity benefits of this system result in significant performance enhancements relative to traditional DS-CDMA with RAKE receivers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.4A
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• pp.200-207
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• 2003

This paper proposes a CDMA receiver structure with time-shifted m-sequence orthogonal reception process, and analyzes the output SNR performance and the characteristics of the orthogonal receiver. This structure can be simply implemented with the converntional receiver adding an additional integrator path in parallel and an adder sums the conventional path and the new path output signals. The structure provides to reference user signal not only increment of signal component but also perfect orthogonal characteristic, canceling the accumulated cross-correlated value out to zero between the reference user and other user signals. Hence, the proposed structure can be applied for channel impulse response measurement, and used for multi-user interference signal cancellation and channel capacity increment by flexible structural inter-working operation of the added path, connection or disconnection, to conventional receiver structure.

• Journal of Broadcast Engineering
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• v.1 no.1
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• pp.1-6
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• 1996

Digital DBS service using Korea Sat starts at Korea Telecom's Yong-in transmission site. Total 6 transmitting stations are needed. At each transmitting station, 4 TV programs are compressed and multiplexed using MPEG-2, modulated into IF, RF signals, then finally transmitted through antenna. At DBS transponder, received signal is down converted, amplified and re-transmitted to earth. At receiver, signal is received by 45cm dish antenna, then wanted program is selected, demultiplexed and decoded. Transmission performance of BER lOE-ll is implemented by using FEe coding and QPSK modulation. For pay TV management, conditional access system, smart card and modem are used.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.53-59
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• 2009

In multi-user MIMO systems, a base station transmits multiple data to multi-user simultaneously in order to improve performance and bandwidth efficiency. When the base station transmits multiple data to multi-user simultaneously, multi-user interference occurs severely. In this paper, we define a post-processing leakage as the total power leaked from desired user to all other users after combining at the output of each user. Using concept of the post-processing leakage, we also define a performance metric, the so called signal-to-post-processing-leakage-plus-noise ratio (SPPLNR). Assuming that the receiver is the minimum mean square error (MMSE) receiver, we propose an iterative SPPLNR-based beamforming that determines beamforming vectors and combining vectors by using an iterative method. The proposed scheme does not impose a condition on the relation between the number of transmit antennas for the base station and the number of receive antennas for users. Simulation results show that the proposed scheme outperforms a beamforming scheme perfectly eliminating the multi-user interference when channel estimation error exists.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.378-390
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• 2001

In this paper, it is analyzed that the error performance of a Multi-Carrier DS-CDMA system in a single cell with multipath Rician fading and multiple access interference (MAI) and the error performance of the system is compared with that of a Sing1e-Carrier DS-CDMA system. Moreover, the convolutional coding techniques with code rate of 1/2, 1/3, and 1/4 are adopted in order to improve the error performance degraded by the multipath fading and MAI and performance improvement through the coding techniques is analyzed. As a result, it is shown that the number of users in each system can be determined by the number of branches of the rake receiver in a Single-Carrier DS-CDMA system and the number of carriers in a Multi-Carrier DS-CDMA system. Furthermore, the convolutional coding should be chosen with considering the trade-off between coding gain and a power limitation in a Multi-Carrier DS-CDMA system. In case of increasing the number of carriers, the processing gain is decreased but the error performance is improved through the effect of frequency diversity and the system can be possibility implemented due to the low chip rate.