• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.8
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• pp.9-15
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• 2010

This paper presents an analysis of asynchronous multicarrier-code division multiple access (MC-CDMA) uplink systems over frequency-selective multipath fading channels when the frequency offsets (FOs) of all users are random variables and the frequency offset for the desired user is compensated. The effect of a residual frequency offset(RFO) on the average bit error rate (BER) is evaluated by the semi-analytical method, then the approximated BER performance is obtained as a closed-form expression. Moreover, the signal to noise ratio (SNR) loss caused by RFO is evaluated. Derived results show that the performance degradation due to RFO is negligible if the estimation error of RFO for the desired user is less than the normalized value of 0.1.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.342-350
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• 2000

In this paper, the bit error performance for the reverse link of a synchronous direct sequence code division multiple access (DS-CDMA) system employing an imperfect power control scheme over a frequency selective Rayleigh fading channel is analyzed. The system capacity degradation due to power control error (PCE), which is approximated by a log-normally distributed random variable, is estimate as a function of a standard deviation of the PCE. In addition, the impact of the multipath intensity profile (MIP) shape and the number of resolvable paths on the performance of the synchronous transmission is investigated. To estimate the system capacity, the coded bit error performance is evaluated and compared with the conventional CDMA. It is found tat synchronous transmission has less sensitivity to imperfect power control and eases the power control requirements. In particular, as the decay constant $\delta$ of MIP increases, the synchronous transmission in the DS-CDMA reverse link results in a significant BER improvement over the asynchronous transmission even in the presence of imperfect power control. We further conclude that the capacity can be improved by employing the synchronous transmission.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12A
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• pp.1146-1152
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• 2005

In this paper, we propose a compressed quantized channel state information (CQCSI) feedback scheme for multi-carrier mobile communication systems. The proposed CQCSI figures out the contiguous subsequences of equal QCSI's as separate types of runs across the subcarriers, and then encodes the types of runs using a truncated Huffman coding algorithm. Computer simulation shows that the proposed algorithm can reduce the QCSI feedback up to one tenth of the uncompressed, while providing a comparable performance with the conventional QCSI feedback schemes. To cope with special cases when the frequency selective fading is very high, we also propose a restricted CQCSI feedback scheme. The restricted CQCSI feedback has been proved under vehicular B channel model.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.87-92
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• 2005

This paper analyzes the performance for an improved multistage parallel interference cancellation (PIC) technique with a reverse-link synchronous transmission technique (RLSTT) for DS-CDMA system in a frequency-selective Rayleigh fading channel with an imperfect power control scheme. The performance degradation due to power control error (PCE), which is approximated by a log-normally distributed random variable, is estimated as a function of the standard deviation of the PCE. The uncoded bit error performance is evaluated in order to estimate the system capacity. Comparing with the conventional one-stage PIC system, we show achievable gain around $60\%$ by the RLSTT even in the presence of PCE. We conclude that the capacity can be further improved via RLSTT, which alleviates the detrimental effects of the PCE

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11C
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• pp.682-693
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• 2011

Energy spreading transform (EST) based modulation is an effective technique to combat frequency-selective fading in broadband wireless communication. It performs close to the inter-symbol interference (ISI)-free matched filter bound (MFB) only at the complexity of a linear detector. Originally, EST-based modulation has been proposed for QPSK. However, to fully utilize the capacity of multipath fading channels, higher-order modulations are also necessary. In this paper, we review the EST based modulation that has originally been proposed for QPSK and discuss its extension to 8 PSK and 16 QAM. The performance of the extended system is verified through simulation in Proakis B and 8-tap fading channel. The EST based modulation for 8 PSK shows the performance which is very close to MFB and the EST based modulation for 16 QAM shows the performance gap between its receiver and MFB.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.10
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• pp.941-950
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• 1991

channel is severely degraded by multipath delay time spread. In this paper. We propose a simple multipath delay time detection method, which has a merit of in serviceable, yet simple H/W realizability for $\pi/4$ shift QPSK by detecting cross channel interference. A $\pi/4$ shift QPSK signal originally has quadrature channel(Q-ch) component. Thus in order to measure CCI between in-phase channel(I-ch) and quadrature channel(Q-ch), which closely related to multipath delay time, Frequency doubling scheme(frequency doubler) and differential detector is proposed, which makes $\pi/4$ shift QPSK signal look like BPSK and also makes it possible for CCI to be detected at I-ch detector output. To get an information from time varying I-ch output signal under the multipath lading environment, a method for obtaining the mean of the absolute value$(V_{MABS}(t))$ and another one for obtaining the root mean square value$(V_{RMS}(t))$ of CCI are proposed. Furthermore, a relationship between delay spread and CCI is also analyzed. In order to confirm theoretical results, computer simulation has been carried out under the quasi-static and Reyleigh distributed two ray multipath fading environments. A fairly good result was obtained. However it was also shown that this method is sensitive to bandwidth restriction to some extent. In addition, some idea for a simple hardware realization for the frequency doubler are given.

• Journal of Korea Society of Industrial Information Systems
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• v.19 no.4
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• pp.25-32
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• 2014

Powerline communications (PLC) is a promising medium for network access technology where smart grid aided network services can be provided. In the presence of frequency selective fading in the PLC channel, orthogonal frequency division multiplexing (OFDM) is a technique for reliable communications. This paper presents a spectral efficient method using a superimposed hidden pilot for OFDM-based PLC systems. Based on the scheme using a hidden pilot, it is possible to estimate the channel with no consumption of bandwidth, but with utilization of power allocated to the hidden pilot. Computer simulations showed that the proposed scheme provides higher achievable data rate than that of the conventional schemes in low voltage and medium voltage transmission lines.

• Journal of Advanced Navigation Technology
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• v.5 no.1
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• pp.11-18
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• 2001

In this paper, we evaluated the performance of Orthogonal MC/FH-CDMA system considering the hit of frequency hopping patterns, and obtained the degree of the performance improvement by adopting TCM scheme under frequency selective Rayleigh fading channel. From the performance analysis, it is known that the error performance is improved, since delay time relative to symbol time is reduced as the number of carrier is increased. On the other hand, it is found that BER performance is improved about $5{\times}10^{-2}$ degree by adopting TCM scheme, and higher S/N is required if the QoS of voice (BER = $10^{-3}$) must be achieved.

• Journal of Communications and Networks
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• v.7 no.1
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• pp.21-28
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• 2005

In this paper, we analyze the performance of code division multiple access (CDMA) systems with orthogonal frequency division multiplexing (OFDM) that employ random spreading sequences in an additive white Gaussian noise (AWGN) channel. We obtain the probability density function (pdf) of the multiple access interference and extend the results to OFDM-CDMA systems to determine the pdf of multiple access and inter-carrier interference in terms of the number of users, the spreading length, the number of sub-carriers, and the frequency offset. We consider the synchronous downlink of cellular multi-carrier CDMA and derive a Gaussian approximation of the multiple access and inter-carrier interference. Overall the effect of frequency offset is shown to vary with the system loading. The analysis in this paper is critical for further development into fading channels and frequency selective multipath channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.803-813
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• 2005

This paper explores the throughput performance of CSMA/CA-based DCF protocol over frequency-selective, slow Ricean fading channels with both the $E_{b}/N_{o}$ and BER at the MAC layer in the 802.1 la wireless LAN. By exploring the throughput of DCF protocol with the data rate of 6Mbps, 12 Mbps, 24 Mbps and 54 Mbps, we find the fact that the higher the $E_{b}/N_{o}$ be and the less the BER be, the higher the throughput be.