• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.63-66
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• 1998

MC-CDMA(Multi-Carrier Code Division Multiple Access) 시스템에서 전송 신호의 피크 전력 대 평균 전력(Peak-to-Average Power: PAP)율을 낮추는 방안을 제시한다. 확산 코드에 의해 결정된 각 부 캐리어의 위상 오프셋은 전송 신호의 복소 포락선 형성에 영향을 주게 되어 전송 신호의 PAP 율을 결정하게 된다. 따라서 각 부 캐리어의 위상 오프셋을 적절히 조정함으로써 PAP율을 낮출수 있다. 본 논문에서는 PAP 율을 감소시키는 부 캐리어 위상 오프셋 코드의 한 예를 제시하며, 모의 실험을 통하여 전송신호의 크기 분포 특성과 PAP 율의 감소를 확인한다.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.2 no.3
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• pp.17-23
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• 2003

Turbo decoding in combination with detection strategy for Multi Access Interference (MAI) cancellation has been shown to be very effective for MC-CDMA system in Rayleigh multi-path fading environment. This paper reports new simulation results on the efficacy of joint decoding and detection for MC-CDMA in nonlinear and fading channel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2623-2631
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• 2010

In this paper, we propose a new interference cancellation(IC) receiver for multirate Multicarrier DS/CDMA(MC DS/CDMA) system based on orthogonal variable spreading factor(OVSF) code. The users are assigned different lengths of OVSF codes as a spreading code according to their data rates and the active users having same representative code split into a group for effective cancellation. The code grouping interference cancellation(IC) receiver performs cancellation between the groups first and cancellation within group. This proposed IC receiver can cancel the interferences using desired user's code information and then desired signals are detected. The results show that the large improvement in performance can be attained by group-wise IC scheme and we can make the effective systems compare to conventional ones. The bit error rate of the system is analytically derived in frequency selective Rayleigh fading channel and we also compare the system performance with that of multirate DS/CDMA system. We also analyze the performance of the proposed system with same bandwidth and processing gain. The results show the large improvement in performance that can be attained by cancellation scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.3
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• pp.319-328
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• 1999

It is necessary to devise the method for increasing bandwidth efficiency in order to provide the high speed mobile multi-media communication services with CDMA under the limited radio bandwidth resources. In this paper the structure for transmitting the high speed data at the half bandwidth of the required bandwidth using the symmetry property of the IFFT output of the binary input MC-CDMA, which enables the time scaling method utilized, is proposed. The processing gain is increased 4 times than the DS-CDMA and its performance is evaluated as better than DS-CDMA with rake receivers under the Rayleigh fading channel and same bandwidth per one channel.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.249-252
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• 2000

In this paper, the performance of a MC-CDMA system applying adaptive subchannel allocation scheme and M-ary orthogonal signaling is analyzed for forward links in Rayleigh fading channel. In the proposed system, each DS waveform is transmitted over the subchannel having the biggest fading among L subchannels. Assuming M-ary orthogonal signaling and 4 subchannels, the BER of 10$\^$-3/ is satisfied if SNRs are 7.33 ㏈, 5.33 ㏈, and 4.47 ㏈ for k=1, 2, and 3, respectively. Also, SNRs which met BER of 10$\^$-3/ are 1.42 ㏈ and 2.33 ㏈ in L=2 and L=8 as k=1 is increased to k=2. It is shown that the MC-CDMA system has performance improvement as a number of subcarriers and M-ary orthogonal signaling.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1996.06a
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• pp.3-7
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• 1996

In this paper, the performances of OFDM and MC-CDMA systems in a slowly-varying multipath fading environment is investigated. Time variation of the multipath channel leads to both a change of an optimal coefficient in one-tap equalizer and a loss of subchannel orthogornality, resulting in significant performance loss. A new simple one-tap equalizer which can reduce the effect of slowly time-varying multipath channel is proposed by taking into account time-variation of multipath profile and modifying the previous equalization techniques. It is demonstrated by computer simulation that the performances of OFDM and MC-CDMA systems can be improved by using the proposed one-tap equalizers when the multipath channel is slowly varying.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.421-428
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• 2009

Inter-cell coordination has been an emerging issue for mitigating inter-cell interference in broadband wireless access networks such as IEEE802.16 and 3GPP LTE (Long Term Evolution). This paper proposes uplink/downlink hybrid inter-cell coordination patterns for a TDD (Time Division Duplex)/MC-CDMA (Multi-Carrier Code Division Multiple Access) system. For the performance analysis, closed forms of inter-cell interferences are derived when uplink and downlink transmissions coexist over a multi-cell environment. In the analysis, we find an optimal ratio of downlink transmit powers of BSs (Base Stations) based on the target outage probability and the performance according to ratios of uplink/downlink transmit powers of MSs (Mobile Stations)/BSs is explored. Our numerical results show that interference mitigation utilizing the characteristics of the uplink and downlink power ratio is very effective in improving system performance in terms of QoS.

• Journal of electromagnetic engineering and science
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• v.9 no.2
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• pp.61-65
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• 2009

Successive interference cancellation(SIC) for the uplink of MC-CDMA mobile communications systems is an effective method to improve performance. We propose a successive interference cancellation(SIC) technique for the uplink of MC-CDMA mobile systems with multiple receive antennas. The destination uses optimum combining(OC) to combine the signals from an OFDM Demodulator with multiple receiving antennas, and applies SIC processing to the combined signals. Achieved interference cancellation order is depends on the signal to interference-plus-noise ratio (SINR) at the output of the optimum combiner. Monte-Carlo simulations are employed to verify the proposed technique.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.470-477
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• 2001

Multucarrier code-division multiple access(MC-CDMA) is one of the promising technique for high capacity wireless communication. Hower the carrier phase error and frequency offest cause the performance degradation of MC-CDMA due to the inter-carrier interference. In this work, downlink performance of the partially coherent MC-CDMA is analytically derived in Rayleigh fading channels. The bit error rate sensitivity by combining method, Maxiaml ratio combining (MRC)and Equal gain combining(EGC), is compared as functions of phase errors. multi-user interference, and received signal-to-noise ratio. The results show that the susceptibility for the performance degradation of EGc and MRC is negligible for loop SNR's of above 15 dB and above 10 dB, respectivtely.

• ETRI Journal
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• v.31 no.2
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• pp.193-200
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• 2009

In this paper, we study the performance of subspace-based multiuser detection techniques for multicarrier code-division multiple access (MC-CDMA) systems. We propose an improvement in the PASTd algorithm by cascading it with the classical Gram-Schmidt procedure to orthonormalize the eigenvectors after their sequential extraction. The tracking of signal subspace using this algorithm, which we call OPASTd, has a faster convergence as the eigenvectors are orthonormalized at each discrete time sample. This improved PASTd algorithm is then used to implement the subspace blind adaptive multiuser detection for MC-CDMA. We also show that, for multiuser detection, the complexity of the proposed scheme is lower than that of many other orthogonalization schemes found in the literature. Extensive simulation results are presented and discussed to demonstrate the performance of the proposed scheme.