• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.47-52
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• 2007

This paper analyzes the output signal-to-interference-plus-noise ratio (SINR) for a multiple-input-multiple-output (MIMO) multicarrier code division multiple access (MC-CDMA) system with minium mean square error receivers in multi-cell environments. A previous work in single cell environments is extended into analysis in multi-cell environments. The use of Haar unitary code matrix for asymptotic analysis causes other cell interferences expressed with a diagonal matrix haying different diagonal values. This paper shows that other cell interferences converge to an identity matrix whose gain is expressed by only other cell interference power in mean square sense and finds asymptotic deterministic SINRs for a given other cell interference. Under the assumption that the sum of lognormal fading components is distributed by other lognormal function, we show the comparison between theoretical performances and simulations from the view point of bit error rate and present average throughput performance according to the cell radius.

• 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 Communications and Information Sciences
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• v.30 no.6C
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• pp.423-433
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• 2005

We present power(in frequency domain) and rate adaptation(in time domain) schemes in multicarrier (MC) direct-sequence code-division multiple-access(DS/CDMA) communications. Utilizing channel state information from the receiver, the adaptation schemes allocate power the user's sub-band with the largest channel gain. In the time domain, the transmission data rate is adapted for a desired transmission quality. In the case of single-user channels, a closed-form expression is derived for an optimal time domain power adaptation that minimizes the average bit error rate(BER). Channel inversion power adaptation is found to provide nearly optimal performance in this case, as the number of sub-bands or available average transmission power increase. Analysis and simulation results show the BER performance of the proposed power and rate adaptations with fixed average transmission power significantly improves the performance over the power allocation in the frequency domain only. Also, we compare the performance of the proposed power and rate adaptation schemes in MC-DS/CDMA systems with that of power and rate adapted single carrier DS/CDMA systems with RAKE receiver.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1300-1310
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• 2003

In this paper, the performance of a multicarrier CDMA system using adaptive modulation and adaptive subchannel allocation scheme is analyzed in Rayleigh fading channel. The proposed adaptive modulator consists of modulation schemes using QPSK 16 QAM, 64 QAM and 256 QAM and constellations are pointed by Gray code. In addition, the threshold of the analysis is average E$\_$b//N$\_$o/ when the BER is 1 %. In the multicarrier system with adaptive subchannel allocation scheme, each DS waveform of user is transmitted over the K subchannels with the biggest fading among L subchannels. In case of the proposed system, total 4 subchannels are used and data are transmitted over 2 subchannels with the biggest fading, which results in the threshold of each channels is 5.2 dB, 9 dB, 13.2 dB and 8.4 dB, 12.2 dB, 16.3 dB. In the case of proposed system, the BER of 10$\^$-3/ is satisfied if average E$\_$b//N$\_$o/ is 8.1 dB. This is increased performance of 12.9 dB in comparison with conventional system. The BPS according to average channel is needed average E$\_$b//N$\_$o/ of about 15 dB in 7 bit. In the case of subchannel error, the BER of 10$\^$-3/ is 13.6 dB and is declined about 5.5 dB.