• ETRI Journal
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• v.26 no.5
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• pp.405-412
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• 2004

MC-CDMA, a multicarrier (MC) modulation scheme based on code division multiple access (CDMA), is the most likely candidate for the next generation of mobile radio communications. The rate compatible punctured turbo (RCPT) coded hybrid automatic repeat request (HARQ) has been found to give improved throughput performance in a direct sequence (DS) CDMA system. However, the extent to which the RCPT HARQ improves the throughput performance of an MC-CDMA system has not been fully understood. In this paper, we apply the RCPT HARQ to MC-CDMA and evaluate by computer simulations its performance in a frequency selective Rayleigh fading channel. We found that the performance of RCPT HARQ MC-CDMA is almost insensitive to channel characteristics. The performance can be drastically improved with receive diversity combined with space-time transmit diversity. In addition, the comparison of RCPT HARQ MC-CDMA, orthogonal frequency division multiplexing, and DS-CDMA shows that under similar conditions the throughput of MC-CDMA is the best in a frequency selective fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1677-1685
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• 2001

In this paper, we propose a call admission control scheme that can be performed within guaranteeing of required QoS(Quality of Services) in DS-CDMA(Direct Sequence-Code Division Multiple Access) reverse link. It has been performed rely on a physical channel numberonly and based on quality of received signal from MODEM(modulator/demodulator) part in established study. In other methods, the standard for services would have been set from statistical analysis of users\` location and using received power level in BTS(Base Transceiver Station). These ways bring about not only system loads but time delay or great differences from real environment. To solve these problems, we propose a call drop rate estimation algorithm for the purpose of call admission control based on measured value at LNA(Low Noise Amplifier) ports of BTS(Base Transceiver Station) in real time. This method proposed in this paper estimates a quality of offered service in real time, reduce system loads and shorten time delay which is needed to determine the standard for call admission control. But it requires a additional 17W complexity which can measure received signal power in BTS and estimate call drop rate.

• 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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1968-1976
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• 2007

This paper proposes a hybrid pseudo-noise (PN) code acquisition scheme for Multicarrier Direct Sequence - Code Division Multiple Access (MC DS-CDMA) mobile communication systems on the code acquisition performance for Nakagami-m fading channel. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time (MAT) slightly inferior to that of the total parallel acquisition. The closed-form expressions of the detection and false-alarm probabilities are derived.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.12A
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• pp.1319-1332
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• 2004

Multicarrier direct sequence code-division multiple access CDMA(MC DS-CDMA) is an attractive technique for achieving high data rate transmission even if the potentially large peak-to-average power ratio(PAPR) is an important factor for its application. On the other hand, code select CDMA(CS-CDMA) is an attractive technique with constant amplitude transmission of multicode signal irregardless of subchannels by introducing code selection method. In this paper we propose a new multiple access scheme based on the combination of MC DS-CDMA and CS-CDMA. Proposed scheme, which we called MC CS-CDMA, includes the sutclasses of MC DS-CDMA and CS-CDMA as special cases. The performance of this system is investigated for multipath Sequency selective fading channel and maximal ratio combining with rake receiver. In addition the PAPR of proposed system is compare with that of both MC BS-CDMA and CS-CDMA. Simulation results show that proposed system improves PAPR reduction than MC DS-CDMA at the expense of the complexity of receiver and the number of available non. Also, the numerical result shows that the proposed system is better performance than MC DS-CDMA due to the increasing processing gain and the number of time diversity gain.

• Proceedings of the KIEE Conference
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• 2005.10a
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• pp.173-175
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• 2005

Two-dimensional orthogonal variable spreading codes are presented for multiplexing of forward link in direct sequence code division multiple access (DS-CDMA) multiple antennas system And the results of code generation and simulation of 2 dimensional orthogonal variable spreading factors on Jacket matrices are also be investigated. The bit error rate(BER) performance under a multi-user environment for the additive white Gaussian noise (AWGN) channel demonstrated that the proposed scheme could provide flexible rates and lower correlation values

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.140-143
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• 2000

In this paper, forward error control coding in multicarrier direct sequence code division multiple access (DS/CDMA) systems is considered. In order to accommodate a number of coding rates easily and make the encoder and do-coder structure simple, we use the rate compatible punctured convolutional (RCPC) code. We obtain data throughputs at several coding rates and choose the coding rate which has the highest data throughput in the SINR sense. To achieve maximum data throughput, a rate adaptive system using channel state information (the SINR estimate) is proposed. The SINR estimate is obtain by the soft decision Viterbi decoding metric. We show that the proposed rate adaptive convolutionally coded multicarrier DS/CDMA system can enhance spectral efficiency and provide frequency diversity.

• Journal of the Korea Computer Industry Society
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• v.5 no.5
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• pp.761-770
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• 2004

The multicarrier direct sequence code-division (MC-DS/CDMA) is a well-known multiple access and data transmission scheme that is applicable for various mobile and wireless communications. Particularly for modern, smart vehicles equipped with multiple sensors, MC-DS/CDMA is one of the possible means for giving the sensors to get connected one another for sending and receiving messages and control information. For intra-vehicalur communicaiton and networking applications, we have proposed a novel MC-DS/CDMA multiple access and data transmission scheme incorporating a new idea of inserting sub-symbol based cyclic prefixes for compromising inter-symbol interference. In the performance investigation of our MC-DS/CDMA, we have looked into system performances related to bandwidth utiltzation, coding gain, and multiple number of sensors. Since the channel delay is comparatively shorter inside of vehicle than any other general mobile channels, the proposed scheme can be a successful candidate for networking wireless sensors simultaneously operting in an intelligent vehicle.

• ETRI Journal
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• v.26 no.5
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• pp.413-422
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• 2004

This paper investigates the impacts of array weight errors (AWE) in an antenna array (AA) on a parallel interference cancellation (PIC) receiver in uplink synchronous and asynchronous direct sequence code division multiple access (DS-CDMA) systems. The performance degradation due to an AWE, which is approximated by a Gaussian distributed random variable, is estimated as a function of the variance of the AWE. Theoretical analysis, confirmed by simulation, demonstrates the tradeoffs encountered between system parameters such as the number of antennas and the variance of the AWE in terms of the achievable average bit error rate and the user capacity. Numerical results show that the performance of the PIC with the AA in the DS-CDMA uplink is sensitive to the AWE. However, either a larger number of antennas or uplink synchronous transmissions have the potential of reducing the overall sensitivity, and thus improving its performance.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.4
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• pp.403-408
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• 2002

In this paper, the performance on the PN code acquisition of DS/CDMA system was analyzed using the Nakagami-m probability density function considered fading environment. The equations on detection probability, $P_D$ and false alarm probability, ($P_{FA}$, decision variables affecting the PN code acquisition time were derived and proved using simulation in order to analyze the performance. In conclusion, It was necessary increasing the gain of PLL for correcting phase errors and improving the acquisition performance of PN code in apply to the rake receiver.