• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.53-60
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• 2013

In this paper, the new multi-beamforming is proposed for Multiple-input multiple-output (MIMO) Multicarrier-Code division multiple access(MC-CDMA) systems to overcome the decrease of performance due to multiuser interference and multiple-antenna interference. Installing the number of multi-beamformer which is equal to the number of multi-transmitter antennas and exploiting the proposed approach at the receiver of MIMO MC-CDMA, the multi-beams are formed toward each multi-antenna of desired user and null beam are formed to other interference. Therefore, the performance of MIMO MC-CDMA system is improved as removing the interference signal. BER performance improvement is investigated through computer simulation by the proposed approach to MIMO MC-CDMA system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.1A
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• pp.55-61
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• 2005

Mobile communication systems are required not only to support high-data-rate transmissions in favorable channel conditions but also to be able to tolerate hostile environments possibly encountered by cellular communications. This paper compares CDMA(Code Division Multiple Access), OFDM(Orthogonal Frequency Division Multiplexing), and MC-CDMA(Multi-Carrier CDMA)with inaccurate channel estimates and low SNR environments. The equations and simulation results show that the performance losses in CDMA systems due to imprecise channel estimates are not considerable while frequency-hopping of OFDM systems can result in more than l0dB SNR losses. Also, this paper show that frequency-spreading of MC-CDMA can be very helpful for channel compensation performances than frequency-hopping or time-spreading of OFDM.

• Journal of electromagnetic engineering and science
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• v.10 no.4
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• pp.290-295
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• 2010

In this paper, an interference analysis method with a site-specific path loss model for a wireless personal area network (WPAN) is proposed. The site-specific path loss model is based on geometrical optics and geometric probability to consider both site-specific radio propagation characteristics and a closed-form expression to obtain the mean interference from which the uniformly distributed multiple interferers are derived. Therefore, the proposed interference analysis method can achieve more computational simplicity than the Monte-Carlo (MC) simulation, which uses the ray-tracing (RT) technique. In addition, better accuracy than the conventional interference analysis model that uses stochastic method can also be achieved. To evaluate the proposed method, a signal to the interference-noise ratio with a mean interference concept for uniformly distributed interferers is calculated and compared in two simulation scenarios. As a result, the proposed method produces not only better matched results with the MC simulation using the RT technique than the conventional interference analysis model, but also simpler and faster calculation, which is due to the site-specific path loss model and closed-form expression for interference calculation.

• Wind and Structures
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• v.17 no.1
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• pp.1-19
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• 2013

A multiscale finite element method is applied to the Spalart-Allmaras turbulence model based detached-eddy simulation (DES). The multiscale arises from a decomposition of the scalar field into coarse (resolved) and fine (unresolved) scales. It corrects the lack of stability of the standard Galerkin formulation by modeling the scales that cannot be resolved by a given spatial discretization. The stabilization terms appear naturally and the resulting formulation provides effective stabilization in turbulent computations, where reaction-dominated effects strongly influence near-wall predictions. The multiscale DES is applied in the context of high-Reynolds flow over the Commonwealth Advisory Aeronautical Council (CAARC) standard tall building model, for both uniform and turbulent inflows. Time-averaged pressure coefficients on the exterior walls are compared with experiments and it is demonstrated that DES is able to resolve the turbulent features of the flow and accurately predict the surface pressure distributions under atmospheric boundary layer flows.

• Journal of Korea Society of Industrial Information Systems
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• v.11 no.4
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• pp.112-120
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• 2006

Multicarrier code division multiple access(MC-CDMA) system that combines multicarrier modulation with CDMA offers robustness to frequency selective fading and can support higher rate data transmission with higher spectral efficiency. A new asynchronous MC-CDMA system to implement multiple data rate communications is proposed in this paper. In a W-CDMA downlink the orthogonal variable spreading factor(OVSF) code is used for variable spreading factor for various multimedia traffic. Proposed system utilizes the OVSF code that generated by generation property for spreading. The proposed MC-CDMA system use different lengths of OVSF code as a spreading code according to their data rate. The groupwise processing is accomplished by code grouping in OVSF code generation tree. For the analysis of average BER performance, numerical method and computer simulation were used. We also compare the system performance with that of a single rate MC-CDMA system used orthogonal code as a spreading code.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1471-1479
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• 1999

This paper presents an adaptive beamforming algorithm for an MC-CDMA system with an adaptive array antenna. By employing an antenna array at the receiver of an MC-CDMA system, the performance of an MC-CDMA system, which is known to be effective for high data rate transmission due to its robustness to multipath fading and its simplicity for using a simple one-tap equalizer, is shown to be significantly improved. The proposed algorithm for adaptive beanforming in an MC-CDMA system is derived by (1) calculating the error signals between the pilot symbols of desired user and the received pilot signals in frequency domain, (2) transforming the frequency-domain error signals into time-domain error signals, (3) updating the filter coefficients of the adaptive beamformer in the direction of minimizing the MSE. Convergence behavior and performance improvement of the proposed approach are demonstrated through computer simulation by applying it to the conventional MC-CDMA system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.6
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• pp.43-48
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• 2021

We propose 2-channel filter bank method instead of FFT method to decrease sub-channel interference for using of efficient frequency resource in MC-CDMA method. Since a prototype filter of filter bank having wavelet characteristic is designed having more less side-lobe, the nearest co-channel interference and inter symbol interference are decreased efficiently. Since the spreading signal of suggesting MC-CDMA system is being demanded for less chip rate and is not being considering for autocorrelation characteristic, the Walsh code can be used as a optimal orthogonal signal set. We consider bit error rate and signal to noise ratio to estimate the performance of suggested system on condition that white noise channel and arbitrary sinusoidal jammer are existing. As a result of comparing to traditional FFT-based MC-CDMA simulation result, our suggested system has shown better performance than traditional MC-CDMA method on the side of minimizing interference effect.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1135-1142
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• 2006

This article presents a new asynchronous MC-CDMA system to implement multiple data rate communications. In a W-CDMA downlink, the OVSF code is used for spreading code for various multimedia traffic. Proposed system utilizes the OVSF code that generated by generation property for spreading. The proposed MC-CDMA system use different lengths of OVSF code as a spreading code according to their data rate. The groupwise processing is accomplished by code grouping in OVSF code generation tree. Between each group, the code grouping interference canceller is performed to cancel other group interference. At that time the proposed receiver does not require any information about interference users. For the analysis of average BER performance, we propose system model and computer simulation were used. We also compare the system performance with that of a single rate MC-CDMA system used orthogonal code as a spreading code.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.53-60
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• 2005

In this paper, we analyze the performance of UWB MC-CDMA system and compareit with DS-CDMA and OFDM systems, which have been drafting in standardization even now. Too many Rake Fingers are needed in the DS-CDMA system to separate multi-path signals, which results in highsystem complexity. OFDM radio power fails to qualify for FCC certification unless frequency hopping. From this reason, MC-CDMA system considered is proposed in this paper. It has lower complexity compared with DS-CDMA and shows good performance against frequency selective fading. In addition, for a wide-band communication, less radio power per spectrum is allowed in the MC-CDMA system than in an OFDM system. Simulation result show that the DS-CDMA system has better performance with single user, but MC-CDMA system shows best performance in case of multi user environment.