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Search Results: 1 - 10 of 12571 matches for " Wideband Code-Division Multiple-Access (WCDMA) "
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BER Performance of Space-Time Coded MMSE DFE for Wideband Code Division Multiple Access (WCDMA)  [PDF]
Sanjay Kumar SHARMA, S. Naseem AHMAD
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2009, DOI: 10.4236/ijcns.2009.24030
Abstract: In recent times, there has been growing interests in integration of voice, data and video traffic in wireless communication networks. With these growing interests, WCDMA has immerged as an attractive access technique. The performance of WCDMA system is deteriorated in presence of multipath fading environment. The paper presents space-time coded minimum mean square error (MMSE) Decision Feedback Equalizer (DFE) for wideband code division multiple access (WCDMA) in a frequency selective channel. The filter coefficients in MMSE DFE are optimized to suppress noise, intersymbol interference (ISI), and multiple access interference (MAI) with reasonable system complexity. For the above structure, we have presented the estimation of BER for a MMSE DFE using computer simulation experiments. The simulation includes the effects of additive white Gaussian noise, multipath fading and multiple access interference (MAI). Furthermore, the performance is compared with standard linear equalizer (LE) and RAKE receiver. Numerical and simulation results show that the MMSE DFE exhibits significant performance improvement over the standard linear equalizer (LE) and RAKE receiver.
A Dynamic MAC Protocol with Adaptive Power Control for WCDMA Networks
S.P.V.Subba Rao,S. Venkata Chalam,D.Sreenivasa Rao
International Journal of Distributed and Parallel Systems , 2011,
Abstract: In Wideband code-division multiple-access (WCDMA) systems, all users share the same time andfrequency resources and may lead to near far problem, where power control forms an effective solution.A power control algorithm aims to reduce transmission power and interference level, and to maximizesystem capacity. In this paper, we propose an adaptive power control mechanism for multimedia trafficin WCDMA networks. The proposed algorithm uses two most recent Transmit Power Control (TPC)commands to compute the Adaptive Factor (AF) based on a predefined Adaptive Control Factor (ACF).We introduce another parameter, Power Determining Factor (PDF) based on the data traffic rate todetermine the power. Based on this parameter, the power is increased or decreased. Depending on thetraffic rate, the PDF factor is updated i.e., if the observed traffic rate is high, then it will increase theparameter and subsequently increases the power and if it is low, then the parameter will be decreasedand correspondingly the power also. By simulation results, we show that the proposed power controlalgorithm reduces the power consumption of multimedia traffic.
A Low-Complexity Joint Synchronization and Detection Algorithm for Single-Band DS-CDMA UWB Communications
Christensen Lars PB
EURASIP Journal on Advances in Signal Processing , 2005,
Abstract: The problem of asynchronous direct-sequence code-division multiple-access (DS-CDMA) detection over the ultra-wideband (UWB) multipath channel is considered. A joint synchronization, channel-estimation, and multiuser detection scheme based on the adaptive linear minimum mean square error (LMMSE) receiver is presented and evaluated. Further, a novel nonrecursive least-squares algorithm capable of reducing the complexity of the adaptation in the receiver while preserving the advantages of the recursive least-squares (RLS) algorithm is presented.
The Application of Optical CDMA-Based Fiber Radio Networks in Wireless Sensor Networks  [PDF]
Chao-Chin YANG
Wireless Sensor Network (WSN) , 2009, DOI: 10.4236/wsn.2009.12010
Abstract: One fiber radio scheme using shifted prime codes for interference elimination is proposed for optical code-division multiple-access (OCDMA) network. By taking advantage of the cyclic property of the shifted prime codes in the same code groups, the proposed compact decoder is low cost and suitable to be used in the task manager node in the applications of wireless sensor networks. The performance comparison for sev-eral OCDMA-based fiber radio networks is also given to clarify the advantage of the proposed one.
A Doherty Amplifier with Envelope Tracking Technique and DSP for High Efficiency
Ambar Saxena,Rakesh Kumar,Sahab Ram
International Journal of Electronics and Computer Science Engineering , 2012,
Abstract: A Doherty amplifier employing input signal envelope tracking technique. In the amplifier, gate bias of peaking amplifier is controlled according to the magnitude of the envelope. The performance of the microwave Doherty amplifier has been compared with class AB amplifier. DSP is used to dynamically adjust the gate bias of the auxiliary (peaking) amplifier at the rate of the signal envelope to obtain gain flatness. DSP is used as a digital predistortor to improve the overall linearity and efficiency.
Performance Improvement of DS-CDMA Wireless Communication Network with Convolutionally Encoded OQPSK Modulation Scheme
Manish Rai,Inderpreet Kaur
International Journal of Advances in Engineering and Technology , 2011,
Abstract: This paper considers the bit error probability analysis of Direct-Sequence Code-Division Multiple Access (DS-CDMA) system. A statistical characterization of the decision variable at transmitter and receiver is obtained. System is simulated with OQPSK modulation scheme which when compared with conventional Binary Phase Shift Keying (BPSK) gives improved performance in terms of Probability of Error (Pe). Convolution coding is further incorporated with both of the modulations schemes and results show that this coding further improves the system when compared without coding. However, mathematical analysis includes exact bit error calculation as well as various approximation methods based on Gaussian modeling of the Multiple-Access Interference (MAI) terms.
Performance Analysis of Normalized Throughput in a Hybrid WDMA-OCDMA System
一种混合WDMA-OCDMA系统归一化吞吐量性能研究

Ji Jianhua,Xu Ming,Yang Shuwen,Ma Junxian,
吉建华
,徐铭,杨淑雯,马君显

光子学报 , 2005,
Abstract: The performance of normalized throughput in a hybrid WDMA-OCDMA system is studied. The effect of optical beat noise on the normalized throughput is analyzed. The scheme of BCH channel coding is proposed to improve the performance of a hybrid WDMA-OCDMA system.The analysis result shows that the normalized throughput is a little decreased when traffic load is light, but can improved greatly when traffic load is medium and heavy. Furthermore, the maximum normalized throughput will increase for the BCH-coded hybrid WDMA-OCDMA system.
BARRIER FUNCTION DESCENT DIRECTION METHOD FOR CDMA MULTI-USER DETECTION
在CDMA系统中实现多用户检测的障碍函数下降方向法

Li Chunguang,Liao Xiaofeng,Yu Juebang,
李春光
,廖晓峰,虞厥邦

电子与信息学报 , 2001,
Abstract: In this paper, A barrier function descent direction method for implementing CDMA multi-user detection (BMD) is proposed. As compared to conventional detectors and neural network optimal algorithms, the method derives a new descent direction from the barrier function other than the gradient direction. Numerical results show that the method is always able to find the global minimization point. It has many advantages featuring near-far effect resistance, able to suppressing multiple access interference and channel noise, etc. The method paves a new way for realizing optimal multi-user detection in CDMA system.
Phase-Induced Intensity Noise Reduction with Improved Group Velocity Dispersion Tolerance in SAC-OCDMA Systems
Hamza M. R. Al-Khafaji,S. A. Aljunid,Angela Amphawan,Hilal A. Fadhil
International Journal of Engineering and Technology , 2013,
Abstract: The demand for efficient optical communication systems has fuelled considerable research in developing techniques for eradicating phase-induced intensity noise (PIIN) in spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA). This paper investigates the use of modified-AND subtraction detection technique to mitigate PIIN in SAC-OCDMA systems. The simulation results show that the modified-AND subtraction detection demonstrates better performance over the conventional AND detection approach. Furthermore, we have found that, from a transmission length of 40 km onwards, group velocity dispersion (GVD) degrades SAC-OCDMA system performance apparently. Dispersion compensating fiber (DCF) is used to lessen the influence of GVD caused by single mode fiber (SMF).
Overloaded Minimum Total Squared Correlation Signatures Based Pilot Aided System for MC-CDMA and STBC MC-CDMA
M.S. Arifianto,A. Chekima,M.Y. Hamid,L. Barukang
Journal of Applied Sciences , 2007,
Abstract: This paper proposes multiple-access schemes based on Overloaded Minimum Total Squared Correlation (TSC) signatures, namely Pilot Aided Multi-Carrier Code-Division Multiple-Access (MC-CDMA) and Pilot Aided Space Time Block Codes (STBC) MC-CDMA. Since overloaded minimum TSC signatures were used as the spreading codes, a number of sub-channels in the MC-CDMA and STBC MC-CDMA schemes were not utilized for data transmission. These empty sub-channels can be exploited for comb-type pilot signaling. To maintain low system complexity, for the pilot sub-channels Least Square (LS) estimation was employed and for interpolating the characteristics of the data sub-channels linear interpolator was applied. The validity of the schemes is confirmed by comparing them with the original MC-CDMA method using Walsh-Hadamard orthogonal codes and also with Walsh-Hadamard based STBC MC-CDMA with block-type pilot. All systems use Equal Gain Combining (EGC) or Maximum Ratio Combining (MRC) in the MC-CDMA block at the receiver. The simulation result shows that although the spreading codes of interest are not fully orthogonal codes, for a low number of users the systems under investigation performed better than their Walsh-Hadamard based counterpart. This will be valuable for Wireless Personal Area Network (PAN) where the number of users is typically low.
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