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Search Results: 1 - 10 of 11186 matches for " Multiple access interference (MAI) "
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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.
Issues in Analysis & Design of IDMA & its Application
International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering , 2013,
Abstract: Interleave Division Multiple Access (IDMA) is one of the competitors for next generation wireless systems .IDMA not only inherits all the advantages of CDMA but also has the capability to overcome its deficiencies.This paper outlines a survey on interleave-division multiple-access (IDMA) technique which exploits the interleaving as only means of user separation instead of by different signatures as in a conventional code-division multiple-access (CDMA) scheme. IDMA scheme can achieve near single user performance in situations with very large numbers of users while maintaining very low receiver complexity. This technique inherits many advantages from CDMA, such as diversity against fading and mitigation of the worst-case user interference problem. The parallel and simultaneous execution of repetitive functions can be used to overcome the significant time delays involved in previous simulations of IDMA system. This paper presents an overview of IDMA and discusses the main features and areas of application as the future air interface access schemes for IMT-2000/UMTS.
Journal of Engineering Science and Technology , 2009,
Abstract: Channel time-variation (or fading) is the major source of impairment in digital wireless communications. This occurs due to mobility of the user or of the objects in the propagation environment. The limited spectral bandwidth necessitates the use of resource sharing schemes between multiple users. As the transmission medium is shared between the users, this leads to interference between the users. Sharing of resource results in interference such as multiple access interference. This paper deals with methods to study and mitigate such interference considering Rayleigh fading channels. There are various classes of fading conditions. The use of CDMA is under active research as a viable alternative to TDMA and FDMA. Performance in this system is limited by narrowband and multiple access interference. Various methods are used to mitigate them. But here, linear MMSE detector is considered. MMSE technique results in interference rejection. Its adaptive form is applied to Rayleigh fading channels, which are reflective and nondispersive. It results into better results than before.
International Journal of Engineering Science and Technology , 2010,
Abstract: In CDMA systems interference is the major problem. Reducing the interference results in direct increase in system capacity. This interference reduction can be controlled by investing additional por per user at the transmitter or by using spreading codes. The use of any orthogonal code spreading sequences provides excellent performance for the downlink of DS-CDMA systems in Additive White Gaussian noise (AWGN) channels. However, the hostile nature of the wireless channel can severely degrade the orthogonality of such sequences and unless compensated for at the receiver it will result in significant Multiple access interference (MAI). The MAI experienced by the different users depends on the cross correlations of the user’s codes as ll as the instantaneous values of the user’s data symbols to be transmitted. The principle of the proposed technique is to exploit the dependency of multiple access nterference on the instantaneous symbol values of active users. Thispaper implements the CDMA transmitter and receiver algorithm for both Adaptive code allocation, fixed code allocation with different loads.
Comparison between a conventional receiver (RC) and conventional receiver with limiting device (RC-LO) for a DS-OCDMA link using OOC codes
Boudaoud Radhwane,Chikh-Bled Mohamed
International Journal of Computer Science Issues , 2012,
Abstract: This article presents the performance of an incoherent optical connection CDMA with direct sequence (DS-OCDMA) by using an orthogonal optical codes (OOC). The influence of the multiple access interference will be studied in the case of a conventional receiver (RC) and Conventional receiver with limiting device (RC-LO).The comparison between both types of receivers enables us to evaluate the performance of the studied system.
Performance Analysis of Optical Zero Cross Correlation in OCDMA System
M.S. Anuar,S.A. Aljunid,R. Badlishah,N.M. Saad
Journal of Applied Sciences , 2007,
Abstract: We propose a new code structure for Spectral-Amplitude Coding Optical Code Division Multiple Access (OCDMA) systems with zero cross-correlation and theoretically demonstrate the performance of this code by using a direct decoding technique. The proposed code can be adapted to any weight and user by using transformation and mapping techniques, respectively. The direct decoding technique is exploited since there is no overlapping occurrence in the code construction. The code performance shows that it outperforms the existing SAC OCDMA codes such as Hadamard, Modified Frequency Hopping (MFH) and Modified Double-Weight (MDW). The system can accommodate 120 simultaneous users for a bit error rate of 10-9.
Performance Analysis of Polarization Modulated DirectDetection Optical CDMA Systems over Turbulent FSO LinksModeled by the Gamma-Gamma Distribution
Fan Bai,Yuwei Su,Takuro Sato
Photonics , 2015, DOI: 10.3390/photonics2010139
Abstract: This paper proposes a theoretical study to characterize the transmission of optical code division multiple access (CDMA) systems deploying polarization shift keying (PolSK) over a free space optical (FSO) link under the impact of atmospheric turbulence. In our analysis, a novel transceiver architecture for atmospheric OCDMA FSO systems based on polarization modulation with direct detection is proposed and discussed. A detailed analytical model for PolSK-OCDMA systems over a turbulent FSO link is provided. Further, we derive a closed-form bit error ratio (BER) and outage probability expressions, taking into account the multiple-access interference (MAI), optical noise and the atmospheric turbulence effect on the FSO link modeled by the Gamma-Gamma distribution. Finally, the results of this study show the most significant parameters that degrade the transmission performance of the PolSK-OCDMA signal over FSO links and indicate that the proposed approach offers improved bit error ratio (BER) performances compared to the on-off-keying (OOK) modulation scheme in the presence of turbulence.
Blind Adaptive Multiuser Detector Based on Robust Kalman Filter

Xue Yi-bing,Li Jian-dong,

电子与信息学报 , 2005,
Abstract: A high performance blind adaptive multiuser detection algorithm is proposed by introducing robust Kalman filter based on a compensation technique of a fictitious noise to estimate the optimal decision vector of asynchronous CDMA multiple-users receiver. This algorithm can converge rapidly, track in high accuracy and has satisfied numeric stability. Simulation results show that this algorithm can eliminate Multiple Access Interference (MAI) efficiently and is robust for numerical calculation.
Capacity Research of Asynchronous OCDMA System

Zhou Xiu-li,Yang Hua-jun,Ma Jun-xian,

电子与信息学报 , 2007,
Abstract: To research the information capacity of the Asynchronous Optical Code Division Multiple Access(OCDMA) system,the system model and its implementation under ideal channel and AWGN channel optical communications are presented. We modeled a discrete memoryless channel OCDMA system and evaluated the aggregate capacity from the probability of the output signal at the chip level. On the condition that the information capacity limited by 1 bit per chip,the results show that the interference caused by asynchronism reduces the capacity limit as the number of users increases,but for a sufficiently large number of users,both the ideal and the AWGN channel throughput limit varies slowly and the limit is around 0.71-0.75 bit/chip. With less number of users of the ideal channel,the more the input probability is lower than 0.50,the lower the largest capacity limit will be. With low noise variance of the AWGN channel,the system with smaller users can attain higher capacity limit. So the information capacity of the asynchronous OCDMA is gotten.
Performance Analysis of Multiple User Optical Code Division Multiple Access  [PDF]
Himanshu Monga, R. S. Kaler
Optics and Photonics Journal (OPJ) , 2014, DOI: 10.4236/opj.2014.42004

In this paper, we discuss and analyze an optical code division multiple access for multiple user system. Media access control implementation has been considered. For fulfilling the huge need of bandwidth services, technology tends to move to optical networks and three major optical systems come into existence. Code division of the optical network is most used and real concept interacted with users up to this time. Optical code division multiple access provides complete spectrum to each and every user for the time of accessing the channel. In the paper, we have proposed network architecture with optical encoder and decoder along with optical code translator which is supporting multiple user systems. We integrate the code translator with encoding and decoding of optical code to use the optical network at full extent and present the simulation validation results of 6 Gb/s 3-hop transmission by use of proposed architecture. Further, we have implemented experimentation with 6 users 3 Gb/s optical code division multiple access network. Through simulation structure, it is shown that the combination of encoding with EDFA in multiple user environment system provides improvement in bit error rate and also improves the multiple access interference. With increase of users in the network, MAI value increases and our proposed scheme controls interference in the network.

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