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1
Mandalapu, Harinath, and B. Murali Krishna. "FPGA implementation of DS-CDMA Transmitter and Receiver." International Journal of Reconfigurable and Embedded Systems (IJRES) 6, no. 3 (May 28, 2018): 179. http://dx.doi.org/10.11591/ijres.v6.i3.pp179-185.
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Direct sequence spread Spectrum (DSSS) is also known as direct sequence code division multiplexing. In direct sequence spread spectrum the stream of information to be transmitted is divided into small pieces each of which is allocated across to a frequency channel across the spectrum. Data signal at the point of transmission is collaborated with a higher data-rate bit sequence (also called chipping code) that divides the data according to a spreading ratio. A redundant chipping code helps the signal resist interference and also enables the original data to be recovered if data bits are damaged during the transmitting. In this project direct sequence spread spectrum principle based code division multiple access (CDMA) transmitter and receiver is implemented on SPARTAN 3E FPGA. The Xilinx synthesis technology (XST) of Xilinx ISE tool used for synthesis of transmitter and receiver on FPGA Spartan 3E.
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Argüello, Francisco, Manuel Bugallo, and Juan López. "Blind Multiuser Receivers for Chaos Based Communications." International Journal of Bifurcation and Chaos 13, no. 08 (August 2003): 2353–59. http://dx.doi.org/10.1142/s0218127403008028.
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Recently, there has been a good deal of interest in the use of chaotic signals for direct sequence code division multiple access (DS-CDMA) communication systems. The capacity of DS-CDMA systems is interference-limited, and can therefore be increased by techniques that suppress interference. This letter is devoted to the evaluation of the impact of blind multiuser detection techniques on chaos based DS-CDMA systems. Blind receivers can suppress multiple access interference and do not require knowledge of the code sequences and propagation channels of the interference. We demonstrate that, for chaotic sequence-based communications, blind multiuser receivers significantly improve the BER with respect to single-user receivers, and that their use is practically essential with a high number of users.
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Alami Hassani, Aicha, Mohcine Zouak, and Mostafa Mrabti. "Contribution to Synchronization and Tracking Modelisation in a CDMA Receiver." Journal of Engineering 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/936495.
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We propose and analyze a noncoherent receiver with PN code tracking for direct sequence code division multiple access (DS-CDMA) communication systems. We employ the delay-lock loop (DLL) architectures for the tracking stage. The choice of DLL parameters is studied with special focus on DS-CDMA communication systems and orthogonality conditions. We described the modeling and simulation of the NCO using hardware description language VHDL. Details of the VHDL implementation are shown.
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Uddin, Jia, Mohammed Faisal, Md Facihul Azam, and A. F. M. Muzahidur Rahman. "Performance Analysis of Multicarrier Code Division Multiple Access over Rayleigh Fading Channel." Advanced Materials Research 457-458 (January 2012): 985–88. http://dx.doi.org/10.4028/www.scientific.net/amr.457-458.985.
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Recently, multi-carrier transmission schemes have been introduced into Code Division Multiple Access (CDMA) systems to gain advantages for high data rate transmission as well as security. Due to pseudorandom code there is no chance to Inter Symbol Interference (ISI). There are different techniques to mitigate multipath fading. One of the method is to transmit identical narrowband direct-sequence (DS) waveforms in parallel over a number of sub-channels using frequency diversity. Implementation this multi-carrier modulation technique in CDMA system is known as multi-carrier CDMA (MC-CDMA). In Rayleigh fading channel, due to multi-carrier modulation, when one subcarrier goes deep fade another subcarrier may remain safe. Therefore it combats multi-path fading and signal can be received in low bit error rate.
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Men, Wei, Liang Zhang, Jing-wei Yin, Xiao Han, and Hong-yu Yin. "Blind beamforming-based strong interference suppression in underwater acoustic direct-sequence code-division multiple-access systems." Journal of the Acoustical Society of America 152, no. 4 (October 2022): 2128–39. http://dx.doi.org/10.1121/10.0014598.
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In an underwater acoustic direct-sequence code-division multiple-access (DS-CDMA) system, the performance of the conventional receiver is severely limited by the strong multiple-access interferences, which is due to the near-far effect. In this paper, a time-frequency-time with eigendecomposition-based blind beamformer (TFT-EBB) method is proposed for a distant user to suppress strong interference from a nearby user in DS-CDMA underwater acoustic communications. When the interference level is moderately higher than that of the desired signal, the TFT-EBB method can estimate the composite steering vector of all multipath components of the weak desired user signal via the eigendecomposition of the array covariance matrix at each frequency bin. Then the proposed energy detection-based RAKE receiver is cascaded to achieve multipath diversity, in which it requires less prior information compared with the conventional RAKE receiver. The proposed method is evaluated by using both simulated and field experimental data, which verifies its effectiveness.
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Bilal Abdalla, Khalid Hamid. "Simulation Performance of CDMA/QA in Mobile Channel." FES Journal of Engineering Sciences 5, no. 1 (October 6, 2011): 14. http://dx.doi.org/10.52981/fjes.v5i1.32.
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The aim of this work is to study, analyze and evaluate software the link performance of mobile communication system under the impairment of the multiple access schemes, down-link thermal noise and the multipath fading in the mobile channel. For this purpose, modeling and simulation has been used to study the effects of nonlinearities in mobile channel using spread spectrum for Direct Sequence Code Division Multiple Access, with Quadrature Amplitude Modulation (DS-CDMA/QAM).
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Liu, Xiao Zhi, Da Wei Feng, and Tian Shuang Zhang. "Multi-User Detection of DS-CDMA Based on Improved-FastICA." Applied Mechanics and Materials 128-129 (October 2011): 633–36. http://dx.doi.org/10.4028/www.scientific.net/amm.128-129.633.
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Multi-user detection (MUD) is used to control multiple access interference (MAI) and promote system performance and capacity, which is one of the key technology for CDMA system. Independent component analysis (ICA) aims to recover a set of unknown mutually independent source signals from theirs observed mixtures without knowledge of the mixing coefficients. FastICA, one of the ICA methods, has been successfully applied in various fields. But the classical FastICA does not converge quickly. In multi-user detection of direct sequence code division multiple access (DS-CDMA) system, we proposes an Improved-FastICA algorithm to reduce multiple access interference (MAI). The improved-FastICA algorithm uses a new Fifth-order Newton iterative method to estimate the negentropy. The experimental results show that the improved algorithm has the advantages of smaller bit error rate than traditional algorithm. The Improved-FastICA is more suitable for applications in DS-CDMA system.
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Hassani, A., Y. Garrouani, F. Mrabti, and F. Abdi. "Acquisition Time and Probabilities of Detection and False Alarm in Direct Sequence Code Division Multiple Access Systems." Jordan Journal of Electrical Engineering 9, no. 1 (2023): 60. http://dx.doi.org/10.5455/jjee.204-1668454435.
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Multiple access interference (MAI) is one of the most important issues to consider in the design, implementation and operation of 5G systems using code division multiple access (CDMA) technique based on spread spectrum that offers a more flexible solution, compared to other techniques. Especially, it permits a much higher user bit rate, due to the bandwidth allocated to the emitted signal; thus, allowing very attractive multimedia services. In this paper, we develop the expressions of the detection probability, false alarm probability and the average acquisition time - in a direct sequence CDMA (DS-CDMA) transmission system - using a serial search and taking into consideration MAI. The evolution of these parameters according to the signal- to-noise ratio (SNR) and the decision threshold leads to study performances of the system in terms of detection and average acquisition time. The obtained results reveal that the acquisition time decreases when the SNR increases. Additionally, it is found that the probability of detection increases when the threshold decreases, and increasing SNR it reaches a constant value for an SNR/chip around 0 dB for all thresholds.
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Litvinenko, A., and E. Bekeris. "Statistical Analysis of Multiple Access Interference in Chaotic Spreading Sequence Based DS-CDMA Systems." Electronics ETF 21, no. 1 (July 14, 2017): 34. http://dx.doi.org/10.7251/els1721034l.
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This paper presents a statistical analysis of multiple access interference (MAI) in Direct Sequence Code Division Multiple Access (DS-CDMA) communication systems based on different types of chaotic spreading sequences. The probability distribution of the interference in a system with K users causing the MAI is studied using MATLAB simulation. For chaotic spreading sequence generation six different 1-D chaotic maps are used: modified Bernoulli, modified Tent, Gauss, Sine-Circle, Cubic and Pinchers map. A brief statistical analysis of the cross-correlation properties of the chaotic sequences generated by the aforementioned maps is also presented.
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Varzakas, Panagiotis. "Capacity Estimation for a DS-CDMA System in Nakagami-m Fading." WSEAS TRANSACTIONS ON COMMUNICATIONS 21 (March 3, 2022): 31–33. http://dx.doi.org/10.37394/23204.2022.21.6.
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Ιn this paper, a novel closed-form expression of the Shannon average channel capacity per user for direct- sequence code-division multiple access (DS-CDMA) systems, operating in Nakagami-m fading, with optimum RAKE reception, is obtained. Numerical results are also presented to illustrate the proposed mathematical analysis and to point out the effect of the fading severity on the user’s average channel capacity.
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Litviņenko, Anna, and Artūrs Āboltiņš. "Computationally Efficient Chaotic Spreading Sequence Selection for Asynchronous DS-CDMA." Electrical, Control and Communication Engineering 13, no. 1 (December 1, 2017): 75–80. http://dx.doi.org/10.1515/ecce-2017-0011.
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Abstract The choice of the spreading sequence for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems plays a crucial role for the mitigation of multiple-access interference. Considering the rich dynamics of chaotic sequences, their use for spreading allows overcoming the limitations of the classical spreading sequences. However, to ensure low cross-correlation between the sequences, careful selection must be performed. This paper presents a novel exhaustive search algorithm, which allows finding sets of chaotic spreading sequences of required length with a particularly low mutual cross-correlation. The efficiency of the search is verified by simulations, which show a significant advantage compared to non-selected chaotic sequences. Moreover, the impact of sequence length on the efficiency of the selection is studied.
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LIM, ALVIN, and KUI MOK. "PERFORMANCE EVALUATION OF ADAPTIVE MEDIA ACCESS CONTROL PROTOCOLS FOR PERVASIVE WIRELESS NETWORKS." Journal of Interconnection Networks 03, no. 03n04 (September 2002): 253–72. http://dx.doi.org/10.1142/s0219265902000665.
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As pervasive and high-density wireless networks become increasingly common, it is critical to address the problems of intermittent disconnection, high error rate and collision that cause degradation in the performance of wireless media access control protocols, such as slotted ALOHA Time Division Multiple Access (slotted ALOHA/TDMA) and Direct Sequence Code Division Multiple Access (DS/CDMA). We propose adaptive techniques for improving performance of media access protocols through awareness of the mobile communication environment. These techniques involve detection of intermittent disconnection, high error rates, and collisions. Upon detection and notification of these conditions by snooping devices, the media access control layer adapts its operation and synchronization accordingly to reduce delay and loss of bandwidth. Results from our simulation studies show that adaptive TDMA improves performance by as much as 12 times over basic TDMA and adaptive CDMA improves by as much as 4 times over basic CDMA in wireless network with high density cells. Overall, adaptive CDMA still performs better than adaptive TDMA by about 4 times.
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Biteur, Kada, Belkacem Benadda, and Ahmed Ayad. "New approach to a DS-CDMA-UWB system using a pseudo orthogonal code (POC)." Facta universitatis - series: Electronics and Energetics 35, no. 4 (2022): 483–93. http://dx.doi.org/10.2298/fuee2204483b.
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Ultra-Wideband Direct Sequences Code Division Multiple Access (DS-DMA) plays an important role in the case of multi-terminal multi-application communications of UWB devices. In the case of UWB systems that exploit the injection of the pulse itself directly to the antenna hence the very wide bandwidth, generation of suitable DS-CDMA codes poses a real challenge. In this paper we will describe our novel UWB transmission which uses pseudo-orthogonal time code (POC) as DS-CDMA sequences. The suggested codes are unipolar sequences with chips that may be dynamically modified to target a certain number of users or applications. Our approach bypasses the modulations schemes commonly used on UWB systems. Moreover, as perspectives to our work, it would be very interesting to realize our new approach based on an FPGA circuit.
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Mvuma, Aloys. "Adaptive IIR Filters for Single Interference Suppression in a BPSK DS CDMA System In Rayleigh Fading Channel." Tanzania Journal of Engineering and Technology 30, no. 1 (June 30, 2007): 65–73. http://dx.doi.org/10.52339/tjet.v30i1.398.
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In this paper, effect of a single narrow-band interference (NBI) on bit error rate (BER) performance for a binary phase shift keying (BPSK) synchronous direct-sequence code-division multiple access (DS CDMA) communication system operating in a frequency nonselective Rayleigh fading channel is analyzed. Second-order adaptive infinite impulseresponse (IIR) notch filters with plain gradient algorithm (GA) for suppression of NBI in the DS CDMA system are proposed. A general closed-form BER expression for the DS CDMA system with NBI suppression second order adaptive IIR notch filters is derived based on the standard Gaussian approximation (SGA) method. BER expressions are then derived for the allpass filter-based adaptive IIR notch filter and adaptive IIR notch filter with constrained poles and zeros, the two structures that are commonly found in literature. It is observed that both adaptive IIR notch filter structures exhibit comparable BER performance. Extensive computer simulation results are presented to verify the accuracy and limitations of the analysis.
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Zope, Rajendrakumar Govinda, and Balasaheb Shrirangrao Agarkar. "Channel Estimation for DS-CDMA Rake Receiver using Sparse Recovery Approach." International Journal of Recent Technology and Engineering (IJRTE) 11, no. 1 (May 30, 2022): 41–46. http://dx.doi.org/10.35940/ijrte.f6841.0511122.
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In the literature of direct-sequence code-division multiple-access (DS-CDMA), for issues related to channel estimation, some exclusive architectures have been proposed, which are characterized by known channel noise statistics and noise observation. But in reality, the channel parameters are frequently assessed utilizing training sequences that lead to difficulty in obtaining the channel noise statistics. Channel estimation quality has been proved to play an important role in the performance of rake receiver. This paper addresses the issues of optimizing DS–CDMA rake receiver channel estimation equipped with an Iterative least square sparse recovery (IL2SR) channel estimator. Moreover, the ambient noises corrupt the signal received and multiple-access interference further aggravates it. Because of this observation noises become hard to acquire. Hence this paper proposes as an iterative least square structure for channel estimation algorithm in rake receiver employed in DS-CDMA communication systems. Further, examination of blind channel estimation problem for rake-based DS-CDMA communication framework having multi-path fading channels with time variation is also attempted. The validity of the proposed techniques has been verified through results obtained from simulation for different channel parameters and spreading codes. Further exploration has been carried out with execution of the IL2SR with Rake receiver in DS-CDMA framework for multi-path fading channels. It is found that better performance is obtained with this framework under various channels with different spreading codes. The proposed system is compared with Kalman based techniques and it was found that DS-CDMA framework under additive white gaussian noise (AWGN)channel with IL2SR receiver reveals better outcomes in terms of bit error rate (BER). Also, there has been improvement in video quality while using the proposed IL2SR receiver with increase in the values of ratio of signal to noise ratio.
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Srinivasa, Rao V., Kumar P. Vinay, S. Balaji, Khan Habibulla, and Kumar T. Anil. "Robust Multiuser Detection in Synchronous DS-CDMA System with MRC Receive Diversity over Nakagami-m Fading Channel." Advanced Engineering Forum 4 (June 2012): 43–50. http://dx.doi.org/10.4028/www.scientific.net/aef.4.43.
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This paper presents the robust multiuser detection in synchronous direct sequence-code division multiple access (DS-CDMA) systems with Maximal Ratio Combiner (MRC) receive diversity over frequency-nonselective, slowly fading Nakagami-m channels in a non-Gaussian environment. Average probability of error is derived for decorrelating detector over single path Nakagami-m fading channel. A new M-estimator proposed to robustify the detector is studied and analyzed. Simulation results show that the new M-estimator outperforms linear decorrelating detector, the Huber, and the Hampel estimator based detectors.
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N. Motade, Sumitra, and Anju V. Kulkarni. "Incremental gradient algorithm for multiuser detection in multi-carrier DS-CDMA system under modulation schemes." International Journal of Engineering & Technology 7, no. 2.6 (March 11, 2018): 311. http://dx.doi.org/10.14419/ijet.v7i2.6.11270.
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Nowadays, Multicarrier Direct sequence code division multiple access (MC DS-CDMA) systems are used in mobile communication. Performance of these systems are limited by multiple access interference (MAI) created by spread-spectrum users in the channel as well as background channel noise. This paper proposes an incremental gradient descent (IGD) multi-user detection (MUD) for MC DS-CDMA system that can achieve near-optimum performance while the number of users is linear in its implementation complexity. The IGD algorithm make an effort to perform optimum MUD by updating one user's bit decision each iteration in the best way. This algorithm accelerates the gradient algorithm convergence by averaging. When a minimum mean square error (MMSE) MUD is employed to initialize the proposed algorithm, in all cases tested the gradient search converges to a solution with optimum performance. Further, the iterative tests denote that the proposed IGD algorithm provides significant performance for cases where other suboptimum algorithms perform poorly. Simulation compares the proposed IGD algorithm with the conventional detectors.
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Cheng, Hao, Na Yu, and Jun Liu. "Improved Natural Gradient Algorithms for Multi-Channel Signal Separation." Applied Mechanics and Materials 651-653 (September 2014): 2326–30. http://dx.doi.org/10.4028/www.scientific.net/amm.651-653.2326.
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In this paper, an Multi-channel blind separation of Direct Sequence Code Division Multiple Access (DS-CDMA) has been introduced. Most of which we assume statistically stationary sources as well as instantaneous mixtures of signals using blind source separation (BSS) algorithms. In practicality, the CDMA sources received are convolute mixing. A more complex blind separation algorithm is required to achieve better source separation. Based on the minimizing the average squared cross-output-channel-correlation, the proposed scheme obtains the better source separation. Simulation results show that the proposed optimal scheme not only achieves superior bit error rate (BER) performance to those of the existing ones, but also provides a guaranteed-convergent solution under different channel conditions.
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Elmissaoui, Taoufik. "Multi-Access Techniques Comparison for Remote Lab System." International Journal of Online and Biomedical Engineering (iJOE) 19, no. 12 (August 31, 2023): 4–15. http://dx.doi.org/10.3991/ijoe.v19i12.39681.
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Remote lab systems are one of the essential requirements for an increased academic productivity in the modern digital world. These systems support and facilitate effective migration from face-to-face classroom education to online education. Digital technology applications and processes are required to easily build a remote lab system. With the availability of multiple access techniques, users can comfortably share laboratory equipment among themselves. The sharing of resources using the remote lab system is highly required for a smooth deployment and implementation of online education. This paper therefore proposed and tested some techniques that combine Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) in remote lab systems. The tested techniques are Multi-Carrier Direct Sequence CDMA (MC-DS-CDMA), Multi-Tone CDMA (MT-CDMA), Multi-Carrier CDMA (MC-CDMA), and Spread Spectrum Multi-Carrier Multiple Access (SS-MC-MA). The first step proposed in this work had to do with the setting of the comparison criteria. At the second step, the solutions cited previously in the real equipment was tested and the best option that met the criteria was selected for the eLab system since the performance technique varies with the laboratory equipment characteristic. The four techniques that were tested demonstrated high performance in telecommunications and online laboratory systems. The implementation of these techniques will benefit universities in several ways, which include reduction of remote lab cost and optimization of sharing of online resources among users. This will further provide students with conducive learning environment by addressing the challenges of reservation and time slot limit. It is therefore recommended that MC-CDMA should be integrated into remote lab system.
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Wang, Wei, and Chunyan Han. "H∞Channel Estimation for DS-CDMA Systems: A Partial Difference Equation Approach." Mathematical Problems in Engineering 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/307342.
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In the communications literature, a number of different algorithms have been proposed for channel estimation problems with the statistics of the channel noise and observation noise exactly known. In practical systems, however, the channel parameters are often estimated using training sequences which lead to the statistics of the channel noise difficult to obtain. Moreover, the received signals are corrupted not only by the ambient noises but also by multiple-access interferences, so the statistics of observation noises is also difficult to obtain. In this paper, we will investigate theH∞channel estimation problem for direct-sequence code-division multiple-access (DS-CDMA) communication systems with time-varying multipath fading channels. The channel estimator is designed by applying a partial difference equation approach together with the innovation analysis theory. This method can give a sufficient and necessary condition for the existence of anH∞channel estimator.
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Tuzlukov, Vyacheslav. "Performance of Generalized Receiver Employed by Broadband Multicarrier DS-CDMA System Using Space-Time Spreading-Assisted Transmit Diversity." WSEAS TRANSACTIONS ON COMMUNICATIONS 20 (September 29, 2021): 152–71. http://dx.doi.org/10.37394/23204.2021.20.21.
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In this paper the multicarrier direct-sequence code-division multiple access (MC DS-CDMA) using space-time spreading assisted transmit diversity is investigated in the context of broadband wireless communi-cations systems constructed based on the generalized approach to signal processing in noise over frequency-se-lective Rayleigh fading channels. We consider the issue of parameter design for the sake of achieving high-ef-ficiency communications in various dispersive environments. In contrast to the conventional MC DS-CDMA wireless communication system employing the time (T)-domain spreading only, in the present paper the broad-band wireless MC DS-CDMA wireless communication schemes employ both the time (T)-domain and frequen-cy (F)-domain spreading, i.e., employ the TF-domain spreading. The bit-error rate (BER) performance of the space-time spreading assisted broadband MC DS-CDMA wireless communications system is investigated for down-link transmissions associated with the single user and multiuser generalized detectors and is compared with that of the single user correlation detector and the multiuser decorrelating detector. Our study demonstra-tes that with appropriately selecting the system parameters, the broadband MC DS-CDMA wireless communi-cation system using the space-time spreading assisted transmit diversity constitutes a promising downlink tran-smission scheme. This scheme is capable to support ubiquitous communications over diverse communication environments without the BER performance degradation
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Dahmane, Adel Omar, and Lotfi Mejri. "FPGA Implementation of Block Parallel DF-MPIC Detectors for DS-CDMA Systems in Frequency-Nonselective Channels." Research Letters in Communications 2008 (2008): 1–5. http://dx.doi.org/10.1155/2008/435756.
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Multistage parallel interference cancellation- (MPIC-) based detectors allow to mitigate multiple-access interference in direct-sequence code-division multiple-access (DS-CDMA) systems. They are considered serious candidates for practical implementation showing a good tradeoff between performance and complexity. Better performance is obtained when decision feedback (DF) is employed. Although MPIC and DF-MPIC have the same arithmetic complexity, DF-MPIC needs much more FPGA resources when compared to MPIC without decision feedback. In this letter, FPGA implementation of block parallel DF-MPIC (BP-DF-MPIC) is proposed allowing better tradeoff between performance and FPGA area occupancy. To reach an uncoded bit-error rate of10−3, BP-DF-MPIC shows a 1.5 dB improvement over the MPIC without decision feedback with only 8% increase in FPGA resources compared to 69% for DF-MPIC.
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Sirithummachak, P., and C. Benjangkaprasert. "Adaptive Equalizer for DS-CDMA Multi-User Communication System Using Sign-Algorithm Based on Laguerre Filter Structure." Applied Mechanics and Materials 548-549 (April 2014): 1231–34. http://dx.doi.org/10.4028/www.scientific.net/amm.548-549.1231.
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This paper proposes a sign-algorithm based on adaptive Laguerre filter structure for improving the performance of the direct sequence-code division multiple access (DS-CDMA) communication system. The proposed adaptive equalizer employs a combination of sign and least mean square (LMS) algorithms to minimizing the effect of inter-symbol interference (ISI) that arises due to multipath propagation, and the computational complexity of equalizer. The performance of proposed equalizer was compared with traditional equalizers such as LMS and RLS algorithms in terms of varying path. The function detail and performance results of the proposed equalizer are described by computer simulations in terms of the bit error rate (BER).
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Tuzlukov, Vyacheslav. "Generalized Receiver with Decision-Feedback Equalizer for Multicode Wideband DS-CDMA." WSEAS TRANSACTIONS ON CIRCUITS AND SYSTEMS 21 (September 1, 2022): 202–22. http://dx.doi.org/10.37394/23201.2022.21.23.
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In the present paper, a chip-level minimum mean-square-error (MMSE) decision-feedback equalizer for the downlink receiver of multicode wideband direct sequence code-division multiple access (DS-CDMA) wireless communication systems over frequency-selective channels is investigated. Firstly, the MMSE per sym-bol achievable by an optimal decision-feedback equalizer is derived, assuming that all interchip interference (ICI) of the desired user can be eliminated. The MMSE of the decision-feedback equalizer is always less than or at most equal to that of linear equalizers. When all the active codes belong to the desired user, the ideal deci-sion-feedback equalizer is able to eliminate multicode interference and approach the performance of the single-code case at high signal-to-noise ratio (SNR) range. Secondly, we apply the hypothesis-feedback equalizer or tentative-chip decision-feedback equalizer in the multicode scenario. The tentative-chip decision-feedback equ-alizer outperforms the chip-level linear equalizer and the decision-feedback equalizer that only feeds back the symbols already decided. The performance gain increases with SNR, but decreases with the number of active codes owned by the other users. When all the active codes are assigned to the desired user, the tentative-chip decision-feedback equalizer eliminates the multicode interference and achieves single-user performance at the high SNR, similarly, to the ideal decision-feedback equalizer. The asymptotic performance of the decision-feed-back equalizer is confirmed through the bit error rate (BER) simulation over various channels.
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Wang, Feng, and Xuan De Ji. "A Joint Chip Equalization Adaptive Rake Receiver for DS-CDMA UWB Systems over ISI Channels." Advanced Materials Research 505 (April 2012): 274–81. http://dx.doi.org/10.4028/www.scientific.net/amr.505.274.
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There is serious inter-symbol interference (ISI) when ultra-wideband (UWB) wireless communication systems work at high data speed since there is much larger channel delay spread. The serious ISI becomes a major factor that affects the performance of UWB systems. In this paper, suppression ISI is developed for direct sequence spread-code division multiple access (DS-CDMA) UWB systems with a high data speed, and a joint chip equalization adaptive Rake (JCE-Rake) receiver is proposed. The proposed JCE-Rake receiver spreads the number of traditional Rake receiver taps to collect multi-path component and equalize the inter-chip interference simultaneously. Then the soft output of JCE-Rake receiver is despreaded with the user's spreading code. Finally the decision is made to recover the transmitted symbol. The simulation results verify that ISI is suppressed effectively and the system performance is improved evidently.
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Khan, Mr Wasim, Mrs Nilofar Khan, and Sanmati Jain. "BER performance analysis of Subtractive interference cancellation (SIC) Using Rayleigh channel in DS-CDMA Receiver system." INTERNATIONAL JOURNAL OF COMPUTERS & TECHNOLOGY 13, no. 6 (June 30, 2014): 4603–14. http://dx.doi.org/10.24297/ijct.v13i6.2523.
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In this paper, we present and analyze the performance of a parallel interference cancellation (PIC) scheme for multicarrier (MC) direct-sequence code-division multiple-access (DS-CDMA) systems. In order to mitigate the multi-path interference (MPI) in the DS CDMA system. At each cancellation stage in the proposed PIC scheme, on each subcarrier, a weighted sum of the soft outputs of the other users in the current stage is cancelled from the soft output of the desired user to form the input to the next stage. At the last stage, the interference cancelled outputs from all the subcarriers are maximal ratio combined (MRC) to form the decision statistic. Parallel interference elimination is first proposed in this paper the multi-path interference are evaluated by tentative decision and known user information. Then the performance over Rayleigh fading channel are analyzed and compared to Matched filter, Decorelator, successive interference cancellation (SIC) and conventional parallel interference cancellation (PIC). It is shown that PIC performance can be improved greatly by using this method with simple structure and easy implementation.
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Umamaheswari, R., M. Ramya Princess, and P. Nirmal Kumar. "Improved Whale Optimized MLP Neural Network-Based Learning Mechanism for Multiuser Detection in MIMO Communication System." Journal of Circuits, Systems and Computers 29, no. 15 (May 6, 2020): 2050239. http://dx.doi.org/10.1142/s0218126620502394.
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Direct-Sequence Code Division Multiple Access (DS-CDMA) is a digital method to spread spectrum modulation for digital signal transmission. We propose to detect signal in DS-CDMA communication using the learning mechanism. Initially, the user signals are spread using the respective pseudo-noise (PN) code where the input signal is multiplied with the code which is then modulated using the quadrature phase shift keying (QPSK) modulator. The modulated signal is then transmitted in a 3G/4G channel considering all types of fading. The transmitted signal is received by the antenna array which is performed by demodulation. We propose to adaptively assign the weights by employing Improved Whale Optimized Multi-Layer Perceptron Neural Network (IWMLP-NN)-based learning mechanism. To design IWMLP-NN, Improved Whale Optimization Algorithm is combined with multilayer perceptron neural network. This is used instead of the normal Multiple Signal Classification (MUSIC) and least mean squares (LMS)/root-mean-square (RMS) algorithms used in beam-forming networks. After assigning weight through IWMLP-NN-based learning mechanism, we de-spread to get the original user data. We have compared our proposed technique with the normal techniques with the help of plots of Bit Error Rate (BER) versus Signal-to-Noise Ratio (SNR). We use both the AWGN channel and fading channel for analysis. Experimental results prove that our proposed method achieves better BER performance results even with deep fading.
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She, Feng, Hsiao Hwa Chen, and Hongyang Li. "Joint Angular and Time Diversity of Multi-Antenna CDMA Systems in Wireless Fading Channels." International Journal of Wireless Networks and Broadband Technologies 1, no. 1 (January 2011): 1–14. http://dx.doi.org/10.4018/ijwnbt.2011010101.
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In this paper, a multi-antenna based receiver structure for direct sequence code division multiple access (DS/CDMA) system is proposed. The proposed scheme exploits the excellent time resolution of a CDMA RAKE receiver and uses an antenna array beamforming structure to resolve multipath returns in both angular and time domains. A much higher diversity gain than that based only on the time domain diversity can be achieved. This work suggests a new space-time diversity paradigm, namely angular-time diversity, which differs from traditional Alamouti-type space-time coded schemes. The impairments caused by multipath and multiuser interference are analyzed. The performance of the proposed receiver in multipath fading channel is explicitly evaluated. An expression for uncoded system bit error probability is derived. Simulation results show the performance improvement in terms of BER due to the use of multi-antenna in the receiver, and the results illustrate that the multi-antenna based receiver works effectively in resolving multipaths in both angular and time domains to achieve performance improvement due to angular and time diversity gain provided by the multi-antenna system.
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Varzakas, P. "Statistics of the Channel Capacity in a Cellular DS/FFH-CDMA Rayleigh Fading System." WSEAS TRANSACTIONS ON INFORMATION SCIENCE AND APPLICATIONS 18 (December 31, 2021): 151–55. http://dx.doi.org/10.37394/23209.2021.18.18.
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In this paper, we derive analytically the probability density function (pdf) of the theoretically achievable average channel capacity per user (in the Shannon sense) for a constant total system’s allocated bandwidth hybrid direct-sequence/fast frequency hopping code-division multiple-access (DS/FFHCDMA) cellular system, when operating in a Rayleigh fading environment. Then, the analysis leads to a theoretical novelclosed form expression for the pdf of the channel capacity, which relates the pdf of the channel capacity per user and all system’s parameters. In addition, the probability that the channel capacity per user does not exceed the available average channel capacity per user, in a Rayleigh fading environment, is calculated and respective numerical results are presented to investigate the sensitivity of this probability value from various system’s parameters. Finally, the derived expression can be useful for the initial practical design of a DS/FFHCDMA cellular system and for a quantitative analysis.
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Rani, Ankita, and Deepak Kedia. "Performance Analysis of 2-D Prime Codes Encoded Optical CDMA System." Journal of Optical Communications 40, no. 4 (October 25, 2019): 463–72. http://dx.doi.org/10.1515/joc-2017-0115.
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Abstract Optical code division multiple access (OCDMA) system provides highly secured transmission in addition to its capabilities to support asynchronous transmission and soft blocking. Two-dimensional OCDMA codes are chosen in this paper due to their high cardinality, good spectral efficiency and flexibility in their construction methods against direct sequence codes. This paper focuses on study of impact of multiple access interference (MAI) at high data rates for 2-D prime codesbased OCDMA system. It is shown that how the change in number of simultaneous users affects the transmission quality. Further, performance of the system is analysed in terms of bit error rate, received electrical power and eye openings. In addition, this paper also shows a comparative analysis of 2-D codes-based OCDMA system and wavelength division multiple access (WDMA) system in order to justify the improved performance of the proposed system. It is observed that the performance of 2-D OCDMA system is much better than WDMA system in terms of quality as well as security.
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Cotae, Paul, and Matt Aguirre. "Method for Minimizing Total Generalized Squared Correlation of Synchronous DS-CDMA Signature Sequence Sets in Multipath Channels." Journal of Communications Software and Systems 2, no. 1 (April 6, 2017): 20. http://dx.doi.org/10.24138/jcomss.v2i1.302.
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We characterize the Total Generalized Squared Correlation (TGSC) for a given signature sequence set used in uplink synchronous code division multiple access (S-CDMA) when channel state information is known perfectly at bothtransmitter and receiver. We give a definition of the TGSC based on the eigenvalues of Gram matrix associated to signature sequences set for multipath channels in the presence of the colored noise. Total Squared Correlation (TSC) and Total Weighted Squared Correlation (TWSC) measures are particular cases of TGSC. We present a method for minimizing TGSC (TSC, TWSC) in multipath channels and in the presence of the colored noise. Numerical results for overloaded synchronous CDMA systems are presented in order to support our analysis.
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Herdiana, Budi, Muhammad Aria, and Jana Utama. "PEMBANGKITAN DATA ACAK TERSEBAR DIRECT SEQUENCE SPREAD SPECTRUM PADA LAJU DATA BERKECEPATAN RENDAH UNTUK APLIKASI TEKNOLOGI CODE DIVISION MULTIPLE ACCESS." SINERGI 21, no. 3 (November 15, 2017): 187. http://dx.doi.org/10.22441/sinergi.2017.3.005.
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Salah satu kelebihan utama sistem komunikasi Spread Spectrum adalah kemampuannya mengirimkan data informasi disertai kode-kode unik sehingga hanya perangkat penerima tertentu saya yang mampu mendeteksinya. Sangat banyak metode pembangkitan kode unik pada spread spectrum ini yang mana salah satunya adalah direct sequence. Penerapan metode ini banyak direalisasikan pada teknologi CDMA dikarenakan kesederhanaan rancangan dan relatif mudah dalam menganalisis karakteristik kerja sistemnya terutama bagian sebaran kode unik pada sebuah lebar pita transmisi radio. Sumber kode unik dalam penelitian ini berasal dari data acak yang dihasilkan oleh pembangkit derau semu atau pseudo noise generator melalui pengaturan panjang kodenya sebesar 16 dengan tingkat kestabilan frekuensi sistem pembangkit kode unik dan frekuensi pembawa masing-masing sebesar 15,020 kHz dan 499,9419 kHz dimana keduanya ini masing-masing menghasilkan nilai persen kesalahannya sebesar 0,0412 % dan 0,000049 % sehingga dampaknya masih cukup baik bagi metode ini apabila diimplementasikan pada teknologi CDMA khususnya diperuntukan untuk laju kecepatan data rendah.
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Zhu, Yun Hang, Qiong Cai, and Xiu Liang Huang. "Research on Key Technologies in Multi-Robotic Spread Spectrum Communication System." Advanced Materials Research 756-759 (September 2013): 2401–5. http://dx.doi.org/10.4028/www.scientific.net/amr.756-759.2401.
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It has become a hot research topic that to improve the coordination performance of multi-robotic system by communication. With rapid development of wireless communication and robot technologies, multi-robotic system based on spread-spectrum technology has become product of combining two technologies. Code Division Multiple Access (CDMA) technology is applied in multi-robotic communication system here. According to the modified m-Walsh sequence got by the way of analyzing the relation characteristic of Walsh-code and m-sequence, the best direct sequence spread spectrum (DSSS) PN code and the improved RAKE receiver scheme are proposed, which satisfied the requirements of real-time performance, reliability and confidentiality in multi-robotic communication system, and have great significance for the research of multi-robotic communication system.
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Gultom, Imeldawaty. "CDMA Modulation for Communication System Environment using Frequency Hopping Spread Spectrum." International Innovative Research Journal of Engineering and Technology 6, no. 1 (September 30, 2020): EC—1—EC—13. http://dx.doi.org/10.32595/iirjet.org/v6i1.2020.131.
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In this paper, an overall framework for a joint Special emphasis is placed on the communication segment of the sensing system at 85 GHz. Code division multiplexing using frequency hopping spread spectrum signals is implemented at 85 ghz to take advantage of reduced interference between ambient communication. The framework, which spans the entire chain of signal processing, mat lab is enabled, explained, and simulated using data networking. A template, able to scatter, fraud detection, including radio frequency-block and synchronization non-idealities are built up and analyzed. Also, the implementation of a channel model is into the Win Prop technology and embedded into the simulation of simu link. In the previous paper, they implemented the code division multiple access using a direct sequence spread spectrum at 77ghz for secure communication. Because of using 77ghz for the direct sequence spread spectrum, there will occur noise distortion and interference in the communication system. So that there will be poor system communication between transmitter and receiver. To overcome these problems, our paper explains the implementation of code division multiple access using frequency hopping spread spectrum for better and secure communications. By using this frequency-hopping spread spectrum technology, we can reduce the noise distortion and interference between the transmitter and the receiver. So that our system will be in proper condition to transmit the signals in the same range of frequency without any interference and distortion. FHSS systems can allow a higher aggregate bandwidth for coverage because FHSS provides more channels in the same range of frequencies. In accordance with the bit-error-rate, the module is assessed. By creating white Gaussian additive noise. The attribute is proven to reconcile the theoretical assumptions with the outcomes. By organizing a Rake-Receiver, the system is further boosted with structure configuration without any distortions.
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Saragih, Hoga, and Fendy Santoso. "Capture Delay Analysis on the Throughputs of Direct-Sequence Code Division Multiple Access (DS-CDMA) with Slotted-ALOHA (S-ALOHA) Systems over Nakagami/Nakagami Fading Channels." International Journal of Wireless Information Networks 18, no. 3 (May 8, 2011): 186–92. http://dx.doi.org/10.1007/s10776-011-0144-2.
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Tuzlukov, Vyacheslav. "Generalized Receiver with Parallel Interference Cancellation for Multiuser Detection." WSEAS TRANSACTIONS ON SYSTEMS AND CONTROL 16 (December 9, 2021): 633–54. http://dx.doi.org/10.37394/23203.2021.16.59.
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Parallel interference cancellation is considered as a simple yet effective multiuser detector for direct -sequence code-division multiple-access (DS-CDMA) systems. However, system performance be deteriorated due to unreliable interference cancellation in the early stages. Thus, a detector with the partial parallel interfere-nce cancellation in which the partial cancellation factors are introduced to control the interference cancellation level has been developed as a remedy. Although the partial cancellation factors are crucial, complete solutions for their optimal values are not available. In this paper, we consider a two-stage decoupled generalized receiver with the partial parallel interference cancellation. Using the minimum bit error rate (BER) criterion, we derive a complete set of optimal partial cancellation factors. This includes the optimal partial cancellation factors for pe-riodic and aperiodic spreading codes in channels with the additive white Gaussian noise and multipath chann-els. Simulation results demonstrate that the considered theoretical optimal partial cancellation factors agree clo-sely with empirical ones. The proposed two-stage generalized receiver with the partial parallel interference can-cellation using the derived optimal partial cancellation factors outperforms not only a two-stage, but also a three-stage conventional generalized receiver with the full parallel interference cancellation.
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Kadhim, Nader Abdullah, Ali jawad Alrubaie, and Ameer Al-khaykan. "Two cross coupled and Madgwicks filter for estimation of multi-channel dividing systems." Indonesian Journal of Electrical Engineering and Computer Science 27, no. 1 (July 1, 2022): 262. http://dx.doi.org/10.11591/ijeecs.v27.i1.pp262-270.
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The estimates of Rayleigh fading channels are rapidly changing in multi carrier direct sequence code division multiple access (MC-DS-CDMA) multiplexing systems. The most widely accepted answer to this issue is the conventional solution least square (LS) or mean square error estimator (MMSE) using the recursive least squares algorithm (RLS) or the least mean squares (LMS) algorithm. In much of the previous work, only one Kalman filter was used for estimation. In this paper, a Kalman filter is used with a Madgwicks filter together to satisfy the fading problems. However, this requires a priori evaluation of auto regressive (AR) parameters. A standard solution involves the first matching of the auto-completion function of the applying the AR method to Jakes' problem and then tackling it (YWE). Even more the results procedure is limited to crowd constraints and is related to an AR+ process of noise, an approximation considered. In fact, depending on simulation findings, high-AR models outperform conventional models on the basis of spectral estimate and bit error margins (BER). Nevertheless, in order to save costs of computing, the 5-D model of AR is a possibility. The proposed process outperforms edge of art competitors in terms of bit error rate as demonstrated by results.
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Kochanska, Iwona, Roman Salamon, Jan H. Schmidt, and Aleksander M. Schmidt. "Study of the Performance of DSSS UAC System Depending on the System Bandwidth and the Spreading Sequence." Sensors 21, no. 7 (April 2, 2021): 2484. http://dx.doi.org/10.3390/s21072484.
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A signal transmitted in an Underwater Acoustic Communication (UAC) system operating in a shallow-water channel suffers from strong time dispersion due to multipath propagation. This causes the Inter-Symbol Interference (ISI) observed in the received signal, which significantly limits the communication system’s reliability and transmission rate. In such propagation conditions, the Direct-Sequence Spread Spectrum (DSSS) method is one of the solutions that make reliable data transmission possible. In systems with one-to-one communication, it ensures communication with a satisfactory Bit Error Rate (BER). Additionally, it makes it possible to implement the Code-Division Multiple Access (CDMA) protocol in underwater acoustic networks. This paper presents the results of simulation and experimental communication tests on a DSSS-based UAC system using three types of spreading sequence, namely m-sequences, Kasami codes and Gold codes, and occupying different bandwidths from 1 kHz to 8 kHz around a carrier frequency equal to 30 kHz. The UAC channel was simulated by impulse responses calculated by the virtual sources method and the UAC chanel models available in the Watermark simulator. The experimental tests were conducted in a model pool. Based on the obtained results, a transmission rate was estimated, which is possible to achieve in strong multipath propagation conditions, assuming reliability expressed as BER less than 0.001.
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Kim, Gunzung, Imran Ashraf, Jeongsook Eom, and Yongwan Park. "Optimal Path Configuration with Coded Laser Pilots for Charging Electric Vehicles Using High Intensity Laser Power Beams." Applied Sciences 11, no. 9 (April 23, 2021): 3826. http://dx.doi.org/10.3390/app11093826.
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Wireless power transmission (WPT) for wireless charging has been gaining wide attention as a promising approach to miniaturizing the battery size and increasing the maximal total range of an electric vehicle (EV). With an appropriate charging infrastructure, WPT holds great potential to accelerate the acceptance of EVs through users’ higher satisfaction, reducing EV cost, and increasing the driving range and capability. A WPT system based on high-intensity laser power beaming (HILPB) provides an optimal solution for wirelessly charging electric vehicles from a distance of several meters. Despite a large number of WPT approaches, the problem of optimal path configuration for charging EV remains an unexplored area. This paper proposes a method to determine the optimal power transmission path in environments where multiple power transmitters (PTXs) and power receivers (PRXs) are operated simultaneously. To this end, we modeled the HILPB power that reaches a PRX equipped with a photovoltaic (PV) array and validated the model by simulating the WPT process in an environment with multiple PTXs and PRXs using a direct-sequence optical code division multiple access (DS-OCDMA) system. In the simulation environment, upon receiving a request from a PRX, a PTX sent its power channel information through optically encoded laser pulses using each available wireless power channel (WPC). The PRX calculated the maximum deliverable power of a PTX and WPC based on the received channel power indicator of the incident laser beam. Based on the calculation results, it selected the optimal PTX and WPC for its maximum power requirement (MPQ). The MPQ of each PRX was satisfied by applying the algorithm for selecting the PTX according to the alignment and characteristics of the PTXs and PRXs. We modeled a power reception model of the PRX based on a PV array using coded laser pilots and validated it through experimentation. We discussed some algorithms that select the most suitable PTX among several PTXs for which several EVs receive the power it needs.
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Kim, Taeyoon, Jeffrey G. Andrews, Jaeweon Kim, and Theodore S. Rappaport. "Multi-code Multicarrier CDMA: Performance Analysis." Journal of Communications Software and Systems 2, no. 1 (April 6, 2017): 12. http://dx.doi.org/10.24138/jcomss.v2i1.301.
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A new multi-code multicarrier code division multiple access (MC-MC-CDMA) system is proposed and analyzed in afrequency selective fading channel. By allowing each user to transmit an M-ary code sequence, the proposed MC-MC-CDMA system can support various data rates as required by next generation standards without increasing the interference which is common in general multicarrier CDMA systems. The bit error rate of the system is analytically derived in frequency selective fading, with Gaussian noise and multiple access interference. The results show that the proposed MC-MC-CDMA system clearly outperforms both single-code multicarrier CDMA (MC-CDMA) and single-carrier multi-code CDMA in a fixed bandwidth allocation.This indicates that MC-MC-CDMA can be considered for next generation cellular systems.
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Taubin, F. A. "MULTIPLE ACCESS IN WIRELESS CHANNELS USING NONORTHOGONAL CODING AND FREQUENCY INTERLEAVING." System analysis and logistics 4, no. 34 (December 20, 2022): 73–82. http://dx.doi.org/10.31799/2077-5687-2022-4-73-82.
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Code division multiple access (CDMA) is currently considered as one of the promising technologies that can significantly improve the efficiency of modern and future communication networks. In code division multiple access systems, users can share a dedicated space-frequency-time resource to simultaneously transmit their own traffic. To ensure the separation of individual user streams on the receiving side, each user is provided with his own code sequence embedded in the broadband signal transmitted by this user, the spectrum of which, as a rule, occupies the entire allocated frequency band. When centimeter-and- millimeter wave wireless channels are used as the transmission medium, such factors as fading, multipath, and Doppler scatter can significantly degrade the performance of a code division multiple access system. The standard solution in this situation is to combine code division multiple access with OFDM (orthogonal frequency division multiplexing) technology, known as multicarrier CDMA (MC-CDMA). To ensure the acceptable level of performance of multiple access systems under oversaturated conditions, many novel approaches based on the use of non-orthogonal multiple access (NOMA) have been proposed. The paper considers a variant of multiple access with non-orthogonal coding that is close in approach to sparse coding multiple access (SCMA). The proposed access procedure is based on dividing the allocated time-frequency resource into relatively small clusters and sharing each cluster with its own group of users, equipped with a non-orthogonal cluster code with the ability to change the loading factor. For the proposed class of cluster codes, a general encoding and decoding scheme is presented. Examples of specific cluster code constructions and numerical results are given that allow one to get a number of the parameters for tradeoffs between an increase of the loading factor in the system and additional energy loss.
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Suresh Babu, Sumith Babu, and R. Kumar. "Multigroup Synchronization in 1D-Bernoulli Chaotic Collaborative CDMA." Wireless Communications and Mobile Computing 2017 (2017): 1–7. http://dx.doi.org/10.1155/2017/7561757.
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Code-division multiple access (CDMA) has played a remarkable role in the field of wireless communication systems, and its capacity and security requirements are still being addressed. Collaborative multiuser transmission and detection are a contemporary technique used in CDMA systems. The performance of these systems is governed by the proper accommodation of the users and by proper synchronization schemes. The major research concerns in the existing multiuser overloaded CDMA schemes are (i) statistically uncorrelated PN sequences that cause multiple-access interference (MAI) and (ii) the security of the user’s data. In this paper, a novel grouped CDMA scheme, the 1D-Bernoulli chaotic collaborative CDMA (BCC-CDMA), is introduced, in which mutually orthogonal chaotic sequences spread the users’ data within a group. The synchronization of multiple groups in this scheme has been analyzed under MAI limited environments and the results are presented. This increases the user capacity and also provides sufficient security as a result of the correlation properties possessed by the chaotic codes. Multigroup synchronization is achieved using a 1D chaotic pilot sequence generated by the Bernoulli Map. The mathematical model of the proposed system is described and compared with the theoretical model of the synchronization in CDMA, the simulation results of which are presented.
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Yen, Chih-Ta, Ing-Jr Ding, and Cheng-Mu Tsai. "PERFORMANCE ANALYSIS OF SEVERAL QUASI-ORTHOGONAL CODES OPTICAL CDMA FOR RADIO-OVER-FIBER SYSTEM." Transactions of the Canadian Society for Mechanical Engineering 37, no. 3 (September 2013): 415–26. http://dx.doi.org/10.1139/tcsme-2013-0031.
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An optical code-division multiple-access (OCDMA) network for radio-over-fiber (RoF) transmissions was proposed. The network encoders/decoders (codecs) were structured based on arrayed-waveguide-grating (AWG) routers coded using modified prime codes (MPCs). In the proposed system, the lower in-phase cross correlation could reduce the beating noise, and in the proposed study, its performance was compared with that of a conventional system that uses M-sequence and Walsh-Hadamard codes. The performance of both systems was numerically evaluated by analyzing the effect of phase-induced-intensity noise (PIIN). The results showed that the new code families that had lower cross correlation can suppress the intensity of the noise and effectively cancel out the multiple-access interference (MAI) in balanced detection processes, which improved system performance. By using the proposed MPC-coded OCDMA ROF network codecs, each network required only two AWG routers to accomplish the spectral coding of radio base stations (RBSs) and the decoding of control stations (CSs), resulting in a simple and low-cost system. Therefore, it is possible to produce interference- and crosstalk-free optical CDMA systems for RoF transmissions.
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Zhang, Zhen Yu, Feng Chun Tian, Fan Xin Zeng, Li Jia Ge, and Gui Xin Xuan. "Symbol Timing Sequence Structure for OFDM-CDMA Communication System under Low SNR." Applied Mechanics and Materials 713-715 (January 2015): 1188–92. http://dx.doi.org/10.4028/www.scientific.net/amm.713-715.1188.
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Symbol synchronization offset of orthogonal frequency division multiplexing (OFDM) communication system will cause the rotation of data constellation at receiver even if such offset falls in the range of the appended cyclic prefix. When OFDM modulation is combined with spread spectrum technique, e.g., OFDM code division multiple access (OFDM-CDMA), the problem becomes more serious since OFDM-CDMA communication system generally works under very low signal-to-noise ratio. This paper focuses on symbol timing synchronization of OFDM-CDMA communication system and proposes an effective sequence structure on the basis of circular conjugate-symmetric properties of discrete Fourier transform. The proposed frequency-domain sequence not only can generate real time-domain signal to reduce calculation complexity, but also can resist peak-to-average power ratio of OFDM modulation by exploiting suitable computer search algorithm. The simulation results show a sharp cross-correlation peak can be obtained, which is quite helpful for accurate symbol timing synchronization of OFDM-CDMA communication system.
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Mrabet, Hichem. "A Performance Analysis of a Hybrid OCDMA-PON Configuration Based on IM/DD Fast-OFDM Technique for Access Network." Applied Sciences 10, no. 21 (October 30, 2020): 7690. http://dx.doi.org/10.3390/app10217690.
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The purpose of this article is to propose a new configuration based on OCDMA and Fast-OFDM techniques for access network applications. A hybrid intensity modulation with direct detection, fast orthogonal frequency-division multiplexing–code division multiplexing access (IM/DD Fast-OFDM-CDMA) system is analytically and numerically evaluated for an amplifier-free access network. Therefore, system performance is analytically investigated in terms of bit error rate/Q-factor as a function of simultaneous users, fiber length and launched optical power. Firstly, the proposed analytical model includes the overlapping effect among OFDM subcarriers, the peak-to-average power ratio (PAPR), and multiple access interference (MAI). Secondly, a simulation setup is performed, allowing four simultaneous users operating at 40 Gb/s in a passive optical network (PON) context. Furthermore, a power budget analysis is made between IM/DD Fast-OFDM-CDMA, all-optical IM/DD OFDM-CDMA (IM/DD AO-OFDM-CDMA) and OCDMA wavelength division multiplexing (OCDMA-WDM) configurations. It is shown that at 40 Gb/s and by using 2D-hybrid coding (2D-HC), the maximum achievable transmission-reach of IM/DD Fast-OFDM-CDMA is 142 km, which is 34 km and 60 km higher than those provided by the IM/DD AO-OFDM-OCDMA and OCDMA-WDM PON configurations, respectively.
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Liu, Peng. "A New Congestion Control Algorithm of CDMA Systems." Advanced Materials Research 255-260 (May 2011): 2220–23. http://dx.doi.org/10.4028/www.scientific.net/amr.255-260.2220.
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A new congestion control algorithm of code division multiple access (CDMA) is developed to reduce the cost of system. Firstly,the paper defines the utility function of resource throughout,and then set up the mathematics model according to the wireless resource characteristic. In the approach only the non-linear compensating term, solution of a sequence of adjoint vector differential equations, is required iteration. By taking the finite iteration of non-linear compensating term of optimal solution sequence, a suboptimal congestion control algorithm of CDMA can be obtained. It is proved by analysis in theory and system level simulation that the congestion control algorithm can enlarge system throughput while controlling system load.
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Wang, Xin, and Jari Nurmi. "Comparison of a Ring On-Chip Network and a Code-Division Multiple-Access On-Chip Network." VLSI Design 2007 (April 5, 2007): 1–14. http://dx.doi.org/10.1155/2007/18372.
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Two network-on-chip (NoC) designs are examined and compared in this paper. One design applies a bidirectional ring connection scheme, while the other design applies a code-division multiple-access (CDMA) connection scheme. Both of the designs apply globally asynchronous locally synchronous (GALS) scheme in order to deal with the issue of transferring data in a multiple-clock-domain environment of an on-chip system. The two NoC designs are compared with each other by their network structures, data transfer principles, network node structures, and their asynchronous designs. Both the synchronous and the asynchronous designs of the two on-chip networks are realized using a hardware-description language (HDL) in order to make the entire designs suit the commonly used synchronous design tools and flow. The performance estimation and comparison of the two NoC designs which are based on the HDL realizations are addressed. By comparing the two NoC designs, the advantages and disadvantages of applying direct connection and CDMA connection schemes in an on-chip communication network are discussed.
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Alshammari, A. S. "Synchronization of Two Chaotic Stream Ciphers in Secure CDMA Communication Systems." Engineering, Technology & Applied Science Research 10, no. 4 (August 16, 2020): 5947–52. http://dx.doi.org/10.48084/etasr.3569.
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In the basic processing of Code Division Multiple Access (CDMA) systems using chaotic code sequences, a pair of chaos generators in the transmitter and the receiver are used to generate the same sequence, in order to synchronize and retrieve the transmitted signals. In addition, a filter with a simple structure should be integrated into chaotic signals to achieve the maximum of the signal to noise ratio and mitigate the harmful effects of multipath. Another effective property of chaos signal is that a wireless multipath channel does not change the amount of contained information. Considering those issues, the present paper describes a practical system for synchronizing two chaotic generators used in a digital CDMA. Chaotic generators were used to spread the data and provide security against attack. Both receiver and transmitter were implemented using two separate Spartan 6 FPGA boards. Experimental results proved the robustness of the proposed method which could contribute towards the synchronization of chaotic signals in secure CDMA communication systems.
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YONG, REN, YONGXIANG XIA, XIUMING SHAN, and YUAN JIAN. "DRIVING SYNCHRONIZATION OF SPATIOTEMPORAL CHAOS AND ITS APPLICATIONS IN CDMA COMMUNICATIONS." International Journal of Bifurcation and Chaos 11, no. 12 (December 2001): 3117–24. http://dx.doi.org/10.1142/s0218127401004042.
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This paper investigates the driving synchronization of spatiotemporal chaos. Using this method, synchronization could be achieved efficiently. By improving the driving sequence generation method, the spatial periodicity in the original system is overcome. Large quantities of chaotic sequences are available, which possess the excellent properties expected in Code Division Multiple Access (CDMA) communications. These chaotic sequences can be used as the spreading sequences in place of the traditional pseudo-noise sequences. We also evaluate the performance of the chaotic CDMA communication systems and compute the average bit error rate caused by the multi-user interference and the noise in the channel. The theoretical and simulation results show the excellent performance of the scheme.
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Plascencia, Emmanuel, Oyunchimeg Shagdar, Hongyu Guan, Olivier Barrois, and Luc Chassagne. "Optical CDMA MAC Evaluation in Vehicle-to-Vehicle Visible Light Communications." Electronics 11, no. 9 (April 30, 2022): 1454. http://dx.doi.org/10.3390/electronics11091454.
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One of the most critical challenges in vehicle-to-vehicle (V2V) visible light communications (VLCs) is the access capability of multi-users over the same channel. VLC links are known to be line of sight (LOS) and highly directional compared to the commonly used radio-frequency (RF) technologies, but multi-user interference can still be problematic. Consequently, it is necessary to develop a medium access control (MAC) protocol for VLC. In the present work, we propose a novel optical code division multiple access (OCDMA) protocol. The fundamentals of the VLC channel are presented, and the interference problem is discussed in more detail. We also explain the CDMA MAC protocol and its adaptation from optical fiber communications. The simulations with our OCDMA protocol based on pseudo-noise (PN) sequence codes are presented, and the results are compared with those obtained using a solution based on VLC and optical orthogonal codes (OOCs) from the OCDMA gold standard. Finally, the results show that PN sequence OCDMA can provide sufficiently high performance and is particularly attractive because there are no synchronization requirements between nodes in real V2V scenarios.