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CDMA Systems (cdma + system)

Distribution by Scientific Domains

Engineering	100%

Selected Abstracts

2-Dimensional code design for an optical CDMA system with a parallel interference cancellation receiver

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 7 2007
Mikaël Morelle
The objective of this paper is to design a two-Dimensional Optical Code Division Multiple Access system (2D-OCDMA) for application in access networks, with coding and decoding functions performed by electronic devices. We present a new construction method of Multi-Wavelength Optical Orthogonal Codes (MWOOC), which permits a high flexibility in the code parameters choice. This work evaluates in the noiseless case, the MWOOC potentialities for two receiver structures: a Conventional Correlation Receiver (CCR) and a Parallel Interference Cancellation receiver (PIC). We show that with a PIC receiver, it is possible to design two-Dimensional codes that respect the access specifications. Copyright © 2007 John Wiley & Sons, Ltd. [source]

On multi-cell admission control in CDMA networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2008
Gábor Fodor
Abstract We consider a multi-cell (MC) code division multiple access (CDMA) system that supports multiple service classes, including peak rate allocated and elastic ones. Peak rate allocated sessions,when admitted into the system,transmit at a constant bit rate, while elastic sessions can be slowed down at the expense of increasing their residency time. Admitted sessions cause an instantaneous bit rate-dependent interference in neighbour cells. In this rather general setting, we propose a method to calculate the class-wise blocking probabilities as the functions of the estimated so-called inter-cell coupling factors. In the paper this coupling factor is the ratio between the uplink path gains to different Node-B:s (that can be easily obtained in a CDMA system from pilot measurement reports), but our model could include other coupling measures as well. We find that when these coupling factors are underestimated, the system may get into false states (FSs) or false rate states (FRSs) that lead to violating the noise rise threshold. As traffic becomes increasingly elastic, the probability of FSs decreases, but the probability of FRSs increases. Based on numerical results, we make the point that as the traffic becomes more elastic, avoiding the underestimation of these coupling factors as well as exercising MC admission control plays an increasingly important role in guaranteeing proper service quality. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Sequential detection CDMA multi-user receiver

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2005
Mitsuhiro Tomita
Abstract This paper proposes a sequential detection technique for a multi-user receiver that is constructed over a CDMA system. In this system, the transmitter transmits a symbol made by spreading the spectrum with an enveloped sequence protected by guard sequences, and a receiver de-modulates the core-sequence part of the received symbol with either a de-correlating detector or an MMSE detector. The advantage is that performance is improved without reducing the number of the active users. This sequential detection system estimates the best user signal from all of the soft outputs, which are obtained by solving a de-correlating system of equations. Once detected, the best user component is removed from the received symbol. The resultant symbol composed of the remaining user signals is then sequentially detected by repeating the method stated above. A computer simulation of this system reveals a remarkable improvement in the bit-error rate performance compared to conventional systems. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Performance analysis of an improved multi-carrier CDMA system under frequency-selective Rayleigh fading channels

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2003
Hsiao-Hwa Chen
Abstract In this article, an analytical method is proposed to study an improved orthogonal multi-carrier DS/CDMA system, which uses QPSK for both spreading and carrier modulations without redundant sub-carriers and time interleavers in each sub-channel. The article concerns in particular such a system and its performance under frequency-selective Rayleigh fading channels with various delay-power profiles. The bit error probabilities under varying multipath-diversity orders (using maximal ratio combing RAKE reception) and different numbers of resolvable multipaths are derived. It has been shown that the system, despite of its structural simplicity, performs well in mitigating frequency-selective fading. The performance is also evaluated taking into account various other parameter sets, such as numbers of users and sub-carriers, lengths of PN codes and the number of fingers in an RAKE receiver, etc. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A multi-user CDMA receiver utilizing decorrelating detector with additional dummy pilot response

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2003
Mitsuhiro Tomita
Abstract A pilot assisted CDMA system which uses extended spreading sequences with guard sequences under a quasi-synchronous condition is capable of separating the interference components included in the input of a de-correlating receiver by solving a system of linear equations. The performance of such a system, however, depends on the property of the de-correlating matrix consisting of the received pilots, which correspond to the respective user spreading sequences and the multi-path channel conditions. That is, the regularity of the matrix often tends to degrade, and the rank reduces occasionally primarily due to the multi-paths, resulting in solutions that are vulnerable to AWGN. The present paper proposes an effective technique to solve this problem by introducing a virtual user into a group of real users that are to be served. The simulation results indicate a remarkable improvement in the bit-error-rate (BER) performance. In addition, based on the BER performance, the system has a RAKE-like function that has power-sum characteristics. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A slotted multicode CDMA protocol for efficient integration of voice and data in cellular networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2002
H. Zhang
Abstract This paper presents a novel radio channel structure based on slotted CDMA technology intended for carrying traffic with diverse bandwidth/QoS requirements in mobile environments, e.g. personal communication systems (PCS). The essence of our approach is a combination of flexible slotting with allocation of multiple codes to high-bandwidth mobiles. As demonstrated by our performance studies, the proposed scheme efficiently integrates multiple traffic classes into a unified CDMA system. It is highly flexible and incurs low overheads for a wide range of realistic traffic conditions. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Performance of a turbo-coded CDMA system in a mobile satellite channel

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2005
Jin Young Kim
Abstract The bit error rate (BER) performance of a turbo-coded code-division multiple-access (CDMA) system operating in a satellite channel is analysed and simulated. The system performance is compared for various constituent decoders, including maximum a posteriori probability (MAP) and Max-Log-MAP algorithms, and the soft-output Viterbi algorithm. The simulation results indicate that the Max-Log-MAP algorithm is the most promising among these three algorithms in overall terms of performance and complexity. It is also shown that, for fixed code rate, the BER performance is improved substantially by increasing the number of iterations in the turbo decoder, or by increasing the interleaver length in the turbo encoder. The results in this paper are of interest in CDMA-based satellite communications applications. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Interference reduction in synchronous fiber-optic PPM,CDMA systems

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2001
T. S. Lee
Abstract A pulse-position modulation (PPM) optical CDMA system with interference estimation and cancellation is proposed. Multiuser interference is estimated with the aid of modified prime code sequence properties. A comparison between the bit-error rate (BER) of both the proposed system and the system without cancellation reveals that the former system improves the BER performance significantly. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 202,205, 2001. [source]

Joint data detection and estimation of time-varying multipath rayleigh fading channels in asynchronous DS-CDMA systems with long spreading sequences,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2007
Pei Xiao
In this paper, we present a joint approach to data detection and channel estimation for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signaling formats and long scrambling codes. Our emphasis is placed on different channel estimation algorithms since the performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigate channel estimation algorithms under different conditions. The estimated channel information is used to enable coherent data detection to combat the detrimental effect of the multiuser interference and the multipath propagation of the transmitted signal. In the considered multiuser detector, we mainly use interference cancellation techniques, which are suitable for long-code CDMA systems. Interference cancellation and channel estimation using soft estimates of the transmitted signal is also proposed in this paper. Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of channel estimation and bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems. Copyright © 2006 AEIT [source]

Multiuser detection techniques with decision statistics combining for layered space-time coded CDMA systems

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2006
Slavica Marinkovic
This paper considers a low-complexity iterative multiuser detection/decoding algorithm in single user layered space-time coded (LST) systems and LST coded code division multiple access (CDMA) systems. We concentrate on the iterative multiuser receiver based on parallel interference cancellation (PIC) and compare it to the iterative PIC with the minimum means square error (MMSE) detection, as these two approaches seem to be most efficient in meeting the performance-complexity trade-off required by practical systems. In iterative PIC structures, a decision statistics bias severely limits the system performance for a large number of multiple access (MA) or multiple-input multiple-output (MIMO) interferers. A decision statistics combining (DSC) method, originally proposed for iterative PIC receivers in CDMA systems, is used to minimize the bias effect in space-time coded systems for iterative PIC receivers. Significant performance improvements have been confirmed with the iterative PIC receiver with DSC (PIC-DSC) relative to the standard iterative PIC receivers in LST systems for both flat and frequency selective fading channels. This advantage is retained in layered coded CDMA systems as well. The proposed iterative PIC-DSC detector approaches the performance of the much more complex iterative PIC-MMSE receiver. Copyright © 2006 AEIT. [source]

Load-Adaptive MUI/ISI-Resilient Generalized Multi-Carrier CDMA with Linear and DF Receivers

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2000
Georgios B. Giannakis
A plethora of single-carrier and multi-carrier (MC) CDMA systems have been proposed recently to mitigate intersymbol interference (ISI) and eliminate multiuser interference (MUI). We present a unifying all-digital Generalized Multicanier CDMA framework which enables us to describe existing CDMA schemes and to highlight thorny problems associated with them. To improve the bit error rate (BER) performance of existing schemes, we design block FIR transmitters and decision feedback (DF) receivers based on an inner-code/outer-code principle, which guarantees MUI/ISI-elimination regardless of the frequency-selective physical channel. The flexibility of our framework allows further BER enhancements by taking into account the load in the system (number of active users), while blind channel estimation results in bandwidth savings. Simulations illustrate the superiority of our framework over competing MC CDMA alternatives especially in the presence of uplink multipath channels. [source]

Dynamic bandwidth recycle algorithm for OVSF,CDMA systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2006
Peng-Jung Wu
Abstract This paper presents a dynamic bandwidth recycle algorithm in the downlink of a WCDMA system using orthogonal variable spreading factor codes (OVSF). It consists of a bandwidth recycle algorithm and a bandwidth reservation algorithm. The bandwidth recycle algorithm is used to recycle bandwidth from current serviced connections when the system does not have enough available bandwidth to support a bandwidth request. The bandwidth reservation algorithm is used to reduce transmission delay caused by suddenly increasing bandwidth requests. Four traffic classes, conversational, streaming, interactive, and background classes, defined by universal mobile telecommunication system (UMTS) are considered. Simulation results show that the bandwidth utilization and block rate are improved, the bandwidth guaranteed to conversational and streaming classes are protected, and the delay time of interactive and background classes are kept under an acceptable value even when the traffic load is heavy. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Semi-random LDPC codes for CDMA communication over non-linear band-limited satellite channels

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2006
Mohamed Adnan Landolsi
Abstract This paper considers the application of low-density parity check (LDPC) error correcting codes to code division multiple access (CDMA) systems over satellite links. The adapted LDPC codes are selected from a special class of semi-random (SR) constructions characterized by low encoder complexity, and their performance is optimized by removing short cycles from the code bipartite graphs. Relative performance comparisons with turbo product codes (TPC) for rate 1/2 and short-to-moderate block sizes show some advantage for SR-LDPC, both in terms of bit error rate and complexity requirements. CDMA systems using these SR-LDPC codes and operating over non-linear, band-limited satellite links are analysed and their performance is investigated for a number of signal models and codes parameters. The numerical results show that SR-LDPC codes can offer good capacity improvements in terms of supportable number of users at a given bit error performance. Copyright © 2006 John Wiley & Sons, Ltd. [source]

A low complexity partially adaptive CDMA receiver for downlink mobile satellite communications

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 1 2003
Gau-Joe Lin
Abstract A novel CDMA receiver with enhanced interference suppression is proposed for pilot symbols assisted mobile satellite systems in the presence of frequency offset. The design of the receiver involves the following procedure. First, adaptive correlators are constructed at different fingers, based on the scheme of generalized sidelobe canceller (GSC), to collect the multipath signals and suppress multi-access interference (MAI). In particular, a partially adaptive (PA) realization of the GSC correlators is proposed based on the Krylov subspace technique, leading to an efficient algorithm without the need of complicated matrix computations. Second, pilot symbols assisted frequency offset estimation, channel estimation and RAKE combining give the estimate of signal symbols. Finally, further performance enhancement is achieved by an iterative scheme in which the signal is reconstructed and subtracted from the GSC correlators input, leading to faster convergence of the receiver. The proposed low complexity PA receiver is suitable or the downlink of mobile satellite CDMA systems, and shown to outperform the conventional fully adaptive MMSE receiver by using a small number of pilot symbols. Copyright © 2003 John Wiley & Sons, Ltd. [source]