A New Approach for Evaluating the BER of a Multirate, Multiclass OFFH-CDMA System

In this letter, we propose a new approach to evaluate the bit error rate (BER) of a multirate, multiclass optical fast frequency hopping code-division multiple-access (OFFH-CDMA) system. This proposed approach does not require knowledge of the generated users' code sequences, which makes the system analysis straightforward. Furthermore, the presented formalism can also be successfully applied to most multi-weight multi-length family of codes, as long as the corresponding code parameters are employed.

S/MIMO MC-CDMA Heuristic Multiuser Detectors Based on Single-Objective Optimization

This paper analyzes the complexity-performance trade-off of several heuristic near-optimum multiuser detection (MuD) approaches applied to the uplink of synchronous single/multiple-input multiple-output multicarrier code division multiple access (S/MIMO MC-CDMA) systems. Genetic algorithm (GA), short term tabu search (STTS) and reactive tabu search (RTS), simulated annealing (SA), particle swarm optimization (PSO), and 1-opt local search (1-LS) heuristic multiuser detection algorithms (Heur-MuDs) are analyzed in details, using a single-objective antenna-diversity-aided optimization approach. Monte- Carlo simulations show that, after convergence, the performances reached by all near-optimum Heur-MuDs are similar. However, the computational complexities may differ substantially, depending on the system operation conditions. Their complexities are carefully analyzed in order to obtain a general complexity-performance framework comparison and to show that unitary Hamming distance search MuD (uH-ds) approaches (1-LS, SA, RTS and STTS) reach the best convergence rates, and among them, the 1-LS-MuD provides the best trade-off between implementation complexity and bit error rate (BER) performance.

New quasi-orthogonal BCH-derived sequences for CDMA applications

European Transactions on Telecommunications, vol. 18

Large-system analysis of a CDMA dynamic channel under a Markovian input process

We study the minimum mean square error (MMSE) and the multiuser efficiency η of large dynamic multiple access communication systems in which optimal multiuser detection is performed at the receiver as the number and the identities of active users is allowed to change at each transmission time. The system dynamics are ruled by a Markov model describing the evolution of the channel occupancy and a large-system analysis is performed when the number of observations grow large. Starting on the equivalent scalar channel and the fixed-point equation tying multiuser efficiency and MMSE, we extend it to the case of a dynamic channel, and derive lower and upper bounds for the MMSE (and, thus, for η as well) holding true in the limit of large signal–to–noise ratios and increasingly large observation time T.

ML approaches to channel estimation for pilot-aided multi-rate DS/CDMA systems

This paper analyzes the asymptotic performance of maximum likelihood (ML) channel estimation algorithms in wideband code division multiple access (WCDMA) scenarios. We concentrate on systems with periodic spreading sequences (period larger than or equal to the symbol span) where the transmitted signal contains a code division multiplexed pilot for channel estimation purposes. First, the asymptotic covariances of the training-only, semi-blind conditional maximum likelihood (CML) and semi-blind Gaussian maximum likelihood (GML) channelestimators are derived. Then, these formulas are further simplified assuming randomized spreading and training sequences under the approximation of high spreading factors and high number of codes. The results provide a useful tool to describe the performance of the channel estimators as a function of basicsystem parameters such as number of codes, spreading factors, or traffic to training power ratio.

Optimización de las redes, mediante canalización, para el acceso múltiple por división de código (CDMA), en el Distrito Capital

En el desarrollo académico de este proyecto se siguieron los procedimientos que se tienen en cuenta para poder gestionar el proyecto, establecidos en la Guía de los Fundamentos de la Dirección de Proyectos (Guía del PMBOK) 3ª edición. El proyecto, en su fase de planeación, describió la etapa de iniciación hasta la de cierre, con sus procesos detallados y como se deben seguir para cumplir el alcance del mismo. Se especifican los requerimientos internos de la organización para llevar al proyecto a su éxito teniendo en cuenta el tiempo, el costo y el alcance. En la fase de control y seguimiento se lleva al lector al entendimiento de los resultados de la planeación del proyecto y de sus diferencias con el resultado obtenido. Anexo al presente documento se encuentran todos los soportes necesarios utilizados para llevar a cabo las tareas de control y seguimiento de cada una de las etapas de diseño y construcción de este. Este ejercicio académico conlleva a poner en practica técnicas avanzadas en la administración de proyectos, desarrolladas por el Project management Institute, entidad Norteamericana especializada en este tema

Uso de la banda 450 MHz con la tecnología de acceso múltiple por división de código; CDMA, en el Ecuador para la ampliación del acceso universal

Es de transcendental importancia el reto de conseguir que las redes de los operadores de servicios de telecomunicaciones brinden el servicio a la mayoría de los sectores de la Patria, dicho concepto es el denominado acceso universal, y constituye el marco teórico del presente estudio. Mediante el presente análisis, se determina la viabilidad técnica del uso de la tecnología de acceso inalámbrico de acceso múltiple por división de código en la banda 450 MHz; CDMA 450, para la ampliación del acceso universal en el Ecuador. Lo indicado debido a sus fortalezas técnicas, en especial por la propagación que brinda la banda de frecuencias 450 MHz. Detalla además, los motivos para su gran aceptación a nivel mundial, particularmente en países latinoamericanos como Argentina y Perú. A la fecha, el Consejo Nacional de Telecomunicaciones; CONATEL, Organismo Rector de las Telecomunicaciones en el Ecuador, ha emitido Resoluciones que faciliten el uso de esta tecnología por parte de la Corporación Nacional de Telecomunicaciones; CNT, empresa estatal de telefonía fija, las cuales son recogidas en la presente investigación. Dichas Resoluciones fueron adoptadas, tomando como referencia los resultados obtenidos con el uso de la tecnología CDMA 470, que brinda la empresa ETAPA en el cantón Cuenca, de la provincia del Azuay. Con estos antecedentes y a fin de validar la investigación realizada, se realizaron estudios teóricos de propagación, en las Provincias de Cotopaxi y Galápagos, obteniéndose la viabilidad técnica para su uso únicamente en Galápagos. Finalmente, se debe señalar que este estudio no pretende plantear a la tecnología CDMA 450 como única herramienta válida para conseguir lo indicado, sino que recomienda la investigación de nuevas tecnologías que permitan que las telecomunicaciones sean una herramienta que faciliten el desarrollo de la población.

Blind channel estimation for multi-rate multicarrier DS/CDMA communications

Multi-rate multicarrier DS/CDMA is a potentially attractive multiple access method for future wireless communications networks that must support multimedia, and thus multi-rate, traffic. Several receiver structures exist for single-rate multicarrier systems, but little has been reported on multi-rate multicarrier systems. Considering that high-performance detection such as coherent demodulation needs the explicit knowledge of the channel, based on the finite-length chip waveform truncation, this paper proposes a subspace-based scheme for timing and channel estimation in multi-rate multicarrier DS/CDMA systems, which is applicable to both multicode and variable spreading factor systems. The performance of the proposed scheme for these two multi-rate systems is validated via numerical simulations. The effects of the finite-length chip waveform truncation on the performance of the proposed scheme is also analyzed theoretically.

Blind adaptive channel estimation for dual-rate DS/CDMA signals

This letter proposes the subspace-based blind adaptive channel estimation algorithm for dual-rate quasi-synchronous DS/CDMA systems, which can operate at the low-rate (LR) or high-rate (HR) mode. Simulation results show that the proposed blind adaptive algorithm at the LR mode has a better performance than that at the HR mode, with the cost of an increasing computational complexity.

Synchronisation error resistant CDMA detection

A bit-level linear CDMA detector is presented which is based on the minimum variance distortionless response (MVDR) principle. Owing to the interference suppression capability made possible by basing the detector on the MVDR principle and the fact that no inversion of the user correlation matrix is involved, the influence of synchronisation errors is greatly suppressed.

Orthogonal on-off BPSK: a convenient signaling scheme for near-far resistant detection in DS/CDMA

This paper proposes a convenient signaling scheme-orthogonal on-off BPSK (O3BPSK)-for near-far (NF) resistant detection in asynchronous direct-sequence code-division multiple-access (DS/CDMA) systems (uplink). The temporally adjacent bits from different users in the received signals are decoupled by using the on-off signaling, and the original data rate is maintained with no increase in transmission rate by adopting an orthogonal structure. The detector at the receiver is a one-shot linear decorrelating detector, which depends upon neither hard decision nor specific channel coding. The application of O3 strategy to the differentially encoded BPSK (D-BPSK) sequences is also presented. Finally, some computer simulations are shown to confirm the theoretical analysis.

Coupling cancellation based multiuser detector for asynchronous DS/CDMA

A three-shot multiuser detector is proposed for the reverse link of asynchronous DS/CDMA systems. By taking advantage of the preceding (already reconstructed) bit and the matched filter output for the following two bits, the coupling between temporally adjacent bits (TABs, which always exists for asynchronous systems) is cancelled in a three step fashion. The obtained detector has several useful advantages over existing schemes.