Generalized Receiver with Parallel Interference Cancellation for Multiuser Detection

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.

Performances enhancement of underwater wireless optical communications (UWOC) using pulse position modulation

In this work, we study the performance analysis of underwater optical wireless communication (UOWC) transmission link by incorporating optical code division multiple access (OCDMA) using pulse position modulation (PPM) to enhance the channel range and cardinality. Bit error rate (BER) variations are examined versus the range, modulation type (on–off keying (OOK), quadrature amplitude modulation (QAM), etc.), number of users as well as the channel attenuation caused by different water types. The power and transmitter inclination angle limitation, of the enhanced system, are also presented in order to determine the threshold for which the minimum BER 10−9 is achievable.

Employment of Generalized Receiver for Group-Blind Intersymbol Detection in Downlink CDMA over Fading Multipath Channels

Group-blind multiuser detectors for uplink code-division multiple-access (CDMA) were developed by Wang and Host-Madsen. These detectors make use of the spreading sequences of known users to construct a group constraint to suppress the intracell interference. However, such techniques demand the estimation of the multipath channels and the delays of the known users. In the present paper, the blind generalized receiver is de-veloped for CDMA in fading multipath channels. The proposed generalized receiver utilizes the correlation in-formation between consecutively received signals to generate the corresponding group constraint. It is shown that by incorporating this group constraint, the proposed generalized receiver can provide different performance gains in both the uplink and downlink environments. Compared with the well-known group-blind detectors, our new methods only need to estimate the multipath channel of the desired user and do not require the channel es-timation of other users. Simulation results demonstrate that the proposed generalized receiver outperforms the conventional blind linear multiuser detectors.

Performance Analysis of Bipolar Optical Code Division Multiple Access with Dual Electro-Optical Modulator Scheme for Free-Space Optical Communication

In this study, the performance of bipolar optical code division multiple access (OCDMA) with dual electro-optical modulator (EOM) scheme for multi-user scenario was tested and analyzed with OptiSystem version 10. The performance measurement was implemented for free-space optical (FSO) communication and includes the common noises in optical communication. Two different channels were used in the measurement, i.e., additive white Gaussian noise (AWGN) and fading channel. Two extreme weather conditions, strong rain and storm, were considered in the simulation. The performance between three spectral amplitude coding (SAC) codes, i.e., Modified M-Sequence code, Walsh-Hadamard code, and random diagonal (RD) code were measured and compared. The simulation results indicate that Modified M-Sequence code had the highest BER while RD code achieved the lowest BER in the short-range and Walsh-Hadamard code got the lowest BER for the medium-range of FSO, both for AWGN only and AWGN with fading channel. In strong turbulence condition, the performance of all codes become comparable after 500 m of FSO range. Modified M-Sequence suffered the lowest performance degradation while RD code endured the highest performance deterioration in all-weather condition. The results show that Modified M-Sequence can be applied for medium to long-range FSO.

Behavior study of EDEU optical code for FE-OCDMA system

The increase in the cardinality of the frequency encoding-optical code division multiple access (OCDMA) system directly affects the length of the optical code, which leads us to find a less expensive solution. In this work, I propose an improved version of the diagonal eigenvalue Unit code (DEU) called Enhanced diagonal eigenvalue Unit code (EDEU) that is much easier in terms of construction and short in code length compared to the DEU code. The results found showed that the performance of the EDEU code exceeds the DEU code in terms of bit error rate (BER), and allowed us to multiplex about 15 more users when using the EDEU code compared to the system using the DEU code. As a result, the EDEU code is very suitable for use in access and OCDMA systems and it can be seen as a strong competitor to existing codes.

Orthogonal Frequency Division Multiplexing and Code Division Multiple Access Systems

Chapter 8 presents modern multi-user and multicarrier communication systems based on code division multiple access technology and orthogonal frequency division multiple access technology. Analogue, digital, and discrete orthogonal frequency division multiple access systems are presented separately and then inter-related from theoretical and practical points of view. A precise mathematical model of discrete baseband and intermediate-frequency blocks is presented, including procedures for signal mapping and the discrete Fourier transform, and then related to the model of an analogue radiofrequency block to make the whole orthogonal frequency division multiple access system. The basic theory of binary and non-binary code division multiple access systems operation is presented. To support deeper theoretical understanding of the design and operation of a code division multiple access system, one project in the supplementary material demonstrates the mathematical modelling, simulation, and design of this system in field-programmable gate array technology and presents the development tools required.