In this paper, we investigate the application of optical code division multiple access (OCDMA) to multimedia transmission (voice, data, video). The various services are differentiated by assigning to each user a specific two-dimensional (2D) code signature. The coding method used is adapted from 2D multi-wavelength optical orthogonal codes (MWOOC). We first generate 2D multi-weight codes to differentiate the quality of service (QoS). Then, by applying a parallel mapping technique, we achieve multi-rate services. The theoretical error probability corresponding to the quality of each service is established in the noiseless case. This permits evaluating the potentiality of such systems in terms of number of communicating users and data rates. This study has been realized considering a conventional correlation receiver (CCR) with and without hard limiting (HL) device.

New sphere decoding algorithms are proposed in this paper. We put the emphasis on an iterative list branch and bound (BB) algorithm which is based on the basic BB algorithm.. When compared to other LSD algorithms, simulation results show that the proposed list BB algorithm can achieve near capacity performance with smaller candidate list size.

This paper introduces new studies on the codes named Super Orthogonal Space Time Trellis Codes (SOSTTC). Using set partitioning rules combined with a set of orthogonal designs, SOSTTC's are able to combine the coding gain of STTC's together with diversity advantage of orthogonal STBC's. We propose new application fields of these codes in the particular context of three transmit antenna systems. We introduce new STTC's built on STBC designs that outperform some STTC's schemes based on the determinant and rank criteria. Further- more, we demonstrate by simulation that the use of these codes in a turbo parallel concatenated scheme permits working very close to the channel outage probability.

In this paper, we study the parallel interference cancellation receiver (PIC) efficiency, in direct sequence optical code division multiple access system (DS-OCDMA) with prime codes (PC). We develop the analytical expression of the error probability in the chip synchronous case, for PC. We show that the PIC receiver permits to suppress totally the effect of multiple access interference (MAI) for prime code, and leads to an error free O-CDMA link in the noiseless case, for whichever PC employed. Simulation results have validated the theoretical analysis. Finally, we show that the PIC receiver permits to reduce the required code length for a given bit error rate

In this paper, we investigate the feasibility of a 2 Dimensional Optical Code Division Multiple Access system (2DOCDMA), with electronic coding and decoding functions. We present a modified construction method of Multi-Wavelength Optical Orthogonal Codes (MWOOC) which permits high flexibility for the code parameters choice. Our objective is to evaluate the 2D code performance, with a Conventional Correlation Receiver (CCR) and a more complex one named Parallel Interference Cancellation receiver (PIC). For example, for a Bit Error Rate (BER)10-9, 30 simultaneous users and an electrical implementation, we show that contrary to the CCR, the use of a PIC receiver leads to workable 2D code solutions.

We present a new architecture of layered space-time codes as a combination of BLAST architecture and of special STTC codes which are variations about the codes first introduced by Jafarkhani et al. and named super orthogonal space-time trellis codes (SOSTTC). Using powerful set partitioning, these codes are able to combine the coding advantage of STTC's together with the advantage diversity of orthogonal space-time block codes (STBC). The system we propose is named super quasi orthogonal horizontal layered space time trellis code (SQOHLSTTC). It consists in a powerful STBC based STTC originally derived for a three transmit antenna system, together with an original block based decoding algorithm which enables to use a higher number of transmit antennas. The decoding of SQOHLSTTC combines group interference suppression and group interference cancellation techniques. To implement the system, we propose a low complexity hard decision iterative decoding method. System performances are illustrated and confirm the great interest of the proposed transmission scheme

This paper addresses maximum-likelihood (ME) time-frequency synchronization algorithm joint with channel estimation for MIMO-OFDM systems in frequency selective fading channels. In proposed algorithm, we use two steps to maximize a proposed metric to obtain first frequency offset and then timing. Using these two estimates, the channel is identified. An iterative algorithm is proposed to improve frequency offset estimation. The performance of the proposed synchronization approach, in terms of timing failure probability and mean square error of the estimated frequency offset, was compared with literature. Based on simulation results, the Cramer-Rao lower bound is obtained with a few iterations

In an incoherent direct-sequence optical code-division multiple-access (DS-OCDMA) system, multiple-access interference (MAI) is one of the principal limitations. To mitigate MAI, the parallel interference cancellation (PIC) technique can be used to remove nondesired users' contribution. In this paper, we study four DS-OCDMA receivers based on the PIC technique with hard limiters placed before the nondesired users or before the desired user receiver, or both. We develop, for the ideal synchronous case, the theoretical upper bound of the error probability for the four receivers. Significant performance improvement is obtained by comparison with conventional receivers in the case of optical orthogonal codes. The paper highlights that the number of active users with null error probability is doubled, compared with conventional receivers. Finally, we show that, thanks to their good performances, the PIC structures permit considerably reducing the minimal code length required to have 30 users with bit-error rate <10/sup -9/. So, the hardware constraints are relaxed for realistic application.

In direct sequence optical code division multiple access system (DS-OCDMA), one of the principal limitations is due to unipolar coding which introduces multiple access interference (MAI). To mitigate MAI, we have applied a parallel interference cancellation technique (PIC) to remove non-desired users' contribution. We study in this paper, the performances of the PIC improved by hard limiters (HL) placed either before the non-desired users receivers (HL+PIC) or before the desired user receiver (PIC+HL). We develop the HL+PIC and PIC+HL theoretical error probability expression, and show the performances improvement due to such receivers

In this paper, we propose a multi-user detector for space-time uplink transmission in multi-carrier CDMA systems using a new combination of STBC, OFDM and CDMA spreading. To achieve high rate, CDMA spreading codes are shared between a few users and we use linear STBC decoding to further separate users. The OFDM codewords are built from chips issued from different symbols. The STBC encoder and decoder are placed at the last stage of our multi-user transmitter and receiver respectively. We show that the system is particularly easy to implement when exploiting the space diversity after CDMA detection. Besides, the performance is comparable to the case of a single user STBC system. The proposed system allows for a very high rate multi-user system compared to the conventional CDMA system or combined array-processing technique previously proposed.