We consider the problem of security in the CDMA. CDMA system has wireless channels to transmit voice or data. By this reason, CDMA communication has a possibility of being eavesdropped by someone. It is known that eavesdropping in CDMA system is impossible because the voice data spreads with the PN. However, we can eavesdrop the CDMA data using FCM protocol in case that we know the ESN and the ...

To solve the degradation of the BER performance of Space-Time Block Code (STBC)/MC-CDMA system when MC-CDMA system has large number of users, we propose Unitary Space-Time Modulation (USTM)/MC-CDMA system. USTM combines STBC and baseband modulation by employing unitary matrix. USTM is designed in order not to receive signals from different transmit antennas simultaneously at the receiver. In th...

In this contribution, we propose a variant of the MC-CDMA system that offers more flexibility than the traditional MC-CDMA system. We investigate the sensitivity of this flexible MC-CDMA system to some types of synchronisation errors. This flexible MC-CDMA system is not affected by a constant phase offset or a constant timing offset, as in the proposed flexible MC-CDMA system the carriers insid...

Optical CDMA has gained increasing attention as a promising access network technology. This paper presents an optical CDMA network simulation environment based on OPNET modeler, with a focus on the simulation module implementation. We discuss the pipeline structure of optical CDMA transceivers and describe its interface with the physical layer for system integration. We also present the archite...

Code Division Multiple Access (CDMA) is probably the most interesting multiple access method provided by spread spectrum technology. CDMA refers to a multiple access method in which the individual terminals use spreadspectrum techniques and occupy the entire spectrum whenever they transmit. This paper focuses on direct-sequence spread-spectrum principles (processing gain, spreading, de-spreadin...

DS-CDMA with minimum mean square error frequency-domain equalization (MMSE-FDE) can provide much better performance than that with rake combining in a frequency-selective fading channel and is comparable to that of MC-CDMA with MMSEFDE. Chip interleaving is a form of channel interleaving that improves the DS-CDMA performance by converting the channel into a highly time-selective channel; the ti...

The goal of this paper is to compare the performance of the linear minimum mean square error (MMSE) detector for a class of code division multiple access (CDMA) systems in time and frequency selective channels. Specifically, we consider direct sequence (DS)-CDMA, multicarrier (MC)-CDMA, and the MC-DS-CDMA systems. Two key tools are used in our development. First, a general time-frequency framew...

In this paper, we consider an integrated voice and data system over CDMA Slotted-ALOHA (CDMA SALOHA). We investigate its performance when multi-code CDMA (MC-CDMA) is applied as a multi-rate scheme to support users which require transmission with different bit rates. Two different classes of data users are transmitted together with voice. Performance measurement is obtained in respect of throug...

In this paper, we compare two signal designs for uplink quasi-synchronous code division multiple access (CDMA) channels in order to optimize the trade-off between bandwidth efficiency and power efficiency. The design we call band-limited DS/CDMA design, is based on the time-domain assignment of Gold sequences, just as in the ordinary DS/CDMA, but with band-constrained cyclic chip interpolation ...

Multi-carrier code division multiple access (MC-CDMA) technique maintains the original signaling interval while it spreads the signal over wide bandwidth like direct-sequence code division multiple access (DS-CDMA) technique. Low amount of delay spread reduces the guard interval in MC-CDMA and make it power efficient. MC-CDMA is sensitive to frequency offset and small Doppler spread is preferre...