Performance Of Multicarrier CDMA System Research Articles

Multiple level orthogonal codes and their application in MC-CDMA systems

This paper proposes the use of multiple level orthogonal (MLO) codes in multicarrier CDMA (MC-CDMA) systems. It is extremely challenging to improve system error probability performance of MC-CDMA systems with binary spreading codes in multi-user conditions, since attainable-diversity performance is severely degraged by multi-user interference (MUI) in frequency-selective fading channel conditions, even with the use of optimum multi-user detection (MUD) methods. MLO codes are shown to improve system error probability performance in heavily-loaded or fully-loaded systems, in comparison to binary codes. Some widely used MLO code generation methods are summarized, and a new generation method is also provided. The performance advantage of MLO codes over binary codes is analyzed by treating the spreading process in MC-CDMA as a coding process and via analysis of pair-wise sequence error probability. Rules for choosing desirable MLO codes for multi-user MC-CDMA are also given. Numerical results show that MLO codes can provide a substantial performance improvement in fully-loaded systems. For example, for a K = 4 user system with spreading gain L = 4, our system can obtain a diversity order of 3, whereas the binary code system diversity order is only slightly larger than 1. The MLO code application provides a new way to compensate for multi-user interference (MUI) and makes MC-CDMA more attractive for future high data-rate transmission systems.

On the down-link performance of multi-carrier CDMA systems with partial equalization

This paper addresses the performance evaluation of multi-carrier code division multiple access systems. A partial equalization technique depending on a parameter adapted to different conditions such as the number of sub-carriers, the number of active users and the mean signal-to-noise ratio is evaluated for the down-link. We analytically derive the performance of this system and the value of the equalization parameter that maximizes the performance. The partial equalization technique is shown to have the same complexity of the well known maximal ratio combining, equal gain combining and orthogonality restoring combining techniques, with significative performance improvement. Analytical results are compared with simulations showing a perfect agreement

Extended Orthogonal Polyphase Codes for Multicarrier CDMA System

The Complete Complementary (CC) codes have been able to improve the performance of multicarrier CDMA system for both downlink and uplink transmission. However, the number of users supported by CC code design is limited as its family size is relatively small. In this letter, an extension to CC codes using Zadoff-Chu sequence is proposed. The proposed codes are able to support large number of users and have perfect auto- and cross-correlation function just like CC codes.

Bit error rate performance of multicarrier CDMA system with application to image transmission

In this paper, we proposed and analyzed a multicarrier CDMA system with application to image signal transmission over wireless communication channels. Instead of the conventional method of transmitting signal with one carrier frequency, the image signal is partitioned into subsets and a different subband carrier modulates each subset. By so doing, the probability that all the subcarrier will simultaneously fade and be in error is minimized. The performance of the proposed system is evaluated in terms of the average bit error rate in the presence of multipath fading and thermal noise and as a function of data rate, bandwidth, delay range, and space diversity. The effectiveness of multicarrier modulation in resisting fading is demonstrated for a maximal ratio combining space diversity system. Results reveal considerable performance improvement using multicarrier modulation, compared to single carrier modulation.

Performance of MC-CDMA system using controlled MRC with power control in Rayleigh fading channel

A modified maximum ratio combining (MRC) technique called controlled MRC which incorporates power control for multicarrier CDMA (MC-CDMA) systems is proposed. A threshold is set to cut off deep fading subcarriers. The channel status is fed back to the transmitter to make efficient use of the subcarriers. The optimal value of the threshold has been obtained by simulation and the improvement of the proposed method over conventional MRC has also been demonstrated by simulation.

Design and performance of multicarrier CDMA system in frequency-selective Rayleigh fading channels

This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/receiver structure and, the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MC-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.