Conventional Multi-carrier CDMA Research Articles

An efficient radon mapped discrete wavelet transform-based algorithm for MC-CDMA system

The proposed work is aimed at improving bit error rate (BER) performance and spectral efficiency, increasing data rate, reducing inter-symbol interference (ISI) and inter-channel interference (ICI). Implementation of a conventional MC-CDMA system normally involves the use of QAM techniques for mapping. In the proposed work a mapping technique based on finite radon transform is used. The use of finite radon transform (FRT) improves orthogonality between the subcarriers. It also reduces ISI and ICI, which is due to the loss of orthogonality between carriers. Since discrete wavelet transform (DWT) is used instead of fast Fourier transform (FFT), which is employed in conventional multi-carrier CDMA techniques, the insertion of guard interval is not required and it offers better spectral efficiency. The result shows that the bit error rate performance of the proposed algorithm is far better than conventional techniques in AWGN channel.

Performance of Multiband Complex-Wavelet-Based MC-CDMA System with Space-Time Coding over Nakagami-m Fading Channels

Space-time coding technique and Multi-carrier CDMA (MC-CDMA) technique have received much interest due to their high frequency spectrum efficiency and high data rate transmission. On the basis of analyzing the two technique principle, utilizing the optimized multiband complex wavelet as multi-carrier basis function, we propose an MC-CDMA system based on multiband complex wavelet and space-time coding for downlink and investigate the system bit error rate (BER) performance over Nakagami-m fading channel. The system has much higher spectrum efficiency and data rate due to no need any cyclic prefix (CP) when compared to the conventional MC-CDMA system. Moreover, the application of space-time coding technique improves the ability against fading channel effectively and perfects the downlink performance further. Simulation results show that the proposed multiband complex-wavelet-based MC-CDMA (MBCW-MC-CDMA) system performs better than conventional MC-CDMA system and real wavelet-packet-based MC-CDMA system due to its superior ability against interferences. Especially, the space-time coded MBCW-MC-CDMA system has superior performance, and it outperforms single antenna MBCW-MC-CDMA and conventional MC-CDMA with space-time coding.

Time-Frequency Cyclic Shift Keying Transceiver for Low PAPR MC-CDMA Uplink System over Multipath Fading Channels

A low peak-to-average-power-ratio (PAPR) transceiver with a time-frequency cyclic shift orthogonal keying (TF-CSOK) technique is proposed for the uplink multi-carrier CDMA (MC-CDMA) system over multiple access interference (MAI) and multipath interference (MPI) channels. The low complexity structure of the TF-CSOK MC-CDMA system is designed to involve the FCSOK and TCSOK techniques to combat MPI and MAI effects, respectively. In particular, at the besestation, the multiuser detector employs the maximum likelihood (ML) rule and the TFSOK despreading and demapping techniques to acquire the M-ary modulation gain and diversity gain. Simulation results show that the multuser receiver has the robustness against strong MAI. Moreover, it outperforms the conventional single-carrier frequency division multiple access (SC-FDMA) system and the conventional MC-CDMA system under MAI and MPI environments.

A Low-PAPR Multiplexed MC-CDMA System with Enhanced Data Rate and Link Quality

Recently, a new multi-carrier CDMA (MC-CDMA) system with cyclic-shift orthogonal keying (CSOK) has been proposed and shown to be more spectral and power efficient than conventional MC-CDMA systems. In this paper, a novel extension called the multiplexed CSOK (MCSOK) MC-CDMA system is proposed to further increase the data rate while maintaining a low peak-to-average power ratio (PAPR). First, the data stream is divided into multiple parallel substreams that are mapped into QPSK-CSOK symbols in terms of cyclic shifted Chu sequences. Second, these sequences are repeated, modulated, summed, and placed on IFFT subcarriers, resulting in a constant-modulus multiplexed signal that preserves the desired orthogonality among substreams. The receiver performs frequency-domain equalization and uses efficient demultiplexing, despreading, and demapping schemes to detect the modulation symbols. Furthermore, an alternate MCSOK system configuration with high link quality is also presented. Simulations show that the proposed MCSOK system attains lower PAPR and BER, as compared to conventional MC-CDMA system using Walsh codes. Under a rich multipath environment, the high link quality configuration exhibits excellent performance with both diversity gain and MCSOK modulation gain.

PERFORMANCE ANALYSIS OF MULTICARRIER CDMA SYSTEM BASED ON COMPLEX WAVELET PACKET AND SPACE–TIME BLOCK CODES IN RAYLEIGH FADING CHANNEL

On the basis of analyzing the principle of multicarrier CDMA (MC-CDMA) technique and space–time coding technique, using the optimized complex wavelet packet as multicarrier modulation, a novel MC-CDMA system based on complex wavelet packet and space–time block codes is proposed. The bit error rate (BER) performance of the system is investigated in Rayleigh fading channel, and the corresponding BER expression is derived in detail. The system can overcome the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix (CP). Moreover, the application of space–time coding technique strengthens the capability against fading channel significantly and perfects the system performance. Theoretical analysis shows that the proposed system with 2-transmitter antenna and 2-receiver antenna space–time block codes performs four times better than the single-antenna MC-CDMA system based on complex wavelet packet (CWP-MC-CDMA); the same conclusion is also reached by the simulation results in fading channel. As a result, the performance of the proposed CWP-MC-CDMA system outperforms a conventional MC-CDMA system based on DFT, it is close or superior to that of the conventional MC-CDMA with CP. Especially, the CWP-MC-CDMA system with space–time coding has superior ability to combat spatial fading and multi-access interference, and it slightly outperforms conventional MC-CDMA with CP and space–time coding.

Single Carrier Cyclic Prefix-Assisted CDMA System with Frequency Domain Equalization for High Data Rate Transmission

Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.