Conventional MC-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 multicarrier complementary-coded CDMA under frequency-selective Nakagami-m fading channels

Multicarrier complementary-coded code division Multiple Access (MC CC-CDMA) is becoming an attractive multiple access technique for high data rate transmission in future wireless communication systems. MC CC-CDMA systems transmitting over frequency-selective channels suffer from multiple access interference (MAI) owing to non-ideal correlation properties of complementary codes (CC). MC CC-CDMA with equalization has recently gained much attention for its ability to offer an excellent performance than traditional systems in frequency-selective fading channels. In this paper, the authors present an analytical study and investigation of MC CC-CDMA downlink system using different combining schemes. The use of parallel interference cancellation (PIC) under frequency-selective Nakagami-m fading channels is also analyzed. A comparison among different combining schemes is provided to show the impact of PIC with minimum mean square error combining (MMSEC) and maximal ratio combining (MRC) on the performance of MC CC-CDMA system. The analytical and simulation results show that the combination of general combining schemes with PIC provides an efficient solution to suppress MAI in downlink MC CC-CDMA system than conventional MC-CDMA systems using Walsh codes under frequency-selective channels.

The novel two-dimensional ICI cancellation scheme for a PB/MC-CDMA system in a frequency selective fading channel

In this paper, we introduce the novel two-dimensional multiple access interference MAI cancellation scheme in order to improve the performance in the partial block multi-carrier code division multiple access PB/MC-CDMA environment. In conventional MC-CDMA systems, interference cancellation is typically accomplished in the frequency domain, however, as is commonly understood, undesired user data used in the cancellation is an estimated value; therefore, the interference cannot be completely eliminated, resulting in the residual MAI limiting improvements in the bit error rate BER performance. In this paper, we apply cancellation in both the frequency and time domains, by combining the signals after two separate domain cancellations, thus obtaining diversity. The disadvantage of this method is that the calculation on the receiver is slightly complicated; however, this two-dimensional cancellation is advocated for situations where there is a strict requirement for low BER performance.

Comparative Analysis of MC-CDMA System with Wavelet Packet Based MC-CDMA System Using Different Modulation Techniques

Recently conventional Multi-Carrier Code Division Multiple Access (MC-CDMA) techniques attract more attention of researcher's due to its high frequency spectrum efficiency and high data rate transmission. MC-CDMA is a Multiple access scheme used in Orthogonal Frequency Division Multiplexing (OFDM) based telecommunication systems, allowing the system to support multiple users at the same time. Specialized wavelet packet waveform set is used as the modulation waveform in a multicarrier CDMA system. The wavelet packet waveform is the waveform generated from a full binary wavelet packet tree. This paper presents a design of conventional MC CDMA and wavelet packets based MC CDMA and their comparison on the basis of performance matrices. The performance parameter used in this comparison is Bit Error Rate (BER). The spectral analysis is done by wavelet.

Low Complexity Channel Estimation for MC-CDMA System Based Chaos under Fast Multipath Channel

Based on interpolation methods, a low complexity channel estimation method for MC-CDMA system based chaos under fast fading multipath channel is proposed.Different interpolation methods are used; Linear interpolation (LI), cubic spline interpolation (CSI), and piecewise cubic Hermite interpolation (PCHI). The multi-carrier scheme is established by using a chaotic generator with different initial conditions, while the pilots are established using another chaotic generator with another different initial conditions. The proposed channel estimator without and with interpolation methods for single user and multiusers is tested under fast frequency selective Rayleigh fading channel. Simulation results demonstrate that the channel estimation of MC-CDMA system based chaos using interpolation methods and when the pilots are chaos signal too, achieves better performance improvement in fast multipath environment compared to the conventional MC-CDMA system when the pilots are considered as Walsh- Hadamard codes. The proposed system is also built and tested using Simulink program.

Performance of an Improved MC-CDMA System Based on DT-OCWDM and Quasi-Orthogonal Matrix

In this paper, we propose a new improved MC-CDMA system which combines spreading codes from Quasi-Orthogonal Matrix with Orthogonal Complex Wavelet Division Multiplexing (OCWDM). The system is implemented by complex wavelet filters which are able to lower computational complexity and increase flexibility. Novel spreading codes from Quasi-Orthogonal Matrix can be expanded randomly. It can increase user number hugely in system. Improved MC-CDMA named OCWDM-CDMA has much higher frequency spectrum efficiency and high data rate than conventional MC-CDMA. The system also has better BER performance in Gaussian channel than conventional system for much more users.

A Proposed Turbo Coded Wavelet Packet Modulation based MC-CDMA

A turbo coded Discrete Wavelet Packet Transform DWPT based Multicarrier CDMA system has been proposed to enhance the bit error rate and complexity of the conventional MC-CDMA which based on Fast Fourier Transform FFT over different channel models. The decoding algorithm used maxlog-MAP algorithm. The computer simulation tests show that the BER of the coded DWPT based MC-CDMA has been improved by 4 dB compared with the coded FFT based MCCDMA over Additive White Gaussian Noise AWGN and 4.5 dB over the multipath fading channel at of BER=10.

Diffused Channel Estimation and Reception for Cyclic Prefix-free MC-CDMA Arrayed-MIMO Communication Systems

An arrayed-MIMO communication system, which employs antenna arrays at both ends of the wireless link is proposed to leverage upon spatial information such as directions-of-arrival to achieve an improvement in performance. This is in contrast with conventional MIMO systems, which typically assume multiple independent antenna elements at the transmitters and receivers. This paper focuses on an arrayed-MIMO communication system operating over a frequency selective fading channel and employs MC-CDMA as the modulation technique. However, in a departure from conventional MC-CDMA systems, cyclic prefixes or guard intervals are not used for the MC-CDMA system employed here so that valuable bandwidth is not wasted on cyclic prefixes or guard intervals. Localized scattering is assumed to occur for each multipath; hence the wireless channel is modelled as a diffused vector channel. A robust blind estimation method is presented to estimate the parameters of the spatially diffused channel, followed by reception based on these parameters. The feasibility of the proposed system is supported by simulation results.

Performance analysis of uplink MIMO MC-CDMA systems based on linear zero-forcing V-BLAST algorithm

A structure was proposed for multiple-input-multiple-output multicarrier code division multiple access (MIMO MC-CDMA) uplink transmission system. Linear zero-forcing V-BLAST (ZF V-BLAST) algorithm and maximum ratio combining (MRC) scheme was applied to the receivers. The average bit error rate (BER) expression was derived on condition that the number of receive antennas was larger than that of transmit antennas and it was verified by simulations. Numerical results show that the number of transmit and receive antennas, as well as the number of subcarriers, all exert significant effects on the BER performance. The space diversity and frequency diversity show different abilities to improve the BER performance. The MIMO MC-CDMA system based on linear ZF V-BLAST algorithm is capable of achieving better BER performance than that of the conventional MC-CDMA system by reducing the number of transmit antennas or increasing the number of receive antennas.

A turbo SDMA receiver for strongly nonlinearly distorted MC-CDMA signals

This paper considers the use of space division multiple access (SDMA) techniques for the uplink of multi-carrier code division multiple access (MCCDMA) systems, where the transmitted signals face strong nonlinear distortion effects. The signal transmitted by each mobile terminal (MT) is submitted to a nonlinear operation consisting of a clipping device followed by a frequency-domain filtering operation, so as to reduce the envelope fluctuations and peak-to-mean envelope power ratio (PMEPR) while maintaining the spectral occupation of conventional MC-CDMA signals. At the base station, an iterative receiver employing multiple antennas jointly performs turbo multi-user detection and the estimation and cancellation of nonlinear distortion effects. Performance results show that the proposed receiver structures can achieve good performances that are very close to those obtained with linear transmitters, even for high system load and/or when a very low-PMEPR MC-CDMA transmission is intended for each MT.

Sensitivity of Carrier Frequency Offset and MAI in DAPSK-MC-CDMA Systems

A less complex system by integrating non-coherent differential amplitude and phase shift keying modulation with multi-carrier code division multiple access (DAPSK-MC-CDMA) is introduced. The proposed DAPSK-MC-CDMA system can reduce the system complexity and also maintain a good performance and high-spectral efficiency. The paper firstly shows that the performance degradation caused by the multiple access interference (MAI) and the carrier frequency offset can be effectively controlled in a DAPSK-MC-CDMA system. Simulation results illustrate that both the MAI and the carrier frequency offset in the DAPSK-MC-CDMA is much less sensitive than the conventional MC-CDMA system. Furthermore, using the DAPSK modulation, the detection methods of equal gain combining, maximum ratio combining, and minimum mean square error combining now can be used in the multiple-ary DAPSK-MC-CDMA system.

Uplink performance of CWP-MC-CDMA with Space Diversity Combining technique over Rayleigh fading channel

In this paper, a Complex Wavelet Packet based Multi-Carrier Code Division Multiple Access (CWP-MC-CDMA) system uplink model is proposed, based on the analysis of the principle of MC-CDMA and the use of the optimized complex wavelet packet. Considering that the base station can adopt multiple receiver antennas in the uplink, we employ the Space Diversity Combining (SDC) technique to improve the system performance via multiple antennas. The uplink performance of proposed CWP-MC-CDMA system with SDC technique is investigated over Rayleigh fading channel, and corresponding bit error rate analysis is given in detail. The system can avoid the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix. Theoretical analysis and simulation result show that the application of SDC technique can improve the CWP-MC-CDMA system ability to combat spatial fading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior Bit Error Rate (BER) performance over the Discrete Fourier Transform (DFT) and SDC based MC-CDMA system and the real wavelet packet and SDC based MC-CDMA system.

Effect of carrier-frequency offset on the performance of group-orthogonal multicarrier CDMA systems

In this letter, the downlink performance of a group-orthogonal multicarrier code-division multiple-access (GO-MC-CDMA) system with binary-phase shift keying (BPSK) modulation is investigated, when communicating over Rayleigh fading channels in the presence of carrier-frequency offset (CFO). The bit error rate (BER) performance of the GO-MC-CDMA is compared with that of a conventional MC-CDMA for given system resources and for a given value of the CFO. Our study and results show that the GO-MC-CDMA system is capable of achieving a better BER performance than that of a conventional MC-CDMA scheme in the presence of CFO, when the number of users per group is relatively small. By contrast, when the number of users per group is high, two MC-CDMA systems considered achieve similar BER performance.

Performance Analysis for OFDM-CDMA With Joint Frequency-Time Spreading

In this paper, a novel OFDM-CDMA system with joint time-frequency spreading methods is proposed. The average bit error probability of the proposed system using maximum-ratio combining (MRC) is derived for a frequency-selective fading channel and that of conventional MC-CDMA is also presented for comparison. Numerical analysis and simulation results indicate that the proposed system outperforms MC-CDMA system.