Carrier Code Division Multiple Access Research Articles

Signal Detection in Multi Carrier–Code Division Multiple Access System using Iterative Block Decision Feedback Equalizer

Signal Detection in Multi Carrier–Code Division Multiple Access System using Iterative Block Decision Feedback Equalizer

Multiuser Detection using Noma Technique in FD-MC-CDMA System in Fading Channels

Non-Orthogonal Multiple Access which is an emerging technique which performs good in any aspects. Multiple users can share the resources that are available and also user can be identified, which adopts successive interference cancelation (SIC). The power domain is considered for detection of power allocation for the base stations. The performance of errors in selective channels like frequency channels is demonstrated with the help of code division multiple access which is a multi carrier (MC-CDMA), in which the frequency diversity can be resolved quickly. Due to high range of multiple access interferences the performance of MC-CDMA is been restricted. To overcome the problems in MC-CDMA, a new technique is proposed i.e frequency division multi carrier code division multiple access by which the multiple access interferences can be reduced by exploiting the available range of frequencies. NOMA is one of the emerging technique used as an answer to boost the spectral potency whereas permitting some extent of accessibility for multiple interferences at receiver end. By using NOMA-FD-MC-CDMA the range of spectrum can be increased and reduced the interferences. Bit error rate(BER) is evaluated and compared with other existing technique. The experimental results are performed using Mat lab tool.

A Novel Detected Peak Samples Combining Technique for PAPR Minimization of MC-CDMA Signal

A new signal scrambling technique is proposed to minimize the peak to average power ratio (PAPR) of multi carrier code division multiple access (MC-CDMA) signal using novel detected peak samples combining technique. This new approach minimizes PAPR by combing the MC-CDMA symbol with a number of copies of the detected peak sample which belong to the same MC-CDMA symbol. The analytical and simulation results show that by the right selection of the number of peak samples; the PAPR for 64 subcarrier system reduces by 4.9 dB at the complementary cumulative distribution function = 10−3. The PAPR can be further reduced by increasing the number of peak samples but it could compromise the data speed. The implementation of this technique is very simple when compared to the existing techniques like selective mapping, partial transmit sequence and tone reservation as it requires lesser number of Inverse Fast Fourier Transform/Fast Fourier Transform blocks, no side information and low processing delay.

Design and Performance of MC-CDMA Transceiver based LDWT –OFDM in Flat Fading Channel

Multi Carrier Code Division Multiple Access (MC-CDMA) is a suitable modulation method for high data rates. In this modulation system, using of combining methods are inevitable for restoring orthogonality between diverse user signals. In this paper, the combining techniques of a MC-CDMA based on lifting discrete wavelet transform strategy (LDWT) are studied. Is presented to keep up the symmetry against the multipath Flat Fading Channels (FFC). Show of MC-CDMA under many channels similar the AWGN channel and FFC, is examined and BER versus SNR graphs are plotted and their presentation is deliberate.

Low Complexity Signal Detector for MIMO MCCDMA System for Longer Delay Channel

In recent years Multiple-input multiple-output (MIMO) Multi carrier code division multiple access (MCCDMA), which combines the advantage of diversities with high spectral efficiency has drawn great attention. In this paper we introduce a novel low-complexity multiple-input multiple-output (MIMO) MMSE detector tailored for MCDCDMA systems, suitable for frequency selective channel. The proposed detector begins with estimation of the minimum mean square error (MMSE) on less reliable symbols followed by iterative de-correlation as post-detection processing for mitigating multiple access interferences. Efficient high-throughput VLSI architecture is used to achieve superior performance compared to the conventional MMSE detectors. The performance of the proposed MMSE detector is close to the efficient maximum likelihood, with significant complexity reduction over higher order constellations. The efficiency of MIMO MCCDMA over high order constellations and its quality retentions are verified through MATLAB BER simulation.

Improving BER and data throughput using adaptive modulation level MC-CDMA technique in underwater wireless communication

Underwater communication has a wide range of applications like environmental monitoring to predict the natural disasters, underwater ex-ploration and military applications. The need for effective underwater communication is the high demand in the present scenario. The im-plementation of precise modulation technique is also important because the underwater channel environment is time variant due to various noises present in the underwater like natural and vehicle noise (mechanical noises). The bandwidth is also highly limited in underwater communication. The existing method is adaptive modulation based OFDM system. This method has low spectral efficiency, however, each symbol is modulated with different carriers. The proposed method is Adaptive Modulation Level MC-CDMA (Multi carrier Code Division Multiple Access). The CDMA techniques share the same carrier frequency to multiple number of users. It adapts the modulation scheme according to the present channel conditions in the underwater. The performance of the proposed system improves the Data Throughput and Bit Error Rate.

Improvement of bit error rate performance of MC-CDMA system by using adaptive digital modulation schemes

In Wireless Communication, the transmission channel suffers due to multipath propagation and channel dispersion due to Inter Symbol Interference (ISI), thereby degrades the system performance greatly. Future communication requires high data rate and effective utilization of bandwidth. Hence, there is a need to improve the Bit Error Rate (BER). The proposed work is Adaptive Modulation (AM), combined with Multi Carrier Code Division Multiple Access (MC-CDMA) based transmission system. It is a promising way to increase the data rate and it uses bandwidth in a efficient manner. The Adaptive Modulation based MC-CDMA systems applied to a wide-area environment, can achieve high data rate up to 100Mbps. In this paper M-ary PSK, M-ary QAM and M-ary CPM modulation techniques are used. The Adap-tive modulation based MC-CDMA systems perform well for around 10 number of users. As a whole, the adaptive MC-CDMA system is found to give the optimum BER performance of given digital modulation schemes for fourth generation environment.

A MC-CDMA system based on orthogonal filter banks of wavelet transforms and partial combining

Multi Carrier Code Division Multiple Access (MC-CDMA) is an appropriate modulation technique for high data rates. In this modulation scheme, employing of combining techniques are unavoidable for restoring orthogonality between different user signals. In this paper, the combining techniques of a MC-CDMA based on wavelet transform are studied. The partial combining of the wavelet based MC-CDMA system is suggested and its performance is compared with the maximum ratio combining (MRC), equal gain combining (EGC), orthogonality restoring combining (ORC) and the minimum mean square error (MMSE) techniques. Orthogonal filter banks of the wavelet transforms provide orthogonality between the wavelets and scaling functions, subcarriers and spreading sequences. Therefore, they provide new dimensions in combatting multipath fading, inter carrier interference (ICI) and narrowband interference in MC-CDMA systems. Furthermore, analysis of partial combining shows that coefficients of this technique can be computed in a simple manner. Simulations results indicate that the bit error rate (BER) performance of the proposed scheme is almost comparable with the MMSE combining scheme and the proposed system has a proper performance in terms of BER versus the signal to noise ratio (SNR) in frequency selective fading channels.

Interference mitigation in uplink STBC MC-CDMA system based on PIC receiver

Multi Carrier Code Division Multiple Access (MC-CDMA) is attractive technique for high speed data transmission in multipath fading channel. MC-CDMA system cannot handle the sudden time variations of the channel which cause the subcarriers to lose their orthogonality. The loss of orthogonality between the subcarriers of a user or unwanted correlation between the spreading codes of different user can lead to increase in Multiple Access Interference (MAI). Space Time Block Code (STBC) based MC-CDMA system is chosen to achieve full diversity and transmission rate without the knowledge of Channel State Information (CSI) at the transmitter. Thus, in the paper STBC is introduced at the transmitter to improve the quality of the receiver. Space Time Block Code-Parallel Interference Cancellation (STBC-PIC) receiver has been proposed for MC-CDMA system. In the proposed STBC-PIC receiver, at each interference cancellation stage, weighted signal of the other user is subtracted from signal of the desired user, thereby reducing the MAI and improving the BER performance. From the simulation results, it is observed that the proposed receiver outperforms STBC-Orthogonal Complete Complementary Code (STBC-OCCC), STBC-Minimum Mean Square Error (STBC-MMSE) and STBC-Zero Forcing (STBC-ZF) receivers for MAI reduction.

Subcarrier Allocation Algorithm Based on Greedy-Like in Multi Carrier Code Division Multiple Access Systems

One of the most important issues to be taken into consideration in multi carrier communication systems with multi users is the assignment of the available resources to the users efficiently. Thus, how to determine the number of subcarriers to be allocated to the users has an important role with regards to data rate and error performance of the system when active users are increased in multi carrier system. In this study by using Greedy-Like algorithm, the subcarriers in MC-CDMA systems are optimal allocated to the users and the efficiency of this algorithm compared with other algorithms in terms of bit error and bit rate performance.DOI: http://dx.doi.org/10.5755/j01.eie.23.4.18726

Robust Neural Network based Multiuser Detector in MC-CDMA for Multiple Access Interference Mitigation

The aim of this paper is to design a multiuser detector technique using artificial Neural Network under multiple access interference mitigation. To improve the performance of Multi Carrier Code Division Multiple Access (MC-CDMA) under multiple access interference, we have used a multilayered perceptron model of Neural Network that has three layers namely, input layer, hidden layer and output layer. The Neural Network is further trained by Levenberg-Marquardt algorithm. This algorithm uses the error function as key factor based on which the weights are adjusted to get the desired output. The Bit Error Rate (BER) performance of the system has been evaluated under Rayleigh and Stanford University Interim (SUI) channels for Binary Phase Shift Keying (BPSK) and Quadrature Amplitude Modulation (QAM) techniques. The proposed Neural Network based receiver is compared with Equal Gain Combining (EGC) and Maximal Ratio Combining (MRC) with varying number of users and Signal to Noise Ratio (SNR). Under SUI channel conditions and for a BER of 10 -3 , the Neural Network based receiver shows an improvement of 1 dB and 8 dB than EGC and MRC receivers, respectively.

Transmission of DWT Block-Based KLT Watermarked Images Through MC-CDMA Wireless Channel

This paper addresses the transmission of watermarked images using two watermarking methods over Multiple Carrier Code Division Multiple Access (MC-CDMA) wireless system. Both of the two proposed watermarking methods depend on combining two adequate mathematical transforms; the discrete wavelet transform (DWT) and Karhunen---Loeve Transform (KLT). The first method named DWT-based KLT watermarking embeds watermark during performing the KLT to selected middle and high frequency bands LH, HL and HH resulted from employing 2-level DWT on the cover image that will be watermarked. The second method named DWT block-based KLT watermarking works by splitting the host image into segments and each segment is subjected to 2-level DWT. Then, the watermark is embedded to every block during applying the KLT to selected middle and high frequency bands LH, HL and HH of each block separately. The watermarked images obtained by the two above mentioned watermarking methods are transmitted over the MC-CDMA wireless system. Then, the receiver manipulates the received watermarked image to extract the watermark. Experiment tests are performed and results ensure the superiority of proposed watermarking methods over the MC-CDMA with different signal-to-noise ratios.

Interference Mitigation in MC-CDMA System with CFO compensation based Modified MMSE-FDE Technique

carrier Code Division Multiple Access (MC-CDMA) has been an attractive technique for wireless communication because it offers high data rate, high spectral efficiency, large system capacity, less transmit power and less implementation complexity. But due to Carrier Frequency Offset (CFO), which comes into account due to asynchrony between transmitter and receiver local oscillators or by Doppler Effect due to high mobility, orthogonality among the subcarriers gets effected resulting in Inter Carrier Interference (ICI) which leads to rapid degradation in performance of MC-CDMA system. In this paper, the performance of Uplink MC-CDMA system with Zero forcing- frequency domain Equalization (ZF-FDE), conventional MMSE equalizer and Modified MMSE-FDE using Walsh-Hadamard spreading sequence in multipath fading channel has been analyzed. Simulation has been performed using 32 subcarriers and 64 subcarriers for these equalization techniques. Simulation results confirm excellent performance of the Modified MMSE-FDE which outperforms the conventional MMSE equalization and ZF- FDE. The further improvement in performance is achieved by employing 64 subcarriers instead of 32 subcarriers. Numerical equations and simulation results are given to support the analysis. Keywords-CDMA, CFO, MMSE-FDE, ZF, ICI, Walsh-Hadamard Sequence.

Performance enhancement of MC-CDMA system through novel sensitive bit algorithm aided turbo multi user detection.

Multi carrier code division multiple access (MC-CDMA) system is a promising multi carrier modulation (MCM) technique for high data rate wireless communication over frequency selective fading channels. MC-CDMA system is a combination of code division multiple access (CDMA) and orthogonal frequency division multiplexing (OFDM). The OFDM parts reduce multipath fading and inter symbol interference (ISI) and the CDMA part increases spectrum utilization. Advantages of this technique are its robustness in case of multipath propagation and improve security with the minimize ISI. Nevertheless, due to the loss of orthogonality at the receiver in a mobile environment, the multiple access interference (MAI) appears. The MAI is one of the factors that degrade the bit error rate (BER) performance of MC-CDMA system. The multiuser detection (MUD) and turbo coding are the two dominant techniques for enhancing the performance of the MC-CDMA systems in terms of BER as a solution of overcome to MAI effects. In this paper a low complexity iterative soft sensitive bits algorithm (SBA) aided logarithmic-Maximum a-Posteriori algorithm (Log MAP) based turbo MUD is proposed. Simulation results show that the proposed method provides better BER performance with low complexity decoding, by mitigating the detrimental effects of MAI.

PAPR Reduction Based on Proposed Rotating Phase Shift Technique in MC-CDMA Using FPGA

FPGA implementation used of Rotating phase shift (RPS) for peak-to-average power ratio (PAPR) reduction in Multi Carrier Code Division Multiple Access (MC-CDMA) signals. Because, MC-CDMA is still suffering from PAPR which is a major drawback in most of the multi carrier communication systems. In addition, the implementation of the system in an FPGA becomes more flexible and scalable. It eliminates the search for optimum phase factors from a given set, which manifests improved PAPR at reduced computational complexity as compared to conventional PTS and SLM. The amplitude of the signal is reduced by rotating each of the partially transmitted sequence anticlockwise by a π/2 degree and the peak power is reduced by circularly shifting the quadrature component of the partially transmitted sequence after phase rotation. A brief description of PTS, SLM is compared with the RPS, which best reduces PAPR from PTS and SLM. It is also presented that VHDL code of the RPS is designed by Xilinx ISE 14.1 implements of FPGA. The peak-to-average power ratio performance of the proposed method has been investigated.

Comparison of the Performance of Group Orthogonal Multi-carrier Code Division Multiple Access and Multi Carrier Code Division Multiple Access Signal in Fading Channels

This paper gives the effectiveness measures of the comparison of the MIMO MC CDMA and MCCDMA modulation technique for wireless radio applications. MIMO is checked as a modulation technique for telephony communication system. A comparative study of MIMO MC CDMA and MC CDMA a variant of MC is done with the CDMA technology for the same application. The study will provide bird eye view of MIMO and CDMA for communication engineering. It was found by study that MIMO performs extremely well, providing a very high tolerance to multipath delay spread and channel noise. This paper attempts to assess wireless communications channels and propose techniques to improve the performance of modern wireless communications. Hence from a strategic perspective, an analytical study into the comparison of performance of MIMO Multi Carrier Code Division Multiple Access (MIMO-MC-CDMA) and multicarrier code division multiple access signal in frequency selective fading channel, the channel bandwidth is the main theme of this paper; from which the problems that may affect the communications link are highlighted and measures to counterbalance and alleviate multi path fading are proposed and investigated.

Research and Simulation on the Performance of Multi-User Detection for MC-CDMA System

The paper makes a brief introduction of Multiple Carrier- Code Division Multiple Access (MC-CDMA) scheme based on the principles of Orthogonal Frequency Division Multiplexing (OFDM) and CDMA, and a mathematical model of the uplink is established in MC-CDMA system. The simulation research on different multi-user detection methods in MC-CDMA system is implemented by using MATLAB software, and it also compares the impacts to system performance by several different multi-user detection methods, such as De-Correlation (DEC) multi-user detection, Minimum Mean Square Error (MMSE) multi-user detection and Parallel Interference Cancellation (PIC) multi-user detection, based on understanding and analyzing the experimental results. In addition, the paper also focuses on the research of multi level PIC multi-user detection performance in different primary detection methods and different series detections.

Performance Enhancement of Grouped MCCDMA-MIMO System through Power Control Using Water Filling Game Theory under Imperfect Channel State Condition

Continuous increase in demand of wireless services such as voice, data and multimedia is fueling the need of spectrally efficient techniques in communication networks. The MCCDMA-MIMO, a system of Multi Carrier Code Division Multiple Access (MCCDMA) technique with multiple antennas at both the transmitter and receiver gets benefits of ability to adopt multiple access capability from MCCDMA technique, achieves high data rate from MIMO concepts and becomes a very attractive multiple access technique for the future wireless communication systems. But, the wireless channels in MCCDMA-MIMO networks are known to display significant variations across active users’ subcarriers as well as among subcarriers of the same user due to simultaneous spectrum utilization. This leads to the undesirable Multiple-Access Interference (MAI) and Inters Carrier Interference (ICI), accordingly degrades the performance of the system. So, the interference mitigation methodology in the MCDMA-MIMO system has received a lot of attention in next generation mobile environment. The power control and sub carrier grouping methods have been long standing open solutions for capacity enhancement. The strategic choice of assigning the transmission power to each individual subcarrier in the MCCDMA-MIMO system is subjected to the knowledge of Channel State Information (CSI), which usually becomes imperfect due to the time varying nature of the channels. The goal of this paper is to allocate proper power to sub-carriers of MCCDMA-MIMO system by playing water filling game theory against the CSI errors to improve the performance of the system.

Performance of Reduced State S–T Trellis Coded MC-CDMA Systems

In this paper, performance of reduced state space-time trellis coded multi carrier code division multiple access (STTC-MC-CDMA) system is evaluated and compared with the performance of original state STTC-MC-CDMA system. The optimum decoding scheme, i.e., maximum likelihood sequence estimation is employed which uses Viterbi algorithm for decoding STTC code. To simplify the implementation of the STTC decoder, the number of states is reduced by reducing the constraint length of the STTC encoder using generating function technique. In this technique, the generator matrix of STTC code is minimized to reduce the number of states of S–T trellis decoder. It is observed that the performance loss in terms of frame error rate of the reduced state STTC-MC-CDMA system is negligible compared to the original state STTC-MC-CDMA system. It is also noted that by using the reduced state technique the STTC decoder can be made faster since it is having lower computational complexity.

Performance Enhancement of MC-CDMA System through Turbo Block Codes

Multi carrier code division multiple access (MC-CDMA), a strong contender for future mobile communication is a combination of orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA). Turbo coding technique can be used for improving the performance of MC-CDMA system in terms of bit error rate (BER). The objective of this work is to form a coding scheme that reduces BER of MC-CDMA system. In this paper a time domain turbo block code (TBC) designed using powerful low density parity check (LDPC) code is used in MC-CDMA system for improving the BER performance and the same is proved through simulation. This code also has error correction capability along with high performance efficiency in terms of BER.