Multi-carrier Code Division Multiple Access Research Articles

New Class of Optimal Z-Complementary Code Sets

Z-complementary code sets (ZCCSs) can support interference-free multi-carrier code-division multiple access (MC-CDMA) in quasi-synchronous channels due to their favourable correlation properties. In this letter, based on the existing optimal ZCCSs and CCCs, we propose new class of optimal ZCCSs using Kronecker product. The resultant sequence sets have enlarged set size and sequence lengths which have not been reported before.

INTERFERENCE MITIGATION BASED ON CARRIER INTERFEROMETRY CODES IN THE DOWNLINK LOW EARTH ORBIT SATELLITE CHANNEL

The multi-carrier code division multiple access (MC-CDMA) system employs the Hadamard-Walsh (HW) code in the low earth orbit (LEO) satellite systems. It has been used as spreading code to maintain the multi-access interference (MAI) in the downlink LEO satellite channel. However, due to the non-orthogonality of the HW codes, these interferences are observed at the MC-CDMA satellite receiver. As a result, the LEO satellite system performance is degraded. In this paper, we propose to employ the orthogonal Carrier Interferometry (CI) code with MC-CDMA in the downlink LEO satellite channel. A new system is called CI/MC-CDMA which is used to mitigate the MAI. Moreover, the performance of the CI/MC-CDMA satellite system in terms of bit error rate (BER) is analyzed and simulated. To confirm the analysis, the system is compared to the HW/MC-CDMA system. It has been shown that CI/MC-CDMA satellite system outperforms HW/MC-CDMA

Performance Evaluation of MC-CDMA Systems with Single User Detection Technique using Kernel and Linear Adaptive Method

Among all the techniques combining multi-carrier modulation and spread spectrum, the multi-carrier code division multiple access (MC-CDMA) system is by far the most widely studied. In this paper, we present the performance of the MC-CDMA system associated with key single-user detection techniques. We are interested in problems related to identification and equalization of mobile radio channels, using the kernel method in Hilbert space with a reproducing kernel, and a linear adaptive algorithm, for MC-CDMA systems. In this context, we tested the efficiency of these algorithms, considering practical frequency selective fading channels, called broadband radio access network (BRAN), standardized for MC-CDMA systems. As far as the equalization problem encountered after channel identification is concerned, we use the orthogonality restoration combination (ORC) and the minimum mean square error (MMSE) equalizer techniques to correct the distortion of the channel. Simulation results demonstrate that the kernel algorithm is efficient for practical channels.

PAPR suppressing matrix transform and dual layered phase sequencing design for a chaos-based multi-carrier CDMA VLC system.

In this paper, we propose a chaos-based visible light communication system, wherein multiple users can access the network via the multi-carrier code division multi-access (MC-CDMA). By utilizing the high security property of chaotic sequences being aperiodic and sensitive to initial values, secure access can be achieved. However, the multi-carrier transmission suffers from high peak to average power ratio (PAPR) due to the superposition of multiple carriers, which reduces the lifetime of the light-emitting diodes (LEDs). In order to suppress the PAPR, we propose a joint matrix transform and dual layered phase sequencing (MT-DLPS) scheme. By reducing the autocorrelations of signals, the PAPR can be reduced. Moreover, the computation complexity is analyzed. Simulations are then conducted to validate that the PAPR is effectively reduced while maintaining satisfactory bit error rate (BER) performances.

Research on anti-jamming and anti-interception performance of MC-CDMA system based on Code-Hopping

In the wireless channel environment, there are all kinds of jamming. With the wide application of OFDM Technology in wireless communication system, the technology of signal analysis is becoming more and more mature. Pure OFDM signal exposed in the wireless channel is no longer safe, facing the risk of jamming and interception, especially in the military field. Multi-carrier Code Division Multiple Access (MC-CDMA) technology is what combines the characteristics of OFDM and CDMA. It has the advantages of OFDM system and CDMA system at the same time. It reduces the transmission rate and improves the reliability. Compared with OFDM system, MC-CDMA has better BER performance in the same SNR environment. Based on the single user MC-CDMA system, the system model and simulation analysis are carried out, and the performance comparison with OFDM system is carried out. Based on the above work, the theory of code hopping spread spectrum is introduced to design a new code hopping spread spectrum system based on MC-CDMA, and the anti-jamming and anti interception performance of the system is analyzed.

UFMC Waveform and Multiple-Access Techniques for 5G RadCom

In recent years, multiple functions traditionally realized by hardware components have been replaced by digital-signal processing, making radar and wireless communication technologies more similar. A joint radar and communication system, referred to as a RadCom system, was proposed to overcome the drawbacks of the conventional existent radar techniques while using the same system for intervehicular communication. Consequently, this system enhances used spectral resources. Conventional orthogonal frequency division multiplexing (OFDM) was proposed as a RadCom waveform. However, due to OFDM’s multiple shortcomings, we propose universal filtered multicarrier (UFMC), a new 5G waveform candidate, as a RadCom waveform that offers a good trade-off between performance and complexity. In addition to that, we propose multicarrier code division multiple access (MC-CDMA) as a multiple-access (MA) technique that can offer great performance in terms of multiuser detection and power efficiency. Moreover, we study how UFMC filter length and MC-CDMA spreading sequences can impact overall performance on both radar and communication separately under a multipath channel. Analysis of the bit error rate (BER) of the UFMC waveform was performed in order to confirm the experiment results.

Three New Constructions of Asymptotically Optimal Periodic Quasi-Complementary Sequence Sets With Small Alphabet Sizes

Quasi-complementary sequence sets (QCSSs) play an important role in multi-carrier code-division multiple-access (MC-CDMA) systems. They can support more users than perfect complementary sequence sets in MC-CDMA systems. It is desirable to design QCSSs with good parameters that are a trade-off of large set size, small periodic maximum magnitude correlation and small alphabet size. The main results are to construct new infinite families of QCSSs that all have small alphabet size and asymptotically optimal periodic maximum magnitude correlation. In this paper, we propose three new constructions of QCSSs using additive characters over finite fields. Notably, these QCSSs have new parameters and small alphabet sizes. Using the properties of characters and character sums, we determine their maximum periodic correlation magnitudes and prove that these QCSSs are asymptotically optimal with respect to the lower bound.

Human opinion dynamics optimization for ICI mitigation in MC-CDMA systems

This paper presents a novel social impact based approach named as Human Opinion Dynamics Optimization (HODO) to detect signals of Multi-Carrier Code Division Multiple Access (MC-CDMA) systems in the presence of Inter Subcarrier Interference (ICI). The ICI occurs because of various factors, such as Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO) and channel mobility. The ICI degrades orthogonality between different subcarriers in MC-CDMA system due to which Multiple Access Interference (MAI) occurs. The HODO is based on the socio-psychological behavior of humans in the society. Opinion dynamics leads to human consensus and consensus builds up due to human interactions in a society. The proposed approach could be used to introduce human opinion based intelligent communication networks. Our method is novel in the sense that with this algorithm, social sciences could be made compatible with wireless communication technology, which will go a long way to bridge the gap between humans and the communication technology. This new method works with very few number of control parameters and reduces the bit error rate (BER) better as compared with other conventional stochastic methods like Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). Numerical simulation results show that the proposed detector also reduces the computational complexity manifold.

Developing Optimal Spectrum Sharing Protocol and Optimal Linear Precoding for Multi-Carrier Code-Division Multiple Access Using Massive Multiple Input Multiple Output in 5G Wireless Networks

Currently, wireless systems are moving towards implementing fifth-generation (5G) wireless networks to compensate for intense growth and surpass demands concerning future wireless services. Consequently, massive multiple-input multiple-output (mMIMO) and multi-carrier code-division multiple access (MC-CDMA) have received considerable attention for addressing the prevailing constraints in developing 5G mobile networks. To meet requirements related to future wireless services such as achieving elevated data rates, avoiding multi-user co-channel interference (CCI), and satisfying other network limitations, implementing MC-CDMA with mMIMO has become mandatory. In this study, a detailed literature review is conducted on research for implementing MC-CDMA and mMIMO, and it is determined that the utilised methods fail to effectively solve previous issues. Thus, this paper proposes combining an optimal spectrum sharing (OSS) protocol and optimal linear precoding (OLP) with MC-CDMA and mMIMO. The OSS protocol provides an optimal allocation of power with improved quality of service. It is utilised to provide resource allocation with energy efficiency and high spectrum efficiency. Additionally, implementing OLP maximises the system capacity of MC-CDMA-based mMIMO wireless networks. Further, the performance of OLP is improved by introducing the salp swarm algorithm, which helps in finding the optimal precoding vector for the respective system. The proposed methods were employed in MATLAB for analysing system parameters, including the bit error rate (BER), signal-to-noise ratio, and system capacity. Moreover, the proposed work is contrasted with existing methods based on zero-forcing (ZF), regularised ZF (RZF), space–time RZF, minimum mean square error, and a relay precoder.

Multi-carrier Visible Light Communication System Using Enhanced Sub-carrier Index Modulation and Discrete Wavelet Transform

This work is aimed at providing a novel design of the Visible Light Communication (VLC) system that uses the Multi-Carrier Code-Division Multiple Access (MC-CDMA) technique to send and receive data through intensity-modulated/direct detected (IM/DD) VLC channel. The state-of-the-art framework of Enhanced Sub-Carrier Index Modulation (ESIM) is utilized to reduce the inherent peak-to-average power ratio (PAPR) in Orthogonal Frequency Division Multiplexing. Additionally, the use of cyclic prefix is omitted through the Discrete Wavelet Transform in the current system. Hence, the performance of the system is optimized in terms of PAPR, Bit Error Rate (BER), and data rate. The work presents the closed-form BER expressions for both conventional and proposed techniques in line-of-sight VLC channel. Correspondingly, the simulation programs are also executed to compared the proposed ESIM based WT-MC-CDMA system with both existing systems followed by an analysis of the results. Simulation results show the superior performance of the proposed system compared to existing systems.

Construction of Gaussian Integer Periodic Complementary Sequence Set with Zero Correlation Zone

Based on aperiodic complementary sequence (ACS) sets and orthogonal matrices, the construction of Gaussian integer (GI) zero correlation zone (ZCZ) periodic complementary sequence (ZPCS) sets is proposed. The constructed GI ZPCS sets can achieve the theoretical bound, and the length of ZCZ can be chosen flexibly. The GI ZPCS sets obtained by this paper can be used in multi-carrier code division multiple access system to obtain higher spectrum efficiency and eliminate interference.

New Image Transmission Schemes for DST-Based MC-CDMA System

In recent years, one important research area for multimedia broadcasting is how to encrypt images over communication systems. However, wireless transmission is usually under many constraints and limitations like multipath fading, InterSymbol Interference and jitter especially for such applications require relatively high data rates compared to voice transmissions. Interleaving techniques with multicarrier code division multiple access system are used to combat multi-path fading environment. This paper proposes three new transmission schemes of encrypted images for downlink discrete sine transform-based multi-carrier code division multiple access (DST-MC-CDMA) system. For each one of them, two or three stages are added to the DST-MC-CDMA system to combat the wireless transmission problems. The three stages are called Randomization stage, Interleaving stage, and PIC stage. The randomization stage encrypts the image using a two dimensional chaotic map before the DST-MC-CDMA modulation. The interleaving stage interleaves the DST-MC-CDMA signal before the transmission. The stage of parallel interference cancellation is used to cancel the multiple access interference from the received image. The main aim is to clarify the received image by combating the wireless channel weaknesses. The results of the experiments reveal that the proposed schemes are superior to conventional one that uses only equalization. Moreover, a significant performance improvement in terms of the mean square error and peak to signal and noise ratio values when applying the proposed schemes is shown in the results.

An Adaptive FH/MC-CDMA to Improve Channel Quality for Multiuser Using Variable Code-Based Carriers

The adaptive variable code-based carriers for multiusers in a common channel of communication is a technique of Multi-Carrier Code Division Multiple Access (MC-CDMA). It is an advanced mode of communication, where multiple users are communicating with different code and a different carrier. The proposed adaptive frequency hopping technique in MC-CDMA will give high signal to noise ratio value mitigating multiple access interference. Proposed adaptive technique detects multi-users with the help of matched filters. The simulation of the above system is done with correlated sub-carriers in the presence of realistic fading channels and even imperfect channel state information for recovering at the transmitter. The performance of an improved allocation algorithm for MC-CDMA system with adaptive frequency hopping is investigated. Imperfect channel state information at the base station does not affect the performance of the proposed technique due to the combined allocation algorithm and multi-user detector employment. The above combination mitigates multiple access interference efficiently, and increases the system capacity in a significant way compared to non-adaptive variable code-based carrier system. The results of the simulation confirm the above said performance factors with realistic correlated sub carriers that are faded with practical communication system parameters.

Pseudo-Boolean Functions for Optimal Z-Complementary Code Sets With Flexible Lengths

This paper aims to construct optimal Z-complementary code set (ZCCS) with non-power-of-two (NPT) lengths to enable interference-free multicarrier code-division multiple access (MC-CDMA) systems. The existing ZCCSs with NPT lengths, which are constructed from generalized Boolean functions (GBFs), are sub-optimal only with respect to the set size upper bound. For the first time in the literature, we advocate the use of pseudo-Boolean functions (PBFs) (each of which transforms a number of binary variables to a real number as a natural generalization of GBF) for direct constructions of optimal ZCCSs with NPT lengths.

Z-Complementary Code Sets With Flexible Lengths From Generalized Boolean Functions

In this paper, new direct constructions of Z-complementary code sets (ZCCSs) from generalized Boolean functions are proposed. In the literature, most ZCCS constructions based on generalized Boolean functions lead to sequences of power-of-two length. In this study, we show that our proposed methods result in ZCCSs of both power-of-two length and non-power-of-two length. Since the monomials of degrees more than 2 are employed in the proposed constructions, more ZCCSs can be obtained. The constructed ZCCSs admit the theoretical upper bound on the size for a ZCCS when the sequence length is a power of two. Also, the corresponding peak-to-average-power ratio (PAPR) is theoretically upper-bounded when a sequence in the set is used in OFDM. The proposed constructions extend the applications of ZCCSs in practical communication systems, e.g., multicarrier CDMA (MC-CDMA) system, by offering flexible sequence lengths, various set sizes, and bounded PAPR. For example, only one percent of sequences in the constructed ZCCS of size 16 and of length 128 have PAPRs larger than 8 whereas the theoretical upper bound is 16.

Implementation of Orthogonal Codes Using MZI

Background: In Code Division Multiple Access (CDMA)/Multi-Carrier CDMA (MCCDMA), Walsh-Hadamard codes are widely used for its orthogonal characteristics, and hence, it leads to good contextual connection property. These orthogonal codes are important because of their various significant applications. Objective: To use the Mach–Zehnder Interferometer (MZI) for all-optical Walsh-Hadamard codes is implemented in this present paper. Method: The Mach–Zehnder Interferometer (MZI) is considered for the Tree architecture of Semiconductor Optical Amplifier (SOA). The second-ordered Hadamard and the inverse Hadamard matrix are constructed using SOA-MZIs. Higher-order Hadamard matrix (H4) formed by the process of Kronecker product with lower-order Hadamard matrix (H2) is also analyzed and constructed. Results: To experimentally get the result from these schemes, some design issues e,g Time delay, nonlinear phase modulation, extinction ratio, and synchronization of signals are the important issues. Lasers of wavelength 1552 nm and 1534 nm can be used as input and control signals, respectively. As the whole system is digital, intensity losses due to couplers in the interconnecting stage may not create many problems in producing the desired optical bits at the output. The simulation results were obtained by Matlab-9. Here, Hadamard H2 (2×2) matrix output beam intensity (I ≈ 108 w.m-2) for different values of inputs. Conclusion: Implementation of Walsh-Hadamard codes using MZI is explored in this paper, and experimental results show the better performance of the proposed scheme compared to recently reported methods using electronic circuits regarding the issues of versatility, reconfigurability, and compactness. The design can be used and extended for diverse applications for which Walsh-Hadamard codes are required.

A Direct Construction of Optimal ZCCS With Maximum Column Sequence PMEPR Two for MC-CDMA System

The high peak-to-mean envelope power ratio (PMEPR) is a major problem in multicarrier code-division multiple-access (MC-CDMA) system. In this letter, we have proposed a new optimal Z-complementary code set (ZCCS) using higher-order (≥ 2) generalized Boolean functions (GBFs). The proposed ZCCS has maximum column sequence PMEPR of 2 and it achieves the theoretical upper bound of optimality.

System Imperfections on the Overall Performance of MC-CDMA-Based Cognitive Radio Network (CRN) System

Cognitive radio network (CRN) is considered to be the future technology for the fifth generation of cellular wireless standards (5G). CRN is based on a complex spectrum allocation system, and licensed primary users (PUs) or unlicensed secondary users (SUs) are allowed to share the spectrum, provided that they do not cause significant interference. In cognitive radio, it is important to control the transmission power of SUs so that the interference should not be harmful to the quality of service of PUs. In this paper, the authors addressed the impact of system imperfections on the overall performance of multi-carrier code division multiple access (MC-CDMA)-based CRN system. A new expression of the signal-to-interference-noise ratio (SINR) for MC-CDMA-based CRN system over a Rayleigh fading channel without any power control condition among the PUs and SUs is derived and investigated. The performance of MC-CDMA-based CRN system over the frequency selective multi-path fading channel is examined by varying the number of users, the signal-to-noise-ratio (SNR) per bit, number of fading path and number of subcarriers, respectively. From the simulation results, we have seen that the SINR performance is affected by these parameters. The analysis presented in this paper shows the impact of lack of a controlling mechanism on transmitted signal power affecting the between PUs and SUs ultimately system performance. The result of the analysis will provide relevant information to design the physical layer protocol for high speed CRN system for 5G.

Construction of Z-Complementary Code Sets With Non-Power-of-Two Lengths Based on Generalized Boolean Functions

$Z$ -complementary code set (ZCCS) plays a major role in modern communication systems. It has applications in multi-carrier code-division multiple access (MC-CDMA) scheme, channel estimation in multiple-input and multiple-output (MIMO) systems, etc. In this letter, we propose a construction of $q$ -ary ZCCS of a length of the form $2^{m}+2$ using generalized Boolean functions (GBFs). The constructed ZCCS is optimal with respect to the theoretical upper bound. Based on the authors’ knowledge, all the existing constructions of ZCCSs based on GBFs are limited to the lengths of power-of-two only.

A Novel Adaptive Optimized Fast Blind Channel Estimation for Cyclic Prefix Assisted Space–Time Block Coded MIMO-OFDM Systems

In this paper an adaptive optimized fast blind channel estimation using cyclic prefix supported with Space Time Block Coded Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (STBC-MIMO-OFDM) system is presented. The main aspire of our technique is to support multiple users at the same time over same frequency band based on the Multi-Carrier Code-Division Multiple Access (MC-CDMA) approach. High complexity and low convergence is the main obstacle in earlier blind channel estimation techniques. Modified flower pollination algorithm is implemented to overcome this problem. The MC-CDMA approach is utilized to implement the blind channel estimation. The proposed MC-CDMA is used to reduce the error rate included in the Blind Channel Estimation. As a part of wireless communications, time block coding technique is utilized to transmit several copies of information across the number of antennas. To develop the consistency of data transfer different received data is used and then MFPA results in lower fuel cost compared to FPA. MFPA produces better results compared with previous methods.