Multi-carrier Code Division Multiple Access Research Articles

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.

Performance Analysis and FPGA Prototype of Variable Rate GO-OFDMA Baseband Transmission Scheme

To fulfill the increasing demand for high speed Variable Bit Rate (VBR) broadcast services with reliable Quality of Service, Group Orthogonal-Orthogonal Frequency Division Multiple Access (GO-OFDMA) and Variable Spreading Length Multicarrier Code Division Multiple Access transmission schemes are examined over Land Mobile Satellite (LMS) channel. This paper presents the performance analysis of aforementioned multiple access transmission schemes in terms of computation complexity, Peak-to-Average-Power-Ratio (PAPR) and the average Bit Error Rate (BER) performance over L-band LMS channel. Minimum Mean Square Equalizer (MMSE) equalizer is employed at the receiver. Based on the simulation results, GO-OFDMA stems out to be a better variable rate transmission scheme in respect of both PAPR and BER performance for higher data rate users. Further, GO-OFDMA based VBR transmitter and MMSE equalizer are prototyped on commercially available virtex5 xc5vlx110t–1ff1136 Field Programmable Gate Array (FPGA) device. A block-by-block analysis of hardware resource utilization and power dissipation for the VBR GO-OFDMA transmitter is provided. The achieved baud rate for VBR GO-OFDMA transmission scheme on FPGA is 103.874 Msps. Thus, GO-OFDMA transmission scheme could be appropriate for VBR communication over LMS channel.

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.

Radio Resource Allocation with The Fairness Metric for Low Density Signature OFDM in Underlay Cognitive Radio Networks.

Low density signature orthogonal frequency division multiplexing (LDS-OFDM), one type of non-orthogonal multiple access (NOMA), is a special case of multi-carrier code division multiple access (MC-CDMA). In LDS-OFDM, each user is allowed to spread its symbols in a small set of subcarriers, and there is only a small group of users that are permitted to share the same subcarrier. In this paper, we study the resource allocation for LDS-OFDM as the multiple access model in cognitive radio networks. In our scheme, SUs are allocated to certain subcarriers based on minimum interference or higher SINR in each subcarrier. To overcome the problem where SUs were allocated less than the subcarriers, we propose interference limit-based resource allocation with the fairness metric (ILRA-FM). Simulation results show that, compared to the ILRA algorithm, the ILRA-FM algorithm has a lower outage probability and higher fairness metric value and also a higher throughput fairness index.

Iterative Channel Estimation Algorithm For Downlink MC-CDMA Systems With Two-Path Successive Relaying Transmission

In this letter, we develop a channel estimation algorithm for a downlink multi-carrier code division multiple access system in the context of two-path successive relaying transmission. We employ the expectation maximization tool to get the maximum likelihood estimate of the channel impulse responses of the direct and relays links. The proposed algorithm proceeds in an iterative structure and utilizes the soft information given by the demodulator as a priori probabilities to refine the estimation process, without causing overhead to the demodulation execution. The simulation experiments are carried out to assess the effectiveness of the proposed estimator.

Performance Improvement of MIMO MC- CDMA System using Relay and ITBF

Objective: In the wireless communication the Inter Symbol Interference (ISI) is a major barrier caused by multipath fading which has a strong negative impact on Bit Error Rate (BER) and affects the high speed data transmission over the wireless channel. Methods: The equalization and channel estimation techniques are available at the receiver (Rx) to reduce the ISI when the channel is affected by multipath propagation effect. Further to decrease the influence of ISI or to improve the quality of the channel condition from the transmitter (Tx), it is reliable to use Relay with Beam-Form (BF) technique because ISI is related to a channel’s spatial property. It is natural to expect BF techniques which are often deployed in Multiple Input Multiple Output (MIMO) systems that help to enhance the performance of the system. Findings: In this model, the half duplex Relaying is provided with MIMO antennas with the Amplify and Forward (AF) Relaying protocol. To reduce the ISI and error rate, this study proposes Improved Transmit Beam-Form (ITBF) with equalizationandRelay to be employed with MIMO Multi-Carrier Code Division Multiple Access (MC-CDMA) system. Application: Simulation result depicts the proposed system with ITBF and Relaying is highly reliable to achieve high speed data transmission. Keywords: Equalization and Improved Transmit Beam-Form (ITBF), Inter Symbol Interference (ISI), Multi-Carrier Code Division Multiple Access (MC-CDMA), Multiple Input Multiple Output (MIMO), Relay

Optimal <inline-formula> <tex-math notation="LaTeX">$Z$ </tex-math> </inline-formula>-Complementary Code Set From Generalized Reed-Muller Codes

Z-complementary code set (ZCCS), an extension of perfect complementary codes (CCs), refers to a set of two-dimensional matrices having zero correlation zone properties. ZCCS can be used in various multi-channel systems to support, for example, quasi-synchronous interference-free multicarrier code-division multiple access communication and optimal channel estimation in multiple-input multiple-output systems. Traditional constructions of ZCCS heavily rely on a series of sequence operations which may not be feasible for rapid hardware generation particularly for long ZCCSs. In this paper, we propose a direct construction of ZCCS using second-order Reed-Muller codes with efficient graphical representation. Our proposed construction, valid for any number of isolated vertices present in the graph, is capable of generating optimal ZCCS meeting the set size upper bound.

Performance analysis of Selective Mapping and clipping based multicarrier-CDMA system with and without MIMO technique

Multicarrier Code Division Multiple Access (MC-CDMA) is a promising choice for next generation wireless communication, offers high spectral efficiency, high capacity and immunity against narrow band interference. On the other hand, it suffers from high Peak to Average Power Ratio (PAPR). This increases nonlinear distortion and reduces efficiency of radio frequency components at the base station. Among the several PAPR reduction techniques, the distortion-less & simple search algorithm based Selective Mapping (SLM) and computationally efficient & less complicated clipping techniques have been applied in MC-CDMA system to mollify PAPR. Then the impact of these techniques on BER performance has been investigated. Results show that this hybrid system (SLM and clipping based MC-CDMA system) substantially reduces PAPR, but at the expense of BER. To improve BER performance while maintaining PAPR, Multiple Input Multiple Output (MIMO) technique has been applied to hybrid system. Results reveal that MIMO based hybrid system significantly improves BER performance with approximately same PAPR compared to that of hybrid system. This work also presents theoretical bit error rate analysis for hybrid system with and without MIMO technique.

可见光通信非对称限幅光多载波码分多址系统的设计及性能分析

可见光通信非对称限幅光多载波码分多址系统的设计及性能分析

Dynamic User Grouping-Based NOMA Over Rayleigh Fading Channels

With the development of wireless communications and internet of things (IoT), non-orthogonal multiple access (NOMA) has been considered as one of effective schemes to meet the rapidly growing user access requirements. Two types of NOMA, i.e., NOMA-2000 and power-domain NOMA (PD-NOMA), have been proposed in recent years. The first one is a superposition of a set of orthogonal frequency division multiple access (OFDMA) signals and a set of spread-spectrum multicarrier-code division multiple access (MC-CDMA) signals while the second one is a direct superposition of a MC-CDMA signal and an OFDMA signal. This paper proposes a dynamic user grouping method for classifying users and then compares the performance between NOMA-2000 and PD-NOMA over Rayleigh fading channels. Simulation results show that the PD-NOMA can always exhibit lower bit error rate (BER) than the NOMA-2000 under different signal-to-noise ratios. Under the Rayleigh fading environment, the performance of the PD-NOMA after user grouping is better than that of NOMA-2000.

Multiuser Detection with Decision-Feedback Detectors and PIC in MC-CDMA System

In this paper we propose an iterative parallel decision feedback (P-DF) receivers associated with parallel interference cancellation (PIC) for multicarrier code division multiple access (MC-CDMA) systems in a Rayleigh fading channel (cost 207). First the most widely detection techniques, minimum mean-squared error MMSE, Maximum Likelihood ML and PIC were investigated in order to compare their performances in terms of Bit Error Rate (BER) with parallel feedback detection P-DFD. A MMSE DF detector that employs parallel decision-feedback (MMSE-P-DFD) is considered and shows almost the same BER performance with MMSE and ML, which present a better result than the other techniques. In a second time, an iterative proposed method based on the multi-stage techniques P-DFD (parallel DFD with two stages) and PIC was exploited to improve the performance of the system.

Patient Monitoring System Using Cognitive Internet of Things.

In this article, we ponder multi-user medical image transmission using Cognitive Multiple-input Multiple-output (MIMO) Multi-carrier Code-division-multiple-access (MC-CDMA) system to monitor patient information. We investigate the performance of such system in the communication layer and application layer of internet of things (IOT). Patient monitoring system plays vital role in the hospital particularly in the emergency ward to resolve certain problems such as maintaining glucose level in the body, maintaining minimum sugar levels under emergency conditions. IOT find tremendous application in the hospital to deal with certain issues such as injection of drug to the patients by doctor from remote places, monitoring patients heart beats, sugar level by the concerned doctors. MIMO finds many applications in medical field to enrich data rate while communication patient information at faster rate. We utilize MC-CDMA system to accommodate large user patients information and to transmit such information with high resolution by eliminating channel impairments. We are utilizing Cognitive spectrum for medical image transmission of higher bandwidth applications. We realize Double-space-time transmit diversity as MIMO profile to boost up throughput. We perform multi-carrier modulation using IDFT at the transmitter .we carryout demodulation employing DFT at the hospital. We introduce Multi-carrier communication to fulfil the need of bandwidth efficiency and to diminish frequency selectivity effects.In the application layer, we estimate patient's information with aid of block-nulling decoding algorithm. Moreover we analyze the quality of image of D-STTD MC-CDMA system with turbo style of channel encoder to manifest medical image with high resolution with less signal strength. We conclude that Cognitive D-STTD MC-CDMA system provides reliable communication for the application of IOT and also transfer high resolution medical image with less signal strength in order to observe patient status by doctor.

Suitable Spreading Sequences for Asynchronous MC-CDMA Systems

In order to meet the demand of high data rate transmission with good quality maintained, the multi-carrier code division multiple access (MC-CDMA) technology is considered for the next generation wireless communication systems. However, their high crest factor (CF) is one of the major drawbacks of multi-carrier transmission systems. Thus, CF reduction is one of the most important research areas in MC-CDMA systems. In addition, asynchronous MC-CDMA suffers from the effect of multiple access interference (MAI), caused by all users active in the system. Degradation of the system’s bit error rate (BER) caused by MAI must be taken into consideration as well. The aim of this paper is to provide a comparative study on the enhancement of performance of an MC-CDMA system. The spreading sequences used in CDMA play an important role in CF and interference reduction. Hence, spreading sequences should be selected to simultaneously ensure low CF and low BER values. Therefore, the effect that correlation properties of sequences exert on CF values is investigated in this study. Furthermore, a numerical BER evaluation, as a function of the signal-to-noise ratio (SNR) and the number of users, is provided. The results obtained indicate that a trade-off between the two criteria is necessary to ensure good performance. It was concluded that zero correlation zone (ZCZ) sequences are the most suitable spreading sequences as far as the satisfaction of the above criteria is concerned.

Using Least Mean p-Power Algorithm to Correct Channel Distortion in MC-CDMA Systems

This work focuses on adaptive Broadband Radio Access Network (BRAN) channel identification and on downlink Multi-Carrier Code Division Multiple Access (MCCDMA) equalization. We use the normalized BRAN C channel model for 4G mobile communications, distinguishing between indoor and outdoor scenarios. On the one hand, BRAN C channel parameters are identified using the Least Mean p-Power (LMP) algorithm. On the other, we consider these coefficients in the context of adaptive equalization. We provide an overview and a mathematic formulation of MC-CDMA systems. According to these fundamental concepts, the equalizer technique is investigated analytically to compensate for channel distortion in terms of the bit error rate (BER). The numerical simulation results, for various signal-to-noise ratios and different p threshold, show that the presented algorithm is able to simulate the BRAN C channel measured with different accuracy levels. Furthermore, as far as the adaptive equalization problem is concerned, the results obtained using the zero-forcing equalizer demonstrate that the algorithm is adequate for some particular cases of threshold p.

Construction of a Near-Optimal Quasi-Complementary Sequence Set from Almost Difference Set

Compared with the perfect complementary sequence sets, quasi-complementary sequence sets (QCSSs) can support more users to work in multicarrier CDMA communications. A near-optimal periodic QCSS is constructed in this paper by using an optimal quaternary sequence set and an almost difference set. With the changes of the values of parameters in the QCSS, the number of users supported by the subcarrier channels in CDMA system has an exponential growth.

Sub-Nyquist Sampling Receiver for Overlay Cognitive Radio Users

The secondary users (SUs) in cognitive radio (CR) networks exploit the underutilized radio spectrum of the primary networks. In overlay CR systems, transmit waveforms can be designed either in orthogonal frequency-division multiplexing or in multicarrier code division multiple access modulation formats by deactivating subcarriers corresponding to primary users’ frequency bands to avoid interference. Transmissions of these overlay CR waveforms are expected to be extremely wideband, occupying up to 1 GHz of bandwidth. As reception of such wideband signals requires very high Nyquist sampling rates, we propose to employ a sub-Nyquist sampling front end. The proposed sub-Nyquist sampling receiver collects as coherently as possible all the SU signals spread across the entire frequency span of interest. Our theoretical analysis and simulation results demonstrate that the proposed receiver performs very close to the Nyquist rate receiver with significantly reduced complexity.

Constructions of Asymptotically Optimal Quasi-Complementary Sequence Sets

Quasi-complementary sequence sets (QCSSs) have the advantage of supporting more users in multi-carrier CDMA systems. Recently, a generic construction of QCSSs from difference sets was developed by Liu et al. In this letter, the idea of Liu et al. is extended, and the constructions of QCSSs from both difference sets and almost difference set are proposed. These constructions produce QCSSs asymptotically achieving the theoretical bound. The QCSSs presented in this letter have new parameters not covered in the literature.

Interference cancellation in cognitive radio-based MC-CDMA system using pre-coding technique

In this article, the authors investigate error rate (ER) analysis of multi-carrier code-division multiple access (MC-CDMA) for cognitive radio network (CRN) using the pre-coding technique. CRN is a type of frequency-sensitive device in wireless communication which can intellect the idle spectrum availability and assign the spectrum dynamically for mobile communication. The spectrum is subdivided and its sub-band frequency of CRN is used for implementing multi-carrier (MC) communication and generating the spread of code frequency generation. In this work, pre-processing technique using singular value decomposition is considered for alleviation of the effects of interferences arising from secondary users to ensure a reliable link between the base station and the active users. The null space of channel matrix of active interference primary users has been exploited for the formulation of pre-processing matrix. A time–frequency domain signature sequence has been constructed to suppress the adverse effects of adjacent cell interference (ACI) and secondary multi-user interferences (S-MUI). Further, iterative decoder has been implemented for the achievement of better coding gain when the primary users’ signals are contaminated by noise. Simulation ER results of CR MC-CDMA with pre-coding technique for Stanford University Interim and Long-term Evolution channels specification has been presented. It is discerned from ER results that coded CR MC-CDMA system established with pre-processing matrix offers robust performance through vindication of ACI and S-MUI effects while retaining a low complexity of primary mobile station for downlink transmission. Additionally, CRN-based MC-CDMA system has been analysed and found to provide an efficient and flexible solution to fulfil the demands of spectrum utilization.

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.

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.