Multi-carrier Code Division Multiple Access Research Articles

Constructed MC-CDMA LR-PON With Colorless Laser Diode and Multicode Interference Cancellation DSP

Performance of multicarrier code division multiple access (MC-CDMA) long reach passive optical network (LR-PON) implemented with colorless laser diode transmitter is evaluated and compared with the same system under typical orthogonal frequency division multiplexing (OFDM) format. The relative amount of the multicode interference (MCI) in the MC-CDMA PON can be efficiently suppressed by applying the minimum mean square error based MCI cancellation processing and be analyzed in term of the error vector magnitude deviation. Due to the double sideband nature of the directly modulated colorless laser diode, both OFDM and MC-CDMA formats suffer from severe power fading after fiber transmission. Partial subcarriers in the OFDM-PON fail to reach the specified forward error correction (FEC) threshold, causing a huge performance deviation among subcarriers and a 3% data loss after 75-km transmission. In contrast, a distance transparency transmitter design for subscribers ranging from back-to-back to 50 km is achieved in the MC-CDMA PON scheme, and the received performance among subcarriers are equalized under the FEC criterion even after 75-km transmission. Therefore, the MC-CDMA exhibits superior performance when comparing with the OFDM format in the directly modulated colorless laser diode based LR-PONs.

Mitigation of co-channel interferences in cognitive multi-carrier code division multiple access system by singular value decomposition techniques

Efficient spectrum usage is important criteria for next generation wireless systems. In this paper, to utilize the spectrum in useful manner, cognitive radio approaches are used along with multi-carrier code division multiple access schemes (MC-CDMA). But MC-CDMA systems are greatly affected by co-channel interference (CCI). To mitigate CCI interference, multi-user detection (MUD) technique is the design choice. When the user population increases complexity level of MUD algorithms are increases linearly. Also power consumption of mobile station also increases. Hence as a design alternate, in this paper we developed a singular value decomposition based pre-processing approaches to mitigate CCI interferences. The proposed technique is tested with real time channel models and the result shows that superior performance obtained with proposed techniques.

Design of MC-CDMA receiver using radial basis function network to mitigate multiple access interference and nonlinear distortion

Multicarrier code division multiple access (MC-CDMA) is a novel wireless communication technology with high spectral efficiency and system performance. However, all multiple access techniques including MC-CDMA were most likely to have multiple access interference (MAI). So, this paper mainly aims at designing a suitable receiver for MC-CDMA system to mitigate such MAI. The classical receivers like maximal-ratio combining and minimum mean square error fail to cancel MAI when the MC-CDMA is subjected to nonlinear distortions, which may occur due to saturated power amplifiers or arbitrary channel conditions. Being highly nonlinear structures, the neural network (NN) receivers such as multilayer perceptron and radial basis function networks could be better alternative for such a case. The possibility NN receiver for a MC-CDMA system under different nonlinear conditions has been studied with respect to both performance and complexity analysis.

Secure Multiple Access Based on Multicarrier CDMA With Induced Random Flipping

In this paper, we study secure multiple access based on multicarrier (MC) code division multiple access (CDMA) systems with induced random (chip) flipping of spreading sequence, which is suitable for machine-type communications (MTC). In MTC, devices may use low-cost hardware-based random number generators for pseudo-random noise (PN) sequences in secure communications. Since PN sequences can be estimated by correlation attacks at an eavesdropper, induced random (chip) flipping of spreading sequences is proposed to make correlation attacks infeasible. However, induced random flipping can also degrade the performance of detection and decoding at a legitimate receiver that only knows original spreading sequences. To avoid the performance degradation, we derive low-complexity iterative receiver algorithms for multiuser signal detection and decoding based on the expectation-maximization (EM) algorithm.

Mean Spectral Efficiency Evaluation of the Uplink of MC-CDMA Cellular Systems

The mean spectral efficiency of the uplink of MC-CDMA cellular systems is evaluated. The complete system employs the multicarrier-code division multiple access (MC-CDMA) technique, a linear antenna array at the base stations, frequency interleaving, maximal ratio combining, adaptive modulation, perfect power control and a cyclic prefix large enough to eliminate the intersymbol and intercarrier interferences effects. This scenario assumes the presence of multiple access interference, co-channel interference, additive white Gaussian noise, exponential path-loss and slow and frequency selective Rayleigh fading channel. In this context, a procedure to calculate the mean spectral efficiency of the cellular network is proposed, which depends of the mean bit error rate, the channel reuse factor, the increase of bandwidth due to the cyclic prefix, the system load, the spreading factor, the cell radius and the modulation schemes. Results show that an unitary channel reuse factor is the most efficient way to use the spectrum, but it is critical in relation to the transmission rates. Also, as orthogonal frequency division multiple access technique is a particular case of MC-CDMA, the spectral efficiency of both techniques is compared.

Multi-code Multicarrier CDMA: Performance Analysis

A new multi-code multicarrier code division multiple access (MC-MC-CDMA) system is proposed and analyzed in afrequency selective fading channel. By allowing each user to transmit an M-ary code sequence, the proposed MC-MC-CDMA system can support various data rates as required by next generation standards without increasing the interference which is common in general multicarrier CDMA systems. The bit error rate of the system is analytically derived in frequency selective fading, with Gaussian noise and multiple access interference. The results show that the proposed MC-MC-CDMA system clearly outperforms both single-code multicarrier CDMA (MC-CDMA) and single-carrier multi-code CDMA in a fixed bandwidth allocation.This indicates that MC-MC-CDMA can be considered for next generation cellular systems.

Compensation of Fading Channels Using Partial Combining Equalizer in MC-CDMA Systems

In this paper the performance of a partial combining equalizer for Multi-Carrier Code Division Multiple Access (MC-CDMA) systems is analytically and numerically evaluated. In the part of channel identification, authors propose a blind algorithm based on Higher Order Cumulants (HOC) for identifying the parameters representing the indoor scenario of Broadband Radio Access Networks (BRAN A) channel model normalized for MC-CDMA systems. Theoretical analysis and numerical simulation results, in noisy environment and for different Signal to Noise Ratio (SNR), are presented to illustrate the performance of the proposed algorithm in the one hand, and the other hand the impact of partial combining equalizer on the performance of MC-CDMA systems.

Performance of Convolution Coded Multicarrier CDMA System in Frequency Selective Rayleigh Channel

Performance of Convolution Coded Multicarrier CDMA System in Frequency Selective Rayleigh Channel

Precoding for the Sparsely Spread MC-CDMA Downlink With Discrete-Alphabet Inputs

Sparse signatures have been proposed for the CDMA uplink to reduce multi-user detection complexity, but they have not yet been fully exploited for its downlink counterpart. In this work, we propose a Multi-Carrier CDMA (MC-CDMA) downlink communication, where regular sparse signatures are deployed in the frequency domain. Taking the symbol detection point of view, we formulate a problem appropriate for the downlink with discrete alphabets as inputs. The solution to the problem provides a power-efficient precoding algorithm for the base station, subject to minimum symbol error probability (SEP) requirements at the mobile stations. In the algorithm, signature sparsity is shown to be crucial for reducing precoding complexity. Numerical results confirm system-load-dependent power reduction gain from the proposed precoding over the zero-forcing precoding and the regularized zero-forcing precoding with optimized regularization parameter under the same SEP targets. For a fixed system load, it is also demonstrated that sparse MC-CDMA with a proper choice of sparsity level attains almost the same power efficiency and link throughput as that of dense MC-CDMA yet with reduced precoding complexity, thanks to the sparse signatures.

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.

A joint cross-layer transmission design with time–frequency coded cooperation HARQ for underground coal mine MC-CDMA WSNs

In this paper, multicarrier code division multiple access (MC-CDMA) modulation is adapted to constitute wireless sensors to improve the monitoring performance of wireless sensor networks (WSNs) for underground coal mine. A subcarrier phase compensation algorithm based on selective mapping (SLM) is proposed to reduce the relatively high PAPR of MC-CDMA signal. To further improve the monitoring performance of the underground MC-CDMA WSNs, a joint cross-layer transmission with time–frequency coded cooperation hybrid automatic repeat request (HARQ) is also proposed. The proposed cross-layer transmission combines time–frequency coded cooperation of physical layer with HARQ of media access control (MAC) layer. In the proposed transmission, the cooperative sensor utilizes time–frequency coded cooperation method to retransmit the monitoring information of source sensor at each retransmission time to obtain the coding gain and spatial diversity gain. Simulation results show that the proposed joint cross-layer transmission for underground coal mine MC-CDMA WSNs based on SLM phase compensation has significantly reduced the PAPR of MC-CDMA signal and improved the monitor performance of the coal mine MC-CDMA WSNs.

AN EFFICIENT CFO ESTIMATION AND ICI REDUCTION IN MC-CDMA SYSTEM THROUGH CONJUGATE WEIGHTED MUSIC BASED RPRCC SCHEME

Multicarrier code division multiple access (MC-CDMA) is one of the most attractive method for future broadband wireless systems and long term evolution (LTE) standard. The performance of MC-CDMA systems is greatly deteriorated by carrier frequency offset (CFO) which is due to oscillator instability and Doppler shifts. CFO leads to loss of orthogonality between the subcarriers and introduces intercarrier interference (ICI). Among the numerous ICI cancellation techniques, the proposed receiver phase rotated conjugate cancellation (RPRCC) offers greater ICI reduction compared to other methods. The distributed nature of networks and concurrent transmission from multiple users in uplink, RPRCC needs multiple frequency offset estimation at the receiver. Multiple signal classification (MUSIC) algorithm is the best suited CFO estimation technique in multiuser environment. However the performance of MUSIC algorithm is inferior for closely spaced CFOs. To achieve precise CFO estimation and greater ICI reduction, RPRCC with conjugate weighted MUSIC based CFO estimation is proposed in this paper. The simulation results depict that the ICI power reduction capability and BER performance of the suggested method outperforms the conventional techniques in both properly and closely spaced CFOs.

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.

RF power fading mitigation for an IMDD multicarrier LR-PON.

In an intensity-modulation direct-detection (IMDD) orthogonal frequency division multiplexing (OFDM) signal format, radio frequency (RF) power fading produces non-uniform receiving performance among the subcarriers due to chromatic dispersion. Hence each subscriber experiences distinct quality of service (QoS) in conventional frequency division multiple access (FDMA). In this paper, a multicarrier code division multiple access (MC-CDMA) signal along with multicode interference (MCI) cancellation process is proposed and experimentally demonstrated to enhance the receiving performance in an IMDD long reach passive optical network (LR-PON). With the proposed scheme, the receiving performance of each subcarrier can be equalized so that a universal transmitter design at central office (CO) can support all the subscribers with their locations ranging from back-to-back to 100 km. Our experimental results also reveal that, even under 20 dB RF power fading, the proposed scheme can still provide over 21.7 dB power budget and only approximately 2 dB sensitivity deviation is observed in an IMDD LR-PON system.

A Blind Recognition Algorithm for Real Orthogonal STBC MC-CDMA Underdetermined Systems Based on LPCA and SCA

This paper proposes a blind recognition algorithm for real orthogonal space---time block code multi-carrier code division multiple access (OSTBC MC-CDMA) underdetermined systems based on Laplacian potential clustering algorithm (LPCA) and sparse component analysis. In our work, the received signal first has been constructed to satisfy the instantaneous underdetermined model, where the mixing matrix (virtual channel matrix) includes the information of space---time block code. The virtual channel matrix is then can be separated by using the LPCA. We show that, for OSTBC, the correlation matrix of virtual channel matrix is a diagonal matrix, while with non-OSTBC (NOSTBC) signal, such correlation matrix of virtual channel matrix was not. According to this property, two characteristic parameters of correlation matrix of virtual channel matrix are extracted, such as sparsity and energy ratio of non-main and main diagonal elements. In recognition process, the energy ratio will be used in pre-decision step, thus it avoids the influence of noise and making sure that the correlation matrix of virtual channel matrix is a diagonal matrix for OSTBC. The last decision will be done through comparing sparsity parameter with the number of transmitted symbols, where the sparsity parameter of OSTBC will be equal the number of transmitted symbols and the such parameter of NOSTBC will not. Simulation results demonstrate the effectiveness of the proposed algorithm.

Low Complexity Joint Blind Equalization and CFO Estimation for MC-CDMA System

Based on the orthogonality between the used and the unused spreading codes (excess codes) subspaces in one hand and on the restoration of guard interval redundancy of Multicarrier Code Division Multiple Access signal in other hand, we propose joint Carrier Frequency Offset and time domain equalizer estimators. A major difficulty arises from the highly complexity of these methods. Use of an approximation method or an adaptive algorithm has been popular approach to ease problem solving. Our derived methods are found to be good in terms of estimation accuracies, computation complexity, and convergence speed when compared to the block processing algorithms.

Sparse index multiple access for multi-carrier systems with precoding

In this paper, we consider subcarrier-index modulation (SIM) for precoded orthogonal frequency division multiplexing (OFDM) with a few activated subcarriers per user and its generalization to multi-carrier multiple access systems. The resulting multiple access is called sparse index multiple access (SIMA). SIMA can be considered as a combination of multi-carrier code division multiple access (MC-CDMA) and SIM. Thus, SIMA is able to exploit a path diversity gain by (random) spreading over multiple carriers as MC-CDMA. To detect multiple users' signals, a lowcomplexity detection method is proposed by exploiting the notion of compressive sensing (CS). The derived low-complexity detection method is based on the orthogonal matching pursuit (OMP) algorithm, which is one of greedy algorithms used to estimate sparse signals in CS. From simulation results, we can observe that SIMA can perform better thanMC-CDMA when the ratio of the number of users to the number of multi-carrier is low.

Game Theory based Hybrid Cognitive Radio Transmission

Background: Overlay based Cognitive radio can utilize only the primary user spectrum opportunistically for transmission. A hybrid overlay and under based cognitive radio is presented with game theory based decision making to facilitate continuous transmission support for the secondary user. Methods: The Hybrid Cognitive Radio (HCR) provides an optimum solution for effective utilization of the spectrum. A hybrid cognitive radio is designed to switch between overlay and under lay mode of transmission to continuously provide transmission opportunity with high data rate support for secondary user. The switching between the two transmission modes and frequency selection is formulated as a game. Decision making in the game is carried out by using the frequency utilization factor of the primary user as the utilization function of the game. Spectrally Modulated Spectrally Encoded (SMSE) framework is employed to efficiently generate the overlay Orthogonal Frequency Division Multiplexing signal and underlay Multicarrier Code Division Multiple Access (MCCDMA) signal with less overhead. Findings: This simple game theory based hybrid cognitive radio show improved bit error rate and throughput performance of the secondary user. The implementation of the hybrid cognitive radio is done using the LabVIEW and Universal Software Radio Peripheral (USRP) Software defined radio hardware platform. Applications/Improvements: The overhead of generation two different waveform in hybrid cognitive radio using Fast Fourier Transform (FFT) is reduced by sharing the common functionality between them under the frame work of the Spectrally Modulated Spectrally Encoded scheme which reduces the switching time and increases the spectral efficiency.

Hybrid Overlay/Underlay Cognitive Radio Network With MC-CDMA

Cognitive radio allows secondary users (SUs) to exploit the underutilized radio spectrum of the primary networks. To fully utilize the primary spectrum and maximize spectral efficiency, overlay and underlay transmissions, which exploit the white and gray spaces, respectively, should be used together. However, for underlay, the SUs need to transmit at low power to avoid causing harmful interference to the primary users (PUs), whereas the PUs will cause high interference to the SUs. Thus, interference mitigation is a major issue in underlay spectrum utilization. In this paper, a hybrid transmission system that exploits both overlay and underlay is proposed using multicarrier code-division multiple access due to its interference rejection and diversity exploitation capabilities. Unlike existing approaches, which separate the use of overlay and underlay spectrum, the proposed schemes utilize the entire spectrum for underlay transmission to minimize the PU interference while using the spectrum holes for overlay transmission to maximize the data rate. Two techniques that operate at full-load and overload scenarios are proposed. The overload system is then extended to the multiuser underlay case to further improve spectrum utilization.

Joint angle and delay estimation for underwater acoustic multicarrier CDMA systems using a vector sensor

In this study, the problem of joint angle and delay estimation for underwater acoustic multicarrier CDMA systems using a vector sensor is addressed. By jointly utilising the temporal, pressure and velocity information inherent in the received signal, the temporal-vector-sensor manifold vector is constructed. Then, a MUSIC-based algorithm that contains several one-dimensional searches for jointly estimating azimuth angle, elevation angle and time-delay parameters of a ‘desired source’ operating in the multi-source and multipath environment is proposed. In addition, a closed-form ESPRIT-based algorithm is also presented for the scenario where the multipath propagation signals are emanated from a single source. Simulation results are finally presented to verify the efficacy of the proposed algorithms.