Exact BEP of cooperative MC-CDMA systems using selective threshold digital relaying

The performance of a multicarrier direct sequence code division multiple access (MC-DS-CDMA) system in fading environment has been extensively analysed in the literatures. The analysis that is available in the literatures did not take into account the impact of jamming and channel estimation errors on the performance of the system. In this study, closed-form expressions of the average bit error probability (BEP) of the MC-DS-CDMA system with channel estimation errors in the presence of partial band, broadband and multitone jamming are derived in a Rayleigh fading channel. The analysis shows that the magnitude of the normalised correlation between the actual and the estimated complex fading channel gain, A, greatly affects the performance of the MC-DS-CDMA system. For large signal-to-noise ratio, the average BEP with A=1 and without multiple access interference (MAI) tends to zero. When A≠1, the BEP of the system exhibits an error floor even without MAI. This error floor increases as the number of users increases. It is also shown that increasing the number of the system subcarriers enhances the system performance against jamming.

In the uplink system, different carrier frequency offsets (CFO) of different users at the receiver resulting multiuser interference (MUI) and thus degrade the performance of Multicarrier Code Division Multiple Access (MC-CDMA) system. In the previous study, Modified Minimum Mean Square Error Frequency Domain Equalization (Modified MMSE-FDE) has been proposed by Agnihotri which results in a better performance than the conventional MMSE. However, the achieved Bit Error Rate (BER) is not smaller than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> for Signal to Noise Ratio (SNR) below 20. This paper proposed a new algorithm to improve Modified MMSE-FDE performance in mitigating multiuser interference (MUI) in single cell MC-CDMA system, that is called as Carrier Frequency Offset Estimation-Minimum Mean Square Error Frequency Domain Equalization (CFO Estimation-MMSE FEQ). CFO Estimation-MMSE FEQ takes into account the rest of MUI as well as Modified MMSE-FDE to design equalization coefficient, but CFO Estimation-MMSE FEQ uses CFO estimation that is not on Modified MMSE-FDE. The value of CFO is estimated and regenerated in the receiver and then used to estimate MUI. In order to get signal processing more efficient, CFO Estimation-MMSE FEQ only takes the real trace of equalization coefficient matrix. MC-CDMA with CFO Estimation-MMSE FEQ has better performance than MC-CDMA with Modified MMSE-FDE. However, the complexity of CFO Estimation-MMSE FEQ is higher than Modified MMSE-FDE. By taking only the real trace of equalization coefficient matrix, the complexity of CFO Estimation-MMSE FEQ is getting simpler than taking the whole of equalization coefficient matrix. Furthermore, CFO Estimation-MMSE FEQ that takes only the real trace of equalization coefficient matrix is 2.9 % more efficient than CFO Estimation-MMSE FEQ that takes the whole of equalization coefficient matrix.

The variation of peak-to-average power ratio (PAPR) for different allocations of spreading code sequences in multi-carrier code division multiple access (MC-CDMA) and multi-carrier direct-sequence code division multiple access (MC-DS-CDMA) systems is investigated. The results show that for a small number of active users, the PAPR performance of an MC-CDMA system can be improved by careful allocation of the spreading code sequences to different users.

In this paper, we derive exact form expressions for the Bit Error Probability (BEP) and throughput of cooperative Direct Sequence-Code Division Multiple Access (DS-CDMA) systems using incremental selective relaying which combines selective relaying with incremental relaying protocols in the presence of multipath propagation. The derived results are valid for any multipath intensity profile of the channel and any path delays. They also consider the correlation of the multipath gains. Simulation results along with analytical studies of BEP and throughput prove that the combination of incremental relaying with selective relaying in cooperative DS-CDMA systems improve significantly the throughput performance and can achieve the maximum possible spatial diversity when it is required by destination.

In conventional system of wireless communication the source and the channel coding are used in different modules that increases the system complexity, cost and overall processing period. To make it more efficient, both the source and channel coding modules are combined in a single processing block, which not only decreases the system complexity but also reduces the overall processing cost. Multi Carrier Code Division Multiple Access (MC-CDMA) technique which is a combination of CDMA and Orthogonal Frequency Division Multiplexing (OFDM) provides higher capacity. The proposed approach combines joint source channel coding with MC-CDMA. Through integrity check and receiver control mechanism, our system is able to subscribe to a desired broadcast session. The proposed approach result in a capacity which is nearly equals to the upper bound of the ratio CH where C is the channel capacity and H is the entropy of the source.

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.

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.

The multicarrier code division multiple access (MC-CDMA) system has received a considerable attention from researchers owing to its great potential in achieving high data rates transmission in wireless communications. Due to the detrimental effects of multipath fading the performance of the system degrades. Similarly, the impact of non-orthogonality of spreading codes can exist and cause interference. This paper addresses the performance of multicarrier code division multiple access system under the influence of frequency selective generalized η-µ fading channel and multiple access interference caused by other active users to the desired one. We apply Gaussian approximation technique to analyse the performance of the system. The avearge bit error rate is derived and expressed in Gauss hypergeometic functions. Maximal ratio combining diversity technique is utilized to alleviate the deleterious effect of multipath fading. We observed that the system performance improves when the parameter η increase or decreasse in format 1 or format 2 conditions respectively.

Multicarrier code division multiple access (MC-CDMA) is a promising technique for high data rate and high capacity (large number of users) transmission. However, rapidly time varying channels degrade the performance due to loosing the orthogonality among the subcarriers as well as code patterns. Channel estimation is very important to design adaptive system for improvement in all round performance. This paper proposes an efficient channel estimation for Rayleigh fading channel in high capacity carrier interferometry /multi-carrier code division multiple access (CI/MC-CDMA) system with variable data rate using Genetic algorithms (GAs). The system implementation is done by allocating all sub-carriers to the users who transmit high data rate and alternate odd and even subcarriers are assigned to the other sets of users transmitting at low data rate. GAs is used to estimate a near optimal solution of the set of parameter values on frequency selective Rayleigh fading channel. Objective function is formed from the weighted average of channel capacity and bit error rate. Simulation results show that both channel capacity and bit error probability are improved with the increase of number of iterations/generations.

Orthogonality restoring combining (ORC) performs better than maximum ratio combining (MRC) and equal gain combining (EGC) in multicarrier code division multiple access (MC-CDMA) systems under high load and high signal-to-noise-ratio (SNR) conditions. However, its exact bit error rate (BER) performance is complicated to evaluate. In this paper, the signal models for the MC-CDMA uplink and downlink channels are first unified. A lower bound and a tight approximation to the BER expressions of MC-CDMA with ORC are then developed. Both the lower bound and approximate BER expressions involve at most one-dimensional integration, hence they can be evaluated much more efficiently. The approximate BER expression is also numerically verified to be very tight under different fading conditions.

Automatic Digital Modulation Recognition (ADMR) is becoming an interesting problem with various civil and military applications. In this paper, an ADMR algorithm in Multi-Carrier Code Division Multiple Access (MC-CDMA) systems using Discrete Transforms (DTs) and Mel-Frequency Cepstral Coefficients (MFCCs) is proposed. This algorithm uses various DT techniques such as the Discrete Wavelet Transform (DWT), Discrete Cosine Transform (DCT) and Discrete Sine Transform (DST) with MFCCs to extract features from the modulated signal and a Support Vector Machine (SVM) to classify the modulation orders. The proposed algorithm avoids over fitting and local optimal problems that appear in Artificial Neural Networks (ANNs). Simulation results shows the classifier is capable of recognizing the modulation scheme with high accuracy up to 90% - 100% using DWT, DCT and DST for some modulation schemes over a wide Signal-to-Noise Ratio (SNR) range in the presence of Additive White Gaussian Noise (AWGN) and Rayleigh fading channel, particularly at a low Signal-to-Noise ratios (SNRs).

A novel transmitter code optimisation technique based on adaptive code-to-user allocation is presented for interference exploitation on the time division duplex downlink of binary phase shift keying-based multiple carrier code division multiple access systems. The principle of the proposed technique is to exploit the dependency of multiple access interference on the instantaneous symbol values of the active users. The objective is to adaptively allocate the available spreading sequences to users on a symbol-by-symbol basis to enhance the ratio between constructive and destructive interference and thus optimise the decision variables at the downlink receivers. The resulting signal-to-interference plus noise improvement happens by making use of the energy inherent in the system so the performance benefit is attained with no additional power-per-user investment. It will be shown that when this optimisation technique is incorporated with common pre- and post-equalisation schemes, a significant bit error rate performance improvement is achieved while the associated adaptation overhead is kept less than 6% of the available bandwidth.

Enhanced connectivity through double RIS uplink MIMO and advanced modulation

This paper introduces new blind time domain equalization (TEQ) techniques for downlink multicarrier code division multiple access (MC-CDMA) systems. This equalization exploits the guard interval (GI) redundancy together with the excess codes (EC) to restore the structural properties of MC-CDMA signal destroyed by multipath fading channels. Indeed, since in CDMA based wireless systems, the number of users per cell is significantly less than the spreading factor, a base station can set apart a subset of the codes, the excess codes that will not be used for spreading. It is shown that the joint use of the EC and GI redundancy improves significantly the equalization performance compared to the GI only or EC only cases. A second contribution consists in exploiting the previous information together with the one given by a pilot sequence in a semi blind scheme to further improve the performance. Finally, we propose a new adaptive algorithm for the estimation and tracking of the equalizer that has a faster convergence rate compared to existing algorithms of similar complexity order. Simulation based performance evaluations are given at the end of this paper to assess the effectiveness of the proposed methods in MC-CDMA.

This letter presents a novel multi-carrier code division multiple access (MC-CDMA) system called time domain synchronous MC-CDMA (TDS-MC-CDMA). Aided by the new training sequence (TS) with perfect autocorrelation in the time domain and flat frequency response in the frequency domain, the proposed TDS-MC-CDMA system outperform the traditional MC-CDMA system in terms of spectrum efficiency by about 10%. Simulations are carried out to demonstrate the good performance of the proposed scheme.