ICA detection for MC-CDMA systems

The multicarrier code division multiple access (MC-CDMA) technique has received considerable interest for its potential application to future wireless communication systems due to its high data rate. A common problem regarding the blind multiuser detectors used in MC-CDMA systems is that they are extremely sensitive to the complex channel environment. Besides, the perturbation of colored noise may negatively affect the performance of the system. In this paper, a new coherent detection method will be proposed, which utilizes the modified fast independent component analysis (FastICA) algorithm, based on approximate negentropy maximization that is subject to the second-order cone programming (SOCP) constraint. The aim of the proposed coherent detection is to provide robustness against small-to-medium channel estimation mismatch (CEM) that may arise from channel frequency response estimation error in the MC-CDMA system, which is modulated by downlink binary phase-shift keying (BPSK) under colored noise. Noncoherent demodulation schemes are preferable to coherent demodulation schemes, as the latter are difficult to implement over time-varying fading channels. Differential phase-shift keying (DPSK) is therefore the natural choice for an alternative modulation scheme. Furthermore, the new blind differential SOCP-based ICA (SOCP-ICA) detection without channel estimation and compensation will be proposed to combat Doppler spread caused by time-varying fading channels in the DPSK-modulated MC-CDMA system under colored noise. In this paper, numerical simulations are used to illustrate the robustness of the proposed blind coherent SOCP-ICA detector against small-to-medium CEM and to emphasize the advantage of the blind differential SOCP-ICA detector in overcoming Doppler spread.

In the present time, there is a rapid increase in demand for faster and reliable transmission of multimedia data through wireless channels. When multimedia data specially an image is to be transferred through the wireless channel, image is highly degraded due to wireless channel errors such as fading, interference and bursty errors. Multi-Carrier Code Division Multiple Access (MC-CDMA) technique is considered as the most promising technique for efficient wireless data transmission. This paper presents the performance comparison of image transmission over MC-CDMA system with two interleaving techniques; Helical interleaving and chaotic interleaving. At the receiver, Linear Minimum Mean Square Error (LMMSE) equalization is employed. System performance is measured through Peak Signal-to-Noise Ratio (PSNR) and Root Mean square Error (RMSE) values. From results, it has been evaluated that MC-CDMA system having chaotic interleaving and LMMSE performs better instead of having helical interleaving for image transmission over wireless channels.

Multi-carrier code division multiple access (MC-CDMA) technique is one of the strong candidates for next generation wireless mobile communication systems. Multi-carrier systems are very much sensitive to carrier frequency offset (CFO) results in intercarrier interference (ICI). To mitigate ICI without any spectral loss, a second order duobinary coded phase rotated conjugate cancellation algorithm is proposed in this paper. In the conventional phase rotated conjugate cancellation (PRCC) technique, one path carries the MC-CDMA signal with a phase spin of ϕ and the other path carries the conjugate of the first path signal with -ϕ phase spin. This artificial phase rotation allows the transmitter to tune the transmitted signals so that the ICI effects could be mutually cancelled at the receiver. Although the PRCC technique reduces the spectral efficiency, the limitation can be overcome by the joint second order duobinary coding scheme with PRCC technique. In the proposed method, the correlative coding between the binary symbols modulated on adjacent subcarriers is used to reduce the ICI without any spectral loss. Simulation results show that the proposed PRCC method provides better carrier to interference ratio (CIR) and bit error rate (BER) performances compared to the conventional conjugate cancellation (CC) technique.

Multi-carrier code division multiple access (MC-CDMA) technique is a combination of two radio access techniques: CDMA and orthogonal frequency division multiplexing and has the advantages of both techniques. The paper presents the design of transmitter and receiver for MC-CDMA radio interface. It also presents encoders and decoders of turbo codes which were used in simulation of the MC-CDMA technique. Two turbo codes with 8-state recursive systematic convolutional were used in the simulation. The simulation results of the transmission quality in additive white Gaussian noise (AWGN) channel presented in the paper show bit error rate and frame error rate performance of MC-CDMA technique with the turbo codes and allow for comparison the performance of both turbo codes.

For future mobile communications, an appropriately chosen multiple access scheme is a critical issue. To support robust frequency planning, multi-operator scenarios, system coexistence and hierarchical cell structures, frequency division multiple access (FDMA) and multicarrier techniques are viable choices. Further multiple access schemes presently under discussion are code division multiple access (CDMA) and time division multiple access (TDMA). A mobile radio system concept deploying a hybrid frequency and time divided code division multiple access (F/T/CDMA) scheme with a multicarrier CDMA (MC-CDMA) component, called MC/JD-CDMA, is proposed and performance results for the uplink are presented. Attractive features of the proposed system concept are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, as well as inherent frequency and interferer diversity.

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.

Multicarrier Code-Division Multiple Access (MC-CDMA) is a foreseen technique for future high data rate and high capacity multiuser wireless communications. However, the often large values of the Peak-to-Average Power Ratio (PAPR) of the transmitted signals pose a problem in multicarrier systems, because they can lead to nonlinear distortion at the High Power Amplifier (HPA) and a subsequent degradation of the system performance. In this paper, we propose a PAPR reduction scheme for MC-CDMA downlink systems based on the addition of peak reduction signals that borrow the spreading codes of idle users. The minimization of the PAPR can then be formulated as a Second-Order Cone Programming (SOCP) problem.

This paper addresses the power assignment problem in multicarrier code-division multiple-access (MC-CDMA) systems. The problem is formulated as finding the correct transmission power to achieve a desired quality of service (QoS), described by an objective signal-to-interference and noise ratio (SINR). First, the model of the MC-CDMA is described, and by considering a matched filter at the receiver, the SINR after data estimation is explicitly characterized. Due to the diversity in MC-CDMA systems, the power assignment problem is approached with a minimum norm perspective restricted to achieve a pre-defined objective SINR per user. Centralized and distributed solutions are presented in the paper. The distributed power allocation strategy is further extended to consider general controllers, and measurement and processing delays. Necessary conditions for closed-loop stability and convergence to the optimal minimum norm solution are derived by using the small-gain theorem. One advantage of the proposed methodology is that it can use power control strategies previously suggested for CDMA systems, as the Foschini-Miljanic scheme and LQ-control.

Multi-carrier code division multiple access (MC-CDMA) has been one of the candidates for the next generation wireless communication systems. In an uplink, the MC-CDMA system suffers from the different access timing, the different fading, and the different frequency offset of each active user. In this paper we analyze the effects of the frequency offset compensation with MMSE-MUD (minimum mean square error based multi-user detection) for MC-CDMA in a quasi-synchronous uplink. We consider the MC-CDMA system with two subcarrier mapping schemes, the continuous mapping scheme and the discrete mapping scheme. From our theoretical analysis and computer simulation, we show that the MMSE-MUD can compensate the different frequency offsets among users. We also show that the MMSE-MUD significantly improves the bit error rate (BER) for the MC-CDMA system with the continuous mapping scheme.

Multi-carrier code division multiple access (MC-CDMA)has been considered as a strong candidate for next generation wireless communication system due to its excellent performance in multi-path fading channel and simple receiver structure. However, like all the multi-carrier transmission technologies such as OFDM, the inter-carrier interference (ICI) produced by the frequency offset between the transmitter and receiver local oscillators or by Doppler shift due to high mobility causes significant BER (bit error rate) performance degradation in MC-CDMA system. Many ICI cancellation methods such as windowing and frequency domain coding have been proposed in the literature to cancel ICI and improve the BER performance for multi-carrier transmission technologies. However, existing ICI cancellation methods do not cancel ICI entirely and the BER performance after ICI cancellation is still much worse than the BER performance of original system without ICI. Moreover, popular ICI cancellation methods like ICI self-cancellation reduce ICI at the price of lowering the transmission rate and reducing the bandwidth efficiency. Other frequency-domain coding methods do not reduce the data rate, but produce less reduction in ICI as well. In this paper, we propose a novel ICI cancellation scheme that can eliminate the ICI entirely and offer a MC-CDMA mobile system with the same BER performance of a MC-CDMA system without ICI. More importantly, the proposed ICI cancellation scheme (namely Total ICI Cancellation) does not lower the transmission rate or reduce the bandwidth efficiency. Specifically, by exploiting frequency offset quantization, the proposed scheme takes advantage of the orthogonality of the ICI matrix and offers perfect ICI cancellation and significant BER improvement at linearly growing cost. Simulation results in AWGN channel and multi-path fading channel confirm the excellent performance of the proposed Total ICI Cancellation scheme in the presence of frequency offset or time variations in the channel, outperforming existing ICI cancellation methods.

This letter presents an analysis of asynchronous multicarrier code-division multiple-access (MC-CDMA) systems with a guard period (GP) in the form of a cyclic prefix over frequency-selective multipath fading channels, which results in closed-form bit-error rate performance. Furthermore, it confirms that the frequency diversity of MC-CDMA systems is identical to the path diversity. The analytical approach proposed here is extended to the case without a GP. The derived analytical results show that a GP is required for MC-CDMA systems in order to mitigate not only the effect of intersymbol interference and intercarrier interference, but also the desired signal power degradation.

Most of the techniques for multiple access interference (MAI) reduction in code-division multiple access (CDMA) systems are applicable to the uplink, where the base-station knows the signature of all users and can apply a multi-user detection (MUD) strategy. A technique is proposed here to reduce the influence of MAI on the downlink of a multi-carrier CDMA (MC-CDMA) system, without resorting to MUD. The technique is based on the use of a spreading sequences pair for each subscriber. Its limiting factor is that the system capacity, in terms of the active users' maximum number, is halved as compared to the case in which a single spreading code per user is adopted

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.

this paper reviews the state of the technique of field programmable gate array (FPGA) for partial Reconfiguration (PR), design methodologies of Wireless Communication System, such as Multi Carrier Code Division Multiple Access (MC-CDMA) technique has been to be suited for future wireless systems that are expected to provide higher data rates and greater flexibility for the services of voice, data, video and Internet to the users due to its property in using the bandwidth in efficient manner. The Software Defined Radio is considered as a wireless system applied by routines so as software. Consequently, the use of SDR allows vehicle manufacturers to familiarize communication applications sustained through cars to appropriate to the standards of the respected country presented in the object oriented programming. FPGAs are playing a very significant role in SDR. However, in modern wireless communication system programs, SDR and CR need to design a wide range of waveforms complex, which it is complicated in design and performance and implementation needs more time. The design of the modulation and demodulation and other signal processing application of PR technique that have the ability to modify blocks of logic dynamically by downloading partial bit files, while the remaining logic is still working without interruption; thus, power consumption and configuration time can be saved for a larger extent. The PR using was allowed to move for fewer or smaller devices as, decrease power and increase system upgradability.

The need for a communication system with a higher data rate and mobility grows along with information and communication technology development. Combining MC-CDMA with the MIMO system and supporting the system with a good transmit diversity technique is a promising idea to provide the needed communication system, especially in high mobility conditions. MC-CDMA can support ubiquitous communications without affecting the achievable BER and is more capable of high-speed mobility. It integrates the benefit of both OFDM and CDMA. On the other hand, QO-STBC increases the bit rate without using additional bandwidth to transmit diversity in the MIMO system. So, this study proposed a system combining the MIMO MC-CDMA system with QO-STBC. The proposed system is investigated under high mobility conditions to see the system's performance. The simulation results show that our system performs better than the MC-CDMA STBC system and the QOSTBC system but not better than the MC-CDMA multilevel coding scheme. To reach the value of BER 10−3, MC-CDMA multilevel Coding requires less power, around 5 dB, than the proposed system.