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For telemedicine purpose, simultaneous transmission of biomedical multichannel signals remains problematic. There is a need to transmit all the channels without creating distortions such as delay, inversion of the signal parts. Multiple access techniques are more indicated. In this paper, we proposed a multi-user direct sequence code division multiple access (DS-CDMA) based chaotic communication system to simulate the transmission of biomedical multichannel electrocardiogram (ECG) signals and electroencephalogram (EEG) signals in the same bandwidth. We used binary chaotic sequences to spread the ECG/EEG signals and the Walsh sequences as pilot signals. The performance of the proposed system is evaluated in the presence of Additive White Gaussian Noise (AWGN) channel and in the presence of the Rayleigh flat fading channel. We achieved the code acquisition that represents the first stage of the synchronization process in the presence of AWGN channel and in the presence of the Rayleigh flat fading channel. We evaluated the code acquisition stage in term of the probability of detection and probability of false alarm. We used the time delay estimated by the code acquisition to despread the received signal. The low bit error rate obtained confirms the effectiveness of the synchronization unit, the effectiveness and the robustness of the proposed system. [ABSTRACT FROM AUTHOR]

This paper presents a subspace blind method to estimate the direction of arrival of direct sequence code division multiple access signals in a multipath fading environment. The proposed method is based on signal/noise subspace approach. For enhancing the results, the problem is formulated based on both signal and noise subspaces to exploit structures of desired signal, self interference and multiple access interference simultaneously. The main idea in this paper is based on fitting the extended subspace spanned by the desired signature waveform in all different paths into the estimated extended signal subspace. The proposed method is blind in the sense that it utilizes only the desired user's code and its corresponding path delays. The performance of the proposed method is compared to the Cramer–Rao lower bound. We also propose a method for estimating relative power of different paths in multipath code division multiple access signals. [ABSTRACT FROM AUTHOR]

The inter-vehicle communication (IVC) systems are based on carrier sense multiple access/orthogonal frequency division multiplexing (CSMA/OFDM) scheme. However, it is concerned that the delay time increases significantly as the number of vehicles increases. In order to reduce the effects of this problem, research has been conducted on simultaneous communication using direct spread-code division multiple access). However, there is concern that the communication performance of applying this scheme is degraded by different and same intersymbol interference (ISI). This paper proposes schemes to reduce two types of ISIs and shows the performance is improved by the proposed method. [ABSTRACT FROM AUTHOR]

Systems based on spread spectrum technique are inherently interference resistant. However, asynchronous transmission and multipath propagation causes manifestation of multiuser interference. Multiuser interference in a multiple access system limits the capacity of the system. Hence, it becomes imperative to mitigate the interference. This work presents the design and mathematical analysis of Hybrid Interference Cancellation (HIC) detector for direct-sequence code division multiple access (DS-CDMA). The detector is analysed for single path as well as multipath propagation over a Rayleigh fading channel. Simulation results are compared with the results of Successive Interference Canceller (SIC). Furthermore, the SIC and HIC detectors are tested for convergence. An HIC detector is proposed for MC-CDMA system. The interference canceller discussed in this paper dispenses with the RAKE receiver for diversity combining and data estimation, which averts the likelihood of errors because of incorrect data estimates.

Nowadays, modern wireless mobile communication systems attempt to increase the number of subscribers simultaneously, starting from the third to fifth generations. The purpose of this research is to explain the correlation between the efficiency of the multi-user communication system and linear phase orthogonal binary codes (LPOBC) like Walsh and Gold codes. Query This work focuses on orthogonal binary sequences that are concurrent distributed over frequency and time domains according to the behavior of the correlation functions. Besides, the effect of using different code lengths with variable number of users will be examined and discussed. The communication system performance will be examined based on the cross-correlation and the autocorrelation behavior. This criterion is affected and influenced by the code length, bit error rate and signal to noise ratio. Furthermore, the impact of using the LPOBC on different modulation schemes is discussed. Finally, a case study utilizing code division multiple access is chosen as a practical case that has the potential of being further developed toward the fifth generation communication system. [ABSTRACT FROM AUTHOR]

An independent component analysis (ICA) based CDMA receiver is proposed, which in addition to the independence of users also exploits the independence of pseudo-codes in user signal separation. The proposed scheme is termed as independent code division multiple access in contrast to orthogonal code division multiple access being used in conventional CDMA receivers. Independence of pseudo-codes has been invoked by introducing the so-called independent Gram-Schmidt process in a deflation based ICA algorithm. The independence via Gram-Schmidt process is claimed by taking the inner product of successive vectors in a nonlinearly transformed Hilbert space, incorporating higher order statistics, instead of that in the original Euclidean space. The proposed receiver has been shown to outperform the existing CDMA receivers, in terms of bit error rate, through simulations. Moreover, the introduction of nonlinear transformation is shown to have no adverse effect on the convergence of the original deflation based ICA algorithm in terms of number of iterations apart from the computational cost of nonlinear transformation at each step. Gold codes are used for the demonstration of the proposed scheme although more work is needed to be done in order to identify the code family more amenable to the independence property. [ABSTRACT FROM AUTHOR]

Systems based on spread spectrum technique are inherently interference resistant. However, asynchronous transmission and multipath propagation causes manifestation of multiuser interference. Multiuser interference in a multiple access system limits the capacity of the system. Hence, it becomes imperative to mitigate the interference. This work presents the design and mathematical analysis of Hybrid Interference Cancellation (HIC) detector for direct-sequence code division multiple access (DS-CDMA). The detector is analysed for single path as well as multipath propagation over a Rayleigh fading channel. Simulation results are compared with the results of Successive Interference Canceller (SIC). Furthermore, the SIC and HIC detectors are tested for convergence. An HIC detector is proposed for MC-CDMA system. The interference canceller discussed in this paper dispenses with the RAKE receiver for diversity combining and data estimation, which averts the likelihood of errors because of incorrect data estimates. [ABSTRACT FROM AUTHOR]

Direct-Sequence Code Division Multiple Access (DS-CDMA) is a digital method to spread spectrum modulation for digital signal transmission. We propose to detect signal in DS-CDMA communication using the learning mechanism. Initially, the user signals are spread using the respective pseudo-noise (PN) code where the input signal is multiplied with the code which is then modulated using the quadrature phase shift keying (QPSK) modulator. The modulated signal is then transmitted in a 3G/4G channel considering all types of fading. The transmitted signal is received by the antenna array which is performed by demodulation. We propose to adaptively assign the weights by employing Improved Whale Optimized Multi-Layer Perceptron Neural Network (IWMLP-NN)-based learning mechanism. To design IWMLP-NN, Improved Whale Optimization Algorithm is combined with multilayer perceptron neural network. This is used instead of the normal Multiple Signal Classification (MUSIC) and least mean squares (LMS)/root-mean-square (RMS) algorithms used in beam-forming networks. After assigning weight through IWMLP-NN-based learning mechanism, we de-spread to get the original user data. We have compared our proposed technique with the normal techniques with the help of plots of Bit Error Rate (BER) versus Signal-to-Noise Ratio (SNR). We use both the AWGN channel and fading channel for analysis. Experimental results prove that our proposed method achieves better BER performance results even with deep fading. [ABSTRACT FROM AUTHOR]

The rapid development of medical sensors has increased the interest in Wireless Body Area Network (WBAN) applications where physiological data from the human body and its environment is gathered, monitored, and analyzed to take the proper measures. In WBANs, it is essential to design MAC protocols that ensure adequate performance and Quality of Service (QoS). This paper investigates Medium Access Control (MAC) protocols used in WBAN, and compares their performance in a high traffic environment with respect to different QoS and network performance metrics. Such scenario can be induced in case of emergency for example, where physiological data collected from all sensors on human body should be sent simultaneously to take appropriate action. This study can also be extended to cover collaborative WBAN systems where information from different bodies is sent simultaneously leading to high traffic. OPNET simulations are performed to compare the performance of the different MAC protocols under the same experimental conditions. A new MAC scheme aiming to enhance the delay, throughput, and energy performance of the system is then proposed and compared to existing protocols, to evaluate its performance in high traffic environment. [ABSTRACT FROM AUTHOR]

This work studies the spectral efficiency achievable when a very large number of terminals are connected simultaneously to a central node (uplink) through independent and identically-distributed flat-fading channels. Assuming that terminals only have statistical channel state information (CSI), the optimum random transmitted-energy allocation is formulated considering a non-orthogonal direct-sequence code-division multiple access (DS-CDMA) where all users transmit using the same modulation and error correcting code and the receiver implements successive interference cancellation (SIC). Focusing on low-power terminals, optimization is carried out by imposing constraints on both the average and peak per-user transmitted energy. Simulations have revealed that a limited number of random energy levels, whose number is determined by the channel power gain variance, is sufficient to achieve approximately the maximum spectral efficiency that would be obtained under direct optimization of the received energy profile. [ABSTRACT FROM AUTHOR]

• This paper analyses some important measures responsible for the performance of ZCZ in quasi synchronous direct sequence (QS-DS) CDMA. • The BER and the MUI interference of binary and ternary spreading codes were investigated as functions of the codes' even and odd periodic correlation functions. • Numerical results based on availability of ZCZ codes in the existing literature is provided. Zero correlation zone (ZCZ) codes have been recently adopted for many communication systems based on code division multiple access (CDMA). In this paper, we focus on the use of ZCZ codes in quasi-synchronous direct-sequence (QS-DS) CDMA. To ensure Interference-free communication, spreading ZCZ codes must be carefully designed. Indeed, numerous ZCZ code constructions with various correlation properties have been proposed and studied in literature. However, most of them are not adequately designed for communication systems. Here, we aim at determining specific criteria in order to choose the suitable ZCZ code family. A new bit error rate (BER) for QS-DS-CDMA as a function of the code's even and odd periodic correlation functions (PCFs) is derived. It is shown that the adequate spreading codes are those with zero even and odd PCFs. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the effect of inserting some randomly generated watermarking chips into known spreading sequences in terms of periodic correlations; moreover, we give two design criteria for good watermarked sequences in the sense of: 1) reducing the average correlation value and 2) minimizing the variance of correlations. For $n=2m$ with even $m$ , we propose a set of $2^{m-1}$ punctured bent function sequences of length $2^{n}-1$ punctured by the Singer difference set. The maximum non-trivial correlation magnitude of the proposed set turns out to be $2^{m}+1$ , which is asymptotically two times the Welch bound. [ABSTRACT FROM AUTHOR]

This paper analyzes the method of power allocation for wireless communication networks, limited by multiple access interference under fading Rayleigh channels. The method takes into account the statistical variation of the desired and interfering signals power and optimally and dynamically allocates the power resources in the system. This allocation is made being taken into account the restrictions imposed by the outage probability for each receiver/transmitter pair. Based on the Perron-Frobenius eigenvalue and geometric programming (GP) theories, some interesting results were found for the optimization problem analyzed. A GP is a special type of optimization problem that can be transformed in a non-linear convex optimization problem simply by the change of variables, and then to be globally solved. Also, an iterative method for fast convergence was shown to find the optimally power allocation seeking to minimize the outage probability in the communication.

In this paper, a blind adaptive detector is proposed for blind separation of user signals and blind estimation of spreading sequences in DS-CDMA systems. The blind separation scheme exploits a charrelation matrix for simple computation and effective extraction of information from observation signal samples. The system model of DS-CDMA signals is modeled as a blind separation framework. The unknown user information and spreading sequence of DS-CDMA systems can be estimated only from the sampled observation signals. Theoretical analysis and simulation results show that the improved performance of the proposed algorithm in comparison with the existing conventional algorithms used in DS-CDMA systems. Especially, the proposed scheme is suitable for when the number of observation samples is less and the signal to noise ratio (SNR) is low.

In this paper, we propose a new hyperchaos-based spreading codes generator (HSCG) for multi-users direct sequence spread spectrum (DSSS) communication systems. For experimental validation, we implement the proposed generator in Xilinx FPGA Virtex-5 technology. Contrary to the traditional spreading codes, the proposed HSCG offers interesting statistical properties such as good autocorrelation, very small cross-correlation, no repetition of the generated spreading codes and high degree of security. In addition, the developed hardware architecture used for implementing the HSCG permits to generate simultaneously an infinite number of multi-length spreading codes with high hardware performances in terms of logic area consumption, throughput and latency. Real-time results are given for 32-, 64- and 128-bit chaotic spreading codes. All of these properties are validated and compared with that of classical codes (Gold sequences, Walsh–Hadamard) through bit error rate (BER) performance evaluation in a DS-CDMA system in AWGN and time-invariant multipath channels. With its interesting performances, the proposed HSCG is very useful for the next generations of mobile communication systems. [ABSTRACT FROM AUTHOR]

Several signal processing problems can be written as the joint eigenvalue decomposition (JEVD) of a set of noisy matrices. JEVD notably occurs in source separation problems and for the canonical polyadic decomposition of tensors. Most of the existing JEVD algorithms are based on a block coordinate procedure and require significant modifications to deal with complex-valued matrices. These modifications decrease algorithms performances either in terms of estimation accuracy of the eigenvectors or in terms of computational cost. Therefore, we propose a class of algorithms working equally with real- or complex-valued matrices. These algorithms are still based on a block coordinate procedure and multiplicative updates. The originality of the proposed approach lies in the structure of the updating matrix and in the way the optimization problem is solved in C N × N . That structure is parametrized and allows to define up to five different JEVD algorithms. Thanks to numerical simulations, we show that, with respect to the more accurate algorithms of the literature, this approach improves the estimation of the eigenvectors and has a computational cost significantly lower. Finally, as an application example, one of the proposed algorithm is successfully applied to the blind source separation of Direct-Sequence Code Division Multiple Access signals. [ABSTRACT FROM AUTHOR]

Direction of Arrival (DOA) estimation using gold -MUSIC is achieved for Uniform Linear Array (ULA) antenna based Direct-Sequence Code Division Multiple Access (DS-CDMA) sources having different Propagation Delay. The DOA is estimated by different MUSIC (Multiple Signal Classification) algorithms for M signal sources with Phase Shift Keying (PSK) transmission in presence of Additive White Gaussian Noise (AWGN). Spatial spectrum, computational efficiency and Root Mean Square Error (RMSE) of DOA estimation using gold -MUSIC over MUSIC and Root-MUSIC algorithms are studied meticulously. The effects of number of ULA elements, Data length and arrival angle on RMSE of DOA are also conferred here. [ABSTRACT FROM AUTHOR]

Generalized RAKE (G-RAKE) reception reduces the total amount of interference and provides enhanced diversity by comprising extra fingers to collect information about interference and further using channel and impairment correlation estimates for fingers allocation. However, the hardware complexity and the excessive computational requirements of GRAKE receivers may restrict their application in real systems; thus, suboptimal solutions are commonly used. In this paper, we propose and evaluate three maximum likelihood G-RAKE structures for colored noise with suboptimal finger placement. In all implementations, the fingers are optimally distributed within a time window that spans from several chip periods before the first arriving multipath to several chip periods after the latest one. The first receiver has its fingers at integer multiples of the chip period while in the rest two structures the search window is segmented in halves and tenths of the chip duration. This work also extends earlier studies by thoroughly investigating the impact of fractionally spaced finger placement on system performance. Our analysis shows that a suboptimal finger allocation reduces hardware complexity with negligible performance loss. The impact of channel delay spread and processing gain on system performance is also investigated and gives interesting results.

In this paper, bit error probability (BEP), outage probability (OP) and channel capacity (CC) of direct-sequence code-division multiple access systems with amplify-and-forward relaying are presented for different fading scenarios. In the first scenario, the source-destination link is assumed to experience Rayleigh fading while it is subject to Nakagami- m fading in the second scenario. The source-relay and relay-destination channels are considered to have Nakagami- m fading conditions in two scenarios. First, analytical expressions for the end-to-end probability density function (PDF) are derived by using the convolution integral. Then, BEP, OP and CC are obtained based on these PDFs in terms of infinite series. Truncation error analyses are presented for different parameter values in order to show that truncation error arising from the infinite series is negligible. Simple and easy-to-compute asymptotic expressions are also introduced for BEP and OP in order to simplify the performance analysis in high signal-to-noise ratio region. Simulation results are provided to show the accuracy of the proposed approximate and asymptotic expressions. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem of time delay estimation (TDE) from single-carrier (SC) or multi-carrier (MC) direct-sequence spread spectrum (DSSS) multipath transmissions in the presence of multiple transmit and/or receive antennas that will characterize future 5G radio interface technologies (RITs), such as coded-domain nonorthogonal multiple access. We derive for the first time a closed-form expression for the Cramer-Rao lower bound (CRLB) and develop two maximum likelihood (ML) multipath TDEs for SC DSSS single-input multiple-output (SIMO) in the non-data-aided (NDA) case. The first TDE, based on iterative expectation maximization (EM), provides accurate estimates whenever a good initial guess of the parameters is available at the receiver. The second TDE implements the ML criterion in a non-iterative way and finds the global maximum of the compressed likelihood function using the importance sampling (IS) technique without requiring any initialization. We also extend both the SC DSSS SIMO CRLB and the two new SC DSSS SIMO ML NDA TDEs to MC DSSS RITs and to multiple-input multiple-output structures with any diversity versus multiplexing pre-coding type before generalizing them all to the data-aided (DA) case. Simulations suggest that the EM TDE is suitable for large observation in space, time, and/or frequency, whereas the IS TDE is preferred in the opposite case of very short data records. Moreover, we show in the NDA case, both analytically and by simulations, that spatial (transmit and receive), temporal, and frequency samples interchangeably have the same impact on estimation accuracy and performance bound regardless of the channel correlation type and amount present in each dimension. Furthermore, we are able to properly cope with such channel correlations that do indeed arise in practice and, hence, become very challenging both in estimation and CRLB derivation in the DA case, but that have been so far overlooked in previous works. [ABSTRACT FROM PUBLISHER]

Bandlimited direct-sequence code division multiple access (DS-CDMA) attracts much attention for its compact spectrum and the ability to suppress inter-symbol interference. Among the various bandlimited DS-CDMA systems available, minimum-bandwidth DS-CDMA (MB-DS-CDMA) is the only realizable Nyquist rate transmission system. But, MB-DS-CDMA only applies to certain kinds of spreading codes. Accordingly, this study proposes a modified DS-CDMA structure which extends the application of MB-DS-CDMA to all common spreading codes at the expense of a negligible reduction in the transmission rate. Additionally, the bit error rate of the proposed schemes adopting either single-user or multi-user detection receiver is analyzed and compared with that of the commonly-used raised-cosine-pulsed DS-CDMA over multipath fading channels. The numerical results show that given a sufficiently large number of users, the bit error rate performance of modified MB-DS-CDMA is comparable to that of the raised-cosine-pulsed DS-CDMA scheme; meanwhile, the realizable modified MB-DS-CDMA approaches the ultimate transmission rate. [ABSTRACT FROM AUTHOR]

Both m -sequences and Gold sequences have been applied as the pseudonoise (PN) code in the code division multiple access (CDMA) scheme to enable distinct users to simultaneously share the available capacity of a common channel, which is called direct sequence CDMA (DS-CDMA). However, this scheme does not provide the required ideal periodic cross-correlation function property among various members of sequences within the same set. This paper proposes a new perfect Gaussian integer sequence (PGIS)-based CDMA scheme called PGIS-CDMA; in this scheme, the PN code of DS-CDMA is replaced by a set of PGISs. The intrinsic orthogonal property of PGIS can be applied to a CDMA system to achieve perfect cochannel interference separability under the ideal synchronism; it can also be adapted at the receiver to obtain diversity gain and improve the carry-to-interference ratio. These two concepts are further developed to implement two PGIS-CDMA configurations, and they can outperform DS-CDMA on the basis of Gold sequences that possess a favorable cross-correlation property for the CDMA scheme. [ABSTRACT FROM AUTHOR]

Recently, Gaussian process has been excellent for proving the effectiveness in solving the multiuser detection issue in code division multiple access system. Even with limited training sequences, Gaussian process-based solutions still surpass other approaches. However, due to the high complexity in terms of computation, the performance of this approach might be degraded. In this letter, we would like to propose an efficient method to reduce the complexity while still maintaining the desired accuracy. Finally, the proposed method is validated via the experiment. [ABSTRACT FROM PUBLISHER]

Over the past decade, wireless sensor network research primarily relied on highly-integrated commercial off-the-shelf radio chips. The rigid silicon implementation of the radio stack restricted access to the lower layers; thus, research focused mainly on the medium access control (MAC) layer and above. SRAM field-programmable gate array (FPGA)-based software-defined radios (SDR), on the other hand, provide a flexible architecture to experiment with any and all layers of the radio stack, but usually require desktop computers and draw high currents that prohibit mobile or longer-term outdoor deployments. To address these issues, we have developed a modular flash FPGA-based wireless research platform, called Marmote SDR, that has computational resources comparable to those of SRAM FPGA-based radio platforms, but at a reduced power consumption, with duty cycling support. We discuss the design decisions underlying Marmote SDR and evaluate its power consumption. Furthermore, we present and evaluate an asynchronous and multiple access communication protocol specifically designed for data-gathering wireless sensor networks.

Chaos based communications have drawn increasing attention over the past years. Chaotic signals are derived from non-linear dynamic systems. They are aperiodic, broadband and deterministic signals that appear random in the time domain. Because of these properties, chaotic signals have been proposed to generate spreading sequences for wide-band secure communication recently. Like conventional DS-CDMA systems, chaos-based CDMA systems suffer from multi-user interference (MUI) due to other users transmitting in the cell. In this paper, we propose a novel method based on radial basis function (RBF) for both blind and non-blind multiuser detection in chaos-based DS-CDMA systems. We also propose a new method for optimizing generation of binary chaotic sequences using Genetic Algorithm. Simulation results show that our proposed nonlinear receiver with optimized chaotic sequences outperforms in comparison to other conventional detectors such as a single-user detector, decorrelating detector and minimum mean square error detector, particularly for under-loaded CDMA condition, which the number of active users is less than processing gain.

In Body Sensor Networks (BSNs), two types of events should be addressed: periodic and emergency events. Traffic rate is usually low during periodic observation, and becomes very high upon emergency. One of the main and challenging requirements of BSNs is to design Medium Access Control (MAC) protocols that guarantee immediate and reliable transmission of data in emergency situations, while maintaining high energy efficiency in non-emergency conditions. In this paper, we propose a new emergency aware hybrid DTDMA/DS-CDMA protocol that can accommodate BSN traffic variations by addressing emergency and periodic traffic requirements. It takes advantage of the high delay efficiency of DS-CDMA in traffic burst, and the high energy efficiency of DTDMA in periodic traffic. The proposed scheme is evaluated in terms of delay, packet drop percentage, and energy consumption. Different OPNET simulations are performed for various number of nodes carrying emergency data, and for various payload sizes. The protocol performance is compared to other existing hybrid protocols. Results show that the proposed scheme outperforms the others in terms of delay and packet drop percentage for different number of nodes carrying emergency data, as well as for different payload sizes. It also offers the highest energy efficiency during periodic observation, while adjusting the energy consumption during emergency by assigning spreading codes only to nodes holding emergency data.

In this work, we try to design a DS-CDMA communication system model for the transmission of different types of images: binary, gray level and color. We adopted a transmission system of multiple users. During transmission of each image, we evaluated the noise and multiple access interference effects on the quality of DS-CDMA transmitted images which are inversely proportional to the length of the spreading sequence. Quality is assessed each time by the bit error rate (BER) estimation between received and original images. By increasing the signal to noise ratio to positive values, the BER tends to decrease, this results in a received image with fewer errors, thus without alteration which confirms Shannon equation. By using one user alone, the inter-user interference is canceled and the BER obtained is far lower than the BER obtained in presence of inter-user interferences. This can be resolved in hardware implementation using adequate filters. [ABSTRACT FROM AUTHOR]

In statistical wireless signal processing, extraction of unobserved signals from observed mixtures can be achieved using Blind Source Separation (BSS) algorithms. Orthogonal Frequency Division Multiplexing (OFDM) and Direct Sequence-Code Division Multiple Access (DS-CDMA) can be pronounced as the well established predominant air interface communication techniques. Consequences of an effort taken and counteractive solutions to diminish the undesirable influences encountered within the wireless air interface of those techniques with aid of BSS schemes are disclosed. Filter coefficients for the receiver are ascertained with the support of a set of energy functions and the iterative fixed point rule. Time correlation properties of the channel are taken advantage for BSS. Performance of the algorithm are evaluated using OFDM and DS-CDMA models under slow fading channel conditions with a receiver containing Equal Gain Combining. The importance is that, this scheme can be promoted as a low computationally complex mechanism. [ABSTRACT FROM AUTHOR]

This work makes a review of the main Adaptives Multi-user Detectors (MuD-Adpt) for Direct Sequence - Code Division Multiple Access (DS-CDMA) systems. The MuD-Adpt based on Minimum Mean Square Error (MMSE) and Decorrelator (MuD-Dec) are focused. Multi-user detectors show great resistance to the near-far effect and combat effectively the Multiple Access Interference (MAI). Comparative numeric results characterize the substantial performance improvement of those detectors in relation to the matched filter conventional receiver (Conv).

Spatial transmit diversity schemes are now well integrated into third-generation cellular mobile communication system specifications. When DS-CDMA-based technology is deployed in typical macro- and microcell environments, multipath diversity and spatial diversity may be exploited simultaneously by a 2D RAKE receiver. The work presented in this paper focuses on taking advantage of spatial transmit diversity in synchronising the 2D RAKE structure. We investigate the use of coherent and noncoherent techniques for tracking the timing parameters of each multipath component. It is shown that both noncoherent and coherent techniques benefit from transmit diversity. Additionally the performance gap between these two techniques increases with the number of antennas.

In this paper, a generalized spectral subtraction approach for reducing additive impulsive noise, narrowband signals, white Gaussian noise and DS-CDMA interferences in MIMO channel DS-CDMA wireless communication systems is investigated. The interference noise reduction or suppression is essential problem in wireless mobile communication systems to improve the quality of communication. The spectrum subtraction scheme is applied to the interference noise reduction problems for noisy MIMO channel systems. The interferences in space and time domain signals can effectively be suppressed by selecting threshold values, and the computational load with the FFT is not large. Further, the fading effects of channel are compensated by spectral modification with the spectral subtraction process. In the simulations, the effectiveness of the proposed methods for the MIMO channel DS-CDMA is shown to compare with the conventional MIMO channel DS-CDMA.

In this paper the continuous dynamic model of Verhulst is used. It had been initially elaborated to describe the population growth of biological species with food restriction and physical space, in order to synthesize a new distributed power control algorithm (DPCA), applicable in direct sequence code division multiple access (DS-CDMA) systems. The discretization of the corresponding differential equation is accomplished via numeric integration Euler method (NIE). The properties of the proposed recursive algorithm, as Euclidian distance from optimum vector after convergence, convergence speed, normalized mean squared error (NSE), average power consumption per user and implementation complexity, are investigated through simulations. The simulation results are confronted with the other DPCAs: the classic algorithm derived by Foschini and Miljanic and the sigmoidal by Uykan and Koivo. With estimate errors, the proposed DPCA showed smaller discrepancy from the optimum power vector allocation after convergence and better convergence. Additionally, the Gerchgorin Circles theory (GC) is applied for the feasibility of the power allocation problem.

Çoklu erişim girişimi, bir doğrudan dizili/kod bölmeli çoklu erişim (DD/KBÇE) sisteminin başarımını sınırlayan temel etkidir ve yayma dizilerinin (kodlarının) bu etki üzerindeki rolü oldukça önemlidir. Bu çalışmada, adım kırmık ağırlıklandırma dalgaformlarıyla ağırlıklandırılmış toparlama dizileri kullanan bir DD/KBÇE sistemi için verilen bir kod seti içerisinde daha düşük bit hata oranları oluşturan dayanak yayma kodlarının belirlenmesine hizmet eden bir kriter önerilmektedir. Nümerik sonuçlar, önerilen kritere göre belirlenen yayma kodlarının, dayanak olarak kullanılmaya en uygun kodlar olduğunu göstermektedir.

This study analyses the performance of directsequence code division multiple access (DS-CDMA) based on two-hop amplify-and-forward protocol over Weibull symmetric fading channels as well as Rayleigh/Rician, Rician/Rayleigh asymmetric fading phenomenas. We investigate the bit-error rate (BER) of the considered system using multiple relays by considering the effect of Weibull fading parameter and Rician K factor on the system performance. Our simulation results demonstrate the positive impacts of the value of fading parameter, Rician K factor and increasing number of relay nodes on BER performance. It is also confirmed that the Rician K factor is more effective on the system performance over Rician/Rayleigh fading channels in comparison with Rayleigh/Rician fading environment. [ABSTRACT FROM AUTHOR]

We propose ANC-CDMA, a CDMA-based analog network coding scheme for underwater acoustic sensor networks (UW-ASNs) that can significantly improve the underwater acoustic channel utilization. First, we analyze a unidirectional multihop network, in which two acoustic nodes separated by two hops are assigned the same code-division channel (i.e., spreading code) to transmit concurrently. The packets transmitted by the two nodes will collide at the intermediate (relay) node. However, we show that, by exploiting a priori information, i.e., the interfered packet previously received from one of the nodes, and applying joint channel estimation through pilot supervision along with a newly designed adaptive RAKE receiver, the relay node can cancel the interference before decoding the packet of interest. We then extend our analysis to a bidirectional network, in which two nodes first concurrently transmit their packets to the relay using the same spreading code. The relay amplifies and forwards the received interfered packet to the two nodes. We show that either node can still decode the packet of interest after equalizing the channel effects introduced during the propagation from the relay to itself and jointly estimating multipath affected channels and suppressing the self-interference signal before applying the adaptive RAKE receiver. The proposed ANC-CDMA scheme is implemented in a testbed based on Teledyne Benthos Telesonar SM-975 underwater modems and tested extensively in Lake LaSalle. Experiments and simulations demonstrate that for a 1–2 dB tradeoff in signal-to-noise ratio (SNR), the proposed scheme can significantly improve the channel utilization of a unidirectional and bidirectional networks by up to 50% and 100%, respectively, compared with conventional multiuser DS-CDMA scheme. [ABSTRACT FROM PUBLISHER]

A compact (20 x 20 mm² size), coplanar waveguide (CPW) fed, octagonal slotted, dual-band antenna is presented in this paper. The proposed antenna has a simple structure consisting of an octagonal slot, L-shape stub, and a two stepped rectangular patch. The introduction of the L-shaped metallic stubs in the ground plane generates a lower resonance frequency at 2.42 GHz. The proposed antenna is fabricated on a low cost FR4 substrate having thickness of 1.6 mm. The measured impedance bandwidth of the proposed antenna is from 2.40 to 2.46 GHz and 3.2 to 6.2 GHz. It is also shown that the proposed antenna has stable radiation patterns of almost dumb-bell shape in the E-plane and omni-directional shape in the H-plane. The effects of various design parameters on the impedance bandwidth are also studied and presented in detail. The proposed antenna can be used for 3.5/5.5 GHz worldwide interoperability for microwave access (WiMAX), 2.4/5.2/5.8 GHz wireless local area network (WLAN) and 3.1-6.0 GHz Direct-Sequence Code Division Multiple Access (DS-CDMA) / Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) ultra wideband (UWB) applications. [ABSTRACT FROM AUTHOR]