Direct Sequence Code Division Multiple Access Research Articles

DSSS-based Channel Access Technique DS-CDMA for Underwater Acoustic Transmission

This paper proposes a novel method for acoustically and wirelessly transmitting data underwater with a high transmission rate. The method uses the most promising physical layer and multiple access technique (i.e., the code division multiple channel access technique) to divide the channel into subchannels. Data is transmitted through these subchannels. The codes are PN (pseudo random) sequences. In the spread-spectrum technique, a signal such as electrical, electromagnetic, acoustic signal generated in a particular bandwidth is deliberately spread in the frequency domain, which results in a signal with a wider bandwidth. This paper reviews the possibility of application of the DS-CDMA (direct sequence-code division multiple access) technique in an underwater system using MATLAB. As the result of our review, we recognize that the DS-CDMA technique can be applied to underwater environments.

A Novel Multiuser Detector Based on Restricted Search Space and Depth-First Tree Search Method in DS/CDMA Communication Systems

In this paper, we consider an improved and efficient algorithm for the multiuser detection (MUD) in direct sequence/code division multiple access (DS/CDMA) communication systems. The optimum detector for MUD is the maximum likelihood (ML) detector, but its complexity is very high and it calls for an optimization problem that involves an exhaustive search. Consequently, there has been considerable interest in suboptimal multiuser detectors with less complexity and reasonable performance. The idea of reducing the complexity by sub-optimum detectors was efficient and applicable but had some defects. The idea proposed in this paper is the restriction of the search space. This idea comprises using a sub-optimum detector such as ordinary genetic algorithm for which the size of the search space is confined to a predetermined region that is smaller than the whole search space. This limited region includes the objective bit sequence. Then by using depth-first tree search algorithm, we could find the optimum bit stream. We compare our algorithm to the ML detector, the genetic algorithm with conventional detector, and the ant colony optimization (ACO) detector which have been used for MUD in DS/CDMA. Simulation results show that the performance of this algorithm is near the optimal detector with very low complexity, and works better in comparison to other algorithms.

SIMULATION OF DS-CDMA PERFORMANCE ESTIMATION USING VISSIM/COMM SOFTWARE

The focus of this paper is to implement a simulator for the Direct Sequence - Code Division Multiple Access (DS-CDMA) communication system and test its performance against certain parameters using the VisSim/Comm Version 6.0.03 software. In this paper, the communication system is considered to consist of a number of users each of which generating binary data of specified rate and is assigned a unique code. There are many major system aspects that associated with the design of a spread spectrum system need to be considered. One of these very important concepts is how to evaluate the performance of the system. The main evaluation method in the simulator for system evaluation is the measurement of the Bit-Error-Rate (BER) for various conditions that are essential in the DS-CDMA design and implementation.

Robust Blind Multiuser Detection Algorithm Using Fourth-Order Cumulant Matrices

A new blind detection algorithm, based on fourth-order cumulant matrices, is presented and applied to the multiuser symbol estimation problem in direct sequence code division multiple access (DS-CDMA) systems. The blind detection is to estimate multiple symbol sequences in the downlink of a DS-CDMA communication system using only the received wireless data and without any knowledge of the user spreading codes. The proposed algorithm takes advantage of higher cumulant matrix properties to reduce the computational load and enhance the performance. Bit error rate simulations of this algorithm are performed for different numbers of users, signal-to-noise ratios, and numbers of symbols per user in comparison with the FastICA and RobustICA algorithms. The results show that the proposed algorithm outperforms both ICA-based detectors in estimating the symbol signals from the received mixed signals. Moreover, the proposed blind detector is computationally fast and exhibits high convergence speed in extracting user symbols.

Modeling and Simulation of CDMA Codes in Scilab

Prior to hardware implementation, simulation is an important step in the study of systems such as Direct Sequence Code Division Multiple Access (DS-CDMA). A useful technique is presented, allowing to model and simulate Linear Feedback Shift Register (LFSR) for CDMA. It uses the Scilab package and its modeling tool for dynamical systems Xcos. PN-Generators are designed for the quadrature-phase modulation and the Gold Code Generator for Global Positioning System (GPS). This study gives a great flexibility in the conception of LFSR and the analysis of Maximum Length Sequences (MLS) used by spread spectrum systems. Interesting results have been obtained, which allow the verification of generated sequences and their exploitation by signal processing tools.

Literature Review of Spread Spectrum Signaling: Performance, Applications and Implementation

In this paper, we will review spread spectrum signaling techniques in terms of performance, applications and implementation. Specifically, we focus on direct sequence spread spectrum signaling and CDMA, as the most important applications of spread spectrum signaling techniques, analyzing them in details. With a number of theoretical derivations and simulations, their mathematical characteristics, merits and drawbacks can be revealed. By reading this paper, the readers are expected to have a broad understanding of spread spectrum signaling as well as of direct sequence spread spectrum signaling and CDMA. Index Terms—Spread spectrum signaling, direct sequence spread spectrum signaling, CDMA, performance analysis

Ant Colony Input Parameters Optimization for Multiuser Detection in DS/CDMA Systems

In this work a simple and efficient methodology for tuning the input parameters applied to the ant colony optimi- zation multiuser detection (ACO-MUD) in direct sequence code division multiple access (DS-CDMA) is proposed. The motivation in using a heuristic approach is due to the nature of the NP complexity posed by the wireless multiuser detection optimization problem. The challenge is to obtain suitable data detection performance in solving the associated hard complexity problem in a polynomial time. Previous results indicated that the application of heuristic search algorithm in several wireless optimization problems have been achieved excellent performance-complexity tradeoffs. Regarding different system operation and channels scenarios, a complete input parameters optimization procedure for the ACO-MUD is provided herein, which represents the major contribution of this work. Furthermore, the performance of the PSO-MUD is analyzed via Monte-Carlo simulations. Simulation results show that, after convergence, the performance reached by the ACO-MUD is much better than the conventional detector, and somewhat close to the single user bound (SuB). Rayleigh flat channel is initially considered, but the results is straightforward extended to selective fading channels, as well as diversity (time and spatial) wireless channels.

System study on direct sequence spectrum of radio-frequency identification

This paper considers points of secure and anti-collision of the Radio-frequency identification (RFID) technology. Source symbols are represented by a special coding, termed Minimum Energy (ME) coding, which exploits redundant bits for saving power when transmitted via RF links with On-Off Keying (OOK). This ME coding is applied to Direct Sequence Spread Spectrum (DSSS) RFID tag in order to enhance security as well as to reduce collision. This synchronized DSSS RFID system is designed and simulation is conducted to verify the advantage of DSSS RFID and present the power efficiency enhance 4 dB, quantities are taken at Bit Error Rate (BER) of 10e-4. When the channel uses the ME coding combined with a DSSS code and OOK without FM0 encoding as is disclosed in the EPC-C1G2/ISO 18000-6 Type C standard. Finally, the maximum number of users in this Direct-Sequence Code Division Multiple Access (DS-CDMA) RFID system is calculated under the condition of successfully acquired.

A study on visual sensor network cross-layer resource allocation using quality-based criteria and metaheuristic optimization algorithms

Visual sensor networks (VSNs) consist of spatially distributed video cameras that are capable of compressing and transmitting the video sequences they acquire. We consider a direct-sequence code division multiple access (DS-CDMA) VSN, where each node has its individual requirements in compression bit rate and energy consumption, depending on the corresponding application and the characteristics of the monitored scene. We study two optimization criteria for the optimal allocation of the source and channel coding rates, which assume discrete values, as well as for the power levels of all nodes, which are continuous, under transmission bit rate constraints. The first criterion minimizes the average distortion of the video received by all nodes, while the second one minimizes the maximum video distortion among all nodes. The resulting mixed integer optimization problems are tackled with a modern optimization algorithm, namely particle swarm optimization (PSO), as well as a hybrid scheme that combines PSO with the deterministic Active-Set optimization method. Extensive experimentation on interference-limited as well as noisy environments offers significant intuition regarding the effectiveness of the considered optimization schemes, indicating the impact of the video sequence characteristics on the joint determination of the transmission parameters of the VSN.

Novel Subcarrier-Allocation Schemes for Downlink MC DS-CDMA Systems

This paper addresses the subcarrier allocation in downlink multicarrier direct-sequence code-division multiple access (MC DS-CDMA) systems, where one subcarrier may be assigned to several users who are then distinguished from each other by their unique direct-sequence spreading codes. We first analyze the advantages and shortcomings of some existing subcarrier-allocation algorithms in the context of the MC DS-CDMA. Then, we generalize the worst subcarrier avoiding (WSA) algorithm to a so-called worst case avoiding (WCA) algorithm, which achieves better performance than the WSA algorithm. Then, the WCA algorithm is further improved to a proposed worst case first (WCF) algorithm. Furthermore, we propose an iterative worst excluding (IWE) algorithm, which can be employed in conjunction with the WSA, WCA, and the WCF algorithms, forming the IWE-WSA, IWE-WCA, and the IWE-WCF subcarrier-allocation algorithms. The complexities of these algorithms are analyzed, showing that they are all low-complexity subcarrier-allocation algorithms. The error performance is investigated and compared, demonstrating that we can now be very close to the optimum performance attained by the high-complexity Hungarian algorithm.

Improved Natural Gradient Algorithms for Multi-Channel Signal Separation

In this paper, an Multi-channel blind separation of Direct Sequence Code Division Multiple Access (DS-CDMA) has been introduced. Most of which we assume statistically stationary sources as well as instantaneous mixtures of signals using blind source separation (BSS) algorithms. In practicality, the CDMA sources received are convolute mixing. A more complex blind separation algorithm is required to achieve better source separation. Based on the minimizing the average squared cross-output-channel-correlation, the proposed scheme obtains the better source separation. Simulation results show that the proposed optimal scheme not only achieves superior bit error rate (BER) performance to those of the existing ones, but also provides a guaranteed-convergent solution under different channel conditions.

Audio watermarking with high embedding capacity based on multiple access techniques

This paper deals with a new digital audio watermarking scheme based on multiple access techniques. In digital communication, multiple access techniques allow several users transmissions by taking the same communication channel. The present work proposes to embed multiple sub-watermarks in the same channel that is the audio signal. Our main objective is to investigate embedding capacity (the amount of information that can be hidden) limitations of our proposed audio watermarking system. Three multiple access techniques have been employed in the new multi-watermarking system: DS-CDMA (Direct-Sequence Code Division Multiple Access), FHMA (Frequency Hopped Multiple Access) and FDMA (Frequency Division Multiple Access). Experimental results allow us to make the choice on the best multiple access technique, in the multi-watermarking system, which significantly permits the highest embedding capacity (a data embedding rate up to 6 kb/s) with almost no loss of data imperceptibility and with acceptable extraction fidelity (BER≃10−2) even in presence of disturbances.

Multicarrier Spread Spectrum Modulation Schemes and Efficient FFT Algorithms for Cognitive Radio Systems

Spread spectrum (SS) and multicarrier modulation (MCM) techniques are recognized as potential candidates for the design of underlay and interweave cognitive radio (CR) systems, respectively. Direct Sequence Code Division Multiple Access (DS-CDMA) is a spread spectrum technique generally used in underlay CR systems. Orthogonal Frequency Division Multiplexing (OFDM) is the basic MCM technique, primarily used in interweave CR systems. There are other MCM schemes derived from OFDM technique, like Non-Contiguous OFDM, Spread OFDM, and OFDM-OQAM, which are more suitable for CR systems. Multicarrier Spread Spectrum Modulation (MCSSM) schemes like MC-CDMA, MC-DS-CDMA and SS-MC-CDMA, combine DS-CDMA and OFDM techniques in order to improve the CR system performance and adaptability. This article gives a detailed survey of the various spread spectrum and multicarrier modulation schemes proposed in the literature. Fast Fourier Transform (FFT) plays a vital role in all the multicarrier modulation techniques. The FFT part of the modem can be used for spectrum sensing. The performance of the FFT operator plays a crucial role in the overall performance of the system. Since the cognitive radio is an adaptive system, the FFT operator must also be adaptive for various input/output values, in order to save energy and time taken for execution. This article also includes the various efficient FFT algorithms proposed in the literature, which are suitable for CR systems.

BER performance analysis of Subtractive interference cancellation (SIC) Using Rayleigh channel in DS-CDMA Receiver system

In this paper, we present and analyze the performance of a parallel interference cancellation (PIC) scheme for multicarrier (MC) direct-sequence code-division multiple-access (DS-CDMA) systems. In order to mitigate the multi-path interference (MPI) in the DS CDMA system. At each cancellation stage in the proposed PIC scheme, on each subcarrier, a weighted sum of the soft outputs of the other users in the current stage is cancelled from the soft output of the desired user to form the input to the next stage. At the last stage, the interference cancelled outputs from all the subcarriers are maximal ratio combined (MRC) to form the decision statistic. Parallel interference elimination is first proposed in this paper the multi-path interference are evaluated by tentative decision and known user information. Then the performance over Rayleigh fading channel are analyzed and compared to Matched filter, Decorelator, successive interference cancellation (SIC) and conventional parallel interference cancellation (PIC). It is shown that PIC performance can be improved greatly by using this method with simple structure and easy implementation.

Multiuser Detection For DS-CDMA Systems Using Honeybees Mating Optimization Algorithm

The future wireless mobile communication systems will be required to support high-speed transmission rate and high quality of service. Direct sequence code division multiple access (DS-CDMA) is an important scheme for high-rate wireless communication. The capacity of DS-CDMA can be impaired by two problems; near-far effect and multiple-access interference (MAI). The use of conventional-matched filter detector for multiple users in DS-CDMA fails to combat any of these problems. The performance degradation caused by MAI can be overcome using multiuser detection (MUD). The use of maximum likelihood (ML) sequence estimation detector provides excellent results, but involves high computational complexity. In this paper, we propose a new meta-heuristic approach for MUD using honeybees mating optimization (HBMO) algorithm to detect the user bits based on the ML decision rule for DS-CDMA systems in additive white-Gaussian noise and flat Rayleigh fading channels. In order to improve the solutions generated by the HBMO, a second meta-heuristic method simulated annealing is used. By computer simulations, the bit error rate performance and the complexity curves show that the proposed HBMO-SA MUD is capable of outperforming the other conventional detectors and genetic algorithm detector.

A High-Security Image Watermarking Scheme Against WOA Attacks Using DS-CDMA and Entropy Criterion

In this paper, we present a digital watermarking scheme in the discrete wavelet transform (DWT) domain that is highly secure to watermark only attacks (WOA). The main idea is that a proper combination of entropy criterion and DS-CDMA is applied to achieve a superior performance in terms of security. In this scheme, the entropy of a random variable is used to opt suitable wavelet blocks where the watermark is to embed. Afterwards, we employ a direct-sequence code division multiple access approach to encode the watermark image. The DS-CDMA encoded watermark is embedded into wavelet blocks, which are determined by entropy criterion. In this context, we quantify the security using an information-theoretic point of view via the equivocation of secret parameters. The resulting watermarking scheme is adequate for private watermarking applications, where the host image is available for watermark detection. To assess the performance of the presented algorithm, we draw an analogy between the security of the proposed watermarking scheme and several important DWT-based watermarking algorithms. Numerical experiments demonstrate that the proposed image watermarking scheme is more secure in comparison with other image watermarking algorithms.

Adaptive Equalizer for DS-CDMA Multi-User Communication System Using Sign-Algorithm Based on Laguerre Filter Structure

This paper proposes a sign-algorithm based on adaptive Laguerre filter structure for improving the performance of the direct sequence-code division multiple access (DS-CDMA) communication system. The proposed adaptive equalizer employs a combination of sign and least mean square (LMS) algorithms to minimizing the effect of inter-symbol interference (ISI) that arises due to multipath propagation, and the computational complexity of equalizer. The performance of proposed equalizer was compared with traditional equalizers such as LMS and RLS algorithms in terms of varying path. The function detail and performance results of the proposed equalizer are described by computer simulations in terms of the bit error rate (BER).

Performance of RAKE-LMMSE Receivers in Wideband Communication Systems

High speed multimedia services with flexible data rate are main cause of popularity of 3 G WCDMA. WCDMA air interface of UMTS has the bandwidth of 5 MHz and chip rate of 3.84 Mcps. The flexibility in data rate is achieved by varying the length of its spreading code. WCDMA supports seamless connections of dynamic data rate ranging from 15 Kbps to 1 Mbps and respective spreading factors are 256 and 4 respectively for indoor and outdoor applications. The conventional RAKE receiver is near far and interference limited. Its performance at high data is limited due to short spreading factor of a code. A simple MIMO receiver structure of LMMSE in downlink asynchronous direct-sequence code division multiple access is proposed in this paper. This paper investigates RAKE receiver characteristics and does the analysis of zero forcing and LMMSE equalizer for MIMO channels.

Affine Projection‐Type Blind Multiuser Detection with Block Length Control under the Multipath Environment

SUMMARYThis paper proposes affine‐projection blind multiuser detection with block length control for improvement of convergence speed in DS‐CDMA (direct sequence code division multiple access) systems in a multipath environment. The traditional method of controlling the block length is discussed for the situation in which the desired signal of the system is given. But due to the difficulty of the application of the above method to blind multiuser detection, some suitable improvements are performed in the proposed method. These give the proposed method advantages over the traditional detectors.

Finite Field Spreading for Multiple-Access Channel

As a generalization of the binary spreading scheme in conventional direct-sequence code-division multiple-access (DS-CDMA) and interleave-division multiple-access (IDMA), a finite field spreading scheme is proposed for a synchronous multiple-access channel (MAC) with Gaussian noise and equal-power users. For each user, each information symbol over a finite field is spread into a length-L field vector by L-field multiplications. At the receiver, an iterative multi-user decoding algorithm on a factor graph is developed to recover each user's information symbol. To estimate the bit error rate performance of an uncoded finite field spreading system, an extrinsic information transfer analysis of the finite field despreading is given. This analysis shows that in addition to overcoming multi-user interference, the finite field spreading scheme can also provide an additional coding gain to overcome Gaussian noise compared with the conventional spreading scheme. This coding gain increases with the field order. The finite field spreading serially concatenated with a nonbinary low-density parity-check (LDPC) code, with field order 64, approaches the MAC capacity within 0.26 dB at a sum rate of 0.25.