Direct Sequence Spread Spectrum CDMA Research Articles

Drivers’ Warning Application Through Personalized DSSS-CDMA Data Transmission by Using the FM Radio Broadcasting Infrastructure

In this paper, a new drivers’ warning application through personalized Direct-Sequence Spread Spectrum Code-Division Multiple Access (DSSS-CDMA) transmissions, performed using the FM radio broadcasting infrastructure is presented. The proposed application is designed to simultaneously transmit a maximum of 15 low-resolution image notifications together with standard FM radio broadcasting in different geographical areas. The application is intended to warn drivers of significant driving events in major traffic areas of a country. The proposed solution is low-cost and rapid to put into practice because the modifications, both on the transmission infrastructure and on the receiver’s side, are relatively easy to implement. The transmission of image notifications is performed in subsidiary bands of commercial FM radio systems. The receiver is implemented using the Software-Defined Radio (SDR) paradigm and is able to extract the audio signal (corresponding to the usual FM transmission) and the data component, depending on the geographical area in which the vehicle is located. The receiver is based on a novel implementation of a modified Costas loop using two new nonlinear limiters. Appropriate image notification is selected using a specific decoding key, generated according to the geographical position of the vehicle. The performance of the data transmission system is analyzed by plotting the Bit Error Rate (BER) versus the signal-to-noise ratio of the data signal for different numbers of image notifications simultaneously transmitted. The proposed radio communication system was validated through an experimental setup based on Universal Software Radio Peripheral (USRP) devices driven by MATLAB/Simulink software.

Multi‐user underwater acoustic communication using binary phase‐coded hyperbolic frequency‐modulated signals

Multi-user communication traditionally uses either code division multiple access (CDMA) or time-division multiple access schemes. The chirp signals resilience to multipath and the Doppler effect makes it suitable for underwater acoustic communication. This paper presents a binary phase-coded hyperbolic frequency-modulated (BPC-HFM) for multi-user underwater acoustic communication. The proposed scheme has the advantage of both linear frequency-modulated signal, which is immune to multipath and Doppler offset, while PN sequence is encoded in such a manner that a waveform possesses either a phase shift of 0 or 180 depending upon the code which results in a unique orthogonal waveform for every user. As a result, it helps to reduce multiple access interference; in addition, the time-reversal mirror technique is used to enhance the performance of the system in the high multipath environment due to the virtue of hydro-acoustic channel. Furthermore, it uses a relatively simple matched filter-based receiver. To substantiate the robustness of the proposed multi-user waveforms three types of hydro-acoustic channels using the different numbers of multiple users are chosen for simulation and the bit error rate (BER) of the system is calculated. Furthermore, the results are compared to binary phase-coded linear frequency-modulated signal and conventional Direct sequence spread spectrum CDMA.

Chirp-rate quasi-orthogonality based DSSS-CDMA system for underwater acoustic channel

Underwater network node positioning is a key supporting technology for underwater networks. Generally, nodes at known locations (anchor nodes) are used to transmit location information to the node to be located, and the node to be located performs location calculation according to the arrival time of the received information, which requires multiple access communication between the anchor nodes and the node to be located. In order to reduce the multiple access interference (MAI) and distinguish the information of different anchor nodes, it is necessary to study the underwater multiple access method. The GPS positioning system uses direct sequence spread spectrum code division multiple access(DSSS-CDMA) technology, and the positioning satellite transmits a signal formed by the BPSK modulation by transmitting a pseudo-random sequence (PN sequence) to the binary code sequence corresponding to the navigation message to the user equipment to be located. The underwater acoustic (UWA) channel has a complex multipath structure and Doppler effect, which causes a large interference to the communication system. Compared with narrowband communication, spread spectrum communication has a strong anti-interference ability, and can maintain the reliability of the communication system in the UWA channel. Based on this, this paper proposes a quasi-orthogonal Chirp-rate based DSSS-CDMA method under UWA channel, and carries out simulation analysis and experimental verification.

A Blind Adaptive Kalman-PIC MUD Algorithm for the Multiple Access Communication Network

In the parallel signal processing, the multi-user detection precision of parallel interference cancellation (PIC) detector is always easily affected by the decision error diffusion. Based on the fast convergence and low complexity of blind adaptive Kalman algorithm, a new blind adaptive Kalman-PIC (KPIC) multi-user detection (MUD) algorithm is proposed for the direct sequence spread spectrum code division multiple access (DS-CDMA) system network with strong multiple access interference (MAI). Compared with traditional standard Kalman filter and PIC algorithm, the proposed combined program can totally track the time-varying channel, effectively estimate unknown noise statistics characteristics on-line while conducting state filtering, possibly minimize the detection error diffusion in the interference cancellation processing of single PIC algorithm, thus effectively suppress MAI. Simulation results show that the KPIC algorithm is of better convergence, dynamic tracking ability and precision

VHDL Implementation of MAC based DSSS-CDMA Protocol for Solving near Far Effect IN Ad-hoc Network

In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique like other spread spectrum technologies; transmitted signal takes up additional bandwidth than the data signal which modulates the carrier frequency. DS-CDMA is beneficial for Ad hoc network because it eliminates the requirement for any frequency or time-slot coordination. The main issue in DS-CDMA (Ad hoc network) is the hindrance of a near-far problem. There are two solutions available for reducing this near far effect, first is Power control and second is Medium access problem. In this paper, we focus on medium access problem, for this, we design multiple access interference (MAI) at the protocol level. The aim is that, use “VHDL implementation” for MAC Based DSSS CDMA design, which consist transmitter & receiver with MAC protocol of a Ad-hoc network, which prevent fast degradation of network throughput. In this design, used DPSK modulation technique is non-coherent and has higher BER performance than BPSK. VHSIC Hardware Description Language (HDL) was used for committal to writing of the design. Model Sim Edition 10.2 C was used for functional simulation and logic verification. The Xilinx Synthesis Technology (XST) 14.1 of Xilinx ISE tool was used for synthesis of this project.

A Blind Adaptive Kalman-SIC MUD Algorithm of the Wireless Multiple Access Mobile Communication System

The multi-user detection precision of successive interference cancellation (SIC) detector is always affected by the decision error diffusion. This paper focuses on the SIC algorithm of direct sequence spread spectrum code division multiple access (DS-CDMA) system with strong multiple access interference (MAI) and inter symbol interference (ISI). A blind adaptive Kalman-SIC multi-user detection (MUD) algorithm is proposed in this paper. This algorithm can totally track the time-varying channel, minimize the detection error diffusion, and thus effectively suppress MAI and ISI. Simulation results show that the blind adaptive Kalman-SIC algorithm is of better tracking ability, convergence and detection precision.  Index Terms—Successive interference cancellation, Kalman, DS-CDMA, multiple access interference.

Soft Decision Parallel Interference Cancellationfor Scrambled/Unscrambled DS-CDMA System

A soft decision linear parallel interference cancellation for the direct sequence spread spectrum CDMA systems which can accommodate more users (K = N+M >N) than the processing gain of the system is analyzed in this paper. The proposed technique accommodates N users without any mutual interference and a number of additional users at the expense of a small signal-to-noise ratio. Two sets of orthogonal Gold codes are used, one for the first N users and the other for the additional users. Both the N users and additional users are overlaid by a set-specific pseudonoise scrambling sequence. The performance of scrambled and unscrambled system for matched filter and linear parallel interference cancellation is analyzed and the scrambled system is found better than unscrambled system. The allowable load of this scheme is investigated, so that the uncoded performance with linear parallel interference cancellation detector using soft (SDIC) decision functions remains close to the single user bound for N= 64 at 33% overloading.

A method for generating chaotic spread-spectrum sequences and their optimized selection algorithm

A method for generating chaotic spread-spectrum sequences based on the combined chaotic map is proposed. An optimized selection algorithm based on the property requirement of spread-spectrum sequences and the performance index of multiple access interference is also presented. Simulation is performed for the optimized chaotic sequence, and an optimized logistic sequence is applied to a direct sequence spread-spectrum CDMA system under different channel conditions. The results show that the chaotic spread-spectrum sequences generated by the proposed method have similar performance as the logistic spread-spectrum sequences and have better security.

Evaluation of SIR statistics in a DS/CDMA system with signal-level-based power control and multipath dispersion

The statistical evaluation of the estimated short-term signal-to-interference ratio (SIR) for power control is presented in many-to-one reverse link. As mentioned in other previous works, the statistical evaluation shows that the estimated short-term SIR can be approximated by a log-normal distribution. The analysis has applications to a cellular system employing direct-sequence spread-spectrum code-division multiple access (CDMA) with M-ary orthogonal modulation on the uplink. Copyright © 2004 AEI.

Spectral Overlay of Direct-Sequence Spread Spectrum in the Instrument Landing System Glideslope Band

In this paper, we examine the effects of intentional spectral overlay between a directsequence spread spectrum (DS-SS) code-division multiple-access (CDMA) system and the glide slope signal of the Instrument Landing System (ILS) currently employed by the Federal Aviation Administration (FAA). The purpose of the overlay system is to enable increased spectral efficiency (higher data throughput), for future potential aeronautical datalink communications, e.g., an “airborne internet.” That is, this overlay would enable simultaneous use of the ILS glideslope band by the current glide slope systems and a new DS-SS CDMA digital communication system. We estimate the performance degradation incurred by both systems for several values of transmit powers, DS-SS bandwidths and data rates, and typical ILS glideslope and CDMA system parameters. Our study uses both analysis and computer simulations. We provide examples that explore both ILS glideslope and CDMA system parameter values appropriate for the successful application of the overlay technique.

Adaptive single-user receivers for direct-sequence spread-spectrum CDMA systems

The capacity of a direct-sequence spread-spectrum code-division multiple-access (DSSS-CDMA) system is limited by multiple-access interference (MAI) and the near-far problem. Multiuser receivers provide a solution to these problems, but they require knowledge of parameters of the MAI and are computationally complex. Adaptive single-user receivers, however, do not require knowledge of MAI parameters and need fewer computations. This paper discusses a wide range of adaptive single-user receivers found in the literature and presents their performance results under a unified framework to provide a basis of comparison. Results indicate that, compared to the conventional receiver, adaptive single-user receivers provide large gains in system capacity and are near-far resistant. It is shown that fractionally spaced adaptive receivers, which exploit spectral correlation due to the cyclostationary nature of the DSSS signal, perform better than adaptive receivers that cannot exploit this correlation. Multipath results presented for two-ray and urban channels indicate that fractionally spaced adaptive receivers act as RAKE receivers.

Blind adaptive detection of DS/CDMA signals on time-varying multipath channels with antenna arrays using high-order statistics

A new approach based on multiscale decomposition and higher-order statistics is presented for the simultaneous solution of multiuser interference and time-varying multipath propagation in the uplink of a cellular direct-sequence spread-spectrum code-division multiple-access (DS/CDMA) system. Each channel between the mobile transmitter and the base-station receiver is unknown and arbitrarily varying with time. The optimum filter achieving separation and multipath compensation is time-variant. The typical approach in many multiuser detectors previously proposed is to assume that the channel is almost static (time invariant) and attempt detection according to this model. Slow variations of the channels are then compensated using adaptive algorithms that force the estimates (of the channels or of the separating filters) to be constantly in search of a convergence point. If the channel coefficients variations in time are fast with respect to the convergence time of the adaptive algorithm, significant degradation may result. In this work, we depart from this traditional approach and we investigate new kernels that more accurately can characterize the time-varying nature of the detection problem. As a first step, we show that the super-exponential framework can still be applied in a time-variant environment. Then, we describe a multiresolution decomposition of the filter components, essentially constraining its variations in time to remain within the solution subspace. The resulting algorithm overcomes some of the drawbacks associated with slow convergence and insufficient tracking capability typical of many blind approaches and several nonblind methods based on the slow fading assumption.

A Novel Direct Sequence Spread Spectrum CDMA System with Analog Frequency Modulation

This paper describes and analyzes a unique combination of analog modulation with code division multiple access. Although the capacity of the analog CDMA system is less than that of the digital CDMA, the analog system has reliable voice quality, economy and ease of implementation, simplified frequency planning, and compatibility with current analog phone systems and devices, which is an especially attractive feature. The FM CDMA system is proposed as a fixed wireless system, e.g., wireless local loop, in which the small scale fading distortion due to Doppler effect is likely to be moderate. This allows the use of simple and cost-efficient receiver structures while maintaining performance.

VLSI implementation of a signal recognition and code acquisition algorithm for CDMA packet receivers

The widespread application of direct-sequence spread-spectrum code division multiple access (DS/SS-CDMA) to wireless communication systems asks for ever faster and more reliable real-time signal processing operations to be performed by highly integrated and low-power consumption digital receivers. One of the most critical signal processing tasks to be performed by the DS/SS-CDMA receiver is signal presence detection and code epoch estimation. This paper deals with the design and realization of an application-specific integrated-circuit (ASIC) for fast signal recognition and code acquisition (SR/CA) in packet DS/SS-CDMA receivers operating in a satellite or terrestrial radio network. In particular, we show how a parallel acquisition circuit can be effectively implemented on a single-chip with a 1.0-/spl mu/m CMOS technology according to the specifications of the ARCANET Ku-band CDMA VSAT satellite network sponsored by the European Space Agency (ESA). It is shown that the ASIC performance closely follows analytical predictions.

PN acquisition and tracking performance in DS/CDMA systems with symbol-length spreading sequences

Direct sequence spread spectrum code-division multiple-access (DS/CDMA) is receiving increasing attention for cellular communications systems. When the users are synchronized and special symbol-length sequences, such as Gold codes, are used, the mutual interference can be substantially reduced relative to a system with very long or purely random spreading sequences. It is shown that this approach degrades the performance of the code phase acquisition and tracking, however. This effect prevents the system from acquiring and tracking long before the data detection is affected by the multiuser interference.

A hybrid spreading/despreading function with good SNR performance for band-limited DS-CDMA

Code-division multiple-access (CDMA) implemented with direct-sequence spread spectrum (DS/SS) signaling is a promising multiplexing technique for cellular telecommunications services. The efficiency of a direct-sequence spread-spectrum code-division multiple-access (DS-CDMA) system depends heavily on the shape of the spectrum of the spread signal. Maximum efficiency is obtained with an ideal brick-wall bandpass spectrum. There are two approaches toward achieving such a spectrum. One is to use a simple spreader that produces a broad spectrum and then follow it with a precise, high order filter to band limit the spectrum. A second approach, which is the approach taken in this paper, is to use a spreader that produces a spectrum close to the ideal spectrum and then employ a simple filter to control the out-of-band power. The proposed spreader/despreader is based on a simple hybrid function and can be easily implemented. An analysis provides a compact expression for the signal-to-noise ratio (SNR) of a RAKE receiver. The expression includes the effects of baseband, intermediate frequency (IF) and RF filtering as well as the effects of the spectral densities of the spreading/despreading functions. The analysis shows that the proposed spreader/despreader yields superior performance over a conventional pseudo noise (PN) spreading/despreading mechanism.

Mathematical modeling and performance analysis for a two-stage acquisition scheme for direct-sequence spread-spectrum CDMA

Acquisition of synchronism is considered for DS/SS CDMA systems. For large systems with large timing uncertainties, it has been shown previously that acquisition in the presence of multiple-access interference may impose a significant limitation on capacity. This leads the authors to consider a system in which timing uncertainties are relatively small and to propose an acquisition scheme which exploits this to reduce complexity and acquisition overhead. The proposal may be appropriate for a microcellular environment for personal communications in which CDMA packet transmission is employed for both voice and data. Packetized transmission would imply that the overhead available for acquisition is small, and the large number of microcells would restrict the cost of the acquisition scheme used in the receiver in each microcell. The acquisition time required for a simple serial search scheme may therefore be unacceptably large. On the other hand, while acquisition using a passive matched filter is fast, the filter length required for reliable acquisition is liable to be excessive in terms of cost and complexity. Motivated by these considerations, the authors propose a two-stage acquisition scheme which employs a short programmable matched filter for initial detection, followed by a correlator for verification. Numerical results based on an approximate analysis of acquisition performance in the presence of multiple access interference are employed to compare the scheme with conventional acquisition schemes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mobile access to an ATM network using a CDMA air interface

The paper presents a possible integrated system concept for a direct sequence spread spectrum CDMA radio access system suitable for third-generation mobile radio. The system has been conceived to take account of such diverse services as low bit rate voice and quasi-broadband services at rates of up to 256 kb/s. Broadband services imply the use of the ATM transmission technique, and particular attention is paid to the mutual impact of CDMA and ATM. An efficient automatic repeat request technique is described which gives a suitably low overall error rate and a soft capacity limit. The proposed solution represents a quantum advance on today's CDMA solutions and integrates well with the ATM fixed network. >