Code division multiple access based visible light communication in vehicle adaptive cruise control under emergency situation

Recently, the emerging Ultra-Wideband (UWB) impulse technology has found numerous applications in the civil as well as the military sectors. In this paper, an UWB multi-user communication system is studied. In a previous work, two systems (DS---CDMA---UWB and Gegenbauer---UWB) were compared in a rather simple case: only two users were considered, and a perfect synchronization between each receiver and transmitter for the two users was assumed. In the present paper, a more general case is studied. Different synchronous (different users detected at the same time or with constant delays) and asynchronous (each user transmitting independantly of other) scenarios are introduced. The interferences between users are also taken into account (for two users and more). Two systems are described and analyzed and their performance in terms of Bit Error Rate (BER), synchronization errors and users interference is studied by simulation. The first system, which is only based on orthogonal UWB waveforms called Modified Gegenbauer functions (MGF), gives a satisfactory multi-user detection in the synchronous case only. The second one uses an hybrid coding technique: an UWB orthogonal coding is associated to a spread spectrum DS---CDMA (Direct Sequence Code Division Multiple Access) technique (in fact a combination of the two systems sudied in the previous work). This allows an efficient multi-user detection in the asynchronous case.

Code division multiple access (CDMA) promises to become the enabling technology for the future generation of satellite communications. For instance, CDMA is being used in Globalstar, Skybridge and is also proposed for the satellite component of UMTS. The evolution of satellite systems towards multimedia communications, necessitates not only wideband CDMA but also requires a hybrid code and time division multiple access (CTDMA) technique because of the packet nature of the data. In this paper, we give an overview of the challenges in designing a wideband CTDMA modem. As a first challenge, the wideband nature of the CDMA modem dictates that the tracking loops of the modem can no longer be executed in software but must be fully integrated in VLSI. Second, the packet based nature of the communication in a CTDMA modem requires ultra fast acquisition for each packet. The extremely low signal-to-noise ratio in satellite communications largely complicates this fast acquisition task.

We analyze the basic principles of the spread-space holographic code division multiple access (CDMA) technique. We describe the structure of the encoder and decoder and present a basic mathematical analysis based on spatial harmonic decomposition for the receiver's processing module, which is comprised of a Fourier transform lens and a holographic matched filter. Subsequently, we study two applications of optical holographic CDMA, namely, free-space holographic CDMA photonic switch and free-space (wireless) multiaccess optical (infrared) indoor communications. For both techniques, we describe the two-dimensional imaging techniques, namely user's code transmission, and highlight the basic parameters and components that need to be optimized. To obtain the bit-error rate (BER) of the proposed application, we first evaluate the probability density function of multiuser interference and then evaluate the BER as a function of the processing gain, number of users, the received power, and the optimum threshold. For BER /spl ap/ 10/sup -9/, the result shows an extraordinary number of users that can be supported via holographic CDMA, for both applications.

This paper introduces four block joint detection (JD) receivers which combining the orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA) techniques, i.e., OFDM-CDMA receiver. The performance of the OFDM-CDMA receiver with orthogonal and non-orthogonal spreading sequences is investigated in mobile radio channels. The sequences considered as spreading codes are orthogonal Walsh-Hadamard, Orthogonal Gold, Gold and maximim length sequences or m - sequences. The JD algorithms for the OFDM- CDMA receiver are Zero Forcing Block Linear Equalizer (ZF- BLE), Minimum Mean Square Error Block Linear Equalizer (MMSE-BLE), with and without decision feedback (DF). Time- domain equalization does not require DFT or FFT operations and can be used to compensate the channel fading effect. Hence for hardware implementation, the time domain interpretation can lead to a more efficient structure when compared with the frequency domain approach. The bit error rate (BER) performance comparisons of different spreading codes and equalizers are shown in the simulations.

Wireless communication with multicarrier modulation is very attractive for present and future communication network due to immunity to delay spread and fading. However, such systems are receptive to carrier frequency offset (CFO) due to Doppler effect in a mobile communication system. Analysis is carried out for a wireless communication system with multi carrier (MC) direct sequence (DS) code division multiple access (CDMA) technique with CFO to find the expression of SINR and the bit error rate (BER) with BPSK coherent detection receiver. The results are checked out in term of SINR and BER for various values of CFO variance, considering Gaussian distribution of CFO. The result shows that there occurs BER floor due to CFO for SC and Multi Carrier (MC) DS-CDMA and there is a power penalty at a given BER which is high for the Multi Carrier (MC) DS-CDMA compared to SC DS-CDMA. It is also observed that increasing the number of subcarriers does not affect much in MC DS-CDMA, which will definitely allow to minimize the delay spread which is a vital limitation of wireless communication system.

This paper analyzes the performance of generalized optical orthogonal codes (OOC) in a wireless infrared system using code division multiple access (CDMA) technique. Since the emergence of generalized OOC s, they have been analyzed in optical fiber media, in which noise can be ignored with good approximation. But in an optical wireless system which inherently suffers from intense noise sources, generalized OOC behaves differently. The main issues of an optical wireless system are intense noise sources which degrades system performance and limited available bandwidth which is caused by multipath distortion in the channel. We believe that these analyses will help the designer of an optical wireless system, to select the best code family which satisfies the desired condition on bit error rate (BER) or required bandwidth.

There are several technologies and techniques available when developing indoor positioning systems (IPS). Recently, the development of positioning systems based on optical signals has aroused great interest, mainly those using visible light from the lighting infrastructure. In this work, we analyze which techniques give better results to lay the foundations for the development of a Visible Light Positioning system (VLP). Working only with a receiver, it is analyzed what the result of determining the position of different emitters is when they emit simultaneously and without any synchronism. The results obtained by Frequency Division Multiple Access (FDMA) (with digital bandpass filters, I/Q demodulation, and FFT) and Code Division Multiple Access (CDMA) are compared. The interference between signals when emitted simultaneously from multiple emitters is analyzed as well as the errors they cause and how these effects can be mitigated. As a result of the research, the advantages and disadvantages using different multiple-access determination techniques are determined. In addition, advantages and disadvantages of using FDMA and CDMA techniques as well as hardware requirements that make one more feasible than the other are presented. The system behavior, in terms of errors, is established using FDMA and different configurations such as: I/Q, RMS, or FFT. The work also determines the error rates that can be obtained with the different FDMA and CDMA configurations, considering different error scenarios and integration time. Synthetic emulations and empirical tests were performed, which concluded that IPS systems based on optical signals and PSD sensors can achieve very high measurement accuracies and a high measurement rate. Obtained positioning errors in a room of 3 m height are less than 1 cm when working in noisy environments.

<div class="section abstract"><div class="htmlview paragraph">Aviation industry is striving to leverage the technological advancements in connectivity, computation and data analytics. Scalable and robust connectivity enables futuristic applications like smart cabins, prognostic health management (PHM) and AI/ML based analytics for effective decision making leading to flight operational efficiency, optimized maintenance planning and aircraft downtime reduction. Wireless Sensor Networks (WSN) are gaining prominence on the aircraft for providing large scale connectivity solution that are essential for implementing various health monitoring applications like Structural Health Monitoring (SHM), Prognostic Health Management (PHM), etc. and control applications like smart lighting, smart seats, smart lavatory, etc. These applications help in improving passenger experience, flight operational efficiency, optimized maintenance planning and aircraft downtime reduction. Intra Aircraft WSNs (IAWSN) used for such applications are expected to provide robust and reliable communication performance. However, IAWSNs, when deployed, must co-exist with other wireless devices and networks based on Wi-Fi and Bluetooth technologies. Sharing of the ISM frequency band (2.4 GHz) among these networks makes the co-existence problem more challenging and has a significant impact on the Quality of Service (QoS) in terms of throughput, latency and Packet Error Rate (PER) of IAWSN. In addition, they are subjected to additional electromagnetic interference from other electronic and avionic systems onboard aircraft. There are various channel management, priority-based scheduling and time-sharing techniques that are deployed currently to address the co-existence problem. However, these methods perform a trade-off among one or more operational parameters like channel bandwidth, number of nodes per channel, throughput, latency, PER, etc. of IAWSN. Code Division Multiple Access (CDMA) technique is a proven one in cellular networks for providing reliable interference free communication performance especially in large scale networks. This paper evaluates the feasibility of deploying CDMA for IEEE 802.15.4 based IAWSN onboard aircraft. A CDMA based communication schema is proposed and simulated for IAWSN operating as per IEEE 802.15.4 protocol. The communication performance of the CDMA based IAWSN is evaluated in comparison with the performance of a standard IEEE 802.15.4 protocol implementation in the presence of interference from the co-nodes of the IAWSN and Wi-Fi devices by analyzing the QoS parameters like signal to noise ratio (SNR), operational bandwidth, Bit-Error Rate (BER) and Process Gain through simulation. Simulations results are evaluated against the desired performance level for a reference use case application. Improvement opportunities are identified and areas for future research are proposed.</div></div>

By introducing a full‐rate space–time coding (STC) scheme, a synchronous CDMA (code division multiple access) system with full‐rate STC is given, and the corresponding uplink performance is investigated in Rayleigh fading channel with imperfect estimation. Considering that existing STC‐CDMA system has high decoding complexity, low‐complexity multiuser receiver schemes are developed for perfect and imperfect estimations, respectively. The schemes can make full use of the complex orthogonality of STC to reduce the high decoding complexity of the existing scheme, and have linear decoding complexity compared with the existing scheme with exponential decoding complexity. Moreover, the proposed schemes can achieve almost the same performance as the existing scheme. Compared with full‐diversity STC‐CDMA, the given full‐rate STC‐CDMA can achieve full data rate, low complexity, and partial diversity, and form efficient spatial interleaving. Thus, the concatenation of channel coding can effectively compensate for the performance loss due to partial diversity. Simulation results show that the full‐rate STC‐CDMA has lower bit error rate (BER) than full‐diversity STC‐CDMA systems under the same system throughput and concatenation of channel code. Moreover, the system BER with imperfect estimation are worse than that with perfect estimation due to the estimation error, which implies that the developed multiuser receiver schemes are valid and reasonable. Copyright © 2010 John Wiley & Sons, Ltd.

Hybrid code division multiple access (CDMA) scheme utilizes advantages of both direct sequence spread spectrum (DS/SS) and frequency hopped spread spectrum (FH/SS) systems, while overcoming some of their shortcomings. To enhance performance of this hybrid system, an efficient modulation scheme must be used that can perform favorably in a fading environment. We have compared the bit error rate (BER) performance of two spectrally efficient schemes namely, quadrature phase shift keying (QPSK) and minimum phase shift keying (MSK), when used in a hybrid system, over a Rayleigh fading channel. Simulation results show that hybrid MSK indeed is a better scheme in a multi-user (CDMA) environment in that, it achieves lower BER than hybrid QPSK. The comparison has been extended by including a predetection diversity reception scheme. >

This paper deals with a new digital audio watermarking scheme based on Code Division Multiple Access (CDMA) technique. In digital communication, CDMA allows several users to share the same communication channel without interference from each other. The present work proposes to embed multiple watermarks in the same audio channel in order to increase the embedded information. Our main objective is to emphasize the impact of spreading codes on the performance of CDMA based watermarking system. This performance will be evaluated in terms of transparency, detection reliability of the watermark and its robustness against various disturbances.

Multiuser detection is an essential part of code division multiple access (CDMA) receivers to be able to exploit the bandwidth efficiency, i.e., to support as many users as possible. In this paper we propose a switching successive interference canceller (SSIC) for CDMA systems which dynamically switches between SIC and matched filter operations depending upon the channel characteristics. The switching detector that we have proposed has a better performance than that of the matched filter and SIC in the presence of AWGN and Rayleigh fading channel conditions. The suggested detector combines good average bit error rate (BER) performance, acceptable complexity and more capacity improvement than the successive interference canceller itself.

In recent years, the joint decoding of combined source and channel coding have shown the capability of delivering performances exceeding that of separately decoded schemes. In this paper, a well-known joint source/channel coding scheme is investigated for possible use in future 4th Generation (4G) direct sequence spread spectrum multiple access (DS/SSMA) code division multiple access (CDMA) communication systems. Due to the availability of potentially large sets of sequences with good correlation characteristics, the DS/SSMA CDMA system considered in this paper employs complex spreading sequences (CSS). A multiuser CSS-based DS/SSMA CDMA communication system was implemented as test platform for the joint source/channel coding scheme. Several families of CSSs, including Zadoff-Chu (ZC), double sideband constant envelope linearly interpolated root-of-unity filtered general chirp-like (DSB CE-LI-RU Filtered GCL), analytical bandlimited complex (ABC) and quadriphase (QPH) sequences are investigated on this platform. Simulated bit error rate (BER) performances are presented for uncoded, separate source and channel coded and joint source/channel coded systems under realistic multipath fading channel conditions.

Code Division Multiple Access (CDMA) and multiple input multiple output- (MIMO-) CDMA systems suffer from multiple access interference (MAI) which limits the spectral efficiency of these systems. By making these systems more power efficient, we can increase the overall spectral efficiency. This can be achieved through the use of improved modulation and coding techniques. Conventional MIMO-CDMA systems use fixed spreading code assignments. By strategically selecting the spreading codes as a function of the data to be transmitted, we can achieve coding gain and introduce additional degrees of freedom in the decision variables at the output of the matched filters. In this paper, we examine the bit error rate performance of parity bit-selected spreading and permutation spreading under different wireless channel conditions. A suboptimal detection technique based on maximum likelihood detection is proposed for these systems operating in frequency selective channels. Simulation results demonstrate that these code assignment techniques provide an improvement in performance in terms of bit error rate (BER) while providing increased spectral efficiency compared to the conventional system. Moreover, the proposed strategies are more robust to channel estimation errors as well as spatial correlation.

A direct sequence optical code division multiple access technique is investigated. This paper introduces, first, the principles definitions of Code Division Multiple Access in radio communications. After that, the performances of Optical Code Division Multiple Access are evaluated in association with a realistic amplified optical channel model.