Code Division Multiple Access System Research Articles

Construction of type-II ZCCS for the MC-CDMA system with low PMEPR

This paper introduces a novel construction method for Type-II Z complementary code set (ZCCS) based on the Kronecker product between complete complementary code and mutually orthogonal sequences. Type-II ZCCS offer significant advantages over their Type-I counterparts, boasting larger zero correlation zone (ZCZ) width and a larger number of codes with identical constituent sequences and lengths. Moreover, we propose a strategy to reduce column peak-to-mean envelope power ratio (PMEPR) to a low values upto smaller than 2. This construction framework also facilitates the creation of Z complementary pairs (ZCPs) with flexible parameters. Furthermore, we present a Type-II ZCCS based multi-carrier code division multiple access (MC-CDMA) system and conduct performance comparisons against existing Type-I ZCCS based counterparts. Simulation results demonstrate the superiority of the proposed system, showcasing improved reliability and efficiency. Additionally, we establish a novel relationship among set size, code size, sequence length, and ZCZ width for Type-II ZCCS.

A 930 m/180 Gbps*User Underwater Coherent Optical Code-Division Multiple-Access Network Based on Hybrid 256-Differential Pulse Position Modulation and Weighted Modified Prime Code Sequence

Currently, there are three types of optical communication networks based on the communication channel between the transmitter and receiver: the optical fiber channel, visible light channel, and optical wireless channel networks. The last type has several advantages for underwater communication, wireless sensors, and military communication networks. However, this type of optical network suffers from weather conditions in free-space communications and attenuation owing to the scattering and absorption mechanisms for underwater communication. In this study, we present a new transceiver architecture of a coherent optical code-division multiple-access (OCDMA) system based on a hybrid M-ary differential pulse position modulation scheme and a spreading code sequence called weighted modified prime code for underwater communication to minimize channel dispersion, increase the transmission rate per second, enhance the network bit error rate (BER) performance, and improve network security. Using an OCDMA system, we can simultaneously expand the network coverage area and increase the number of users sharing the network over the same channel bandwidth. The simulation results in this study proved that the proposed system can accommodate 1310 active users and a network throughput of 180 Gbps*user over a transmission distance of 930 m without any repeater at a 10−9 BER performance, compared to the 45 Gbps*user network throughput and 100 m transmission distance reported in the literature.

Chaotic Code Division Multiple Access

Chaotic signals are gaining importance in the field of communication these days. The chaotic Pseudo Noise sequences give a uniform spread over the entire frequency bandwidth. The sequences produce good performance as Pseudo random patterns when used in Code Division Multiple Access (CDMA) systems. This paper introduces to the field of chaotic signals and demonstrates how it is used in CDMA systems Key Words: Chaotic signals, DS CDMA, Nonlinear systems, PN sequences.

Performance analysis of 2D optical code division multiple access through underwater wireless optical medium

The performance of a two-dimensional optical code division multiple access (2D-OCDMA) system using an underwater wireless optical (UWO) medium is assessed in this work. The optical source is an LED with a working wavelength of 532 nm, and the optical detector is a p–i–n photodiode. When calculating the bit error rate (BER), the phase-induced intensity noise (PIIN), thermal noises, and shot sounds are taken into account. The user code address is set using 2D perfect difference (2D-PD) codes. Link distance, inclination angle, beam divergence angle, transmitter power, and the number of concurrent users are all taken into account when determining the BER performance. For various water media, such as pure sea water (PSW), clear ocean water (CLOW), and coastal ocean water (CSOW), the performance of the suggested system is examined.

Complete Complementary Coded Excitation Scheme for SNR Improvement of 2D Sparse Array Ultrasound Imaging.

Driving the numerous elements of 2D matrix arrays for 3D ultrasound imaging is very challenging in terms of cable size, wiring and data rate. The sparse array approach tackles this problem by optimally distributing a reduced number of elements over a 2D aperture while preserving a decent image quality and beam steering capabilities. Unfortunately, reducing the number of elements significantly reduces the active probe footprint reducing as a consequence the sensitivity and at the end the signal-to-noise ratio. Here we propose a new coded excitation scheme based on complete complementary codes to increase the signal-to-noise ratio in 3D ultrasound imaging with sparse arrays. These codes are known for their ideal auto-correlation and cross-correlation properties and have been widely used in Code-Division Multiple Access systems (CDMA). An algorithm for generating such codes is presented as well as the adopted imaging sequence. The proposed method has been compared in simulations to other coded excitation schemes and showed significant increase in the signal-to-noise ratio of sparse arrays with no correlation artifacts and no frame rate reduction. The gain in signal-to-noise ratio compared to the case where no coded excitation is used was around [Formula: see text] and the contrast was also improved by [Formula: see text] while the resolution was unchanged.

Non Orthogonal Multiple Access for Multi-carrier Code Division Multiple Access Systems with Energy Harvesting

Non Orthogonal Multiple Access for Multi-carrier Code Division Multiple Access Systems with Energy Harvesting

Analysis of Multiuser Detectors and Performance improvement in DS-CDMA system using Multistage Multiuser Detection Techniques

The Direct Sequence Code Division Multiple Access (DS-CDMA) system faces several disruptions, this is most crucial of which is the Multi Access Interference (MAI) caused by its users. The efficiency of the system gradually declines as every quantity rises, and the MAI rises, especially in faded environments. This work proposes a multiple-phase multiuser identification approach called Differencing Partial Parallel Interference Cancellation (DPPIC), which improves the overall efficiency. The methods known as Differencing Parallel Interference Cancellation (DPIC) and Partial Parallel Interference Cancellation (PPIC) are combined in this methodology. Current solutions for Parallel Interference Cancellation (PIC) and PPIC have enhanced overall effectiveness; however, this has come at the expense of increasing the complexity of computation. As the variety of consecutive stages grows, the MAI falls. Using the DPIC approach may reduce the computational burden without improving system functionality. The use of the Partial Differencing Parallel Interference Cancellation (PDPIC) technique can enhance system performance while lowering the level of complexity. According to the simulation findings, Bit Error Rate (BER) vs normalized signal strength (i.e., Eb / N0) performs more effectively for the suggested DPPIC approach than for PIC, the PPIC, and PDPIC.

Influence of different codes on the performance of SAC‐OCDMA over FSO link

SummaryThis paper evaluates the performance of a spectral‐amplitude‐coding optical code division multiple access (SAC‐OCDMA) system over a free space optical (FSO) communication link under various weather conditions such as fog, snow, and rain. The system uses different code families, including modified quadrature congruence (MQC), random diagonal (RD), and diagonal eigenvalue unity (DEU), to address user codes and reduce the effects of multiple access interference (MAI). The system's bit error rate (BER) performance has been analyzed taking into account receiver noises and MAI, and calculates the required optical power for a BER value of 10−9 under different weather conditions. The results show that fog has the most significant impact on the system's performance, while rainy conditions require the lowest optical power. The performance of the system also declines with increasing transmission length and concurrent user count. Finally, the paper compares the performance of different code families under unfavorable weather conditions and concludes that DEU performs better than MQC and RD in bad weather.

Notice of Removal: Applications of Advanced Computer Communication and Control Technology for Modern Substations

This paper proposes a novel approach to achieve monitoring and control of modern substations using advanced computer communication and control technology. The proposed approach is based on a code division multiple access (CDMA) and interleave division multiple access (IDMA) system joining with optical-fiber communication technology to realize the utility infrastructure of Smart Grid. Recently, owing to the rapid growth on optical-fiber communication, it can offer standardized communication technology for wide-area, metropolitan-area, and local-area networks. Moreover, optical-fiber communication technologies offer not only significant benefits on connection among different CDMA-IDMA systems such as rapid deployment, higher baud rate (equal or higher than 14 Tb/s), enhanced bandwidth, less bit error rate (equal or less than 10-9), less optical-amplifier quantities, reduced interference among them, lower signal attenuation, etc. but also the advantages of being more suitable for remote-end applications in Smart Grid environment. With spreading spectrum modulation and demodulation combing encoding, it can be used to transmit data and images over power lines to accomplish opportunities and challenges in the effort on comparisons and assure safety, security, and reliability in order to achieve reliability and demand efficiency for modern substations of the utility system as a supervisory control and data acquisition (SCADA) system.

Design of spread spectrum communication system based on multipath signal synthesis

AbstractA low‐complexity anti‐multipath interference spread spectrum communication system is proposed to address shortcomings in traditional anti‐multipath technology, such as complex structures and high resource consumption. The system utilizes a fast Fourier transform to capture pseudo‐noise code signals and simultaneously detect multipath signals. Moreover, the signal‐to‐noise ratio (SNR) of each path signal is calculated, and the multipath signal is synthesized through the designed optimal SNR synthesis method to improve the SNR of the demodulated signal to reduce the bit error rate. MATLAB is used to perform functional simulations of the system to verify its feasibility. The simulation results show that the system can successfully detect and synthesize multipath signals and achieve lower communication error rates than traditional code division multiple access (CDMA) systems.

Complementary Coded Identical Code Cyclic Shift Multiple Access Under Asynchronous Frequency-Selective Fading Channels

A complementary coded code-division multiple-access (CC-CDMA) system is built on the direct sequence (DS) spread spectrum technique, which can suppress multipath interferences and multiple-access interferences due to the ideal correlation property of complementary codes (CCs). However, the DS spread spectrum technique will cause poor bandwidth efficiency; the CC-CDMA system suffers from serious interferences due to the ideal correlation of CCs may not be reconstructed at the receiver after passing through asynchronous frequency selective fading channels. In this paper, we propose a complementary coded identical code cyclic shift multiple access (CC-ICCSMA) system under asynchronous frequency selective fading channels, which allows multiple data streams to transmit in parallel by sharing one spreading code for improving the bandwidth efficiency. Considering the impact of interferences, we propose an ICCS matched filterbank to tackle the interferences, which can decode the data under all paths and achieve a high multipath diversity gain. Simulation results show that the proposed CC-ICCSMA system can achieve higher bandwidth efficiency than that of traditional CC-CDMA and can outperform the traditional DS-CDMA schemes in terms of bit-error rates and transmission rates.

Smoothed Sparse Blind DOA Estimation for MC-CDMA Systems Based on Tensor Decomposition

We propose a blind direction of arrival (DOA) estimation method for multicarrier code-division multiple access (MC-CDMA) systems, which does not require knowledge of the spreading codes of transmitters. Our method involves reconstructing a fourth-order tensor with observations from the antenna array at the receiver. We then apply higher-order singular value decomposition (HOSVD) to separate the signal subspace from the noise subspace. To enhance the sparsity of the solution, we develop a smoothed ℓ0-norm sparse reconstruction method by designing continuous functions with reweighted vectors. Finally, DOA estimates are obtained by searching the spectrum of the sparse solution using an iterative method that ensures fast convergence. Numerical simulations show its superiority over previous work.

A Secure Optical Body Area Network Based on Free Space Optics and Time-Delayed 2D-Spectral/Spatial Optical CDMA

Free space optics (FSO)-based optical body area networks (OBANs) are receiving massive attention as an opportunity to address the limitations of their radio frequency (RF)-based counterparts. This boom in research interests is primarily due to multitude of benefits, including high capacity, immunity to electromagnetic interference (EMI), rapid installation, cost efficiency, and license-free use of spectrum. Securing the transmission of patient health data against interception in OBANs using insecure FSO channels is a challenging task. Therefore, we propose a low-cost, flexible, and secure OBAN based on FSO technology and a time-delayed two dimensional (2D) spectral/spatial optical code-division multiple access (OCDMA) system. The proposed architecture consists of eight sensors attached to the bodies of patients. The sensors operate at a rate of 50 kbps. Electrical data generated from each sensor are used to modulate an optical carrier and then encoded using 2D-spectral/spatial double weight–zero cross correlation (DW-ZCC) code. The 2D encoded optical signals are then time delayed to eliminate the multiple parallel FSO channels between the transmitter and medical center. The combined optical signal consists of eight 2D-encoded time-delayed optical signals transmitted towards a remote medical center over an FSO channel with a range of 1 km. The received signal is decoded and the data from each sensor are recovered after photodetection at the medical center for further analysis. The overall performance of the sensors is analyzed using bit-error rate (BER) and quality factor (Q-factor) plots for different weather conditions and lengths of the FSO channel, considering the log-normal channel model. The capital expenditure (CAPEX) of the proposed architecture is analyzed and compared with the conventional 2D-spectral/spatial FSO system to determine the overall impact of introducing time delay units on the cost of implementation.

Performance improvements of a VLC system, in a V2X context, using a different multiplexing technique

This paper scrutinizes visible light communication (VLC) employing hybrid optical time division multiplexing (OTDM) wavelength division multiplexing (WDM). It also demonstrates the simulation of VLC using the direct sequence optical code division multiple access (DS-OCDMA) system developed by OptiSystem-Matlab Co-simulation. The profits of WDM and OTDM capacities have been combined using two levels of freedom to build up of the system. The performances are demonstrated in the simulated findings of the bit error rate (BER) in relationship with the data rate and the number of users. First, the simulated results display the usefulness of the system. Then, the number of users has been significantly enhanced. Besides, the OCDMA functions by appointing a specific code to each user and could provide asynchronous and simultaneous access to numerous users. One drawback is multiple access interference (MAI). The use of very long code sequences is crucial in order to lessen this effect. Hence, very large bandwidths are essential. This study aims at demonstrating, through system simulation, the practicability of an all-optical conventional correlation receiver dedicated to a DS-OCDMA access network link. Again, OptiSystem has been used to realize our blocks.

Performance Evaluation and Comparison Between LDPC and Turbo Coded MC-CDMA

This work presents a comparison between the Convolutional Encoding CE, Parallel Turbo code and Low density Parity Check (LDPC) coding schemes with a MultiUser Single Output MUSO Multi-Carrier Code Division Multiple Access (MC-CDMA) system over multipath fading channels. The decoding technique used in the simulation was iterative decoding since it gives maximum efficiency at higher iterations. Modulation schemes used is Quadrature Amplitude Modulation QAM. An 8 pilot carrier wereused to compensate channel effect with Least Square Estimation method. The channel model used is Long Term Evolution (LTE) channel with Technical Specification TS 25.101v2.10 and 5 MHz bandwidth bandwidth including the channels of indoor to outdoor/ pedestrian channel and Vehicular channel. The results showed that the performance of the proposed system was better when the LDPC was used as a coding technique

Channel Identification Using Chaos for an Uplink/Downlink Multicarrier Code Division Multiple Access System

A scheme of chaotic spreading sequence for multicarrier code division multiple access system (MC-CDMA) iproposed to estimate the transmission channel. This systespreads spectrum and identifies the channel, simultaneously. The proposed scheme uses a chaotic sequence generated by a logistic map as a training signal and estimate channel parameters according to dynamics of the chaotic sequence. Encoding data by chaotic sequences is first built and then the orthogonal codes are used to spread the encrypted data for multiusers scheme. At the reception, first the channel parameters are identified using a training chaotic sequence in order to equalize the received data, and then the encrypted information is decoded for the desired user. The studies reveal that the proposed system (chaos plus orthogonal codes) significantly outperforms the Walsh-Hadamard code spreading in MC-CDMA system. The performance of the system is considered in the multiuser case by means of simulation. The simulation result shows that the proposed chaotic code spreading approach for channel identification achieves significant improvement in the channel identification, comparing to using others training sequence or the least square method.

Channel Identification Using Chaos for an Uplink/Downlink Multicarrier Code Division Multiple Access System

A scheme of chaotic spreading sequence for multicarrier code division multiple access system (MC-CDMA) is proposed to estimate the transmission channel. This system spreads spectrum and identifies the channel, simultaneously. The proposed scheme uses a chaotic sequence generated by a logistic map as a training signal and estimate channel parameters according to dynamics of the chaotic sequence. Encoding data by chaotic sequences is first built and then the orthogonal codes are used to spread the encrypted data for multiusers scheme. At the reception, first the channel parameters are identified using a training chaotic sequence in order to equalize the received data, and then the encrypted information is decoded for the desired user. The studies reveal that the proposed system (chaos plus orthogonal codes) significantly outperforms the Walsh- Hadamard code spreading in MC-CDMA system. The performance of the systemis considered in the multiuser case by means of simulation. The simulation result shows that the proposed chaotic code spreading approach for channel identification achieves significant improvement in the channel identification, comparing to using others training sequence or the least square method.

Higher Order Cumulants for Identification and Equalization of Multicarrier Spreading Spectrum Systems

This paper describes two blind algorithms for multicarrier code division multiple access (MC-CDMA) system equalization. In order to identify, blindly, the impulse response of two practical selective frequency fading channels called broadband radio access network (BRAN A and BRAN E) normalized for MC-CDMA systems, we have used higher order cumulants (HOC) to build our algorithms. For that, we have focussed on the experimental channels to develop our blind algorithms able to simulate the measured data with high accuracy. The simulation results in noisy environment and for different signal to noise ratio (SNR) demonstrate that the proposed algorithms are able to estimate the impulse response of these channels blindly (i.e., without any information about the input), except that the input excitation is i.i.d. (identically and independent distributed) and non-Gaussian. In the part of MC-CDMA, we use the zero forcing and the minimum mean square error equalizers to perform our algorithms. The simulation results demonstrate the effectiveness of the proposed algorithms.

Maximal (v, k, 2, 1) Optical Orthogonal Codes with k = 6 and 7 and Small Lengths

Optical orthogonal codes (OOCs) are used in optical code division multiple access systems to allow a large number of users to communicate simultaneously with a low error probability. The number of simultaneous users is at most as big as the number of codewords of such a code. We consider (v,k,2,1)-OOCs, namely OOCs with length v, weight k, auto-correlation 2, and cross-correlation 1. An upper bound B0(v,k,2,1) on the maximal number of codewords of such an OOC was derived in 1995. The number of codes that meet this bound, however, is very small. For k≤5, the (v,k,2,1)-OOCs have already been thoroughly studied by many authors, and new upper bounds were derived for (v,4,2,1) in 2011, and for (v,5,2,1) in 2012. In the present paper, we determine constructively the maximal size of (v,6,2,1)- and (v,7,2,1)-OOCs for v≤165 and v≤153, respectively. Using the types of the possible codewords, we calculate an upper bound B1(v,k,2,1)≤B0(v,k,2,1) on the code size of (v,6,2,1)- and (v,7,2,1)-OOCs for each length v≤720 and v≤340, respectively.

Performance Analysis of Coherent Source SAC OCDMA in Free Space Optical Communication Systems

In this paper, we investigate the performance of spectral amplitude coding optical code division multiple access (SAC OCDMA) systems under the effect of beat noise and turbulence. Three different multi-laser source configurations are considered in this analysis: shared multi-laser, separate multi-laser, and carefully controlled center frequency separate multi-laser. We demonstrate through Monte Carlo simulation that the gamma–gamma probability density function (pdf) cannot adequately approximate the measured intensity of overlapping lasers and that an empirical pdf is required. Results also show it is possible to achieve error-free transmission at a symmetrical data rate of 10 Gbps for all active users when only beat noise is taken into account by precisely controlling the center frequencies. However, only 30% of the active users can be supported when both beat noise and turbulence are considered.