Code Division Multiple Access Scheme Research Articles

Wheel-Based MDM-PON System Incorporating OCDMA for Secure Network Resiliency

Wheel-based network resilience passive optical network (PON) based on mode division multiplexing (MDM) can be integrated with optical code division multiple access (OCDMA) schemes efficiently for the fixed and backhaul traffic under normal and break/failure fiber operating conditions. In this work, a bidirectional 10/2.5 Gbit/s hybrid MDM-OCDMA-PON system using multi-weight zero cross-correlation (MWZCC) code is proposed. Donut modes 0 and 1 are incorporated by the MDM technique in the proposed system. The benefit of this work is to offer an inexpensive, high-bandwidth and advanced long-haul network with satisfactory resource utilization ability for fiber links with protection against faults and to improve the reliability along with survivability of the network. The simulation results show the successful realization of the multimode fiber (MMF) link at 1.6 km in the uplink and 1.2 km in the downlink directions under an acceptable bit error rate (BER). The minimum accepted received power of −31 dBm in uplink and −27 dBm in downlink over 1 km link at 10/2.5 Gbit/s rate is obtained. Moreover, the minimum received power of −20 dBm in uplink and −30 dBm downlink is achieved by using MWZCC code compared to other codes handling 58 simultaneous end users. Further, the influence of fiber impairments and connected devices on the proposed approach is numerically evaluated. Moreover, it is shown that the wheel based proposed approach performs well than other topologies for the bidirectional network resilience transmission.

Achievable Rates and Resource Allocation for CDMA-Based Overlay Cognitive Radio With RF Energy Harvesting

This article introduced a cognitive wireless powered communication network with an uplink (UL) code-division multiple access (CDMA) scheme consisting of one hybrid access point (H-AP) and multiple energy harvesting secondary users (SUs), which are coexisted with a primary wireless network. The frame structure is coordinated through the two-phase harvest-then-transmit protocol. The energy-limited SUs first harvest wireless energy in the downlink phase and then transmit their information signals simultaneously to H-AP with the CDMA scheme in the UL phase. An overlay spectrum sharing model is also considered where H-AP has access to the primary transmitter's codebook and primary network's channel. Our goal is to maximize the sum-throughput optimization problem of SUs via jointly optimizing power and time allocation. The considered joint optimization problem is generally nonconvex due to coupled variables. As a solution, we first transform it into the equivalent convex form using proper variables and then we solve it using the convex optimization technique. The closed-form solutions for time and power allocations are given. We also confirm from various simulations’ results that our proposed CDMA scheme is superior to the conventional time-division multiple access schemes.

An improved optimal energy aware data availability approach for secure clustering and routing in wireless sensor networks

AbstractMaintaining high residual energy is one of the major challenges of wireless sensor networks (WSNs), where nodes are moving at a random speed. In addition, data availability is also a major concern that must be maintained constantly during the packet transmission phase. In this research work, a Residual‐Energy‐Based Data Availability Approach (REDAA) for WSNs is developed to increase the network lifetime by focusing on the selection of stable routing paths and cluster heads. During the first phase of the work, the network model, and assumptions for route creations are adopted to effectively initialize the data transmission phase. During the second phase, a cluster was formed, and two categories of cluster heads were created based on quadrature low energy adaptive clustering hierarchy (Q‐LEACH) and multi‐hop low energy adaptive clustering (MH‐LEACH) algorithms to formalize the route and to make data available whenever requested. During the third phase, energy conservation routes are initialized, and data gathering is improved through slot‐based code division multiple access schemes. Simulation results demonstrate that the proposed REDAA approach can achieve an improvement in terms of throughput and energy consumption by 37% and 70% respectively when compared to MH‐LEACH approach, whereas in comparison to Q‐LEACH approach, these improvements are found to be 30% and 73% respectively.

Integration of Spatial Modulation Scheme With Code Division Multiple Access for VIVO Based Frequency Selective Nano Sensor Networks

Due to their suitability for human-body based communications, in-VIVO nano sensor networks are envisioned to use the promising Terahertz signals in order to ensure the forthcoming high-rate communication needs of the modern medicine. However, the propagation losses at these frequency bands are quite significant and dependent on the operation frequency as well as on the physiological characteristics, thus impeding the use of Terahertz rates to their utmost benefit. Using numerous emitting elements is likely to improve the quality of the received signal, but gives rise to multi-channel interference (MCI) emanating from multi-antenna signaling reception, which necessitates a relatively complex signal processing to mitigate it. When multiple physiological signals are of interest, detecting them necessitates to mitigate multiple-access interference (MAI). In this perspective, orthogonal frequency division multiplexing (OFDM) allows to combat the channel frequency selectivity, whereas code division multiple access (CDMA) scheme cancels MAI. In this paper, we propose to embed the novel spatial modulation technique with CDMA architecture in an OFDM framework to ensure a viable communication in in-VIVO frequency selective Nano channels. The immunity of our proposed solution to such an interference is confirmed, since less than −2 dB in SNR level is required to support 5 users simultaneously communicating with a BER which is inferior to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${10}^{-{3}}$ </tex-math></inline-formula> when the operating frequency is equal to 1THz. This hybrid scheme is shown to efficiently combat the MCI while enabling a safe retrieval of the useful signal at the very-high data rate communications.

Enhancement of code division multiple access system performance using raptor codes

Some kinds of communication systems work in very low signal-to-noise (LSNR) environments. For these systems to function reliably, &lt;span&gt;specific techniques and methodologies have to be used to mitigate the degrading effects of the channel. The channel coding method is the key element in most LSNR communication systems, but emphasizing the code division multiple access (CDMA) is a new transmission technique in these channels. To enhance the CDMA scheme's system capacity and reach unprecedented ranges of LSNR values in wireless sensor network. This paper suggests combining CDMA with certain types of channel coding algorithms, such as the raptor codes. The raptor channel encoding technique has improved the CDMA system's performance when using binary phase-shift keying (BPSK) modulation in additive white gaussian noise (AWGN) channels. It has achieved a low bit error rate in range of 10-7 at Eb/No value of (-3) dB and about 10-6 at shannon's limit. The Raptor-coded CDMA scheme works well for channel signal to noise ration (SNR) values of greater than -9 dB, showing an improvement of about 7 dB compared with turbo/convolutional channel coding methods used with the CDMA system bit error rate (BER) and throughput. On the other hand, it has been shown that the convolutional encoder presents the weakest performance compared to both the turbo and raptor codes.&lt;/span&gt;

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.

Fault detection and location in power distribution systems: The usefulness of the HS-OFDM scheme for time-domain reflectometry

This study discusses key characteristics and benefits of using time-domain reflectometry (TDR) systems based on the Hermitian symmetric orthogonal frequency-division multiplexing (HS-OFDM) scheme for fault detection and location in power distribution networks. In this context, a system model with power line modems injecting signals and capturing reflections in a power distribution network is outlined. Next, two reflectogram processing approaches, namely digital pulse compression and channel estimation, are examined. Also, the effects of different parametrizations and multiple access schemes on the performance of the HS-OFDM-based TDR system are addressed. Numerical results confirm that HS-OFDM-based TDR systems making using of channel estimation outperforms their counterparts based on pulse compression. The frequency range for narrowband power line communication provides fair range resolution and maximum unambiguous range values. Also, it is seen that the use of frequency-division multiple access schemes implies different signal-to-interference-plus-noise ratio (SINR) performance among different power line modems (PLMs) connected to a power distribution network. Time-division and code-division multiple access schemes, on the other hand, provide fair SINR performance among the PLMs at the cost of obtaining a small number of reflectograms during a time interval.

Integrating ultra-wideband and free space optical communication for realizing a secure and high-throughput body area network architecture based on optical code division multiple access

Nodes in a body area network (BAN) are miniature wearable or implantable battery-powered wireless sensors which continuously transmit real-time vital physiological data of a patient to remote health-care center while remaining in close proximity to the human body. Therefore, BAN nodes should have the features of high data rates and low transmit powers to protect the human body, environment and bio-medical equipment from harmful exposure of electromagnetic radiations and electromagnetic interference (EMI). Ultra-wideband (UWB) signals have low allowable transmission power and high data rates. Therefore, we propose a low cost, low powered and secure optical body area network (OBAN) composed of four UWB-BAN nodes each transmitting at a data rate of 30 Mbps. At the control node, UWB signals from UWB-BAN nodes are encoded using spectral amplitude coding-optical code division multiple access (SAC-OCDMA) scheme and the combined signal is transmitted over free space optics (FSO) channel towards remote health-care center. At the health-care center, the combined signal is decoded and UWB signal of each UWB-BAN node is photo-detected for analysis of patient’s data. Log-normal channel model is considered between control node and the health-care center. The signal received from each UWB-BAN after propagation through the FSO channel is analyzed through Bit error rate (BER) results. Similarly, cost efficiency of the proposed architecture is also evaluated through a detailed cost analysis. It was observed that the proposed architecture requires the UWB-BAN nodes to have low receiver sensitivities with the added benefits of cost-efficiency and data security.

Construction of Z-Complementary Code Sets With Non-Power-of-Two Lengths Based on Generalized Boolean Functions

$Z$ -complementary code set (ZCCS) plays a major role in modern communication systems. It has applications in multi-carrier code-division multiple access (MC-CDMA) scheme, channel estimation in multiple-input and multiple-output (MIMO) systems, etc. In this letter, we propose a construction of $q$ -ary ZCCS of a length of the form $2^{m}+2$ using generalized Boolean functions (GBFs). The constructed ZCCS is optimal with respect to the theoretical upper bound. Based on the authors’ knowledge, all the existing constructions of ZCCSs based on GBFs are limited to the lengths of power-of-two only.

Super-Sparse On-Off Division Multiple Access: Replacing Repetition With Idling

A very low-complexity on-off division multiple access (ODMA) scheme is proposed for $K$ -user non-orthogonal multiple access (NOMA) systems. At the transmission side, each user employs the same length- $m$ channel code whose coded bits, after modulation, are sent in a random time-hopping manner. Specifically, $m$ coded bits are randomly scheduled and sent using $n$ time slots with $n\gg m$ , i.e., only $m$ slots are used for signal transmission and the other $n-m$ slots are idle. The slot selection, referred to as an on-off pattern, is unique to each user, and it is the only means of user separation. Consequently, at each time slot only a very few users (i.e., 2 or 3) may simultaneously access the channel, leading to a super-sparse access system. Due to the sparse access property, a very low-complexity iterative multi-user decoding method can be implemented on an almost tree-like factor graph. Compared with existing iteratively decodable code division multiple access (CDMA) schemes, such as sparse-CDMA and interleave division multiple access (IDMA), ODMA does not rely on repetition (spreading) or user interleaving. In fact, we show that in using extrinsic information transfer (EXIT) analysis and simulation, idling is more effective than repetition in terms of enhancing the multi-user iterative decoding performance. By replacing repetition with idling, a remarkable multi-user decoding performance gain is achieved and, at the same time, the decoding complexity is significantly reduced.

Design and Performance analysis of data encrypted two dimensional coding technique for wavelength hopping time spreading Optical CDMA

This paper presents a novel two dimensional (2D) wavelength/time (W/T) code with zero cross correlation property to minimize the multiple access interference (MAI) referred as two dimensional multi-diagonal prime hop code (2D MDPHC) in optical fiber network. This 2D MDPHC code is constructed using various features of two different one dimensional (1D) codes i.e. multi-diagonal code (MD) and prime code (PC). The proposed 2D MDPHC code is generated using java software version 8.1 and implemented in an optical system using the optisystem software version 14 for the spectral amplitude coded optical code division multiple access (SAC-OCDMA) scheme. The proposed 2D MDPHC code exhibits zero cross correlation property which reduces the multiple access interference (MAI) and improves system performance. Simulation results reveal that the OCDMA system based on the proposed 2D MDPHC code can accommodate large number of simultaneous users with higher data rate transmission, lower bit error rates (BER) and longer travelling distance without compromising the signal quality as compared to the existing SAC-OCDMA codes. Further, security provision at the photonic layer of the OCDMA network is addressed by transmitting the data through a novel encrypted circuit in order to prevent the hacking by an eavesdropper or by an unauthorized user to disrupt the communication.

Capacity Enhancement using Game Theory-Based Power Assignment for 5G Cellular Network

The increasing demand for high data rate services necessitates technology advancement and adoption of beyond 4G termed as 5G cellular standards. In this paper, game theory-based power assignment for capacity enhancement is investigated for 5G cellular network. Specifically, in this work, we analyze a multiple input and multiple output (MIMO) multi-carrier (MC) code division multiple access (CDMA) scheme as a possible air interface for next generation wireless network with capacity enhancement techniques. A pricing methodology and two non-cooperative MIMO power control games using recreation hypothesis are proposed in this work. The study shows that the proposed pricing scheme and power control games prove to be powerful techniques for attaining an enhanced performance as it results in 10% growth in equilibrium with less power usage in a MIMO MC-CDMA uplink communication.

A New Polarization-SAC Scheme Suitable for Compact OCDMA-FSO Networks

A free-space optics communication network with the mitigation of multiuser interference was developed on the basis of a polarization spectral amplitude coding (P-SAC) optical code division multiple access (OCDMA) scheme. With the cyclic property of the used cyclic ternary perfect codes, a common codec can be constructed using the arrayed waveguide grating routers. Moreover, the complementary keying and polarization encoding schemes could both be applied to generate superior spectral efficiencies. According to a theoretical analysis, our P-SAC OCDMA-based network design outperformed those of previous networks.

Collaborative Reader Code Division Multiple Access in the Harmonic RFID System

Reading reliability is a critical aspect in the ultrahigh-frequency radio frequency identification (RFID) system when a large amount of tags are in the reading zone with complex multi-path interferences. The read failure incidences can be caused not only by the random tag position and orientation but also by the RF shadowing of other objects and tags, both of which can misalign the main lobes of the tag and reader antennas. To increase the system coverage and total read yield in practical indoor ambient, a possible solution is to employ multiple readers with overlapping reading zones. However, when the tags are within the reading zones of multiple readers, the conventional tag singulation protocol will suffer serious reader-to-reader collision (R2RC) unless the conflicting readers can agree on proper collaborative time or space division schemes. The uncertain delay of the time division multiple access and the lack of definitive time sequence can further affect the reading process, especially when the RFID system is employed for applications requiring real-time accessing, tracking, and sensing. In this paper, we introduce a collaborative reader code division multiple access (CDMA) protocol in the harmonic RFID system, which provides synchronous tag access for all readers within range. The tag can distinguish the downlink commands from multiple readers simultaneously and then formulate the response accordingly. The proposed reader CDMA is demonstrated in a simple experimental prototype to verify R2RC resolution and read yield improvement. The tworeader collaborative CDMA scheme achieved below 10−5 in the read failure rate when individual readers had 0.05 – 0.2 failure rates in the complex multi-path scenarios due to rich channel exploitation and anti-correlation in the failure incidences.

A PSSS Approach for Wireless Industrial Communication Applying Iterative Symbol Detection

Wireless industrial communication requires high reliability and low latencies. In order to fulfill both requirements simultaneously, wireless approaches are being developed. One of these technologies is parallel sequence spread spectrum (PSSS). In comparison to direct sequence spread spectrum approaches, which employ a set of appropriate pseudonoise (PN) sequences, PSSS data symbols are spread based on a single cyclically shifted m -sequence. Each cyclic shift of the chosen m -sequence is used as an individual PN-sequence. This enables a code division multiple access (CDMA) scheme with simple processing and thus, a fast hardware implementation. In order to investigate the impact of an inaccurate time synchronization, this paper presents a theoretical and simulative PSSS evaluation. Moreover, an iterative symbol detection is introduced, which neutralizes the impact of the nonorthogonal m -sequences and mitigates the degradation due to inaccurate synchronization. In addition, several reasonable resource allocation schemes are presented, which emphasize the PSSS systems flexibility.

A CDMA system implementation with dimming control for visible light communication

Visible light communication (VLC), using solid-state lightings to transmit information, has become a complement technology to wireless radio communication. As a realistic multiple access scheme for VLC system, code division multiple access (CDMA) has attracted more and more attentions in recent years. In this paper, we address and implement an improved CDMA scheme for VLC system. The simulation results reveal that the improved CDMA scheme not only supports multi-users’ transmission but also maintains dimming value at about 50% and enhances the system efficiency. It can also realize the flexible dimming control by adjusting some parameters of system structure, which rarely affects the system BER performance. A real-time experimental VLC system with improved CDMA scheme is performed based on field programmable gate array (FPGA), reaching a good BER performance.

Broadband acoustic local positioning system for mobile devices with multiple access interference cancellation

This paper presents an Acoustic Local Positioning System (ALPS) suitable for indoor localization of mobile devices, based on the transmission of high frequency Code Division Multiple Access (CDMA) audio signals from a fixed beacon network to a tablet computer. The system permits positioning of the device (and the user carrying it) within a few centimeters, which is accurate enough for most location-based applications. It also implements a CDMA scheme for localization, including compensation for the limited transmission frequency band of the sensors which causes Intersymbol Interference (ISI), as well as Multiple Access Interference (MAI) between the different beacons. Signal reception, processing and estimation of position all take place within the tablet, operating at real time and with an update rate of 2 Hz. Experimental results show that the MAI/ISI compensation algorithm increase both the system’s robustness (availability ⩾90%) and accuracy (errors ⩽10 cm) under adverse circumstances such as near-far effect or noisy conditions.

Mitigation of co-channel interferences in cognitive multi-carrier code division multiple access system by singular value decomposition techniques

Efficient spectrum usage is important criteria for next generation wireless systems. In this paper, to utilize the spectrum in useful manner, cognitive radio approaches are used along with multi-carrier code division multiple access schemes (MC-CDMA). But MC-CDMA systems are greatly affected by co-channel interference (CCI). To mitigate CCI interference, multi-user detection (MUD) technique is the design choice. When the user population increases complexity level of MUD algorithms are increases linearly. Also power consumption of mobile station also increases. Hence as a design alternate, in this paper we developed a singular value decomposition based pre-processing approaches to mitigate CCI interferences. The proposed technique is tested with real time channel models and the result shows that superior performance obtained with proposed techniques.

An Efficient Method to Reduce an MAI’s Effect in Spectral Amplitude Coding OCDMA Network

Multiple access interference (MAI) in spectral-amplitude coding, optical code division multiple access (SAC-OCDMA) scheme hardly limits the system performance. This problem increases proportionally with the amount of concurrent users. In addition, phase induces intensity noise (PIIN) coming from the spontaneous emission process of light source is extra impairment leads to system drop needs to be tackled too. Towards overcome the specified problems, vector combinatorial (VC) codes which based on grouping of certain vectors is proposed. Any positive integer number can be used in both weighs and user parameters in code building procedure, these technique nominees our code to be a potential reliable applicant for future optical communication schemes. Such flexibility is an exceptional property for VC compared to SAC-OCDMA counterparts’ codes. Compared with the systems employing Hadamard, Modified Frequency Hopping (MFH), Modified Quadratic-Congruence (MQC), and Modified Double Weight (MDW), numerical results show that, the VC is effective to reduce the power of MAI and PIIN. It has been exposed that, performance can be superior significantly when VC is used.

An Efficient Method to Reduce an MAI’s Effect in Spectral Amplitude Coding OCDMA Network

Multiple access interference (MAI) in spectral-amplitude coding, optical code division multiple access (SAC-OCDMA) scheme hardly limits the system performance. This problem increases proportionally with the amount of concurrent users. In addition, phase induces intensity noise (PIIN) coming from the spontaneous emission process of light source is extra impairment leads to system drop needs to be tackled too. Towards overcome the specified problems, vector combinatorial (VC) codes which based on grouping of certain vectors is proposed. Any positive integer number can be used in both weighs and user parameters in code building procedure, these technique nominees our code to be a potential reliable applicant for future optical communication schemes. Such flexibility is an exceptional property for VC compared to SAC-OCDMA counterparts’ codes. Compared with the systems employing Hadamard, Modified Frequency Hopping (MFH), Modified Quadratic-Congruence (MQC), and Modified Double Weight (MDW), numerical results show that, the VC is effective to reduce the power of MAI and PIIN. It has been exposed that, performance can be superior significantly when VC is used.