Code Division Multiple Access Networks Research Articles

Implementation of Shared Laser–LED Sources in a Free Space Optics (FSO) Network under Environmental Impact

This paper is devoted to evaluating the combined coherent and incoherent sources (CCIS) technique for different applications in the optical domain and future optical code division multiple access (OCDMA) networks. Spectral amplitude coding (SAC) has gained significant attention in optical processing systems due to its increased capabilities in dealing with multiple-access interference (MAI) efficiently. Fixed right shift (FRS) is adopted as a signature code in this study. Furthermore, performance analysis is studied in terms of bit error rate (BER) for the system using CCIS in both the free space optics (FSO) and sky mesh network using an aerial altitude platform system (AAPS). Simulation results confirmed that a CCIS design significantly improves system performance with moderate cost. An acceptable BER value of 10−9 at 1.25 Gbps data rate and 60 km, 38 km, and 6 km distances for the laser, CCIS, and LED sources, respectively, can be supported. In particular, at Q-factor ~4.5, the FSO ranges under low haze, moderate haze, and heavy haze are, respectively, 3.7 km, 2.5 km, and 1.5 km. The reason is that a CCIS design causes an increase in the effective transmitted power. It can be summarized that a CCIS design can provide reliable solutions and an affordable cost for future optical fiber and wireless network applications.

Two code keying using optical CDMA system with 2D multi-method codes

We propose a novel family of two-dimensional multi-methods with two codes keying (2D MM with TCK) in spectral amplitude coding optical code division multiple access (OCDMA) networks. The idea transfers one code keying (OCK) of one-dimensional (1D) MM codes into two code keying (TCK) of 2D MM codes. The rationale has OCK transferred into TCK, 2D matrix formulations using the 2D MM codes, and modified cross-correlation. The research solution resolves the first item using two OCKs of 2D MM codes to become TCK of 2D MM codes to call 2D MM codes with TCK, the second item using two sets of 1D MM codes to produce 2D matrix formulations using 2D MM codes, and the third item using the cross-correlation to transfer into a modified cross-correlation. The modified cross-correlation eliminates multiuser interference. The proposed analysis utilizes a modified photocurrent to suppress phase-induced intensity noise. In the numerical results, the number of simultaneous users, data transmission rate, and effective source power using 2D MM codes with TCK are 294, 4.72 Gbps, and − 12 dBm, respectively.

Linear programming-aided power allocation for large OCDMA networks

To provide a suitable operation in optical code division multiple access (OCDMA) networks, it is paramount to balance the powers received at the destination optical node. This work presents a solution strategy for the power allocation (PA) problem in OCDMA by rewriting it as a linear programming (LP) problem and applying two LP methods based on the Simplex method and the Interior Point method (IPM). Such LP methods proposed in the PA OCDMA context were compared with two methods available in the literature: a) hybrid ALPSO PA method, which is based on the particle swarm optimization (PSO) strategy combined with the augmented Lagrangian (AL) analytical method and the solver GUROBI; b) the high-complexity benchmark solution matrix inversion method (MIM), which is used to verify the quality of the Simplex and IPM solutions. Numerical result reveal the effectiveness and efficiency of both LP methods when compared with other competitive methods. Numerical results in terms of floating-point operations (FLOPS), normalized mean squared error (NMSE), convergence, and the evolution of the allocated power reveal the effectiveness and efficiency of both LP methods when compared with the literature methods, mainly under higher network dimensions (K≥32 optical nodes), achieving better accuracy-complexity tradeoffs. For 32≤K≤512 users, the IPM has resulted in perfect feasibility (F=0) and little complexity, i.e., an order less in terms of Flops than Simplex, twice to five times less than MIM procedure, and at least four orders less complexity than the hybrid analytical-heuristic ALPSO method.

Multiservice transmissions in optical code-division multiple access networks of spectral amplitude coding based on hypothesis testing and multiple chip decoding

I propose a multiservice scheme in optical code-division multiple access (OCDMA) networks by adapting hypothesis testing to a receiver design of multiple chip decoding. Each transmitted bit of a single user is divided into several time-domain chips carrying an identical spectral amplitude coding (SAC) signature. Multiservice transmissions are achieved by assigning the users with different chip numbers based on the user classes. Hypothesis testing is employed to derive the required chip number supporting the desired bit-error rate (BER) performance. Numerical results have shown that efficient BER classifications are achieved among distinctive classes for multiple conditions of user numbers and power levels. The proposed multiservice scheme can be transparently applied to SAC-OCDMA systems with existing optical codes and various user class numbers.

Phase Carrier approach based on Optical Code Division Multiple Access Networks

A technique for optical code-division multiple-access (OCDMA) spectral amplitude coding is proposed and analyzed. The proposed approach is based on combining both OCDMA systems over a phase carrier. Compared with conventional OCDMA systems, this approach exhibits numerous advantages such as simplicity in the system design and cost efficiency. The phase shift based on phase modulation is adopted in the proposed system, and the orthogonal function based on the random diagonal code is applied. The proposed scheme is considered cost-effective because only one laser source is used; which minimizes interference for access network passive optical network applications and improves the system performance of bit-error rate (BER 10-12).

Numerical Modeling of Smartphones with WCDMA, LTE, and WLAN Bands for Epidemiological Studies

This paper presents the representative numerical modeling of smartphones with wideband code division multiple access (WCDMA), long-term evaluation (LTE), and wireless local area network (WLAN) bands for epidemiological studies. For this purpose, based on specific absorption rate (SAR) test reports for commercial smartphones released in South Korea from 2013 to 2019, we determined the smartphone size, frequency band categorization, antenna locations, and target 1-g peak-spatial SAR (psSAR) values for a specific anthropomorphic mannequin (SAM) phantom. Numerical results showed that the designed numerical smartphone models yielded good matching and radiation performance, and more importantly, their 1-g psSAR values were within ±16% of the target 1-g psSAR values.

Enhanced overloaded code division multiple access for network on chip

The Code-division multiple access (CDMA) method is commonly used as the network infrastructure in multi-core chips. One of its advantages is the simultaneous connection of all network components. Another advantage is the constant delay of this method. On the other hand, one drawback is that the number of transmitters is limited to the number of encoding bits. In this study, the authors used the combination of Walsh codes and their inverses, as well as the simultaneous application of the time-division multiple access (TDMA) method, to increase the transmission capacity of this protocol more than four times the standard mode. In the proposed design, although the circuit area does not increase significantly, a fourfold increase in the throughput of the CDMA network is seen. Using the method proposed in this study, it will be possible to increase the capacity further.

A New Hybrid Prime Code for OCDMA Network Multimedia Applications

This paper presents a new family of spreading code sequences called hybrid prime code (HPC), to be used as source code for the optical code division multiple access (OCDMA) network for large network capacity. The network capacity directly depends on the number of available code sequences provided and their correlation properties. Therefore, the proposed HPC is designed based on combining two or more different code words belonging to two or more different prime numbers. This increases the number of code sequences generated. The code construction method utilized allows the generation of different code sets, each with different code length and weight, according to the number of prime numbers used. In addition, the incoherent pulse position modulation (PPM) OCDMA system is proposed based on the HPC code. Furthermore, the bit error rate (BER) performance analysis is introduced versus the received optical power and the number of active users. Moreover, the error vector magnitude (EVM) is calculated versus the optical signal-to-noise ratio. This work proves that using two prime numbers simultaneously generates far more codes than using prime numbers separately. It also achieved an OCDMA system capacity higher than the system that uses the optical orthogonal codes (OOCs), modified prime codes (MPCs) families, and two code families with separate simultaneously prime numbers, at a BER below 10−9 which is the optimum level.

Noncoherent optical CDMA system of 2-D subtracted square codes using two code keying by eliminating the multiple use interferences

We propose the new two-dimensional subtracted square (SS) codes to achieve the new family in the spectral amplitude coding (SAC) optical code division multiple access (OCDMA) networks. The proposed codes give the multiplication between the 1-D subtracted square codes and 1-D subtracted square codes to become the code sequences of the 2-D SS codes. The proposed structure using the 2-D SS codes constructs the proposed transmitter and proposed receiver to build the code sequences of the 2-D SS codes and recovered bits using the modified cross-correlation, respectively. The proposed transmitter activates the 2-D SS codes to convert the code sequences of the 2-D SS codes. The proposed receiver gets the code sequences of the 2-D SS codes to decode the recovered bits, which cancel the interferences in the powers called the multiple user interferences (MUI). The proposed receiver transfers the cross-correlation to the modified cross-correlation, which eliminates the MUI. The modified cross-correlation takes the photodiodes to suppress the phase-induced intensity noise (PIIN), simultaneously. In numerical results, the bit error rate (BER) gets the number of the simultaneous users in the proposed system using the 2-D SS codes to accomplish the all users with 84 users. And the BER takes the data transmission rate in the proposed system using the 2-D SS codes to attain the 7.1 Gbps.

Halton-Chaos and ALPSO power allocation methods for passive optical CDMA networks

The allocation of minimum power with guarantee of minimum rate in passive optical network optical code division multiple access (PON-OCDMA) networks is analyzed considering heuristic optimization methods such as Particle Swarm Optimization (PSO) and four variants. The base of the power-rate adaptive PON-OCDMA is the multi-length 2-D wavelength-hopping/time-spreading code called multiple-length extended wavelength-hopping prime code (MLEWHPC) to support the services of different media in accordance with the bit-rate and quality of service (QoS). The Halton-Chaos-β-PSO (HC-PSO) algorithm is proposed for solving the optimal power and rate allocation in order to maximize the EE of the optical system, subject to QoS restrictions based on the signal-to-interference plus-noise ratio (SINR) in each class of optical user and minimum required power. The proposed HC-PSO and the analytical–iterative–heuristic approach based on the augmented Lagrangian and PSO (ALPSO) method demonstrate promising performance-complexity trade-off, specially for high dimensionality OCDMA systems. The proposed hybrid analytical-evolutionary resource allocation method is corroborated by numerical simulation results, considering the tuning of heuristic evolutionary input parameters, which have demonstrated to improve the EE of the optical system when the power-rate allocation procedure is deployed dynamically in real time applications.

Optimal Power Allocation for Cooperative Pattern Division Multiple Access Systems

This study focuses on the power allocation (PA) problem in code division multiple access (PDMA) networks with amplify-and-forward (AF) relays. We provide two wireless communication technical performance indexes, which are system throughput and outage probability. A multiobjective version of particle swarm optimization is proposed to solve Pareto-optimal solutions for optimal PA problems. A novel programming model is built based on improvement of constraint functions, and the accuracy and efficiency of solution can be improved via compact constraints. The technique for order preference by similarity to an ideal solution is proposed to balance the performance indicators, which include outage probability and system throughput. It has been calculated that the proposed approach for optimal PA is verified and performs better than a genetic algorithm approach.

Energy and spectral efficiency trade-off in OCDMA-PON assisted by non-linear programming methods

Two important metrics for performance evaluation in optical code division multiple access networks (OCDMA) are energy efficiency (EE) and spectral efficiency (SE). Both metrics are investigated in this work through the bi-objective optimization approach by analyzing the trade-off between SE and EE. We first formulate the SE–EE optimization as a bi-objective optimization (BOO) problem with minimum rate requirement constraints. Then, considering the non-convexity of the BOO problem, it is converted into a single-objective optimization (SOO) problem by utilizing weighted sum method. Nonlinear programming methods as sequential quadratic programming method (SQP) and majoration–minimization (MaMi) are applied to solve the BOO problem, with QoS guarantees for the OCDMA networks. Resource efficiency (RE) is able to explore the trade-off between EE and SE in OCDMA networks. The optimization methods were applied and their performance-complexity trade-offs are compared with the exhaustive search (ES) method. Numerical results were performed considering practical and realistic scenarios, including a wide range of nodes, while the solutions obtained by the methods are represented in the Pareto front.

Performance analysis of incoherent PPM‐OCDMA networks based on optimised modified prime code for multimedia applications

This study presents the design analysis and correlation properties of a new spreading code for the incoherent synchronous pulse position modulation-optical code division multiple access (PPM-OCDMA) networks. The proposed code called optimised modified prime code (OMPC), which refers to the modified prime codes (MPCs) family. Additionally, this new code designed at a higher code length, optimised code weight and good correlation characteristics to enhance communication security and improve the bit error rate (BER) performance. In this study, the proposed code is used as source code for different kinds of multimedia services such as data, voice, and video. Furthermore, the characteristics and correlation properties of the OMPC in comparison with the other MPCs families that utilised in the PPM-OCDMA networks are presented. Moreover, for the PPM-OCDMA networks, the effect of OMPC auto- and cross-correlation properties on the multiple access interference (MAI) was investigated. Consequently, the MAI is considered in the BER analysis and calculations. Finally, the results show that the proposed OMPC is better than the other existing codes with respect to the channel capacity and system performance.

Bounds and constructions for multilength variable-weight optical orthogonal codes

Multilength variable-weight optical orthogonal codes (MLVWOOCs) are recently proposed for supporting multirate and integrated multimedia services in optical code division multiple access (OCDMA) networks. In this paper, we consider (N,M,W,1,Q;λ)-MLVWOOCs with λ=2 (the minimum nontrivial intercross-correlation). Some upper bounds on code size are obtained under certain restrictions, an (N,M,W,1,Q;λ) compatible difference packing (CDP) set system is introduced to construct an MLVWOOC, and an equivalence relation between a CDP set system and an MLVWOOC is established. Recursive constructions for MLVWOOCs are also presented. By using cyclotomic classes, disjoint skew starters and recursive constructions, infinite classes of MLVWOOCs with W={3,4} and λ=2 are obtained which are of optimal sizes reaching the upper bounds.

Spectral and energy efficiency tradeoff in optical code division multiple access networks

AbstractA paradigm on the energy efficiency (EE) and spectral efficiency (SE) tradeoff named resource efficiency (RE) exploits the EE‐SE equilibrium, which is formulated as Pareto optimal set based on two objectives balancing power consumption against occupied bandwidth. In optical code division multiple access (OCDMA) networks, the EE‐SE tradeoff is discussed by formulating a multiobjective optimization problem, while solutions are compared by deploying the weighted sum (WS) and ‐Constraint (‐C) scalarization procedures combined with nonlinear programming methods. The generalized RE optimization problem with QoS guarantees for the OCDMA networks is formulated considering that such methods result in the same Pareto boundaries. Theoretical results demonstrate that the obtained numerical optimized solutions are efficient due to the multiobjective characteristics of the optimization problem. Also, considering the numerical tests performed, it is noteworthy that the ‐C procedure found a greater diversity of solutions inside the Pareto front when compared with the WS method.

BER performance of OCDMA system based on optimised 2D PhC passive encoder

This study introduces an accurate design and optimisation of a passive optical code division multiple access (OCDMA) network encoder using the coupled cavity waveguide (CCW) as an optical delay line. Such CCW has the capability of providing more time delay with minimum encoder size. The proposed design and analysis are based on the two-dimensional (2D) photonic crystal (PhC) structure. Additionally, two different 2D-PhC structures are studied, in which a silicon material with an effective refractive index of 3.487 is used. The first structure is a silicon bar in air background, whereas the second one is air holes in a silicon substrate. Furthermore, the behaviour of the proposed 2D-PhC structures is studied over the wavelength, ranging from 1300 to 1600 nm. Since the structure geometry is simple with a clear operating principle, it is sufficient to use in the photonic integrated circuits. Moreover, the performance analysis of such design is investigated in terms of the bit error rate (BER) calculations. Finally, the results showed that a 21% BER performance enhancement was achieved using the optimised silicon bars in air background encoder model and this model can be utilised for the multimedia applications in the OCDMA networks.

Performance analysis of OCDMA wireless communication system based on double length modified prime code for security improvement

In this study, a construction analysis and design of a new spreading code set are presented. This code is designed to be used as a source code in optical wireless communication (OWC) system to achieve better performance and security enhancement. The new proposed code is called double length modified prime code (DLMPC), which is constructed based on the popular modified prime code that is commonly applied in the optical code division multiple access (OCDMA) networks. The correlation properties and characteristics of the DLMPC are investigated in this study. Based on the new code, the OWC system architecture and channel model are illustrated and further analysed. Additionally, the transmitted and received data bits encoding and decoding scenarios are discussed. Moreover, a low power consumption optical light source and photo-detector are utilised for a transmitter and receiver, respectively. The overall OWC performance in terms of the bit error rate (BER) has been evaluated considering the multi-user interference as the only source of noise. Finally, the results show that the proposed DLMPC outperforms the popular codes with respect to the channel capacity, security, and system BER performance.

A mixed construction of variable-weight optical orthogonal code for optical code division multiple access networks

Optical orthogonal codes play an important role in optical code-division multiple access systems. In order to support heterogeneous quality of service, it is of interests to employ optical orthogonal codes in which different codewords may have different Hamming weights. In this paper a construction method of variable-weight optical orthogonal codes combining meta-heuristic search algorithm and combinatorial block designs is studied. This method is capable of producing variable-weight optical orthogonal codes with large and flexible parameters. We construct three infinite families of optimal variable-weight optical orthogonal codes using the proposed method.

New asymptotically optimal three-dimensional wave-length/space/time optical orthogonal codes for OCDMA systems

We present new families of three-dimensional (3-D) optical orthogonal codes for applications to optical code-division multiple access (OCDMA) networks. The families are based in the extended rational cycle used for the 2-D Moreno-Maric construction. The new families are asymptotically optimal with respect to the Johnson bound.

CDMA design for on-Chip Communication Network

Network on chip is used to implement the communication features on a Silicon chip. To increase the performance of Code Division Multiple Access (CDMA) Network On Chip (NOC) ,a Standard-basis (SB) Method is Proposed.In this Method, a source code from various transmitters are encoded separately using an orthogonal code . These coded data are Combined together by an Exclusive-OR operation and it is then sent to their destinations through the communication interface.By Performing AND operartion between original coded data and their Orthogonal code, chip sequence can be obtained. The Standard basis (SB) encoding and decoding technique is compared with the Walsh Based (WB) code in terms of power, area and throughput and the Proposed Standard basis encoding and decoding technique is proven to be more efficient.