Search

Summary: As the core technology of mobile communication system, multiple access technology directly determines the performance and capacity of the system. However, with the rapid growth of the number of mobile communication system users and the high rate service demand, these orthogonal multiple access technologies are limited by the spectrum efficiency and access capacity, so it is difficult to meet the future mobile communication demand. Therefore, for the fifth generation mobile communication system (5G), the research of non‐orthogonal multiple access (NOMA) technology to effectively improve the system capacity has been widely concerned. The purpose of this paper is to analyze the influence of interference and power distribution on system performance simulation based on the simulation results of two most representative NOMA technologies, sparse code division multiple access (SCMA) and NOMA. This paper firstly briefly analyzes the SCMA system model and key technologies and, on this basis, introduces the SCMA system simulation platform, including basic platform parameters and platform simulation flow chart. Furthermore, the influence of adaptive modulation coding on the performance improvement of SCMA system is analyzed by simulation. Then, based on the NOMA system model, this paper carried out the research on fairness among NOMA users. Based on Lagrange multiplier method, this paper simulates fairness under the restriction of power allocation optimization algorithm, the number of users in different area, different radius and different transmission power, the village of village fair index, the change of the frequency spectrum efficiency and energy efficiency curve, the throughput rate between 0.8 and 1.4 changes, and the conclusion that has a guiding significance for NOMA system design. [ABSTRACT FROM AUTHOR]

Increasing demand for mobility and high data rates has brought more attention and the need for wireless technologies. Ultra-Wide Band (UWB) waveforms have the ability to deliver megabits of information while maintaining a low average power consumption. Since UWB systems operates under the noise floor, they are an excellent choice to solve the problem of radio frequency (RF) congestion. But, UWB communication systems experience severe Inter Symbol Interference (ISI) due to the existence of the long root-mean square delay spread of UWB channels. Hence, employing a rake receiver is essential to minimize the effect of ISI, as the various multipath components of the UWB channel are resolvable and carry important information. A more effective rake receiver scheme is the MMSE rake receiver which has shown better performance in Wideband Code Division Multiple Access (WCDMA) systems. Since the selection of optimal subset of multipath components is crucial in MMSE rake receivers, this paper proposes a Genetic Algorithm (GA) based optimum finger selector for a Minimum Mean Square Error (MMSE) rake receiver in a Direct Sequence-Code Division Multiple Access (DS-CDMA) UWB system. The proposed GA based MMSE Rake outperforms the conventional Maximal Ratio Combining (MRC) rake receiver. The simulation results also show that by adding a simple 3-tap linear equalizer on a 10 finger MMSE Rake, it is possible to achieve almost the same Bit Error Rate (BER) performance as an MRC A-Rake receiver which requires hundreds of fingers. [ABSTRACT FROM AUTHOR]

In this paper an adaptive mapping technique (AMT) is proposed for spectral amplitude coding-optical code division multiple access (SAC-OCDMA) system. The main purpose of the proposed technique is to construct codes whose length varies adaptively with the number of users. This task can be easily accomplished by successive offsets of the basic code matrix. The important benefit is that all the codes resulting from this technique have a zero cross-correlation property even if the basic code matrix doesn't check it. Therefore, the AMT technique effectively reduces both MAI and PIIN. SAC-OCDMA system employing AMT is mathematically analyzed and then numerically simulated using Matlab. The results show the improvement given by this mapping technique to the SAC-OCDMA system. It illustrate that the proposed mapping technique can supports more users with a higher bit rate compared to the existing mapping techniques in the literature. The advantages of this technique have made it a compelling candidate for future OCDMA applications. [ABSTRACT FROM AUTHOR]

In this paper, a method based upon combination of duo-binary (DB) and carrier suppressed return-to-zero (CSRZ) format has been proposed that has significantly improved the performance of optical code division multiple access (OCDMA) system by means of two dimensional (2D) codes based on two parameters; wavelength and time. The various investigations divulge that highest Q2 (dB) of minimum and maximum value [18,23]; [14,17]; [9,12] and [1,6] has been obtained at a power variation of -10 to 20 dBm for DCRZ, DB, CSRZ and RZ modulation formats respectively for a communication distance of 80 kilometers. It has also been identified that maximum OSNR of [37-29] dB is obtained by using DCSRZ modulation format for the same distance. The maximum opening of eye for DCSRZ format has further proved its robustness to suppress the channel impairments at a high-power level of 20 dBm for 10 GHz optical CDMA systems. [ABSTRACT FROM AUTHOR]

In an orthogonal frequency division multiplexing (OFDM) system, cyclic prefix (CP) has to be added to eliminate multipath-induced inter-symbol interference (ISI) with a severely sacrificed bandwidth efficiency. Peak-to-average ratio (PAPR) may impair its performance further if a large number of carriers are used. On the other hand, traditional multi-carrier modulation suffers a prohibitive complexity, which can not be implemented with colorred current available silicon technologies. This work proposes a cost-effective way to implement multi-carrier modulation, namely multi-layer quadrature (MLQ) modulation, which requires only two oscillators. As an application example, we apply MLQ modulation to a complementary coded code division multiple access (MLQ-CC-CDMA) system, whose multi-carrier transmission is based on MLQ modulation to mitigate ISI and multi-user interference (MUI) with ideal auto- and cross-correlations of complementary codes. Compared to a frequency domain (FD) CC-CDMA system, MLQ-CC-CDMA has a lower RF complexity. Compared to OFDM direct sequence (DS) CDMA and single carrier frequency division multiple access (SC-FDMA) CDMA schemes, MLQ-CC-CDMA achieves a higher spectrum efficiency (SE) and a lower bit error rate with Rake and minimum mean square error (MMSE) detection due to its powerful multipath and multi-carrier diversity gains. [ABSTRACT FROM AUTHOR]

Quasi-complementary sequence sets (QCSSs) can be seen as a generalized version of complete complementary codes (CCCs), which enables multicarrier communication systems to support more users. The contribution of this work is two-fold. First, we propose a systematic construction of Florentine rectangles. Secondly, we propose several sets of CCCs and QCSSs, using Florentine rectangles. The CCCs and QCSSs are constructed over $\mathbb {Z}_{N}$ , where $N\geq 2$ is any integer. The cross-correlation magnitude of any two of the constructed CCCs is upper bounded by $N$. By combining the proposed CCCs, we propose asymptotically optimal and near-optimal QCSSs with new parameters. [ABSTRACT FROM AUTHOR]

This paper has been focused to utilize the m-sequence (matrix) code in spectral/time/spatial OCDMA domain in a bipolar mode (Three Dimensional modes). The scheme has elegantly incorporated the design of an encoder and decoder such that the system efficiently generates the code in three-dimensional bipolar mode. The decoder design is such that it effectively suppresses the multiple user interference (MUI) of three-dimensional code. System analyses are carried for defining the BER performance variation with users acceptability and received power. The observed results demonstrate that the cardinality of m- matrix three-dimensional bipolar code is larger than the existing 3D Pascal code, 2D-MDW, 3D-PDC, 2D-PDC, 1D-CWH and 1D-MS codes. The received power in proposed system is − 5.8 dBm lesser than the 3D Pascal Code at 10–18 BER and the users in system more than 210% can be accomplished as compared to 3D Pascal code. [ABSTRACT FROM AUTHOR]

Complementary coded multicarrier code-division multiple access (CC MC-CDMA) has a strong potential to offer frequency diversity gain in frequency selective fading channels due to its ideal correlation characteristics. However, in uplink transmissions the use of single-user detection techniques will reduce the diversity gain achievable with complementary codes (CCs). Multiuser detection schemes such as successive interference cancellation (SIC) has a strong potential to overcome multiple access interference (MAI) in near-far environments. In this paper, SIC is analyzed in the context of improving the error rate performance of CC MC-CDMA operating under asynchronous uplink environments. The probability of error (POE) analysis for M-branch diversity system using alternate form of Q-function is derived and its performance is verified using SIC with maximal ratio combining (MRC) and minimum mean square error (MMSE) combining. The analysis of CC MC-CDMA systems under equal and unequal power variations is performed in asynchronous channel conditions and it was shown that considerable improvement in system capacity is achieved through multiuser detection. [ABSTRACT FROM AUTHOR]

Almost all existing studies on inter-satellite radio-frequency (RF) measurement have focused on two-satellite formations. Although some frequency division multiple access and code division multiple access multisatellite RF measurement schemes have been proposed, their poor scalability does not satisfy the inter-satellite measurement requirements of multisatellite formations, especially large-scale formations. Two-way ranging (TWR), which is based on a time division mechanism, is an effective solution that has been used for inter-satellite links in the global positioning system and Beidou navigation constellations. However, the high measurement accuracy achieved with TWR in these navigation constellations is heavily reliant on high-performance atomic clocks and the assistance of navigation ephemeris, which are not available on microsatellite platforms. This work focuses on a scalable multisatellite measurement scheme that adopts a distributed broadcast-based time division multiple access mechanism as the media access control layer and uses an asymmetric double-side TWR method as the physical layer. The measurement performance of the proposed scheme is evaluated through in-depth theoretical modeling, simulation verification, and experimental validation, along with a comprehensive comparison with the conventional TWR method. The experimental results show that centimeter-level measurement accuracy can be achieved with the proposed scheme when only a common miniaturized frequency source is used. This accuracy level is two orders of magnitude better than that of the TWR method, and thus satisfies the application requirements of general large-scale microsatellite formations. [ABSTRACT FROM AUTHOR]

This paper investigates shortcomings that limit the performance of optical code division multiple access (OCDMA) systems including the low cardinality and data rate as well as the high power at reception. The main drawback for such systems known as multiple access interference accompanying by phase induced intensity noise is also investigated to effeciencly propose a novel two dimensional cyclic shift (2D-CS) code to be implemented in non-coherent OCDMA systems. The developed code is based on a one dimensional cyclic shift (1D-CS) code previously provided by research works processing spectral amplitude coding for optical code division multiple access (SAC-OCDMA) systems. Numerical results obtained by this study are therefore compared to previous studies employing different codes like two dimensional extended double weight (2D-EDW), two dimensional flexible cross correlation/modified double weight (2D-FCC/MDW), two dimensional perfect difference (2D-PD), two dimensional diluted perfect difference (2D-DPD), two dimensional multi service (2D-MS) and two dimensional zero cross correlation/multi diagonal (2D-ZCC/MD) codes. Accordingly, it is demonstrated that the proposed 2D-CS code outperforms all codes given previously in terms of system capacity where the small increasing percentage is about 40% compared to 2D-ZCC/MD and 2D-MS. Systems using 2D-CS code can support until 203 simultaneous users with a total code length equal to 171. System performance investigation leads to a BER and Q-Factor closely to1.0E−12 and 1.0E−27, and 6.6 dB and 10.6 dB at 20 km of single mode fiber length using white light source and Laser, respectively. Furthermore, such a code can be easily adopted by OCDMA systems for a long distance up to approximately 55 and 100 km. [ABSTRACT FROM AUTHOR]

In this proof-of-principle paper, the application of 2-D optical code-division multiple-access (OCDMA) modulation to long-range automotive time-of-flight (ToF) light detection and ranging (LiDAR) is studied. The regulations and physical constraints that govern the design parameters are reviewed. Using 2-D carrier-hopping prime codes (CHPCs), the modulation model and a novel 2-D hard-limiting decoder are designed and validated with OptiSystem$^{\rm {TM}}$ simulations. Based on the design parameters, the 2-D CHPCs have six times as many distinct sequences (for sensor identification) as 1-D code sequences. Analytical and simulation studies show that the proposed 2-D OCDMA modulation model can eliminate the near-far (power) problem and support more LiDAR sensors with distinctive ToF tags, greater interference robustness for more simultaneous ToF measurements, and better performance than the 1-D counterparts. The simulation results show that the 2-D model can support four times as many simultaneous emitting sensors without false detections as the 1-D model. In summary, the 2-D OCDMA modulation has more benefits and is more cost efficient overall, even though it is more complex.

For the diverse traffic requirements of the wireless communication multiple access system and the characteristics of VLC, a new orthogonal variable spreading factor zero cross correlation (OVSF-ZCC) code set was proposed for multi-rate VLC code division multiple access (CDMA) system, which consisted of unipolar spreading sequences with variable lengths, and zero cross correlation properties.Assuming the radiation of LED light source was Lambert distribution, a multi-rate CDMA-VLC system with proposed code set was further presented.The effects of construction parameters, transmission rate and distance on system performance were evaluated.The results show that the new code set can effectively reduce multiple access interference (MAI), and support multiple transmission rate requirements of different users in multiple access systems.

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. [ABSTRACT FROM AUTHOR]

Fiber-Wireless (Fi-Wi) networks play a crucial role in broadband wireless communication. A hybrid Fi-Wi architecture integrating Optical Code Division Multiple Access (OCDMA) based Next-Generation Passive Optical Network (NGPON) with Long Term Evolution (LTE) is proposed that can provide a higher capacity to the mobile end users, thereby achieving scalability and mobility. Maximal length sequence (M-sequence) codes of code length 31 used can support six users. A simulation study is carried out for the proposed integrated architecture considering multiple users and multiple services, and the performance is analyzed in terms of the received Bit Error Rate (BER) and Error Vector Magnitude (EVM) values. A high capacity of 160 Gbps and a spectral efficiency of 2–4 bps/Hz are achieved for the multi-user and multi-service links with six users. [ABSTRACT FROM AUTHOR]

In an incoherent optical code division multiple access (OCDMA) system using amplitude spectral coding (SAC), which exceeds 1.5 Gbps, it is difficult or impossible to make a transmission with a bit error rate better than 10–9. For this, it is necessary to associate an error correction code (ECC) to the SAC-OCDMA system. In this paper, we proposed an architecture of a two-dimensional SAC-OCDMA system (spectral (w) and spatial (s)) using multi-diagonal code (MD) as spreading code and low-density parity check code (LDPC) as ECC. According to the properties of the MD code and the proposed architecture, the phase induced intensity noise is eliminated, which has improved the performance of the system. The theoretically results shows that LDPC/2D-SAC-OCDMA allowing more than 40 users to be multiplexed compared to a non-coded 2D SAC-OCDMA system. This combination allowed us to increase the cardinality of the LDPC/SAC-OCDMA (W/S) system without using an optical hard limiter. [ABSTRACT FROM AUTHOR]

Spectral amplitude coding optical code division multiple access (SACOCDMA) is a multiplexing technique, which provides faster speed, efficiency, security and unlimited bandwidth. It is widely preferred because of its ability to eliminate multiple access interference (MAI). Free space optics (FSO) provides a wireless link to transmit data securely at higher rates for last mile access. In this work, a 100 Gb/s hybrid FSO-SACOCDMA is designed using direct detection. The performance of FSO using SACOCDMA utilizing NZCC (New Zero Cross Correlation) code is evaluated under different weather conditions (clear weather, haze and fog) for ten users where each user carries 10 Gb/s. The results indicate that in clear weather FSO distance can be extended up to 13 km. Moreover, after using preamplifier in clear weather, FSO enhances the maximum distance to 35 km with acceptable signal to noise ratio and bit error rate. Using an amplifier in the link not only makes the quality of the signal better but it also increases the communication range. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Future telecommunication systems and networks are expected to provide a variety of integrated broadband services to the customers. There has been a tremendous interest in applying Code Division Multiple Access (CDMA) techniques to fiber optic communication systems. This technique is one of the multiple access schemes that is becoming popular because of the flexibility in the allocation of channels, ability to operate asynchronously, enhanced privacy and increased capacity in bursty networks. This project is focusing on designing 2D OCDMA system with the hardware implementation of design using FPGA. The coding techniques in OCDMA are time versus wavelength and amplitude versus phase. 2D OCDMA coding incorporates both wavelength selection and time distribution. The data bit would be encoded as consecutive chips with various wavelengths. The code architecture seeks to produce codes with high autocorrelation and low cross-correlation properties. Code length is an essential aspect of code and device architecture for coding characteristics. The hardware implementation of the system is designed by using FPGA De1-SoC. The FPGA have the abilities to enhance the transmission of data to the receiver in a short period of time. The performance of 2D OCDMA system is expected to surpass 1D OCDMA system in terms of BER and the number of simultaneous users that can be supported. The system encoder and decoder were designed using optical switch, splitter, combiner and modulator. The performance of 2D OCDMA system in terms of time spreading and wavelength spreading is also compared which shown a huge difference in the results. The best performance of the system is when the number of wavelength (M) is fixed to 18 and the number of times spreading (N) is 31 which can support 350 more simultaneous users.dc [ABSTRACT FROM AUTHOR]

Polyphase sequences with low aperiodic autocorrelation levels, assessed in terms of the integrated sidelobe level (ISL), can be applied in many engineering fields, such as radars, sonars, and code-division multiple access communication systems. In practice, a polyphase sequence that is optimal in some sense (for example, minimum ISL) could be significantly distorted, thus reducing the detection performance of the radar system. Hence in this article, we focus on designing ISL minimization-based polyphase sequences with spectral distortion taken into consideration, where we first derive an expression for the ISL under spectral distortion, i.e., distorted ISL (DISL), and then we propose an iterative algorithm based on majorization-minimization framework to solve the DISL minimization problem. The proposed algorithm is proved to be nonincreasing and is guaranteed to converge to a stationary point. A variety of design results utilizing the proposed algorithm in different scenarios are presented and compared with those by other methods or some known sequences. The proposed algorithm is proved to be effective to design polyphase sequences with low DISL. [ABSTRACT FROM AUTHOR]

Spectrum efficiency is a critical performance metric in wireless communications due to an increasing demand for radio spectrum to support high data rate applications. Direct sequence spread spectrum technology enables a code division multiple access (CDMA) system a strong anti-interference capability but with a relatively low spectrum efficiency. To address this issue, complementary coded scrambling multiple access (CCSMA) (X. Liu et al., in 2018) was proposed to use three-dimensional (space-time-frequency) resources for performance enhancement. However, in a CCSMA system, if the number of multipath returns is larger than the number of transmit (Tx) antennas, a code reuse problem occurs to degrade bit error rate performance significantly. This work designs a new scrambling code, namely generalized complementary coded scrambling multiple access (GCCSMA) codes, to overcome the code reuse problem in CCSMA. GCCSMA uses complementary codes, scrambling modulation, and multiple-input-multiple-output (MIMO) techniques jointly, which works well even in multipath channels with more paths than the number of Tx antennas. The analysis and simulations are conducted to validate the effectiveness of the proposed GCCSMA system. [ABSTRACT FROM AUTHOR]

Low-complexity detectors are conceivedfor the spatial modulation-aided sparse code-division multiple-access (SM-SCDMA). Firstly, the approximate message passing (AMP) algorithm is adapted for the detection of SM-SCDMA, which has less than 1% detection complexity of the state-of-the-art message passing-aided (MPA) detection albeit at a bit error ratio (BER) degradation. Therefore, inspired by the benefits of interference cancellation (IC) and the unique characteristics of SM, an enhanced AMP (EAMP) detector is proposed for mitigating BER degradation without increasing the detection complexity. Finally, the classic expectation propagation (EP) is intrinsically amalgamated with our EAMP detector, leading to a novel EAMP-EP detector, which further reduces the detection complexity of the EAMP algorithm. The three detectors are compared both in terms of their coded and uncoded BER, as well as complexity. [ABSTRACT FROM AUTHOR]

In this proof-of-principle paper, the application of 2-D optical code-division multiple-access (OCDMA) modulation to long-range automotive time-of-flight (ToF) light detection and ranging (LiDAR) is studied. The regulations and physical constraints that govern the design parameters are reviewed. Using 2-D carrier-hopping prime codes (CHPCs), the modulation model and a novel 2-D hard-limiting decoder are designed and validated with OptiSystem $^{\rm {TM}}$ simulations. Based on the design parameters, the 2-D CHPCs have six times as many distinct sequences (for sensor identification) as 1-D code sequences. Analytical and simulation studies show that the proposed 2-D OCDMA modulation model can eliminate the near-far (power) problem and support more LiDAR sensors with distinctive ToF tags, greater interference robustness for more simultaneous ToF measurements, and better performance than the 1-D counterparts. The simulation results show that the 2-D model can support four times as many simultaneous emitting sensors without false detections as the 1-D model. In summary, the 2-D OCDMA modulation has more benefits and is more cost efficient overall, even though it is more complex. [ABSTRACT FROM AUTHOR]

This paper presents the work on the efficient scheme of Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA). This is one of the promising solution to the emerging need of high data rates. The systems based on OCDMA suffer from Multiple User Interference (MAI) and Phase-Induced Intensity Noise (PIIN). The SAC-OCDMA systems are able to eliminate them by using better code structuring. This script presents the numerical analysis and detailed comparison of logical interference cancellation of used 1D codes which are Enhanced Double Weight (EDW) and Modified Double Weight (MDW) codes. The three-user system is simulated and designed for associating BER and other performance parameters with respect to the length of the optical cable. The receiver side is using Single Photo Diode Detection (SPD) technique. The results reveal that EDW performs better than the MDW codes moreover, the transmission length for standard error free transmission is 120 km with EDW codes and 102 km for MDW codes. For comparative study PIN as well as APD detectors are used for the same parameters where a significant increase up to 45 km is seen while using APD. [ABSTRACT FROM AUTHOR]

Free space optics (FSO) communication is a very recent mechanism. It is mainly needed when physical connection between the transmitter and the receiver is practically impossible and when high bandwidth data transmission is expected. This paper walks through the investigation of the performance of FSO communication adopting spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems at different weather scenarios. The suggested system uses enhanced double weight codes as signature codes by 3 clients, simultaneously. To eliminate multiple access interference and phase induced intensity noise, two different detection schemes are used; single photodiode (SPD) and modified-AND subtraction detection schemes. Furthermore, a comparison between PIN and APD detectors is performed. The performance is evaluated through its propagation distance, received power, Q-factor and bit error rate (BER). The obtained numerical results reveal both Q-factor and BER are modified by 30%. Accordingly, the system performance is enhanced by 30%, when using SAC-OCDMA-FSO with SPD detection technique compared with modified-AND subtraction technique. [ABSTRACT FROM AUTHOR]

This paper reports the simulative analysis of NRZ, RZ, carrier-suppressed RZ (CSRZ) and duo-binary (DB) modulation formats for optical code division multiple access (OCDMA) system for two different types of encoders at 10 Gbps. The investigations reveal that highest Q²(dB) of the order of 16.5;14.5;6.2 and 3.8 has been obtained when we use combination of optical filters and time delay components as optical encoders in OCDMA system for CSRZ, DB, RZ and NRZ formats respectively. It is also observed that for fiber Bragg grating (FBG's) as optical encoders, Q² (dB) of the order of 17.7;11.8;7 and 4 is achieved in case of DB, CSRZ, RZ and NRZ formats respectively. CSRZ and duo-binary formats have shown the robustness over other formats for OCDMA system using filter, time delay components and fiber Bragg gratings (FBGs) as optical encoders respectively. The maximum eye opening in case of these formats further proved their efficiency. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) is the preferred scheme for high-speed communication in the field of underwater acoustic communication. However, it is very sensitive to the carrier frequency offset (CFO). This study used a time-varying CFO estimation method aided by the differential evolution (DE) algorithm to accurately estimate the CFO of an OFDM system. This method was based on the principle that the received OFDM signal with inter-carrier interference could be considered by a Multi Carrier-code division multiple access (MC-CDMA) system on the receiver side because MC-CDMA is a technology that combines OFDM and code division multiple access (CMDA). Because it is suitable for solving problems where there are dependencies between adjacent variables, the DE algorithm was used to capture the varying CFO values on the adjacent blocks. The spreading code of the MC-CDMA was obtained based on the estimated CFO values, which were elements in the DE solutions. Then the received signal was reconstructed. The Root-Mean-Square Error between the reconstructed and actual received signals was used as the cost function, and the CFO was estimated using the DE algorithm because of its powerful parallel search capability. The simulation results showed that the proposed method had a high estimation accuracy. Compared with other intelligent optimization algorithms such as the genetic algorithm and simulated annealing mutated-genetic algorithm, the time-varying CFO estimation performance of the DE algorithm was better because of its unique ability to solve problems with dependencies between adjacent variables. Specifically, under the condition of a high signal-to-noise ratio, the improvement of estimation accuracy reaches 36.13%, and the Bit Error Rate of demodulation is thus reduced by 75%, compared with the reference algorithms. In addition, the proposed method also has good applicability to modulation methods. For phase-shift keying and quadrature amplitude modulation, in particular, the proposed method not only achieved high-precision time-varying CFO estimation values, but also reduced the demodulation deterioration caused by noise.

Inter-satellite optical wireless communication (IsOWC) is a developing free-space optical technology used to communicate among satellites in space. At the same time, SAC-OCDMA (spectral amplitude coding optical code division multiple access) is an encouraging research area in the domain of optical communication because of its high bandwidth, speed, huge capacity, and ability to carry bursty and asynchronous information transmission. The present paper is concerned with the hybrid IsOWC non-coherent SAC-OCDMA system based on PM-ZCC (Permutation Matrix Zero Cross-Correlation) code for long-range high data rate transmission. The advanced modulation format (CSRZ) and direct detection (DD) techniques have been used to design the proposed system. The system is designed for five stations (each carrying 10 Gb/s). The system's performance is investigated for pointing error (with and without) over a space distance up to 12000 km in terms of Q factor, eye diagrams, BER and SNR. Moreover, the performance of a single IsOWC link has also been compared with multiple IsOWC links for a distance of 6500 km at 10 Gb/s data rate. The results show that system performance improves by using CSRZ format and multiple ISL links. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mode division multiplexing (MDM) is an emerging multiplexing technique that simultaneously transmits independent channels through a spatial light modulator (SLM). Further, Spectral amplitude coding optical code division multiple access (SAC-OCDMA) is an encouraging invention because it gives an appealing answer for burst and asynchronous environment. In addition, free space optics (FSO) provides a cost-effective, secure, high data rate for last mile access compared to other systems. In this paper, a hybrid 100 GB/s SACOCDMA-FSO-MDM system is proposed, and its performance is estimated by using four SAC-OCDMA codes that are Zero Cross Correlation (ZCC), Random Diagonal (RD), Multi Diagonal (MD), and Enhanced double weight (EDW) under atmospheric turbulences such as haze, rain, and clear weather. Laguerre Gaussian (LG) modes (used for MDM) and direct detection (DD) method are used for the construction of the system using 10 channels; each carries 10 Gb/s data. Results specify that the ZCC code is more suitable under all the atmospheric conditions as it possesses no cross-correlation, lesser noise that diminishes the hardware's complexity. For clear weather, the ZCC code gives a BER of 10–29 at a maximum distance of 22 km. [ABSTRACT FROM AUTHOR]

A two dimensional spectral/spatial cyclic shift (2D-CS) optical code division multiple access (OCDMA) systems is proposed for a potentially next generation passive optical network (NG-PON) implementation called (2D-CS NG-OCDMA-PON) system. The2D-CS proposed code is characterized by a high capacity and a zero cross correlation property leads to completely eliminating the multiple access interference (MAI) effect that is considered as the main OCDMA system drawback. Firstly, the 2D-CScode construction is investigated from 1D-CS code. Secondly, a system description is provided by exhibiting the transmitter and receiver architecture in the PON context. Analytical analysis reveals that our proposed 2D-CScode outperforms similar codes such as perfect difference (2D-PD) and dynamic cyclic shift (2D-DCS) codes in terms of spectral efficiency, simultaneous network subscribers and data bit rate. In addition, based on numerical analysis 2D-CS NG-OCDMA-PON system shows a good system performance by means of avery low BER and a high Q-factor values equal to 10 - 26 and 10.41 dB, respectively. Likewise, for four users and free-amplification the achievable reach ability distance of the NG-OCDMA-PON system is 63.21 km, 43.57 km and 33.2 km while Q-factor is equal to 6 dB at a bit rate of 622 Mb/s, 1 Gb/s and 1.5 Gb/s, respectively. On the other side, according to the system setup the number of single mode fiber (SMF) is reduced to the half compared to other 2D-OCDMA-PON systems based on enhanced multi diagonal (EMD) and single weight ZCC (SWZCC) codes. [ABSTRACT FROM AUTHOR]

Among all the techniques combining multi-carrier modulation and spread spectrum, the multi-carrier code division multiple access (MC-CDMA) system is by far the most widely studied. In this paper, we present the performance of the MC-CDMA system associated with key single-user detection techniques. We are interested in problems related to identification and equalization of mobile radio channels, using the kernel method in Hilbert space with a reproducing kernel, and a linear adaptive algorithm, for MC-CDMA systems. In this context, we tested the efficiency of these algorithms, considering practical frequency selective fading channels, called broadband radio access network (BRAN), standardized for MC-CDMA systems. As far as the equalization problem encountered after channel identification is concerned, we use the orthogonality restoration combination (ORC) and the minimum mean square error (MMSE) equalizer techniques to correct the distortion of the channel. Simulation results demonstrate that the kernel algorithm is efficient for practical channels. [ABSTRACT FROM AUTHOR]

In the case of emergency scenarios communication infrastructure might be destroyed, impairing communication abilities in the disaster area. In such situation device‐to‐device (D2D) communication networking plays an essential role to overcome the communication loss. To provide a reliable communication network, D2D devices are combined with airborne drones. The D2D devices provide a relay service while being able to transmit their own data. The airborne drones offer additional relay functionality and provide considerably reduced latency compared with D2D communication networks without any airborne drones. In this article, we will illustrate a large dynamic communication network (LDCN) and demonstrate its feasibility for even more than 64 000 D2D communication devices in the case of realistic channel conditions including path loss and fading. It will be shown that the illustrated LDCN is truly infrastructure‐less, that is, no infrastructure or backbone or base station functionality need to be reinstalled. Therefore, the airborne drones do not take over any coordination services. The illustrated LDCN has a simple packet switching architecture and since all communication is localized it is robust and fully flexible. In addition, no specific radio interface or preferred multiple access scheme such as code division multiple access or time division multiple access are required. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is a prominent 5G wireless communication technique which ensures higher spectral efficiency, low latency and user fairness. As power-domain NOMA exploits different power levels assigned to each user for decoding, therefore, performance of this scheme degrades badly in a network having approximately equidistant users. To address this challenge, a novel hybrid CDMA–NOMA scheme for 5G downlink is proposed in this paper. Superposition coding is done at the transmitter side while successive interference cancellation (SIC) is performed at the receiver. The proposed scheme differentiates inter-cluster users on the basis of spreading codes, whereas intra-cluster users are differentiated on the basis of different power levels. Interference in the system is mitigated through two different techniques, inter-cluster interference through spreading codes (PN and Walsh codes) while intra-cluster interference through SIC technique. We implement an accurate power allocation strategy with users clustering best with poor model (users with nearest and farthest distances to BS) which is based on the distance of each user from base station. Considering user's distance and channel coefficient, the proposed technique adapts intelligently among NOMA and hybrid CDMA–NOMA. BER performance of the hybrid CDMA–NOMA system is analyzed in NYUSIM channel model. The proposed approach improves the capacity without increasing the bandwidth and/or number of antennas, and results in reduced interference in congested NOMA systems. [ABSTRACT FROM AUTHOR]

A new architecture for Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system based on two Dimensional Multi Diagonal (2D-MD) codes named 2D-MD SAC-OCDMA and utilizing a laser optical source is proposed for Long-Reach Passive Optical Network (LR-PON). In this work, a computer simulator tool is used, for the first time, as a SAC-OCDMA simulation set-up utilizing the unique combination of a coherent laser array and 2D-MD codes. In addition, the system performance is addressed numerically by taking into account Multiple Access Interference (MAI), optical coherent source noise, first, second and third order fiber dispersion, nonlinear effects and photo-detector noise. Simulation results indicate that for a single user (i.e., without considering MAI), the system can operate at a maximum bit rate of 55 Gb/s over 250 km of Single Mode Fiber (SMF), with a Bit Error Rate (BER) below 10−9 (Q-limit = 15.5 dB), when only first order fiber dispersion is considered. However, including the effects of second and third order fiber dispersion as frequency domain parameters, results in a reduction of the maximum bit rate to 40 Gb/s, while maintaining a Q-factor above the Q-limit under the same transmission distance. Furthermore, we demonstrate that the proposed architecture extends the SMF transmission reach up to 600 km and 480 km, when considering linear and nonlinear effects, respectively. Finally, we show that our proposed 2D-MD SAC-OCDMA system outperforms existing solutions presented in the literature for LR-PON configuration, in terms of both aggregate bit rate and transmission reach. [ABSTRACT FROM AUTHOR]

The implemented method for data recovery in some practical code division multiple access (CDMA) systems is the matched filter detector which has zero decision threshold in the symmetric modulations. Because in the multiuser communication systems, the cochannel interference changes the observation noise model to Non- Gaussian one, using zero thresholds is not optimal anymore. In this paper, we obtain the optimal threshold of the matched filter detector in the presence of the block faded interference and fast frequency flat Rayleigh faded desired user signal. We show that the probability of error for this system can be decreased using the obtained optimal threshold. To this end, we derive the analytic probability of error of the communication system with interference which leads to the condition of having an optimal threshold for this system and its value. We have also compared the obtained analytic results with the Monte Carlo simulation curves to validate the derived analytic expressions. [ABSTRACT FROM AUTHOR]

Non-Orthogonal Multiple Access (NOMA) is an efficient multiple access scheme which augments the capacity and overall throughput in LTE and 5G networks. Tackling the high system throughput and device connectivity of multiple users with different channel state information is a key challenge at this juncture. The joint detection and decoding using parity check polar coding (PCPC) and the utilization of Sparse Code Multiple Access (SCMA) in Code domain NOMA improves throughput supporting an overloaded number of users. Also, Multiple-Input Multiple-Output (MIMO)-SCMA scheme has potential in providing spectrum and energy efficiency. MIMO-SCMA superimposes multiple users in the code domain and utilizes the channel gain difference between multiplexed users. Hence, this paper aims to propose a proficient code domain NOMA scheme, the PCPC SCMA multiplexed over Orthogonal Frequency Code Division Multiple Access (OFCDMA), implementing a joint detection and decoding with user scheduling. Signals of numerous users are superimposed and transmitted over a channel. At the receiver, Multi-User Detection (MUD) exploiting the Message Passing Algorithm (MPA) is used to identify the desired user. To ensure proper resource utilization of multiple data blocks, the users are scheduled by implementing the Invasive Weed Optimization (IWO) technique along with the MPA. The proposed scheme, which engages an IWO-MPA based MUD scheme, improves the convergence rate, in terms of the number of iterations thereby leading to lower complexity, as well as reduces the Bit Error Rate (BER). Computer simulations reveal that the proposed scheme achieves high spectrum and energy efficiency, higher throughput and overloaded user fairness compared with recent researches. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One dimensional encoding in optical communications has limitations in terms of the number of supported users and large bandwidth consumption. This study presents a new algorithm to generate two-dimensional (2D) encoding utilizing permutation vectors (PV) theory for incoherent multiple access network to suppress multiple access interference (MAI) and system complexity. The proposed code design approach is based on spectral/spatial techniques for code generation. All possible combinations of PV code-sets are obtained by utilizing all permutations of the vectors with the repetition of each vector weight (W) times. Furthermore, the 2D-PV code-set is constructed by combining two code sequences of the 1D-PV code. Furthermore, the transmitter–receiver architecture of the 2D-PV spectral/spatial (S/S) code based OCDMA system is presented. The Gaussian approximation is used to analyze the performance of the proposed OCDMA system with 2D- PV code by considering various noise sources (shot, thermal, and PIIN). Results indicate that the 2D-PV code provides increased cardinality by eliminating phase induced intensity noise (PIIN) effects with a minimum likelihood of interference between multiple user data. Simulation implementations validate the proposed system performance for an agreeable bit error rate (BER) of 10–9 [ABSTRACT FROM AUTHOR]

Quasi-complementary sequence sets (QCSSs) play an important role in multi-carrier code-division multiple-access (MC-CDMA) systems. They can support more users than perfect complementary sequence sets in MC-CDMA systems. It is desirable to design QCSSs with good parameters that are a trade-off of large set size, small periodic maximum magnitude correlation and small alphabet size. The main results are to construct new infinite families of QCSSs that all have small alphabet size and asymptotically optimal periodic maximum magnitude correlation. In this paper, we propose three new constructions of QCSSs using additive characters over finite fields. Notably, these QCSSs have new parameters and small alphabet sizes. Using the properties of characters and character sums, we determine their maximum periodic correlation magnitudes and prove that these QCSSs are asymptotically optimal with respect to the lower bound. [ABSTRACT FROM AUTHOR]

The performance of two dimensional (2D) hybrid wavelength/time optical code division multiple access (OCDMA) system is affected severely by the presence of noise at its physical layer. This noise is present in the guise of multiple access interference (MAI) and beat noise in OCDMA systems and degrades its performance. In this paper an attempt has been made to analyze the impact of noise in OCDMA system using four different coding schemes. The mitigation of noise is then done by using either optical hard limiter (OHL) or by utilizing coherent detection for all these schemes. These codes use synchronized quadratic congruence sequences (SQC), synchronized prime procession (SPP), prime code sequences (PC) and synchronized prime sequences (SPS) for wavelength hopping and (n, w, λa, λc) one dimensional optical orthogonal codes for time spreading respectively. The code with heavier code weight or lower values of auto-and cross-correlation function performs the best with noise mitigation techniques. Investigations reveal that SQC/OOC coding scheme in combination with OHL and PC/OOC scheme in combination with coherent detection outperforms in comparison to other techniques. [ABSTRACT FROM AUTHOR]