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Free space optical (FSO) systems offer an attractive and cost-effective solution for providing communication services in remote regions, as they allow secure transmission without the need for licensing and with lower deployment costs. However, the performance of FSO systems can be significantly impacted by atmospheric turbulences, creating considerable challenges to their deployment. To meet the expanding bandwidth requirements in optical networks, dense wavelength division multiplexing (DWDM) has emerged as a viable option. The development of a 400-Gbps DWDM-FSO system with advanced modulation formats is the subject of this paper. To ensure efficient energy conservation in such a system, power consumption needs to be minimized while maintaining performance level; this calls for optimization of different components within the system. The system is made up of 10 channels and each channel can transmit data at 40 Gbps. Various modulation schemes like carrier-suppressed return-to-zero, modified duo binary return-to-zero, differential phase shift keying, and duo binary return-to-zero are studied for their impact on system performance parameters Q-factor and bit error rate (BER) in C-band around 1550 nm wavelengths. The assessment is also extended to the effects that changing FSO length, input power, and data rate have on these two parameters as well as an evaluation regarding how differing atmospheric conditions influence the FSO system's effectiveness. [ABSTRACT FROM AUTHOR]

In the present study, a model for analyzing the performance of laser-based satellite uplinks that account for beam wander and atmospheric turbulence is presented. The developed scintillation index model is a continuation of the recent works considering the effects of non-Kolmogorov turbulence on the propagation of Gaussian beams across turbulent media. We specifically concentrate on the specific regime under the tilt-corrected beam wander. The on-axis scintillation index is developed assuming an isotropic non-Kolmogorov spectrum model where the power law exponent (PLE) effective value, α , is taken to be 3 < α < 4. Within that regime, effective irradiance models for tilt-corrected beam wander are presented, using the Gamma and Gamma-Gamma distributions. Closed-form expressions of the average bit error rate (BER) are derived to evaluate the performance of the optical communication system considering coherent detection of differential phase shift keying. The obtained numerical results show the impact of the Gaussian beam radius at the transmitter, the PLE effective value, and the zenith angle on the on-axis scintillation index and the average BER of the system under consideration. Due to beam wander, the link performance in terms of scintillation index and average BER depends on the beam radius at the transmitter. With tilt-corrected beam wander the link performance becomes best at an intermediate value of beam radius. With the non-Kolmogorov turbulent medium model, the PLE effective value has a major effect on the beam radius with the best performance. The obtained results guide the choice of the optimum beam radius for best performance for each PLE effective value. [ABSTRACT FROM AUTHOR]

Wavelength division multiplexing (WDM) is one of the emerging technologies for data transmission in 5G access network assembly between the antenna unit (AU) and the distribution unit (DU). Here, in this work, we evaluate and analyze a dense wavelength division multiplexing (DWDM) — passive optical networks (PONs) employing erbium–ytterbium-doped fiber amplifier (EYDFA) + Raman hybrid optical amplifier (HOA) using two modulation schemes — modified duobinary return to zero (MDRZ) and differential phase shift keying (DPSK) for alternate channels, where the channel count has been varied from 8 to 40. The system has been analyzed over the wavelength span of 1550–1558.8 nm with a channel spacing, input power and data rate of 25 GHz, 0 dB and 40 Gb/s, respectively. An average gain, gain ripple and optical signal-to-noise ratio (OSNR) of 20.87, 0.95 and 30 dB, respectively have been observed in the case of HOA along with the achievement of Q-factor of up to 9 at the receiving end of the system. The DPSK-modulated channels result in higher values of gain and OSNR along with lower gain ripple as compared to MDRZ channels making the proposed system a good option for 5G access network applications. [ABSTRACT FROM AUTHOR]

A quantum conference key agreement (QCKA) protocol based on differential-phase-shift quantum key distribution is presented, which provides a common secret key for secure communication between more than two parties. In the proposed protocol, one party simultaneously broadcasts a weak coherent pulse train with {0, π} phases to multiple parties that measure the phase differences between adjacent pulses using a delay interferometer followed by photon detectors, and the transmitter and receivers share secret key bits from the coincident counts in the receivers. The system setup and operation are simpler than those of conventional QCKA schemes that use a multipartite quantum entanglement state. The key creation performance is evaluated by considering the eavesdropping probability. The results indicate that the proposed scheme offers better performance than the conventional entanglement-based QCKA system. [ABSTRACT FROM AUTHOR]

Two-wave with diffuse power (TWDP) is one of the most promising distributions for describing multipath fading in the emerging millimeter-wave (mmWave) band. However, traditional error performance analysis in these channels is mostly based on the approximate expressions, accurate only for specific combinations of TWDP parameters that describe particular channel conditions. Considering the aforementioned, this paper begins with an extensive literature overview of the existing average bit/symbol error probability (ABEP/ASEP) expressions in TWDP channels, revealing the absence of the exact expressions that could be used to accurately evaluate error performance in all channel conditions, for most modulation and diversity techniques. Next, the exact ASEP expressions are derived for M-ary rectangular quadrature amplitude modulation with coherent detection and for M-ary differential phase shift keying modulation. These expressions are then used to derive corresponding computationally simple closed-form asymptotic ASEPs, which accurately evaluate error performance for signal-to-noise ratios (SNR) greater than 30 dB. All the results are verified through Monte-Carlo simulation. [ABSTRACT FROM AUTHOR]

Mobile communications systems are affected by what is known as fading, which is a well-known problem largely studied for decades. The direct consequence of fading is the complete loss of signal (or a large decrease of the received power). Rayleigh fading is a reasonable model for wireless channels although, Nakagami-m distribution seems better suited to fitting experimental data. In this paper we obtain the Nakagami-m distribution as a composite (mixture) of the Rayleigh distribution, a result which as far as we know it has not been shown in the literature. This representation of the Nakagami-m distribution facilitates computations of the average BER (Bit Error Rate) for DPSK (Differential Phase Shift Keying) and MSK (Minimum-Shift Keying) modulations for this distribution and higher moments of them, which is of great applicability to modeling wireless fading channels. Furthermore, a simple, not depending on any special function, apart of the Gamma function, bivariate version of the Nakagami-m distribution is also proposed as a special case of the multivariate version which is also presented. The proposed composite distribution is simulated through the standard procedure of summation of phasors, and results for the new closed-form measures for the MSK modulation are also shown. From that it is clear that the alternative formulation of the Nakagami-m distribution allows for easier modeling of fading fading-shadowing wireless channels through the new explicit second order statistics metrics. is well suited for modelling fading-shadowing wireless channels. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of free space optical (FSO) communication that incorporates the orthogonal frequency division modulation (OFDM) system with differential quadrature phase shift keying (DQPSK) modulation scheme. FSO has become a significant area of research in the optical communication field due to efficient communication systems with higher data transmission rates and lower energy requirements. While transmitting signals through free space, the efficiency of the system is constantly compromised by atmospheric turbulence. In this research, the Gamma-Gamma fading model is considered to incorporate atmospheric turbulence which offers better protection against signal fading and scintillation. Convolutional coding is introduced as the forward error correction (FEC) code with the OFDM technique to ensure better and easier encoding of the signal. The system performance is evaluated in terms of bit error rate (BER). All complex calculations and final result are computed with the help of a hyper-geometrical function, Meijer G. Final results are obtained in graphical form with the help of MATLAB software. System performance is analyzed in terms of BER by varying different system's parameters including the number of OFDM sub-carrier and link distance. Significant amount of coding gain almost 32 dB was found at a BER of 10–9, when the system link length is 2000 m and the refractive index structure parameter is 10–14 m−2/3. [ABSTRACT FROM AUTHOR]

The article presents the results of a method based on asynchronous delay-tap sampling (ADTS) and convolutional neural network (CNN) for determining simultaneously occurring disturbances described using the chromatic dispersion (CD), crosstalk and optical signal-tonoise ratio (OSNR) parameters. The ADTS method was used to generate training and test data for the convolutional network, which in turn was used to learn to recognize interference from said data. The tests were carried out for a transmission speed of 10 Gbit/s and for onoff keying (OOK) and differential phase shift keying (DPSK) modulation. Very good results were obtained in recognizing simultaneously occurring phenomena. Accuracy of over 99% was achieved for CD and crosstalk for DPSK modulation and over 98% for OOK modulation. In the case of amplified spontaneous emission (ASE) noise, slightly weaker results were obtained, above 95-96% for both modulations. Based on the conducted research, it was determined that the use of ADTS and CNN methods enables monitoring of simultaneously occurring CD, crosstalk, and ASE noise in the physical layer of the optical network, while maintaining the requirements for modern monitoring systems. [ABSTRACT FROM AUTHOR]

In this research, we investigated and analyzed the performance of an optical video transmission system. We combined the benefits of HEVC compression techniques and OTDM multiplexing using the Differential Phase Shift Keying (DPSK) scheme. Source and channel coding are separately designed and then cascaded. The intra-prediction module used in HEVC encoder has been implemented using the Matlab tool to show its ability to select the coding prediction threshold and block size using all prediction unit sizes and modes (PUs). The obtained results have been implemented for the second contribution concerning the proposed fiber transmission system using the OptiSystem software. To evaluate the proposed system, several metrics were used, including the signal-to-noise ratio (SNR), Q-factor, and bit error rate (BER). The simulation results show that the optimization criterion led to better performance in terms of transmission quality, in improving Q-factor and minimizing (BER), thus providing a significant resolution reduction of the video stream, which reduces the amount of data before being transmitted on the optical fiber. [ABSTRACT FROM AUTHOR]

Optical wireless technologies like Free Space Optics (FSO) have proven to be a perfect choice for 5G communication systems. FSO can offer low latency, high capacity, extensive connectivity, and high reliability at a low cost. However, the major limitation of FSO is its susceptibility to atmospheric turbulences, especially rain at high frequencies. In this paper, a rain efficient 10 Gbps 5G communication system using multibeam FSO and multilevel Differential Phase Shift Keying (M-ary DPSK) encoder is proposed. To evaluate the system performance at different rain intensities, the state-of-the-art Charbonneau channel model for rain attenuation has been used. The performance efficiency of the proposed system is evaluated in terms of quality factor (Q-factor), bit error rate (BER), optical signal-to-noise ratio (OSNR), and received power. The results convey that the proposed system can perform well up to 4.25 km, 3.24 km, and 2.55 km under below average, average, and above average rain conditions, respectively, with attenuation of 6.28 dB/km, 9.65 dB/km, and 19.27 dB/km, respectively. Moreover, the comparative analyses show that the proposed system performs better than the recent conventional systems in terms of bandwidth and power efficiency. [ABSTRACT FROM AUTHOR]

Underwater communication is one of the most important and difficult challenges facing researchers due to the high attenuation of the signal, communication with the surface because of the harsh medium of water, and data transmission performance degradation as a result of various effects. Underwater acoustic communication (UWA) has a low data rate, which describes the disadvantage of this type of communication. In addition, it has a low bandwidth range and high latency but has a long transmission range as an advantage. Multicarrier wireless transmission systems increase the data rate by sending the data using more than one carrier. We proposed a noncoherent orthogonal frequency division multiplexing (OFDM) method to increase the data rate in UWA communication systems. In addition, doubling the data rate in the OFDM using Subcarrier Power Modulation (OFDM-SPM) system can save half of the bandwidth. The MATLAB simulation program was used to implement the system in the underwater acoustic environment to increase its throughput. The proposed design uses Differential Phase Shift Keying (DPSK) with power control, and the data stream is transmitted through two-dimensional modulation schemes, the DPSK, and the power level of each subcarrier in the OFDM system with cyclic prefix (CP). The underwater channel was designed using a Rician fading multipath with a spreading loss formula as a function of distance and frequency. We designed an equalizer at the receiver side to recover the original signal as a function of three parameters which are: the channel effect as a rate between transmitting and receiving symbols, the Rician channel response, and the UWA spreading loss. OFDM-Subcarrier Power Modulation (OFDM-SPM) using the proposed equalizer performed better than the theoretical OFDM-SPM in the Rayleigh channel. The designed equalizer increased the performance of the OFDM-SPM system by 25% which helped to enhance the system's throughput and doubled the data rate compared with the OFDM system, doubling the data rate using OFDM-SPM had been validated in laboratory experiments in the Time domain. [ABSTRACT FROM AUTHOR]

With the development of the Internet and information technology, optical fiber communication systems need to meet people's information demand for large capacity and high speed. High-order phase modulation and channel multiplexing can improve the capacity and data rate of optical fiber communication systems, but they also bring the problem of bit error. To improve the transmission quality and reliability of optical fiber communication systems, forward error correction (FEC) coding techniques are commonly used, which serve as the fundamental approach to enhance the quality and reliability of fiber optic communication systems, ensuring that the received data remain accurate and reliable. The FEC in optical fiber communication systems is divided into three generations. The first generation FEC is mainly hard decision codewords, represented as RS code. The second generation FEC is mainly cascaded code, which stands for interleaved cascaded code. The third generation of FEC mainly refers to soft decision codes, which are represented as low-density parity-check (LDPC) codes. As a kind of FEC, LDPC codes stand out as pivotal contributors in the field of optical communication and have gained remarkable attention due to exceptional error correction performance and low decoding complexity. Based on IEEE802.16e standard, LDPC code with specific code length and rate is compiled and simulated in MATLAB and VPItransmissionMaker 10.1 and successfully incorporated into polarization multiplexed differential quadrature phase shift keying (PM-DQPSK) coherent optical transmission system. The simulation results indicate that the bit error rate (BER) can be reduced to 10−3 when the optical signal-to-noise ratio (OSNR) reaches 14.2 dB, and the BER experiences a reduction by nearly three orders of magnitude when the OSNR is 17.2 dB. These findings underscore the efficacy of LDPC codes in significantly improving the performance of optical communication systems, particularly in scenarios demanding robust error correction capabilities. This study provides valuable, significant results regarding the potential of LDPC codes for enhancing the reliability of optical transmission in real-world applications. [ABSTRACT FROM AUTHOR]

Free space optical (FSO) communication is a wireless alternative to fiber-based communication as it may provide a backbone emergency communication link in disaster-hit areas. This paper proposes a full duplex millimeter wave (mm-wave) enabled FSO system to provide a high data rate communication link for search and rescue operations. The proposed system consists of a central unit which is connected to multiple unmanned aerial vehicles (UAVs) through an optical-amplify and forward relay over an FSO channel represented by Log-Normal channel model. An optical comb is generated and Laguerre-Gaussian modes of each wavelength of the optical comb are exploited to carry 10 Gbps differential phase shift keying modulated signals. 60 GHz mm-wave signals are generated at the remote UAVs by employing optical heterodyne detection for downlink transmission towards the user equipment. For the uplink transmission, a dedicated wavelength is used to carry 10 Gbps on-off keying baseband data for live streaming of the disaster-hit area. Furthermore, a single hop scheme is employed to counter the non-line of sight issue of the FSO link. The performance of the proposed model is evaluated under different weather conditions and refractive index structure parameter values. A maximum distance of 3.3 km is achieved for clear sky under low turbulence conditions. Moreover, the effect of misalignment due to hovering of the UAVs on the system performance is also investigated and tolerance in the x (horizontal) and y (vertical) directions is observed at the forward error correction BER limit of 10 - 9 . The simulation results reveal that the proposed system has the potential to provide reliable and quick emergency communication services in disaster-struck areas. [ABSTRACT FROM AUTHOR]

At key optical network nodes the efficient deployment of WDM/DWDM technologies can be made possible by wavelength conversion. In this research, Cross-Polarization Modulation (XpolM) based All-Optical Wavelength Conversion (AOWC) using wide band Semiconductor Optical Amplifier (SOA) is obtained. The effectiveness of various optical differential phase modulations on wavelength conversion is analysed. NRZ-DPSK/DPSK, 33%RZ-DPSK, 50%RZ-DPSK and 67%RZDPSK/CSRZ-DPSK are investigated here. The data rate is 80 Gb/s and the conversion bandwidth is 1.04 nm. The analysis is extended for Linear, Lorentzian and No-approximation material gain simulation models. The NRZ-DPSK performs better in terms of maximum coupled intensity and ellipticity. CSRZ-displays a power spectral gain of up to 12 dB and shows narrower spectral width. [ABSTRACT FROM AUTHOR]

Wavelength division multiplexed passive optical is promising technique to achieve a high data rate and large number of user. The notable advantages of WDM PON is the combination of reliability, cheap in cost, accessible bandwidth, high security, large optical reach and it can support large number of ONU. There are multiple approaches to achieve high-speed WDN PON using different transmission techniques. In WDM, multiple lasers are required which increase the cost of the system. To reduce cost, an optical multicarrier generation system is proposed. An economical multiple carrier generation with the incorporation of sine generator and Mach–Zehndar modulator is demonstrated. Utmost work of sine generator and dual drive modulator was to attain low cost functioning of passive optical networks. Multicarrier generation was done and replacement of laser carriers with optical multicarrier generator. Carriers were generated with the frequency spacing of 20 GHz and these carriers were used in the passive optical networks with the tone-to-noise ratio of 40 dB, amplitude difference of 1.4 dB. For the transmission of downstream in the PON, differential phase shift keying was employed at 10 Gbps data speed. Transmission distance achieved was 30 km using single-mode fiber and this was a part of optical distribution network. Optical network unit was next part after ODN and signals were received with balanced receiver. Moreover, half signal was given to intensity modulator for the signal re-modulation. Bit error rate of 10–9 was achieved at all channels in the downstream. An upstream of 10 Gbps was accomplished in the passive optical network. [ABSTRACT FROM AUTHOR]

The development of communication technology requires a new type of passive optical network (PON) architecture. The architecture needs to be based on time division multiplexing (TDM) of 40 Gbit/s downstream and 10 Gbit/s upstream, and it can realize TDM PON prototype. The PON system achieved the system distance of 120 km supporting 128 ONU with power budget of 53.5 dB via polarization multiplexing differential quadrature phase shift keying format signal which employs the coherent receiver and the digital signal processing. [ABSTRACT FROM AUTHOR]

Optical wireless communication in space is attracting great consideration due to high speed, high capacity, no EMI, high security, and wide bandwidth. OWC has edge over microwave communication because in laser based communication, relay feature saves the time of the system. In this paper, different interference reduction techniques in wavelength division multiplexing based inter-satellite optical wireless system are presented at different data rates 10, 20, and 40 Gbps. Hybrid multiplexing using wide division multiplexing and time division multiplexing is proposed first and second technique proposed is polarization interleaving in IsOWC systems. Dense channel spacing system with diverse modulations is investigated further such as Chirped, differential phase shift keying, and alternate mark inversion (AMI). Q factor is the performance evaluation parameters for different distances. [ABSTRACT FROM AUTHOR]

Free-space optical (FSO) communication system provides several advantages over radio frequency (RF) system offering high bandwidth, low cost, small space requirements and more secure transmission which is free from Electromagnetic Interference (EMI). However, when the transmitted light signal passes through the atmosphere it experiences attenuation and fluctuations due to atmospheric turbulence. This paper analyzes the bit error rate (BER) performance of FSO communication systems under strong atmospheric turbulence for on-off keying (OOK), binary phase-shift keying (BPSK), differential phase shift keying (DPSK), quadrature phase shift keying (QPSK) and 8-phase shift keying (8-PSK) for link distances of 500, 1,000, 1,500 and 2,000 m. The probability density function (pdf) of the received irradiance is modelled using the gamma-gamma distribution model. It is found that the system exhibits the best BER performance and compensates the lowest power penalty at BER of 10 - 9 for BPSK modulation compared with other modulation techniques which makes BPSK more appropriate to be used with FSO turbulent system. [ABSTRACT FROM AUTHOR]

In the current research work, an analysis of differential phase shift quantum key distribution using InGaAs/InP and Silicon-APD (avalanche photodiode) as single photon detectors is performed. Various performance parameters of interest such as shifted key rate, secure key rate, and secure communication distance obtained are investigated. In this optical fiber-based differential phase shift quantum key distribution, it is observed that Si-APD under frequency conversion method at telecommunication window outperforms the InGaAs/InP APD. [ABSTRACT FROM AUTHOR]

The congestion in the radio frequency spectrum has posed a serious challenge for mobile service providers. Radio-over-free space optics (Ro-FSO) technology has been considered as a front runner to deal with the problem of spectrum congestion and to provide future generation high-capacity wireless networks. This work proposes designing and numerical analysis of differential phase shift keying (DPSK) modulation-based 20 Gbit/s–40 GHz hybrid mode division multiplexing-radio-over-free space optics (MDM-Ro-FSO) link up to 40 km transmission range under clear weather. Quality Factor (Q Factor), log of bit error rate (BER), signal to noise ratio (SNR), and received power are the key metrics used to probe the proposed system performance. The impact of increasing divergence angle and different fog weather conditions on the proposed system performance is also numerically evaluated. Further, the decomposition analysis of different spatial modes at the receiving unit is carried out in this work. [ABSTRACT FROM AUTHOR]

Underwater Optical Wireless Communication is not a newly coined idea but it has recently created renewed interest to the scientific community. In comparison to acoustic and RF counter parts it has many advantages like higher bandwidth, higher data rates at low latency levels and lower power consumption. The conventional methods such as intensity modulation (IM) schemes with direct detection, On/Off Keying, Pulse Position Modulation, Pulse Width Modulation in UWOC systems has certain disadvantages such as high latency, high BER etc. and also it is not suitable for some kind of practical applications like in video signal processing and transmission applications. Most of the modulation schemes in underwater has lower range of communication efficiency. Communication in the ranges of km is required for underwater vehicle sensors and observatories. Therefore, for better communication range we can use PSK modulations in underwater. So, in this paper we propose an UWOC system by using Differential Phase Shift Keying (DPSK) and Quadrature Phase Shift Keying (QPSK) modulation and Avalanche Photo Diode detection. The underwater medium is simulated with the proper adjustment of parameters in the optical wireless channel. The bit rate of optical link considered is at 10 Gbps for all the types of sea water. The efficiency is analysed in terms Q-Factor, Bit Error Rate (BER) and from the result it can be seen that both the QPSK and DPSK are suitable for underwater optical communications with a minimum BER of zero. However, in comparison DPSK has much better Q-Factor in underwater wireless optical links. [ABSTRACT FROM AUTHOR]

In this paper, an electroabsorption modulator-based relay is employed for the transmission of on-off keying (OOK) and differential phase shift keying (DPSK) signals over a free space optical (FSO) communication link. The FSO link is based upon the Gamma-Gamma (Γ - Γ ) channel model considering both medium and strong atmospheric turbulence conditions. 10 Gbps modulated OOK and DPSK signals are transmitted over the FSO link by employing all-optical amplify and forward (AOAF) and all-optical regenerate and forward (AORF) relay-assisted techniques. The bit-error-rate results are analyzed with respect to received optical power for the proposed model. It is observed that AORF relay-assisted OOK is performing better than AOAF at high data rates under medium atmospheric turbulence, whereas for DPSK-modulated signals, the performance is almost the same for both AORF and AOAF relay-based FSO links. The AORF-based relay for the transmission of OOK- and DPSK-modulated signals show significant improvement under strong atmospheric turbulence compared to the AOAF-based relay link. Furthermore, under multiple relay scenario for DPSK signal, AOAF results degraded while AORF remains almost the same under strong atmospheric turbulence. [ABSTRACT FROM AUTHOR]

A free-space optic (FSO) system model considering non-Hermitian orthogonal frequency division multiplexing (OFDM) modulation followed by optical differential quadrature phase shift keying (DQPSK) modulation is proposed. Analysis is presented for an OFDM-DQPSK FSO link considering an optical direct detection receiver based on dual detection optical QPSK demodulator. Analytical approach is developed to find the expressions for output current and signal to noise ratio (SNR) in presence of atmospheric turbulence. The conditional bit error rate (BER) for a given turbulence-induced fading is also derived. Average SNR and BER are obtained considering the turbulence-induced fading to be log-normal distribution. Results are evaluated in terms of average SNR and BER for different link distances, number of OFDM subcarriers, background current and different wavelengths. It is noticed that the proposed OFDM FSO system suffers 4 and 1.4 dB power penalty at a BER of 10−12 due to the effect of atmospheric turbulence and background radiation respectively for 512 number of OFDM subcarrier and link distance of 2,000 m. Comparison of the results is made with simulation results as well as experimental results reported earlier. The proposed OFDM FSO system provides better performance, with an almost 3 dB improvement in receiver sensitivity compared to the experimental results on OFDM-QPSK FSO link reported earlier at a BER of 10−6. Finally, the analytical results are verified by numerical simulation. [ABSTRACT FROM AUTHOR]

This paper investigates the error performance of various modulation techniques like on–off keying, binary phase shift keying, differential phase shift keying, and binary pulse position modulation against misalignment parameters. Misalignment parameter is related to the effective beam radius at the receiver plane with respect to the pointing error deviation at the same receiver plane. This manuscript considers a new approach of limiting the deviation of beam centre by using larger beam radius and subsequently considers the reduction of power flux density even when there is less pointing error. The intensity (power flux density) reduction due to misalignment and the losses taking place due to absorption by fog, snow, clouds and many more, are considered in this article. However, the atmospheric absorption losses are modelled using Beers–Lambert Law. In addition to that a simplest form of diversity known as aperture averaging is used to curb the losses due to misalignment. This manuscript unveils the scientific cause of decrease in error performance with increasing pointing error parameter. [ABSTRACT FROM AUTHOR]

Differential phase shift keying (DPSK) modulation and multi-aperture receiving are effective means for suppressing flickering, deviation, and fragmentation of the light spot by atmospheric turbulence. What is challenging in coherent beam combination of such an array receiver system is to detect and compensate for phase deviation of sub-apertures. In this paper, a method of phase alignment of an array optical telescope system using balanced detection was proposed and demonstrated. The improved Mach Zehnder Interferometer (MZI) can demodulate the digital signal and recover the phase difference at the same time. It also brings a 3 dB gain to the receiver and improves the detection sensitivity of the system. Adequate simulations with OptiSystem and MATLAB were carried out to show that the power value remains near the ideal state of 2.75 mW, and the bit error rate is less than 10−9 after phase compensation, which indicates the effectiveness and accuracy of the proposed method. Furthermore, taking the communication interruption difference of ninety degrees as an example, the system bit error rate was reduced from 1 to 10−35, and communication was established again. [ABSTRACT FROM AUTHOR]

Differential phase shift keying (DPSK) signals are widely employed in optical communication systems due to the high sensitivity and simple self-delay interference demodulation scheme. In this paper, we demonstrate a broadband on-chip Mach-Zehnder interferometer (MZI) for multiple channel DPSK signal demodulation. The chip is constructed using a single-mode high-index doped silica glass waveguide with fiber-to-fiber insert loss less than 3 dB and small second-order dispersion. The MZI interference fringe extinction ratio is over 25 dB in the range of C- and L-bands. The MZI is employed to demodulate four parallel DPSK signals simultaneously with similar performance, indicating that the broad bandwidth MZI is suitable for a receiver of massive parallel optical communications. • A broadband DPSK signal demodulator for massively parallel optical communication. [ABSTRACT FROM AUTHOR]

We propose a single laser source-based free space optical link for transmission of bidirectional data of three different channels between modular data centers, where each channel has a data rate of 20 Gbps. The downlink channels are transmitted using a combination of differential quadrature phase shift keying (DQPSK) and pulse amplitude modulation (PAM). The uplink channels are transmitted using On-Off keying (OOK). The optical signals are transmitted over a 500-m free space optical (FSO) link based on Gamma–Gamma channel model. A regenerative wavelength converter is used to generate multiple optical pulsed carriers from the received downlink optical signals. The performance of the proposed architecture is evaluated under medium turbulence condition, which represents the FSO channel in a data center scenario. Our simulation results show that the proposed architecture gives acceptable bit-error-rate (BER) results. The architecture can be used as a potential substitute to fiber-based interconnects in a data center or a general point link in a passive optical network (PON), enabling high data-rate and cost-efficient transmission. [ABSTRACT FROM AUTHOR]

Acoustic and optical communication are the best options for data transmission in underwater communication. This paper presents the simulation model of an underwater wireless optical communication channel using the Errorless Channel Selection Using Forward Error Rectification and Modulation Progression (ECFM). The suitable modulation methods are used to encode and transfer the packets properly, the data is encoded in differential phase shift key mode at the phase of the light wave carrier. In addition, to send and receive data, an error rectification method is developed in the transport layer, which improves network speed. In addition, we create connections by observing the impact of the refractive index of the optical channel and the reflections formed on the surface of the water. As well as the distance the data travels, throughput, packet delivery ratio, energy consumed, and delay are calculated and discussed using a network simulator. We also look at the losses caused by the operation of the channels running on the network and its location points. [ABSTRACT FROM AUTHOR]

In this paper, we have designed an ultra-dense wavelength division multiplexing system for 450 channels with a bit rate of 160 Gb/s per channel based on the high spectral efficient differential quadrature phase shift keying (DQPSK) modulation technique and investigated the performance of the system using different pulse shapes such as nonreturn-to zero, return-to-zero, carrier suppressed return-to-zero (CSRZ), modified duobinary return-to-zero and manchester, under the effect of various transmission impairments such as amplified spontaneous emission, group velocity dispersion, self-phase modulation and cross-phase modulation. Bit error rate (BER) and quality factor (Q-factor) have analyzed with variation in transmission distance and input power. It has also observed from the simulation results that the CSRZ pulse scheme serves the best performance in terms of BER and Q-factor due to its high tolerance towards linear and nonlinear effects. The maximum Q-factor of 14 dB and minimum BER of around 10− 13 have reported for CSRZ for a distance from 50 to 400 km. In the end, the eye diagrams for all the pulse shapes have compared under the influence of the combined effect of the above mentioned transmission impairments and found better eye-opening in CSRZ–DQPSK modulated system as compared to others. [ABSTRACT FROM AUTHOR]

Optical performance monitoring (OPM), particularly the optical power and optical signal-to-noise ratio (OSNR) of each wavelength channel, are of great importance and significance and need to be implemented to ensure stable and efficient operation/maintenance of wavelength division multiplexing (WDM) networks. However, the critical monitoring module of existing solutions generally are too expensive, operationally inconvenient and/or functionally limited to apply over WDM systems with numerous nodes. In this paper, a low-cost and high-efficiency OPM scheme based on differential phase shift keying (DPSK)-modulated digital optical labels is proposed and demonstrated. Each pilot tone is modulated by digital surveillance information and treated as an identity indicator and performance predictor that ties up to each wavelength channel and thereby can monitor the performance of all wavelength channels simultaneously by only one low-bandwidth photoelectric detector (PD) and by designed digital signal processing (DSP) algorithms. Simulation results showed that the maximum errors of channel power monitoring and OSNR estimation were both less than 1 dB after 20-span WDM transmission. In addition, offline experiments were also carried out and further verified the feasibility of our OPM scheme. This confirms that the optical label based OPM has lower cost and higher efficiency and thereby is of great potential for mass deployment in practical WDM systems. [ABSTRACT FROM AUTHOR]

Although LoRa modulation can achieve low-power and long-range transmission, its performance is significantly affected by fading channels. On the other hand, its low data rate limits the capacity. To mitigate these disadvantages, a new reconfigurable intelligent surface (RIS) assisted LoRa uplink system is proposed in this paper, where the reflection coefficients of the RIS are generated by utilizing an $M$ -ary differential phase shift keying modulator. Moreover, a low-complexity non-coherent receiver is designed for the proposed system. The new system is able to inherit the non-coherent detection of the conventional LoRa system and also transmit additional information of $\log _{2}{M}$ bits while reducing the impact of the fading channels. Furthermore, the bit-error-rate, symbol-error-rate and throughput expressions of the system are derived in closed form. Theoretical and simulated results show that the system has better performance than the conventional LoRa system and single-relay LoRa system. [ABSTRACT FROM AUTHOR]

Switching ripple communication (SRC), which modulates the PWM carrier with digital data and takes the switching ripple as a signal carrier, helps power electronic converters to transfer digital data along with power. This article discusses the theory and implementation of SRC technology. It proves that the modulation using square wave and sinusoidal wave carriers is compatible. The fundamental principles of frequency hopping–differential phase shift keying (FH–DPSK) modulation are then analyzed in detail, and an improved FH–DPSK scheme is proposed to suppress output voltage disturbances, thereby maintaining power quality, reducing communication noise, and separating power control and data modulation. Furthermore, to evaluate the reliability of the communication technique, the effect of power conversion on communication is discussed in detail. Finally, a buck converter with a switching frequency of 100/83.3 kHz is set up, and the experiment achieves a 16.7 kbps bit rate using quaternary modulation, demonstrating the correctness of the scheme. [ABSTRACT FROM AUTHOR]

The aim of this study is to present a proposed chromatic dispersion compensation model for single mode optical fiber. The proposed model consists of 4-stages of cascaded identical linear chirped fiber Bragg grating (CFBG) in post-compensation connection scheme. It is based on differential phase shift keying modulation format. To evaluate the performance of the proposed model, a comparative study is conducted using offset quadrature phase shift keying modulation technique. This comparative study includes four cases with and without using CFBG. For system performance evaluation, a 10 Gbps wavelength division multiplexing link is simulated at a distance of 70 km under conventional operating parameters. Optisystem 7.0 has been used for simulation and evaluation process. Quality factor (Q-factor) and bit error rate (BER) are used as evaluation metrics. The proposed model shows the best performance in case of using CFBG compared to the other cases. A maximum Q-factor of 7.22, and a corresponding minimum BER of 2.59 × 10−13are obtained. The proposed system performance is enhanced by at least 53% as compared to related work. [ABSTRACT FROM AUTHOR]

We consider a dual-function radar communication (DFRC) system employing frequency hopping (FH) radar waveforms. Each communication symbol is represented by a phase-modulated pulse sequence that multiplies the radar hops in fast-time and transmitted from a multiple-input multiple-output radar platform. In this respect, the DFRC system considered follows the code-shift keying (CSK) signal embedding strategy. The phase modulations include phase-shift keying (PSK), derivative PSK, and continuous phase modulation. The CSK pulse sequences and the FH code are jointly designed to reduce range sidelobe levels (RSLs) and combat range sidelobes modulation. It is shown that the joint optimization using the genetic algorithm yields desired CSK sequences and FH code matrix with less computational complexity compared to the exhaustive search algorithm. The power spectral density and detection performance of various DFRC systems are analyzed, underscoring the tradeoff between RSLs and spectral sidelobe levels. The proposed DFRC system with optimum phase sequences and hopping code achieves high data communication rates by permitting frequencies to be reused in the radar hops. [ABSTRACT FROM AUTHOR]

In this work we consider a multiple-input multiple-output (MIMO) dual-function radar-communication (DFRC) system, which senses multiple spatial directions and serves multiple users. Upon resorting to an orthogonal frequency division multiplexing (OFDM) transmission format and a differential phase shift keying (DPSK) modulation, we study the design of the radiated waveforms and of the receive filters employed by the radar and the users. The approach is communication-centric, in the sense that a radar-oriented objective is optimized under constraints on the average transmit power, the power leakage towards specific directions, and the error rate of each user, thus safeguarding the communication quality of service (QoS). We adopt a unified design approach allowing a broad family of radar objectives, including both estimation- and detection-oriented merit functions. We devise a suboptimal solution based on alternating optimization of the involved variables, a convex restriction of the feasible search set, and minorization-maximization, offering a single algorithm for all of the radar merit functions in the considered family. Finally, the performance is inspected through numerical examples. [ABSTRACT FROM AUTHOR]

The primary goal of this paper is to assess the performance of an Orthogonal Frequency Division Multiplexing Access (OFDMA) transmission system with a High Power Amplifier (HPA) at the transmitter edge. Differential Phase Shift Keying (DPSK) and Quadrature Amplitude Modulation (QAM) modulation techniques are used to generate the OFDMA signal. For modulation and demodulation, the Complex Wavelet Transform (CWT) is proposed instead of the Fast Fourier Transform (FFT). As a result, an algorithm is demonstrated that shows the effect of HPA on the modulated signal at the transmitter end. Reducing the high Peak to Average Power Ratio (PAPR) of an OFDMA signal is a difficult problem that is still being researched. As a result, the issue of PAPR performance evaluation in OFDMA systems is being investigated. As a result, a signal recovery algorithm is being researched in order to overcome the OFDMA system's limitation. This algorithm is based on detecting the highest peak. These peaks are estimated to be equal to the average value of the OFDMA signal as well as the detected peaks above the OFDMA signal's threshold limit. Furthermore, the results of the algorithm are compared to the results of the general clipping method. Bit error rate (BER) analysis is used to evaluate the performance of the transmitted OFDMA signal over fading channels. Rayleigh with Rician channel noise fading introduces the highest BER on the transmitted signal, according to the results. Furthermore, the accuracy of the highlighted algorithms is assessed using statistical measurements. The effect of contaminated channel impairments on the received modulated OFDMA signal, on the other hand, is investigated. As a result, recognizing the OFDMA signal is of primary importance. As a result, the Power Density Spectrum (PDS) and High Order Statistics (HOS) algorithms are proposed for identifying OFDMA signals. [ABSTRACT FROM AUTHOR]

In this paper, we present a differential modulation and detection scheme for use in the uplink of a system with a large number of antennas at the base station, each equipped with low-resolution analog-to-digital converters (ADCs). We derive an expression for the maximum likelihood (ML) detector of a differentially encoded phase information symbol received by a base station operating in the low-resolution ADC regime. We also present an equal performing reduced complexity receiver for detecting the phase information. To increase the supported data rate, we also present a maximum likelihood expression to detect differential amplitude phase shift keying symbols with low-resolution ADCs. We note that the derived detectors are unable to detect the amplitude information. To overcome this limitation, we use the Bussgang Theorem and the Central Limit Theorem (CLT) to develop two detectors capable of detecting the amplitude information. We numerically show that while the first amplitude detector requires multiple quantization bits for acceptable performance, similar performance can be achieved using one-bit ADCs by grouping the receive antennas and employing variable quantization levels (VQL) across distinct antenna groups. We validate the performance of the proposed detectors through simulations and show a comparison with corresponding coherent detectors. Finally, we present a complexity analysis of the proposed low-resolution differential detectors. [ABSTRACT FROM AUTHOR]

To overcome the power jitters in satellite-to-ground communications caused by atmospheric turbulence, a type of DPSK free-space communication system, assisted by a self-designed real-time phase lock controller, has been established. The system can effectively compensate for power swings in communication links and hence achieve high sensitivity. The wavelength division multiplexing technique is applied to a four-channel DPSK system to provide greater link capacity. With the data rate of a single channel as 2.5 Gbps and unencoded BER as 1 × 10–3, reception sensitivity has been obtained at −53.58 dBm (13.69 photons/bit), −53.59 dBm (13.66 photons/bit), −53.61 dBm (13.59 photons/bit), and −53.63 dBm (13.53 photons/bit) for each independent channel, respectively. The gap between our sensitivity result and the theoretical limit has narrowed to about −3.5 dB. Simultaneously, the DPSK receiver, with our self-designed phase lock controller, has stabilized reception of optical power fluctuations that range from 0 to 40 dB. Additionally, the impact of a four-wave mixing effect on multi-channel system performance has been investigated in detail. Our experimental results present a novel solution for the superior performance of free-space communication links.

The Costas loop is an important technology for synchronous demodulation in space coherent communication. However, due to the limitation of the loop device and processing technology, it is difficult to achieve high-precision locking, which results in the Costas loop phase deviation and further affects the quality of the demodulation signal. In this paper, a closed-form bit error rate (BER) model is derived to evaluate the Costas loop phase deviation effect on BER performance in the space differential phase shift keying (DPSK) modulation and heterodyne detection communication system, considering laser phase noise, atmospheric turbulence, and detector noise. Based on the BER model, analytical solution simulation is conducted. The results show that the BER performance deteriorates varying with the increase of the Costas loop phase deviation. In addition, we research how to better balance the laser linewidth and Costas loop accuracy in the system design to ensure good communication status. We find that the wider the laser linewidth, the more stringent the Costas loop accuracy. Furthermore, the BER performance versus the Costas loop phase deviation under different satellite-to-ground communication system parameter settings including divergence angle, receiving aperture, signal laser power, and data rate are analyzed. This work provides valuable references for space optical coherent communication systems design. [ABSTRACT FROM AUTHOR]

This document Designing system with Free-space optical (FSO) communication can supply high-speed digital data linkages to rural regions where geography, setup costs, and groundwork safety are major obstacles. Transmission impairments and space loss could be considered major challenges for handling the FSO system. This work, it has been designed and analyzed a system based on the combination of Dual Polarization Differential Quadrature Phase Shift Keying (DP-DQPSK) and Dense Wavelength Division Multiplexing (DWDM) using the Direct Detection (DD) technique. The proposed system has been utilized with a hybrid transmission medium of Single-Mode Fiber (SMF) with a fixed length of 60 km and FSO with a varied length of (5, 7, and 9) km. The system was designed with Optisystem software 18 and consist of 64 channels and 14 Gbps of data rate per channel to make the system 5G communication compatible, 3.5 GHz RF electrical signals have been used to modulate the optical carrier. The channels 1, 6, 12, …, 64 were selected as samples among all channels to be investigated and analyzed along with four different atmospheric weather conditions. Additionally, the proposed system is designed to investigate based on different weather attenuation that affected the parameters of Quality Factor (QF) and Bit Error Rate (BER). The significant advantage of the proposed system by using the DD technique is no reference wave is required. Hence, make the system less complex and possible to be implemented and tested via different weather conditions. Results obtained indicate reverse relation between the QF and both the FSO distance and attenuation. While BER-based parameters showed a direct relation. For light air and haze, the results showed that the system has higher reliability for all the three investigated FSO distances. For the medium haze, the system has shown the capability to transfer as far as 7 km. And for the rain condition, the system capability was set to 5 km. [ABSTRACT FROM AUTHOR]

In this research article, we investigate the impact of different atmospheric turbulence along with polarization crosstalk on the bit error rate (BER) performance of a non-Hermitian orthogonal frequency division modulated (OFDM) free-space optical (FSO) system with polarization diversity. Analysis is carried out for a non-Hermitian coherent optical OFDM followed by differential quadrature phase shift keying FSO system with polarization diversity in presence of atmospheric turbulence for all weather conditions. We considered Log-normal, Gamma-Gamma and Negative exponential turbulence fading model for weak, medium and strong atmospheric turbulent channel respectively and for cross polarization induced crosstalk, the random misalignment angle is Maxwellian distributed. The system average BER is calculated by averaging the conditional BER over the probability density function of the channel irradiance along with Maxwellian distributed random misalignment angle. Results are evaluated in terms of BER, power penalty due to polarization crosstalk along with atmospheric turbulence and receiver sensitivity due to OFDM. Results show that the system suffers almost 7.5, 11 and 16 dB power penalty due to polarization crosstalk along with weak, medium and strong turbulence respectively at a constant BER of 10–12 when the system link length is 3000 m. It is clearly observed that, almost 19, 16 and 10 dB receiver sensitivity is achieved when number of subcarriers increase into 512 for weak, medium and strong turbulence conditions, respectively at a constant BER of 10–12. [ABSTRACT FROM AUTHOR]

Multiplexing concepts like WDM and DWDM are being employed for effective utilization of fiber bandwidth. Wavelength conversion at key network nodes can allow the deployment of these technologies in addition to wavelength routing, contention resolution and it makes the networks all-optical communication networks. Cross polarization modulation (XPolM) is used in wideband semiconductor optical amplifiers (SOA) to implement all-optical wavelength converter (AOWC) as SOAs offer the necessary nonlinearity. In this paper, the effectiveness of CSRZ-DPSK data format in wavelength conversion is assessed for the data rate of 80 Gbps. The input pump power dependent polarization rotation of the signal is demonstrated. Input pump power of -12 dBm which falls in the sub-mW range and the bias current of 260 mA in SOA are optimized numerically. Error free all-optical wavelength conversion is achieved with BER of 2.25 × 10− 117 along with the Q factor of 66.2. The investigation is extended for both up and down conversions and the proposed system works well for up conversion relatively. The numerical simulations expose that the optical CSRZ-DPSK data modulation has better jitter tolerance than the optical OOK and has insignificant phase noise. [ABSTRACT FROM AUTHOR]

Here, the amplification performance of distributed Raman amplifier in a dense wavelength division multiplexed (DWDM) system is analyzed. We aim to compare the performance of distributed Raman amplifier using different digital modulation formats accordant with the bit error rate (BER) and Q factor through simulations. The various pumping methods like forward pumping, backward pumping, and bidirectional pumping for different pump powers have been compared by varying the modulation formats. Binary phase shift Keying (BPSK), differential phase shift keying (DPSK), carrier suppressed DPSK (DPSK‐CS), and quadrature phase shift keying (QPSK) with RZ and NRZ are analyzed as their spectral efficiency is found to be better than OOK systems. Our simulation results indicate that the bit error rates are much lesser for Raman Amplifier systems with QPSK‐NRZ modulation format having SNR improvement of almost 6 dB. [ABSTRACT FROM AUTHOR]

Summary: Optical transmission networks (OTxNs) provide a cost‐effective solution towards ultrahigh data intercontinental transmission. However, nonlinear effects such as four‐wave mixing (FWM) and cross‐phase modulation (XPM) are the major performance limiting factors for OTxNs. This paper proposes the use of differential quadrature phase shift keying (DQPSK) modulation format and uneven channel spacings for dispersion compensation and investigates the nonlinear mitigation performance for a 32 channels ultradense wavelength division multiplexing (UDWDM) with data rate of up to 10 Gbps per channel. In addition, this paper presents an analysis on power budget and power penalties with a cost benefit analysis (CBA) for the proposed framework. The transmission link of the proposed UDWDM model is analyzed in terms of bit error rate (BER) for various lengths of optical fiber in long‐haul transmission, launch power, nonlinear effective area, and nonlinear refractive index. The analytical model is developed for mitigation of nonlinearity for the modeled UDWDM long‐haul and ultrahigh‐capacity system, beyond 1200‐km path span. The simulation results show systems advantages of having narrower spectrum than on‐off‐keying (OOK) modulation, significant tolerance to nonlinearities and low cost, compared with current OTxNs with 2.8‐dB optical signal‐to‐noise ratio (OSNR) improvement and successful mitigation of nonlinearities for as high launch powers as +4 dBm for such long distance transmission in dispersive channel. [ABSTRACT FROM AUTHOR]

We consider a power constrained downlink communication scenario where energy efficiency, reliability, and latency take precedence over rate, as in some Internet of Things (IoT) applications. To reduce its receiver power consumption and complexity, we assume that the IoT device has a single RF chain and investigate the finite-resolution analog-to-digital converter (ADC) operation with differential Phase Shift Keying (PSK) modulation. A lower ADC resolution leads to an exponential decrease in power consumption, while adopting differential PSK enables the use of a low-cost detector with no channel state information (CSI) or carrier phase recovery circuitry. Our main goal in this article is to compare, both analytically and numerically using representative IoT system design parameters, the receiver energy efficiency of the proposed differential PSK system with a coherent PSK system that uses estimated CSI under reliability and latency constraints in Rayleigh slow-fading and ADC quantization distortion conditions. To mitigate the ADC finite-resolution effects without requiring CSI at the receiver or transmitter, we propose and analyze a PSK differentially-modulated Alamouti space-time block transmission scheme with only two RF chains at the transmitter while still restricting the IoT device to have a single RF chain. Our results demonstrate that in the considered low-rate, and outage and latency-constrained scenario with stringent power consumption requirements, differentially-modulated Alamouti transmissions to a single RF-chain IoT device with a low-resolution ADC is an attractive choice in terms of receiver energy efficiency, reliability, and transmission latency.

Free space optical (FSO) communication is a remarkable transmission technique and offers many benefits such as faster rate of data transfer, immunity to electromagnetic interferences (EMI), security and enormous bandwidth. In this research article, a spectrum sliced (SS) FSO system at 2.5 Gbps is demonstrated by using Supercontinuum generation in highly nonlinear fiber for spectrum broadening. Modulations plays crucial role in the final performance of FSO system and therefore, differential phase shift keying (DPSK) based SS-FSO system is investigated at different FSO distances, beam divergences, transmitter and receiver antenna diameters in terms of Q factor and log BER. Further, in order to evaluate the performance of proposed systems, it is compared with non-return to zero (NRZ), return to zero (RZ) and compressed spectrum RZ (CS-RZ). Result revealed that proposed DPSK-SS-FSO system surpassed the performance of rest of investigated modulations formats. [ABSTRACT FROM AUTHOR]

The present work deals with the use of biphasic codes for their application as an exciting signal in pulse compression radars. Its main characteristics are exposed and the digital design of sections for modulation, reception and compression is described. Very High-Speed Integrated Circuit Hardware Description Language (VHDL) was used for its implementation and MATLAB® for simulation, modelling and synthesis in VHDL of functional blocks. A 32-bits code is used with witch a 20.56 dB Peak to Sidelobe Level Ratio (PSR) is guaranteed. The contribution of the proposal lies in the demonstration of two convolution synthesis methods for the BPSK signal. Is presented and described its finite difference equation that define both of the convolution methods and also presented main resources used for their synthesis on DE10-Standard Development Kit. [ABSTRACT FROM AUTHOR]

The hybrid optical code-division multiple-access over wavelength-division multiplexing (OCDMA/WDM) scheme has attractive features of supporting system reach, multi Gbps data rates, security, and robustness for optical communication networks. This paper presents the performance of such scheme under DPSK and QPSK modulation formats using spectral direct detection technique. The modified double weight (MDW) code is used as spectral amplitude coding which also acts as a signature address code for the OCDMA system. The MDW code has the advantage of reducing the multiple access interference (MAI) and enhancing the security of the proposed hybrid system. The study focuses on the comparison between the two advanced modulation techniques (DPSK, QPSK) using spectral direct detection. Simulation results show bit-error-rate (BER) ≤10–09 for up to 25 km distance at the bit rate of 1 Gbps for optical communication networks. [ABSTRACT FROM AUTHOR]