Phase shift keying

Circular harmonic expansion-based carrier frequency offset estimation is investigated for optical MQAM communication systems. The proposed method, combined with a gradient-descent algorithm, shows better performance compared to already proposed VVMFOE and 4 th power methods.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

All-optical nonlinear phase noise reduction using an InP-over-SOI PhC nanocavity is experimentally demonstrated for 20-Gbit/s NRZ-QPSK signals. The phase-preserving intensitylimiting function results in an OSNR penalty reduction of 3.5 dB at a BER of 10 -3 .

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

We present a simple alternative method for the compensation of quadrature imbalance in optical quadrature phase-shift-keying (QPSK) coherent systems. The method is based on the determination and the compensation of the phase mismatch by the introduction of a relevant signal-to-noise ratio metric. The principle is validated numerically and the algorithm is validated experimentally through bit-error-rate (BER) and error vector magnitude (EVM) measurements. A 20 Gb/s optical QPSK experiment reveals a good agreement of the proposed method with the Gram-Schmidt orthogonalization procedure (GSOP). Moreover, the robustness of both methods was verified with up to 30° phase misalignment by comparing the signal after phase imbalance compensation to that without compensation. A 10% reduction of EVM is achieved with our method for a high phase misalignment of 30 .

We investigate the cascadability of a microcavity-saturable-absorber-based phase-preserving amplitude regenerator for RZ-DPSK signals. The results show that the tolerance of phase-encoded signals to nonlinear phase noise is increased. A distance improvement ratio up to 1.6 is experimentally demonstrated.

This paper presents a theoretical and experimental comparison of two techniques of optical fiber current sensors (OFCS) based on the Faraday Effect: the power and the degree of polarization (DOP) methods. The DOP method is shown to be insensitive to state of polarization (SOP) changes induced by environmental conditions. A maximum variation of 0.4% in the DOP value in the entire range of applied current from 0 to 100 A was measured. It is the first time to our knowledge that this fact was experimentally verified. Also, for the first time known it is reported that zero current response, DOP = 0.996, is in agreement with the theoretical expected value of unitary DOP. Besides, the theoretical and experimental normalized DOP is shown to have a maximum difference of 0.33% in the entire range of applied current. On the other hand, the power method OFCS is greatly affected by SOP changes. In order to be used in a practical application, its complexity must be increased by the use, for example, of polarization maintaining fibers instead of standard fibers used in the DOP method, increasing the cost of the sensor element.

MIMO is a modern mobile scheme used for the transmission of digitized data at high speed, which has a large number of narrow band subcarriers. It needs multiple antennas at both the transmitter and receiver side. In real time, the implementation of Multiple-Input Multiple-Output (MIMO) is more complicated. To overcome this problem, one new method was implemented, that is SEC(Stepwise Exponential Companding) based Quadrature Phase Shift Key (QPSK) detection which is implemented in Field Programmable Gate Array (FPGA) device. This method has a better feature for both Communications as well as the VLSI domain. This method has a great future for the wireless 5G system because of its spectral competence and robustness of the channel. Our investigation observed results are promising one to minimize MIMO detection complexity which can enhance the MIMO scheme operation.

Automatic modulation classification (AMC) is an essential task in intelligent receivers. AMC research papers over multipath fading channels have two problems. The first problem is the Higher-order moment (HOM)based normalized channel coefficients estimator is not valid for some types of digital modulations. The second problem is poor classification accuracy. This paper solves these problems through significant steps, first, by finding a new HOM-based normalized channel coefficients estimator for all cases of digital modulation types, and second, by finding the mathematical forms of the transmitted signal's estimated normalized HOMs and Higherorder cumulants (HOCs), and third, by selecting the most discriminative estimated HOCs for AMC using features selection algorithms. The simulation results show that the classification accuracy of the selected estimated HOCs, for M-array Phase Shift Keying (MPSK) and M-array quadrature amplitude shift modulation (MQAM) classification is highly improved compared with reference papers. It's 100% for the three-tap multipath channel case, and Signal-to-noise ratio (SNR) values greater than 6 dB. Keywords Automatic Modulation Classification, Higher-order Cumulants, Multipath fading channel, Feature selection algorithms. The automatic modulation classification (AMC) algorithm determines the modulation type of the received signal. This task is somehow simple over the Additive white Gaussian noise (AWGN) channel, but it becomes more complicated over the multipath fading channel. Research papers [1-3] improved the AMC performance using HOCs over AWGN channels. Our work focuses on improving the AMC performance using HOCs but over multipath fading channels. Research papers classify the digital modulation types over multipath fading channels through two steps [4-6]: First, the normalized channel coefficients are estimated using the HOM of the received signal. Second, some of the normalized cumulants of the transmitted signal are estimated based on the previously estimated normalized coefficients. In , the author shows the performance accuracy of binary phase-shift keying (BPSK) and Quadrature Phase-Shift Keying (QPSK) classification, using the estimated normalized cumulant 42, ˆx C of the transmitted signal for the four-tap multipath case and SNR value of 10 dB is 89%. The performance accuracy of 4-quadrature amplitude modulation (4QAM), 16QAM, and 64QAM classification is 77%. In [5], the author shows the performance accuracy of BPSK and QPSK classification, using the estimated normalized cumulant 63, ˆx C of the transmitted signal for the four-tap multipath case, and SNR value of 10 dB is 91%. The performance accuracy of QPSK, 16QAM, and 64QAM classification is 45%. In [6], the author shows the performance accuracy of BPSK, QPSK, 8PSK, 16QAM, and 64QAM classification, using three normalized estimated cumulants 40, ˆx C , 41, ˆx C , and 42, ˆx C of the transmitted signal for the four-tap multipath case and SNR value of 10 dB is 82%. As a result, the AMC performance degrades for lower SNR values cases. So, the selected estimated HOCs in have poor performance for AMC over the multipath fading channel. Deep learning techniques have also been used to classify digital modulations over multipath channels . In [7], the author uses the convolutional neural network technique (CNN) to classify PSK, QAM, frequency-shift keying (FSK), Pulse-amplitude modulation (PAM), and analog modulation. The performance accuracy for SNR value of 10 dB is 90%.In [8], the author uses 60, y C and 63, y C of the received signal as input features to the stacked convolutional auto-encoder to classify BPSK, QPSK, 16-QAM, and 64-QAM over the multipath channel. The performance accuracy for the 5-tap multipath Rayleigh fading channel and SNR value of 10 dB is 91%. ' ' / 2 / 2 21 21 Estimate the normalized channel coefficients (Section 4)

Free space optical communication is gaining importance in the field of optical communication due to its high speed and high bandwidth applications. Free space optical communication system (FSOCS) provides many benefits as compared to traditional wireless communication system and fiber optic cables. This makes this technology the reasonable extension of metropolitan area network and also provides the quick recovery during natural disaster. This system performance is limited due to the atmospheric turbulence effect and various atmospheric losses such as rain, and fog. Gamma gamma atmospheric turbulent model is used to analyze the system performance in the presence of moderate to strong atmospheric turbulence. We have designed the FSO gamma gamma turbulent model with non-return to zero (NRZ) modulation format employing wavelength division multiplexing (WDM), spatial diversity multiple input multiple output (MIMO) (8×8) at various atmospheric turbulence levels and attenuation loss of 10 dB/km at the distance of 2-4 km. Using the proposed model, the link distance is enhanced up to 4km in the presence of turbulence and atmospheric losses with minimum laser transmitted power.

In this search, an important methodology has been presented for communicated information rectification utilizing advanced channel windowing approach. The modern data communication technologies are ensured with numerous challenges because of their unpredictability and arrangement. Various digital transmission topologies in 4G can't fulfill the requirements in future arrangements, therefore, alternative multicarrier modulation (MCM) becoming the nominated approaches among all other data transmission techniques. Wherein prototype filter configuration is a fundamental system based on which the synthesis and analysis filters are derived. This paper presents a complete review on the ongoing advances of finite impulse response (FIR) filter plan procedures in MCM based correspondence frameworks. Initially, the essential issues are tried, taking into consideration the presentation of available data signal applicants and the FIR filter design concept. At that point the techniques for FIR filter configuration are summed up in subtleties and are center around the accompanying three group’s recurrence testing strategies, windowing based strategies and advancement-based techniques. At last, the exhibitions of different FIR structure strategies are assessed and measured by power spectral density (PSD) and bit error rate (BER), and variable MCM plots as well as their potential prototype filters are examined.

An inverter circuit is promoted in this paper, using series-connected switched dc sources along with an H-bridge circuit with optimized circuit elements like switching devices and diode clamped (DC) sources. This configuration uses DC supplies that can be strung together in series to create a significant voltage level. This topology consists of two parts, namely: 1) level production part and 2) polarity production part. The combination of some of the dc sources and switching devices completes the level production part. The H-bridge in the presented structure produces the polarity generation part. The DC-link capacitors are not needed in this design. There is a full presentation of the operating modes and modeling process of the proposed converter. Finally, in the MATLAB/SIMULINK setting the proposed topology is simulated and output current and voltage results have been examined.

The system diagrams for the digital radio compatible with NASA's S-Band Space Network operating from 2025.8 -2117.9 MHz (forward link) to 2200 -2300 MHz (return link) are presented. The digital radio implementation includes binary phase shift keying (BPSK), quadrature phase shift keying (QPSK) and staggered quadrature phase shift keying (SQPSK). We have derived the system requirements for these modulation schemes from the Space Network User Guide (SNUG) and thereafter, derived system diagrams for the communication links. The designed system diagrams for the transceiver were implemented using Simulink models and USRP2 platform.

In the article, we present an ad hoc (AH) detector for two differentially encoded BPSK sources in the Hierarchical MAC (H-MAC), i.e., for the case when the receiver sees the superposition of non-orthogonal signals from individual sources. (Prefix “H-” means Hierarchical, it emphasizes that the entity is related to the many-to-one principle.) The AH detector decodes the XOR H-map of the two BPSK streams—in other words, it decides whether the transmitted symbols from the two sources are the same or opposite. The BER of the detection in H-MAC is denoted as H-BER. The H-BER is compared with the other two differential detectors, with the coherent (Coh) detector, and with an approximate coherent (ApC) detector. The exact analytical H-BER formula is derived for the ad hoc and coherent detectors. The proposed ad hoc detector is very simple for evaluation, does not require the estimation of subchannel phases, does not depend on noise variance, and it is uniformly only roughly 3.5 dB worse th...

Cognitive radio systems provide an intelligent solution to spectrum scarcity by dynamically accessing underutilized frequency bands licensed to primary users. Among various sensing techniques, energy detection (ED) is extensively adopted due to its inherent simplicity and minimal computational requirements, but suffers from poor performance at low signal-to-noise ratio (SNR) environments under channel impairments such as additive white gaussian noise (AWGN) and multipath fading. This paper proposes an enhanced spectrum sensing approach by integrating ED with entropy-based techniques, specifically Kapur and Renyi entropy measures. The proposed methods are evaluated under AWGN and various fading environments with binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) modulations. Simulation results demonstrate substantial improvements in detection performance. The results show that entropybased enhancements significantly improve the reliability of spectrum sensing in cognitive radio (CR) systems operating under challenging channel conditions. Among the fading models, the Nakagami channel causes the greatest degradation in detection probability, followed by the Rayleigh fading channel. ED with Renyi entropy improves Pd by 15-fold and 8-fold, compared to ED under Nakagami and Rayleigh channels respectively.

The soliton optical phase stability versus amplified spontaneous noise is investigated in a recirculation loop experiment in the presence of in-line filters. The behavior of phase fluctuations is shown to be in good agreement with numerical simulations. The phase standard deviation is kept below 0 15 for distances up to 8000 km. We, therefore, demonstrate the feasibility of phase-shift keying on solitons for long-haul transmission systems.

This paper details the design of integrated balanced PSK modulator using finline coplanar line hybrid junction. The PSK signal output is in suspended stripline with incident wave carrier in finline. Schottky barrier Diode MA4E2037 has been used for modulation. The balanced configuration offers high isolation between the carrier input port and the modulated carrier output port and thus the pulse width variations and amplitude deviations are suppressed. An insertion loss imbalance of±1.5 dB with an average loss of 2 dB in the two switching states has been achieved over 38.9 to 40 GHz. The phase imbalance is±10 degrees with phase switching from 180 to 199 degrees As the PSK output signal is in suspended stripline, two BPSK modulators can be easily combined together to work as QPSK modulator.

Data Encryption and User Authentication are the major communications security (ComSec) approaches used in today's communications networks. While these methods provide an efficient means to secure the sensitive information, they do not prevent a hostile opponent from jamming the signal or tapping the link. We present here an analysis of a coherent optical communications system providing secure communications in free-space or over fiber. Communications we present a system using polarization/frequency agility to secure the data link at the optical layer. The key building blocks will be presented, including a QPSK transmitter, and an optical hybrid combined with a coherent digital receiver. A description of CeLight's LiNbO 3 integrated implementation of the transmitter and the receiver will be detailed. Next, a theoretical analysis demonstrating the capabilities of such a secure communications system to send data over fiber and in free space eliminating the need for optical filtering and lambda-based de-multiplexing. Finally, we present an experiment demonstrating the ability of the proposed frequency hopping solution to avoid an eavesdropper from intercepting the data channel.

We describe a relatively simple but effective closed-loop bias control of LiNbO 3 quadrature modulator (QM) for optical quaternary phase-shift-keyed (QPSK) transmission. Simulation and experimental results of the feedback control loop for maintaining near optimal operating points of the QM are described for 12.5-GSym/s optical QPSK. The control loop uses nonhigh-speed off-the-shelf components independent of the symbol rate. Similar performance of the control loop at higher symbol rates using the same components is expected.

In this correspondence our aim is to use some tight lower and upper bounds for the differential quaternary phase shift keying transmission bit error rate in order to deduce accurate approximations for the bit error rate by improving the known results in the literature. The computation of our new approximate expressions are significantly simpler than that of the exact expression.

We report on the transmission experiment of seven 12.5-GHz spaced all optical-orthogonal frequency division multiplexed (AO-OFDM) subcarriers over a 35-km fiber link, using differential quadrature phase shift keying (DQPSK) modulation and direct detection. The system does not require chromatic dispersion compensation, optical time gating at the receiver (RX) or cyclic prefix (CP), achieving the maximum spectral efficiency. We use a wavelength selective switch (WSS) at the transmitter (TX) to allow subcarrier assignment flexibility and optimal filter shaping; an arrayed waveguide grating (AWG) AO-OFDM demultiplexer is used at the RX, to reduce the system cost and complexity.

For over 40-Gbps optical communication systems, phase coded modulation formats, like differential phase shift keying (DPSK) and quadrature phase shift keying (QPSK), are very important for signal frequency efficiency and long-reach transmission. In such systems, differential receivers which regenerate phase signals are key components. Dual Photo Diodes (dual PDs) are key semiconductor devices which determine the receiver performance. Each PD of the dual PDs should realize high speed performance, high responsibility and high input power operation capability. Highly symmetrical characteristics between the two PDs should be also realized, thus the dual PDs are desired to be monolithically integrated to one chip. In this paper, we describe the design, fabrication, characteristics and reliability of monolithically integrated dual evanescently coupled waveguide photodiodes (EC-WG-PDs) for the purpose described above. The structure of the EC-WG-PDs offers the attractive advantages of high speed performance, high responsivity and high input power operation. Furthermore, their fabrication process is suitable for the integration of two PDs on one ship. First, the optimization was done for high products of 3-dB bandwidth and responsivity for 43-Gbps DPSK receivers. Excellent characteristics (50 GHz bandwidth with a responsivity of 0.95 A/W), and high reliability were demonstrated. The other type of optimization was done for ultra high speed operation up to 100-Gbps. The fabricated PDs exhibited the 3 dB-bandwidth of 80 GHz with a responsivity of 0.25 A/W. Furthermore, 43-Gbps RZ-DPSK receivers including the dual EC-WG-PDs based on the former optimization and differential transimpedance amplifiers (TIAs) newly developed for the purpose were also presented. Clear and symmetrical eye openings were observed for both ports. The OSNR characteristics exhibited 14.3 dB at a bit error rate of 10 -3 that is able to be recovery with FEC. These performances are enough for practical use in 43-Gbps RZ-DPSK systems.

We demonstrate an AO-OFDM system with a WSS-based transmitter and time-lens based receiver for spectral magnification, achieving BER~10 -9 for a 28×10 Gbit/s DPSK AO-OFDM signal. Furthermore, the receiver performance for DPSK and DQPSK is investigated using Monte Carlo simulations.

Recent advances in satellite communication technologies in the tropical regions have led to significant increase in the demand for services and applications that require high channel quality for fixed and mobile satellite terminals. Due to lack of reliable investigations regarding accurate performance evaluation, experiments, and analysis on the satellite communication link in tropical regions under atmospheric impairments for both scenarios, accurate signal quality performance analysis is necessary. This paper presents the link characteristics observations and performance analysis with propagation measurements done in tropical region to provide an accurate database regarding rain attenuation in the tropics for fixed and mobile scenarios. The paper also presents a newly developed extension attached to the measurements setup for improved packet error rate (PER) performance evaluation related to the degradations occur in channel quality for different types of impairments (rain, mobility, and physical obstacles) for 4 modulation schemes, namely QPSK, 8-PSK, 16-QAM and 32-QAM. The results show that the rain impairments at Ku band cause up to 12.5 dB and 23 dB at 77.5 • and 40.1 • elevation angles respectively in two tropical regions inside Malaysia for fixed scenario with a significant increase in PER at higher M-ary modulation schemes. For mobile scenario the PER appeared at higher M-ary scheme due to the lower signal power degradation in which, in turn, exceeded 1 dB when the vehicle speed exceed 100 km/hr

In this paper we propose an improved version of a single receiver DF system that combines a PLL scheme with the MUSIC algorithm to obtain both azimuthal and zenithal angles. The new approach uses a more efficient algorithm to remove the typical ambiguities of PLL-based schemes. We carry out several experiments to assess the algorithm performance. Among them, we consider complex environments, such as wireless communication channels where the received signal is corrupted by noise and suffers from distortion, interference, and multipath effects. The new scheme is tested for BPSK and QPSK signals under these conditions. The simulated results show superior performance of the proposed PLL algorithm when compared to previous techniques.

The concept of modulation is a key factor in communication, because without an appropriate modulation method or scheme, getting an expected throughput in such a communication effort would be impossible to achieve. Communication engineers and researchers have not relented in trying to find the best modulation methods aimed at achieving an expected throughput, bandwidth/power efficiency, low error performance, etc in digital communication networks. Digital modulation is preferred to the analogue modulation due to their error-free capability.Moreso, this choice of digital modulation is dependent on the type of communication network that is to be established. However, trade-offs must be made between the bandwidth efficiency, power efficiency and the cost of implementation of such a network. This paper focuses onsome methods usually employed in the process of modulation in digital communication networks. Specifically, binary phase shift keying, quadrature phase shift keying, eight phase ...

Reliability is an inherent challenge for the emerging nonvolatile technology of racetrack memories, and there exists a fundamental relationship between codes designed for racetrack memories and codes with constrained periodicity. Previous works have sought to construct codes that avoid periodicity in windows, yet have either only provided existence proofs or required high redundancy. This paper provides the first constructions for avoiding periodicity that are both efficient (average-linear time) and with low redundancy (near the lower bound). The proposed algorithms are based on iteratively repairing windows which contain periodicity until all the windows are valid. Intuitively, such algorithms should not converge as there is no monotonic progression; yet, we prove convergence with average-linear time complexity by exploiting subtle properties of the encoder. Overall, we both provide constructions that avoid periodicity in all windows, and we also study the cardinality of such constraints.

Conventional approaches of digital modulation schemes make use of amplitude, frequency and/or phase as modulation characteristic to transmit data. In this paper, we exploit circular polarization (CP) of the propagating electromagnetic carrier as modulation attribute which is a novel concept in digital communications. The requirement of antenna alignment to maximize received power is eliminated for CP signals and these are not affected by linearly polarized jamming signals. The work presents the concept of Circular Polarization Modulation for 2, 4 and 8 states of carrier and refers them as binary circular polarization modulation (BCPM), quaternary circular polarization modulation (QCPM) and 8-state circular polarization modulation (8CPM) respectively. Issues of modulation, demodulation, 3D symbol constellations and 3D propagating waveforms for the proposed modulation schemes are presented and analyzed in the presence of channel effects, and they are shown to have the same bit error performance in the presence of AWGN compared with conventional schemes while provide 3dB gain in the flat Rayleigh fading channel.

This paper presents new visualization techniques for 4D Quadrature-Quadrature Phase Shift Keying (Q2PSK), Saha's Constant Envelope (CE) Q2PSK, and Cartwright's CEQ2PSK in ideal bandlimited channels. The signal diagrams analyzed are: time-signal eye patterns for 4D passband signals, 2D complex trajectory diagrams of baseband signals, and time-signal eye patterns for the 1D outputs of the baseband matched filter. These methods may be applied to other multidimensional modulation systems to obtain insight into the effects of noise, interference, and channel filtering.

The authors present theoretical performance analysis and simulation results for Quadrature-Quadrature Phase Shift Keying (Q2 PSK), Constant Envelope (CE) Q2 PSK, and trellis coded 16D CEQ2 PSK in ideal bandlimited channels of various bandwidths. The performance of receivers with and without channel estimation is reported. Spectral analysis is presented for each system, in addition to MSK and expanded uncoded 16D CEQ2 PSK. We show that the effects of bandlimiting are most severe for Q2 PSK. Knowledge of the channel information aids 4D CEQ2 PSK the least. Only 6.8 dB of SNR is needed for the TCM system for a bit error rate of 10-5 for the narrowest channel bandwidth studied here, if the receiver has knowledge of the channel.

This paper presents a TCM scheme that uses a new expanded 16-Dimensional Constant Envelope Q2PSK constellation along with a simple convolutional encoder of rate 2/3. An effective gain of 2.67 dB over uncoded CEQ2PSK is achievable with low complexity, and without suffering from constellation expansion penalty. Larger coding gains are easily achieved with encoders of higher rates. In addition, an optimal hardware implementation of the required decoders is described.

It has been well reported that the use of multidimensional constellation signals can help to reduce the bit error rate in Additive Gaussian channels by using the hyperspace geometry more efficiently. Similarly, in fading channels, dimensionality provides an inherent signal space diversity (distinct components between two constellations points), so the amplitude degradation of the signal are combated significantly better. Moreover, the set of Ndimensional signals also provides great compatibility with various Trellis Coded modulation schemes: N-dimensional signaling along with a convolutional encoder uses fewer redundant bits for each 2D signaling interval, and increases intra-subset minimum squared Euclidean distance (MSED) to approach the ultimate capacity limit predicted by Shannon’s theory. The multidimensional signals perform better for the same complexity than two-dimensional schemes. The inherent constellation expansion penalty factor paid for using classical mapping structure...

We propose and demonstrate a novel 4-level DD-PolSK system with phase modulators and alternative allocation of constellations, which lead to a greatly simplified transceiver architecture. A 5Gb/s (2.5GS/s) testbed has been built to demonstrate the feasibility of the 4-PolSK transceiver.

The basic criteria for best modulation scheme depends on Bit Error Rate (BER), Signal to Noise Ratio (SNR), Available Bandwidth, Power efficiency, better Quality of Service, cost effectiveness. The performance of each modulation scheme is measured by estimating its probability of error produced by noise and interference induced in the channel. Modulation methods which are capable of transmitting more bits per symbol are more vulnerable to error caused by noise. The modulation technique used for OFDM-LTE (4G) syatems are M-PSK and QAM, so in this paper the Bit error rate (BER) of M-PSK and QAM digital modulation schemes are compared under AWGN, and Rayleigh fading channels to identify a suitable digital modulation scheme for OFDM application. The research has been performed by using MATLAB SIMULINK for simulation and evaluation of Bit Error Rate (BER) and Signal-to-Noise Ratio (SNR) for OFDM system models.

The basic criteria for best modulation scheme depends on Bit Error Rate (BER), Signal to Noise Ratio (SNR), Available Bandwidth, Power efficiency, better Quality of Service, cost effectiveness. The performance of each modulation scheme is measured by estimating its probability of error produced by noise and interference induced in the channel. Modulation methods which are capable of transmitting more bits per symbol are more vulnerable to error caused by noise. The modulation technique used for OFDM-LTE (4G) syatems are M-PSK and QAM, so in this paper the Bit error rate (BER) of M-PSK and QAM digital modulation schemes are compared under AWGN, and Rayleigh fading channels to identify a suitable digital modulation scheme for OFDM application. The research has been performed by using MATLAB SIMULINK for simulation and evaluation of Bit Error Rate (BER) and Signal-to-Noise Ratio (SNR) for OFDM system models.

We compare 2×2 and 4×4 multi-mode interference (MMI) couplers with respect to performance of D(Q)PSKdemodulators. We shall provide simulation and experimental data of MMI-devices realized in 4µm silicon-on-insulator (SOI) rib waveguide technology.