Bobby Barua

Analysis the performance of a LDPC coded FSO system with Q-ary pulse-position modulation

Free-space optical communication is an attractive and cost-effective solution for high-rate image, voice, and data transmission. However, optical wave propagation through the air experiences fluctuation in amplitude and phase due to atmospheric turbulence. In this paper, an analytical approach is presented to evaluate the bit error rate performance of a free space optical link using LDPC coded Q-ary optical PPM through atmospheric turbulence channel. Performance results are evaluated for multiple-laser and multiple photo-detector combination without and with LDPC code to combat the effect of atmospheric turbulence. The performance results are evaluated in terms of bit error rate (BER) and coding gain. It is found that LDPC coded system provides significant coding gain of 10 to 20dB over uncoded system can be evaluated at BER 10−12 for multiple source and photo-detector combinations. It also provides better performance under strong turbulence rather than weak turbulence conditions.

Free Space Optical Communication with OOK and BPSK modulation under different turbulent condition

Free Space Optical (FSO) Communications are able to deliver us to an age of unprecedented bandwidth, low signal attenuation, small space requirements and ultimately low cost. In FSO communications the influence of atmospheric effects can be specified by the attenuation and fluctuations of the transmitted optical power, caused by the atmospheric turbulence. This paper investigate the bit error rate (BER) performance of FSO communication systems employing on-off keying (OOK) and subcarrier binary phase-shift keying (BPSK) modulation in turbulence regimes from weak to strong, In addition, we try to compare the BER performance of FSO communication systems employing subcarrier BPSK and OOK as modulation technique.

Evaluate the effect of Stimulated Raman Scattering in DWDM transmission system with direct detection binary WSK receiver

Dense wavelength division multiplexing (DWDM) is usually used on fiber optic backbones and long distance data transmission. Due to the feature of constant light intensity, the WSK modulation is used to reduce the unwanted cross gain modulation in a semiconductor optical amplifier and the four-wave mixing in a WDM system. This paper analyses the effect of fiber nonlinearity, Stimulated Raman Scattering (SRS) in DWDM transmission system with direct detection binary WSK receiver. The performance results are evaluated in terms of Bit Error Rate (BER) by changing system parameters at a bit rate of 10 Gb/s and above. It is noticed that the system performance degrades with power penalty and the maximum amount of power penalty for 32 channels at 10-9 BER is -36.95 dB for channel spacing 80 GHz and the length of the fiber of 120 Km.

Evaluate the Performance of a LDPC Coded FSO System Employing Q-PPM as Modulation Technique

249 Abstract—Free space optics (FSO) is a promising solution for the need to very high data rate point-to point communication. It is one of the future technologies of wireless networks as it meets most of the quality parameters at low implementation cost. The main drawback in communicating via the FSO channel is the detrimental effect the atmosphere has on a propagating laser beam. This paper investigates the use of multiple lasers and multiple apertures to mitigate the effects of the atmospheric turbulence without and with low density parity check (LDPC) code. Here an analytical approach is presented to evaluate the bit error rate performance of a free space optical link using LDPC coded Qary optical PPM through atmospheric turbulence channel. The performance results are evaluated in terms of bit error rate (BER) and coding gain. It is found that LDPC coded system provides significant coding gain of 10 to 20dB over uncoded system can be evaluated at BER 10-12 for multiple source and photo-detector combinations. It is also found that LDPC code provides better performance under strong turbulence rather than weak turbulence conditions.

LDPC coded FSO communication system under strong turbulent condition

Atmospheric turbulence-induced fading is one of the main impairments affecting free-space optics (FSO) communications. To design a high-performance communication link for the atmospheric FSO channel, it is of great importance to characterize the channel from the perspective of information and coding theory. In this paper, we consider FSO multiple-input multiple-output (MIMO) channel with Q-ary pulse position modulation (QPPM) and transmit repetition under the assumption of non-ideal photodetection is analyzed in terms of its ergodic channel capacity. Instead of using a simple binary channel code, we suggest using low density parity-check (LDPC) code to perform iterative soft demodulation (demapping) and channel decoding at the receiver. The simulation results confirm the analytical findings of this paper.

Characterization of low index Si waveguides

In recent years, silicon photonics has attracted attention as an emerging technology for optical telecommunications and for optical interconnects in microelectronics. The refractive index contrast plays a fundamental role in determining the characteristics of an optical dielectric waveguide and a higher index contrast permits to move towards larger scales of integration and to access new devices and functionalities. But high contrast waveguides are more difficult to realize and more critical but there are no serious impediments in their use. The aim of this contribution is to investigate the dependence of the waveguide characteristics with respect to the index contrast and explore the difficulties. In this paper, the impact of the index contrast on the characteristics of dielectric waveguides such as single mode regime, losses, fiber to waveguide coupling, technological constraints and available materials are investigated. The investigation shows that the dependence of the sensitivity in optical waveguide sensors on the polarization of guided modes is less in small refractive index difference waveguide compare than the silicon on silica waveguides but it provide flexibility to the design engineers.

Free-space optical communication with m-ary pulse position modulation under strong turbulence with different type of receivers

With the exponential increase in demand for high speed precision communication system, free-space optics (FSO) has been proven to be a viable solution to this problem. This relatively new technology has gained popularity because of its wider bandwidth, comparatively greater security and relatively economical configuration. However, in FSO links, due to the atmospheric turbulence which is one of the characterizing elements in the system between the transmitter and the receiver, the magnitude of received signal intensity and also the phase of the received light signal wavers. To diminish fading in FSO systems combination of single or multiple transmitter and receiver are used. Moreover, the efficiency of the FSO systems are enhanced by utilizing the most pertinent modulation technique and channel model, making a suitable compromise between system implementation complexity and overall performance. Taking everything into account, we focus our attention in this paper on m-ary pulse position modulation (PPM) with gamma-gamma atmospheric turbulence model, under strong turbulent condition. Furthermore, APD and PIN photodiodes are used as receiver and a comparison of performance is also been made between them. The overall performance of the system are computed in the form of bit error rate (BER) and the simulation results confirm the analytical findings.

Evaluate the effect of FWM on the performance of an M-ary WSK-DWDM transmission system with the energy efficient convolution code

Dense Wavelength Division Multiplexing (DWDM) enables the utilization of a significant portion of the available fiber bandwidth by allowing many independent signals to be transmitted simultaneously on one fiber, with each signal located at a different wavelength. The DWDM systems with long repeater-less spans, the simultaneous requirements of high launched power and low dispersion fibers lead to the generation of new waves by four-wave mixing (FWM), which degrades the performance of a multi-channel transmission system. Several methods have been proposed to mitigate the effect of FWM crosstalk. All these works are performed considering only binary WSK scheme. In this paper we include the effect of FWM on the performance of an M-ary WDM system and try to mitigate the effect by employing the energy efficient convolution code.

Analysis the Performance of Transceiver Circuits for Pulse Based Ultra Wideband

Ultra-wideband is a technology that can be use at very low energy levels for short-range high bandwidth communications by using a large portion of the radio spectrum. In this paper we is specifically focused on the performance of software radio transceiver design for impulse-based UWB with the ability to transmit a raw data rate of 100 Mbps yet encompasses the adaptability of a reconfigurable digital receiver. To complete the analysis we introduce a transmitter and receiver of pulse based ultra wideband modulation. Direct sequence spread spectrum has become the modulation method of choice for wireless local area networks, and personal communication systems, because its numerous advantages such as jammer suppression, code division multiple access, and ease of implementation. Again spread spectrum techniques are most favourable for indoor communication needs and digital radio links, where most of the applications are found. We also observe its characteristics and complete the modulation techniques. Finally we examine UWB communication systems paying particular attention to transmitter and receiver design. Index Terms—Code division multiple access (CDMA). direct sequence spread spectrum (DSSS), personal communication systems (PCS), ultra-wideband (UWB), wireless local area networks (WLANs).