A. Arockia Bazil Raj

Implementation of high-speed LFSR design with parallel architectures

Linear feedback shift register (LFSR) is an important component of the cyclic redundancy check (CRC) operations and BCH encoders. The contribution of this paper is two fold. First, this paper presents linear transformation of serial LFSR architecture into the transformation of parallel LFSR architecture. This transformation achieves a full speed-up compared to the serial architecture at the cost of an increase in hardware overhead. This method applies to all generator polynomials used in CRC operations and BCH encoders. Second, a new formulation is proposed to modify the parallel LFSR into the form of pipelining and retiming algorithm. We propose a high-speed parallel LFSR architecture based on pipelining and retiming algorithms to reduce the critical path. Finally, we are calculating the Bit Error Rate (BER) tester for the proposed LFSR design. The advantage of this proposed approach over the previous architectures is that it has both feed forward and feedback paths. Also it has the advantage of further increasing the speed-up and it increases the throughput rate. We further propose to apply combined parallel and pipelining techniques to eliminate the fan-out effect in long generator polynomials. The proposed scheme can be applied to any generator polynomial, i.e., any LFSR in general. The proposed parallel architecture achieves better area-time product compared to the previous designs.

Comparison of Different Models for Ground-Level Atmospheric Attenuation Prediction with New Models According to Local Weather Data for FSO Applications

A dedicated Free Space Optical Link (FSOL) for the range of 0.5 km at an altitude of 15.25 m is established and explained. The power levels of the received signal with meteorological parameters are continuously measured using the opto-electronic assembly and developed weather station respectively and stored in a computer. The existing models selected for comparative analysis are briefed. Measured meteorological parameters and optical attenuation of size [2000 4] are used for linear regression analysis as well as to design the mathematical models more suitable at the test field. In addition, the prediction accuracy of the proposed and selected models during different seasons in one-year period are investigated and validated in terms of RMSE. The average Root Mean Square Error (RMSE) of 0.041 dB/km for the optical attenuation is achieved in the longer range dynamic of meteorological parameters during different local seasons.

A direct and neural controller performance study with beam wandering mitigation control in free space optical link

The beam wander on the detector plane is one of the main causes for major power loss which severely degrades the performance of Free Space Optical (FSO) link. Designing a suitable controller to correct the beam motion at a faster rate to increase the beam stability becomes significant. This paper presents an investigation on the performance of two types of controller designed for aiming a laser beam to be at a particular point under dynamic disturbances. The first design is based on the Taguchi’s method (direct controller) while the second is the Artificial Neural Network (ANN) method (neural-controller). These controllers process the beam location information and generate the necessary outputs to mitigate the beam wandering. The pipelined-parallel architecture for both controllers are developed in a Field Programmable Gate Array (FPGA) and installed at the receiver station. Evidence of the suitability and the effectiveness of the proposed controller in terms of prediction exactness, prediction error, reduction of focal point wander, response to impulse and scintillation are provided through experimental results from the FSO link established for the horizontal range of 0.5 km at an altitude of 15.25 m.

Seasonal investigation on prediction accuracy of atmospheric turbulence strength with a new model at Punalkulam, Tamil Nadu

Atmospheric parameters strongly affect the performance of free space optical communication systems when an optical wave is propagating through an inhomogeneous turbulence transmission medium. Developing models to get an accurate prediction of the turbulence strength (Cn2) according to meteorological parameters becomes significant to understand the behavior of the channel in different seasons. A dedicated free space optics link for the range of 0.5 km at an altitude of 15.25 m is established and explained. The power level and beam centroid information of the received signal with meteorological parameters at the same time are continuously measured using the optoelectronic assembly and developed weather station, respectively, and stored in a data logging computer. The existing models selected, based on exhibiting relatively less prediction error, for comparative analysis are briefed. Measured meteorological parameters (as input factors) and Cn2 (as a response factor) of size [2000×4] are used for linear regression analysis and to design the empirical models more suitable at the test field. Along with the model formulation methodologies, the contributions of the input factors’ individual and combined effects on the response surface and coefficient of determination (R2) estimated using Analysis of Variance tools are presented. Model equation-V (R2=98.93%) is finalized for predicting Cn2. In addition, the prediction accuracy of the proposed and selected models for different seasons in a one year period are investigated and validated in terms of the sum of absolute error (SAE). The average SAE of 0.000641×10−9 m−2/3 for Cn2 is achieved using the new model in a longer range dynamic of meteorological parameters during different local seasons.

Lower-order adaptive beam steering system in terrestrial free space point-to-point laser communication using fine tracking sensor

The Terrestrial Free Space Point to Point Laser Communication (TFSPPLC) offers an attractive alternatives for transferring high -bandwidth data. The wave propagation takes place in optically inhomogeneous atmospheric channel. Various deleterious effects of the atmospheric channel leads the optical wave to serious signal fading, misalignments of fixed position and even complete loss of signal altogether. Therefore, understanding the atmospheric behavior to the optical wave propagation with the real time experimental data collected over long duration become significant. A TFSPPLC opto-electronic architecture is established for the range of 500m and 28.5m altitude above the surface of the earth. An Adaptive Optics (AO) based steering technique is incorporated in the experimental test-bed to mitigate the lower order temporal and spatial distortions measured at the receiver aperture. The technique of incorporating 2 Dimensional - 4 Quadrant fine tracking sensor (2D-4QS) and Fast Steering Tip-Tilt Mirror (FSTTM) in the adaptive receiver in a closed loop control configuration is presented. An Adaptive Fuzzy Logic Controller (AFLC) is developed in the Field Programmable Gate Array (FPGA) and its performance is tested in real time with generating the control signal to drive the piezoelectric actuators of FSTTM. The method of compensating the atmospheric effects using FSTTM is described. The statistical analyses of the experimental data are also presented.

Terrestrial free space line of sight optical communication (TFSLSOC) using adaptive control steering system with laser beam Tracking, Aligning and Positioning (ATP)

Free Space Optical Communication (FSOC) is the most promising approach for addressing the emerging broadband access network. Quick link setup, high transmission security, large bandwidth and light weight are some of the important features of this system. However, the laser power attenuation due to adverse weather conditions and scattering due to turbulence are to be mitigated. In this paper, a Position Sensing Detector (PSD) and Stochastic Parallel Gradient Descent Algorithm (SPGDA) based control system using Field Programmable Gate Array (FPGA) in a Closed Loop Control Configuration (CLCC) are developed and presented for Aligning, Tracking and Positioning (ATP) the laser beam to improve the performance of the FSOC.