Informatics Publishing Limited

Rajkumar Goswami ¹, G. Sasi Bhushana Rao ²

Affiliations
1 Andhra University, Visakhapatnam, IN
2 Electronics and Communication Department, Andhra University Visakhapatnam, IN

Abstract

The corruption of the transmission signal in the channel has always been a cause of worry for communication engineers, especially in the multipath environment where it necessitates the additional processing in order to mitigate the errors those creep in because of the fading effect created due to this multipath phenomenon. Various Forward Error Correction (FEC) Schemes have evolved over a period of time such as Block Codes, Convolutional codes, TCM Codes and in the recent past Turbo Coding Schemes have become more popular due to its high performance. In this paper the use of turbo coding scheme based on Serially Concatenated Convolutional Codes (SCCC) has been presented for achieving the better BER in respect of fading channel. A design of convolutionalencoder of rate 3/4, 16 states has been presented which forms the integral part of the Turbo Coder. The performance analysis of this turbo coding scheme has been undertaken in respect of fading environment. The complete analysis has been undertaken in MATLAB. The fading channel has been simulated through Rician Multipath Model and the performance of the proposed Turbo Coding Scheme has been compared with the performance of the Convolutional coding Scheme for the same convolutional encoder and with the uncoded 8PSK. The performance of the same has also been evaluated in the case of AWGN channel.

Keywords

Convolutional Code, Fading Channel, TCM, Turbo Codes.

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Nagamani Modalavalasa ¹, G. Sasi Bhushana Rao ², K. Satya Prasad ³

Affiliations
1 Department of Electronics & Communication Engineering, State Board of Technical Education & Training, Andhra Pradesh, IN
2 Department of Electronics & Communication Engineering, Andhra University Engineering College, Visakhapatnam, AndhraPradesh, IN
3 Jawharlal Nehru Technological University, Kakinada, Andhra Pradesh, IN

Abstract

The SONAR (Sound Navigation and Ranging) images are perturbed by a multiplicative noise called speckle noise, due to the coherent nature of the scattering phenomenon. Removing noise from the SONAR image is still a challenging problem for researcher. There is no unique technique for image enhancement for noise reduction. Several approaches have been introduced and each has its own assumption, advantages and disadvantages. This paper proposes performance comparison of frequency domain filtering techniques such as low pass, high pass and band pass filters based on fast fourier transform method for the removal of underwater speckle noise from the real Sector Scan SONAR images. These three filters are compared by computing the error metrics such as Peak Signal to Noise Ratio (PSNR) and Mean Square Error (MSE). Low pass filter is found to be the suitable filter in frequency domain which tends to reduce the speckle, preserving the structural features and textural information of the scene.

Keywords

Mean Square Error (MSE), Peak Signal to Noise Ratio (PSNR), SONAR Images, Speckle Noise.

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Rajkumar Goswami ¹, G. Sasi Bhushana Rao ², S. Swapna Rani ¹, M. N. V. S. S. Kumar ³, S. Deva Prasad ³, G. Hemanth Kumar ⁴

Affiliations
1 Andhra University, IN
2 Electronics and Communication Department, Andhra University, Visakhapatnam, IN
3 Andhra University, Visakhapatnam, IN
4 GNITS, Hyderabad, IN

Abstract

With the advancement of technology, the imaging sonars have become the reality and their usage has been extensive in the area of obstacle avoidance in respect of Autonomous Underwater Vehicle (AUV). The underwater environment being heterogeneous, the sonar images have a very complex background, low contrast, and deteriorative edges. These characteristics, therefore, pose the difficulties for extracting the objects from the sonar images. In this paper we have reviewed the various existing image processing techniques in respect of the sonar images and discussed their shortcomings. After discussing the existing image processing techniques and their limitations, an algorithm has been proposed for processing these sonar images effectively and the results have also been compared with the results of existing techniques. Extracting the obstacle (objects) aspects such as range, bearing, size, shape, speed and course from the images received from Sonar are very important for the AUV in order to avoid the collision from the obstacles those may come into its path. Another very important criterion is the time taken to process the image, which must be as least as possible in order to provide more time for the AUV to take evasive action. For achieving this, proper segmentation of sonar images is a very important step in order to identify the objects (or obstacles) correctly in the least possible time. Several algorithms have been developed in the past for segmentation of images, however these methods did not provide the desired results when subjected to the real sonar images. Therefore a new segmentation method for processing the underwater Sonar images was developed by taking into account the available techniques and domain knowledge. This method is based on the thresholding of the image in which the threshold is calculated adaptively on iterative basis by taking the parameters of image histogram into consideration. The initial threshold value for each individual region of image has been selected by taking the histogram of the region under consideration. Adaptive thresholding utilizes a local window for each individual pixel and computes the new intensity value, based on the local histogram defined in the local window. This is then followed by the morphological, dilation and erosion operations before producing the final segmented image. The performance of the proposed algorithm has been compared with the other existing methods such as Edge detection, Adaptive Thresholding, Fuzzy C Means Clustering (FCM) and Adaptive Histogram Equalization. The results have also been presented in the tabulated form in addition to the segmented images. It has been concluded from the results that the proposed segmentation method achieves better segmentation results in respect of sonar images and is also highly efficient as it takes the least time for segmentation amongst all the methods.

Keywords

Adaptive Threshold, Histogram, Segmentation, Sonar.

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G. Sasi Bhushana Rao ¹, Rajkumar Goswami ², S. Deva Prasad ³, M. N. V. S. S. Kumar ⁴, S. Swapna Rani ⁵

Affiliations
1 Electronics & Communication Engineering Department, Andhra University Engineering College, Visakhapatnam, IN
2 Andhra University College of Engineering, Visakhapatnam, IN
3 University College of Engineering, Andhra University, Visakhapatnam-530003, IN
4 Department of Electronics & Communication Engineering, University College of Engineering, Andhra University, Visakhapatnam-530003, IN
5 Electronics and Communication Engineering Department, Andhra University, Visakhapatnam, IN

Abstract

With the advent of Imaging SONAR, the field of underwater imaging has been gaining lot of importance especially for Autonomous Underwater Vehicle (AUV) for obstacle avoidance.AUV is the underwater robot used for detecting the underwater mines, monitoring and surveillance of coastline and important dense traffic movement ports and other vital defence installations. The AUV applications include the obstacle trajectory tracking, obstacle avoidance and intelligence surveillance and reconnaissance(IRS). The heart of the AUV system depends on the performance of the SONAR. SONAR provides the navigation and guidance by mounting it on the AUV and operates on the principle of acoustic wave propagation. SONAR provides only the location of the object in terms of range and bearing and the objects dimensions (length and thickness) but not the obstacle depth information. For effective maneuvering and for analyzing the target features especially for collision avoidance, the depth information of the object in 3Dimensions is important. In order to know the depth of the obstacle using 2D SONAR, the 2-Dimensional images of the obstacle at different elevation angles are obtained and are used to reconstruct the 3D. This is achieved by scanning the object at various depths. There can be two conditions one in which the SONAR beam partially covers the object, and the second in which SONAR beam covers the complete object. The algorithms developed for this analysis of SONAR data demonstrate the usefulness of the proposed system in the process of converting 2D to 3D information. In this paper a method along with the algorithm that has been designed and developed to calculate the aspect of the target in 3 Dimensions from the 2 Dimension images received from the imaging SONAR by scanning the objects at the various depths is presented. It has been concluded that by using the proposed method and by implementing the proposed algorithm in the 2D SONAR, the high precision 3D aspect of objects has been achieved. The main advantages of proposed algorithm are cost saving and high precision of reconstructed objects.

Keywords

2-Dimensional, 3-Dimensional, AUV, SONAR.

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G. Sasi Bhushana Rao ¹, V. B. S. Srilatha Indira Dutt ²

Affiliations
1 Department of Electronics & Communication Engineering, University College of Engineering, Andhra University, Visakhapatnam-530003, IN
2 Department of Electronics & Communication Engineering, Andhra University, Visakhapatnam, IN

Abstract

Global Positioning System (GPS) is a satellite-based navigation system that provides three-dimensional position of a user (latitude, longitude and altitude) anywhere on or above the surface of the earth. The Navigation accuracy of GPS is affected by various errors. Among all the errors, the delay contribution is more due to ionosphere and is termed as ionospheric delay. Ionospheric delay is a function of the Total Electron Content (TEC). TEC can be determined using either the code or carrier phase measurements. TEC is defined as the number of electrons along the ray path between a transmitter and a receiver. This number is significant in determining ionospheric effects such as refraction, dispersion, and group delay on radio waves. The TEC is strongly affected by solar activity, earthquakes, Tsunami and geomagnetic activity. In this paper, an attempt is made to analyze the TEC variations along the satellite propagation path in the upper atmospheric layers during the total solar eclipse on 22nd July, 2009. The GPS receiver data from IISc, Bangalore is collected on the day of the eclipse and two days before the eclipse for analysis. Data is sampled at a sampling rate of 30 seconds for analysis. TEC is estimated for the day long data of the corresponding days and response of total TEC to the eclipse was analyzed. The results show that: 1) Eclipse led to depression of TEC mounted to 2-6TECU 2) maximum TEC depression (6TECU) occurred during eclipse maximum.3)better Navigation solution is obtained during the eclipse time.

Keywords

Solar Eclipse Navigation Solution Total Electron Content.

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