M Tech Dissertations
Permanent URI for this collectionhttp://drsr.daiict.ac.in/handle/123456789/3
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Item Open Access Digital implementation of orthogonal frequency division multiplexing(Dhirubhai Ambani Institute of Information and Communication Technology, 2017) Bhanushali, Artiben; Pillutla, Laxminarayana; Bhatt, Amit"OFDM (Orthogonal Frequency Division Multiplexing) is the most important part of 4G and 5G technology which is adopted by many standards because of its various advantages. In this thesis, firstly prototype of OFDM system is designed according to 802.11a standard in MATLAB to check its performance and then to implement the same in Verilog using Xilinx ISE 14.4 design suite. FFT (Fast Fourier Transform) and IFFT (Inverse Fast Fourier Transform) are the most complex part of the design which are implemented using radix-2 algorithm. For channel estimation, scattered pilot arrangement is used to insert pilots at regular period in OFDM frame. At receiver side, least-square estimation is used to estimate the channel’s impulse response at known pilot tones. The system analysis is done using MATLAB-Verilog co-simulation in which Verilog transmitter and receiver are connected with MATLAB channel using testbench to generate the text files. This files are used as connecting platform between MATLAB and Xilinx. Performance of channel estimation at different number of multipath is observed which shows that the combination of time interpolation followed by frequency interpolation performs better over only frequency interpolation. In later part, BER (bit error rate) vs. SNR (signal to noise ratio) is analyzed for different number of multipath. From graphs, it is clearly denoted that, BER performance improves with respect to increase in SNR. Finally, fixed point and floating point comparison is carried out which depicts that fixed point system implemented in Verilog performs almost similar to the floating point implementation done in MATLAB."Item Open Access Frequency offset estimation in OFDM signals using particle filtering along with resampling methods(Dhirubhai Ambani Institute of Information and Communication Technology, 2008) Jayanthi, V. Ravisankar; Vijaykumar, ChakkaFrequency offset is one of the main effects the Bit Error Rate(BER) in orthogonal frequency division multiplexing (OFDM). There are many applications which depend on OFDM. The present method describes the estimation of frequency offset for OFDM irrespective of the distribution of the channel noise. This method uses Particle Filtering for the estimation of frequency offset. As Particle Filter is a non-linear and non-Gaussian estimator, there will be no constraint on the channel noise. This method also uses the resampling methods, which are essential in modifying the weight approximates during the iterations. Here the performance of the Particle Filter in estimating the frequency offset for the OFDM is observed along with the resampling methods.Item Open Access Multirate signal processing in digital communications(Dhirubhai Ambani Institute of Information and Communication Technology, 2008) Arya, Krishna Kumari; Chakka, VijaykumarFundamentals of multirate signal processing and perfect reconstruction filter banks are revisited. An attempt is made to develop a good understanding of concepts by connecting the filter bank design issues to the concepts of linear algebra. An interpretation of multicarrier systems in the form of transmultiplexers is provided and the notion of resampling of channel is introduced. A pulse shaping filter for the OFDM systems is proposed to remove the constraint of Cyclic Prefix. A comparison of performance of OFDM and filter bank based multicarrier systems in terms of stop band attenuation is provided. Notion of MIMO biorthogonal partners and the conditions for existence of FIR biorthogonal partners are studied. Emphasis is put on finding out the Greatest Right Common Divisor (GRCD) of polynomial matrices.Item Open Access Model based channel shortening technique for IEEE 802.11a OFDM system(Dhirubhai Ambani Institute of Information and Communication Technology, 2007) Patidar, Pravin; Chakka, VijaykumarChannel shortening tehniques for IEEE802.11a OFDM system are studied. Their performance is evaluated for various standard channel models. A model based channel shortening technique is presented, which reduces the computational comlexity, both during initialization and data transmission. The method is based on modeling of channel impulse response by a pole-zero system, and using the denominator coefficients as the equalizer. Further, it is shown that for channel shortening, calculation of zeros of the model is not required. Comparison of proposed technique with MMSE and MSSNR channel shortening techniques is presented.Item Open Access Performance evaluation of OFDM technique for high speed communication applications(Dhirubhai Ambani Institute of Information and Communication Technology, 2005) Kabra, Mukul; Maskara, S. L.The Internet revolution has created the need for wireless technologies that can deliver data at high speeds in a spectrally efficient manner. However, supporting such high data rates with sufficient robustness to radio channel impairments requires careful selection of modulation techniques. The demand for high-speed mobile wireless communications is rapidly growing. OFDM technology promises to be a key technique for achieving the high data capacity and spectral efficiency requirements for wireless communication systems of the near future. Orthogonal frequency division multiplexing (OFDM) is a special case of multi-carrier transmission, where a single data stream is transmitted over a number of lower rate sub-carriers. OFDM is currently being used in Europe for digital audio and video broadcasting. The IEEE standardization group decided to select OFDM as the basis for their new 5-GHz standard, targeting a range of data stream from 6 up to 54 Mbps. This standard was the first one to use OFDM in packet-based communications, while the use of OFDM until now was limited to continuous transmission systems. OFDM is also being considered as a serious candidate for fourth generation cellular systems. In this project, transmitter, channel and receiver were simulated with various parameters, to evaluate the performance and different possibilities in the implementation. Also, some considerations about forward error correction coding, interleaving, synchronization and channel estimation are given to improve the system performance.Item Open Access Enhancing data efficiency in OFDM (IEEE 802.11a) using equalization (11A)(Dhirubhai Ambani Institute of Information and Communication Technology, 2005) Reddy, S. Gangadhar; Chakka, VijaykumarIEEE 802.11a OFDM signal passed through a dispersive channel introduces ISI & ICI. To avoid ISI & ICI, cyclic prefix (guard interval) is introduced between the OFDM symbols. But the cyclic prefix contributes about 20% (0.8us/4us) of the total symbol duration. Transmission of OFDM symbols without cyclic prefix increases the data efficiency, but introduces ICI & ISI. The ISI & ICI can be removed by equalization at the receiver. Spill over in the frequency domain is same as ICI & ISI. This spill over can be observed at the unused carriers also (carriers numbered from 0-6, 33, 59-64 are unused in IEEE 802.11a). Equalization is done in the frequency domain by making use of spill over in unused carriers. A relationship is brought between the length of the channel impulse response and the number of unused carriers for perfect equalization in the absence or very little AWGN-channel noise. To avoid the noise amplification caused by Zero Forcing equalization and to satisfy the relationship derived, a methodology using Time domain equalizer (TEQ) is proposed and simulation results are presented supporting it. Alternatively, computational efficient algorithm for indoor environment is suggested by transmitting data in unused carriers with the combination of used carriers. By this method, ICI & ISI is removed at the transmitter itself and it even doesn’t amplify the noise.