M Tech Dissertations

Permanent URI for this collectionhttp://ir.daiict.ac.in/handle/123456789/3

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Subject: search.filters.subject.Multiplexing

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Now showing 1 - 5 of 5
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    Pulse shaping for linear time varying channels
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2011) Doshi, Savankumar; Chakka, Vijaykumar
    Pulse shaping is the one of the important an critical area for wireless communication. In this article we show the relation between pulse shaping for wide sense stationary uncorrelated scattering (WSSUS) channels and the notion of approximate eigenstructure for time-varying channels. Optimal link adaption to the scattering function of WSSUS channel is still an unsolved problem. In ulticarrier transmission such link adaption is performed by pulse shaping by properly adjusting transmitter and receiver filters. We consider pulse shaping for general signaling scheme called Weyl-Heisenberg signaling which includes Orthogonal Frequency Division Multiplexing (OFDM) and Offset Quadrature amplitude modulation (OQAM). We establish a general mathematical framework for joint transmitter and receiver pulse shape. Pulse design problem in the view of optimal averaged SINR is an interplay between localization and optimization strategies. The Localization problem can be expressed in terms of eigenvalues of approximate eigenstructure of Linear Time Varying (LTV) channel operators. In this thesis, we will show approximate eigenstructure and its relation with pulse design and several iterative algorithms for optimization.
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    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, Chakka
    Frequency 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.
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    Orthogonal frequency division multiplexing synchronization techniques
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2008) Ravikanth, Sivangi; Vijaykumar, Chakka
    Synchronization plays a major role in the design of a digital communication system. Essentially, this function aims at retrieving some reference parameters from the received signal that are necessary for reliable data detection. The OFDM is very sensitive to symbol timing and frequency offset. The loss of orthogonality among the subcarriers causes degradation of the OFDM system performance. so, the timing and frequency offset must be estimated and compensated before demodulating the OFDM signals. This report presents the study of different synchronization schemes for OFDM receiver. Different methods like Schmidl-Cox synchronizer, The Coulson synchronizer, The Minn-Zeng Bhargava synchronizer, Blind carrier offset estimation using unused subcarriers etc. Matlab experiments are conducted to study the performance of different synchronization schemes. The simulations results shows that Blind estimation method is more advantage over training symbol and Cyclic Prefix (CP) based methods in terms of Bandwidth saving.
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    Enhancing data efficiency in OFDM (IEEE 802.11a) using equalization (11A)
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2005) Reddy, S. Gangadhar; Chakka, Vijaykumar
    IEEE 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.
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    Study of MPLS traffic engineering with constraint-based routing
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2004) Modi, Bhavesh; Maitra, Anutosh
    Multi-protocol Label Switching (MPLS) is fast becoming popular for future communication networks running applications demanding high speed and Quality of Service. In this work, we have studied the evolution of MPLS, various issues related to MPLS and the architecture ofMPLS. The simplicity and functional capabilities ofMPLS enables various important applications over it such as Virtual Private Networks, Provisioning of Quality of Service and Traffic Engineering. The traffic engineering perspective of MPLS is studied in a greater detail as MPLS protocol has certain advantageous features in traffic engineering applications, the major being that it allows explicit routing, through which separately calculated routes can be specified for different traffic flows. The process of route calculation can be automated with the help of Constraint-based Routing. The thesis also presents a study on Constraint-based routing in MPLS environment. After that, a few classical constraint-based routing algorithms that consider bandwidth as constraint are investigated. The effectiveness of these algorithms is ascertained by means of simulation results. The concept of minimum interference routing and the corresponding algorithm MIRA is studied in greater detail in this work and presented in the thesis. The performance of MIRA was analyzed and factors that affect the performance were identified. Finally, the work suggests two modifications over MIRA based on the observations and analysis mentioned above. The primary philosophy behind the modifications are identifying the criticality of the resources and quantifying the order of the criticality. The performance of the suggested modified algorithms is benchmarked against classical MIRA algorithm and the simulation results are presented.