R-3 Repository :: Browsing by Author "Sengupta, Chaitali"

Browsing by Author "Sengupta, Chaitali"

Now showing 1 - 20 of 23

Algorithms and Architectures for Channel Estimation in Wireless CDMA Communication Systems
(1998-12-20) Sengupta, Chaitali; Center for Multimedia Communications (http://cmc.rice.edu/)
Wireless cellular communication is witnessing a rapid growth in markets, technology, and range of services. An attractive approach for economical, spectrally efficient, and high quality digital cellular and personal communication services is the use of code division multiple access (CDMA) technology. The estimation of channel delays along with channel attenuation and phases of different users constitutes the first stage in the detection process at the receiving base station in a CDMA communication system. This stage, called channel parameter estimation, forms the bottleneck for the detection of users' bitstreams; both in terms of accuracy as well as execution time. In this thesis, we develop new algorithms and architectures to solve the CDMA channel estimation problem. We have first developed a framework that facilitates a computationally efficient solution to the combined problem of channel estimation and detection in a scenario involving multiple users, multiple paths, and multiple sensors at the receiver. The channel estimation approaches presented in this thesis, consist of two categories: (1) maximum likelihood based schemes, and (2) signal and noise subspace based schemes. The maximum likelihood approach is used to solve the complex multidimensional problem of channel estimation in the presence of multipath effects and concurrently using an antenna array at the base station receiver. Once the composite channel impulse response of each user is estimated, it is directly used in the detection process instead of first extracting the individual channel parameters, such as path delays and attenuation factors. This technique benefits from better performance as well as lower computational cost. Further, implementation issues of this algorithm, such as complexity reduction and fixed point error behaviour have also been addressed. Our contribution to the subspace-based solution includes extension of the basic algorithm to tracking of the channel parameters in a time varying environment. We have also applied algorithmic optimizations to reduce the computation required for the algorithm and developed architectural enhancements to improve the execution time, such as parallel processing and implementation on fixed point hardware.
Algorithms and architectures for channel estimation in wireless CDMA communication systems
(1999) Sengupta, Chaitali; Cavallaro, Joseph R.
Wireless cellular communication is witnessing a rapid growth in markets, technology, and range of services. An attractive approach for economical, spectrally efficient, and high quality digital cellular and personal communication services is the use of code division multiple access (CDMA) technology. The estimation of channel delays along with channel attenuation and phases of different users constitutes the first stage in the detection process at the receiving base station in a CDMA communication system. This stage, called channel parameter estimation, forms the bottleneck for the detection of users' bitstreams; both in terms of accuracy as well as execution time. In this thesis, we develop new algorithms and architectures to solve the CDMA channel estimation problem. We have first developed a framework that facilitates a computationally efficient solution to the combined problem of channel estimation and detection in a scenario involving multiple users, multiple paths, and multiple sensors at the receiver. The channel estimation approaches presented in this thesis, consist of two categories: (1) maximum likelihood based schemes, and (2) signal and noise subspace based schemes. The maximum likelihood approach is used to solve the complex multidimensional problem of channel estimation in the presence of multipath effects and concurrently using an antenna array at the base station receiver. Once the composite channel impulse response of each user is estimated, it is directly used in the detection process instead of first extracting the individual channel parameters, such as path delays and attenuation factors. This technique benefits from better performance as well as lower computational cost. Further, implementation issues of this algorithm, such as complexity reduction and fixed point error behaviour have also been addressed. Our contribution to the subspace-based solution includes extension of the basic algorithm to tracking of the channel parameters in a time varying environment. We have also applied algorithmic optimizations to reduce the computation required for the algorithm and developed architectural enhancements to improve the execution time, such as parallel processing and implementation on fixed point hardware.
An integrated CAD framework linking VLSI layout editors and process simulators
(1995) Sengupta, Chaitali; Cavallaro, Joseph R.
This thesis presents an Integrated CAD Framework which links VLSI layout editors to lithographic simulators and provides information on the simulated resolution of a feature to the circuit designer. This will help designers to design more compact circuits, as they will be able to see the effect on manufactured silicon. The Framework identifies areas in a layout (in Magic or CIF format) that are more prone to problems arising out of the photolithographic process. It then creates the corresponding inputs for closer analysis with a process simulator (Depict) and analyzes the simulator outputs to decide whether the printed layout will match the designed mask for a particular set of process parameters. The designer can modify the original layout based upon this analysis. The Framework has been used to evaluate layouts for various process techniques. These evaluations illustrate the use of the Framework in determining the limits of any lithographic process.
Arithmetic Acceleration Techniques for Wireless Communication Receivers
(1999-10-20) Das, Suman; Rajagopal, Sridhar; Sengupta, Chaitali; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
We develop techniques to accelerate the implementation of the next generation wireless communication algorithms in hardware. We discuss an implementation of a key computationally intensive baseband algorithm for joint multiuser channel estimation and detection for this purpose and study its real-time requirements. An analysis of the bottlenecks present in the algorithm is made. We present an acceleration technique using task decomposition to take advantage of the existing pipelining and parallelism flow in the algorithm. We show that an application specific system design with multiple processing elements is more effective than the conventional single processor approach as it can satisfy the high data rate requirements of the next generation wireless communication systems. Our analysis is done independent of the final mapping of the processing elements in hardware.
Automated Evaluation of Critical Features in VLSI Layouts Based on Photolithographic Simulations
(SME Press, 1996-01-01) Cavallaro, Joseph R.; Sengupta, Chaitali; Tittel, Frank K.; Wilson, William L. Jr.; Center for Multimedia Communication
This paper describes a CAD tool (An Integrated CAD Framework) which links VLSI layout editors to lithographic simulators and provides information on the simulated resolution of a feature to the circuit designer. The designer can modify the original layout based upon this analysis to create compact circuits with better yield capabilities. The objective of this project is to improve the manufacturability of high density VLSI integrated circuits.
Automated Evaluation of Critical Features in VLSI Layouts Based on Photolithographic Simulations
(IEEE, 1997-11-01) Sengupta, Chaitali; Cavallaro, Joseph R.; Wilson, William L.; Tittel, Frank K.; Center for Multimedia Communication
In this paper, we address the problem of identifying and evaluating “critical features” in an integrated circuit (IC) layout. The “critical features” (e.g., nested elbows and open ends) are areas in the layout that are more prone to defects during photolithography. As feature sizes become smaller (sub-micron range) and as the chip area becomes larger, new process techniques (such as, using phase shifted masks for photolithography), are being used. Under these conditions, the only means to design compact circuits with good yield capabilities is to bring the design and process phases of IC manufacturing closer. This can be accomplished by integrating photolithography simulators with layout editors. However, evaluation of a large layout using a photolithography simulator is time consuming and often unnecessary. A much faster and efficient method would be to have a means of automatically identifying “critical features” in a layout and then evaluate the “critical features” using a photolithography simulator. Our technique has potential for use either to evaluate the limits of any new and nonconventional process technique in an early process definition phase or in a mask house, as a postprocessor to improve the printing capability of a given mask. This paper presents a CAD tool (an Integrated CAD Framework) which is built upon the layout editor, Magic, and the process simulator, Depict 3.0, that automatically identifies and evaluates “critical features”
Efficient Multiuser Receivers for CDMA Systems
(1999-09-20) Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
We focus on the design of multiuser receiver structures for Code Division Multiple Access (CDMA) communication systems, in the presence of multipath elects and multiple sensors at the base station receiver. We present a exible and extensible framework that allows the use of an estimated elective spreading code from the channel estimation phase, in the multiuser detection process. The effective spreading code captures all the channel parameters such as path delays, attenuation factors, and directions of arrival. Hence estimation of this one composite vector removes the necessity of estimating each individual parameter, thus reducing computational complexity. Our results also show that this approach leads to better performance for multiuser detection, especially when the channel consists of a number of low energy paths in addition to a few discrete strong paths.
Enhanced Microlithography Using Combined Phase Shifting and Off-axis Illumination
(Japanese Journal of Applied Physics, 1995-12-01) Erdelyi, Miklos; Bor, Zsolt; Cavallaro, Joseph R.; Szabo, Gabor; Wilson, William L.; Sengupta, Chaitali; Smayling, Michael C.; Tittel, Frank K.; Center for Multimedia Communication
Off-axis illumination is a promising optical microlithography technique which can be used to improve the image quality of line-space patterns. With this method the image is produced by the zero and first order diffracted beams. Due to the intensity difference between these two order diffracted beams the contrast of the image cannot be unity. This paper demonstrates the optical enhancement that can be achieved by a combination of interferometric phase shifting and off-axis illumination. In such an arrangement the mask is illuminated symmetrically from both the front and back sides, and not two but in fact four–(two zero and two first)–order beams produce the image. We show experimentally that the contrast of the image can be improved if the phase difference between the reflected and transmitted beams is π, and the intensity of the transmitted beam is about 13% of the reflected beam. This improved quality image with feature sizes of 0.4 µm was recorded in a photoresist using an Ar+ ion laser operating at 457.9 nm.
Fixed Point Error Analysis Of Multiuser Detection and Synchronization Algorithms For CDMA Communication Systems
(1998-04-20) Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
Conventional correlation based single-user techniques for Direct Sequence Code Division Multiple Access (DS-CDMA) wireless communication systems are susceptible to performance degradation due to interference from other users. Recent research has focused on development of several multiuser techniques where information about multiple users is used to improve performance for each individual user. Due to performance benefits of these methods, they are attractive candidates for implementation in future cellular systems. In this paper we present an error analysis of fixed point implementation of some of these techniques.
Hardware design issues for a mobile unit for next generation CDMA systems
(1998-07-20) Das, Suman; Sengupta, Chaitali; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
This paper addresses hardware design issues of a mobile receiver for future generation direct sequence CDMA wireless communication systems. In the design of a mobile unit, fixed-point hardware is an attractive alternative because of increased speed, reduced power consumption, and reduced hardware costs. In this paper, we focus on the fixed-point implementation of `blind' detection and channel estimation schemes that do not require knowledge of spreading codes of the other users. The error pattern of the 'blind' algorithms, wordlength requirements, and the operation count required for implementation of such algorithms are evaluated. Our results show that the blind maximum likelihood channel estimation along with the blind MMSE detection algorithm can achieve approximately five times improvement in performance over the conventional correlator based receivers. These newer algorithms require slightly higher wordlength but similar computational complexity.
An Integrated CAD Framework Linking VLSI Layout Editors and Process Simulators
(1995-05-20) Sengupta, Chaitali; Center for Multimedia Communications (http://cmc.rice.edu/)
This thesis presents an Integrated CAD Framework which links VLSI layout editors to lithographic simulators and provides information on the simulated resolution of a feature to the circuit designer. This will help designers to design more compact circuits, as they will be able to see the effect on manufactured silicon. The Framework identifies areas in a layout (in Magic or CIF format) that are more prone to problemsmask for a particular set of process parameters. The designer can modify the original layout based arising out of the photolithographic process. It then creates the corresponding in-puts for closer analysis with a process simulator (Depict) and analyzes the simulator outputs to decide whether the printed layout will match the designed upon this analysis. The Framework has been used to evaluate layouts for various process techniques. These evaluations illustrate the use of the Framework in determining the limits of any lithographic process.
An Integrated CAD Framework Linking VLSI Layout Editors and Process Simulators
(SPIE, 1996-03-01) Sengupta, Chaitali; Erdelyi, Miklos; Bor, Zsolt; Cavallaro, Joseph R.; Smayling, Michael C.; Szabo, Gabor; Tittel, Frank K.; Wilson, William L.; Center for Multimedia Communication
As feature sizes in VLSI circuits extend into the far sub-micron range, new process techniques, such as using phase shifting masks for photolithography, will be needed. Under these conditions, the only means for the circuit designer to design compact and efficient circuits with good yield capabilities is to be able to see t he effect of different design approaches on manufactured silicon, instead of solely relying on conservative general design rules. The Integrated CAD Framework accomplishes this by providing a link between a layout editor (Magic), advanced photolithographic techniques such as phase shifted masks, and a process simulator (Depict). This paper discusses some applications of this tool. A non-conventional process technique involving interferometric phase shifting and off-axis illumination has been evaluated using the tool. Also, a feature of the CAD Framework which allows representation of a phase shifted mask, together with its layout analysis capability has been used to compact a piece of layout by inserting phase shifted elements into it.
Joint Multiuser Channel Estimation and Detection for CDMA Systems
(1999-02-20) Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
We focus on the design of multiuser receiver structures for Code Division Multiple Access (CDMA) communication systems, in the presence of multipath effects and multiple sensors at the base station receiver. The joint channel estimation and detection approach presented in this paper uses a miximum likelihood approach to estimate an effective spreading code [1] vector of each user. We design our channel estimation algorithm to estimate this vector in a computationally efficient manner, instead of focusing on estimation of the individual channel parameters, such as path delays, attenuation factors, and direction of arrival. We present a framework that allows the use of the estimated effective spreading code in the detection process [2] and facilitates the development of a computationally efficient solution to the combined problem of channel estimation and multi-shot detection in a scenario involving multiple users, multiple paths, and multiple sensors.
Maximum Likelihood Multipath Channel Parameter Estimation in CDMA Systems
(1998-03-01) Sengupta, Chaitali; Hottinen, Ari; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communication
The problem addressed in this paper is the estimation of the channel parameters in a Code Division Multiple Access(CDMA) communication system, in the presence of multipath effects. Maximum likelihood estimation of these parameters has been investigated in the past with the main drawback being the complexity of the multi-dimensional algorithms. The algorithm presented in this paper elegantly decomposes the multiuser problem into a series of single user problems. The algorithm first estimates a composite channel impulse response of each user and then extracts the channel parameters of all the paths of each user from the channel impulse response. We evaluate the performance of the algorithm through simulation studies.
Maximum Likelihood Multipath Channel Parameter Estimation in CDMA Systems Using Antenna Arrays
(1998-09-20) Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
The problem addressed in this paper is the estimation of the chan-nel parameters in a Code Division Multiple Access (CDMA) communication system, in the presence of multipath effects and multiple sensors at the base station receiver. The algorithm presented in this paper solves the problem by estimating a composite channel impulse response of each user, which can be directly used in the detection process to appropriately modify the spreading code of the user. In addition, the algorithm combines the benefit of spatial processing in the form of an antenna array at the receiver to gain an increase in performance of the system.
A New Interferometric Phase-Shifting Technique for Sub-half-micron Laser Microlithography
(SPIE, 1995-02-01) Erdelyi, Miklos; Sengupta, Chaitali; Bor, Zsolt; Cavallaro, Joseph R.; Kido, Motoi; Smayling, Michael C.; Tittel, Frank K.; Wilson, William L.; Szabo, Gabor; Center for Multimedia Communication
This paper reports recent progress in achieving sub-half-micron feature sizes with UV laser illumination based on a novel interferometric phase shifting (IPS) technique. In the IPS arrangement, the intensity and amount of phase shift of the shifted beam can be controlled continuously and independently using the same mask. Consequently the method can be considered as a convenient general testbed for practical phase shifting concepts such as strong, weak and attenuated phase shifting. Recent measurements of the lithographic performance of a new concept are reported where phase shifting is combined with off-axis illumination. Experimental as well as simulation data are used to demonstrate this new method. A lithography simulator, Depict from Technology Modeling Associates, Inc. and a related Integrated CAD Framework which is being developed at Rice University was used to simulate and evaluate the performance of the IPS scheme.
A New Phase Shifting Technique for Deep UV Excimer Laser Based Lithography
(SPIE, 1995-02-01) Bor, Zsolt; Cavallaro, Joseph R.; Erdelyi, Miklos; Kido, Motoi; Sengupta, Chaitali; Smayling, Michael; Szabo, Gabor; Tittel, Frank; Wilson, William; Center for Multimedia Communication
This paper reports simulation and experimental details of a novel phase shifting technique based o laser interferometry. Phase shifting is one of the most promising techniques for the fabrication of high density DRAM's. In recent years many kinds of phase shifting methods have been proposed to extend the resolution limit and contrast of image patterns. These techniques however, have several problems that result from the phase shift elements on the mask, especially when applied to UV excimer laser illumination. A new technique will be described that is based on a one-layered reticle which is used as both a reflective and transmissive mask, irradiated from both the front and the back sides. A combination of both off-axis illumination, as well as phase shift are used in this method. Both the relative path length of the two beams as well as their amplitude can be manipulated in such a way that near 100% contrast can be achieved in the final image. Experimental as well as simulation data are used to demonstrate this new method.
On Multipath Channel Estimation for CDMA Systems Using Multiple Sensors
(2001-03-20) Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
This paper focuses on the design of a multiuser receiver structure for the reverse link of a code-division multiple-access communication system, in the presence of multipath effects and using an antenna array at the base station receiver. The algorithm presented in this paper solves the complex multidimensional problem of channel estimation in this complex scenario using a maximum-likelihood approach. This channel estimation technique requires the transmission of a training sequence or feedback of detected data. Once a composite channel-impulse response of each user is estimated, it is directly used in the detection process instead of first extracting the individual channel parameters, such as path delays and attenuation factors. The paper presents a framework that facilitates a computationally efficient solution to the combined problem of channel estimation and detection in a scenario involving multiple users, multiple paths, and multiple sensors at the receiver.
Parallel algorithms and architectures for subspace based channel estimation for CDMA communication systems
(1996-08-20) Sengupta, Chaitali; Kota, Kishore; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
This paper presents an overview and results from an ongoing research project to study parallel algorithms for the acquisition of Code Division Multiple Access (CDMA) communication signals. The goal of this research isto evaluate a class of related algorithms and architectures for the acquisition problem and map them onto parallel architectures containing DSPs. The algorithms used are generally termed subspace-based algorithms, since they involve computation of subspaces of the vector space spanned by certain observation vectors. This paper presents results from some preliminary implementations of such a subspace-based algorithm on the Texas Instruments TMS320C40 Parallel Processing Development System.
Solving the SVD updating problem for subspace tracking on a fixed sized linear array of processors
(1997-04-20) Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
None

Browsing by Author "Sengupta, Chaitali"

Results Per Page

Sort Options