Rice Wireless

Permanent URI for this collection

https://hdl.handle.net/1911/21945
Formerly the Center for Multimedia Communications, Rice Wireless is part of the university's Electrical and Computer Engineering Department. More information about the group can be found at http://wireless.rice.edu/.

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Browsing Rice Wireless by Author "Bhashyam, Srikrishna"

Now showing 1 - 6 of 6
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    Edge Localized Image Sharpening via Reassignment with Application to Computed Tomography
    (2000-07-01) Dorney, Timothy D.; Bhashyam, Srikrishna; Doran, Andrew; Choi, Hyeokho; Flandrin, Patrick; Baraniuk, Richard G.; Center for Multimedia Communications (http://cmc.rice.edu/); Digital Signal Processing (http://dsp.rice.edu/)
    Traditional filtering methods operate on the entire signal or image. In some applications, however, errors are concentrated in specific regions or features. A prime example is images generated using computed tomography. Practical implementations limit the amount of high frequency content in the reconstructed image, and consequently, edges are blurred. We introduce a new post-reconstruction edge enhancement algorithm, based on the reassignment principle and wavelets, that localizes its sharpening exclusively to edge features. Our method enhances edges without disturbing the low frequency textural details.
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    Efficient VLSI Architectures for Baseband Signal Processing for Wireless Base-Station Receivers
    (2000-07-20) Rajagopal, Sridhar; Bhashyam, Srikrishna; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
    A real-time VLSI architecture is designed for multiuser channel estimation, one of the core base-band processing operations in wireless base-station receivers. Future wireless basestation receivers will need to use sophisticated algorithms to support extremely high data rates and multimedia. Current DSP architectures are unable to fully exploit the parallelism and bit level arithmetic present in these algorithms. These features can be revealed and efficiently implemented by task partitioning the algorithms for a VLSI solution. We modify the channel estimation algorithm for a reduced complexity fixed-point hardware implementation. We show the complexity and hardware required for three different area-time tradeoffs: an area-constrained, a time-constrained and an area-time efficient architecture. The area-constrained architecture achieves low data rates with minimum hardware, which may be used in picocell base-stations. The time-constrained solution exploits the entire available parallelism and determines the maximum theoretical data rates. The area-time efficient architecture meets real-time requirements with minimum area overhead. The orders-of-magnitude difference between area and time constrained solutions reveals significant inherent parallelism in the algorithm. All proposed VLSI solutions exhibit better time performance than a previous DSP implementation.
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    Efficient VLSI architectures for multiuser channel estimation in wireless base-station receivers
    (Kluwer Academic Pubishers, 2002-06-20) Rajagopal, Sridhar; Bhashyam, Srikrishna; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
    This paper presents a reduced-complexity, fixed-point algorithm and efficient real-time VLSI architectures for multiuser channel estimation, one of the core baseband processing operations in wireless base-station receivers for CDMA. Future wireless base-station receivers will need to use sophisticated algorithms to support extremely high data rates and multimedia. Current DSP implementations of these algorithms are unable to meet real-time requirements. However, there exists massive parallelism and bit level arithmetic present in these algorithms than can be revealed and efficiently implemented in a VLSI architecture. We it re-design an existing channel estimation algorithm from an implementation perspective for a reduced complexity, fixed-point hardware implementation. Fixed point simulations are presented to evaluate the precision requirements of the algorithm. A dependence graph of the algorithm is presented and area-time trade-offs are developed. An area-constrained architecture achieves low data rates with minimum hardware, which may be used in pico-cell base-stations. A time-constrained solution exploits the entire available parallelism and determines the maximum theoretical data processing rates. An area-time efficient architecture meets real-time requirements with minimum area overhead.
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    Real-Time Algorithms and Architectures for Multiuser Channel Estimation and Detection in Wireless Base-Station Receivers
    (IEEE, 2002-07-20) Rajagopal, Sridhar; Bhashyam, Srikrishna; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
    This paper presents alogrithms and architecture designs that can meet real-time requirements of multiuser channel estimation and detection in future wireless base-station receivers. Sophisticated algorithms proposed to implement multiuser channel estimation and detection make their real-time implementation difficult on current Digital Signal Processor (DSP)-based receivers. A maximum-likelihood based multiuser channel estimation scheme requiring matrix inversions is redesigned from an implementation perspective for a reduce complexity, iterative scheme with a simple fixed-point VLSI architecture. A reduced-complexity, bit-streaming multiuser detection algorithm that avoids the need for multishot detection is also developed for a simple, pipelined VLSI architecutre. Thus, we show that real-time solutions can be achieved for third generation wireless systems by (1) designing the alogrithms from a fixed-point implementation perspective, without significant loss in error rate performance, (2) task partitioning and (3) designing bit-streaming fixed-point VLSI architectures that explore pipelining, parallelism and bit-level computations to achieve real-time with minumum area overhead.
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    Signal and Information Processing for Wireless Communication Systems
    (2001-04-20) Bhashyam, Srikrishna; Center for Multimedia Communications (http://cmc.rice.edu/)
    Next generation wireless communication systems need to support access to multimedia data available on the internet. This universal wireless access to multimedia data requires data rates and quality of service that are orders of magnitude better than those available in current wireless systems. The two major problems posed by the wireless channel, multipath fading and multiple access interference, are addressed here. The time-varying and shared nature of the wireless channel lead to multipath fading and multiple access interference (MAI) respectively. In this work, signal and information processing algorithms are developed to combat these problems and, consequently, increase data rates and improve performance. First, multiuser signal processing algorithms that combat MAI are developed for code division multiple access (CDMA) systems. Although multiuser signal processing has been extensively studied in the past, very little attention has focused on the practically important case of CDMA with long spreading codes that forms the basis of next generation wireless cellular communications. This work proposes new multiuser channel estimation and tracking algorithms for long code CDMA and demonstrates the significant gains achievable in performance. We also propose new channel estimation algorithms for short code CDMA systems that support multiple data rates to achieve multimedia communication. The new problems posed by the multirate nature of this system, key to support multimedia communication, are studied. Then, in the rest of this work, the use of multiple antenna systems with channel feedback is studied to combat fading. Multiple antenna systems provide multiple independent channels for communication and can effectively combat fading. The following practical issues, ignored in most existing work, are considered in the analysis and design: (i) the channel information is imperfect both at the receiver and at the transmitter, and (ii) part of the total available resources for the system need to be used for channel estimation and feedback. Feedback and power control schemes are designed to achieve significant gains in performance (in terms of outage probability) and data rates. These gains, based on the information-theoretic analysis, are then translated into frame error rate improvements for practical systems that employ space-time codes.
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    Time-Selective Signaling and Reception for Communication over Multipath Fading Channels
    (2000-01-20) Bhashyam, Srikrishna; Sayeed, Akbar M.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
    The mobile wireless channel affords inherent diversity to combat the effects of fading. Existing code division multiple access (CDMA) systems, by virtue of spread-spectrum signaling and RAKE reception, exploit only part of the channel diversity via multipath combination. Moreover, their performance degrades under fast fading commonly encountered in mobile scenarios. In this paper, we develop new signaling and reception techniques that maximally exploit channel diversity via joint multipath-Doppler processing. Our approach is based on a canonical representation of the wireless channel which leads to a time-frequency generalization of the RAKE receiver for diversity processing. Our signaling scheme facilitates joint multipath-Doppler diversity by spreading the symbol waveform beyond the inter-symbol duration to make the channel time-selective. A variety of detection schemes are developed to account for the inter-symbol interference (ISI) due to overlapping symbols. However, our results indicate that the effects of ISI are virtually negligible due to the excellent correlation properties of the pseudo-random codes. Performance analysis also shows that relatively small Doppler spreads can yield significant diversity gains. The inherently higher level of diversity achieved by time-selective signaling brings the fading channel closer to an additive white Gaussian noise channel, thereby facilitating the use of powerful existing coding techniques for Gaussian channels.