Browsing by Author "Livingston, Frank"

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    Blind Algorithms for Channel Estimation and Detection in Wireless Handsets
    (2000-05-20) Livingston, Frank; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
    Multiple access is an important consideration in the design and implementation of wireless communications systems. Code division multiple access (CDMA) is one method for providing multiple access in a wireless system. In CDMA, each user is assigned a unique code that identifies the user to the system. This code is used to modulate and demodulate the user's data. CDMA has several advantages over other more traditional multiple access methods like frequency-division multiple access (FDMA) and time-division multiple access (TDMA), one of the most important being its inherent noise-rejection capability. Because of its advantages over other multiple access methods, CDMA is being designed into many current and next-generation wireless systems. Two important functions in a wireless system are channel estimation and detection. Signals transmitted through a wireless channel are attenuated and delayed by the channel, and the purpose of channel estimation is to estimate this attenuation and delay. The purpose of detection is to detect the information symbols contained in the received signal. For reasons of size, power, and cost, the handsets in a wireless system have fewer resources than the base stations in the system and less knowledge than the base stations concerning the other users in the system. Because of this, channel estimation and detection techniques applicable to base stations are not always applicable to handsets, and algorithms that perform these functions on handsets must do so in a manner that is driven more by a need for efficiency and cost effectiveness than by a need for optimal performance. The research presented in this paper is concerned with "blind" algorithms for channel estimation and detection in handsets, where the term "blind" refers to the fact that the handset only has knowledge of the code of its own user. The focus of this research is on algorithmic and architectural improvements to such algorithms that will enable the algorithms to execute more efficiently in a hardware/software environment typifying those used in actual handsets. A goal of this work is to investigate issues related to real-time constraints and fixed-point quantization that would be encountered in the design and implementation of a wireless handset for a CDMA system. Two algorithms for channel estimation and two for detection are considered. One algorithm for channel estimation and one for detection are actually implemented on a Texas Instruments 'C5410 digital signal processor. As of the writing of this paper, these algorithms have only been implemented in floating-point C. It is expected, however, that with little additional effort, the algorithms will be implemented in fixed-point assembly language on the 'C5410.
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    Handset Algorithms & Architectures for Blind Channel Estimation & Detection
    (2000-05-20) Livingston, Frank; Center for Multimedia Communications (http://cmc.rice.edu/)
    Multiple access is an important consideration in the design and implementation of wireless communications systems. Code division multiple access (CDMA) is one method for providing multiple access in a wireless system. In CDMA, each user is assigned a unique code that identifies the user to the system. This code is used to modulate and demodulate the userâ s data. CDMA has several advantages over other more traditional multiple access methods like frequency-division multiple access (FDMA) and time-division multiple access (TDMA), one of the most important being its inherent noise-rejection capability. Because of its advantages over other multiple access methods, CDMA is being designed into many current and next-generation wireless systems.
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    Handset Detector Architectures for DS-CDMA Wireless Systems
    (2002-05-20) Livingston, Frank; Chandrasekhar, Vikram; Vaya, Mani; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
    This paper investigates detector architectures for wireless handsets employing DS-CDMA. The code-matched filter (MF) and minimum output energy (MOE) detectors are analyzed with respect to fixed-point arithmetic behavior. Architectures employing fixed-point arithmetic are then proposed for these detectors. The maximum throughput of these architectures and the associated costs in terms of area usage and power consumption are evaluated. Results of the fixed-point analysis indicate that the MOE detector is more susceptible to quantization than the MF detector. Results of implementation indicate that the superior performance of the MOE detector is achieved at a considerably higher cost in terms of area usage and power consumption. Finally, comparison of hardware implementation with software-based DSP implementation indicates that software approaches result in considerably lower throughputs.
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    Reducing Dynamic Power Consumption in Next Generation DS-CDMA Mobile Communication Receivers
    (2003-06-20) Chandrasekhar, Vikram; Livingston, Frank; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
    Reduction of the power consumption in portable wireless receivers is an important consideration for next-generation cellular systems specified by standards such as the UMTS, IMT2000. This paper explores the architectural design-space and methodologies for reducing the dynamic power dissipation in the Direct Sequence Code Division Multiple Access (DS-CDMA) downlink RAKE receiver. Starting with a reference implementation of the DS-CDMA RAKE receiver, we demonstrate design methodologies for achieving significant power reduction, while highlighting the corresponding performance trade-offs. At the algorithm level, we investigate the tradeoffs of reduced precision and arithmetic complexity on the receiver performance. We then present two architectures for implementing the reference and reduced complexity receivers, and analyze these architectures with respect to their dynamic power dissipation. Our findings report that reduction in precision from a 16 bit to a 10 bit data-path is found to yield significant power savings of 25.6% in the reference RAKE receiver architecture, with a performance loss of less than 1 dB. Further, a power reduction of upto 24.65% is achieved in a 16 bit data-path for the reduced complexity RAKE receiver compared to the reference architecture, with a performance loss of less than 2 dB. Although there is a tradeoff in performance, adaptive power saving is very important for mobile wireless terminals. The combined effect of reduced precision and complexity reduction leads to a 37.44% savings in baseband processing power.
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    Reducing dynamic power consumption in next generation DS-CDMA mobile communication receivers
    (Inderscience Enterprises Ltd., 2008-09-01) Chandrasekhar, Vikram; Livingston, Frank; Cavallaro, Joseph R.; Center for Multimedia Communication
    Reduction of the power consumption in portable wireless receivers is important for cellular systems, including UMTS and IMT2000. This paper explores the architectural design-space and methodologies for reducing the dynamic power dissipation in the Direct Sequence Code Division Multiple Access (DS-CDMA) downlink RAKE receiver. At the algorithm level, we investigate the tradeoffs of reduced precision and arithmetic complexity on the receiver performance. We then present and analyse two architectures for implementing the reference and reduced complexity receivers, with respect to dynamic power dissipation. The combined effect of reduced precision and complexity reduction leads to a 37.44% power savings.