The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform
Tolga M. Duman - One of the best experts on this subject based on the ideXlab platform.
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Soft input soft output Kalman equalizer for MIMO frequency selective fading channels
IEEE Transactions on Wireless Communications, 2007Co-Authors: S. Roy, Tolga M. DumanAbstract:We consider the Kalman filter for equalization of a multiple-input multiple-output (MIMO), frequency selective, quasi-static fading channel. More specifically, we consider a coded system, where the Incoming Bit stream is convolutionally encoded, interleaved and then spatially multiplexed across the transmit antennas. Each substream is modulated into M-ary symbols before being transmitted over a frequency selective channel. At the receiver, we propose to use the Kalman filter as a low complexity MIMO equalizer, as opposed to the trellis based maximum a-posteriori (MAP) equalizer whose computational complexity grows exponentially with the channel memory, the number of transmit antennas and the spectral efficiency (Bits/s/Hz) of the system. We modify the structure of the Kalman filter and enable it to process the a-priori (soft) information provided by the channel decoder, thereby allowing us to perform iterative (turbo) equalization on the received sequence. The iterative equalizer structure is designed for general M-ary constellations. We also propose a low complexity version of the above algorithm whose performance is comparable to its full complexity counterpart, but which achieves a significant complexity reduction. We demonstrate via simulations that for higher order constellations, when sufficient number of receive antennas are available (e.g. for a 2 transmitter, 3 receiver system, QPSK), the performance of the proposed algorithms after 4 iterations is within 1.5 dB of the non-iterative MAP algorithm with close to an order of magnitude complexity reduction. By objectively quantifying the complexity of all the considered algorithms we show that the complexity reduction for the proposed schemes becomes increasingly significant for practical systems with moderate to large constellation sizes and a large number of transmit antennas
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Soft input soft output Kalman equalizer for MIMO frequency selective fading channels
IEEE 60th Vehicular Technology Conference 2004. VTC2004-Fall. 2004, 1Co-Authors: S. Roy, Tolga M. DumanAbstract:We consider the Kalman filter for equalization of a multiple-input multiple-output (MIMO), frequency selective, quasi-static fading channel. More specifically, we consider a coded system, where the Incoming Bit stream is convolutionally encoded, interleaved and then spatially multiplexed across the transmit antennas before being transmitted over a frequency selective channel. At the receiver, we use a Kalman filter as the MIMO equalizer and modify its structure, enabling it to process the a-priori (soft) information provided by the outer decoder, thereby allowing us to perform iterative (turbo) equalization on the received sequence. The proposed equalizer has a comparable performance with the optimal symbol-by-symbol, maximum a-posteriori probability (MAP) equalizer and provides a considerable complexity reduction, especially for systems with a large number of transmit antennas or long ISI spans.
Eduardo Tovar - One of the best experts on this subject based on the ideXlab platform.
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WiDom: A Dominance Protocol for Wireless Medium Access
IEEE Transactions on Industrial Informatics, 2007Co-Authors: Nuno Pereira, Björn Andersson, Eduardo TovarAbstract:Wireless networks play an increasingly important role in application areas such as factory-floor automation, process control, and automotive electronics. In this paper, we address the problem of sharing a wireless channel among a set of sporadic message streams where a message stream issues transmission requests with real-time deadlines. For this problem, we propose a collision-free wireless medium access control (MAC) protocol, which implements static-priority scheduling and supports a large number of priority levels. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus, a proven communication technology for various industrial applications. However, unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel. The evaluation of the protocol with real embedded computing platforms is presented to show that the proposed protocol is in fact collision-free and prioritized. We measure the response times of our implementation and find that the response-time analysis developed for the protocol indeed offers an upper bound on the response times
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Collision-free prioritized medium access in the presence of hidden nodes without relying on out-of-band signaling
2006Co-Authors: Björn Andersson, Nuno Pereira, Eduardo TovarAbstract:Consider the problem of sharing a wireless channel between a set of computer nodes. Hidden nodes exist and there is no base station. Each computer node hosts a set of sporadic message streams where a message stream releases messages with real-time deadlines. We propose a collision-free wireless medium access control (MAC) protocol which implements static-priority scheduling. The MAC protocol allows multiple masters and is fully distributed. It neither relies on synchronized clocks nor out-of-band signaling; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel. Our protocol has the key feature of not only being prioritized and collision-free but also dealing successfully with hidden nodes. This key feature enables schedulability analysis of sporadic message streams in multihop networks. Collision-Free Prioritized Medium Access in the Presence of Hidden Nodes Without Relying on Out-of-Band Signaling Bjorn Andersson, Nuno Pereira, Eduardo Tovar IPP Hurray Research Group Polytechnic Institute of Porto, Portugal {bandersson, npereira, emt}@dei.isep.ipp.pt
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OPODIS - Static-priority scheduling of sporadic messages on a wireless channel
Lecture Notes in Computer Science, 2006Co-Authors: Björn Andersson, Eduardo TovarAbstract:Consider the problem of scheduling sporadic messages with deadlines on a wireless channel. We propose a collision-free medium access control (MAC) protocol which implements static-priority scheduling and present a schedulability analysis technique for the protocol. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel.
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Static-priority scheduling of sporadic messages on a wireless channel
Lecture Notes in Computer Science, 2006Co-Authors: Björn Andersson, Eduardo TovarAbstract:Consider the problem of scheduling sporadic messages with deadlines on a wireless channel. We propose a collision-free medium access control (MAC) protocol which implements static-priority scheduling and present a schedulability analysis technique for the protocol. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel.
S. Roy - One of the best experts on this subject based on the ideXlab platform.
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Soft input soft output Kalman equalizer for MIMO frequency selective fading channels
IEEE Transactions on Wireless Communications, 2007Co-Authors: S. Roy, Tolga M. DumanAbstract:We consider the Kalman filter for equalization of a multiple-input multiple-output (MIMO), frequency selective, quasi-static fading channel. More specifically, we consider a coded system, where the Incoming Bit stream is convolutionally encoded, interleaved and then spatially multiplexed across the transmit antennas. Each substream is modulated into M-ary symbols before being transmitted over a frequency selective channel. At the receiver, we propose to use the Kalman filter as a low complexity MIMO equalizer, as opposed to the trellis based maximum a-posteriori (MAP) equalizer whose computational complexity grows exponentially with the channel memory, the number of transmit antennas and the spectral efficiency (Bits/s/Hz) of the system. We modify the structure of the Kalman filter and enable it to process the a-priori (soft) information provided by the channel decoder, thereby allowing us to perform iterative (turbo) equalization on the received sequence. The iterative equalizer structure is designed for general M-ary constellations. We also propose a low complexity version of the above algorithm whose performance is comparable to its full complexity counterpart, but which achieves a significant complexity reduction. We demonstrate via simulations that for higher order constellations, when sufficient number of receive antennas are available (e.g. for a 2 transmitter, 3 receiver system, QPSK), the performance of the proposed algorithms after 4 iterations is within 1.5 dB of the non-iterative MAP algorithm with close to an order of magnitude complexity reduction. By objectively quantifying the complexity of all the considered algorithms we show that the complexity reduction for the proposed schemes becomes increasingly significant for practical systems with moderate to large constellation sizes and a large number of transmit antennas
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Soft input soft output Kalman equalizer for MIMO frequency selective fading channels
IEEE 60th Vehicular Technology Conference 2004. VTC2004-Fall. 2004, 1Co-Authors: S. Roy, Tolga M. DumanAbstract:We consider the Kalman filter for equalization of a multiple-input multiple-output (MIMO), frequency selective, quasi-static fading channel. More specifically, we consider a coded system, where the Incoming Bit stream is convolutionally encoded, interleaved and then spatially multiplexed across the transmit antennas before being transmitted over a frequency selective channel. At the receiver, we use a Kalman filter as the MIMO equalizer and modify its structure, enabling it to process the a-priori (soft) information provided by the outer decoder, thereby allowing us to perform iterative (turbo) equalization on the received sequence. The proposed equalizer has a comparable performance with the optimal symbol-by-symbol, maximum a-posteriori probability (MAP) equalizer and provides a considerable complexity reduction, especially for systems with a large number of transmit antennas or long ISI spans.
Björn Andersson - One of the best experts on this subject based on the ideXlab platform.
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WiDom: A Dominance Protocol for Wireless Medium Access
IEEE Transactions on Industrial Informatics, 2007Co-Authors: Nuno Pereira, Björn Andersson, Eduardo TovarAbstract:Wireless networks play an increasingly important role in application areas such as factory-floor automation, process control, and automotive electronics. In this paper, we address the problem of sharing a wireless channel among a set of sporadic message streams where a message stream issues transmission requests with real-time deadlines. For this problem, we propose a collision-free wireless medium access control (MAC) protocol, which implements static-priority scheduling and supports a large number of priority levels. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus, a proven communication technology for various industrial applications. However, unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel. The evaluation of the protocol with real embedded computing platforms is presented to show that the proposed protocol is in fact collision-free and prioritized. We measure the response times of our implementation and find that the response-time analysis developed for the protocol indeed offers an upper bound on the response times
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Collision-free prioritized medium access in the presence of hidden nodes without relying on out-of-band signaling
2006Co-Authors: Björn Andersson, Nuno Pereira, Eduardo TovarAbstract:Consider the problem of sharing a wireless channel between a set of computer nodes. Hidden nodes exist and there is no base station. Each computer node hosts a set of sporadic message streams where a message stream releases messages with real-time deadlines. We propose a collision-free wireless medium access control (MAC) protocol which implements static-priority scheduling. The MAC protocol allows multiple masters and is fully distributed. It neither relies on synchronized clocks nor out-of-band signaling; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel. Our protocol has the key feature of not only being prioritized and collision-free but also dealing successfully with hidden nodes. This key feature enables schedulability analysis of sporadic message streams in multihop networks. Collision-Free Prioritized Medium Access in the Presence of Hidden Nodes Without Relying on Out-of-Band Signaling Bjorn Andersson, Nuno Pereira, Eduardo Tovar IPP Hurray Research Group Polytechnic Institute of Porto, Portugal {bandersson, npereira, emt}@dei.isep.ipp.pt
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OPODIS - Static-priority scheduling of sporadic messages on a wireless channel
Lecture Notes in Computer Science, 2006Co-Authors: Björn Andersson, Eduardo TovarAbstract:Consider the problem of scheduling sporadic messages with deadlines on a wireless channel. We propose a collision-free medium access control (MAC) protocol which implements static-priority scheduling and present a schedulability analysis technique for the protocol. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel.
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Static-priority scheduling of sporadic messages on a wireless channel
Lecture Notes in Computer Science, 2006Co-Authors: Björn Andersson, Eduardo TovarAbstract:Consider the problem of scheduling sporadic messages with deadlines on a wireless channel. We propose a collision-free medium access control (MAC) protocol which implements static-priority scheduling and present a schedulability analysis technique for the protocol. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an Incoming Bit from the channel while transmitting to the channel.
Mohammed Ghanbari - One of the best experts on this subject based on the ideXlab platform.
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Buffer analysis and control in CBR video transcoding
IEEE Transactions on Circuits and Systems for Video Technology, 2000Co-Authors: Pedro Assuncao, Mohammed GhanbariAbstract:In video distribution services, various networks of different capacity may be linked together to form the branches of a multicasting tree. In order to efficiently use the available bandwidth of each subnetwork, a video transcoder capable of reducing the Bit rate of the Incoming Bit stream must be used at those nodes whose output links have less bandwidth than the input one. In this paper, we analyze the buffering implications of inserting a video transcoder within the transmission path. For transcoders with either fixed or variable compression ratio, we show that the encoder buffer size can be maintained as if no transcoder existed while the decoder has to modify its own buffer size according to both the Bit rate conversion ratio and transcoder buffer size. We derive the conditions that have to be met by both the encoder and transcoder buffers for preventing the decoder buffer from underflowing or overflowing. Furthermore, based on the characteristics of constant Bit rate (CBR) MPEG coded video, we show that efficient Bit rate control can be implemented in CBR video transcoders such that the picture quality of transcoded sequences is practically the same as those directly encoded from the original sequence at the same reduced Bit rates.
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Heterogeneous video transcoding to lower spatio-temporal resolutions and different encoding formats
IEEE Transactions on Multimedia, 2000Co-Authors: Tamer Shanableh, Mohammed GhanbariAbstract:In this work, transcoding of pre-encoded MPEG-1, 2 video into lower Bit rates is realized through altering the coding algorithm into H.261/H.263 standards with lower spatio-temporal resolutions. For this heterogeneous transcoding, we extract and compose a set of candidate motion vectors, from the Incoming Bit stream, to comply with the encoding format of the output Bit stream. For the spatial resolution reduction we generate one motion vector out of a set of input motion vectors operating on the higher spatial resolution image. Finally, for the temporal resolution reduction we compose new motion vectors from the dropped frames motion vectors. Throughout the paper, we discuss the impact of motion estimation refinement on the new motion vectors and show that for all cases a simple half-pixel refinement is sufficient for near-optimum results.
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ICASSP - Transcoding of video into different encoding formats
2000 IEEE International Conference on Acoustics Speech and Signal Processing. Proceedings (Cat. No.00CH37100), 1Co-Authors: Tamer Shanableh, Mohammed GhanbariAbstract:In this paper, transcoding of pre-encoded MPEG-1,2 video into lower Bit rates is realized through altering the coding algorithm into H.261/H.263 standards with lower spatial resolutions. We extract and compose a set of candidate motion vectors, from the Incoming Bit stream, to comply with the encoding format of the output Bit stream. For the spatial resolution reduction, we generate one motion vector out of a set of input motion vectors operating on the higher spatial resolution image. We discuss the impact of motion estimation refinement on the new motion vectors and show that for all cases a simple half-pixel refinement is sufficient for near-optimum results.
