ahmed badr - Academia.edu (original) (raw)
Papers by ahmed badr
The column Hamming distance of a convolutional code determines the error correction capability wh... more The column Hamming distance of a convolutional code determines the error correction capability when streaming over a class of packet erasure channels. We introduce a metric known as the column sum rank, that parallels column Hamming distance when streaming over a network with link failures. We prove rank analogues of several known column Hamming distance properties and introduce a new family of convolutional codes that maximize the column sum rank up to the code memory. Our construction involves finding a class of super-regular matrices that preserve this property after multiplication with non-singular block diagonal matrices in the ground field.
IEEE Transactions on Information Theory, 2018
The burst rank loss channel is an extension of the burst erasure channel where the channel matrix... more The burst rank loss channel is an extension of the burst erasure channel where the channel matrix between the sender and receiver becomes rank-deficient for a certain period of consecutive time-slots. We study streaming communication over the burst rank loss channel, propose a new class of codes, ROBIN codes, and establish their optimality. Our construction uses the Maximum Rank Distance (MRD) and Maximum Sum Rank (MSR) codes from previous works as constituent codes, and combines them in a layered fashion. Our results generalize previous work on both the single-link and multiple-parallel-link streaming setups over burst erasure channels. We perform simulations over statistical network models to show that ROBIN codes attain low packet loss rates in comparison to existing codes. I. INTRODUCTION Streaming communication is characterized by two factors: causality and delay. Source packets arrive sequentially at a transmitter, which generates channel packets causally. The receiver collecting the transmitted packets must reconstruct the source within a decoding deadline, using only what it has observed up to that point. A receiving user is interested in sequential playback, meaning if a packet has not been recovered within the deadline, the decoder considers it lost and moves to the next packet. Error correcting codes capable of low delay decoding have previously been designed in the context of a single-link erasure channel connecting the transmitter and receiver [1]-[5]. In Internet communication, packet erasures primarily occur in bursts [6], and consequently the works of [1], [3]-[5] focus primarily on low-delay recovery from a burst of consecutive erasures. Alternatively, [2], [3], [5] also consider arbitrary loss patterns and guarantee low-delay recovery when there are fewer than the maximum tolerable number of erasures in a window. The above mentioned works consider the case of a single communication link between the sender and receiver. As communication methods increase in sophistication, it is natural to consider streaming over a network where there are multiple links and paths connecting the source and destination nodes [7], [8]. The simplest extension of a single-link setting is the case when there are multiple parallel links. This extension has been previously studied for streaming in [7, Chapter 8], [9]. In the network setting. multiple parallel links correspond to separate paths chosen by a naive routing algorithm. Link failures in the network then lead to packet erasures over the associated path. It was shown that joint coding across packets transmitted over different paths, can outperform separate coding applied to individual paths only. An alternative to path routing is generationbased linear network coding, where the received packets are a linear transformation of the transmitted packets [10]-[12]. Links failures in the network now can potentially reduce the channel rank [13]. Rank metric codes such as Gabidulin codes can be used as end-to-end codes for protecting packets in such rank-deficient channels [14]-[17]. In this work, we extend streaming under the burst packet loss model, see e.g., [18], to a rank-deficient matrix channel. In the context of network coding, the rank is equal to the min-cut of the network, decreasing to a minimum tolerable rank when links fail in a burst [10], [13], [19]. For such a burst rank loss model, we design an end-to-end code with a layered structure and establish its optimality. Our approach generalizes the prior work in [7, Chapter 8], which addressed a network with naive routing and permitted at most one link to fail during a burst. While there, the problem simplified to multiple parallel links with one behaving as a periodic burst erasure channel, we permit both multiple bursts and linear transformations of the channel packets that can ensue as a result of network coding. Furthermore, their code construction involved diagonally interleaving
IEEE Transactions on Information Theory, 2017
We propose a new class of error correction codes for low-delay streaming communication. We consid... more We propose a new class of error correction codes for low-delay streaming communication. We consider an online setup where a source packet arrives at the encoder every M channel uses, and needs to be decoded with a maximum delay of T packets. We consider a sliding-window erasure channel-C(N, B, W)-which introduces either up to N erasures in arbitrary positions, or B erasures in a single burst, in any window of length W. When M = 1, the case where source-arrival and channel-transmission rates are equal, we propose a class of codes-MiDAS codes-that achieve a near optimal rate. Our construction is based on a layered approach. We first construct an optimal code for the C(N = 1, B, W) channel, and then concatenate an additional layer of parity-check symbols to deal with N > 1. When M > 1, the case where source-arrival and channel-transmission rates are unequal, we characterize the capacity when N = 1 and W ≥ M (T + 1), and for N > 1, we propose a construction based on a layered approach. Numerical simulations over Gilbert-Elliott and Fritchman channel models indicate significant gains in the residual loss probability over baseline schemes. We also discuss the connection between the error correction properties of the MiDAS codes and their underlying column distance and column span.
IEEE Transactions on Information Theory, 2015
2015 IEEE International Symposium on Information Theory (ISIT), 2015
The column Hamming distance of a convolutional code determines the error correction capability wh... more The column Hamming distance of a convolutional code determines the error correction capability when streaming over a class of packet erasure channels. We introduce a metric known as the column sum rank, that parallels column Hamming distance when streaming over a network with link failures. We prove rank analogues of several known column Hamming distance properties and introduce a new family of convolutional codes that maximize the column sum rank up to the code memory. Our construction involves finding a class of superregular matrices that preserve this property after multiplication with non-singular block diagonal matrices in the ground field.
IEEE Journal of Selected Topics in Signal Processing, 2015
2013 Proceedings IEEE INFOCOM, 2013
2013 13th Canadian Workshop on Information Theory, 2013
2013 IEEE International Symposium on Information Theory, 2013
We study near optimal error correction codes for real-time communication. In our setup the encode... more We study near optimal error correction codes for real-time communication. In our setup the encoder must operate on an incoming source stream in a sequential manner, and the decoder must reconstruct each source packet within a fixed playback deadline of T packets. The underlying channel is a packet erasure channel that can introduce both burst and isolated losses. We first consider a class of channels that in any window of length T + 1 introduce either a single erasure burst of a given maximum length B, or a certain maximum number N of isolated erasures. We demonstrate that for a fixed rate and delay, there exists a tradeoff between the achievable values of B and N, and propose a family of codes that is near optimal with respect to this tradeoff. We also consider another class of channels that introduce both a burst and an isolated loss in each window of interest and develop the associated streaming codes. All our constructions are based on a layered design and provide significant improvements over baseline codes in simulations over the Gilbert-Elliott channel.
2013 Asilomar Conference on Signals, Systems and Computers, 2013
IEEE Journal on Selected Areas in Communications, 2011
Error-Correcting Codes for Low-Delay Streaming Communications Ahmed Badr Doctor of Philosophy Gra... more Error-Correcting Codes for Low-Delay Streaming Communications Ahmed Badr Doctor of Philosophy Graduate Department of Electrical and Computer Engineering (ECE) University of Toronto 2014 This thesis develops a new class of error-correcting codes for low-delay streaming over packet-erasure channels. Such codes must operate sequentially on the incoming source stream, and must reconstruct each source packet within a fixed delay of T packets. We show that both the fundamental limits, as well as structural properties of such streaming codes, are different from classical codes. In our study, we consider successively finer approximations of burst erasure channels, that capture the dominant error events associated with the streaming setup. In the basic model, we consider a channel that in any sliding window of length W , introduces either an erasure burst of length B, or up to N erasures in arbitrary positions. We show that there is an inherent tradeoff between the achievable values of B and...
2017 IEEE International Symposium on Information Theory (ISIT), 2017
We study a setting where two source streams with different decoding deadlines must be transmitted... more We study a setting where two source streams with different decoding deadlines must be transmitted over a burst erasure channel. The source streams are multiplexed into a single stream of channel-packets at the encoder and transmitted over a packet erasure channel. The decoder must recover the source-packets within each stream sequentially, by their corresponding deadlines. We consider the burst-erasure channel model and characterize the capacity region for a certain range of system parameters. We show that the operation of the system can be divided into three different regimes based on the relative values of decoding deadlines. On the achievability side, we show that jointly coding across the two streams, despite their different deadlines, is necessary to achieve capacity. On the converse side we develop information theoretic outer bounds on the capacity region. We find that the capacity region exhibits a “corner point” where we can transmit the urgent stream at a positive rate, yet...
Journal of Infrastructure Systems
The Egyptian Journal of Haematology
Introduction Vaso-occlusion is a determinant for most manifestations of sickle cell anemia (SCA).... more Introduction Vaso-occlusion is a determinant for most manifestations of sickle cell anemia (SCA). Elevated concentration of homocysteine contributes to thrombosis, a frequent event in SCA. Folic acid deficiency leads to increase in plasma homocysteine. The aim of study was to test whether children with SCA have elevated serum homocysteine with diminished folate level and to determine whether hyperhomocysteinemia has a correlation with the frequency of vaso-occlusive crisis. Patients and methods A case–control study was carried over a period of 1 year (January to December 2014) in the hematology clinic, Abo El-Reesh Hospital, Cairo University. A total of 50 patients with SCA were included together with 30 age-matched and sex-matched healthy children recruited from Menoufia Hospital. Venous blood samples were obtained from both groups to measure serum homocysteine and folic acid levels. Results The mean±SD of age of the patients and controls were 6.20±2.55 and 6.03±2.64 years, respectively. Homocysteine level was significantly higher in the patients group compared with control group, with a mean±SD of 44.68±9.096 and 18.81±3.76 µmol/l, respectively (P>0.01). Folic acid level was lower in the patients group than control group, with 12.02±2.76 and 14.68±2.99 ng/ml, respectively (P<0.05). Significant inverse correlation was found between homocysteine and folic acid (correlation coefficient −0.337 and P=0.017). A strong positive correlation between homocysteine level and the frequency of vaso-occlusive crisis was found (P=0.04). Conclusion Patients with sickle cell disease have high serum homocysteine with low folate levels. This hyperhomocysteinemia is positively correlated with the frequency of vaso-occlusive crisis.
IEEE Signal Processing Magazine
Many current and emerging applications require low-latency communication, including interactive v... more Many current and emerging applications require low-latency communication, including interactive voice and video communication, multiplayer gaming, multiperson augmented/virtual reality, and various Internet of Things (IoT) applications. Forward error correction (FEC) codes for low-delay interactive applications have several characteristics that distinguish them from traditional FEC. The encoding and decoding operations must process a stream of data packets in a sequential fashion. Strict latency constraints limit the use of long block lengths, interleaving, or large buffers. Furthermore, these codes must achieve fast recovery from burst losses and yet be robust to other types of loss patterns.
Rheumatology International, 2017
We conducted this systematic reviews and meta-analysis to investigate the safety and efficacy of ... more We conducted this systematic reviews and meta-analysis to investigate the safety and efficacy of ocrelizumab in patients with active rheumatoid arthritis (RA) who exhibited resistance or intolerance to methotrexate or biological therapy. We performed a web-based literature search of PubMed, Google Scholar, EBSCO, Scopus, Embase, and Web of science for studies that compared ocrelizumab plus methotrexate versus methotrexate plus placebo in RA patients. Data were extracted from eligible studies and pooled as risk ratios (RR), using RevMan software. Pooling data from four RCTs (2230 patients) showed that ocrelizumab plus methotrexate were superior to methotrexate plus placebo at 24 weeks in terms of improvement on the American college of rheumatology (ACR20, ACR50, and ACR70) criteria (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001), disease activity score 28-ESR (RR = 3.77, 95% CI [2.47, 5.74], p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001), and Sharp/van der Heijde radiological score (RR = 1.63, 95% CI [1.43, 1.85], p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001). These effects were consistent among all ocrelizumab doses. The rates of serious adverse events were comparable between the ocrelizumab and placebo containing groups (RR = 1, 95% CI [0.78, 1.28], p = 0.98). However, infusion related reactions were significantly higher in ocrelizumab group (RR = 2.13, 95% CI [1.69, 2.68], p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001), compared to placebo group. The combination of ocrelizumab plus methotrexate was superior to methotrexate plus placebo on all clinical and radiographic improvement scales. The incidence of adverse events, including serious adverse events, was comparable between both groups. Future trials should investigate the efficacy of ocrelizumab alone and develop strategies to alleviate its related infusion reactions.
2016 IEEE International Symposium on Information Theory (ISIT), 2016
The burst rank loss channel is an extension of the burst erasure channel where the channel matrix... more The burst rank loss channel is an extension of the burst erasure channel where the channel matrix between the sender and receiver becomes rank-deficient for a certain period of consecutive time-slots. We study streaming communication over the burst rank loss channel, propose a new class of codes, ROBIN codes, and establish their optimality. Our construction uses the Maximum Rank Distance (MRD) and Maximum Sum Rank (MSR) codes from previous works as constituent codes, and combines them in a layered fashion. Our results generalize previous work on both the single-link and multiple-parallel-link streaming setups over burst erasure channels. We perform simulations over statistical network models to show that ROBIN codes attain low packet loss rates in comparison to existing codes. I. INTRODUCTION Streaming communication is characterized by two factors: causality and delay. Source packets arrive sequentially at a transmitter, which generates channel packets causally. The receiver collecting the transmitted packets must reconstruct the source within a decoding deadline, using only what it has observed up to that point. A receiving user is interested in sequential playback, meaning if a packet has not been recovered within the deadline, the decoder considers it lost and moves to the next packet. Error correcting codes capable of low delay decoding have previously been designed in the context of a single-link erasure channel connecting the transmitter and receiver [1]-[5]. In Internet communication, packet erasures primarily occur in bursts [6], and consequently the works of [1], [3]-[5] focus primarily on low-delay recovery from a burst of consecutive erasures. Alternatively, [2], [3], [5] also consider arbitrary loss patterns and guarantee low-delay recovery when there are fewer than the maximum tolerable number of erasures in a window. The above mentioned works consider the case of a single communication link between the sender and receiver. As communication methods increase in sophistication, it is natural to consider streaming over a network where there are multiple links and paths connecting the source and destination nodes [7], [8]. The simplest extension of a single-link setting is the case when there are multiple parallel links. This extension has been previously studied for streaming in [7, Chapter 8], [9]. In the network setting. multiple parallel links correspond to separate paths chosen by a naive routing algorithm. Link failures in the network then lead to packet erasures over the associated path. It was shown that joint coding across packets transmitted over different paths, can outperform separate coding applied to individual paths only. An alternative to path routing is generationbased linear network coding, where the received packets are a linear transformation of the transmitted packets [10]-[12]. Links failures in the network now can potentially reduce the channel rank [13]. Rank metric codes such as Gabidulin codes can be used as end-to-end codes for protecting packets in such rank-deficient channels [14]-[17]. In this work, we extend streaming under the burst packet loss model, see e.g., [18], to a rank-deficient matrix channel. In the context of network coding, the rank is equal to the min-cut of the network, decreasing to a minimum tolerable rank when links fail in a burst [10], [13], [19]. For such a burst rank loss model, we design an end-to-end code with a layered structure and establish its optimality. Our approach generalizes the prior work in [7, Chapter 8], which addressed a network with naive routing and permitted at most one link to fail during a burst. While there, the problem simplified to multiple parallel links with one behaving as a periodic burst erasure channel, we permit both multiple bursts and linear transformations of the channel packets that can ensue as a result of network coding. Furthermore, their code construction involved diagonally interleaving
2006 6th International Conference on ITS Telecommunications, 2006
We propose the multicast encryption security protocol MESP. It is driven form the IPSEC ESP. The ... more We propose the multicast encryption security protocol MESP. It is driven form the IPSEC ESP. The specification of the protocol are discussed and applied the existing IPSEC ESP. We use the existing implementation of the IPSEC ESP; modify it to meet the MESP specifications to implement the MESP. A multicast chat system is used as an application for this protocol.
Neurological Research, 2001
Even though cerebral vasospasm after subarachnoid hemorrhage (SAH) causes cerebral ischemia or in... more Even though cerebral vasospasm after subarachnoid hemorrhage (SAH) causes cerebral ischemia or infarction, the metabolic alterations in cerebrospinal fluids (CSF) after SAH have not been studied. This study was undertaken to measure the levels of glucose, lactate, pyruvate and glutamate in CSF from double hemorrhage dog models. Thirty-two mongrel dogs of either sex, weighing 18-24 kg, underwent double hemorrhage by percutaneous needle puncture of the cistema magna and injection of autologous blood on day 0 and day 2. The dogs were then sacrificed on day 3, 5 and 7, after collecting CSF. In another study, the dogs were treated with mitogen-activated protein kinase (MAPK) inhibitors PD98059 and U0126, and caspase-2 and caspase-3 inhibitors from day 3 to day 6 after initial blood injection. CSF was collected on day 7 before dogs were sacrificed. The concentration of glucose, lactate, pyruvate and glutamate in CSF was measured by photometrical method. Compared with CSF collected on day 0, glucose was decreased on days 5-7, lactate was increased on days 2-7, pyruvate was increased on days 2-7, and glutamate was increased on days 3-7 (p < 0.05). In the groups treated with MAPK or caspase inhibitors, most of the metabolic alterations remained unchanged as compared with CSF from untreated dogs. Clinically, caspase inhibitors-2 and -3, and MAPK inhibitor U0126 all failed to prevent vasospasm. MAPK inhibitor PD98059 partially prevented vasospasm. Our data demonstrated a metabolic alteration of glucose, glutamate, lactate and pyruvate in CSF during cerebral vasospasm. This metabolic change in consistent with the time course of cerebral vasospasm. This study suggests that brain energy metabolites and excitative amino acids are altered during cerebral vasospasm.
The column Hamming distance of a convolutional code determines the error correction capability wh... more The column Hamming distance of a convolutional code determines the error correction capability when streaming over a class of packet erasure channels. We introduce a metric known as the column sum rank, that parallels column Hamming distance when streaming over a network with link failures. We prove rank analogues of several known column Hamming distance properties and introduce a new family of convolutional codes that maximize the column sum rank up to the code memory. Our construction involves finding a class of super-regular matrices that preserve this property after multiplication with non-singular block diagonal matrices in the ground field.
IEEE Transactions on Information Theory, 2018
The burst rank loss channel is an extension of the burst erasure channel where the channel matrix... more The burst rank loss channel is an extension of the burst erasure channel where the channel matrix between the sender and receiver becomes rank-deficient for a certain period of consecutive time-slots. We study streaming communication over the burst rank loss channel, propose a new class of codes, ROBIN codes, and establish their optimality. Our construction uses the Maximum Rank Distance (MRD) and Maximum Sum Rank (MSR) codes from previous works as constituent codes, and combines them in a layered fashion. Our results generalize previous work on both the single-link and multiple-parallel-link streaming setups over burst erasure channels. We perform simulations over statistical network models to show that ROBIN codes attain low packet loss rates in comparison to existing codes. I. INTRODUCTION Streaming communication is characterized by two factors: causality and delay. Source packets arrive sequentially at a transmitter, which generates channel packets causally. The receiver collecting the transmitted packets must reconstruct the source within a decoding deadline, using only what it has observed up to that point. A receiving user is interested in sequential playback, meaning if a packet has not been recovered within the deadline, the decoder considers it lost and moves to the next packet. Error correcting codes capable of low delay decoding have previously been designed in the context of a single-link erasure channel connecting the transmitter and receiver [1]-[5]. In Internet communication, packet erasures primarily occur in bursts [6], and consequently the works of [1], [3]-[5] focus primarily on low-delay recovery from a burst of consecutive erasures. Alternatively, [2], [3], [5] also consider arbitrary loss patterns and guarantee low-delay recovery when there are fewer than the maximum tolerable number of erasures in a window. The above mentioned works consider the case of a single communication link between the sender and receiver. As communication methods increase in sophistication, it is natural to consider streaming over a network where there are multiple links and paths connecting the source and destination nodes [7], [8]. The simplest extension of a single-link setting is the case when there are multiple parallel links. This extension has been previously studied for streaming in [7, Chapter 8], [9]. In the network setting. multiple parallel links correspond to separate paths chosen by a naive routing algorithm. Link failures in the network then lead to packet erasures over the associated path. It was shown that joint coding across packets transmitted over different paths, can outperform separate coding applied to individual paths only. An alternative to path routing is generationbased linear network coding, where the received packets are a linear transformation of the transmitted packets [10]-[12]. Links failures in the network now can potentially reduce the channel rank [13]. Rank metric codes such as Gabidulin codes can be used as end-to-end codes for protecting packets in such rank-deficient channels [14]-[17]. In this work, we extend streaming under the burst packet loss model, see e.g., [18], to a rank-deficient matrix channel. In the context of network coding, the rank is equal to the min-cut of the network, decreasing to a minimum tolerable rank when links fail in a burst [10], [13], [19]. For such a burst rank loss model, we design an end-to-end code with a layered structure and establish its optimality. Our approach generalizes the prior work in [7, Chapter 8], which addressed a network with naive routing and permitted at most one link to fail during a burst. While there, the problem simplified to multiple parallel links with one behaving as a periodic burst erasure channel, we permit both multiple bursts and linear transformations of the channel packets that can ensue as a result of network coding. Furthermore, their code construction involved diagonally interleaving
IEEE Transactions on Information Theory, 2017
We propose a new class of error correction codes for low-delay streaming communication. We consid... more We propose a new class of error correction codes for low-delay streaming communication. We consider an online setup where a source packet arrives at the encoder every M channel uses, and needs to be decoded with a maximum delay of T packets. We consider a sliding-window erasure channel-C(N, B, W)-which introduces either up to N erasures in arbitrary positions, or B erasures in a single burst, in any window of length W. When M = 1, the case where source-arrival and channel-transmission rates are equal, we propose a class of codes-MiDAS codes-that achieve a near optimal rate. Our construction is based on a layered approach. We first construct an optimal code for the C(N = 1, B, W) channel, and then concatenate an additional layer of parity-check symbols to deal with N > 1. When M > 1, the case where source-arrival and channel-transmission rates are unequal, we characterize the capacity when N = 1 and W ≥ M (T + 1), and for N > 1, we propose a construction based on a layered approach. Numerical simulations over Gilbert-Elliott and Fritchman channel models indicate significant gains in the residual loss probability over baseline schemes. We also discuss the connection between the error correction properties of the MiDAS codes and their underlying column distance and column span.
IEEE Transactions on Information Theory, 2015
2015 IEEE International Symposium on Information Theory (ISIT), 2015
The column Hamming distance of a convolutional code determines the error correction capability wh... more The column Hamming distance of a convolutional code determines the error correction capability when streaming over a class of packet erasure channels. We introduce a metric known as the column sum rank, that parallels column Hamming distance when streaming over a network with link failures. We prove rank analogues of several known column Hamming distance properties and introduce a new family of convolutional codes that maximize the column sum rank up to the code memory. Our construction involves finding a class of superregular matrices that preserve this property after multiplication with non-singular block diagonal matrices in the ground field.
IEEE Journal of Selected Topics in Signal Processing, 2015
2013 Proceedings IEEE INFOCOM, 2013
2013 13th Canadian Workshop on Information Theory, 2013
2013 IEEE International Symposium on Information Theory, 2013
We study near optimal error correction codes for real-time communication. In our setup the encode... more We study near optimal error correction codes for real-time communication. In our setup the encoder must operate on an incoming source stream in a sequential manner, and the decoder must reconstruct each source packet within a fixed playback deadline of T packets. The underlying channel is a packet erasure channel that can introduce both burst and isolated losses. We first consider a class of channels that in any window of length T + 1 introduce either a single erasure burst of a given maximum length B, or a certain maximum number N of isolated erasures. We demonstrate that for a fixed rate and delay, there exists a tradeoff between the achievable values of B and N, and propose a family of codes that is near optimal with respect to this tradeoff. We also consider another class of channels that introduce both a burst and an isolated loss in each window of interest and develop the associated streaming codes. All our constructions are based on a layered design and provide significant improvements over baseline codes in simulations over the Gilbert-Elliott channel.
2013 Asilomar Conference on Signals, Systems and Computers, 2013
IEEE Journal on Selected Areas in Communications, 2011
Error-Correcting Codes for Low-Delay Streaming Communications Ahmed Badr Doctor of Philosophy Gra... more Error-Correcting Codes for Low-Delay Streaming Communications Ahmed Badr Doctor of Philosophy Graduate Department of Electrical and Computer Engineering (ECE) University of Toronto 2014 This thesis develops a new class of error-correcting codes for low-delay streaming over packet-erasure channels. Such codes must operate sequentially on the incoming source stream, and must reconstruct each source packet within a fixed delay of T packets. We show that both the fundamental limits, as well as structural properties of such streaming codes, are different from classical codes. In our study, we consider successively finer approximations of burst erasure channels, that capture the dominant error events associated with the streaming setup. In the basic model, we consider a channel that in any sliding window of length W , introduces either an erasure burst of length B, or up to N erasures in arbitrary positions. We show that there is an inherent tradeoff between the achievable values of B and...
2017 IEEE International Symposium on Information Theory (ISIT), 2017
We study a setting where two source streams with different decoding deadlines must be transmitted... more We study a setting where two source streams with different decoding deadlines must be transmitted over a burst erasure channel. The source streams are multiplexed into a single stream of channel-packets at the encoder and transmitted over a packet erasure channel. The decoder must recover the source-packets within each stream sequentially, by their corresponding deadlines. We consider the burst-erasure channel model and characterize the capacity region for a certain range of system parameters. We show that the operation of the system can be divided into three different regimes based on the relative values of decoding deadlines. On the achievability side, we show that jointly coding across the two streams, despite their different deadlines, is necessary to achieve capacity. On the converse side we develop information theoretic outer bounds on the capacity region. We find that the capacity region exhibits a “corner point” where we can transmit the urgent stream at a positive rate, yet...
Journal of Infrastructure Systems
The Egyptian Journal of Haematology
Introduction Vaso-occlusion is a determinant for most manifestations of sickle cell anemia (SCA).... more Introduction Vaso-occlusion is a determinant for most manifestations of sickle cell anemia (SCA). Elevated concentration of homocysteine contributes to thrombosis, a frequent event in SCA. Folic acid deficiency leads to increase in plasma homocysteine. The aim of study was to test whether children with SCA have elevated serum homocysteine with diminished folate level and to determine whether hyperhomocysteinemia has a correlation with the frequency of vaso-occlusive crisis. Patients and methods A case–control study was carried over a period of 1 year (January to December 2014) in the hematology clinic, Abo El-Reesh Hospital, Cairo University. A total of 50 patients with SCA were included together with 30 age-matched and sex-matched healthy children recruited from Menoufia Hospital. Venous blood samples were obtained from both groups to measure serum homocysteine and folic acid levels. Results The mean±SD of age of the patients and controls were 6.20±2.55 and 6.03±2.64 years, respectively. Homocysteine level was significantly higher in the patients group compared with control group, with a mean±SD of 44.68±9.096 and 18.81±3.76 µmol/l, respectively (P>0.01). Folic acid level was lower in the patients group than control group, with 12.02±2.76 and 14.68±2.99 ng/ml, respectively (P<0.05). Significant inverse correlation was found between homocysteine and folic acid (correlation coefficient −0.337 and P=0.017). A strong positive correlation between homocysteine level and the frequency of vaso-occlusive crisis was found (P=0.04). Conclusion Patients with sickle cell disease have high serum homocysteine with low folate levels. This hyperhomocysteinemia is positively correlated with the frequency of vaso-occlusive crisis.
IEEE Signal Processing Magazine
Many current and emerging applications require low-latency communication, including interactive v... more Many current and emerging applications require low-latency communication, including interactive voice and video communication, multiplayer gaming, multiperson augmented/virtual reality, and various Internet of Things (IoT) applications. Forward error correction (FEC) codes for low-delay interactive applications have several characteristics that distinguish them from traditional FEC. The encoding and decoding operations must process a stream of data packets in a sequential fashion. Strict latency constraints limit the use of long block lengths, interleaving, or large buffers. Furthermore, these codes must achieve fast recovery from burst losses and yet be robust to other types of loss patterns.
Rheumatology International, 2017
We conducted this systematic reviews and meta-analysis to investigate the safety and efficacy of ... more We conducted this systematic reviews and meta-analysis to investigate the safety and efficacy of ocrelizumab in patients with active rheumatoid arthritis (RA) who exhibited resistance or intolerance to methotrexate or biological therapy. We performed a web-based literature search of PubMed, Google Scholar, EBSCO, Scopus, Embase, and Web of science for studies that compared ocrelizumab plus methotrexate versus methotrexate plus placebo in RA patients. Data were extracted from eligible studies and pooled as risk ratios (RR), using RevMan software. Pooling data from four RCTs (2230 patients) showed that ocrelizumab plus methotrexate were superior to methotrexate plus placebo at 24 weeks in terms of improvement on the American college of rheumatology (ACR20, ACR50, and ACR70) criteria (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001), disease activity score 28-ESR (RR = 3.77, 95% CI [2.47, 5.74], p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001), and Sharp/van der Heijde radiological score (RR = 1.63, 95% CI [1.43, 1.85], p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001). These effects were consistent among all ocrelizumab doses. The rates of serious adverse events were comparable between the ocrelizumab and placebo containing groups (RR = 1, 95% CI [0.78, 1.28], p = 0.98). However, infusion related reactions were significantly higher in ocrelizumab group (RR = 2.13, 95% CI [1.69, 2.68], p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.00001), compared to placebo group. The combination of ocrelizumab plus methotrexate was superior to methotrexate plus placebo on all clinical and radiographic improvement scales. The incidence of adverse events, including serious adverse events, was comparable between both groups. Future trials should investigate the efficacy of ocrelizumab alone and develop strategies to alleviate its related infusion reactions.
2016 IEEE International Symposium on Information Theory (ISIT), 2016
The burst rank loss channel is an extension of the burst erasure channel where the channel matrix... more The burst rank loss channel is an extension of the burst erasure channel where the channel matrix between the sender and receiver becomes rank-deficient for a certain period of consecutive time-slots. We study streaming communication over the burst rank loss channel, propose a new class of codes, ROBIN codes, and establish their optimality. Our construction uses the Maximum Rank Distance (MRD) and Maximum Sum Rank (MSR) codes from previous works as constituent codes, and combines them in a layered fashion. Our results generalize previous work on both the single-link and multiple-parallel-link streaming setups over burst erasure channels. We perform simulations over statistical network models to show that ROBIN codes attain low packet loss rates in comparison to existing codes. I. INTRODUCTION Streaming communication is characterized by two factors: causality and delay. Source packets arrive sequentially at a transmitter, which generates channel packets causally. The receiver collecting the transmitted packets must reconstruct the source within a decoding deadline, using only what it has observed up to that point. A receiving user is interested in sequential playback, meaning if a packet has not been recovered within the deadline, the decoder considers it lost and moves to the next packet. Error correcting codes capable of low delay decoding have previously been designed in the context of a single-link erasure channel connecting the transmitter and receiver [1]-[5]. In Internet communication, packet erasures primarily occur in bursts [6], and consequently the works of [1], [3]-[5] focus primarily on low-delay recovery from a burst of consecutive erasures. Alternatively, [2], [3], [5] also consider arbitrary loss patterns and guarantee low-delay recovery when there are fewer than the maximum tolerable number of erasures in a window. The above mentioned works consider the case of a single communication link between the sender and receiver. As communication methods increase in sophistication, it is natural to consider streaming over a network where there are multiple links and paths connecting the source and destination nodes [7], [8]. The simplest extension of a single-link setting is the case when there are multiple parallel links. This extension has been previously studied for streaming in [7, Chapter 8], [9]. In the network setting. multiple parallel links correspond to separate paths chosen by a naive routing algorithm. Link failures in the network then lead to packet erasures over the associated path. It was shown that joint coding across packets transmitted over different paths, can outperform separate coding applied to individual paths only. An alternative to path routing is generationbased linear network coding, where the received packets are a linear transformation of the transmitted packets [10]-[12]. Links failures in the network now can potentially reduce the channel rank [13]. Rank metric codes such as Gabidulin codes can be used as end-to-end codes for protecting packets in such rank-deficient channels [14]-[17]. In this work, we extend streaming under the burst packet loss model, see e.g., [18], to a rank-deficient matrix channel. In the context of network coding, the rank is equal to the min-cut of the network, decreasing to a minimum tolerable rank when links fail in a burst [10], [13], [19]. For such a burst rank loss model, we design an end-to-end code with a layered structure and establish its optimality. Our approach generalizes the prior work in [7, Chapter 8], which addressed a network with naive routing and permitted at most one link to fail during a burst. While there, the problem simplified to multiple parallel links with one behaving as a periodic burst erasure channel, we permit both multiple bursts and linear transformations of the channel packets that can ensue as a result of network coding. Furthermore, their code construction involved diagonally interleaving
2006 6th International Conference on ITS Telecommunications, 2006
We propose the multicast encryption security protocol MESP. It is driven form the IPSEC ESP. The ... more We propose the multicast encryption security protocol MESP. It is driven form the IPSEC ESP. The specification of the protocol are discussed and applied the existing IPSEC ESP. We use the existing implementation of the IPSEC ESP; modify it to meet the MESP specifications to implement the MESP. A multicast chat system is used as an application for this protocol.
Neurological Research, 2001
Even though cerebral vasospasm after subarachnoid hemorrhage (SAH) causes cerebral ischemia or in... more Even though cerebral vasospasm after subarachnoid hemorrhage (SAH) causes cerebral ischemia or infarction, the metabolic alterations in cerebrospinal fluids (CSF) after SAH have not been studied. This study was undertaken to measure the levels of glucose, lactate, pyruvate and glutamate in CSF from double hemorrhage dog models. Thirty-two mongrel dogs of either sex, weighing 18-24 kg, underwent double hemorrhage by percutaneous needle puncture of the cistema magna and injection of autologous blood on day 0 and day 2. The dogs were then sacrificed on day 3, 5 and 7, after collecting CSF. In another study, the dogs were treated with mitogen-activated protein kinase (MAPK) inhibitors PD98059 and U0126, and caspase-2 and caspase-3 inhibitors from day 3 to day 6 after initial blood injection. CSF was collected on day 7 before dogs were sacrificed. The concentration of glucose, lactate, pyruvate and glutamate in CSF was measured by photometrical method. Compared with CSF collected on day 0, glucose was decreased on days 5-7, lactate was increased on days 2-7, pyruvate was increased on days 2-7, and glutamate was increased on days 3-7 (p < 0.05). In the groups treated with MAPK or caspase inhibitors, most of the metabolic alterations remained unchanged as compared with CSF from untreated dogs. Clinically, caspase inhibitors-2 and -3, and MAPK inhibitor U0126 all failed to prevent vasospasm. MAPK inhibitor PD98059 partially prevented vasospasm. Our data demonstrated a metabolic alteration of glucose, glutamate, lactate and pyruvate in CSF during cerebral vasospasm. This metabolic change in consistent with the time course of cerebral vasospasm. This study suggests that brain energy metabolites and excitative amino acids are altered during cerebral vasospasm.