338 results on '"Jafar, Syed A."'
Search Results
2. The Impact of CEO Characteristics on the Financial Performance of Family Businesses Listed in the Euronext Exchange.
- Author
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El Abiad, Zouhour, Abraham, Rebecca, El-Chaarani, Hani, Skaf, Yahya, Binsaddig, Ruaa Omar, and Jafar, Syed Hasan
- Subjects
FINANCIAL performance ,FAMILY-owned business enterprises ,ORGANIZATIONAL performance ,RATE of return ,CHIEF executive officers - Abstract
This paper identifies the CEO characteristics that have an impact on the performance of family businesses listed in the Euronext in the post-COVID 19 period. CEO characteristics are evaluated on two dimensions, i.e., personal characteristics and corporate governance mechanisms. A sample of 137 firm-year observations from Portugal, Luxembourg, the Netherlands, Ireland, France, and Belgium was chosen. CEO attributes of age, gender, education, and family membership were combined with corporate governance mechanisms of ownership concentration, CEO duality, CEO directorships, and CEO tenure, to predict return on assets and return on equity, using OLS regression. GMM estimation and Two-Stage Least Squares were employed to establish the robustness of the results. Among CEO personal characteristics, CEO family membership has a positive impact on return on assets, and a positive impact on return on equity. Among corporate governance mechanisms, CEO duality had a negative impact on return on assets, and a negative impact on return on equity. CEO ownership, and CEO tenure had a positive impact on return on assets, and a positive impact on return on equity. This paper's value lies in its evaluation of the under-researched area of family businesses of Euronext-listed firms. It can be used by family businesses in the region, for the selection and training of CEOs to fulfill the goal of achieving superior financial performance. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
3. The coccolithophore family Calciosoleniaceae with report of a new species : Calciosolenia subtropicus from the southern Indian Ocean
- Author
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Patil, Shramik, Mohan, Rahul, Jafar, Syed A., Gazi, Sahina, Choudhari, Pallavi, and Crosta, Xavier
- Published
- 2019
4. Attraction of Bus Rapid Transit (BRT) for Car and Bike Owners
- Author
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Abid Malik Muneeb, Ayaz Altaf, Nawaz Nabeel, Iqbal Muhammad, Yang Hongtai, Tehseen Ahmad Salar, and Jafar Syed Taseer Abbas
- Subjects
bus rapid transit ,metro bus service ,mode shift ,multinomial logistic regression model (mnl) ,stated preference ,Transportation engineering ,TA1001-1280 - Abstract
This study aims to find the potential of Bus Rapid Transit (BRT) to attract the vehicle owners from their personal vehicles i.e., motorcars and motorcycles. Stated preference survey (questionnaires) and interviews were conducted at BRT (Metro Bus) Stations for the prediction of the individuals shifting from their private vehicles to BRT. Questions were designed critically as per the requirements of the research related to numerous aspects of BRT use i.e., vehicle ownership of the travelers, driving license holder, demographic characteristics, choice to use BRT if the fare increases, trip purpose and their prior mode of transportation for the same trip. A total of 374 responses, as per the population of the study area (Islamabad-Rawalpindi, Pakistan), were collected. The Multinomial Logistic Regression (MNL) model has been employed for four categories of vehicle ownerships i.e., “Car owners using BRT”, “Bike owners using BRT”, “Both Car and Bike owners using BRT” and the last one which has been taken as reference category is “BRT users with no vehicle ownership”. The analysis indicated that BRT has attracted considerably private vehicle users specially the bike owners. Some socio-economic factors like income and residence location (accessibility) additionally have a major effect on the selection of BRT. In addition, it has been observed that fare increase can alter the mode choice of the BRT users and they will again prefer their own vehicles. The Travel choice model developed in the study can be very useful for policy makers and transport planners to enhance the BRT service and attraction, to mitigate traffic congestion and car ownership.
- Published
- 2020
- Full Text
- View/download PDF
5. Fusion of Blockchain and Sustainable Development Goals: A Bibliometric Analysis for Future Trends.
- Author
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Salim, Mohd, Khan, Parvez Alam, Jalil, Nasir Abdul, Johl, Satirenjit Kaur, Jafar, Syed Hasan, Irfan, Fatima, and Khan, Mantasha
- Subjects
SUSTAINABLE development ,LITERATURE reviews ,BLOCKCHAINS ,TREND analysis ,SCIENCE databases ,BIBLIOMETRICS ,CITATION indexes - Abstract
Blockchain technology has emerged as a transformative solution for enhancing transparency and accountability across various dimensions of sustainable development. Given the limited exploration of Blockchain's synergy with sustainable development goals, there exists a compelling rationale to undertake a bibliometric literature review aimed at identifying forthcoming research trajectories. Employing the "Blockchain" AND "Sustainable Development Goals" keywords, an extensive search was conducted across Scopus and Web of Science databases. This endeavor yielded a corpus of 271 articles published within the span of 2017 to 2023. Subsequent adherence to inclusion and exclusion criteria refined this collection to 183 documents for meticulous Bibliographic Analysis through the Biblioshiny application of the Bibliometrix R package. The study charts a promising trajectory characterized by upward trends in recent years, unveiling the most prolific authors, productive nations, frequency of keywords, thematic evaluation, and collaborative endeavors. Delving into the systematic literature review, the research introduces five discernible future trends, along with a comprehensive research framework designed to amplify the generalizability of findings to pertinent stakeholders. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
6. Biogeographic distribution of extant Coccolithophores in the Indian sector of the Southern Ocean
- Author
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Patil, Shramik M., Mohan, Rahul, Shetye, Suhas S., Gazi, Sahina, Baumann, Karl-Heinz, and Jafar, Syed
- Published
- 2017
- Full Text
- View/download PDF
7. Microstructure-Dictated Resistance Properties of Some Indian Dinosaur Eggshells: Finite Element Modeling
- Author
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Sahni, Ashok, Jafar, Syed A., and Mishra, Sanjay
- Published
- 2005
8. Forecasting of NIFTY 50 Index Price by Using Backward Elimination with an LSTM Model.
- Author
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Jafar, Syed Hasan, Akhtar, Shakeb, El-Chaarani, Hani, Khan, Parvez Alam, and Binsaddig, Ruaa
- Subjects
PRICE indexes ,RELATIVE strength index (Securities) ,DEEP learning ,ARTIFICIAL intelligence ,PRICES - Abstract
Predicting trends in the stock market is becoming complex and uncertain. In response, various artificial intelligence solutions have emerged. A significant solution for predicting the trends of a stock's volatile and chaotic nature is drawn from deep learning. The present study's objective is to compare and predict the closing price of the NIFTY 50 index through two significant deep learning methods—long short-term memory (LSTM) and backward elimination LSTM (BE-LSTM)—using 15 years' worth of per day data obtained from Bloomberg. This study has considered the variables of date, high, open, low, close volume, as well as the 14-period relative strength index (RSI), to predict the closing price. The results of the comparative study show that backward elimination LSTM performs better than the LSTM model for predicting the NIFTY 50 index price for the next 30 days, with an accuracy of 95%. In conclusion, the proposed model has significantly improved the prediction of the NIFTY 50 index price. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
9. Quantum Cross Subspace Alignment Codes via the $N$-sum Box Abstraction
- Author
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Lu, Yuxiang and Jafar, Syed Ali
- Subjects
FOS: Computer and information sciences ,Information Theory (cs.IT) ,Computer Science - Information Theory - Abstract
Cross-subspace alignment (CSA) codes are used in various private information retrieval (PIR) schemes (e.g., with secure storage) and in secure distributed batch matrix multiplication (SDBMM). Using a recently developed $N$-sum box abstraction of a quantum multiple-access channel (QMAC), we translate CSA schemes over classical multiple-access channels into efficient quantum CSA schemes over a QMAC, achieving maximal superdense coding gain. Because of the $N$-sum box abstraction, the underlying problem of coding to exploit quantum entanglements for CSA schemes, becomes conceptually equivalent to that of designing a channel matrix for a MIMO MAC subject to given structural constraints imposed by the $N$-sum box abstraction, such that the resulting MIMO MAC is able to implement the functionality of a CSA scheme (encoding/decoding) over-the-air. Applications include Quantum PIR with secure and MDS-coded storage, as well as Quantum SDBMM., arXiv admin note: substantial text overlap with arXiv:2304.07561
- Published
- 2023
10. $N$-Sum Box: An Abstraction for Linear Computation over Many-to-one Quantum Networks
- Author
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Allaix, Matteo, Lu, Yuxiang, Yao, Yuhang, Pllaha, Tefjol, Hollanti, Camilla, and Jafar, Syed A
- Subjects
FOS: Computer and information sciences ,Quantum Physics ,Information Theory (cs.IT) ,Computer Science - Information Theory ,FOS: Physical sciences ,Quantum Physics (quant-ph) - Abstract
Linear computations over quantum many-to-one communication networks offer opportunities for communication cost improvements through schemes that exploit quantum entanglement among transmitters to achieve superdense coding gains, combined with classical techniques such as interference alignment. The problem becomes much more broadly accessible if suitable abstractions can be found for the underlying quantum functionality via classical black box models. This work formalizes such an abstraction in the form of an "$N$-sum box", a black box generalization of a two-sum protocol of Song \emph{et al.} with recent applications to $N$-server private information retrieval. The $N$-sum box has a communication cost of $N$ qudits and classical output of a vector of $N$ $q$-ary digits linearly dependent (via an $N \times 2N$ transfer matrix) on $2N$ classical inputs distributed among $N$ transmitters. We characterize which transfer matrices are feasible by our construction, both with and without the possibility of additional locally invertible classical operations at the transmitters and receivers. Furthermore, we provide a sample application to Cross-Subspace Alignment (CSA) schemes to obtain efficient instances of Quantum Private Information Retrieval (QPIR) and Quantum Secure Distributed Batch Matrix Multiplication (QSDBMM). We first describe $N$-sum boxes based on maximal stabilizers and we then consider non-maximal-stabilizer-based constructions to obtain an instance of Quantum Symmetric Private Information Retrieval.
- Published
- 2023
11. Late Cretaceous (Santonian-Maastrichtian) Integrated Coccolith-Globotruncanid Biostratigraphy of Pelagic Limestones from the Accretionary Prism of Manipur, Northeastern India
- Author
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Chungkham, Prithiraj and Jafar, Syed A.
- Published
- 1998
- Full Text
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12. Trigonium curvatus sp. nov. and Trigonium arcticum (Bacillariophyceae) from the surface sediments of Prydz Bay, East Antarctica
- Author
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Nair, Abhilash, Mohan, Rahul, Shetye, Suhas, Gazi, Sahina, and Jafar, Syed A.
- Published
- 2015
13. Petasaria heterolepis (Prymnesiaceae) from the Southern Indian Ocean
- Author
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Patil, Shramik, Mohan, Rahul, Gazi, Sahina, Shetye, Suhas, and Jafar, Syed A.
- Published
- 2015
14. Morphological variability of Emiliania huxleyi in the Indian sector of the Southern Ocean during the austral summer of 2010
- Author
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Patil, Shramik M., Mohan, Rahul, Shetye, Suhas, Gazi, Sahina, and Jafar, Syed
- Published
- 2014
- Full Text
- View/download PDF
15. Diatom burst-driven silica depletion under the Antarctic sea ice: evidence from sponge spicules
- Author
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Shetye, Suhas, Mohan, Rahul, Jafar, Syed A., Nair, Abhilash, Patil, Shramik, Jawak, Shridhar, Asthana, Rajesh, and Gazi, Sahina
- Published
- 2014
16. Prymnesium neolepis (Prymnesiaceae), a siliceous Haptophyte from the Southern Indian Ocean
- Author
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Patil, Shramik, Mohan, Rahul, Shetye, Suhas, Gazi, Sahina, and Jafar, Syed A.
- Published
- 2014
17. The Extremal GDoF Gain of Optimal versus Binary Power Control in $K$ User Interference Networks Is $\Theta(\sqrt{K})$
- Author
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Chan, Yao-Chia, Pezeshkpour, Pouya, Geng, Chunhua, and Jafar, Syed A.
- Subjects
Computer Science - Information Theory - Abstract
Using ideas from Generalized Degrees of Freedom (GDoF) analyses and extremal network theory, this work studies the extremal gain of optimal power control over binary (on/off) power control, especially in large interference networks, in search of new theoretical insights. Whereas numerical studies have already established that in most practical settings binary power control is close to optimal, the extremal analysis shows not only that there exist settings where the gain from optimal power control can be quite significant, but also bounds the extremal values of such gains from a GDoF perspective. As its main contribution, this work explicitly characterizes the extremal GDoF gain of optimal over binary power control as $\Theta\left(\sqrt{K}\right)$ for all $K$. In particular, the extremal gain is bounded between $\lfloor \sqrt{K}\rfloor$ and $2.5\sqrt{K}$ for every $K$. For $K=2,3,4,5,6$ users, the precise extremal gain is found to be $1, 3/2, 2, 9/4$ and $41/16$, respectively. Networks shown to achieve the extremal gain may be interpreted as multi-tier heterogeneous networks. It is worthwhile to note that because of their focus on asymptotic analysis, the sharp characterizations of extremal gains are valuable primarily from a theoretical perspective, and not as contradictions to the conventional wisdom that binary power control is generally close to optimal in practical, non-asymptotic settings., Comment: 18 pages, 5 figures; Typo corrections
- Published
- 2022
18. On Single Server Private Information Retrieval with Private Coded Side Information
- Author
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Lu, Yuxiang and Jafar, Syed Ali
- Subjects
FOS: Computer and information sciences ,Information Theory (cs.IT) ,Computer Science - Information Theory ,Computer Science::Cryptography and Security - Abstract
Motivated by an open problem and a conjecture, this work studies the problem of single server private information retrieval with private coded side information (PIR-PCSI) that was recently introduced by Heidarzadeh et al. The goal of PIR-PCSI is to allow a user to efficiently retrieve a desired message $\bm{W}_{\bm{\theta}}$, which is one of $K$ independent messages that are stored at a server, while utilizing private side information of a linear combination of a uniformly chosen size-$M$ subset ($\bm{\mathcal{S}}\subset[K]$) of messages. The settings PIR-PCSI-I and PIR-PCSI-II correspond to the constraints that $\bm{\theta}$ is generated uniformly from $[K]\setminus\bm{\mathcal{S}}$, and $\bm{\mathcal{S}}$, respectively. In each case, $(\bm{\theta},\bm{\mathcal{S}})$ must be kept private from the server. The capacity is defined as the supremum over message and field sizes, of achievable rates (number of bits of desired message retrieved per bit of download) and is characterized by Heidarzadeh et al. for PIR-PCSI-I in general, and for PIR-PCSI-II for $M>(K+1)/2$ as $(K-M+1)^{-1}$. For $2\leq M\leq (K+1)/2$ the capacity of PIR-PCSI-II remains open, and it is conjectured that even in this case the capacity is $(K-M+1)^{-1}$. We show the capacity of PIR-PCSI-II is equal to $2/K$ for $2 \leq M \leq \frac{K+1}{2}$, which is strictly larger than the conjectured value, and does not depend on $M$ within this parameter regime. Remarkably, half the side-information is found to be redundant. We also characterize the infimum capacity (infimum over fields instead of supremum), and the capacity with private coefficients. The results are generalized to PIR-PCSI-I ($\theta\in[K]\setminus\mathcal{S}$) and PIR-PCSI ($\theta\in[K]$) settings.
- Published
- 2022
19. The impact of liquidity on the financial performance of banks during the post-Covid-19
- Author
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EL-Chaarani, Hani, EL-Abiad, Zouhour, and Jafar, Syed Hasan
- Published
- 2022
- Full Text
- View/download PDF
20. Flexible Distributed Matrix Multiplication.
- Author
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Li, Weiqi, Chen, Zhen, Wang, Zhiying, Jafar, Syed A., and Jafarkhani, Hamid
- Subjects
MATRIX multiplications ,FINITE fields ,POLYNOMIALS - Abstract
The distributed matrix multiplication problem with an unknown number of stragglers is considered, where the goal is to efficiently and flexibly obtain the product of two massive matrices by distributing the computation across $N$ servers. There are up to $N - R$ stragglers but the exact number is not known a priori. Motivated by reducing the computation load of each server, a flexible solution is proposed to fully utilize the computation capability of available servers. The computing task for each server is separated into several subtasks, constructed based on Entangled Polynomial codes by Yu et al. The final results can be obtained from either a larger number of servers with a smaller amount of computation completed per server or a smaller number of servers with a larger amount of computation completed per server. The required finite field size of the proposed solution is less than $2N$. Moreover, the optimal design parameters such as the partitioning of the input matrices are discussed. Our constructions can also be generalized to other settings such as batch distributed matrix multiplication and secure distributed matrix multiplication. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
21. Capacity of 2-User Linear Computation Broadcast With Partially Informed Server.
- Author
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Yao, Yuhang and Jafar, Syed A.
- Abstract
A linear computation broadcast (LCBC) setting is comprised of data that is stored at a server and $K$ users who wish to retrieve their respective desired linear functions of the data, while utilizing knowledge of certain other linear functions available to each user as prior side-information. The goal is to determine the smallest amount of broadcast information from the server that will simultaneously satisfy all the users’ demands. The reciprocal of the optimal broadcast cost is called the capacity of LCBC. The capacity is known for the 2-user setting, and recent studies of 3-user LCBC have revealed new insights into the need for sumset inequalities for LCBC. This letter introduces a generalization of the LCBC problem, where instead of storing all the data, the server may have partial knowledge in the form of some arbitrary linear function of the data. Building upon recent advances, the exact capacity is found for 2-user linear computation broadcast with partially informed server. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
22. DoF region of the decentralized MIMO broadcast channel - How many informed antennas do we need?
- Author
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Bazco-Nogueras, Antonio, Davoodi, Arash, de Kerret, Paul, Gesbert, David, Gresset, Nicolas, Jafar, Syed, Bazco-Nogueras, Antonio, Davoodi, Arash, de Kerret, Paul, Gesbert, David, Gresset, Nicolas, and Jafar, Syed
- Published
- 2020
23. X -Secure T -Private Federated Submodel Learning With Elastic Dropout Resilience.
- Author
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Jia, Zhuqing and Jafar, Syed Ali
- Subjects
- *
DISTRIBUTED databases , *INFORMATION retrieval , *MATRIX multiplications - Abstract
Motivated by recent interest in federated submodel learning, this work explores the fundamental problem of privately reading from and writing to a database comprised of $K$ files (submodels) that are stored across $N$ distributed servers according to an $X$ -secure threshold secret sharing scheme. One after another, various users wish to retrieve their desired file, locally process the information and then update the file in the distributed database while keeping the identity of their desired file private from any set of up to $T$ colluding servers. The availability of servers changes over time, so elastic dropout resilience is required. The main contribution of this work is an adaptive scheme, called ACSA-RW, that takes advantage of all currently available servers to reduce its communication costs, fully updates the database after each write operation even though the database is only partially accessible due to server dropouts, and ensures a memoryless operation of the network in the sense that the storage structure is preserved and future users may remain oblivious of the past history of server dropouts. The ACSA-RW construction builds upon cross-subspace alignment (CSA) codes that were originally introduced for $X$ -secure $T$ -private information retrieval and have been shown to be natural solutions for secure distributed batch matrix multiplication problems. ACSA-RW achieves the desired private read and write functionality with elastic dropout resilience, matches the best results for private-read from PIR literature, improves significantly upon available baselines for private-write, reveals a striking symmetry between upload and download costs, and exploits storage redundancy to accommodate arbitrary read and write dropout servers up to certain threshold values. It also answers in the affirmative an open question by Kairouz et al. for the case of partially colluding servers (i.e., tolerating collusion up to a threshold) by exploiting synergistic gains from the joint design of private read and write operations. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
24. Sum-GDoF of Symmetric Multi-Hop Interference Channel Under Finite Precision CSIT Using Aligned-Images Sum-Set Inequalities.
- Author
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Wang, Junge and Jafar, Syed Ali
- Subjects
- *
CHANNEL coding , *FINITE, The , *SPREAD spectrum communications , *BROADCAST channels , *DEGREES of freedom - Abstract
Aligned-Images Sum-set Inequalities are used in this work to study the Generalized Degrees of Freedom (GDoF) of the symmetric layered multi-hop interference channel under the robust assumption that the channel state information at the transmitters (CSIT) is limited to finite precision. First, the sum-GDoF value is characterized for the $2\times 2\times 2$ setting that is comprised of 2 sources, 2 relays, and 2 destinations. It is shown that the sum-GDoF does not improve even if perfect CSIT is allowed in the first hop, as long as the CSIT in the second hop is limited to finite precision. The sum GDoF characterization is then generalized to the $2\times 2\times \cdots \times 2$ setting that is comprised of $L$ hops. Remarkably, for large $L$ , the sum-GDoF value approaches that of the one-hop broadcast channel that is obtained by full cooperation among the two transmitters of the last hop, with finite precision CSIT. Previous studies of multi-hop interference networks either identified sophisticated GDoF optimal schemes under perfect CSIT, such as aligned interference neutralization and network diagonalization, that are powerful in theory but too fragile to be practical, or studied robust achievable schemes like classical amplify/decode/compress-and-forward without claims of information-theoretic optimality. In contrast, under finite precision CSIT, we show that the benefits of fragile schemes are lost, while a combination of classical random coding schemes that are simpler and much more robust, namely a rate-splitting between decode-and-forward and amplify-and-forward, is shown to be GDoF optimal. As such, this work represents another step towards bridging the gap between theory (optimality) and practice (robustness) with the aid of Aligned-Images Sum-set Inequalities. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
25. $X$-Secure $T$-Private Federated Submodel Learning with Elastic Dropout Resilience
- Author
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Jia, Zhuqing and Jafar, Syed A.
- Subjects
FOS: Computer and information sciences ,Information Theory (cs.IT) ,Computer Science - Information Theory - Abstract
Motivated by recent interest in federated submodel learning, this work explores the fundamental problem of privately reading from and writing to a database comprised of $K$ files (submodels) that are stored across $N$ distributed servers according to an $X$-secure threshold secret sharing scheme. One after another, various users wish to retrieve their desired file, locally process the information and then update the file in the distributed database while keeping the identity of their desired file private from any set of up to $T$ colluding servers. The availability of servers changes over time, so elastic dropout resilience is required. The main contribution of this work is an adaptive scheme, called ACSA-RW, that takes advantage of all currently available servers to reduce its communication costs, fully updates the database after each write operation even though the database is only partially accessible due to server dropouts, and ensures a memoryless operation of the network in the sense that the storage structure is preserved and future users may remain oblivious of the past history of server dropouts. The ACSA-RW construction builds upon CSA codes that were originally introduced for XSTPIR and have been shown to be natural solutions for secure distributed matrix multiplication problems. ACSA-RW achieves the desired private read and write functionality with elastic dropout resilience, matches the best results for private-read from PIR literature, improves significantly upon available baselines for private-write, reveals a striking symmetry between upload and download costs, and exploits redundant storage dimensions to accommodate arbitrary read and write dropout servers up to certain threshold values. It also answers in the affirmative an open question by Kairouz et al. by exploiting synergistic gains from the joint design of private read and write operations.
- Published
- 2020
26. Degrees of freedom of the K user M x N MIMO interference channel
- Author
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Gou, Tiangao and Jafar, Syed A.
- Subjects
Company business management ,Antennas (Electronics) -- Mechanical properties ,Communications circuits -- Management ,Degrees of freedom (Mechanics) -- Research - Published
- 2010
27. Interference alignment with asymmetric complex signaling - settling the Host-Madsen-Nosratinia conjecture
- Author
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Cadambe, Viveck R., Jafar, Syed Ali, and Wang, Chenwei
- Subjects
Wireless technology ,Company business management ,Computer networks -- Capacity ,Information networks -- Capacity ,Degree of freedom -- Analysis ,Electromagnetic interference -- Management ,Signal theory (Telecommunication) ,Mobile communication systems ,Wireless communication systems - Published
- 2010
28. Duality of MIMO multiple access channel and broadcast channel with amplify-and-forward relays
- Author
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Gomadam, Krishna S. and Jafar, Syed A.
- Subjects
Wireless technology ,Technology application ,Communications circuits -- Equipment and supplies ,Communications circuits -- Technology application ,Duality theory (Mathematics) -- Research ,Mobile communication systems -- Equipment and supplies ,Wireless communication systems -- Equipment and supplies - Published
- 2010
29. Interference alignment and the degrees of freedom of wireless X networks
- Author
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Cadambe, Viveck R. and Jafar, Syed A.
- Subjects
Wireless technology ,Company business management ,Degree of freedom -- Analysis ,Mobile communication systems -- Research ,Wireless communication systems -- Research - Published
- 2009
30. Degrees of freedom of the MIMO interference channel with cooperation and cognition
- Author
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Huang, Chiachi and Jafar, Syed A.
- Subjects
Company business management ,Antenna arrays -- Methods ,Degrees of freedom (Mechanics) -- Methods ,Degrees of freedom (Mechanics) -- Usage - Published
- 2009
31. Parallel Gaussian interference channels are not always separable
- Author
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Cadambe, Viveck R. and Jafar, Syed A.
- Subjects
Communications circuits -- Research - Published
- 2009
32. Degrees of freedom of wireless networks with relays, feedback, cooperation, and full duplex operation
- Author
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Cadambe, Viveck R. and Jafar, Syed Ali
- Subjects
MIMO communications -- Analysis ,Wireless networking -- Equipment and supplies ,Wireless networking -- Analysis - Abstract
We find the degrees of freedom of a network with S source nodes, R relay nodes, and D destination nodes, with random time-varying/frequency-selective channel coefficients and global channel knowledge at all nodes. We allow full-duplex operation at all nodes, as well as causal noise-free feedback of all received signals to all source and relay nodes. An outer bound to the capacity region of this network is obtained. Combining the outer bound with previous interference alignment based achievability results, we conclude that the techniques of relays, feedback, full-duplex operation and noisy cooperation do not increase the degrees of freedom of interference and X networks. As a second contribution, we show that for a network with K full-duplex nodes and K(K - 1) independent messages with one message from every node to each of the other K - 1 nodes, the total degrees of freedom are bounded above and below K(K - 1)/(2K - 2) and K(K - 1)/(2K - 3), respectively. Index Terms--Capacity, degrees of freedom, interference alignment, interference channel, multiple-input multiple-output (MIMO), X channel.
- Published
- 2009
33. The effect of noise correlation in amplify-and-forward relay networks
- Author
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Gomadam, Krishna Srikanth and Jafar, Syed Ali
- Subjects
Relay control systems -- Design and construction - Abstract
In wireless relay networks, noise at the relays can be correlated possibly due to common interference or noise propagation from preceding hops. A parallel relay network with noise correlation is considered in this network. For the relay strategy of amplify and forward (AF), the optimal rate maximizing relay gains when correlation knowledge is available at the relays are determined. Interestingly, it is shown that, on average, noise correlation is beneficial regardless of whether the relays know the noise covariance matrix. However, the knowledge of correlation can greatly improve the performance. Typically, the performance improvement from correlation knowledge increases with the relay power and the number of relays. With perfect correlation knowledge the system is capable of canceling interference if the number of interferers is less than the number of relays. For a two-hop multiple-access parallel network, closed-form expressions for the maximum sum rate and the optimal relay strategy are determined. Relay optimization for networks with three hops is also considered. Based on the result of two-hop network with noise correlation, an iterative algorithm is proposed for solving the relay optimization problem for three-hop networks. Index Terms--Amplify and forward (AF), common interference, multiple hop, noise correlation, parallel relay network, relay optimization.
- Published
- 2009
34. Interference alignment on the deterministic channel and application to fully connected Gaussian interference networks
- Author
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Cadambe, Viveck R., Jafar, Syed A., and Shamai, Shlomo 'Shitz'
- Subjects
Gaussian processes -- Analysis ,Interference (Linguistics) -- Analysis - Abstract
An interference alignment example is constructed for the deterministic channel model of the K-user interference channel. The deterministic channel example is then translated into the Gaussian setting, creating the first known example of a fully connected Gaussian K-user interference network with single antenna nodes, real, nonzero and constant channel coefficients, and no propagation delays where the degrees of freedom outerbound is achieved. An analogy is drawn between the propagation delay based interference alignment examples and the deterministic channel model which also allows similar constructions for the two-user X channel as well. Index Terms--Capacity, degrees of freedom, interference alignment, interference channel, X channel.
- Published
- 2009
35. Robust Optimality of Secure TIN.
- Author
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Chan, Yao-Chia, Geng, Chunhua, and Jafar, Syed A.
- Abstract
In order to discover larger networks and parameter regimes where sharp Generalized Degrees of Freedom (GDoF) characterizations may be found based on the optimality of robust schemes for interference and broadcast networks with channel state information at the transmitters (CSIT) limited to finite precision, we explore the impact of secrecy constraints. In the absence of secrecy constraints, the largest such parameter regime for $K$ user interference networks is the CTIN regime (so named for the Convexity of the GDoF region achieved by Treating Interference as Noise (TIN)) originally discovered by Yi and Caire, whose optimality was established by Chan et al. For the corresponding broadcast networks the largest regime is the SLS (Simple Layered Superposition) regime discovered by Davoodi and Jafar, but only for small networks with $K\leq 3$ users. By including secrecy constraints, we identify much larger regimes, the STIN regime and the SLS regime, where GDoF are fully characterized for arbitrary number of users under finite precision CSIT, for interference networks and broadcast networks, respectively. The optimal achievable scheme in both cases is based on TIN along with power control and jamming. Proofs of optimality rely on a combination of secrecy constraints and Aligned Images sum-set inequalities. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
36. Privacy in Retrieval, Computing, and Learning.
- Author
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Ulukus, Sennur, Avestimehr, Salman, Gastpar, Michael, Jafar, Syed, Tandon, Ravi, and Tian, Chao
- Subjects
CODING theory ,PRIVACY ,DATA privacy ,DISTRIBUTED computing ,INFORMATION theory ,GRID computing - Abstract
The increasing prevalence of massive datasets makes the outsourcing of storage and computation tasks to distributed servers a necessity. This raises a number of concerns regarding the security and integrity of stored information, the privacy of accessing desired information, the communication overhead of distributed systems, the latency, reliability, and complexity of distributed computing, and privacy in distributed training and learning systems. Recent breakthroughs from coding, communication, and information-theoretic perspectives have opened up exciting new research avenues for these topics. There are many theoretical and practical open problems. This Special Issue is dedicated to communication theory, coding theory, information theory, signal processing, and networking aspects of privacy in information retrieval, privacy in coded computing over distributed servers, and privacy in distributed learning. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
37. Private Retrieval, Computing, and Learning: Recent Progress and Future Challenges.
- Author
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Ulukus, Sennur, Avestimehr, Salman, Gastpar, Michael, Jafar, Syed A., Tandon, Ravi, and Tian, Chao
- Subjects
INTERNET privacy ,DISTRIBUTED computing ,DATA privacy ,CYBERSPACE ,INFORMATION retrieval ,GRID computing ,PARALLEL processing - Abstract
Most of our lives are conducted in the cyberspace. The human notion of privacy translates into a cyber notion of privacy on many functions that take place in the cyberspace. This article focuses on three such functions: how to privately retrieve information from cyberspace (privacy in information retrieval), how to privately leverage large-scale distributed/parallel processing (privacy in distributed computing), and how to learn/train machine learning models from private data spread across multiple users (privacy in distributed (federated) learning). The article motivates each privacy setting, describes the problem formulation, summarizes breakthrough results in the history of each problem, and gives recent results and discusses some of the major ideas that emerged in each field. In addition, the cross-cutting techniques and interconnections between the three topics are discussed along with a set of open problems and challenges. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
38. Canonical Conditions for K /2 Degrees of Freedom.
- Author
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Gul, Recep, Stotz, David, Jafar, Syed Ali, Bolcskei, Helmut, and Shamai Shitz, Shlomo
- Subjects
DEGREES of freedom ,RANDOM variables ,INTEGRATING circuits ,INTEGRATED circuits ,MATRICES (Mathematics) - Abstract
We present a condition for 1/2 degree of freedom for each user in constant $K$ -user single-antenna interference channels. This condition is sufficient for all and necessary for almost all channel matrices. Moreover, it applies to all channel topologies, i.e., to fully-connected channels as well as channels that have individual links absent, reflected by corresponding zeros in the channel matrix. Moreover, it captures the essence of interference alignment by virtue of being expressed in terms of a generic injectivity condition that guarantees separability of signal and interference. Finally, we provide codebook constructions achieving 1/2 degree of freedom for each user for all channel matrices satisfying the condition we identified. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
39. Interference alignment and degrees of freedom of the K-user interference channel
- Author
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Cadambe, Viveck R. and Jafar, Syed Ali
- Subjects
Electromagnetic interference -- Control ,Communications circuits -- Design and construction ,MIMO communications -- Research ,Digital multiplexing -- Methods ,Multichannel communication -- Methods ,Multiplexing -- Methods - Abstract
For the fully connected K user wireless interference channel where the channel coefficients are time-varying and are drawn from a continuous distribution, the sum capacity is characterized as C(SNR) = K/2 log(SNR) + o(log(SNR)). Thus, the K user time-varying interference channel almost surely has K/2 degrees of freedom. Achievability is based on the idea of interference alignment. Examples are also provided of fully connected K user interference channels with constant (not time-varying) coefficients where the capacity is exactly achieved by interference alignment at all SNR values. Index Terms--Capacity, degrees of freedom, interference alignment, interference channel, multiple-input-multiple-output (MIMO), multiplexing.
- Published
- 2008
40. Degrees of freedom region of the MIMO X channel
- Author
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Jafar, Syed A. and Shamai, Shlomo
- Subjects
Electromagnetic interference -- Control ,MIMO communications -- Research ,Information theory -- Research - Abstract
We provide achievability as well as converse results for the degrees of freedom region of a multiple-input multiple-output (MIMO) X channel, i.e., a system with two transmitters, two receivers, each equipped with multiple antennas, where independent messages need to be conveyed over fixed channels from each transmitter to each receiver. The inner and outer bounds on the degrees of freedom region are tight whenever integer degrees of freedom are optimal for each message. With M = 1 antennas at each node, we find that the total (sum rate) degrees of freedom are bounded above and below as 1 [less than or equal to] [[eta].sup.*.sub.X] [less than or equal to] 4/3. If M > 1 and channel matrices are nondegenerate then the precise degrees of freedom [[eta].sup.*.sub.X] = 4/3 M. Thus, the MIMO X channel has noninteger degrees of freedom when M is not a multiple of 3. Simple zero forcing without dirty paper encoding or successive decoding, suffices to achieve the 4/3 M degrees of freedom. If the channels vary with time/frequency then the X channel with single antennas (M = 1) at all nodes has exactly 4/3 degrees of freedom. The key idea for the achievability of the degrees of freedom is interference alignment--i.e., signal spaces are aligned at receivers where they constitute interference while they are separable at receivers where they are desired. We also explore the increase in degrees of freedom when some of the messages are made available to a transmitter or receiver in the manner of cognitive radio. Index Terms--Capacity, cognitive radio, degrees of freedom, dirty paper coding, interference alignment, multiple-input multiple-output (MIMO), zero forcing.
- Published
- 2008
41. On the optimality of beamforming with quantized feedback
- Author
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Jafar, Syed Ali and Srinivasa, Sudhir
- Subjects
Beamforming -- Analysis ,MIMO communications -- Usage ,Antennas (Electronics) -- Usage - Abstract
The ergodic capacity of a fading vector channel with multiple transmit antennas and a single receive antenna is explored. Perfect channel information is assumed to be available at the receiver while the transmitter has only partial knowledge of the direction of the user's channel vector based on quantized feedback. We present necessary and sufficient conditions for the optimality of beamforming in such systems. The conditions are applicable to all quantized feedback scenarios regardless of the channel distribution, number of transmit antennas, number of quantization vectors or transmit power. The optimality conditions are closely related to the iteration conditions of the Lloyd algorithm, revealing an interesting link between the optimality of beamforming and the optimality of the vector quantizers. Using the conditions, we prove the capacity optimality of beamforming for several quantized feedback scenarios such as the antenna-selection scheme. We also point out examples of quantized feedback scenarios where beamforming is not optimal. We find that for the independent identically distributed Rayleigh fading channel with more than a single bit of quantized feedback, there is no capacity benefit from increasing the number of antennas beyond the number of quantization vectors. Extensions of the necessary and sufficient optimality condition to the multiple-input multiple-output case are also provided. Index Terms--Beamforming, ergodic capacity, multiple-input, multiple-output (MIMO) channels, partial/limited feedback, quantized feedback.
- Published
- 2007
42. Duality and rate optimization for multiple access and broadcast channels with amplify-and-forward relays
- Author
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Jafar, Syed Ali, Gomadam, Krishna Srikanth, and Huang, Chiachi
- Subjects
Radio relay systems -- Usage ,Radio relay systems -- Properties ,Data communications -- Research - Abstract
In this paper, we consider multihop multiple access (MAC) and broadcast channels (BC) where communication takes place with the assistance of relays that amplify and forward (AF) their received signals. For a two-hop parallel AF relay MAC, assuming a sum power constraint across all relays we characterize optimal relay amplification factors and the resulting optimal rate regions. We find the maximum sum rate and the maximum rate for each user in closed form and express the optimal rate pair ([R.sub.1], [R.sub.2]) that maximizes [[micro].sub.1] R.sub.1] + [[micro].sub.2] [R.sub.2] as the solution of a pair of simultaneous equations. We find that the parallel AF relay MAC with total transmit power of the two users [P.sub.1] + [P.sub.2] = P and total relay power [P.sub.R] is the dual of the parallel AF relay BC where the MAC source nodes become the BC destination nodes, the MAC destination node becomes the BC source node, the dual BC source transmit power is [P.sub.R] and the total transmit power of the AF relays is P. The duality means that the rate region of the AF relay MAC with a sum power constraint P on the transmitters is the same as that of the dual BC. The duality relationship is found to be useful in characterizing the rate region of the AF relay BC as the union of MAC rate regions. The duality is established for distributed multiple antenna AF relay nodes and multiple (more than 2) hops as well. Index Terms--Amplify-and-forward (AF), broadcast, capacity, duality, multiple-input multiple-output (MIMO), multiple access.
- Published
- 2007
43. Degrees of freedom for the MIMO interference channel
- Author
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Jafar, Syed Ali and Fakhereddin, Maralle Jamal
- Subjects
MIMO communications -- Analysis ,Zero balancing -- Analysis - Abstract
In this correspondence, we show that the exact number of spatial degrees of freedom (DOF) for a two user nondegenerate (full rank channel matrices) multiple-input-multiple-output (MIMO) Gaussian interference channel with [M.sub.1],[M.sub.2] antennas at transmitters 1, 2 and [N.sub.1]\[N.sub.2] antennas at the corresponding receivers, and perfect channel knowledge at all transmitters and receivers, is min{[M.sub.1] + [M.sub.2] + [N.sub.2], max([M.sub.1], [N.sub.2]). max([M.sub.2], [N.sub.1]) }. A constructive achievability proof shows that zero forcing is sufficient to achieve all the available DOF on the two user MIMO interference channel. We also show through an example of a share-and-transmit scheme how the gains of transmitter cooperation may be entirely offset by the cost of enabling that cooperation so that the available DOF are not increased. Index Terms--Broadcast, degrees of freedom (DOF), interference, multiple--input--multiple--output (MIMO), multiple access, zero forcing.
- Published
- 2007
44. The optimality of transmit beamforming: a unified view
- Author
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Srinivasa, Sudhir and Jafar, Syed Ali
- Subjects
Beamforming -- Analysis ,MIMO communications -- Analysis ,Numerical analysis - Abstract
The optimality of transmit beamforming for a multiple antenna system with partial/limited feedback is investigated and a single general necessary and sufficient condition for beamforming to achieve ergodic capacity is derived. The condition obtained is universal--applicable to all partial/limited feedback scenarios in all ergodic fading channel distributions regardless of the number of transmit/ receive antennas or transmit power, Using the universal condition we explore the optimality of beamforming for the quantized mean feedback scheme, which unifies previous results for the separate cases of mean feedback and quantized feedback. Numerical results are provided to complement the analysis. Index Terms--Beamforming, ergodic capacity, multiple-input-- multipl-eoutput (MIMO) channels, partial feedback, quantized feedback, quantized mean feedback.
- Published
- 2007
45. Modulation and detection for simple receivers in rapidly time-varying channels
- Author
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Gomadam, Krishna Srikanth and Jafar, Syed Ali
- Subjects
Frequency modulation -- Analysis - Abstract
We investigate the performance degradation of basic modulation schemes in a rapidly time-varying channel using a first-order autoregressive channel model. Various performance metrics are used to indicate the relative advantages of each modulation scheme. We find that noncoherent frequency-shift keying (FSK) is suitable for operating at very high mobility and high signal-to-noise ratio, ideal for some military applications. We then propose a partially coherent detector for FSK and differential phase-shift keying that exploits partial channel knowledge to enable the receiver to operate effectively in both fast and slow fading. The maximum-likelihood rule obtained for the partially coherent FSK turns out to be a linear combination of coherent and noncoherent detection rules. Results demonstrate that significant performance improvement can be achieved over the best of coherent and noncoherent FSK detection. The detector is robust to estimation errors present in the channel statistics. We also propose a few adaptive schemes that employ various combinations of modulation schemes to increase the robustness of the system in fast fading. Index Terms--Fast fading, interblock adaptation, intrablock adaptation, partially coherent detection, rapidly time-varying channel.
- Published
- 2007
46. Capacity with causal and noncausal side information: a unified view
- Author
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Jafar, Syed
- Subjects
Information theory -- Research - Abstract
In this correspondence, we identify the common underlying form of the capacity expression that is applicable to both cases where causal or noncausal side information is made available to the transmitter. A genie-aided outerbound is developed that states that when a genie provides n bits of side information to a receiver the resulting capacity improvement cannot be more than n bits. Using the genie-bound we are able to bound the relative capacity advantage of noncausal side information over causal side information for both the single user point-to-point channel as well as the multiple-access channel (MAC) with independent side information at the transmitters. Applications of these capacity bounds are demonstrated through examples of random access channels. Interestingly, the capacity results indicate that the excessive MAC layer overheads common in present wireless systems may be avoided through coding across multiple-access blocks. It is also shown that even one bit of side information at the transmitter can result in unbounded capacity improvement. Index Terms--Capacity, causal, feedback, multiple access, mutual information, noncausal, side information.
- Published
- 2006
47. On the capacity of the vector MAC with feedback
- Author
-
Jafar, Syed and Goldsmith, Andrea
- Subjects
Antennas (Electronics) -- Design and construction ,Gaussian processes -- Analysis - Abstract
In this correspondence, we determine the feedback capacity region of a two user Gaussian multiple-access channel (MAC) with multiple antennas at the base station and a single antenna at each user. The vector MAC with a single antenna at the base station and multiple antennas at each user is shown to be equivalent to a scalar MAC. We also determine the capacity enhancement due to feedback at high signal-to-noise ratio (SNR) for the scalar and vector MAC for any number of users. Extensions of the high SNR results to the vector broadcast channel are also provided. Index Terms--Broadcast, capacity, feedback, multiple access, multiple antennas.
- Published
- 2006
48. Too much mobility limits the capacity of wireless ad hoc networks
- Author
-
Jafar, Syed Ali
- Subjects
Wireless network ,Wireless LAN/WAN system ,Information theory -- Research ,Wireless local area networks (Computer networks) -- Research - Abstract
We show that for highly mobile ad hoc networks, the benefits of mobility are overshadowed by the cost of mobility in terms of the increased channel uncertainty and network homogeneity. We assume a block-fading channel model with jointly isotropic fading. We allow relays which can transmit and receive simultaneously. Under fairly general assumptions for the users' channel fades and additive noise distributions we show that increasing the number of transmit antennas M at any node beyond the channel coherence time [T.sub.c] (measured in units of channel uses) does not affect the capacity region of the ad hoc network. For a fast-fading (coherence time [T.sub.c] [less than or equal to] M) homogeneour network, we determine the exact capacity region of the ad hoc network for any partition of the nodes into source, destination, and relay nodes. The optimal strategy is such that only one pair of source--destination nodes is active at a time while all the other nodes are inactive. There is no benefit from relaying and at high signal-to-noise ratio (SNR) the total throughput grows at most double-logarithmically with the number of nodes. Even for the case of slow fading, where the channel variations are slow enough that the receiver can track the channel perfectly, the inability of the transmitter to track the network topology limits the total throughput growth rate to no more than logarithmic in the number of nodes. Spatial correlation is shown to enhance the capacity region of the Rayleigh-fading ad hoc network. Index Terms--Ad hoc networks, capacity, fading, mobility, relay.
- Published
- 2005
49. Sum power iterative water-filling for multi-antenna gaussian broadcast channels
- Author
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Jindal, Nihar, Rhee, Wonjong, Vishwanath, Sriram, Jafar, Syed Ali, and Goldsmith, Andrea
- Subjects
Algorithm ,Information theory -- Research ,Antennas (Electronics) -- Research ,Algorithms -- Research - Abstract
In this correspondence, we consider the problem of maximizing sum rate of a multiple-antenna Gaussian broadcast channel (BC). It was recently found that dirty-paper coding is capacity achieving for this channel. In order to achieve capacity, the optimal transmission policy (i.e., the optimal transmit covariance structure) given the channel conditions and power constraint must be found. However, obtaining the optimal transmission policy when employing dirty-paper coding is a computationally complex nonconvex problem. We use duality to transform this problem into a well-structured convex multiple-access channel (MAC) problem. We exploit the structure of this problem and derive simple and fast iterative algorithms that provide the optimum transmission policies for the MAC, which can easily be mapped to the optimal BC policies. Index Terms--Broadcast channel, dirty-paper coding, duality, multiple-access channel (MAC), multiple-input multiple-output (MIMO), systems.
- Published
- 2005
50. Isotropic fading vector broadcast channels: the scalar upper bound and loss in degrees of freedom
- Author
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Jafar, Syed Ali and Goldsmith, Andrea J.
- Subjects
Antennas (Electronics) -- Research ,Information theory -- Research - Abstract
We propose a scalar upper bound on the capacity region of the isotropic fading vector broadcast channel in terms of the capacity region of a scalar fading broadcast channel. The scalar upper bound is applicable to the broad class of isotropic fading broadcast channels regardless of the distribution of the users' channel magnitudes, the distribution of the additive noise experienced by each user, or the amount of channel knowledge available at the receiver. Using this upper bound, we prove the optimality of the Alamouti scheme in a broadcast setting, extend the recent results on the capacity of nondegraded, fading scalar broadcast channels to nondegraded fading vector broadcast channels, and determine the capacity region of a fading vector Gaussian broadcast channel with channel magnitude feedback. We also provide an example of a Rayleigh-fading broadcast channel with no channel state information available to the receiver (CSIR), where the bound on the capacity region obtained by a naive application of the scalar upper bound is provably loose, because it fails to account for the additional loss in degrees of freedom due to lack of channel knowledge at the receiver. A tighter upper bound is obtained by separately accounting for the loss in degrees of freedom due to lack of CSIR before applying the scalar upper bound. Index Terms--Broadcast channel, channel capacity, channel state information, degrees of freedom, fading channels, multiple antennas.
- Published
- 2005
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