| 1. |
- Angelakis, Vangelis, et al.
(författare)
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Minimum-Time Link Scheduling for Emptying Wireless Systems: Solution Characterization and Algorithmic Framework
- 2014
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 60:2, s. 1083-1100
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Tidskriftsartikel (refereegranskat)abstract
- We consider a set of transmitter-receiver pairs, or links, that share a wireless medium and address the problem of emptying backlogged queues with given initial size at the transmitters in minimum time. The problem amounts to determining activation subsets of links, and their time durations, to form a minimum-time schedule. Scheduling in wireless networks has been studied under various formulations before. In this paper, we present fundamental insights and solution characterizations that include: 1) showing that the complexity of the problem remains high for any continuous and increasing rate function; 2) formulating and proving sufficient and necessary optimality conditions of two baseline scheduling strategies that correspond to emptying the queues using one-at-a-time or all-at-once strategies; and 3) presenting and proving the tractability of the special case in which the transmission rates are functions only of the cardinality of the link activation sets. These results are independent of physical-layer system specifications and are valid for any form of rate function. We then develop an algorithmic framework for the solution to this problem. The framework encompasses exact as well as sub-optimal, but fast, scheduling algorithms, all under a unified principle design. Through computational experiments, we finally investigate the performance of several specific algorithms from this framework.
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| 2. |
- Björnson, Emil, et al.
(författare)
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Massive MIMO Systems With Non-Ideal Hardware : Energy Efficiency, Estimation, and Capacity Limits
- 2014
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Ingår i: IEEE Transactions on Information Theory. - : IEEE Press. - 0018-9448 .- 1557-9654. ; 60:11, s. 7112-7139
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Tidskriftsartikel (refereegranskat)abstract
- The use of large-scale antenna arrays can bring substantial improvements in energy and/or spectral efficiency to wireless systems due to the greatly improved spatial resolution and array gain. Recent works in the field of massive multiple-input multiple-output (MIMO) show that the user channels decorrelate when the number of antennas at the base stations (BSs) increases, thus strong signal gains are achievable with little interuser interference. Since these results rely on asymptotics, it is important to investigate whether the conventional system models are reasonable in this asymptotic regime. This paper considers a new system model that incorporates general transceiver hardware impairments at both the BSs (equipped with large antenna arrays) and the single-antenna user equipments (UEs). As opposed to the conventional case of ideal hardware, we show that hardware impairments create finite ceilings on the channel estimation accuracy and on the downlink/uplink capacity of each UE. Surprisingly, the capacity is mainly limited by the hardware at the UE, while the impact of impairments in the large-scale arrays vanishes asymptotically and interuser interference (in particular, pilot contamination) becomes negligible. Furthermore, we prove that the huge degrees of freedom offered by massive MIMO can be used to reduce the transmit power and/or to tolerate larger hardware impairments, which allows for the use of inexpensive and energy-efficient antenna elements.
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| 3. |
- Blom, Rolf
(författare)
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Bounds on key equivocation for simple substitution ciphers
- 1979
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Ingår i: IEEE Transactions on Information Theory. - : IEEE. - 0018-9448 .- 1557-9654. ; 25:1, s. 8-18
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Tidskriftsartikel (refereegranskat)abstract
- The equivocation of the key for a simple substitution cipher is upper and lower hounded, when the message source is memoryless. The hounds are shown to be exponentially tight. The results are compared with random ciphering. It is observed that the exponential behavior of the equivocation of the key is not determined by the redundancy in the message source, but by the symbol probabilities which are closest in a certain sense.
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| 4. |
- Cederlöf, Jörgen, et al.
(författare)
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Security aspects of the Authentication used in Quantum Cryptography
- 2008
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 54:4, s. 1735-1741
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Tidskriftsartikel (refereegranskat)abstract
- Unconditionally secure message authentication is an important part of Quantum Cryptography (QC). We analyze security effects of using a key obtained from QC for authentication purposes in later rounds of QC. In particular, the eavesdropper gains partial knowledge on the key in QC that may have an effect on the security of the authentication in the later round. Our initial analysis indicates that this partial knowledge has little effect on the authentication part of the system, in agreement with previous results on the issue. However, when taking the full QC protocol into account, the picture is different. By accessing the quantum channel used in QC, the attacker can change the message to be authenticated. This together with partial knowledge of the key does incur a security weakness of the authentication. The underlying reason for this is that the authentication used, which is insensitive to such message changes when the key is unknown, becomes sensitive when used with a partially known key. We suggest a simple solution to this problem, and stress usage of this or an equivalent extra security measure in QC.
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| 5. |
- Danev, Danyo, et al.
(författare)
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On a sequence of cyclic codes with minimum distance six
- 2000
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 46:2, s. 673-674
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Tidskriftsartikel (refereegranskat)abstract
- A sequence of q-ary cyclic codes is analyzed. For each finite field GF (q), q=4, there is a code with parameters [n, k, d, q] = [q(q-1)+1, q(q-1)-6, 6,q]. All these codes are n-, k-, and d-optimal, with only one exception. The dual codes are considered. Their true minimum distances are calculated in the range 4=q=32.
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| 6. |
- He, Qing, 1979-, et al.
(författare)
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Optimal Link Scheduling for Age Minimization in Wireless Systems
- 2018
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Ingår i: IEEE Transactions on Information Theory. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9448 .- 1557-9654. ; 64:7, s. 5381-5394
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Tidskriftsartikel (refereegranskat)abstract
- Information age is a recently introduced metric to represent the freshness of information in communication systems. We investigate age minimization in a wireless network and propose a novel approach of optimizing the scheduling strategy to deliver all messages as fresh as possible. Specifically, we consider a set of links that share a common channel. The transmitter at each link contains a given number of packets with time stamps from an information source that generated them. We address the link transmission scheduling problem with the objective of minimizing the overall age. This minimum age scheduling problem (MASP) is different from minimizing the time or the delay for delivering the packets in question. We model the MASP mathematically and prove it is NP-hard in general. We also identify tractable cases as well as optimality conditions. An integer linear programming formulation is provided for performance benchmarking. Moreover, a steepest age descent algorithm with better scalability is developed. Numerical study shows that, by employing the optimal schedule, the overall age is significantly reduced in comparison to other scheduling strategies.
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| 7. |
- He, Qing, 1979-, et al.
(författare)
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Optimal Scheduling for Emptying a Wireless Network : Solution Characterization, Applications, Including Deadline Constraints
- 2020
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Ingår i: IEEE Transactions on Information Theory. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9448 .- 1557-9654. ; 66:3, s. 1882-1892
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Tidskriftsartikel (refereegranskat)abstract
- Link scheduling, i.e., which links should transmit together and for how long, has been and remains a cornerstone optimization problem in wireless networking. In minimum-time scheduling, the task is to minimize the amount of time before emptying the data demand residing at the source nodes. We derive a complete structural characterization of the solution that unifies and significantly extends the known results. First, we approach link scheduling with a general system model without restrictions on the shape of the achievable rate region. Then, we give and prove a solution characterization of optimality that is conceptually simple yet powerful. We demonstrate several applications of this characterization for analysis of optimality and problem tractability. Next, we consider a significant extension by including deadline constraints, under which optimal scheduling becomes much more complex. Yet, we show how our formulation yields a solution description for that problem as well.
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| 8. |
- Kailath, Thomas, et al.
(författare)
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Fast Time-Invariant Implementations of Gaussian Signal Detectors
- 1978
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Ingår i: IEEE Transactions on Information Theory. - : IEEE Information Theory Society. - 0018-9448 .- 1557-9654. ; 24:4, s. 469-477
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Tidskriftsartikel (refereegranskat)abstract
- A new implementation is presented for the optimum likelihood ratio detector for stationary Gaussian signals in white Gaussian noise that uses only two causal time-invariant filters. This solution also has the advantage that fast algorithms based on the Levinson and Chandrasekhar equations can he used for the determination of these time-invariant filters. By using a notion of "closeness to stationarity,' there is a natural extension of the above results for nonstationary signal processes.
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| 9. |
- Kapetanovic, Dzevdan, et al.
(författare)
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Lattice Structures of Precoders Maximizing the Minimum Distance in Linear Channels
- 2015
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 61:2, s. 908-916
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates linear precoding over nonsingular linear channels with additive white Gaussian noise, with lattice-type inputs. The aim is to maximize the minimum distance of the received lattice points, where the precoder is subject to an energy constraint. It is shown that the optimal precoder only produces a finite number of different lattices, namely perfect lattices, at the receiver. The well-known densest lattice packings are instances of perfect lattices, but are not always the solution. This is a counter-intuitive result as previous work in the area showed a tight connection between densest lattices and minimum distance. Since there are only finite many different perfect lattices, they can theoretically be enumerated offline. A new upper bound on the optimal minimum distance is derived, which significantly improves upon a previously reported bound, and is useful when actually constructing the precoders.
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| 10. |
- Lindkvist, Tina, et al.
(författare)
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A class of traceability codes
- 2002
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 48:7, s. 2094-2096
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Tidskriftsartikel (refereegranskat)abstract
- Traceability codes are identifiable parent property (IPP) codes with the additional requirement that Hamming distance can be used to trace a parent of a word. Traceability codes can be used for constructing digital fingerprints in order to deter users from illegally copying digital data. We construct a class of traceability codes and determine the exact parameters of some of the codes in this class.
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