| 21. |
- 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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| 22. |
- Asraf, Daniel, et al.
(författare)
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An analytical series expansion solution to the problem of noncoherent detection
- 2004
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 50:12, s. 3369-3375
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Tidskriftsartikel (refereegranskat)abstract
- The well-known noncoherent detection problem concerns optimal detection of an amplitude-modulated sinusoid, with an unknown phase angle, corrupted by additive Gaussian noise. The classical solution to this problem is the noncoherent detector which is known to be optimal if the envelope belongs to a specific set of functions or satisfies the narrow-band approximation i.e., that the bandwidth of the envelope is narrow in comparison with the (carrier) frequency of the sinusoid. In this work, an analytical series expansion solution to the likelihood ratio for the noncoherent detection problem is derived. This solution offers a generalization of the noncoherent detector in which the conditions imposed on the envelope stated above have been relaxed. Analytical expressions for the joint probability density functions (pdfs) of the in-phase and quadrature components, jointly expressed in polar coordinates, are also derived under the signal-plus-noise and the noise-only hypotheses, respectively. Numerical simulations of the detector performance are presented in the form of receiver operating characteristics (ROC) and minimum probability of error curves. The results from a comparison of the general analytical solution with the classical noncoherent detector show significant differences between the two detectors when the narrow-band approximation does not hold.
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| 23. |
- Asraf, Daniel, et al.
(författare)
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Detection of Multiple Transient Signals with Unknown Arrival Times
- 2005
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 51:5, s. 1856-1860
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Tidskriftsartikel (refereegranskat)abstract
- The problem of optimal detection of signal transients with unknown arrival times contaminated by additive Gaussian noise is considered. The transients are assumed to be time continuous and belong to a parameterized family with the uncertainty about the parameters described by means of an a priori distribution. Under the assumption of a negligible probability that the independent transient observations overlap in time, a likelihood ratio is derived for the problem of detecting an unknown number of transients from the family, each transient with unknown arrival time. The uncertainty about the arrival times is assumed to be equal for all transients and is also described by means of a distribution. Numerical simulations of the performance of detecting a particular transient signal family are presented in the form of receiver operating characteristics (ROCs) for both the optimal detector and the classical generalized likelihood ratio test (GLRT). The results show that the optimal detector yields noticeable performance improvements over the GLRT. Moreover, the results show that the optimal detector may still outperform the GLRT when the true and modeled uncertainties about arrival times no longer agree.
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| 24. |
- Aulin, Tor, 1948
(författare)
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Comment on “Improved Analysis of List Decoding and Its Application to Convolutional Codes and Turbo Codes”
- 2009
-
Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 55:8, s. 3892-
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper (Bai et al, IEEE Trans. Inf. Theory, 2007) an improved analysis concerning the analysis of List Decoding was presented. The event that the correct codeword is excluded from the list is central. For the additive white Gaussian noise (AWGN) channel an important quantity is the in (Bai et al, IEEE Trans. Inf. Theory, 2007) called effective Euclidean distance. This was earlier considered in (Aulin, IEEE Trans. Commun., 1999) under the name Vector Euclidean Distance, where also a simple mathematical expression for this quantity was easily derived for any list size. In (Bai et al, IEEE Trans. Inf. Theory, 2007), a geometrical analysis gives this when the list size is 1, 2 or 3.
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| 25. |
- Austrin, Per, et al.
(författare)
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A Simple Deterministic Reduction for the Gap Minimum Distance of Code Problem
- 2014
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 60:10, s. 6636-6645
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Tidskriftsartikel (refereegranskat)abstract
- We present a simple deterministic gap-preserving reduction from SAT to the minimum distance of code problem over F-2. We also show how to extend the reduction to work over any fixed finite field. Previously, a randomized reduction was known due to Dumer, Micciancio, and Sudan, which was recently derandomized by Cheng and Wan. These reductions rely on highly nontrivial coding theoretic constructions, whereas our reduction is elementary. As an additional feature, our reduction gives hardness within a constant factor even for asymptotically good codes, i.e., having constant positive rate and relative distance. Previously, it was not known how to achieve a deterministic reduction for such codes.
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| 26. |
- Austrin, Per, 1981-, et al.
(författare)
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Sharper Upper Bounds for Unbalanced Uniquely Decodable Code Pairs
- 2018
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Ingår i: IEEE Transactions on Information Theory. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9448 .- 1557-9654. ; 64:2, s. 1368-1373
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Tidskriftsartikel (refereegranskat)abstract
- Two sets of 0-1 vectors of fixed length form a uniquely decodeable code pair if their Cartesian product is of the same size as their sumset, where the addition is pointwise over integers. For the size of the sumset of such a pair, van Tilborg has given an upper bound in the general case. Urbanke and Li, and later Ordentlich and Shayevitz, have given better bounds in the unbalanced case, that is, when either of the two sets is sufficiently large. Improvements to the latter bounds are presented.
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| 27. |
- Bassi, German, et al.
(författare)
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The Wiretap Channel With Generalized Feedback : Secure Communication and Key Generation
- 2019
-
Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 65:4, s. 2213-2233
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Tidskriftsartikel (refereegranskat)abstract
- It is a well-known fact that feedback does not increase the capacity of point-to-point memoryless channels, however, its effect in secure communications is not fully understood yet. In this paper, an achievable scheme for the wiretap channel with generalized feedback is presented. This scheme, which uses the feedback signal to generate a shared secret key between the legitimate users, encrypts the message to be sent at the bit level. New capacity results for a class of channels are provided, as well as some new insights into the secret key agreement problem. Moreover, this scheme recovers previously reported rate regions from the literature, and thus it can be seen as a generalization that unifies several results in the field.
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| 28. |
- Battaglioni, Massimo, et al.
(författare)
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Girth Analysis and Design of Periodically Time-Varying SC-LDPC Codes
- 2021
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448. ; 67:4, s. 2217-2235
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Tidskriftsartikel (refereegranskat)abstract
- Time-varying spatially coupled low-density parity-check (SC-LDPC) codes with very large period are characterized by significantly better error rate performance and girth properties than their time-invariant counterparts, but the number of parameters they require to be described is usually very large and unpractical. Time-invariant SC-LDPC codes, which can be seen as periodically time-varying codes with unitary period, are represented through a small number of parameters and designed exploiting few degrees of freedom, but their error rate performance and girth properties are sub-optimal. In this paper, we show that the limits of time-invariant SC-LDPC codes can be overcome by transforming them into time-varying SC-LDPC codes with very small period. In particular, we show that periodically time-varying SC-LDPC codes with small period may exhibit significantly better girth properties than the corresponding time-invariant codes by exploiting a larger number of degrees of freedom in the code design, which however scale at most linearly with the product of the code period and the size of the considered base matrix.
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| 29. |
- Björnson, Emil, et al.
(författare)
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Massive MIMO Systems With Non-Ideal Hardware : Energy Efficiency, Estimation, and Capacity Limits
- 2014
-
Ingår i: IEEE Transactions on Information Theory. - : IEEE Press. - 0018-9448 .- 1557-9654. ; 60:11, s. 7112-7139
-
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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| 30. |
- 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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