| 51. |
- Cervia, Giulia, et al.
(författare)
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Strong Coordination of Signals and Actions Over Noisy Channels With Two-Sided State Information
- 2020
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 66:8, s. 4681-4708
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Tidskriftsartikel (refereegranskat)abstract
- We consider a network of two nodes separated by a noisy channel with two-sided state information, in which the input and output signals have to be coordinated with the source and its reconstruction. In the case of non-causal encoding and decoding, we propose a joint source-channel coding scheme and we develop inner and outer bounds for the strong coordination region. While the inner and outer bounds do not match in general, we provide a complete characterization of the strong coordination region in three particular cases: i) when the channel is perfect; ii) when the decoder is lossless; and iii) when the random variables of the channel are independent from the random variables of the source. Through the study of these special cases, we prove that the separation principle does not hold for the joint source-channel strong coordination. Finally, in the absence of state information, we show that polar codes achieve a subset of the best known inner bound for the strong coordination region, therefore offering a constructive alternative to random binning and coding proofs.
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| 52. |
- Charalambous, Themistoklis, et al.
(författare)
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Optimal Merging Algorithms for Lossless Codes With Generalized Criteria
- 2014
-
Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 60:9, s. 5486-5499
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents lossless prefix codes optimized with respect to a payoff criterion consisting of a convex combination of maximum codeword length and average codeword length. The optimal codeword lengths obtained are based on a new coding algorithm, which transforms the initial source probability vector into a new probability vector according to a merging rule. The coding algorithm is equivalent to a partition of the source alphabet into disjoint sets on which a new transformed probability vector is defined as a function of the initial source probability vector and scalar parameter. The payoff criterion considered encompasses a tradeoff between maximum and average codeword length; it is related to a payoff criterion consisting of a convex combination of average codeword length and average of an exponential function of the codeword length, and to an average codeword length payoff criterion subject to a limited length constraint. A special case of the first related payoff is connected to coding problems involving source probability uncertainty and codeword overflow probability, whereas the second related payoff compliments limited length Huffman coding algorithms.
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| 53. |
- Chen, Eric Zhi
(författare)
-
An explicit construction of 2-generator quasi-twisted codes
- 2008
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers Inc.. - 0018-9448 .- 1557-9654. ; 54:12, s. 5770-5773
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Tidskriftsartikel (refereegranskat)abstract
- Quasi-twisted (QT) codes are a generalization of quasi-cyclic (QC) codes. Based on consta-cyclic simplex codes, a new explicit construction of a family of 2-generator quasi-twisted (QT) two-weight codes is presented. It is also shown that many codes in the family meet the Griesmer bound and therefore are length-optimal. New distance-optimal binary QC [195, 8, 96], [210, 8, 104] and [240, 8, 120] codes, and good ternary QC [208, 6, 135] and [221, 6, 144] codes are also obtained by the construction.
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| 54. |
- Chen, Eric Zhi
(författare)
-
New quasi-cyclic codes from simplex codes
- 2007
-
Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers Inc.. - 0018-9448 .- 1557-9654. ; 53:3, s. 1193-1196
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Tidskriftsartikel (refereegranskat)abstract
- As a generalization of cyclic codes, quasi-cyclic (QC) codes contain many good linear codes. But quasi-cyclic codes studied so far are mainly limited to one generator (1-generator) QC codes. In this correspondence, 2-generator and 3-generator QC codes are studied, and many good, new QC codes are constructed from simplex codes. Some new binary QC codes or related codes, that improve the bounds on maximum minimum distance for binary linear codes are constructed. They are 5-generator QC [93 17 34] and [254,23, 102] codes, and related [96, 17, 361, [256, 23,104] codes.
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| 55. |
- Chepyshov, V.V, et al.
(författare)
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The free distance of fixed convolutional rate 2/4 codes meets the Costello bound
- 1992
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448. ; 38:4, s. 1360-1366
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Tidskriftsartikel (refereegranskat)abstract
- The long standing question whether the free distance of fixed rate convolutional codes is as good as the Costello bound was almost solved by K.S. Zigangirov and J.L. Massey (1987). They proved that this is indeed the case for codes with long branch length and rates 2/c, c>or=5. It is shown that there exist fixed convolutional codes of rate 2/4 whose free distance d/sub free/ meets the Costello bound originally derived for time varying convolutional codes
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| 56. |
- Cho, Jeong-woo, 1978-, et al.
(författare)
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Fundamentals of the Backoff Process in 802.11 : Dichotomy of the Aggregation
- 2015
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Ingår i: IEEE Transactions on Information Theory. - : IEEE Press. - 0018-9448 .- 1557-9654. ; 61:4, s. 1687-1701
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Tidskriftsartikel (refereegranskat)abstract
- This paper discovers fundamental principles of the backoff process that governs the performance of IEEE 802.11. A simplistic principle founded upon regular variation theory is that the backoff time has a truncated Pareto-type tail distribution with an exponent of $ { (log gamma !)/log m}$ ( $boldsymbol {m}$ is the multiplicative factor and $ {gamma }$ is the collision probability). This reveals that the per-node backoff process is heavy-tailed in the strict sense for $ { gamma > 1/m^{2}}$ , and paves the way for the following unifying result. The state-of-the-art theory on the superposition of the heavy-tailed processes is applied to establish a dichotomy exhibited by the aggregate backoff process, putting emphasis on the importance of time-scales on which we view the backoff processes. While the aggregation on normal time-scales leads to a Poisson process, it is approximated by a new limiting process possessing long-range dependence (LRD) on coarse time-scales. This dichotomy turns out to be instrumental in formulating short-term fairness, extending existing formulas to arbitrary population, and to elucidate the absence of LRD in practical situations. A refined wavelet analysis is conducted to strengthen this argument.
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| 57. |
- Cho, Jeong-woo, 1978-, et al.
(författare)
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On the Asymptotic Validity of the Decoupling Assumption for Analyzing 802.11 MAC Protocol
- 2012
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Ingår i: IEEE Transactions on Information Theory. - : IEEE Press. - 0018-9448 .- 1557-9654. ; 58:11, s. 6879-6893
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Tidskriftsartikel (refereegranskat)abstract
- Performance evaluation of the 802.11 MAC protocol is classically based on the decoupling assumption, which hypothesizes that the backoff processes at different nodes are independent. This decoupling assumption results from mean field convergence and is generally true in transient regime in the asymptotic sense (when the number of wireless nodes tends to infinity), but, contrary to widespread belief, may not necessarily hold in stationary regime. The issue is often related with the existence and uniqueness of a solution to a fixed point equation; however, it was also recently shown that this condition is not sufficient; in contrast, a sufficient condition is a global stability property of the associated ordinary differential equation. In this paper, we give a simple condition that establishes the asymptotic validity of the decoupling assumption for the homogeneous case (all nodes have the same parameters). We also discuss the heterogeneous and the differentiated service cases and formulate a new ordinary differential equation. We show that the uniqueness of a solution to the associated fixed point equation is not sufficient; we exhibit one case where the fixed point equation has a unique solution but the decoupling assumption is not valid in the asymptotic sense in stationary regime.
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| 58. |
- Chuang, Allen, et al.
(författare)
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Optimal throughput-diversity-delay tradeoff in MIMO ARQ block-fading channels
- 2008
-
Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 54:9, s. 3968-3986
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider an automatic-repeat-request (ARQ) retransmission protocol signaling over a block-fading multiple-input-multiple-output (MIMO) channel. Unlike previous work, we allow for multiple fading blocks within each transmission (ARQ round), and we constrain the transmitter to fixed rate codes constructed over complex signal constellations. In particular, we examine the general case of average input-power-constrained constellations with a fixed signaling alphabet of finite cardinality. This scenario is a suitable model for practical wireless communications systems employing orthogonal frequency division multiplexing (OFDM) techniques over a MIMO ARQ channel. Two cases of fading dynamics are considered, namely, short-term static fading wherechannel fading gains change randomly for each ARQ round, and long-term static fadingwhere channel fading gains remain constant over all ARQ rounds pertaining to a given message. As our main result, we prove that for the block-fading MIMO ARQ channel with a fixed signaling alphabet satisfying a short-term power constraint, the optimal signal-to-noise ratio (SNR) exponent is given by a modified Singleton bound, relating all the system parameters. To demonstrate the practical significance of the theoretical analysis, we present numerical results showing that practical Singleton-bound-achieving maximum distance separable codes achieve the optimal SNR exponent.
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| 59. |
- Como, Giacomo
(författare)
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Group codes outperform binary-coset codes on nonbinary symmetric memoryless channels
- 2010
-
Ingår i: IEEE Transactions on Information Theory. - 0018-9448. ; 56:9, s. 4321-4334
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Tidskriftsartikel (refereegranskat)abstract
- Typical minimum distances and error exponents are analyzed on the 8-PSK Gaussian channel for two capacity- achieving code ensembles with different algebraic structure. It is proved that the typical group code over the cyclic group of order eight achieves both the Gilbert-Varshamov bound and the expurgated error exponent. On the other hand, the typical binary-coset codes (under any labeling) is shown to be bounded away both from the Gilbert-Varshamov bound (at any rate) and the expurgated exponent (at low rates). The reason for this phenomenon is shown to rely on the symmetry structure of the 8-PSK constellation, which is known to match the cyclic group of order eight, but not the direct product of three copies of the binary group. The presented results indicate that designing group codes matching the symmetry of the channel guarantees better typical-code performance than designing codes whose algebraic structure does not match the channel. This contrasts the well-known fact that the average binary-coset code achieves both the capacity and the random-coding error exponent of any discrete memoryless channel.
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| 60. |
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