By Topic

Information Theory Workshop, 2009. ITW 2009. IEEE

Date 11-16 Oct. 2009

Filter Results

Displaying Results 1 - 25 of 133
  • [Front cover]

    Page(s): c1
    Save to Project icon | Request Permissions | PDF file iconPDF (629 KB)  
    Freely Available from IEEE
  • [Copyright notice]

    Page(s): 1
    Save to Project icon | Request Permissions | PDF file iconPDF (36 KB)  
    Freely Available from IEEE
  • Welcome

    Page(s): 1
    Save to Project icon | Request Permissions | PDF file iconPDF (580 KB)  
    Freely Available from IEEE
  • Technical program

    Page(s): 1 - 13
    Save to Project icon | Request Permissions | PDF file iconPDF (170 KB)  
    Freely Available from IEEE
  • The broadcast approach over fading Gaussian wiretap channels

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB) |  | HTML iconHTML  

    A (layered) broadcast approach is studied for fading wiretap channels. The basic idea is to employ superposition coding to encode information into a number of layers and use stochastic encoding for each layer to keep the corresponding information secret from an eavesdropper. The legitimate receiver successively decodes information one layer after another by canceling the interference caused by the layers that the receiver has already decoded. The advantage of this approach is that the transmitter does not need to know the channel states to the legitimate receiver and the eavesdropper, but can still securely transmit certain layers of information to the legitimate receiver. The layers that can be securely transmitted are determined by the channel states to the legitimate receiver and the eavesdropper. The Gaussian wiretap channel with fixed channel gains is first studied to illustrate the idea of the broadcast approach. Three cases of block fading wiretap channels with a stringent delay constraint are then studied, in which either the legitimate receiver's channel, the eavesdropper's channel, or both channels are fading. For each case, the secrecy rate that can be achieved by using the broadcast approach is obtained, and the optimal power allocation over the layers (or the conditions on the optimal power allocation) is also derived. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • ARQ secrecy: From theory to practice

    Page(s): 6 - 10
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (311 KB) |  | HTML iconHTML  

    Inspired by our earlier work on automatic repeat request (ARQ) secrecy, we propose a simple, yet efficient, security overlay protocol to existing 802.11 networks. Our work targets networks secured by the wired equivalent privacy (WEP) protocol because of its widespread use and vulnerability to a multitude of security threats. By exploiting the existing ARQ protocol in the 802.11 standard, our proposed opportunistic secrecy scheme is shown to defend against all known passive WEP attacks. Moreover, our implementation on the madwifi-ng driver is used to establish the achievability of a vanishing secrecy outage probability in several realistic scenarios. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A multiple access approach for the compound wiretap channel

    Page(s): 11 - 15
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    The compound wiretap channel generalizes the classical problem in broadcast information-theoretic secrecy by allowing a class of potential eavesdroppers. This represents uncertainty in the eavesdropper channel and the characterization of its secrecy capacity is an open question. In this paper we present a new coding scheme that generalizes known approaches to this problem. The scheme prefixes an artificial multiple access channel to the transmission scheme in order to design a structured transmit codebook. The idea is that such a structure can potentially increase the perfect secrecy rate for the legitimate users in the presence of the class of eavesdroppers. We develop the achievable secrecy rate of this scheme and provide examples where this scheme is optimal. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Asymptotic capacity of multi-user MIMO communications

    Page(s): 16 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    This paper introduces two new formulas to derive explicit capacity expressions of a class of communication schemes, which include single-cell multi-user MIMO and single-user MIMO with multi-cell interference. The extension of a classical theorem from Silverstein allows us to assume a channel Kronecker model between the base stations and the cellular terminals, provided that they all embed a large number of antennas. As an introductory example, we study the single-user MIMO setting with multi-cell interference, in the downlink. We provide new asymptotic capacity formulas when single-user decoding of the incoming data or MMSE decoding are used. Simulations are shown to corroborate the theoretical claims, even when the number of transmit/receive antennas is not very large. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On upper bounds for the achievable rates of LDPC codes

    Page(s): 21 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    Upper bounds on the mutual entropy of syndrome components of low-density parity-check (LDPC) codes are developed. Using these bounds, an upper bound is derived on the rates of LDPC codes for which reliable communication over a memoryless binary-input symmetric-output (MBIOS) channel is achievable. This bound improves on the earlier known bounds due to Gallager, Burshtein et al., and Weichmann-Sason. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • RQ precoding for the cooperative broadcast channel

    Page(s): 26 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB) |  | HTML iconHTML  

    We consider a broadcast channel with multiple transmit antennas, where receiving terminals (users), with single antenna, can cooperate by exchanging information through a secondary local channel. Similar to zero-forcing dirty paper coding (ZF-DPC) in, we consider a RQ precoding, which is based on the RQ decomposition of the channel matrix and transforms the channel matrix into an upper triangular matrix. Without DPC, the RQ precoding is used in conjunction with successive interference cancellation by the users, which send to each other their respectively detected information symbols. We conduct error probability performance analysis for the RQ precoded cooperative broadcast channel and show how errors on the local link degrade the overall performance. Finally we compare the RQ precoding to standard beamforming precoding where the users do not cooperate and observe: (i) improvements in the overall error rates and throughput, (ii) different diversity gains for the different users, (iii) performance degradation resulting in an error floor due to errors on the local channels. This last feature enables either the application of RQ precoding to a system with different quality of service users or the possibility of scheduling the users in order to improve the overall error rates and throughput. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ascending-bid auction for unequal-erasure-protected network coding

    Page(s): 31 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    According to our previous paper, global encoding kernels (GEKs) describing linear network codes have different levels of built-in unequal-erasure-protecting (UEP) capability. This creates conflicts among sink nodes in a multicast session since a particular assignment of GEKs favors one sink node over another. This paper proposes a resolution to the conflict by means of a simple ascending-bid auction scheme which has three obvious benefits. First, it frees all the nodes from the complicated optimization algorithms that might otherwise be used. Second, it provides the source node with some revenue. Lastly, it allows the richer sink nodes to receive the data with better quality. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A static protocol to achieve optimal Diversity-Multiplexing Tradeoff for high diversity gains in half-duplex relay channels

    Page(s): 36 - 40
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB) |  | HTML iconHTML  

    In this paper, we study the diversity-multiplexing tradeoff (DMT) of a novel decode or quantize and forward (DoQF) protocol for the half duplex single relay channel. It is well-known that the so-called dynamic decode and forward (DDF) achieves the multiple-input-single-output (MISO) bound in the range of multiplexing gains r < 0.5. But to the best of our knowledge, no practical coding scheme allows the implementation of the DDF, so that it essentially remains a theoretical protocol. On the opposite, the proposed DoQF protocol is based on a practical static coding-decoding strategy. Our results show that the DoQF achieves the MISO bound in the range of multiplexing gains r < 0.25 (and still has an attractive performance for r < 0.37). To the best of our knowledge, this makes the DoQF the only static protocol that achieves the MISO upperbound without any feedback link between nodes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Randomly select and forward: Erasure probability analysis of a probabilistic relay channel model

    Page(s): 41 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (194 KB) |  | HTML iconHTML  

    This paper proposes a semi-analytical framework for estimating the erasure probability in single-hop multi-relay networks. Specifically, we consider a system, in which relays do not decode the information but simply forward coded packets that have been previously received from the source. This allows for uncoordinated, low-complexity processing at the relays. We present a detailed analysis of the proposed network model, which represents an instance of a new coding scheme that we refer to as distributed fountain coding. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bounding the minimal Euclidean distance for any PSK block codes of alphabet size 8

    Page(s): 46 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (255 KB) |  | HTML iconHTML  

    We consider a bound for the minimal Euclidean distance of any PSK block code with eight symbols. The main result was established in [6] - here we prove that the bound is in fact stronger than was proven there. The bound is deduced by generalizing Elias' method of a critical sphere. It is not asympthotic, as previous Elias' sphere bounds, but valid for any specific word length and code size. Many known codes fulfil the bound with equality, proving the sharpness of the bound for these parameter values as well as the optimality of these codes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Outage behavior of bidirectional half-duplex relaying schemes

    Page(s): 50 - 54
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (261 KB) |  | HTML iconHTML  

    Two-phase and three-phase decode-and-forward schemes with network coding for the two-way (bidirectional) relay channel with Rayleigh-fading are considered. All nodes are half-duplex constrained. Closed form expressions of the outage probability for the two-phase scheme and the three-phase scheme with symmetric rate and time-allocation with Gaussian distributed channel inputs are derived, necessary conditions on achieving diversity for discrete channel inputs are given and practical coding schemes based on turbo codes are considered. It is shown analytically as well as by simulating the practical coding schemes that a diversity gain is achievable for the three-phase scheme as opposed to the two-phase scheme. Moreover, it is shown that for discrete channel inputs the three-phase scheme allows a diversity gain for higher rates compared to a conventional relaying scheme without network coding. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Linear analog coding of general multivariate Gaussian sources

    Page(s): 55 - 59
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (650 KB) |  | HTML iconHTML  

    In this paper we study the performance of linear analog coding of multivariate Gaussian sources and compare it to the theoretical limits. A general performance analysis is presented for both random and optimal linear encoders. Simulation results show the agreement between the theoretical analysis and the practical implementation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Exposing pseudoweight layers in regular LDPC code ensembles

    Page(s): 60 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (213 KB) |  | HTML iconHTML  

    A solution is presented for the asymptotic growth rate of the AWGN-pseudoweight distribution of regular low-density parity-check (LDPC) code ensembles for a selected graph cover degree M ¿1. The evaluation of the growth rate requires solution of a system of 2M +1 nonlinear equations in 2M +1 unknowns. Simulation results for the pseudoweight distribution of two regular LDPC code ensembles are presented for graph covers of low degree. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On random construction of a bipolar sensing matrix with compact representation

    Page(s): 65 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (123 KB) |  | HTML iconHTML  

    A random construction of bipolar sensing matrices based on binary linear codes is introduced and its RIP (restricted isometry property) is analyzed based on an argument on the ensemble average of the weight distribution of binary linear codes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An application of the relative network Generalized Hamming weight to erroneous wiretap networks

    Page(s): 70 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (298 KB) |  | HTML iconHTML  

    This paper demonstrates that the relative network generalized Hamming weight (RNGHW) of a nested code fully characterizes the security performance of the corresponding nested coset coding scheme for erroneous wiretap networks with a given linear network code. Specifically, when the nested coset coding specified by a nested code (C1, C2) is applied at the source node, the RNGHW of the nested code (C2 ¿, C1 ¿) characterizes the equivocation of the wiretapper about the secure message, where C2 is a subcode of linear code C1, and C1 ¿ (C2 ¿) is the dual code of C1 (C2). View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Reconstruction of punctured convolutional codes

    Page(s): 75 - 79
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (217 KB) |  | HTML iconHTML  

    We present here a new technique to reconstruct punctured convolutional codes from a noisy intercepted bit-stream. Compared to existing techniques our algorithm has two major advantages: it can tolerate much higher noise levels in the bitstream and it is able to recover the best possible decoder (in terms of decoding complexity). This is achieved by identifying the exact puncturing pattern that was used and recovering the parent convolutional code. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • MIMO downlink scheduling with non-perfect channel state knowledge

    Page(s): 80 - 84
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB) |  | HTML iconHTML  

    Downlink scheduling schemes are well-known and widely investigated. In the multiuser MIMO (broadcast) case, downlink scheduling in the presence of non-perfect CSI is only scantly treated. In this paper we provide a general framework within which the problem can be addressed systematically. Then, we focus on the special case of proportional fairness and ¿hard fairness¿, with Gaussian coding and linear beamforming. We find that the naive scheduler that ignores the quality of the channel state information may be very suboptimal. We propose novel simple schemes that perform very well in practice. Also, we illuminate the key role played by the channel state prediction error: our schemes treat in a fundamentally different way users with ¿predictable¿ or ¿non-predictable¿ channels, and allocate these classes of users over time in a near-optimal fashion. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiple description coding based on LDGM codes

    Page(s): 85 - 89
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (381 KB) |  | HTML iconHTML  

    This work addresses practical multiple description coding for uniform binary sources in the no excess sum-rate case. For this case Zhang and Berger have shown that the EGC* region defined by El Gamal and Cover coincides with a portion of the boundary of the MD rate-distortion region, and proposed a construction of the auxiliary variables U and V to achieve this bound. We introduce a sequential coding technique for the corner points of this EGC* region and implement it using low-density generator matrix based codes. Furthermore we use timesharing to approach any point on the dominant face of the EGC* region. Our experimental results show very good practical performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the channel statistics in Hybrid ARQ systems for correlated channels

    Page(s): 90 - 94
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB) |  | HTML iconHTML  

    This paper discusses a result for error control techniques based on retransmissions, most notably hybrid automatic repeat request schemes. We assume that the underlying coding technique is described by the so-called reliable region. Under this assumption, we derive the channel distribution after a frame is either acknowledged or discarded. This is derived within an entirely analytical framework, where we show that such a distribution can be found as the result of an iterative process. Remarkably, this distribution is not the same as the steady-state channel distribution, and can be significantly different from it. Thus, using one instead of the other can lead to evaluation errors, which instead are avoided by our model. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • LDPC codes for the Gaussian wiretap channel

    Page(s): 95 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (469 KB) |  | HTML iconHTML  

    A coding scheme for the Gaussian wiretap channel based on low-density parity-check (LDPC) codes is presented. The messages are transmitted over punctured bits to hide data from eavesdroppers. It is shown by means of density evolution that the BER of an eavesdropper, who operates below the code's SNR threshold and has the ability to use a bitwise MAP decoder, increases to 0.5 within a few dB. It is shown how asymptotically optimized LDPC codes can be designed with differential evolution where the goal is to achieve high reliability between friendly parties and security against a passive eavesdropper while keeping the security gap as small as possible. The proposed coding scheme is also efficiently encodable in almost linear time. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A unified framework for key agreement over wireless fading channels

    Page(s): 100 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (183 KB) |  | HTML iconHTML  

    A framework that unifies existing source and channel models for key agreement over wireless fading channels is developed in this paper. It is shown that, in general, to fully exploit the resources provided by time-varying channel gains, one needs to combine both the channel model and the source model. Asymptotic analyses suggest that in the long coherence time regime, the channel model is asymptotically optimal. On the other hand, in the high SNR regime, the source model is asymptotically optimal. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.