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ABSTRACT: It is known that the worst case near-far resistance of optimum multiuser detectors for asynchronous Gaussian multiple-access channels can be expressed in terms of a class of block-tridiagonal matrices, and the minimal eigenvalues of such a class of block-tridiagonal matrices serve as a good measure of the worst case near-far resistance. In this paper, we focus on the two-user scenario where each block-tridiagonal matrix under consideration is a tridiagonal matrix. We derive closed-form expressions for the minimal eigenvalues of such a class of tridiagonal matrices in terms of the largest real solution of a trigonometric equation in [0,pi] . We also obtain lower bounds and upper bounds on the minimal eigenvalues which improve on previously known results in the literature.
IEEE Transactions on Information Theory 12/2009; · 3.01 Impact Factor
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ABSTRACT: In this correspondence, we show that solutions to the multiple description coding problem and the broadcast channel coding problem share a common encoding procedure: successive source encoding. We use this connection as the basis for establishing connections between the achievable multiple description rate region and Marton's region for broadcast channels. Specifically, we show that Marton's encoding scheme can be viewed as a multiple description coding procedure. We also explore the dual problem, namely, the relationship between successive channel decoding in multiple access communication and distributed source coding. By illuminating these connections to multiple description, we hope to motivate a solution to what remains a mostly unsolved problem
IEEE Transactions on Information Theory 07/2007; · 3.01 Impact Factor
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ABSTRACT: The multiple description (MD) problem has received considerable attention as a model of information transmission over unreliable channels. A general framework for designing efficient MD quantization schemes is proposed in this paper. We provide a systematic treatment of the El Gamal-Cover (EGC) achievable MD rate-distortion region, and show it can be decomposed into a simplified-EGC (SEGC) region and a superimposed refinement operation. Furthermore, any point in the SEGC region can be achieved via a successive quantization scheme along with quantization splitting. For the quadratic Gaussian case, the proposed scheme has an intrinsic connection with the Gram-Schmidt orthogonalization, which implies that the whole Gaussian MD rate-distortion region is achievable with a sequential dithered lattice-based quantization scheme as the dimension of the (optimal) lattice quantizers becomes large. Moreover, this scheme is shown to be universal for all independent and identically distributed (i.i.d.) smooth sources with performance no worse than that for an i.i.d. Gaussian source with the same variance and asymptotically optimal at high resolution. A class of MD scalar quantizers in the proposed general framework is also constructed and is illustrated geometrically; the performance is analyzed in the high-resolution regime, which exhibits a noticeable improvement over the existing MD scalar quantization schemes
IEEE Transactions on Information Theory 01/2007; · 3.01 Impact Factor
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ABSTRACT: In this paper, we propose guided broadcast algorithms (GB) - a family of distributed broadcast algorithms for wireless sensor networks (WSNs). GB is based on the recently proposed self-organizing redundancy cellular architecture (SoRCA) for WSNs. It utilizes spatial diversity to cover the sensor nodes in the WSN for a tunable number of times to ensure that at least n portion, a parameter specified by QoS-requirements, of nodes will receive the broadcast message (BM), instead of striving for a 100% delivery ratio which can be costly and unnecessary in some WSN applications. Specifically, the coverage assurance algorithm (CAA) in the GB family ensures that, in the ideal scenario, all nodes in the WSN receive any BM with probability that is at least n; the propagation assurance algorithm (PAA) is invoked to circumvent obstacles and to ensure that BMs propagate through the entire WSN. Additionally, the load balancing and equal exposure scheme (LBEE) is proposed to balance broadcast energy cost. Our performance evaluations show that the proposed schemes possess several nice characteristics that fit well for many applications of WSNs
Mobile Adhoc and Sensor Systems Conference, 2005. IEEE International Conference on; 12/2005
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ABSTRACT: Due to constraints inherent in RF systems, it is commonly agreed that collision detection is not feasible for CSMA-based wireless networks. However, by applying ideas from the busy-tone solution for hidden terminals and engineering together existing solutions for RF communications, we devise a simple method to reliably detect collisions for the wireless channel. We investigate the throughput gain delivered by CSMA/CD and its cross-layer designed version for multipacket-reception capable physical layers. We show that collision detection can help the system operate closer to its channel capacity. Our novel performance-improving protocols can be applied as beneficial extensions to the IEEE 802.11 wireless LAN standards
Personal, Indoor and Mobile Radio Communications, 2005. PIMRC 2005. IEEE 16th International Symposium on; 10/2005
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ABSTRACT: We propose a new class of universal multiple description lattice quantizers based on the method of quantization splitting. For Gaussian sources and squared error distortion measure, our scheme can achieve the whole multiple description rate-distortion region, as the dimension of the (optimal) lattice quantizers becomes large
Information Theory, 2005. ISIT 2005. Proceedings. International Symposium on; 10/2005
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ABSTRACT: This paper addresses the problem of bit allocation among frames in a predictively encoded video sequence. Finding optimal solutions to this problem potentially requires making an exponential number of calls to the encoder. To better understand the structure of the rate-distortion data output by video encoders, a simple model of a sequentially encoded autoregressive Gaussian random field is theoretically investigated. The rate-distortion data for the model exhibits an additive-separability property, i.e. the rate can be decomposed into a sum of independent functions of single distortion variables. This property implies the near-optimal behavior of a non-backtracking steepest-descent (SD) based bit allocation algorithm. The SD algorithm when applied to video coding produces near-optimal solutions by making a linear number of calls to the encoder. Results are presented for MPEG-2 encoding of standard video sequences.
Data Compression Conference, 2005. Proceedings. DCC 2005; 04/2005
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ABSTRACT: We propose self-organizing redundancy-cellular architecture (SoRCA) - a cell-based architecture for wireless sensor networks (WSN). SoRCA conserves energy by significantly reducing redundant data admitted to the network. It is scalable, robust and guarantees coverage. At a cost of extra energy, it can supply adjustable resolution. SoRCA also significantly simplifies the network models and may serve as a framework for mathematical analysis and simulation of WSNs. A formula for network lifetime is derived for location-based SoRCA and is verified by simulations. In addition, a scheme for extending network lifetime is proposed. We also evaluate various partitions from practical perspectives and show that hexagonal partitions are best for the class of cell-based WSNs.
Wireless Communications and Networking Conference, 2005 IEEE; 04/2005
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ABSTRACT: We consider a class of finite-state Markov channels with feedback. We first introduce a simplified equivalent channel model, and then construct the optimal stationary and nonstationary input processes that maximize the long-term directed mutual information. Furthermore, we give a sufficient condition under which the channel's Shannon capacity can be achieved by a stationary input process. The corresponding converse coding theorem and direct coding theorem are proved.
IEEE Transactions on Information Theory 04/2005; · 3.01 Impact Factor
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ABSTRACT: With the improvement of the physical layer's ability to decode more than one packets from multiple users, the classical collision model no longer applies and a cross-layer approach should be employed when designing multiple access protocols. This is especially the case for CSMA communications, which previously have not been studied under a multipacket reception (MPR) model. Since CSMA is used in the IEEE 802.11 wireless LAN standards and other wireless networks, improving its performances could have widespread benefits. In here, we investigate the impact of MPR on CSMA and propose a performance-improving cross-layer designed CSMA protocol for wireless networks.
Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on; 12/2004
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ABSTRACT: The recently proposed self-organizing redundancy-cellular architecture (SoRCA) can significantly simplify wireless sensor network (WSN) topologies. We present three additional components for SoRCA: the distributed resource allocation algorithm (DRAA), the optimal path algorithm (OPA) and the distributed probabilistic routing algorithm (DPRA). The number of channels required for SoRCA is calculated and channels can be assigned by applying DRAA. Various WSN properties such as network lifetime are analytically derived assuming channelized MAC protocols and traffic models predicted based on OPA and DPRA.
Modeling, Analysis, and Simulation of Computer and Telecommunications Systems, 2004. (MASCOTS 2004). Proceedings. The IEEE Computer Society's 12th Annual International Symposium on; 11/2004
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ABSTRACT: We consider a distributed sensor network in which several observations are communicated to the fusion center using limited transmission rate. The observation must be separately encoded so that the target can be estimated with minimum average distortion. We address the problem from an information theoretic perspective and establish the inner and outer bound of the admissible rate-distortion region. We derive an upper bound on the sum-rate distortion function and its corresponding rate allocation schemes by exploiting the contra-polymatroid structure of the achievable rate region. The quadratic Gaussian case is analyzed in detail and the optimal rate allocation schemes in the achievable rate region are characterized. We show that our upper bound on the sum-rate distortion function is tight for the quadratic Gaussian CEO problem in the case of same signal-to-noise ratios at the sensors.
IEEE Journal on Selected Areas in Communications 09/2004; · 3.41 Impact Factor
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ABSTRACT: The finite battery power in wireless portable computing devices is a motivating factor for developing energy efficient wireless network technologies. This paper investigates energy efficiency, relating it to throughput and packet delay for both non-persistent and p-persistent CSMA, two protocols popularly applied in current wireless networks; for example, the widely adopted IEEE 802.11 WLAN standards are based on p-persistent CSMA. For high message generation by the members of a finite population, we find that non-persistent CSMA has a markedly higher energy efficiency than p-persistent CSMA for all network configurations, though the latter attains a moderately lower packet delay. We also show that when non-persistent CSMA is optimized for energy efficiency, throughput and delay are impacted negatively, whereas p-persistent CSMA can effectively optimize all three with the same network settings. Our results help illuminate the suitability of each CSMA scheme for various wireless environments and applications.
Wireless Communications and Networking Conference, 2004. WCNC. 2004 IEEE; 04/2004
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ABSTRACT: We present an integrated system with structural Gaussian mixture models (SGMMs) and a neural network for purposes of achieving both computational efficiency and high accuracy in text-independent speaker verification. A structural background model (SBM) is constructed first by hierarchically clustering all Gaussian mixture components in a universal background model (UBM). In this way the acoustic space is partitioned into multiple regions in different levels of resolution. For each target speaker, a SGMM can be generated through multilevel maximum a posteriori (MAP) adaptation from the SBM. During test, only a small subset of Gaussian mixture components are scored for each feature vector in order to reduce the computational cost significantly. Furthermore, the scores obtained in different layers of the tree-structured models are combined via a neural network for final decision. Different configurations are compared in the experiments conducted on the telephony speech data used in the NIST speaker verification evaluation. The experimental results show that computational reduction by a factor of 17 can be achieved with 5% relative reduction in equal error rate (EER) compared with the baseline. The SGMM-SBM also shows some advantages over the recently proposed hash GMM, including higher speed and better verification performance.
IEEE Transactions on Speech and Audio Processing 10/2003; · 2.29 Impact Factor
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ABSTRACT: We consider a hybrid selection/maximal-ratio combining (HS/MRC) diversity system and assume independent Nakagami fading on the diversity branches with unequal fading parameters and unequal signal-to-noise ratios (SNR's). We use the virtual branch technique and two series expressions for the characteristic function (CF) of the sum of independent gamma random variables to derive closed-form expressions for CF, the probability density function (PDF), the mean, and the variance of the instantaneous combiner output SNR. We also obtain closed-form expressions for the outage probability, the channel capacity under different transmission policies, and the average symbol error probability (SEP) for a general class of M-ary modulation schemes (including MPSK, MQAM, BFSK, and MSK) with coherent detection. Our approach provides a canonical structure for the closed-form expressions, which are the closed-form expressions for a single-branch system in different Nakagami fading environments.
Communications, 2003. ICC '03. IEEE International Conference on; 06/2003
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ABSTRACT: In this paper, we consider a diversity system with M-ary orthogonal FSK and hybrid selection/equal-gain combining (HS/EGC) which combines, per the EGC rule, the L<sub>c</sub> strongest diversity branches out of the L available ones. We assume independent Nakagami fading on the diversity branches with unequal fading parameters and unequal signal-to-noise ratios (SNRs) and derive different closed-form expressions for the average symbol error probability (SEP). The closed-form expressions are in canonical form as a weighted sum of elementary closed-form expressions, which are the closed-form expressions for a diversity system with EGC in various Nakagami fading environments.
Vehicular Technology Conference, 2003. VTC 2003-Spring. The 57th IEEE Semiannual; 05/2003
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ABSTRACT: In this paper, we derive closed-form expressions for the channel capacity of a diversity reception system with maximal-ratio combining (MRC) or postdetection equal-gain combining (EGC) over a slowly varying Nakagami-q (Hoyt) fading channel under different adaptive transmission policies when the channel side information is available at the transmitter and the receiver. We consider the situation that the branches are independent and identically distributed (i.i.d.). We first derive three different canonical-form expressions for the probability density function (PDF) of the instantaneous combiner output signal-to-noise ratio (SNR) as a weighted sum of gamma PDFs. Then the channel capacity is obtained in different canonical forms as a weighted sum of channel capacities for single-branch systems in gamma fading environments.
Communication Technology Proceedings, 2003. ICCT 2003. International Conference on; 05/2003
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ABSTRACT: In this paper, we provide a unified analysis of average symbol error probability (SEP) for a diversity system over generalized gamma fading channels, which is a generalization of Rayleigh, Nakagami, and Ricean fading channels. We consider independent generalized gamma fading on the diversity branches and derive different closed-form expressions of the average SEP for a general class of M-ary modulation schemes (including MPSK, MQAM, BFSK, and MSK) with maximal-ratio combining (MRC) and for M-ary orthogonal FSK with postdetection equal-gain combining (EGC). The results apply to the situations where some branches are Nakagami faded and the others are Ricean faded. Furthermore, the results are applied to obtain closed-form expressions of the average SEP for the cases of arbitrarily correlated and not necessarily identically distributed Nakagami and Ricean faded branches with the help of virtual branch technique by Win et al. Our approach provides a canonical structure for the average SEP as a weighted sum of elementary closed-form expressions, which are the closed-form expressions for the average SEP of a diversity system in independent and identically distributed (i.i.d.) Nakagami fading environments.
Wireless Communications and Networking, 2003. WCNC 2003. 2003 IEEE; 04/2003
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ABSTRACT: We adapt methods originally developed in information and coding
theory to solve some testing problems. The efficiency of two-stage pool
testing of n items is characterized by the minimum expected number E(n,
p) of tests for the Bernoulli p-scheme, where the minimum is taken over
a matrix that specifies the tests that constitute the first stage. An
information-theoretic bound implies that the natural desire to achieve
E(n, p) = o(n) as n → ∞ can be satisfied only if p(n) →
0. Using random selection and linear programming, we bound some
parameters of binary matrices, thereby determining up to positive
constants how the asymptotic behavior of E(n, p) as n → ∞
depends on the manner in which p(n) → 0. In particular, it is shown
that for p(n) = n<sup>-β+o(1)</sup>, where 0 < β < 1,
the asymptotic efficiency of two-stage procedures cannot be improved
upon by generalizing to the class of all multistage adaptive testing
algorithms
IEEE Transactions on Information Theory 08/2002; · 3.01 Impact Factor
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ABSTRACT: We formulate quantum rate-distortion theory in the most general
setting where classical side information is included in the tradeoff.
Using a natural distortion measure based on entanglement fidelity and
specializing to the case of an unrestricted classical side channel, we
find the exact quantum rate-distortion function for a source of
isotropic qubits. An upper bound we believe to be exact is found in the
case of biased sources. We establish that in this scenario optimal
rate-distortion codes produce no entropy exchange with the environment
of any individual qubit
IEEE Transactions on Information Theory 07/2002; · 3.01 Impact Factor
