Browsing by Author "Chen, PN"

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A combination logic design for a high speed IEEE 802.11 MAC controller
(2003-03-01)
Li, RZ
;
Huang, SP
;
Lin, FS
;
Hong, MT
;
Chen, PN
In this paper, we propose a pure combinational logic design for the implementation of IEEE802.11 Medium Access Control (MAC) protocol, in contrast to firmware implementation based on an embedded micro-engine. In order to have a timely response, a Control Frame Handler is also included in our MAC controller. A further improvement for timely manipulation on the time-critical management frames (such as Beacon, ATIM and Probe Response) is subsequently developed in our revised edition. Equipped with a self-developed PCMCIA unit, the functions of our MAC controller have been verified using two Altera EPF 10K-100 ARC240-2 FPGAs in an on-line MAC-to-MAC data exchange fashion. Experimental results show that a pure combinational logic design can easily achieve a baseband-interfacing throughput of over-100Mbps with a cost-effect gate count of 21702.
A maximum-likelihood soft-decision sequential decoding algorithm for binary convolutional codes
(2002-02-01)
Han, YSS
;
Chen, PN
;
Wu, HB
;
電信工程研究所
;
Institute of Communications Engineering
In this letter, we present a trellis-based maximum-likelihood soft-decision sequential decoding algorithm (MLSDA) for binary convolutional codes. Simulation results show that, for (2, 1, 6) and (2, 1, 16) codes antipodally transmitted over the AWGN channel, the average computational effort required by the algorithm is several orders of magnitude less than that of the Viterbi algorithm. Also shown via simulations upon the same system models is that, under moderate SNR, the algorithm is about four times faster than the conventional sequential decoding algorithm (i.e., stack algorithm with Fano metric) having comparable bit-error probability.
A note on the Poor-Verdu upper bound for the channel reliability function
(2002-01-01)
Alajaji, F
;
Chen, PN
;
Rached, Z
;
電信工程研究所
;
Institute of Communications Engineering
In an earlier work, Poor and Verdu established an upper bound for the reliability function of arbitrary single-user discrete-time channels with memory. They also conjectured that their bound is tight for all coding rates. In this note, we demonstrate via a counterexample involving memoryless binary erasure channels (BECs) that the Poor-Verdu upper bound is not tight at low rates. We conclude by examining possible improvements to this bound.
A rate-distortion theorem for arbitrary discrete sources
(1998-07-01)
Chen, PN
;
Alajaji, F
;
電信工程研究所
;
Institute of Communications Engineering
A rate-distortion theorem for arbitrary (not necessarily stationary or ergodic) discrete-time finite-alphabet sources is given, This result, which provides the expression of the minimum epsilon-achievable fixed-length coding rate subject to a fidelity criterion, extends a recent data compression theorem by Steinberg and Verdu.
An efficient collision resolution scheme for wireless multiple access
(1998)
Chen, PN
;
Wu, CS
;
Ma, GK
;
電信工程研究所
;
Institute of Communications Engineering
This paper presents a contention resolution scheme for multiple random access based on tree algorithms. The proposed scheme, called Dynamic Collision Resolution (DCR), is a variation of the tree algorithm. Given that plural users are transmitting packets to a shared communication medium, the free algorithm will divide the transmitting users into n parts upon detecting a collision condition and, in the later retransmission, collisions will only occur in between the users that fall into the same part. It was well known that the optimal value of n is 3 under the condition that n is fixed and the number of users is infinite. The proposed DCR scheme adopts a dynamically change on the value of n for a better contention resolution. The performance is evaluated through the simulation over a finite number of users and the result shows that the DCR scheme gives a non-trivial improvement on the tree algorithms under a moderate number of users.
Analysis of decoding complexity using the Berry-Esseen theorem
(2002)
Chen, PN
;
Han, YS
;
Hartmann, CRP
;
Wu, HB
;
電信工程研究所
This work presents a novel technique to analyze the computational efforts of an ordering-free variant of the generalized Dijkstras's algorithm (GDA) and the maximum-likelihood sequential decoding algorithm (MLSDA) based on the Berry-Esseen theorem. Different from the theoretical bounds determined by the conventional central limit theorem argument, which often holds only for sufficiently large blocklength, the new bounds are valid for any blocklength.
Asymptotic minimum covering radius of block codes
(2001)
Chen, PN
;
Han, YSS
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we restudy the covering radius of block codes from an information theoretic point of view by ignoring the combinatorial formulation of the problem. In the new setting, the formula of the statistically defined minimum covering radius, for which the probability mass of uncovered space by M spheres can be made arbitrarily small, is reduced to a minimization of a statistically defined spectrum formula among codeword-selecting distributions. The advantage of the new view is that no assumptions need to be made on the code alphabet (such as finite, countable, etc.) and the distance measure ( such as additive, symmetric, bounded, etc.) in the problem transformation, and hence the spectrum formula can be applied in most general situations. We next address a sufficient condition under which uniform codeword-selecting distribution minimizes the spectrum formula. With the condition, the asymptotic minimum covering radius for block codes under J-ary quantized channels and constant weight codes under Hamming distance measure are determined to display the usage of the spectrum formula.
Asymptotic performance analysis for minimum-hamming-distance fusion
(2005)
Chen, PN
;
Wang, TY
;
Han, YSS
;
Varshney, PK
;
Yao, C
Distributed (M-ary) detection and fault-tolerance have been considered as two fundamental functions in the context of large-scale sensor networks. Distributed multiclass classification fusion using error correcting codes (DCFECC) has been proposed to provide good fault-tolerance capability in wireless sensor networks. Minimum Hamming distance fusion is an essential part of the DCFECC approach. In this paper, we study the asymptotic performance of minimum Hamming distance fusion for both fault-free and faulty situations when the number of sensors tends to infinity. We conclude that the error probability vanishes asymptotically as long as the minimum Hamming distance d(min) of the DCFECC code approaches infinity, and the probabilities of correct local classification for all hypotheses are greater than one half. In case d(min)/2, normalized by the number of sensors, can be made larger than the largest local classification error, an explicit expression for the error exponent of the DCFECC system in terms of the Kullback-Leibler divergence can be established. A converse where the DCFECC decoding error is bounded away from zero is also addressed.
Broadband service creation and operations
(1997-12-01)
Lin, YD
;
Lin, YT
;
Chen, PN
;
Choy, MM
;
資訊工程學系
Three challenges for deploying broadband services are the time-consuming process of service creation, the interoperability over heterogeneous platforms, and the gap between the needs of service management and the functionalities of network management. In this article we describe a methodology to attack the first two challenges, namely, to simplify the process of service creation and provide a platform-independent framework for service operations. A set of broadband service-independent building blocks (SIBs) are designed and used to create and customize SIB graphs for broadband services. During service running time, the service agent interprets a SIB graph and executes SIB procedures which are all downloaded from the service provider. Web, Java, and CORBA are the technological elements of this methodology. Two examples, video conferencing and video on demand, are given to demonstrate the feasibility of this approach.
Broadband service creation and operations
(1997-12-01)
Lin, YD
;
Lin, YT
;
Chen, PN
;
Choy, MM
;
資訊工程學系
Three challenges for deploying broadband services are the time-consuming process of service creation, the interoperability over heterogeneous platforms, and the gap between the needs of service management and the functionalities of network management. In this article we describe a methodology to attack the first two challenges, namely, to simplify the process of service creation and provide a platform-independent framework for service operations. A set of broadband service-independent building blocks (SIBs) are designed and used to create and customize SIB graphs for broadband services. During service running time, the service agent interprets a SIB graph and executes SIB procedures which are all downloaded from the service provider. Web, Java, and CORBA are the technological elements of this methodology. Two examples, video conferencing and video on demand, are given to demonstrate the feasibility of this approach.
Csiszar's cutoff rates for arbitrary discrete sources
(2001-01-01)
Chen, PN
;
Alajaji, F
;
電信工程研究所
;
Institute of Communications Engineering
Csiszar's forward beta -cutoff rate (given a fixed beta > 0) for a discrete source is defined as the smallest number Ro such that for every R > R-0, there exists a sequence of tired-length codes of rate R with probability of error asymptotically vanishing as e(-n beta (R-R0)). For a discrete memoryless source (DMS), the forward beta -cutoff rate is shown by Csiszar [6] to be equal to the source Renyi entropy. An analogous concept of reverse beta -cutoff rate regarding the probability of correct decoding is also characterized by Csiszar in terms of the Renyi entropy. In this work, Csiszar's results are generalized by investigating the beta -cutoff rates for the class of arbitrary discrete sources with memory. It is demonstrated that the limsup and liminf Renyi entropy rates provide the formulas for the forward and reverse beta -cutoff rates, respectively. Consequently, new fixed-length source coding operational characterizations for the Renyi entropy rates are established.
Csiszar's cutoff rates for the general hypothesis testing problem
(2004-04-01)
Alajaji, F
;
Chen, PN
;
Rached, Z
;
電信工程研究所
;
Institute of Communications Engineering
In [6], Csiszar established the concept of forward beta-cutoff rate for the error exponent hypothesis testing problem based on independent and identically distributed (i.i.d.) observations. Given beta < 0, he defined the forward beta-cutoff rate as the number R-0 greater than or equal to 0 that provides the best possible lower bound in the form beta(E - (R) over bar (0)) to the type 1 error exponent function for hypothesis testing where 0 < E < R-0 is the rate of exponential convergence to 0 of the type 2 error probably. He then demonstrated that the forward beta-cutoff rate is given by where D1/(1-beta)(Xparallel to(X) over bar) denotes the Renyi alpha-divergence [19], alpha > 0, alpha not equal 1. Similarly, for 0 < beta < 1, Csiszar also established the concept of reverse beta-cutoff rate for the correct exponent hypothesis testing problem. In this work, we extend Csiszar's results by investigating the forward and reverse beta-cutoff rates for the hypothesis testing between two arbitrary sources with memory. We demonstrate that the lim inf Renyi a-divergence rate provides the expression for the forward beta-cutoff rate. We also show that if the log-likelihood large deviation spectrum admits a limit, then the reverse beta-cutoff rate equals the liminf a-divergence rate, where alpha and 1/1-beta and 0 < beta < beta(max), where beta(max) is the largest beta < 1 for which the lim inf 1/1-beta-divergence rate is finite. For beta(max) less than or equal to beta < 1, we show that the reverse cutoff rate is in general only upper-bounded by the lim inf Renyi divergence rate. Unlike in [4], where the alphabet for the source coding cutoff rate problem was assumed to be finite, we assume arbitrary (countable or continuous) source alphabet. We also provide several examples to illustrate our forward and reverse beta-cutoff rates results and the techniques employed to establish them.
Distance-spectrum formulas on the largest minimum distance of block codes
(2000-05-01)
Chen, PN
;
Lee, TY
;
Han, YS
;
電信工程研究所
;
Institute of Communications Engineering
A general formula for the asymptotic largest minimum distance (in block length) of deterministic block codes under generalized distance functions (not necessarily additive, symmetric, and bounded) is presented. As revealed in the formula, the largest minimum distance can be fully determined by the ultimate statistical characteristics of the normalized distance function evaluated under a properly chosen random-code generating distribution. Interestingly, the new formula has an analogous form to the general information-spectrum expressions of the channel capacity and the optimistic channel capacity, respectively derived by Verdu-Han [29] and Chen-Alajaji [7], [8], As a result, a minor class of distance functions for which the largest minimum distance can be derived is characterized. A general Varshamov-Gilbert lower bound is next addressed. Some discussions on the tightness of the general Varshamov-Gilbert bound are also provided. Finally, lower bounds on the largest minimum distances for several specific block coding schemes are rederived in terms of the new formulas, followed by comparisons with the known results devoted to the same codes.
Distributed fault-tolerant classification in wireless sensor networks
(2005-04-01)
Wang, TY
;
Han, YSS
;
Varshney, PK
;
Chen, PN
;
電信工程研究所
Fault-tolerance and data fusion have been considered as two fundamental functions in wireless sensor networks. In this paper, we propose a novel approach for distributed multiclass classification using a fault-tolerant fusion rule for wireless sensor networks. Binary decisions from local sensors, possibly in the presence of faults, are forwarded to the fusion center that determines the final classification result. Classification fusion in our approach is implemented via error correcting codes to incorporate fault-tolerance capability. This new approach not only provides an improved fault-tolerance capability but also reduces computation time and memory requirements at the fusion center. Code matrix design is essential for the design of such systems. Two efficient code matrix design algorithms are proposed in this paper. The relative merits of both algorithms are also studied. We also develop sufficient conditions for asymptotic detection of the correct hypothesis by the proposed approach. Performance evaluation of the proposed approach in the presence of faults is provided. These results show significant improvement in fault-tolerance capability as compared with conventional parallel fusion networks.
General formulas for Csiszar's source coding cutoff rates
(2000)
Chen, PN
;
Alajaji, F
;
電信工程研究所
;
Institute of Communications Engineering
In this work, Csiszar's fixed-length source coding beta -cutoff rates are investigated for the class of arbitrary discrete sources with memory. It is demonstrated that the limsup and liminf Renyi entropy rates provide the formulas for the forward and reverse beta -cutoff rates, respectively. Consequently, new fixed-length source coding operational characterizations for the Renyi entropy rates are established.
Generalization of Gartner-Ellis theorem
(2000-11-01)
Chen, PN
;
電信工程研究所
;
Institute of Communications Engineering
A generalization of the Gatner-Ellis Theorem for arbitrary random sequences is established. It is shown that the conventional formula of the large deviation rate function, based on the moment generating function techniques, fails to describe the general (possibly nonconvex) large deviation rate for an arbitrary random sequence. An (nonconvex) extension formula obtained by twisting the conventional large deviation rate function around a continuous functional is therefore proposed. As a result, a new Gartner-Ellis upper bound is proved. It is demonstrated by an example that a tight upper bound on the large deviation rate of an arbitrary random sequence can be obtained by choosing the right continuous functional, even if the true large deviation rate is not convex. Also proved is a parallel extension of the Gartner-Ellis lower bound with the introduction of a new notion of Gartner-Ellis set within which the upper bound coincides with the lower bound (for countably many points).
Generalized source coding theorems and hypothesis testing: Part I - Information measures
(1998-05-01)
Chen, PN
;
Alajaji, F
;
電信工程研究所
;
Institute of Communications Engineering
Expressions for epsilon-entropy rate, epsilon-mutual information rate and epsilon-divergence rate are introduced. These quantities, which consist of the quantiles of the asymptotic information spectra, generalize the inf/supentropy/information/divergence rates of Han and Verdu. The algebraic properties of these information measures are rigorously analyzed, and examples illustrating their use in the computation of the E-capacity are presented. In Part II of this work, these measures are employed to prove general source coding theorems for block codes, and the general formula of the Neyman-Pearson hypothesis testing type-II error exponent subject to upper bounds on the type-I error probability.
Generalized source coding theorems and hypothesis testing: Part II - Operational limits
(1998-05-01)
Chen, PN
;
Alajaji, F
;
電信工程研究所
;
Institute of Communications Engineering
In light of the information measures introduced in Part I, a generalized version of the Asymptotic Equipartition Property (AEP) is proved, General fixed-length data compaction and data compression (source coding) theorems for arbitrary finite-alphabet sources are also established, Finally, the general expression of the Neyman-Pearson type-II error exponent subject to upper bounds on the type-I error probability is examined.
On the optimistic capacity of arbitrary channels
(1998)
Chen, PN
;
Alajaji, F
;
電信工程研究所
;
Institute of Communications Engineering
A formula for the optimistic capacity of arbitrary channels is established. It is shown to equal the supremum, over all input processes, of the input-output zero-sup-information rate. A general expression for optimistic epsilon-capacity is also provided.
Optimistic Shannon coding theorems for arbitrary single-user systems
(1999-11-01)
Chen, PN
;
Alajaji, F
;
電信工程研究所
;
Institute of Communications Engineering
The conventional definitions of the source coding rate and or channel capacity require the existence of reliable codes for all sufficiently large block lengths. Alternatively, if it is required that good codes exist for infinitely many block lengths, then optimistic definitions of source coding rate and channel capacity are obtained. In this work, formulas for the optimistic minimum achievable fixed-length source coding rate and the minimum epsilon-achievable source coding rate for arbitrary finite-alphabet sources are established, The expressions for the optimistic capacity and the optimistic epsilon-capacity of arbitrary single-user channels are also provided. The expressions of the optimistic source coding rate and capacity are examined for the class of information stable sources and channels, respectively, Finally, examples for the computation of optimistic capacity are presented.