Stack Algorithm Research Articles

The Crawfish and the Aztec treasure maze

Teaching data structures and other CS1/CS2 subjects can be challenging. Previous research has shown that using manipulatives and visualization tools may help students comprehend these abstract concepts. This paper illustrates how students can use a pez dispenser as a stack to gain first hand experience with many CS1/CS2 topics. In addition to giving students candy, we appeal to their sense of adventure by presenting a fictitious account of how the Aztecs might have used pez-like stacks. This tale is meant to supplement homework and class discussion concerning stack definition, algorithm design, recursion, tree traversal, and operation pre- and post-conditions.

A maximum-likelihood soft-decision sequential decoding algorithm for binary convolutional codes

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.

STABILITY AND PERFORMANCE OF STACK ALGORITHMS FOR RANDOM ACCESS COMMUNICATION MODELED AS A TREE STRUCTURED QBD MARKOV CHAIN

In this paper, we introduce an analytical model to study the stability and the main performance measures of a binary stack algorithm for random multiple access communication. The input traffic is a discrete time Batch Markovian Arrival Process (D-BMAP). The analytical model is nearly exact (one minor approximation is required) and the analysis is based on recent results obtained from tree structured Quasi-Birth-Death (QBD) Markov chains. Apart from studying the stability of the protocol, we are also able to calculate the mean delay and other important performance measures. The method deployed in this paper can also be extended to evaluate other medium access control (MAC) protocols with an underlying stack structure.

One stochastic process and its application to multiple access in supercritical region

A discrete-argument stochastic process is presented. The process is a generalization of the Cinlar (1975) semiregenerative process and process /spl eta/(t) given in Tsybakov (1993). For this process, the theorem, which is similar to the Smith regenerative process theorem, is given. We use this theorem to find the transmission rate and mean packet delay for stack and part-and-try random multiple access algorithms in their supercritical regions. For the part-and-try algorithm, the results are new. For the stack algorithm, we give a new method of finding the rate and delay.

A deadlock model for a multi-service medium access protocol employing multi-slot N -ary stack algorithm (msSTART)

Many modern multi‐service medium access protocols (MACs) use a collision based capacity request signaling channel as part of a hybrid TDMA frame structure. Multi‐slot Stack Random Access Algorithm (msSTART) is proposed for use in IEEE 802.14 hybrid fiber/coaxial network and will be highly relevant for the S‐MAC development of evolving WATM MAC specifications. This paper studies the performance of msSTART as an example of a Q‐ary tree contention resolution algorithm (CRA) in the wireless environment using the novel Basic Deadlock model. We contrast approximate results for msSTART performance obtained by simulation under extreme inter‐station correlation with analytical results for the more popular p‐persistence CRA used in several testbed WATM implementations. Using three signaling channel schemes designed to provide support for increased system stability, to implement priority in the wireless MAC, and maximise efficiency, we provide comparative results for evaluation of msSTART and p‐persistence ALOHA under what the IEEE 802.14 working group has termed the “disaster scenario”. We find that of the three schemes evaluated the full Contention Mini‐Slot (CMS) sharing scheme employing multiple CMSs per data region extends the protocol's useable load region the furthest. We conclude that Q‐ary tree contention resolution algorithms (in particular msSTART) are best adapted to the wireless environment, providing less case sensitive performance.

Channel identification and sequential sequence estimation using antenna array for broad-band mobile communications

This paper proposes the joint use of an antenna array and sequential sequence estimation (SSE) technique for the equalization of multipath fading channels suffering from severe intersymbol interference (ISI). It is shown that with the proper use of the multiple stack algorithm (MSA), exploiting the redundant structure of the signal received by multiple antenna array elements can enhance the uniqueness of the sequence estimation, thereby significantly reducing the frame erasure probability. Three new algorithms are derived for vector channel identification, the results of which are used to calculate the Fano metric for SSE. The first algorithm uses just a temporal reference, and others use both temporal and spatial references. Impacts of using the temporal and spatial references are investigated in terms of the channel identification accuracy as well as overall frame erasure rate (ERR) and bit error rate (BER). Results of computer simulations are then presented to compare the performances of the three algorithms for vector channel identification. The propagation scenario assumed in the simulations is equal-power 12-path propagation, in which, even with binary phase shift keying (BPSK), maximum likelihood sequence estimation (MLSE) requires 2048 states. It is shown that even in such a complicated situation, the MSA algorithm can achieve excellent ERR and BER performances with reasonable computational complexity.

Free access stack algorithms for microcellular radio systems

We evaluate the data traffic performance of a centralized packet access protocol for microcellular radio systems supporting both speech and data users. A time-slotted radio channel is assumed. Speech contention is decoupled from data contention to give speech priority over data. A free access stack algorithm is used for handling data contention. An out-slot access scheme is used in which the slots are divided into user-information transmission slots and contention slots for sending transmission requests. The contention slots are subdivided in minislots to improve the access capacity. The out-slot algorithm performances are compared with the performances of a previously proposed in-slot one in which all slots can be used for sending user information. A memoryless channel, with capture and errors, is considered. The effects of speech traffic on data performance are evaluated. Moreover, the paper presents a method for evaluating the packet error probability of a packet cellular system. This method is used for evaluating the proposed algorithm in a microcellular system. An access technique with coordinated operation among cochannel cells is studied. The effects of sectorization on data performances and protocol unfairness are investigated. Different frequency reuse factors are taken into consideration.

Representing group codes as permutation codes

Given an abstract group /spl Gscr/, an N-dimensional orthogonal matrix representation G of /spl Gscr/, and an "initial vector" x/spl isin/R/sup N/, Slepian defined the group code generated by the representation G to be the set of vectors Gx. If G is a group of permutation matrices, the set Gx is called a "permutation code". For permutation codes a "stack algorithm" decoder exists that, in the presence of low noise, produces the maximum-likelihood estimate of the transmitted vector by using far fewer computations than the standard decoder. In this correspondence, a new concept of equivalence of codes of different dimensions is presented which is weaker than the usual definition of equivalent codes. We show that every group code is (weakly) equivalent to a permutation code and we discuss the minimal degree of this permutation code.

A bidirectional multiple stack algorithm

Bidirectional sequential decoding (BSD) substantially reduces the computational variability of conventional sequential decoding without compromising the error performance. However, BSD does not completely eliminate the erasure problem. We propose an erasure-free decoding algorithm which combines the idea of BSD in conjunction with that of the multiple stack algorithm (MSA). It is found that the new bidirectional multiple stack algorithm (BMSA) offers substantial advantages over the MSA in terms of computational effort, memory requirements, and error performance. The BMSA appears as an attractive alternative to the Viterbi algorithm (VA) where low error probabilities and high decoding speeds are required.

Data-parallel load balancing strategies

Programming irregular and dynamic data-parallel algorithms must consider the effect of data distribution. The implementation of a load balancing algorithm is quite a difficult task for the programmer. However, a load balancing strategy may be developed independently of the application. The integration of such a strategy into the data-parallel algorithm may be relevant to a library or a data-parallel compiler run-time. We propose load distribution data-parallel algorithms for a class of irregular data-parallel algorithms called stack algorithms. Our algorithms allow the use of regular and/or irregular communication patterns to exchange the works between processors. The results of theoretical analysis of these algorithms are presented. They allow different load balancing algorithms to be compared and the identification of criteria to choose between them.

On hybrid stack decoding algorithms for block codes

This correspondence presents sequential algorithms for soft decision decoding of linear block codes. They use a stack algorithm based on the trellis of the code. We are interested in the trellis as a means to avoid path-decoding repetitions. As well, the possibility of bidirectional decoding offers a chance to increase the likelihood of explored paths. We have developed three successive algorithms that offer a good decrement in the overall complexity, and mainly in the most complex decoding case, while giving near-maximum-likelihood performance. This is important since it determines the maximum buffer size necessary in the decoder.

Linear Time Simulation of Invertible Non-Deterministic Stack Algorithms

Linear Time Simulation of Invertible Non-Deterministic Stack Algorithms

The n -ary stack algorithm for the wireless random access channel

The emergence of wireless and personal communication networks has brought random access protocols for packet radio networks back to the research forefronts. Most such protocols are based on the ever popular ALOHA protocol. Unfortunately, this protocol is inherently unstable and requires sophisticated schemes to stabilize it. Another class of random access schemes, called limited sensing or stack algorithms, has been proposed that is stable and allows for the dynamic incorporation of new stations into the network. In this paper, we will review the simple to implement n-ary stack algorithm, and we will study its performance under various system parameters in the presence of capture, and also in the presence of feedback errors. Finally, we will investigate its maximum system throughput under various traffic generation processes.

Modified multiple stack algorithm for decoding convolutional codes

The multiple stack algorithm (MSA), devised by Chevillat and Costello, is an efficient algorithm for erasurefree decoding of long constraint length convolutional codes. In the MSA, substack size and the number of transferred survivors (or successors) are assumed to be small. Lower error probabilities can be achieved by increasing the first stack size and/or increasing the computational limit. A large storage capacity for survivors is required to prevent memory overflow and achieve a low error probability. The authors present a modified MSA, in which the storage capacity for survivors is kept as a constant, while the substacks are arranged in a ring-like structure to handle the overflow problem of storage for survivors. In addition, the substack size and the number of transferred survivors are made large to improve performance. The performance of the modified MSA in decoding a convolutional code with constraint length m = 23 is investigated and compared with the performance of the unmodified MSA.

Monochromatic body waves excited by great subduction zone earthquakes

Large quasi‐monochromatic body waves were excited by the 1995 Chile Mw=8.1 and by the 1994 Kurile Mw=8.3 events. They are observed on vertical/radial component seismograms following the direct P and Pdiff arrivals, at all azimuths. We devise a slant stack algorithm to characterize the source of the oscillations. This technique aims at locating near‐source isotropic scatterers using broadband data from global networks. For both events, we find that the oscillations emanate from the trench. We show that these monochromatic waves are due to localized oscillations of the water column. Their period corresponds to the gravest ID mode of a water layer for vertically traveling compressional waves. We suggest that these monochromatic body waves may yield additional constraints on the source process of great subduction zone earthquakes.

A sequential soft-decision decoder for Reed-Solomon codes applied to encoded PSK in Rayleigh-fading channels

A soft-decision stack algorithm with a variable-bias-term branch metric and accurate channel state information estimate is applied to a Reed-Solomon-encoded phase-shift keying (PSK) system in the presence of memoryless Rayleigh fading. To compensate for the variable decoding delay inherent in sequential decoding algorithms, a time-out mechanism is used by the inner decoder: if a time-out occurs before complete decoding of a given block, the decoder declares an erasure. An erasures-and-errors correction decoding algorithm is implemented at the outer decoder to recover any incorrect or incompletely decoded inner code words. Simulation results show that significant improvement over uncoded modulation can be achieved with this approach with moderate cost in decoding complexity.

Efficient stack simulation for set-associative virtual address caches with real tags

Stack simulation is a powerful cache analysis approach to generate the number of misses and write backs for various cache configurations in a single run. Unfortunately, none of the previous work on stack simulation has efficient stack algorithm for virtual address caches with real tags (VIR-type caches). In this paper, we devise an efficient stack simulation algorithm for analyzing VIR-type caches. Using markers with a valid range for synonym lines, our algorithm is able to keep track of stack distances for different cache configurations. In addition to cache miss ratios and write back ratios, our approach generates pseudonym frequency for all cache configurations under investigation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multiple-inputs systolic priority queue for fast sequential decoding of convolutional codes

The operating speed of a sequential decoder with stack algorithm is usually limited by the time to search the best node for further extension. This problem can be completely alleviated by using the systolic priority queue to replace the stack memory. However, the systolic priority queues developed previously are accessible only in the cases when the number of inputs processed is small. This is because the complexity of a queue grows up quickly as the volume of data flowing through it increases. Since the largest amount of data flowing through a systolic priority queue is equal to the number of inputs to this queue, the systolic priority queue is not suitable for a system with many inputs. A modified version of previously developed circuits is proposed. The number of transmission gates required in this circuit is proportional to 3N instead of N/sup 2/, where N is the number of inputs. Also the total number of control signals is proportional to 3N/sup 2/ instead of N/sup 3/. But the number of comparators required is proportional to C/sub 2//sup N+1/, as before. This modified circuit can be used in cases where the number of inputs is small (N/spl les/8). A new algorithm for the multiple-inputs systolic priority queue (MISPQ) is proposed. By using this algorithm, a MISPQ may be implemented with several smaller queues, each is used to process a part of data in the MISPQ. Since the volume of data flowing through each queue is small, these queues will be simpler. However, some additional circuits should be used for the interactions between queues. A circuit for implementing this algorithm is presented and its complexity is analysed. The number of transmission gates for the MISPQ is proportional to 3N, the number of control signals is proportional to (3N/sup 2//2), and the number of comparators is proportional to 4C/sub 2//sup N/2+1/. Thus this new architecture is feasible for large N (e.g.N/spl ges/8).

Optimising delay and throughput in packet-switched CDMA network with collision resolution using stack algorithm

The authors address the effect of code division multiple access (CDMA) on the performance of wireless packet-switched networks. Although CDMA can enhance throughput, the delay at small traffic loads suffers from bandspreading. For imperfect signal separation at the receiver, performance benefits from CDMA may be lost. The capacity of the particular stack algorithm addressed for collision resolution can be enhanced from 0.32 to approximately 0.40 if a 10 dB spreading gain with perfect signal separation is employed. >

Error probability for maximum likelihood sequence estimation of trellis-coded modulation on ISI channels

A method is presented for upper bounding the error probability of trellis-coded modulation on multipath-fading ISI channels that uses one-directional stack algorithm. The method provides a tighter upper bound than transfer function bounding techniques, and is useful for large-state systems, because the transfer function is not required. The stack algorithm exploits the symmetry properties of the trellis code to reduce computing time. >