DPCM Encoding of Regenerative Composite Processes

Fixed (nonadaptive) and forward adaptive differential pulse code modulation of regenerative composite sources is investigated. In the fixed code, an approximate formula is given for the optimal value of the prediction coefficient. This is then used as an initial guess to optimize the code (predictor and quantizer) through a numerical method. In the forward adaptive scheme, the state of the switch in the composite source is estimated using a MAP sequence estimation algorithm, and the code is then matched to the mode process corresponding to the estimated switch state. The performance of the two systems is evaluated with quantizers of 4, 8, and 16 levels. The results show that the forward adaptive scheme significantly outperforms optimized fixed DPCM in the sense of meansquared error. Stochastic stability of the code is also established for the fixed DPCM scheme as well as for an adaptive scheme which receives the switch state as side information. © 1994 IEE

Conditional Connectivity Measures for Large Multiprocessor Systems

Introduces a new measure of conditional connectivity for large regular graphs by requiring each vertex to have at least g good neighbors in the graph. Based on this requirement, the vertex connectivity for the n-dimensional cube is obtained, and the minimal sets of faulty nodes that disconnect the cube are characterize

Peer-to-Peer Communication in Wireless Local Area Networks

A new MAC protocol which supports peer-to-peer direct communication is introduced for a packet switched wireless network. Terminals that are located within range of each other and are sufficiently isolated from the base station can communicate with their peers directly without the use of the base station as a relay. Slotted Aloha is used as the access protocol. Throughput and delay of the protocol are evaluated. Numerical results are presented which show that significant improvements in throughput/delay performance can be obtained over a system using slotted Aloha without peer-to-peer communication. Index Terms--- Wireless LAN, MAC protocol, peer-to-peer communication, slotted Aloha, throughput and delay. 2 1 Introduction Interconnection of data terminals to LAN's by means of wireless links allows for flexible location of these terminals, thus eliminating the need for wiring when terminals are added, removed or relocated. Furthermore, the mobility offered by such systems is highly..

Throughput optimization in multi-cell CDMA networks

In this paper, we investigate the performance of a multi-cell CDMA network by determining the maximum throughput that the network can achieve for a given gradeof-service requirement, quality-of-service requirement, network topology and call arrival rate profile. Our analysis is restricted to the reverse link and accounts for mobility of users between cells. A constrained nonlinear optimization problem is formulated that maximizes the network throughput subject to upper bounds on the blocking probabilities and a lower bound on the bit energy to interference ratio. The goal is to optimize the usage of network resources, provide consistent grade-of-service for all the cells in the network, and maintain a pre-specified quality-of-service. The solution to the optimization problem yields the maximum network throughput as well as the maximum number of calls that should be admitted in each cell for a given topology and call arrival rate profile. Our optimization algorithm yields significantly higher throughput compared with traditional call admission schemes. © 2005 IEEE

Convolutional codes for finite state channels

Summary form only given, as follows. Error control strategies for finite-state channels often utilize decoders designed for use over memoryless channels (memoryless decoders). These are used with either specifically designed codes, such as burst-error-correcting codes, or with random-error-correcting codes in conjunction with interleaving. It may be possible, however, to improve the error probability performance of coding schemes by employing decoders which exploit the memory in the channel. Such decoders would utilize, directly or indirectly, the channel state sequence information obtained in the channel output sequence. The notion of state in convolutional codes and the existence of efficient decoding algorithms which are sequential (e.g., Viterbi algorithm) make convolutional codes suitable for adaptation for use with decoders which utilize the memory in the finite-state channel without greatly increasing the concomitant complexity. Several new decoders for the use of convolutional codes over such channels are proposed. The main feature of these decoders is that they can be implemented sequentially on a trellis by a Viterbi-like algorithm. The performance of these decoders is evaluated by simulation and compared with the performance of memoryless decoders with and without interleaving. The results indicate that in cases in which the channel is bursty, these decoders significantly outperform the memoryless decoders. The cost of this improved performance is a somewhat moderate increase in the decoders\u27 complexity

A comparison of two neural network architectures for vector quantization

The authors investigate the performance of two neural network architectures for vector quantization (VQ). The two architectures are the multilayer feedforward network and the Hopfield analog neural network. It is found that for the feedforward network to have reasonably good performance, the number of hidden units must be unrealistically high: exponential in the number of dimensions and codewords. For the Hopfield analog model, on the other hand, the number of processors required is equal to the number of codewords and the resulting performance is very close to the optimum mean squared error

Development and evaluation of new clinical methods of age estimation in children based on the eruption status of primary teeth

Background: Age estimation methods in the permanent dentition are numerous in number and well established and evaluated. However, there exists a dearth of methods available for the estimation of age based on the eruption status of primary teeth, despite various studies displaying greater accuracy using such methods. Aim: The purpose of this study was to develop the methods of age estimation based on the eruption status of primary teeth and based on previous methods developed for permanent teeth and to assess the accuracy of the methods in a clinical situation. Materials and Methods: A total of 50 children were randomly selected between the age group of 6 and 38 months for the assessment of primary tooth emergence in the oral cavity. New methods of age estimation (triangles and regression equations) were developed for used in the Indian population. Results: Data were analyzed using receiver operating characteristics curve and intraclass correlation coefficient. Our results conducted in a validation sample of 30 children suggested high levels of accuracy using the new methods, with greater accuracy displayed using the regressive equation (0.928) as compared to the new triangle of age estimation (0.897). Conclusion: Such methods of age estimation will be of unparalleled importance in rural setups, which cannot afford the luxury of panoramic radiography

Convolutional coding for finite-state channels

We propose new decoders for decoding convolutional codes over finite-state channels. These decoders are sequential and utilize the information about the channel state sequence contained in the channel output sequence. The performance of these decoders is evaluated by simulation and compared to the performance of memoryless decoders with and compared to the performance of memoryless decoders with and without interleaving. Our results show that the performance of memoryless decoders with and without interleaving. Our results who that the performance of these decoders is good whenever the channel statistics are such that the joint estimate of the channel state sequence and the channel input sequence is good, as, for example, when the channel is bursty. In these cases using even a partial search decoder such as the Fano decoder over the appropriate trellis is nearly optimal. However, when the information between the output sequence and the sequence of channel states and input diminishes, the memoryless decoder with interleaving outperforms even the optimal decoder which knows the channel state