J. T. Lim

Joint and tandem source-channel coding with complexity and delay constraints

Two common source-channel coding strategies, joint and tandem, are compared on the basis of distortion versus complexity and distortion versus delay by analyzing specific representatives of each when transmitting analog data samples across a binary symmetric channel. Channel-optimized transform coding is the joint source-channel strategy; transform coding plus Reed-Solomon coding is the tandem strategy. For each strategy, formulas for the mean-squared error, computational complexity, and delay are found and used to minimize distortion subject to constraints on complexity and delay, for source data modeled as Gauss-Markov. The results of such optimizations suggest there is a complexity threshold such that when the number of operations per data sample available for encoding and decoding is greater than this threshold, tandem coding is better, and when less, channel-optimized transform coding is better. Similarly, the results suggest there is also a delay threshold such that tandem coding is better than joint coding when the permissible encoding and decoding delay is greater than this threshold.

Joint and tandem source-channel coding with delay constraints

Two common source-channel coding strategies, joint and tandem, are compared on the basis of distortion vs. delay by analyzing specific representatives of each when transmitting analog data samples across a binary symmetric channel. Channel-optimized transform coding is the joint source-channel coding strategy; transform coding with Reed-Solomon coding is the tandem strategy. For each strategy, formulas for the mean-squared error and delay are found and used to minimize distortion subject to a delay constraint, for data modeled as Gauss-Markov. The results of such optimizations suggest there is a threshold such that when the permissible delay is above this threshold, tandem coding is better, and when below the threshold, channel-optimized transform coding is better.

Dynamics in production-inventory-assembly manufacturing systems

Extending the approach presented in [1], a mathematical model which describes the interaction between production, inventory and assembly subsystems of a manufacturing process is postulated. The model consists of a set of nonlinear, stochastic, difference equations and contains a set of explicit feedback loops from the state variables (inventory stock levels) to the output of the production subsystem. A set of implicit feedback loops from the final assembly to subassemblies is also present. The normalized output of the final assembly is referred to as the production rate.

Performance of Markovian access protocols in satellite channels

The theory developed by J.-T. Lim and S.M. Meerkov (see ibid., vol.COM-35, p.1278-88, Dec. 1987) is extended to channels with long propagation delays. The performance characteristics of Markovian access control protocols in satellite channels are evaluated. It is shown that the channel propagation delay may lead to improvements in systems behavior, i.e. to elimination of the saturation effects and to stabilization of the network in a steady state with relatively high performance characteristics. >

Distributed communications in collision channels with errors

Analysis of distributed communication networks in noisy collision channels is given. Both feedback and feedforward channel errors are considered. Finite number of buffered users is addressed. It is shown that channel errors lead to stabilization of unstable access control protocols, i.e., to elimination of the saturation phenomena and to stabilization of a network in a unique, globally asymptotically stable steady state with relatively high performance characteristics. Thus, channel noise, possibly introduced intentionally, could be viewed as a decentralized stabilizing controller.

Asymptotic analysis of a simple model of an assembly line

A model of an assembly line, consisting of a buffer storage and an assembly workstation, is introduced. It is assumed that the input flow of parts has a random character and the capacity of the buffers is sufficiently large. An asymptotic formula is obtained that evaluates the steady state production rate and the buffer occupancy, given the capacity of the storage. Conversely, this formula may be used for the buffer storage design so that the production rate is maximized.

Source-channel coding strategies: tandem coding vs. channel-optimized quantization

Two source-channel coding strategies, tandem coding and channel-optimized quantization, are compared on the basis of distortion vs. complexity. For each, formulas for the mean-squared error and complexity used to minimize distortion subject to a complexity constraint. The results suggest there is a threshold such that tandem coding is better than channel-optimized quantization when and only when the complexity constraint is larger than the threshold.

Asymptotic analysis of multi-hop networks with Markovian access control protocols

The theory developed by J.-T. Lim and S.M. Meerkov (1987) is applied to multi-hop networks. The effect of coupling between the hops on the degradation of the performance characteristics is investigated using two-hop networks with ALOHA-TDMA and TDMA-ALOHA architectures. The resulting throughput-delay characteristics and the probability of blocking are investigated, and the issue of hop decoupling is addressed.<<ETX>>

Simplified description of slow-in-the-average Markov walks

The averaging theory for the slow Markov walks is extended to the slow-in-the-average Markov processes where the jump vector takes arbitrarily large values with sufficiently small probabilities. The results obtained are important for applications in communication networks and manufacturing systems.<<ETX>>

Asymptotic analysis of adaptive Markovian access control protocols

In this paper, the technique developed in [1], [2] is applied to adaptive access control protocols. Both an adaptive ALOHA-type system and an adaptive TDMA-type system are considered. It is shown that for a large number of users both systems can utilize the same set of adaptation parameters, even though in the adaptive TDMA-type system the switching mode is required in order to achieve the maximum stable throughput. It is also shown that the adaptive TDMA-type system has superior throughput characteristics. In addition, the behavior of adaptive protocols in noisy environment is analyzed and it is shown that the throughput degradation is negligible if the probability of channel error is less than 0.15.