Dispatching rules for scheduling in assembly jobshops - Part 1

Research on jobshop scheduling has tended to concentrate on the development of dispatching rules for jobs that are independent, i.e. single-component jobs. However, in real-life situations, many jobs involve assembly operations that require scheduling of multiple components through the jobshop where both serial and parallel operations take place. In this two-part paper, we consider the problem of scheduling in assembly jobshops, i.e. jobshops that manufacture multi-level assembly jobs. The development of new and efficient dispatching rules with a view to address various measures of performance related to flowtime and staging delay of jobs is first undertaken. A new concept, called 'operation synchronization date' is introduced and made use of in the new dispatching rules. The best existing dispatching rules and the proposed dispatching rules are relatively evaluated by an exhaustive simulation study. The results indicate that the proposed rules emerge to be superior to the existing ones for most measures of performance.     

Dispatching rules for scheduling in assembly jobshops - Part 2

In this part of the paper, we present the development and evaluation of dispatching rules for scheduling in jobshops manufacturing multi-level assembly jobs with the performance measures reated to tardiness. We present a new definition of 'operation due date' in the context of assembly jobs and use it in the development of dispatching rules. A simulation study is carried out to evaluate the performances of the existing and the proposed dispatching rules with respect to different measures of tardiness. We also measure their performances with respect to different measures of flowtime and staging delays. The results of the study indicate that the proposed rules perform better than the existing rules.     

New focusing scheme for DOA estimation of multipath clusters in WiMedia UWB systems without coarse estimation of angle of arrival

Ultra wideband (UWB) systems are expected to coexist with narrowband systems as well as other UWB systems. By estimating the direction of arrival of the multipaths, one would be able to limit the transmission to these directions and limit the interference to other systems. The focussing of subspaces is used to improve the resolution performance in direction of arrival estimation of wideband signals. The focussing matrix is calculated based on initial coarse estimation of DOA. The error in initial estimation results in an irreducible bias in final estimated DOA. By making use of the known pilot signals in Wimedia systems, a new focussing scheme is proposed in this paper that does not require coarse estimation. Computer simulation experiments validating this scheme are also presented. The bias in final estimation is drastically reduced.