Total System Delay Research Articles

Scheduling Interdependent Waterway Projects through Simulation and Genetic Optimization

The evaluation, selection, sequencing, and scheduling of lock reconstruction and rehabilitation projects is a major concern for inland waterway systems. As traffic increases and existing lock conditions deteriorate, users suffer substantially longer processing times and delays. Lock projects tend to be interdependent as improvements at one lock may shift bottlenecks elsewhere. A generalized waterway simulation model that is independent of network geometry was developed to evaluate the system over a multiyear planning horizon. A genetic algorithm was also developed in order to efficiently explore the solution space of this large investment optimization problem. The proposed combination of two stochastic models can solve selection, sequencing, and scheduling problems for interdependent projects in large waterway networks but requires long computation times. Due to lock interdependency, the benefits of multiple projects are not directly obtainable by adding individual project benefits; they are measured from the marginal increment of total system delays. The results show how interdependent projects should be scheduled and how operational lock control improvements can sometimes improve delays significantly without requiring major construction investments.

High-performance DSPs

The processing delay is a serious constraint for speech communication. A one-way end-to-end delay of more than 150 ms can severely degrade the quality of real-time conversations. The components of the total system delay includes the speech frame size, the look ahead, other algorithmic delays, multiplexing delay, processing delay for computation, and transmission delay. At the transcoder rate adaptor unit (TRAU), the only delay that can be manipulated is the processing delay. The TRAUs are generally positioned remote to the base transceiver station (BTS). The channel codec units (CCUs) are located in the BTS. In general, 16 kbit/s traffic channels can be used for full rate speech between the TRAU and BTS. By putting the TRAU remote to the BTS, DSPs for speech coding can be utilized more efficiently to cut system cost. High performance DSPs, such as the Lucent DSP16000, can be used to further cut the cost per speech channel. This article presents an implementation of GSM enhanced full rate (EFR) codec on the Lucent Technologies' DSP16000. The original European Telecommunications Standards Institute (ETSI) C code has been restructured to address the issues of MIPS (million instructions per second), RAM usage, and processing delay. We give a performance overview of vocoder implementations on some existing fixed-point DSPs and discuss the architecture of the DSP16000. Details on how the ETSI C code is restructured are presented. The DSP16210 implementation results are then discussed.

Lead/Lag Dynamics to Compensate for Display Delays

Problems of control produced by delays in flight simulators are reviewed and related data that were available from an earlier experiment are analyzed. That study used a lead/lag transfer function to compensate for delays inserted into a closed-loop system, and pilot control performance was measured using various amounts of lag for a given setting of lead. Those data indicated that—based upon the changes of phase and gain associated with subjects' best control performance—an optimal ratio of lead to lag could be determined. Best performance was produced by a maximum phase lead of approximately 0.08 deg per 1 ms of delay for total system delays greater than 175 ms.