System Design Issues

System Design IssuesSystem Design Issues•Product, process, and support life-cycles

System EffectivenessSystem Effectiveness

Design Iteration with System-Design Iteration with System-Level EvaluationLevel Evaluation

• Design processes should ideally consider multiple parameterso Life-cycleo Various technical performance measures

• Potential benefitso Allows trade-offso Correct design problems earlyo More effective designs

• Methodso Concurrent engineeringo Life-cycle engineering

Cont..

Design Iteration with System-Design Iteration with System-Level EvaluationLevel Evaluation

Simple Cost AnalysisSimple Cost Analysis

• System life-cycle costs are a function ofo Design-dependent parameters, e.g. total cost for componentso Design-independent parameters, e.g. labor costs

• Minimum set of cost contributorso Design costs (fixed)o Production setup costs (fixed)o Parts and assembly cost (per unit)o Support costs (per year of utilization)

• Should also consider the “time value of money”o Discount rate allows money spent in future to be compared to

present costs

Cont..

Simple Cost AnalysisSimple Cost Analysis

Life-Cycle Cost ComponentsLife-Cycle Cost Components

• Design costs -- salaries, offices, labs, ...o Conceptual design and specificationo Design and developmento Test and validation

• Production costso Setupo Partso Assemblyo Testo Packagingo Distribution

Cont..

Life-Cycle Cost ComponentsLife-Cycle Cost Components

• Support costso Customer supporto Repairo Diagnosis and repair equipmento Distribution

Example: Design-Independent Example: Design-Independent ParametersParameters

Example: Design-Dependent Example: Design-Dependent Parameters (1)Parameters (1)

•Component and board costs ...

Example: Design-Dependent Example: Design-Dependent Parameters (2)Parameters (2)

•Other design-dependent costs ...

Example: Model SummaryExample: Model Summary•The baseline design ...

Example: Design Alternative 1Example: Design Alternative 1

•Design alternative 1:

oCheaper, but less reliable SRAM part ($3.25 versus $4.25)

oTwo days per year support costs for alternative 1 versus 1 day per year for baseline

•Comparison to baseline Baseline Alternative 1

oSimple total cost per unit: $148 $152

oAdjusted total cost per unit: $125 $129

Cont..

Example: Design Alternative 1Example: Design Alternative 1

Example: Design Alternative 2Example: Design Alternative 2

Cont..

• Design alternative 2:o More expensive, but less complex/more familiar SRAM part

($7.00 versus $4.25)o 3 days hardware design time for alternative 2 versus 4 days for

baseline

• Comparison to baseline Baseline Alternative 2o Simple total cost per unit: $148 $148o Adjusted total cost per unit: $125 $124

Example: Design Alternative 2Example: Design Alternative 2