## 3 Integrated Method for SoS Architecture Selection and Reconfiguration
### Architecture Reconfiguration Process and Enablers  
Consistent with the decisions at the design time, the reconfiguration decisions at the operational phase primarily considers re-arranging the architecture, including re  
Figure 1: SoS architecture and potential reconfiguration options analysis.  
connecting operational activities, re-connecting systems, and re-allocating systems to activities when disruptions occur and performance degrades, as illustrated in Figure 1. The reconfiguration decisions are constrained by the reconfigurability of the designed architecture and are expected to recover SoS performance responsively.  
An architecture reconfiguration example is illustrated in Figure 2. If disruptions occur to system Sys2 that consist of sense (S in Figure 2), decide (D in Figure 2), influence (I in Figure 2, referring to firing/striking) functions and fail Sys2, the performance of function/activity FcnS2 would be degraded. In this case, the surviving systems can be re-allocated to the operational architecture to recover partial SoS capability. Meanwhile, the connections between systems might change accordingly to optimize the information exchange process.  
The reconfigurability of the initial architecture is a prerequisite quality for conducting SoS architecture reconfiguration. Many factors can influence reconfigurability, such as function redundancy, function capacity, system redundancy, communication bandwidth, communication type, reconfiguration cost, ease of reconfiguration, and willingness of re-configuration.  
Function redundancy indicates the number of alternative ways in an SoS to perform a particular function. For example, long-range detection of an air threat can be performed by early warning aircraft, fighters, patrol aircraft, ground-based radar, etc. Function capacity is a system-level ability that affects the number of functions/activities to be supported simultaneously by a particular system. For instance, a phased array radar could support the target searching function and target tracking function at the same time. System redundancy refers to the number of the same backups for a system in an SoS; this is one of the most commonly applied methods for reliability and resilience.  
Figure 2: SoS architecture reconfiguration process.  
Communication bandwidth influences the reconfiguration because different activity-system mapping and system-system connections differ in their requirements for bandwidth resources. Communication type determines whether two systems can be re-connected. If two systems are equipped with different types of communication links (e.g., Link 16, satellite communication), they cannot be connected during reconfiguration.  
Reconfiguration costs affect reconfigurability from the perspective of economic constraints. Ease of reconfiguration that depends on the physical and control structure of component systems can influence the rapidness of the reconfiguration process. The modular open system approach (MOSA) that has been advocated again by the U.S. DoD explains the two important prerequisites for the ease of reconfiguration--modular design and open standard. Willingness of reconfiguration is a special SoS consideration due to the operational and managerial independence of the constituent systems. If a participant refuses to reconfigure the current structure, the reconfiguration process affected by this participant cannot proceed. This paper does not plan to include all the enablers because some factors impact the reconfiguration in similar ways and it is difficult to explain the results when too many intertwined factors are involved.