You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Review of Protocol Implementations and Energy Efficient Cross-Layer Design for Wireless Body Area Networks 
Chapter Title:  Layering as Optimization Decomposition 
1. Abstract of Cited Paper (BIB001):  This book presents an in-depth study on recent advances and research in Wireless Sensor Networks (WSNs). Existing WSN applications are described, followed by discussing the ongoing research efforts on some WSNs applications that show the usefulness of sensor networks. Theoretical analysis and factors influencing protocol design are highlighted. The state-of-the-art protocol for WSN protocol stack is explored for transport, routing, data link and physical layers. Moreover, the open research issues are discussed for each of the protocol layers. Furthermore, the synchronization and localization problems in WSNs are investigated along with the existing solutions and open research issues. Finally, the existing evaluation approaches for WSNs including physical testbeds and software simulation environments are overviewed.

Literature Review:
This method of cross-layer design effectively dispenses with the traditional protocol stack and replaces it with a completely new architecture. Layering as optimization decomposition is a concept that effectively decouples the traditional protocol stack and provides a framework for cross-layer design BIB001 . In this method the traditional protocol stack is dispensed with and replaced by a single integrated solution. The research by Chiang et al. BIB001 positions this theory as carrying out an asynchronous distributed computation over the network to implicitly solve a global optimization problem modeling the network. The theory exposes the interconnections between layers as different ways to modularize and distribute a centralized computation. Separate vertical decompositions (functions) of an optimization problem in the form of a generalized network utility maximization (NUM) are mapped to a layer or the interfaces between specific layers. The NUM can take the form of vertical or horizontal decomposition. Vertical decomposition: entails the decoupling of the protocol stack where network protocol functions such as energy detection, congestion management, routing, error control etc are coordinated as part of modules that perform the same functions as the separate layers. Horizontal decomposition: can be carried out to further optimize and control the functional layer interaction. The net effect of this is to decompose the optimization problem into sub-problems each associated or mapped to a specific protocol layer with defined functions managing the interfaces between the layers. Layering as Optimization Decomposition presents a "clean sheet" approach to the design of a protocol stack. Chiang et al. positions the theory as being outside of and separate to the existing research on cross-layer design. However, Layering as Optimization Decomposition does not supersede the need for cross-layer design. The decomposition process involves the development of modules that retain coupling between layers and could be seen as justifying the requirement for cross-layer design BIB002 . The need for cross-layer design solutions is reinforced in cases of architecture mismatch between an existing protocol stack and an optimal decomposition method. Layering as Optimization Decomposition provides a top down approach to designing network architecture from first principles. The resulting conceptual simplicity stands in contrast to the ever increasing complexity of communication networks  . Although the case for Layering as Optimization Decomposition is still to be fully made in terms of its practical application, it can provide benefits for the modeling of a decomposition scenario in providing a direct comparison to an existing protocol stack identifying which layers to integrate.