Improvement of wireless and sensing technology enabled the design of a new network technology called Wireless Sensor Network (WSN). However, its applications are greatly limited due to the resource constraint nature of wireless sensor nodes and the lack of flexibility in protocol design. Until recently, almost all the WSN protocols were developed for different layers independently based on traditional OSI layered architecture. Nowadays, researchers are envisioning optimized resource utilization by breaking the barrier of layer abstraction. In this chapter, the authors present basic concepts of layered architecture design and its pros and cons for WSN applications followed by a survey on different applications of Cross-Layer Design (CLD) in WSNs. All the different techniques used for CLD are also discussed in detail. They then highlight some guidelines provided for stable and efficient cross-layer design. Finally, the authors indicate some open issues to show the future direction of research in cross-layer protocol design for WSNs. They conclude the chapter with a great hope that the CLD will have widespread use in next generation WSNs communication.
TopIntroduction
In recent years, wireless technologies have improved significantly in terms of cost, size, and efficiency. Microminiaturization has enabled the designing and fabrication of very small sized and low cost wireless sensor nodes (Akyildiz, et al., 2002a). These sensor nodes are designed to be very efficient, and the applications and protocols designed for them can function with limited amount of energy (Akyildiz, et al., 2002b). This advancement has spiraled into the development of a new network technology, called Wireless Sensor Network (WSN) (Akyildiz, et al., 2002b; Karl & Willig, 2003). In a WSN, the nodes sense the environment and communicate with one another through the wireless medium with certain objectives.
A WSN consists of very small-sized nodes (a.k.a “motes”) having sensing, computation and wireless communication capabilities, and powered by small amount of energy unit. They have constraints on storage capacity, computation power and energy supply. In spite of these constraints, the WSNs have been envisioned to be used in a wide range of application domains such as surveillance, inventory system, environmental observation, event forecasting, health monitoring, habitat monitoring and military (Akyildiz, et al., 2002b). Despite the potential applicability of WSN, their actual use in solving real-life problems have been greatly limited due to different constraints on the network as a whole, the nodes that constitute it and the protocols and algorithms that are executed on them (Jambli & Tully, 2007). The adoption of conventional layered communication architectures that are akin to the conventional OSI model can help in handling the communication challenges in WSNs as well (Kawadia & Kumar, 2005).
In a layered architecture, there exist a series of layers endeavoring to reduce the complexity of the network by splitting it into smaller modules with different functionalities. Each layer receives certain services from the lower layer and offers certain others to the higher layers. This enables the shielding of other layers from the details of how the services are implemented in a specific layer. In order to meet these requirements, exhaustive research has been done to design protocols for supporting functionalities in different layers. Most of the communication protocols proposed so far have simple computation requirements and improved energy efficiency characteristics.
The layered design has many disadvantages like non-adaptive and non-optimized. In this regard, the network architecture and the protocol design based on cooperative approaches between layers, called Cross-Layer Design (CLD), shows a promising alternative to help solve some of the inefficiencies of the layered design.
In fact, a recent trend on research to develop protocol using multilayer integration and design techniques has shown a significant improvement in terms of energy conservation and efficiency. The issues are even more challenging in WSNs because of limited energy and computation power (Mendes & Rodrigues, 2011; Vuran, et al., 2005; Hoesel, et al., 2004; Safwat, et al., 2003). A considerable amount of work has been done using cross-layer design on different issues of WSNs such as resource allocation and optimization, network lifetime and throughput maximization, providing real-time heterogeneous packet transmission, error control, adaptive routing, target tracking, and security. However, a systematic classification of different applications based on cross-layer design is still missing. Keeping all these perspectives in mind, this chapter is written with two objectives. The first is to present a brief overview of the CLD approaches. In doing so, we make an overview of layered architecture used in WSN. Then, we present the advantages or stipulations of CLD over layered design in WSN. We discuss basic types of CLD techniques used in WSN with examples taken from literature. Finally, we present some concerns and precautionary guidelines regarding CLD in WSN. Our second objective is to present a brief survey on different applications of CLD in WSN. In doing so, we take stock of ongoing works and try to put in perspective to categorize them based on their application. We then draw attention to few potential open problems and new opportunities for CLD in WSN.