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(More customer reviews)Of the plentitude of topics covered in this book, the overarching theme is that energy efficiency is the most important property of a wireless sensor network [WSN]. A typical WSN has sensor nodes deployed with very limited energy. The only exception tends to be when nodes have solar panels, but as the reader will see, this is considered by the editors to be a rare instance of a WSN. The book points out that a TCP/IP implemention of a WSN can be prone to energy overuse, since TCP was never designed with energy efficiency as a constraint.
Chapter 5 has a good explanation of Medium Access Control, including the important case of the hidden terminal problem. Overhearing is also a significant problem. This is where a node listens but has no data to transmit. The act of listening on a wireless channel consumes as much energy as transmitting. The typical solution is for nodes to periodically or even most of the time to sleep, to minimise the active duty cycle when the antenna is on.
Reservation based protocols seem best, out of the various protocols in Chapter 5, because of collision free communication. This is aided by the common case of many WSN nodes having little data to transmit. However the book warns that the disadvantages are higher latency and overhead, compared to contention based protocols.
Chapter 7 on the network layer suggests that the simplest algorithm is to flood. Gossiping is more efficient but can be much slower. However, a hierarchical protocol is often needed, to avoid exhaustion of nodes near the sink, as they are involved in relaying messages from nodes that are further away. The answer to go to a set of clusters, and only the cluster heads in each cluster are involved in relaying messages between clusters and to the sink.
The transport layer is discussed in chapter 8. The main idea is that messages from the sink to a node need to be reliable, though the latency can be long, with no dropped messages. These messages are often control commands. However, messages from a node to the sink can tolerate losses, since there is often a redundancy in such data coming from nearby nodes.
Chapter 9 on the application layer looks at trying to reduce the amount of data sent by nodes. Savings in reduced transmission energies often are greater than the cost of increased computational energy at the nodes doing the data compression. Where possible, in-network processing should be done.
The idea of a WSN is extended to a Wireless Sensor and Actor Network [WSAN] in chapter 14. The actor refers to nodes that can perform actions, like follow a target object. As can be seen, an actor could be mobile, unlike a typical stationary sensor node. Also, an actor is likely to have more computational power and memory and communication bandwidth. The actors let the network close a control loop.
Chapter 15 covers a wireless multimedia sensor network. These sensors might be directional, instead of scalar [omnidirectional]. The best example is where a sensor is a camera in the visible wavelengths. Such sensors have an orientation and also perhaps a focal length that can be varied; ie. a dynamic field of view is possible. The control logic for such sensors can be quite involved.
The chapter also raises an intriguing idea. It talks about Multiple Input Multiple Output [MIMO] abilities, where sensors close to each other form a joint antenna. Each sensor acts as 1 antenna in a composite MIMO approach. Very complex, and it is unclear if anyone has yet to implement such a network.
Chapter 16 on wireless underwater sensor networks has an error on page 401 - "In contrast to electromagnetic waves, optical waves do not such from such high attenuation". Well, optical waves are indeed also electromagnetic radiation.
This book could usefully be read in conjunction with another recent text, Mobile Intelligence (Wiley Series on Parallel and Distributed Computing). While the latter concerns mostly cases where the nodes are mobile, there are many overlaps in problems encountered. And notably, energy efficiency is also the most common constraint in both types of networks.
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This book presents an in-depth study on the recent advances in Wireless Sensor Networks (WSNs). The authors describe the existing WSN applications and discuss the research efforts being undertaken in this field. Theoretical analysis and factors influencing protocol design are also highlighted. The authors explore state-of-the-art protocols for WSN protocol stack in transport, routing, data link, and physical layers. Moreover, the synchronization and localization problems in WSNs are investigated along with existing solutions. Furthermore, cross-layer solutions are described. Finally, developing areas of WSNs including sensor-actor networks, multimedia sensor networks, and WSN applications in underwater and underground environments are explored. The book is written in an accessible, textbook style, and includes problems and solutions to assist learning.
Key Features:
The ultimate guide to recent advances and research into WSNs
Discusses the most important problems and issues that arise when programming and designing WSN systems
Shows why the unique features of WSNs – self-organization, cooperation, correlation -- will enable new applications that will provide the end user with intelligence and a better understanding of the environment
Provides an overview of the existing evaluation approaches for WSNs including physical testbeds and software simulation environments
Includes examples and learning exercises with a solutions manual; supplemented by an accompanying website containing PPT-slides.
Wireless Sensor Networks is an essential textbook for advanced students on courses in wireless communications, networking and computer science. It will also be of interest to researchers, system and chip designers, network planners, technical mangers and other professionals in these fields.
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