With the advances in the technology of micro-electromechanical system (MEMS), developments in wireless communications and WSNs have also emerged. WSNs have become the one of the most interesting areas of research in the past few years. Here, we look into the recent advances and future trends in WSNs.

WSNs are usually composed of small, low-cost devices that communicate wirelessly and have the capabilities of processing, sensing and storing. The development of WSNs was motivated by military applications such as battlefield surveillance. WSN are being used in many industrial and civilian application areas, including industrial process monitoring and control [1, 2], machine health monitoring [3], environment and habitat monitoring, healthcare applications, home automation, and traffic control [1, 4].

A WSN generally consists of a base-station (also called as gateway sometimes) that can communicate with a number of wireless sensors via a radio link. Wireless sensor nodes collect the data, compress it, and transmit it to the gateway directly or indirectly with the help of other nodes. The transmitted data is then presented to the system by the gateway connection.

This paper discusses the recent advances in WSNs that enable a wide range of applications and future development in applications like underwater acoustic sensor systems; sensing based cyber-physical systems, time-critical applications, cognitive sensing and spectrum management, and security and privacy management. Rest of the paper is organized as follows. Section 2 describes the recent advances in WSNs. We discuss future trends in WSN in Section 3. Section 4 describes the research challenges for WSN. Finally Section 5 presents the conclusion.

RECENT ADVANCES

Recent advances in wireless and electronic technologies have enabled a wide range of applications of WSNs in military sensing, traffic surveillance, target tracking, environment monitoring, healthcare monitoring, and so on. Here we describe such type advances in WSN and their applications in various fields.

Sensor Localization and Location-Aware Services

Smart Home/Smart Office

Smart home environments can provide custom behaviors for a given individual. Considerable amount of research has been devoted to this topic. The research on smart homes is now starting to make its way into the market. It takes a considerable amount of work and planning to create a smart home. There are many examples of products currently on the market which can perform individual functions that are considered to be part of a smart home. Several useful applications which take advantage of information collected by WSN are presented in [5].

Military

New and emerging technologies, such as networks, support military operations by delivering critical information rapidly and dependably to the right individual or organization at the right time. This improves the efficiency of combat operations. The new technologies must be integrated quickly into a comprehensive architecture to meet the requirements of present time. Improvement in situation awareness [6] is must requirement. Other important application is detection of enemy units’ movements on land/sea, sensing intruders on bases, chemical/biological threats and offering logistics in urban warfare [7]. Command, control, communications, computing, intelligence, surveillance, reconnaissance, and targeting systems are well described in [8].

Industrial & Commercial

Since the long time wireless transmission of data is being done in industrial applications, but recently it has gained importance. Successful use of wireless sensors in systems such as supervisory control and data acquisition has proved that these devices could effectively address the needs of industrial applications. The critical process applications of WSNs in industry are monitoring temperature, flow-level, and pressure parameters.

With the rapidly increasing technological advances in wireless technology and its subsequently decreasing prices, numerous wireless applications are being developed in industry. WSN in manufacturing industries can monitor and optimize quality control.

Traffic Management and Monitoring

Every big city is suffering from traffic congestion around the world. A sincere effort is being made to solve the traffic congestion. Congestion can be alleviated by planning managing traffic. A real-time automatic traffic data collection must be employed for efficient management of rush-hour traffic. Research on this topic is considered as part of the Intelligent Transport System (ITS) research community. ITS is the application of the computers, communications, and sensor technology to surface transportation [9].

The vehicle tracking application is to locate a specific vehicle or moving object and monitor its movement. This work also describes design of WSN for vehicular monitoring. As the power source (battery) is limited, it is important that a design of sensor node is power efficient.

Structural Healthcare

Structures are inspected at regular time intervals, and repairing or replacing based on the time of use, rather than on their working conditions. Sensors embedded into structures enable condition-based maintenance of these assets [10]. Wireless sensing will allow assets to be inspected when the sensors indicate that there may be a problem. This will reduce the cost of maintenance and preventing harmful failure. These applications include sensors mounted on heavy duty bridges, within concrete and composite materials [11], and big buildings.

Agriculture

Agriculture can also be benefited by the deployment of WSN to get the information regarding soil degradation and water scarcity [12]. With help of WSNs we can check the clean water consumed in irrigation and manage it.

Topology and Coverage Control

Topology control is one of the fundamental problems in WSNs. It has great importance for prolong lifetime, reducing radio interference, increasing the efficiency of media access control protocols and routing protocols. It also ensures the quality of connectivity & coverage and increase in the network service as well. A significant progress in research can be seen in WSNs topology control. Many topology control algorithms have been developed till date, but problems such as lack of definite and practical algorithm, lack of efficient measurement of network performance and idealness of mathematical model still exist.

Several graph models used in topology control, the present hot spots and the future trends on the research of topology control are presented in [13].

Quality of Service (QoS) Provision

QoS support is challenging due to severe energy and computational resource constrains of wireless sensors. Various service properties such as the delay, reliability, network lifetime, and quality of data may conflict; for example, multi-path routing can improve the reliability, however it can increase the energy consumption and delay due to duplicate transmissions. Modeling such relationships, measuring the provided quality, and providing means to control the balance is essential for QoS support.

There are various research opportunities in enhancing the QoS of WSNs. One of the researches is the project described in [14] that analyzes and enhances the performance of a WSN by deploying a simple max-min fairness bandwidth allocation technique.

Mobility management

Mobility is one of the most important issues in next generation networks. As WSNs are becoming the next elements of the future Internet, it is crucial to study new models that also support mobility of these nodes. WSNs are applicable in variety of cases that make it difficult to produce a standard mobility scenario. Following are some cases where the mobile support is necessary [15].

Intra-WSN device movement is probably the most common scenario in WSNs architectures, where each sensor node has the ability to change from its local position at run time without losing the connectivity with the sensor router (SR). In the case of inter-WSN device movement, sensor nodes move between different sensor networks, each one with its SR responsible to configure and manage all the aggregated devices.

A research project of IETF working group NEMO [16] is an example of WSN movement. Sensor network deployed in a moving bus is a real scenario of this type. It is possible to have a scenario where a sensor network can use another sensor network in order to be connected through Internet. MANEMO [17] project is also an example.

Security and Privacy Concern

The field that paid less attention is the privacy concern on information being collected, transmitted, and analyzed in a WSN. Such private information of concern may include payload data collected by sensors and transmitted through the network to a centralized data processing server. The location of a sensor initiating data communication, and other such context information, may also be the focus of privacy concerns.

In real world applications of WSNs, effective countermeasures against the disclosure of both data and context-oriented private information are indispensable prerequisites. Privacy protection in various fields related to WSNs, such as wired and wireless networking, databases and data mining, has been extensively studied in [18]. Effective privacy-preserving techniques are needed for the unique challenges of WSN security.

Biomedical/Medical

The uses of WSNs in biomedical and medical are in growing phase. Biomedical wireless sensor networks (BWSNs) show the future opportunities for supporting mobility while monitoring vital body functions in hospital and home care. There is a requirement for BWSN to develop in order to cover security handling, improved signal integration and visualization. They can also be used to achieve extended mobility outside the surgery room, monitoring of several patients/persons at the same time, and further adaptations to medical experts needs for information.

As the Internet usage has become popular among people, e-services for the healthcare which is commonly known as e-Health, have recently attracted significant attention within both the research society and industry. Followings are several ongoing projects for healthcare using WSN:

CodeBlue [19] – an architecture proposed for tracking and monitoring of patients.

ALARM-NET [20] – a WSN built for assisted-living and residential monitoring.

AMON [21] – a Wireless Body Area Sensor Network System

GlucoWatch G2 [22] – use WSN to research wearable personal health system that will monitor and evaluate human vital signs.

FUTURE TRENDS

The future developments in sensor nodes must produce very powerful and cost-effective devices, so that they may be used in applications like underwater acoustic sensor systems, sensing based cyber-physical systems, time-critical applications, cognitive sensing and spectrum management, and security and privacy management. In this section we will look into all possibilities of further development in WSN applications.

Cognitive Sensing

Cognitive sensor networks are used for acquiring localized and situated information of the sensing environment by the deploying a large number of sensors intelligently and autonomically. Managing a large number of wireless sensors is a complex task. A significant research interest can be seen in bio-inspired sensing [23] and networking. Two well known examples of cognitive sensing are swarm intelligence and quorum sensing:

Swarm intelligence is developed in artificial intelligence for studying the collective behavior of decentralized, self-organized systems.

Quorum sensing is an example of bio-inspired sensing and networking. Quorum sensing is the ability of bacteria to communicate and coordinate behavior via signaling molecules.

Spectrum Management

As application of low-power wireless protocols is increasing, we can envision a future in which wireless devices, such as wireless keyboards, power-point presenters, cell phone headsets, and health monitoring sensors will be ubiquitous. But the pervasiveness of these devices leads to increased interference and congestion within as well as between networks, because of overlapping physical frequencies.

Cognitive radios and multi-frequency MACs are some approaches that have been developed to utilize multiple frequencies for parallel communication. A generic solution is provided by SAS [24]: a Self-Adaptive Spectrum Management middleware for WSNs, which can be easily integrated with an existing single frequency.

The inherent nature of WSNs makes them deployable in a variety of circumstances. They have the potential to be everywhere, on roads, in our homes and offices, forests, battlefields, disaster struck areas, and even underwater in oceans. This paper surveys the application areas where WSNs have been deployed such as military sensing, traffic surveillance, target tracking, environment monitoring, and healthcare monitoring as summarized in Table 2. The paper also surveys the various fields where WSNs may be deployed in the near future as underwater acoustic sensor systems, sensing based cyber-physical systems, time-critical applications, cognitive sensing and spectrum management, and security and privacy management. These application areas are being researched extensively by various people across the industry and academician [7, 9, 22, 24, 28].