Wireless Sensor Networks Challenges and Solutions

Abstract

In this field, many research works have been done. And there is still emerging and trending domain for all researchers. Sub domains are also interested like WBAN, WPAN etc. as well as advance domains of this WSN is also interested and trending topic as IoT, IoE etc. In this fifth generation, IoT is everywhere. So, researchers can easily research on this topic and publish paper. Although advancement of this domain have been trending, but core WSN has many issues as disadvantages. Such as, it has seven layers. Each and every layer has many issues as challenges like simulator tools are very old configuration and simulator softwares are becoming obsolete. Hardware issues are there like devices should be supported with computer. Another important issues are sensor battery, energy consumption etc. Rather than those issues, most serious issue is security, because the lack of privacy constraints.

1. Introduction

A sensor based network system that performs wirelessly has given birth to the coinage ‘Wireless Sensor Network’ or simply ‘WSN’. ‘WSN’ [1] has become essential in many fields including infrastructure, healthcare, agriculture, environment, military defense, automation and so on.

As technological advancement is gaining its momentum day by day, it has been trying to replicate some of the biological receptive and cognitive faculties in order to develop more intelligent devices and systems to overcome real world hindrances. Thus ‘sensors’ [2] are used to imitate human sense organs to collect information about certain physical parameters like temperature [3], light, speed, movement, moisture etc. for any desired action taken thereafter.

Wireless Sensor Network is a system for the transmission of data through such a networking process which is independent of any physical cables. Here the sensors deployed receive some physical quantities like temperature, pressure, sound, humidity etc. from the environment and process them. They not only monitor the sense but also have the communication capability. Thus we can define Sensor as a device which measures any physical quantity and converts it to such a format which an observer or an instrument can understand (Figure 1).

Figure 1.

Brief structure of WSN.

2. Architecture of WSN

A wireless sensor network [4, 5, 6, 7] consists of Base station and many sensor nodes. The primary constituent of a Wireless Sensor Network is a cluster of interconnected sensor nodes. Wireless sensors are highly distributed, lightweight nodes deployed in large number to monitor the environment or system. These sensors constitute a network which is distributed on ad-hoc basis, which means they work on wireless connectivity and sensor nodes are fitted with on board processor.

These sensor nodes can have many features namely Sensor Subsystem, Processing system and Communication System. Now we are going to discuss these features briefly.

1. Sensor Sub-system: This is a combination of proprioception, visual, audio, inertial and tactile units. Proprioceptors are the sensory receptors which receives stimuli from within the body, especially one that responds to position and movement. Visual unit comprises high speed and high definition cameras. Similarly an audio system equipped with microphones, inertial measurement unit, force sensitive resistors are used to construct the sensor subsystem.

2. Processing system: The processing unit comprises Microcontroller unit (MCU), Memory and an operating system. The MCU performs computations on the received data, computes the next hop to the sink, controls and monitor battery power etc. In the Memory part program code is stored and it computes the procedure by nonvolatile RAM. Sensor uses operating systems like Contiki, TinyOS etc.

3. Communication system: Here data are exchanged between the sensors through radio transceiver. This unit receives query and transmits the processed data from MCU to the devices.

4. Power generator – It provides energy for sensor node and has two parts within namely Battery and DC-DC converter.

Optional components –

1. Location finding system: This system comes into use if the user requires the knowledge of location with high accuracy.

2. Mobilizer: It is needed to move sensors when it is required to carry out the assigned tasks based on its decisions on its mission depending on the routing algorithms used.

On the other hand Base Station is an end point device that gets all the processed data from the sensor nodes and it performs aggregation as well as fusion for the purpose of analysis and controlling it.

Now we will see how a wireless sensor network works. A number of interconnected sensor nodes are arranged and rearranged to make a group and it is connected to a Base Station. As mentioned earlier, Base Station acts as the terminal point of a sensor network system and collects all the information from the group of sensor nodes. This Base Station is eventually linked to the internet. There could be other sensor node- Base Station systems connected to the internet. Thus a complex network of sensors are formed to get various data communicated through the internet so that the information can be used for different purpose according to the user’s need like processing, mining, storing or analysis (Figure 2).

Figure 2.

Architecture of WSN.

3. Different kinds of wireless network

Network means a group of devices interconnected to perform specified task. To achieve that purpose we have two distinct technologies namely ‘wired network’ and ‘wireless network’. Between these two, ‘wireless network technology’ is often preferred in terms of flexibility, user mobility, network access and so on. In ‘wireless sensor network’ data is transferred through radio frequency unlike a wired network where data transmission takes place through Physical cables. There are different types of wireless network system in vogue depending on the data rate or coverage area (Figure 3).

Figure 3.

Different kinds of WSN.

W-WAN (Wireless Wide Area Network):-

As the name suggests, this is a network system that can provide long distance transmission of data, voice, image and video information over a large geographical area. The range of W-WAN is beyond 100 km. This kind of network is used in GSM, telephonic calls, surfing web pages etc.

Technologies used in W-WAN:

1. ISDN (Integrated Service Digital Network) – It is one of the technologies that is used to transmit data, voice and signaling and it is a circuit-switched telephone network system. It is well known for providing better speed and quality than traditional connections.

2. SMDS (Switched Multimegabit Data Service) – It is a packet-switched telecommunication service and is designed for high speed broadband networking technology.

3. SONET (Synchronous Optical Network) – It is a communication protocol used to transmit a great amount of data over large distances.

4. HDLC (High Data Link Control) – This is a data link protocol and data is organized into frames those are transmitted through the network to the destination that verifies its successful arrival.

5. SDLC (Synchronous Data Link Control) – An error-free movement of data is possible between the Network Addressable Units within a given communication network through this protocol.

W-MAN (Wireless Metropolitan Area Network):

This is a wireless network system which has the capability to cover an area of approximately the size of a city and it sits somewhere between W-LAN and W-WAN. The connections can be point to point or point to multiple networks.

W-LAN (Wireless Local Area Network):

A wireless LAN is a wireless computer network two or more devices using wireless connection to form a local area network within a limited area such as home, school, computer laboratory, campus or office building.

W-PAN (Wireless Personal Area Network):

A personal area network is a computer network for interconnecting electronic devices within an individual person’s workplace. A PAN provides data transmission among devices such as computers, smartphones, tablets [8] and personal digital assistants.

4. Application of wireless sensor network

With the advent of new technology like WSN a plethora of areas in modern civilization has been redefined with newer prospects. WSN is introduced in the following applications:

1. Battlefield – Surveillance and monitoring the movement of enemies and own military forces.

2. Disaster relief operation – receiving data and analyzing situation of the affected area.

3. Environmental use – monitoring different environmental parameters of a particular region like temperature [9], air pressure, rain etc.; tracking related data of flora and fauna of certain biosphere.

4. Agriculture – monitoring data regarding soil, weather, irrigation for agricultural use.

5. Health care [10]– monitoring patients’ physical condition and giving necessary feedback in alarming situation.

6. IoT [11, 12]– The Internet of Things works on the basis of physical world of devices and objects connected over the network using the wireless sensors.

4.1 Challenges of WSN

In spite of their highly practical usefulness there are some challenges [13] in wireless sensor network system –.

1. Scalability – There are a vast difference in scale of such sensor networking system as the number of sensor nodes may vary from few to several. Added to this the deployment density is correspondingly adjustable.

2. Energy efficiency [14, 15]– As wireless sensor nodes have to work on a limited power supply, the designing of the software and the hardware has to be so optimized that it can perform efficiently the designated job.

3. Maintenance [16, 17] – WSN has several constraints like power supply, storage, large amount of algorithms, so there is a serious challenge in maintenance of all these.

4. Security [18] – Like all internet dependent applications, WSN also has insecurity scare. Proper data transmission management should be adopted to counter data theft by every possible way.

5. Quality of service – The data must be provided in time as the real time based applications heavily dependent on the timely distributed data.

4.2 Advantage of WSN

It is scalable and can accommodate any new node or device at any home. It is flexible and open to physical partitions.

• All the WSN nodes can be accessed through a centralized monitoring system.

• WSN can be applied on large scale and in various domains such as mines, agriculture, health care and so on.

• It uses different security algorithms as per wireless technologies and hence provide reliable network for customer user.

Disadvantage of WSN:

• It cannot be used in high speed communication as it is designed for low speed application.

• It is quite expensive to build such network, so cost-effectiveness of such system may be a concern for some users.

• WSN has limited computation and communication resources. It is prone to security threat.

5. Research issues on WSN

In this field, many research works have been done. And there is still emerging and trending domain for all researchers. Sub domains are also interested like WBAN, WPAN etc. as well as advance domains of this WSN is also interested and trending topic as IoT, IoE etc. In this fifth generation, IoT is everywhere. So, researchers can easily research on this topic and publish paper. Although advancement of this domain have been trending, but core WSN has many issues as disadvantages. Such as, it has seven layers. Each and every layer has many issues as challenges like simulator tools are very old configuration and simulator softwares are becoming obsolete. Hardware issues are there like devices should be supported with computer. Another important issues are sensor battery, energy consumption etc. Rather than those issues, most serious issue is security, because the lack of privacy constraints. Some main challenges are followed as:

1. Node deployment:- In WSN, sensor node deployment is the main challenge. Deployment should be always in proper way. If useless deployment is there i.e. in any vital area, there is needed more sensor to collect data, but rather that important deployment, remote area is getting more sensor which is totally useless.

2. Selection of Relay node:-Sometimes, sensor data is sent from source to destination (sink/base station) for collection of information. To get shortest path, sometimes source nodes information are sent through via node(relay node) to destination. To choose this relay node and shortest path, various methods must be followed. This is very hectic process to choose which method is best for this purpose. And this is very time consuming.

3. Selection of cluster head:- Like relay node, cluster head selection is very challenging. Because, some area has grouping node deployment. In that case, Cluster nodes, cluster node size, cluster head should be selected to send data to coordinator (base station). Basis on this selection, routing protocol has been designed.

4. Energy consumption:- WSN is based on sensor node. So, if sensor node battery is dead, communication will be disrupted. Therefore, battery power is needed to save for longtime rather consumes more energy.

5. Security issues:- In this domain, this is a big issue. Anytime any data can be lost, hacked, misled via attacker. Malicious nodes, corrupted messages are also treated as security issues.

6. Heterogeneity:- Sometimes this is very much confused, at where in which node structures are needed. For health monitoring purpose, heterogeneous nodes are preferable.

7. Pathloss:- To get multipath for sending data in shortest way, many problems have been faced. Most of those, pathloss is very crucial problem. This is not only happened with multipath but also happened with single/direct path.

8. Delay:- During data transmission, messages communication, time is very critical measurement. Because, a nanosecond delay in WSN means a lot. Message deliver, acknowledgement can be failed due to this delay.

9. System failure:- Primary reason behind this is hardware-software failure, physically damage sensor node etc. Both client server architecture in WSN may face this type of situation.

6. Effective solutions

Although this field has so many issues, but still researchers are trying to solve those problems doing researches on it. Advance Simulator with compatible hardware, devices are being upgraded by computer engineers, so this will be helpful to research work and researchers do many update researches on WSN. More or less, researches are trying to put idea about network lifetime of sensor battery. Also, they are making cryptography algorithm to provide more security about field. Some solutions are given as followed below:

1. Node deployment structure should be maintained non-adhoc network structure i.e. well organized way and well planned protocol manner.

2. Relay node selection should be based on Euclidean distance manner i.e. equal distance from relay to source node should be followed.

3. Cluster head node selection should be based on k-means clustering, KNN algorithm. Other better algorithm can be fitted.

4. Energy consumption can be less and it can be happened due to following multi hop routing protocol. If shortest path is chosen, then energy can be less consumed. It is direct proportional to network lifetime. So more energy saving means more longevity of sensor battery node and as well as total network longevity.

5. To give security, data confidential, data integrity, data authentication concept is there. To stop stealing data, data should be kept in confidential way using cryptography techniques. Some mechanisms such as verification should be implemented to check for authenticated data. Data integrity always check receiving data is matched with previous sending data or not.

6. Fault tolerance is the technique to tolerate all types of failure within WSN, it measures failure of the system.