Mang cam bien khong day wireless sensor network

Wireless sensor network (WSN) is one of the most suitable candidate areas where cognitive radio (CR) technology can be used for opportunistic spectrum access, in the purpose of decreasing significant amount of energy consumption for the whole system. Research in this area is still in its infancy, but it is rapidly progressing. In this project, the basics overview of conventional WSN and CR technology will be provided, and then I investigate the use of CR in WSN in order to show the advantage of CRWSN in saving energy consumption. Some certain prospects and challenges are also illustrated for further development of CRWSN.

Contents

Abstract 2

I Introduction 2

II Conventional wireless sensor network 4

i Sensor nodes 4

ii Common WSNs standards and topologies 5

III Cognitive radio technology 10

IV Cognitive radio-based wireless sensor network 13

i CRSN architecture 14

ii CRSN hardware 15

iii CRSN topologies 16

iv Potential application areas of CR-WSNs 18

V CR-WSNs for energy saving 20

i System model 20

ii Result and discussion 22

iii Conclusion 22

VI Challenges and prospects of CRWSNs 22

VII Conclusion and future work 23

References 23

Abstract

Wireless sensor network (WSN) is one of the most suitable candidate areas where cognitive radio (CR) technology can be used for opportunistic spectrum access, in the purpose of decreasing significant amount of energy consumption for the whole system Research in this area is still in its infancy, but it is rapidly progressing In this project, the basics overview of conventional WSN and CR technology will be provided, and then I investigate the use of CR in WSN in order to show the advantage of CRWSN in saving energy consumption Some certain prospects and challenges are also illustrated for further development of CRWSN

Nowadays, communication networks are indispensable part of human life in modern world They have huge applications, ranging from social networking [1], security networks [2], trade and commerce to educational research and development networks [3] Among the leading area of research and developments in wireless communications are techniques and mechanisms to implement the most cost effective and efficient utilization of radio frequency spectrum and energy Radio frequency is considered as the most vital and scarce resource among all wireless network resources, and it is closely followed by energy consumption, especially in low energy, battery powered sensor network devices [4] However, it has been observed that the scarcity of the frequency spectrum is mainly due to the adoption of a static spectrum assignment policy which gives exclusive right-of-use (RoU) to a licensed user

of a licensed particular spectrum This exclusive right has led to scarcity of spectrum in licensed spectrum band, while in the unlicensed bands where WSNs operate, there will be overcrowding due to increase in the number of users in this band

Recently, Wireless sensor networks (WSNs) have proved itself as one of the most promising technologies for the future [5, 6] A wireless sensor network is a network formed

by a large number of sensor nodes, embedded CPUs, working together to monitor a region

in order to obtain data about the environment Each node is equipped with a sensor to detect physical phenomena such as light, heat, pressure, etc and uses one or more specific wireless communication technologies to form a network [7, 8] WSNs have gained world-wide attention and were much improved in recent years Today, smart grid [9-11], smart homes [12, 13], smart water networks [14], intelligent transportation [15-17], are infrastructure systems that connect our world more than we ever thought possible, the

common vision of such systems is usually associated with one single concept, the internet of things (IoT) [18, 19], where through the use of sensors, the entire physical infrastructure is closely coupled with information and communication technologies WSNs are regarded as a revolutionary information gathering method to build the information and communication system which will greatly improve the reliability and efficiency of infrastructure systems Compared with the wired solution, WSNs feature easier deployment and better flexibility of devices With the rapid technological development of sensors as well as wireless communication technologies, WSNs will become the key technology for IoT

Increasing usage of wireless communications triggered the development of dynamic spectrum access schemes The key enabling technology providing dynamic, i.e opportunistic, spectrum access is the cognitive radio CR is defined as a radio capable of being aware of its surroundings, learning and adaptively changing its operating parameters

in real time with the objective of providing reliable ubiquitous spectrally efficient communication With these capabilities, CRs can operate in licensed bands as well as in unlicensed band CRs have three main features; self-awareness, re-configurability and intelligent adaptive behaviour which help static spectrum allocation and utilization give way

to a dynamic spectrum access and efficient utilization Dynamic spectrum access, allows the unlicensed user (regarded as secondary user-SU) opportunistic use the licensed band belonging to another user (regarded as primary user-PU) while PU is not currently available

As posited by [20], cognitive radio utilizes the underutilized spectrum resources along time and frequency and provides efficient dynamic spectrum access

Leveraging on the advantages of the opportunistic spectrum access provided by CR technology, wireless sensor networks have the potential of operating at lower licensed spectrum band, for example the TV band with efficient spectrum usage and higher energy efficiency due to range extension [21] A CR-based WSN (CRWSN) of CR-based sensor network (CRSN) is multichannel wireless network in which sensor nodes dynamically adapt themselves to the available communication channel [22] The objective of this project report

is to provide a clear picture of potentials of CRSNs, the current state-of-the-art and the research about the energy efficiency in integrating WSN with CR technology

The remained content of the project report is organized as followed In section II and III, the basic concept and specifications of conventional WSN is provided and CR technology are provided CR-based WSN and CRSN architecture including CR sensor node structure and

possible architecture topologies of CRSN will be presented in section IV The follow section will be the challenges and prospects of CRWSN and the last section I state the concluding and further works in the future

Due to recent technological advances, the manufacturing of small and low-cost sensors has become technically and economically feasible These sensors measure ambient conditions in the environment surrounding them and then transform these measurements into signals that can be processed to reveal some characteristics about phenomena located

in the area around these sensors (Figure 1) A large number of these sensors can be networked in many applications that require unattended operations, hence producing a wireless sensor network (WSN).Typically, WSNs contain hundreds or thousands of these sensor nodes and these sensors have the ability to communicate either among each other or directly to an external base station (BS) A greater number of sensors allows for sensing over larger geographical regions with greater accuracy

Figure 1: Conventional wireless sensor network

i Sensor nodes

The sensor node is one of the main parts of a WSN The hardware of a sensor node generally includes four parts: the power and power management module, a sensor, a microcontroller, and a wireless transceiver The power module offers the reliable power needed for the system The sensor is the bond of a WSN node which can obtain the environmental and equipment status A sensor is in charge of collecting and transforming the signals, such as light, vibration and chemical signal, in to electrical signals and then transferring them to the microcontroller, and in each application we use many different kinds of sensors which depend on the property of each project to make sure the system or network working on the highest efficiency and optimal power consumption In fact, I took a research on sensor field, about many kind of sensor but more detailed about temperature, humidity, light, soil moisture sensors…which are available in the workshop such as temperature sensor LM 35, temperature and humidity sensor DHT11 and soil moisture sensor etc

LM 35 Soil moisture sensor DHT11

These sensors are used commonly in simple projects or applications that not required high accuracy and they are very simple to synchronize with MCU

After the sensor sensing the environment, it’ll receive a package of the data, and then it transfers data to the microcontroller processing the data accordingly The Wireless Transceiver (RF module) then transfers the data, so that the physical realization of communication can be achieved It’s important that the design of the all parts of a WSN node consider the WSN node features of tiny size and limited power

ii Common WSNs standards and topologies

The access network, whose length ranges from a few hundred meters to several miles, includes all the devices between the backbone network and the user terminals It is thus aptly call “the last mile” Because the backbone network usually uses optical fiber structure with a high transmission rate, the access network has become the bottleneck of the entire network system Due to the open property of wireless channels, conflicts will happen in time, space or frequency dimension when the channel is shared among multiple users The function of access network technologies is to manage and coordinate the use of channels resources to ensure the interconnection and communication of multiple users on the shared channel

According to the distance and speed of access, existing access technologies can be classified into four categories in Figure 2: wireless local area network (WLAN), wireless metropolitan area network (WMAN), wireless personal area network (WPAN) and wireless wide area network (WWAN)

Figure 2: Existing access technologies

However, the overall developing trend of high transmission rates is not suitable for the application requirements of WSNs The representative access technologies that are more systematic and noteworthy are Bluetooth 4.0 oriented towards medical WSN; IEEE 802.15.4 oriented towards industrial WSN and WLAN IEEE 802.11TM in view of the IoT

In some basic, simple projects and applications such as monitoring temperature, humidity, smoke, light, pressure which not required far distance between nodes or high speed

transmission … we use radio frequency (RF) module, technique which included in IEEE 802.15.4 standard for communicating among nodes or among nodes and BS, with a little bit higher requirement we can use GPRS, 3G technology to upload the data to the base data then the client can access the data from computer or smartphone with internet connected IEEE 802.15.4 is a standard which specifies the physical layer and media access control for low-rate wireless personal area network (LR-WPANs) It’s main standardized technology for low cost, low power, low date rate, short range wireless networks It operates in 3 ISM bands, 868MHz, 915 MHz, 2.4GHz and was seen as the main wireless communication technology for automation and control applications The over-the-air data rates in this standard are 250kb/s, 40kb/s, 20kb/s and use star or peer-to-peer topologies with 16bits or 64bits addressing schema

Every wireless communication devices in a network need to assemble as a “team”, WSNs are the same way In WSNs network, nodes or devices are connected together in several different layouts or topologies to give the network its structure, these topologies define the way the devices are logically connected to each other but their physical arrangement may be different There are some common topologies used in WSNs network such as: Pair, Star, Mesh or Cluster Tree, each of them is used in specific applications and projects to give the best efficiency [23, 24]

Pair topology

This is the simplest network topology with only two nodes or devices One node must be

a FFD or PAN coordinator to form the network and the other can be configured as an end device or a router [23]

Star topology

The star topology network is formed by a FFD - PAN coordinator placed in the centre of the network and surrounded by several RFDs – End devices Any data packet exchange between ends devices must pass through the coordinator, which routes them as needed between devices The advantage of star topology is simple and packets go through at most two hops to the destination but it also has some drawbacks such as; there is no alternative path from the source to the destination and the network totally depends too much on the coordinator so that the coordinator may become bottlenecked

Cluster tree topology

In cluster tree topology, the PAN coordinator of the clusters forms a tree structure, and acts as intermediate aggregators and routers of data between different devices Routers in this topology form a backbone of softs, with end devices clustered around each router and it’s nearly the same as a mesh configuration [23, 27]

Furthermore, several hybrid topologies are being developed and researched for maximizing efficiency of power consumption, routing, and gathering data Depending on the purpose of each project, a WSN uses one or combined wireless communication technologies to exchange data within the network to achieve the highest efficiency of transmitting and energy consumption Table 1 depicts the specifications of some common wireless communication technologies which are usually used in WSN

Specifications

Standards

Working Frequency

Latency

Entries Max data

rate

Application References

ZigBee

868/915 MHz, 2.4 GHz

Up to 1500m

Star, Mesh,

Monitoring Smart girds, home

Smart phone, IoT, Health, Sport & Fitness

Small Star, Mesh,

Tree

Automation, Entertainment Applications

Navigation systems, WMSN, military

Up to

60 Kbit/s

Fitness monitoring [45,46]

Z Wave 15 ISM

bands

40m

Control and sensor applications

[47]

Table 1: Comparison of common wireless communication technologies used in WSN

III Cognitive radio technology

CRs are borne out of a software radio, which is a transceiver whose communication functions are realised as programs running on a suitable processor It comprises all layers to the application layer [48] A software-defined radio (SDR) is a practical implementation of a software radio in which received signals are sampled after a suitable band selection filter instead of directly sampling antenna output If in addition, a SDR can sense its environment, track changes, and react upon its findings, then it is referred to as a CR CRNs can provide high bandwidth wireless communication to users through dynamic spectrum access (DSA)

techniques and heterogeneous architectures In CR terminology, primary users (PUs), also known as incumbent users, are licensed users with legacy rights or higher priority to utilise a particular part of the spectrum Secondary users (SUs), also referred to as cognitive users,

are unlicensed users with a lower priority, and exploit the spectrum opportunistically such that PUs do not suffer harmful interference from them SUs as a result must possess CR capacity, such as dynamic spectrum access techniques, that will allow them to function in the most favourable channel Only users with a tangible legal or regulatory right to spectrum are considered PUs In unlicensed bands, e.g in ISM frequency bands where most of the industrial wireless network technology operates, there are no PUs Despite the perceived importance of some applications, SUs compete equally for the same resource A CRN can be multiband, multichannel, multiservice and multi-standard [48] CR shall give SUs the ability

to (1) detect licensed PUs and evaluate which parts of the wireless spectrum are available for use (spectrum sensing), (2) select the best available spectrum channel (spectrum decision), (3) coordinate access to this channel with other SUs (spectrum sharing) and (4) vacate the channel when a licensed user is detected (spectrum mobility) [49] The dynamic spectrum access operation where CRs use temporarily unused spectrum, also known as white space or a spectrum hole is illustrated in Fig 4

Figure 4: Spectrum holes concept

The two main characteristics of a CR are its cognitive capability and re-configurability

[28]

Cognitive capability: This enables the platform to determine the current occupancy of

the spectrum Information on spectrum utilisation should be available on an on-going basis and updated on the platforms spectrum allocation module in order for the transmission parameters to be set Spectrum sensing approaches can be of two types, wideband and narrowband The accuracy of spectrum access decisions when using wideband sensing is negatively affected by delays in getting spectrum utilisation information Narrowband sensing, however, investigates a small portion of the spectrum and as a result, spectrum access opportunities can be missed Nonetheless, the fast response time of narrowband sensing can more accurately track the dynamic nature of spectrum utilisation

Re-configurability: This enables the configuration of the transceiver’s operating

parameters to be changed in real time without modifying the hardware components that affect the radio transmission Configured transceiver parameters include the operating frequency, modulation type, and error control scheme and transmission power Using MIMO antennas can produce significant increases in spectral efficiently and gives rise to a cognitive MIMO radio that offers the ultimate in flexibility with four degrees of freedom: carrier frequency, channel bandwidth, transmit power and multiplexing gain [50] To provide the above capabilities a new structure for the radio frequency (RF) transceiver is required The

most important parts are shown in Fig 5 These include the baseband processing unit and the radio front end, that in the beginning were proposed for SDRs [51] The RF front-end amplifies, mixes, and performs analog-to-digital (A/D) conversion on the received signal, while the baseband processing unit modulates and demodulates the signal To accommodate the dynamic RF environment, a control bus can be used to re-configure each constituent part A unique feature of the CR transceiver is that it has a wideband RF front-end that can sense over a wide range of frequencies simultaneously [52] The RF hardware should be adjusted to operate anywhere in a large spectrum range and this is leveraged by hardware technologies which include an adaptive filter, a power amplifier and a wideband antenna

Figure 5: Cognitive radio transceiver architecture

There are several advantages of using CR solutions CRs can prolong the useful service life of communication systems by allowing the possibility to change radio configurations on CR equipment that has already been placed into service CR applications that have already been invested in can be ported to new SDR platforms that are more capable It becomes easier to keep up with the rapid evolution of communications standards [53] as base stations and other radios can have their software upgraded Some challenges exist, however, concerning the CR transceiver Receiving transmissions from several radios that operate using different bandwidths, at different power levels and in different locations means that the CR transceiver needs to sense weak signals in a large dynamic range, which is a major design problem [51]

IV Cognitive radio-based wireless sensor network

CR-wireless sensor networks (CR-WSNs) are a specialized ad hoc network of distributed

wireless sensors that are equipped with cognitive radio capabilities CR-WSN is different in many aspects with a conventional WSN and conventional distributed cognitive radio

networks (CRNs) The following section details the differences in the aspects among ad hoc

CRNs, WSNs, and CR-WSNs CR-WSNs normally involve a large number of spatially distributed energy-constrained, self-configuring, self-aware WS nodes with cognitive capabilities They require cognition capacity for a high degree of cooperation and adaptation to perform the desired coordinated tasks They have not only to transfer data packets, but also to protect incumbent license users More explicitly, this is a system that employs most of the capabilities required for a CR system, as defined by International Telecommunication Union (ITU) [54] and also for WSNs

According to Akan et al [55], a CR-WSN is defined as a distributed network of wireless

cognitive radio wireless sensor (CRWS) nodes, which sense an event signal and collaboratively communicate their readings dynamically over the available spectrum bands

in a multi-hop manner, ultimately to satisfy the application-specific requirements

Figure 6: CR-WSN model

In CR-WSNs, a wireless sensor node selects the most appropriate channel once an idle channel is identified and vacates the channel when the arrival of a licensed user on the channel is detected The cognitive radio technique is probably one of the most