Overview Of Wireless Sensor Networks

Published Date: 02 Nov 2017

The patients are providing with well-located health amenities at very less price has been a great challenge for health service providers. In the present world, the rapid changing life style and the cause of aging society pose an emergency requirement to modernize such amenities. It involves devising cheaper and smarter ways of providing healthcare to victims of age related illness. As well, stress has to be paid on providing health monitoring in out-of-hospital conditions for older individual and patients who need regular supervision, especially in remote access. In national healthcare services, trends are expected to include shorter hospital stays and good community care.

Even though, it is difficult to provide a healthcare monitoring and assistance services without any bother and interference reasoned by the measuring equipment, older peoples and patients are always monitored both at home and hospital ecology by wireless specific network technology. The above technology satisfies the needs of ‘wireless health state monitoring, including minimum intervention by medical health professionals. In this kind, ecology is built by using wireless sensor network (WSN) technology, which allows the coverage area of single wireless network to be elaborated by specific network technology, competent of handing over wireless information to adjacent wireless networks.

1.2 Overview of Wireless Sensor Networks

It is defined as a network of devices which is called as nodes. It sense given objects/ entities and communicate the sensed data via wireless links. The data is transmitted through a single hop/ multi-hops, to a base station or PDA/cell phone, which can be connected to other networks, for example, Internet.

A wireless sensor node consists of one/ more sensors for sensing physical variables, main processing unit, analog-to-digital converter (ADC), flash memory, and RF transceiver. It has limited power source.

The Figure 1 presents, the basic elements of a typical wireless sensor node. Most WSN nodes use an 8051 microcontroller as their main processing unit because of its less price and low power consumption in addition to their limited size.

According to Chai & Yang (2008), some systems use the SOC (system on chip) like CC2430 which includes the ADC, flash memory, and RF transceiver. Because of the small size of SOC, one develops a small and low power sensor node; but its limitations are the low quality of ADC and small memory size. Some sensor nodes are developed by using a microcontroller unit (MCU), like MSP430F1611 and Atmel with external RF transceiver. The Other developers use MCU with external ADC/ external extra flash memory to achieve higher quality of service.

1.3 Combining telecommunication and information technology for medical practice

Telemedicine is an emerging technology which combining telecommunication and information technology for medical practice. It gives a new way to deliver health care services when the distance between doctor and patient is significantly away. Telemedicine can deliver health care services to the patient even in remote area.

According to Pavlopoulos et al. (1998) has presented an example of telemedicine advantage with execution on ambulatory patient care at remote area. As per Sudhamony et al. (2008), another application has been done for cancer care in rural area. In surgery, high technology telemedicine application has been developed by Xiaohui et al. (2007).

Currently, the telemedicine uses available wired and wireless infrastructures. Telemedicine infrastructures was suggested by Al-taei (2005), with wired network by using Integrated Service Digital Network (ISDN), Asynchronous Transfer Modes (ATM) by Cabral & Kim (1996), Very Small Aperture Terminal (VSAT) by Pandian et al. (2007) and Asymmetric Digital Subscriber Line (ADSL) by Ling et al. (2005). Telemedicine has been executed in wireless network using Wireless

LAN (WLAN) was proposed by Kugean et al. (2002), Worldwide Interoperability for Microwave Access (WIMAX) by Chorbev et al. (2008), Code Division Multiple Access (CDMA) 1X-EVDO by Yoo et al. (2005), General Packet Radio Switch (GPRS) by Gibson et al. (2003) and 2G Groupe Special Mobile (GSM) by Pavlopoulos et al. (1998).

According to Nanda et al. (2007), each infrastructure has its own obstacle, when they are executed in a remote area. For example, Asynchronous Transfer Mode (ATM) and Multi Protocol Label Switching (MPLS) had some mobility and scalability limitation; even both networks provide high Quality of Service (QoS) and have stability on delivering data. The fragility of 3G UMTS network for telemedicine has been explored by Y. E. Tan et al. (2006), where the implementation costs are high and does not provide enough QoS. Comparison of available network infrastructures and technologies for telemedicine system are summarized in Table 1. It can be shown that based on cost, data rate and mobility, the optimal solution for telemedicine system is Wireless Mesh Network (WMN).

1.4 Problem description

A wireless physiological data monitoring system uses a radio channel to send real time critical sign data from wearable biomedical sensor devices to a coordinator. Patient’s wears wireless devices that sense physiological conditions and send the sensed data to their doctors in real time. Wireless health monitoring systems have various benefits compare to wired healthcare equipment

First, patients no longer waste waiting time to meet their doctor. Furthermore, the use of wireless healthcare systems outside the hospital helps to save the healthcare cost for care providers. It allows many patients to work when they are under their doctor’s care.

Second, such systems can alert any medical emergency if specific vital signs change drastically, for example, heart rate is beyond the norm.

Heart attack occurs due to the heart muscle death because of blood clot blockage in coronary. If blood flow is not restored to the heart muscle within the time frame of 20 to 40 minutes, heart muscle passes its way towards to death. Based on the statistics, roughly around 1million Americans suffer a heart attack every year. 40 % of people die from heart attack [http://www.medicinenet.com]. Because heart attack suddenly happens to old people/ patients, continuous real time heart rate monitoring certainly saves lives.

Currently, most heart beat monitors, e.g. ECG, are available at certain locations, for example, hospitals and doctor's offices. They require several wired electrodes on the skin of a patient. Medical professionals frequently use stethoscopes to check the heart beat sound of a patient. Unfortunately, these have critical limitation in heart beat monitoring. As mentioned before, it is highly desired to monitor heart beat continuously for unexpected heart attack. Nevertheless, it is impossible with the existing medical apparatus. Thus, wireless health monitoring systems carry many benefits compared to the current wired healthcare equipment. The telemedicine technology is used as the method send real time vital sign data from wearable biomedical sensor devices to a coordinator.

1.5 Design issues and challenges in wireless healthcare

In ever-present healthcare applications, the most substantial limitations of wireless networks are the slow data transfer rate and lack of a single connectivity standard that which enables devices to communicate with one another and exchange data. Other limitations include wireless devices, which are in their infancy stages and slower in speed than desktop computers, high initial costs involved in setting up wireless systems and lack of real-time connectivity due to device mobility.

In the healthcare setting, in order to achieve efficiency gains, there are 3 main issues in wireless development need to be addressed:

Suitable growth methodology is developed to enable proper integration of new solutions with existing wireless solutions.

Data access, communication and synchronization issues among mobile devices and existing databases are resolved.

Suitable user interfaces are designed in order to capture and access data accurately and timely.

When many prototypes of healthcare solutions have been found to be successful, they have suffered from limitations with regard to code, integration with existing applications, user interfaces and data transmission. To allow flexibility, code is written as generic as possible and parameters are kept as variables. During real-time testing, some of these parameters have caused run time errors, as the compiled code has not been able to resolve certain data types prior to the run. It has created the necessity to re-visit the code and examine every instance of the run in order to fix the problem. Also integration with existing applications has caused concern, as the healthcare industry lacks uniform standards.

1.6 Outline of Dissertation

2 Background

2.1 Local networks

As known a network is a connection of computers (and/or) devices connected to each other. The need of data transferring from a computer or a device to another and the massive progress in data communication had led to the development of various network types, topologies and communication protocols.

2.2 Types of networks

One way to categorize the different types of computer network designs is by their scope or scale. The networking industry refers to nearly every type of design as some kind of area network. Some examples of area network types are:

LAN - Local Area Network

WLAN - Wireless Local Area Network

WAN - Wide Area Network

MAN - Metropolitan Area Network

SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network

CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area

PAN – Personal Area Network

BAN – Body Area Network

DAN – Desk Area Network

A LAN (Local Area Network) is a network that connects devices at a relatively short distance. (Connection is done with the use of a media like wire or optic fibre). A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs and occasionally a LAN will span a group of nearby buildings.

A WAN (Wide Area Network) is two or more LAN that is connected together over a wide geographic area. This may be networks located across town, across a state, across a country or across the world.

A WLAN (Wireless local area network) is a type of a LAN that uses high frequency radio waves (or even a laser beam) rather than wire or optical-fiber to achieve communication between different nodes. WLAN is a flexible communication system, because it can be used as an expansion of a wired LAN, or even as an alternative solution, in order not to be used a wired LAN. WLANs transmit and receive data over the air, by using electromagnetic waves. Thus, WLANs combine data connectivity with user mobility and through a simplified configuration enable movable LANs. The radius of coverage for a typical WLAN system is up to 150m, but it can be increased by adding APs. Although this range can be increased when high gain directional antennas are used. APs connect wired and wireless networks together.

- A MAN (Metropolitan Area Network) typically covers an area of between 5 and 50 km diameter. Many MANs cover an area in the size of a city, although in some cases MANs may be as small as a group of buildings.

- A CAN (Campus Area Network) is generally a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus. But there is also the CAN-bus type that is a serial protocol that is also a type of network used specially in automotive applications (and must not be confused with that of computer communications) for control and monitoring of the ECUs (Electronic Control Unit) of a car or truck.

- A PAN (Personal Area Network) consists of a dynamic group of less than 255 devices that communicate within about a 10m range. Unlike with wireless LANs, only devices within this limited area typically participate in the network, and no online connection with external devices is defined. One device is selected to assume the role of the controller during wireless PAN initialization, and this controller device mediates communication within the WPAN. The controller broadcasts a beacon that lets all devices synchronize with each other and allocates time slots for the devices. The detailed function of this type of network is going to be further discussed in this chapter.

-BAN (Body Area Network) is a limited range network and it is used for medical purposes like health monitoring. This network consists of various types of wireless sensors attached in the human body.

2.3 Basic Network Topologies

Network topology is the arrangement of the elements of a network. These elements are nodes or links. When two computers or devices are connected directly through a link then this topology is called peer-to-peer and is the simplest topology of all. The most wide spreading topologies are

-The BUS topology

-The RING topology

-The STAR topology

-The TREE topology

-The Mesh topology

In Bus topology (Figure 2-1) the base stations are connected to a common shared physical mean. The frames that are being sent by a base station go through the physical mean (wire, optic fiber) and then directly to the other base station or to the base stations. A necessary requirement in order to reach the right frame the right base station is to have the specific address of that specific base station.

In Ring topology (Figure 2-2) there is a close way of the natural mean and all the base stations connected sequentially. All the frames are transmitted to every base station in proportion to their destination address. The information’s flow is only one-way.

In Star topology (Figure 2-3) all the base stations are connected to a central service unit. The network’s reliability depends on this unit. The frames that this unit sends to all the other base stations must have a destination address. This topology can expand, if extra service units added.

The Tree (Figure 2-4) topology is a generalization of the Bus topology. A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network.

In a mesh topology, (Figure 2-5) in contrast to the tree topology, there are no hierarchical relationships. Any device in a mesh topology is allowed to attempt to contact any other device either directly or by taking advantage of routing-capable devices to relay the message on behalf of the message originator. In mesh topology, the route from the source device to the destination is created on demand and can be modified if the environment changes. The capability of a mesh network to create and modify routes dynamically increases the reliability of the wireless connections. If, for any reason, the source device cannot communicate with the destination device using a previously established route, the routing-capable devices in the network can cooperate to find an alternative path from the source device to the destination device [6]. This is clarified further in the route discovery and maintenance subsections.

Finally there are some other types of topologies which are the result of the combination of the previous topologies. These are:

-The Star-Bus topology

-The Star-Ring topology

Rate of Death in U.S:

As the main cause of death in U.S is about due to the heart disease which is the first cause for death and due to cancer about 23% people are dying which was the second cause according to the year 2007.

Infant mortality rate is about 6.75 of deaths per 1,000 infant births which is according to the year 2007 and 2 % less when compared to the year 2000

In the year 2007 ,for about 13 of deaths are caused due to the cancer of the age group between 45-64 years of age while considering the years 1997-2007, death rate of cancer in this age group is decreased to 14%,for about 1,00,000 population 200 deaths are caused.

Cancer disease among the children of age 18 years by sex and age in 1999-2009

Overall Death rate in the World :

As according to the age group of 65 years and over heart disease is the main problem for death between 1997-2007.As it is decreased to 26% to 1,309 deaths in the year 2007.Most the people die due to the motor –vehicle traffic .As the death rate in Mississippi is about 31 percent of 1,00,000 population.

When comparing the year from 1997 -2007 death rate is dropped for about 30% in the age of 1-14 years of children which was caused due to the unintentional injury death rate for about (7% deaths/100,000 population ).

Between 15-24 years age group for about ½ of deaths are occurred due to unintentional injuries .Out of 100,000 population 5% to 37 deaths are occurred due to unintentional injury among this group during the years 1997-2007.

Death among all age groups ,age and cause of death in 2007

Due to lack of facilities most of the people died in hospital about 36% and 22% in nursing homes in the year 2007.

Patients in the hospital are offered by medical services ,bereavement services to 85% in the year 2007.Also ¼ of family member’s are offered with services from care giver health.About one and half of the patients in the hospital has difficult in breathing and also last visit after death suffered with one third of the pain.

Life Expectancy :

For males the life expectancy is increased to 1.3 years at birth rate over 2000-2007 years and for females about 1.1 years.

As compared with white population the life expectancy at birth is increased more for the black from the year 2000-2007.

Health measures and Disease Prevalence :

Over the past few years ,asthma is attacked to the 5% of the children of 18 years age in the year 2007-2009.Skin Allergy is attacked to the 11% of the people and about 6% of ear infections over few years.

Children’s condition at the age of 18 years from 1997-1999 and 2007-2009

People with age 18-44 years reported that their health as good (or) bad in the year 2009 and 75 years age people will be about 29% in this condition.

A most common high blood pressure (or) hyper tension is observed for about 33-34% of men ,women at particular age of 45-54 years . It is observed more at the age of 25 years for men at 67% and women 80% .

Adults with the age of 20 years are suffering from diabetes about 11% in the year 2005-2008.

Infant Mortality :

In the year 1997-2007 , about 5%-8% infant mortality rates had been declined .This is mainly caused due to the public health practice ,health of the mother ,availability and usage of the health care for pregnant women and infants .

Mortality rates of infant, neonatal ,post neonatal from 1997-2007

According to the year 2007 , the rate of infant mortality is about 6.7 per 1000 births and as per 1997 it is 7% less. Before the 28 days of age deaths have been decreased to 8% to 4.41 per 1000 births .The main reason of infant deaths are 3 causes they are low birth weight ,sudden infant death syndrome(SIDS) ,malformation which lead to deaths for about 45% of 29,000 infants.

Child mortality rate for Economic Cooperation and Development Country :

As the age group from 1-19 years ,the mortality rate of child are lower than for other age people .For about 32.7 per 100,000 children are died which was the second highest U.S mortality rate among different countries .

Rate of death among children of age group 1-19 years by OECD country from 2001-2006

Child mortality rate about 14.8/100,000 children are died in Luxembourg in the year 2003-2005 .

In Portugal child mortality rate is 34.6/100,000 of children are died in an average of the year 2001-2003.

Most of the people are died due to injury death caused by the motor vehicle accidents which is mainly seen in the age of 1-4 years old in Europe and U.S .Many of the people are died in the world are due to measles ,malaria ,HIV/AIDS, Diarrhoea ,malnutrition .

Impact of Telehealth :

After completion of pilot program, by the clients which was one of the impact of telehealth technology and it generally measures the level of both acceptance ,intrusion by nurse monitoring and telehealth monitoring .

a)Monitors are flexible and easy to use by 100% of people .

b)The process of interview ,monitors are not officious which is felt by 87% of people.

c)Serious problems are been prevented and monitored by nurse which is felt by 73%

d)Life quality ,independence ,improvement in security is felt by 80%

Client sentiment

Client responses

Strongly agree

Agree

Neutral

Disagree

Strongly Disagree

Easy to use device monitoring

15

87%

13%

0%

0%

0%

Monitoring devices are Intrusive

15

7%

7%

0%

40%

47%

Serious problems are prevented by monitoring calls

15

40%

33%

27%

0%

0%

Technology is managed better

15

67%

27%

7%

0%

0%

More independence can be obtained by technology

15

80%

30%

7%

0%

0%

Security can be improved by technology

15

53%

27%

20%

0%

0%

Life quality has been improved by technology

15

40%

40%

20%

0%

0%

Table : Usage of Telehealth technology by client

Telehealth impact on Care managers :

Inorder to access the technology impact for 18 telehealth clients , the survey at pilot program of beginning ,end has been responded by care managers.

Reports provided by significance care managers are :

a)Over 65% of cases are being monitored the clients chronic condition .

b)For about 29% of clients cases are managed at home.

c)35% of patients required permanent care which were at the end of the pilot program.

d)41% of patients (or)clients are being provided by improved care

Care management

Responses of care manager

Yes

No

No change

Independence of client is improved

17

29%

18%

53%

Need for day care is decreased

17

18%

6%

76%

Need for nursing is decresed

17

18%

12%

71%

Decrease in undetected falls

17

53%

12%

35%

Client chronic conditions with improved ability

17

65%

6%

29%

Permanent care need is decreased

17

35%

12%

53%

Client care management is improved at home

17

29%

12%

59%

Holistic management strategic is improved for client

17

41%

18%

41%

Table : Telehealth impact on care managers

In the year 2009/2010 the health care spent by government of Australia was growing rapidly from 4% to 7% of GDP in2049/2050 years.

Telehealth client group :

Factors (or)medical conditions which are benefited from the technology is been selected by telehealth client group.

For about 65 to 90 years of the age includes 18 clients in telehealth group.Telecare equipment is provided to 11 of the telehealth client group.

Carers of Telehealth :

In the below table the near to clients homes the proximity of the carer’s living arrangements are present .A person who lives with client(or)family friend’s are said to be primary carers who will not live close to them.

Group

With client

With in 5kms

With in 20kms

Distance >20kms

Telecare

9

6

4

3

Telehelath

3

3

1

Both

3

5

3

Total

15

14

4

7

Table : Proximity of carer to client

Telehealth Interventions :

According to the pilot program period there are 34 interventions which they use of telehealth technology .These are caused when client is being called by nurse and 15 of the other resulted in home visits.

Nature of intervention

RN phone client

RN visited client

Readings are out of range

28

32

Responses are very poor to interview question

7

2

Missed interviews

14

0

Table :Interventions of Telehealth

Death analysis in U.K :

In the year 2009 ,85% of 65 age group people are died in England out of 491,348 people .

People with age more than 85 are died in hospital are 85% due to cancer comparing with 20% of cancer death

Most of the people died about 33% of age 85

Deaths are caused by circulatory ,respiratory diseases are 41% and 13% are due to cld weather and less heating.

More than 65 years of age are 18% died in home ,age group 15-64 are died about 31%

People who are receiving hospital care (Advance care Planning ) are died about 10%.

Death rate of people receiving care from hospital at home are 40%

Effects of death in UK due to winter cold :

1)In the year 2011/2012 the people with the age group of 65 are died due to winter about 23,380

2)About 21,700 deaths are occurred in England and Wales during the year 2012.

3)People with age 65 ,are dying daily due to winter of an average 193 ,8 per hour.

4)Mortality rate rises from 1 to 2 % for increase in every degree of 20 C

5)8,000 deaths are occurred for increase in degree in a year

6)Mortality rate for heart and circulatory diseases are main cause of death over the age 65.

Deaths due to heart disease and strokes in U.K :

The men with age 65-74 are facing heart disease problem of 20.8% people ,28.4% for aged 75 and above.

Every year rate of heart stroke by people in U.K are 1,50,000.

Due to heart stroke every year 60,000 patients are admitted in the hospital

Heart disease among the age 18-75 by sex and age in 1999-2009

Death analysis of the World due to various Diseases :

WORLDWIDE DEVELOPING DEVELOPED

RANKS DEATHS % RANKS DEATHS % RANKS DEATHS %

Heart diseases

1

8,923

15.1

1

7,342

14.5

2

1,563

Malignant neoplasms

2

7,424

12.6

2

5,255

10.4

1

2,154

Cerebrovascular diseases

3

5,712

9.7

3

4,949

9.8

3

757

Lower respiratory infections

4

4,177

7.1

4

3,910

7.7

4

305

Perinatal conditions*

5

3,180

5.4

5

3,141

6.2

35

Chronic obstructive pulmonary

6

3,025

5.1

6

2,737

5.4

5

285

HIV/AIDS

Tuberculosis

9

1,464

2.5

9

1,448

2.9

15

Road traffic accidents

10

1,275

2.2

10

1,158

2.3

114

Diabetes mellitus

11

1,141

1.9

914

1.8

7

221

Malaria

12

889

1.5

888

1.8

0

Suicide

13

844

1.4

707

1.4

9

118

Cirrohsis of the liver

14

772

1.3

655

1.3

10

116

Nephritis and nephrosis

15

739

1.3

611

1.2

8

126

All causes

58,772

100.0

50,582

100.0

8,095

Table :Causes of death in Worldwide,Developing,Developed countries according to year 2004

2.4 Sort range wireless technologies

2.5 The IEEE 802 working groups ................................................................................. - 28 -

2.5.1 Wi-Fi.........................................................6

2.5.2 Bluetooth......................................................6

2.5.3 ZigBee Standard ................................................7

2.5.4 ZigBee source code stack.....................................8

2.5.5 Network Topologies .........................................9

CHAPTER 2 LITERATURE REVIEW

OVERVIEW OF WIRELESS SENSOR NETWORKS

2.1 Basic Components in Wireless Sensor Nodes

Wireless Sensor Networks is identified as a new class of disturbed systems which is defined as a set of network wireless devices. These are named as Nodes. WSN, unlike computers they sense through allotted objects or entities and communicate the bridge of sensed data through wireless links. Bridge between the data transmission is processed through Single or multi hops or to a base station or PDA/cell phones which can be connected to other networks.

Each wireless sensor node consists of more than one sensor to process sensing of physical variables, main processing unit (which is used to consume low power cut or a microcontroller), analog to digital converter (ADC), flash memory and RF transceiver. Wireless sensor node is often limited to low power source.

As shown in figure 2.1, the screen represents basic components of typical wireless sensor node. Most of the WSN nodes executes 8051 microcontroller which is defined as their main processing unit. These are used due to its low cost, low power consumption and also with their limited size as specified in Barth, et al., 2009; Chen and Wang, 2008; Choi, et al., 2007; Choi and Song, 2008; Zhang, et al., 2009.

Most of the systems use SOC process which is defined as (System-on-chip). This chip consists of CC2430 processor that includes ADC, Flash memory and RF transceiver as specified by Chai and Yang, 2008. The size of the chip is small in dimensions and easy to develop low power consuming sensor nodes. Nodes are limited to low quality of ADC and small memory size.

Sensor nodes are also developed by using Micro Controller Unit such as MSP430F1611 or Atmel with external RF transceiver as specified by Jovanov, et al., 2005. There are some more developers specified by Mangharam, et al., 2006 who use MCU with external ADC or external extra flash memory to achieve higher quality of service.

2.2 Wireless Sensor Networks in Health Monitoring

The wireless sensor networks uses a physiological data monitoring system. These systems are used for radio channel signals to send real-time vital sign data from wearable biomedical sensor devices to a coordinator. The usage is prolonged to patients who wear wireless devices that support and sense physiological conditions and forwards the sensed data to their doctors in real time scenarios. This proves to know that wireless health monitoring systems have several advantages when they are compared to wired healthcare equipments.

This helps the patients to save their time in meeting their doctor and also improves to save the health care expenses for care providers. Also, it allows lots of patients to work while they are under observations at doctor’s care. A system automatically alerts all or many medical emergency if the vital signs are changed specifically. e.g., heart rate is beyond the norm. A heart attacked is the death caused due to the sudden blockage of heart muscles of a coronary artery of a blood clot.

Therefore if the blood flow is restored between 20 to 40 minutes, deaths of the heart muscles begin to occur. Americans suffer from heart attacks which are approximately one million each year. That results in 40% of death due to their heart attack by medicine net by 2010.

2.3 Technologies for WSN in Health Monitoring

Technologies for WSN in health monitoring is categorized into three wireless standards i.e. IEEE 802.15.1 (Bluetooth), IEEE 802.15.4 (ZigBee), and IEEE 802.15.3a (UWB) for PAN, and one IEEE 802.11 a/b/g (Wi-Fi). Wireless sensor networks are briefly reviewed as WLAN for their applications in wireless health monitoring systems.

The Wireless Sensor Networks technology engages very small and low power consuming devices for collection medical data. The nodes are sensed through PDA, cell phone or PAN coordinator to collect data and communicate to a coordinator or a remote monitoring device using wireless data transfer technology.

The data collected by the PAN coordinator have equipments in large size memory and fast processors to analyze the data received. The central server, nodes and between a node the interface among them defines the operating frequency, modulation scheme, network data rate and hardware edge of physical radio layer. Various medical objectives depending on continuous periodic monitoring, dimensions of a physiological data packet, range of transmissions, network speed, and network size, can be adopted.

2.3.1 ZigBee

Wireless Sensor Network applications are considered into standard based protocols i.e. IEEE 802.15.4 and ZigBee that provides basic network infra structures. These layers have its own identity – IEEE 802.15.4 defines both physical and MAC layers, and Zigbee defines network and application layers. The layers are developed based on low data rate, low complexity, low power consumption, and low cost WSNs.

Zigbee is bonded with physical layer (PHY) which is supported by three radio bands i.e. 2.4GHz ISM band (which is activated globally) embedded with 16 channels, 915MHz ISM band (Americas) embedded with 10 channels, and 868MHz band (Europe) embedded with a single channel. Data rates vary from each band and are 250kbps at 2.4GHz, 40kbps at 915MHz, and 20kbps at 868MHz.

All these layers are controlled by MAC layer which has the access to all the radio channels through Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism.

Usage of IEEE 802.15.4 PHY utilizes direct sequence spread spectrum coding in order to reduce packet loss which is caused due to noise and interference. The mechanism also supports two PHY layer modulation options into consideration.

The 868/915 MHz PHY equipments adopt all the binary phase shift key modulations, where as 2.4 GHz PHY uses off set phase shift key (Quadrature).

Zigbee defines three types of devices which serves as a network coordinator or a regular device i.e. coordinator (MAC Full Function Device-FFD), Router (MAC FFD), and end device (MAC Reduced Function Device- RFD). Full Function device can effortlessly communicate with any other devices, where as RFD is suitable for simple application which include light switch or simple sensor device. RFD can communicate with FFD only.

Zigbee coordinator acts as a base station node. The node automatically initiates the thorough composition of networks and controls all the network process. The controlling power needs lots of memory and high processing source. A router is also linked to FFD that easily links groups together and wires all multi-hoping for packet transmissions.The transmissions are easily connected to various routers and end devices. The end devices are named as Zigbee and communicate only with a Full Function Device (FFD) and are limited in functionality.

Zigbee supports around 65,536 nodes and for security reasons the usage is 128-bit which enables Advanced Encryption Standard (AES) encryption and validation. Transmission range starts from 10m to 75m which is totally dependent on applications power output and various environmental features. These devices are expected to run through a battery and the life ranges from several months to years.

2.3.2 Bluetooth

Bluetooth device is also acknowledged as IEEE 802.15.1. This device is of low cost, consumes low power wireless radio frequency and communicates for a very short distance. The protocol related to Bluetooth is complicated to compare with other IEEE networks, where it defines several components above PHY and MAC layers. As specified by Hackmann, 2006, there are some optional complications to its whole protocol.

The operations performed by Bluetooth are operated under supervision of unlicensed 2.4 GHz ISM band which is occupied by 79 channels.

The PHY layer uses frequency hopping spread spectrum coding to reduce interference

and fading. The maximum data rate is up to 3Mbps in the enhanced data rate mode.

However, the actual data payload is usually reduced due to different units’ address and

other header information to guarantee the compatibility among all Bluetooth sensor

nodes.

Bluetooth's basic connectivity technology is the piconet based on a star network

topology. It consists of one master device that communicates directly with up to seven

active slave network devices. In a given piconet, all devices are synchronized using the

clock and frequency hopping pattern of the master, and slave devices communicate only

with their master in the one-to-one way. Bluetooth has three power saving modes. At the

hold mode, devices just process reserved slots for synchronous links. After that they enter

the sleep status. At the sniff mode, a device is in the sleep mode for most of the time. It

wakes up periodically in a given time for communication. At the parked mode, the device

just holds the parked slave broadcast (PSB) link and turns off any other links to the

master device. If the latter would like to wake up parked devices, it sends beacons to

them over the PSB link [Hackmann, 2006]. A slave device at the active mode can reduce

the power consumption by entering the above power saving modes.

2.3.3 Ultra Wide Band (UWB)

A wireless radio technology used for short-range, and communication of high-bandwidth at low energy levels are defined as UWB (IEEE 802.15.3a). The energy levels are proved to use larger portions of the radio spectrum. Among IEEE 802.11 standards UWB is one of the hidden competitors. These proved to be the largely comfortable properties with its huge bandwidth. The wireless technology delivers a bandwidth of 480 Mbps currently for 3 meters and 110 Mbps at 10 meters.UWB supports all the multimedia applications which include audio and video transmission in home networks.

UWB is also used a wireless cable replacement which includes a very high speed serial bus such as USB 2.0 and IEEE 1394 as specified by Lee, et al.,2007.Infact acts a data networking which is more intended to IEEE 802.11 that uses WLAN and are replaced with Ethernet cables. Bluetooth is accepted for small PAN-covering area applications, which includes wireless mouse and cell phone set. Bluetooth supports lesser bandwidth than UWB. It is also used as low-powered, short-pulse radio signals to transfer data from minimum frequency to over a wide spectrum of frequencies.

2.3.4 Wireless Fidelity (WIFI)

Wi-Fi represents a general term defined for any type of IEEE 802.11 network. Certain examples are distinct here i.e. 802.11 networks which are categorized into 802.11a (up to 54 Mbps), 802.11b (up to 11 Mbps), and 802.11g (up to 54 Mbps). The networks are used as WLANs and all the three 802.11 networks differ based on their bandwidth, coverage, security support and also through applications. The categorized networks in the application are better suited for various sources. 802.11a is suitable for multimedia voice, video playing and large sized image applications in a user friendly environment. Compared to 802.11a with their bandwidth, coverage of 802.11b it relatively provides shorter range. This type of network requires very few access points for coverage of larger areas. 802.11g is compatible compared to 802.11b due to its higher bandwidth and enhanced security.

2.4 Technology Comparison

2.1 Health monitoring system

2.1.1 Common architectures for health monitoring system

2.1.2 A mobile architecture for diabetes management

2.2 Health support system 8

2.2.1 On-line personal health records management platform

3.1 Review of Wireless Sensor Networks in Health Monitoring

3.2.1 Reliability

3.2.2 Power

3.2.3 Portability

3.2.4 Network Interference

3.2.5 Real Time and Continuous Monitoring

3.3 Limitation and Challenges in WSN