Overview of four emerging mechanisms for e-health communications

Abstract

The ever-advancing miniaturisation and low-power consumption of electronic devices led to the emergence of wireless body area networks. This revolutionary technology provides new possibilities for high-quality medical and healthcare services. In this paper, we expose an overview of the main standards adopted for WBANs particularly: ANT, Bluetooth low energy (BLE), IEEE 802.15.4 and IEEE 802.15.6. We perform subsequently a comparison between these different standards in order to provide useful insights about their main differences and facilitate standard choice depending on WBAN application requirements.

Full text

Int. J. Systems, Control and Communications, Vol. X, No. Y, xxxx 1
Copyright © 20XX Inderscience Enterprises Ltd.
Overview of four emerging mechanisms for e-health
communications
Hend Fourati*, Hanen Idoudi and
Leila Azouz Saidane
National School of Computer Sciences,
University of Manouba,
Tunisia
Email: hend.fourati@ensi.rnu.tn
Email: hanen.idoudi@ensi.rnu.tn
Email: leila.saidane@ensi.rnu.tn
*Corresponding author
Abstract: The ever-advancing miniaturisation and low-power consumption of
electronic devices led to the emergence of wireless body area networks. This
revolutionary technology provides new possibilities for high-quality medical
and healthcare services. In this paper, we expose an overview of the main
standards adopted for WBANs particularly: ANT, Bluetooth low energy (BLE),
IEEE 802.15.4 and IEEE 802.15.6. We perform subsequently a comparison
between these different standards in order to provide useful insights about their
main differences and facilitate standard choice depending on WBAN
application requirements.
Keywords: IEEE 802.15.6; Bluetooth low energy; BLE; wireless body area
networks; WBANs; e-health; MAC protocol; IEEE 802.15.4; ANT.
Reference to this paper should be made as follows: Fourati, H., Idoudi, H. and
Azouz Saidane, L. (xxxx) ‘Overview of four emerging mechanisms for e-health
communications’, Int. J. Systems, Control and Communications, Vol. X, No. Y,
pp.xxx–xxx.
Biographical notes: Hend Fourati is a PhD student at the National School of
Computer Science (ENSI), University of Manouba, Tunisia since 2014. She
received her Engineering degree in Computer Science from the Faculty of
Sciences of Tunis (FST), Tunisia. Her research explores QoS in MAC
protocols for WBAN-based e-health applications.
Hanen Idoudi is an Associate Professor at the National School of Computer
Science, University of Manouba, in Tunisia and a member researcher in the
CRISTAL laboratory. She earned her Engineering and Master’s degrees in
Computer Science at the National School of Computer Science, Tunisia in 2001
and 2002, respectively. She received her PhD degree jointly from the
University of Rennes 1, France (where she was also member of IRISA, INRIA,
Rennes), in 2008. Her research focuses on issues related to wireless
networking: MAC protocols optimisation, networks modelling and
performances, routing, quality of service (QoS), energy conservation,
cross-layer designs, etc.

2 H. Fourati et al.
Leila Azouz Saïdane is a Professor at the National School of Computer Science
(ENSI), at The University of Manouba, in Tunisia and the Chairperson of the
PhD Commission at ENSI. She was the Director of this school and the
Supervisor of the Master’s degree program in Networks and Multimedia
Systems. She is the Co-Director of RAMSIS group of CRISTAL Research
Laboratory (Center of Research in Network and System Architecture,
Multimedia and Image Processing) at ENSI. She collaborated on several
international projects. She is author and co-author of several papers in refereed
journals, magazines and international conferences.
1 Introduction
The rapid growth of the world population is increasing the life expectancy, as a natural
effect, leading to aging population. Knowing that, for example, more than 33% of 65 and
over aged persons fall every year (Wang et al., 2014) is not very reassuring, since it is
impossible to have qualified personnel alongside each one of them 24 hours a day and
seven days/seven. This fact, most likely, explodes healthcare costs especially as a
majority of the elderly prefer to receive the medical care at home and, at the same time,
benefit from quality conditions and optimal safety.
That’s why the idea of an e-health solution concept becomes interesting. Especially, if
it is easy to use, remotely handled and it has a low-cost. E-health covers several activities
such as the telemedicine, electronic health records, medical remote monitoring, cyber
medicine (the use of the internet to deliver medical services), etc.
One of the means to fulfil those emerging needs is through wearable monitoring
systems capable of supervising vital signals such as heart rate, body temperature, etc.
These small devices (sensors) monitor the health state and vital parameters of the elderly
person and send periodically or if necessary, the related information to a network
coordinator. The latest is responsible for forwarding these data to the family doctor or a
family member (Ullah et al., 2012). Networks of smart sensors can be placed or
implanted on/in the human body to provide real time data. So the implementation of
WBAN-based e-health applications is often based on two elements:
• A network of tiny sensor nodes, which are spatially distributed to communicate
information gathered from the monitored field through wireless links. The data
collected by different nodes is sent to other networks, for example, the internet
through a hub.
• A network coordinator (hub) which allows the collection of data and its transmission
(to the smartphone of the family doctor, for instance).
Such networks are commonly known as wireless body area networks (WBAN). In
addition to saving lives, prevalent use of WBANs will cover three areas (Wang and
Wang, 2012).
• medical check up: collect data for monitoring brain electrical activity, heart activity,
etc.
• physical rehabilitation: tilt sensors for monitoring accidental falls, foot sensors for
monitoring steps, etc

Overview of four emerging mechanisms for e-health communications 3
• physiological monitoring: acceleration sensors for monitoring instant behaviours,
breathing sensors for monitoring respiration, etc.
So old people will be able to engage in their normal activities instead of staying at home
or close to a medical centre. The data from the sensors are collected using the on-body/
in-body communication techniques (WBAN) and are then sent to a doctor or a family
member for analysis and control through the internet and other existing wireless
technologies like ZigBee, WSNs, Bluetooth, wireless local area networks (WLAN),
wireless personal area network (WPAN), video surveillance systems and cellular
networks, etc.
To get a reliable e-health communication over a WBAN, it is necessary to provide
simultaneously several QoS criteria since it manipulates vital data:
• High reliability of data transmission: very reduced data loss, an acceptable
transmission delay and transmission error rate, support of high data rates and
real-time aspect, etc.
• Low energy consumption: the nodes are small and their batteries are often difficult to
replace.
• Support of high mobility and coexisting WBANs: on one hand, the sensors are
usually placed on non-fixed devices (such as a walking cane) or on the human body.
Thus, they have to support the most extreme movements (suddent falling, running,
jumping, skipping, etc.). On the other hand, body networks (WBANs) should
mitigate interferences to provide a good QoS in the presence of several other
WBANs nearby as in hospitals or healthcare centres.
• Support of various traffic periodicities: regular traffic, unscheduled and improvised
access, urgent traffic and vital traffic (with highest priority).
• Support of different data rates: light and heavy medical traffics.
• Reliable service differentiation: based on data priority, a medical WBAN has to
provide a balance between providing an acceptable delay for lowest-priority traffic
and making sure that ‘vital’ traffic is still favoured enough to prevent life-threatening
or eventual increasing of health problems (Gama et al., 2008; Cavallari et al., 2014;
Juneja and Jain, 2015; Agrawal et al., 2014).
Since the beginning of this century, considerable research efforts have been dedicated to
propose/investigate new protocols that could satisfy these crucial WBAN requirements as
well as studies of applicability of existing wireless sensor network (WSN) protocols in
WBAN scenarios such as e-health applications. But how does it technically work?
According to the position of the communicating devices, the following classification
can be drawn:
• on-body communications: all the devices are located on the body of the same person,
most of the radio channel is on the surface of the body
• in-body communications: at least one of the end-points of the communication link is
implanted in the body, a significant part of the channel is thus inside the body
• off-body communications: one of the devices is placed on the body, while the other
one is located outside it, being an external device, such as a router or a gateway

4 H. Fourati et al.
• body-to-body communications: the communication takes place between devices
placed on the body on at least two different subjects (Studiorum, 2013).
The primary standard solutions for wireless body area communication, treated
in this paper are: advanced and adaptive network technology (ANT) (ANT protocol
website), Bluetooth low energy (BLE) (Bluetooth website), IEEE 802.15.4 (Heile et al.,
2003) and IEEE 802.15.6 (Astrin et al., 2012). ANT has been proposed for the first time
in 2005 and was designed for applications with periodic transfer of small amounts of
sensor information. The main application domain targeted by this standard is essentially
the sport sector, such as cycling performance monitoring.
BLE technology is a robust, low power consumption and low cost configuration of
Bluetooth standard. Several types of devices are now equipped with BLE such as mobile
phones and PCs.
IEEE 802.15.4 (Salman et al., 2010) has also long been considered as an efficient
protocol for WBAN since it is a well known short-range wireless communication
standard, developed in 2000, specifically designed to support low power, low cost, and
low data rate networks, as WSNs.
IEEE 802.15.6 (Kwak et al., 2010), whose final version was released in February
2012, has been specially developed for WBANs. In this paper, we present each of the
major WBAN standards and their features, then we briefly overview their physical layer
specifications and a comprehensive study of MAC Layer specificities. We will finish the
paper by presenting a comparative study and a discussion.
2 Advanced and adaptive network technology: ANT
ANT whose last version (5.1) appeared in April 2014, is one of the newest
communication protocols for WPANs with low power consumption (LR-WPANs) (ANT
protocol website). This commercial technology aims at providing a trade off between
device’s battery lifetime and bandwidth.
2.1 ANT specifications
As shown in Figure 1, ANT protocol handles data link, network, transport and low level
security layers. The light ANT stacks provide a simple solution easily integrable into
small devices like mobile phones (ANT protocol website; Khsibi et al., 2013).
Figure 1 ANT/ANT+ Layers Model (see online version for colours)

Overview of four emerging mechanisms for e-health communications 5
The ANT specification defines a bandwidth rate of up to 1Mbps by using the 2.4 GHz
ISM band divided into 125 of 1MHz-width channels (Khsibi et al., 2013; Patel and
Wang, 2010).
• Network topology
ANT technology runs under different network topologies such as peer-to-peer, star,
tree and fixed mesh topologies. Two kinds of nodes are defined in an ANT network:
master and slave nodes. A single node can handle the two roles at once according to
the network in which it is placed. Masters ensure the control of the channel
communication, and each slave is responsible of synchronisation with its master
(Khsibi et al., 2013).
• Channel specifications
a Channel ID is the most important descriptor of a channel. It allows the channel
establishment and management (e.g., device pairing). The channel ID value,
coded on 4-byte, is composed of three fields: transmission type (8 bits), device
type (8 bits), and device number (16 bits).
b The device type is a number, representing the class of the master device.
c The device number, being unique, permits the specification of the master device
considered.
d The transmission type, defines the transmission specifications of a device.
e Channel type (type of communication): ANT protocol defines four data types for
data transmission on ANT network channels: broadcast, acknowledged, burst and
advanced burst.
1 broadcast: in this mode, master and slave communicate with each other
without any acknowledgment
2 acknowledged: during the establishment of two-way connection, the
acknowledged mechanism is used for data transmission with acknowledgment
3 burst: this type is dedicated to transmit a large amount of data especially
frames of high priority
4 advanced burst: the advanced burst transfer operates in the same way of burst
type. In addition, it increases the maximum data throughput to 60kbps (ANT
protocol website; Khsibi et al., 2013).
• Channel management
In order to ensure communication between different nodes, three channel types are
supported by ANT protocol: independent channels, shared channels and continuous
scanning mode.
a independent channels: there is only one master and one slave in this type of
channels in order to reduce the risk of interference
b shared channels: when many nodes have to send data to one central node (the
single master), shared channels are used
c continuous scanning mode: being permanently in listening state, a node can
receive data from multiple transmitting masters at any time (ANT protocol
website; Khsibi et al., 2013).

6 H. Fourati et al.
• Channel establishment
As shown in Figure 2, the first step to establish a channel between two nodes is to set
a network key. If the concerned node (master or slave) uses the default public
network key, then, it is automatically assigned to network number ‘0’. Otherwise, to
use another network (a private one), the network number have to be set to the
corresponding value. Next, depending on the type of data exchanges, the same
channel type is assigned to each node (master and slave). After the channel
assignment, channel parameters (timeouts, channel period, etc.) will be defined to the
appropriate values. In case there is no correspondence between the master and slave
for a given value of a parameter, this value may be changed. Once the channel is
opened and the master is detected (by the slave), the master starts sending data
continuously to the slave until the channel is closed by the application. If the defined
timeout period is elapsed without finding the master, the slave channel then will be
closed (ANT protocol website).
Figure 2 Channel establishments between master and slave nodes
2.2 ANT+
ANT+ is a function that can be optionally added to the basic ANT structure to provide
the interoperable collection and exchange of data between different nodes of a managed
network. So the transmission type in such a network can be pre-defined in an ANT+
managed network.
As shown in Figure 1, the additional layers defined by ANT+ allow not only the
network management but also the definition of device profiles according to the nature of
the target application. The determination of ANT+ device profiles is meant to specify
data formats and different channel parameters. It can be used for several kinds of
operations in different devices such as speed and distance monitoring, fitness equipments
and heart rate monitoring (ANT protocol website; Khsibi et al., 2013; Patel and Wang,
2010).

Overview of four emerging mechanisms for e-health communications 7
ANT technology is thus a simple protocol that does not handle any QoS oriented
services. In this way, it is commonly used for applications that do not generate important
data rate and do not have any QoS constraints such as sports and wellness.
3 Bluetooth low energy
Introduced in 1999, Bluetooth is one of the first standardised technologies for WPAN
communications (Mackensen et al., 2012). It can connect wireless sensors via radio
channels to different devices, such as cell phones, via applications providing both
monitoring and short range control. However, this traditional version of Bluetooth shows
some limitations such as high power consumption of transceiver chips and high
complexity of protocol stack. To overcome these aspects, BLE specification was
introduced in the 4.0 version published in 2010 (Mackensen et al., 2012; The Bluetooth
SIG, 2010). Being an emerging short range technology, the main feature of BLE is its
low power consumption (only 10% of the power consumed by classic Bluetooth) and low
cost for point-to-multipoint data transfer in WPANs and WBANs through different
devices like laptops, tablets and smartphones (Gonzalez et al., 2011). This standard
supports star topology only, known as piconet, where the network is composed of a single
master device that coordinates the activity of all the other devices (one or many slaves)
whose maximum number is 232 (Mackensen et al., 2012; Cavallari et al., 2014).
3.1 BLE protocol stack
As shown in Figure 3, the BLE protocol stack is composed of two parts, the controller
and the host part. Controller part is compound of the physical and link layer (Tabish
et al., 2013). The role of host controller interface (HCI) is to assure the connection of the
controller part with the host part in a BLE device.
Figure 3 BLE protocol stack (see online version for colours)

8 H. Fourati et al.
3.2 BLE physical layer
The BLE system operates in the 2.4 GHz ISM band, and uses 40 channels, three of
them as advertising channels and 37 as data channels (Mackensen et al., 2012; Cavallari
et al., 2014). The advertising channels features are: discovering devices, connection
establishment and broadcast. Data channels ensure communication and data transfer
between devices (Tabish et al., 2013). Two transceiver chip types are proposed in BLE
specification: single mode chips [Figure 4(a)] for BLE support only and dual mode chips
[Figure 4(b)] which supports both BLE and Bluetooth BR/EDR (Mackensen et al., 2012).
Figure 4 Host and controller BLE combinations (see online version for colours)
3.3 BLE link layer
The link layer defines six states for a BLE device: standby, advertiser, scanner, initiator,
master and slave. As shown in Figure 5, a device is in standby state when it is neither
transmitting nor receiving any data, and is not connected to any other device. However,
the link layer of a given device may have multiple instances of the link layer state
machine (some combinations are banned).
Other states will be explained in the following.
Figure 5 BLE link layer: states flow chart (see online version for colours)

Overview of four emerging mechanisms for e-health communications 9
• Broadcast phase:
In order to broadcast promiscuously or to advertise their presence to a device trying
to connect, Bluetooth devices utilise a method named advertisement. It consists of
sending messages (announcing that they are connectable devices) over BLE
advertising channels to other Bluetooth devices in the way of non-connection. The
device which needs to broadcast data periodically is the advertiser and the devices
aiming to find advertisers and receive data from them during BLE connectionless
advertisement are called scanners. An advertising event is the periodic time frame
during which the advertiser broadcasts advertising packets. Only the advertiser can
interrupt, at any time, the current advertising event and restart eventually another
one. If a scanner is listening to advertised messages, it becomes an initiator when it
tries actively to initiate a connection with an advertiser by sending a connection
request message. So the point-to-point connection is established and the exchange of
data between the two devices can begin.
• Connection phase
During the communication phase, only two device roles are considered: master and
slave. The master (which acted as initiator during the connection creation) monitors
the connection to the slaves (named the advertisers during the previous phase) of the
network and fixes their sleep/wake-up periods (Tabish et al., 2013). By default,
slaves are in idle state and wake up periodically according to the master instructions
to receive data packets. BLE combines two channel access strategies: frequency
division multiple access (FDMA) and time division multiple access (TDMA)
(Wendt, 2010, Wendt and Reindl, 2008; Gomez et al., 2012). Connection events are
non-overlapping time units, which form data channels. During each of them data
packets are transmitted through the physical channel with the same data channel
frequency. When both master and slave have no more data to communicate, the
connection event is closed and the slave returns to its default state (sleep) until the
master launches a new connection event with it. The conInterval parameter, specified
at Figure 6, takes values in (7.5ms, 4s) and have to be a multiple of 1.25ms. It
designates the duration between two consecutive connection events starts (Gomez
et al., 2012).
Figure 6 Connection events (see online version for colours)

10 H. Fourati et al.
3.4 1L2CAP
The logical link control and adaptation protocol (L2CAP) layer is mainly responsible for
channel management (creation, configuration and tear down) and the multiplex of upper
layers data (Gomez et al., 2012; Wang, 2014).
BLE is a powerful and widely used short-range communication technology.
Nevertheless, it supports only WBAN applications with a limited number of sensors and
networks organised as the star topology only.
4 IEEE 802.15.4 standard
In 2003, the IEEE working group proposed a standard for low-rate wireless personal area
networks (LR-WPANs), named 802.15.4. This standard defines the characteristics of the
physical and MAC layers for data communication devices using low data rate, low
power, low complexity, and short-range radio frequency (RF) transmissions (Heile et al.,
2003). Since then, several revisions of this standard were performed, whose last one
appeared in 2013, making changes basically to the PHY layer (Abdeddaim, 2013). In
addition to the first proposed version of IEEE 802.15.4, several revisions appeared later:
an enhanced version of IEEE 802.15.4 (IEEE Computer Society, 2011; Heile et al., 2003)
in 2006, 802.15.4a (Desai et al., 2013), 802.15.4b (Desai et al., 2013), 802.15.4c (Desai
et al., 2013), 802.15.4d (Desai et al., 2013), 802.15.4e (Desai et al., 2013; IEEE
Computer Society, 2012a), 802.15.4f (IEEE Computer Society, 2012b), 802.15.4g (IEEE
Computer Society, 2012c), 802.15.4j (IEEE Computer Society, 2013a) and 802.15.4k
(IEEE Computer Society, 2013b), etc.
4.1 Network topology
The network topologies supported under IEEE 802.15.4 standard are star and peer-to-
peer. The choice between those two topologies depends on the type of applications. As
shown in Figure 7, two different device types can participate in an LR-WPAN network; a
full function device (FFD) and a reduced-function device (RFD) (Heile et al., 2003).
Figure 7 IEEE 802.15.4 network topologies (see online version for colours)

Overview of four emerging mechanisms for e-health communications 11
• FFD: this kind of devices can be either a coordinator, a coordinator of a WPAN or a
simple device. It works under all topologies and communicates with all types of
devices.
• RFD: an RFD cannot be a WPAN coordinator. It is limited to star topology or in a
peer-to-peer network as a final device and can only communicate with an FFD.
4.2 IEEE 802.15.4 physical layer specifications
The IEEE 802.15.4 standard specifies two options for PHY layer, as shown in Table 1,
with the frequency band as a fundamental difference: the 2.4 GHz band which is
available worldwide and divided into 16 channels each providing a transmission rate of
250 kbps, and the 868/915 MHz PHY, which specifies operation in the 868 MHz band in
Europe and 915 MHz ISM band in the USA, and provides data rates of 20 kb/s and 40
Mb/s respectively (Abdeddaim, 2013; Eroglu, 1998).
Table 1 IEEE 802.15.4 frequency bands and data rates
Frequency bands Coverage Sub-channels Data rate
2.4 GHz Worldwide 16 250 kbits/s
868 MHz Europe 1 20 kbits/s
915 MHz Americas 10 40 kbits/s
Source: Ullah et al. (2010)
4.3 IEEE 802.15.4 MAC layer specifications
4.3.1 Access modes
4.3.1.1 Beacon enabled mode (or slotted mode)
In beacon mode, the WPAN coordinator manages the network communication, mainly
the access to the channel, through a superframe, as illustrated in Figure 8. The beginning
and end are both marked by a periodic packet called beacon. The superframe structure is
composed of an active and optional inactive periods. The interaction between the
coordinator and network nodes is only authorised during the active part which consists of
a contention access period (CAP; nine slots of equal duration), and a contention free
period (CFP; seven slots) (Ali et al., 2010). During the CAP, nodes communicate with
their coordinator using the slotted CSMA/CA mechanism (slotted carrier sense multiple
access with collision avoidance). As for the CFP part, a node may request the allocation
of exclusive guaranteed time slots (GTS). If there is still at least one free GTS, this
request will be fulfilled and the concerned node may use the time slot allocated to it via
the TDMA access mechanism (TDMA) (Khsibi et al., 2013; Cavallari et al., 2014).

12 H. Fourati et al.
Figure 8 IEEE 802.15.4 superframe structure (see online version for colours)
4.3.1.2 Non-beacon enabled mode (or unslotted mode)
In non-beacon-enabled mode, nodes use an unslotted CSMA/CA protocol to access the
channel: there is neither a duty cycle mechanism nor synchronisation. This mode is more
suitable for applications or nodes with no energy constraints (Heile et al., 2003; Khssibi
et al., 2014).
Various researchers, such as the authors of Timmons (2004), have considered IEEE
802.15.4 for WBANs thanks to its various features mentioned previously. However, their
results indicate that even if IEEE 802.15.4 can provide an acceptable compromise
between power consumption and QoS in some scenarios, there are situations (e.g.,
co-existence with multimedia and heavy data traffic) in which both performance criteria
cannot be met simultaneously. Therefore, this technology is neither power efficient, nor
scalable to meet the requirements of various WBAN applications. And this highlights the
need for proposing new solutions capable of guaranteeing both extremely low power and
QoS for WBANs, such as IEEE 802.15.6 std specially designed for WBANs (Alam and
Hamida, 2014).
5 IEEE 802.15.6 standard
The IEEE 802.15.6 TG developed the IEEE 802.15.6 Standard to provide an international
standard supporting low complexity, low cost, ultra-low power consumption, and
extremely reliable wireless communication for short range within the surrounding area of
the human body. IEEE 802.15.6 also supports a vast range of data rates from 75.9 Kbps
(narrowband) up to 15.6 Mbps (ultra wide band), to serve a variety of applications both in
the medical/healthcare and in the non-medical fields.
5.1 Network topology
A 802.15.6 WBAN consists of one and only one central node (coordinator or hub),
whereas the number of nodes varies from 0 tomMaxBANSize (under the IEEE 802.15.6
specification, mMaxBANSize=64). The communication range should be around a few
meters (typically 3 m), and it should support the one-hop or two-hop star topology. In a
one-hop star, frame exchanges occur directly between nodes and the hub of the WBAN
[Figure 9(a)]. In a two-hop extended star WBAN, the hub and a node are to exchange
frames optionally via a relay-capable node to form a two-hop restricted tree topology as
shown in Figure 9(b) (Astrin et al., 2012).

Overview of four emerging mechanisms for e-health communications 13
Figure 9 IEEE 802.15.6 network topology: centralised star network, (a) one-hop star topology
(b) two-hop extended star topology (see online version for colours)
(a) (b)
5.2 Layer model
As depicted in Figure 10, all nodes and hubs incorporate both PHY and MAC layers. For
transmission, MAC frames are sent by the MAC client (higher layer) to the MAC
sub-layer through the MAC service access point (SAP). Then, MAC frames are passed
from the MAC layer to the PHY layer through the PHY SAP. Upon reception,
MAC frames are delivered from the PHY layer to the MAC sub-layer through the
PHY SAP, and MAC frames from the MAC sub-layer to the MAC client through
the MAC SAP (Optical Zeitgeist Laboratory, IEEE 802.15.6 description). Additionally,
there can be a logical node management entity (NME) or hub management entity (HME)
that exchanges network management information with the PHY and MAC as well as with
other layers. The HME is a superset of the NME in terms of the management
functionality they each support. However, the presence of the NME or HME and the
partitioning between each one of them and the MAC or the PHY layer is not mandated
(Astrin et al., 2012).
Figure 10 Layer model (see online version for colours)
Source: Optical Zeitgeist Laboratory, IEEE 802.15.6 description

14 H. Fourati et al.
5.3 IEEE 802.15.6 physical layer specification
The IEEE 802.15.6 standard defines an unique medium access control (MAC) layer and
three different physical (PHY) layers in order to establish a reliable physical link to
transmit binary data (through a wide range of frequencies): human body communications
(HBC), narrowband (NB) PHY and ultra wideband (UWB) PHY. The choice between
those independent PHY layers defined in the IEEE 802.15.6 standard depends on the
target application: medical/non-medical, in, on or off-body.
5.3.1 Narrowband PHY (NB)
NBPHY is aimed at communication with wearable nodes on body and the implantation
nodes in body under several frequency bands:
• 402–405 MHz: medical implant communication system (MICS) band, which is used
for communication with medical implants
• 420–450 MHz: wireless medical telemetry system (WMTS) band (available in
Japan), for transmission of data related to a patient’s health (biotelemetry)
• 863–870 MHz: WMTS band (available in Europe)
• 902–928 MHz: the industrial, scientific and medical ‘ISM’ band, it is available for
use without a license in North America, Australia and New Zealand
• 950–956 MHz: available in Japan
• 2,360–2,400 MHz: this frequency band is proposed by the standardisation group to
be adopted in WBAN applications
• 2,400–2,483.5 MHz: ISM band, it is available worldwide, but there could be issues
of coexistence with other IEEE standards that use the same band.
It functions mainly in three aspects, i.e., activation and deactivation of the radio
transceiver, clear channel assessment (CCA: when there is carrier detection energy on the
channel, the node considers that the channel is busy, else it is free) and data transmission
and reception (Li and Zhuang, 2012). The data rates available under the IEEE 802.15.6
standard scale from 50 kbits/s to 970 kbits/s (depending on frequency band).
5.3.2 Ultra wideband PHY (UWB)
This physical layer is used for communication between on-body devices and for
communication between on-body and off-body devices (Movassaghi et al., 2014). In
UWB, the frequency range varies between 3.1 GHz and 10.6 GHz and it provides a
relatively wide range of data rates varying from 1 Kbps to 1 Mbps. The UWB PHY layer
has been designed in order to improve the robustness of the WBAN, and to provide
opportunities for high performance implementation, low complexity and low power
consumption operation. There are two different types of UWB technologies included in
the UWBPHY: impulse radio UWB (IR-UWB) and wideband frequency modulation
(FM-UWB). For IRUWB, there are two released IEEE standards: the UWB physical
layer option of IEEE Std 802.15.4-2011 (previously named IEEE 802.15.4a) which
provides for features that are desirable in medical applications such as very low power.

Overview of four emerging mechanisms for e-health communications 15
The data rates supported are 110 Kb/s, 851 Kb/s, 1.70 Mb/s, 6.81 Mb/s, and 27.24 Mb/s.
However, it does not support the levels of safety, quality of service (QoS), and security
features required in many of those applications. Thus, the latest standard including
the IR-UWB definitions have been created under IEEE 802.15.6 standard which has
features specifically designed to support medical applications (Pomalaza-Ráez and
Taparugssanagorn, 2012). The specification of this standard defines two modes of
operation: default mode and high QoS mode (Li and Zhuang, 2012). The default mode is
used in medical and non-medical applications whereas the high QoS mode is dedicated
for high priority medical applications (Hernandez, 2014).
5.3.3 Human body communications PHY (HBC)
HBC PHY provides the electrostatic field communication (EFC) requirements that cover
modulation, preamble/start frame delimiter (SFD) and packet structure, for the frequency
range of 5–50 MHz for implanted devices and their interaction with coordinating device,
with a data rate up to 2 Mb/s (Movassaghi et al., 2014; Alam and Hamida, 2014). In order
to provide a common platform for the multiple PHY layers (which are detailed in the
previous section), the IEEE 802.15.6 TG defined a new common MAC layer for the
purpose of channel access control. In this section, we present the medium access protocol
specificities including different access modes, phases and access mechanisms.
5.3.4 Time-base
According to 802.15.6, time axis is divided, as illustrated in Figure 11, into beacon
periods (superframes) of equal length and each beacon period (superframe) is composed
of allocation slots of equal length and numbered from 0 to s, where s < 255.
So every allocation interval may be referenced in terms of the numbered allocation
slot comprising it (Astrin et al., 2012).
Figure 11 IEEE 802.15.6 time reference-base (see online version for colours)
Source: Optical Zeitgeist Laboratory, IEEE 802.15.6 description
5.3.5 Access modes
To communicate with other nodes in an IEEE 802.15.6 network, a node must be
associated with this network. First, it has to scan its environment by listening to beacons
transmitted by coordinators. The node will then choose the coordinator to join (the closest
coordinator).
Then, the association phase comes. It consists of the exchange between the node and
the selected coordinator by:

16 H. Fourati et al.
• association request: transmitted from the node to the hub device to start the
association (or connection) process
• association response: received in case the hub device accepts the connection request.
Once this step is performed for each node of the network, the hub (or coordinator) sets
the time axis and the allocated slots. The hub also chooses beacon periods to bind the
superframes. The offsets of the beacon periods can also be shifted by the hub. The
beacons are usually sent in each beacon period unless prohibited by inactive superframes
(Movassaghi et al., 2014). In the beacon mode, a hub shall divide each active beacon
period into applicable access phases. It may also instantly define some superframes
(beacon periods) as inactive superframes when it transmits no beacons and provides no
access phases (just in case there are no allocation intervals scheduled in those
superframes) (Hur et al., 2013). The channel access coordination within a coordinated
network is provided by the coordinator through one of the following three access modes.
5.3.5.1 Beacon mode with beacon periods (or superframes)
In this channel access mode, the hub transmits beacon frames in active superframes
which may be followed by several inactive superframes whenever there is no scheduled
transmission. As illustrated in Figure 12, the superframe structure is divided into a
Beacon, transmitted in the first slot of each superframe. In this way, it identifies the
coordinator, allows power management and devices synchronisation and establishes a
common time-base, to enable time referenced allocations.
Figure 12 Beacon mode with beacon period (see online version for colours)
Source: Optical Zeitgeist Laboratory, IEEE 802.15.6 description
There are two exclusive access phases (EAP1 and EAP2) for highest priority traffic such
as reporting emergency events. There are also Random Access Phases (RAP1 and RAP2)
announced via a beacon frame for random access to the medium by nodes in the WBAN
of the hub. This applies to regular traffic only.
In addition, there is a managed access phase (MAP) for scheduled, unscheduled and
improvised access options and a contention access phase (CAP) which starts at the end of
the second beacon frame and ends at the end of the current beacon period, for contention
access to the medium by the nodes of the WBAN. This phase is for regular traffic only.
The Beacon2 frame is transmitted in order to indicate the beginning and the end of
the CAP phase. Any of these periods can be disabled when the hub sets their duration
length to zero except RAP1 period which is mandatory (Astrin et al., 2012; Optical
Zeitgeist Laboratory, IEEE 802.15.6 description; Alam and Hamida, 2014).

Overview of four emerging mechanisms for e-health communications 17
5.3.5.2 Non-beacon mode with superframes
The hub can access only the MAP in any superframe without using beacons. To inform
about the superframe boundaries, the hub transmits timed frames (T-Poll frames) also
containing their transmit time relative to the start time of current superframe. The total
superframe duration is covered either by only one types 1 or 2 access phase.
Type-1 access phase: this access phase is used for uplink and downlink allocation
intervals. It can improvise type-1 and type-2 polled and posted allocation intervals
anywhere outside the scheduled allocation intervals and provide type-1 and type-2 polled
allocation intervals within scheduled bilink (a communications link for transfer of
management and data traffic from a hub to a node or/and vice versa) allocation intervals.
In a type-1 access phase, type-1 polled allocation is conveyed in terms of its time
duration. The allocation intervals and access methods in a type-1 access phase are
presented in Figure 13 (Astrin et al., 2012; Bradai et al., 2013). Type-2 access phase: the
type-2 access phase is used for bilink and delayed bilink allocation intervals. The
difference (between type-1 and type-2) is that type-2 shall not schedule any bilink
allocation intervals after delayed bilink allocation intervals in the same type-2 access
phase. It can improvise type-2 polled and posted allocation intervals anywhere outside
the scheduled and delayed bilink allocation intervals. The allocation intervals and access
methods in a type-2 access phase are shown in Figure 14 (Bradai et al., 2013).
Figure 13 Allocation intervals and access method in a type-1 access phase (see online version
for colours)
Source: Bradai et al. (2013)
Figure 14 Allocation intervals and access method in a type-2 access phase (see online version
for colours)
Source: Bradai et al. (2013)

18 H. Fourati et al.
5.3.5.3 Non-beacon mode without superframes
In this mode, superframe and allocation slot boundaries are not established because there
is no time reference involved in accessing the medium. As shown in Figure 15, the
non-beacon mode without superframe medium access is based on unscheduled access
with type-2 polled uplink and post allocation for downlink by using CSMA/CA
mechanism (Alam and Hamida, 2014).
Figure 15 Non-beacon mode without superframes (see online version for colours)
5.3.6 Access mechanisms
5.3.6.1 Random access mechanism
Slotted ALOHA protocol: in this access method, the access to the channel by the nodes is
done with different traffic priorities named commonly contention probabilities (randomly
selected from the interval [0, 1]). A node have to maintain his probability to guess if it
obtains a new contended allocation (an uplink allocation, suitable for servicing
‘unpredictable’ uplink traffic) in an Aloha slot. A node is also able to start, use, modify,
abort and end a contended allocation (Bradai et al., 2011).
Slotted CSMA/CA protocol: in CSMA/CA, in order to get a new allocation, each node
sets its back-off counter to a random integer over the interval [1, CW]. The CW is
selected from the interval (CWmin, CWmax) where the values of CWmin and CWmax
vary according to the user priorities. When the timer expires, the algorithm then performs
one CCA operation at the BP boundary.
Every idle CSMA slot, the back-off counter is decremented by one and if the channel
is assessed to be idle, CW is decremented. The CCA is repeated if CW 6 = 0.
When the back-off counter reaches zero, the data is transmitted and theCWis
configured as follows (Optical Zeitgeist Laboratory, IEEE 802.15.6 description):
• it is set to CWmin, if the node did not get any allocation slot or if the frame
transmission was successful
• the CW is not changed, if the transmitter node does not require an ACK frame or if
this is its mth time where the node has failed consecutively, with m being odd
• the CW is doubled, if the node has failed consecutively n (even) times.
If after doubling CW, it exceeds CWmax, the CW is set to CWmin.
The back-off counter is locked by the node until the end of the current frame
transmission if the channel is busy. It is also locked by the node, if the current time is
outside of RAP and CAP for regular traffic or if the current time is outside of EAP, RAP,

Overview of four emerging mechanisms for e-health communications 19
and CAP for emergency traffic. Moreover, when there is not enough time to finish the
current transmission, the back-off counter is also blocked. On the other hand, the back-off
counter is unlocked when the channel is idle for the short interframe space period (pSIFS)
within a CAP or RAP for regular traffic and when there is enough time to finish the
current transmission (Optical Zeitgeist Laboratory, IEEE 802.15.6 description).
5.3.6.2 Improvised and unscheduled access mechanism
Improvised access mechanism: this method is employed to permit a hub to send poll or
post commands outside the scheduled allocation intervals (in beacon and non-beacon
modes): the poll frames (control frames) are used to start one or more transmissions and
the post frames (management frames) are used to send network information.
Unscheduled access mechanism: to obtain an unscheduled bilink allocation either in
beacon or non-beacon mode, a hub can use unscheduled polling and posting access to
send poll and post frames at any time. So it will permanently be in active state ready to
receive unscheduled polls or posts.
6 Discussion
With the emergence of a wide range of e-health applications requiring strict QoS
constraints, many studies tried to adapt existing mechanisms to handle the required QoS.
Yet, this comes frequently with an added complexity and energy consumption.
Table 2 General characteristics of studies technologies
Technology Frequency Data rate Coverage Type
Channel access
mechanisms
ANT 2.4 GHz ISM 1 Mbps 10 m (on-body
only) PAN TDMA
BLE 2.4 GHz ISM 1 Mbps 10–100 m
(on-body only) PAN FDMA, TDMA
IEEE
802.15.4 868 MHz, 915
MHz, 2.4 GHz
ISM
20 Kbps, 40
Kbps, 250 Kbps 75 m PAN CSMA/CA,
TDMA
IEEE
802.15.6 868 MHz ISM,
915 MHz ISM,
2.4 GHz ISM
;1 Gbps 10 m WBA
N CSMA/CA,
TDMA, slotted,
aloha, etc.
Table 2 shows the general differences between ANT, BLE, IEEE 802.15.4 and the newly
defined IEEE 802.15.6 whereas Table 3 summarises the types of applications each
mechanism is designed for. As our study shows, it is notable that 802.15.6 is a very
flexible standard especially regarding the variety of data rates and its MAC layer
mechanisms. This standard is designed in a way that it could be customised to adapt to a
wide range of application requirements while offering special features to support e-health
applications. At this level, 802.15.6 is the only existing standard that dedicates special
functions to QoS constrained e-health applications while being able to handle any other
type of low energy and low complexity application.

20 H. Fourati et al.
Table 3 Main applications of the studied technologies
Technology The main target
applications Advantages Disadvantages
ANT Sport, fitness and health
products A lightweight protocol
stack, an ultra-low power
consumption
A proprietary technology
BLE E-health and
entertainment
applications
Robustness, low cost, low
power consumption,
better mobility (use of
powerful devices: such as
tablets and smartphones)
Lack of multi-hop
communication, limited
scalability (only star
topology is supported)
IEEE
802.15.4 Different applications in
medicine and
entertainment
Low complexity, low
cost, low power
consumption, low bit rate
transmissions, large
coverage
Does not support
adequate QoS for all
WBANs applications
IEEE
802.15.6 E-health and sport
applications A wide range of bit rates
is supported Some of the bands are not
suitable for WBANs
applications (e.g.: HBC
cannot support video or
voice transmission)
With the introduction of IEEE 802.15.6, it is clear that the focus will be the definition of
an enhanced framework that comes to overcome all limitations of existing mechanisms,
yet to fuse their advantages.
7 Conclusions
With the rapidly increasing demand for medical and non-medical applications using
ubiquitous communications, in/on (around) the human body, WBAN is playing today an
important role in the daily lives of many people around the world. Revolutionising
healthcare systems as well as non-medical services, WBAN are taking advantage of the
advancements provided by different standards designed to provide low complexity and
low energy consumption communications.
In this paper, we briefly presented ANT, BLE, IEEE 802.15.4 and IEEE 802.15.6 key
characteristics and studied their PHY and MAC layers specifications. In addition, we
made a comparison between those standards based on their different features.
IEEE 802.15.6 standard is the newest standard and the only one that was specifically
designed for e-health applications. Its wide range of data rates and different MAC access
modes, handling different QoS constrains, make it a very promising technology that can
replace existing ones and bring new opportunities for healthcare systems.
Future work should investigate deeply the performances of IEEE 802.15.6 MAC
layer when applied in critical and QoS-constrained e-health applications.

Overview of four emerging mechanisms for e-health communications 21
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