Wireless body area networks : A comparative [601262]

Wireless body area networks : A comparative
overview between the IEEE Zigbee and the IEEE
BAN standards

Reda CHEFIRA
LAMAI, Faculty of Sciences and Technologies
Cadi Ayyad University
Marrakesh , Morocco
[anonimizat] Said RAKRAK
LAMAI, Faculty of Sciences and Technologies
Cadi Ayyad University
Marrakesh, Morocco
[anonimizat]

Abstract— Wireless body area networks is a forthcoming
technology which interconnect devices all around a body. Related
to Wireless sensor networks and to Internet of Things, t his smart
technology is closely connected to many fields such as health,
gaming and sports. Due to similarities of the standardization , this
paper proposes a technical review about the functions of WBANs.
Topologies, PHY and MAC layers are deeply examined to explain
the possibility of using the two norms , the IEEE 802.15.4 Zigbee
and the IEEE 802.15.6 BAN in a WBAN project.
Keywords —WBANs; IE EE standards; zigbee; BAN; WSN ;
WPANs
I. INTRODUCTION
Because of the recent advancements in electronics and
computing sciences, the development of efficient smart sensors
become handy. This gave a powerful boost to the development
of technology in the service of humanity in goal t o enhance
one’s quality of life [1]. Nowadays, many fields are closely
connected to w ireless sensor networks viz. Healthcare[2],
military [6] and entertainement[13] . Sensors are responsible of
exchanging sensed data among network nodes and then send
all data or targeted ones to base station. To monitor vital body
parameters and movements, d eveloping small -devices that
needs short -range and large data rates considers many technical
challenges to perform well. Designed for this purpose, Wireless
body area networks are a typical variant of Wireless Sensor
Networks , can interact with Internet Of Things to incorporate
limited number de tiny sensors implanted on, in or around
bodies in order to gather vital data. WBANs use proprietary
PHY and MAC protocols[3] simultaneously with existing
WPAN standards. The literature discusses mainly two used
technologies: the IEEE 802.15.4 Zigbee standard and the IEEE
802.15.6 BAN standard [4]. This paper is organized as follows:
after this Introduction, section II gives a brief overview of used
standards in Wireless Personal Area networks including those
used in Wireless Body Area network project s. A complete
investigation of the IEEE 802.15.4 and Zibgee standard s is
provided in section III. Section IV describes the IEEE 802.15.6
BAN standard, its topologies, PHY and MAC layers. Current
work has been concluded in s ection V. II. IEEE 802.15 WPAN S
The 802.15 group of IEEE standards specifies a diversity of
wireless personal area networks (WPANs) for different
applications. The current list of active projects can be found
on[5]. This group is d ivided into ten task groups w ith different
specificities. We describe the three common used ones:
A. IEEE 802.15.1
The first task group of WPAN i s based on Bluetooth
technology [7]. It supports ad hoc, terrestrial and wireless
standard for short -range communication. Moreover, it defines
PHY and MAC characteristics for wireless connectivity.
Designed for low cost devices, this technology includes three
classes supporting variable ranges from one to 100 meters.
B. IEEE 802. 15.4
Zigbee is a low tier, ad hoc, terrestrial and wireless standard
based on 802.15.4 standard. It is used to create PAN with small
and low -power digital radios. Its low power consumption limits
transmission distances to 1 –10m line-of-sight , depending on
power output and environmental characteristics.
C. IEEE 802.15.6
BAN task group is formed in November 2007 to focus on a
low-power, low -complexity and short -range wireless standard.
With its special design, it aims to optimiz e devices and
operation on, in, or around bodies. The task group serves a
variety of applications including medical (e-health) and also
entertainment (gaming, sports). This make the communication
much easier and more comfortable.
Fig.1 shows a power level comparison between all the
standards cited above. We can conclude the required
specificities of WBANs in power and data rate .
III. IEEE 802.15.4 – ZIGBEE STANDARD
Based on previous ve rsion of IEEE 802.15.4 standard [8],
Zigbee defines layer 3 and above . It diffe rs from its
predecessor in its ability to use aside physical and MAC layers,
RF communication [9] and an efficient network system capable
of allowing poin t to point energy communication . This
standard can implement routing, encryption, application

Fig. 1 : Power and Data Rate Requirements for the IEEE 802.15.6 WBAN
[18]
services on star, mesh and tree topologies, even authorize to
reduce power while keeping the main node waiting for
communication (semi -centralized network) .
A. Topolo gies
Zigbee standard proposes three topology types out of four
supported by 802.15.4. These common topologies are depicted
below and illustrated in Fig. 2. It defines the network layer
architecture for star, tree and mesh network topologies and
affords in the application layer, a framework for application
programming.
 Star topology: Nodes communicates only with the
coordinator. Because of this packet exchange
condition, the coordinator may become bottlenecked
which can decrease the network’s lifetime.
 Mesh topology: Like tree topology, it consists of a
coordinator, several routers and end devices too. This
scalable topology supports a multiple -hop access for
packets to rich their destination. Unlike the star
topology, the node has alternative to choose sever al
paths if the principal chosen one fails.
 Tree topology: The network consists of a central node,
which is a coordinator, routers, and end devices. Only
a coordinator and a router can have children. Its
functions are similar to a cluster tree topology.
Table. 1 shows a brief comparative overview of the main
technical aspects for the star, mesh and tree topologies. It
contains benefits and drawbacks of each topology.
B. PHY : Physical layer
The physical layer of the IEEE 802.15.4 supervises many
functions vi z. channel selection, energy and link quality
estimation. It supports three frequency bands. Each one
gathers a certain number of channels that use the direct
sequence spread spectrum access mode.

Fig. 2 : Zigbee Topologies
C. MAC layer
In this layer, two different types of nodes, RFDs an d FFDs
define the MAC behavior . Reduced Function Devices nodes
(RFD s) can only operate in a mode serving end device , and
exchange sensed data with a single FFD. If nodes are Full
Function Devices ( FFDs), they can both act like a coordinator
(PAN coordinator) , and manage synchronization services, or
like an end device and gather data with appropriate actuators .
Generally, the IEEE 802.15.4 standard aims to ease
installation and use s a short -range app roach in order to
optimize battery life. So a Personal Area Network act as a
coordinator and may use a super frame under an active or an
inactive portion. This depend s on its energy status. Fig. 3
shows the super frame structure under active and inactive
portions . In the Inactive part, all devices sleep . Active portion
consists of 16 slots that can be further divided into CAP and
CFP. The c ompetitive n odes use a slotted CSMA -CA protocol
to contend for the usage of channel. If a node gets access to
the Conte ntion Access Period (CAP ), it transmit s its data once
an access is guaranteed to the Contention Free Period (CFP).
When an end -device needs to send data to a coordinator (non
GTS) it must wait for the beacon to synchronize and later
contend for channel access[17]. End devices use to sleep most
of the time in order to save their battery life and wake up only
to check if there is a need to receive a message from the
coordinator. A GTS, allocated by the PAN coordinator allows
devices to operate on the channel within a portion of the
superframe.
D. Upper layers
Zigbee aims to standardize the higher layers of the IEEE
802.15.4. The Network layer (NWK) manages not only the
routing protocols in the network but also assur es reliability
and security for transmissions among devices. Zigbee uses the
mentioned above topologies. In a Tree network topology,
address assignment is utilized to retrieve the routing paths.
While receiving a packet, the node checks if it is destined to it
or to one of its end devices. If so, the package is forwarded,
otherwise, the node’s role is to relay the package to other
nodes along the tree. The Mesh topology is characterized by
two different options, reactive routing and tree routing,
depending on the routing capacity. The Application Supp ort
Sublayer (APS) affords the necessary services for endpoints
and the Zigbee Device Object (ZDO) in order to transfer data
in a unified communication structure.

Table. 1 : Benefits and drawbacks of Zigbee topologies

Topologie s Technical analysis
Benefits Drawbacks
Star Synchronization
Low latency
Low power operations Small scale
Mesh Resilience
Expandability
Low latency Sleep mode
Storage
Tree Support sleep mode
Multihop communication Long latency

Fig. 3 : Super frame for Mac Layer

managing role to control device types, network and check for
security services.
IV. IEEE 802.15.6 – BAN STANDARD
A. Topologies
BAN proposes two topology types. Since all nodes and the
coordinator are directly connected and exchange data in the
network, the topology seems to define itself as a one -hop star.
A two -hop extended star topology can also occur if there is a
relay capable of exchanging data between the hub and a node.
Fig. 4 shows these two possible topologies.
Star topology allows two different communication
methods, beacon and non -beacon modes. In beacon mode, the
network coordinator controls communication, defines the start
and the end of a super frame. T he user manages the length of
the beacon and defin es the d uty cycle of the system [12].
However, in the non -beacon mode, a node poll the coordinator
after powering up to receive data.
B. PHY : Physical Layer
The IEEE 802.15.6 standard defines three PHY distinct
layers viz. Narrow Band (NB), Ultra -wide Band (UWB) and
Human Body Communications (HBC) [10]. Every BAN has
one coordinator (or hub); while there can be up to 64 nodes
[11]. The function of the hub is to establish a time base
dividable into beacon periods.
 NB: The Narrow Band physical layer
activate s/deactivates , along the channel, both the node
sensors and data transmission. NB is also clearing
channel assessment (CCA) within the current channel
that is responsible of transmitting the signal. A
physical -layer service data unit (PSDU) becomes a
physical -layer pro tocol data unit (PPDU). Both
physical -layer preamble and physical -layer header serve to decode and demodulate the PSDU. Fig. 5
illustrates the schema description.
 UWB: Ultra Wide Band layer supports two frequency
bands, a low er and a high er one. The lower bandwidth
consists of eight channels, whereas the higher band
has 3 channels. Each channel has its own specified
frequency and number. To be compatible with UWB,
a device needs to support at least one of these
channels.
 HBC: The Human Bod y Communications PHY
technology is based on electric field communication
(EFC) and has two frequency bands. It contains a
PLCP preamble, a frame check sequence (FSC), a
PLCP header and a payload (PSDU).
C. MAC layer
In Wireless body area networks the entire channel is
divided into super frame structures. A beacon period bounds
each super frame and the hub selects these boundaries in order
to opt for the allocation slots[16]. The MAC layer supports
three different modes and any phases are active in these
methods viz. Exclusi ve Access Phase (EAP), Random Access
Phase (RAP), Contention Access Phase (CAP) and finally
TYPE I/II phases :
 Beacon mode with super frame boundaries, where
every beacon period receives a beacon frame or a
signal sent by the hub. Super frames contains man y
slots. Beacons in this mode are characterized by the
role of initialization , identification and network
management.
 In the non -beacon mode with super frame boundaries,
the transmission time depends on the start of the
current super frame. It is given by a T-poll period that
control both timestamp and synchronization.
 Finally the non -beacon mode without superframe
boundaries, unlike the other modes, there are no super
frame boundaries and only an unscheduled type II
polling access method is provided by t he hub.

Fig. 4. BAN topologies [11]

Fig. 5. PPDU structure [15]
D. Access mechanisms
CSMA/CA and slotted aloha a ccess are the main access
method s employed in BAN standard together with Exclusive
Access Phase (EAP), Random Access Phase (RAP) and
Content ion Access Phase (CAP) for the allocations. The EAP
is used for high priority traffic when a node sends data types
frame s in an emergency access phase, whereas the CAP and
RAP are used for regular traffic. We explain briefly the three
mechanisms depicted b elow as follows:
 Slotted Aloha Access: In the network, a node obtains
an allocation based on contention probability. This
mechanism allows nodes the same privileges that a
CSMA/CA mechanism offers.
 CSMA/CA : This mechanism grants some privileges
like initia te, modify abort and en to contend new
allocations.
 Unscheduled and Improvised Access: The hub may
use these two mechanisms in some particular
conditions such as emergency communication
service. Depending on the allocation, nodes can sleep
to save their b attery life. Both employ unscheduled
polling and posting access but unlike unscheduled
access, improvised access has the privileges in poll
and post allocations of a RAP.
V. CONCLUSION
In this paper, we presented an overview of the two main
standards used in Wireless Body Area Networks, namely the
IEEE 802.15.4 Zigbee and the IEEE 802.15.6 BAN. We
highlighted the t opologies, PHY and MAC layers in order to
illustrate the major specificities of each standard. This paper
can be useful for a common usage to under stand the key
concepts of WBANs standards . As a future work, the
challenges in these protocols will be examined and an
application oriented Internet of Things will be done.
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