1. 4 4 ZigBee and Bluetooth are different
by design and are optimised for
different applications. Real
industrial wireless networks will
inevitably be hybrids including
both in complementary roles.
IEE Computing i Control Engineering | April/May 2005

2. ZigBee and Bluetooth
ONLY IN THE LAST 10 YEARS OR SO, WITH CONTINUING ADVANCES IN
SEMICONDUaOR, RADIO AND BATTERY TECHNOLOGY HAS SIGNIFICANT EFFORT BEEN
MADE TO DEFINE AND DEVELOP WIRELESS TECHNIQUES FOR DATA NETWORKS.
Bluetoothstrengths and Weaknesses
for Industrial applicationsBy Nick Baker
Most industry analysts are fore-
casting explosive growth in the use of
wireless data network technologies in
industrial applications in the next few
years.
Figure 1 depicts the wireless spectrum
in terms of two key performance characteristics - wireless
radio range aiid data transmission rate. Other performance
characteristics will be discussed later but in terms of these
two parameters it is important to recognise that the two
IEEE standards that underpin ZigBee (802.15.4) and
Bluetooth (802.15.1) are intended to differentiate them from
each other.
The IEEE defmes only the Physical (PHY)
and Medium Access Control (MAC) layers in
its standards. Eor both ZigBee and Bluetooth
separate alliances of companies worked to
develop specifications covering the network/
link, security and application profOe layers so
that the coniniercial potential of the standards
could be realised.
Bluetooth originated in 1994 when Ericsson
began to examine alternatives to cahles tbat
linked mobile phone accessories. In 1998
Ericsson was joined hy IBM, Nokia. Intel, and
Toshiba to form the Bluetooth Special Interest
Group (SIG) which defined the initial
specification. In mid-1999 the SIG approached the IEEE and
asked them to formally adopt the Bluetooth specifications.
The 802.15.1 Standard was published in 2002. Thousands of
Promoter. Associate, and Adopter companies have since
joined the SIG which develops, publishes and promotes
Bluetooth and runs a qualification program to foster device
interoperability
ZigBee's origins date only from 1998 when Motorola
started work on this type of low power mesh networking.
The IEEE 802.15.4 standard was based on Motorola's mid-
2001 proposal and was ratified in May 2003. Phillips,
Motorola, Invensys, Honeywell, and Mitsubishi -^
WAN
Fig I: The wireless landscape
IEE Computing & Control Engineering | April/May 2005

3. joined together and formed the ZigBee Alliance in mid-2002
to develop and promote this technology and leverage the
standard. Ember. Freescale and Samsung joined as
promoters later. They worked together on defining the
network, security and application layers of the ZigBee
specification, which was ratified in December 2004. There
are now well over 100 affiliate members of the ZigBee
Alliance representing semiconductor manufacturers,
technology development companies, OEMs, end user
coinpanies and systems integrators.
TECHNOLOGY OBJEaiVES
So wbat are the objectives behind the two technologies?
Looking in a little more detail we can see some clear
differences and some similarities.
Firstly looking at Bluetooth, the SIG mission statement
defines an objective targeting short range and mobile
Direct Connection
• Wire replacement
• Point to point
Star
• One central routing and controi point
> Singie-iiop-point to multi-point
' All data flows through centrai point
< Exampies are UVifl. Bluetooth. CSM
Mesh
• Multipie data paths
• Muilt-hop
• Seif configuring, seif healing
• Examples are ZigBee, EmberNet SensiNet
Fig 2: Wireless network topologies
products and this is echoed by the IEEE in defining a
'Personal Operating Space" (POS) of 10m radius and
allowing for mobility The use of the word 'personal' links
this technology at its core to provision of ad-hoc
connections hetween devices used by humans.
The types of device interoperability profiles that bave
been developed for Bluetooth [cordless telephony headset,
LAN access, fax, printing, hands-free, etc.] and the types of
application areas in which products bave been developed
are very much in line with the intent of the SIG and tbe
standard.
Looking at ZigBee the key additions or differences in
terms of the alliance mission statement are low power,
networked |as opposed to connected], and open standard.
The 802.15.4 standard also speaks of a POS and 10m range
but recognises the possibility for greater range at lower
data rates.
These mesh self-bealing networks, which allow mobility
of end nodes within tbe network and, by virtue of their
multi-hop capability can cover large areas, will have a very
wide range of applications from industrial sensing and
control to huilding automation and security, home
automation and even in interactive toys.
DESIRABLE CHARAaERiSTiCS OF NETWORKS
Let's focus our attention on industrial wireless data
networks and their desirable characteristics.
Range: At least 50m in "cluttered" industrial RF
environments where there is often a lot of metal in
equipment and building structure and increasing amounts
of radio interference.
Data rate: In industrial sensing and control applications
required data rates vary widely by application but are often
low and/or intermittent.
Network latency [or how long the data takes to getfrom
origin to destination/: This varies
widely by application. It should
ideally be possible to tune tbe
network availability or response to
tbe application i-equirement at the
end-node to optimise performance.
A second consideration is how
long new devices take to join the
network.
Powerprofile: Ideally under all
circumstances devices would be
battery-operated to avoid both
power and data wiring costs and
increase tlexihility
Security: At the lowest level:
How sure can I be that the data did
get from origin to end point
accurately and completely? This is
critical in sensing and control applications where humans
do not normally validate data at the operating time
interval. At the highest level: How sure can I be that my
network and its data cannot be 'hacked' and the data
misappropriated or meddled with? Am I able to control
which devicesjoin my network?
Operating Frequency: The main requirement here is
operation in one of the unlicensed bands for operating cost
and regulatory reasons. Globally tbe 2.4GHz ISM band is
emerging as the preferred band, which brings increased
risk of interference from otber devices. Much of the
overhead of wireless network protocols involves strategies
to avoid interference degradation of network integrity
Engineering and design complexity: More complexity
will drive up cost for product developers, implementers and
end-users. The technology should ideally be relatively
simple to understand and engineer into products, have low
overheads in I^^s of system operation and design, and be
lEE Computing & Control Engineering i April/May 2005

4. ZigBee and Bluetooth
simple to implement and support.
Network topology: Increasing the number of possible
communication paths through the network increases the
likelihood that the message will be received at its
destination, even if after multiple hops. Tbis makes
network traffic more complex but will increase the network
resilience and reliability Ideally the fuH range of topologies
[Figure 2] sbould be supported.
Number of devices: The numher of required
measurement points is increasing significantly often in a
'retrofit' manner, to more completely measure industrial
environments and processes for better control and for
compliance and audit purposes. In most real industrial
applications many tens, hundi'eds and possibly thousands
of devices could he required in a network.
Scalability/Extendability: Industrial environments
constantly change - growing or shrinking in size and the
number and nature of measurement points. Sometimes
this is short term - for example. Intensifying measurement
during commissioning stages of a new plant. Tbe wireless
network must be capable of accommodating these changes
without significant support overhead to tbe enterprise.
Flexibility:The networking technology should be flexible
in terms of tbe uses to which it might be put. It should be
agnostic to the type of sensors or output devices attached
and able to be implemented for different device types
without a lot of device-specific requirements within the
network or tbe protocol stack.
Resilience and reliability: It must have the real world"
Bluetooth is 'always on' and must
be recharged frequently; ZigBee
'sleeps' most of the time and has
years of battery life , ,
performance capability to deal with transient interference
and obstacles. It must be able to manage and adjust the
network configuration, ideally automatically and know or
be alerted when the network encounters a situation that it
cannot resolve. During the network implementation it
should be possible to design out unnecessary single points
of failure.
COMPARING ZICBEE WITH BLUETOOTH
We turn now to a comparison of the two technologies
in terms of tbe desirable features above and reference
Fig 3.
Range: As designed and without special equipment it is
clear that ZigBee has the potential to operate over a greater
range especially in 'low clutter'-radio environments. Tbe
upper range limit has really only been possible with
proprietary mesh networking protocols, such as SensiNet.
running over 802.15.4 radios.
Data rate: Where higher data rates are important
Bluetooth clearly has the advantage and can support a
wider range of traffic types than ZigBee. ->
characteristic
Range
As designed
Special kit or outdoors
Data rate „ ,,.,-,,,,„,.„
Network Latency (typical)
New slave enumeration
Sleeping slave changing to active
Active slave channel access
Power profile
Security
Operating Frequency
Complexity
Networii Topology
Number of devices per network
Scalability/Extendability
Flexibility
Resilience and reliability
ZigBee
10-100 metres
up to 400 metres
30ms
15ms
15ms
Years
Optimizes slave power requirements
128 bit AES and application layer user definable
868 Mhz, 902-928 MHz, 2.4 GHz ISM
Simple
Adhoc star, mesh hybrid
2 to 65,000
Very High/Yes
Very High
Very High
Bluetooth
10 metres
100+ metres dep. on radio
20s
3S
2ms
Oays
Maximises adhoc functionality
64 bit 128 bit
2.4 GHz ISM -^M
Complex
Adhoc piconets •^^^.
8
-:flHK^ Low/No
Medium, profile dependent
Fig 3: Comparison of desirable characteristics
IEE Compjtmg & Control Engineering | April/May 2005

5. Focus on remote sensing and control
• Warehouses, Fle«t management Factory, Supennarhets, Office
complexes
• Cas/Water/Eiectric meter, HVAC
• Smoke, CO, H,0 detector
• Refrigeration case or appliance
• Equipment management services ft Preventative maintenance
• Security services
• Lighting control
• Assembly line and work fiow. Inventory
• Materiait processing systems (heat gas flow, cooiing, chemical)
Temp sensor
Energy, diagnostics, e-Business services
• Gateway or Field 5ervice links to sensors ft equipment
Monitored to suggest PM. product updates, status changes
• Nodes iink to PC for database storage
PC Modem calls retailer. Service Provider, or Corp headquarters
Corp headquarters remoteiy monitors assets, billing, energy
management
Fieid Service or
mobiie worker
1004 Tba Zi(BM MHanca, Inc
Materiais handDng
Fig 4: ZigBee industrial applications
Service
Provider Retailer
Network latency: To be able to sleep for extended periods
to conserve power and achieve acceptable network latency
ZigBee end devices need to wake up very quickly, transmit
and/or receive and go back to sleep. The multi-hop nature
of mesh networks also increases latency. Bluetooth is
clearly designed for single hop device-to-device where the
nodes do not sleep for much of the time and as a result
network access is fast.
Powerprofile: Bluetooth devices are constantly alert for
available networks for them tojoin. To do that they have to
be awake. The power profile is 'always on" to maximise this
ad hoc networking functionality with days of battery life
and regular recharging required. ZigBee has been
developed specifically to permit low power consumption
and years of battery life.
Security: Both protocols have security huilt in. 802.15.4
specifies use of the 128 bit Advanced Encryption Standard
High speed Bluetooth embodies
device profiles for equipment
interoperability whereas ZigBee is
intended to be an open global
standard
and the ZigBee specification defines how to handle
encryption key change and multi-hop transmission
security Security is also user definable within the
application layer for ZigBee networks. Beyond encryption
each ZigBee node retreives a unique short address from the
network coordinatoi' and each ZigBee network has a unique
ID. In addition ZigBee networks can also be open or locked
to new devices. Bluetooth uses 64 or 128-bit encryption
based on the SAFER+ algorithm for authentication and key
generation.
Operatingfrequency:ZigBee supports most of the widely
used unlicensed ISM bands in Europe, NA. and around the
world whereas Bluetooth operates solely on the 2.4GHz
band. Although the 2.4 GHz band is becoming a defacto
global standard (many companies in North America now
prefer it to 915 MHz) support for other bands can he
important to industry for legacy reasons.
Complexity: We have mentioned the relative complexity
of the Bluetooth protocol stack compared to ZigBee and the
fact that Bluetooth embodies device profiles for equipment
interoperability whereas ZigBee is intended to be an open
global standard - a ZigBee compliant device from any
manufacturer should interoperate with any other.
Deployment complexity and operational support of pure
ZigBee networks are as yet untested in the real world but
makers of proprietary 802.15.4-based mesh networking
technology such as Sensicast have found that
implementation and support with networks of several
hundred nodes is relatively simple. Bluetooth complexity
is, in practice, limited by the small numher of devices
allowed in each network.
iEE Computing & Control Engineering | Apnl/May 2005

6. ZigBee and Bluetooth
Network topology and number of devices: The increased
range of options in terms of topology and the significantly
larger numher of devices per network would suggest that
ZigBee will have much greater capahility to address the
spectrum of industrial situations.
Scalabiiity/Extendabiiity: ZigBee has a significant
advantage here in terms of the ease of network growth to
quite large scale implementations and the ahility to use the
flexible topologies to accommodate real-world situations.
Flexibility: In theory both protocols are tlexible and can
carry any type of data. In practice the profile dependency
of Bluetooth carries some built in inflexibility. In some
ways this category could be seen as a qualitative
amalgamation of all the preceding categories which
suggest that ZigBee is the more flexible approach for
industrial applications except where there is a need for
higher data rates.
Resilience and Reliability: From the purely technical
perspective ZigBee wins here in terms of the range of
industrial situations that are likely to be encountered, due
to its data packet acknowledgement. CSMA-CA approach,
encryption, mesh multi-path transmission redundancy and
ahility to physically worii ai'ound the buUt enviromnent due
to the hybrid network configuration options. Within its
constraints Bluetooth is resilient - it works very well for
certain application types.
ZIGBEE APPLICATIONS
Figure 4 shows the wide variety of foreseen applications
for ZigBee and other 802.15.4-hased proprietary
technologies. There is a focus on remote sensing and
control reflecting the ZigBee mission statement, and the
possibilities are virtually limitless.
Many of these applications apparently require the
adoption of ZigBee by OEMs on a large scale. Before that
happens there is a huge opportunity to retrofit enhanced
sensing and control into existing huilt environments using
ZigBee/802.15.4 technology through 'off-the-shelf
production-ready mesh networking elements linked to any
of the wide range of existing sensor types and actuators.
Clear advantages over classical wired installations are
speed, low cost, tlexihility and long-term re-usability all of
which can help increase enterprise productivity
ZigBee is not yet field-tested for these applications. Many
organisations are developing ZigBee products but this is
still in the early stages hecause the initial specification was
only ratified a few months ago, in December 2004. Since
802.15.4 was published many companies have been
developing 802.15.4-based mesh networks. All the existing
products in this sector use proprietary non-ZigBee network
protocols on top of 802.15.4 although many are designed to
support the ZigBee protocol stack on the same hardware.
Examples are EmherNet. SensiNet and Millennial Net.
Looking at Bluetooth there is clearly an intended focus
on short-range cahle replacement for medium bandwidth
device to device connections. Beyond this. Bluetooth access
points can extend LANs and corporate networks to
Bluetooth devices.
In the industi'ial world the most likely uses for Bluetooth
are for machine to machine communication and for ad hoc
connectivity between mobile computing devices and fixed
equipment. This could he for diagnostics, data transfer or
configuration, especially in cases where use of temporarily
connected cahles would be difficult such as in certain types
of hazardous environments.
Examples of current uses largely follow this trend
because Bluetooth has been established as a useful standard
for at least two years longer than ZigBee. It has reached an
early level of maturity but is still heing promoted into new
usage areas and extended in capability and refmed.
In summary it seems clear that ZigBee and Bluetooth
are different by design and are optimised for different
In industry Bluetooth will most likely be used
for machine-to-machine communication and
for adhoc connectivity between mobile
computing devices and fixed equipment
applications. Real industrial wireless networks will
inevitably be hybrids including ZigBee/802.15.4 and
Bluetooth in complementary roles that suit the
characteristics of each. The key to success will be in
deploying the right wireless technologies for the
requirements of the application and avoiding the
temptation of trying to make one technology meet all
needs.
However, considering the wide range of typical
iTidustrial opportunities for wireless network use it seems
clear that ZigBee and 802.15.4-hased proprietary protocols
can meet a wider variety of real needs than Bluetooth. The
key reasons are the intrinsic value to the industrial
enterprise of long-term "unattended" battery operation,
greater useful range, flexihility In a number of dimensions
that were highlighted earlier and finally the inherent
resilience and reliability of the mesh networking
architecture. •
The author, Nick Baker, is the managing director of Adaptive
Wireiess Solutions. He many be reached at nbaker@adaptive-
wireless.co.uk
IEE Computing i Control Engineering | April/May 2005 25