BLUESTAR CHAPTER-1 INTRODUCTION Bluetooth is a wireless communication technology that provides short-range, semi-autonomous radio network connections, and offers the ability to establish ad hoc networks, called piconets. It has also been chosen to serve as the baseline of the IEEE 802.15.1 standard for wireless personal area networks (WPANs). WPAN can be integrated with large wide area networks (WANs) to provide Internet connectivity in addition to access among these devices. It is much likely that Bluetooth devices and wireless local area networks (WLANs) stations operating in the 2.4 GHz frequency band should be able to coexist as well as cooperate with each other, and access each other’s resources. These cooperative requirements have encouraged an intuitive architecture, called Bluestar, whereby few selected Bluetooth devices, called Bluetooth wireless gateways (BWG), are also members of a WLAN, empowering low-cost, short-range devices to access the global Internet infrastructure through the use of WLAN basedhigh-powered transmitters [1]. Bluetooth Wireless Gateways (BWGs), are also IEEE 802.11 enabled so that these BWGs could serve as egress/ingress points to/from the IEEE 802.11 wireless network. An important challenge in defining the Bluestar architecture is that both Bluetooth and WLANs employ the same 2.4 GHz ISM band Dept. of Electronics and Communication Page 1
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BLUESTAR
CHAPTER-1
INTRODUCTION
Bluetooth is a wireless communication technology that provides short-range, semi-
autonomous radio network connections, and offers the ability to establish ad hoc networks,
called piconets. It has also been chosen to serve as the baseline of the IEEE 802.15.1 standard for
wireless personal area networks (WPANs). WPAN can be integrated with large wide area
networks (WANs) to provide Internet connectivity in addition to access among these devices. It
is much likely that Bluetooth devices and wireless local area networks (WLANs) stations
operating in the 2.4 GHz frequency band should be able to coexist as well as cooperate with each
other, and access each other’s resources. These cooperative requirements have encouraged an
intuitive architecture, called Bluestar, whereby few selected Bluetooth devices, called Bluetooth
wireless gateways (BWG), are also members of a WLAN, empowering low-cost, short-range
devices to access the global Internet infrastructure through the use of WLAN basedhigh-powered
transmitters [1]. Bluetooth Wireless Gateways (BWGs), are also IEEE 802.11 enabled so that
these BWGs could serve as egress/ingress points to/from the IEEE 802.11 wireless network.
An important challenge in defining the Bluestar architecture is that both Bluetooth and
WLANs employ the same 2.4 GHz ISM band and can possibly impact the performance. The
interference generated by WLAN devices over the Bluetooth channel called as persistent
interference, while the presence of multiple piconets in the vicinity creates interference referred
to as intermittent interference. To combat both of these interference sources and provide
effective coexistence, authors proposed a unique hybridapproach of adaptive frequency hopping
(AFH) and a new mechanism called Bluetooth carrier sense (BCS) in Blue-Star. AFH seeks to
mitigate persistent interference by scanning the channels during a monitoring period. BCS takes
care of the intermittent interference by sensing channel before transmission.
Bluestar takes advantage of the widely available WLAN installed base as it is advantageous
to use pre-existing WLAN infrastructure. This can easily support long-range, large-scale
mobility as well as provide uninterrupted access to Bluetooth devices.
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CHAPTER-2
BLUETOOTH
Ad hoc networks such as Bluetooth are networks designed to dynamically connect remote
devices such as cell phones, laptops, and PDAs. These networks are termed “ad hoc” because of
their shifting network topologies. Whereas WLANs use a fixed network infrastructure, ad hoc
networks maintain random network configurations, relying on a master-slave system connected
by wireless links to enable devices to communicate. In a Bluetooth network, the master of the
piconet controls the changing network topologiesof these networks. It also controls the flow of
data between devices that are capable of supporting direct links to each other.
Bluetooth was designed as a low-cost, low-power wireless networking technology to be used
in a person’s operating space,i.e. the space that typically extends up to 10m. Bluetooth is a short-
range (up to 10 m) wireless technology aimed at replacing cables that connect phones, laptops,
and other portable devices [3]. Bluetooth operates in the ISM frequency band 2.4 GHz. The
Bluetooth radio transmission uses a slotted protocol with a FHSS (Frequency Hopping Spread
Spectrum) technique. A total of 79 RF channels of 1 MHz width are defined, where the raw data
rate is 1 Mbit/s. Channel is divided into 625 µs slots and, with a 1 Mbit/s symbol rate, a slot can
carry up to 625 bits. Transmission occurs in packets that occupy 1, 3 and 5 slots. Each packet is
transmitted on a different hop frequency with a maximum frequency hopping rate of 1600
hops/s.
Fig-1 Packet transmission in Bluetooth
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Communication of Bluetooth devices follows a strict master-slave scheme, i.e. there is no
way for slave devices to communicate directly with each other. Master periodically polls the
Slave devices and only after receiving such a poll is a Slave allowed to transmit. The Master for
a particular set of connections is defined as the device that initiated the connections. A Master
device can directly control up to seven active Slave devices. The Bluetooth network supports
both point-to-point and point-to-multi-point connections. In order to fulfill this function, two
terms are defined:
2.1 Piconet
The Bluetooth devices which have been setup using the same frequency hopping channel
and clock form a Piconet. In every Piconet, one Bluetooth device is in charge of setting the
communications, deciding the queue of frequency hopping and synchronizing the network. It is
so-called Master. Other devices are joined to this piconet as slave.
2.2 Scatternet
Agroup of Piconet in which connections consists between different Piconet is called a
Scatternet. Between two Piconet in a Scatternet, at least one Bluetooth device is acting as a
bridge to connect two Piconet. Each piconet is established by a different frequency hopping
channel. All users participating on the same piconet are synchronized to this channel.
The Bluetooth specification defines two distinct types of links for the support of voice
and data applications, namely, SCO (synchronous connection-oriented) andACL (asynchronous
connectionless). The first link type supports point to point voice switched circuits while the latter
supports symmetric as well as asymmetric data transmission. The frequency hopping scheme is
combined with fast ARQ (Automatic Repeat Request), CRC (Cyclic Redundancy Check) and
FEC (Forward Error Correction) to achieve appropriate reliability on the wireless link.
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2.3 Bluetooth Stack
Bluetooth is a lower-layer specification by the view of OSI. Figure below shows the
main protocols of Bluetooth. The key parts of it are radio (RF) layer, baseband and link
layer(link manager and L2CAP).
Fig-2: Bluetooth protocol
Radio or RF part of Bluetooth is the lowest layer that defines the frequency bands and
channel arrangement, transmitter and receiver characteristics.
Baseband define packet format, physical and logical channels, channel control, hop
selection etc. It establishes the Bluetooth physical link between devices forming a
piconet.
Link Manager Protocol (LMP) is used for link set-up and control. Other functions of the
link manager include security, negotiation of Baseband packet sizes, power mode and
duty cycle control of the Bluetooth device, and the connection states of a Bluetooth
device in a piconet..
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The interfaces between the hardware and software are such common ones as
USB and UART which are include in Host Controller Interface (HCI) to make them
universal to the different vendor.
L2CAP supports higher-level protocol multiplexing, packet segmentation and
reassembly, and the conveying of quality of service information. It provides the upper
layer protocols with connectionless and connection-oriented services.
Bluetooth also includes other important protocols, such as service discovery protocol
(SDI), audio and some Bluetooth-specific adaptation protocol (RFCOMM).
RFCOMM protocol, which allows for the emulation of serial ports over the L2CAP. It is
a transport protocol that provides serial data transfer. In other words, it enables legacy
software applications to operate on a Bluetooth device.
The Service Discovery Protocol (SDP) provides the means for Bluetooth applications to
discover the services and the characteristics of the available services that are unique to
Bluetooth.SDPprovides service discovery specific to Bluetooth. That is, one device can
determine the services available in another connected device by implementing the SDP.
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CHAPTER-3
Wireless LAN
WLANs allow greater flexibility and portability than do traditional wired local area networks
(LAN). Unlike a traditional LAN, which requires a wire to connect a user’s computer to the
network, a WLAN connects computers and other components to the network using an access
point device[5]. An access point communicates with devices equipped with wireless network
adaptors; it connects to a wired Ethernet LAN via an RJ-45 port. Access point devices typically
have coverage areas of up 100 meters. This coverage area is called a cell or range. Users move
freely within the cell with their laptop or other network device. Access point cells can be linked
together.
WLANs are based on the IEEE 802.11 standard, which the IEEE first developed in 1997.
The IEEE designed 802.11 to support medium-range, higher data rate applications, such as
Ethernet networks, and to address mobile and portable stations. 802.11 is the original WLAN
standard, designed for 1 Mbps to 2 Mbps wireless transmissions. 802.11b standard was
completed in 1999, which operates in the 2.4 - 2.48 GHz band and supports 11 Mbps. The
802.11b standard is currently the dominant standard for WLANs, providing sufficient speeds for
most of today’s applications.
Fig-3 wireless LAN
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CHAPTER-4
The proposed Bluestar architecture
BlueStars produces a mesh-like connected scatternet with multiple routes between pairs
of nodes. It is a distributed solution. That is, all the nodes participate in the formation of the
scatternet. But they do so with minimal, local topology knowledge (nodes only knowabout their
one-hop neighbors). BlueStars, a new scatternet formation protocol for multi-hop Bluetooth
networks, that overcomes the drawbacks of previous solutions in that it is fully distributed, does
not require each node to be in the transmission range of each othernode and generates a
scatternet whose topology is a mesh[4].
The protocol proceeds in three phases:
1. The first phase, topology discovery, concerns the discovery of neighboring devices. This
phase allows each device to become aware of its one hop neighbors’ ID and weight.By
the end of this phase, neighboring devices acquire a “symmetric” knowledge of each
other.
Fig-4 First Phase Topology
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2. The second phase takes care of BlueStar (piconet) formation. Given that each piconet is
formed by one master and a limited number of slaves that form a star-like topology, we
call this phase of the protocol BlueStars formation phase. Based on the information
gathered in the previous phase, namely, the ID, the weight, and synchronization
information of the discovered neighbors, each device performs the protocol locally. A
device decides whether it is going to be a master or a slave depending on the decision
made by the neighbors with bigger weight. By the end of this phase, the whole network is
covered by disjoint piconets.
Fig-5 Second phase Topology
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3. The final phase
The final phase concerns the selection of gateway devices to connect multiple BlueStars.
The purpose of the third phase of our protocol is to interconnect neighboring BlueStars by
selecting inter-piconet gateway devices so that the resulting scatternet is connected whenever
physically possible. The main task accomplished by this phase of the protocol is gateway
selection and interconnection.
Fig-6 Third Phase Topology
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This noval architecture is expected to be capable of accessing networked information,
especially through a WAN such as the Internet. This allows dynamic content to be delivered to
the piconets and to the devices that may not otherwise have such WAN access, but can
communicate with other Bluetooth devices that do have access, either within the piconet or
scatternet. Bluetooth access to the WAN and take advantage of the existing IEEE 802.11
WLANs by using bluetooth selected devices – which possess botha WLAN interface and a
Bluetooth interface – as Bluetooth wireless gateways (BWGs). The interaction between the
Bluetooth network and the outside world is managed by the BWGs[1]. Figure below illustrates
the BlueStar architecture with a scatternet, composed of total of four piconet, where each piconet
has several slaves (indicated by the letter Si,j) and one master (indicated by the letter Mi ). In this
figure, two BWGs provide the scatternet Bluetooth devices access to the local WLAN which, in
turn, provides communication to the local LAN, MAN, or WAN, and possibly the Internet.
Fig-7 Bluestar proposed architecture
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The interaction between the Bluetooth network and the outside world is managed by the
BWGs. The possible protocol stacks to carry IP packets over Bluetooth could be employed
within BWGs. the Bluetooth SIG has published a native way for carrying IP traffic over
Bluetooth by a protocol called Bluetooth network encapsulation protocol(BNEP) wherein IP
packets are encapsulated in Ethernet packets which are then carried over Bluetooth links.
Fig-8 Protocol stack for each entity
In order for Bluetooth devices to be directly addressed, authors assumed that every
Bluetooth device possesses an IP address and any of the well-known routing algorithms is
available
A crucial challenge in the design of BlueStar is to enable an efficient and concurrent
operation of both Bluetooth and WLANs as they both employ the same 2.4 GHz ISM band. To
combat the interference sources, BlueStar employs a unique hybrid approach of an adaptive
frequency hopping (AFH) and the Bluetooth carrier sense (BCS).
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4.1.Bluetooth carrier sense (BCS)
BlueStar employs carrier sense so that intermittent-like interference can be avoided.
Carrier sensing is fundamental to any efficient interference mitigation with other technologies
using the same ISM frequency band, and among Bluetooth piconets Themselves[1]. Author has
incorporated BCS into Bluetooth without any modifications to the current slot structure. Carrier
sensing is shown in figure :
Fig-9 Carrier sensing mechanism in Bluetooth
In figure the dashed block denotes the sense window of size WBCS. Before starting
packet transmission, the next channel is checked (i.e., sense) in the turn around time of the
current slot. If the next channel is busy or becomes busy during the sense window, the sender
simply withholds any attempt for packet transmission, skips the channel, and waits for the next
chance. Otherwise, packet transmission is carried out. A direct consequence of this approach is
that, eventually, an ARQ (automatic retransmission request) packet will be sent when the slot is
clear and the communication is carried out.
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The nature of intermittent interference :
As packet transmission in different piconets are asynchronous and are transmitted with
period Tp, which depends upon the Bluetooth packet type p. For instance, if p is equal to DH1 or
DM1 we have that Tp= 2 · slotsize, where slotsizeis the size of a Bluetooth slot, and is equal to
625 µsec. Figure 4 illustrates the timing of two Bluetooth packets p and z generated at piconetsi
and j with sizes Sp,iand Sz,j, respectively.
Fig-10 Timing of two Bluetooth pockets on different piconets
The probability of packet collision between piconetsI and j is :