Blue star seminar report dated 18 march

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.

Dept. of Electronics and Communication Page 1

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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).


BLUESTAR

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 :

pc(i, j ) = (Sp,i+ Sz,j ) /((max _slotsperpacket(p),slotsperpacket(z)) + 1)* slotsize)*1/C

whereC is the number of available frequency channels

slotsperpacket(X) gives the number of slots occupied by a Bluetooth packet X

The packet collision probability with a packet originated at the ithpiconet is given by (N

piconets) :

pc(i) = 1 − (1 - pc(i, j ))N−1

.


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Fig-11 Packet collision and withdrawal probabilities for different slot length packets

As we can see from figure 5, even though both packet probabilities increase with the

number of piconets, the packet withdrawal probability increases at a slower rate, indicating that a

large fraction of packet collisions are being avoided with the adoption of BCS. Moreover, the

rate of increase is also distinct for different slot length packets. Bluetooth with BCS not only

significantly increases the overall throughput but alsonables a larger number of nearby piconets

to operate efficiently.


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4.2. Bluetooth adaptive frequency hopping (AFH)

Given that a IEEE 802.11 DATA frame has a maximum size of up to 2346

octets and a Bluetooth slot occupies 625 bits , in the worst case, so a IEEE 802.11

DATA frame can overlap with up to 30 Bluetooth slots[1]. Figure 7 shows two

potential cases of packet collisions.

Fig-12 Potential packet collisions between IEEE 802.11 and Bluetooth

Although the IEEE 802.11WLAN senses the channel before transmission, it

cannot sense the Bluetooth activities, since the Bluetooth signal is narrowband and

low power as compared to WLANs. Therefore, when the Bluetooth packet (from

piconeti) is ahead of the WLAN, packet collision (with the next IEEE 802.11 packet)

takes place even after employing BCS. On the other hand, when the WLAN packet is

ahead of the Bluetooth packet BCS successfully senses activity in the medium and

withdraws packet transmission.

Bluetooth devices scan every T SCAN seconds for each of the 79 channels

used by Bluetooth and collect PER statistics. If the PER is above a threshold

PERTHRES, it is labeled as “bad”; otherwise it is labeled as “good”. All devices

within a piconet carry out this procedure and when the piconet master request this,

the slaves send their measured “good” and “bad” channel marks. The master, in

turn, conducts a referendum process based on information collected by itself and

provided by the slaves. The final mapping sequence is then determined and sent

back to each slave device, which follow this new sequence thereafter. Authors have


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implemented this scheme by a bitmap comprising of 79 bits where a one indicates

that a frequency can be used while a zero indicates otherwise. The overall effect on

Bluetooth is that the total number of available channels C decreases as some

channels may be labeled as “bad”.

4.3 Capacity allocation scheme

In the BlueStar architecture, theBWGs have to act as forwarding units between the

wireless systems besides serving as source or destination for their own applications. Thus, a

BWG must spend a proportional amount of time in receiving data as in forwarding it[1].

Obviously, because of mismatch in packet sizes and the eventual segmentation and reassembly

overheads, the time spent in one network may not be exactly the time spent in the other. Since a

BWG can be present only in one piconet at a time, the total capacity a BWG can provide to the

users it serves is bounded by half the piconet capacity. This prevents the fair distribution of the

capacity when a BWG serves more than half the total number of users in the scatternet.


BLUESTAR

CHAPTER-5

Simulation of BlueStar

Authors have implemented all functionalities of BlueStar in the network simulator (ns-2)

andBlueHoc. In addition, authors consider that the interfering range of Bluetooth devices is

about two times larger than the transmission range and an IEEE 802.11b DSSS running at 11

Mbps for all simulations[1]. Authors have developed a hybrid Bluetooth-802.11 model that has

been incorporated into the BWGs.

5.1Bluetooth-only simulation environment

Initial experiment employs an environment comprised of only Bluetooth devices without

any external sources of interference. Therefore, since we are mainly concerned with intermittent

interference and BCS, AFH is not employed. Figure 8 illustrates the topology used for this

evaluation. Within a total area of 500 m × 500 m, we have considered a network composed

initially of 10 piconets. For each of the twenty simulation runs, we increase the number of

piconets by 10 up to a total of 200 piconets, where each piconet comprises of four devices.

Fig-13 Bluetooth only network topology model


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Bluetooth with BCS greatly reduces the number of collisions and defers packet transmission

until a safe channel is found and BCS can drastically increase throughput.

.

5.2 Combined Bluetooth and WLAN simulation

environment

In this section authors carried out experiments with both intermittent and persistent

interferences. For that, we utilize the implementations of both BCS and AFH[1].

TCP/IP traffic simulation

Similar to earlier simulations, we have considered a network initially comprising of 10

piconets, and increase the number of piconets in steps of 10 till 200 piconets. As for the WLAN

axis, it is composed of an AP, located at (0, 200) m, which has a radio range of 250 m.

Fig-14 WLAN and Bluetooth network simulation model

The traffic between the WLAN AP and Bluetooth network also consists of FTP traffic.

The WLAN packet is of total size of approximately 1.5 KByte. Authors had set the offered load


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in each piconet to 30% of its total capacity, and assume Bluetooth stations to be stationary as

currently assumed by BlueHoc.

Four possible scenarios as follows:

Scenario A:

The flow of data packets is from the WLAN AP to the BWG, reflecting an application

where Bluetooth devices downloading contents from the WAN.

Scenario B:

This scenario is the opposite of the previous one with the Bluetooth devices uploading

information to the WAN, i.e., the flow of data packets is from the BWG to the WLAN AP.

Scenario C:

A BWG might find itself in a situation where it simultaneously receives data packets

from both the WLAN AP and the Bluetooth devices in order to synchronize information in the

BWG.

Scenario D:

This scenario models the opposite situation as described in scenario C. In other words, it

is the case where the BWG simultaneously transmits data packets to both the Bluetooth devices

and the WLAN AP.


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Results obtained for different scenarios after Simulation

are:

Scenarios B and D:

scenarios B and D experience a sizeable degradation in throughput as compared to

scenarios A and C, with scenario B having the largest impact. This is particularly true in these

scenarios because when the BWG is transmitting data packets towards the AP, there is a high

persistent interference in the Bluetooth network causing a high PER. On the other hand, in

scenarios A and C the BWG is sending acknowledgments (ACKs) to the AP, therefore reducing

the probability of packets being corrupted. The reason why scenario B suffers a higher

performance drop (and higher PER) than scenario D is because the WLAN transmissions corrupt

the Bluetooth data packets in scenario B, while in scenario D only Bluetooth ACK packets are

susceptible to be corrupted by WLAN transmissions.

Since these scenarios are more impacted by persistent interference, AFH is effective for a larger

number of piconets until it reaches a point where the intermittent interference levels becomes

significant. At these points, BCS performs better by effectively mitigating intermittent

interference sources. Despite the high interference levels, BlueStar, employing both AFH and

BCS, accomplishes enhanced performance by achieving the highest throughput and lowest PER.

Scenarios A and C :

AFH is now effective only for a smaller number of piconets as the larger impact comes

from intermittent interference. In scenarios A and C (especially in scenario A) the regular

Bluetooth implementation shows performance sometimes comparable to that of the AFH


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scheme, which is primarily due to the TCP congestion control mechanisms employed in the

WLAN interface. When collisions in the WLAN traffic occur, the frame has to be completely

retransmitted as IEEE 802.11 WLANs do not employ any kind of FEC (forward error

correction). In scenario A the WLAN transmissions have been corrupting the Bluetooth ACK

packets, while in scenario C Bluetooth data packets are more impacted. Therefore, scenario A

performs slightly better due to the shorter and less frequent duration of the ACK packets.

Scenarios C and D:

A higher drop in throughput for scenario D, especially for the ordinary Bluetooth

implementation. As expected, AFH outperforms BCS when most of the interference is of

persistent type, however degrades nearly at the same rate as the ordinary Bluetooth

implementation when the number of piconets become larger than 50 and 65 for scenarios C and

D, respectively. Likewise, BlueStar approximately doublesthe throughput achieved in Bluetooth

by combining AFH and BCS.

Moreover, it is also important to highlight the performance of AFH as it outperforms

BCS under a small number of piconets, since most of the interference is of persistent type.

However, as the number of piconets increase, and hence the intermittent interference level, the

performance of AFH degrades and BCS becomes more efficient both in terms of PER and

throughput. More specifically, in scenarios B and D AFH is more efficient than BCS up to 90

and 72 piconets respectively, whereas in scenarios A and C AFH performs better when the

number of piconets is approximately less than 55.

In all scenarios, BlueStar achieves the best throughput and the lowest PER by taking

advantage of both AFH and BCS.

5.3 Placement and number of BWGs in bluestar

This section deals with number of BWGs are needed to provide adequate and uninterrupted

coverage to all devices in a Bluetooth scatternet, as well as where to place these BWGs. Authors

refer to these as the placement and the number problems. The topology of interconnection has

influence on the number of resulting BWGs. Authors has proposed a model in which a BWG


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serve as bridge node between exactly two neighboring piconets and piconets have a circular

shape and are centered on the master[1]. BWG between two piconet

While in figure A the addition of a piconet resulted in the addition of only one more

BWG, the same piconet might also result in the addition of two more BWGs as shown in figure

However, since major interest is in an upper bound (worst-case) on the number of

BWGs, this task is simplified by considering only the topology which results in the highest

interconnection, as exemplified in the sketch of figure C. In Bluetooth, it is possible to have all

eight devices of a piconet working as bridge nodes.

Fig D

Fig.A Fig. B


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Fig. C

Fig-15 Placement and number of BWGs in Bluestar

For mathematical simplicity, we impose a restriction that only the master device is not

allowed to work as a BWG. Thus, among seven BWGs of a piconet, each BWG is shared by two

piconets. It is clear that we can have at most [7n/2] BWGs in a scatternet composed of n

piconets. In fact, the total number of BWGs required will be fewer than these as there is no need

to have a BWG on non-bridge devices as shown in the outer parts of figures .

Proposition 1.

For a scatternet comprised of n (n >0) piconets, where piconets have a circular (or near-

circular) shape (figure B), the number of BWGs needed is at most [7n/2] − 2[4√n − 4] .

Proposition 2.

For a scatternet comprised of n (n >0) piconets, the maximum number of BWGs needed

is [7n/2] − 2[4√n − 4] .


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CHAPTER-6

Conclusion

This paper introduces a novel architecture called BlueStar, which employs a combinationof

adaptive frequency hopping and Bluetooth carrier sensing to efficiently provide advanced wide

area services to Bluetooth devices. BlueStar can take advantage of the existing installed base of

IEEE 802.11 wireless networks by assigning selected Bluetooth devices, called Bluetooth

wireless gateways (BWG), with IEEE 802.11 capabilities. These BWG are responsible for

providing uninterrupted access to the WAN, such as the Internet, to the entire Bluetooth network

(piconet or scatternet). BlueStar is observed to greatly outperform existing Bluetooth under

different traffic condition. The incorporation of BlueStar into Bluetooth is simple, does not incur

much overhead, and hence is an excellent enabler for co-existence and cooperation of Bluetooth

and IEEE 802.11.

Future work in BlueStar includes defining a more elaborate capacity allocation algorithm. In

addition, we plan to investigate the correlation amongst the various simulation parameters in

order to assess their impact on BCS and AFH. Mobility of both IEEE 802.11 and Bluetooth

devices and its impact on both systems are also part of our future research.


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CHAPTER-7

References

[1] Bluestar: enabling efficient integration between Bluetooth WPANs

and IEEE 802.11 WLANs

Mobile Networks and Applications archive

Volume 9 , Issue 4 (August 2004) ,Pages: 409 – 422

Carlos De M. Cordeiro, SachinAbhyankar, Rishi Toshiwal,

Dharma P. Agrawal

[2] Ascatternet operation protocol for Bluetooth ad hoc networks

Wireless Personal Multimedia Communications, 2002

27-30 Oct. 2002,pages: 223 – 227, Volume: 1

Tadashi Sato, KenichiMase

[3] Bluetooth - The Fastest Developing Wireless Technology

May 2000 , pages: 1657 – 1664


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ZhangPei, Li Weidong, Wang Jing, Wang Yotizhen

[4] Bluetooth scatternet models

December 2004/ January 2005, pages : 36 – 39

Patricia McDermott-Wells
