Paper

2nd International Conference on Emerging Trends in Computer and Image Processing (ICETCIP'2012) June 30-July 1, 2012 Bali

Location Based Computation Sharing
Framework for Mobile Devices
Samiul. Islam, Boraq. Ammourah, and Mohamad. Mahmoud

today’s mobile phones and smart phones and we have
Abstract— Third generation and fourth generation mobile proposed our process sharing framework for mobile devices,
devices are providing various online services and applications to based on this technology.
facilitate users with their rich web interfaces. Limited computing In section II and III of this paper, we have provided an
power and shorter battery life of mobile devices caused computation
overview of cellular network and working principle of
intensive application components to migrate to the external
computing resources. By elastic resource provisioning and the ability Bluetooth. We have described our proposed framework in
to support large scale service deployment, mobile cloud computing section IV. Section VI contains some part of evaluation of our
introduced an attractive platform for offloading the computational framework and we concluded with section VII.
processes among mobile devices. In this paper we proposed a
location based computation sharing framework for mobile devices in II. OVERVIEW OF CELLULAR NETWORK
which mobile devices locating in the same cell can share their
processing power. We introduced a certification technique by which Modern mobile phone networks use cells (Fig. 1) because
all mobile devices within 10 meters ranges can share their processing radio frequencies are a limited, shared resource. Cell-sites and
power using Bluetooth technique without traditional 2 step handsets change frequency under computer control and use
verification process. low power transmitters so that a limited number of radio
frequencies can be simultaneously used by many callers with
Keywords— Bluetooth Connectivity, Computational Process less interference. A cellular radio system provides a wireless
Sharing, Mobile Computing, Wireless Ad-hoc Network.
connection to the public telephone network for any user
location within the radio range of the system. The term mobile
I. INTRODUCTION
has traditionally been used to classify a radio terminal that can

T ECHNOLOGICAL advance in radio communication
introduced to us with wireless ad-hoc networks. These are
self-organizing networks that are formed from wireless
be moved during communication. Cellular systems
accommodate a large number of mobile units over a large area
within a limited frequency spectrum [3].
devices communicating with each other without the need of
any infrastructure. In these networks, each device (or node)
works as a terminal and a router at the same time. The nodes
are allowed to join or leave the network at any time. Nodes
may also move from one geographical position to another at
any time. Different wireless radio technologies were proposed
to enable wireless ad hoc networks; one of them is Bluetooth
[1]. The technology is promising in many ways. First,
Bluetooth devices are efficient with respect to power
consumption. Second, Bluetooth devices use a communication
mechanism that is noise-resistant and robust against
interference with neighboring Bluetooth devices. Third, the
cost of Bluetooth radio devices is relatively low. Bluetooth
also offers ad-hoc networking capabilities [2]. These Fig.1 Mobile cell architecture.
advantages of Bluetooth led its deployment in a wide range of
A cellular network is used by the mobile phone operator to
Samiul. Islam is with the Department of Computer Science, College of achieve both coverage and capacity for their subscribers.
Computer Science and Information System in Najran University, Najran, Large geographic areas are split into smaller cells to avoid
Saudi Arabia (phone: +966 75428610 ; Mobile: +966 501343118; e-mail: line-of-sight signal loss and to support a large number of
samiul80@gmail.com).
Boraq. Ammourah is with the Department of Computer Science, College active phones in that area. All of the cell sites are connected
of Computer Science and Information System in Najran University, Najran, to telephone exchanges (or switches), which in turn connect to
Saudi Arabia (phone: +966 75428615 ; Mobile: +966569596556; e-mail: the public telephone network. Each cell contains at least a
mr.boraq@gmail.com).
Mohamad. Mahmoud is with the MIS department in Salman bin Abdulaziz
University, Hot at Bani, Tamim, Saudi Arabia. (Phone: +966 543170968; e-
mail: m_awni1983@yahoo.co.uk ).

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Legend: M- Master device, S- Slave device

M S
S M

S S
S
S

Piconet- A Piconet- B

Fig. 3 Scatternet in a mobile cell
Fig. 2 Communication of BTS and mobile phones
i.e. a node can be a master in one piconet and a slave in
base transceiver station (BTS), under which all cell phones of another. This permits the connection of several piconets as the
that cell are registered. The base transceiver station, or BTS, nodes functioning in master/slave mode act gateways between
contains the equipment for transmitting and receiving radio piconets. In the Bluetooth concept the network topology
signals (transceivers), antennas, and equipment for encrypting resulting by the connection of piconets is called a scatternet
and decrypting communications with the base station (Fig. 3). A node can be active in only one piconet at time, and
controller (BSC). Fig. 2 shows BTS functionality in a simple to operate as a member of another piconet, a node must switch
manner. to the hopping frequency sequence of the other piconet [5].
The base station subsystem (BSS) is the section of a The Bluetooth Core Specification provides for the
traditional cellular telephone network which is responsible for connection of two or more piconets to form a scatternet, in
handling traffic and signaling between a mobile phone and which certain devices simultaneously play the master role in
the network switching subsystem. The BSS carries one piconet and the slave role in another. A master Bluetooth
out transcoding of speech channels, allocation of radio device can communicate with a maximum of seven devices in
channels to mobile phones, paging, transmission a piconet (an ad-hoc computer network using Bluetooth
and reception over the air interface and many other tasks technology), though not all devices reach this maximum. The
related to the radio network. Typically a BTS will have several devices can switch roles, by agreement, and the slave can
transceivers (TRXs) which allow it to serve several different become the master.
frequencies and different sectors of the cell (in the case of
sectorized base stations). A BTS is controlled by a parent base A. Operations
station controller via the base station control function (BCF). Bluetooth uses a radio technology called frequency-hopping
The BCF is implemented as a discrete unit or even spread spectrum, which chops up the data being sent and
incorporated in a TRX in compact base stations. The BCF transmits chunks of it on up to 79 bands (1 MHz each;
provides an operations and maintenance (O&M) connection to centered from 2402 to 2480 MHz) in the range 2,400–
the network management system (NMS), and manages 2,483.5 MHz (allowing for guard bands). This range is in the
operational states of each TRX, as well as software handling globally unlicensed Industrial, Scientific and Medical (ISM)
and alarm collection. The basic structure and functions of the 2.4 GHz short-range radio frequency band. It usually performs
BTS remains the same regardless of the wireless technologies 800 hops per second, with AFH enabled [6].
[4]. Bluetooth operation relies on packet-based protocol with
a master-slave structure. One master may communicate with
III. BLUETOOTH: WORKING PRINCIPLE up to 7 slaves in a piconet; all devices share the master's clock.
Bluetooth is a short-range radio technology that enables Packet exchange is based on the basic clock, defined by the
wireless connectivity between mobile devices. When two master, which ticks at 312.5 µs intervals. Two clock ticks
Bluetooth devices come into each other’s communication make up a slot of 625 µs; two slots make up a slot pair of 1250
range, one of them assumes the role of master of the µs. In the simple case of single-slot packets the master
communication and the other becomes the slave. This simple transmits in even slots and receives in odd slots; the slave,
“one hop” network is called a piconet, and may include up to conversely, receives in even slots and transmits in odd slots.
seven active slaves connected to one master. As a matter of Packets may be 1, 3 or 5 slots long but in all cases the master-
fact, there is no limit on the maximum number of slaves transmit will begin in even slots and the slave-transmit in odd
connected to one master but only seven of them can be active slots. The master chooses which slave device to address;
at time, others have to be in so called parked state. The typically, it switches rapidly from one device to another in
specification also allows multiple roles for the same device, a round-robin fashion. Since it is the master that chooses
which slave to address, whereas a slave is (in theory) supposed

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to listen in each receive slot, being a master is a lighter burden state, they do not have addresses, but only listen enough to
than being a slave. keep their synchronization with the master and check for
Bluetooth devices can be in 3 different power classes [7], broadcast messages.
[8]:
C. Security Method
Class 3: The lowest power, the max. range of this is 10m
Class 2: Max range is about 50m (150ft) Authentication ensures the identity of Bluetooth devices. It
Class 1: Max range is about 100m (300ft) authenticates the device at the other end of the link.
These ranges (Table-I) can be affected by environmental Authentication is accomplished by using a stored link key or
conditions i.e. furniture, walls, people so ranges can easily be by pairing (entering a PIN). Pairing is a procedure that
reduced. Bluetooth is not a line of sight connection so it can be authenticates two devices based on a common passkey,
used through walls and floors. thereby creating a trusted relationship between those devices.
An arbitrary but identical passkey must be entered on both
TABLE I devices. As long as both devices are paired, the pairing
BLUETOOTH CLASSES procedure is not required when connecting those devices again
Maximum permitted power Range (the existing link key is used for authentication). Devices
Class without any input method, like headsets, have fixed passkeys.
(mW) (dBm) (m)
Authorization is a process of deciding if a device is allowed
Class 1 100 20 ~100 to have access to a specific service. User interaction may be
Class 2 2.5 4 ~10 required unless the remote device has been marked as
"trusted." Usually the user can set authorization on/off to
Class 3 1 0 ~5 every remote device separately. Authorization always requires
The effective range varies due to propagation conditions, authentication.
material coverage, production sample variations, antenna Encryption protects communication against eavesdropping.
configurations and battery conditions. In most cases the For example, it ensures that nobody can listen to what a laptop
effective range of class 2 devices is extended if they connect transmits to a phone. The length of the encryption key can be
to a class 1 transceiver, compared to a pure class 2 network. between 8 and 128 bits.
This is accomplished by the higher sensitivity and
transmission power of Class 1 devices. IV. PROPOSED FRAMEWORK
B. Connection Protocols All mobile devices under a BTS can be grouped in a
Bluetooth connections are established via the following multiple piconets, where the number of piconets depends on
techniques [9], [10]: the cell size of that specific BTS depending on geographical
Standby: Devices not connected in a piconet are in standby position. Each piconet can contain maximum n number of
mode. In this mode, they listen for messages every 1.28 s over mobile devices at any given time, where 0≤ n. When an
32 hop frequencies (fewer in Japan, Spain, and France). application initiates in any node of a piconet of our proposed
Page/inquiry: If a device wishes to make a connection with framework, it has been marked as an active node and acquire a
another device, it sends out a page message if the address is certificate from local BTS with a time stamp for that node.
known, or an inquiry followed by a page message if it is When an active node has been selected, it discovers the idle
unknown. The master unit sends out 16 identical page nodes asynchronously within its piconet and use the certificate
messages on 16 hop frequencies to the slave unit. If there is no to create a private channel with the idle nodes to share their
response, the master retransmits on the other 16 hop processing powers. If the time stamp of an active node
frequencies. The inquiry method requires an extra response exceeds the duration more than 300 seconds, and/or the
from the slave unit, since the address is unknown to the master number of idle nodes drop below a level m, where 1≤ m≤7,
unit. the active node share its processes with the other available idle
Active: Data transmission occurs. nodes in different piconets through BTS. The proposed
Hold: When either the master or slave wishes, a hold mode framework is composed of several algorithms implemented in
is established or no data is transmitted in order to conserve middle layer of BTS and in the application layer of cell
power. Otherwise, there is a constant data exchange. A typical phones. Those can be categorized as mentioned in later sub
reason for going into hold mode is the connection of several sections.
piconets. A. Certificates:
Sniff: The sniff mode, applicable only to slave units, is for Subscriber, MS (Mobile Station) or mobile phone connects
power conservation, though not at as reduced a level as hold. to mobile network through BTS. When a mobile phone
During this mode, the slave does not take an active role in the switches on, it registers with the corresponding BTS of its cell.
piconet, but listens at a reduced level. This is usually a In our proposed framework, during the registration process of
programmable setting. mobile devices, it will acquire a certificate from the
Park: Park mode is a more reduced level of activity than the corresponding BTS, containing subscriber’s information and
hold mode. The slave is synchronized to the piconet, thus not service provider’s information. This certificate authenticated
requiring full reactivation, but is not part of the traffic. In this

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the device with a device generated 64 bit encrypted security finding other devices listening to the same frequency hop at
key. An active node shares this key in the idle node discovery the same time. The inquirer keeps alternating in a range of
process within the piconets. During the link establishment frequencies - 32 out of the 79 available hops known to all the
process and data exchange process between these two types of devices. On the opposite side of the connection, a node that
nodes, the security key will automatically authorize an active wants to be discovered has to switch to the query scan state
node to send and retrieve its data from an idle node without and keeps listening to ID packets generated from the inquirers.
prompting the user. The scanner switches between the frequencies hops at a slower
rate than the inquirer’s in order to increase the chance of
B. Discover idle nodes with timestamp:
finding each other in the same hop. When the scanner receives
We require time synchronization between mobile nodes. one of those ID packets, it replies to it with a special packet
We assume clock ticking speeds of different nodes to be called the FHS [11], [12] packet. An FHS packet contains its
comparable. It means that when a idle node B i receives a clock address and its clock value. The clock value is used for
value from an active node A i , node B i can synchronize with synchronization purposes to make the link establishment
node A i , using A i ’s clock value. There is no globally common procedure faster. In the paging procedures, the active node
clock for the mobile network, say MN. Assume that MN has switches to the page state and the idle must switch to the page
M channels available for its operations. Let this channel set be scan state. Using the information obtained from the FHS
Cglobal = {C1, C2 , ... , CM}. packet, the active node adds an offset value to its clock to have
Each node in MN is assigned a unique identifier (Node ID) the same clock value of the idle node so they are both become
in the range 1 to N. Each node knows its unique Node ID, but synchronized to each other. After that, the active node
does not know how many other nodes there are and what their attempts to contact the idle node by broadcasting again a
IDs are. Nodes are equipped with one transceiver (Transmitter number of ID packets. If the idle node listens to one of these
& Receiver) capable of either receiving or transmitting at any ID packets, it replies with another ID packet and go to the idle
given time. Nodes know about the global channel set Cglobal response state. When this ID packet is received by the active
and the value of N. Also each node finds its set of usable node, it changes its state to the active response state. Then, the
channels (available channel set) by a periodic scanning active node sends an FHS packet.
mechanism. We assume nodes can detect collisions. An active
node transmits and receives alternatively on each channel of V. RELATED WORK
its available channel set. During the transmit period it sends a
Salonidis et. al. presents a distributed topology construction
query referred to as Active Node Query (ANQ) with node ID,
scheme in Bluetooth networks [13]. The basic assumption
clock value of the node, available channel set and remaining
behind the scheme is that all nodes are within transmission
time in ANQ. Every ANQ has limited time validity, Q t .
range of each other. The nodes conduct a leader election
During the receiving period, inquiring node listens on the
algorithm. The winner knows the identity of all nodes and uses
same channel that it transmitted previously, for duration of Q t .
this information to design the desired topology. Existing
If a valid reply (Query Reply) is received, the queering node
service discovery protocols such as Universal Plug and Play
sends an Acknowledgment (Ack) message, during the current
(UPnP) [14], Service Location Protocol (SLP) [15] and
receiving period or during the next receiving period, on the
Salutation focused on auto configuration issues allowing
same channel that it received the reply. Upon receiving a
devices to automatically join the network and learn about its
Query Reply message, inquiring node discovers the sender of
capabilities. However such approaches were designed for
the Query Reply.
resource rich networks and are not suitable for resource
C. Sharing and synchronization of process: constrained systems. Energy efficient service discovery has
Bluetooth operates in the range of frequencies 2.4000 GHz been done using power efficient wake-up scheduling
to 2.4835 GHz. It divides the medium to 79 channels each of 1 protocols, such as [16][17][18]. Bhagwat et al. presents a
MHz. The rest of the available frequencies are considered as source routing mechanism for Bluetooth networks [19]. Das et
lower and upper band edges, in order to comply with the radio al. [20] and Johanson et al. [21] present distributed scheduling
regulations of different countries. To establish a link between policies for Bluetooth networks. Existing middleware
an active and idle node, the communicating nodes must solutions for wireless sensor networks usually have plug-in
perform two operations; the first is the query; in which one system [22] for service discovery protocols or use their own
node gets the address of (or discovers) another node. The mechanisms [23]. TeenyLime [23] is a data-sharing
second is the paging, in which a link is constructed. The middleware designed for mobile sensors. It uses an operational
specifications of Bluetooth state that for one node to discover setting where sensors are fixed and relatively powerful mobile
others, it must switch to the query state, and then, keeps sinks are used to collect data from sensors.
broadcasting small special packets (of 68 bits size), called the
ID packets. The contents of these packets are common to all VI. EVALUATION
Bluetooth devices, and although called ID packets, they do not Evaluation of certificate is our future work. The time
contain the identity of their senders. The inquirer’s ID packets duration of idle node discovery procedure has been evaluated
must be broadcast in different frequency hops in hope of

159


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implementation and evaluation of certification algorithm,
Synchronization with BTS to share processing with the idle
node of different piconets within the same cell.. Few critical
concerns also need to be considered in future work, e.g. when
two active nodes try to share an idle node in concurrent time.
Fault tolerance mechanism need to be implemented as any
shared node can be switched of or change location without
prior notice.

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