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Improved Channel Assignment Scheme in Cellular Mobile Communication

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Volume 1, Issue 3, September – October 2012                                    ISSN 2278-6856



           Improved Channel Assignment Scheme in
               Cellular Mobile Communication
                                      Swati Sonavane1 and Dr. R. R. Sedamkar2
                             1
                              University of Mumbai, Thakur College of Engineering & Technology,
                                                       Mumbai, India.
                             2
                              University of Mumbai, Thakur College of Engineering & Technology,
                                                       Mumbai, India.



Abstract: This technique is giving an efficient dynamic            resource flexibility is one of the most important
allocation of communications channels which is essential for       requirements in third-generation networks.
ensuring good performance of cellular networks. The work in        This thesis proposes a distributed channel allocation
this project demonstrates that intelligent agent acting            scheme using intelligent software agents for cellular
collaboratively in a multi-agent system is able to increase the
robustness of the cellular network as a whole, to distribute the
                                                                   mobile networks. The main reason for using intelligent
knowledge and to allow negotiation of radio resources.             software agents is to give greater autonomy to the base
The performance of the Distributed Fixed Channel Allocation        stations; this autonomy allows
& Dynamic Channel Allocation schemes are compared and
the we found that the average call dropping probability of         decrease in centralized information.
FCA scheme is 96% to 98% and the average call dropping             Agent technology is an interdisciplinary area of research
probability of DCA is 26% to 28% in different conditions, so
                                                                   that has received special
the Distributed Dynamic Channel Allocation scheme is
efficient than the FCA scheme.                                                                                    1990s. The
Keywords: Efficiency, Intelligent Agent, Mobile                    definition of an agent is controversial, but in general
communication, Resource flexibility, Traffic Profiles.             terms an agent can be described as a hardware or software
                                                                   system with social ability that performs tasks with specific
1. INTRODUCTION                                                    aims in a complex and dynamic environment. Agents are
                                                                   capable of autonomous
Techniques for increasing the efficiency of channel usage
in mobile networks are essential in order to handle the
                                                                            unexpected events.
complexity of third generation mobile communications.
                                                                   This thesis applies agents to the problem of mobile
Previous work on analogue and second generation mobile
                                                                   resource allocation in such a way that they do not work in
communications has led to several algorithms being
                                                                   isolation, but as a community. A community of agents is a
proposed to maximize the channel usage and minimize
                                                                   multi-agent system, such a system being defined as a
the call blocking probability. Some channel assignment
                                                                   group of agents with specific roles in an organisational
schemes presented in the literature [1]-[7] have improved
                                                                   structure. The agents interact with the environment and
the performance of the basic fixed channel assignment
                                                                   with each other in a co-ordinate way, as collaborators or
strategy for different traffic densities (macro/micro/pico
                                                                   competitors, seeking to fulfill the local or global aims of the
cellular networks) over different traffic load conditions.
                                                                   organization.
However, most of the solutions proposed have an entirely
reactive approach: the response to a series of events
follows an algorithm that is prepared to react to specific
situations. This limits their efficiency. Even those
                                                                   A multi-agent system is able to provide this flexibility and
schemes that contain adaptive features are not ideal.
                                                                   also is able to increase the robustness of the network by
Some schemes are completely centralized (which is
                                                                   allowing negotiation when conflicts occur. This project
impractical for real implementation because of
                                                                   describes the framework we are adopting to verify the
computational complexity making them too slow, or
                                                                   feasibility of multi-agent systems in controlling resource
because the network would become overloaded with
                                                                   assignment in mobile networks. Our agent architecture is
signaling messages) or are distributed, but restricted to
                                                                   hierarchical, with a reactive part and a deliberative part.
individual base stations which again limits their
                                                                   The reactive part is the lowest layer, ensuring fast
efficiency.
                                                                   response to the needs of the cells in terms of channel
In order to accommodate multiple networks and services
                                                                   allocation. The deliberative part is concerned with
with multiple bit rates within a limited frequency band,
                                                                   optimization of the allocation of channels among cells
Volume 1, Issue 3, September – October 2012                                                                           Page 186
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Volume 1, Issue 3, September – October 2012                                    ISSN 2278-6856


and consists of two layers: one to meet the local goals of    America, additional standards were introduced for digital
the individual base stations and another (the co-operative    cellular systems using the same frequency spectrum as
layer) for load balancing in the network.                     AMPS. These standards integrated other multiple access
We are assuming a macro-cellular scenario where base          techniques in addition to FDMA.
stations are not able to share information by interference    The IS-54 standard, known as North American TDMA
measurements, but only by explicit exchange of                (NA-TDMA) or Digital AMPS (D-AMPS), has integrated
information, and the resources are complete frequency         the Time Division Multiple Access (TDMA) technique,
carriers. Although the results in this paper are based on     where each frequency carrier is shared using time
an AMPS [8] model, the concept is completely generic          division by up to 6 mobile users (currently 3 mobile
and the work could be extended to TDMA/CDMA.                  users).
Different cell structures (such as microcellular or           In 1994, the IS-95 standard introduced the Code Division
hierarchical) could also be included.                         Multiple Access (CDMA) technique. It is based on the
                                                              spread-spectrum modulation in which multiple users have
2. MOBILE NETWORK                                             access to the same band. Each mobile user is assigned a
The first generation of mobile communication started in       unique orthogonal code called a Walsh code. The 12.5
1974; the Federal Communication Commission (FCC)              MHz of a band is divided in 10 CDMA bands of 1.25
allocated a 40 MHz band in the 800 to 900 MHz                 MHz Each CDMA band supports 64 Walsh codes.
frequency range for cellular communications. The              CDMA can offer about eight times the capacity of
Advanced Mobile Phone Systems (AMPS) standard was             analogue [8].
introduced in 1979 and adopted by the FCC [4]. Licenses       The drastic growth in the use of mobile communications
were issued in the market in 1982. An additional 10 MHz       by public and business sectors increased the pressure to
band was allocated in 1988 and called Expanded                integrate fixed and mobile networks. Now, mobile
Spectrum (ES). The licenses were divided into bands:          networks are expected to have the same diversity of
Band A and band B. Cellular communication is full-            services offered by fixed networks with the same quality
duplex and the frequency band is divided between both         of service and security. Also, full mobility capability is
communication paths: 25 MHz is allocated to the forward       expected. The mobile system needs to have the flexibility
path, which is the path from the base station transmitter     to integrate world-wide the different types of mobile
towards the mobile terminal receiver. The other half is for   communication systems available today, such as public
the reverse path in the opposite direction. The paths are     and private cellular systems, data radio and satellite
separated by a 45 MHz guard band in order to avoid            systems. These demands are beyond the technological
interference between the transmission and reception           capabilities of the second generation of mobile
channels.                                                     communications. These pressures and developments in
Bands A and B each occupy 12.5 MHz: 10 MHz is Non-            component technology, network management and service
Expanded Spectrum (NES) and 2.5 MHz is ES. The 12.5           engineering made inevitable the emergence of a third
MHz bands are divided into 30 kHz channels, making a          generation of mobile communications. The aim of third
total of 416 channels per band. Twenty-one of these           generation systems is to provide communication services
channels are used for specific procedure like channel         from any person to any person at any place and at any
assignment, paging, messaging, etc. they are called           time through any medium using a compact light-weight
control channels. The remaining channels are used for         terminal with guaranteed quality of service and security.
conversation and called voice channels. In AMPS, each         Frequency management in mobile networks has been a
frequency channel corresponds to a frequency carrier and      hot topic for research in the past 20 years and the
only one mobile can be assigned per channel. Therefore,       solutions proposed still present a lack of intelligence and
AMPS is solely Frequency Division Multiple Access             flexible behaviour. The technological advances made in
(FDMA) and is an analogue cellular system.                    software and hardware in the last decade is providing the
                                                              means to introduce intelligence in control and
                                                              management of networks. The introduction of more
                                                              intelligence and flexible behaviour in the management of
                                                              channel allocation is the objective of this work.
                                                              3. The Cellular Concept
                                                              The cellular concept, conceived by Bell Systems under the
                                                              AMPS standard in 1979[9], is a mobile network
           Figure 1 Cellular Band Allocation                  architecture composed ideally of hexagonal cells. The
The second generation of mobile communications, i.e. the      cells represent geographic areas. Inside the cells, the
digital cellular systems, emerged in the 1990’s. In North     users, called mobile telephone switching office (MTSO)

Volume 1, Issue 3, September – October 2012                                                                   Page 187
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Volume 1, Issue 3, September – October 2012                                    ISSN 2278-6856


responsible for controlling the calls and acting as a               To greatly increase the number of simultaneous calls
gateway to other networks. When an active user (i.e. a           that can be covered by the same number of allocated
mobile station using a frequency channel) reaches the            channel frequencies.
boundary of the cell, it needs to change its current             Cell splitting is the reconfiguration of a cell into smaller
frequency channel for another belonging to the                   cells. This feature makes it possible for the same network to
neighbouring cell. This network procedure is known as            service different densities of demand for channels. Larger
handoff or handover. Hand over can be either soft                cells can serve low demand areas and smaller cells high
handover or hard handover.                                       demand areas. Cell splitting is a long-term configuration
                                                                 planning that allows the system to adjust to a

                                                                                         increase in the spectrum allocation.
                                                                 Frequency Reuse the distribution of the frequency
                                                                 channels in a cellular network is dependent on several
                                                                 parameters, such as cellular geometry, signal propagation
                                                                 characteristics and signal interference [10].
                                                                 The assignment of frequency channels in the cellular
                                                                 concept is fixed, i.e. a set of frequency channels is
                                                                 statically allocated to a cell. This same set is reused in
          Figure 2 Handoff between MS and BS                     another
The main objectives of AMPS for supplying a large-scale          cell distant enough to allow the use of the frequency
mobile-telephone service were [9]:                               channels with acceptable signal interference. Cells that
  Large subscriber capacity                                      use the same set of frequency channels are called co-
  Efficiency use of spectrum                                     channel
                                                                 cells and the distance between them is called co-channel
  Nationwide compatibility
                                                                 reuse distance. The total number of frequency carriers
  Widespread availability
                                                                 allocated to a network operator is divided in sets and
  Adaptability to traffic density
  Service to vehicles and portables
                                                                                                pattern. The pattern is
  Regular telephone services and special services
                                                                 reused according to the co-channel reuse distance. The
  Quality of service in telephony                                choice
  Affordability
                                                                                                   considerations. A better
                                                                 understanding about signal propagation and cellular
                                                                 geometry is needed in order to understand how frequency
                                                                 assignment is performed in a mobile cellular system (e.g.
                                                                 AMPS).
                                                                 One main issue in cellular system design reduces to one
                                                                 of economics. Essentially we have a limited resource
                                                                 transmission spectrum that must be shared by several
                                                                 users. Unlike wired communications which benefits from
                                                                 isolation provided by cables, wireless users within close
            Figure 3 Cellular Band Allocation                    proximity of one another can cause significant
                                                                 interference? To address this issue, the concept of cellular
The essential features of the cellular system that made          communications was introduced around in 1968 by
possible the achievement of the above objectives were            researchers at AT&T Bell Labs. The basic concept being
frequency reuse and cell splitting.                              that a given geography is divided into polygons called
Frequency reuse refers to the use of the same frequency          cells.
carrier in different areas that are distant enough so that the   Each cell is allocated a portion of the total frequency
interference caused by the use of the same carrier is not a      spectrum. As users move into a given cell, they are then
problem. The reason for the application of frequency reuse is    permitted to utilize the channel allocated to that cell. The
twofold:                                                         virtue of the cellular system is that different cells can use
   To reduce the cost of the land transmitter/receiver site by   the same channel given that the cells are separated by a
placing several moderate                                         minimum distance according to the system propagation
                                                                 characteristics; otherwise, intercellular or co channel
network operator.                                                interference occurs. The minimum distance necessary to
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Volume 1, Issue 3, September – October 2012                                    ISSN 2278-6856


reduce co channel interference is called the reuse
distance. The reuse distance is defined as the ratio of the    transmission from the neighbouring cell almost as well as
distance, D, between cells that can use the same channel       that in their own. When there is a call attempt and no
without causing interference and the cell radius, R. Note      more available channels [11] or when the channel
that R is the distance from the centre of a cell to the        occupancy reaches a pre-defined threshold, the MSC may
outermost point of the cell in cases when the cells are not    advise some mobile users of the cell to check the
circular.                                                      transmission quality of channels in neighbouring cells.

4. CHANNEL ALLOCATION SCHEME                                                                neighbouring cell, a handoff
Channel allocation deals with the allocation of channels       request will be made to that cell and the mobile moved,
to cells in a cellular network. Once the channels are
allocated, cells may then allow users within the cell to                                          mobile user. In this way,
communicate via the available channels. Channels in a          the congested cell can have some of its nominal channels
wireless communication system typically consist of time        freed and use them in the new call requests. This load
slots, frequency bands and/or CDMA pseudo noise                sharing strategy is also known as directed retry.
sequences, but in an abstract sense, they can represent any    Schemes using a channel borrowing strategy differ from the
generic transmission resource. There are three major           original FCA concept by allowing a cell to use some of the
categories for assigning these channels to cells (or base-     channels of other channel sets apart from its
stations). They are                                            own. The channel borrowing is performed when there are
                                                               no more nominal channels to serve call requests (new
          Fixed Channel Allocation Scheme,
                                                               calls or handoffs) or when the channel occupancy reaches
          Dynamic Channel Allocation Scheme and
                                                               a pre-defined threshold. Borrowed channels normally
          Hybrid Channel Allocation Scheme which is a
                                                               belong to other sectors of the cell, neighbouring cells and in
combination of the first two methods.
                                                               some cases from the cells of the compact pattern which
Fixed Channel Allocation Scheme
                                                               are not neighbours of the borrowing cell site.
                                                               Channel borrowing with channel locking strategy
                                                               borrows a channel from an adjacent cell, but prevents
                                                               (totally or partially)the use of the borrowed channel in the
                                                               co-channel cells of the lender that are near to the
                                                               borrower, taking into account the co-channel interference
                                                               constraints. Channel locking reduces the traffic capability
                                                               of the network. To overcome this penalty, the schemes
                                                               have also adopted channel reassignment strategies.
               Figure 4 Reuse of Channel                       Channel reassignment is an intra cellular handoff, i.e. a
The frequency channel assignment in the cellular concept is    mobile user is asked to change its current frequency
static, i.e. after careful frequency planning, channels are    channel          for        another         one         under
assigned to cell sites and these sets will not change          the control of the same base station. The channel
except for a new long-term reconfiguration. Cell sites will    reassignment is performed in such a
only make use of the assigned channel set or individual
assigned channel sets per sector. This frequency channel
assignment strategy is known as fixed channel                  Channel borrowing without locking (CBWL) [12]
assignment (FCA). After the cellular system has been           strategy proposes the use of a channel of a neighbouring
configured, the fixed channel assignment is simple to use.     cell. However, the borrowed channel is used with
However, it does constrain channel utilisation. If the         reduced transmission power to avoid interference with the
traffic demand in a cell is greater than the number of         co-channel cells of the lender that are near the borrower
nominal channels, (i.e. the frequency channels assigned        (inside the co-channel reuse distance).Fixed Channel
to that cell) all the excess demand is blocked, regardless     Allocation (FCA) systems allocate specific channels to
of the traffic conditions in other cells. This constraint is   specific cells. This allocation is static and cannot be
very limiting for mobile networks and several strategies       changed. For efficient operation, FCA systems typically
have                                                           allocate channels in a manner that maximizes frequency
                                      probability.             reuse. Thus, in a FCA system, the distance between cells
                                                               using the same channel is the minimum reuse distance for
         borrowing (with or without channel locking).          that system. The problem with FCA systems is quite
                                                               simple and occurs whenever the offered traffic to a
                                                               network of base stations is not uniform. Consider a case
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Volume 1, Issue 3, September – October 2012                                    ISSN 2278-6856


in which two adjacent cells are allocated N channels each.       an agent can be described as a hardware or software system
There clearly can be situations in which one cell has a          with social ability that performs tasks with specific
need for N+k channels while the adjacent cell only               aims in a complex and dynamic environment. Agents are
requires N-m channels (for positive integer’s k and m). In       capable of autonomous actions to pursue their objectives,
such a case, k users in the first cell would be blocked from     despite the occurrence of expected or limited unexpected
making calls while m channels in the second cell would           events. This thesis interests in the application of
go unused. Clearly in this situation of non-uniform spatial      intelligent co-operative software agents.
offered traffic, the available channels are not being used       The characteristics of software agents have inherited
efficiently. FCA has been implemented on a widespread            aspects from distributed computing, such as; modularity,
level to date.                                                   speed (parallelism) and reliability (redundancy), and
Dynamic Channel Allocation Scheme                                from Artificial Intelligence (AI) in the knowledge
                                               assignment of     level; easier maintenance, reusability and platform
frequency channels to the cells of the cellular network.         independence.
All frequency                                                    Agents can present different degrees of complexity,
                                            station, the MSC     normally known as granularity. Simple agents with little
chooses the appropriate frequency channel that gives             or no intelligence regarding their behaviour are called
maximum channel efficiency taking into account all the           reactive agents. More complex agents such as those
signal interference constraints. The channels are assigned       possessing symbolic internal models, capable of knowing
for the duration of a call; after the call has finished, the     their environment and able to reason about their goals are
channel is returned to the central pool or reallocated to a      called cognitive or deliberative agents. As the complexity
mobile user inside the same cell site that was controlling       of agents can be so broad, it is difficult to find the
the channel before.                                              boundary between an agent and other types of control
Dynamic Channel Allocation (DCA) attempts to alleviate           software. However, agents do present special properties
the problem mentioned for FCA systems when offered               that distinguish them from other software systems. The
traffic is non-uniform. In DCA systems, no set                   main properties that software agents exhibit are autonomy,
relationship exists between channels and cells. Instead,         social ability and reactivity.
channels are part of a pool of resources. Whenever a             Autonomy is the ability to have control over its own actions
channel is needed by a cell, the channel is allocated under      and states. An agent is able to make decisions and
the constraint that frequency reuse requirements cannot          complete actions based on its internal representation of
be violated. There are two problems that typically occur         the world without direct intervention of a human or a
with DCA based systems.                                          central entity.
          First, DCA methods typically have a degree of
randomness associated with them and this leads to the                                      homogeneous or heterogeneous
fact that frequency reuse is often not maximized unlike          software agents) via some kind of communication
the case for FCA systems in which cells using the same           language in a co-ordinate manner. Agents may co-operate
channel are separated by the minimum reuse distance.             in order to solve a problem or to achieve a task. The terms
          Secondly, DCA methods often involve complex            and conditions of the co-operation may be negotiated at
algorithms for deciding which available channel is most          runtime.
efficient. These algorithms can be very computationally          Reactivity is the ability to perceive changes in the
intensive and may require large computing resources in           environment and react timely and appropriately.
order to be real-time.                                           Software agents may also present other properties such as
Hybrid Channel Allocation                                        pro-activity, learning, adaptability or mobility.
The third category of channel allocation methods includes        Pro-activity is the ability to plan ahead and take the
all systems that are hybrids of fixed and dynamic channel        initiative to perform actions that will contribute to the
allocation systems. Several methods have been presented          goal achievement without waiting for external
that fall within this category and in addition, a great deal     instructions or only responding to events in the environment.
of comparison has been made with corresponding
simulations and analyses [1]-[2].                                                            actions as the agent reacts with
                                                                 the environment and/or with other agents, in order to
5. INTELLIGENT AGENT                                             avoid past mistakes or increase performance over time.
                                                                 Adaptability is the ability to adapt to changes in the
Agent based technology is an interdisciplinary area of
                                                                 environment, in order to continue to pursue its objectives.
research and it has received special attention from the
                                                                 Learning is one of the factors that allow agents to have an
research community since the beginning of the 1990’s. The
                                                                 adaptive behaviour.
definition of an agent is controversial, but in general terms,
                                                                 Mobility is the ability to move around a network.
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                                                                FCA-based schemes. However, the near-optimum channel
                                                                allocation is at the expense of high overheads through its
                                                                use of centralized allocation schemes. This overhead
                                                                means that such schemes are not practicable for large
                                                                networks.
                                                                Distributed DCA schemes with limited inter-cell
                                                                communication suffer less overhead, but lead to sub-
                                                                optimum allocations. Such schemes are being proposed
                                                                for microcellular systems as this cell structure allows
                                                                inter-cell     information    sharing    by interference
                                                                measurements and passive non-intrusive monitoring at
   Figure 5 Agent Types Based In Their Predominant              each base station (busy/idle status of the carriers). For
                      Features.                                 macro cellular systems, where explicit communication is
A different approach to defining agents by classifying          needed, FCA with channel borrowing offers good results
them uses different criteria: mobility, granularity,            and less computational complexity than DCA. However,
predominant attributes and roles. In the first two criteria,    those FCA schemes with the best results used centralized
the agents can be mobile or static and deliberative or          control inside the Mobile Switching Centre (MSC).
reactive. Cooperation, autonomy and learning are the            Although that is less complex than DCA schemes, there
three basic attributes of agents and from them three types      is still a need to maintain an up-to-date global knowledge
of agents can be identified: collaborative agents, interface    of the entire mobile network, leading to a slow response
agents and smart agents, as can be seen in Figure 4.1.1.        and a heavy signaling load. To alleviate this problem,
Each type giving more emphasis to                               several authors have proposed modifications to make the
                                                                schemes more distributed. One example is the distributed
       attributes equally, but the applicability of the agent   load balancing with selective borrowing scheme (D-
to certain problem will dictate which type of agent is more     LBSB) [6] that performs better than its centralized
suitable for each case.                                         version [5] and also outperforms other existing schemes
The last criterion to classify agents is by their roles, for    like direct retry [3] and CBWL [4]. The D-LBSB scheme
example, World Wide Web                                         is a distributed FCA algorithm with selective borrowing,
                                                         Web    channel locking and channel reassignment. It takes into
Crawlers, Lycos and Spiders.                                    consideration the position of the mobile users when
Of course, the total classification of an agent would be a      borrowing and reassigning channels; it triggers the
combination of these criteria. For example, an agent            execution of the algorithm when the usage of the nominal
could be a mobile deliberative information agent or a           channels in a cell reaches a pre-determined threshold (h,
                                                                when a previously cold cell becomes hot). It also controls
                                                                the number of the channels to be borrowed from or lent to
                                                                a cell according to the traffic load of the whole cellular
     deliberative part inside a single agent. These agents      network. We selected this algorithm as the basic
would be classified as hybrid agents.                           comparison for our work.

6. PROBLEM DEFINITION                                           7. ARCHITECTURE DESIGN
Fixed channel assignment (FCA) is too limiting for              There are 49 cells and each cell has 10 nominal channels.
mobile networks and several strategies have been                The compact pattern is a 7-cell cluster with the reuse
proposed to maximize frequency channel allocation and           distance being three cell units. Mobile users have their
minimize call blocking probability. A detailed survey           own trajectories inside the mobile network. Call
describing dynamic channel assignment (DCA) schemes             establishments and handoff requests are simulated as they
and FCA-based schemes, including those with channel             are requested in AMPS systems. For each cell, a Poisson
borrowing is given in [7]. In that paper it is noted that       distribution is used to generate calls, which have an
there is a trade-off between the implementation                 exponentially distributed duration with a mean of three
complexity of the channel allocation algorithms and             minutes. Each call attempt is performed by an idle mobile
spectrum utilization efficiency. DCA schemes perform            inside the cell, chosen randomly. This is a more detailed
better under low traffic intensity; modified FCA schemes        simulation than those presented in the literature, which
have superior performance in high traffic loads. DCA            make broader assumptions. These differences need to be
schemes use channels more efficiently and for the same          taken into account when comparing results. A distributed
blocking rate have a lower forced call termination than         borrowing algorithm based on D-LBSB was implemented

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Volume 1, Issue 3, September – October 2012                                    ISSN 2278-6856


generally following the descriptions in [5], [6]. The
distribution elements of the system were located in the
base stations, the messages between base stations passing
through the MSC. We used a value of 0.2 for the cold/hot
threshold (h). Unlike the original algorithm where the
departing region (r) varies with the number of channels to
be borrowed and the average density of mobile users in
the cell, we chose r to be constant and dependent on
signal strength. Some necessary parameters for
implementation have not been described fully in the
references so that while our algorithm generally follows
that of D-LBSB it is not exactly the same. We refer to our
scheme as the distributed borrowing algorithm (BA). To                     Figure 8 Total Loads on Network
analyze the performance of the scheme, we chose the
system layout with non-uniform traffic distributions. The
number in the bottom of each cell is the cell
identification; the number in the middle gives the Poisson
arrival rates in calls/hour (ranging from 20 to
200calls/hour). Simulation result 1 shows the blocking
rate of our BA compared with the FCA as the traffic rates
increase over the load. Overall, BA outperforms FCA
from moderate to heavy load; the maximum improvement
achieved in this case is a reduction in call blocking
probability by around 20%. However, individual cells
with higher traffic rates present a better improvement.
                                                                      Figure 9 Percentage of Call Drop for FCA




Figure 6 Seven-Cell Clusters with Frequency Reuse Plan
                & Hexagonal Model

8. SIMULATION RESULTS
                                                                     Figure 10 Percentage of Call Drop for DCA


                                                             9. CONCLUSION
                                                             The cellular network implemented has nineteen cells, ten
                                                             nominal frequency channels per cell in a 7-cell cluster.
                                                             The network is a macro cellular structure. In each cell a
                                                             source call generator process generates the call requests
                                                             and randomly chooses an idle mobile station located
                                                             inside the cell to place the call. The pdf for the call inter-
                                                             arrival time and its mean value are changeable simulation
                                                             parameters. In the scenarios simulated in this work, a
                                                             negative exponential distribution was selected for call
                                                             inter-arrival time with different mean values depending
                                                             on the desired traffic load in the cell. The call length
           Figure 7 Inputs given for simulation              distribution is also a simulation parameter. Constant and
                                                             exponential call length distributions were used in the
Volume 1, Issue 3, September – October 2012                                                                    Page 192
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Volume 1, Issue 3, September – October 2012                                    ISSN 2278-6856


simulations.                                                      Communications Magazine, vol. 3, no. 3, pp. 10-31,
The performance of Distributed DCA scheme of a cellular           June 1996.
network using the multi-agent system was compared with     [8]
the distributed FCA scheme. The simulation results                                          Systems Implementation.
demonstrated that the use of intelligent software agents          Prentice Hall Communication Engineering and
brought more flexibility than the other approaches and            Emerging Technologies. Series Editor - Theodore S.
the distributed DCA scheme is more efficient than the             Rapp port. Prentice Hall PTR. 2000
other schemes of FCA.                                      [9]    V. H. MacDonald, “Advanced mobile phone
                                                                  services: the cellular concept,” Bell Systems
The performances of the Distributed FCA & DCA
                                                                  Technology Journal, vol. 58, no. 1, pp. 15-41,
schemes are compared and the results are given in table
                                                                  January 1979.
1.                                                         [10]   William     C.     Y.     Lee.   Mobile    Cellular
   Table 1 Performance of the Distributed FCA & DCA               Telecommunications: Analog and Digital Systems.
                        Schemes                                   Second Edition. McGraw-Hill, Inc. ISBN 0-07-
     Ch. Allocation Call Drop Rate Status                         038089-9. 1995.
     Scheme           (%)                                  [11]   E. L. Bodanese and L. Cuthbert, “Distributed
     FCA              96% To 98%          High                    channel allocation scheme for cellular networks
     DCA              26% To 28%          Low                     using intelligent agents,” 7th International
                                                                  Conference in Telecommunication Systems, pp. 156-
Overall, the distributed DCA scheme using multi-agent             165, Nashville TN, USA, March 18-21 1999.
system proved to be efficient and feasible.                [12]   R. G. Smith, “The contract net protocol: high-level
                                                                  communication and control in a distributed problem
                                                                  solver,” In Readings in Distributed Artificial
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Volume 1, Issue 3, September – October 2012                                                               Page 193

				
DOCUMENT INFO
Description: International Journal of Emerging Trends & Technology in Computer Science (IJETTCS) Web Site: www.ijettcs.org Email: editor@ijettcs.org, editorijettcs@gmail.com Volume 1, Issue 3, September – October 2012 ISSN 2278-6856