Location Management Cost Strategies in Cellular Networks
Rizal Munadi
Electrical Engineering Department, Engineering
Faculty
Syiah Kuala University
Mahamod Ismail, Mardina Abdullah, Norbahiah
Misran
Electrical, Electronics and System Department -
Engineering Faculty
Universiti Kebangsaan Malaysia
{mahamod, mardina, bahiah} @vlsi.eng.ukm.my
Abstract-The growth of cellular users using to
communicate at any place and any time increases the
signaling activities among the cellular networks. To
reduce the network costs and better usage of radio
resources, an efficient location management scheme:
location updating and paging strategies are essential to
improve the network performance. This paper presents
a mixed location management strategy that combines
some strategies of location update and paging schemes
to minimize the overall cost. Simulation results
indicates that the location management performance of
using larger memory system, shows better result in
reducing the location management costs.
Keyword: Location Management, Cellular user,
Location Update, Paging, Cost
1. Introduction
The growth of cellular users and the intense of
communication activities will increase signaling traffic
in which the available spectrum for radio resources is
limited. Increasing the number of active users in service
area have influenced the grade of service of the
network, which is dependent on the size of the cell
employed. On the other hand, increasing the user
mobilities will increase uncertainty of user locations in
a network with respect to the size of the cell employed.
Increased signaling incurs additional cost to operators
by consuming network resources that effected to
revenue-generating traffic.
The cost of mobility tracking depends primarily on
the costs of location update (LU) and paging.
Intuitively, the location accuracy depends in the LU
frequency. The more frequent the LU, the more
accurate the location information of cellular user . In
other word, this frequent LU activity will increase the
cost of signaling and on the other hand the paging cost
may decrease. If the cellular user performs the lower
LU activities, it will increase the task of the system to
page cellular user when it delivers the incoming call.
This situation will decrease the LU cost but increase the
paging cost. This cost problem is the main interest of
this study and a mixed strategy using a combination of
different LU and paging schemes is implemented to
obtain the minimal signaling cost.
The rest of the paper is organized as follows. In
Section 2, the concept of location management is briefly
introduced and followed the review of the current
research in this area. In Section 3, the procedure for
mixed strategy LU and paging schemes developed is
described. Section 4 gives the simulation results and
finally Section 5 concluded the paper.
2. Location Management Concepts and
Review of Previous Works
In order to provide fast and smooth mobile services
to users, Location Management (LM) becomes a
primary issue in cellular communication system. The
location management system resides in Mobile
Switching Center (MSC) that contains two databases to
facilitate the tracking of cellular user: Home Location
Register (HLR) and Visitor Location Register (VLR).
The HLR contains the user permanent data (e.g.,
directory number, profile information, current location,
and validation period) of the cellular user whose
primary subscription is within the area. The VLR is
associated with an MSC in the networks. The VLR
retrieve information for handling calls to or from a
visiting cellular user.
Location management is concerned with the
procedures required to enable the network to maintain
location information for each active cellular user and to
efficiently handle the establishment of incoming calls.
There are two basic procedures in LM: LU and Paging.
These two-stage process in LM enables the network to
discover the current attachment point of the mobile user
for call delivery [1]. LU is initiated by the mobile
terminal, and informed the network of the subscriber’s
current location. The network initiates paging when an
incoming call arrives. It means that the paging process
always performs after the completion of the LU
transaction. Paging messages are broadcast in one or
more paging areas, contained within the current
location, and inform the target user of the incoming call.
Rizal Munadi,Mahamod Ismail,Mardina Abdullah,Norbahiah Misran, Int. J. Comp. Tech. Appl., Vol 2 (1), 188-192
188
ISSN : 2229-6093
There are two tracking strategies to maintain user
location, static and dynamic strategy. Static strategy is
defined that the network decides when and where the
mobile user or mobile terminal should report to the
network of their location, and in dynamic strategy the
cellular user informed the network of its location when
and where it could be. The cellular user transmits
update message according to their movement and not in
predetermined cells. The location tracking strategy
currently used by most PCS is fixed paging area
strategy [2, 3]. In this strategy, all cells of the network
are partitioned into service area that called registration
areas (RA) or location area (LA). A cellular user in this
system is required to update its new location when it
entered to a new LA. Whenever a call arrives, the exact
location of the called is queried by paging all cells of
the LA the active cellular user lastly updated. Designing
appropriate LAs could reduce the location tracking cost
of the PCS effectively [4]. Although the fixed paging
area (PA) strategy could be easily implemented but the
drawback it could not reach the optimal location
tracking cost since the PA defined in this approach may
be large (for low mobility mobiles) or small (for high
mobility mobiles) to make unnecessary updates. There
should be a complicated work in designing the optimal
paging size.
In the last few years some strategies have been
proposed related to LU and paging. For LU, the
proposed strategies that frequently appear in literatures
can be summed up into time-based [5], movement-
based [6], distance-based [7] and zone-based scheme [8,
9].
In the time-based strategy, the cellular user
updates its location periodically every certain time
interval as a threshold. In the distance-based update
strategy, a cellular user updates its location whenever
the distance between the current cell and the last
registered cell exceeds a predefined threshold value. In
the movement-based update strategy, a cellular user
updates its location if the number of cells it has traveled
since the last LU exceeds a pre-defined threshold value.
Finally, in zone-based strategy, the entire cellular
network is partitioned into LA and the user updates
whenever a LA boundary is crossed. In case of an
incoming call, the current LA of the user (where the last
updated) is paged.
Another scheme, Profile Based Strategy (PBS) was
proposed in [10] and [11] as a technique to reduce the
cost of LU. In the PBS, the system maintains a record of
each user’s most likely itinerary. This technique
considers that the user location is known in advance.
A number of authors have proposed paging
strategies. In [12], a sequential paging strategy has
investigated with given an assumed probability
distribution on the user location. In this strategy, when
there is an incoming call to a target cellular user, the
PAs are sequentially paged for the cellular user
following a pre-defined paging strategy, which defines
the order for paging the PAs. To improve the
probability of finding the cellular user and reduce the
paging cost, in [13], based on the velocity and direction
information of a cellular user, the system estimates the
most possible cell that the cellular user is residing.
It is difficult to compare various mobility
management strategies since as yet there exist no
absolute bounds on optimum performance can be
applied to any procedure regardless of assumptions
about mobility, network structure, and the like [14]. On
the other hand, it has been shown that the distance-
based LU with sequential paging would be the most
efficient strategy in the case of saving radio resource
and reducing the network signaling [2]. Among various
method in LU and paging schemes, in this paper a
combination of distance and zone-based method is
analyzed to achieve the minimal cost.
3. Mixed LU and Paging Schemes
The distance-based LU [15, 16] was selected among
the schemes in this work. The basic idea of this
algorithm is as follows. Each cell having a base station
and having its own id (identifier), with cellular user
resides in each cell for some time interval before
moving on the next cell. It is assumed that when cellular
user leaves a cell, there is an equal probability that any
one of the immediate neighboring cells is selected as the
destination. The distance-based scheme is determined
by measuring the cell-to-cell distance. The updating
cost will be processed only if the information about the
cell is changed or in another word the cellular user
moves to a different cell. For paging, a cluster of seven
cells called PA is defined. When the cellular user moves
to another cell, the system will check whether the new
cell belongs to the same PA profile or not.
The mixed strategy LU and paging scheme to reduce
the cost of signaling is described as follows:
A. Location update procedures
Four different LU strategies are proposed and
implemented in this paper. There are 49 cells. Denoting
the base station in every cell as BS1 up to BS49 and
suppose that the initial location of the cellular user is in
cell 1, the system will register the cellular user as BS1
data. Every time cellular user moves to a different cell,
the system will count as a cost. Figure 1 shows a sketch
of a sample path, showing cellular user travels from cell
47 38 6 5 4 1. The strategies are as follows:
1. If the current cell id (n) is different to (n-1) the cost
is LUA. This strategy is similar to Lin [17] and
Abutaleb [18].
2. If the current cell id (n) is different to (n-1) and
(n+1), the cost is LUB.
3. If the current cell id (n) is different to (n-1) and (n-
2), the cost is LUC.
4. If the system can record larger data set for each user
state (ni), where i = 1 to m and m is the maximum of
Rizal Munadi,Mahamod Ismail,Mardina Abdullah,Norbahiah Misran, Int. J. Comp. Tech. Appl., Vol 2 (1), 188-192
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length of the data set. The difference in cell id in the
data set gives the cost, LUD.
Figure 1. Cellular coverage using 49 cells
B. Paging procedures
For paging scheme, an analysis using single PA and
zone-based strategy are employed in this work. In zone-
based, the system is divided into equal size (weight)
area, among MSCs to keep the network overhead
minimal. For this purpose, seven symmetrically PAs of
equal size, in which each cluster consists of seven cells
is defined, as shown in Table 1. The paging schemes
will process any incoming signal by identifying the cell
id of each active cellular user. The system will count as
a cost if the current cell id is different to the previous
one. The mechanisms are as follow:
1. Based on zone area, the system will check whether
cellular user belongs to a certain PA. If it is
different, the system will count as a paging cost,
PgA.
2. The system will detect individually to the paged
cellular user in a single cell, the paging cost PgB.
3. Based on the zone concept, but assuming the system
can store previous information and detect if cellular
user stays in different PA, the paging cost is PgC.
Table 1. Symmetrical Cell Clustering
Cell Cluster Cell Number
1 1, 2, 3, 4, 5, 6, 7
2 8, 9, 10, 11, 12, 13, 14
3 15, 16, 17, 18, 19, 20, 21
4 22, 23, 24, 25, 26, 27, 28
5 29, 30, 31, 32, 33, 34, 35
6 36, 37, 38, 39, 40, 41, 42
7 43, 44, 45, 46, 47, 48, 49
4. Results
The simulation generates a hundred cellular users
randomly with starting at different points. Eight
possible directions of cellular user positions are
implemented in the simulation and cellular user
movement depends on system processing as shown in
Figure 2. Each position of the cellular user has been
investigated using the strategies described in Section 3.
Figure 2. Mobile Terminal Activities
4.1. Location update performance
Four different LU strategies as describe in Section 3
are investigated and compared. The performance of
these strategies is analyzed to obtain the lower signaling
activities using the cumulative distribution function
(cdf) as shown in Figure 3. The LU abbreviation
followed by alphabet A, B, C, and D respectively are
the initial of each LU strategy. With LU_A as the
benchmark, the results show that LU_D is superior with
respect to LU_B and to LU_C in this order, with each
cdf values of 76%, 52%, and 30% respectively.
Figure 3. Location Update Performance
4.2. Paging performance
As mentioned in Section 3, only three procedures in
Paging strategy are evaluated in this simulation. Figure
4 shows cdf of the average number of paging for the
three paging strategies described. The result shows that
using only a single cell will waste the network resources
and increase the paging cost. With this single cell
paging strategy, PG_A as the benchmark, the cdf for
PG_C is 93% and the cdf for PG_B is 65%. PG_C is
shown to be superior to PG_B and PG_A respectively.
Rizal Munadi,Mahamod Ismail,Mardina Abdullah,Norbahiah Misran, Int. J. Comp. Tech. Appl., Vol 2 (1), 188-192
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Figure 4. Paging Performance
4.3. Mixed LU-Paging performance
From the LU and paging strategies that have been
investigated in the previous section, twelve possible
combinations can be employed for the mixed LU-
paging strategies. Figure 5 shows performance of this
scheme, where each LU and Paging combination is
mixed as pair in term of signaling activities. As shown
in this figure, the PG_A and LU_A pair is the worst pair
and the PG_C and LU_D is the best pair in terms of
paging and updating cost reductions.
Figure 5. A Mixed LU and Paging Signaling
Activities
Another way to examine the performance of the
mixed LU-paging strategy is by looking at the cdf plot
as shown in Figure 6. For simplicity, only the best four
combined strategies as given in Table 2 are plotted and
evaluated, these are:
Table 2. Strategy for Mixed LU-Paging pair
Strategy Mixed LU-paging pair
A LU_D and PG_C
B LU_B and PG_C
C LU_D and PG_B
D LU_C and PG_C.
With strategy D as the benchmark, the cdf of strategy A,
B, and C are 84%, 33%, and 32% respectively. Again,
the result shows that the mixed strategy A is superior to
others that will give the lower signaling activities and
the best choice to implement.
Figure 6. Mixed LU-Paging Strategies
Performance
5. Conclusion
In this paper, we have studied a practical mixed
strategy of LU and Paging. The cost function of the
analysis is counted as a number of signaling activities in
LU and paging strategies in cumulative distribution
function. Simulation results showed the performance of
LU case: Strategy LU_D gives superior performance
(76%) with respect to the other three (LU_B, LU_C and
LU_A) respectively. In the Paging case: Strategy PG_C
gives the best result (93%) with respect to Paging
strategy PG_A and PG_B. Both of these LU and Paging
strategy employed larger data set. The strength of these
strategies is that it minimizes the cost of calculating the
redundant data. The mixed strategy results show that
strategy A, a combination of LU_D and PG_C, give the
lower signaling activities with cumulative distribution
function (cdf) value of 84 % with respect to the worst
case combination of strategy D.
References
[1] I. F. Akyildiz, et al., “Mobility Management in Next-
generation Wireless Systems”, Proc. of the IEEE, 1999, Vol.
87, No. 8, pp. 1347-1384.
[2] I. F. Akyildiz, and J. S. M. Ho, “On Location
Management for Personal Communication Networks”, IEEE
Communication Magazine, 1996, Vol. 34, No. 9, pp 138-145.
[3] S. Tabanne. “Location Management Methods for Third
Generation Mobile Systems”, IEEE Communication
Magazine, 1997, Vol. 35, No. 8, pp. 72-78; 83-84.
[4] T.-P. Wang, S.-Y. Hwang, and C.-C. Tseng, “Registration
Area Planning for PCS Networks Using Genetic Algorithms”,
IEEE Transactions on Vehicular Technology, August, 1998,
Vol. 3, No. 47, pp. 987-995.
Rizal Munadi,Mahamod Ismail,Mardina Abdullah,Norbahiah Misran, Int. J. Comp. Tech. Appl., Vol 2 (1), 188-192
191
[5] C. Rose, “Minimizing the Average Cost of Paging and
Registration: A Timer-Based Method”, Wireless Networks,
June, 1996, Vol. 2, No. 2, pp. 109-116.
[6] A. Bar-Noy, I. Kessler, and M. Sidi, “Mobile users: To
Update or not to Update?”, Wireless Networks, July, 1995,
Vol. 2, No. 1, pp. 175-185.
[7] Y.-B. Lin, “Reducing Location Update Cost in a PCS
Network”, IEEE/ACM Transaction on Networking, February,
1997, Vol.5, No.1, pp. 25-33.
[8] S. Madhavapeddy, K. Basu, and A. Roberts, “Adaptive
Paging Algorithms for Cellular Systems”, Wireless
Information Networks: Architecture, Resource Management
and Mobile Data, J.M. Holtzman ed., Kluwer Academic,
1996, pp. 83-101.
[9] S. Subramanian and S. Madhavapeddy, “System
Partitioning in a Cellular Network”, Proc. 46th IEEE
Vehicular Technology Conference, Atlanta, April-May, 1996,
pp. 106-110.
[10] G. Wan and E. Lin, “Cost Reduction in Location
Management Using Semi-Real Time Movement Information”,
Wireless Network Journal, July 1999, Vol. 5, No. 4, pp. 245-
256.
[11] K. Kim, M. Cho, S. Kwon, K. Cho, and K. Cho. “An
Optimal Location Area Decision Method Considering Mobile
Power Status”, Proc. IEEE 5th ICUPC, September 29-
October 2, 1996, Vol. 2, pp. 612-616.
[12] C. Rose and R. Yates, “Minimizing The Average Cost of
Paging Under Delay Constraints”, Wireless Network, 1996,
Vol. 2, No. 3, pp. 109-116.
[13] S. Subramanian and S. Madhavapeddy, “System
Partitioning in a Cellular Network”, Proc. 46th IEEE
Vehicular Technology Conference, Atlanta, April-May, 1996,
pp. 106-110.
[14] C. Rose and R. Yates, “Location Uncertainty in Mobile
Networks: A Theoritical Framework”, IEEE Communication
Magazine, February, 1997, Vol. 35, No. 2, pp. 94-101.
[15] J. S. M. Ho and I. F. Akyildiz, “Mobile User Location
Update and Paging under Delay Constraints”, Wireless
Networks, December, 1995, Vol. 4, No. 1, pp. 413-425
[16] U. Madhow, M. L. Honig, and K. Steiglitz,
“Optimization of Wireless Resources for Personal
Communications Mobility Tracking”, Proc. IEEE INFOCOM
'94, Toronto, June, 1994, pp. 577-584.
[17] Y.-B. Lin, “Reducing Location Update Cost in a PCS
Network”, IEEE/ACM Transaction on Networking, February,
1997, Vol. 5. No.1, pp. 25-33.
[18] A. Abutaleb and V. Li, “Location Update Optimization
in Personal Communication Systems”, Wireless Networks,
July, 1997, Vol. 3, pp. 205-216.
Rizal Munadi,Mahamod Ismail,Mardina Abdullah,Norbahiah Misran, Int. J. Comp. Tech. Appl., Vol 2 (1), 188-192
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