E E E TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL 45, NO. 1, FEBRUARY 1996
82
ing and Analysis of the ynamic
ation and Paging in icrocellu
Seok J. Kim and Ghae Y. Lee, Member, IEEE
Ahtruct- A 0-1 integer programming model is considered
to determine the most appropriate dynamic location registration (LR) area of each subscriber in microcellular systems.
The minimization model of the LR area updating and paging
signal costs is examined. The model is based on the subscriber
characteristics, such as the call arrival rate and the velocity, as
well as the regional information. The control channel blocking
probabilities are considered as constraints to meet the service
level of subscribers. A dynamic scheme which adaptively updates
the size and shape of the LR area is developed by solving the
minimization problem. Paging and location updating procedures
are presented based on the dynamic procedure. The superiority off
the proposed scheme is demonstrated with various computational
results.
I. INTRODUCTION
ECENT increase of the mobile communication subscribers is in great need of the capacity expansion of
the cellular system. In order to accommodate the increasing
number of subscribers, the cell size will have to be much
smaller than the current one, even in the code division multiple
access (CDMA) system. The advance of microcells is thus
necessary to serve the subscribers in metropolitan areas. One
emerging problem in the microcellular system is the paging
and location updating. Since the mobility of each subscriber
largely depends on the flow of the traffic and the individual
velocity, the visitor location registration and paging becomes
an important issue in the microcellular system.
In paging, a subscriber is located for its land-originated
call setup within an established paging area. For rapid and
efficient paging, determination of the most appropriate paging
area is essential. When all cells in a city are in one paging
area, the location updating procedure is not required in the
city. However, the number of paging signals required for
one call setup increases with the number of base stations. In
microcellular systems note that the number of base stations
may be 10-100 times larger than that in the traditional cellular
system. Thus, in the one-paging area system the number of
required paging signals rapidly increases as the number of
call setups increases.
To reduce the paging signals in the one-paging area system,
Munoz-Rodriguez [ 11 introduces the cluster-paging scheme. In
the scheme, a subscriber is first paged within a cluster of base
stations, including the home location cell. If the subscriber
Manuscript received August 19, 1994, revised February 9, 1995 and May
10, 1995
The authors are with the Department of Management Science, Korea
Advanced Institute of Science and Technology, Taejon 305-701, Korea.
Publisher Item Identifier S 0018-9545(96)00200-9
does not exist in the cluster, other clustered base stations are
searched. This procedure is repeated until the subscriber is
reached. In the worst case, all the base stations may have to
be searched for the subscriber. Thus, the call setup time in the
cluster-paging scheme may be greater than that in one paging
area procedure.
One natural selection to improve the one-paging area
method is to divide the paging area into fixed subareas [2]. In
the fixed location registration (LR) area, it is easy to manage
paging and location registration. The location of a subscriber
who moves in or out of a particular fixed LR area is updated
in the visitor location registration and used for paging. Also in
the system, since the location updating procedure is activated
when a subscriber leaves the fixed area, the updating signal
occurs only at a boundary cell of the fixed LR area. Thus in
the boundary cells, since the occurrence of updating signals is
proportional to the mobility, congestion in the control channel
occurs. Clearly, the effect becomes serious when the velocity
of each mobile increases.
To reduce the overload at LR borders, a method with fixed
layered LR area is employed by Okasaka et al. [2].In the
scheme, each cell is included in one or more layers, depending
on the amount of traffic at the cell. When a subscriber leaves
one area, the location is updated to another area of the same
layer or to an area in a different layer. The determination of
the layer is controlled by the traffic density at each cell.
A dynamic LR area scheme in which each subscriber has
its own LR area is proposed by Goodman et al. [3]. They
provide a dynamic scheme that determines the LR area by
reflecting the call arrival rate and average velocity of each
subscriber. The size of the LR area is thus controlled by the
two factors. However, the type of LR area is always identical
regardless of the location of the subscriber. Therefore, the
regional information, such as the physical type of cells and
the direction of the mobile, is not considered in the procedure.
Also, the determination of the LR area is under the assumption
of equal-sized cells and uniform call arrivals at each cell.
Another paging scheme proposed by Taketsugu et al. [4]
employs the overlapped LR area to reduce the updating signals
in the boundary cells. Each LR area is composed of a central
cell and its neighboring cells. The inclusion of neighboring
cells is determined by reflecting the route information around
the central cell. The LR area thus reflects the flows at each
cell around the subscriber. However, the characteristics of each
subscriber are not considered in the system.
To avoid the inefficiency of the previous work, we consider
a minimization model of the signal costs, which flexibly reflect
0018-9545/96$05,00 0 1996 IEEE
KIM AND LEE DYNAMIC LOCATION REGISTRATION AND PAGING IN MICROCELLULAR SYSTEMS
both the regional information and the mobile characteristics.
An adaptive dynamic location registration scheme is developed
to determine the most appropriate LR area size.
OF THE DYNAMIC
LR AREA
11. DETERMINATION
As discussed in the previous section, recent research on
the decision of the LR area has several disadvantages to be
applied in microcellular systems. First, the control channels
of boundary cells are overloaded in the fixed LR area system
due to the location updating signals. The overload in boundary
cells is more serious in the heavy traffic region. Second, the
research on dynamic schemes did not reflect the regional and
mobile characteristics at the same time.
In this paper we consider a new dynamic LR area decision
scheme, which continuously reflects the regional information
and mobile characteristics such that the required number
of paging and location updating signals is minimized. The
minimization of the use of these two signals will eventually
increase the capacity of the cellular system, even if the total
usage might be restricted by the service level preserved at each
cell. For the modeling of the decision problem, we introduce
the two signal costs as follows:
Paging-cost = a * #of_CallArrivals * #-of-CellsinLR-area
Updating-cost = P * #-of-Updates
where a and /3 are weights (bitslsignal) of paging and updating
signals, respectively. Note that the updating cost is proportional to the velocity of a subscriber, while the paging cost is
proportional to the call arrival rate and the size of the area.
If we assume the uniform distribution of subscribers in a
region, the LR area size may be defined by either the radius
or the length of the side of the area. However, under the
nonuniform assumption, the density of subscribers and the
moving tendency at each cell are not identical. Thus, the
optimization of the LR area must be based on each cell. A cell
may or may not be contained in the LR area of a particular
subscriber.
Now, at each cell included in the LR area of a mobile,
a certain service level has to be met. In other words, a
prespecified standard o€blocking probability has to be satisfied
by the forward and reverse control channel between the
subscribers and a base station.
Before introducing a model for the determination of the
dynamic LR area, the following notation needs to be defined.
2 , = 1 If cell i is in the LR area of the subscriber
= 0: otherwise.
U
Call arrival rate to the subscriber.
U
Average velocity of the subscriber.
Visiting
rate of cell i when the average velocity of
f,(u)
the subscriber is U .
Weight of paging signal (bitdsignal).
a
Weight of updating signal (bitshignal).
P
Average number of paging signals to cell i.
Pa
Average number of updating signals from cell i .
u,
Mean service time of paging signal.
71
Mean service time of updating signal.
72
Forward control channel blocking probability re81
quirement.
83
Reverse control channel blocking probability requirement.
Set of all cells.
Set of the boundary cells not included in the LR
area.
The number of cells.
O2
TC
BC
N
The determination of the dynamic LR area is formulated as
the following 0-1 integer programming problem
Min
ax,
+ PC f z ( v ) ( l-
s.t.
. 1+PZ71
u,7 2
1
+
2%)
(1)
i E TC
(2)
2
2
ut72
z, = 0
2,
5 10-@1
(1 - 2 , ) 5 10-@z i E BC
or
(3)
1.
In the formulation, the first term of the cost function (1)
represents the paging cost of each subscriber. If cell i belongs
to the LR area of a subscriber, the paging signal occurs a times
for a unit time period. The second term represents the LR area
updating cost. Since the updating occurs when a subscriber
moves out of its current LR area, the cost at cell i can be
computed by examine the visiting rate of cell i . To reduce the
updating cost, a cell with a large visiting rate will have to be
included in the current LR area, while that with a small one
may be excluded. In this study, the visiting rate f,(v) of cell
i is computed by including the regional information at each
cell as follows:
f%(.)=
kv x E[number of visits to cell i with free flow]
driving distance
(4)
where 5 is a constant.
The visiting rate of cell i is proportional to the velocity
of a subscriber and the expected number of visits to cell z
when no blocking is assumed in the flow. The rate is inversely
proportional to the driving distance from the current cell. Note
in the cost function that the increase of the paging cost is
proportional to the number of cells in the LR area while that
of the updating cost is inversely proportional to the size of
the LR area.
The constraint (2) in the model represents the blocking
probability of paging signals. It is assumed that the paging
signals arrive in each cell in Poisson manner and that the
blocking probability is defined by Erlang-B formula. The
blocking probability of the location updating signals is also
represented, as in the constraint (3). The location updating
is assumed to occur as soon as a mobile moves out of the
current LR area.
Note in the above formulation that the problem cannot
be solved easily. The boundary cells to which the second
constraints are applied cannot be identified before the problem
is solved. Thus, we first need to solve the problem by relaxing
the second constraint. After deciding the LR area of the
relaxation problem, we then consider the constraint ( 3 ) at the
boundary cells. Now, suppose that the blocking probability of
the control channel is greater than that of the voice channel,
then a large portion of calls will be blocked because of the
IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 45, NO. 1, FEBRUARY 1996
84
paging and location updating. Therefore, constraint on the
control channel needs to be tighter than that on the voice
channel to prevent bottleneck effects.
In the optimization problem, the objective function is transformed as follows
i
i
2
a
By relaxing the constraint (3),the problem is now decomposed
into the following decision problems P ( i ) ,each of which is
to decide whether cell z is included in the LR area or not.
Decomposed Problem
Pi
d) endif
e) do while (all the boundary cells are considered)
if not satisfy the second constraint
if satisfy the first constraint by letting IC, = 1
then x, = 1
else z,= 0
endif
endif
f) enddo
2) end.
The computational complexity of the proposed scheme is
Q ( N ) ,which is linear to the number of cells. For each location
update, the scheme decides whether a cell z is included in
the new LR area or not by computing the coefficient of
the objective function of P(z). However, the computational
demand can be reduced in real implementation by sorting the
cell Est according to the flow rates and distance. Thus, the
computation of the objective function is not applied to every
cell in the microcell region.
The LR area is determined by solving each decomposed
problem. In the problem P(z),if 2, = 1 satisfies the constraint
and the coefficient of the objective function is negative or
equal to zero, then cell z is included in the new LR area of the
II€. PAGINGAND LOCATIONUPDATING
subscriber. Otherwise, if x, = 1 does not satisfy the constraint
PROCEDURES WITH THE DYNAMIC
SCHEME
or the coefficient is positive, then it is better to exclude the
Two types of control signals are needed for paging and
cell from the new LR area. That is, by letting x, = 0, the
location registration. A paging signal from each base station
decomposed problem can be minimized.
After solving each decomposed problem, it may be possible pages a mobile for a call setup. A location updating signal on
that the LR area is not connected. In this case, the area to the other hand requests the telephone switching office to enroll
which the subscriber belongs is considered the new LR area. and update the location of the mobile.
Fig. 1 illustrates a simplified structure of the paging and
Other cells that are not connected to the area are discarded.
Now that we have determined the LR area of the relaxation location registration system. As shown in the figure, two
problem, we consider the boundary cells that are not contained database systems-the visitor location registration (VLR) and
in the LR area. At a boundary cell of the LR area, if the the home location registration (HLR)-are necessary for the
constraint (3) is satisfied, then the cell is included in the paging and location update. The HLR keeps information on
LR area. Otherwise, if the constraint (3) is not satisfied, the phone number, home location, and current registered VLR
the constraint (2) is checked by letting xa = 1.If the boundary cell numbers of each subscriber. When a call arrives, the
cell satisfies the first constraint, then the cell is included in current registered VLR cell numbers of the subscriber are
the LR area. This has an effect of avoiding location updating first seached. If they exist, an exact cell of the mobile is
at cells where reverse control channel is extremely busy. searched within the LR area. Based on the system of Fig. 1, the
However, when the boundary cell does not satisfy the two procedures of location registration and paging are summarized
below.
constraints, it is not included in the LR area.
The decision scheme discussed above updates the LR area
of a subscriber each time a mobile moves out of the current LR
area. The size and shape of the new LR area is dynamically A. Paging Procedure
updated by reflecting the call arrival rate, velocity, and regional
When a mobile telephone switching office (MTSO) receives
flow rates
a call request, it first scans the VLR in which the location of
A Dynamic LRarea Decision Scheme
each subscriber is recorded. It decides the location according
to the level of the response from each base station. The MTSQ
1) begin
then sends a paging signal to each registered cell of the
a) for z = 1 to the last number of cells
subscriber.
solve P(z) and decide z,
Paging Procedure
b) endfor
Step 1) The MTSO that received a paging request scans
c) If LR area is disconnected then
the VLR.
* if cell z is in the area to which the mobile belongs
Step 2) The MTSO sends the paging request to registered
* then x, = 1
LR area cells of the subscriber.
* else z, = 0
Step 3) Each cell sends the paging signal and receives the
endif
response of the subscriber.
85
KIM AND LEE: DYNAMIC LOCATION REGISTRATION AND PAGING IN MICROCELLULAR SYSTEMS
MTSO
BascStation
Basestation
BaseStation
BasoStation
Fig. 1. Simplified structure of cellular system components, presented in [5]. OMC: operation and management center; HLR: home location register; VLR:
visitor location register; MTSO: mobile telephone switching office.
Step 4) If a response returns, each cell sends the response
level to the MTSO.
Step 5) The MTSO decides the location of the subscriber
with the response level of each cell.
B. LR-area Updating Procedure
To help a mobile update its new LR area, each cell broadcasts its cell identification in the region. Each subscriber
then decides his location with the cell identification. When
a subscriber moves out of the current LR area, the LR area
updating procedure is activated as follows:
LR-area Updating Procedure
Step 1) A subscriber sends an updating signal to a new cell.
Step 2) The cell sends the LR area updating request to the
MTSO for the subscriber.
Step 3) The MTSO decides the new LR area based on the
Dynamic LR-area Decision Scheme.
Step 4) Cell identifications of the new LR area are updated in the database of the subscriber’s VLR. The
MTSO informs cell identifications of the new LR
area to the current base station.
Step 5) The current base station sends the cell identifications of the new LR area to the subscriber.
IV. COMPUTATIONAL RESULTSAND DISCUSSION
To analyze the performance of the proposed dynamic LR
area scheme, experimentations are performed on two environmental settings: the square cell structure and the irregular
cell structure. In the model of Section 11, the unit paging and
updating cost are assumed to be a = 1 and p = 10, as in [ 3 ] .
The call arrivals are assumed to follow Poisson distribution.
The visiting rate is obtained by approximating the expected
number of visits to cell i with free flow. The expected number
is obtained by the following equation.
E[number of visits to cell i with free flow]
-
f Z O Z 1 fZlZ,
--...&, 6 . 1
fin%
6%
where {io, i l , iz,... ,in, i} is shortest path to cell i from
current cell io
6%= density of subscribers at cell i
fi, = flow amount of subscribers from cell i to cell j
The density of subscribers at each cell is set to be uniform in
the square cell and time variant in the irregular cell structure.
The service times of paging and updating are assumed to
have exponential distribution with mean 0.03 and 0.3 s,
respectively. The blocking probability requirement of the two
control channels is assumed to be 0.001, i.e., 81 = 62 = 3.
A. Experiments on the Square Cell Structure
A square cell structure to be tested is shown in Fig. 2. In
the figure, the length of each cell is assumed to be 500 m
and the effect of boundary cell is excluded by duplicating
the cell numbers. A simulation on the square cell structure
is performed with 100 subscribers during 10 hours. Only
horizontal or vertical move is allowed to each subscriber. In
the experiment it is assumed that the call arrivals are Poisson
and the velocity of each subscriber has normal distribution.
1) Experiments with Uniform Flow Rates of Subscribers:
In this experiment, we assume the uniform flow rate of
subscribers among square cells. The flow rate is assumed to
have uniform distribution over [go, 1101. Thus, no regional
characteristic is considered in the experiment. Table I shows
the result with various call arrival rates and velocities.
In the table, it is illustrated that the proposed dynamic
scheme outperforms the other three schemes in every case. The
IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 45, NO. 1, FEBRUARY 1996
86
TABLE I
SIGNAL
COSTSWITH UNIFORMFLOWRATES
Of
1101 1 1 2 1 3 14 1 5 / 6 1 7 1 8 1 9 1101 1
I
Fig. 2. A square cell structure.
result is shown in Figs. 3 and 4. Fig. 3 shows the total signal
costs with different velocities, while Fig. 4 presents those with
different call arrival rates. Even though the dynamic scheme
by [3] is less expensive than the layered and overlapped
schemes, it requires 5-20% additional signal costs, compared
to the proposed scheme. Since the dynamic scheme [3] makes
velocity adaptive LR area, it starts to perform better than the
layered and overlapped schemes after 20 km/h. However, the
scheme is dominated by the proposed method. The reason is
mainly due to that in the proposed dynamic scheme the signal
costs reflects both the subscriber’s mobility and the regional
information.
2) Experiments with Nonuniform Flow Rates of Subscribers:
In the square cell structure of Fig. 2, let us assume there exist
three high-traffic roads: one vertical road and two horizontal
roads. The flow rate on high-traffic roads is assumed to be
twice of that on the other roads. We also assume a river runs
vertically, which has no traffic except on the two high-traffic
bridges.
Table I1 shows the signal costs of four schemes with regiondependent nonuniform flow rates. As shown in the table, the
proposed scheme dominates all three methods. Approximately
0
I
I
I
5
10
15
I
I
I
I
20
25 30 35
Velocity (km/hour)
I
I
40
45
50
Fig. 3. Signal costs with vanant velocities with uniform flow rates (call
arrival rate = 0 6 callsh). -a-layered scheme [2],
overlapped scheme
[4],-0-d y n m c scheme [3], -x- proposed scheme.
-+-
200
180
____ ____....
...-...
----.--~
a:.,-,
40-
20
*
I
I
I
I
I
KIM AND LEE DYNAMIC LOCATION REGISTRATION AND PAGING IN MICROCELLULAR SYSTEMS
TABLE I1
NONUNIFORM
FLOWRATES
SIGNAL. COSTS WITH
5
1
50
180
4
140-
f
120-
h
B$
0
.v)
100-
8060-
40- &,'
0'
0
b
Ib
-.45
I
20
25 30 d5
Velocity (km/hour)
40
45
50
Fig. 5. Signal costs with variant velocities with nonuniform flow rates (call
layered scheme [2];
overlapped scheme
arrival rate = 0.6 callsh).
[4]; -0- dynamic scheme [ 3 ] ; -x- proposed scheme.
-+-
20
I
,
I
I
I
Fig. 6. Signal Costs with variant call amVal rates with nonuniform flow rates
overlapped scheme [4];
(velocity = 20 kmh). -C layered scheme [2];
-0- dynamic scheme [3]: -x- proposed scheme.
-+-
flow rates. The results with variant velocities and variant
call arrival rates are shown in Figs. 5 and 6, respectively.
The overlapped scheme constructs the LR areas by reflecting
the regional flow rates, while the dynamic scheme always
constructs the equal-shaped LR area. Thus, the performance
of the overlapped scheme is better than that of the dynamic
scheme [3], in some cases.
B. Experiments on the Irregular Cell Structure
The performance of the proposed dynamic scheme is examined on an irregular cell structure. The downtown area in
Seoul, which is depicted in Fig. 7, is tested for the experiment.
The radius of the largest cell in the region is about 1.5 km,
while the smallest is 250 m.
To obtain an appropriate fixed-layered LR area, a graph
coloring algorithm [6] is employed. The link cost cy of a pair
of cells ( i , j ) is obtained by reflecting the call arrivals and
flow rates such that cZg = a ( u , + u 3 ) - ,l?(fz,f,%).Notice
that if a pair of cells is included in the same LR area, the two
cells share the paging cost together. Otherwise, the location
+
Fig. 7. The downtown area in Seoul.
base station.
~
2-partition; -3-partition:
updating cost occurs that is proportional to the flow rate. The
k-coloring algorithm provides k-partition of cells such that
sum of link costs in each partition is minimized. Therefore, a
pair of cells with high flow rates are supposed to be in the same
LR area. Also, if the sum of paging costs of any two cells are
small, then they may probably be included in the same area.
IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 45, NO. 1, FEBRUARY 1996
88
Proposed Scheme
Layered Scheme [21
calldOverlapped Scheme [41
Proposed Scheme
hour
hour
3.0
43%
6634
5760
4341
4967
8372
7690
7724
6243
12952
1ZB5
9047
8854
12119
13630
116940
22631
32610
35225
17688
01
0
0.5
15119
23315
16094
30h
25-
8
20-
8t;
15-
a
z6
10-
5Oi
0
I
I
I
5
10
15
I
,
I
25
30
Velocity (kmhour)
20
I
35
,
40
I
45
50
Fig. 8. Signal costs with variant velocities on irregular cell structure (call
arrival rate = 0.6 callsh). -E- layered scheme [2];
overlapped scheme
[4];-x- proposed scheme.
-+-
The k-coloring algorithm applied to the irregular cell structure
presented the least cost partition when k = 3. A good second
partition was obtained when k = 2. The result of two and
three partitioning is shown in Fig. 7. In the experiments, we
thus employed two partitioning in the first layer and three
partitioning in the second layer.
To determine the LR area in the overlapped scheme, the
flow rate fi, is employed. The LR &ea of cell z is constructed
by including each neighboring cell j whose flow rate fi3 is
above a predetermined threshold value. The threshold value is
computed such that the average number of cells in a LR area
equals that of the three partition in the fixed layered scheme.
Table I11 shows the result of experiments on the irregular cell
structure. Note that the dynamic scheme [3] is not included
in the experiment since the procedure is based on the square
cell structure.
In the table, it is clear that the proposed dynamic scheme is
superior to the two other schemes. Especially, the subscribers
who have a high call arrival rate and low velocity or a low call
arrival rate and high velocity pay a lower signal cost in the
I
,
-.-
I
8
1
1.5
2
Call Arrival Rates (callsihour)
I
2.5
3
Signal costs with variant call arrival rates on irregular cell structure
layered scheme [2];
overlapped scheme [4];
(velocity = 20 km/h).
-x- proposed scheme.
-+-
proposed dynamic scheme. This shows the effectiveness of the
proposed dynamic scheme. The proposed scheme minimizes
the two signal costs by reducing the LR area size when a
subscriber’s call arrival rate is high and the velocity is low.
The scheme, on the other hand, enlarges the LR area when a
subscriber has a low call arrival rate and high velocity. Fig. 8
shows the total signaling cost with variant velocities. In the
figure, the cost of the layered scheme and overlapped scheme
are approximately six times larger than that of the proposed
scheme in the case of 50 km/h. Fig. 9 shows the result with
variant call arrivals. The effectiveness of the proposed dynamic
scheme is illustrated especially when the call arrival rate is
low.
Results with Mixed Types of Subscribers: To investigate
the real world situation, we assume two types of subscribers:
30% of them are car-phone users and the rest are pedestrians.
The velocity of car-phone users is assumed 10-20 km/h in
rush hour and 50 km/h at midnight. The call arrival rate is
assumed to be 0.3-1.0 callsh through the day. Pedestrians
are assumed to move 1-5 km/h with the call arrival rates at
1.0-3.0 callsh. Variant call arrival rates are applied to both
89
KIM AND LEE DYNAMIC LOCATION REGISTRATION AND PAGING IN MICROCELLULAR SYSTEMS
I
//
-.-
Fig. 10. Signal costs with mixed types of subscriber during a day.
layered scheme [2];
overlapped scheme [4]; -x- proposed scheme.
-+-
TABLE IV
SIGNALCOSTSWITH MIXEDTYPESOF SUBSCRIBERS
DURING
A DAY
call arrival rate, as well as the regional information, are taken
into account as the factors that influence the two signal costs.
To meet the service level of subscribers, the control channel
blocking probabilities are considered as the constraints of the
model.
By relaxing the reverse control channel constraints, the 0-1
integer programming problem is decomposed into a number
of decision problems each of which is to decide whether cell
i is included in the LR area or not. A cell is included in
the LR area when the updating cost is greater than the paging
cost. Paging and LR area updating procedures are suggested in
microcellular systems based on the proposed dynamic scheme.
The performance of the proposed dynamic LR area updating
scheme is tested and compared with other existing methods.
The computational results demonstrate that the proposed dynamic scheme is superior to other methods both in square
cell and irregular cell structures. Particularly in irregular cell
structure, the saving in updating and paging cost was 17-23%,
with the average velocity and call arrival rate of 20 k m h
and 0.6 callsh, respectively. The excellence of the proposed
dynamic scheme is mainly due to the fact that the size and
shape of the LR area of each subscriber is determined based
on the minimization model that reflects both the subscriber’s
characteristics and the regional flow information.
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of the two cases, i.e., high rates from 11 a.m. to 8 p.m., and
low rates for the rest of the day.
Table IV and Fig. 10 show the total signal costs of each
scheme. The proposed dynamic scheme is demonstrated to be
superior to the other two methods. The simulation result shows
that the paging cost at 2 p.m. is very high in the layered and
the overlapped schemes, which is mainly due to the increased
number of call arrivals from 11 a.m. In the proposed dynamic
scheme, however, the paging cost is drastically reduced with
the aid of small LR area of each subscriber. The computational
result also shows that the updating cost at midnight is higher
than in the daytime in the layered and overlapped schemes.
However, in the proposed scheme, the increased LR area
effectively reduces the updating cost.
V. CONCLUSION
A dynamic location registration scheme is developed in
microcellular systems. The procedure is based on the minimization model of the LR area updating and paging signal
costs. The subscriber characteristics such as the velocity and
,
I
Seok J. Kim received the B.A. degree in business
administration from Seoul National University, in
1990, and the M.S. degree in management science
from the Korea Advanced Institute of Science and
Technology in 1992. He is working toward the
Ph.D. degree in industrial management at the Korea
Advanced Institute of Science and Technology.
He is interested in digital cellular telecommunication systems, personal communication services, and
artificial intelligence.
90
IEEE TRANSACTTONS ON VEHICULAR TECHNOLOGY, VOL. 45, NO. 1, FEBRUARY 1996
Chae Y. Lee (M’93) received the B.S. degree in
industrial engineering from Seoul National University, in 1979, and the M.S. and Ph.D. degrees in
O.R. from the Georgia Institute of Technology, in
1981 and 1985, respectively.
He is Associate Professor of Industrial Management at the Korea Advanced Institute of Science
and Technology. His professional interests include
wireless personal communication, telecommunication network design, and genetic algorithm and
scheduling.