Selective broadcasting of charge rates

A cellular phone system, optimizing user demand by charging system subscribers according to a Variable Charge Rate (VCR) that is based on the price elasticity of the subscribers. According to the present invention, the service provider monitors the load in each cell and, for each cell, the service provider continuously determines a charge rate that can be tailored to specific subscriber category according to a number of variables, offering subscribers a VCR that is optimized for the individual cell's capacity and overall system capacity. According to an exemplary embodiment, subscribers may use mobile stations supporting the Short Message Service (SMS) to provide the subscribers with the broadcast VCR. The system can determine, in real time, optimal VCRs for individual cells to maximize revenue generated by the cell for any time of day. The VCRs may be selectively broadcast to the VCR-mobile station to inform subscribers of the current rate of charge for calls. VCRs may be tailored to specific categories of subscribers to provide better price differentiation between subscribers based on price elasticity of the subscribers categories.

BACKGROUND 
The present invention relates to cellular telephone systems and, in 
particular, to a method and apparatus for controlling and optimizing the 
utilization of cellar telephone systems. 
A cellular telephone system normally services an area populated by a number 
of users. Looking at FIG. 1, the service area of the system typically is 
divided up into cells (C1-C10), each equipped with a base station 
(BS1-BS10) capable of communicating with a number of users (M1-10) within 
the cell. Inherently, each cell has a maximum number of users that can be 
handled simultaneously. This is referred to as the cell's capacity. In 
addition, the service area containing the cells has an overall capacity. A 
critical factor which is taken into account in providing cellular 
telephone service to subscribers is the overall capacity of the system. 
A basic problem with designing any cellular system is how much overall and 
individual cell capacity should be provided to ensure adequate service 
while maximizing revenues generated from the users of the cellular system. 
Complicating the design of such a system is the fact that the number of 
calls, or demand for use of the system, varies dramatically in each cell 
according to the time of day. On one hand, insufficient capacity during 
peak hours of system operation will cause congestion, and the inability to 
provide adequate service to users. On the other hand, providing too much 
unused capacity during off-hours under utilizes resources that increases 
overall cost of system operation. Therefore, it is important to optimize 
the trade-off between adequate capacity to handle anticipated subscriber 
demand for the system during peak usage while minimizing the unused 
capacity during off-hours. The more difficult of these two is how to 
maximize system usage during the hours when the system's capacity is 
largely idle. 
Various methods and systems have been devised in order to maximize usage of 
the overall capacity of a cellular system at every time of day. In the 
past this has been attempted by varying the rate charged to subscribers of 
the system and its services at different times. For example, during peak 
hours, such as business hours when demand is at its greatest, all 
subscribers pay a full rate. However, as subscriber demand decreases, for 
example, during the evening and weekend hours, rates are reduced in one or 
more steps in order to encourage increased utilization of the system. 
Varying the price is an effective means for regulating system demand 
because of the price sensitivity of subscribers. Certain subscribers are 
more price sensitive than others. This is known as a subscriber's price 
elasticity. For example, a personal use subscriber's price elasticity is 
much greater than a business use subscriber because, unlike a business use 
subscriber, a personal use subscriber's need to make a call is usually 
much less urgent or necessary. As a result, personal use subscribers may 
delay or make fewer calls for no other reason than the price of the call 
or because it comes out of their own pocket. Accordingly, personal use 
subscribers are more likely to be induced to use a system when rates are 
lower. 
Cellular service providers often charge higher rates during the week, 
especially during working hours, for cellular calls. Because of these 
higher rates, certain subscribers who would otherwise use the cellular 
phone system are discouraged from making calls due to the higher rates. 
During peak hours, when the system is being used to near capacity, this is 
not a problem for the service provider because maximum revenue is being 
generated from system usage. However, when the system is not being used to 
near capacity, the service provider is not deriving any revenue from the 
unused system capacity and thus would like to be able to attract 
additional subscribers to make use of the system. 
Further complicating the problem of maximizing use of available system 
capacity is that, even during peak hours of the overall system, certain 
cells may have surplus capacity and, therefore, are not generating their 
potential maximum revenue. For example, in FIG. 1 a cell in a city center 
(C1) may have its peak hour in the middle of the day, while a cell in a 
suburb (C9) may have its peak hour later in the afternoon. FIGS. 2A and 2B 
illustrate this problem in another way. FIG. 2A is an example of a 
macro-cell 21 with one micro-cell 22 indicated within. As illustrated in 
FIG. 2B while the load approaches maximum capacity for the macro-cell 21, 
a micro-cell 22 may only be at 60% capacity and thus have an unused 
surplus capacity even though the macro-cell 21 is congested. Typically, 
with state of the art cellular systems, service providers are forced to 
take all cells into account when choosing the time of day for rate 
reduction. Because the macro-cell 21 is at near capacity, the service 
provider cannot reduce the rate to increase revenues from the micro-cell 
22. Additionally complicating matters is that by instantly lowering the 
rate the load on the entire system might sharply increase. In other words, 
these systems fail to take into account that different types of 
subscribers display different price elasticities and thus fail to maximize 
revenue for the system providers. These systems also do not address the 
problem that cheaper rates can only be offered when there is a substantial 
system wide excess capacity, because the load on the system might sharply 
increase with any broadcast of the lowering of the rate. Thus, if there is 
insufficient excess capacity, and a lower rate is offered, congestion will 
likely result. 
Various systems have been contemplated in an attempt to address some of 
these problems. According to one approach described in U.S. Pat. No. 
5,303,297 to Hillis, it has been suggested that system demand be 
monitored, and based on demand, a charge rate is dynamically calculated 
and broadcast to subscribers to encourage subscribers to use the system 
during non-peak times. However, Hillis does not describe how this charge 
rate is calculated. While the broadcast rate message solution does provide 
more flexibility than previous systems, it is not a complete solution to 
maximizing overall use of a system's excess capacity. The system of Hillis 
fails to consider a particular subscriber's price elasticity and thus the 
system indiscriminantly discourages some subscribers use of the system. 
This further results in inefficient use of the system's excess capacity 
and loss of potential revenue. 
It has also been suggested that mobile phone calls could be charged 
according to where the calls are made, for instance, one price in an 
office, another on the street, and a third at home, etc. However, in this 
solution, as with the one described above, overload which might result 
from a decreased rate can only be alleviated by indiscriminately 
discouraging certain subscribers service and therefore cannot provide 
overall optimization of generating maximum revenues from the system. 
SUMMARY 
The present inventor has recognized because subscriber price elasticity 
does vary, by optimizing price differentiation between subscribers, the 
service provider can increase revenue and more effectively regulate system 
capacity. 
It is therefore an object of the present invention to improve use of system 
capacity regardless of time of day without indiscriminately discouraging 
subscriber service. 
It is another object of the invention to improve overall revenue generated 
by the cellular system through optimized subscriber price differentiation. 
It is a further object to provide increased subscriber satisfaction due to 
increased flexibility of when subscribers can use the system because it is 
their choice to place a call at a higher rate or wait until a lower rate 
is broadcast. The rates being adjusted for the category of user. 
The foregoing and other objects are accomplished through implementation of 
a cellular system, providing a user subscription that is charged according 
to a Variable Charge Rate (VCR) that is based on the price elasticity of 
the subscribers. According to one embodiment of the present invention, the 
service provider monitors the load in each cell and, for each cell, the 
service provider continuously determines a charge rate that can be 
tailored to specific subscriber groups according to a number of variables, 
offering subscribers a VCR that is optimized for the individual cell's 
capacity and overall system capacity. In one embodiment, subscribers may 
use mobile stations supporting the Short Message Service (SMS) to provide 
the subscribers with the broadcast VCR (VCR mobile stations). The system 
can determine, in real time, optimal VCRs for an individual cell to 
maximize revenue generated by the cell for any time of the day. The VCRs 
may be selectively broadcast to VCR-mobile stations to inform subscribers 
of the current rate of charge for calls. According to an exemplary 
embodiment of the invention, the VCRs may be tailored to specific 
categories of subscribers to provide better price differentiation between 
subscribers based on price elasticity of the subscriber categories.

DETAILED DESCRIPTION 
The various features of the invention will now be described with respect to 
the figures, in which like parts are identified with the same reference 
characters. 
Referring to FIG. 1, a conventional cellular radio communication system 
which may be used with the present invention is illustrated. FIG. 1 shows 
an geographic area divided into a plurality of contiguous radio coverage 
areas or cells labeled C1 through C10. Associated with each of the cells 
C1 through C10 is a base station designated B1 through B10. Each base 
station generally includes a transmitter, a receiver and a base station 
controller, all of which are well known in the art. It is noted that the 
representation of the cellular radio system according to FIG. 1 is for 
purposes of illustration only and is not intended as a limitation on the 
possible implementations of a mobile radio telecommunication system within 
which the Variable Charge Rate (VCR) system of the present invention may 
be implemented. For example, the number and size of cells could be varied 
along with the position of the base station relative to a cell. The VCR 
according to the present invention may also be used with any of the 
multiple access communication systems such as GSM, AMPS, D-AMPS, CDMA, or 
the like. 
Also shown in FIG. 1 are a plurality of mobile stations M1 through M10. 
These mobile stations may roam from one location in the cell to another, 
from one cell to an adjacent cell, or even from one cellular radio system 
served by a mobile switching center (MSC) to another such system all while 
receiving and placing calls both within the cellular system as well as to 
and from a public switch telecommunications network (PSTN). 
Each of the mobile stations M1 through M10 is capable of initiating or 
receiving a call through one or more of the base stations B1 through B10 
in conjunction with the MSC. The MSC is connected by communication links, 
e.g., cables, to each of the base stations B1 through B10 and to the PSTN 
(not shown) of a similar fixed network which may include an integrated 
services digital network (ISDN) facility. According to an embodiment of 
the present invention, the mobile stations supported by the system can be 
both VCR-mobile stations and non-VCR-mobile stations. The VCR mobile 
stations, base stations, and MSC are described in further detail below. 
Fixed Charged Rates 
Turning to FIG. 3 it can be seen that the available capacity of the service 
area sharply changes with the time of day. An example of the usage levels 
of a fixed rate system is shown by curve 30. By fixed rate it is meant 
that the same, unvarying rate is offered to everyone within the system or 
cell at the same time of day. Normally, demand for the system will be 
greatest in daylight hours, for example, between the hours of 8:00 to 
18:00, the time when most people are awake and active. In addition, the 
majority of business is also conducted during this period of time. As the 
business day ends, demand by subscribers to the cellular system 
continually drops and system capacity increases with demand reaching its 
lowest in the early morning hours. 
In a response to the time dependent change in demand, service providers 
have developed a time based charge rate for the local comlink 50 in FIG. 
4. FIG. 3 illustrates this concept with three different time dependent 
charge rates. During the hours between 7:00 and 19:00 when demand is high, 
a full rate is charged to subscribers making calls. According to FIG. 3 it 
can be seen that the demand for the system reaches full capacity or near 
full capacity in mid-morning and late afternoon with a dip in capacity 
near mid-day, for example, when people are at lunch. As demand steadily 
declines beginning around 17:00, the service provider offers a cheaper 
rate in order to induce additional customer demand for the system. It 
should be noted that immediately after the cheaper rate is introduced 
demand for the system increases before peaking and slowly dropping as the 
evening continues. Conversely in the morning when rates go up around 7:00 
demand momentarily sharply drops in a fixed rate system. A second cheaper 
rate is offered in the early morning hours when user demand is at its 
lowest. 
As only one fixed rate is offered at any particular time within a cell 
according to prior systems, some subscribers are indiscriminantly 
discouraged from making calls. For example, suppose a mobile station M7 in 
cell C1 was used by a student who wanted to make a call in the afternoon. 
The student may decide to not make the call because the fixed rate charged 
for a call at this time is too high. However, if cell C1 has unused 
capacity at this time, the service provider would like to be able to 
encourage others, such as the student, to make a call thereby using the 
excess capacity thereby maximizing revenue generated by the cell C1. This 
is accomplished according to the present invention by determining VCRs for 
a cell tailored to various subscriber categories. According to the present 
invention, the service provider can determine that there is an excess 
capacity in the cell C1 and further determine to offer a lower charge to a 
particular subscriber category located in the cell C1, such as students, 
and therefore encourage subscribers such as students to place a call. 
By determining various VCRs for each cell over the entire service area, the 
service provider can maximize the use of the excess system capacity. This 
can be seen from the VCR curve 35 shown in FIG. 3. By providing VCRs the 
load on the system is increased over the entire day. In addition, there 
are fewer sudden drops or spikes in system demand. It should be noted that 
the VCR would generally be calculated for the local com link 50 shown in 
FIG. 4. Additional charges may have to be added, for example long distance 
charges, to determine a total charge rate. Further description of the VCR 
is provided below. 
Variable Charge Rates (VCRs) 
According to an exemplary embodiment of the invention, a new type of 
subscription is introduced. As an alternative to the conventional time of 
day based charge rates typically used by service providers, according to 
the present invention, subscribers are offered a VCR. A VCR may also be 
set for terminating calls in systems in which subscribers also pay for 
call termination (e.g., in the United States). The service provider 
monitors the load in each cell and for each cell continuously determines a 
specific VCR for an individual subscriber or group of subscribers, such 
that the overall system excess capacity is used and revenue increased. 
While it is possible to provide an individual VCR for each subscriber, the 
following description is directed to VCRs for groups of subscribers based 
on subscriber categories. 
In order to provide increased overall demand and revenue generated by the 
system, a number of factors other than time of day and location are used 
when determining a specific VCR for a subscriber. 
The following list, while not exhaustive, includes some of the factors 
which may be taken into account by the service provider when determining 
the VCR: 
A. the load of calls charged at a variable rate in the cell (l.sub.v); 
B. the load of calls charged at a fixed rate in the cell (l.sub.f); 
C. the desired "safety margin", i.e., how close the load may be to 
congestion (m); 
D. the total load in the switch; 
E. the number of VCR-mobiles registered in the cell; 
F. the average power radiated by the base station; 
G. an estimated current demand curve; and 
H. the average co-channel disturbance caused by the cell. 
Through utilization of these factors a service provider is given greater 
control in determining an optimum price to charge each user such that 
overall system usage and revenue can be maximized. Through use of the VCR 
the provider is no longer limited to time and location but may adjust the 
various factors such that prices are optimized for the specific system in 
question. Such optimization may be carried out through use of empirically 
derived estimate demand curves based on the specific area and subscriber 
make-up serviced by the system from the factors given above. 
Subscriber Demand 
According to one embodiment of the present invention an estimate demand 
curve is used to determine subscriber price elasticity that is in turn 
used to determine a VCR. The estimate demand curve is a representation of 
quantity (q) in relation to the price (p). The demand curve can be 
estimated from the service provider's records of prior system use or 
through measuring system use over a representative period of time. Use of 
the estimate demand curves allows the price elasticity of subscribers to 
be taken into account unlike prior systems. The estimate demand curve may 
depend on various factors, such as: 
G1. the time of day; 
G2. the day of week; 
G3. the time of year; 
G4. the type of district (for instance, business district, residential, 
industrial, or a hybrid), etc; and 
G5. the category of subscriber. 
Estimation of a Demand Curve 
For each VCR charged call, the service provider records time of day, the 
duration of the call, and the charge rate. The system may continuously 
record the charge rate and the number of VCR mobiles registered in each 
cell. When a sufficient amount of data has been accumulated the various 
demand curves can then be accurately estimated. According to one exemplary 
embodiment, the day could be divided into a plurality of intervals, and 
labelled "time of day". For each time of day and each charge rate the 
service provider determines the duration of all conversations of the 
subscribers making calls and the duration of exposure to a charge rate of 
the number of mobile stations registered or in conversation. For any cell, 
the probability of a mobile station being in conversation at a certain 
time of day and for a certain charge rate can be estimated. Along the same 
lines, the system can then estimate demand curves with respect to a 
plurality of factors, such as day of the week, the time of the year, the 
type of district, the various subscriber categories, etc. or demand curves 
may even be split as further described below. 
For the purpose of illustrating the general principles according to one 
exemplary embodiment of the invention, the following simplification has 
been made: the probability of a subscriber being in conversation does not 
vary due to say time of day, location, etc. 
Assuming that there are r different charge rates, for each charge rate the 
system sums up (1) the duration of conversations, and (2) the duration of 
offer, i.e., the duration that mobile stations have been offered that 
charge rate (either registered in cells or in conversation). The 
probability p of a mobile station being in conversation at a given charge 
rate then can be estimated as: 
##EQU1## 
Numerical Example 
Consider a system with 50 subscribers, one cell, and two charge rates: $1.5 
and $3.00. The system is run for 10 hours, varying the charge rate. During 
this time the subscribers are offered calls at $1.50 and $3.00 for a 
duration of 6 hours and 4 hours respectively. If it turns out that the 
subscribers as a whole have been in conversation for 24 hours when calls 
were cheap and for 6 hours when they were more expensive, by inserting in 
Equation (1) the probability of a mobile station being in conversation 
during the cheap period can be estimated as being p.sub.1.50 =24 
h/(50.times.6 h)=8%. The probability for both rates is shown in Table 1 
below. 
TABLE 1 
______________________________________ 
Duration of Duration of 
Charge Rate 
Offer Calls p 
______________________________________ 
$1.50. 300 hours 24 hours 8% 
$3.00. 200 hours 6 hours 3% 
______________________________________ 
Sufficient Data 
A sufficient amount of data is obtained when the estimations of p.sub.1, . 
. . , p.sub.r differ significantly. This can be determined as described 
below. 
The example is simplified by reducing the number of charge rates to two. In 
addition, only the duration of the calls is taken into account, and the 
number of calls is disregarded. 
If there are n calls at rate.sub.1, the duration of each call could be 
perceived as the outcome of independent exponentially distributed random 
variables X.sub.1, . . . , X.sub.n, where the expected duration is 
.beta..sub.1. Likewise at rate.sub.2 : the expected duration of Y.sub.1, . 
. . , Y.sub.m, is .beta..sub.2. Assuming .beta..sub.1 &gt;.beta..sub.2 the 
test variable is: 
##EQU2## 
The test variable is used to verify that the change of call duration is 
caused by the change of the charge rate and not just as an accidental 
coincidence. The critical area of a test at significant level .alpha. is 
represented according to an "F" distribution as: 
z&gt;F(2n, 2m).sub.1-.alpha. 
where z is the observed value of the test variable Z. Therefore the 
duration of calls is summed up until z is in the critical area. 
NUMERICAL EXAMPLE 
Assume, for example, that the duration of 50 random calls at $1.50 is 
.SIGMA.x.sub.i =9000s; and at $3.00 .SIGMA.y.sub.i =6400. The observed 
value of the test variable, according to equation 2, would be: 
##EQU3## 
The critical area for a test at a 5% level is z&gt;F(100,100).sub.0.95 =1.39. 
Therefore, the hypothesis that the expected duration is the same for both 
charge rates can be rejected and instead it is concluded that .beta..sub.1 
=180s and .beta..sub.2 =128s. 
One of skill in the art would appreciate that the above method can be 
generalized to include the case of a greater plurality of charge rates. 
Splitting of Demand Curves 
If for one reason or another it is suspected that the behavior of a 
subscriber category differs due to a factor, such as time of day, week, 
district, etc, then the general demand curve may be split into new 
(estimated) demand curves for the identified factor, provided that the 
demand curves differ significantly. Two demand curves differ significantly 
if and only if the probability of conversation of at least one charge rate 
differs significantly. For example, if a category of subscribers in New 
York city were professionals, a number of demand curves could be derived 
based on the factor of time of day. However, additional factors might 
govern professionals' behavior within NY. If a service provider suspected 
that professionals on Wall Street made a large number of calls of short 
duration, by isolating these calls from the rest of professionals' calls 
in New York, additional demand curves for Wall Street could be split from 
the rest of New York's professionals. 
Price Elasticity 
Subscriber price elasticity .epsilon. is the derivative of a subscriber 
estimated demand curve. It is defined as: 
##EQU4## 
where q is "quantity", i.e. load, and here p is "price", i.e., VCR. By 
rearranging the following equation is obtained: 
##EQU5## 
In intervals where price elasticity .epsilon. can be considered constant 
the following relationship exists: 
EQU q=Ap.sup..epsilon. EQUATION (5) 
where A is a positive constant. If the estimate demand curve is discrete, 
i.e. quantity q is only known for finite number of values of p, then 
.epsilon. between p.sub.i and p.sub.i+1 can be calculated as: 
##EQU6## 
Single Category of VCR-Mobiles 
Congestion 
The following is an example of how the VCR may be calculated. According to 
this example, a simplified case is considered where there are only two 
categories of mobile stations in a cell: fixed charge rate (FCR)-mobile 
stations and VCR-mobile stations. The load caused by the two categories is 
l.sub.f (load caused by FCR-mobile stations) and l.sub.v (load caused by 
VCR-mobile stations). When l.sub.f +l.sub.v =1 the system is congested or, 
in other words, at full capacity. According to the invention, only the VCR 
mobile stations can be influenced, therefore q=l.sub.v. The change that is 
desired is .DELTA.q=1-m-l.sub.f -l.sub.v. Dynamically determining the VCR 
the VCR.sub.new =VCR.sub.old +.DELTA.VCR. By insertion in Equation 4, a 
new VCR is determined: 
##EQU7## 
Surplus Capacity 
As described above, when there is surplus capacity in a cell then the 
charge rate should be set so that the revenue is maximized. Based on 
economics theory one skilled in the art would appreciate that this is 
obtained when .vertline..epsilon..vertline.=1. When the VCR calculated 
according to Equation 7 reaches a level so that 
.vertline..epsilon.(VCR).vertline.=1 the VCR will no longer be reduced (in 
a simplified case where the demand curve is constant over time). 
Multiple Categories of VCR-Mobiles 
As example of multiple categories one category could be "normal private 
citizens", and another could be "students" (here considered more price 
sensitive). Both categories are attributed a specific estimate demand 
curve. 
In the case of congestion the lowest charge rate would normally be 
increased (and broadcasted to the corresponding subscriber category). This 
charge rate can be calculated according to Equation (7), where the load of 
the "affluent" subscriber category may be lumped together with the fixed 
rate mobiles l.sub.f. If the two charge rates become identical, then the 
two categories of VCR-mobiles could be combined. The common charge rate 
would then be calculated according to Equation (7) and broadcasted to both 
categories. In contrast, when there is excess capacity the charge rates 
would be lowered according to subscriber category and broadcast to the 
corresponding subscribers. 
System Applications 
The VCR may be determined in real time by the service provider. This can be 
implemented in a number of ways. For example, the determination can be 
made at the MSC or other central location within the service provider by 
any calculation means, such as a computer or processor, for instance. In 
an alternative embodiment, calculation of the charge rate could be 
decentralized, for example, by allowing the MSC to inform the base 
stations of a minimum acceptable charge rate, but otherwise let the base 
stations calculate the VCR and then broadcast it. According to this 
exemplary embodiment the VCRs would be calculated by a computer or 
processor located at each base station. 
Another embodiment of the invention will now be discussed in conjunction 
with FIG. 4. Once a VCR has been determined (either centrally or at the 
base station), the VCR is then broadcast from a base station 62 from its 
antenna 65 over communications channels 50 where it is received by the 
antennas 45 of any registered mobile stations 40. The service provider 60 
would have at least one mobile switching center 64 linked to a PSTN 70, as 
is conventional. According to the present invention the mobile stations 40 
may refer to any information or communication device that may be used to 
communicate information, for example, a fixed wire telephone, a cellular 
phone, facsimile receiver, modem, computer or other communication means. 
The VCR could then be displayed on a display 42, for example, at the 
mobile unit 40 for the subscriber. 
The VCR could be transmitted to the mobile stations in many different ways. 
According to one embodiment the VCR could be broadcast to the mobiles 
stations 40 using the user group short message service (SMS) as provided 
in the (D)-AMPS system. According to this embodiment there could be a 
special user group for each subscriber category associated with the VCR 
mobile stations 40, so that other mobile stations are not inadvertently 
informed. It follows that all system users do not have to belong to a VCR 
subscriber category. Of course, as the number of VCR mobile stations 
increases, the greater the overall demand control and revenue generated 
becomes. 
Alternatively, according to another embodiment, an existing message (such 
as the system identity message described in EIA standard IS-136.1 
6.4.1.1.1.5) on the forward control channel (CC) could have a new 
information element added indicating current VCRs in a cell. Another 
embodiment would be to send the VCRs individually to each mobile station 
using point-to-point short message services (SMS). Alternatively, a new 
message containing an information element indicating current VCRs in a 
cell could be added, or, an existing information element in an existing 
message, e.g., "display" in registration accept could be used to convey 
the VCR as provided in IS-136 6.4.3.14. According to another exemplary 
embodiment of the invention the VCRs broadcast could be repeated either 
intermittently or at regular predefined intervals. However, in all cases 
the VCR should be broadcast whenever it changes. 
When a mobile station 40 not in conversation is registered in one cell and 
then moves to a neighboring cell, the mobile station will register in the 
new cell, via channel re-allocation, as known by those skilled in the art. 
If the new cell has a different VCR for the subscriber the mobile station 
40 should be informed as soon as possible. The simplest method of 
informing the subscriber of the new rate would be to use the information 
element "display" in the registration accept, of course any of the 
alternative methods described above could also be used. When the mobile 
station 40 performs its initial registration the same information element 
could be used; however, several of the methods described above could also 
be used. 
If during a conversation a mobile station 40 is handed off to another cell 
a service provider 60 could then send a message to the mobile station 40 
informing that the VCR will be changed after a predefined period, and what 
the future VCR will be. The decision to change the VCR could depend on a 
plurality of factors, such as the difference between the current VCR and 
the potential future VCR, the subscriber category, the individual 
subscriber, the load situation, etc. Similarly, the mobile station could 
also alert the subscriber if the VCR changes during a conversation 
allowing the subscriber to determine if they wish to continue the call at 
the new rate. The mobile station could provide the alert either visually 
or audibly. 
According to another embodiment the mobile stations 40 could continuously 
read the relevant broadcast message and display the current VCR of the 
cell for the associated subscriber. Additionally the mobile station 40 
could alert the subscriber when the VCR drops below a predetermined 
threshold entered by the user through a user interface in the mobile 
station (e.g., key pad 44). The alert could be provided either visually or 
audibly through an additional circuit or processor included at the mobile 
station which would determine when a VCR has dropped below the 
predetermined threshold. Alternatively, the service provider could 
determine when the VCR is below the threshold and alert the mobile 
stations. According to this embodiment the subscriber could inform the 
service provider of his threshold (e.g., by submitting an SMS message). 
The display 42 at the mobile unit 40 could be of any type able to display 
human readable characters, (e.g., LCD, LED, etc.) Alternatively, the 
present invention could be practiced on mobile units 40 without displays 
42 by allowing a subscriber to receive a broadcast audio message conveying 
the current VCR to the mobile station 40. 
In situations where a device, such as a telefax or computer, needs to react 
to a VCR the VCR can be broadcasted in machine-readable form. For example, 
the charge rate could be converted to a string of ASCII characters that 
are formatted according to a standard so that the VCR may be understood by 
machine as well as humans. Alternatively, the VCR could be coded as a 
binary string. In cases where the mobile station has a display the mobile 
station could translate the binary string to ASCII characters and then 
display it. 
In yet another embodiment according to the present invention, the 
initiating subscriber could actively enter a number to which the user 
desires to be connected via keypad 44. Accordingly, the calling mobile 
station 40 transfers the desired phone number being called via comlink 50 
to the service provider 60 through the base station 62. The service 
provider 60 could then determine a VCR, add any additional charges 
necessary, for example for long distance, and transfer the total charge 
rate information back to the mobile station 40 via the comlink 50. The 
total charge rate information is indicated to the mobile station via the 
display 42 or other means as described above. The subscriber could then be 
given the option to actually place the call. Any number of means could 
also be used to alert the user to the arrival of such a message, such as a 
flashing light, highlighted display, tone, etc. 
According to the present invention, many further enhancements and 
refinements of the charge function can also be introduced. As described 
above, a plurality of subscription categories designed for specific 
customers possessing unusual price elasticity (for instance such as 
students, businessmen, according to household income, etc.) could be 
formed. Charge rate policies could then be tailored for each category and 
broadcast accordingly. Estimate demand curves would then be determined for 
each identified category. As described above in the example for splitting 
of demand curves, the categories may depend on the area, and sub-area 
where the service provider is located as described in the Wall Street 
demand curve. Alternatively, in certain areas there may be a concentration 
of one or more existing subscriber categories, (e.g., students and 
teachers on a university campus). In this situation the service provider 
could merely use the existing estimated demand curves for these groups 
instead of determining new ones. 
According to the present invention, with expedient setting of parameters 
the system will virtually never become congested simply because as traffic 
increases, the price of a call will go up until a given number of 
subscribers are priced out of making a call. In order to know where to 
increase system capacity, for example by splitting cells or adding 
micro-cells, the service provider 60 may estimate and record the potential 
load in the cells, in other words, what the load would have been if the 
VCR had to be set to a certain value. 
The present invention has been described by way of example, and 
modifications and variations of the exemplary embodiments will suggest 
themselves to skilled artisans in this field without departing from the 
spirit of the invention. The preferred embodiments are merely illustrative 
and should not be considered restrictive in any way. The scope of the 
invention is to be measured by the appended claims, rather than the 
preceding description, and all variations and equivalents which fall 
within the range of the claims are intended to be embraced therein.