Multiplex communications – Channel assignment techniques – Combining or distributing information via code word channels...
Reexamination Certificate
1998-08-21
2002-05-21
Rao, Seema S. (Department: 2732)
Multiplex communications
Channel assignment techniques
Combining or distributing information via code word channels...
C375S147000, C455S067150, C370S342000, C370S441000
Reexamination Certificate
active
06393030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for maximizing a cellular capacity in a code division multiple access (hereinafter, referred to as “CDMA”) system by controlling a transmission rate of data calls.
2. Description of Prior Art
In the CDMA system its capacity is decided by an interference caused in a data and voice traffic. Therefore it is important to restrain some unnecessary interference at maximum so as to gain an acceptable quality of service for voice.
In order to maintain a good service quality in the CDMA system, the total interference quantity caused in a communicative traffic should be lessened, in other words, a transmission quantity of information such as data and invoice calls from other subscribers should be reduced to obtain a good service, since the transmission quantity of other subscribers' calls becomes a source of the interference and the total interference quantity also increases systematically in proportion to the transmission rate of other subscribers' calls. Thereby the total interference quantity may be reduced.
By the way a transmission rate of data calls is changeable but a transmission rate of voice calls is not changeable, namely is fixed. The transmission rate of data calls may be thus an important considerable point in the system.
That is, in the data calls, in a case of a service in which a delay is permissible, a data transmission rate may be easily controlled to thereby restrict the interference quantity to a constant standard.
In specialty when a long data call occupies a resource of the system for a long time and in a state of an overload capacity at a cell of the system a voice call of which priority is higher than that of data call in a real time processing is received, a problem such as a cutoff of the call is caused. Accordingly an adequate management for the call is necessary.
In the conventional CDMA technique it was considered that all the voice and data calls were transmitted as a fixed transmission rate and under such consideration, a system capacity was computed, thus the transmission rate of the call caused the increasing of a difficulty in a receipt of a new call.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method for receiving a new call that substantially obviates one or more of the limitations and disadvantages of the related art.
An object of the present invention is to provide a method for receiving a new call by controlling a transmission rate of a data call being under a service in case that a call having a higher priority is newly received under a state that a data call of a high speed occupying a resource of a system for a long time is being transmitted thereto.
Another object of the present invention is to provide a method for receiving more calls by controlling the total interference quantity in such a way as restraining a transmission rate of respective data calls according to diminution factors of a linear, a parabola and a hyperbola, in which the transmission rate of the data call is increased in case a traffic load is small and the transmission rate of the data call is decreased in a case of an overload in the traffic so that the number of subscribers having a service of voice and data calls in a CDMA circumstances may be allowed most suitably.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure as illustrated in the written description and claims hereof, as well as the appended drawings.
To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described, in a case of a data call, the maximum transmission rate is serviced if a load in a cellular capacity is small, and if the cellular capacity is an overload state, the transmission rate of data is lessened to thus match the total interference quantity to a target value in a service quality and receive a new call is received.
In the CDMA system, the capacity in a system for only a voice service is computed by modeling an interference of an outer cell user as a gaussian random variable with a means and a variance of a corresponding interference.
Similarly to this, an inference of an outer cell user under a multi-media circumstances can be modeled as a gaussian random variable in the following numerical expression 1, e.g.,
[Numerical Expression 1]
I
=
∫
∫
(
φ
S
V
ρ
v
+
∑
i
=
1
N
-
1
S
d
i
ρ
d
i
)
(
r
m
r
0
)
d
{
10
(
ξ
0
-
ξ
m
)
}
φ
{
ξ
0
-
ξ
m
r
0
r
m
}
ⅆ
A
where r
o
indicates a distance from a user of other cell to a target base station and r
m
represents a distance from that user to his own base station, m being an index of the base station.
In the above, &phgr; indicates a voice action variable and has a binomial distribution with a mean &agr;, thus its numerical expression 2 may be gained as follows.
A path loss between a base station and a user is in proportion to 10
&xgr;/10
r
−4
and &xgr; has a normal distribution with a mean is ‘0’ and a standard variation is 8 dB.
S
v
presents supply power on voice calls and S
a
provides supply power for data calls.
φ
(
ξ
0
-
ξ
m
r
0
r
m
)
=
(
1
,
if
(
r
m
r
o
)
d
10
(
ξ
0
-
ξ
m
)
10
≤
1
0
,
otherwise
)
[
Numerical
Expression
2
]
In the above numerical expression 1, &rgr;
v
is a user density of voice call and &rgr;
a
indicates a user density of a data call group I.
This is a case for an incomplete power control actually, and the interference I is described as a set of a unit random variable with a logarithmic normal distribution.
Accordingly, when we limit the service area to the second tier, under an assumption that it is impossible one more user exist at the some position, a mean and a variance of the interference from the outer cell user may be obtained through a numerical calculation by a voice call Nv and a data call N
a
as the following numerical expression 3,
E
(
I
)
≤
0.241
N
v
S
v
+
∑
i
=
1
N
-
1
N
d
i
S
d
i
Var
(
I
)
≤
0.078
N
v
S
v
2
+
0.183
∑
i
=
1
N
-
1
N
d
i
S
d
i
2
[
Numerical
Expression
3
]
Further, if we define an SIR is a signal-to-interference ratio for considering an influence from a capacity of the outer cell user interference, a numerical expression 4 may be provided as follows,
r
v
N
v
+
∑
i
=
1
N
-
1
r
d
i
N
d
i
≤
1
-
z
,
[
Numerical
Expression
4
]
where z may be obtained as follows,
z
=
I
S
v
1
(
SIR
)
-
1
v
requirred
+
α
=
I
S
d
i
1
(
sir
)
-
1
d
required
+
1
therefore, a mean and a variance of the gaussian random variable z may be obtained by a numerical expression 5, e.g.,
E
(
z
)
≤
0.659
r
v
N
v
+
0.659
∑
i
=
1
N
-
1
r
d
i
N
d
i
Var
(
z
)
≤
0.555
r
2
vN
v
+
0.183
∑
i
=
1
N
-
1
r
d
i
2
N
d
i
[
Numerical
Expression
5
]
and a probability satisfing a required service in the system may be represented as the following numerical expression 6, e.g.,
P
=
P
r
{
(
E
b
/
N
0
)
≥
(
E
b
/
N
0
)
required
}
=
P
r
{
r
v
N
v
+
∑
i
=
1
N
-
1
r
d
i
N
d
i
≤
1
-
z
}
≥
0.99
[
Numerical
Expression
6
]
An unequal expression such as the following numerical expression 7 can be obtained from the numerical expression 6 since z is the gaussian random variable with the mean and the variance such as the expression 5,
r
v
N
v
i
+
∑
i
=
1
N
Ahn Jee Hwan
Kim Ki Seon
Kim Kyung Soo
Lee Hun
Electronics and Telecommunications Research Institute
Rao Seema S.
Sam Phirin
LandOfFree
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