Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-03-04
2002-11-05
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S332000, C370S335000, C455S434000, C455S442000
Reexamination Certificate
active
06477155
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to communication systems, and in particular, to a method for calculating capacity variation and effective channel rate per sector in connection with the soft handoff rate in a CDMA network.
DESCRIPTION OF THE RELATED ART
Mobile communication networks and personal communication systems employing CDMA technology do not limit accommodation capacity to a fixed value, but rather, accommodate user flexibly in accordance with the constantly changing network environment. CDMA technology makes it possible for a mobile to maintain a simultaneous connection (i.e., occupy a radio link) with two or three base stations as it transitions between them. This process is referred to as soft handoff and represents an important characteristic of CDMA technology. However, one effect of soft handoffs is that the accommodation capacity of a CDMA network and base station varies in accordance with the soft handoff rate. A drawback of conventional cellular mobile communication networks is that call-drops frequently occur when a mobile station experiences a serious fading within a handoff area. To overcome this, CDMA technology utilizes soft handoffs to improve the percentage of successful handoffs in CDMA networks. Soft handoffs provide an additional advantage in eliminating audible “impulse” noises that are often heard in mobile stations during handoff procedures.
However, CDMA networks have other problems, in that network capacity is decreased by the soft handoff method employed. This is because a mobile station performing a soft handoff occupies two or three radio links at the same time and accordingly utilizes the capacity of two or three stations during this procedure. This means that the capacity of a CDMA network may vary according to the ratio of soft handoff areas in a network to total service area in a network or by the rate at which channels within base stations perform soft handoffs.
Conventional CDMA network design methods have used the terms “ratio of soft handoff area to total service area” and “soft handoff channel rate” interchangeably. For example, in conventional CDMA network design methods, the soft handoff channel rate is assumed to be 40% which has resulted in the ratio of the soft handoff area to the total service area also assumed to be 40%. Adopting these values decreases the call success rate over the whole network. The number of users who can communicate simultaneously is also reduced as the accommodation capacity of whole network is significantly reduced as compared with a conventional radio network design. Therefore, CDMA networks often require additional equipment to achieve the service quality that the network was designed for, or service quality can only be maintained with a smaller number of users than contemplated in the original system design.
Other examples of conventional CDMA network design approaches include U.S. Pat. No. 5,710,758 (“the '758 patent”). In the '758 patent, a method for simulating and analyzing the operation of a CDMA wireless network is described. In particular, an electronic representation of a wireless telecommunications system is configured for a given market area and the operation of that wireless telecommunications system simulated. An analysis of the reverse and forward links are performed to determine which locations within a demand and service vector will be able to establish reverse and forward links, respectively, with base stations placed at desired locations throughout the service area.
In contrast to the present invention, the '758 patent is directed to the design of a CDMA network and, as such, does not address accommodation capacity and/or the handoff rate.
SUMMARY OF THE INVENTION
The present invention provides a method for establishing and/or optimizing the handoff rate and accommodation capacity of a CDMA network by calculating capacity variation and effective channel rate per sector as a function of the soft handoff channel rate.
The soft handoff channel rate is used as a basis for determining the handoff rate and the accommodation capacity because it can be easily converted to a ratio of soft handoff area to the total service area. The ratio then readily confirms whether the target design value of accommodation capacity can be satisfied.
In accordance with a first aspect of the present invention, there is provided a method for determining the number of effective channels, and an effective channel rate in a code division multiple access network, comprising the steps of: calculating the ratio of the soft handoff area to the total service area, H
AT
; calculating the soft handoff channel rate, H
CT
as a function H
AT
; and determining the number of the effective channels, N
EFFECTIVE
, and the effective channel rate, R
CH-EFFECTIVE
, as a function of H
CT
and H
AT
.
According to the method of the present invention, the ratio of the soft handoff area to the total service, H
AT
is related to &Dgr;R and D such that &Dgr;R=D·(
1−{square root over (1−H
AT
)}), where
0≦H
AT
≦1 where R is a cell radius, D is a radius of coverage that the corresponding sector can service with the best signal quality, C is a radius of coverage that only the corresponding sector can service and &Dgr;R is radius-difference between R and D or between C and D satisfying 0 &Dgr;R D.
In accordance with the present invention, H
AT
, the ratio of the soft handoff area to the total service, is preferably calculated as the sum of H
A3
and H
A2
where H
A3
is the ratio of the 3-way soft handoff area in the total service area, and H
A2
is the ratio of the 2-way soft handoff area in the total service area.
H
A3
is preferably derived as a function of H
AT
as H
A3
=2·(
1−{square root over (1−H
AT
)})
2
and H
A2
is preferably derived as a function of H
AT
as H
A2
=H
AT
−2·(
1−{square root over (1−H
AT
)})
2
.
The soft handoff channel rate is preferably calculated as a function of H
AT
H
CT
=
4
·
(
1
-
1
-
H
AT
)
(
2
-
1
-
H
AT
)
2
.
H
CT
is preferably calculated as the sum of HC
3
and H
C2
, H
CT
=H
C3
+H
C2
, where H
C3
is a 3-way handoff channel ratio for the total service area, and the H
C2
is a 2-way handoff channel ratio for the total service area.
The 3-way handoff channel ratio, H
C3
is related to &Dgr;R and D such that H
C3
=6·(AR)
2
/(D+&Dgr;R)
2
, where R is a cell radius, D is a radius of coverage that the corresponding sector can service with the best signal quality, C is a radius of coverage that only the corresponding sector can service and &Dgr;R is the radius-difference between R and D or between C and D satisfying 0 &Dgr;R D.
H
C2
is preferably derived as a function of
H
AT
:
(
1
-
1
-
H
AT
)
·
(
6
·
1
-
H
AT
-
2
)
(
2
-
1
-
H
AT
)
2
.
The number of effective channels, N
EFFECTIVE
is preferably derived as N
EFFECTIVE
=N
MAX
·((1−H
CT
)+H
C2
/2+H
C3
/3), where
N
MAX
is the maximum number of channels at a system loading environment defined in a practical system design,
H
CT
is the handoff channel rate,
H
C2
is the 2-way handoff channel ratio for the total service area and the H
C3
is the 3-way handoff channel ratio for the total service area.
In accordance with another aspect of the present invention, the number of effective channels, N
EFFECTIVE
is derived as a function of
H
AT
:
N
EFFECTIVE
=
N
MAX
·
1
(
2
-
1
-
H
AT
)
2
.
In accordance with another aspect of the present invention, the effective channel rate, R
CH-EFFECTIVE
is derived as R
CH-EFFECTIVE
=(1−H
CT
)+H
C2
/2+H
C3
/3, where H
CT
is handoff channel rate, H
C2
is 2-way handoff channel ratio for the total service area and, H
C3
is 3-way handoff channel ratio for the total service area.
In accordance with another aspect of the present invention, the effective channel rate, R
CH-EFFECTIVE
is derived as a function of H
AT
, the ratio of the soft handoff area to the total service area:
R
CH
-
EFFECTIVE
=
1
(
2
-
1
-
Dilworth & Barrese LLP
Hsu Alpus H.
Qureshi Afsar M.
Samsung Electronics Co,. Ltd.
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