Communications: directive radio wave systems and devices (e.g. – Directive – Including antenna pattern plotting
Reexamination Certificate
2002-09-25
2004-05-18
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including antenna pattern plotting
Reexamination Certificate
active
06738016
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a smart antenna array technology used in a cellular mobile communication system, and more particularly to a method that can improve smart antenna array coverage.
BACKGROUND OF THE INVENTION
In a cellular mobile communication system using a smart antenna array, the smart antenna array is built into a radio base station, in general. The smart antenna array must use two kinds of beam forming for transmitting and receiving signals: one kind is the fixed beam forming, while another is the dynamic beam forming. The fixed beam forming, such as omnidirectional beam forming, strip beam forming or sector beam forming, is mainly used for transmitting omnidirectional information, such as broadcasting, paging etc. The dynamic beam forming is mainly used for tracing subscribers and transfers a subscriber's data and signaling information, etc. to a specific user.
FIG. 1
shows a cell distributing diagram of a cellular mobile communication network. Coverage is the first issue to be considered when designing a cellular mobile communication system. In general, a smart antenna array of a wireless base station is located at the center of a cell, as shown by the black dots
11
in FIG.
1
. Most cells have normal circle coverage, as shown by
12
. Some cells have non-symmetric circular coverage, as shown by
13
, and “strip” coverage, as shown by
14
. The normal circle coverage
12
, non-symmetric circular coverage
13
and strip coverage
14
are overlapped for non-gap coverage.
It is well known that a power radiation diagram of an antenna array is determined by the parameters such as: geometrical arrangement shape for antenna units of the antenna array, characteristics of each antenna unit, phase and amplitude of radiation level of each antenna unit, etc. When designing an antenna array, in order to make the design one that can be commonly used, the design is taken under a relatively ideal environment, which includes free space, equipment works normally, etc. When a designed antenna array is put in practical use, the real power coverage of the antenna array will certainly be changed because of different installing locations and positions, different landforms and land surface features, different building heights and different arrangements of antenna units, etc.
FIG. 2
(part of
FIG. 1
) shows a difference of an expected coverage
21
(normal circle) and a real or actual coverage
22
, as such real coverage is caused because of different landforms and land surface features, etc. The real coverage can be measured at a cell's site. It is possible that every cell has this kind of difference, so unless adjustments are made at a cell's site, real coverage of a mobile communication network may be very bad. Besides, there is a need to reconfigure an antenna array when an individual antenna unit of the antenna array does not work normally or coverage requirement has been changed, at this time the coverage of the antenna array must be adjusted in real time.
The principle of the adjustment is: based on fixed beam forming for omnidirectional coverage of a cell, a smart antenna array implements dynamic beam forming (dynamic directional radiation beam) for an individual subscriber.
For formula (1): A(&phgr;) represents the shape parameter of the expected beam forming, (i.e., the needed coverage), wherein 4) represents polar coordinate angle of an observing point, and A(&phgr;) is the radiation strength in the &phgr; direction, with same distance.
Shape Parameter Of The Expected Beam Forming=A(&phgr;) (1)
Suppose there are N antennas for a smart antenna array, wherein any antenna n has a position parameter D(n), a beam forming parameter W(n) and an emission power P in angle &phgr; direction, then the real coverage is represented by formula (2):
P
(
φ
)
=
&LeftBracketingBar;
∑
n
=
1
N
f
(
φ
,
D
(
n
)
)
×
W
(
n
)
&RightBracketingBar;
2
(
2
)
Wherein the form of the function f(&phgr;,D(n)) is related with the type of a smart antenna array.
In a land mobile communication system, taking into account two dimensional coverage on a plane is enough, in general. When dividing antennas in an arrangement, there are linear arrays and a ring arrays. A circular array can be seen as a special ring array (refer to China Patent 97202038.1, “A Ring Smart Antenna Array Used For Radio Communication System”). In a cellular mobile communication system, when implementing sector coverage, a linear array is generally used, and when implementing omnidirectional coverage, a circular array is generally used. In the present invention, a circular array is used as an example.
Suppose it is a circular array, then D(n)=2×(n−1)×&pgr;/N;
f
(&phgr;,
D
(
n
))=
exp
(
j×
2×
r
/&lgr;×&pgr;×cos(&PHgr;−
D
(
n
)) (find exponent).
Wherein r is the radius of a circular antenna array and &lgr; is the working wavelength.
FIG. 3
, for example, shows a power directional diagram of an omnidirectional beam forming for a normal circle antenna array with 8 antennas. Squares of digits 1.0885, 2.177, 3.2654, shown in
FIG. 3
, represent power.
Using a minimum mean-square error algorithm, the mean square error &egr; in formula (3) is the minimum one:
ϵ
=
1
K
∑
i
=
1
K
&LeftBracketingBar;
P
(
φ
i
)
1
/
2
-
A
(
φ
i
)
&RightBracketingBar;
2
×
C
(
i
)
(
3
)
In formula (3), K is the number of sampling points, when using an approximation algorithm; and C(i) is a weight. For some points, if the required approximation is high, then C(i) is set larger, otherwise C(i) is set smaller. When required approximations for all points are coincident, C(i) will be set as 1, in general.
Further, considering that transmission power of every antenna unit is limited, when taking the amplitude of W(n) to represent the transmission power of an antenna unit, and setting the maximum transmission power of each antenna unit as T(n), the limited condition can be expressed as:
|
W
(
n
)|≦
T
(
n
)
1/2
(condition 1)
Obviously, to find out an optimal value of the transmission power within the limit for every antenna unit, in general it only can be solved by selection and exhaustion of unsolved W(n) accuracy, except for some special situations which can be directly solved by a formula. Nevertheless, when using such an exhaustive solution, the calculation volume is very large and has an exponential relationship with the number of antenna units N. Although, the calculation volume can be decreased by gradually raising the accuracy and decreasing the scope of the value to be solved, but even only to solve for this sub-optimal value, the calculation volume is still too large.
SUMMARY OF THE INVENTION
In order to effectively improve smart antenna array coverage, a method to improve smart antenna array coverage has been designed. The improvement includes having the real coverage of an antenna array approach the design coverage; and when part of an antenna unit is shut down because of trouble, the antenna radiation parameter of other normal working antenna units can be immediately adjusted to rapidly recover the cell coverage.
The purpose of the invention is to provide a method, which can adjust parameters of antenna units of an antenna array according to a practical need. With this method, an antenna array has a specific beam forming satisfying requirement, and the emission power optimal value of each antenna unit can be rapidly solved within a limit to obtain a local optimization effect.
The method of the present invention is one kind of baseband digital signal processing methods. The method changes the size and shape of the coverage area of a smart antenna array, by adjusting parameter of each antenna (excluding those shut down antennas) of the smart antenna array, to obtain a local optimization effect coinciding with requirement under minimum mean-square error criterion. The specific adjusting scheme is that accord
Li Feng
Ran Xiaolong
Alston & Bird LLP
China Academy of Telecommunications Technology
Phan Dao
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