Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2000-03-15
2001-09-18
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S118000
Reexamination Certificate
active
06292138
ABSTRACT:
CLAIM OF PRIORITY
This application claims priority to an application entitled “Method of Determining Distance between Diversity Antennas” filed in the Korean Industrial Property Office on Mar. 22, 1999 and assigned Serial No. 99-9590.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to diversity antenna placement, and in particular, to a method of determining an appropriate distance between two receiving antennas in a radio telecommunications base station (BS) to provide good diversity performance.
2. Description of the Related Art
A cellular radio telecommunications system divides the whole service area into a plurality of base stations cells, i.e., small service areas, and the base stations are centrally controlled through an exchange system. An antenna is implemented to transmit or receive radio signals throughout the service area in the radio telecommunications system. However, the radio frequency (RF) signal (voice or electrical wave) is susceptible to fading. Accordingly, the base stations employ more than one antenna to compensate for the fading over the communication channel via diversity. That is, the radio telecommunication system selects the optimal signal among the RF signals received through a plurality of receiving antennas in a complex propagation environment. Typically, a base station uses two receiving antennas spaced by a predetermined distance to achieve the space diversity. At least two antennas are separately placed at a prescribed distance to reduce the multipath fading of the received signals and to achieve a good space diversity performance.
FIG. 1
illustrates a schematic view of a conventional base station employing the diversity antennas. As shown in
FIG. 1
, the base station is comprised of a first antenna
110
for transmitting or receiving radio signals, a second antenna
120
exclusively used only for receiving the radio signals, and an indoor system
130
connecting the first antenna
110
to the second antenna
120
. That is, the first antenna
110
serves the dual purpose of transmitting and receiving radio signals, and the second antenna
120
is exclusively used for the reception of radio signals. The distance between the receiving antennas is a very important factor in improving diversity performance in a radio telecommunications system. A diversity antenna placement method varies with the operation frequency band of the antenna, and the optimal antenna placement maximizes the diversity effect to overcome fading over the communication channel. In particular, the distance between the receiving antennas should be varied according to the operation frequency range of the antennas.
Most existing radio telecommunications systems use a frequency band of 900 MHz or 1.8 GHz. However, the antenna diversity technology of such system is not adaptable to a wireless local loop (WLL) system operating at 2.3 GHz band. As the RF signal experiences different phases of fading depending on the operation range of the frequency band, an optimal diversity antenna placement distance is necessary to bring good diversity performance at 900 MHz or 1.8 GHz band is not affective at 2.3 GHz band. Accordingly, the conventional diversity antenna placement method has its limitation in determining the optimum distance between the diversity antennas to achieve good diversity performance in a new radio environment that operates at a higher frequency band.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a method for determining a diversity antenna placement in which a correlation coefficient is set at a prescribed level to compensate the intended degree of fading, wherein the antenna placement distance is calculated according to the correlation coefficient.
To achieve the above object, there is provided a diversity antenna-distance determining method. According to one aspect of the present invention, the ratio &eegr; of an effective antenna height relative to the distance between two receiving antennas is selected with respect to one of the statistical correlation coefficients (&rgr;) of signals received through the antennas in a first frequency band. Then, a first distance d
1
between the two antennas is calculated in the first frequency band based on the calculated &eegr;, and a second distance d
2
between the two antennas is calculated in a second frequency band based on the calculated d
1
.
According to another aspect of the present invention, an allowable or desirable correlation coefficient of the signals received through the first and the second antennas at a first frequency band is derived, a first distance d
1
between the antennas, which satisfies the requirement to operate within the determined correlation coefficient in the first frequency band, is calculated. A second distance d
2
between the two antennas is calculated using the calculated first distance (d
1
) at a second frequency band, wherein the second frequency band differs from the first frequency band.
In the present invention, an optimal distance between antennas at a given frequency is calculated using the parameters measured from another frequency.
REFERENCES:
patent: 5574466 (1996-11-01), Reed et al.
patent: 5663990 (1997-09-01), Bolgiano et al.
patent: 6104768 (2000-08-01), Speight
Cha Steve
Klauber & Jackson
Phan Dao
Samsung Electronics Co,. Ltd.
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