Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Reexamination Certificate
2001-08-24
2002-12-10
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C342S375000, C342S377000, C370S335000
Reexamination Certificate
active
06492958
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an adaptive antenna reception apparatus for receiving code division multiple access (CDMA) signals and adaptively forming antenna directivity beams to receive a desired user signal while suppressing other user interference signals.
The CDMA scheme has the potential of increasing the subscriber capacity and is expected as a radio access scheme for a next-generation mobile communication cellular system. On the base station receiving side, however, a problem arises in terms of interference with other user signals due to simultaneous access with the same carrier. As a method of eliminating such interference, a method using an array antenna is available.
An array antenna receives signals through a plurality of antennas and performs weighted combining of complex numbers. With this operation, the amplitude and phase of the signal received through each antenna are controlled to form a directivity beam so as to receive a desired user signal, and other user interference signals are suppressed. An adaptive array antenna is an apparatus for forming such a directivity beam by adaptive control.
FIG. 6
shows a conventional adaptive antenna reception apparatus. Referring to
FIG. 6
, the adaptive antenna reception apparatus has L path processing sections
107
-
1
to
107
-L corresponding to the number of paths in accordance with multipath propagation channels in a mobile communication environment. The adaptive antenna reception apparatus forms directivity beams for the respective L paths to receive signals therefrom, and combines the reception signals to obtain a high-quality reception signal. The path processing sections
107
-
1
to
107
-L have the same arrangement. Each section is comprised of a beam former
101
and adaptive control section
106
.
The beam former
101
receives a despread signal obtained at each path timing by using the spreading code of a desired user, and performs weighted combining of complex numbers to form a directivity beam for each path.
A combiner
102
combines outputs from the respective beam formers
101
. A determination unit
103
determines a transmission signal with the highest possibility of being a reception signal, and outputs a user determination symbol. A switch
104
is switched to output a known reference signal as a reference signal to a subtracter
105
if the known reference signal is present and to output a determination signal as a reference signal to the subtracter
105
if no known reference signal is present. The subtracter
105
generates an error signal by subtracting the reception signal sent from the combiner
102
from the reception signal sent from the switch
104
.
The adaptive control section
106
obtains an antenna weighting factor used by each beam former
101
by adaptive control using an error signal and a reception signal before beam forming. Adaptive control, minimum mean square error (MMSE) control is generally used. As adaptive update algorithms for antenna weighting factors using error signal, LMS (Least Mean Square), NLMS (Normalized LMS), and RLS (Recursive Least Square) algorithm are known.
FIG. 9
shows the gains of beam patterns formed by the beam formers for the respective paths.
FIG. 9
shows a case of two paths. In this case, high gains are directed to the respective path directions of desired signals, while the gains in the interference signal directions are suppressed low. In an array antenna using adaptive control, a beam is directed to a desired signal direction, and a point (null) where the gain is extremely low is directed to an interference direction to maximize the reception SINR (Signal to Interference and Noise Ratio).
Other conventional adaptive antenna reception apparatuses are disclosed in “Pilot Symbol-Assisted Decision-Directed Coherent Adaptive Array Diversity for DS-CDMA Mobile Radio Reverse Link”, IEICE Trans. vol. E80-A, pp. 2445-2454, December 1997 (reference 1) and “Performance of Coherent Adaptive Antenna Array Diversity Receiver Using the Common Antenna Weights for Rake Combined Paths for W-CDMA Reverse Link”, Technical Report of IEICE, RCS 99-100, August 1998 (reference 2).
FIG. 7
shows the basic arrangement of this scheme. A beam former
121
receives a despread signal obtained at each path timing by using the spreading code of a desired user, and performs weighted combining of complex numbers to form a directivity beam for each path. A combiner
122
combines outputs from the respective beam formers
121
. A determination unit
123
determines a transmission signal with the highest possibility of being a reception signal.
A switch
124
is switched to output a known reference signal as a reference signal to a multiplier
125
if the known reference signal is present and to output a determination signal as a reference signal to the multiplier
125
if no known reference signal is present. The multiplier
125
multiplies the reference signal output from the switch
124
and the reference signal level output from an averaging section
130
. A subtracter
126
generates an error signal by subtracting the reception signal from the output from the multiplier
125
.
An adaptive control section
127
obtains an antenna weighting factor used by the beam former
121
by adaptive control using the error signal output from the multiplier
125
and the reception signal before beam forming. According to the above reference, antenna weighting factors are updated by using the NLMS algorithm.
A reference signal level A(n) is calculated on the basis of the transmission channel estimation value output from the beam former
121
. A reception level detection section
128
detects the reception level of each path from a corresponding transmission channel estimation value, and outputs it to an adder
129
. The adder
129
adds the reception levels of the respective paths output from the reception level detection section
128
. The averaging section
130
averages the sum level output from the adder
129
and outputs the resultant value to the multiplier
125
. The presence/absence of the averaging section
130
or its averaging time is arbitrarily determined.
FIG. 8
shows an example of the reception level detection section
128
. Referring to
FIG. 8
, an amplitude detection section
141
detects the absolute value (amplitude) of a transmission channel estimation value (complex number). A squaring section
142
calculates the square (power) of an output from the amplitude detection section
141
. The reference signal level A(n) is given by
A
(
n
)
=
∑
n
=
0
N
AVR
∑
i
=
0
L
-
1
&LeftBracketingBar;
h
(
i
,
n
)
&RightBracketingBar;
2
(
1
)
where N
AVR
is the averaging time of the averaging section
130
.
The conventional adaptive antenna reception apparatus exhibits excellent steady-state characteristics owing to low-speed MMSE adaptive control in which antenna weighting factors are long-term-averaged. In a high-speed fading environment or the like, amplitude and phase variations due to fading cannot be corrected. For this reason, to correct phase variations, a transmission channel correction section is connected to the output terminal of each beam former.
With regard to reception level variations, however, when a prescribed value is used as a reference signal, a level difference is produced between the reception signal and the reference signal, resulting in an error in the desired signal itself. This leads to unstable operation. If high-speed transmitting power control (TPC) is used together, a desired signal is suppressed in a short period of time in the process of initial convergence, and TPC diverges.
According to a method of determining a reference signal in accordance with a reception level, when a reception level after beam forming is used as a reference signal, the reference signal level drops as the beam gain decreases, as in the prior art. For this reason, the gain decreases for a long term because of the absence of power that adjusts the gain direction of a beam. In this method, therefo
Phan Tho
Whitham Curtis & Christofferson, PC
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