Communications: directive radio wave systems and devices (e.g. – Directive – Utilizing correlation techniques
Reexamination Certificate
2002-06-05
2003-12-02
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Utilizing correlation techniques
C375S347000, C375S349000, C455S137000
Reexamination Certificate
active
06657590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an adaptive antenna reception apparatus. More particularly, the present invention is directed to an adaptive antenna reception apparatus which receives a CDMA (code division multiple access) signal by arrays of antennas and generates a demodulation signal.
2. Description of the Related Art
A CDMA system has a possibility that the number of subscribers can be increased, and is expected as a radio access system of a mobile communication celler system. However, there is a problem that a signal from a user acts as an interference signal to another signal from another user in a base station receiving end.
An adaptive array antenna reception apparatus is known as a method of receiving only a desired signal while removing these interference signals. The adaptive array antenna reception apparatus receives a signal by a plurality of antennas and carries out a complex weighting and combining operation, controls the amplitude and phase of the reception signal by each antenna to form a directional beam to receive the desired user signal, and to suppress the other user interference signals.
The reception characteristic of the adaptive array antennas strongly depends on the arrangement of the array of antennas and the antenna interval between the antennas. Generally, the fading correlation of reception signals becomes high when the antenna interval is made narrow. As a result, the directionality needs be made narrow. However, there is a problem that the diversity effect decreases at the same time. In the environment severe in fading as in mobile communication, it is sometimes better in improvement of the reception characteristic to carry out diversity-combining and to compensate the fading rather than to control the directionality to be narrow.
A sub-array arrangement is known as the array antenna arrangement having the directionality control effect and the diversity effect. The array antenna arrangement with a sub-array structure is shown in FIG.
1
. Referring to
FIG. 1
, the array antenna is comprised of a sub-array of antennas
31
-
1
-
1
to
31
-
1
-N and a sub-array of antennas
31
-
2
-
1
to
31
-
2
-N. The antenna interval between the antennas in the sub-array is set narrow so that it is possible to carry out the directionality control. The antenna interval in the sub-array is generally set to be 0.5 wavelengths. The sub-array interval between the sub-arrays is set wide for the diversity effect so as to be obtained. The sub-array interval is generally set to be equal to or more than 10 wavelengths.
FIG. 2
shows the circuit structure of a conventional example of an adaptive antenna reception apparatus which uses this sub-array arrangement. Referring to
FIG. 2
, the conventional example of the adaptive antenna reception apparatus receives a CDMA signal by the antennas of sub-arrays with the sub-array structure, independently carries out adaptive directionality forming for every sub-array, diversity-combines the reception signals and outputs a demodulation signal.
A receiving and demodulating section corresponding to two sub-arrays is comprised of L (L is a positive integer) path receiving sections
41
-
1
-
1
to
41
-
1
-L,
41
-
2
-
1
to
41
-
2
-L for the number of paths of a transmission multi-path, combining units
49
-
1
and
49
-
2
, decision units
50
-
1
and
50
-
2
, switches
51
-
1
and
51
-
2
, subtractors
52
-
1
and
52
-
2
and an adder
53
which combines the outputs of two combining units
49
-
1
and
49
-
2
.
The path receiving sections
41
-
1
-
1
to
41
-
1
-L have the same circuit structure and carry out the same operation. Therefore, the path receiving section
41
-
1
-
1
will be described. The path receiving section
41
-
1
-
1
is comprised of a beam former
42
-
1
-
1
, a channel estimating section
43
-
1
-
1
, a complex conjugate calculating section
44
-
1
-
1
, a multiplier
45
-
1
-
1
, a normalizing section
46
-
1
-
1
, a multiplier
47
-
1
-
1
, and an antenna weight adaptive control section
48
-
1
-
1
.
The beam former
42
-
1
-
1
receives antenna-corresponding despread signals #
1
-
1
to #
1
-N as a path #
1
despread signal for a user and outputs a path-corresponding beam former signal from the antenna-corresponding despread signals #
1
-
1
to #
1
-N with an antenna directionality using adaptive weights peculiar to the user and generated adaptively.
The channel estimating section
43
-
1
-
1
estimates a channel estimation signal from the path-corresponding beam former signal outputted from the beam former for the path #
1
. The complex conjugate calculating section
44
-
1
-
1
carries out a complex conjugate calculating operation of the channel estimation signal for the path #
1
and outputs a complex conjugate signal. The multiplier
45
-
1
-
1
multiplies the path-corresponding despread signal from the beam former outputs for the path #
1
and the complex conjugate signal from the complex conjugate calculating section
44
-
1
-
1
. At this time, the multiplier
45
-
1
-
1
corrects a phase change in the path #
1
and carries out a weighting operation for the maximum ratio combining. The maximum ratio combining is a method of weighting and combining such that SINR (signal power vs. interference noise power ratio) after the combining becomes maximum.
The combining unit
49
-
1
adds or combines the outputs of the multipliers
45
-
1
-
1
for path combining and generates a path-corresponding demodulation signal for the path #
1
and for the sub-array
31
-
1
. The decision unit
50
-
1
determines a transmission signal with a high transmission possibility from the user from the demodulation signal for the sub-array
31
-
1
. The switch
51
-
1
selects as a reference signal, a known reference signal when there is the known reference signal, and the transmission signal from the decision unit
50
-
1
when there is not any known reference signal. The subtractor
52
-
1
subtracts the demodulation signal for the sub-array
31
-
1
from the reference signal and generates an error signal. The error signal is distributed to the path receiving sections
41
-
1
-
1
to
41
-
1
-L.
The normalizing section
46
-
1
-
1
carries out a normalizing operation to the channel estimation signal estimated by the channel estimating section
43
-
1
-
1
. Here, the normalizing section
46
-
1
-
1
may be omitted to reduce a calculation quantity. The multiplier
47
-
1
-
1
multiplies the normalized channel estimation signal from the normalizing section and the error signal. The antenna weight adaptive control section
48
-
1
-
1
updates the antenna weights adaptively by using the antenna-corresponding despread signals for the path #
1
and for the sub-array
31
-
1
and the output of the multiplier
47
-
1
-
1
. In the antenna weight adaptive control section
48
-
1
-
1
, minimum mean squared error (MMSE) control is generally used. In the MMSE control, the control is carried out so as to maximize the reception SINR, in addition to direct the beam to the desired user signal.
The path receiving sections
41
-
2
-
1
to
41
-
2
-L have the same circuit structure as the path receiving section
41
-
1
-
1
and carry out the same operation as the path receiving section
41
-
1
-
1
. Also, the combining unit
49
-
2
, the decision unit
50
-
2
, the switch
51
-
2
, and the subtractor
52
-
2
carry out the same operations as those of the combining unit
49
-
1
, the decision unit
50
-
1
, the switch
51
-
1
, and the subtractor
52
-
1
, respectively.
The adder
53
adds the demodulation component signal for the first set and the demodulation component signal for a second set and outputs a demodulation signal for the user.
In the adaptive update algorithm using the above-mentioned determination error signal, algorithms such as LMS (Least Mean Square) algorithm and RLS (Recursive Least Square) algorithm are known. For example, the antenna weights w
1
(l,n), w
2
(l,n) (l is a path number and n is a symbol number) of the respec
McGinn & Gibb PLLC
Mull Fred H
NEC Corporation
Tarcza Thomas H.
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