Communications: radio wave antennas – Antennas – Plural antennas spaced a fractional or full wave length apart
Reexamination Certificate
1999-02-17
2001-05-15
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Plural antennas spaced a fractional or full wave length apart
C343S853000, C342S375000
Reexamination Certificate
active
06232927
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an array antenna apparatus for use in spread spectrum communications, wherein the array antenna apparatus includes a plurality of antenna elements aligned on a straight line, and wherein the array antenna apparatus is provided for use in a receiving station which receives a spread-spectrum modulated radio signal having a wavelength of a predetermined carrier frequency transmitted from transmitting stations, using a two-dimensional RAKE receiving method, and which performs spread spectrum communications in code division multiple access.
2. Description of the Prior Art
In conventional spread spectrum communication methods, there has been available such a technique (a so-called RAKE receiving method) such that, by heightening a spreading ratio of spread-spectrum modulation and by broadening a frequency bandwidth (spreading bandwidth) of a spread-spectrum modulated signal, namely, by sufficiently shortening the chip duration of the spread-spectrum modulated signal relative to the change in the delay time (delay broadening or delay range) of multi-path waves, the multi-path wave signals are separated into individual wave signals as delayed pulses on the delay time base by the despread-spectrum technique, using a cross correlation between received signals and spreading codes, and then, the separated delayed pulses are combined. When enough spreading bandwidth cannot be taken so that multi-path waves cannot be separated into individual waves only by differences of the delay time, it is effective to adopt such a two-dimensional RAKE receiving method such that the multi-path wave signals are received by an antenna array in which antenna elements are arrayed or aligned on a straight line at an interval of a half-wavelength distance, and then, the multi-path wave signals are separated into individual waves by using both the differences of delay time, and differences of arrival angle (for example, See Takashi Inoue et al., “Channel Capacity Improvement in the Uplink of DS/CDMA Systems by Means of 2-Dimensional RAKE Reception Scheme”, Technical Report of the Institute of Electronics, Information and Communication Engineers in Japan, A.P97-103, RCS97-118, October 1997).
FIG. 2
is a block diagram showing an implementation of a spread spectrum communication system of a prior art example, and
FIG. 3
is a perspective view showing the concept of a two-dimensional RAKE receiving method of a prior art example.
Referring to
FIG. 2
, transmitting stations
100
-
1
to
100
-K are equipped with data modulation sections
1
-
1
to
1
-K, spreading modulation sections
2
-
1
to
2
-K, RF transmitting sections (radio frequency transmitting sections)
3
-
1
to
3
-K, and transmitting antennas
4
-
1
to
4
-K, respectively. Spread spectrum signals S
1
-
1
to S
1
-K transmitted from the plurality of K transmitting stations
100
-
1
to
100
-K, respectively, arrive at a receiving station
200
via a multi-path transmission line
300
.
In the receiving station
200
, the signals are received by an array antenna
500
comprising a plurality of M antenna elements
5
-
1
to
5
-M arrayed or aligned on a straight line at an antenna element interval D of, for example, a half-wavelength (&lgr;/2). Individual received signals S
2
-
1
to S
2
-K are converted into intermediate frequency signals or baseband frequency signals by RF receiving sections (radio frequency receiving sections)
6
-
1
to
6
-M, respectively, and then, the converted signals are converted into M types or kinds of beam space signals S
3
-
1
to S
3
-M by a multi-beam forming circuit
7
. In this case, the multi-beam forming circuit
7
as shown in
FIG. 4
is a well circuit configuration and comprises an embodiment where eight beam space signals S
31
-
1
-S
3
-
8
are generated based on eight input signals S
1
-
1
-S
1
-
8
as an example. The multi-beam forming circuit
7
comprises:
(a) 180° phase shifters PS
11
to PS
14
, PS
21
to PS
24
, PS
41
and PS
44
, 90° phase shifters PS
31
to PS
32
, 1350 phase shifters PS
33
and PS
34
, and 215° phase shifters PS
35
and PS
36
; and
(b) in-phase combiners (or adders) AD
11
to AD
18
, AD
21
to AD
28
and AD
31
to AD
38
.
Next, the individual beam space signals S
3
-
1
to S
3
-M outputted from the multi-beam forming circuit
7
are distributed or divided into a plurality of K signals, and then, the divided K signals are inputted to K two-dimensional RAKE receiving sections
8
-
1
to
8
-K, respectively. For example, the two-dimensional RAKE receiving section
8
-
1
of the first user channel, as shown in
FIGS. 2 and 5
, comprises a plurality of M despreading circuits
811
-
1
to
811
-M, a plurality of M RAKE receiving circuits
812
-
1
to
812
-M, a combining circuit
813
, and a data demodulation section
814
. In the two-dimensional RAKE receiving section
8
-
1
of the first user channel, the distributed m-th (m=1, 2, . . . , M) beam space signal S
3
-m of the first user channel is despread by the despreading circuit
811
-m, and a RAKE combined signal S
41
-m of the m-th beam in the first user channel is generated by the RAKE receiving circuit
812
-m. The RAKE combined signals S
41
-
1
to S
41
-M of the first to M-th beams in the first user channel are maximum-ratio combined so as to generate a two-dimensional RAKE combined signal S
5
-
1
of the first user channel. After that, the generated two-dimensional RAKE combined signal S
5
-
1
of the first user channel is demodulated so as to generate a demodulated signal S
6
-
1
of the first user channel by the data demodulation section
814
. The other two-dimensional RAKE receiving sections
8
-
2
to
8
-K of the second to K-th user channels also operate in a similar manner, so as to generate demodulated signals S
6
-
2
to S
6
-K of the second to K-th user channels, respectively.
That is, since the two-dimensional RAKE receiving sections
8
-
1
to
8
-K obtain their outputs by maximum-ratio combining the input signals in a two-dimensional domain of time and space, the multi-path waves can be separated into individual waves with both differences of delay time and differences of arrival angle, this results in advantageous effects such that higher-quality data transmission can be realized by efficiently separating multi-path waves.
FIG. 6
is a plan view showing a multi-path transmission line of the spread spectrum communication system of
FIGS. 1 and 2
.
FIG. 6
shows only one transmitting station
100
and one receiving station
200
, wherein spread-spectrum radio signals transmitted from the transmitting stations
100
are received by the receiving station
200
via, for example, seven paths P
0
to P
6
. In this case, the receiving station
200
, as shown in
FIG. 7
, receives spread spectrum radio signals with a delay range.
In a case of less broadening of the arrival angle of multi-path waves that arrive at the receiving station
200
, in order to separate the individual multi-path waves based on differences of arrival angle, it is necessary to utilize an array antenna having a very large number of antenna elements. In other words, the hardware scale becomes relatively large.
SUMMARY OF THE INVENTION
An essential object of the present invention is to provide an array antenna apparatus for spread spectrum communications, wherein the array antenna apparatus includes a plurality of antenna elements arrayed or aligned on the straight line and is provided for use in a receiving station that receives spread-spectrum modulated radio signals having a wavelength of a predetermined carrier frequency transmitted from transmitting stations by a two-dimensional RAKE receiving method and performs spread spectrum communications in code division multiple access, and wherein the array antenna apparatus is capable of compensating degradations of signal quality due to multi-path fading by efficiently separating multi-path waves with a limited number of antenna elements, which is due to the hardware scale restriction, and is thus capable of prov
Inoue Takashi
Karasawa Yoshio
ATR Adaptive Communications Research Laboratories
Ho Tan
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