Variation compensating unit

Details Variation compensating unit Variation compensating unit

2002-03-01

2003-11-25

Le, Thanh Cong (Department: 2684)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S277100, C455S277200, C455S278100, C455S281000, C375S347000

Reexamination Certificate

active

06654618

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a variation compensating unit and, more particularly, to a variation compensating unit for compensating variation including at least one of an amplitude variation and phase variation which will occur in the case of transmitting signals via transmission paths.
2. Description of the Related Art
In recent years attention has been riveted on cellular mobile communication systems in which digital signal processing is performed on signals to be transmitted or received by locating a plurality of antenna elements, such as multiple beam antennas or adaptive array antennas, at a radio base station.
FIG. 18
is a schematic view showing the structure of a system using an adaptive array antenna.
FIG. 18
shows the structure of a receiving section. In this example, four antennas
101
a
through
101
d
are located on transmission paths respectively. On the first transmission path, a low-noise amplifier (LNA)
102
a
, frequency converters
103
and
105
, an amplifier
104
a
, an A/D converter
106
a
, a multiplier
107
a
, and a combining section
108
are located. On the second transmission path, a low-noise amplifier (LNA)
102
b
, the frequency converters
103
and
105
, an amplifier
104
b
, an A/D converter
106
b
, a multiplier
107
b
, and the combining section
108
are located. On the third transmission path, a low-noise amplifier (LNA)
102
c
, the frequency converters
103
and
105
, an amplifier
104
c
, an A/D converter
106
c
, a multiplier
107
c
, and the combining section
108
are located. On the fourth transmission path, a low-noise amplifier (LNA)
102
d
, the frequency converters
103
and
105
, an amplifier
104
d
, an A/D converter
106
d
, a multiplier
107
d
, and the combining section
108
are located. The frequency converters
103
and
105
include a local oscillator (LO) and mixers.
Signals are received by the antenna
101
a
and are transmitted to the LNA
102
a
. Signals output from the LNA
102
a
, the amplitude of which is far higher than that of the original signals, are converted from RF signals into IF signals by the frequency converter
103
. These IF signals are amplified by the amplifier
104
a
, are converted into base band signals by the frequency converter
105
, are converted into digital signals by the A/D converter
106
a
, and are given weight W by the multiplier
107
a
. This is the same with the antennas
101
b
through
101
d
. The weighted signals are combined by the combining section
108
. Received (or transmitted) signals are expressed as functions of complex variables with amplitude as a and phase as &thgr;.
FIG. 19
is a view showing a beam pattern obtained by an array antenna. As shown in
FIG. 18
, it is assumed that radio signals which arrive from direction &psgr; to the antennas
101
a
through
101
d
are received. There arise path differences among the antennas
101
a
through
101
d.
These path differences are expressed as A
1
through A
3
, respectively, with the antenna
101
a
as a standard. These path differences will lead to phase differences. The radio signals are weighted by the multipliers
107
a
through
107
d
so that these phase differences will be canceled out, and then are combined by the combining section
108
. Signals output from the combining section
108
are equivalent to signals received as beam pattern B
1
shown in FIG.
19
.
Beam pattern B
1
obtained by receiving with an adaptive array antenna and beam pattern B
2
obtained by receiving with one antenna will now be compared. It is assumed that desired user signals arrive from direction &psgr;, that interference user signals arrive from direction&eegr;, that the levels of the desired and interference user signals received as the beam pattern B
1
are P
1
and P
2
respectively, and that the levels of the desired and interference user signals received as the beam pattern B
2
are P
3
and P
4
respectively. With the beam pattern B
2
, the difference in level (La) between P
3
and P
4
is small, but, with the beam pattern B
1
, the difference in level (Lb) between P
1
and P
2
is significant. Therefore, the beam pattern B
1
gives greater S/I than the beam pattern B
2
.
That is to say, with cellular mobile communication systems in which multiple beam antennas, adaptive array antennas, or the like are used, a beam pattern equivalently becomes sharp. As a result, interference in areas can be reduced. In addition, higher gain is obtained, so the number of users who can be accommodated in one cell can be increased.
In order to realize beam forming by the above system, nonlinear elements, such as the LNAs
102
a
through
102
d
and mixers, are needed on the receiving side for converting RF signals received by the antennas
101
a
through
101
d
into base band signals, as shown in FIG.
18
.
Moreover, on the transmitting side (a transmitting section is not shown), nonlinear elements, such as mixers for converting base band signals into IF signals, then into RF signals and a high power amplifier (HPA) for RF signals, are needed on each antenna branch.
However, these nonlinear elements included in each circuit differ in characteristic. Their characteristics also change according to environmental conditions, such as temperature, and input levels and suffer aged deterioration. As a result, amplitude and phase variations differ among different antenna branches, so efficient beam forming cannot be performed. This will lead to degradation in characteristic.
Compensating these amplitude and phase variations therefore is essential for the introduction of a multiple beam antenna or adaptive array antenna.
Conventionally, calibration between antenna branches has usually been performed on regular basis (once a day, for example).
Alternatively, there is the prior art of compensating amplitude and phase variations on each antenna branch by sending a pilot signal.
FIG. 20
is a view for describing the prior art.
Circuits
110
a
through
110
d
each including various nonlinear elements (LNAs, mixers, and the like) are located on four transmission paths respectively. The antennas
101
a
through
101
d
are also located on these transmission paths respectively.
As shown in
FIG. 20
, pilot signal
a
·exp(
j
&thgr;) is sent to the antennas
101
a
through
110
d
from a direction so that phase differences will not arise. It is assumed that signals which are processed in and output from the circuits
110
a
through
110
d
are
a
1
·exp(
j
&thgr;
1
) through
a
4
·exp(
j
&thgr;
4
).
The value of the ratio of signal
a
1
·exp(
j
&thgr;
1
) output from the branch on which the antenna
101
a
is located and signal
a
2
·exp(
j
&thgr;
2
) output from the branch on which the antenna
101
b
is located is (
a
1
/
a
2
)·exp[
j
(&thgr;
1
−&thgr;
2
)]. By multiplying this value and the original signal
a
2
·exp(
j
&thgr;
2
), which is output from the branch on which the antenna
101
b
is located, together,
a
1
·exp(
j
&thgr;
1
) is obtained. That is to say, the amplitude and phase variation between the branch on which the antenna
110
a
is located and the branch on which the antenna
101
b
is located are compensated. This value therefore should be used as a compensation value for the branch on which the antenna
101
b
is located. This is the same with the other branches.
Conventionally, such a compensation value has been calculated for each antenna branch by the use of a pilot signal to compensate an amplitude variation and phase variation.
However, with the above conventional method in which calibration between antenna branches is performed on regular basis, beam forming will be performed on the basis of uncertain compensation conditions because of dynamic amplitude and phase variations. As a result, the reliability of a system is low.
On the other hand, with the above conventional method in which a pilot signal is used, a dedicated unit for generating a pilot signal must be located in all of the cells or sectors, resulting in a heavy economic burden.
Further, this pilot signal w

Affiliated with

Also associated with

Rating

Variation compensating unit does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Variation compensating unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variation compensating unit will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3169964