Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
2000-06-01
2004-05-04
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S148000, C375S349000, C455S296000, C329S320000
Reexamination Certificate
active
06731704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a cross polarization interference eliminating apparatus and a bit shift method for eliminating cross polarization interference. More particularly, the invention is directed to such apparatus and bit-shift method for eliminating cross polarization interference, which are useful in a digital radio multiplex transmitting system.
2. Description of the Related Art
In recent years, for the advantage of the high efficiency of frequency use and bi-directional transmission of large amount data, an increasing number of cross polarization transmission systems have been put on the market as compared to mono-polarization transmission systems, particularly in the field of a digital multiplex radio transmission using microwaves or submillimeter waves.
The cross polarization transmitting system is a kind of radio transmission system for transmitting data using two different polarized waves as carrier waves of a common frequency. The two polarized waves are a vertical polarized plain wave and a horizontal polarized plain wave (hereinafter called the V-polarized wave and the H-polarized wave) as described below.
First, an object signal to be transmitted is modulated in a transmitting apparatus, divided into a V-polarized wave and an H-polarized wave, whereupon they are transmitted in the form of signal-
1
on the V-polarized wave and signal-
2
on the H-polarized wave. Namely, signal-
1
is transmitted by the V-polarized wave and signal-
2
is transmitted by the H-polarized wave whose frequency is identical with the frequency of the V-polarized wave. The orthogonalized V-polarized wave and H-polarized wave interfere each other when they are transmitted via radio space. Therefore, a receiving apparatus has to eliminate the interference on both the two polarized waves for preventing any loss of original data.
An apparatus for eliminating the interference is called a cross polarization interference eliminating apparatus or cross polarization compensating apparatus. This apparatus is designated in an effect to make the optimum adjustment as by shifting the sampling timing of the H-polarized wave for eliminating cross polarization interference as much as possible if interference elements from the H-polarized wave is superimposed on the V-polarized wave.
Namely, the V-polarized wave and the H-polarized wave are received in a receiving apparatus and down-converted to be inputted to cross polarization wave interference eliminating apparatuses, where the V-polarized wave and the H-polarized wave are analog-to-digital converted into and demodulated as respective desired baseband signals. The demodulated output signals are equalized in deterioration due to fading or the like in a transversal equalizer, and added in the adding section installed in a subsequent stage where they are converted into desired signal-
1
and signal-
2
, respectively.
FIG. 14
of the accompanying drawings shows the manner in which cross polarization interference-component is eliminated from one of the received polarized plain waves. In the polarization transmitting system
86
of
FIG. 14
, the transmitted V-polarized wave and H-polarized wave separately propagate through radio space and separately received in a receiving apparatus
84
. Interference is developed in antennas on a transmitting apparatus (not shown) and those on receiving apparatuses
90
a
,
90
b
and the radio space, and results in a major cause fault-receiving.
The receiving apparatus
84
of
FIG. 14
is composed of a signal demodulating section
91
and an interference eliminating section
92
. The V-polarized wave is received in the antenna
90
a
, down-converted in a mixer
82
a
, and analog-to-digital converted in an analog-to-digital converter
91
b
, whereupon the digital signal is inputted to a first demodulator
91
c
. The demodulated digital signal is equalized in a transversal equalizer
91
d
, added in an adding section
91
f
to the demodulated signal of the other polarization, and inputted to an error detecting section
93
to output a detection signal.
On the other hand, the H-polarized wave is received in the antenna
90
b
, and the analog signal of the H-polarized wave is delayed by a delay element
83
for adjustment to conform the signal time to the V-polarized wave. Then the H-polarized wave is analog-to-digital converted in an analog-to-digital converter
92
b
and the digital signal is inputted to a second demodulator
92
c
. The demodulated signal is equalized in a transversal equalizer
92
d
, and is inputted into the adding section
91
f
where the resulting signal is added to the demodulated baseband signal to eliminate the interference-component.
The equalizations of the transversal equalizers
91
d
,
92
d
are signal processing using delay taps constituting the transversal equalizers
91
d
,
92
d
. The transversal equalizers
91
d
,
92
d
include a plurality of taps, which are flip-flops connected in series, shifting the bit time of the input signal. Accordingly, the transversal equalizers
91
d
,
92
d
equalize and eliminate multipath-components by correlation arithmetic of shifted digital signals on the delay taps, respectively. The amount of interference is extracted in the transversal equalizers
91
d
,
92
d
and is input to controllers (CONTROL)
91
e
,
92
e
as interference-component signals to ensure an error-free interference eliminating operation. In addition, the amount of interference is utilized to control the operation speed of the analog-to-digital converter
91
b
,
92
b
and the delay amount of the delay element
83
.
The delay element
83
delays an analog signal by a predetermined time, which is controlled by the controller
92
e
and is set so that the sampling is carried out at the optimum timing. At the final stage, the error detector
93
outputs a canceling signal. Then the error signal outputted from the error detector
93
is inputted to the transversal equalizer
92
d
to change the tap coefficients. The oscillator
91
n
inputs the converting clocks of the analog-to-digital converters
91
b
,
92
b
, being controlled by the controller
91
e.
However, according to the receiving apparatus
84
, unless the receiving wave signal input to the demodulating section
91
and other polarized wave signal input to the interference eliminating section
92
are inputted simultaneously, the interference-component cannot be eliminated sufficiently, and an accurate correlation value cannot be obtained to cancel the amount of interference, resulting in inadequate performance of the polarization interference elimination.
Further, the delay element
83
cannot change the amount of delay without cell breathing; with the setting being fixed, the delay element
83
cannot make a change of the delay amount while the system is working.
Furthermore, the delay element
83
, being an analog element, can change the amount of delay due to change of environment, such as temperature, and would be affected by on which signals are transmitted. Therefore, the delay element
83
should be set with taking the foregoing influences into consideration. Setting the amount of delay requires manipulation by an operator watching a monitor on which target values are displayed. Consequently, new technology has been cherished which realizes a polarization interference eliminating apparatus that enables an error-free adjustment, is compact in size, and is stabilized in operation.
SUMMARY OF THE INVENTION
With the foregoing problems in view, it is an object of the present invention to provide apparatus and bit-shift method for eliminating cross polarization interference in which an amount of delay is changed without cell breathing irrespective to an operator and which operates stably without an adjustment and which is constituted to be high-density.
Therefore, according to the first aspect of the present invention, there is a provided the cross polarization interference eliminating apparatus comprising a signal demodulating section for receiving a first
Fujitsu Limited
Ghebretinsae Temesghen
Katten Muchin Zavis & Rosenman
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