Calibration device

Details Calibration device Calibration device

2000-03-20

2004-03-16

Cumming, William (Department: 2683)

Telecommunications

Transmitter and receiver at separate stations

Distortion, noise, or other interference prevention,...

C455S114100, C455S226100, C342S173000, C342S368000

Reexamination Certificate

active

06708020

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a calibration apparatus applicable to a TDMA (Time Division Multiple Access) based and a CDMA (Code Division Multiple Access) based digital radio communication.
BACKGROUND ART
In conventional digital radio communications, a multiple access system is used and there are cases where an adaptive array antenna is used as the antenna. The multiple access system refers to a channel access system when a plurality of stations perform communications simultaneously using a same band. The TDMA system included in this multiple access system is called “time division multiple access system.” This TDMA system implements multiple accesses by allowing a plurality of stations to use carriers of the same frequency, converting signals transmitted from those stations to intermittent signals (here, referred to as “burst signals”) and aligning the burst signals of those stations in such a way that they do not collide with each other on the time scale.
However, the TDMA system has the difficulty in fully suppressing interference with other stations and this originates various problems such as increasing the number of interference signals as the number of multiplexing stations increases, making it difficult to acquire synchronization, deteriorating the communication quality and making communications impossible. If interference with other stations described above can be fully suppressed, it will be possible to improve the frequency utilization efficiency, improve the communication quality of each station in the same cell (area) and increase its capacity (multiplexing number or the number of channel accesses).
On the other hand, the adaptive array antenna is a system that determines a weight of each antenna output based on a control algorithm and controls directivity according to changes in the surrounding conditions. In the array antenna made up of a plurality of antennas, combining antenna outputs with an amplitude/phase shift added changes array directivity.
This adaptive array antenna is explained with reference to FIG.
18
.
FIG. 18
shows an overall configuration of a reception adaptive array antenna. In
FIG. 18
, antenna outputs
1802
from a plurality of antennas
1801
are multiplied by weights
1803
and combined into array output
1804
. Here, weights are controlled by weight control section
1807
based on the following 3 pieces of information:
{circle around (1)} Combined array output (
1805
)
{circle around (2)} Each antenna output (
1802
)
{circle around (3)} Advance knowledge of desired signal (
1806
)
There are also cases where combined array output (
1805
) is not used for weight control.
Conventionally, the adaptive array antenna has been researched and developed as an antenna system to maximize SINR (Signal to Interference plus Noise Ratio) of a reception signal. The adaptive array antenna is also used as a countermeasure against interference among different stations in TDMA transmission. This adaptive array antenna in TDMA transmission is explained with reference to FIG.
19
.
FIG. 19
shows an overall configuration of a TDMA reception adaptive array. In
FIG. 19
, reception outputs
1903
from radio sections
1902
connected to a plurality of antennas
1901
are multiplied by weights
1904
and combined into array output
1905
. Weight control is performed in the same way as the control in
FIG. 18
above. Reception data
1906
is obtained from array output
1905
.
FIG. 20
is a conceptual diagram of TDMA transmission using an adaptive array antenna on the receiving side. Suppose BS
2001
is provided with a reception adaptive array antenna and is communicating with first MS
2002
equipped with a non-array antenna. At this time, BS
2001
eliminates delayed signals (
2003
and
2004
) by controlling directivity and suppresses interference signal from another station, second MS
2005
, using the same frequency.
However, in
FIG. 19
, the amount of variation (D
1
, D
2
, . . . , Dn) made up of phase variation and amplitude variation generally varies among different radio sections
1902
due to variations in the delay characteristics and amplitude characteristics of elements such as amplifier and filter. Therefore, different phase variations and amplitude variations are added in different radio sections
1902
and the phase and amplitude of the reception signal at the antenna reception end and the phase and amplitude of the input signal to weight control section vary from one antenna to another. Because of this, the directivity pattern including a null point obtained from a weight convergence result is different from the actual directivity pattern.
Furthermore, when transmission directivity is controlled using the reception weights above, correct directivity control is not possible. To prevent the phenomena above, it is indispensable to retain the phase difference and amplitude ratio of the reception signal at each antenna reception end in the stage of signal input to weight control section
1907
, too. To do this, it is necessary to detect the delay (D
1
, D
2
, . . . , Dn) and amplitude of each radio section beforehand and compensate the variations (differences) of the amount of delay and amount of amplitude using some method.
One possible compensation method is the method of multiplying reception outputs
1903
from the radio sections in
FIG. 19
by phase offsets corresponding to the delay difference and gain offsets corresponding to the amplitude ratio. Regarding detection of variations in the phase and amplitude characteristics of an adaptive array apparatus, there is a report in the thesis G. V. Tsoulos, M. A. Beach “Calibration and Linearity issues for an Adaptive Antenna System” (IEEE VTC, Phoenix, pp.1597-1660, May 1997). The thesis above proposes a system using a tone signal as the calibration signal.
A calibration apparatus of radio sections in conventional TDMA transmission using this tone signal is explained with reference to FIG.
21
.
FIG. 21
is a block diagram showing an overall configuration of the calibration apparatus in the conventional radio section.
FIG. 21
illustrates a case where the number of antennas is
2
.
Tone signal (sine wave signal)
2102
generated from calibration signal generator
2101
is input to radio transmission section
2103
. In this example, the reception sections perform quadrature modulation and sin(&ohgr;t) and cos(&ohgr;t) are input as orthogonal IQ signals. Suppose tone signal cycle T at this time is 2&pgr;/&ohgr; and for information symbol frequency fs, &ohgr;=fs/m (m>1).
FIG. 22
shows a constellation of the tone signal in the IQ plane. The signal rotates on the circumference in the figure with a constant cycle of 2&pgr;/&ohgr;.
Radio transmission section
2103
has a function of transmitting signals with reception carrier frequency fc of the radio reception sections that carry out delay detection. The signal output with carrier frequency fc is sent via a cable, etc. from transmission terminal
2104
to antenna connection terminals
2107
and
2108
of radio reception sections
2105
and
2106
, respectively. At this time, suppose these cables are equal in length with sufficient accuracy relative to the wavelength of the carrier frequency. Quadrature detection outputs
2109
and
2110
of their respective radio reception sections are input to detection circuit
2111
. Detection circuit
2111
compares input tone signal
2102
and detection output
2109
and detects:
(Amplitude ratio, phase difference)=(
Ar
1
, &Dgr;&phgr;
r
1
) (2112)
Detection circuit
2111
also compares tone signal
2102
and detection output
2110
and detects:
(Amplitude ratio, phase difference)=(
Ar
2
, &Dgr;&phgr;
r
2
) (2113)
FIG. 23
is a constellation example of tone signal a(t) and detection output b(t) at time t. At this time, the relationship between b(t) and a(t) is expressed using phase difference &ohgr; and amplitude ratio A as follows:
b
(
t
)=
A
·exp(
j
&phgr;)·
a
(
t
)
Here, phase difference &phgr; represents a delay (amount of phase) of the remainder (Dmod&lgr;:

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