Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-12-14
2004-02-10
Vuong, Quochien (Department: 2685)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S424000, C342S174000, C342S368000
Reexamination Certificate
active
06690952
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an adaptive array antenna transceiver apparatus that carries out transceiving a wireless signal using an adaptive array antenna, and in particular, in a communication system using a signals having different frequencies for transmission and reception, such as the FDD (Frequency Division Duplex) systems, relates to an adaptive array antenna transceiver apparatus for automatically calibrating the amplitude and phase differences between branches of the antenna for the respective transmitter and receiver.
This application is based on patent applications No. Hei-11-355995, Hei 11-365352, and 2000-113316 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Accompanying the rapid increasing use of mobile communication systems such as cellular telephones and PHS (Personal Handyphone System), it has become necessary to secure communication channels for as many subscribers as possible in a limited frequency band.
In order to do this, using a method of allocating as necessary a particular channel (multichannel access method) for multiple subscribers in mobile communications is the currently the main practice.
In the present mobile communication systems represented by cellular systems or PHS, for example, the TDMA (Time Division Multiple Access) is mainly used as the multichannel access method. Among these, the FDD system is used to enlarge the transmission area in GSM (Global System for Mobile Communications) and PDC (Personal Digital Cellular Telecommunication System), represented by cellular telephone systems.
However, in order to increase the efficiency of the use of the frequencies in a wireless area, it is necessary to decrease the influence of interference from adjacent cells. As technologies for decreasing the interference, the adaptive array antenna is known. This type of technology is disclosed in Citation 1, Monzingo et al.,
Introduction to Adaptive Arrays
, John Willy and Sons, New York, 1980.
In an adaptive array antenna, an array antenna is formed by a plurality of antenna elements arranged in an array. In addition, the radiation pattern of the array antenna is controlled by weighting the amplitude and phase with respect to an input signal for each of the branches of the array antenna. This means that the null direction of the radiation pattern of the array antenna is formed in the direction of the interference, and thus the influence if the interference is decreased.
An apparatus combining an adaptive array antenna and an FDD system is formed as shown in FIG.
34
.
In recent years, considering the ease and flexibility of control, the general method for the control of the amplitude and phase necessary for adaptive arrays is realized by digital signal processing, using a processor such as a DSP (Digital Signal Processor), in the baseband. This is disclosed in T. Ohgane, et al., “Implementation of a CMA Adaptive array for high speed GMSK transmission in mobile communications”,
IEEE Trans.,
Vol. 42, No. 3, pp. 282-288, August, 1993.
Therefore, in the case of realizing an adaptive array antenna by control of the baseband, a transmitter and receiver are necessary for each antenna of the array antenna. For the transmitter and receiver using this type of adaptive array antenna, ideally the amplitudes and phases between each of the branches are equal. However, in practice due to individual differences in high frequency circuits and cables of the electrical amplifiers, etc., fluctuations of the temperature characteristics of the installation location, etc., frequently the amplitudes and phases between branches are different.
Due to the influence of this type of difference in amplitude and phase, in the radiation pattern of an adaptive array antenna, a shrinking in the null direction and a bulging of the side lobe occurs with respect to the ideal radiation pattern, and this becomes a factor causing deterioration of the inherent interference suppression characteristics of the adaptive array antenna. This is disclosed for example in Citation 3, J. Litva et al.,
Digital Beamforming in Wireless Communications,
Artech House Publishers, 1996.
An example of this phenomenon is explained referring to FIG.
31
and FIG.
32
.
FIG. 31
shows the structure of the array antenna and the radiation pattern, and
FIG. 32
shows the relationship of the amplitude and phase error to the null depth. That is, using as a reference the case in which the amplitude and phase shown in
FIG. 31
are given as ideal conditions for each of three array antenna elements arranged in a circle shown in
FIG. 31
, the null depth of the radiation pattern in the case that the amplitude and phase of each element deviates from the ideal conditions is shown in FIG.
32
.
Under the ideal conditions, a radiation pattern having a null direction at 180° is formed, as shown in
FIG. 32
, and the depth of the null direction is becomes very large. However, in the case that the amplitude and phase of each element deviates from the ideal conditions serving as the reference, the radiation pattern of the array antenna deteriorates, and the depth in the null direction as shown in
FIG. 32
decreases depending on the amplitude error and the phase error.
Therefore, in order to make the radiation pattern of the transmission and the radiation pattern in the reception of the adaptive array antenna agree when using an FDD system having a transmission frequency and reception frequency that are different, technology for calibrating the amplitude and phase between each of the branches of the array antenna becomes necessary. In addition, in the case that the adaptive array antenna in the FDD system is used, because the frequency of transmission and reception are different, the weighting coefficient for each element of the adaptive array antenna required during reception cannot be applied during transmission as-is.
Therefore, normally in order to determine that weighting coefficient of the adaptive array antenna during transmission, it is necessary to estimate the direction of the desired signal and the interference signal using some kind of technology that estimates the incoming direction during reception, and the radiation pattern is controlled by determining the weighting coefficient during transmission using this information about direction. Thus, in order to use an adaptive array in an FDD system, respectively carrying out individual calibration during reception and during transmission is necessary.
Conventionally, in the case of calibrating the amplitude and phase of each of the transmitters and receivers, a reference signal for calibration output by an oscillator built into the apparatus is used. This type of technology is disclosed, for example, in Citation 4, H. Steyscal et al., “Digital Beamforming for Radars”, in Microwave Journal, vol. 32, no. 1, pp. 122-136.
The calibration circuit for such a conventional example is shown in FIG.
33
. The calibration procedure in the case of using the calibration circuit shown in
FIG. 33
is as follows:
(1) A reference signal from a reference signal oscillator is sent as a common signal to each of the branches to the receivers of each of the branches via a coupler having a branching means. The calibration value for each receiver is found using the value obtained at the receiver of each of the branches and the reference value. The value of a particular branch determined in advance and detected by the receiver is used as this reference value.
(2) The signal output from the transmitter is sent to the receiver via an attenuator, and the calibration value for all transmitters and receivers is found for each of the branches using the value obtained for each of the branches and the reference value. The reference value used here is the value obtained by the receiver of the branch serving as the reference when the calibration value of the receiver is found in step 1 above.
(3) The calibration value of the receiver found in step 1 above is subtracted from the cal
Cho Keizo
Hori Toshikazu
Nishimori Kentaro
Takatori Yasushi
Nippon Telegraph & Telephone Corporation
Thelen Reid & Priest LLP
Vuong Quochien
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