Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2002-02-11
2003-07-29
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S174000
Reexamination Certificate
active
06600445
ABSTRACT:
FIELD OF THE TECHNOLOGY
The present invention relates generally to smart antenna technology for wireless communication systems, and more particularly to a method for calibrating smart antenna arrays, as well as to a device for calibrating smart antenna arrays.
BACKGROUND OF THE INVENTION
In modern wireless communication systems, especially in CDMA wireless communication systems, smart antennas are generally used to increase system capacity, system sensitivity and communication distance with lower emission power.
The Chinese patent named “Time Division Duplex Synchronous Code Division Multiple Access Wireless Communication System with Smart Antenna” (CN 97 1 04039.7) discloses a base station structure for a wireless communication system with a smart antenna. The base station includes an antenna array consisting of one or more antenna units, corresponding radio frequency feeder cables and a set of coherent radio frequency transceivers. Each antenna unit receives signals from user terminals. The antenna units direct the space characteristic vectors and directions of arrival (DOA) of the signals to a baseband processor. The processor then implements receiving antenna beam forming using a corresponding algorithm. Among them, any one of the antenna unit, corresponding feeder cable and coherent radio frequency transceiver together is called a link. By using weight getting from the up link receiving beam forming of each link in the down link transmitting beam forming, the entire functionality of smart antennas can be implemented, under symmetrical radio wave propagation conditions.
In the above Chinese patent, for the smart antenna to combine receive and transmit beam accurately, the difference between each antenna unit of the smart antenna array, radio frequency feeder cable and radio frequency transceiver, should be known, i.e. the difference of amplitude and phase variation after the radio frequency signal passes each link should be known. A procedure for determining the difference among links of the smart antenna system is just one concern addressed by the smart antenna calibration of the invention.
Calibration of a smart antenna array is a kernel technology of smart antenna. A characteristic of electronic elements, which comprise radio frequency systems of smart antennas, especially active elements, is sensitivity to working frequency, environment temperature and working duration etc. Characteristics for each link, as a result of such variation, are typically never the same, thus requiring constant calibration of smart antenna systems.
At present, there are generally two kinds of calibration methods for smart antennas. One is a direct measure method. This method measures every set of radio frequency transceivers to obtain data related to its amplitude and phase. Then the measured amplitude and phase characteristics of the antenna units and feeder cables are added to form a set of calibration data. This calibration procedure is very complicated. It is difficult to obtain all measurements in the field, especially for wireless communication systems that are in operation. Another method is to calibrate the system using a pilot transceiver at an antenna far-field region. This method requires the pilot transceiver to be located at a far-field region without multipath propagation. This, however, is also difficult to implement in practice.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a method and device for calibrating smart antenna arrays in real-time, so as to render the use of smart antenna systems practicable. The device of the invention allows the method of the invention to work effectively.
A further object of the invention is to provide two designs and calibration methods of couple structures for calibrating smart antenna arrays, which also allows the method of the invention to work effectively.
A method of the invention for calibrating a smart antenna array comprises:
1) providing a calibration link with a coupling structure, a feeder cable and a pilot transceiver, wherein the coupling structure is coupled with N antenna units of the smart antenna array and the pilot transceiver is connected to a baseband processor of a base station by a digital bus;
2) calibrating the coupling structure with a vector network analyzer before the smart antenna array is put into operation, and recording its receiving transmission coefficient and transmitting transmission coefficient, respectively;
3) calibrating receiving of the smart antenna array by: transmitting a defined voltage level signal at a set working carrier frequency by an analog transmitter of the pilot transceiver, and setting N receiving links, in a base station to be calibrated, in a receiving state; detecting the output of each receiving link, respectively, by the baseband processor in the base station and calculating the ratio of the transmission coefficient of each link to the transmission coefficient of a reference link during receiving, according to the output of each receiving link; controlling the output of each receiving link by controlling a variable gain amplifier in an analog receiver present in each link r, so that the amplitude ratio of the receiving transmission coefficient of each link to the transmission coefficient of the reference link equals to 1; and recording and storing the phase difference &PHgr; between each receiving link and the reference link in the baseband processor; and
4) calibrating transmitting of the smart antenna array by: setting one link in a transmitting state at one time while all other transmitting links of the N transmitting links are in a closing state, and receiving signals coming from each transmitting link, respectively, at a set working carrier frequency with an analog receiver, in the pilot transceiver; processing the signals by the baseband processor of the base station and calculating the ratio of the transmission coefficient of each link to the transmission coefficient of a reference link during transmission; controlling the output of each transmitting link by controlling a variable gain amplifier which is present in an analog transmitter in each link, so that the amplitude ratio of the transmission coefficient of each link transmission to the transmission coefficient of the reference link equals to 1, during transmission; and recording and storing the phase difference &psgr; between each transmitting link and the reference link in the baseband processor.
The method of calibrating a coupling structure with a vector network analyzer in accordance with the present invention, further comprises: setting a pilot antenna in spatial coupling mode; connecting the vector network analyzer to a feeder cable terminal of a pilot signal and antenna unit terminal of the antenna link to be calibrated, connecting an antenna unit terminal of a non-calibrated link to a matched load, measuring and recording the receiving and transmitting transmission coefficient of the link to be calibrated under each necessary working carrier frequency; and repeating the above steps until all receiving and transmitting transmission coefficients of N links have been measured and recorded.
The method of calibrating a coupling structure with a vector network analyzer of the invention further comprises: connecting a passive network coupling structure consisting of N couplers and a 1:N passive distributor/combiner, wherein the N couplers are connected with the antenna terminal of the N antenna units of the smart antenna array, respectively, and the output of the passive distributor/combiner is a feeder cable terminal of the pilot signal; connecting the vector network analyzer to a feeder cable terminal of the pilot signal and antenna unit terminal of the antenna link to be calibrated, connecting the antenna unit terminal of the non-calibrated link with matched load, measuring and recording the receiving transmission coefficient and transmitting transmission coefficient of the link to be calibrated under each necessary working carrier frequency; and repeating the steps above until all receiv
Alston & Bird LLP
China Academy of Telecommunications Technology
Phan Dao
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