Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-09-20
2001-11-13
To, Doris H. (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S025000, C455S063300, C342S354000, C342S147000
Reexamination Certificate
active
06317611
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a communication device using an adaptive antenna which is suited to be the wireless base station of a mobile communications system or the like.
The next-generation mobile communications system named IMT-2000 is required to deliver not only voice communications services, had also video and other relatively large-volume data communications services. Because of these demands, as more advanced technology for increasing the system capacity of the wireless base stations, adaptive antennas (adaptive array antennas), which can improve the SIR (signal-to-interference ratio) of each user signal and increase the system capacity, have become strong candidates.
These adaptive antennas consist of a plurality of antenna elements provided at the base station of the mobile communications system, and arbitrary weights, (amplitude, phase) are applied to the signals input to the respective elements to perform beam formation in the desired direction. However, it is necessary to be able to control the weights applied to the antenna branches so that portions of the beam with a high gain are directed to the desired user (the user to be communicated with) and portions of the beam with low gain are directed to interfering users (users not to be communicated with).
Description of the Prior Art
FIG. 12
shows a conventional example of a configuration of a communicative device with an array antenna. In the figure,
1
is an array antenna consisting of a plurality of antenna branches (antenna elements).
2
is a duplexer, which is used to obtain isolation of a transmit/receive, path in the case that one antenna branch is used for both transmitting, and receiving,
3
are weighting multipliers
3
, and when an adaptive array antenna (AAA) is used in the uplink, these weighting multipliers
3
multiply the weights by the uplink signals of each antenna branch.
4
is an adder that adds the outputs of these weighting multipliers
3
.
5
is the adaptive processor (AAA weighting block) for the uplink, and this adaptive processor
5
calculates the weights of each antenna branch based on the uplink signals of each antenna branch, the combined signal from the adder
4
and an arbitrary reference signal set. The weights of each antenna branch calculated by the adaptive processor
5
are provided as input to weighting multipliers
9
corresponding to each antenna branch.
11
is a data generator, in which data generation is performed according to the coding and frame format required, and the data thus generated is branched through a signal splitter
10
and provided as input to the respective weighting multipliers
9
, where it is multiplied by the weights from the adaptive processor
5
. The output corresponding to each antenna branch (user signals) is multiplexed with the user signals in the same cell or the same sector for each branch by the user signal multiplexers
12
, passes through the duplexer
2
and is provided as output from the array antenna
1
.
In the system as described above, on the downlink, particularly in the case of FDD (Frequency Division Duplex) wherein the frequencies are different on the uplink and downlink, as shown in “The Effect of Interference Suppression in Forward Link by Adaptive Array Antenna Transmitting for W-CDMA Mobile Radio” (RCS
98-72
), adaptive control is performed on the uplink but transmission is performed on the downlink using exactly the same adaptive weightings as those generated for the unlink, but the beam shape of an array antenna has properties that vary depending on the frequency, so the afore-described, method has a limitation in that it can be used only under conditions wherein the difference between the transmit frequency and the receive frequency is no more than roughly 10%.
In this case, since the weights of the uplink are used for the downlink in the prior art system, when the difference between the receive frequency and the transmit frequency is large in the case of FDD, the high-gain portion of the beam may not necessarily be directed in the desired user direction, and similarly there is no guarantee that the low-level beam is directed in the interfering user directions. This tendency worsens particularly in the case in which the frequency difference exceeds 10%, leading to deterioration of characteristics.
In addition, in the case of simultaneous communications by a number of users in excess of the degrees of freedom (N-1) of the antenna (number of antenna elements: N) such as in CDMA, the efficient improvement to characteristics is not feasible.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid the above disadvantages. It is another object of this invention to permit adaptive control of the weights provided as input to each antenna element of the downlink based on uplink arrival angle information regardless of the difference between the uplink and downlink frequencies, and thereby increase the system capacity of the communications system.
The above and other objects of the present invention are attained by a communications device using an adaptive antenna, comprising an array antenna consisting of a plurality of antenna elements wherein beam shaping is performed by adaptively giving arbitrary weights to signals input to the respective antenna elements.
In the communications device using an adaptive antenna of the present invention, in the arrival angle information for each user is extracted from uplink user signal information, simulated user signals corresponding to each antenna branch are generated based on the arrival angle of a desired user, and the weights of the downlink applied to the respective antenna branches are controlled based on an arbitrary adaptive algorithm using these simulated user signals.
Generating simulated user signals and controlling the weights as described above is performed by: setting the arrival angle of a desired user and simulated first and second arrival angles that bracket the arrival angle of said desired user, setting N-3 or more simulated arrival directions (third, fourth, . . . ) (N: number of antenna elements, N>3) in addition to these arrival angles, and generating simulated user signals corresponding to each antenna branch using this arrival direction information, phase information determined from the antenna arrangement, etc., and uncorrelated or poorly-correlated signals, respectively, and using these simulated user signals in an arbitrary adaptive algorithm to control the weights and applied to the respective antenna branches.
In addition, the simulated first and second arrival directions that bracket the arrival angle of the desired user are set to the direction that is closest to the main beam among the null directions at the time of pointing the beam such that the gain in the desired user direction is maximum.
In addition, representative values from each angle range selected based on the arrival angles of each user and the first and second arrival angles aggregated in each cell or each sector are used to set third, fourth, . . . simulated arrival angles.
Furthermore, in changing the weights sequentially applied to each antenna branch, a function is provided for calculating the level of the desired-direction user and the level in each interfering user direction at arbitrary time intervals from information on the beam pattern formed from various user functional blocks and information on the desired-user direction and the interfering user directions, and comparing [these levels] against the previous levels, so that if the characteristics would be improved by changing to new weights then the change to the new weights is made, but if the converse is true and the characteristics were better in the previous state then those weights are kept, and the adaptive algorithm calculations the next weights based on the new weights regardless of this selection.
Thereby, the adaptive algorithm will not necessarily update optimal values in the process of convergence, but rather the error function will fluctua
Fujitsu Limited
Rosenman & Colin LLP
To Doris H.
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