Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-09-24
2002-12-24
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S148000, C375S347000, C375S349000
Reexamination Certificate
active
06498804
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a directive reception method using an array antenna and an adaptive array antenna apparatus.
BACKGROUND ART
One of directivity antennas used in the digital radio communication field such as CDMA (Code Division Multiple Access) is an adaptive array antenna.
The adaptive array antenna is an antenna system that allows directivity to be changed by adaptively controlling the amplitude and phase of signals received through a plurality of antennas placed at regular intervals or signals to be transmitted through those antennas according to the communication environment. This provides effects such as enhancing the effect of eliminating interference or selectively receiving only a radio wave coming from a specific direction via a predetermined path, that is, reception based on a RAKE system.
However, implementing a practical adaptive array antenna requires overcoming numerous problems. In mobile bodies such as automobiles in particular, which change their position each moment, it is not easy to achieve high-speed and high-accuracy adaptation to a communication environment at the same time.
That is, if a mobile body on the transmitting side is moving, the receiving side must change reception directivity quickly to adapt itself to changes in the communication environment. However, the greater the variation in reception directivity per unit time by attaching importance to high-speed follow-up, the lower the accuracy of convergence to a target control value becomes. On the contrary, attaching importance to the accuracy of convergence may allow accurate convergence to a target control value, but would require longer time to converge.
Thus, when carrying out adaptive diversity reception, it is an important issue to determine the level of adaptability to the communication environment. However, a mobile body in mobile ratio communications may be stationary or moving slowly or fast and the direction of an incoming radio wave changes all the time, which makes it difficult to implement optimum follow-up to the communication environment.
DISCLOSURE OF INVENTION
It is one of the objectives of the present invention to provide a method and apparatus that will quickly follow up changes in a communication environment in mobile radio communications, etc. and realize accurate directive reception at the same time.
A directive reception method using an array antenna system of the present invention operates a plurality of diversity reception circuits with different environment follow-up characteristics placed in parallel and selects one of the outputs of the diversity reception circuits as a reception signal. Each of a group of diversity reception circuits with different communication environment follow-up characteristics operates so as to follow up the communication environment and the most appropriate one of the resultant reception signals is selected, achieving high-speed and high-accuracy directive reception.
A preferred mode of the present invention dynamically updates the environment follow-up characteristics of other diversity reception circuits based on the environment follow-up characteristic of the selected diversity reception circuit. The environment follow-up characteristics can be updated by changing parameter values that determine the environment follow-up characteristics.
In another preferred mode of the present invention, when changing the values of parameters that determine the environment follow-up characteristics, suppose the value of a basic parameter is &mgr;
1
, and &mgr;A and &mgr;B that satisfy a relationship of &mgr;A<&mgr;
1
<&mgr;B are obtained and at least one of &mgr;A or &mgr;B is used as a parameter value of another diversity reception circuit. It is desirable that both &mgr;A and &mgr;B be values close to &mgr;
1
. This makes the follow-up performance of a plurality of diversity reception circuits adaptively change while maintaining close correlation with each other, enabling quick formation of desired directivity.
In still another preferred mode of the present invention, only a diversity reception circuit with high environment follow-up capability is operated in an initial state of directivity formation, then the environment follow-up characteristics of other non-operating diversity reception circuits are updated and their operations started based on its environment follow-up characteristic. This reduces power consumption of the circuits.
The directive reception mode using the adaptive array antenna of the present invention multiplies reception signals of a plurality of antenna elements by weighting coefficients, then uses a plurality of diversity reception circuits that combine those signals as the reception output to carry out directive reception and selects the optimum signal from the reception signals output in parallel. It is possible to update weighting coefficients step by step and change the environment follow-up characteristic of each diversity reception circuit by changing the amount of update per step. It is desirable that the amount of update per step of the weighting coefficient in a non-selected diversity reception circuit be changed based on the amount of update of the selected diversity reception circuit.
It is also possible to receive a baseband-spread signal transmitted from a mobile body using the adaptive directive reception method of the present invention and restrain the field intensity of the transmission wave to reduce interference between signals on a same frequency band.
The directivity communication method using the adaptive array antenna of the present invention not only performs high-speed reception directivity formation by selecting the outputs of a plurality of diversity reception circuits but also carries out directivity transmission using directivity formation information of a selected diversity reception circuit.
The adaptive array antenna apparatus of the present invention comprises at least one directive reception circuit that selectively receives only radio waves passing through a specific path from among incoming radio waves via a plurality of antenna elements and a plurality of paths. The directive reception circuit comprises a plurality of diversity reception circuits operating in parallel each having a different environment follow-up characteristic and selects the most appropriate output from the outputs of those diversity reception circuits as a reception signal. It is desirable to update the environment follow-up characteristics of diversity reception circuits which have not been selected in every selection. It is also possible to operate only diversity reception circuits with higher environment follow-up performance in an initial stage of the reception directivity formation and make other diversity reception circuits non-operable, thus reducing power consumption of the circuit.
Another mode of the present invention provides a combination circuit that applies RAKE-combination to the reception outputs of a plurality of directive reception circuits. This makes it possible to increase reception power.
Still another mode of the present invention also carries out directivity transmission using information to form reception directivity. This improves the communication quality in mobile communications.
The adaptive array antenna apparatus of the present invention can be used for a CDMA-based communication apparatus and a base station apparatus for CDMA communications.
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Futagi Sadaki
Hiramatsu Katsuhiko
Ide Minako
Yukitomo Hideki
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Tran Khanh
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