Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-02-18
2003-05-27
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S442000, C455S444000, C455S277100, C455S277200, C455S437000, C370S332000, C370S331000
Reexamination Certificate
active
06571097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an adaptive antenna directivity control method and a system therefore in a mobile communication system applied a code division multiple access (CDMA) system or so forth. More particularly, the invention relates to an adaptive antenna directivity control method and a system therefore, in which amplitudes and a phases of transmission signals and reception signals of respective of a plurality of antenna elements are varied to form a combined radiation pattern for a particular orientation and to cancel output signals for other orientation, for forming a directivity.
2. Description of the Related Art
Conventionally, in radio communication, when a plurality of communication terminals perform communication simultaneously particularly at the same or close frequencies, communication jamming due to mutual interference, such as intermodulation or so forth, can be caused frequently. Therefore, multiplexed communication system permitting multiple simultaneous communication, such as known CDMA system, A frequency division multiple access (FDMA) and a time division multiple access (TDMA) have be employed. Even in such radio communication, it is still possible to cause mutual interference by a large number of communications in a limited frequency band and whereby to limit use efficiency of the frequency. On the other hand, it is also possible to cause interference due to adverse affect of a multiplexed wave propagation path (multipath) in metropolitan where many reflecting bodies, such as buildings, are present.
The CDMA system distinguishes each communication terminal from others by assigning an orthogonal code which has high auto-correlation and low cross-correlatioin. Thus, all of the terminals are performing communication using the same frequency. Particularly, in a mobile communication system, such as in a digital cellular mobile telephone system, propagation characteristics can be varied abruptly according to movement of the mobile terminal. In such wave propagating condition, orthogonality of the code can be broken to possibly cause degradation of communication quality due to mutual interference of communication. Therefore, in the CDMA system, a transmission power control for maintaining interference at respective terminals uniform, RAKE reception for effectively use a plurality of multipath waves having different delay periods, path capture and so forth according to IS-95 standard or so on, are performed.
In such mobile communication system according to the CDMA system, employment of an adaptive antenna has been attracting attention for the purpose of improvement of communication quality and improvement of use efficiency of the frequency. The adaptive antenna is constructed by regularly arraying a plurality of antenna elements for forming a special filter by appropriate weighting of amplitude and phase components for reception signals of different amplitudes and phases through respective antenna elements, in reception. In transmission, similarly to reception, by appropriate weighting of amplitude and phase components, arbitrary directivity characteristics (beam pattern and occasionally simply referred to as directivity) is established in antenna radiation.
As a result, in the mobile communication system, to which the CDMA system is applied, by use of the adaptive antenna, communication of a plurality of mobile terminals at the same frequency can be spatially separated to reduce mutual interference. Thus, use efficiency of the frequency can be improved.
In case of the cellular mobile communication system applied the CDMA system, associating with movement of the mobile terminal (occasionally referred to as mobile station), switching between cell base stations (occasionally referred to as base station) to establish radio channel connection is performed. Namely, so-called handoff is performed. In the cellular mobile communication system performing handoff, in particular the cellular mobile communication system according to the CDMA system, all base stations and mobile stations performs communication by spread spectrum using the same frequencies in respective of up-link and down-link. Thus, the mobile station can simultaneously communicate with both of the base station connected before handoff and the base station to be newly connected by handoff before the mobile station switches the base station. Namely, soft handoff can be performed.
In the mobile communication system employing the adaptive antenna which performs directivity control set forth above, in handoff of the CDMA system, directivity to the base station connected between handoff can be established stably and satisfactorily follow to the movement of the mobile station, however, sharp directivity (the beam pattern having small half value angle) to the base station to be connected cannot be established initially since orientation (direction/angle) of the mobile station cannot be determined. Accordingly, all orientation is retrieved at once to gradually predict the orientation of the mobile station to finally establish sharp directivity for the mobile station.
FIG. 15
is an illustration for explaining initial directivity control in the up-link in the base station to be connected by handoff to the mobile station when the conventional adaptive antenna is used.
In
FIG. 15
, the mobile station
3
is initially located in a cell area
5
(service area) where only transmission wave of the base station
1
reaches, and thus establishes radio channel connection with only base station
1
. Thereafter, the mobile station
3
moves toward the base station
2
to be located near a cell area
6
(service area) of the base station
2
. Then, soft handoff is initiated.
FIG. 15
shows directivities of respective up-links of the base station
1
and the base station
2
immediately after initiation of soft handoff in the mobile station
3
. The up-link of the base station
1
as the base station connected before handoff appropriately follows to moving position of the mobile station and thus establishes sharp directivity (beam pattern
7
).
In contrast to this, the up-link of the base station
2
establishes initial directivity (area
9
) for retrieving all of orientations or only particular orientation (sector) since the position of the mobile station cannot be determined. Accordingly, the directivity (area
9
) of the up-link of the base station
2
is the same area as the cell area
6
of the base station
2
.
Broad (beam pattern having wide −3 dB gain position) of the directivity (area
9
) of the up-link of the base station
2
should increase possibility of mutual interference to receive a transmission wave of the up-link from another mobile station
4
located at the position of the orientation where the mobile station is not present. Furthermore, as set forth above, from the condition of omnidirectional retrieval, adaptive antenna directivity control has been initiated to take a significant period for restoring the normal state of control.
FIG. 16
is a sequence chart between a supervisory station, the base station and the mobile station in the case where the conventional adaptive antenna directivity control set forth above.
FIG. 16
shows a sequence including a supervisory station upon initiating soft handoff of the mobile station
3
from the base station
1
to the base station
2
. The mobile station regularly notifies a received pilot channel strength. The notice from the mobile station is notified to the supervisory station via the base station
1
. In the supervisory station, judgment is made whether the mobile station
3
can handoff with the base station other than the base station
1
on the basis of the content of notice. (“H” in FIG.
16
).
Here, if there is no base station to be an object of handoff, no event occurs. On the other hand, if there is the base station to handoff (base station
2
in
FIG. 15
) (“I” in FIG.
16
), the supervisory station commands for the base station
2
to assign communication channel for the mob
Le Thang
Sughrue & Mion, PLLC
Trost William
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