Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-04-23
2001-07-17
Vo, Nguyen T. (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S522000, C455S069000
Reexamination Certificate
active
06263205
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a mobile radio communication system of the cellular system wherein a base station and a mobile station are connected to each other, and more particularly to a mobile radio communication system wherein soft hand-off processing is performed with regard to a forward link transmission signal when a mobile station moves between cells.
In a cellular system of the direct spread CDMA (Code Division Multiplex Access) system, in order to maximize the communication capacity for reverse link transmission signals, transmission power control of mobile stations is usually performed to avoid a near-far problem. To this end, in a descending channel, a base station transmits transmission power control signals to mobile stations. On the other hand, in a cellular system of the direct spread CDMA system, each of a base station and a mobile station has a plurality of demodulators so that it may perform separation of multi-path components and soft hand-off processing.
The soft hand-off processing is performed because, as shown in
FIG. 5
, when a mobile station
103
moves from a cell
101
to another cell
102
and comes to a position in an overlapping portion
104
between the two cells
101
and
102
, deterioration of the quality of a signal which the mobile station
103
receives from a base station
105
a
of the cell
101
occurs. Thus, as the soft hand-off processing, substantially same signals are transmitted from the base station
105
a
and another base station
105
b
of the cell
102
to the mobile station
103
so that the mobile station
103
may demodulate and compose the signals from the two base stations
105
a
and
105
b
to obtain a signal of an improved signal quality. Also with regard to a reverse link, a signal transmitted from the mobile station
103
is de modulated and composed by the base stations
105
a
and
105
b
to improve a signal quality.
In this instance, transmission power control signals from the base stations
105
a
and
105
b
are each generated independently by the base stations
105
a
and
105
b
, respectively. This is because, when a transmission power control signal is transmitted only from the base station
105
a
to the mobile station
103
provided the mobile station
103
performs such processing as described above to control the transmission power, so that the base station
105
a
can receive the signal of an optimum level and then performs transmission with the controlled transmission power, there is the possibility that the signal transmitted from the mobile station
103
may be an unexpected signal and may be a significant disturbance to the other base station
105
b
. Then, the mobile station
103
demodulates the transmission power control signals from the two base stations
105
a
and
105
b
independently of each other and composes the demodulated transmission power control signals. More particularly, the mobile station
103
increases its transmission power only when, for example, the transmission power control signals from both of the base stations
105
a
and
105
b
exhibit “up”, but when the transmission power control signal from at least one of the base stations
105
a
or
105
b
exhibits “down”, the mobile station
103
decreases the transmission power. The mobile station
103
transmits a reverse link signal with an appropriate transmission power to the base stations
105
a
and
105
b
by receiving and demodulating the transmission power signals from the base stations
105
a
and
105
b
independently of each other in this manner.
As described above, for a cellular system which adopts the direct spread CDMA system, transmission power control of a mobile station is an essentially required technique. Further, in the cellular system, in order to maximize the communication capacity of the entire system, interference must be suppressed to the minimum. To this end, in the cellular system, soft hand-off processing is performed. Upon such soft hand-off, the mobile station
103
must perform transmission power control by demodulating and composing different transmission power control signals from the two base stations
105
a
and
105
b.
In this instance, if the threshold level of the communication quality with which soft hand-off is to be started is set at a lower level, then the number of mobile stations which must perform soft hand-off when a communication resource for a plurality of channels is used increases, and this gives rise to a problem that the communication capacity of the entire system decreases.
On the contrary if the threshold level of the communication quality with which hand-off is to be started is set at a higher level, then since the probability that the mobile station
103
may be present in a region in which hand-off is to be performed decreases, the frequency of soft hand-off can be decreased, and thus the communication capacity of the entire system can be increased. However, the possibility that a communication signal to the adjacent base station
105
b
may be disturbed increases, and this gives rise to a problem that not only the capacity of the entire system is decreased due to the interference, but also the stability of the entire system is deteriorated.
Further, when the mobile station
103
is positioned in the region in which hand-off is to be performed, if the communication capacity of the base station
105
b
of the destination of the hand-off has reached its limit value, then soft hand-off is not performed, but hard hand-off by which the frequency channel is changed is performed. In this instance, if a communication channel is transmitted from the mobile station
103
in a reverse link in a frequency channel which has been used before the hard hand-off is performed, this gives an unexpected significant disturbance to communication signals being handled by the base station
105
b
, presenting a problem that communication of other mobile stations is disturbed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a mobile radio communication system which assures a maximum capacity of the entire system while performing soft-hand off and performs control of the mobile station transmission power appropriately to secure the safety of the entire system.
In order to attain the object described above, according to the present invention, there is provided a mobile radio communication system, comprising at least two adjacent base stations, a mobile station movable between cells formed by and connectable to the base stations, and means for performing transmission power control such that, at least with regard to a control signal, soft hand-off control wherein the mobile station and the base stations are connected simultaneously to each other is performed, but with regard to any signal other than the control signal, hard hand-off control is performed.
In the mobile radio communication system, when hand-off processing is to be performed, since each of the base stations performs soft hand-off control for connecting the base stations simultaneously to the mobile station at least with regard to a forward link control signal but performs hard hand-off control with regard to any signal other than the forward link control signal, the communication capacity of the entire system is increased when compared with an alternative system wherein each base station performs soft hand-off control with regard to both a forward link control signal and an information signal representing voice and so forth other than the forward link control signal. Further, with the mobile radio communication system, since at least a forward link control signal is transmitted to the mobile station, the stability of the entire system can be maintained. Furthermore, with the mobile radio communication system, even if the communication capacity of the entire system is used fully, since the base station of the destination of hand-off transmits only a forward link control signal to the mobile station to perform soft hand-off processing in order to minimize possible interference which may
Sakoda Kazuyuki
Suzuki Mitsuhiro
Yamaura Tomoya
Maioli Jay H.
Nguyen Duc
Sony Corporation
Vo Nguyen T.
LandOfFree
Mobile radio communication system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mobile radio communication system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mobile radio communication system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2531348