Title: Transmission power control method and mobile station
Abstract: An object of the present invention is to prevent communication quality from being degraded when a mobile station 30.sub.2 is conducting DHO using a first signal, by means of simple control without greatly altering the scale of the apparatus. A mobile station 30.sub.2 according to the present invention receives signals from a first base station 10.sub.1 and a second base station 10.sub.2 during DHO. The mobile station 30.sub.2 includes reception means 32 for receiving a first signal DCH and a second signal SCH from the first base station 10.sub.1 and receiving a third signal DCH from the second base station 10.sub.2, reception quality measuring means 37 for measuring a reception quality of the first signal DCH or the second signal SCH, control command generation means 39 for generating a control command for controlling the transmission power of the signals from the first base station 10.sub.1 and the second base station 10.sub.2 on the basis of a result of the measurement of the reception quality, and transmission means 32, 41 and 42 for transmitting the control command to the first base station 10.sub.1 and the second base station 10.sub.2.
Patent Number: 6,853,844 Issued on 02/08/2005 to Iwamura
| Inventors:
|
Iwamura; Mikio (Zushi, JP)
|
| Assignee:
|
NTT DoCoMo, Inc. (Tokyo, JP)
|
| Appl. No.:
|
259304 |
| Filed:
|
September 30, 2002 |
Foreign Application Priority Data
| Sep 28, 2001[JP] | 2001-304273 |
| Current U.S. Class: |
455/442; 455/436; 455/522; 455/226.2; 455/69; 370/331; 370/332 |
| Intern'l Class: |
H04Q 007//20; H04B 007//00 |
| Field of Search: |
455/436,437,438,439,442,443,444,522,69,68,226.2,226.3,13.4
370/331,332,335,342
|
References Cited [Referenced By]
U.S. Patent Documents
| 5771451 | Jun., 1998 | Takai et al. | 455/442.
|
| 5845212 | Dec., 1998 | Tanaka | 455/437.
|
| 6263205 | Jul., 2001 | Yamaura et al. | 455/442.
|
| 6539226 | Mar., 2003 | Furukawa et al. | 455/442.
|
| 6650905 | Nov., 2003 | Toskala et al. | 455/522.
|
| 2002/0115440 | Aug., 2002 | Hamabe | 455/442.
|
| Foreign Patent Documents |
| 1 239 689 | Sep., 2002 | EP.
| |
| WO 99/03291 | Jan., 1999 | WO.
| |
| WO 02/01893 | Jan., 2002 | WO.
| |
Other References
3rd Generation Partnership Project; Technical Specification Group Radio
Access Network; DSCH power control improvenent in soft handover (Release
4), XP-002246941, pp. 1-13, "3GPP TR 25.841 V4.1.0", Mar. 31, 2001.
Derwent Publications, AN 2001-251276, JP 2001-045539, Feb. 16, 2001.
Derwent Publications, AN 1993-341900, JP 5-252100, Sep. 28, 1993.
|
Primary Examiner: Nguyen; Duc M.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the
prior Japanese Patent Applications No. P2001-304273, filed on Sep. 28,
2001, the entire contents of which are incorporated herein by reference.
Claims
What is claimed is:
1. A transmission power control method for controlling, in a mobile station
receiving signals from a first base station and a second base station
during a diversity handover, the transmission power of the signals from
the first base station and the second base station, said transmission
power control method comprising the steps:
a) receiving a first signal and a second signal from the first base station
and receiving a third signal from the second base station;
b) measuring a reception quality of the first signal or the second signal;
c) generating a control command for controlling the transmission power of
the signals from the first base station and the second base station on the
basis of a result of the measurement of the reception quality; and
d) transmitting the control command to the first base station and the
second base station.
2. The transmission power control method according to claim 1, wherein
in said step a), the second signal is received intermittently, and
in said step b), the reception quality of the first signal or the second
signal is measured in an interval during which the second signal is being
received, whereas a reception quality of a signal obtained by conducting a
diversity combination on the first signal and the third signal is measured
in an interval during which the second signal is not being received.
3. The transmission power control method according to claim 2, comprising a
step of:
e) monitoring the first signal to determine whether signaling is occurring
to notify the mobile station that the second signal is being transmitted,
wherein, in said step b), it is determined whether an interval is the
interval during which the second signal is being received, according to
whether the signaling is occurring.
4. The transmission power control method according to claim 2,
wherein, in said step b) the reception quality is measured with RAKE
reception by switching between a finger assignment to the first signal or
the second signal and a finger assignment to the first signal and the
third signal, according to whether an interval is the interval during
which the second signal is being received.
5. The transmission power control method according to claim 1,
wherein the first signal and the third signal are dedicated channels (DCHs)
provided for each mobile station, whereas the second signal is a shared
channel (SCH) shared by a plurality of mobile stations in a time division
form.
6. A mobile station for receiving signals from a first base station and a
second base station during a diversity handover, said mobile station
comprising:
a receiver configured to receive a first signal and a second signal from
the first base station and receive a third signal from the second base
station;
a reception quality measurer configured to measure a reception quality of
the first signal or the second signal;
a control command generator configured to generate a control command for
controlling the transmission power of the signals from the first base
station and the second base station on the basis of a result of the
measurement of reception quality; and
a transmitter configured to transmit the control command to the first base
station and the second base station.
7. The mobile station according to claim 6, wherein
said receiver receives the second signal intermittently, and
said reception quality measurer measures the reception quality of the first
signal or the second signal in an interval during which the second signal
is being received, whereas said reception quality measurer measures a
reception quality of a signal obtained by conducting a diversity
combination on the first signal and the third signal in an interval during
which the second signal is not being received.
8. The mobile station according to claim 7, comprising:
a monitor configured to monitor the first signal to determine whether
signaling is occurring to notify the mobile station that the second signal
is being transmitted,
wherein said reception quality measurer determines whether an interval is
the interval during which the second signal is being received, according
to whether the signaling is occurring.
9. The mobile station according to claim 7,
wherein said reception quality measurer measures the reception quality with
RAKE reception by switching between a finger assignment to the first
signal or the second signal and a finger assignment to the first signal
and the third signal, according to whether an interval is the interval
during which the second signal is being received.
10. The mobile station according to claim 6,
wherein the first signal and the third signal are dedicated channels (DCHs)
provided for each mobile station, whereas the second signal is a shared
channel (SCH) shared by a plurality of mobile stations in a time division
form.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission power control method for
conducting transmission power control of a downlink while a mobile station
is effecting a diversity handover, and a mobile station suitable for use
with this method.
2. Description of the Related Art
FIG. 1 shows a configuration of a mobile communication system such as a
portable telephone system currently in wide use. In the mobile
communication system shown in FIG. 1, the whole service area is divided
into comparatively small radio zones called "cells 1 to 5". Such a mobile
communication system includes a plurality of base stations 10.sub.1 to
10.sub.5 respectively covering the cells 1 to 5, and mobile stations
30.sub.1 to 30.sub.5 which set radio channels and communicate with the
base stations 10.sub.1 to 10.sub.5 respectively.
In such a mobile communication system, radio waves transmitted from the
base stations 10.sub.1 to 10.sub.5 are attenuated when they are propagated
through space, and they arrive at the mobile stations 30.sub.1 to
30.sub.5. The radio waves are influenced in the degree of attenuation not
only by the distances between the base stations 10.sub.1 to 10.sub.5 and
the mobile stations 30.sub.1 to 30.sub.5, but also by the configuration of
the land and buildings around the base stations 10.sub.1 to 10.sub.5 and
the mobile stations 30.sub.1 to 30.sub.5.
When the "transmission power of radio waves" (hereafter referred to as
transmission power) from the base stations 10.sub.1 to 10.sub.5 is
constant, the "reception power of radio waves" (hereafter referred to as
reception power) of the mobile stations 30.sub.1 to 30.sub.5 varies
violently according to the movement of the mobile stations 30.sub.1 to
30.sub.5. Such variation is called "fading".
Conventionally, as a technique for keeping the communication quality
constant even in an environment with fading, there is known a transmission
power control method of a feedback type (conventional first transmission
power control method) based upon the "reception quality of radio waves"
(hereafter referred to as reception quality).
To be more concrete, so as to track the variation of the propagation level
caused by fading or the like, in the conventional first transmission power
control method, the reception side (such as a mobile station) measures the
reception quality, compares the measured reception quality with a desired
value, and feeds back the comparison result to the transmission side (such
as a base station) with a sufficiently short period of radio frames, time
slots, or the like, and the transmission side adjusts the transmission
power on the basis of the comparison result.
The first transmission power control method not only mitigates the
influence of fading and keeps the reception quality constant, but also is
effective in mitigating the variation in the reception quality caused by
the location of the mobile station 30.sub.1 to 30.sub.5 in the service
area, suppressing the transmission power to the minimum, and improving
power utilization efficiency.
As a reference for the reception quality, a "signal to interference power
ratio" (SIR), "reception power", and a "result of error detection using
CRC" (cyclic redundancy check) can be utilized.
Typically, in the mobile communication system, each of the mobile stations
30.sub.1 to 30.sub.5 suitably switches base stations 10.sub.1 to 10.sub.5
to which a radio channel is established, as it moves. This operation is
called "handover".
As the "handover", the "hard handover (HHO) scheme" and the "diversity
handover (DHO) scheme" have been considered. In the hard handover (HHO)
scheme, a mobile station 30 moving across a boundary between the cells 1
to 5 instantaneously switches the base stations 10.sub.1 to 10.sub.5 to
which a radio channel is established, and a radio channel is constantly
established between the mobile station 30 and a single base station 10. In
the diversity handover (DHO) scheme, a mobile station 30 moving across a
boundary between the cells 1 to 5 establishes a radio channel between a
new base station 10.sub.2 and the mobile station 30 before opening a radio
channel between a base station 10.sub.1 under communication and the mobile
station 30 and thus the mobile station 30 temporarily communicates with a
plurality of base stations 10.sub.1 and 10.sub.2 at the same time.
The DHO scheme has an advantage over the HHO scheme that interruption is
not caused at the time of switching of the base stations 10.sub.1 to
10.sub.5.
If the mobile station 30 is located at an end of the cells 1 to 5 and the
mobile station 30 communicates with a single base station 10, then the
base station 10 needs large transmission power in order to keep the
reception quality constant, which causes problems.
In such a case, there is a possibility that sufficient reception power
capable of coping with a fall in the propagation level caused by fading
cannot be obtained in the mobile station 30.
If the DHO scheme is applied, however, then the mobile station 30 can
simultaneously receive radio waves (signals) transmitted from a plurality
of base stations 10 and combine them. As a result, the problem can be
solved.
Fading differs for each base station 10. By using the DHO scheme,
therefore, falls in the propagation level caused by fading can be
compensated for between a plurality of base stations 10. Thus there can be
obtained effects such as the stabilization of communication quality and
reduction of transmission power to the base station 10.
For the transmission scheme in the mobile communication system, there is a
"dedicated scheme" and a "shared scheme". In the "dedicated scheme", a
dedicated channel (DCH) is established for each mobile station 30. In the
"shared scheme", one (or more) shared channels (SCH) having a large
transmission capacity is prepared and a plurality of mobile stations 30
share the "SCH" in a time division form using scheduling.
The "dedicated scheme" has an advantage in that the transmission rate for
each mobile station 30 is ensured. However, the "dedicated scheme" has a
drawback in that the transmission rate for each mobile station 30 is kept
down to a low value and as many hardware resources (radio channels) as the
number of the mobile stations 30 that can communicate simultaneously are
needed.
On the other hand, the "shared scheme" has a drawback in that the
transmission rate for each mobile station 30 is not ensured. However, the
"shared scheme" has an advantage in that a high transmission rate for each
mobile station 30 can be achieved when the number of the mobile stations
30 that communicate simultaneously is small, and the required hardware
resource (radio channel) is only one "SCH".
The "dedicated scheme" is suitable for communication that varies slightly
in transmitted information content with time, makes strong demands
regarding transmission delay, and always needs a constant communication
band, such as audio communication.
On the other hand, the "shared scheme" is suitable for intermittent
communication whose transmitted information content varies greatly with
time and comparatively does not make strong demands regarding transmission
delay.
If information directed to a specific mobile station 30 exists on the SCH
in the shared scheme, then the mobile station 30 is "notified" (signaled)
to that effect. The signaling may be conducted on a dedicated DCH
established for each mobile station 30, or may be conducted on an
established SCH for signaling.
Information transmitted on the SCH for a specific mobile station 30 might
become intermittent, because a plurality of mobile stations 30 share the
SCH. If the conventional first transmission power control method is
applied using the reception quality of the SCH when controlling the
transmission power of the SCH, then the transmission power control becomes
intermittent and trouble is caused, resulting in a problem.
In order to solve this problem, the "second transmission power control
method" can be used. During an interval having a possibility that an SCH
will be transmitted to a mobile station 30, a DCH is established
incidentally for the mobile station 30 and the conventional first
transmission power control method is applied continuously by using the
reception quality of the DCH. If there is transmission of an SCH, then the
transmission power of the SCH is linked with the transmission power of the
DCH with a certain offset.
According to the second transmission power control method, the transmission
power of the SCH can be controlled indirectly by linking the transmission
power of the SCH directed to the mobile station 30 with the transmission
power of the DCH directed to the mobile station 30 as shown in FIG. 2.
In FIG. 2, the transmission power (FIG. 2B) of a "DCH (physical channel A)"
has a shape obtained by nearly inverting vertically that of a variation of
a propagation level (FIG. 2A) caused by fading or the like. As a result,
the "DCH (physical channel A)" has a constant reception quality FIG. 2C.
In other words, in FIG. 2, the variation (FIG. 2A) of the propagation level
of the "SCH (physical channel B)" is similar to the "variation of the
propagation level of the "DCH (physical channel A)". If the transmission
power (FIG. 2B) of the "SCH (physical channel B)" is linked with the
transmission power (FIG. 2B) of the "DCH (physical channel A)", then the
reception quality (FIG. 2C) of the "SCH (physical channel B)" also becomes
constant.
Such a conventional second transmission power control method can also cope
with a multi-call in which the same mobile station 30 conducts a plurality
of communication operations, such as the case where the mobile station 30
receives electronic mail while the mobile station 30 is conducting audio
communication on the DCH.
When application of the DHO scheme is considered, it becomes necessary in
the shared scheme to adjust scheduling of transmission timing between the
base stations 10.sub.1 to 10.sub.5 and consequently the control load of
the network increases.
Furthermore, in a mobile communication system in which the number of base
stations 10.sub.1 to 10.sub.5 is large and the cells 1 to 5 are
continuous, it is difficult for the mobile station 30 to adjust the
scheduling of the timing of transmission to the same mobile station 30
between a plurality of base stations 10.sub.1 to 10.sub.5.
Typically in the shared system, therefore, it is simpler to apply the HHO
scheme.
However, it is effective to apply the DHO scheme to the DCH in expectation
of no interruption occurring at the time of handover, the stabilization of
quality of the DCH, and the reduction of the transmission power required.
In such a case, one of the base stations 10 transmitting the DHOs may
transmit an SCH to a specific mobile station 30 that is conducting DHO
using a plurality of DCHs.
When the mobile station 30 is conducting DHO using specific physical
channels A, i.e., first signals (DCHs in the above described example),
there is a method of simultaneously communicating by using a different
physical channel B, i.e., a second signal (SCH in the above described
example).
As in the above described example of DCH and SCH, a base station group B
(such as 30.sub.1) transmitting the physical channel B is a subset of a
base station group A (such as 30.sub.1 to 30.sub.5) transmitting the
physical channels A. However, the base station group A does not coincide
with the base station group B in some cases.
According to the conventional second transmission power control method,
transmission power of the physical channel A and transmission power of the
physical channel B are simultaneously controlled in such a case, on the
basis of a result of a reception quality measurement of the physical
channel A obtained after a diversity combination.
In other words, in the conventional second transmission power control
method, the transmission power of the physical channel A is controlled on
the basis of the result of the reception quality measurement of the
physical channel A obtained after the diversity combination, and the
transmission power of the physical channel B is controlled indirectly by
linking with the transmission power of the physical channel A.
In the conventional second transmission power control method, the reception
quality of the physical channel A obtained after the diversity combination
is kept constant. However, the reception quality of the physical channel B
cannot be kept constant. An example is shown in FIG. 3.
FIG. 3 shows an example of the case where the base station 10.sub.1
transmits the physical channel B (SCH) to the mobile station 30.sub.2,
which is conducting DHO between two base stations, i.e., the base station
10.sub.1 and the base station 10.sub.2, using the physical channels A
(DCHs) (see FIG. 1).
The propagation level of the base station 10.sub.1 (FIG. 3A) and the
propagation level of the base station 10.sub.2 (FIG. 3B) are varied by
independent fading phenomena, respectively.
The mobile station 30.sub.2 conducts a diversity combination on received
signals of the "physical channels A (DCHs)" transmitted from the base
stations 10.sub.1 and 10.sub.2, and controls the transmission power of the
"physical channels A (DCHs)" of the base stations 10.sub.1 and 10.sub.2 so
as to keep the received signal quality obtained after the diversity
combination constant (see FIG. 3E).
The "physical channel B (SCH)" is transmitted only from the base station
10.sub.1. The transmission power of the "physical channel B (SCH)" is
controlled so as to be linked with the transmission power of the "physical
channel A (DCH)" of the base station 10.sub.1 controlled as described
above (see FIG. 3C and FIG. 3D).
Therefore, the reception quality of the "physical channel B (SCH)" received
in the mobile station 30.sub.2 does not become constant, but varies
violently.
In other words, the case where the reception quality of the "physical
channel B (SCH)" does not satisfy the "required quality of the physical
channel B" frequently occurs, and the communication quality of the
"physical channel B (SCH)" is degraded (see FIG. 3E).
Furthermore, there frequently occurs the case where although the reception
quality of the "physical channel B (SCH)" satisfies the "required quality
of the physical channel B", the reception quality of the "physical channel
B (SCH)" is unnecessarily high and the "physical channel B (SCH)" is
transmitted with excessive power (i.e., "excessive quality" state).
Excessive transmission power lowers the power utilization efficiency in
the mobile communication system, and in addition increases interference on
the surroundings. Therefore, excessive transmission power lowers the
efficiency of the whole mobile communication system.
Thus, the conventional second transmission power control method has a fatal
problem in that the reception quality of the "physical channel B (SCH)" is
degraded when the mobile station 30 is conducting DHO using the "physical
channels A (DCHs)".
Furthermore, there is a problem that the transmission power of the
"physical channel B (SCH)" becomes excessive and power utilization
efficiency in the mobile communication system is lowered. Furthermore,
this results in a problem that excessive transmission power increases
interference and lowers the efficiency of the whole mobile communication
system.
BRIEF SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a transmission
power control method that prevents communication quality degradation of
the physical channel A and the physical channel B using a simple control
without greatly altering the scale of the apparatus, when the base station
group B transmitting the physical channel B is a subset of the base
station group A transmitting the physical channels A, but the base station
group A does not coincide with the base station group B and the mobile
station is conducting DHO using the physical channels A, and to provide a
mobile station suitable for the transmission power control method.
In accordance with a first aspect of the present invention, there is
provided a transmission power control method for controlling, in a mobile
station receiving signals from a first base station and a second base
station during a diversity handover, the transmission power of the signals
from the first base station and the second base station, the transmission
power control method including a first step of receiving a first signal
and a second signal from the first base station and receiving a third
signal from the second base station, a second step of measuring a
reception quality of the first signal or the second signal, a third step
of generating a control command for controlling the transmission power of
the signals from the first base station and the second base station on the
basis of a result of the measurement of the reception quality, and a
fourth step of transmitting the control command to the first base station
and the second base station.
Preferably, in the first aspect of the present invention, in the first
step, the second signal is received intermittently, and in the second
step, the reception quality of the first signal or the second signal is
measured in an interval during which the second signal is being received,
whereas a reception quality of a signal obtained by conducting a diversity
combination on the first signal and the third signal is measured in an
interval during which the second signal is not being received.
Preferably, in the first aspect of the present invention, there is included
a step of monitoring the first signal to determine whether signaling is
occurring to notify the mobile station that the second signal is being
transmitted, and in the second step it is determined whether an interval
is an interval during which the second signal is being received, according
to whether the signaling is occurring.
Preferably, in the first aspect of the present invention, in the second
step the reception quality is measured with RAKE reception by switching
between a finger assignment to the first signal or the second signal and a
finger assignment to the first signal and the third signal, according to
whether an interval is the interval during which the second signal is
being received.
Preferably, in the first aspect of the present invention, the first signal
and the third signal are dedicated channels (DCHs) provided for each
mobile station, whereas the second signal is a shared channel (SCH) shared
by a plurality of mobile stations in a time division form.
In accordance with a second aspect of the present invention, there is
provided a mobile station for receiving signals from a first base station
and a second base station during a diversity handover, the mobile station
including a receiver configured to receive a first signal and a second
signal from the first base station and receive a third signal from the
second base station, a reception quality measurer configured to measure a
reception quality of the first signal or the second signal, a control
command generator configured to generate a control command for controlling
the transmission power of the signals from the first base station and the
second base station on the basis of a result of the measurement of
reception quality, and a transmitter configured to transmit the control
command to the first base station and the second base station.
Preferably, in the second aspect of the present invention, the receiver
receives the second signal intermittently, and the reception quality
measurer measures the reception quality of the first signal or the second
signal in an interval during which the second signal is being received,
whereas the reception quality measurer measures a reception quality of a
signal obtained by conducting a diversity combination on the first signal
and the third signal in an interval during which the second signal is not
being received.
Preferably, in the second aspect of the present invention, there is
included a monitor configured to monitor the first signal to determine
whether signaling is occurring to notify the mobile station that the
second signal is being transmitted, and the reception quality measurer
determines whether an interval is the interval during which the second
signal is being received, according to whether the signaling is occurring.
Preferably, in the second aspect of the present invention, the reception
quality measurer measures the reception quality with RAKE reception by
switching between a finger assignment to the first signal or the second
signal and a finger assignment to the first signal and the third signal,
according to whether an interval is the interval during which the second
signal is being received.
Preferably, in the second aspect of the present invention, the first signal
and the third signal are dedicated channels (DCHs) provided for each
mobile station, whereas the second signal is a shared channel (SCH) shared
by a plurality of mobile stations in a time division form.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a schematic configuration diagram of a mobile communication
system according to an embodiment of the present invention;
FIGS. 2A to 2C is a diagram showing how transmission power is controlled
according to a conventional technique;
FIGS. 3A to 3E is a diagram showing how transmission power is controlled
according to a conventional technique;
FIG. 4 is a schematic configuration diagram of a mobile station according
to an embodiment of the present invention;
FIG. 5 is a flow chart showing operation of a mobile station according to
an embodiment of the present invention;
FIGS. 6A to 6E is a diagram showing how transmission power is controlled
according to an embodiment of the present invention;
FIG. 7 is a schematic configuration diagram of a mobile station according
to an embodiment of the present invention;
FIG. 8 is a flow chart showing operation of a mobile station according to
an embodiment of the present invention; and
FIG. 9 is a diagram showing how transmission power is controlled according
to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
(Configuration of Mobile Station According to First Embodiment of Present
Invention)
A configuration of a mobile station according to a first embodiment of the
present invention will now be described with reference to the drawings.
FIG. 4 is a diagram showing a schematic configuration of a mobile station
30.sub.2 according to the present embodiment. In the present embodiment,
the mobile station 30.sub.2 is receiving "physical channels A (DCHs)",
i.e., "a first signal and a third signal" respectively from a base station
10.sub.1 and a base station 10.sub.2, and simultaneously receiving a
"physical channel B (SCH)", i.e., a "second signal" only from the base
station 10.sub.1. Propagation levels of signals from the base station
10.sub.1 and the base station 10.sub.2 are varied violently by mutually
independent fading phenomena.
When the mobile station 30.sub.2 according to the present embodiment is
conducting DHO between the base station 10.sub.1 and the base station
10.sub.2 using the "physical channels A (DCHs)", a mobile communication
system including the mobile station 30.sub.2 conducts a transmission power
control on both the "physical channel A (DCH)" and the "physical channel B
(SCH)" in a down direction (a direction directed from the base station 10
to the mobile station 30).
The mobile station 30.sub.2 is formed of, for example, a portable telephone
terminal, a PDA terminal, or the like. In the present embodiment, mobile
stations 30.sub.1 to 30.sub.5 have the same configuration. In the ensuing
description, therefore, the mobile station 30.sub.2 is handled as a
representative station.
During a diversity handover (DHO), the mobile station 30.sub.2 receives
signals ("physical channels A (DCHs)" and "physical channel B (SCH)") from
a first base station 10.sub.1 and a second base station 10.sub.2.
To be more concrete, the mobile station 30.sub.2 includes a radio antenna
31, a transceiver 32, a physical channel A receiver 33, a physical channel
A received information output 34, a physical channel B receiver 35, a
physical channel B received information output 36, a reception quality
measurer 37, a comparator 38, a transmission power control command
generator 39, a transmission information input 40, a transmission signal
generator 41, and a transmitter 42, as shown in FIG. 4.
In the present embodiment, the transceiver 32 forms a receiver configured
to receive a first signal ("physical channel A (DCH)") and a second signal
("physical channel B (SCH)") from the first base station 10.sub.1 and
receiving a third signal ("physical channel A (DCH)") from the second base
station 10.sub.2.
The reception quality measurer 37 forms a reception quality measurer
configured to measure the reception quality of the first signal ("physical
channel A (DCH)") or the second signal ("physical channel B (SCH)").
The transmission power control command generator 39 forms a control command
generator configured to generate a control command (transmission power
control command) in order to control the transmission power of a signal
from the first base station 10.sub.1 and the second base station 10.sub.2
on the basis of a measurement result of reception quality.
The transceiver 32, the transmission signal generator 41, and the
transmitter 42 form a transmitter configured to transmit the control
command (transmission power control command) to the first base station
10.sub.1 and the second base station 10.sub.2.
The transceiver 32 is connected to the radio antenna 31, the physical
channel A receiver 33, the physical channel B receiver 35, the reception
quality measurer 37, and the transmitter 42. The transceiver 32 has a
function of transmitting a transmission signal transmitted from the
transmitter 42 via the radio antenna 31. Furthermore, the transceiver 32
has a function of transferring a received signal received via the radio
antenna 31 to the physical channel A receiver 33 or the physical channel B
receiver 35, and the reception quality measurer 37.
In the present embodiment, the transceiver 32 receives the "physical
channel A (DCH)") and the "physical channel B (SCH)" from the base station
10.sub.1 and receives the "physical channel A (DCH)" from the base station
10.sub.2.
The physical channel A receiver 33 is connected to the transceiver 32 and
the physical channel A received information output 34. The physical
channel A receiver 33 conducts a diversity combination on the "physical
channels A (DCHs)" from the base station 10.sub.1 and the base station
10.sub.2 transferred from the transceiver 32.
The physical channel A receiver 33 conducts reception processing, such as
despreading, demodulation and decoding, on the diversity-combined
"physical channel A (DCH)", and reproduces the "physical channel A
received information" transmitted on the physical channel A.
Furthermore, the physical channel A receiver 33 transmits the reproduced
"physical channel A received information" to the physical channel A
received information output 34. Herein, the "physical channel A received
information" is, for example, audio information, data contents
information, and control information.
The physical channel A received information output 34 is connected to the
physical channel A receiver 33, and outputs physical channel A received
information transmitted from the physical channel A receiver 33. If the
physical channel A received information is audio information, the physical
channel A received information output 34 outputs it via a speaker. If the
physical channel A received information is data contents information, the
physical channel A received information output 34 displays it via a
display.
The physical channel B receiver 35 is connected to the transceiver 32 and
the physical channel B received information output 36. The physical
channel B receiver 35 conducts reception processing, such as despreading,
demodulation and decoding, on the "physical channel B (SCH)" from the base
station 10 transferred from the transceiver 32, and reproduces the
"physical channel B received information" transmitted on the physical
channel B.
Furthermore, the physical channel B receiver 35 transmits the reproduced
"physical channel B received information" to the physical channel B
received information output 36. Herein, the "physical channel B received
information" is, for example, audio information, data contents
information, and control information.
If the "physical channel B (SCH)" is transmitted from a plurality of base
stations 10, such as the base station 10.sub.1 and the base station
10.sub.2, then the physical channel B receiver 35 may conduct a diversity
combination on a plurality of received "physical channels B (SCHs)" and
conduct reception processing on the diversity-combined "physical channel B
(SCH)".
The reception quality measurer 37 is connected to the transceiver 32 and
the comparator 38. The reception quality measurer 37 measures the
reception quality in the mobile station 10.sub.2 using only the "physical
channel A (DCH)" or the "physical channel B (SCH)" from the base station
10.sub.1 transferred from the transceiver 32.
As the measured reception quality, the "signal to interference power ratio
(SIR), the "reception power", and the "result of error detection using the
CRC" can be mentioned. Furthermore, the reception quality measurer 37
transmits the measured reception quality to the comparator 38.
In the present embodiment, the "physical channel B (SCH)" is transmitted
only from the base station 10.sub.1. However, the application range of the
present invention is not restricted to this. For example, if the "physical
channel B (SCH)" is transmitted from a plurality of base stations 10.sub.1
to 10.sub.5 and the "physical channel A (DCH)" is transmitted from a
plurality of base stations 10.sub.1 to 10.sub.5, then it is also possible
for the reception quality measurer 37 to conduct a diversity combination
on the "physical channels A (DCHs)" from the base stations 10.sub.1 to
10.sub.5 transferred from the transceiver 32 and measure the reception
quality in the mobile station 10.sub.2 using the diversity-combined
"physical channel A (DCH)".
The comparator 38 is connected to the reception quality measurer 37 and the
transmission power control command generator 39. The comparator 38
compares the reception quality transmitted from the reception quality
measurer 37 with a predetermined desired value, and transmits a result of
the comparison to the transmission power control command generator 39.
The transmission power control command generator 39 is connected to the
comparator 38 and the transmission signal generator 41. According to the
comparison result transmitted from the comparator 38, the transmission
power control command generator 39 generates the "transmission power
control command" for controlling the transmission power of the "physical
channel A (DCH)" and the "physical channel B (SCH)" of the base station
10.sub.1 and the transmission power of the "physical channel A (DCH)" of
the base station 10.sub.2. The transmission power control command
generator 39 transmits the generated "transmission power control command"
to the transmission signal generator 41.
For example, if the reception quality (reception power) of the "physical
channel A (DCH)" is less than the desired value for the comparison result,
then the "transmission power control command" gives an order for the
transmission power of the "physical channels A (DCHs)" of the base station
10.sub.1 and the base station 10.sub.2 to be increased.
On the other hand, if the reception quality (reception power) of the
"physical channel A (DCH)" is greater than the desired value for the
comparison result, then the "transmission power control command" gives an
order for the transmission power of the "physical channels A (DCHs)" of
the base station 10.sub.1 and the base station 10.sub.2 to be decreased.
The transmission information input 40 is connected to the transmission
signal generator 41. The transmission information input 40 transfers
transmission information input by the user to the transmission signal
generator 41. The transmission information input 40 is formed of, for
example, push buttons and a touch panel type display.
The transmission signal generator 41 is connected to the transmission power
control command generator 39, the transmission information input 40, and
the transmitter 42. The transmission signal generator 41 generates a
transmission signal by multiplexing the transmission power control command
transmitted from the transmission power control command generator 39 and
the transmission information (of the up direction) transferred from the
transmission information input 40, and transmits the generated
transmission signal to the transmitter 42.
The transmitter 42 is connected to the transceiver 32 and the transmission
signal generator 41. The transmitter 42 conducts transmission processing,
such as coding, modulation and spreading, on the transmission signal
transmitted from the transmission signal generator 41, and transmits the
transmission signal subjected to the transmission processing to the
transceiver 32.
(Operation of Mobile Station According to First Embodiment of Present
Invention)
Operation of the mobile station 30.sub.2 having the above described
configuration will now be described with reference to FIG. 5.
FIG. 5 is a flow chart showing operation conducted when a mobile
communication system including a mobile station 30.sub.2 effects
transmission power control on the "physical channel A (DCH)" and the
"physical channel B (SCH)" in the down direction when the mobile station
30.sub.2 according to the present embodiment is conducting DHO between the
base station 10.sub.1 and the base station 10.sub.2 using the "physical
channel A (DCH)".
As shown in FIG. 5, the transceiver 32 receives a "physical channel A
(DCH)" and a "physical channel B (SCH)" from the base station 10.sub.1 via
the radio antenna 31 and receives a "physical channel A (DCH)" from the
base station 10.sub.2 via the radio antenna 31 at step 301. The
transceiver 32 transfers the received "physical channels A (DCHs)" and
"physical channel B (SCH)" to the physical channel A receiver 33, the
physical channel B receiver 35, and the reception quality measurer 37.
At step 302, the physical channel A receiver 33 conducts reception
processing, such as despreading, demodulation, and decoding, on the
"physical channel A (DCH)" from the base station 10.sub.1 or the base
station 10.sub.2 transferred from the transceiver 32, reproduces "physical
channel A received information" transmitted on the physical channel A, and
transmits the "physical channel A received information" thus reproduced to
the physical channel A received information output 34.
Furthermore, the physical channel B receiver 35 conducts reception
processing, such as despreading, demodulation, and decoding, on the
"physical channel B (DCH)" from the base station 10.sub.1 transferred from
the transceiver 32, reproduces "physical channel B received information"
transmitted on the physical channel B, and transmits the "physical channel
B received information" thus reproduced to the physical channel B received
information output 36.
At step 303, the physical channel A received information output 34 outputs
the "physical channel A received information" transmitted from the
physical channel A receiver 33. Furthermore, the physical channel B
received information output 36 outputs the "physical channel B received
information" transmitted from the physical channel B receiver 35.
At step 304, the reception quality measurer 37 measures the reception
quality in the mobile station 30.sub.2 using only the "physical channel A
(DCH)" or the "physical channel B (SCH)" from the base station 10.sub.1
transferred from the transceiver 32, and transmits the measured reception
quality to the comparator 38.
At step 305, the comparator 38 compares the reception quality transmitted
from the reception quality measurer 37 with a predetermined desired value,
and transmits a result of the comparison to the transmission power control
command generator 39.
At step 306, the transmission power control command generator 39 generates
a "transmission power control command" for controlling the transmission
power of the "physical channel A (DCH)" and the "physical channel B (SCH)"
to the base station 10.sub.1 and the transmission power of the "physical
channel A (DCH)" to the base station 10.sub.2 on the basis of the
comparison result transmitted from the comparator 38, and transmits the
generated "transmission power control command" to the transmission signal
generator 41.
At step 307, the transmission information input 40 transfers transmission
information input by the user to the transmission signal generator 41.
At step 308, the transmission signal generator 41 generates a transmission
signal by multiplexing the transmission power control command transmitted
from the transmission power control command generator 39 and the
transmission information (of the up direction) transferred from the
transmission information input 40, and transmits the generated
transmission signal to the transmitter 42.
At step 309, the transmitter 42 conducts transmission processing, such as
coding, modulation and spreading, on the transmission signal transmitted
from the transmission signal generator 41, and transmits the transmission
signal subjected to the transmission processing to the transceiver 32.
At step 310, the transceiver 32 transmits the transmission signal
transmitted from the transmitter 42 via the radio antenna 31.
FIG. 6 shows how the mobile station 30.sub.2 controls the transmission
power of the "physical channel A (DCH)" and "physical channel B (SCH)"
transmitted from the base station 10.sub.1 and the transmission power of
the "physical channel A (DCH)" transmitted from the base station 10.sub.2.
The propagation level of signals from the base station 10.sub.1 (FIG. 6A)
and the propagation level of signals from the base station 10.sub.2 (FIG.
6B) are varied by respective independent fading phenomena.
In FIG. 6C, the transmission power of the "physical channel A (DCH)"
transmitted from the base station 10.sub.1 to the mobile station 30.sub.2
is indicated by a solid line, whereas the transmission power of the
"physical channel B (SCH)" transmitted from the base station 10.sub.1 to
the mobile station 30.sub.2 is indicated by a broken line. In FIG. 6D, the
transmission power of the "physical channel A (DCH)" transmitted from the
base station 10.sub.2 to the mobile station 30.sub.2 is indicated by a
solid line.
Unlike the conventional technique in which the reception quality of a
signal obtained by conducting diversity a combination on the "physical
channels A (DCHs)" of the base station 10.sub.1 belonging to the base
station group B and the base station 10.sub.2 belonging to the base
station group A, is measured, the mobile station 30.sub.2 measures the
reception quality of the signal ("physical channel A (DCH)") from the base
station 10.sub.1 as described above. On the basis of a result of the
measurement, the mobile station 30.sub.2 conducts transmission power
control on the "physical channels A (DCHs)" of the base station 10.sub.1
and the base station 10.sub.2.
As shown in FIG. 6E, therefore, the reception quality (indicated by a
dotted line in FIG. 6E) of the "physical channel A (DCH)" from the base
station 10.sub.1 becomes constant at a predetermined desired value. The
transmission power of the "physical channel A (DCH)" of the base station
10.sub.1 thus compensates for the variation in the propagation level of
signals from the base station 10.sub.1.
Furthermore, the transmission power of the "physical channel B (SCH)" is
controlled so as to be linked with the transmission power of the "physical
channel A (DCH)" of the base station 10.sub.1 (see FIG. 6C).
Therefore, the reception quality (indicated by a broken line in FIG. 6E) of
the "physical channel B (SCH)" in the mobile station 30.sub.2 coincides
with a predetermined desired value and becomes constant.
The transmission power of the "physical channel A (DCH)" of the base
station 10.sub.2 is controlled in the same way as the transmission power
of the "physical channel A (DCH)" of the base station 10.sub.1. In actual
data reception, therefore, the mobile station 30.sub.2 may conduct a
diversity combination on the "physical channels A (DCHs)" of the two base
stations 10.sub.1 and 10.sub.2 (as indicated by a solid line in FIG. 6E).
In other words, it is possible to utilize only the "physical channel A
(DCHs)" from the base station 10.sub.1 in the reception quality
measurement for transmission power control and conduct a diversity
combination on the "physical channels A (DCHs)" of the base station
10.sub.1 and the base station 10.sub.2 in actual data reception.
When the diversity combination is conducted in data reception, the
reception quality of the physical channel always exceeds the predetermined
desired valued. Furthermore, the handover causes no interruption, and
stable communication can be maintained.
(Action and Effect Obtained by Mobile Station According to the First
Embodiment)
In the mobile station 30.sub.2 according to the present embodiment, the
transmission power of the "physical channel B (SCH)" in the base station
10.sub.1 is controlled on the basis of only the measurement result of the
reception quality of the "physical channel A (DCH)" or the "physical
channel B (SCH)" (which are not subjected to a diversity combination).
Even when the mobile station 30.sub.2 is conducting DHO using the
"physical channel A (DCH)", the reception quality of the "physical channel
B (SCH)" can be prevented from being degraded.
Furthermore, in the mobile station 30.sub.2 according to the present
embodiment, the problem that the transmission power in the base station
10.sub.1 becomes excessive for the above described reason and the power
utilization efficiency is lowered thereby can be solved.
Furthermore, in the mobile station 30.sub.2 according to the present
embodiment, the problem that the transmission power in the base station
10.sub.1 becomes excessive for the above described reason and that it
increases the interference and lowers the efficiency of the whole mobile
communication system can be solved.
(Configuration of Mobile Station According to the Second Embodiment)
A configuration of a mobile station 30.sub.2 according to a second
embodiment of the present invention will now be described with reference
to the drawings. FIG. 7 is a diagram showing a schematic configuration of
a mobile station 30.sub.2 according to the present embodiment.
In the present embodiment, the mobile station 30.sub.2 receives "physical
channels A (DCHs)", i.e., "a first signal and a third signal" respectively
from a base station 10.sub.1 and a base station 10.sub.2, and
simultaneously receives a "physical channel B (SCH)", i.e., a "second
signal" only from the base station 10.sub.1.
As an example, the "physical channel B" is a shared channel "SCH" whereby a
plurality of mobile stations 30.sub.1 to 30.sub.5 transmit packets in a
time division multiplex form, and the "physical channel A" is a "DCH" for
"signaling (notice)" that indicates that there is a packet being directed
to the mobile stations 30.sub.1 to 30.sub.5 on the "physical channel B
(SCH)".
In other words, the mobile station 30.sub.2 is in the DHO state between the
base station 10.sub.1 and the base station 10.sub.2. The mobile station
30.sub.2 receives "physical channels A (DCHs)" from two base stations
10.sub.1 and 10.sub.2. At the same time, the mobile station 30.sub.2
receives the "physical channel B (SCH)" from only the base station
10.sub.1 intermittently. Propagation levels of signals from the base
station 10.sub.1 and the base station 10.sub.2 are varied violently by
mutually independent fading phenomena.
In the mobile communication system, the mobile station 30.sub.2 according
to the present embodiment conducts transmission power control on both the
"physical channels A (DCHs)" and the "physical channel B (SCH)" in the
down direction when the mobile station 30.sub.2 is conducting DHO between
the base station 10.sub.1 and the base station 10.sub.2 using the
"physical channels A (DCHs)".
The mobile station 30.sub.2 according to the present embodiment has the
same basic configuration as the mobile station 30.sub.2 according to the
first embodiment does except that a control circuit 43 connected to the
physical channel A receiver 33, the physical channel B receiver 35 and the
reception quality measurer 37 is provided and the physical channel A
received information output 34 is removed.
In the present embodiment, the control circuit 43 forms monitor configured
to effect monitoring on a first signal ("physical channel A (DCH)") to
determine whether signaling is occurring as notification that a second
signal ("physical channel B (SCH)") is being transmitted to the mobile
station 30.sub.2.
Since the "physical channel A" is defined as "DCH" for "signaling
(notice)", the mobile station 30.sub.2 according to the present embodiment
has been supposed not to have the physical channel A received information
output 34. Of course, however, the mobile station 30.sub.2 according to
the present embodiment may have the physical channel A received
information output 34.
The control circuit 43 monitors the physical channel A receiver 33 to
determine whether signaling is occurring on the "physical channel A
(DCH)". If signaling is sensed, then the control circuit 43 starts
reception processing on the "physical channel B (SCH)" by activating the
physical channel B receiver 33.
When the control circuit 43 senses signaling in the physical channel A
receiver 33, the control circuit 43 orders the reception quality measurer
37 to measure the reception quality of the "physical channel A (DCH)" or
the "physical channel B (SCH)" from the base station 10.sub.1 that
transmits the "physical channel B (SCH)".
When the reception processing of the "physical channel B (SCH)" conducted
by the physical channel B receiver 35 finishes and a return to the
"physical channel B (SCH)" waiting state is effected, the control circuit
43 orders the reception quality measurer 37 to conduct a diversity
combination on "physical channels A (DCHs)" from all base stations
10.sub.1 and 10.sub.2 transmitting "physical channels A (DCHs)" and to
measure the reception quality obtained after the diversity combination.
In the case of a mobile communication system, such as a CDMA system,
capable of conducting RAKE combination, the reception quality measurer 37
conducts the RAKE combination. In this case, the reception quality
measurer 37 can measure the reception quality according to the order of
the control circuit 43 (according to whether the physical channel B (SCH)
is being received) by suitably switching fingers in the RAKE combination.
(Operation of Mobile Station According to the Second Embodiment of Present
Invention)
Operation of the mobile station 30.sub.2 having the above described
configuration will now be described with reference to FIG. 8.
FIG. 8 is a flow chart showing operation conducted when transmission power
control is effected on the "physical channel A (DCH)" and the "physical
channel B (SCH)" in the down direction when the mobile station 30.sub.2
according to the present embodiment is conducting DHO between the base
station 10.sub.1 and the base station 10.sub.2 using the "physical channel
A (DCH)".
Only operations that differ from that of the mobile station 30.sub.2
according to the first embodiment of the present invention will now be
described.
As shown in FIG. 8, the transceiver 32 receives a "physical channel A
(DCH)" and a "physical channel B (SCH)" from the base station 10.sub.1 via
the radio antenna 31 and receives a "physical channel A (DCH)" from the
base station 10.sub.2 via the radio antenna 31 at step 601. The
transceiver 32 transfers the received "physical channels A (DCHs)" and
"physical channel B (SCH)" to the physical channel A receiver 33, the
physical channel B receiver 35, and the reception quality measurer 37.
At step 602, the control circuit 43 monitors the physical channel A
receiver 33 to determine whether signaling is occurring on the "physical
channel A (DCH)". In the initial state, the reception quality measurer 37
conducts a diversity combination on "physical channels A (DCHs)" from all
the base stations 10 and 10.sub.2 transmitting the "physical channel A
(DCH)", and measures the reception quality obtained after the diversity
combination.
At step 603, if the control circuit 43 has sensed signaling on the
"physical channel A (DCH)" in the physical channel A receiver 33 ("YES" of
the step 603), then the control circuit 43 starts reception processing on
the "physical channel B (SCH)" by activating the physical channel B
receiver 35.
If the control circuit 43 has sensed signaling in the physical channel A
receiver 33 ("YES" of the step 603), then the cont
