U.S. patent application number 08/810707 was filed with the patent office on 2001-08-02 for mobile communication terminal and transmission power control method therefor.
Invention is credited to KUBO, TOKUROU, MINOWA, MORIHIKO, NAKAMURA, SATOSHI, OBUCHI, KAZUHISA, SAWADA, KENSUKE.
Application Number | 20010010686 08/810707 |
Document ID | / |
Family ID | 16951374 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010686 |
Kind Code |
A1 |
KUBO, TOKUROU ; et
al. |
August 2, 2001 |
MOBILE COMMUNICATION TERMINAL AND TRANSMISSION POWER CONTROL METHOD
THEREFOR
Abstract
A mobile communication terminal receives a control command
transmitted on a down-link from a base station and controls a
transmission power so that a reception state on an up-link becomes
approximately constant at the base station. The mobile
communication terminal is provided with a moving speed inferring
unit which infers a moving speed of the mobile communication
terminal, and a transmission power controller which varies a
varying width of the transmission power depending on the moving
speed of the mobile communication terminal.
Inventors: |
KUBO, TOKUROU;
(KAWASAKI-SHI, JP) ; MINOWA, MORIHIKO;
(KAWASAKI-SHI, JP) ; NAKAMURA, SATOSHI;
(KAWASAKI-SHI, JP) ; SAWADA, KENSUKE;
(KAWASAKI-SHI, JP) ; OBUCHI, KAZUHISA;
(KAWASAKI-SHI, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
700 11TH STREET, NW
SUITE 500
WASHINGTON
DC
20001
US
|
Family ID: |
16951374 |
Appl. No.: |
08/810707 |
Filed: |
March 3, 1997 |
Current U.S.
Class: |
370/335 ;
455/522; 455/69 |
Current CPC
Class: |
H04W 52/282
20130101 |
Class at
Publication: |
370/335 ;
455/522; 455/69 |
International
Class: |
H04B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 1996 |
JP |
8-233203 |
Claims
What is claimed is:
1. A mobile communication terminal which receives a control command
transmitted on a down-link from a base station and controls a
transmission power so that a reception state on an up-link becomes
approximately constant at the base station, said mobile
communication terminal comprising: a moving speed inferring unit
inferring a moving speed of the mobile communication terminal; and
a transmission power controller varying a varying width of the
transmission power depending on the moving speed inferred in said
moving speed inferring unit.
2. The mobile communication terminal as claimed in claim 1, wherein
said moving speed inferring unit infers the moving speed based on a
number of times a reception level on the down-link per unit link
crosses a reference level.
3. The mobile communication terminal as claimed in claim 1, wherein
said moving speed inferring unit infers the moving speed based on
an accumulated value of fluctuation values of a reception level on
the down-link per unit time.
4. The mobile communication terminal as claimed in claim 1, wherein
said moving speed inferring unit includes means for sampling
fluctuations of a reception level on the down-link at predetermined
sampling intervals, and means for inferring the moving speed based
on a number of times the fluctuations exceed a threshold value per
unit time.
5. The mobile communication terminal as claimed in claim 4, wherein
said moving speed inferring unit further includes means for
changing the predetermined sampling intervals.
6. The mobile communication terminal as claimed in claim 1,
wherein: said up-link and said down-link employ a direct sequence
code division multiple access (DS-CDMA), and said moving speed
inferring unit infers the moving speed based on one of a signal
level which is obtained by subjecting a received signal on the
down-link to a reverse spread and a correlation value of the
received signal and a spread code.
7. The mobile communication terminal as claimed in claim 1,
wherein: said up-link and said down-link employ a direct sequence
code division multiple access (DS-CDMA), a pilot signal is
transmitted on the down-link, and said moving speed inferring unit
infers the moving speed based on a frequency change of a pilot
signal which is obtained by subjecting a received signal to a
reverse spread and a demodulation.
8. The mobile communication terminal as claimed in claim 1, which
further comprises: a rake receiver; and a varying width
determination unit determining a varying width of the transmission
power based on the moving speed inferred by said moving speed
inferring unit and a path number of the down-link obtained in said
rake receiver and a path level ratio of reception levels in the
paths.
9. A transmission power control method adapted to a mobile
communication terminal which receives a control command transmitted
on a down-link from a base station and controls a transmission
power so that a reception state on an up-link becomes approximately
constant at the base station, said mobile communication terminal
including a moving speed inferring unit inferring a moving speed of
the mobile communication terminal, and a transmission power
controller varying a varying width of the transmission power
depending on the moving speed inferred in said moving speed
inferring unit, said transmission power control method comprising
the steps of: (a) employing a direct sequence code division
multiple access (DS-CDMA) on the up-link and the down-link and
transmitting a pilot signal on the up-link using an extrapolation
technique; (b) varying, in said transmission power controller, a
ratio of transmission powers of a pilot transmission signal and an
information data transmission signal on the up-link depending on
the moving speed inferred by said moving speed inferring unit; and
(c) accumulating, in the base station, control commands to be
transmitted to the mobile communication terminal and varying a
passing bandwidth of a filter which is provided with respect to a
reverse spread pilot signal on the up-link depending on an
accumulated value.
10. The transmission power control method as claimed in claim 9,
which further comprises the steps of: (d) inferring, in said moving
speed inferring unit, the moving speed based on a number of times a
reception level on the down-link per unit link crosses a reference
level.
11. The transmission power control method as claimed in claim 9,
which further comprises the steps of: (d) inferring, in said moving
speed inferring unit, the moving speed based on an accumulated
value of fluctuation values of a reception level on the down-link
per unit time.
12. The transmission power control method as claimed in claim 9,
which further comprises the steps of: (d) sampling, in said moving
speed inferring unit, fluctuations of a reception level on the
down-link at predetermined sampling intervals; and (e) inferring,
in said moving speed inferring unit, the moving speed based on a
number of times the fluctuations exceed a threshold value per unit
time.
13. The transmission power control method as claimed in claim 12,
which further comprises the steps of: (f) changing, in said moving
speed inferring unit, the predetermined sampling intervals.
14. The transmission power control method as claimed in claim 9,
which further comprises the steps of: (d) inferring, in said moving
speed inferring unit, the moving speed based on one of a signal
level which is obtained by subjecting a received signal on the
down-link to a reverse spread and a correlation value of the
received signal and a spread code.
15. The transmission power control method as claimed in claim 9,
which further comprises the steps of: (d) inferring, in said moving
speed inferring unit, the moving speed based on a frequency change
of a pilot signal which is obtained by subjecting a received signal
to a reverse spread and a demodulation.
16. The transmission power control method as claimed in claim 9,
which further comprises the steps of: (d) determining a varying
width of the transmission power based on the moving speed inferred
by said moving speed inferring unit and a path number of the
down-link obtained in a rake receiver of the mobile communication
terminal and a path level ratio of reception levels in the paths.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to mobile
communication terminals and transmission power control methods
therefor, and more particularly to a mobile communication terminal
which guarantees stable operation even when the mobile
communication terminal moves at a high speed, and to a transmission
power control method applicable to such a mobile communication
terminal.
[0002] In mobile communication systems, there are demands to
develop a system having a high frequency utilization efficiency.
Among various systems proposed, a direct sequence code division
multiple access (DS-CDMA) is regarded as the most prominent system
that can improve the communication capacity.
[0003] When the DS-CDMA is applied to the mobile communication,
received levels of up-link signals transmitted from a plurality of
mobile communication terminals must be approximately the same at a
base station. Otherwise, signal interference rates of the up-links
from each of the mobile communication terminals will not become
approximately the same, and it will be impossible to reproduce the
up-links from the mobile communication terminals due to the poor
signal interference rates.
[0004] For this reason, in the mobile communication employing the
DC-CDMA, it is essential to control the reception power of each
mobile communication terminal at a high speed with a high accuracy
and large dynamic range depending on changes in the distance from
each mobile communication terminal to the base station, the
shadowing of each mobile communication terminal caused by buildings
or the like, and instantaneous fluctuations in the multipath of
each mobile communication terminal.
[0005] The changes in the distance from the mobile communication
terminal to the base station and the shadowing similarly occur on
the up-links having different frequency bands. Hence, it is
possible to cope with the changes in the distance from the mobile
communication to the base station and the shadowing, by carrying
out an open loop control which controls the transmission level of
the up-link on which the mobile communication terminal transmits
depending on the reception level of the down-link received by the
mobile communication terminal. However, it is only possible to cope
with the instantaneous fluctuations in the multipath by a closed
loop control because the correlation between the up-link and the
down-link is low when the frequency bands greatly differ. The
closed loop control controls the transmission level of the up-link
on which the mobile communication terminal transmits by sending a
control command from the base station to the mobile communication
terminal depending on the reception level of the up-link received
by the base station.
[0006] According to the conventional DS-CDMA mobile communication
system, a receiver of the base station detects the reception level
from the mobile communication terminal which is to be controlled,
and the instantaneous SIR and bit error rate (BER) are inferred. In
addition, based on the above reception level, SIR and BER, a
control command for controlling the transmission power of the
mobile communication terminal is generated and transmitted to the
mobile communication terminal with the down signal. The
transmission rate of the control command for controlling the
transmission power must be high to such an extent that it is
possible to follow the instantaneous fluctuations in the reception
level, SIR or BER generated on the up-link. For example, according
to the standard IS-95, the control command rate is 800 bps, and an
amount of control per command is 0.5 dB.
[0007] When the mobile communication terminal is located in a
vehicle and the mobile communication terminal moves at a high
speed, the fluctuating rate of the instantaneous fluctuations
(Rayleigh fluctuations) of the multipath also becomes high, and the
fluctuation width per unit time becomes large. In order to obtain a
desired BER in such a case, the rage of the control command for
controlling the transmission power of the mobile communication
terminal must be made high compared to that of a slowly moving
mobile communication terminal. However, when the control command
rate is set high, the ratio of the control command with respect to
the entire communication capacity of the down-link becomes large,
and there was a problem in that the usable communication capacity
becomes small.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is a general object of the present invention
to provide a novel and useful mobile communication terminal and
transmission power control method therefor, in which the problems
described above are eliminated.
[0009] Another and more specific object of the present invention is
to provide a mobile communication terminal in which the
transmission power is controlled so that a reception state on an
up-link of a base station becomes approximately constant without
being affected by instantaneous fluctuations even when the mobile
communication terminal moves at a high speed, without having to
increase the transmission rate of a control command that is
transmitted from the base station to the mobile communication
terminal, and to a transmission power control method for use in
such a mobile communication terminal.
[0010] Still another object of the present invention is to provide
a mobile communication terminal which receives a control command
transmitted on a down-link from a base station and controls a
transmission power so that a reception state on an up-link becomes
approximately constant at the base station, which mobile
communication terminal comprises a moving speed inferring unit
inferring a moving speed of the mobile communication terminal, and
a transmission power controller varying a varying width of the
transmission power depending on the moving speed inferred in the
moving speed inferring unit. According to the mobile communication
terminal of the present invention, it is possible to make the
varying width of the transmission power larger as the moving speed
becomes faster and the instantaneous fluctuation becomes faster.
For this reason, it is possible to make the reception state on the
up-link of the base station approximately constant, without the
need to increase the transmission rate of the control command of
the base station. It is also possible to prevent the communication
capacity of the down-link from decreasing. Furthermore, since the
basic structure of the base station does not require modification,
it is possible to prevent the cost of the system from
increasing.
[0011] A further object of the present invention is to provide a
transmission power control method adapted to a mobile communication
terminal which receives a control command transmitted on a
down-link from a base station and controls a transmission power so
that a reception state on an up-link becomes approximately constant
at the base station, where the mobile communication terminal
includes a moving speed inferring unit inferring a moving speed of
the mobile communication terminal, and a transmission power
controller varying a varying width of the transmission power
depending on the moving speed inferred in the moving speed
inferring unit, and the transmission power control method comprises
the steps of (a) employing a direct sequence code division multiple
access (DS-CDMA) on the up-link and the down-link and transmitting
a pilot signal on the up-link using an extrapolation technique, (b)
varying, in the transmission power controller, a ratio of
transmission powers of a pilot transmission signal and an
information data transmission signal on the up-link depending on
the moving speed inferred by the moving speed inferring unit, and
(c) accumulating, in the base station, control commands to be
transmitted to the mobile communication terminal and varying a
passing bandwidth of a filter which is provided with respect to a
reverse spread pilot signal on the up-link depending on an
accumulated value. According to the transmission power control
method of the present invention, it is possible to set the
transmission power of the pilot transmission signal on the up-link
to a minimum required value depending on the moving speed of the
mobile communication terminal. In addition, it is possible to vary
the passing bandwidth of the reverse spread pilot signal on the
up-link depending on the power variation of the pilot signal on the
up-link in accordance with the moving speed of the mobile
communication terminal. Therefore, it is possible to reproduce the
pilot signal in an optimum state.
[0012] Other objects and further features of the present invention
will be apparent from the following detailed description when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a system block diagram showing a first embodiment
of a mobile communication terminal according to the present
invention;
[0014] FIG. 2 is a system block diagram showing a first embodiment
of a moving speed inferring unit;
[0015] FIG. 3 is a diagram for explaining the operation of the
first embodiment of the moving speed inferring unit;
[0016] FIG. 4 is a system block diagram showing a second embodiment
of the moving speed inferring unit;
[0017] FIGS. 5A and 5B respectively are diagrams for explaining the
operation of the second embodiment of the moving speed inferring
unit;
[0018] FIG. 6 is a system block diagram showing a third embodiment
of the moving speed inferring unit;
[0019] FIG. 7 is a diagram for explaining the operation of the
third embodiment of the moving speed inferring unit;
[0020] FIG. 8 is a system block diagram showing a modification of
the third embodiment of the moving speed inferring unit;
[0021] FIG. 9 is a diagram for explaining the operation of the
modification of the third embodiment of the moving speed inferring
unit;
[0022] FIG. 10 is a system block diagram showing a fourth
embodiment of the moving speed inferring unit;
[0023] FIG. 11 is a system block diagram showing a fifth embodiment
of the moving speed inferring unit;
[0024] FIG. 12 is a system block diagram showing the construction
of a correlation value detector shown in FIG. 11;
[0025] FIG. 13 is a system block diagram showing a sixth embodiment
of the moving speed inferring unit;
[0026] FIG. 14 is a system block diagram showing a seventh
embodiment of the moving speed inferring unit;
[0027] FIG. 15 is a system block diagram showing a part of a second
embodiment of the mobile communication terminal using a rake
receiver;
[0028] FIG. 16 is a flow chart for explaining the operation of a
varying width determination unit shown in FIG. 15;
[0029] FIG. 17 is a system block diagram showing a part of a third
embodiment of the mobile communication terminal using the rake
receiver;
[0030] FIG. 18 is a flow chart for explaining the operation of a
varying width determination unit shown in FIG. 17;
[0031] FIG. 19 is a diagram showing a DS-CDMA radio wave
propagation characteristic;
[0032] FIG. 20 is a system block diagram showing a fourth
embodiment of the mobile communication terminal according to the
present invention;
[0033] FIG. 21 is a flow chart for explaining the operation of a
transmission power controller shown in FIG. 20;
[0034] FIG. 22 is a system block diagram showing a fifth embodiment
of the mobile communication terminal according to the present
invention; and
[0035] FIG. 23 is a system block diagram for explaining a reverse
spread filter control at a base station.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] FIG. 1 shows a first embodiment of a mobile communication
terminal according to the present invention. This embodiment of the
mobile communication terminal employs a first embodiment of a
transmission power control method according to the present
invention.
[0037] In FIG. 1, a base station (BS) receives an up-link signal
transmitted from a mobile communication terminal (MS) at an antenna
12, and a reverse spread in a receiver (Rx) 14. The receiver 14
further carries out a narrow band demodulation, and outputs a
reproduced information data from a terminal 16. In addition, the
receiver 14 detects the reception level, that is, a received signal
strength indicator (RSSI), and infers an instantaneous signal
interference rate (SIR) and a bit error rate (BER). The receiver 14
supplies the RSSI, instantaneous SIR and BET to a transmission
power control command generator 18.
[0038] The transmission power control command generator 18
generates a control command for increasing or decreasing the
transmission power of the mobile communication terminal depending
on the received RSSI, instantaneous SIR and BER. For example, a
control command for increasing the transmission power is generated
when the SIR is less than or equal to a threshold value, and a
control command for decreasing the transmission power is generated
when the SIR exceeds the threshold value. The control command is
passed through a mixer 20 and is supplied to a transmitter (Tx) 22
together with information data supplied via a terminal 21. The
transmitter 22 carries out a narrow band modulation using the
information data and the control command, and further carries out a
spread modulation, thereby transmitting a down-link signal from an
antenna 24. The control command is made up of 1 bit, and a bit
value "1" indicates an increase while a bit value "0" indicates a
decrease. A transmission rate of the control command is 800 bps,
for example, and is constant.
[0039] At the mobile communication terminal, an antenna 32 receives
the down-link signal, and a receiver 34 carries out a reverse
spread and a narrow band demodulation. As a result, reproduced
information data from the receiver 34 are output via a terminal 36.
On the other hand, a reproduced control command from the receiver
34 is supplied to a transmission power controller 38. In addition,
the RSSI detected by the receiver 34 is supplied to a moving speed
inferring unit 40.
[0040] The moving speed inferring unit 40 infers the moving speed
from the change in the RSSI, and supplies the inferred speed data
to the transmission power controller 38. The transmission power
controller 38 instructs the increasing or decreasing direction of
the transmission power of a transmitter 42 based on the reproduced
control command which is periodically supplied from the receiver
34, and instructs the varying width (step quantity) based on the
speed data supplied from the moving speed inferring unit 40. The
increasing direction is indicated when the value of the reproduced
control command is "1", and the decreasing direction is indicated
when the value of the reproduced control command is "0". For
example, a varying width of 0.5 dB is indicated when the inferred
moving speed is 0 km/h, a varying width of 1.0 dB is indicated when
the inferred moving speed is 20 km/h, a varying width of 2.5 dB is
indicated when the inferred moving speed is 40 km/h, and a varying
width of 4.0 dB is indicated when the inferred moving speed is 60
km/h. If the transmission frequency is denoted by , the inferred
moving speed by v and the speed of light by C, a Doppler frequency
f.sub.D can be described by f.sub.D=v.multidot./C, and if =2 GHz,
f.sub.D=37 Hz when v=20 km/h. In other words, it is possible to
describe the inferred moving speed by the Doppler frequency
f.sub.D.
[0041] The transmitter 42 carries out a narrow band modulation
using information data supplied from a terminal 41, and further
carries out a spread modulation, thereby transmitting an up-link
signal from an antenna 24. In this state, the transmission power is
varied in steps depending on the instruction from the transmission
power controller 38.
[0042] Accordingly, the moving speed is inferred from the RSSI in
the mobile communication terminal, and the varying width of the
transmission power is varied depending on the inferred moving
speed. For this reason, even if the moving speed of the mobile
communication terminal is high and the instantaneous fluctuations
of the up-link at the base station occur at a high speed and the
fluctuation width per unit time becomes large, it is possible to
vary the transmission power of the mobile communication terminal
with a varying width matching the fluctuation width. Moreover,
since it is unnecessary to increase the control command rate, the
communication capacity that may be used will not decrease.
[0043] FIG. 2 shows a first embodiment of the moving speed
inferring unit 40. In FIG. 2, the RSSI output from the receiver 34
is supplied to a reference value detector 50 and a crossing counter
52 within the moving speed inferring unit 40. An reference value
detector 50 obtains as a reference value a root-mean-square of an
instantaneous value of the RSSI waveform indicated by a solid line
in FIG. 3, and supplies this reference value to the crossing
counter 52.
[0044] As shown in FIG. 3, the crossing counter 52 counts the
number of times the RSSI waveform crosses the reference value per
unit time. This number of times crossed (that is, the number of
crossings) for every unit time is supplied to a speed inferring
circuit 54 which converts the number of time crossed into a moving
speed, and speed data of the obtained moving speed is supplied to
the transmission power controller 38.
[0045] Because the number of crossings is counted using the
root-mean-square of the instantaneous value of the RSSI as the
reference value, the number of crossings is equal to the Doppler
frequency when the unit time is 1 second. This may be understood
from the following formula, where N.sub.RS denotes a crossing level
number, R.sub.S denotes a level, and b.sub.0 denotes an average
reception power. 1 N RS = 2 f D { ( R S / ( 2 b 0 ) } exp ( - R S /
2 b 0 ) 2
[0046] By setting the crossing level equal to the root of the
average reception power, that is R.sub.S={square root}{square root
over (b.sub.0)}, it is possible to obtain the following formula. 2
N RS , max = f D exp ( 1 / 2 ) f D
[0047] Therefore, by using a conversion table of the Doppler
frequency and the varying width in the transmission power
controller 38, it is possible to integrate the speed inferring
circuit 54 and the transmission power controller 38 into one
unit.
[0048] FIG. 4 shows a second embodiment of the moving speed
inferring unit 40. In FIG. 4, the RSSI output from the receiver 34
is supplied directly to a subtracter 56 on one hand, and is
supplied to the subtracter 56 after being delayed by 1 sampling
time in a 1 sampling delay circuit 58 on the other. The subtracter
58 obtains a fluctuation value of the RSSI for 1 sampling time.
This fluctuation value is supplied to an accumulator 60 which
accumulates absolute values of the fluctuation values per unit
time.
[0049] The RSSI waveform becomes as shown in FIG. 5A when the
moving speed is large, and the accumulated value becomes large. On
the other hand, the RSSI waveform becomes as shown in FIG. 5B when
the moving speed is small, and the accumulated value becomes small.
A speed inferring circuit 62 infers the moving speed from the
accumulated value, and supplies the obtained speed data to the
transmission power controller 38. By using a conversion table of
the accumulated value and the varying width in the transmission
power controller 38, it is possible to integrate the speed
inferring circuit 62 and the transmission power controller 38 into
one unit.
[0050] FIG. 6 shows a third embodiment of the moving speed
interring unit 40. In FIG. 6, the RSSI having a waveform indicated
by a solid line in FIG. 7 is output from the receiving 34 and is
supplied to a level detector 64. The level detector 64 detects the
level of the RSSI signal at a sampling interval T which is
specified by a sampling timer 66. The detected level is supplied to
a difference circuit 70 via a sampling circuit 68, and the
difference circuit 70 calculates a level difference during a
predetermined time .DELTA.t which is determined by the sampling
circuit 68. The calculated level difference is supplied to a
comparator 72.
[0051] The comparator 72 compares the level difference and a
predetermined threshold value received from a threshold circuit 74,
and generates and supplies a pulse to a counter 76 when the level
difference is larger than the predetermined threshold value. In
FIG. 7, portions where the level difference exceeds the
predetermined threshold value are indicated by symbols "o", and
portions where the level difference is less than or equal to the
predetermined threshold value are indicated by symbols "x". The
counter 76 counts the pulses received from the comparator 72 per
unit time, and supplies a counted value to a speed inferring
circuit 78. The speed inferring circuit 78 infers the moving speed
from the counted value, and the obtained speed data is supplied to
the transmission power controller 38. By using a conversion table
of the counted value and the varying width in the transmission
power controller 38, it is possible to integrate the speed
inferring circuit 78 and the transmission power controller 38 into
one unit.
[0052] FIG. 8 shows a modification of the third embodiment of the
moving speed interring unit 40. In FIG. 8, the RSSI having the
waveform indicated by a solid line in FIG. 9 is output from the
receiver 34 and is supplied to a level detector 64. The level
detector detects the level of the RSSI signal during a sampling
interval T.sub.1 which is specified by a sampling timer 79 or
during a sampling interval T.sub.2 specified by a sampling timer
80. The detected level is supplied to a difference circuit 70 via a
sampling circuit 68, and the difference circuit 70 calculates a
level difference during a predetermined time .DELTA.t which is
determined by the sampling circuit 68. The calculated level
difference is supplied to a comparator 72.
[0053] The comparator 72 compares the level difference and a
predetermined threshold value received from a threshold circuit 74,
and generates and supplies a pulse to a counter 76 when the level
difference is larger than the predetermined threshold value. In
FIG. 9, portions where the level difference exceeds the
predetermined threshold value are indicated by symbols "o", and
portions where the level difference is less than or equal to the
predetermined threshold value are indicated by symbols "x". The
counter 76 counts the pulses received from the comparator 72 per
unit time, and supplies a counted value to a speed inferring
circuit 78. The speed inferring circuit 78 infers the moving speed
from the counted value, and the obtained speed data is supplied to
the transmission power controller 38. In FIG. 9, the sampling
interval T.sub.1 is used since the sampling interval T.sub.2 is too
long.
[0054] In this modification, a plurality of sampling intervals are
provided and a suitable sampling interval is selectively used. For
this reason, it is possible to infer the moving speed with a high
accuracy in a wide speed range from a low speed to a high speed,
and to vary the varying width of the transmission power.
[0055] According to each of the moving speed inferring units 40
described heretofore, the moving speed is inferred from the RSSI
which is output from the receiver 34. Next, a description will be
given of embodiments of the moving speed inferring unit 40 which
infer the moving speed without the use of the RSSI.
[0056] FIG. 10 shows a fourth embodiment of the moving speed
inferring unit 40. In FIG. 10, a spread modulated signal received
by a receiver 34 of the mobile communication terminal is supplied
to a multiplier 92. The multiplier 92 also receives a reverse
spread signal and carries out a reverse spread. A reverse spread
signal output from the multiplier 92 is supplied to a speed
inferring circuit 96 via a narrow bandpass filter 94. The speed
inferring circuit 96 infers the moving speed from the level
fluctuation of the reverse spread signal, and supplies the inferred
moving speed to the transmission power controller 38. The speed
inferring circuit 96 infers that the moving speed is lower as the
level fluctuation of the reverse spread signal becomes larger.
[0057] FIG. 11 shows a fifth embodiment of the moving speed
inferring unit 40. In FIG. 11, the spread modulated signal received
by the receiver 34 of the mobile communication terminal is supplied
to a correlation value detector 98. The correlation value detector
98 also receives a spread code, and detects a correlation value of
the spread modulated signal and the spread code (signal). The
correlation value output from the correlation value detector 98 is
supplied to a speed inferring circuit 99. The speed inferring
circuit 99 infers the moving speed depending on the fluctuation of
the correlation value so that the moving speed becomes lower as the
fluctuation of the correlation value becomes larger. The inferred
moving speed is supplied from the speed inferring circuit 99 to the
transmission power controller 38.
[0058] FIG. 12 shows the construction of a matched filter which is
used as the correlation value detector 98. In FIG. 12, the spread
modulated signal input to a terminal 102 is supplied to a
multiplier 106.sub.1 and a unit delay element 104.sub.1. An output
of the unit delay element 104.sub.1 is successively supplied to
unit delay elements 104.sub.2 through 104.sub.n-1. An output of a
unit delay element 104.sub.i is supplied to a multiplier
106.sub.i+1, where i=1, 2, . . . , n-1. In addition, the spread
code input to a terminal 108 is stored in a register 110, and bits
of the spread core are supplied to the corresponding multipliers
106.sub.1 through 106.sub.n and multiplied with the spread
modulated signal or the delayed spread modulated signal. Output
values of the multipliers 106.sub.1 through 106.sub.n are added in
an adder 112, and an output of the adder 112 is output via a
terminal 114 as the correlation value. In the fourth and fifth
embodiments of the speed inferring unit 40, the varying width of
the transmission power is varied depending on the fluctuation of
the reverse spread signal or the correlation value, and thus, it is
possible to infer the moving speed even if the fluctuation of the
reception level is buried in thermal noise when the signal level at
the receiver 34 is lower than the thermal noise level of the
receiver 34.
[0059] In the DS-CDMA, a pilot signal which is used for
synchronization detection and the like is transmitted from the base
station to each of the mobile communication terminals. As methods
of transmitting the pilot signal, there are the extrapolation
technique and the interpolation technique. According to the
extrapolation technique, a pilot signal is transmitted by carrying
out a narrow band modulation using a signal having all "0" s or all
"1"s, and carrying out a spread modulation. On the other hand,
according to the interpolation technique, a pilot signal is
transmitted by inserting the pilot signal having all "0" s or all
"1"s by a time division multiplexing with information, and carrying
out a narrow band modulation and a spread modulation together with
the information data.
[0060] FIG. 13 shows a sixth embodiment of the moving speed
inferring unit 40. In this embodiment, the pilot signal is
transmitted using the extrapolation technique. In FIG. 13, the
spread modulated signal received from the receiver 34 of the mobile
communication terminal is supplied to a multiplier 120. The
multiplier 120 also receives a reverse spread code of the pilot
signal from a terminal 122, and carries out a reverse spread. A
narrow band modulated pilot signal which is output from the
multiplier 120 is supplied to a narrow band demodulator 125 via a
narrow bandpass filter 124. The narrow band demodulator 125 carries
out a narrow band demodulation with respect to the narrow band
modulated pilot signal, and an output pilot signal of the narrow
band demodulator 125 is supplied to a frequency counter 126.
[0061] The pilot signal supplied to the frequency counter 126 has
all "0" s or all "1" if no instantaneous fluctuation exists.
However, as the moving speed becomes high and the instantaneous
fluctuation becomes faster, the demodulated pilot signal value
changes from "0" to "1" and from "1" to "0", and the number of
changes becomes larger as the instantaneous fluctuation becomes
faster. The frequency counter 126 counts the frequency at which the
pilot signal value changes, and supplies a counted value to a speed
inferring circuit 128. The speed inferring circuit 128 converts the
counted value, that is, the frequency, into the moving speed, and
supplies the obtained speed data to the transmission power
controller 38.
[0062] FIG. 14 shows a seventh embodiment of the moving speed
inferring unit 40. In this embodiment, the pilot signal is
transmitted using the interpolation technique. In FIG. 14, the
spread modulated signal received by the receiver 34 of the mobile
communication terminal is supplied to a multiplier 130. This
multiplier 130 also receives from a terminal 132 a reverse spread
code of the mobile communication terminal to which the multiplier
130 belongs, and carries out a reverse spread. A narrow band
modulated signal output from the multiplier 130 is supplied to a
narrow band demodulator 135 via a narrow bandpass filter 134. The
narrow bandpass filter 135 carries out a narrow band demodulation,
and an output of the narrow bandpass filter 134 is supplied to a
pilot signal separation circuit 136. The pilot signal separation
circuit 136 separates the pilot signal which is inserted into the
reproduced information data by the interpolation technique, and
outputs reproduced information data via a terminal 138. On the
other hand, the separated pilot signal is supplied to a frequency
counter 140.
[0063] The pilot signal supplied to the frequency counter 140 has
all "0" s or all "1"s if no instantaneous fluctuation exists.
However, as the moving speed becomes high and the instantaneous
fluctuation becomes faster, the demodulated pilot signal value
changes from "0" to "1" and from "1" to "0", and the number of
changes becomes larger as the instantaneous fluctuation becomes
faster. The frequency counter 140 counts the frequency at which the
pilot signal value changes, and supplies a counted value to a speed
inferring circuit 142. The speed inferring circuit 142 converts the
counted value, that is, the frequency, into the moving speed, and
supplies the obtained speed data to the transmission power
controller 38.
[0064] Of course, in each of the embodiments of the speed interring
unit 40 shown in FIGS. 10 through 14, it is possible to integrate
the speed inferring circuit and the transmission power controller
into one unit by appropriately setting the conversion table.
[0065] If the receiver of the base station has diversity, the
varying width of the transmission power is controlled by taking
diversity information into consideration. The diversity may be
categorized into space diversity and path diversity of rake
reception. The space diversity information includes the antenna
number, while the path diversity information includes the path
synthesizing number, and the effect of suppressing the
instantaneous fluctuation of the transmission power becomes larger
as such numbers become larger, thereby making it to make the
varying width of the transmission power narrower. The mobile
communication terminal obtains the diversity information when an
access is made to the base station.
[0066] FIG. 15 shows a part of a second embodiment of the mobile
communication terminal according to the present invention using a
rake receiver as the receiver 34. This embodiment of the mobile
communication terminal employs a second embodiment of the
transmission power control method according to the present
invention.
[0067] In FIG. 15, a spread modulated signal received by a terminal
150 is supplied to rake demodulators 152.sub.1 through 152.sub.3
and to a reverse spread code reproducer 154. The reverse spread
code reproducer 154 reproduces reverse spread codes by setting
delay times dependent on each of a plurality of paths, and supplies
the reverse spread codes to the rake demodulators 152.sub.1 through
152.sub.3. The rake demodulators 152.sub.1 through 152.sub.3
respectively demodulate (reverse spread) the reverse spread codes
having mutually different delay times, and supply narrow band
modulated signals to a rake combiner 156. The rake combiner 156
synthesizes the narrow band modulated signals, and supplies a
synthesized signal to a circuit in a subsequent stage.
[0068] The reverse spread code reproducer 154 supplies path number
information of the received signal to a varying width determination
unit 160. In addition, the rake demodulators 152.sub.1 through
152.sub.3 supply the levels of the narrow band modulated signals to
the varying width determination unit 160. The varying width
determination unit 160 determines the varying width of the
transmission power depending on a path number and a path level
ratio, and supplies the varying width to the transmission power
controller 38. The path level ratio is the ratio of the reception
levels in the paths. In a case where the receiver 34 has the space
diversity in addition to the path diversity, the varying width is
varied by adding the path number and the level difference of each
path from a rake receiver which is provided in another system.
[0069] FIG. 16 is a flow chart for explaining the operation of the
varying width determination unit 160. In FIG. 16, a step S10
discriminates the path number, that is, the number of paths. If the
discriminated path number is 1, a step S12 sets the varying width
of the transmission power to 3.0 dB. If the discriminated path
number is 2, a step S14 discriminates the path level ratio .DELTA.
between the paths. If the path level ratio .DELTA. is less than 3.0
dB, a step S16 sets the varying width to 1.0 dB. If the path level
ratio .DELTA. is greater than or equal to 3.0 dB but less than or
equal to 6.0 dB, a step S18 sets the varying width to 2.0 dB.
Further, if the path level ratio .DELTA. is greater than 6.0 dB, a
step S20 sets the varying width to 3.0 dB.
[0070] In addition, if the path number discriminated in the step
S10 is 3, a step S22 discriminates the path level ratio .DELTA.
between a path m1 having the largest level and a path m2 having a
second largest level. The process advances to a step S24 if this
discriminated path level ratio .DELTA. is less than 3.0 dB, and the
process advances to a step S26 if the discriminated path level
ratio is greater than or equal to 3.0 dB but less than or equal to
6.0 dB. Further, the process advances to a step S28 if the
discriminated path level ratio .DELTA. is greater than 6.0 dB.
[0071] The step S24 discriminates the path level ratio .DELTA.
between the second largest level of the path m2 and a third largest
level of a path m3. A step S30 sets the varying width to 0.5 dB if
the path level ratio .DELTA. is less than 3.0 dB, and a step S32
sets the varying width to 1.0 dB if the path level ratio .DELTA. is
greater than or equal to 3.0 dB.
[0072] The step S26 discriminates the path level ratio .DELTA.
between the second largest level of the path m2 and the third
largest level of the path m3. A step S34 sets the varying width to
1.5 dB if the path level ratio .DELTA. is less than or equal to 6.0
dB, and a step S36 sets the varying width to 2.0 dB if the path
level ratio .DELTA. is greater than 6.0 dB.
[0073] The step S28 discriminates the path level ratio .DELTA.
between the second largest level of the path m2 and the third
largest level of the path m3. The step S36 sets the varying width
to 1.5 dB if the path level ratio .DELTA. is less than 3.0 dB, and
a step S38 sets the varying width to 3.0 dB if the path level ratio
.DELTA. is greater than or equal to 3.0 dB.
[0074] FIG. 17 shows a part of a third embodiment of the mobile
communication terminal according to the present invention using a
rake receiver as the receiver 34. This embodiment of the mobile
communication terminal employs a third embodiment of the
transmission power control method according to the present
invention.
[0075] In FIG. 17, the spread modulated signal received by a
terminal 150 is supplied to rake demodulators 152.sub.1 through
152.sub.3 and to a reverse spread code reproducer 154. The reverse
spread code reproducer 154 reproduces reverse spread codes by
setting delay times dependent on each of a plurality of paths, and
supplies the reverse spread codes to the rake demodulators
152.sub.1 through 152.sub.3. The rake demodulators 152.sub.1
through 152.sub.3 respectively demodulate (reverse spread) the
reverse spread codes having mutually different delay times, and
supply narrow band modulated signals to a rake combiner 156. The
rake combiner 156 synthesizes the narrow band modulated signals,
and supplies a synthesized signal to a circuit in a subsequent
stage.
[0076] The reverse spread code reproducer 154 supplies path number
information of the received signal to a varying width determination
unit 162. In addition, the rake demodulators 152.sub.1 through
152.sub.3 supply the levels of the narrow band modulated signals to
the varying width determination unit 162.
[0077] A moving speed inferring unit 40 receives the RSSI detected
by the rake receiver 34 and infers the moving speed from the
fluctuation of the RSSI. The inferred moving speed is supplied as
speed data to the varying width determination unit 162. The varying
width determination unit 162 sets the varying width of the
transmission power depending on the inferred moving speed, and
corrects the varying width depending on the path number and the
path level ratio. The varying width determination unit 162 supplies
the determined varying width to the transmission power controller
38.
[0078] FIG. 18 is a flow chart for explaining the operation of the
varying width determination unit 162. In FIG. 18, a step S40 sets
the varying width to 2 dB if the inferred moving speed is described
by the Doppler frequency of 10 Hz, for example, sets the varying
width to 4 dB if the Doppler frequency is 60 Hz, and sets the
varying width to 6 dB if the Doppler frequency is 120 Hz. A step
S50 discriminates the path number. If the discriminated path number
is 1, a step S52 makes no correction of the varying width. If the
discriminated path number is 2, a step S54 discriminates the path
level ratio .DELTA.. If the discriminated path level ratio .DELTA.
is less than 3.0 dB, a step S56 corrects the varying width by
adding -1.0 dB to the set value. If the discriminated path level
ratio .DELTA. is greater than or equal to 3.0 dB but is less than
or equal to 6.0 dB, a step S58 corrects the varying width by adding
-0.5 dB to the set value. Further, if the discriminated path level
ratio .DELTA. is greater than 6.0 dB, a step S60 makes no
correction of the varying width.
[0079] If the discriminated path number in the step S50 is 3, a
step S62 discriminates the path level ratio .DELTA. between the
path m1 having the largest level and the path m2 having the second
largest level. The process advances to a step S64 if the
discriminated path level ratio .DELTA. in the step S62 is less than
3.0 dB, and to a step S66 if the discriminated path level ratio
.DELTA. is greater than or equal to 3.0 dB but less than or equal
to 6.0 dB. The process advances to a step S76 if the discriminated
path level ratio .DELTA. in the step S62 is greater than 6.0
dB.
[0080] The step S64 discriminates the path level ratio .DELTA.
between the path m2 having the second largest level and the path m3
having the third largest level. If the discriminated path level
ratio .DELTA. in the step S64 is less than 3.0 dB, a step S70
corrects the varying width by adding -1.5 dB to the set value. On
the other hand, if the discriminated path level ratio A in the step
S64 is greater than or equal to 3.0 dB, a step S72 corrects the
varying width by adding -1.0 dB to the set value.
[0081] The step S66 discriminates the path level ratio .DELTA.
between the path m2 having the second largest level and the path m3
having the third largest level. If the discriminated path level
ratio .DELTA. in the step S66 is greater than 6.0 dB, the step S76
makes no correction of the varying width. On the other hand, if the
discriminated path level ratio .DELTA. in the step S66 is less than
or equal to 6.0 dB, a step S74 corrects the varying width by adding
-0.5 dB to the set value.
[0082] In FIG. 18, it is assumed for the sake of convenience that
the varying width is variable in steps of 0.5 dB, however, the
varying steps is of course not limited to such. In addition, the
path level ratios among the paths m1, m2 and m3 and the varying
widths are not limited to those used in FIG. 18.
[0083] FIG. 19 shows a radio wave propagation characteristic of the
DS-CDMA. In FIG. 19, the Rayleigh distribution is indicated by a
solid line. A broken line Ia indicates a characteristic curve for a
case where the bandwidth is 1 MHz, a broken line Ib indicates a
characteristic curve for a case where the bandwidth is 4 MHz, a
broken line Ic indicates a characteristic curve for a case where
the bandwidth is 8 MHz, and a broken line Id indicates a
characteristic curve for a case where the bandwidth is 16 MHz. As
may be seen from FIG. 19, the characteristic curve changes towards
a direction in which the distribution width becomes smaller from
the Rayleigh distribution as the bandwidth becomes wider. For this
reason, it is possible to make the transmission power controller of
the mobile communication terminal recognize the transmission and
reception bandwidth when making a communication, so that the
transmission power controller controls the varying width by
itself.
[0084] FIG. 20 shows a fourth embodiment of the mobile
communication terminal according to the present invention. This
embodiment of the mobile communication terminal employs a fourth
embodiment of the transmission power control method according to
the present invention. In FIG. 20, those parts which are the same
as those corresponding parts in FIG. 1 are designated by the same
reference numerals.
[0085] In FIG. 20, a mobile communication terminal (MS) receives a
down-link signal by an antenna 32, and carries out a reverse spread
and a narrow band demodulation in a receiver 34. Reproduced
information data obtained in the receiver 34 are output via a
terminal 36. In addition, a reproduced control command obtained in
the receiver 34 is supplied to a transmission power controller 164.
The receiver 34 also detects the RSSI, and the detected RSSI is
supplied to a moving speed inferring unit 40.
[0086] The moving speed inferring unit 40 infers the moving speed
from the change in the RSSI, and supplies the inferred moving speed
as speed data to the transmission power controller 164. The
transmission power controller 164 instructs the increasing or
decreasing direction of the transmission power of a transmitter 42
based on the reproduced control command which is periodically
supplied from the receiver 34. In addition, the transmission power
controller 164 instructs the varying width (step quantity) of the
transmission power of the transmitter 42 based on the speed data
supplied from the moving speed inferring unit 40. For example, the
increasing direction of the transmission power is indicated when
the reproduced control command has a value "1", and the decreasing
direction of the transmission power is indicated when the
reproduced control command has a value "0". In addition, the
varying width is set to 0.5 dB when the inferred moving speed
(Doppler frequency) is 0 km/h (0 Hz), set to 1.0 dB when the
inferred moving speed (Doppler frequency) is 20 km/h (37 Hz), set
to 2.5 dB when the inferred moving speed (Doppler frequency) is 40
km/h (74 Hz), and set to 4.0 dB when the inferred moving speed
(Doppler frequency) is 60 km/h (111 Hz), for example. Further, the
transmission power controller 164 corrects the varying width
depending on spread bandwidth information which is supplied from a
terminal 166, and supplies a corrected varying width to the
transmitter 42.
[0087] The transmitter 42 carries out a narrow band modulation
using information data supplied from a terminal 41, and further
carries out a spread modulation to transmit an up-link signal from
an antenna 24. In this state, the transmission power of the
transmitter 42 is varied in steps depending on the instruction from
the transmission power controller 164.
[0088] FIG. 21 is a flow chart for explaining the operation of the
transmission power controller 164. In FIG. 21, a step S80 sets the
varying width depending on the inferred moving speed which is
supplied from the moving speed inferring unit 40. Then, a step S82
discriminates a spread bandwidth Bw. More particularly, the step
S82 discriminates whether the spread bandwidth Bw is less than or
equal to 1 MHz, greater than 1 MHz but less than or equal to 4 MHz,
greater than 4 MHz but less than or equal to 8 MHz or, greater than
8 MHz.
[0089] A step S84 makes no correction of the varying width if the
discriminated spread bandwidth Bw is less than or equal to 1 MHz. A
step S86 corrects the varying width by adding -0.5 dB to the set
value if the discriminated spread bandwidth Bw is greater than 1
MHz bit less than or equal to 4 MHz. A step S88 corrects the
varying width by adding -1.0 dB to the set value if the
discriminated spread bandwidth Bw is greater than 4 MHz but less
than or equal to 8 MHz. In addition, a step S90 corrects the
varying width by adding -1.5 dB to the set value if the
discriminated spread bandwidth Bw is greater than 8 MHz. It is
assumed for the sake of convenience that the varying width is
variable in steps of 0.5 dB in this embodiment.
[0090] Next, a description will be given of a fifth embodiment of
the mobile communication terminal according to the present
invention. This embodiment of the mobile communication terminal
employs a fifth embodiment of the transmission power control method
according to the present invention. This embodiment is applied to a
system which transmits the pilot signal from the mobile
communication terminal to the base station using the extrapolation
technique.
[0091] FIG. 22 shows the fifth embodiment of the mobile
communication terminal. In FIG. 22, a moving speed inferring unit
40 of a mobile communication terminal (MS) infers the moving speed
from the RSSI or the like detected by a receiver 34, and the
inferred moving speed is supplied as speed data to a transmission
power controller 168. The transmission power controller 168
variably controls the transmission power of a sum of an information
data transmission signal and a pilot transmission signal, similarly
to the transmission power controller 38 shown in FIG. 1. In
addition, the transmission power controller 168 varies the ratio of
the transmission power of the information data transmission signal
with respect to the transmission power of the pilot transmission
signal. In order to carry out such a control, the transmission
power controller 168 supplies a control signal with respect to an
attenuator 170 which receives the information data signal and
supplies a control signal with respect to an attenuator 172 which
receives the pilot transmission signal, so that the ratio of the
transmission power of the pilot transmission signal becomes larger
as the inferred moving speed becomes faster and the rate of the
transmission power of the pilot transmission signal becomes smaller
as the inferred moving speed becomes slower. The information data
transmission signal passed through the attenuator 170 and the pilot
transmission signal passed through the attenuator 172 are mixed in
a mixer 174 and transmitted from an antenna 178.
[0092] The slower the moving speed, the narrower the narrow
bandwidth of the pilot signal becomes at the base station for use
in inferring the transmission path and detecting synchronization.
Hence, the bandwidth of a filter (reverse spread filter) which
separates the band of the reverse spread pilot signal can be made
narrow, and a correct transmission path can be inferred at a low
transmission power. As the moving speed becomes faster, the phase
variation in the transmission path becomes larger, and it is
necessary to make the transmission power higher because the
bandwidth of the reverse spread filter for the pilot signal becomes
wider.
[0093] In this embodiment, the moving speed of the mobile
communication terminal is inferred in a moving speed inferring unit
180 of the base station (BS) based on the RSSI, the correlation
value, the reverse spread signal level or the like. This moving
speed inferring unit 180 controls the number of taps (stages) of a
filter (reverse spread filter) 182 which separates the band of the
reverse spread pilot signal so as to vary the passing bandwidth of
the filter 182.
[0094] FIG. 23 shows a reverse spread filter control at the base
station. In FIG. 23, a signal received by an antenna 12 is supplied
to a receiver 14, and is then supplied to a multiplier 192 which is
provided to carry out a reverse spread. The multiplier 192
multiplies the received signal and a reverse spread code of a pilot
signal of an arbitrary mobile communication terminal, and supplies
a reverse spread signal to a filter 194. Of course, a plurality of
other multipliers are provided to carry out a reverse spread of the
pilot signal and the information data on the up-link of each of the
mobile communication terminals. The RSSI, instantaneous SIR and BER
detected in the receiver 14 are supplied to a transmission power
control command generator 18 which generates a control command for
increasing or decreasing the transmission power of the mobile
communication terminal. For example, the control command has a
value "1" when instructing an increase of the transmission power,
and has a value "0" when instructing a decrease of the transmission
power. This control command is transmitted on the down-link
together with the information data, and is also supplied to a data
accumulator 196.
[0095] The data accumulator 196 is made up of an up-down counter,
and carries out an accumulation by making an up-count when the
control command has the value "1" and making a down-count when the
control command has the value "0". An accumulated data from the
data accumulator 196 is supplied to a speed inferring unit 198, and
the moving speed is inferred as being higher as the accumulated
data becomes larger. A filter tap controller 200 controls the
number of taps (stages) of the filter 194 by increasing the number
of taps as the inferred moving speed becomes lower, so as to narrow
the passing bandwidth.
[0096] Further, the present invention is not limited to these
embodiments, but various variations and modifications may be made
without departing from the scope of the present invention.
* * * * *