CDMA type mobile communication system capable of realizing soft handoff between cells having different cell diameters

Each radio base station (12-1, 12-2) receives an upward communication channel signal from a mobile station (13-2), calculates a transmission power control signal on the basis of the upward communication channel signal, and transmits the transmission power control signal. A host station (11A) receives the transmission power control signals from the radio base stations as received transmission power control signals, selects, as a selected transmission power control signal, one of the received transmission power control signals that makes upward transmission power for the mobile station the lowest power level, and transmits the selected transmission power control signal to a particular one of the radio base stations that communicates with the mobile station. The particular radio base station receives the selected transmission power control signal and transmits the selected transmission power control signal. The mobile station receives the selected transmission power control signal and controls the upward transmission power on the basis of the selected transmission power control signal.

BACKGROUND OF THE INVENTION 
This invention relates to a mobile communication system and, in particular, 
to transmission power control of a upward communication channel on soft 
handoff peculiar to a CDMA (code division multiple access) type mobile 
communication system. 
As is well known in the art, various multiple access types have been 
adopted in a mobile communication system. One of the multiple access types 
is a CDMA type. The CDMA type mobile communication system assigns to each 
channel with a particular code, transmits to the same repeater a modulated 
wave to which a carrier having the same carrier frequency is 
spectrum-spread with the code, establishes code synchronization in each 
receiving side, and identifies a desired channel. The CDMA type mobile 
communication system may be called a SSMA (spread spectrum multiple 
access) type mobile communication system. 
The CDMA type mobile communication system comprises a plurality of 
terminals (mobile stations) and a plurality of radio base stations each of 
which serving as a repeater. Each radio base station is called a base 
transceiver station in the art. As described above, inasmuch as the 
plurality of terminals carry out communication using the carrier with the 
same carrier frequency, it is necessary for the CDMA type mobile 
communication system to uniformly receive energy of the upward 
communication channel from each terminal communicating with the radio base 
station without a position of the terminal. 
In order uniformly receive energy in the radio base station, the CDMA type 
mobile communication system carries out transmission power control for the 
upward communication channel as described in TIA (Telecommunication 
Industry Association)/EIA (Electronic Industries Association)/IS-95. 
It is assumed that a specific terminal carries out soft hand-off with radio 
base stations covering cells having different cell diameters. In addition, 
it is assumed that the specific terminal provides access to a particular 
radio base station covering the cell having a relatively larger cell 
diameter to depart from an area of soft hand-off. In this event, when an 
upward transmission power is controlled by a conventional transmission 
power control method, the specific terminal rapidly raises transmission 
power therefor. This is because the specific terminal communicates with 
the particular radio base station alone. In other words, the specific 
terminal can receive a downward communication channel signal from the 
particular radio base station alone. Under the circumstances, other radio 
base stations covering the cells each having a relatively small cell 
diameter receive larger interference energy from the specific terminal 
than those from other terminals communicating therewith. In other words, 
reception ratio Eb/N0 for each other terminal is less than a reference 
ratio Eb/N0. As a result, each of the other terminals raise their upward 
transmission power so that the reception ratio Eb/N0 is equal to the 
reference ratio Eb/N0. This means that interference energy in the cell 
having the relatively small cell diameter is further raised and it results 
in decreasing subscriber capacity held in the cell having the relatively 
small cell diameter. In addition, inasmuch as it is necessary for each 
other of the other terminals covering the cell having the relatively small 
cell diameter to raise its upward transmission power, it results in 
increasing consumed power in each other terminal and in shortening the 
life of its battery. 
Various mobile communication systems related to the present invention are 
already known. By way of example, Japanese Unexamined Patent Publication 
of Tokkai No. Hei 5-252,098 or JP-A 5-252,098 discloses a mobile 
communication system which is capable of covering entirely a town and a 
premises with large traffic and a suburb and a thinly populated area with 
small traffic, using the frequency utilizing efficiently, and suppressing 
increase in the traffic due to hand-off. According to JP-A 5-252,098, the 
mobile communication system comprises a plurality of cells each of which 
has at least one radio base station in which mobile stations move in an 
area covered by the cells. The plurality of cells are made up of cells 
having various radii from a minimum cell to a maximum cell. In addition, 
each mobile station comprises means for varying its transmission power in 
accordance with the size of the cell. Specifically, each mobile station 
comprises a transmitter section which includes a variable amplifier for 
increasing and decreasing an amplitude of a signal in accordance with a 
control signal. However, JP-A 5-252,098 only discloses that each mobile 
station varies its transmission power in accordance with the size of the 
cell and is entirely different from a technical idea to vary an upward 
transmission power of each mobile station in accordance with reception 
energy in a radio base station from the mobile station (in other words, in 
accordance with a distance between the radio base station and the mobile 
station). In addition, JP-A 5-252,098 does not concretely explain how to 
generate the control signal supplied to the variable amplifier in the 
transmitter section of the mobile station. 
Another example is disclosed in U.S. Pat. No. 4,613,990 issued to Samuel W. 
Halpern. According to Halpern, power levels in first and second stations 
in a cellular radiotelephone system are dynamically adjusted from only one 
of them. The second station receives signals from the first and, on the 
basis of the level of those signals, first adjusts its own transmitter 
power level to be within a predetermined range and then directs the 
adjustment of the power level of the first station to be within a 
predetermined range. Parameters used in processing call handoffs are also 
adjusted to correspond to the power level adjustments to prevent false 
handoffs due to the power level changes. However, Halpern does not 
perceive the above-mentioned problems in a case where a mobile station 
departs from an area of soft hand-off and therefore does not provide means 
for solving the above-mentioned problems. 
Japanese Unexamined Patent Publication of Tokkai No. Hei 4-290,098 or JP-A 
4-290,098 discloses a mobile communication system which is capable of 
performing mobile switching without interrupting speech even when the 
service area of a base station is changed while the speech is being 
performed in the mobile communication system for broad band cordless 
telephone in building connected to an exchange and city area. According to 
JP-A 4-290,098, the above-mentioned purpose can be attained by learning a 
cell boundary line where electric field strength between base stations are 
set equal by a central station in advance, and calculating the position 
and the travel speed of mobile machines by measuring the electric field 
strength of the mobile machines. In such a way, (a) the arithmetic rule of 
the mobile machine can be simplified even in the building in which cell 
shape is complicated, and (b) urgency can be decided by calculating a time 
when the mobile machine arrives at the boundary line, which reduces 
arithmetic processing quantity, and also, (c) it is possible to realize 
soft mobile switching for the switching of the base station with a simple 
arithmetic rule and to improve speech quality. However, JP-A 4-290,098 
only discloses technique to perform mobile switching without interrupting 
speech even when the mobile machine changes the service area of the base 
station during telephone conversation and is entirely different from a 
technical idea to control an upward transmission power of each mobile 
machine. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a CDMA type mobile 
communication system which is capable of realizing soft hand-off among 
cells having different cell diameters although it is necessary to change a 
cell diameter of each cell due to traffic density. 
It is another object of this invention to provide a mobile communication 
system which is capable of inhibiting subscriber capacity held in a cell 
from decreasing. 
It is still another object of this invention to provide a mobile 
communication system of the type described, which is capable of decreasing 
consumed power in each terminal by lowering its upward transmission power. 
It is yet another object of this invention to provide a mobile 
communication system of the type described, which is capable of 
lengthening the life of battery in each terminal. 
Other objects of this invention will become clear as the description 
proceeds. 
According to an embodiment of the invention a mobile communication system 
comprises a plurality of radio base stations covering respective service 
areas, at least one mobile station moving in the service areas to carry 
out radio communication between the mobile station and the radio base 
stations, and a host station connected to the radio base stations. 
According to this invention, each of the radio base stations comprises 
means for receiving an upward communication channel signal from the mobile 
station, means for calculating, on the basis of the upward communication 
channel signal, a transmission power control signal for controlling 
transmission power for the mobile station, and means for transmitting the 
transmission power control signal to the host station. The host station 
comprises means for receiving the transmission power control signals from 
the radio base stations as received transmission power control signals, 
means for selecting, as a selected transmission power control signal, one 
of the received transmission power control signals that makes the 
transmission power for the mobile station the lowest power level, and 
means for transmitting the selected transmission power control signal to a 
particular one of the radio base stations that communicates with the 
mobile station. Each of the radio base stations comprises means for 
receiving the selected transmission power control signal from the host 
station and means for transmitting the selected transmission power control 
signal to the mobile station. The mobile station comprises means for 
receiving the selected transmission power control signal from the radio 
base station communicating with the mobile station and means for 
controlling the transmission power on the basis of the selected 
transmission power control signal. 
According to another aspect of this invention, a mobile communication 
system comprises a plurality of radio base stations covering respective 
service areas and at least one mobile station moving in the service areas 
to carry out radio communication between the mobile station and the radio 
base stations. According to this invention, each of the radio base 
stations comprises means for receiving an upward communication channel 
signal from the mobile station, means for calculating, on the basis of the 
upward communication channel signal, a transmission power control signal 
for controlling transmission power for the mobile station, means for 
transmitting the transmission power control signal to the radio base 
stations, means for receiving the transmission power control signals from 
the radio base stations as received transmission power control signals, 
means for selecting, as a selected transmission power control signal, one 
of the received transmission power control signals that makes the 
transmission power for the mobile station the lowest power level, and 
means for transmitting the selected transmission power control signal to 
the mobile station. The mobile station comprises means for receiving the 
selected transmission power control signal from the radio base station 
communicating therewith and means for controlling the transmission power 
therefor on the basis of the selected transmission power control signal. 
According to yet another aspect of this invention, a method of controlling 
transmission power for a mobile station for use in a mobile communication 
system comprising a plurality of radio base stations covering respective 
service areas and a host station connected to the radio base stations. The 
mobile station moves in the service areas to carry out radio communication 
between the mobile station and the radio base stations. According to this 
invention, the above-understood method comprises the steps of: receiving, 
in each of the radio base stations, an upward communication channel signal 
from the mobile station; calculating, in each of the radio base stations, 
a transmission power control signal for controlling the transmission power 
of the mobile station on the basis of the upward communication channel 
signal; transmitting the transmission power control signal from each of 
the radio base stations to the host station; receiving, in the host 
station, the transmission power control signals from the radio base 
stations as received transmission power control signals; selecting, in the 
host station, as a selected transmission power control signal, one of the 
received transmission power control signals that makes the transmission 
power for the mobile station the lowest power level; transmitting, from 
the host station, the selected transmission power control signal to a 
particular one of the radio base stations that communicates with the 
mobile station; receiving, in the particular one of the radio base 
stations, the selected transmission power control signal from the host 
station; transmitting, from the particular one of the radio base stations, 
the selected transmission power control signal to the mobile station; 
receiving, in the mobile station, the selected transmission power control 
signal from the particular one of the radio base stations; and 
controlling, in the mobile station, the transmission power on the basis of 
the selected transmission power control signal. 
According to another aspect of this invention, a method of controlling 
transmission power for a mobile station for use in a mobile communication 
system comprising a plurality of radio base stations covering respective 
service areas is described. The mobile station moves in the service areas 
to carry out radio communication between the mobile station and the radio 
base stations. According to this invention, the afore-mentioned method 
comprises the steps of: receiving, each of the radio base stations, an 
upward communication channel signal from the mobile station; calculating, 
each of the radio base stations, a transmission power control signal for 
controlling the transmission power for the mobile station on the basis of 
the upward communication channel signal; transmitting the transmission 
power control signal from each of the radio base stations to the radio 
base stations; receiving, in each of radio base stations, the transmission 
power control signals from the radio base stations as received 
transmission power control signals; selecting, in each of radio base 
stations, as a selected transmission power control signal, one of the 
received transmission power control signals that makes the transmission 
power of the mobile station the lowest power level; transmitting the 
selected transmission power control signal from each of the radio base 
stations to the mobile station; receiving, in the mobile station, the 
selected transmission power control signal from the radio base station 
communicating therewith; and controlling, in the mobile station, the 
transmission power on the basis of the selected transmission power control 
signal. 
On describing the gist of a further aspect of this invention, it is 
possible to understand that a radio base station carries out radio 
communication with a mobile station in a mobile communication system. The 
radio base station is connected to a host station in the mobile 
communication system. According to this invention, the above-mentioned 
radio base station comprises means for receiving an upward communication 
channel signal from the mobile station, means for calculating, on the 
basis of the upward communication channel signal, a transmission power 
control signal for controlling transmission power for the mobile station, 
means for transmitting the transmission power control signal to the host 
station, means for receiving a selected transmission power control signal 
from the host station, and means for transmitting the selected 
transmission power control signal to the mobile station. 
According to a further aspect of this invention, a host station for use in 
a mobile communication system comprises a plurality of radio base stations 
each described above. According to this invention, the abovementioned host 
station comprises means for receiving the transmission power control 
signals from the radio base stations as received transmission power 
control signals, means for selecting, as the selected transmission power 
control signal, one of the received transmission power control signals 
that makes the transmission power for the mobile station the lowest power 
level, and means for transmitting the selected transmission power control 
signal to a particular one of the radio base stations that communicates 
with the mobile station. 
According to a yet a further aspect of this invention, a radio base station 
carries out radio communication with a mobile station in a mobile 
communication system. The radio base station is one of a plurality of 
radio base stations in the mobile communication system. According to this 
invention, the above-mentioned radio base station comprises means for 
receiving an upward communication channel signal from the mobile station, 
means for calculating, on the basis of the upward communication channel 
signal, a transmission power control signal for controlling transmission 
power for the mobile station, means for transmitting the transmission 
power control signal to the radio base stations, means for receiving the 
transmission power control signals from the radio base stations as 
received transmission power control signals, means for selecting, as a 
selected transmission power control signal, one of the received 
transmission power control signals that makes the transmission power for 
the mobile station the lowest power level, and means for transmitting the 
selected transmission power control signal to the mobile station.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a conventional CDMA type mobile communication system 
will be described in order to facilitate an understanding of the present 
invention. The illustrated CDMA type mobile communication system comprises 
a host station 11, first through n-th radio base stations 12'-1, 12'-2, . 
. . , and 12'-n, and a plurality of terminals or mobile stations (only one 
terminal (or mobile station) 13 is illustrated in the drawing), where n 
represents an integer which is not less than two. The host station 11 is 
called a base station controller in the art while the radio base station 
is called a base transceiver station in the art. 
The host station 11 comprises a host station speech coding/decoding section 
14 and a speech frame signal selecting section 15. The host station 11 is 
connected to the first through the n-th radio base stations 12'-1 to 
12'-n. The first base station 12'-1 comprises m first channel control 
sections 30'-1-1, 30'-1-2, . . . , and 30'-1-2, a first base station 
transmitter (TX) 40-1, a first base station receiver (RX) 50-1, and a 
first base station antenna 60-1, where m represents an integer which is 
not less than two. Although illustration is omitted, the second through 
the n-th radio base stations 12'-2 to 12'-n are similar in structure to 
the first radio base station 12'-1. A second and an n-th channel antennas 
60-1 and 60-n alone are illustrated. The first through the n-th radio base 
stations 12'-1 to 12'-n cover first through n-th service areas (not 
shown), respectively. The terminal 13 moves in the first through the n-th 
service areas to communicate with the first through the n-th radio base 
stations 12'-1 to 12'-n. 
The following is a description of the operation of the CDMA type mobile 
communication system illustrated in FIG. 1. 
Transmitted from the terminal 13 to the host station 11 through the first 
radio base station 12'-1, an upward communication channel signal is sent 
via the first antenna 60-1 to the first base station receiver 50-1 to be 
demodulated. Demodulated by the first base station receiver 50-1, a 
demodulated signal is decoded by either one of the m first channel control 
sections, for example, the first channel control section 30'-1-1 to obtain 
a first base station output speech frame signal 300 as illustrated in FIG. 
2. The speech frame signal 300 comprises speech data 310 and speech data 
signal quality information 320 as shown in FIG. 2. Produced by the first 
radio base station 12'-1, the first base station output speech frame 
signal 300 is sent to the host station 11 as a first host input speech 
frame signal via a communication line connecting the first base station 
12'-1 with the host station 11. 
Sent to the host station 11, the first host input speech frame signal 300 
is supplied via the speech frame signal selecting section 15 to the host 
station speech coding/decoding section 14 to be converted to a host output 
speech signal. The speech frame signal selecting section 15 selects, as a 
selected speech frame signal, one of the host input speech frame signals 
300 sent from the first through the n-th radio base stations 12'-1 to 
12'-n that has the best signal quality on the basis of the speech data 
signal quality information 320. The speech frame signal selecting section 
15 sends the selected speech frame signal to the host speech 
coding/decoding section 14. The host input speech frame signals 300 are 
sent to the speech frame signal selecting section 15 from at least two of 
the first through the n-th radio base stations 12'-1 to 12'-n on soft 
hand-off where the terminal 13 communicates therewith. 
In the CDMA type mobile communication system of the CDMA system where a 
plurality of terminals communicate using a carrier having the same carrier 
frequency, the soft hand-off is not the only means for decreasing upward 
interference by inhibiting transmission power in an upward communication 
channel from the terminal which lies of the boundary of the service area 
of each radio base station but means for decreasing downward interference 
by inhibiting transmission power in downward communication channels from 
the radio base stations can also be used. 
Attention is directed to a signal sent from the host station 11 to the 
terminal 13 via the first radio base station 12'-1. At first, a host input 
speech signal is converted by the host station speech coding/decoding 
section 14 into a host output speech frame signal. The host output speech 
signal is sent, as a first base station input speech frame signal, to the 
first channel control section 30'-1-1 of the first radio base station 
12'-1 connected to the host station 11. The first base station input 
speech frame signal is coded by the first channel control section 30'-1-1, 
modulated by the first base station transmitter 40-1, and transmitted, as 
a first downward communication channel signal, to the terminal 13 from the 
first base station antenna 60-1 using a downward communication channel. 
Referring to FIGS. 3 and 4, an upward transmission power control in an 
upward communication channel. FIG. 3 is a block diagram of the first radio 
base station 12'-1 with only the channel control section 30'-1-1 for use 
in communicating with the terminal 13 picked up among the m first channel 
control sections 30'-1-1 to 30'-1-m in order to describe a method of an e 
upward transmission power control of the upward communication channel in 
detail. FIG. 4 is a block diagram of the terminal 13. 
As shown in FIG. 3, the channel control section 30 (suffix omitted) of the 
radio base station 12' (suffix omitted) comprises a channel main control 
section 31, a channel encoding section 32, a channel decoding section 33, 
a transmission power control section 34, a channel downward spreading code 
generating section 35, a channel upward spreading code generating section 
36, a channel output multiplier 3A, and a channel input multiplier 3B. 
As shown in FIG. 4, the terminal 13 comprises a terminal antenna 71, a 
terminal receiver 72, a terminal transmitter 73, an output gain control 
section 74, a terminal downward spreading code generating section 75, a 
terminal decoding section 76, a terminal encoding section 77, a terminal 
upward spreading code generating section 78, a terminal speech 
coding/decoding section 79, and first through third multipliers 7A, 7B, 
and 7C. 
Referring to FIG. 3, the radio base station 12' receives an upward 
communication channel signal from the terminal 13 by the base station 
antenna 60 (suffix omitted), and the upward communication channel signal 
is demodulated by the base station receiver 50 (suffix omitted) into a 
base station demodulated signal. Supplied from the base station receiver 
50, the base station demodulated signal is correlation demodulated using a 
terminal intrinsic spreading code by the channel input multiplier 3B into 
a base station correlation demodulated signal and then the base station 
correlation demodulated signal is supplied to the transmission power 
control section 34 and the channel decoding section 33. The terminal 
intrinsic spreading code is set in the channel upward spreading code 
generating section 36 of the channel control section 30' in the radio base 
station 12' communicating with the terminal 13 at the same time that the 
host station 11 assigns a communication channel to the terminal 13. The 
transmission power control section 34 measures a reception ratio Eb/N0 in 
the base station correlation demodulated signal that is a ratio of 
reception energy to interference energy per bit in the upward 
communication channel from the terminal 13. Subsequently, the transmission 
power control section 34 compares the measured reception ratio Eb/N0 with 
a reference ratio Eb/N0 set by the channel main control section 31 to 
produce a transmission power control signal for controlling the upward 
transmission power of the terminal 13. 
Specifically, when the reception ratio Eb/N0 is greater than the reference 
ratio Eb/N0, the transmission power control section 34 produces the 
transmission power control signal indicative of lowering the upward 
transmission power. This is because the terminal 13 transmits the upward 
communication channel signal using an excess of transmission power. 
Conversely, if the reception ratio Eb/N0 is less than the reference ratio 
Eb/N0, the transmission power control section 34 produces the transmission 
power control signal indicative of raising the upward transmission power. 
This is because the terminal 13 transmits the upward communication channel 
signal at insufficient transmission power. 
Set by the channel main control section 31, the reference ratio Eb/N0 has 
the same value in all of the channel control sections 30' so as to 
maintain the same communication quality in all of the terminals. Produced 
by the transmission power control section 34, the transmission power 
control signal is supplied to the channel encoding section 32. 
The channel coding section 32 encodes a base station input speech frame 
signal 300 sent from the host station 11 into a base station encoded 
signal and then superimposes the transmission power control signal on the 
base station encoded signal. An output signal from the channel coding 
section 32 is spread by a base station intrinsic spreading code into a 
base station spread signal which is supplied to the base station 
transmitter 40. The base station transmitter 40 modulates a carrier with 
the base station spread signal to produce a base station modulated signal 
which is transmitted to the terminal 13 via the base station antenna 60 as 
a downward communication channel signal using a downward communication 
channel. The base station intrinsic spreading code has a different value 
for each radio base station so that the terminal 13 differentiates the 
radio base stations 12'. The base station intrinsic spreading code is 
generated by the channel downward spreading code generating section 35. 
Referring to FIG. 4, transmitted from the radio base station 12', the 
downward communication channel signal is supplied to the terminal receiver 
72 via the terminal antenna 71 and is demodulated by the terminal receiver 
72 into a terminal demodulated signal. The terminal demodulated signal 
from the terminal receiver 72 is correlation demodulated using the base 
station intrinsic spreading code produced by the terminal downward 
spreading code generating section 75 into a terminal correlation 
demodulated signal. The base station intrinsic spreading code to be set in 
the terminal downward spreading code generating section 75 is delivered 
from the host station 11 each time the host station 11 assigns the 
communication channel to the terminal 13. On soft hand-off where the 
terminal 13 simultaneously communicates with two different radio base 
stations, two different base station intrinsic spreading codes are 
assinged to the terminal 13 by the host station 11 and then the two 
different base station intrinsic spreading codes are produced by the 
terminal downward spreading code generating section 75. 
The terminal correlation demodulated signal is separated into a terminal 
reception speech frame signal 300 and the transmission power control 
signal by the terminal decoding section 76. The terminal reception speech 
frame signal 300 is sent to the terminal speech coding/decoding section 79 
while the transmission power control signal is sent to the output gain 
control section 74. Sent to the terminal speech coding/decoding section 
79, the terminal reception speech frame signal 300 is converted into a 
terminal output speech signal by the terminal speech coding/decoding 
section 79. 
Attention is directed to a signal transmitted from the terminal 13 to the 
radio base station 12'. A terminal input speech signal is converted by the 
terminal coding/decoding section 79 into a terminal transmission speech 
frame signal which is encoded by the terminal coding section 77 into a 
terminal encoded signal. The terminal encoded signal is spread by the 
third multiplier 7C using the terminal intrinsic spreading code produced 
by the terminal upward spreading code generating section 78 into a 
terminal spread signal. A power level of the terminal spread signal is 
controlled by the output gain control section 74 using the transmission 
power control signal into a power controlled signal and then the power 
controlled signal is sent to the terminal transmitter 73. 
The terminal transmitter 73 modulates a carrier with the power controlled 
signal to produce a terminal modulated signal which is transmitted to the 
radio base station 12' from the terminal antenna 71 as the upward 
communication channel signal. 
As described above, the radio base station generates the transmission power 
control signal for the terminal on the basis of the reception energy in 
the upward communication channel signal transmitted from the terminal to 
the radio base station and transmits the transmission power control signal 
using the downward communication channel signal. The terminal receives the 
transmission power control signal and controls the upward transmission 
power for the upward communication channel on the basis of the 
transmission power control signal. Therefore it is possible to maintain a 
signal quality of the communication channel by keeping the reception ratio 
Eb/N0 to the reference ratio Eb/N0. 
Referring to FIG. 5 in addition to FIGS. 3 and 4, description is made as 
regards the upward transmission power control on the soft hand-off that is 
peculiar to a CDMA type mobile communication system. As described above, 
the CDMA type mobile communication system can carry out the soft hand-off 
where a terminal simultaneously communicates with two or more different 
radio base stations. This is because all radio base stations communicate 
using the carrier having the same carrier frequency. 
FIG. 5 is a view showing a connection state in the CDMA type mobile 
communication system on the soft hand-off. It will be assumed as follows. 
One skilled in the art will appreciate the following is an exemplary 
description and that other configurations are possible. The first radio 
base station 12'-1 covers a first service area or cell 16-1 while the 
second radio base station 12'-2 covers a second service area or cell 16-2. 
In addition, the terminal 13 lies in an area which is overlapped in the 
first and the second service areas 16-1 and 16-2. Under the circumstances, 
the terminal 13 can simultaneously communicate with the first and the 
second radio base stations 12'-1 and 12'-2. This is the soft hand-off. 
Herein, the service area is a receivable area where the terminal can 
receive the downward communication channel signal from the radio base 
station disposed therein. It is noted that the radio base station can 
receive not only an upward communication channel signal from a terminal 
which lies within the service area converted thereby but also another 
upward communication channel signal from another terminal which is apart 
from the service area in question but is lies close to the service area in 
question. 
It will be also presumed as follows that downward communication channel is 
assigned with a first carrier frequency f1 while the upward communication 
channel is assigned with a second carrier frequency f2. The first and the 
second radio base stations 12'-1 and 12'-2 have first and second base 
station intrinsic spreading codes C1 and C2 while the terminal 13 has the 
terminal intrinsic spreading code depicted at C3. 
In this event, transmitted from the terminal 13 to the first and the second 
radio base stations 12'-1 and 12'-2, the upward communication channel 
signal is transmitted using the second carrier frequency f2 with the 
upward communication channel signal spread by the terminal intrinsic 
spreading code C3. Each of the first through the second radio base 
stations 12'-1 and 12'-2 receives the upward communication channel signal 
from the terminal 13 using the terminal intrinsic spreading code C3 set by 
the host station 11. After receiving, in the manner which is described in 
conjunction with FIG. 3, the first and the second radio base stations 
12'-1 and 12'-2 generate first and second transmission power control 
signals by comparing the reception ratio Eb/N0 with the reference ratio 
Eb/N0. The first and the second radio base stations 12'-1 and 12'-2 
superimpose the first and the second transmission power control signals on 
first and second downward communication channel signals, respectively. The 
first and the second radio base stations 12'-1 and 12'-2 transmit, as 
first and second downward communication channel signals, first and second 
superimposed signals using the first carrier frequency F1 with the first 
and the second superimposed signals spread by the first and the second 
base station intrinsic spreading codes C1 and C2, respectively. Inasmuch 
as the first carrier frequency F1 for the downward communication channel 
is used all of the radio base stations, the terminal 13 can differentiate 
the first and the second radio base stations 12'-1 and 12'-2 by spreading 
the first and the second downward communication channel signals using the 
first and the second base station intrinsic spreading codes C1 and C2 for 
the first and the second radio base stations 12'-1 and 12'-2. 
During the soft hand-off, the terminal 13 receives the first and the second 
downward communication channel signals from the first and the second radio 
base stations 12'-1 and 12'-2 using the first and the second base station 
intrinsic spreading codes C1 and C2. If the first and the second 
transmission power control signals coincide with each other, the terminal 
13 controls the upward transmission power in accordance with one of the 
first and the second transmission power control signals. If the first and 
the second transmission power control signals differ from each other, the 
terminal 13 controls the upward transmission power so as to make the 
lowest power level. That the first and the second transmission power 
control signals differ from each other means that the reception ratio 
Eb/N0 of the upward communication channel in one radio base station is 
higher than that in another radio base station. Under the circumstances, 
the terminal 13 can maintain quality of the upward communication channel 
from the terminal 13 if the upward transmission power is controlled in 
accordance with the transmission power control signal supplied from the 
radio base station having a higher reception ratio Eb/N0. That the first 
and the second transmission power control signals differ from each other 
occurs in a case where the terminal 13 during the soft hand-off approaches 
either of the radio base stations 12'-1 and 12'-2. 
It will now be assumed that the terminal 13 approaches the second radio 
base station 12'-2. In this event, the reception ratio Eb/N0 of the upward 
communication channel received by the second radio base station 12'-2 
exceeds the reference ratio Eb/N0. This is because the terminal 13 carries 
out transmission at the upward transmission power before control is made 
although propagation loss decreases because the terminal 13 approaches the 
second radio base station 12'-2. Inasmuch as the reception ratio Eb/N0 of 
the upward communication channel exceeds the reference ratio Eb/N0 in the 
second radio base station 12'-2, the second radio station 12'-2 transmits 
to the terminal 13 the second transmission power control signal indicative 
of lowering the upward transmission power. On the other hand, the 
reception ratio Eb/N0 of the upward communication channel received by the 
first radio base station 12'-1 is less than the reference ratio Eb/N0. 
This is because the terminal 13 carries out transmission at the upward 
transmission power before control is made although propagation loss 
increases because the terminal 13 is apart from the first radio base 
station 12'-1. Inasmuch as the reception ratio Eb/N0 of the upward 
communication channel is less than the reference ratio Eb/N0 in the first 
radio base station 12'-1, the first radio station 12'-1 transmits to the 
terminal 13 the first transmission power control signal indicative of 
raising the upward transmission power. On reception of the first and the 
second transmission power control signals, the terminal 13 lowers the 
upward transmission power for the upward communication channel signal 
because the terminal 13 complies with the second transmission power 
control signal supplied from the second radio base station 12'-2. 
As a result, in general, the first radio base station 12'-1 has a signal 
quality of the upward communication channel from the terminal 13 that is 
less than that of the second radio base station 12'-2. However, inasmuch 
as temporal variation in strength of an electric wave frequently occurs in 
the mobile communication system, the radio base station with a shorter 
propagation distance may not always have a better signal quality. 
For this purpose, the host station 11 is provided with the speech frame 
signal selecting section 15 for selecting a signal with a better quality 
on the basis of the speech data signal quality information 320 in the 
speech frame signals 300 transmitted from the the first and the second 
radio base stations 12'-1 and 12'-2. 
Referring to FIG. 6, description will be made as regards problems in the 
conventional CDMA type mobile communication system of the CDMA system. In 
FIG. 6, the first radio base station 12'-1 covers the first cell 16-1 
having a relatively small cell diameter while the second radio base 
station 12'-2 covers the second cell 16-2 having a relatively large cell 
diameter. A first terminal 13-1 communicates with the first radio base 
station 12'-1 alone. A second terminal 13-2 carries out soft hand-off 
between the first radio base station 12'-1 and the second radio base 
station 12'-2. 
It is assumed that the second terminal 13-2 lies in an area of the soft 
hand-off at a position P0. In this event, the second terminal 13-2 can 
receive both of the first and the second downward communication channel 
signals from the first and the second radio base stations 12'-1 and 12'-2. 
Control of the upward transmission power is carried out in accordance with 
both of the first and the second transmission power control signals 
supplied from the first and the second radio base stations 12'-1 and 
12'-2. Under the circumstances, the second radio base station 12'-2 cannot 
carry out reception operation to the second terminal 13-2 at sufficient 
energy in comparison with the first radio base station 12'-1. This is 
because there is a long distance between the second radio base station 
12'-2 and the second terminal 13-2. In contrast with this, the first radio 
base station 12'-l can carry out reception operation to the second 
terminal 13-2 at sufficient energy. As a result, the upward transmission 
power of the second terminal 13-2 is controlled mainly in accordance with 
the first transmission power control signal supplied from the first radio 
base station 12'-1. The reception ratio Eb/N0 of the second radio base 
station 12'-2 is kept in a state less than the reference ratio Eb/N0. 
That is, although the second terminal 13-2 at the position P0 can receive 
both of the first and the second downward communication channel signals 
from the first and the second radio base stations 12'-1 and 12'-2, the 
first radio base station 12'-1 can receive from the second terminal 13-2 
the upward communication channel signal having the reception ratio Eb/N0 
satisfied with the reference ratio Eb/N0 while the second radio base 
station 12'-2 cannot receive from the second terminal 13-2 the upward 
communication channel signal having the reception ratio Eb/N0 satisfied 
with the reference ratio En/N0. 
It will be presumed that the second terminal 13-2 shift from the position 
P0 to another position P1 in the second cell 16-2 that is close to the 
first cell 16-1 but is apart from the first cell 16-1. In other words, a 
first distance L1 between the second terminal 13-2 and the first radio 
base station 12'-1 is shorter than a second distance L2 between the second 
terminal 13-2 and the second radio base station 12'-2, namely: 
EQU L1&lt;&lt;L2. 
In this event, the second terminal 13-2 can receive only the second 
downward communication channel signal from the second radio base station 
12'-1 and control of the upward transmission power for the second terminal 
13-2 is carried out in accordance with the second transmission power 
control signal supplied from the second radio base station 12'-2. 
Inasmuch as the second terminal 13-2 is controlled by the second 
transmission power control signal supplied from the second radio base 
station 12'-2 which is a long distance (the second distance L2) from the 
second radio base station 12'-2, the first radio base station 12'-1 
receives large energy from the second terminal 13-2 which is a short 
distance (the first distance L1) from the first radio base station 12'-1. 
The large energy serves as interference energy in the first radio base 
station 12'-1 and it results in lowering the reception ratio Eb/N0 for the 
first terminal 13-1 so as to be less than the reference ratio Eb/N0. As a 
result, the first radio base station 12'-1 controls the first terminal 
13-1 so as to raise its upward transmission power. 
For the above-mentioned reason, each terminal in the first cell 16-1 
carries out transmission operation at extra electric power and it results 
in raising the interference energy in the first cell 16-1 further. As a 
result, subscriber capacity held in the first cell 16-1 decreases. In 
addition, inasmuch as it is necessary for each terminal in the first cell 
16-1 to raise its transmission power and it results in increasing consumed 
power and in shortening the life of its battery. 
Referring to FIG. 7, the description will proceed to a CDMA type mobile 
communication system system according to a first embodiment of this 
invention. The illustrated CDMA type mobile communication system comprises 
a host station 11A, first and second radio base stations 12-1 and 12-2, 
and a terminal or mobile station 13. The host station 11A is connected to 
the first and the second radio base stations 12-1 and 12-2. 
The host station 11A comprises not only the host station speech 
coding/decoding section 14 and the speech frame signal selecting section 
15 but also a transmission power signal selecting section 21, first and 
second host station signal multiplexing sections 22-1 and 22-2, and first 
and second host station signal demultiplexing sections 23-1 and 23-2. 
The host station speech coding/decoding section 14 codes a host input 
speech signal into a host transmission speech frame signal. In addition, 
the host station speech coding/decoding section 14 decodes a selected host 
reception speech frame signal (which will later become clear) into a host 
output speech signal. 
The first host station signal demultiplexing section 23-1 is supplied from 
the first radio base station 12-1 with a first host input multiplexed 
signal which will later become clear. The first host station signal 
demultiplexing section 23-1 separates the first host input multiplexed 
signal into a first transmission power control signal and a first host 
reception speech frame signal. The first transmission power control signal 
is supplied to the transmission power signal selecting section 21 while 
the first host reception speech frame signal is supplied to the speech 
frame signal selecting section 15. Likewise, the second host station 
signal demultiplexing section 23-2 is supplied from the second radio base 
station 12-2 with a second host input multiplexed signal which will later 
become clear. The second host station signal demultiplexing section 23-2 
separates the second host input multiplexed signal into a second 
transmission power control signal and a second host reception speech frame 
signal. The second transmission power control signal is supplied to the 
transmission power signal selecting section 21 while the second host 
reception speech frame signal is supplied to the speech frame signal 
selecting section 15. 
The speech frame signal selecting section 15 selects, as the selected host 
reception speech frame signal, one of the first and the second host 
reception speech frame signals that has the best signal quality on the 
basis of the speech data signal quality information 320 included therein. 
The transmission power signal selecting section 21 selects, as a selected 
transmission power control signal, one of the first and the second 
transmission power control signals so as to make upward transmission power 
in the terminal 13 the lowest power level. 
Each of the first and the second host station signal multiplexing sections 
22-1 and 22-2 is supplied with the selected transmission power control 
signal and the host transmission speech frame signal from the transmission 
power signal selecting section 21 and the host station speech 
coding/decoding section 14, respectively. The first host station signal 
multiplexing section 22-1 multiplexes the host transmission speech frame 
signal and the selected transmission power control signal into a first 
host output multiplexed signal. Similarly, the second host station signal 
multiplexing section 22-2 multiplexes the host transmission speech frame 
signal and the selected transmission power control signal into a second 
host output multiplexed signal. The first and the second host output 
multiplexed signals are delivered to the first and the second radio base 
stations 12-1 and 12-2, respectively. 
The first radio base station 12-1 comprises m first channel control 
sections 30-1-1, 30-1-2, . . . , and 30-1-m, a first base station 
transmitter (TX) 40-1, a first base station receiver (RX) 50-1, and a 
first base station antenna 60-1, where m represents an integer which is 
not less than two. The first base station transmitter 40-1 modulates each 
signal from the m first channel control sections 30-1-1 to 30-1-m. The 
first base station receiver 50-1 demodulates a signal from the terminal 
13. 
Each of the m first channel control sections 30-1-1 to 30-1-m comprises a 
first main control section 31-1, a first base station encoding section 
32-1, a first base station decoding section 33-1, a first base station 
transmission power control section 34-1, a first base station downward 
spreading code generating section 35-1, a first base station upward 
spreading code generating section 36-1, a first base station signal 
demultiplexing section 37-1, a first base station signal multiplexing 
section 38-1, a first base station output multiplier 3A-1, and a first 
base station input multiplier 3B-1. 
The first base station signal demultiplexing section 37-1 is supplied from 
the host station 11A with the first host output multiplexed signal as a 
first base station input multiplexed signal. The first base station signal 
demultiplexing section 37-1 separates the first base station input 
multiplexed signal into a first base station reception speech frame signal 
and the selected transmission power control signal. The first base station 
encoding section 32-1 encodes the first base station reception speech 
frame signal into a first encoded speech signal and then superimposes the 
selected transmission power control signal on the first encoded speech 
signal. The first base station downward spreading code generating section 
35-1 generates a first base station intrinsic spreading code C1 which is a 
code for spreading an output signal from the first base station encoding 
section 32-1. 
The first base station upward spreading code generating section 36-1 
generates the terminal intrinsic spreading code which is a code for 
correlation demodulating an output signal from the first base station 
receiver 50-1. The first base station decoding section 33-1 decodes a 
first base station correlation demodulated signal into a first base 
station output speech frame signal which comprises speech data and quality 
information for the speech data. The first base station transmission power 
control section 34-1 calculates, on the basis of the first base station 
correlation demodulated signal, a first reception ratio Eb/N0 which is a 
ratio of reception energy to interference energy in an upward 
communication channel signal. The first base station transmission power 
control section 34-1 is supplied from the first main control section 31-1 
with a first reference ratio Eb/N0. The first base station transmission 
power control section 34-1 compares the first reception ratio Eb/N0 with 
the first reference ratio Eb/N0 to a first transmission power control 
signal for an upward communication channel. The first base station signal 
multiplexing section 38-1 multiplexes the first base station output speech 
frame signal and the first transmission power control signal into a first 
base station output multiplexed signal. The first base station output 
multiplexed signal is supplied to the host station 11A as the first host 
input multiplexed signal which is described above. 
The second radio base station 12-2 is similar in structure to the first 
radio base station 12-1. That is, the second radio base station 12-2 
comprises m second channel control sections 30-2-1, 30-2-2, . . . , and 
30-2-m, a second base station transmitter (TX) 40-2, a second base station 
receiver (RX) 50-2, and a second base station antenna 60-2. The second 
base station transmitter 40-2 modulates each signal from the m second 
channel control sections 30-2-1 to 30-2-m. The second base station 
receiver 50-2 demodulates a signal from the terminal 13. 
Each of the m second channel control sections 30-2-1 to 30-2-m comprises a 
second main control section 31-2, a second base station encoding section 
32-2, a second base station decoding section 33-2, a second base station 
transmission power control section 34-2, a second base station downward 
spreading code generating section 35-2, a second base station upward 
spreading code generating section 36-2, a second base station signal 
demultiplexing section 37-2, a second base station signal multiplexing 
section 38-2, a second base station output multiplier 3A-2, and a second 
base station input multiplier 3B-2. 
The second base station signal demultiplexing section 37-2 is supplied from 
the host station 11A with the second host output multiplexed signal as a 
second base station input multiplexed signal. The second base station 
signal demultiplexing section 37-2 separates the second base station input 
multiplexed signal into a second base station reception speech frame 
signal and the selected transmission power control signal. The second base 
station encoding section 32-2 encodes the second base station reception 
speech frame signal into a second encoded speech signal and then 
superimposes the selected transmission power control signal on the second 
encoded speech signal. The second base station downward spreading code 
generating section 35-2 generates a second base station intrinsic 
spreading code which is a code for spreading an output signal from the 
second base station encoding section 32-2. 
The second base station upward spreading code generating section 36-2 
generates the terminal intrinsic spreading code which is a code for 
correlation demodulating an output signal from the second base station 
receiver 50-2. The second base station decoding section 33-2 decodes a 
second base station correlation demodulated signal into a second base 
station output speech frame signal which comprises speech data and quality 
information for the speech data. The second base station transmission 
power control section 34-2 calculates, on the basis of the second base 
station correlation demodulated signal, a second reception ratio Eb/N0 
which is a ratio of reception energy to interference energy in the upward 
communication channel signal. The second base station transmission power 
control section 34-2 is supplied from the second main control section 31-2 
with a second reference ratio Eb/N0. The second base station transmission 
power control section 34-2 compares the second reception ratio Eb/N0 with 
the second reference ratio Eb/N0 to a second transmission power control 
signal for the upward communication channel. The second base station 
signal multiplexing section 38-2 multiplexes the second base station 
output speech frame signal and the second transmission power control 
signal into a second base station output multiplexed signal. The second 
base station output multiplexed signal is supplied to the host station 11A 
as the second host input multiplexed signal which is described above. 
Turning to FIG. 8, the terminal 13 is similar in structure to that 
illustrated in FIG. 4. That is, the terminal 13 comprises the terminal 
antenna 71, the terminal receiver (RX) 72, the terminal transmitter (TX) 
73, the output gain control section 74, the terminal downward spreading 
code generating section 75, the terminal decoding section 76, the terminal 
encoding section 77, the terminal upward spreading code generating section 
78, the terminal speech coding/decoding section 79, and the first through 
the third multipliers 7A, 7B, and 7C. 
The terminal receiver 72 receives the first and the second downward 
communication channel signals from the first and the second radio base 
stations 12-1 and 12-2 via the terminal antenna 71. The terminal receiver 
72 demodulates the first and the second downward communication channel 
signals into a terminal demodulated signals, respectively. The terminal 
downward spreading code generating section 75 generates first and second 
base station intrinsic spreading codes C1 and C2 for use in correlation 
demodulating the terminal demodulated signal for the first and the second 
radio base stations 12-1 and 12-2. The first multiplier 7A correlation 
demodulates the terminal demodulated signal using the first base station 
intrinsic spreading code C1 to produce a first terminal correlation 
demodulated signal. The second multiplier 7B correlation demodulates the 
terminal demodulated signal using the second base station intrinsic 
spreading code C2 to produce a second terminal correlation demodulated 
signal. The terminal decoding section 76 decodes the first and the second 
terminal correlation demodulated signals into a terminal decoded signal 
and then separates the terminal decoded signal into a terminal reception 
speech frame signal and the selected transmission power control signal. 
The terminal speech coding/decoding section 79 converts the terminal 
reception speech frame signal into a terminal output speech signal. 
In addition, the terminal speech coding/decoding section 79 is supplied 
with a terminal input speech signal. The terminal speech coding/decoding 
section 79 converts the terminal input speech signal into a terminal 
transmission speech frame signal. The terminal encoding section 77 encodes 
the terminal transmission speech frame signal into a terminal encoded 
signal. The terminal upward spreading code generating section 78 generates 
the terminal intrinsic spreading code C3. The third multiplier 7C spreads 
the terminal encoded signal using the terminal intrinsic spreading code C3 
to produce a terminal spread signal. The terminal spread signal is 
supplied to the output gain control section 74 which is supplied with the 
selected transmission power control signal from the terminal decoding 
section 76. The output gain control section 74 controls upward 
transmission power of the terminal spread signal for the upward 
communication channel on the basis of the selected transmission power 
control signal to produce a power controlled signal. The terminal 
transmitter 73 modulates a third carrier signal with the power controlled 
signal to produce a terminal modulated signal which is transmitted to the 
first and the second radio base stations 12-1 and 12-2 from the terminal 
antenna 71 as an upward communication channel signal. 
Referring to FIGS. 7 and 8, the description will proceed to operation of 
the CDMA type mobile communication system. It is assumed that the terminal 
13 communicates with the first and the second radio base stations 12-1 and 
12-2. Accordingly, the upward communication channel signal transmitted 
from the terminal 13 is received in both of the first radio base station 
12-1 and the second radio base station 12-2. 
In the first radio base station 12-1, the first base station receiver 50-1 
receives the upward communication channel signal via the first base 
station antenna 60-1 and demodulates it into a first base station 
demodulated signal. With respect to the first base station demodulated 
signal, one of the first channel control sections 30-1 (suffix omitted) is 
assigned every terminal 13. In the first channel control section 30-1, the 
first base station demodulated signal is supplied to the first base 
station input multiplier 3B-1. The first base station input multiplier 
3B-1 correlation demodulates the first base station demodulated signal 
using the terminal intrinsic spreading code C3 supplied from the the first 
base station upward spreading code generating section 36-1 to produce the 
first base station correlation demodulated signal. The first base station 
correlation demodulated signal is supplied to the first transmission power 
control section 34-1 and to the first base station decoding section 33-1. 
Responsive to the first base station correlation demodulated signal, the 
first transmission power control section 34-1 measures a first reception 
ratio Eb/N0 which is a ratio of reception energy to interference energy 
per bit in the upward communication channel signal. Subsequently, the 
first transmission power control section 34-1 compares the first reception 
ratio Eb/N0 with a reference ratio Eb/N0 set by the first main control 
section 31-1 to produce a first transmission power control signal for 
controlling the upward transmission power of the terminal 13. The 
reference ratio Eb/N0 set by the first main control section 31-1 has the 
same value in all of the first channel control sections 30-1-1 to 30-1-m 
so as to maintain the same communication quality in all terminals. 
Specifically, when the first reception ratio Eb/N0 is greater than the 
reference ratio Eb/N0, the first transmission power control section 34-1 
produces the first transmission power control signal indicative of 
lowering the upward transmission power. This is because the terminal 13 
transmits the upward communication channel signal at excess transmission 
power. Conversely, if the first reception ratio Eb/N0 is less than the 
reference ratio Eb/N0, the first transmission power control section 34-1 
produces the first transmission power control signal indicative of raising 
the upward transmission power. This is because the terminal 13 transmits 
the upward communication channel signal at insufficient transmission 
power. 
The first base station decoding section 33-1 decodes the first base station 
correlation demodulated signal into the first base station output speech 
frame signal. The first base station signal multiplexing section 38-1 
multiplexes the first base station output speech frame signal and the 
first transmission power control signal into the first base station output 
multiplexed signal. The first base station output multiplexed signal is 
supplied to the host station 11A as the first host input multiplexed 
signal. 
Likewise, the second radio base station 12-2 receives the upward 
communication channel signal from the terminal 13 and transmits to the 
host station 11A the second base station output speech frame signal and 
the second transmission power control signal multiplexed. 
More specifically, the second base station receiver 50-1 receives the 
upward communication channel signal via the second base station antenna 
60-2 and demodulates it into a second base station demodulated signal. 
With respect to the second base station demodulated signal, one of the 
second channel control sections 30-2 (suffix omitted) is assigned every 
terminal 13. In the second channel control section 30-2, the first base 
station demodulated signal is supplied to the second base station input 
multiplier 3B-1. The second base station input multiplier 3B-1 correlation 
demodulates the second base station demodulated signal using the terminal 
intrinsic spreading code C3 supplied from the the second base station 
upward spreading code generating section 36-2 to produce the second base 
station correlation demodulated signal. The second base station 
correlation demodulated signal is supplied to the second transmission 
power control section 34-2 and to the second base station decoding section 
33-2. Responsive to the second base station correlation demodulated 
signal, the second transmission power control section 34-2 measures the 
second reception ratio Eb/N0 which is the ratio of reception energy to the 
interference energy per bit in the upward communication channel signal. 
Subsequently, the second transmission power control section 34-2 compares 
the second reception ratio Eb/N0 with the reference ratio Eb/N0 set by the 
second main control section 31-2 to produce the second transmission power 
control signal for controlling the upward transmission power of the 
terminal 13. The reference ratio Eb/N0 set by the second main control 
section 31-2 has the same value in all of the second channel control 
sections 30-2-1 to 30-2-m so as to maintain the same communication quality 
in all terminals. 
Specifically, when the second reception ratio Eb/N0 is greater than the 
reference ratio Eb/N0, the second transmission power control section 34-2 
produces the second transmission power control signal indicative of 
lowering the upward transmission power. This is because the terminal 13 
transmits the upward communication channel signal at excess transmission 
power. Conversely, if the second reception ratio Eb/N0 is less than the 
reference ratio Eb/N0, the second transmission power control section 34-2 
produces the second transmission power control signal indicative of 
raising the upward transmission power. This is because the terminal 13 
transmits the upward communication channel signal at insufficient 
transmission power. 
The second base station decoding section 33-2 decodes the second base 
station correlation demodulated signal into the second base station output 
speech frame signal. The second base station signal multiplexing section 
38-2 multiplexes the second base station output speech frame signal and 
the second transmission power control signal into the second base station 
output multiplexed signal. The second base station output multiplexed 
signal is supplied to the host station 11A as the second host input 
multiplexed signal. 
In the host station 11A, the first and the second host station signal 
demultiplexing sections 23-1 and 23-2 receive the first and the second 
host input multiplexed signals from the first and the second radio base 
stations 12-1 and 12-2, respectively. The first host station signal 
demultiplexing section 23-1 separates the first host input multiplexed 
signal into the first transmission power control signal and the first host 
reception speech frame signal. Likewise, the second host station signal 
demultiplexing section 23-1 separates the second host input multiplexed 
signal into the second transmission power control signal and the second 
host reception speech frame signal. The first and the second host 
reception speech frame signals are supplied to the speech frame signal 
selecting section 15 while the first and the second transmission power 
control signals are supplied to the transmission power signal selecting 
section 21. 
The speech frame signal selecting section 15 selects, as the selected 
reception speech frame signal, one of the first and the second reception 
speech frame signals that has the best signal quality on the basis of the 
speech data signal quality information included therein. The selected 
reception speech frame signal is sent to the host station speech 
coding/decoding section 14. As shown in FIG. 4, the selected reception 
speech frame signal comprises the speech data and the speech data signal 
quality information. The host station speech coding/decoding section 14 
converts the selected reception speech frame signal into the host output 
speech signal. 
The transmission power signal selecting section 21 selects, as the selected 
transmission power control signal, one of the first and the second 
transmission power control signals so as to make the upward transmission 
power in the terminal 13 the lowest power level. 
Temporarily referring to FIG. 9, the description will proceed to processing 
in the transmission power control signal selecting section 21. The first 
transmission power control signal is denoted at A while the second 
transmission power control signal is denoted at B. The transmission power 
control signal section 21 first compares the first transmission power 
control signal A with the second transmission power control signal B at a 
step 200. If the first transmission power control signal A is not less 
than the second transmission power control signal B, the step 200 is 
succeeded by a step 210 at which the transmission power control signal 
selecting section 21 selects the second transmission power control signal 
B as the selected transmission power control signal. If the second 
transmission power control signal B is greater than the first transmission 
power control signal A, the step 200 is followed by a step 220 at which 
the transmission power control signal selecting section 21 selects the 
first transmission power control signal A as the selected transmission 
power control signal. 
As apparent from the above-mentioned processing, when any one radio base 
station makes control so as to lower the upward transmission power from 
the terminal, the host station makes all radio base stations transmit the 
selected transmission power control signal indicative of lowering the 
upward transmission power. In other words, only when all radio base 
stations require the terminal to raise the upward transmission power, the 
selected transmission power control signal indicative of raising the 
upward transmission power is sent to the terminal from all radio base 
stations. 
The host station speech coding/decoding section 14 converts the host input 
speech signal into the host transmission speech frame signal. The host 
transmission speech frame signal is supplied to both of the first and the 
second host station signal multiplexing sections 22-1 and 22-2 which are 
supplied with the selected transmission power control signal from the 
transmission power control signal selecting section 21 in the manner which 
is described above. The first host station signal multiplexing station 
22-1 multiplexes the host transmission speech frame signal and the 
selected transmission power control signal into the first host output 
multiplexed signal. Similarly, the second host station signal multiplexing 
station 22-2 multiplexes the host transmission speech frame signal and the 
selected transmission power control signal into the second host output 
multiplexed signal. The first and the second host output multiplexed 
signals are delivered to the first and the second radio base stations 12-1 
and 12-2, respectively. 
In the first base station 12-1, the first host output multiplexed signal is 
received by the first base station signal demultiplexing section 37-1 as 
the first base station input multiplexed signal. The first base station 
signal demultiplexing section 37-1 separates the first base station input 
multiplexed signal into the first base station reception speech frame 
signal and the selected transmission power control signal which are 
supplied to the first base station encoding section 32-1. The first base 
station encoding section 32-1 encodes the first base station reception 
speech frame signal into the first encoded speech signal and then 
superimposes the selected transmission power control signal on the first 
encoded speech signal to produce a first encoder output signal. The first 
encoder output signal is supplied to the first base station output 
multiplier 3A-1 which is supplied with the first base station intrinsic 
spreading code C1 from the first base station downward spreading code 
generating section 35-1. The first base station output multiplier 3A-1 
spreads the first encoder output signal using the first base station 
downward spreading code C1 to produce the first base station spread 
signal. The first base station spread signal is supplied to the first base 
station transmitter 40-1. The first base station transmitter 40-1 
modulates a first carrier signal with the first base station spread signal 
to produce a first base station modulated signal. The first base station 
modulated signal is transmitted from the first base station antenna 60-1 
to the terminal 13 as the first downward communication channel signal. 
Similarly, the second base station 12-2 spreads the speech frame signal and 
the selected transmission power control signal using the second base 
station intrinsic spreading code C2 and transmits it from the second base 
station antenna 60-2. 
More specifically, the second host output multiplexed signal is received by 
the second base station signal demultiplexing section 37-2 as the second 
base station input multiplexed signal. The second base station signal 
demultiplexing section 37-2 separates the second base station input 
multiplexed signal into the second base station reception speech frame 
signal and the selected transmission power control signal which are 
supplied to the second base station encoding section 32-2. The second base 
station encoding section 32-2 encodes the second base station reception 
speech frame signal into the second encoded speech signal and then 
superimposes the selected transmission power control signal on the second 
encoded speech signal to produce a second encoder output signal. The 
second encoder output signal is supplied to the second base station output 
multiplier 3A-2 which is supplied with the second base station intrinsic 
spreading code C2 from the second base station downward spreading code 
generating section 35-2. The second base station output multiplier 3A-2 
spreads the second encoder output signal using the second base station 
downward spreading code C2 to produce the second base station spread 
signal. The second base station spread signal is supplied to the second 
base station transmitter 40-2. The second base station transmitter 40-2 
modulates a second carrier signal with the second base station spread 
signal to produce a second base station modulated signal. The second base 
station modulated signal is transmitted from the second base station 
antenna 60-2 to the terminal 13 as the second downward communication 
channel signal. 
Transmitted from the first and the second radio base stations 12-1 and 
12-2, the first and the second downward communication channel signals are 
received in the terminal receiver 72 via the terminal antenna 71 of the 
terminal 13. The terminal receiver 72 demodulates the first and the second 
downward communication channel signals into the terminal demodulated 
signal. The terminal demodulated signal is supplied to the first and the 
second multiplier 7A and 7B in common. The first and the second multiplier 
7A and 7B are supplied from the terminal downward spreading code 
generating section 75 with the first and the second base station intrinsic 
spreading codes C1 and C2, respectively. The first multiplier 7A 
correlation demodulates the terminal demodulated signal using the first 
base station intrinsic spreading code C1 to produce the first terminal 
correlation demodulated signal. Likewise, the second multiplier 7B 
correlation demodulates the terminal demodulated signal using the second 
base station intrinsic spreading code C2 to produce the second terminal 
correlation demodulated signal. 
It is noted that the base station intrinsic spreading code to be set in the 
terminal downward spreading code generateing section 75 is delivered from 
the host station 11A each time the host station 11A assigns the 
communication channel to the terminal 13. On soft hand-off where the 
terminal 13 simultaneously communicates with two different radio base 
stations, two different spreading codes are assigned to the terminal 13 by 
the host station 11A and therefore the terminal downward spreading code 
generating section 75 generates the two different spreading codes. 
The first and the second terminal correlation demodulated signals are 
supplied to the terminal decoding section 76. The terminal decoding 
section 76 decodes the first and the second terminal correlation 
demodulated signals into the terminal decoded signal. Subsequently, the 
terminal decoding section 76 separates the terminal decoded signal into 
the terminal reception speech frame signal and the selected transmission 
power control signal. The terminal reception speech frame signal is 
supplied to the terminal speech coding/decoding section 79 while the 
selected transmission power control signal is supplied to the output gain 
control section 74. The terminal speech coding/decoding section 79 
converts the terminal reception speech frame signal into the terminal 
output speech signal. 
Attention is now directed to a communication signal from the terminal 13 to 
the host station 11A. The terminal input speech signal is supplied to the 
terminal speech coding/decoding section 79. The terminal speech 
coding/decoding section 79 converts the terminal input speech signal into 
the terminal transmission speech frame signal. The terminal transmission 
speech frame signal is supplied to the terminal encoding section 77. The 
terminal encoding section 77 encodes the terminal transmission speech 
frame signal into the terminal encoded signal. The terminal encoded signal 
is supplied to the third multiplier 7C which is supplied with the terminal 
intrinsic spreading code C3 from the terminal upward spreading code 
generating section 78. The third multiplier 7C spreads the terminal 
encoded signal using the terminal intrinsic spreading code C3 to produce 
the terminal spread signal. The terminal spread signal is supplied to the 
output gain control section 74 which is supplied with the selected 
transmission power control signal from the terminal decoding section 76. 
The output gain control section 74 controls the upward transmission power 
of the terminal spread signal on the basis of the selected transmission 
power control signal to produce the power controlled signal. The power 
controlled signal is supplied to the terminal transmitter 73. The terminal 
transmitter 73 modulates the third carrier signal with the power 
controlled signal to produce the terminal modulated signal. The terminal 
modulated signal is transmitted from the terminal antenna 71 to the first 
and the second radio base stations 12-1 and 12-2 as the upward 
communication channel signal. 
In the manner which is described above, the reception ratio Eb/N0 is 
maintained the reference radio Eb/N0 in each radio base station. 
The description will proceed to merits in the CDMA type mobile 
communication system according to the first embodiment of this invention. 
A signal from a terminal is received in two radio base stations. Each 
radio base station generates, on the basis of reception energy, a 
transmission power control signal for controlling upward transmission 
power of the terminal and transmits it to a host station. The host station 
selects, as a selected transmission power control signal, one of two 
transmission power control signals that makes upward transmission power 
for the terminal the lowest power level and transmits it to the two radio 
base stations. As a result, it is possible to realize soft hand-off 
between cells having different cell diameters without decreasing 
subscriber capacity held in each cell. In addition, it is possible to 
inhibit the upward transmission power in the terminal to lower consumed 
power. As a result, it is possible to make the life of a battery of the 
terminal longer. 
Referring to FIG. 10, the description will proceed to operation of the 
mobile communication system illustrated in FIG. 7 in more detail. In FIG. 
10, the first radio base station 12-1 covers the first cell 16-1 having a 
relatively small cell diameter while the second radio base station 12-2 
covers the second cell 16-2 having a relatively large diameter. As shown 
in FIG. 10, the first and the second cells 16-1 and 16-2 are overlapped 
with each other. A first terminal 13-1 communicates with the first radio 
base station 12-1 alone. A second terminal 13-2 carries out communication 
by shifting from a position P0 (FIG. 6) to another position P1 in the 
second cell 16-2. A first distance Li between the second terminal 13-2 
(the position P1) and the first radio base station 12'-1 is shorter than a 
second distance L2 between the second terminal 13-2 (the position P1) and 
the second radio base station 12'-2, namely, L1&lt;&lt;L2. In other words, the 
position P1 closes to the first cell 16-1 but is apart from the first cell 
16-1. That is, the second terminal 13-2 communicates at the position P1 
which is nearer the first radio base station 12-1 than the second radio 
base station 12-2. 
Transmitted from the second terminal 13-2, the upward communication channel 
signal is received by both of the first radio base station 12-1 and the 
second radio base station 12-2. It is assumed that reception ratio Eb/N0 
in the first radio base station 12-1 is equal to 5 dB and reception ratio 
Eb/N0 in the second radio base station 12-2 is equal to 2 dB. That is, the 
reception ratio Eb/N0 in the second radio base station 12-2 is less than 
that in the first radio base station 12-1. This is because the second 
radio base station 12-2 has a larger propagation loss in comparison with 
the first radio base station 12-1. It is also assumed that the reference 
ratio Eb/N0 of 7dB is set in both of the first and the second radio base 
stations 12-1 and 12-2 because of keeping signal quality of the upward 
communication channel at error rate of 1%. Under the circumstances, the 
first radio base station 12-1 generates the first transmission control 
signal indicative of raising the upward transmission power of the second 
terminal 13-2 by (7-5) dB or 2 dB and transmits it to the host station 
11A. In contrast with this, the second radio base station 12-2 generates 
the second transmission control signal indicative of raising the upward 
transmission power of the second terminal 13-2 by (7--2) dB or 5 dB and 
transmits it to the host station 11A. 
The host station 11A selects, as the selected transmission power control 
signal, the first transmission power control signal so as to make the 
upward transmission power of the second terminal 13-2 the most low. The 
host station 11A transmits the selected transmission power control signal 
(or the first transmission power control signal indicative of lowering the 
upward transmission power of the second terminal 13-2 by 2 dB) to the 
second terminal 13-2 through the second radio base station 12-2. 
Responsive to the selected transmission power control signal, the second 
terminal 13-2 raises its upward transmission power by 2 dB. Inasmuch as 
the second terminal 13-2 raises its upward transmission power by 2 dB, the 
reception ratio Eb/N0 in the first radio base station 12-2 is equal to the 
reference ratio Eb/N0 of 7 dB. 
Referring to FIG. 11, the description will proceed to a CDMA type mobile 
communication system according to a second embodiment of this invention. 
The illustrated mobile communication system comprises the host station 11, 
first and second radio base stations 12A-1 and 12A-2, the terminal 13, and 
a private or leased line 80. The first and the second radio base stations 
12A-1 and 12A-2 are connected to each other by the private line 80. That 
is, transmission/reception of the transmission power control signal is 
carried out via the private line 80. 
The host station 11 is similar in structure to that illustrated in FIG. 1. 
The first and the second radio base stations 12A-1 and 12A-2 are similar 
in structure to the first and the second radio base station 12-1 and 12-2 
illustrated in FIG. 7 except that the channel control sections in the 
first and the second radio base station 12-1 and 12-2 are modified in the 
manner which will become clear as the description proceeds. The first 
radio base station 12A-1 includes m first channel control sections 
30A-1-1, 30-A-1-2, . . . , and 30A-1-m while the second radio base station 
12A-2 includes m second channel control sections 30A-2-1, 30-A-2-2, . . . 
, and 30A-2-m. 
Each of the m first channel control sections 30A-1-1 to 30A-1-m in the 
first radio base station 12A-1 is similar in structure to each of the m 
first channel control sections 30-1-1 to 30-1-m in the first radio base 
station 12-1 except that it comprises a first private line interface 
section 81-1 in lieu of the first base station signal demultiplexing 
section 37-1 and the first base station signal multiplexing section 38-1. 
Likewise, each of the m second channel control sections 30A-2-1 to 30A-2-m 
in the second radio base station 12A-2 is similar in structure to each of 
the m second channel control sections 30-2-1 to 30-2-m in the second radio 
base station 12-2 except that it comprises a second private line interface 
section 81-2 in lieu of the second base station signal demultiplexing 
section 37-2 and the second base station signal multiplexing section 38-2. 
It is assumed that the terminal 13 is assigned with a terminal 
identification number while the first and the second radio base stations 
12A-1 and 12A-2 are assigned with first and second base station 
identification numbers, respectively. 
In the first radio base station 12A-1, the first private line interface 
section 81-1 generates a first transmission power control packet by adding 
the terminal identification number and the first base station 
identification number to the first transmission power control signal sent 
from the first transmission control section 34-1 and transmits the first 
transmission power control packet to the private line 80. The first 
private line interface section 81-1 searches for the transmission power 
control packets having the terminal identification number to receive them. 
After all of the transmission power control packets having the terminal 
identification number are collected, the first private line interface 
section 81-1 selects, as a selected transmission power control signal, one 
of their transmission power control packets that lowers the upward 
transmission power in the terminal 13 to the lowest power level and then 
sends the selected transmission power control signal to the first base 
station encoding section 32-1. 
Similarly, in the second radio base station 12A-2, the second private line 
interface section 81-2 generates a second transmission power control 
packet by adding the terminal identification number and the second base 
station identification number to the second transmission power control 
signal sent from the second transmission control section 34-2 and 
transmits the second transmission power control packet to the private line 
80. The second private line interface section 81-2 searches for the 
transmission power control packets having the terminal identification 
number to receive them. After all of the transmission power control 
packets having the terminal identification number are collected, the 
second private line interface section 81-2 selects, as a selected 
transmission power control signal, one of their transmission power control 
packets that lowers the upward transmission power in the terminal 13 to 
the lowest power level and then sends the selected transmission power 
control signal to the second base station encoding section 32-1. 
The host station 11 delivers to the first and the second radio base 
stations 12A-1 and 12A-2 a signal indicative of the radio base stations 
communicating with the the terminal 13 using the terminal identification 
number and the base station identification numbers. As a result, each 
radio base station can recognize how many transmission power control 
packets are sent each terminal identification number. 
The private line 80 connecting the first radio base station 12A-1 with the 
second radio base station 12A-2 may be a local area network (LAN). 
The description will proceed to operation of the CDMA type mobile 
communication system illustrated in FIG. 11. Inasmuch as operation for 
generating the first and the second transmission power control signals are 
similar to that described in conjunction with FIGS. 7 and 8, description 
thereof is omitted. 
In the first radio base station 12A-1, the first private interface section 
81-1 is supplied with the first transmission power control signal 
generated by the first transmission power control section 34-1. The first 
private line interface section 81-1 adds the terminal identification 
number for the terminal 13 and the first base station identification 
number for the first radio base station 12A-1 to the first transmission 
power control signal to produce the first transmission power control 
packet and transmits the first transmission power control packet to the 
private line 80. 
The second radio base station 12A-2 carries out similar operation in the 
first radio base station 12A-2. Specifically, the second private interface 
section 81-2 is supplied with the second transmission power control signal 
generated by the second transmission power control section 34-2. The 
second private line interface section 81-2 adds the terminal 
identification number for the terminal 13 and the second base station 
identification number for the second radio base station 12A-2 to the 
second transmission power control signal to produce the second 
transmission power control packet and transmits the second transmission 
power control packet to the private line 80. 
Each of the first and the second private line interface sections 81-1 and 
81-2 of the first and the second radio base stations 12A-1 and 12A-2 
searches for the transmission power control packets having the terminal 
identification number in the transmission power control packets flowing on 
the private line 80 to receive them. In this event, each of the first and 
the second private line interface sections 81-1 and 81-2 determines 
whether or not all of the transmission power control packets having the 
terminal identification number on the basis of the base station 
identification numbers each terminal identification number delivered from 
the host station 11. 
After all of the transmission power control packets having the terminal 
identification number are collected, the first and the second private line 
interface sections 81-1 and 81-2 select, as the selected transmission 
power control signal, one of the transmission power control packets that 
lowers the upward transmission power in the terminal 13 to the lowest 
power level and send the selected transmission power control signal to the 
first and the second base station encoding sections 32-1 and 32-2, 
respectively. A following operation where the selected transmission power 
control signal is sent from the first and the second encoding sections 
32-1 and 32-2 to the terminal 13 and the upward transmission power of the 
terminal 13 is controlled is similar to those described in conjunction 
with FIGS. 7 and 8, description thereof is omitted. 
Referring to FIG. 12, the description will proceed to operation of the 
mobile communication system illustrated in FIG. 11 in more detail. In FIG. 
12, the illustrated CDMA type mobile communication system comprises first 
through eighth radio base stations 12A-1, 12A-2, 12'-3, 12A-4, 12A-5, 
12'-6, 12A-7, and 12A-8 which serve under the host station 11. The first 
through the eight radio base stations 12A-1 to 12A-8 cover first through 
eighth cells 16-1, 16-2, 16-3, 16-4, 16-5, 16-6, 16-7, and 16-8. Each of 
the first, the fourth, and the seventh cells 16-1, 16-4, and 16-7 has a 
relatively small cell diameter while each of the second, the third, the 
fifth, the sixth, and the eighth cells 16-2, 16-3, 16-5, 16-6, and 16-8 
has a relatively large cell diameter. A private line 80 connects among the 
first, the second, the fourth, the fifth, the seventh, and the eighth 
radio base stations 12A-1, 12A-2, 12A-4, 12A-5, 12A-7, and 12A-8 each of 
which covers the cell adjacent to that having the different cell diameter. 
The first, the second, the fourth, the fifth, the seventh, and the eighth 
radio base stations 12A-1, 12A-2, 12A-4, 12A-5, 12A-7, and 12A-8 carry out 
transmission/reception on the transmission power control packets via the 
private line 80. But, inasmuch as the third and the sixth radio base 
stations 12'-3 and 12'-6 cover the third and the sixth cells 16-3 and 16-6 
adjacent to those having the same cell diameter, it is unnecessary to 
connect the third and the sixth radio base stations 12'-3 and 12'-6 
through the private line 80. This is because it is possible for the third 
and the sixth radio base stations 12'-3 and 12'-6 to control the upward 
transmission power of each terminal in accordance with the conventional 
transmission power control method. 
In FIG. 12, a first terminal 13-1 communicates with both of the first radio 
base station 12A-1 covering the first cell 16-1 having the relatively 
small cell diameter and the second radio base station 12A-2 covering the 
second cell 16-2 having the relatively large cell diameter. A second 
terminal 13-2 communicates with both of the seventh radio base station 
12A-7 covering the seventh cell 16-7 having the relatively small cell 
diameter and the eighth radio base station 12A-8 covering the eighth cell 
16-8 having the relatively large cell diameter. 
It is assumed that the first and the second terminal 13-1 and 13-2 are 
assigned with first and second terminal identification numbers NT1 and NT2 
which are equal to one and two, respectively. It is also assumed that the 
first through the eight radio base stations 12A-1 to 12A-8 are assigned 
with first through eighth base station identification numbers NB1, NB2, 
NB3, NB4, NB5, NB6, NB7, and NB8 which are equal to one, two, three, four, 
five, six, seven, and eight,respectively. 
The first terminal 13-1 transmit a first upward communication channel 
signal which are received in the first and the second radio base stations 
12A-1 and 12A-2. The first radio base station 12A-1 covering the first 
cell 16-1 having the relatively small diameter sends to the private line 
80 a first transmission power control packet obtained by adding the first 
terminal identification number and the first base station identification 
number to a first transmission power control signal indicative of lowering 
the upward transmission power of the first terminal 13-1. On the other 
hand, the second radio base stations 12A-2 covering the second cell 16-2 
having the relatively large diameter sends to the private line 80 a second 
transmission power control packet obtained by adding the first terminal 
identification number and the second base station identification number to 
a second transmission power control signal indicative of raising the 
upward transmission power of the first terminal 13-1. 
Similarly, the second terminal 13-2 transmit a second upward communication 
channel signal which are received in the seventh and the eighth radio base 
stations 12A-7 and 12A-8. The seventh radio base station 12A-7 covering 
the seventh cell 16-7 having the relatively small diameter sends to the 
private line 80 a seventh transmission power control packet obtained by 
adding the second terminal identification number and the seventh base 
station identification number to a seventh transmission power control 
signal indicative of lowering the upward transmission power of the second 
terminal 13-2. On the other hand, the eighth radio base stations 12A-8 
covering the eighth cell 16-8 having the relatively large diameter sends 
to the private line 80 an eighth transmission power control packet 
obtained by adding the second terminal identification number and the 
eighth base station identification number to an eighth transmission power 
control signal indicative of raising the upward transmission power of the 
second terminal 13-2. 
In this event, four transmission power control packets, namely, the first, 
the second, the seventh, and the eighth transmission power control packets 
flow on the private line 80. 
The first radio base station 12A-1 receives the transmission power control 
packets each having the first terminal identification number. After 
reception of the first and the second transmission power control packets 
having the first and the second base station identification numbers, the 
first radio base station 12A-1 selects, as a selected transmission power 
control signal, the first transmission power control signal so as to lower 
the upward transmission power of the first terminal 13-1 to the lowest 
power level and transmits the selected transmission power control signal 
to the first terminal 13-1. Likewise, the second radio base station 12A-2 
receives the transmission power control packets each having the first 
terminal identification number. After reception of the first and the 
second transmission power control packets having the first and the second 
base station identification numbers, the second radio base station 12A-2 
selects, as a selected transmission power control signal, the first 
transmission power control signal so as to lower the upward transmission 
of the first terminal 13-1 to the lowest power level and transmits the 
selected transmission power control signal to the first terminal 13-1. 
Similarly, communicating with the second terminal 13-2, each of the seventh 
and the eighth radio base stations 12A-7 and 12A-8 receives the seventh 
and the eighth transmission power control packets from the private line 80 
and transmits a selected transmission power control signal to the second 
terminal 13-2. Specifically, the seventh radio base station 12A-7 receives 
the transmission power control packets each having the second terminal 
identification number. After reception of the seventh and the eighth 
transmission power control packets having the seventh and the eighth base 
station identification numbers, the seventh radio base station 12A-7 
selects, as the selected transmission power control signal, the seventh 
transmission power control signal so as to lower the upward transmission 
power of the second terminal 13-2 to the lowest power level and transmits 
the selected transmission power control signal to the second terminal 
13-2. Likewise, the eighth radio base station 12A-8 receives the 
transmission power control packets each having the second terminal 
identification number. After reception of the seventh and the eighth 
transmission power control packets having the seventh and the eighth base 
station identification numbers, the eighth radio base station 12A-8 
selects, as the selected transmission power control signal, the seventh 
transmission power control signal so as to lower the upward transmission 
power of the second terminal 13-2 to the lowest power level and transmits 
the selected transmission power control signal to the second terminal 
13-2. 
As described above, in the CDMA type mobile communication system according 
to the second embodiment of this invention, the radio base stations in an 
area having the different cell diameter are connected via the private line 
or LAN to carry out transmission and reception on the transmission power 
control signals for controlling the upward transmission power of the 
terminals. As a result, is is possible to eliminate overhead in the host 
station. In addition, inasmuch as the radio base stations in the area 
having the different cell diameter alone are connected via the private 
line (LAN), it is possible to reduce transmission capacity of the private 
line in comparison with communication lines for connecting the host 
station with the radio base stations as described in the above first 
embodiment. 
While this invention has thus far been described in conjunction with a few 
preferred embodiments thereof, it will now be readily possible for those 
skilled in the art to put this invention into practice in various other 
manner. For example, the number of the radio base stations is restricted 
to two. In addition, the mobile communication system may be applicable to 
not only the CDMA type but also a TDMA type or a FDMA type.