U.S. patent application number 11/907537 was filed with the patent office on 2008-02-21 for cdma communication system and its transmission power control method.
This patent application is currently assigned to HITACHI COMMUNICATION TECHNOLOGIES, LTD.. Invention is credited to Nobukazu Doi, Keiji Hasegawa, Katsuhiko Tsunehara, Takaki Uta, Takashi Yano.
Application Number | 20080045261 11/907537 |
Document ID | / |
Family ID | 18188449 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080045261 |
Kind Code |
A1 |
Tsunehara; Katsuhiko ; et
al. |
February 21, 2008 |
CDMA communication system and its transmission power control
method
Abstract
An uplink channel transmission power control method is provided
for a CDMA mobile communication system performing one way
communication. A base station measures the received level of data
transmitted from each mobile terminal at each channel, and
generates a transmission power control signal of each uplink
traffic channel. The generated transmission power control signals
are multiplexed, and the multiplexed common transmission power
control signal is transmitted to all mobile terminals by using the
common channel shared by the mobile terminals. Each mobile terminal
derives the transmission power control signal of the uplink traffic
channel used by the terminal, from the received common transmission
power control signal, and controls the transmission power of a data
packet.
Inventors: |
Tsunehara; Katsuhiko;
(Yokohama-shi, JP) ; Yano; Takashi;
(Tokorozawa-shi, JP) ; Doi; Nobukazu;
(Hachioji-shi, JP) ; Uta; Takaki; (Yokohama-shi,
JP) ; Hasegawa; Keiji; (Higashimurayama-shi,
JP) |
Correspondence
Address: |
MATTINGLY, STANGER, MALUR & BRUNDIDGE, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Assignee: |
HITACHI COMMUNICATION TECHNOLOGIES,
LTD.
|
Family ID: |
18188449 |
Appl. No.: |
11/907537 |
Filed: |
October 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11300354 |
Dec 15, 2005 |
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11907537 |
Oct 15, 2007 |
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10262935 |
Oct 3, 2002 |
7006463 |
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11300354 |
Dec 15, 2005 |
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09818510 |
Mar 28, 2001 |
6483816 |
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10262935 |
Oct 3, 2002 |
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08985281 |
Dec 4, 1997 |
6307844 |
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09818510 |
Mar 28, 2001 |
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Current U.S.
Class: |
455/522 |
Current CPC
Class: |
H04W 52/58 20130101;
H04W 52/146 20130101; H04W 88/08 20130101; H04W 52/245 20130101;
H04W 52/54 20130101 |
Class at
Publication: |
455/522 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 1996 |
JP |
08-326493 |
Claims
1-26. (canceled)
27. A base station for communicating with a plurality of terminals
in a CDMA method, comprising: a control signal generator that
generates transmission power control signals 1-n corresponding to
uplink traffic channels 1-n for uplink data transmission with the
plurality of terminals; and a spreader that spreads the
transmission power control signals constituted in an order of 1-n,
wherein the transmission power control signals thus spread are
transmitted to the terminals via a channel in common to the
plurality of terminals.
28. The base station according to claim 27, further comprising an
adder that multiplexes the spread transmission power control
signals with downlink traffic channels 1-n for downlink data
transmission.
29. The base station according to claim 27, further comprising a
receiver that receives a signal from a terminal, wherein the
control signal generator generates the transmission power control
signal corresponding to the signal thus received.
30. A terminal for communicating with a base station in a CDMA
method, comprising a despread circuit that despreads spread
transmission power control signals by using a spread code in common
to a plurality of terminals, with the spread transmission power
control signals being transmitted from the base station via a
channel in common to the plurality of terminals, and being
configured in an order of 1-n corresponding to uplink traffic
channels 1-n for uplink data transmission.
31. The terminal according to claim 30, further comprising a
transmitter that transmits a signal in accordance with transmission
power determined based on the transmission power control signal
thus received.
32. The terminal according to claim 30, further comprising a
transmission power correction unit that selects a transmission
power control signal corresponding to the own terminal, from the
transmission power control signals transmitted via the channel in
common to the plurality of terminals.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a code division multiple
access mobile communication system and its transmission power
control method. More particularly, the present invention relates to
a packet communication system and its transmission power control
method using reservation based access control.
[0002] In a CDMA method, a plurality of mobile terminals share the
same frequency band to communicate with a single base station.
Therefore, for example, if mobile terminals A and B transmit
modulated signal waves to the base station, the signal (not desired
to be received) transmitted by the mobile terminal B interferes
with the signal (desired to be received) transmitted by the mobile
terminal A, and the communication of the mobile terminal A with the
base station is obstructed. The degree of interference depends on
the received level of a signal (not desired to be received) at the
base station. If the degree of interference becomes large to some
level or more, communication between the mobile terminal and base
station becomes impossible.
[0003] If the transmission power of each mobile terminal can be
controlled to always limit the signal level received at the base
station to a minimum necessary reception power, it becomes possible
to maximize the number of channels capable of being communicated by
the base station. The more the transmission power shifts from the
minimum necessary reception power, the less the number of channels
capable of being communicated by the base station.
[0004] As transmission power control techniques of CDMA mobile
communication, an IS-95 transmission power control method is known
and described in TIA/EIA/IS-95 which is a standard system of
digital cellular phones adopted in North America. The IS-95
transmission power control method will be described in the
following.
[0005] Since two way communication is essential for cellular
phones, a pair of an uplink traffic channel and a downlink traffic
channel is used for the communication between the base station and
a mobile terminal. The uplink traffic channel is a channel for
transmitting data from a mobile terminal to the base station, and a
downlink traffic channel is a channel for transmitting data from
the base station to the mobile terminal.
[0006] The base station measures the reception power of data
transmitted from each mobile terminal and generates a transmission
power control signal in accordance with the measured reception
power. If the reception power of data is larger than a target
reception power, the base station generates a transmission power
control signal "1" for this mobile station. Conversely if the
reception power of data is smaller than the target reception power,
the base station generates a transmission power control signal "0"
for this mobile station. The generated transmission power control
signal is inserted into data to be transmitted from the base
station to a mobile terminal, and the transmission data with the
transmission power control signal is transmitted to the mobile
terminal. The mobile terminal controls to reduce the transmission
power if the received transmission power control signal is "1", and
to increase it if "0".
[0007] This transmission power control will be described
specifically with reference to FIG. 12. Each mobile terminal 1 to n
and the base station communicate with each other by using a pair of
an uplink traffic channel and a downlink traffic channel. The upper
row of each pair represents transmission data of the downlink
traffic channel, and the lower row represents transmission data of
the uplink traffic channel. The width of transmission data,
particularly uplink transmission data, is drawn to correspond to a
reception power of the uplink data at the base station.
[0008] When the base station communicates with the mobile terminal
1, it inserts transmission power control signals 132a, 132b, 132c,
. . . into a downlink traffic channel 130a to the mobile terminal
1. The mobile terminal 1 changes its transmission power of the
uplink transmission data in accordance with the transmission power
control signal obtained from the received channel 130a. As above,
the transmission power control of the mobile terminal 1 is
performed by using the downlink traffic channel 130a. Similar
transmission power control is performed also for other mobile
terminals 2 to n.
SUMMARY OF THE INVENTION
[0009] With advancement of mobile communication techniques, needs
of not only a voice communication function (cellar phone) but also
a data communication function are becoming large.
[0010] For one way communication typical to data communication,
CDMA packet communication systems have been proposed from the
viewpoint of efficiently using channels. One proposal of such CDMA
packet communication systems is described in "Development on CDMA
Packet Mobile Communication System" by Yano, Uta, Hasegawa, and
Doi, Communication Society Meeting, the Institute of Electronics,
Information and Communication Engineers, B-389 (1996).
[0011] Voice communication is two way communication using uplink
and downlink traffic channels, whereas data communication is one
way communication using only one of uplink and downlink traffic
channels. In such one way communication, a conventional
transmission power control method for cellular phones cannot be
adopted because this method is established on the assumption that
there is one pair of uplink and downlink traffic channels.
[0012] If a paired downlink channel is provided only for the
transmission power control of the uplink traffic channel, one
downlink traffic channel is occupied by the transmission power
control of only the uplink traffic channel. The use efficiency of
traffic channels is lowered.
[0013] To solve this problem, the invention provides a CDMA packet
data communication system in which a base station controls the
transmission power of each of a plurality of mobile terminals by
using a single downlink traffic channel common for all mobile
stations.
[0014] The base station measures the received level of data
transmitted from each mobile terminal at each channel, and
generates a transmission power control signal of each channel in
accordance with the measured reception level. The generated
transmission power control signals are collected together into a
format predetermined for the system, and transmitted to all mobile
terminals by using the common channel shared by the mobile
terminals.
[0015] Each mobile terminal derives the transmission power control
signal of the uplink traffic channel used by the terminal, from the
collected transmission power control signals transmitted from the
base station, and transmits data at the transmission power changed
in accordance with the derived transmission power control
signal.
[0016] These and other objects, features and advantages of the
present invention will become more apparent in view of the
following detailed description of the preferred embodiments in
conjunction with accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a diagram showing the structure of a mobile
communication network.
[0018] FIG. 2 is a diagram illustrating a packet data communication
system using reservation based access control.
[0019] FIG. 3 is a diagram showing a first example of the structure
of a base station embodying transmission power control of the
present invention.
[0020] FIG. 4 is a diagram showing the structure of an answer
packet.
[0021] FIG. 5 is a diagram showing the structure of a unit for
measuring a received level of a traffic channel.
[0022] FIG. 6 is a diagram showing the structure of a unit for
generating a transmission power control signal of a traffic
channel.
[0023] FIG. 7 is a diagram illustrating insertion of a transmission
power control signal between answer packets.
[0024] FIG. 8 is a diagram showing a first example of the structure
of a mobile terminal embodying the transmission power control of
the invention.
[0025] FIG. 9 is a diagram illustrating a transmission power
control state of an uplink traffic channel realized by the
operations of a base station and mobile terminals according to the
present invention.
[0026] FIG. 10 is a diagram showing a second example of the
structure of a base station embodying the transmission power
control of the invention.
[0027] FIG. 11 is a diagram showing a second example of the
structure of a mobile terminal embodying the transmission power
control of the invention.
[0028] FIG. 12 is a diagram illustrating an uplink traffic channel
transmission power control method of a conventional portable
telephone system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] FIG. 1 shows the structure of a mobile communication network
applied to the present invention. A public switched telephone
network (PSTN) 200 is connected with a fixed terminal 201 such as a
telephone and a mobile communication network 202. The mobile
communication network 202 is connected with a plurality of base
stations 203a, 203b, . . . Each base station 203 communicates with
mobile terminals 204a, 204b, . . . in its service area (cell) via
radio channels 205.
[0030] In the following, the invention will be detailed by applying
it to a CDMA packet communication system using reservation based
access control shown in FIG. 2.
[0031] In the CDMA packet communication system using reservation
based access control, channels shared by a plurality of mobile
terminals in the service area include a reservation channel 1
(uplink channel), an answer channel 2 (downlink channel) and a
pilot channel 8 (downlink channel). The pilot channel 8 is a
channel used for transmitting a pilot signal 9 as a reference
signal to each mobile terminal.
[0032] A mobile terminal having a data transmission request
transmits a reservation packet 4 at a desired timing by using the
reservation channel 1. The base station is performs scheduling of
received reservation packets. The base station selects (schedules)
a channel and a time slot (a time slot 7 is defined in an uplink
traffic channel 3) via which each mobile terminal can transmit
data, from a plurality of uplink traffic channels 3. In order to
transmit the scheduling results to each mobile terminal, the base
station generates an answer packet 5 corresponding to the
reservation packet. The generated answer packet 5 is transmitted to
the corresponding mobile terminal in the area by using the answer
channel 2. The mobile terminal identifies the answer packet
destined to it from received answer packets 5, and transmits a data
packet by using the uplink traffic channel and time slot designated
by the base station.
[0033] In the example shown in FIG. 2, the mobile terminal
transmitted the reservation packet 4a receives the answer packet 5a
transmitted to it, selectively from answer packets transmitted from
the base station, and transmits a data packet 6a by using the time
slot 7a of the traffic channel 3a designated in the received answer
packet 5a.
[0034] With reference to FIGS. 3 to 9, a first embodiment will be
described which realizes a method of controlling the transmission
power of an uplink channel.
[0035] FIG. 3 shows an example of the structure of a base station.
A signal received by an antenna 30 is input via a circulator 31 to
a reception radio module 32. The reception radio module 32 performs
a high/middle frequency reception process to demodulate a signal in
a carrier frequency band into a baseband signal. Since the received
signal has a plurality of multiplexed channel signals, it is input
to an acquisition/despread circuit (33, 42a-42n) to be spectrum
despread.
[0036] A reservation channel output from the reservation channel
acquisition/despread circuit 33 is supplied via a signal line 50 to
a detector 35 whereat it is detected and then supplied to a decoder
36 whereat an error correction decode process such as Viterbi
decoding is performed. A packet interpretation unit 37 interprets
the decoded reservation packet to obtain a terminal ID of the
mobile terminal which transmitted the reservation packet and the
reservation contents such as transmission data, and transfers the
reservation contents to an answer packet generator unit 38.
[0037] The reservation packet is also input via a signal line 51 to
a unit 39 for measuring the received level of the reservation
channel. This unit 39 measures a signal to noise power ratio (SN
ratio) of the reservation packet. The measurement result of the
received level is compared with a reference reception level by an
initial transmission power control signal generator 40. In
accordance with this comparison result, a transmission power
control signal is generated which designates a transmission power
when the mobile terminal starts transmitting a data packet. The
generated transmission power control signal is input to an answer
packet generator 38.
[0038] In accordance with the reservation contents interpreted by
the packet interpretation unit 37 and the transmission power
control signal generated by the initial transmission power control
signal generator 40, the answer packet generator 38 generates an
answer packet. An example of the structure of an answer packet is
shown in FIG. 4. A mobile terminal ID is an ID of a mobile terminal
which transmitted a reservation packet. This ID is used as a
destination of the answer packet. An allocated channel 101 and an
allocated slot number 102 indicate an uplink traffic channel and a
time slot to be used by the mobile terminal and are designated by
the answer packet generator 38. An initial transmission power 103
indicates a transmission power when the mobile terminal starts
transmitting data and is designated by the transmission power
control signal input from the initial transmission power control
signal generator 40. This initial transmission power control signal
may designate an increase/decrease relative to the transmission
power when the reservation packet was transmitted, or may be an
absolute value (increased/decreased value) of the transmission
power, whichever of them is determined by the system. A CRC (Cyclic
Redundancy Check) 104 is a code added to the answer packet for
error detection/correction.
[0039] The answer packet generated in the above manner is input to
a coder 47 whereat an error correction coding such as convolutional
coding is performed. The coded answer packet is input to a unit 41
for inserting a traffic channel transmission power control
signal.
[0040] The other acquisition/despread circuits 42a to 42n provided
for a plurality of uplink traffic channels each output a data
packet transmitted via each uplink traffic channel. The data packet
of each channel is supplied via a signal line 52 to a detector
43a-43n and a decoder 44a to 44n to be detected and decoded, and
the reception data is output from a signal line 54.
[0041] The data packet is also supplied via a signal line 53 to a
unit 45 for measuring the received level of the traffic channel.
The structure of this unit 45 is shown in FIG. 5. The received
level measurement units 45a to 45n corresponding to the uplink
traffic channels 53a to 53n measure the received level such as an
SN ratio.
[0042] The received level measurement result of each traffic
channel is input to a traffic channel transmission power control
signal generator 46. The structure of the generator 46 is shown in
FIG. 6. Each of the transmission power control signal generators
46a to 46n provided for each uplink traffic channel compares the
received level with a target reception level, and generates a
transmission power control signal for making the mobile terminal
renew the transmission power when it continues data transmission.
Similar to the initial transmission power control signal, this
renewal designation transmission power control signal is determined
by the system. The generated transmission power control signal is
input to the unit 41 for inserting the traffic channel transmission
power control signal.
[0043] As shown in FIG. 7, the traffic channel transmission power
control signal insert unit 41 inserts a common transmission power
control signal 111 generated by the traffic channel transmission
power control signal generator 46 at a predetermined interval
between answer packets 110 input from the answer packet generator
38. The common transmission power control signal 111 is constituted
of transmission power control signals 111a to 111n of respective
traffic channels 1 to n.
[0044] In order to suppress a fluctuation of the received level of
a data packet, the base station is required to perform a
transmission power control of each mobile terminal at a
sufficiently high occurrence frequency. The data packet is made of
several tens of bits to allow information of some amount to be
transmitted at the same time. In contrast, the common transmission
power control signal 111 can be made of n bits assuming the same
system as IS-95. As shown in FIG. 4, the answer packet can be made
sufficiently small relative to the size of a data packet.
Therefore, as in this embodiment, even if the answer channel and
the transmission power control channel are shared, the transmission
power control can be performed at a sufficiently high occurrence
frequency. If the answer packet and the common transmission power
control signal are received by the same channel, the mobile
terminal can use a common receiver both for the answer packet and
common transmission power control signal. In this manner, the
circuit scale of each mobile terminal can be made small.
[0045] It is also possible to transmit the common transmission
power control signal at a transmission power larger than that of
the answer packet in order to reliably perform the transmission
power control.
[0046] The answer packet and common transmission power control
signal are spectrum spread by a spreader 48 for answer channel. The
spectrum spread answer packet and common transmission power control
signal are multiplexed with other downlinks by an adder 58,
modulated from the baseband signal into a signal in the carrier
frequency band by a transmission radio module 49, and transmitted
from the antenna 30 via the circulator 31.
[0047] An example of the structure of a mobile terminal is shown in
FIG. 8.
[0048] The operation of transmitting a reservation packet from a
mobile terminal will be described.
[0049] A signal received by an antenna 30 is input via a circulator
61 to a reception radio module 62. The reception radio module 62
performs a high/middle frequency reception process to demodulate a
signal in the carrier frequency band into a baseband signal. A
pilot signal output from an acquisition/spread circuit 150 for a
pilot channel is input to a unit 151 for measuring a received
level. This unit 152 measures the received level (e.g., SN ratio)
of the pilot signal. The measurement result of the received level
is input to a reservation channel gain calculator 152 which
determines the transmission power of a reservation packet in
accordance with the received level of the pilot signal.
[0050] In the mobile communication system provided with independent
pilot channels, the pilot signal is transmitted from the base
station always at a constant transmission power level. Therefore,
if an SN ratio of the received pilot signal is large, it is
conceivable that the mobile terminal is near at the base station so
that the reservation channel gain calculator 152 calculates a small
gain. Conversely, if an SN ratio of the received pilot signal is
small, it is conceivable that the mobile terminal is far from the
base station so that the reservation channel gain calculator 152
calculates a large gain. In order to determine the transmission
power of a reservation packet in the above manner, another signal
different from the pilot signal may be used so long as it allows
the mobile terminal to know the transmission power of the base
station. For example, the pilot signal whose transmission power is
determined by the system or a control signal transmitted with the
transmission power value can satisfy the above conditions.
[0051] Next, an operation will be described in which a mobile
terminal that transmitted a reservation packet to the base station
receives an answer packet transmitted from the base station.
[0052] An answer packet output from the despread circuit 63 for an
answer channel is detected with a detector and subjected to an
error correction/decode process such as Viterbi decoding. With the
above processes, it becomes possible to obtain the information of
an allocated traffic channel and an allocated time slot contained
in the answer packet. An initial transmission power holder 125
holds an initial transmission power signal contained in the answer
packet, and inputs the initial transmission power signal to a data
channel gain calculator 124 which calculates a gain so that a data
packet can be transmitted at a transmission power designated by the
initial transmission power signal. The calculated gain is set as
the gain of a variable gain amplifier 68.
[0053] The data packet transmitted from the mobile terminal is
amplified by the variable gain amplifier 68 at the gain designated
by the data channel gain calculator 124. The amplified signal is
modulated from the baseband signal into a signal in the carrier
frequency band by a transmission radio module 69 and transmitted
from the antenna 60 via the circulator 61.
[0054] Next, transmission power control while a mobile terminal
transmits a data packet to the base station will be described.
[0055] A transmission power correction unit 123 derives the common
transmission power control signal from a signal of the answer
channel processed by the answer channel acquisition/despread
circuit 63 and detector 64. The transmission power correction unit
123 selects a transmission power control signal of the uplink
traffic channel now in use by its mobile terminal, from the common
transmission power control signal. For example, in the example
shown in FIG. 7, the mobile terminal transmitting a data packet by
using the transmission channel 1 selects its transmission power
control signal 111a. The selected transmission power control signal
is input to the gain calculator 124 which calculates a gain so that
a data packet can be transmitted at a transmission power designated
by the transmission control signal, and thereafter renews the gain
of the variable gain amplifier 68. The amplified signal is
modulated by the transmission radio module 69 from the baseband
signal into a signal in the carrier frequency band, and transmitted
from the antenna 60 via the circulator 61.
[0056] FIG. 9 illustrates the state of transmission power control
realized by the above operations of the base station and a mobile
terminal.
[0057] The base station inserts common transmission power control
signals 142a, 142b, 142c, . . . into a common answer channel shared
by mobile terminals in the area and transits them. The common
transmission power control signal 142 contains transmission power
control signals for the respective traffic channels 1 to n. Each of
the mobile terminals 1 to n transmitting data packets 1 to n to the
base station derives the transmission power control signal of the
traffic channel now in use by the mobile terminal, from the common
transmission power control signals 142a, 142b, 142c, . . . In
accordance with the derived transmission power control signal, the
mobile terminal changes the transmission power of the data
packet.
[0058] In the state shown in FIG. 9, the width of a data packet is
drawn to correspond to the receive level of the data packet at the
base station. For example, in the uplink traffic channel 1, the
mobile terminal controls the transmission power such that the
transmission powers are increased, reduced, and increased in
response to the reception of the common transmission power control
signals 142a, 142b, and 142c.
[0059] While a data packet is not transmitted by a mobile station,
the transmission power control signal is neglected. The
transmission power control signal is also neglected if it is
received before a lapse time (called "control delay time")
necessary for measuring the received level of a data packet at the
base station after the mobile terminal transmitted the data packet.
The reason for this is a possibility that the transmission power
control information received before the lapse of the control delay
time may be the transmission power control information of a data
packet transmitted by another mobile terminal, resulting in
erroneous control to be made.
[0060] With the above operations, it becomes possible for the base
station to perform transmission power control of the uplink traffic
channels 1 to n by using the common control channel shared by the
mobile terminals.
[0061] This first embodiment has the structure suitable for data
communication, particularly for one way data communication. Two way
data communication is performed in some case. In this case, the
transmission power control signal may be contained in data of a
downlink traffic channel. In the following, a mobile communication
system of the second embodiment will be described which is suitable
for two way communication and has a simple circuit structure,
particularly of a mobile terminal.
[0062] FIG. 10 shows an example of the structure of a base station
according to the second embodiment.
[0063] In FIG. 10, like constituent elements to those of the base
station of the first embodiment are represented by identical
reference numerals. The operation of the base station when a
reservation packet is received is similar to the first
embodiment.
[0064] The base station operates in the manner similar to the first
embodiment to decode a received data packet and obtain reception
data from the signal line 54. The unit 45 for measuring the
received level of a traffic channel and the traffic channel
transmission power control signal generator 46 generate
transmission power control signals of respective uplink traffic
channels.
[0065] In the second embodiment, if a mobile terminal transmits and
receives a data packet to and from the base station by using an
uplink traffic channel i and a downlink traffic channel k, the base
station inputs the transmission power control signal of the uplink
traffic channel i to the traffic channel transmission power control
signal insert unit 59 of the downlink traffic channel k to insert
the transmission power control signal into the data packet.
[0066] The operation will be detailed by taking as an example the
case wherein the base station transmits a data packet by using a
downlink traffic channel n to a mobile terminal which transmits a
data packet to the base station by using an uplink traffic channel
1. In this case, the transmission power control signal of the
uplink traffic channel 1 generated by the traffic channel
transmission power control signal generator 46 is input to a
traffic channel transmission power control signal insert unit 59n
of the downlink transmission channel n. The is traffic channel
transmission power control signal insert unit 59n inserts the
transmission power control signal in the data packet. This data
packet is spectrum spread by the spreader 57n and multiplexed with
other channel signals by the adder 58. The multiplexed signal is
modulated by the transmission radio module 49 from the baseband
signal into a signal of the carrier frequency band, and transmitted
from the antenna 30 via the circulator 31.
[0067] An example of a mobile terminal of the second embodiment is
shown in FIG. 11.
[0068] In FIG. 11, like constituent elements to those of the mobile
terminal of the first embodiment shown in FIG. 8 are represented by
identical reference numerals. A switch 70 is connected to 70a to
perform similar operations to the first embodiment, if the mobile
terminal transmits a reservation packet, receives an answer packet
transmitted from the base station, or only transmits a data packet
to the base station (one way communication).
[0069] Next, an operation (two way communication) will be described
in which a mobile terminal transmits and receives a data packet to
and from the base station. In this case, the switch 10 is turned to
the 70b side.
[0070] A data packet is received via the antenna 60, circulator 61
and reception radio module 62, and subjected to a reception process
by the traffic channel acquisition/despread circuit 63b and
detector 64. The data packet output from the detector is subjected
to error correction/decoding by the decoder 65 to obtain reception
data from the signal line 66. The data packet is also input to the
transmission power correction unit 123 which derives the
transmission power control signal inserted in the data packet and
inputs it to the traffic channel gain calculator 124. The traffic
channel gain calculator 124 calculates a gain of the variable gain
amplifier 68 to renew the gain, similar to the first is
embodiment.
[0071] With the base station and mobile terminals having the above
structures and operating in the above manner, it becomes possible
for a mobile terminal to perform transmission/reception of a data
packet to/from the base station and reception of transmission power
control by the base station, by using either the answer channel or
traffic channel. Therefore, it is sufficient if only the mobile
terminal has one set of a detector and a decoder, and so the
circuit scale of the mobile terminal can be prevented from becoming
large.
[0072] In the above embodiments, the invention has been applied to
a mobile communication system of a reservation based access control
scheme in which a base station transmits a transmission power
control signal to each mobile terminal by using an answer channel.
The invention is also applicable to a channel other than the answer
channel if it is a common channel shared by mobile terminals.
Namely, if a system uses a common channel shared by mobile
terminals, the base station can perform transmission power control
of a plurality of mobile terminals by transmitting transmission
power control signals via the single common channel. Obviously, a
channel dedicated to transmission power control may be provided to
perform transmission power control of mobile terminals by
transmitting transmission power control signals from the base
station by using this dedicated channel.
[0073] While the present invention has been described above in
conjunction with the preferred embodiments, one of ordinary skill
in the art would be enabled by this disclosure to make various
modifications to this embodiment and still be within the scope nd
spirit of the invention as defined in the appended claims.
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