Title: Communication system that rejects connections based on total transmission energy
Abstract: When a base station and a plurality of terminal stations communicate with each other by radio, power control information for controlling electric power of a signal transmitted to the base station is multiplexed at the base station and transmission energy is adjusted such that total transmission energy of the multiplexed power control information becomes substantially a predetermined value if the total transmission energy of the multiplexed power control information is lower than a predetermined value. Therefore, information such as power control information that should be individually instructed to respective terminal stations can satisfactorily be transmitted by a simple arrangement and a simple processing.
Patent Number: 6,909,704 Issued on 06/21/2005 to Sakoda
| Inventors:
|
Sakoda; Kazuyuki (Tokyo, JP)
|
| Assignee:
|
Sony Corporation (Tokyo, JP)
|
| Appl. No.:
|
798582 |
| Filed:
|
March 2, 2001 |
Foreign Application Priority Data
| Mar 03, 2000[JP] | P2000-059028 |
| May 11, 2000[JP] | P2000-139043 |
| Current U.S. Class: |
370/335; 370/342; 455/522 |
| Intern'l Class: |
H04B 007/21.6 |
| Field of Search: |
370/311,335,342
455/522
|
References Cited [Referenced By]
U.S. Patent Documents
| 6307844 | Oct., 2001 | Tsunehara et al.
| |
| 6496706 | Dec., 2002 | Jou et al.
| |
| 6603752 | Aug., 2003 | Saifuddin et al.
| |
| 6633552 | Oct., 2003 | Ling et al.
| |
| 2002/0064135 | May., 2002 | Chen et al.
| |
Primary Examiner: Vanderpuye; Kenneth
Assistant Examiner: Haile; Feben Micael
Attorney, Agent or Firm: Maioli; Jay H.
Claims
1. A communication system in which a base station and a plurality of terminal
stations communicate by radio, comprising:
a base station having:
data processing means for processing data transmitted to each of said plurality
of terminal stations;
power control information processing means for generating power control information
for controlling a transmission of electric power at each of said terminal stations
and adjusting a transmission energy such that a total transmission energy of multiplexed
power control information becomes substantially a predetermined value when said
total transmission energy of multiplexed power control information is lower than
a predetermined threshold value; and
transmission processing means for multiplexing and transmitting signals processed
by said data processing means and said multiplexed power control information processed
by said power control information processing means; and
said plurality of terminal stations each have:
measuring means for measuring a communication state of a signal transmitted from
said base station; and
transmission processing means for transmitting information on said communication
state measured by said measuring means by electric power controlled based upon
said power control information transmitted from said transmission processing means
of said base station,
wherein said base station includes communication connection setting means for
rejecting a setting of a connection with each of said plurality of terminal stations
when said total transmission energy obtained before said power control information
multiplexed by said power control information processing means of said base station
is adjusted is higher than said predetermined threshold value.
2. The communication system according to claim 1, wherein said communication
connection setting means forces a connection with a low priority to end and sets
a connection with a high priority when it is determined by said communication connection
setting means that another connection requested to be set has a high priority.
3. A communication system in which a base station and a plurality of terminal
stations communicate by radio, comprising:
a base station having:
data processing means for processing data transmitted to each of said plurality
of terminal stations;
power control information processing means for generating power control information
for controlling a transmission of electric power at each of said terminal stations
and adjusting a transmission energy such that a total transmission energy of multiplexed
power control information becomes substantially a predetermined value when said
total transmission energy of multiplexed power control information is lower than
a predetermined threshold value;
transmission processing means for multiplexing and transmitting signals processed
by said data processing means and said multiplexed power control information processed
by said power control information processing means; and
said plurality of terminal stations each have:
measuring means for measuring a communication state of a signal transmitted from
said base station; and
transmission processing means for transmitting information on said communication
state measured by said measuring means by electric power controlled based upon
said power control information transmitted from said transmission processing means
of said base station,
wherein said base station includes communication connection setting means for
forcing an end of a connection with any currently accommodated one of said terminal
stations when said total transmission energy obtained before said power control
information multiplexed by said power control information processing means of said
base station is adjusted is higher than said predetermined threshold value.
4. The communication system according to claim 3, wherein said power control
information processing means adaptively sets and multiplexes said transmission
energy of power control information of said terminal stations for each of said
plurality of terminal stations and said connection forced to end by said communication
connection setting means is selected from among connections whose transmission
energy is set large by said power control information processing means.
5. The communication system according to claim 3, wherein said connection forced
to end by said communication connection setting means is selected from among a
predetermined group of connections with a low priority.
6. A communication method in which a base station and a plurality of terminal
stations communicate by radio, comprising the steps of:
generating power control information for controlling electric power for a signal
transmitted to said base station from said plurality of terminal stations;
adjusting transmission energy such that a total transmission energy of multiplexed
power control information becomes substantially a predetermined value when said
total transmission energy of said multiplexed power control information is lower
than a predetermined threshold value;
transmitting said multiplexed power control information from said base station
to said plurality of terminal stations; and
rejecting a setting of a connection with one of said terminal stations when said
total transmission energy obtained before said multiplexed power control information
is adjusted is higher than said predetermined threshold value.
7. The communication method according to claim 6, further comprising the step
of forcing a connection with a low priority to end and setting a connection with
a high priority when a priority of another connection requested to be set is high.
8. A communication method in which a base station and a plurality of terminal
stations communicate by radio, comprising the steps of:
generating power control information for controlling electric power for a signal
transmitted to said base station from said plurality of terminal stations;
adjusting transmission energy such that a total transmission energy of multiplexed
power control information becomes substantially a predetermined value when said
total transmission energy of said multiplexed power control information is lower
than a predetermined threshold value;
transmitting said multiplexed power control information from said base station
to said plurality of terminal stations; and
forcing an end of a connection with any currently accommodated said terminal
stations when said total transmission energy obtained before said multiplexed power
control information is adjusted is higher than said predetermined threshold value.
9. The communication method according to claim 8, further comprising the steps of:
adaptively setting and multiplexing transmission energy of power control information
toward said plurality of terminal stations for each of said plurality of terminal
stations individually; and
selecting said connection forced to end from a connection group in which transmission
energies are set large.
10. The communication method according to claim 8, further comprising the step
of selecting said connection forced to end from among a predetermined group of
connections with a low priority.
11. A communication apparatus for communicating with a plurality of terminal
stations by radio, comprising:
data processing means for processing data transmitted to each of said terminal
stations;
power control information processing means for individually generating power
control information for controlling transmission electric power at each of said
terminal stations and adjusting a transmission energy such that a total transmission
energy of multiplexed power control information becomes substantially a predetermined
value when said total transmission energy of said multiplexed power control information
is lower than a predetermined threshold value;
transmission processing means for multiplexing and transmitting a signal processed
by said data processing means and said multiplexed power control information processed
by said power control information processing means; and
communication connection setting means for rejecting a setting of a connection
with another terminal station when said total transmission energy obtained before
said power control information multiplexed by said power control information processing
means is adjusted is higher than said predetermined threshold value.
12. The communication apparatus according to claim 11, wherein said communication
setting means forces an end of a connection with a low priority and sets a connection
with a high priority when it is determined by said communication connection setting
means that a priority of a requested connection is high.
13. A communication apparatus for communicating with a plurality of terminal
stations by radio, comprising:
data processing means for processing data transmitted to each of said terminal
stations;
power control information processing means for individually generating power
control information for controlling transmission electric power at each of said
terminal stations and adjusting a transmission energy such that a total transmission
energy of multiplexed power control information becomes substantially a predetermined
value when said total transmission energy of said multiplexed power control information
is lower than a predetermined threshold value;
transmission processing means for multiplexing and transmitting a signal processed
by said data processing means and said multiplexed power control information processed
by said power control information processing means; and
communication connection setting means for forcing an end of a connection with
any currently accommodated terminal stations when said total transmission energy
obtained before said power control information multiplexed by said power control
information processing means is adjusted is higher than said predetermined threshold
value.
14. The communication apparatus according to claim 13, wherein said power control
information processing means adaptively sets and multiplexes said transmission
energy of power control information toward each of said plurality of terminal stations
individually and said connection forced to end by said communication connection
setting means is selected from among connections in which transmission energy is
set large by said power control information processing means.
15. The communication apparatus according to claim 13, wherein said connection
forced to end by said communication connection setting means is selected from among
a predetermined group of connections with a low priority.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a communication system and a communication
method suitable for use for a cellular wireless communication system and a communication
apparatus for use in a base station of this communication system. More particularly,
this invention relates to a communication system, a communication method and a
communication apparatus suitable for use in a system which transmits a CDMA (code
division multiple access) signal by radio, for example.
2. Description of the Related Art
There is proposed a digital cellular wireless communication system for effecting
a data communication between a base station and a plurality of terminal stations,
in which down-link communications are transmitted from the base station to the
terminal stations with a frame arrangement shown in FIGS. 1A and 1B. This digital
cellular wireless communication system shows an example of a transmission arrangement
of a system called an HDR (high data rate). FIG. 1A is a diagram showing a frame
arrangement in which slots of a unit length are located continuously. FIG. 1B shows
an arrangement of one slot in which there are disposed a first data interval, a
first pilot interval, a second data interval, a third data interval, a first power
control information interval, a second pilot interval, a second power control information
interval and a fourth data interval, in that order. In FIG. 1B, each power control
information interval is shown as RPC for simplicity.
As shown in FIG. 1B, a preamble signal is disposed at a part of the starting
portion
of the first data interval. Data within the preamble signal indicates a terminal
station to which the data within the slot is transmitted. The first to fourth data
intervals are set to be of the same duration. To be concrete, the first to fourth
data intervals are respectively set to be 464 chips, the first and second pilot
intervals are respectively set to be 96 chips, the first and second power control
information intervals are set to be 64 chips, respectively, and the length of one
slot is set to be 2176 chips, for example.
In the case of this digital cellular wireless communication system, a data interval
within one slot is allocated as an interval for transmitting data to one terminal
station. Accordingly, when data should be transmitted from the base station to
a plurality of specific terminal stations, a plurality of terminal stations, for
example, transmit data by sequentially using one slot each. The power control information
intervals (RPC) located ahead of and behind the second pilot interval individually
transmit power control information to respective terminal stations which are communicating
with the base station. The pilot interval is fundamentally the interval in which
data is received by all terminal station. This power control information is data
for designating a transmission electric power of an up-link through which data
is transmitted from each terminal station to the base station and instructs individual
terminal stations either to increase a transmission power or decrease a transmission power.
In order to simultaneously and individually transmit the power control information
to individual terminal stations, in the proposed system according to the related
art, power control information for each terminal station is spread by using a code
allocated to every terminal station and the power control information thus spread
for each terminal station are multiplexed and then transmitted. The processing
in which a plurality of data thus spread by using the code corresponds to a CDMA
(code division multiple access) system processing.
FIG. 1C is a diagram showing the manner in which power control information is
transmitted in the first and second power control information intervals. In this
example, power control information is simultaneously transmitted to six terminal
stations of users #0 to #5, and power control information for six terminal stations
are held at the same transmission electric power, spread, multiplexed and then transmitted.
Transmission electric powers of all signals transmitted from the base
station during each slot period are set at the same value (fixed value), and the
total transmission electric powers of the power control information transmitted
during the first and second power control information intervals also are set to
be this fixed value. Accordingly, as shown in FIG. 1C, for example, when the power
control information is simultaneously transmitted to the six terminal stations,
a transmission electric power of each power control information becomes ⅙
of the fixed value. While the power control information to the six users #0 to
#5 are illustrated in the state that they are simply added for simplicity in the
example shown in FIG. 1C, in actual practice, the power control information that
has been spread by using the code is added.
In the case of this digital cellular wireless communication system, a modulation
system and a coding rate of data transmitted from the base station during the data
interval is adaptively set in response to the communication state between the base
station and the terminal station of the called party so that even the arrangement
in which the transmission electric power is fixed as described above can cope with
the change of the wireless communication state between the base station and the
terminal station.
FIG. 2 (formed of FIGS. 2A and 2B drawn on two sheets of drawings to permit
a use of a suitably large-scale) is a block diagram showing an example of an arrangement
of a transmission system of a base station for transmitting data to each terminal
station with the arrangement of the frame shown in FIGS. 1A and 1B, for example.
As shown in FIG. 2, there is provided a transmission data generating section
10
which is a circuit for generating data transmitted to a terminal station. A reception
power management section
11 is a circuit for generating power control information
transmitted to the terminal stations. Power control information to individual terminal
stations are supplied to separate terminals (these terminals will hereinafter be
referred to as "power control information input terminals")
12a to
12n. A pilot channel input terminal
13 is a terminal to which
pilot data is supplied from a pilot data setting circuit (not shown).
Transmission data generated from the transmission data generating section
10 is supplied to a data transmission processing section
14, in which
it is subjected to processings for transmission such as transmission coding processing,
modulation processing and interleave processing. The data processed herein is data
located in the first to fourth data intervals of the slot arrangement shown in
FIGS. 1A and 1B, and the preamble data located at the starting portion of the first
data interval also is processed. Since data allocated in the first to fourth data
intervals are fundamentally allocated to one terminal station by the slot unit
as earlier noted, during a period in which data of one slot is processed, the coding
system and the modulation system suited for the terminal station for effecting
a communication in that slot are set by the data transmission processing section
14 and the transmission processing is executed.
The coding system and the modulation system suitable for the terminal station
are set based on bit rate information supplied from a data rate control section
15 to the data transmission processing section
14. To be concrete,
when data which is to be transmitted to a terminal station of which communication
state (receiving situation at the terminal station) is satisfactory is transmitted,
transmission data is coded by a multivalued modulation such as a 16QAM (16-quadrature
amplitude modulation) and a high coding rate and transmitted at a high throughput.
When transmission data which is to be transmitted to a terminal station whose communication
state is not satisfactory is transmitted, transmission data is coded at a low coding
rate and a QPSK (quadrature phase shift keying)-modulated signal is spread or transmitted
a plurality of times and thereby transmitted at a low throughput. Transmission
data (I-channel data and Q-channel data) processed by the data transmission processing
section
14 are supplied to a channel multiplex circuit
16.
Power control information supplied to the power control information input terminals
12a to
12n are information prepared individually at
a plurality of terminal stations with which the base station communicate in the
same period, and individual information is separately supplied to the power control
information input terminals
12a to
12n at every terminal
station. Accordingly, power control information are generated and supplied in response
to the number of terminal stations which communicate with the base station in the
same period. Power control information supplied to one terminal station is 1-bit
information per slot. Such 1-bit information is used to instruct the corresponding
terminal station to increase transmission electric power or to decrease transmission
electric power.
Respective power control information obtained by the power control information
input terminals
12a to
12n are supplied to repetitive
processing sections
17a to
17n, in which each 1-bit
data is broken into four-times data, i.e., 4-bit data in which 1-bit data is repeated
four times. The 4-bit power control information per slot are respectively supplied
to respective spread processing circuits
18a to
18n,
in which they are spread and modulated into data having a predetermined-time bit
rate (bit rate of 32 times) by using a predetermined code (e.g., Walsh Code) set
at every terminal station and thereby I-channel power control information and Q-channel
power control information are obtained. Since the 4-bit data is spread by 32 times,
there may be obtained data having a data rate of 128 chips/slot.
The data spread and modulated by the respective spread processing circuits
18a
to
18n are supplied to a symbol multiplex circuit
19,
in which they are mixed into signals of one system. The signals thus mixed are
supplied to a variable gain setting circuit
20. The variable gain setting
circuit
20 adjusts the gains of the mixed power control information in a
way that the gains may become constant values. Specifically, in the case of this
example, the gain of the signal transmitted from the base station is a predetermined
constant value. The number of data which are multiplexed by the symbol multiplex
circuit
19 is changed in response to the number of terminal stations which
are communicating with the base station at that time. Therefore, in response to
the number of data multiplexed by the symbol multiplex circuit
19, the variable
gain setting circuit
20 generates a signal having a constant gain by adjusting
the gain of the transmission signal. The signals whose gain has been adjusted by
the variable gain setting circuit
20 are supplied to a channel multiplex
circuit
16.
Pilot data obtained by a pilot channel input terminal
13 are all null
data and hence supplied to the channel multiplex circuit
16 as they are.
The channel multiplex circuit
16 multiplexes the respective signals supplied
thereto in a time-division manner such that the slot arrangement shown in FIG.
1B may be obtained. The signals thus multiplexed in a time-division manner by the
channel multiplex circuit
16 are supplied to a scramble processing circuit
21. The scramble processing circuit
21 is supplied with spread codes
of both I-channel and Q-channel set for the base station from terminals
22i,
22q and spreads data by using these spread codes. The spread transmission
signals of the I-channel and Q-channel are supplied to a digital-to-analog (D/A)
converter
23, in which they are converted from digital data into analog
data. The analog transmission signal is supplied to a high-frequency (radio-frequency)
circuit
24, in which it is processed as a high-frequency signal and thereby
converted into a signal having a predetermined transmission frequency channel.
Then, the signal having the converted transmission frequency is supplied to an
antenna
25, from which it is transmitted to each terminal station by radio.
Since the transmission signal is transmitted from the base station to each
terminal station as described above, the base station is able to individually communicate
with respective terminal stations at the unit of slots and is able to simultaneously
transmit the power control information for instructing the transmission state of
each terminal station to all terminal stations at every slot. With respect to the
wireless transmission of up-link information from each terminal station to the
base station, the transmission electric power can properly be set based on the
power control information transmitted from the base station and the base station
can satisfactorily receive the signal from each terminal station. With respect
to the wireless transmission of down-link information from the base station to
each terminal station, since the coding ratio and the modulation system are set
adaptively although the transmission power is fixed to the constant value, the
transmission signal can be satisfactorily received by any terminal station. Specifically,
if each terminal station is a mobile station, then although a distance or a communication
state between each terminal station and the base station is changed at any time,
the above processing is effected on the transmission signals of up-link information
and down-link information respectively, whereby the transmission processing following
the change of the distance or the communication state is set adaptively so that
wireless communication can constantly be carried out satisfactorily.
Since the power control information multiplexed and simultaneously transmitted
are spread by an individual code at every terminal station and transmitted, each
terminal station can receive only its own power control information by despreading
the received signal with the code allocated thereto, and hence each terminal station
can receive power control information properly.
In the above transmission system, let it be assumed that many users (terminal
stations) want a connection at the same time. At that time, since the traffic channel
of down-link transmitted from the base station is adapted to be shared by a plurality
of users, many users can be accommodated by decreasing a time occupying ratio per
user from a principle standpoint. With respect to the traffic channel of up-link
transmitted from the terminal station, if the transmission electric power is decreased
by decreasing the transmission bit rate per user, then the time occupying ratio
can be decreased and hence the number of users can be increased. If a communication
between the base station and the terminal station is data communication, then data
transmission periods are generated in a burst fashion and hence there occurs a
time zone in which there exists no transmission data even though the connection
is established. Accordingly, there frequently occurs the situation in which one
base station accommodates many terminal stations whose connections are established
between them and the base station.
In the above transmission channel, if the number of users having connections
established
increases, electric power distributed to power control information (PC information)
per channel decreases. The reason for this is as follows:
An electric power distributed to power control information per channel, for example,
is expressed as:
Further, in order that interference by a terminal station accommodated in
an adjacent cell comprised of another base station can be controlled, (with respect
to a terminal station which will become a large interference source terminal station),
power control information should be transmitted to a terminal station which does
not transmit and receive data between it and its own station. Consequently, since
one terminal station monopolizes power control information intervals of transmission
signals of a plurality of base stations, there should be provided more power control
information transmission channels than the number of the accommodated terminal stations.
In this case, since [Electric power of PC information per channel (connection)]=total
transmission power/number of channels in power control information interval and
[number of channels in power control information]>[number of connections]
are established, there are required more channels of the power control information intervals.
If the number of accommodated connections increases excessively, then the number
of transmitted control information increases in response thereto and transmission
electric power of control information distributed to one channel decreases. As
a result, when the terminal station receives power control information, there arises
a problem that the terminal station cannot receive the power control information
correctly because of a shortage of electric power. If the terminal station becomes
unable to correctly receive the power control information, then a receiving electric
power at the reception side of the up-link cannot be kept constant. As a consequence,
it is unavoidable that a quality of an up-link network line is degraded.
SUMMARY OF THE INVENTION
In view of the aforesaid aspect, it is an object of the present invention to
provide
a communication system, a communication method and a communication apparatus in
which information such as power control information that should be individually
instructed to respective terminal stations can satisfactorily be transmitted to
all terminal stations by simple arrangement and simple processing.
According to an aspect of the present invention, there is provided a communication
system in which a base station and a plurality of terminal stations communicate
with each other by radio. This communication system is comprised of a base station
which is comprised of data processing means for processing data transmitted to
each of the terminal stations, power control information processing means for individually
generating and multiplexing power control information for instructing a transmission
electric power at each of the terminal stations and adjusting transmission energy
such that total transmission energy of multiplexed power control information becomes
substantially a predetermined value if the total transmission energy of multiplexed
power control information is lower than a predetermined threshold value and transmission
processing means for multiplexing and transmitting signals processed by the data
processing means and the multiplexed power control information processed by the
power control information processing means and each of the terminal station which
is comprised of measuring means for measuring a receiving situation of a signal
transmitted from the base station and transmission processing means for transmitting
information of the receiving situation measured by the measuring means by an electric
power set based on power control information transmitted from the transmission
processing means of the base station.
According to other aspect of the present invention, there is provided a
communication method in which a base station and a plurality of terminal stations
communicate with each other by radio. This communication method is comprised of
the steps of generating power control information for instructing an electric power
of a signal transmitted to the base station from the base station to the plurality
of terminal stations, adjusting transmission energy such that total transmission
energy of multiplexed power control information becomes substantially a predetermined
value if the total transmission energy of the multiplexed power control information
is lower than a predetermined threshold value, and transmitting the multiplexed
power control information from the base station to the plurality of terminal stations.
According to a further aspect of the present invention, there is provided
a communication apparatus for communicating with a plurality of terminal stations
by radio which is comprised of data processing means for processing data transmitted
to each of the terminal stations, power control information processing means for
individually generating power control information for instructing transmission
electric power at each of the terminal stations and adjusting the transmission
energy such that total transmission energy of multiplexed power control information
becomes substantially a predetermined value if a total transmission energy of the
multiplexed power control information is lower than a predetermined threshold value
and transmission processing means for multiplexing and transmitting the multiplexed
power control information processed by the data processing means and a signal processed
by the power control information processing means.
According to the present invention, when a base station and a plurality
of terminal stations are communicated with each other by radio, control information
for instructing an electric power of a signal transmitted to the base station are
multiplexed from the base station to a plurality of terminals and a transmission
energy is adjusted such that the transmission energy becomes substantially a predetermined
value if a total transmission energy of the multiplexed power control information
is lower than the predetermined value.
According to the present invention, the total transmission energy of the
power control information multiplexed and transmitted from the base station is
adjusted to become substantially the predetermined value and the transmission state
of the power control information becomes satisfactory.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1C are explanatory diagrams showing an example of a frame
format of down-link from a base station to a terminal station and an example of
an electric power distribution according to the related art, respectively;
FIG. 2 (formed of FIGS. 2A and 2B drawn on two sheets of drawings so as to permit
a use of a suitably large-scale) is a block diagram showing an example of an entire
arrangement of a transmission system of a base station according to the related art;
FIG. 3 (formed of FIGS. 3A and 3B drawn on two sheets of drawings so as to permit
a use of a suitably large-scale) is a block diagram showing an example of an overall
arrangement of a transmission system according to an embodiment of the present invention;
FIGS. 4A and 4B are explanatory diagrams showing an example of a part of a
slot arrangement and an example of an electric power distribution, respectively;
FIG. 5 is a flowchart to which reference will be made in explaining how to control
a signal power and the manner in which a new channel is accepted;
FIGS. 6A and 6B are explanatory diagrams showing the manner in which electric
power of power control information is set (when a new channel is accepted), respectively;
FIGS. 7A and 7B are explanatory diagrams showing the manner in which electric
power of power control information is set (when a new channel is not accepted), respectively;
FIG. 8 is a flowchart to which reference will be made in explaining power control
and the manner in which a new channel is accepted;
FIG. 9 is a flowchart to which reference will be made in explaining power control
and the manner in which a new channel is accepted;
FIG. 10 is an explanatory diagram showing an example of a transmission state
according to an embodiment of the present invention; and
FIG. 11 is a block diagram showing an example of an arrangement of a terminal
station according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A communication system, a communication method and a communication apparatus
according
to an embodiment of the present invention will be described below with reference
to FIGS. 3 to
11. In FIGS. 3 to
11, elements and parts identical
to those of FIGS. 1A to
1C and FIG. 2 of the related art are identified
with identical reference numerals.
In this embodiment, the present invention is applied to a communication system
in which a CDMA system wireless signal is transmitted between the base station
and a plurality of terminal stations in a bidirectional fashion. A fundamental
slot arrangement used when a down-link signal is transmitted from the base station
to each terminal station is the same as that shown in FIG. 1B as the example of
the related art. Specifically, under the condition that the down-link transmission
from the base station to each terminal station is based on a TDMA (time division
multiple access) system with the frame arrangement shown in FIG.
1A and
in which one slot is allocated to one terminal station, the power control information
transmission interval is applied to an HDR (high data rate) system in which signals
to a plurality of terminal stations and which had been spread by using different
spread codes for every terminal are multiplexed. In the case of this embodiment,
the transmission processing of the power control information within the power control
information transmission interval is executed by processings different from those
of the related art.
FIG. 3 (formed of FIGS. 3A and 3B drawn on two sheets of drawings so as to permit
a use of a suitably large-scale) is a block diagram showing an example of an arrangement
of a transmission system of a base station according to this embodiment.
As shown in FIG. 3, transmission data outputted from the transmission data generating
section
10 is supplied to the data transmission processing section
14,
in which it is processed in a transmission processing fashion such as a coding
processing, a modulation processing and an interleave processing. When the transmission
data is generated from the transmission data generating section
10, transmission
data to a designated terminal station is generated based on control data generated
from a control data generating section
28. The control data generating section
28 is adapted to generate control data under control of a channel management
section
27. The channel management section
27 is a control section
which manages the base station when the base station communicates with a specific
terminal station.
When the data transmission processing section
14 processes transmission
data, suitable factors such as a coding rate, a modulation system and the number
of repeated data are adaptively set based on bit rate information supplied from
the data rate control section
15 to the data transmission processing section
14. This data rate control section
15 is adapted to generate bit
rate information based on information concerning a communication state transmitted
from a terminal station, for example. Information concerning communication states
transmitted from respective terminal stations is one which results from converting
the reception state (by way of example, a level difference called a CIR between
received electric power of a desired wave and received electric power of an interference
wave) of the signal into absolute values based on a predetermined conversion table.
The following table 1 indicates an example of a relationship among coding rates,
modulation systems and the number of repeated data which are set when the data
transmission processing section
14 transmits data to the corresponding terminal
station based on the information concerning the communication state. The table
1 sets 11 stages of the communication states and shows examples of data rates.
| TABLE 1 |
| |
| Value of |
|
|
|
|
|
| Com- |
|
Cod- |
Modu- |
Number |
| munica- |
Measured |
ing |
lation |
of |
| tion state |
CIR value |
rate |
system |
repetitions |
Data rate |
| |
| |
| 0 |
CIR < -;7 [dB] |
¼ |
QPSK |
16 |
0.03125 |
| |
|
|
|
|
[bit/symbol] |
| 1 |
-;7 [dB] < CIR < |
¼ |
QPSK |
8 |
0.0625 |
| |
-;8 [dB] |
|
|
|
[bit/symbol] |
| 2 |
-;6 [dB] < CIR < |
¼ |
QPSK |
6 |
0.0833 |
| |
-;4 [dB] |
|
|
|
[bit/symbol] |
| 3 |
-;4 [dB] < CIR < |
¼ |
QPSK |
4 |
0.1250 |
| |
-;3 [dB] |
|
|
|
[bit/symbol] |
| 4 |
-;3 [dB] < CIR < |
¼ |
QPSK |
3 |
0.1667 |
| |
-;2 [dB] |
|
|
|
[bit/symbol] |
| 5 |
-;2 [dB] < CIR < |
¼ |
QPSK |
2 |
0.2500 |
| |
-;1 [dB] |
|
|
|
[bit/symbol] |
| 6 |
1 [dB] < CIR < |
¼ |
QPSK |
1 |
0.5000 |
| |
3 [dB] |
|
|
|
[bit/symbol] |
| 7 |
3 [dB] < CIR < |
⅜ |
QPSK |
1 |
0.7500 |
| |
5 [dB] |
|
|
|
[bit/symbol] |
| 8 |
5 [dB] < CIR < |
½ |
QPSK |
1 |
1.0000 |
| |
9 [dB] |
|
|
|
[bit/symbol] |
| 9 |
9 [dB] < CIR < |
½ |
8PSK |
1 |
1.5000 |
| |
12 [dB] |
|
|
|
[bit/symbol] |
| 10 |
12 [dB] < CIR |
½ |
16QAM |
1 |
2.0000 |
| |
|
|
|
|
[bit/symbol] |
| |
In this manner, the data rates are adaptively set in response to the communication
states with the respective terminal stations. Then, the transmission data (data
of I-channel and data of Q-channel) processed by the data transmission processing
section
14 are supplied to the channel multiplex circuit
16.
Power control information supplied from the reception power management section
11 to the power control information input terminals
12a to
12n is information individually prepared for a plurality of terminal
stations with which the base station communicates in the same period. For every
terminal station, individual information is separately supplied to the input terminals
12a to
12n. Power control information to one terminal
station is information of one bit per slot. Such one-bit information is used to
instruct the corresponding terminal station such that the corresponding terminal
station increases the transmission electric power or decreases the transmission
electric power.
Respective power control information obtained by the input terminals
12a
to
12n is respectively supplied to power control circuits
31a
to
31n and thereby converted into multivalued signals. FIG. 3
shows the case in which respective power control information is converted by the
power control circuits
31a to
31n into 2-bit information
(2-bit parallel data) per slot in which transmission energy setting bit is added.
This transmission energy setting bit is generated based on the bit rate information
supplied from the data rate control section
15. To be concrete, when a transmission
setting bit rate to the destination terminal station of information handled by
the power control circuit of the system is higher than a reference rate, a bit
for setting low transmission energy is added to the power control information based
on the bit rate information from the data rate control section
15, for example.
When on the other hand a transmission setting bit rate to the destination terminal
station of information handled by the power control circuit of the system is lower
than the reference rate, a bit for setting high transmission energy is added to
the power control information.
The power control information with transmission energy setting bits added by
the respective power control circuits
31a and
31n are
respectively supplied to other direct sequence processing sections
32a
to
32n, in which they are converted into data of 4 times in which
the same information is repeated 4 times per slot. The power control information
converted into the data of 4 times by the respective direct sequence processing
sections
32a to
32n are respectively supplied to separate
spread processing circuits
33a to
33n, in which it
is spread and modulated into data of predetermined times (32 times) by using a
predetermined code (e.g., Walsh Code) set at every terminal station and thereby
power control information of I-channel and Q-channel are obtained.
The data that had been spread and modulated by the respective spread processing
circuits
33a to
33n are supplied to a symbol multiplex
circuit
34, in which they are mixed as signals of one system. As a mixing
processing executed at that time, the mixing states are adaptively set based on
transmission energy set bit information. To be concrete, based on the transmission
energy setting bit, there are changed a mixing ratio of power control information
instructed to set low a transmission energy and a mixing ratio instructed to set
a high transmission energy. Here, the mixing ratio is such one obtained from a
signal electric power (amplitude) standpoint.
FIGS. 4A and 4B are respectively diagrams showing examples in which mixing
ratios of power control information are set. As shown in FIG. 4A, it is assumed
that first and second power control information intervals (RPC) are located ahead
of and behind the second pilot interval. Respective data intervals are assumed
to be 464 chips, a pilot interval is assumed to be 96 chips, and the first and
second power control information intervals are respectively assumed to be 64 chips.
Let it be assumed that power control information should simultaneously be transmitted
to six terminal stations of users #0 to #5 in the power control information interval,
data to the users #0 and #1 are power control information instructed to set a high
transmission energy and data with respect to the remaining users #2 to #5 are power
control information instructed to set a low transmission energy. At that time,
as shown in FIG. 4B, power control information of the users #0, #1 are mixed in
such a manner that they become a signal electric power about twice as large as
those of the power control information for other users #2 to #5. When it is instructed
that all mixed power control information is mixed at a low mixing ratio or at a
high mixing ratio, as a result, the mixing ratios of information become equal to
each other.
Referring back to FIG. 3, the power control information mixed into the
signal of one system by the symbol multiplex circuit
34 as described above
is supplied to the variable gain setting circuit
20. The variable gain setting
circuit
20 adjusts the mixed power control information such that the total
gain of the mixed power control information becomes substantially a constant value.
Specifically, in the case of this embodiment, the gain of the signal transmitted
from the base station is a predetermined constant value and the variable gain setting
circuit
20 adjusts the gain in such a manner that the output from the symbol
multiplex circuit
34 may become constant electric power. Since the gain
adjustment is effected on the mixed power control information, mixing ratios (electric
power ratios) of amplitudes of power control information for respective users are
still those set when power control information are mixed by the symbol multiplex
circuit
34.
The variable gain setting circuit
20 adjusts power control information
under control of a total RPC power control section
26. Bit rate information
is supplied to the total RPC power control section
26 from the data rate
control section
15. The total RPC power control section
26 controls
power control information with reference to bit rate information. The total RPC
power control section
26 communicates with the channel management section
27 and manages the channel setting situation based on the transmitted state
of power control information. The situation in which the variable gain setting
circuit
20 sets the total gain of the power control information under control
of the total RPC power control section
26 will be described later on. The
signal whose gain has been adjusted by the variable gain setting circuit
20
is supplied to the channel multiplex circuit
16.
Pilot data obtained by the pilot channel input terminal
13 are all null
data and therefore supplied to the channel multiplex circuit
16 as they are.
The channel multiplex circuit
16 multiplexes supplied signals in a time-division
manner in a way that a predetermined slot arrangement (slot arrangement shown in
FIG. 1B) may be obtained. The power control information supplied from the variable
gain setting circuit
20 is multiplexed in such a manner that data of each
slot unit is divided into data of first half and data of second half and the data
of first half is located in the first power control information interval and the
data of the second half is located in the second power control information interval.
The signals thus multiplexed by the channel multiplex circuit
16 in a
time-division manner are supplied to the scramble processing circuit
21.
This scramble processing circuit
21 is supplied with the spread codes of
I-channel and Q-channel set for this base station from the terminals
22i,
22q and spreads the transmission signals by using these spread codes.
The transmission signals of the I-channel and Q-channel are supplied to the digital-to-analog
(D/A) converter
23, in which they are converted into an analog transmission
signal. The analog transmission signal from the D/A converter
23 is supplied
to the high-frequency (RF) circuit
24, in which it is converted into a channel
signal having a predetermined transmission frequency by a high-frequency signal
processing. The converted signal having the above transmission frequency is transmitted
from the antenna
25 by radio and thereby transmitted to each terminal station
within the area by radio.
Next, the manner in which the transmission electric power of the power control
information is controlled and the channel is managed based on the control of the
transmission electric power of the power control information within the above base
station will be described below. The control of the transmission electric power
of the power control information is executed by the variable gain setting circuit
20 under control of the total RPC power control section
26. The total
RCP power control section
26 instructs the channel management section
27
in channel management in response to the state in which the power control information
is being transmitted at that time.
An example of control of the transmission electric power of the power control
information and channel management executed by the total RPC power control section
26 will be described below with reference to a flowchart of FIG. 5 (this
example will be referred to as an "example 1").
Referring to FIG. 5, and the following the start of operation, at a step
101, the total RPC power control circuit
26 detects a total gain
of mixed power control information outputted from the symbol multiplex circuit
34. It is detected at the next decision step
102 whether or not the
detected gain is lower than a previously-set threshold value Pth. For example,
as shown in FIG. 6A, when a maximum power Pmax of a transmission electric power
of power control information is set, the threshold value Pth is set to a value
which is about 75% of the maximum power Pmax. The maximum value Pmax corresponds
to an output level of power control information adjusted by the variable gain setting
circuit
20 and is substantially a maximum electric power which falls within
a tolerance range as signals transmitted from this base station, namely the same
level as data intervals, pilot intervals etc., for example (or an electric power
slightly lower than the maximum electric power).
If the total gain is less than the threshold value Pth as represented by a YES
at the decision step
102, then control goes to a step
103, whereat
the gain of the signal (power control information) is increased by the variable
gain setting circuit
20 and is thereby set to the maximum power Pmax. Then,
the transmission signal is transmitted at that maximum power. For example, when
the total power judged at the step
102 is lower than the threshold valu
