JP3657850B2 - Multicast transmission downlink transmission power control method and base station - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multicast transmission downlink transmission power control method and a base station for reducing interference power in a mobile station and effectively using transmission power in a base station in mobile communication.
[0002]
[Prior art]
FIG. 4 is a diagram illustrating a configuration example of a conventional multicast transmission system.
[0003]
The system shown in FIG. 4 includes a base station 1 that transmits a multicast signal and a plurality of mobile stations 5 that receive the multicast signal.
[0004]
In the base station 1, the multicast signal input from the multicast signal input terminal 2 is input to the transmitter 3 and modulated into a transmission wave, and then transmitted with a predetermined transmission power.
[0005]
On the other hand, after demodulating the multicast signal received by the receiver 6, the mobile station 5 outputs the demodulated multicast signal from the multicast signal output terminal 7.
[0006]
As described above, in the conventional multicast transmission system, since there is no means for adaptively controlling the transmission power of the multicast signal in the base station, the multicast signal cannot be transmitted with the transmission power suitable for the reception quality of the mobile station. It was.
[0007]
Therefore, the base station needs to transmit with a transmission power larger than the required transmission power so that all mobile stations in the cell can satisfy the required reception quality.
[0008]
That is, the base station always transmits with transmission power with a margin added.
[0009]
[Problems to be solved by the invention]
However, if there is a bias such as the presence of a mobile station near the base station, the set transmission power becomes excessive, which not only causes interference to mobile stations in other cells or mobile stations that do not receive multicast signals. There is also a problem in that the transmission power is not effectively used.
[0010]
The present invention has been made in view of the above problems, and reduces downlink transmission power while maintaining the reception quality of a mobile station that receives a multicast signal, and interferes with mobile stations in other cells and mobile stations that do not receive the multicast signal. The purpose is to reduce power and to effectively use base station transmission power.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.
[0012]
The invention described in claim 1 is a multicast transmission downlink transmission power control method in a multicast transmission system that transmits the same information from a base station to a plurality of mobile stations. Error detection means for detecting an error; means for transmitting a retransmission request signal to the base station based on the detection result; the base station transmitting a multicast signal; and the mobile station Characterized in that it has means for receiving a retransmission request signal for the multicast signal transmitted by the receiver and means for controlling transmission power of the multicast signal based on the received retransmission request signal.
[0013]
According to a second aspect of the present invention, in the multicast transmission downlink transmission power control method according to the first aspect, the base station increases the transmission power when receiving one or a predetermined number of retransmission request signals. Alternatively, the transmission power is reduced when a predetermined number of retransmission request signals are not received.
[0014]
According to a third aspect of the present invention, in the multicast transmission downlink transmission power control method according to the first aspect, the base station obtains and calculates a ratio of the number of mobile stations that have transmitted retransmission request signals to the total number of mobile stations. The transmission power is increased when the ratio is greater than or equal to a predetermined value, and the transmission power is decreased when the determined ratio is equal to or less than the predetermined value.
[0015]
According to a fourth aspect of the present invention, in a base station in a multicast transmission system that transmits the same information to a plurality of mobile stations, means for transmitting a multicast signal, and retransmission for the multicast signal transmitted by the mobile station It has means for receiving a request signal and means for controlling the transmission power of the multicast signal based on the received retransmission request signal.
[0016]
In the invention described in claim 5, when the base station according to claim 4 receives one or a predetermined number of retransmission request signals, the transmission power is increased and one or a predetermined number of retransmission request signals are not received. The transmission power is lowered.
[0017]
According to a sixth aspect of the present invention, in the base station according to the fourth aspect, the ratio of the number of mobile stations that have transmitted retransmission request signals to the total number of mobile stations is obtained, and when the obtained ratio is equal to or greater than a predetermined value, The transmission power is increased, and when the obtained ratio is equal to or less than a predetermined value, the transmission power is decreased.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0019]
In the following description, it is assumed that the multicast signal transmitted by the base station is a signal transmitted in units of blocks, and each block is added with a CRC (Cyclic Redundancy Check) for error detection.
(First embodiment)
A first embodiment of the present invention will be described with reference to FIG.
[0020]
The first embodiment is a case where the base station performs transmission power control based on the retransmission request signal.
(System configuration)
The system in FIG. 1 includes a base station 11 that transmits a multicast signal and a plurality of mobile stations 21 that receive the multicast signal.
[0021]
The base station 11 includes a receiver 12, a signal number measuring device 13, a transmitter 3, and a transmission power controller 17. The signal number measuring device 13 is a circuit for measuring a retransmission request signal, and controls the transmission power controller 17 according to the contents thereof, as will be described later.
[0022]
The mobile station also includes a receiver 6, an error detection / ARQ unit 22, and a transmitter 23. The error detection / ARQ unit 22 is a circuit that sends a retransmission request signal (ARQ signal) 24 to the transmitter 23 when an error is detected in the received and demodulated multicast signal.
(Operation)
In the base station 11, the multicast signal input from the multicast signal input terminal 2 is input to the transmitter 3, modulated into a transmission wave, and then transmitted to the transmission power controller 17 with a predetermined power.
[0023]
On the other hand, the mobile station 21 demodulates the multicast signal 4 received by the receiver 6 and outputs a multicast signal from the multicast signal output terminal 7.
[0024]
The demodulated multicast signal is applied to the error detection / ARQ unit 22. The error detection / ARQ unit 22 detects an error.
[0025]
The error detection / ARQ unit 22 performs error detection for each block on the received multicast signal, and sends an retransmission request signal 24 to the transmitter 23 when an error is detected. The transmitter 23 that has received the retransmission request signal 24 transmits the retransmission request signal 24 to the base station 11 through the uplink channel 32.
[0026]
In addition, when no error is detected in the block, the mobile station 21 waits for reception of the next block.
[0027]
The base station 11 receives the uplink channel 32 by the receiver 12. Then, the retransmission request signal 24 demodulated by the receiver 12 is input to the signal number measuring device 13 and a retransmission request signal is output from the retransmission request signal output terminal 15. Note that, when receiving the retransmission request signal, the base station 11 performs a retransmission process on the error detected block, which is not shown.
[0028]
The signal number measuring device 13 first stores the input retransmission request signal. Next, the signal number measuring device 13 measures the number of retransmission request signals stored at an arbitrarily designated interval.
[0029]
In the present embodiment, the following description will be continued assuming that this interval is twice as long as the round trip delay.
[0030]
If even one retransmission request signal is stored in the signal number meter 13, the transmission power controller 17 is requested to increase transmission power. Conversely, if none is stored, the transmission power controller 17 is requested to reduce transmission power. The variable range of the transmission power here is determined in advance. The transmission power controller 17 receives a signal obtained by modulating the multicast signal from the multicast signal input terminal 2 into a transmission wave, and transmits the multicast signal with the controlled transmission power.
[0031]
This series of operations is repeated until there are no more multicast signal blocks to be transmitted.
[0032]
The state of the transmission power control will be described in detail with reference to FIG. Here, for ease of explanation, it is assumed that the number of mobile stations is one.
[0033]
2A shows the transmission power of the base station, FIG. 2B shows the transmission block of the base station, and FIG. 2C shows the reception block at the mobile station.
[0034]
A multicast signal composed of a series of blocks to which a CRC is added is sequentially transmitted from the base station to the mobile station as shown in FIG. In this example, the round trip delay is 2 blocks long. That is, the timing at which the retransmission request signal from the mobile station for block 1 reaches the base station is before the transmission of block 3.
[0035]
In the following description, the transmission power control timing in the base station is set to be twice as long as the round trip delay. In this case, transmission power control is performed at intervals of 4 blocks.
[0036]
First, as shown in FIG. 2A, since the retransmission request signals of blocks 1 and 2 transmitted at transmission power P1 are not detected before transmission of blocks 3 and 4, the transmission output is increased by one stage. Decrease to P2 and send block 5 and later. In blocks 1 to 4, the transmission power is P1.
[0037]
Next, since the retransmission request signals of blocks 5 and 6 transmitted with the transmission power P2 are not detected before the transmission of blocks 7 and 8, the transmission output is further lowered by one step to P3 and the blocks 9 and thereafter are transmitted.
[0038]
Next, since retransmission request signals for the blocks 9 and 10 transmitted with the transmission power P3 are detected, the transmission power is increased by one level to P2, and the blocks 11 and thereafter are transmitted.
[0039]
Subsequent blocks are sent out in the same manner.
[0040]
In the above description, an example in which transmission power control is performed based on the presence / absence of a retransmission request signal has been described. However, in this case, there is no need to count the retransmission request signal by the signal number measuring device 13, and the signal number measuring device 13 can also be omitted.
[0041]
In the above description, the example in which transmission power control is performed based on the presence / absence of a retransmission request signal has been described. However, transmission power control may be performed based on the presence / absence of a predetermined number of retransmission request signals.
(Second embodiment)
A second embodiment of the present invention will be described with reference to FIG.
[0042]
The second embodiment is a case where transmission power control is performed when the ratio of the number of mobile stations that have transmitted retransmission request signals to the number of mobile stations that receive multicast signals is less than or equal to a certain value.
(System configuration)
The system of FIG. 3 includes a base station 31 that transmits a multicast signal and a plurality of mobile stations 41 that receive the multicast signal.
[0043]
The base station 31 includes a receiver 12, a signal number measuring device 33, a transmitter 3, and a transmission power controller 17. The signal number measuring device 33 is a circuit for measuring the retransmission request signal and the arrival confirmation signal, and controls the transmission power controller 17 according to the contents thereof, as will be described later.
[0044]
The mobile station also includes a receiver 6, an error detection / ARQ unit 42, and a transmitter 23. When the error detection / ARQ unit 42 detects an error in the received and demodulated multicast signal, the error detection / ARQ unit 42 transmits a retransmission request signal 44 to the transmitter 23 and does not detect an error in the demodulated multicast signal. , A circuit for sending an arrival confirmation signal 45 to the transmitter 23.
(Operation)
In the base station 31, a multicast signal input from the multicast signal input terminal 2 is input to the transmitter 3 and modulated into a transmission wave, and then transmitted by the transmission power controller 17 while being controlled to a predetermined power.
[0045]
On the other hand, the mobile station 41 demodulates the multicast signal 4 received by the receiver 6 and outputs a multicast signal from the multicast signal output terminal 7.
[0046]
The demodulated multicast signal is applied to the error detection / ARQ unit 42. The error detection / ARQ unit 42 detects an error.
[0047]
The error detection / ARQ unit 42 sends a retransmission request signal 44 to the transmitter 23 when an error is detected in the received multicast signal block. If no error is detected in the received block, the error detection / ARQ unit 42 An arrival confirmation signal 45 is sent out.
[0048]
Upon receiving the retransmission request signal 44 or the arrival confirmation signal 45, the transmitter 23 transmits the retransmission request signal 44 or the arrival confirmation signal 45 to the base station 11 through the uplink channel 32.
The base station 31 receives the uplink channel 32 by the receiver 12. Then, the retransmission request signal 44 or the arrival confirmation signal 45 demodulated by the receiver 12 is inputted to the signal number measuring device 33 and the retransmission request signal 44 or the arrival confirmation signal 45 is outputted from the retransmission request / arrival confirmation signal output terminal 35. Note that, when receiving the retransmission request signal, the base station 11 performs a retransmission process on the error detected block, which is not shown.
[0049]
The signal number measuring device 33 first stores the input retransmission request signal 44 or arrival confirmation signal 45.
[0050]
Next, the signal number measuring device 33 measures the stored retransmission request signal 44 and arrival confirmation signal 45 at arbitrarily designated intervals as in the first embodiment.
[0051]
Next, the ratio of the number of mobile stations that have transmitted the retransmission request signal to the number of mobile stations that receive the multicast signal is obtained. That is, the number of retransmission request signals / (number of retransmission request signals + number of arrival confirmation signals) is calculated. If this value is equal to or less than a predetermined value, the transmission power controller 17 is requested to reduce transmission power. Conversely, if it is greater than the predetermined value, the transmission power controller 17 is requested to increase transmission power.
[0052]
The variable range of the transmission power is determined in advance as in the first embodiment. The transmission power controller 17 receives a signal obtained by modulating the multicast signal from the multicast signal input terminal 2 into a transmission wave, and transmits the multicast signal with the controlled transmission power.
[0053]
In the above description, the example of obtaining the ratio of the number of mobile stations that transmitted the retransmission request signal has been described. However, the present invention provides the ratio of the number of mobile stations that transmitted the arrival confirmation signal (number of arrival confirmation signals / (retransmission request signal The transmission power control may be performed by calculating (the number + the number of arrival confirmation signals), but in this case, the transmission power control is the reverse of the ratio of the number of mobile stations that have transmitted the retransmission request signal. It becomes control.
[0054]
【The invention's effect】
As described above, in the present invention, a retransmission request signal requested from a mobile station that receives a multicast signal is detected by the base station, and based on the number of retransmission request signals or the ratio of the number of mobile stations that have transmitted the retransmission request signal. By controlling to reduce or increase the transmission power, it is possible to reduce interference with mobile stations in other cells and mobile stations that do not receive multicast signals, and to make effective use of base station transmission power.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example for explaining a first embodiment of the present invention;
FIG. 2 is a diagram showing an example of a state of transmission power control in the first embodiment.
FIG. 3 is a diagram showing a configuration example for explaining a second embodiment of the present invention;
FIG. 4 is a diagram illustrating a configuration example of a conventional multicast transmission system.
[Explanation of symbols]
2 Multicast signal input terminal 3 Transmitter in base station 4 Multicast signal 5, 21, 41 Mobile station 6 Receiver in mobile station 7 Multicast signal output terminal 1, 11, 31 Base station 12 Receiver in base station 13 Signal number measuring device 15 Retransmission request Signal output terminal 17 Transmission power controller 22, 42 Error detection / ARQ unit 23 Intra-mobile station transmitters 24, 44 Retransmission request signal 32 Upstream channel 35 Retransmission request / arrival confirmation signal output terminal 45 Arrival confirmation signal

Claims (2)

In a multicast transmission downlink transmission power control method in a multicast transmission system that transmits the same information from a base station to a plurality of mobile stations,
The mobile station has error detection means for detecting an error with respect to the received multicast signal, and means for sending a retransmission request signal to the base station to the base station based on the detection result,
A base station for transmitting a multicast signal; means for receiving a retransmission request signal for the multicast signal transmitted by the plurality of mobile stations; and means for controlling transmission power of the multicast signal based on the received retransmission request signal Have
The base station obtains the ratio of the number of mobile stations that have sent retransmission request signals to the total number of mobile stations. If so, a multicast transmission downlink transmission power control method, wherein the transmission power is reduced. In a base station in a multicast transmission system that transmits the same information to a plurality of mobile stations,
Means for transmitting a multicast signal; means for receiving a retransmission request signal for the multicast signal transmitted by the plurality of mobile stations; and means for controlling transmission power of the multicast signal based on the received retransmission request signal;
The means for controlling the transmission power obtains a ratio of the number of mobile stations that have transmitted retransmission request signals to the total number of mobile stations. If the obtained ratio is equal to or greater than a predetermined value, the transmission power is increased and the obtained ratio is The base station characterized by lowering the transmission power when it is equal to or less than a predetermined value.

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