JP2014216819A - Radio communication system and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication system which improves accuracy of determining whether or not to control multicast transmission (retransmission control or transmission rate control).SOLUTION: A radio communication system includes: a base station device for transmitting communication data by multicast; and a plurality of radio terminal devices 30 for receiving the communication data transmitted by multicast. The base station device includes an information generation unit which generates information on transmission power of the communication data and makes the information and the communication data be multiplexed. Each of the plurality of radio terminal devices includes: a reception power measurement unit 382 for measuring reception power of the communication data; and a transmission power setting unit 383 which acquires the information multiplexed with the communication data, and sets transmission power of a response signal to be transmitted to the base station device from transmission power of the communication data shown by the information and the reception power of the communication data measured by the measurement unit.

Description

  The present invention relates to a wireless communication system and a wireless communication method, and more particularly to a multicast transmission control technique such as retransmission control and transmission rate control.

  In a wireless communication system, one-to-many transmission may be performed from a base station device to a wireless terminal device. Such one-to-many transmission is generally called multicast transmission. In contrast, one-to-one transmission is called unicast transmission. In multicast transmission in a commercial radio communication system, the number of radio terminal apparatuses that receive communication data multicast-transmitted by one base station apparatus may be 1000 or more.

  By the way, in wireless communication, communication data often contains errors during transmission due to radio wave propagation conditions and the like. Therefore, by including a cyclic redundancy code in the communication data at the time of transmission, the receiving device can detect an error, and the receiving device returns a retransmission request when an error is detected. When a retransmission request is received, it is widely performed to retransmit communication data requested to be retransmitted (communication data in which an error is detected).

  Multicast transmission and unicast transmission are the same in that retransmission request processing is performed. However, in the case of multicast transmission, a large number of wireless terminal devices receive the same communication data at a time, and a large number of retransmission requests at a time. Will be sent. For this reason, if radio resources are exclusively allocated to each radio terminal device and a retransmission request is transmitted using the radio resources, there may be a shortage of radio resources.

  As a technique for solving such a problem, there is a technique described in Patent Document 1 by the present applicant. In this technique, the power of the reception state notification signal for notifying the base station device from the wireless terminal device that the communication has arrived, and the retransmission request for requesting retransmission of the packet from the wireless terminal device to the base station device Multicast transmission is controlled using a predetermined reference retransmission request rate determined by a ratio with the signal power as an index.

  Specifically, the first total value is obtained by statistically multiplexing the received power of each subcarrier of the first subcarrier group constituting the OFDM symbol of the reception status notification signal transmitted from a plurality of radio terminal apparatuses. Then, the value obtained by multiplying the first total value by the reference retransmission request rate is obtained as a threshold value. Then, the reception level of each subcarrier of the second subcarrier group constituting the OFDM symbol of the retransmission request signal transmitted from a plurality of radio terminal apparatuses is statistically multiplexed to obtain a second total value, When the total value of 2 is higher than the threshold, multicast transmission control is performed such as reducing the transmission rate of multicast transmission or retransmitting the packet.

As described above, in the technique described in Patent Literature 1, the first total value of the power values of the reception status notification signals of the plurality of wireless terminal devices and the second total value of the power of the retransmission request signals of the plurality of wireless terminal devices. Is used as an index to significantly determine the presence of wireless terminal devices that require control of multicast transmission, and multicast resources according to the number of wireless terminals without allocating wireless resources exclusively to each wireless terminal device. It is possible to control transmission.
In addition, since the power of reception status notification signals or retransmission request signals of a plurality of wireless terminal devices is simply added without considering the phase relationship in the base station device, and this power is measured, the base station device Thus, it is possible to avoid complication of the apparatus such as demodulating each signal from the wireless terminal apparatus by a method according to the communication method.

JP 2008-277913 A

  According to the technique described in Patent Literature 1 described above, the power value of the retransmission request signal that arrives from the wireless terminal device to the base station device tends to increase as the wireless terminal device is closer to the base station device. For this reason, as will be described below, it may not be possible to appropriately control multicast transmission according to the number of wireless terminal devices that require retransmission of packets and the like.

  When the transmission power of the wireless terminal device is fixed, the power value of the response signal received from the wireless terminal device at the base station device decreases as the distance between the base station device and the wireless terminal device increases. In other words, the power value of the response signal received from the nearby radio terminal apparatus in the base station apparatus is relatively larger than the power value of the response signal received from the far radio terminal apparatus. For this reason, when the base station apparatus determines the presence of a wireless terminal apparatus that requires retransmission of a packet or the like from the power value of the response signal, the nearby wireless terminal apparatus has a greater influence than the far wireless terminal apparatus. Have.

  For example, due to the difference in distance between the base station device and the wireless terminal device, the power value of the retransmission request signal received from a distant wireless terminal device becomes the received power of the retransmission request signal received from a nearby wireless terminal device. In this case, the wireless terminal device close to the base station device has an influence 10 times that of a remote wireless terminal device in determining whether or not to control multicast transmission. As a result, the distance between the base station device and the wireless terminal device is reflected in the second total value described above, and the number of wireless terminal devices that have transmitted the retransmission request signal is not necessarily reflected appropriately. In this case, since it becomes difficult to accurately determine the presence of a wireless terminal device that needs to control multicast transmission such as packet retransmission, it is necessary to accurately determine whether or not to perform multicast transmission control. Becomes difficult.

  Accordingly, one of the problems of the present invention is to provide a wireless communication system and a wireless communication method capable of improving the accuracy of determination as to whether or not to perform multicast transmission control (for example, retransmission control or transmission rate control). It is in.

A wireless communication system according to the present invention for solving the above-described problems is a wireless communication system including a base station device that multicasts communication data and a plurality of wireless terminal devices that receive the communication data transmitted by multicast. The base station device includes an information generation unit that generates information related to transmission power of the communication data and multiplexes the information with the communication data, and each of the wireless terminal devices of the plurality of wireless terminal devices includes: The received power measuring unit that measures the received power of the communication data, the information multiplexed on the communication data is acquired, and the transmission power of the communication data indicated by the information and the communication measured by the measuring unit A transmission power setting unit configured to set transmission power of a response signal to be transmitted to the base station apparatus from received data power, and the plurality of wireless terminals When the ratio of the received power to the transmission power of the communication data exceeds a specified value, the transmission power setting unit included in each wireless terminal device of the apparatus determines the amount exceeding the specified value from the transmission power of the communication data. A value obtained by subtraction is set as the transmission power of the response signal.
In general, when the base station device performs multicasting with respect to the information generation unit, there are many cases in which transmission frequency information, base station position information, and the like are broadcasted as notification information toward an area covered by the base station device. The information generation unit may be configured by including transmission power information in such broadcast information.

According to this configuration, each wireless terminal device can know the attenuation (loss) of the power of the radio frequency signal in the transmission path from the transmission power in the base station device and the received power in each wireless terminal device. Accordingly, each wireless terminal device can set the transmission power of the response signal so that the reception power of the response signal in the base station device becomes a substantially constant value. When the transmission power of the response signal is set in each wireless terminal device in this way, the response signal from each terminal device received in the base station device becomes a substantially constant value, and it is determined whether to control multicast transmission. In the above, even if the response signals from the wireless terminal devices are added and received, the influences can be made equal. Therefore, it is possible to accurately determine whether or not to perform multicast transmission control according to the number of wireless terminal devices, and it is possible to appropriately perform the control.
Also, according to this configuration, the value obtained by subtracting the ratio of the reception power to the transmission power of the communication data that exceeds the specified value from the transmission power of the communication data is set as the transmission power of the response signal. If the characteristics of the transmission path and the characteristics of the downstream transmission path are substantially the same, the received power of the response signal in the base station apparatus can be adjusted to the specified value. Thereby, in determining whether the base station apparatus controls multicast transmission, the influence of each wireless terminal apparatus can be made equal. Therefore, the base station apparatus can control multicast transmission according to the number of wireless terminal apparatuses that have transmitted response signals.

In the wireless communication system, for example, the specified value is used to determine whether or not there is a wireless terminal device that has transmitted the response signal based on power of the response signal received by the base station device from the plurality of wireless terminal devices. It may be a value that gives a standard of.
According to this configuration, the base station apparatus can determine the presence / absence of the wireless terminal apparatus that has transmitted the response signal according to the number of wireless terminal apparatuses that have transmitted the response signal.

  In the wireless communication system, for example, each wireless terminal device further receives one or more subcarriers (first subcarriers) selected from the first subcarrier group when the communication data is received. Group), a reception state notification signal transmission unit that transmits a reception state notification signal indicating that the wireless terminal device is performing a reception operation, and a determination unit that determines whether or not the communication data is normally received, One or a plurality of subcarriers selected from a second subcarrier group that does not overlap the first subcarrier group when the determination unit determines that the communication data is not normally received. The base station apparatus further receives the first subcarrier group and configures the first subcarrier group. A first total value acquisition unit that acquires a first total value that is a total value of the reception levels of each subcarrier, and each subcarrier that receives the second subcarrier group and constitutes the second subcarrier group A second total value acquisition unit that acquires a second total value that is a total value of the reception levels, and a multicast transmission control unit that controls multicast transmission based on a ratio of the second total value to the first total value; , May be included.

A wireless communication method according to the present invention for solving the above problem is a wireless communication method in which a base station device multicasts communication data and a plurality of wireless terminal devices receive the communication data multicast-transmitted. The base station device generates information related to the transmission power of the communication data, and an information generation step of multiplexing the information into the communication data; and each of the wireless terminal devices of the plurality of wireless terminal devices includes the communication data A reception power measurement step of measuring reception power; and each wireless terminal device acquires the information multiplexed in the communication data, and is measured by the transmission power of the communication data indicated by the information and the measurement unit And a transmission power setting step for setting a transmission power of a response signal to be transmitted to the base station apparatus from the reception power of the communication data. In the transmission power setting step, when the ratio of the reception power to the transmission power of the communication data exceeds a specified value, a value obtained by subtracting the amount exceeding the specified value from the transmission power of the communication data is It is set as transmission power of a response signal.
In addition, regarding the above information generation step, when the base station apparatus performs multicasting, the transmission power is transmitted to broadcast information that broadcasts transmission frequency information, base station position information, and the like as broadcast information toward an area covered by the base station apparatus. An information generation step may be configured including information.

  In the wireless communication method, for example, when each wireless terminal apparatus receives the communication data, a reception state notification signal is transmitted by one or more subcarriers selected from the first subcarrier group. A reception state notification signal transmission step for transmitting the data, a determination step for determining whether or not the communication data is normally received by each wireless terminal device, and a method for determining whether or not each wireless terminal device performs the communication in the determination step. When it is determined that data is not normally received, a retransmission request signal is transmitted by one or more subcarriers selected from the second subcarrier group that does not overlap with the first subcarrier group. A retransmission request signal transmission step for transmitting, and the base station apparatus receives the first subcarrier group, and each subkey constituting the first subcarrier group. A first total value acquisition step of acquiring a first total value that is a total value of rear reception levels; and the base station apparatus receives the second subcarrier group and configures the second subcarrier group A second total value acquisition step of acquiring a second total value that is a total value of reception levels of the subcarriers to be transmitted, and the base station apparatus performs multicast transmission based on a ratio of the second total value to the first total value A multicast transmission control step for performing the above control.

In the wireless communication system, for example, the multicast transmission control unit compares the calculated threshold value with the second total value based on the first total value. Comparison means, and the multicast transmission control means may control multicast transmission based on a comparison result of the comparison means.
According to this, for example, the total value acquired by the first reception level total value acquisition means is set to a retransmission request rate (a retransmission request signal for the number of wireless terminal devices that transmitted the reception status notification signal) as a reference for multicast transmission control. The ratio can be calculated by multiplying by the ratio of the number of transmitted wireless terminal devices (hereinafter referred to as a reference retransmission request rate). Then, multicast transmission can be controlled using the reference retransmission request rate as an index.

In the wireless communication system, for example, the reception state notification signal transmission unit transmits a reception state notification signal using a first number of subcarriers selected from the first subcarrier group. The retransmission request signal transmitting means transmits a retransmission request signal by a second number of subcarriers selected from the second subcarrier group, and the multicast transmission control means is configured to transmit the retransmission request signal to the first total value. Multicast transmission may be controlled based on the ratio of the second total value and the ratio of the second number to the first number.
According to this, even if the first number and the second number are different, the multicast transmission control means appropriately controls multicast transmission using the ratio of the second total value to the first total value as an index. It can be performed.

Also, in the above wireless communication system, for example, the reception status notification signal transmission means sets each power level of one or a plurality of subcarriers selected from the first subcarrier group as a first predetermined value. To transmit a reception status notification signal, and the retransmission request signal transmission means sets each power level of one or a plurality of subcarriers selected from the second subcarrier group to a second predetermined value. The multicast transmission control means, based on the ratio of the second total value to the first total value and the ratio of the second predetermined value to the first predetermined value, Control of multicast transmission may be performed.
According to this, even when the first predetermined value and the second predetermined value are different, the multicast transmission control means appropriately performs multicast transmission using the ratio of the second total value to the first total value as an index. Can be controlled.

In the wireless communication system, for example, the reception state notification signal transmission unit transmits a reception state notification signal using a first number of subcarriers selected from the first subcarrier group. The retransmission request signal transmission means transmits a retransmission request signal using a second number of subcarriers selected from the second subcarrier group, and the threshold calculation means includes the first total value, The threshold value may be calculated based on the ratio of the second number to the first number.
According to this, the threshold value calculation means can appropriately calculate the threshold value even when the first number and the second number are different.

Also, in the above wireless communication system, for example, the reception status notification signal transmission means sets each power level of one or a plurality of subcarriers selected from the first subcarrier group as a first predetermined value. To transmit a reception status notification signal, and the retransmission request signal transmission means sets each power level of one or a plurality of subcarriers selected from the second subcarrier group to a second predetermined value. The retransmission request signal may be transmitted, and the threshold value calculation unit may calculate the threshold value based on the first total value and a ratio of the second predetermined value to the first predetermined value.
According to this, the threshold value calculation unit can appropriately calculate the threshold value even when the first predetermined value and the second predetermined value are different.

  ADVANTAGE OF THE INVENTION According to this invention, the precision of determination of whether to control multicast transmission can be improved.

It is a figure which shows the system configuration | structure of the radio | wireless communications system concerning embodiment of this invention. It is explanatory drawing of the outline of the multicast transmission concerning embodiment of this invention. It is a schematic block diagram which shows an example of a structure of the radio | wireless terminal apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows an example of the resending request signal which the radio | wireless terminal apparatus which concerns on Embodiment 1 of this invention transmits. It is a figure which shows an example of the resending request signal which the base station apparatus which concerns on Embodiment 1 of this invention received. It is a schematic block diagram which shows an example of a structure of the base station apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows an example of the flow of operation | movement of the radio | wireless communications system which concerns on Embodiment 1 of this invention, and is a figure which shows an example of the setting procedure of the transmission power of a response signal. It is explanatory drawing for demonstrating the operation principle of the radio | wireless communications system which concerns on Embodiment 1 of this invention, and is explanatory drawing for demonstrating the setting principle of the transmission power of a response signal. It is a schematic block diagram which shows an example of a structure of the radio | wireless terminal apparatus which concerns on Embodiment 2 of this invention. It is a schematic block diagram which shows an example of a structure of the radio | wireless terminal apparatus which concerns on Embodiment 3 of this invention. It is a schematic block diagram which shows an example of a structure of the radio | wireless terminal apparatus which concerns on Embodiment 4 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Embodiment 1]
FIG. 1 is a diagram showing a system configuration of a wireless communication system 1 according to the present embodiment. As shown in the figure, the wireless communication system 1 includes a base station device 10 and a large number of wireless terminal devices 30. The base station apparatus 10 transmits communication data by multicast, and each wireless terminal apparatus 30 receives the communication data transmitted by multicast transmission. The number of wireless terminal devices 30 that receive communication data multicast-transmitted by the base station device 10 may actually be 1000 or more. In the present embodiment, communication between the base station apparatus 10 and the wireless terminal apparatus 30 including the multicast transmission is performed by the OFDM method, but is not limited to this example.

FIG. 2 is a schematic explanatory diagram of multicast transmission. Base station apparatus 10, to a plurality of wireless terminal devices 30 (the wireless terminals 30-1 to 5 in FIG. 2), at the same time sends a packet _(t 1 _~t 2 in FIG. 2). Each wireless terminal apparatus 30 performs error detection of the received packet using, for example, a cyclic redundancy code or the like. Each wireless terminal device 30 generates and transmits a reception status notification (ACK: ACKnowledge) signal regardless of the presence or absence of error detection. When an error is detected in a received packet, a retransmission request (NAK: Negative) AcKnowledge) signal is generated and transmitted.

  The reception status notification signal transmitted here is different from normal ACK. That is, the normal ACK indicates that “communication has arrived without error”, but the reception state notification signal simply indicates that “communication has arrived”. Hereinafter, the reception status notification signal and the retransmission request signal are collectively referred to as a response signal as appropriate.

  In this embodiment, the reception status notification signal and the retransmission request signal are composed of one OFDM symbol. Normally, an OFDM symbol is generated by superimposing a modulation signal on N subcarriers orthogonal to each other and performing IFFT (inverse Fourier transform) processing. In this embodiment, a part of N subcarriers is generated. A retransmission request signal is generated using this. Further, a retransmission request signal is generated using a part of N subcarriers. Details of the method of generating these signals will be described later.

Time slot by the base station apparatus 10 broadcasts a packet (t ₁ ~t 2 in FIG. _2), time slot (in FIG. 2 t ₂ the terminal station to the packet responds the reception state notification signal and the retransmission request signal ˜t ₃ ) is determined by a prior procedure, and each wireless terminal device 30 uses the designated time slot (t ₂ ˜t _{3 in} FIG. 2) to receive the reception status notification signal and the retransmission request signal. Transmit to station apparatus 10.

Next, details of the wireless terminal device 30 will be described. FIG. 3 is a schematic block diagram illustrating an example of the configuration of the wireless terminal device 30. As shown in the figure, the wireless terminal device 30 includes an antenna 31, an RF (Radio Frequency) unit 32, an OFDM symbol detector 33, a P / S (Parallel).
/ Serial) converter 34, demodulator 35, separation unit 36, encoder 37, control unit 38, first number storage unit 39, first predetermined value storage unit 40, second number storage unit 41, second The predetermined value storage unit 42, the encoder 42, the multiplexing unit 43, the modulator 44, the S / P (Serial / Parallel) converter 45, the OFDM symbol generator 46, and the RF unit 47. The control unit 38 includes a reception state notification signal transmission unit 380, a retransmission request signal transmission unit 381, a reception power measurement unit 382, and a transmission power setting unit 383 therein.

  The RF unit 32 down-converts the radio frequency signal of the communication data received by the antenna 31 and performs orthogonal demodulation. The OFDM symbol detector 33 performs an FFT (Fast Fourier Transform) process on the output of the RF unit 32 to detect an OFDM symbol of communication data. The P / S converter 34 performs parallel / serial conversion on the OFDM symbol. The demodulator 35 demodulates the OFDM symbol of the serially converted communication data. Separating section 36 separates transmission power information TP, which will be described later, from the OFDM symbol of the demodulated communication data. The encoder 37 functions as a determination unit that determines whether or not communication data is normally received by performing error detection of a demodulated signal using a cyclic redundancy code or the like.

  The reception state notification signal transmission unit 380 (reception state notification signal transmission means) receives a communication data and receives a first number selected from the first subcarrier group (hereinafter referred to as Lo). The reception state notification signal is transmitted by performing modulation processing on the subcarriers and setting the power level of each subcarrier to a first predetermined value (hereinafter referred to as Po). The retransmission request signal transmission unit 381 (retransmission request signal transmission means) is a second that does not overlap with the first subcarrier group when the encoder 37 determines that the communication data is not normally received. Modulation processing related to a second number (hereinafter referred to as L) of subcarriers selected from the subcarrier group of the subcarrier group, and the power level of each subcarrier is set to a second predetermined value (hereinafter referred to as P and The retransmission request signal is transmitted.

  The Lo, L, Po, and P are determined by the user and are respectively a first number storage unit 39, a second number storage unit 41, a first predetermined value storage unit 40, and a second predetermined value storage unit. 42. The reception state notification signal transmission unit 380 and the retransmission request signal transmission unit 381 read and use Lo, L, Po, and P from each storage unit. In the present embodiment, it is assumed that Lo = L and Po = P.

In addition, here, the first subcarrier group is Mo among the subcarriers constituting the OFDM symbol transmitted at time t _{2 to} t ₃ shown in FIG. 2, and the second subcarrier group is The other M subcarriers transmitted at times t _{2 to} t ₃ shown in FIG. The first subcarrier group and the second subcarrier group are determined in advance.

  Reception state notification signal transmission section 380 and retransmission request signal transmission section 381 select Lo subcarriers and L subcarriers from Mo subcarriers and M subcarriers, respectively. This selection method includes a method of randomly selecting each time, a method of selecting at random only at the start of communication, a method of selecting the same subcarrier thereafter, a method of selecting a fixed subcarrier, etc. You may choose. Then, the modulation signal is superimposed only on the selected Lo or L subcarriers, and a signal sequence is generated such that the other subcarriers are null.

  The received power measuring unit 382 measures the received power of the communication data received from the base station apparatus 10 and outputs information RP related to this received power. In the present embodiment, the received power measuring unit 382 acquires the received power of the radio frequency signal received by the antenna 31 from the RF unit 32. The transmission power setting unit 383 obtains transmission power information TP relating to transmission power multiplexed in advance on the communication data received from the base station apparatus 10 from the separation unit, and transmits and receives the transmission power of the communication data obtained from the information. Based on the received power of the communication data measured by the power measuring unit 382, the transmission power of the reception status notification signal and the retransmission request signal, which are response signals transmitted to the base station apparatus 10, is set. Here, the transmission power information TP multiplexed on the communication data received from the base station apparatus 10 is information indicating the transmission power when the base station apparatus 10 transmits the communication data.

  In this embodiment, when the ratio of the received power to the transmission power of the communication data exceeds the specified value S, the transmission power setting unit 383 obtains the amount exceeding the specified value S from the transmission power of the communication data. Is set as the transmission power of the response signal. As a result, the power value of each response signal received from each of the plurality of wireless terminal devices 30 in the base station device 10 is made substantially constant. Here, the prescribed value S is an arbitrary value that is equal to or less than the maximum transmission power of the wireless terminal device 30 and at least larger than that assumed to be attenuation in the transmission path. The specified value S provides a reference for determining whether or not there is a wireless terminal device that has transmitted this response signal based on the power of response signals received from the plurality of wireless terminal devices 30 by the base station device 10. Details of the setting method of the transmission power of the response signal by the transmission power setting unit 383 will be described later.

  The encoder 42 encodes the signal for transmission and generates a signal sequence. The multiplexing unit 43 multiplexes each signal sequence generated by the encoder 42, the reception status notification signal transmission unit 380, and the retransmission request signal transmission unit 381 to generate a multiplexed signal. The modulator 44 modulates the generated multiplexed signal. The S / P converter 45 converts the modulated signal obtained by the modulation performed by the modulator 44 into a parallel signal. The OFDM symbol generator 46 performs an IFFT (Inverse Fast Fourier Transform) process on the output of the S / P converter 45 to generate an OFDM symbol. The RF unit 47 modulates the OFDM symbol and up-converts it to a radio frequency. The output of the RF unit 47 is transmitted from the antenna 31.

  The processing of the multiplexing unit 43 will be described in detail. When the reception state notification signal transmission unit 380 does not generate the reception state notification signal and the retransmission request signal transmission unit 381 does not generate the retransmission request signal, the multiplexing unit 43 uses the signal sequence generated by the encoder 42. Output. On the other hand, when reception state notification signal transmission section 380 generates a reception state notification signal or retransmission request signal transmission section 381 generates a retransmission request signal, a signal sequence corresponding to the generated signal and encoder 42 Is multiplexed with the signal sequence generated.

  Although the drawing shows only the minimum configuration for explaining the present invention, for example, when performing interleaving and error correction (FEC: Forward Error Collection), an interleaver and an encoder are provided immediately after the encoder 42. A deinterleaver or the like is required immediately before 37.

  FIG. 4 is a diagram illustrating an example of a retransmission request signal transmitted by the wireless terminal device 30, and particularly illustrates a case where L = 1. On the other hand, FIG. 5 is a diagram illustrating an example of a retransmission request signal received by the base station apparatus 10. In FIGS. 4 and 5, the hatched portion indicates the retransmission request signal.

As illustrated in FIG. 5, the base station device 10 receives the retransmission request signal transmitted by each wireless terminal device 30. In addition, since each radio | wireless terminal apparatus 30 has selected L subcarriers by the independent process, the same subcarrier may be selected. In this case, if the phases of the retransmission request signals transmitted by the wireless terminal devices 30 are opposite to each other, they cancel each other and the reception level decreases.
4 and 5, the retransmission request signal has been described, but the same applies to the reception state notification signal.

  Next, details of base station apparatus 10a that is base station apparatus 10 according to the present embodiment will be described. FIG. 6 is a schematic block diagram showing the internal configuration of the base station apparatus 10a. As shown in the figure, the base station apparatus 10a includes a control unit 11, an encoder 12, a multiplexing unit 13, a modulator 14, an S / P converter 15, an OFDM symbol generator 16, an RF unit 17, an antenna 18, an RF Unit 19, OFDM symbol detector 20, first reception level total value acquisition unit 21, second reception level total value acquisition unit 22, P / S converter 23, demodulator 24, encoder 25, and multicast transmission control unit 26a. Consists of including. The control unit 11 further includes an information generation unit 110 therein, and the multicast transmission control unit 26a is further configured to include a reference retransmission request rate input reception unit 260, a threshold value calculation unit 261a, and a comparison unit 262 therein. .

  The RF unit 19 performs quadrature demodulation by down-converting the radio frequency signal received by the antenna 18. The OFDM symbol detector 20 performs an FFT process on the output of the RF unit 19 to detect an OFDM symbol.

  The first reception level total value acquisition unit 21 (first total value acquisition unit) receives the first subcarrier group (Mo subcarriers) and detects the reception level of the signal component for each subcarrier. Then, by summing the detected reception levels (statistical multiplex addition), a total value (first total value) of the reception levels of the subcarriers constituting the first subcarrier group is obtained. Similarly, the second reception level total value acquisition unit 22 (second total value acquisition unit) receives the second subcarrier group (M subcarriers) and determines the reception level of the signal component for each subcarrier. To detect. Then, by summing the detected reception levels (statistical multiplex addition), a total value (second total value) of the reception levels of the subcarriers constituting the second subcarrier group is obtained.

  The P / S converter 23 performs parallel / serial conversion on the OFDM symbol. The demodulator 24 demodulates the serially converted OFDM symbol. The encoder 25 performs error detection based on the demodulated signal. The control unit 11 receives the demodulated signal after error detection. The information generation unit 110 included in the control unit 11 generates transmission power information TP indicating the transmission power of communication data to be multicast transmitted, and the multiplexing unit 13 multiplexes the transmission power information TP with the communication data.

  The multicast transmission control unit 26a (multicast transmission control means) controls multicast transmission based on the ratio of the second total value to the first total value. Hereinafter, the processing of the multicast transmission control unit 26a will be described in detail.

  First, the reference retransmission request rate input receiving unit 260 receives the input of the reference retransmission request rate by the user. The reference retransmission request rate input here is a reference value of the ratio of the number of wireless terminal devices that have transmitted retransmission request signals to the number of wireless terminal devices that have transmitted reception status notification signals.

The threshold value calculation unit 261a (threshold value calculation means) calculates the threshold value of the second total value by multiplying the first total value by the reference retransmission request rate. Formula (1) is a formula for calculating this threshold value.
Threshold = first total value × reference retransmission request rate (1)

  The comparison unit 262 (comparison means) compares the threshold value calculated by the threshold value calculation unit 261a with the second total value acquired by the second reception level total value acquisition unit 22. Then, based on the comparison result, multicast transmission of communication data by the control unit 11 is controlled. As a specific example, when the comparison result indicates that the second total value is higher than the threshold value, the transmission rate of multicast transmission can be lowered to reduce the error rate. Further, only when the comparison result indicates that the second total value is higher than the threshold value, the control unit 11 can be controlled to perform retransmission control for retransmitting a packet corresponding to the retransmission request signal. Which control is used for this embodiment depends on the setting of the reference retransmission request rate. The control unit 11 performs transmission rate control and packet retransmission control according to the control of the comparison unit 262.

  The encoder 12 encodes a signal for transmission to generate a signal sequence. The multiplexing unit 13 multiplexes the transmission power information TP generated by the information generation unit 110 with respect to each signal sequence of the communication data generated by the encoder 12. The modulator 14 modulates each signal sequence in which the transmission power information TP is multiplexed. The P / S converter 15 converts the modulated signal into a parallel signal. The OFDM symbol generator 16 performs an IFFT process on the output of the P / S converter 15 to generate an OFDM symbol. The RF unit 17 orthogonally modulates the OFDM symbol and up-converts it to a radio frequency. The output of the RF unit 17 is transmitted from the antenna 18.

  When the control unit 11 transmits a packet, the control unit 11 buffers the packet for a certain time. When the comparison unit 262 instructs to retransmit, the buffered packet is read out and multicasted. However, the buffering of the packet is not necessarily performed by the control unit 11. For example, a signal modulated by the modulator 14 or an OFDM symbol generated by the OFDM symbol generator 16 may be buffered. In this case, the control of the comparison unit 262 may be sent to the buffering location.

  FIG. 6 shows only a minimum configuration for explaining the present invention. Similar to the wireless terminal device 30, an interleaver, a deinterleaver, and the like are required when performing interleaving and error correction. Become.

  Next, referring to FIG. 7 and FIG. 8, a method for setting the transmission power of the response signal in the wireless terminal device 30 will be described. FIG. 7 is a flowchart showing an example of the operation flow of the radio communication system 1 according to the present embodiment, and shows an example of a procedure for setting the transmission power of the reception state notification signal and the retransmission request signal that are response signals. FIG. FIG. 8 is an explanatory diagram for explaining the operation of radio communication system 1 according to the present embodiment, and is an explanatory diagram for explaining the principle of setting the transmission power of the response signal.

  According to the response signal transmission power setting method described below, the reception power of the response signal that the base station apparatus 10a receives from each of the plurality of radio terminal apparatuses 30 is the same as the base station apparatus 10a and the radio terminal apparatus 30. Regardless of the distance between them, the value is almost constant. This means that when the base station apparatus 10a determines whether or not multicast transmission control is necessary from the received power of the response signal, the wireless terminal apparatus 30 near the base station apparatus 10a and the wireless terminal far from the determination are determined. This means that the device 30 has the same influence. If this influence is equal, the sum of received power of response signals received from a plurality of wireless terminal devices 30 in the base station device 10a is approximately proportional to the number of wireless terminal devices 30 that have transmitted response signals. Therefore, the base station device 10a can accurately determine the presence of the wireless terminal device 30 that requires packet retransmission and the like, and can accurately determine whether or not to perform multicast transmission control. it can. Therefore, it is possible to appropriately control multicast transmission according to the number of wireless terminal devices 30 that have transmitted response signals.

The procedure for setting the transmission power of the response signal will be described in detail along the flow shown in FIG.
In the base station apparatus 10a shown in FIG. 6, the information generation unit 110 provided in the control unit 11 generates transmission power information PT indicating transmission power of communication data to be multicast transmitted (step S1), and this transmission power information TP. Is supplied to the multiplexing unit 13. The transmission power in this case is set in the same way as in normal multicast transmission, for example. The multiplexing unit 13 multiplexes the transmission power information TP supplied from the information generation unit 110 into communication data (step S2). The communication data in which the transmission power information TP is multiplexed by the multiplexing unit 13 is transmitted as a radio frequency signal via the antenna 18 via the modulator 14, the S / P converter 15, the OFDM symbol generator 16, and the RF unit 17. Is done.

  On the other hand, the radio terminal device 30 illustrated in FIG. 3 receives the radio frequency signal transmitted from the base station device 10 a via the antenna 31. The received radio frequency signal is demodulated into communication data through an RF unit 32, an OFDM symbol detector 33, a P / S converter 34, a demodulator 35, a separation unit 36, and an encoder 37. In this demodulation process, the separation unit 36 separates the transmission power information TP from the received communication data and supplies it to the transmission power setting unit 383 (step S3). The reception power measurement unit 382 measures the reception power of the radio frequency signal of the communication data obtained in the RF unit 32, generates reception power information RP indicating the reception power, and supplies the reception power information RP to the transmission power setting unit 383 ( Step S4). The difference between the reception power indicated by the reception power information RP and the transmission power indicated by the transmission power information TP corresponds to the amount of signal attenuation in the transmission path between the base station device 10a and the wireless terminal device 30.

  The transmission power setting unit 383 sets the transmission power of the response signal to be transmitted to the base station apparatus 10a from the transmission power information TP supplied from the separation unit 36 and the reception power information RP supplied from the reception power measurement unit 382. (Step S5). Specifically, the transmission power setting unit 383 determines that the ratio (RW / TW) between the transmission power TW indicated by the transmission power information TP and the reception power RW indicated by the reception power information RP exceeds the specified value S. Then, a value obtained by subtracting the amount exceeding the specified value S from the transmission power of the communication data is set as the transmission power of the response signal.

  Setting of transmission power by the transmission power setting unit 383 will be specifically described with reference to FIG. In FIG. 8, the horizontal axis represents the distance from the base station apparatus 10a to the radio terminal apparatus 30, and the vertical axis represents the transmission power [dBm] or the reception power [dBm] in the base station apparatus 10a or the radio terminal apparatus 30. . As shown in FIG. 8 (a), the maximum transmission power value U (hereinafter referred to as "maximum transmission power U") set at the time of conventional multicast transmission is set as the transmission power TW, and the base station apparatus 10a When communication data is transmitted, the received power RW in the wireless terminal device 30 tends to decrease as the distance from the base station device 10a increases. In the example of FIG. 5A, the reception power RW is reduced by the attenuation (propagation loss) D1 on the transmission path in the nearby wireless terminal device 30, but the decibel value of the reception power RW has a specified value S. The excess is indicated by “E”. On the other hand, the attenuation D2 on the transmission path between the remote radio terminal apparatus 30 and the base station apparatus 10a is larger than the attenuation D1 on the transmission path between the nearby radio terminal apparatus 30 and the base station apparatus 10a. As a result, the decibel value of the received power RW in the remote radio terminal device 30 is lower than the specified value S.

  If the characteristics of the downlink and downlink transmission paths between the base station device 10a and the wireless terminal device 30 are the same, and each wireless terminal device 30 transmits a response signal with the same transmission power as the base station device 10a. Then, the received power of the response signal received from each wireless terminal device 30 in the base station device 10a is substantially equal to the received power RW in each wireless terminal device 30 shown in FIG. Similarly, in the base station device 10a, the reception power of the response signal changes according to the distance between the base station device 10a and the wireless terminal device 30.

  In order to suppress such a change in the reception power of the response signal in the base station apparatus 10a, in the present embodiment, as described above, each wireless terminal apparatus 30 transmits a response signal according to the reception power RW of the communication data. Set the power. That is, when the ratio (decibel value) of the reception power RW to the transmission power TW of the communication data exceeds the specified value S, the transmission power setting unit 383 of each wireless terminal device 30 converts the excess E into the transmission power information TP. Is subtracted from the value of the transmission power TW of the communication data indicated by, and the value obtained by this subtraction is used as the transmission power of the response signal.

  Specifically, as shown in FIG. 8A, for example, in the wireless terminal device 30 near the base station device 10a, the received power RW represented by the ratio of the received power RW to the transmission power TW of the communication data. It is assumed that the value exceeds the specified value S. In this case, the nearby wireless terminal device 30 subtracts the excess E of the received power RW from the maximum transmission power U indicated by the transmission power information TP as shown in FIG. The value (U-E) is set as the transmission power TRW of the response signal.

  As described above, by setting the transmission power TRW of the response signal in the wireless terminal device 30, if the characteristics of the downlink and downlink transmission paths between the base station device 10a and the wireless terminal device 30 are substantially the same, As shown in FIG. 8B, the transmission power TRW of the response signal transmitted from the wireless terminal device 30 is attenuated to the same extent as the uplink in the downlink transmission path, and decreases by the attenuation D1. As a result, the received power RTW of the response signal received at the base station apparatus 10a is approximately equal to the reference value S. Thereby, in the base station apparatus 10a, the value of the reception power RTW of the response signal received from each of the plurality of nearby radio terminal apparatuses 30 becomes substantially constant.

  Next, as shown in FIG. 8A, when the reception power RW of communication data in the remote wireless terminal device 30 is lower than the specified value S, the wireless terminal device 30 is shown in FIG. The maximum transmission power U is set as the transmission power TRW of the response signal. In this case, if the characteristics of the downlink and uplink transmission paths between the base station apparatus 10a and the line terminal apparatus 30 are the same, the reception power RTW of the response signal received by the base station apparatus 10a is the maximum transmission power. As a result of attenuation from U by the attenuation D2, the prescribed value S is not reached. For this reason, when the remote radio terminal apparatus 30 is included, the reception power RTW of each response signal received from the plurality of arbitrary radio terminal apparatuses 30 in the base station apparatus 10a may not be constant.

  In such a case, for example, if the specified value S is set according to the reception power RTW of the response signal received from the remote radio terminal device 30, each base station device 10a receives each of the multiple radio terminal devices 30. The reception power RTW of the response signal is substantially equal to the reception power RTW of the response signal received from the remote wireless terminal device 30. As a result, regardless of the distance between the base station device 10a and the wireless terminal device 30, the received power RTW of each response signal received from the plurality of wireless terminal devices 30 in the base station device 10a becomes substantially constant, The distance between the station device 10a and the wireless terminal device 30 is not reflected in the received power RTW of the response signal. As a result, when the base station apparatus 10a determines whether or not multicast transmission control is necessary from the received power of the response signal, the nearby radio terminal apparatus 30 and the far radio terminal apparatus 30 have the same influence. Thus, the total value of the received power of response signals received from a plurality of wireless terminal devices 30 is approximately proportional to the number of wireless terminal devices 30 that have transmitted response signals.

Therefore, according to the present embodiment, the response signal is transmitted according to the number of the wireless terminal devices 30 that transmitted the response signal without being affected by the distance between the base station device 10a and the wireless terminal device 30. Whether or not to perform multicast transmission control by accurately determining the presence / absence of the wireless terminal device 30 requiring packet retransmission or the like from a second predetermined value indicating the power level of the second subcarrier group to be used The accuracy of the determination can be improved.
It should be noted that the reference value S can be arbitrarily set within an allowable range of accuracy required for determining the presence / absence of the wireless terminal device 30 that requires packet retransmission or the like.
Further, in the example illustrated in FIG. 8C, for the sake of simplicity, the transmission power TRW [dBm] of the wireless terminal device 30 and the transmission power TW [dBm] of the base station device 10a are equal to the maximum transmission power U of the same power. However, it is sufficient that the received power at each base station apparatus 10a from each wireless terminal apparatus 30 is substantially the same, the transmission power TRW [dBm] of the wireless terminal apparatus 30 and the transmission power TW [dBm] of the base station apparatus 10a. Need not be identical. In particular, the case where the wireless terminal device 30 does not have the ability to transmit the transmission power as much as the base station device 10a is usual. In such a case, the received power RTW [dBm] received by the base station device 10a may be assumed to be equal to or less than thermal noise. In this case, it is difficult to receive and demodulate a signal from a single wireless terminal device 30, but when a signal from a plurality of wireless terminal devices is added and operated (in the case of a multicast operation), the wireless terminal Since only the number of devices is added, the added value of the reception status notification signal and the retransmission request signal which are response signals can be set to be equal to or higher than the thermal noise. For this reason, even if the transmission power RTW [dBm] of the wireless terminal device 30 is sufficiently lower than the transmission power TW [dBm] of the base station device 10a, it is possible to operate the wireless communication system without any problem. More specifically, it will be described later in [Supplementary explanation on setting method of transmission power of retransmission request signal].

Also, according to the present embodiment, multicast transmission can be controlled using the ratio of the second total value to the first total value as an index.
Further, since the threshold is calculated by multiplying the first total value by the reference retransmission request rate, multicast transmission can be controlled using the reference retransmission request rate as an index.
Furthermore, since the threshold is determined based on the first total value, it is possible to reduce the false detection probability and the missed detection probability of the retransmission request signal.

[Supplementary explanation on setting method of retransmission request signal transmission power]
Next, a supplementary description will be given of a method for setting the transmission power TRW of the response signal in the wireless terminal device 30 described above. In the downlink from the base station apparatus 10a that is a broadcasting station that performs the multicast transmission described above to each wireless terminal apparatus 30 that is a mobile station, the transmission power TW of the base station apparatus 10a is set to P _dl-tx [dBm], If the received power RW of the wireless terminal device 30 is P _dl-rx [dBm], the propagation loss (attenuation) Ldl in the downlink is Ldl = P _dl-tx -P _dl-rx [dB].

Here, since the transmission power P _dl-tx [dBm] of the base station apparatus 10a can be included in the communication data transmitted from the base station apparatus 10a as the above-described transmission power information TP, each wireless terminal The device 30 can know the transmission power P _dl-tx [dBm] of the base station device 10 a from the transmission power information TP. In addition, since the received power P _dl-rx [dBm] of the wireless terminal device 30 is measured in each wireless terminal device 30 as described above, each wireless terminal device 30 and the transmission power TW of the base station device 10 a itself. From the received power RW at the station, it is possible to know the propagation loss (attenuation) Ldl in the downlink from the base station apparatus 10a to the own station.

On the other hand, in the uplink from each wireless terminal device 30 to the base station device 10, the maximum transmission power U of the wireless terminal device 30 is P _ul-tx-max [dBm], and the transmission power TRW of the wireless terminal device 30 is P _{ul. -Tx} [dBm], and the received power RTW from each radio terminal apparatus 30 in the base station apparatus 10a is Pul _-rx [dBm], the uplink propagation loss Lul is Lul = Pul _-tx- Pul _-rx [dB].

  Here, when the uplink and downlink frequencies are the same, Lul = Ldl [dB] because of the reciprocity of the propagation path. Even if the frequency is slightly different and the propagation loss varies with time, the relationship Lul≈Ldl [dB] holds.

The assumed received power of the base station device 10a corresponding to the above-mentioned specified value S (that is, the desired value of the received power RW of the response signal from one wireless terminal device 30 in the base station device 10a) is P _ul-rx-set [dBm ], The required transmission power of the wireless terminal device 30 (that is, the transmission power of the wireless terminal device 30 for obtaining the assumed reception power P _ul-rx-set in the base station device 10a in consideration of the propagation loss) P _{ul -Tx-set} is Pul _-tx-set = Pul _-rx-set + Lul [dBm]. The value of the required transmission power P _ul-tx-set of the wireless terminal device 30 is expressed by P _ul-tx-set ≈P _ul-rx-set + Ldl [dBm] because of the relationship Lul≈Ldl [dB]. . Therefore, each wireless terminal apparatus 30 determines the transmission power of the uplink of its own station in consideration of the propagation loss if the assumed reception power of the base station apparatus 10a corresponding to the above-mentioned specified value S is given. be able to.

Here, for example, the transmission power P _ul-tx of the wireless terminal device 30 is determined as follows.
・ When P _ul-tx-set ≤ P _ul-tx-max : P _ul-tx = P _ul-tx = P _ul-tx-set [dBm]
・ When P _ul-tx-set > P _ul-tx-max : P _ul-tx = P _ul-tx = P _ul-tx-max [dBm]

When the transmission power P _ul-tx of each wireless terminal device 30 is determined in this manner, each wireless signal in the base station device 10a is determined unless the maximum transmission power of each wireless terminal device 30 reaches P _ul-tx-max [dBm]. The received power (per radio terminal apparatus) of the terminal device 30 is a constant value, and the received power (per radio terminal apparatus) of the base station apparatus 10a is assumed to be the assumed received power P _ul-rx-set [dBm]. I can do it.

Next, supplementary explanation will be given regarding the assumed reception power P _ul-rx-set of the base station apparatus 10a.
If the base station device 10a individually demodulates the received signal from each wireless terminal device 30, the received power P _ul-rx of the base station device 10a per wireless terminal device 30 is thermal noise. Alternatively, the received power P _ul-rx-1 of the base station device 10a per one wireless terminal device 30 that is equal to or greater than the value obtained by adding the required C / N [dB] for demodulation to the environmental noise No [dBm] is required. . That is, Expression (2) is established.
P _ul-rx-set -1 = P _ul-rx ≧ No + C / N [dBm] (2)

On the other hand, according to the present embodiment, signals from a plurality of wireless terminal devices 30 are detected by vector addition (synthesis) instead of individually demodulating the signals from each wireless terminal device 30. . Here, the phase of the signal from each radio terminal apparatus 30 is random at the receiving end of the base station apparatus 10a. Therefore, for the sake of simplicity, it is assumed that each wireless terminal device 30 is equidistant from the base station device 10a, and the number of wireless terminal devices 30 equidistant from the base station device 10a is m. and total received power _{P ul-rx-m} of 10a, the following relationship exists between the reception power _{P ul-rx} from each wireless terminal 30.
P _ul-rx-m = P _ul-rx + 10Log (m) [dBm]
Here, 10 Log (m) [dBm] represents the addition effect of the wireless terminal device.

According to the present embodiment, in the case of wireless terminal devices 30 at different distances, that is, when the distances between base station device 10 and a plurality of wireless terminal devices 30 are not equidistant, transmission of wireless terminal device 30 The power P _ul-tx is corrected and set in each radio terminal apparatus 30 by the amount of uplink propagation loss Lul (≈Ldl) [dB]. For this reason, unless the transmission power of the wireless terminal device 30 reaches the maximum transmission power P _ul-tx-max [dBm], the reception power P _ul-rx of each wireless terminal device 30 in the base station device 10a becomes equal to each other. When the number of all wireless terminal devices 30 is M, the total received power P _ul-rx-all in the base station device 10 a is P _ul-rx-all = P _ul-rx +10 Log (M) [dBm] It becomes.

Therefore, in the present embodiment, the necessary received power P _ul-rx-set-2 of the base station device 10a per wireless terminal device 30 only needs to satisfy the following expression (3).
P _ul-rx-set-2 = P _ul-rx = P _ul-rx-all -10Log (M) ≧ No-10Log (M) [dBm] (3)

Comparing Equation (2) and Equation (3), the received power P _ul-rx-set-1 in the base station device 10a per wireless terminal device 30 of the former Equation (2) is _either thermal noise or environmental noise. A level higher by the required C / N [dB] than No [dBm] is required. On the other hand, according to the latter equation (3) according to the present embodiment, the received power P _ul-rx-set-2 in the base station device 10a per one wireless terminal device 30 is _{equal to} thermal noise or environmental noise No. It may be lower by 10 Log (M) [dB] due to the addition effect of the wireless terminal device 30 than [dBm].

Therefore, according to the present embodiment, the received power of the base station apparatus 10a per radio terminal apparatus 30 is (C / C) as compared with the case where the signal from each radio terminal apparatus 30 is demodulated (the former). N + Log (M)) [dB] may be low, and the thermal noise or environmental noise No [dBm] may be reduced by 10 Log (M) [dB] due to the addition effect of the wireless terminal device 30. Further, when the number of wireless terminal devices 30 is sufficiently large (M >> 1), the received power in the base station device 10a per wireless terminal device 30 is a value that is sufficiently low with respect to thermal noise or environmental noise No [dBm]. Good. In each wireless terminal device 30, when the number M of wireless terminal devices 30 is sufficiently larger than 1 and the condition of M >> 1 is satisfied, the required transmission power P _ul-tx-set of each wireless terminal device 30 is sufficiently low. Can be set to a value. Therefore, the transmission power of each wireless terminal device 30 is unlikely to reach the maximum transmission power P _ul-tx-max [dBm] of each wireless terminal device 30. For this reason, the reception power P _ul-rx per radio terminal apparatus 30 in the base station apparatus 10a is a constant value, that is, the assumed reception power (per radio terminal apparatus) of the base station apparatus 10a is P _ul-rx-set. The number of wireless terminal devices 30 that can be set to [dBm] (the number of wireless terminal devices that ensure equality among wireless terminal devices) can be sufficiently increased.

[Embodiment 2]
In the first embodiment, the case where Lo = L and Po = P has been described. In the second embodiment, the case where Lo ≠ L and Po = P will be described. There is a difference in the configuration of the base station apparatus 10 between the present embodiment and the first embodiment, and the difference will be mainly described below.
Note that the method for setting the transmission power of a response signal such as a retransmission request signal in each wireless terminal device 30 is the same as in the first embodiment.

  FIG. 9 is a schematic block diagram showing an internal configuration of a base station apparatus 10b that is the base station apparatus 10 according to the present embodiment. As shown in the figure, the base station device 10b includes a first number storage unit 271 and a second number storage unit 272 in addition to the configuration of the base station device 10a. Further, a multicast transmission control unit 26b is included instead of the multicast transmission control unit 26a. The multicast transmission control unit 26b is different from the multicast transmission control unit 26a in that it includes a threshold value calculation unit 261b instead of the threshold value calculation unit 261a.

  The multicast transmission control unit 26b controls multicast transmission based on the ratio of the second total value to the first total value and the ratio of the second number to the first number. This will be specifically described below.

The first number storage unit 271 and the second number storage unit 272 store Lo and L, respectively. The threshold calculation unit 261b reads the Lo and L from each storage unit, and calculates the threshold based on the first total value and the ratio L / Lo of the second number to the first number. Formula (4) is a formula for calculating this threshold value.
Threshold = first total value × reference retransmission request rate × (L / Lo) (4)
Processing after the threshold is calculated is the same as that in the first embodiment.

  According to the present embodiment, even if the first number and the second number are different, the multicast transmission control unit 26b appropriately uses the ratio of the second total value to the first total value as an index. Multicast transmission can be controlled.

[Embodiment 3]
In the third embodiment, a case where Lo = L and Po ≠ P will be described. There is a difference in the configuration of the base station apparatus 10 between the present embodiment and the first and second embodiments, and the difference will be mainly described below.
Note that the method for setting the transmission power of a response signal such as a retransmission request signal in each wireless terminal device 30 is the same as in the first embodiment.

  FIG. 10 is a schematic block diagram showing an internal configuration of a base station apparatus 10c that is the base station apparatus 10 according to the present embodiment. As shown in the figure, the base station device 10c includes a first predetermined value storage unit 273 and a second predetermined value storage unit 274 in addition to the configuration of the base station device 10a. Further, a multicast transmission control unit 26c is included instead of the multicast transmission control unit 26a. The multicast transmission control unit 26c is different from the multicast transmission control unit 26a in that it includes a threshold value calculation unit 261c instead of the threshold value calculation unit 261a.

  The multicast transmission control unit 26c controls multicast transmission based on the ratio of the second total value to the first total value and the ratio of the second predetermined value to the first predetermined value. This will be specifically described below.

The first predetermined value storage unit 273 and the second predetermined value storage unit 274 store Po and P, respectively. The threshold calculation unit 261c reads Po and P from each storage unit, and calculates the threshold based on the first total value and the ratio P / Po of the second predetermined value to the first predetermined value. Formula (5) is a formula for calculating this threshold value.
Threshold = first total value × reference retransmission request rate × (P / Po) (5)
Processing after the threshold is calculated is the same as in the first and second embodiments.

  According to the present embodiment, even if the first predetermined value and the second predetermined value are different, the multicast transmission control unit 26b uses the ratio of the second total value to the first total value as an index. Multicast transmission can be appropriately controlled.

[Embodiment 4]
In the fourth embodiment, a case where Lo ≠ L and Po ≠ P is described. There is a difference in the configuration of the base station apparatus 10 between the present embodiment and the first to third embodiments, and the difference will be mainly described below.
Note that the method for setting the transmission power of a response signal such as a retransmission request signal in each wireless terminal device 30 is the same as in the first embodiment.

  FIG. 11 is a schematic block diagram showing an internal configuration of a base station apparatus 10d that is the base station apparatus 10 according to the present embodiment. As shown in the figure, in addition to the configuration of the base station device 10a, the base station device 10d includes a first number storage unit 271, a second number storage unit 272, a first predetermined value storage unit 273, a second A predetermined value storage unit 274 is included. Each of these storage units is the same as that described in the second or third embodiment. Further, a multicast transmission control unit 26d is included instead of the multicast transmission control unit 26a. The multicast transmission control unit 26d is different from the multicast transmission control unit 26a in that it includes a threshold value calculation unit 261d instead of the threshold value calculation unit 261a.

  The multicast transmission control unit 26d is based on the ratio of the second total value to the first total value, the ratio of the second number to the first number, and the ratio of the second predetermined value to the first predetermined value. Control of multicast transmission. This will be specifically described below.

The threshold calculation unit 261d reads the Lo, L, Po, and P from each storage unit, and the first total value, the ratio L / Lo of the second number to the first number, and the second for the first predetermined value. The threshold value is calculated based on the ratio P / Po of the predetermined value. Formula (6) is a formula for calculating this threshold value.
Threshold = first total value × reference retransmission request rate × (L / Lo) × (P / Po) (6)
Processing after the threshold is calculated is the same as in the first to third embodiments.

  According to the present embodiment, the multicast transmission control unit 26d uses the first total value even when the first number and the second number, and the first predetermined value and the second predetermined value are different from each other. Multicast transmission can be appropriately controlled using the ratio of the second total value to the index.

  While the first to fourth embodiments of the present invention have been described above, the optimum values of Lo, L, Po, and P will be described here. As described above, these are determined by the user, but it is preferable to use values determined as follows. That is, the ratio of L to Lo (L / Lo) is preferably determined based on the reference retransmission request rate. For example, it is preferable to make the reference retransmission request rate equal to Lo / L. Further, the ratio of P to Po (P / Po) is also preferably determined based on the reference retransmission request rate. For example, it is preferable to make the reference retransmission request rate equal to Po / P.

  As described above, the multicast transmission control unit 26a and the like perform multicast transmission control based on the ratio of the second total value to the first total value, but the first reception level total value acquisition unit 21 and the second reception level total The first total value and the second total value respectively acquired by the value acquisition unit 22 include a noise component. And the above-mentioned ideal ratio which does not contain a noise component and the ratio calculated | required based on the 1st total value and 2nd total value which were actually acquired have a big difference of a 1st total value and a 2nd total value. The farther away. Therefore, it is not preferable that the difference between the first total value and the second total value becomes too large. However, if the Lo, L, Po, and P are determined as described above, the first total value and the first total value The difference between the two total values can be prevented from becoming too large.

  The present invention is not limited to Embodiments 1 to 4 described above, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention.

For example, in each of the above embodiments, the first subcarrier group is set to Mo among the subcarriers constituting the OFDM symbol transmitted at times t _{2 to} t ₃ shown in FIG. The carrier group is the other M carriers among the subcarriers transmitted at times t _{2 to} t ₃ shown in FIG. 2, but for example, as shown in FIG. and Mo pieces of the sub-carriers constituting the OFDM symbols transmitted ₂ ~t _3, sub transmitted the second set of subcarriers, time _t 3 _{~t 4 (t} 4 after the _{t 3)} to Other M carriers may be used. In this way, more subcarriers can be used for transmission of the reception state notification signal and retransmission request signal.

  In the above embodiment, the Lo, L, Po, and P have been described as being determined by the user. However, the base station apparatus 10 determines that the reference retransmission request rate received by the reference retransmission request rate input reception unit 260 is the same as the reference retransmission request rate. Based on the above, the optimum values of Lo, L, Po, and P are calculated, and the calculated values are used as the first number storage unit 271, the second number storage unit 272, the first predetermined value storage unit 273, the second The data may be stored in the predetermined value storage unit 274 and transmitted to each wireless terminal device 30. In this case, each wireless terminal device 30 converts the received Lo, L, Po, P into the first number storage unit 39, the second number storage unit 41, the first predetermined value storage unit 40, and the second predetermined value. It is preferable to store the value in the value storage unit 42.

Further, a program for realizing the functions of the base station apparatus 10 and the wireless terminal apparatus 30 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed. The above-described processes of each device may be performed.
Here, the “computer system” may include an OS and hardware such as peripheral devices. Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
The “computer-readable recording medium” means a flexible disk, a magneto-optical disk, a ROM, a writable nonvolatile memory such as a flash memory, a portable medium such as a CD-ROM, a hard disk built in a computer system, etc. This is a storage device.
Furthermore, the “computer-readable recording medium” includes a volatile memory (for example, DRAM (DRAM) in a computer system that becomes a server or a client when a program is transmitted through a network such as the Internet or a communication line such as a telephone line. Dynamic Random Access Memory)) that holds a program for a certain period of time is also included.
The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.
Further, the program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve each function mentioned above in combination with the program already recorded on the computer system, what is called a difference file (difference program) may be sufficient.

1 wireless communication system,
10, 10a, 10b, 10c, 10d base station apparatus,
11, 38 control unit,
12, 25, 37, 42 encoder,
13,43 Multiplexer,
14,44 modulator,
15,45 S / P converter,
16,46 OFDM symbol generator,
17, 19, 32, 47 RF section,
18,31 antenna,
20, 33 OFDM symbol detector,
21 first reception level total value acquisition unit,
22 Second reception level total value acquisition unit,
23, 34 P / S converter,
24, 35 demodulator,
26a, 26b, 26c, 26d multicast transmission control unit,
30 wireless terminal device,
36 separation units 39, 271 a first number storage unit,
41,272 second number storage unit,
40, 273 a first predetermined value storage unit,
42, 274 second predetermined value storage unit,
110 Information generator,
260 Reference retransmission request rate input reception unit,
261a, 261b, 261c, 261d threshold value calculation unit,
262 comparison unit,
380 reception state notification signal transmission unit,
381 retransmission request signal transmission unit,
382 received power measurement unit,
383 A transmission power setting unit.

Claims (5)

A wireless communication system including a base station device that multicasts communication data and a plurality of wireless terminal devices that receive the communication data multicast-transmitted,
The base station device
An information generating unit that generates information about transmission power of the communication data and multiplexes the information with the communication data;
Each wireless terminal device of the plurality of wireless terminal devices is
A received power measuring unit for measuring the received power of the communication data;
A response to acquire the information multiplexed in the communication data and transmit to the base station apparatus from the transmission power of the communication data indicated by the information and the reception power of the communication data measured by the measurement unit A transmission power setting unit for setting the transmission power of the signal;
Including
The transmission power setting unit included in each wireless terminal device of the plurality of wireless terminal devices,
When the ratio of the received power to the transmission power of the communication data exceeds a specified value, a value obtained by subtracting the amount exceeding the specified value from the transmission power of the communication data is set as the transmission power of the response signal And a wireless communication system. The wireless communication system according to claim 1, wherein
The specified value is
The base station apparatus is a value that provides a reference for determining whether or not there is a radio terminal apparatus that has transmitted the response signal based on the power of the response signal received from the plurality of radio terminal apparatuses. Communications system. In the radio | wireless communications system of any one of Claim 1 or 2,
Each wireless terminal device further includes:
A reception state notification signal transmitter that transmits a reception state notification signal by one or a plurality of subcarriers selected from the first subcarrier group when the communication data is received;
A determination unit for determining whether the communication data is normally received;
One or a plurality of subcarriers selected from a second subcarrier group that does not overlap the first subcarrier group when the determination unit determines that the communication data is not normally received. A retransmission request signal transmission unit for transmitting a retransmission request signal, and
Including
The base station device further includes:
A first total value acquisition unit that receives the first subcarrier group and acquires a first total value that is a total value of reception levels of the subcarriers constituting the first subcarrier group;
A second total value acquisition unit that receives the second subcarrier group and acquires a second total value that is a total value of reception levels of the subcarriers constituting the second subcarrier group;
A multicast transmission control unit that controls multicast transmission based on a ratio of the second total value to the first total value;
A wireless communication system comprising: A wireless communication method in which a base station device multicasts communication data and a plurality of wireless terminal devices receive the communication data multicast-transmitted,
An information generating step in which the base station apparatus generates information on the transmission power of the communication data and multiplexes the information with the communication data;
A reception power measuring step in which each wireless terminal device of the plurality of wireless terminal devices measures the reception power of the communication data;
Each wireless terminal device acquires the information multiplexed on the communication data, and from the transmission power of the communication data indicated by the information and the reception power of the communication data measured by the measurement unit, A transmission power setting step for setting transmission power of a response signal to be transmitted to the base station device, and
In the transmission power setting step, when the ratio of the reception power to the transmission power of the communication data exceeds a specified value, a value obtained by subtracting the amount exceeding the specified value from the transmission power of the communication data is A wireless communication method characterized by setting as transmission power of a response signal. The wireless communication method according to claim 4, further comprising:
A reception state notification signal transmission step of transmitting a reception state notification signal by one or a plurality of subcarriers selected from the first subcarrier group when each of the wireless terminal devices has received the communication data; ,
Each wireless terminal device determines whether or not the communication data is normally received; and
When each wireless terminal apparatus determines that the communication data is not normally received in the determination step, the wireless terminal apparatus is selected from a second subcarrier group that does not overlap with the first subcarrier group. A retransmission request signal transmission step of transmitting a retransmission request signal by one or a plurality of subcarriers;
The base station apparatus receives the first subcarrier group and acquires a first total value that is a total value of reception levels of the subcarriers constituting the first subcarrier group. Steps,
The base station apparatus receives the second subcarrier group and acquires a second total value that is a total value of reception levels of subcarriers constituting the second subcarrier group. Steps,
A multicast transmission control step in which the base station apparatus controls multicast transmission based on a ratio of the second total value to a first total value;
A wireless communication method comprising: