JP2008167164A - Communication system, base station, communication method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for determining a DL CQI level at a base station without notifying DL CQI information by a mobile station and individually setting transmission parameters of response signals to random access for each mobile station. <P>SOLUTION: According to this invention, a mobile station using a signature meeting a detection criterion is detected and delay time at a propagation path is measured with respect to a reception random access signal from the detected mobile station. Then, a table in which relation between the delay time and the DL CQL level is preliminarily defined is prepared, the DL CQI level is determined using the measured delay time and the table and the transmission parameters of the random access response which are the response signals to the random access are individually set for each mobile station based on the determined DL CQI level. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio communication system in which a plurality of mobile stations share radio resources and randomly access a base station.

  In 3GPP Long Term Evolution (LTE), individual time and frequency are appropriately allocated for transmission of uplink data signals, and orthogonality between mobile stations is maintained. However, this requires uplink Layer 1 (L1) symbol synchronization.

  For this reason, a mobile station that is not synchronized with the L1 symbol performs random access for transmitting a signal by setting a no-signal interval (GP) in advance so as not to interfere with the signals of the preceding and succeeding frames. . The base station measures the delay time in the propagation path of the random access signal of each mobile station in which the preamble is detected, and notifies the mobile station of the transmission timing correction value, thereby establishing L1 symbol synchronization.

  In random access in LTE, it has been studied to transmit several bits of information on a preamble. Therefore, each mobile station transmits DL CQI (Channel Quality Indicator) level information indicating the channel quality of the downlink (DL) to the base station side and transmits a response signal for random access. It is possible to set power (or other transmission parameters such as a modulation scheme and an error correction code coding rate) to an appropriate value for each mobile station.

  However, since the number of bits that can be transmitted in the preamble is extremely limited to 4 to 8 bits, a situation in which notification of the DL CQI level is impossible is easily assumed. In that case, as in the case of random access in the WCDMA scheme, it is conceivable to transmit a response to random access to all detected mobile stations with the same transmission power (for example, Non-Patent Document 1 or Non-Patent Document). 2).

  The configuration of a conventional random access communication apparatus that transmits a response to random access with the same transmission power to all mobile stations will be described below with reference to FIG.

In the mobile station 301 of FIG. 8, the signature selection unit 102 selects one of the predetermined signatures and outputs it as signature information S _SGN . The random access signal generation unit 103 generates a random access signal S _TX from the signature information S _SGN and transmits it to the base station 302.

In base station 302, the preamble detection unit 105 performs detection of the received random access signal S _RX signature used in the preamble of which corresponds to the random access signal S _TX, and outputs the result as received signatures information S _RSGN. The delay time measuring unit 106 measures and outputs the delay time S _RTD in the propagation path from the received random access signal S _RX and the received signature information S _RSGN . The timing control unit 107 calculates a necessary transmission timing correction value for each mobile station detected from the delay time S _RTD and outputs it as transmission timing control information _STA . Transmission power control section 303 uses transmission power S _POW of a random access response, which is a response signal to random access, from the transmission power of the common pilot channel (CPICH: Common Pilot Channel) and the power offset value with respect to the preset CPICH transmission power. Is calculated and output. The random access response generation unit 304 generates a random access response S _ACK from the reception signature information S _RSGN , the transmission timing control information S _TA, and the transmission power S _POW and transmits it to the mobile station.
3GPP TS25.211 V6.7.0 (2005-12) "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical channels and mapping of transport channels onto physical channels (FDD) (Release 6)", Section 5.3 .3.7, pp. 34-35 3GPP TS25.101 V7.1.0 (2005-09) "3rd Generation Partnership Project, Technical Specification Group Radio access Network (Radio Access Network, User Equipment) (3rd Generation Partnership Project) pp. 53

In the background art described above, a random access response is transmitted with the same transmission power regardless of the distance between the mobile station and the base station.
For mobile stations with a high CQI level, the problem is that the transmission power becomes excessive. The same can be said for not only the transmission power of the random access response but also other transmission parameters such as the modulation scheme and the coding rate of the error correction code.

The first invention for solving the above-described problems is
A communication system,
A mobile station transmitting a random access signal;
A base station that detects the mobile station by the random access signal,
The base station
A measurement unit for measuring a delay time of the random access signal;
A setting unit configured to set a transmission parameter of a random access response to be transmitted as a response signal of the random access signal based on the measured delay time.

According to a second invention for solving the above-mentioned problem, in the first invention,
The setting unit determines a downlink channel quality level of the mobile station based on the measured delay time, and controls the transmission parameter based on the level.

According to a third invention for solving the above-described problem, in the first or second invention,
The setting unit determines the level based on the measured delay time and a table that defines a relationship between the delay time and the level prepared in advance.

A fourth invention for solving the above-mentioned problems is any one of the first to third inventions,
The setting unit calculates a reception success probability of the random access response based on a response confirmation transmitted from the mobile station in response to the random access response, and determines the transmission parameter from the reception success probability and the level. It is characterized by setting.

A fifth invention for solving the above-mentioned problems is the above-mentioned fourth invention,
The setting unit determines the transmission parameter based on an offset defined according to the reception success probability and the level.

A sixth invention for solving the above-described problem is
A base station,
A measurement unit for measuring the delay time of the random access signal transmitted;
A setting unit configured to set a transmission parameter of a random access response to be transmitted as a response signal of the random access signal based on the measured delay time.

The seventh invention for solving the above-mentioned problems is the above-mentioned sixth invention,
The setting unit determines a channel quality level of a mobile station downlink based on the measured delay time, and controls the transmission parameter based on the level.

An eighth invention for solving the above-described problems is the above sixth or seventh invention,
The setting unit determines the level based on the measured delay time and a table that defines a relationship between the delay time and the level prepared in advance.

A ninth invention for solving the above-described problems is any one of the sixth to eighth inventions,
The setting unit calculates a reception success probability of the random access response based on a response confirmation transmitted in response to the random access response, and sets the transmission parameter from the reception success probability and the level. It is characterized by.

A tenth aspect of the invention for solving the above-described problem is the ninth aspect of the invention,
The setting unit determines the transmission parameter based on an offset defined according to the reception success probability and the level.

An eleventh invention for solving the above-mentioned problems is
A communication method,
A transmission step of transmitting a random access signal;
A measuring step of measuring a delay time of the random access signal;
And setting a transmission parameter of a random access response to be transmitted as a response signal of the random access signal based on the measured delay time.

A twelfth invention for solving the above-mentioned problems is the above-mentioned eleventh invention,
The setting step includes
A determination step of determining a downlink channel quality level of the mobile station based on the measured delay time;
And a control step of controlling the transmission parameter based on the determined level.

The thirteenth invention for solving the above-mentioned problems is the above-mentioned eleventh or twelfth invention,
The setting step includes a determination step of determining the level based on the measured delay time and a table in which a relationship between the delay time and the level is defined in advance.

A fourteenth aspect of the invention for solving the above-described problems is the invention according to any one of the eleventh to thirteenth aspects,
The setting step calculates a reception success probability of the random access response based on a response confirmation transmitted in response to the random access response;
And a setting step for setting the transmission parameter from the calculated reception success probability and the level.

A fifteenth aspect of the present invention for solving the above problem is the fourteenth aspect of the present invention,
The setting step sets the transmission parameter based on an offset defined according to the reception success probability and the level.

The sixteenth invention for solving the above-mentioned problems is
A program of a base station, wherein the program identifies the base station,
A measurement unit for measuring the delay time of the random access signal transmitted;
It is made to function as a setting part which sets the transmission parameter of the random access response transmitted as a response signal of the said random access signal based on the measured delay time.

In the present invention, a plurality of mobile stations share radio resources and transmit a random access signal to a base station, and the base station detects a signature detected based on a received random access signal corresponding to the random access signal transmitted by the mobile station The delay time generated in the propagation path is measured based on the random access signal and the signature information, the DL CQI level is determined based on the delay time, and the response to the random access signal is based on the DL CQI level. The transmission parameter of the random access response is determined. The determination of the DL CQI level based on the delay time is performed using a table in which a relationship between the delay time and the DL CQI level is prepared in advance. Further, the transmission parameter of the random access response is determined from the determined DL CQI level. Further, there is a method of defining an offset for a transmission parameter based on the reception success probability of the random access response and adding the offset to the transmission parameter determined from the table of delay time and DL CQI level. Here, as transmission parameters, transmission power, modulation scheme, coding rate of error correction code, and the like can be considered.
As described above, according to the present invention, the DL CQI level can be determined in the base station without the mobile station notifying the DL CQI information, and the transmission parameter of the random access response is individually set for each mobile station. It is characterized by setting.

  According to the present invention, the DL CQI level can be determined at the base station without the mobile station notifying the DL CQI information. This is because the DL CQI level can be determined based on the propagation loss calculated from the delay time in the propagation path measured by the base station. Furthermore, by using the determined DL CQI level, it is possible to set a random access response transmission parameter for each mobile station.

  In order to explain the features of the present invention, it will be specifically described below with reference to the drawings.

  A first embodiment for carrying out the present invention will be described in detail with reference to the drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of a random access communication system according to the first embodiment of the present invention.

  The random access communication system of the present invention includes a mobile station 101 and a base station 104. The mobile station and the base station communicate with each other using a random access method.

  The mobile station 101 includes a signature selection unit 102 and a random access signal generation unit 103. Moreover, although not shown in figure, it has a transmission / reception part.

The signature selecting unit 102 randomly selects one of predetermined types of signatures, that is, signatures satisfying the detection criteria, and outputs signature information S _SGN indicating the number of the selected signature.

In order to start communication with the base station, the random access signal generation unit 103 generates a random access signal S _TX from the signature information S _SGN and transmits it to the base station via the transmission / reception unit.

  The base station 104 includes a preamble detection unit 105, a delay time measurement unit 106, a timing control unit 107, a DL CQI determination unit 108, a transmission parameter control unit 109, and a random access response generation unit 110. Moreover, although not shown in figure, it has a transmission / reception part.

The preamble detection unit 105 detects a signature used for the preamble from the received random access signal S _RX corresponding to the random access signal S _TX from the mobile station 101 received by the transmission / reception unit, and outputs it as reception signature information S _RSGN .

The delay time measuring unit 106 measures and outputs a delay time S _RTD generated in the propagation path from the received random access signal S _RX and the received signature information S _RSGN . The method for measuring the delay time S _RTD generated in the propagation path from the received random access signal S _RX and the received signature information S _RSGN is not particularly limited in the present invention, and any method may be used.

The timing control unit 107 calculates a transmission timing correction value necessary in the mobile station from the delay time S _RTD and outputs it as transmission timing control information S _TA .

The DL CQI determination unit 108 determines the DL CQI level (downlink _channel quality) from the delay time S _RTD and outputs the DL CQI information S _RCQI . The determination of the DL CQI level in the DL CQI determination unit 108 is performed using a table in which a relationship between the delay time and the DL CQI level is defined in advance, and using the delay time S _RTD and the table.

  Here, a table defining the relationship between the delay time and the DL CQI level will be described.

2 and 3 are diagrams for explaining determination of the DL CQI level in the first embodiment according to the present invention. In this embodiment, the determination is made using a table in which the relationship between the delay time and the DL CQI level is defined in advance. For the derivation of the relationship between the delay time and the distance used to generate the table and the relationship between the distance and the propagation loss, the following equations (1) and (1), which are used in the examination of the 3GPP LTE standard method as an example: (2) is used.
R = T _RTD / 6.7 (1)
L = 128.1 + 37.6 log ₁₀ (R) (2)
Here, _TRTD is the delay time [us], R is the distance [km] between the mobile station and the base station, and L is the propagation loss [dB]. In generating the table of the relationship between the delay time and the DL CQI level, first, the relationship between the DL CQI level and the propagation loss is defined. At this time, the table is generated so that the difference in propagation loss between adjacent DL CQI levels becomes a constant value.

Next, the delay time corresponding to the propagation loss that becomes the boundary of the DL CQI level is calculated, and the relationship between the delay time and the DL CQI level is defined. In this embodiment, assuming that the cell radius is 5 km, the relationship between the delay time and the DL CQI level is defined so that the difference in propagation loss between the DL CQI levels is 20 dB. FIG. 2 is a table in such a case. In FIG. 2, for example, the propagation loss corresponding to the lower limit value 0.9 us of the delay time when the DL CQI level is Lv2 (High) is L = 12.81 + 37.6 log ₁₀ (0. 0 from Equation (1) and Equation (2). 9 / 6.7) = 94.4 dB, while the propagation loss corresponding to the lower limit value 3.0 us of the delay time when the DL CQI level is Lv3 (Middle) is L = 128 from Equation (1) and Equation (2). .1 + 37.6 log ₁₀ (3.0 / 6.7) = 114.4 dB, and the difference is 20 dB.

  Furthermore, in this embodiment, in order to control the transmission power of the random access response from the determined DL CQI level, the relationship between the DL CQI level and the transmission power is also defined in advance. The transmission power is set so as to be inversely proportional to the DL CQI level and to satisfy an error rate target (for example, 1% Packet Error Rate: PER) of the random access response for each DL CQI level.

  Here, it is assumed that the transmission power required for the Lv4 mobile station having the lowest DL CQI level is 30 dBm, and the transmission power increases as the DL CQI level increases on the assumption that the target error rate is satisfied. Is set small, and a relationship as shown in FIG. 2 is defined.

In random access, each mobile station ideally transmits a random access signal so as to be received at the timing shown in FIG. However, due to the delay in the propagation path, the random access signal is actually received with a delay as shown in FIG. Here, it is assumed that mobile station 1 and mobile station 2 are detected as shown in FIG. At this time, the delay times of the random access signals of the mobile station 1 and the mobile station 2 were measured, and as a result, T _{RTD, 1} = 1.6 [us] and T _{RTD, 2} = 10.4 [us], respectively. When the DL CQI level of each mobile station is determined using the relationship between the predefined delay time and the DL CQI level shown in FIG. 2, the DL CQI level of the mobile station 1 is “High”, and the DL CQI level of the mobile station 2 is “ Low ".

  Based on the DL CQI level determination result, the transmission power of the random access response is controlled. As a transmission power control method, a method in which the relationship between the DL CQI level and the transmission power is defined in advance as shown in FIG. 2 is used. In this embodiment, the transmission power of mobile station 1 whose DL CQI level is “High”. Is set to 10 dBm, and the transmission power of the “Low” mobile station 2 is set to 30 dBm.

Transmission parameter control section 109 outputs transmission parameter control information S _CTRL indicating a transmission parameter of random access response signal S _ACK that is a response signal from DL CQI information S _RCQI to random access.

The random access response generation unit 110 generates a random access response signal S _ACK that is a response signal to the random access from the mobile station 101. The random access response signal S _ACK is generated from the reception signature information S _RSGN , the transmission timing control information S _TA, and the transmission parameter control information S _CTRL, and is transmitted to the mobile station via the transmission / reception unit.

  Subsequently, the operation of the present embodiment will be described.

When the mobile station 101 connects to the base station 104, the signature selection unit 102 randomly selects one of predetermined types of signatures and outputs signature information S _SGN indicating the number of the selected signature To do.

The random access signal generation unit 103 generates a random access signal S _TX based on the signature information S _SGN from the signature selection unit 102 and transmits the random access signal S _TX to the base station 104 via the transmission / reception unit.

When the transmission / reception unit of the base station 104 receives the access signal S _TX , the preamble detection unit 105 detects the signature used for the preamble from the reception random access signal S _RX corresponding to the random access signal S _TX , and receives the received signature information S _Output as _RSGN .

The delay time measuring unit 106 measures a delay time S _RTD generated in the propagation path from the received random access signal S _RX and the received signature information S _RSGN .

The timing control unit 107 calculates a transmission timing correction value necessary in the mobile station 101 from the measured delay time _SRTD and outputs it as transmission timing control information _STA .

The DL CQI determination unit 108 determines the DL CQI level from the delay time S _RTD and outputs the DL CQI information S _RCQI . The determination of the DL CQI level in the DL CQI determination unit 108 is performed using a table in which a relationship between the delay time and the DL CQI level is defined in advance, and using the delay time S _RTD and the table.

Transmission parameter control section 109 outputs transmission parameter control information S _CTRL indicating a transmission parameter of random access response S _ACK , which is a response signal from DL CQI information S _RCQI to random access. This random access response S _ACK describes information necessary for the mobile station 101 to communicate with the base station 104.

Random access response generation section 110 randomly receives reception signature information S _RSGN from preamble detection 105, transmission timing control information S _TA from timing control section 107, and transmission parameter control information S _CTRL from transmission parameter control section 109. An access response S _ACK is generated and transmitted to the mobile station 101 via the transmission / reception unit.

When the transmission / reception unit of the mobile station 101 receives the random access response S _ACK transmitted from the base station 104, the mobile station 101 communicates with the base station 104 based on the information of the random access response S _ACK .

<Second Embodiment>
Next, a second embodiment will be described.

  FIG. 4 is a block diagram showing a configuration of a random access communication apparatus according to the second embodiment of the present invention. In addition, about the structure similar to the said embodiment, the same number is attached | subjected and detailed description is abbreviate | omitted.

In the mobile station 101, the signature selection unit 102 randomly selects one from predetermined types of signatures and outputs signature information S _SGN indicating the number of the selected signature.

The random access signal generation unit 103 generates a random access S _TX from the signature information S _SGN and transmits the random access S _TX to the base station via the transmission / reception unit. Further, when a random access response is received from the base station 104 via the receiving unit, a response confirmation (ACK) is transmitted via the transmitting / receiving unit in response thereto.

When the transmission / reception unit of the base station 104 receives the random access S _TX from the mobile station, the preamble detection unit 105 detects the signature used for the preamble from the reception random access S _RX corresponding to the random access S _TX and receives it. Output as signature information S _RSGN .

The delay time measuring unit 106 measures and outputs a delay time S _RTD generated in the propagation path from the received random access S _RX and the received signature information S _RSGN .

The timing control unit 107 calculates a transmission timing correction value necessary in the mobile station from the delay time S _RTD and outputs it as transmission timing control information S _TA .

The DL CQI determination unit 108 determines the DL CQI level from the delay time S _RTD and outputs the DL CQI information S _RCQI .

The DL detection probability calculation unit 203 calculates and outputs a reception success probability S _DLDP of a random access response that is a response signal to DL random access.

Transmission parameter control section 204 outputs transmission parameter control information S _CTRL indicating transmission parameters of random access response S _ACK from DL CQI information S _RCQI and reception success probability S _DLDP of random access response.

The random access response generation unit 110 generates a random access response S _ACK from the reception signature information S _RSGN , the transmission timing control information S _TA, and the transmission parameter control information S _CTRL and transmits it to the mobile station via the transmission / reception unit.

The DL CQI determination unit 108 determines the DL CQI level by preparing a table in advance that defines the relationship between the delay time and the DL CQI level, using the delay time S _RTD and the table, and randomly accessing the determined DL CQI level. Used to determine response transmission parameters. In the determination of the transmission parameter of the random access response in the transmission parameter control unit 204 of the present embodiment, an offset corresponding to the reception probability of successful reception of the random access response is added to the transmission parameter determined from the DL CQI level. It is realized by doing.

  Here, there is a method of using, as the reception success probability of the random access response in the DL detection probability calculation unit, the probability that the base station receives ACK transmitted from the mobile station in response to the random access response.

  In this embodiment, the cell radius is set to 5 km, and the relationship between the DL CQI level (High, Middle, Low) in three stages and the delay time based on the propagation loss calculated from the delay time, and further corresponds to each DL CQI level. The transmission power of the random access response is defined as shown in FIG. Here, the predefined transmission power shown in FIG. 5 is set to satisfy a value necessary to achieve 1% PER. From the viewpoint of the reception success probability of the random access response, this 1% PER is considered to correspond to a 99% reception success probability. Therefore, when the reception success probability is less than 99%, a positive offset is added to the transmission power in common to all mobile stations in order to increase the reception success probability. In this embodiment, the relationship between the reception success probability of the random access response shown in FIG. 6 and the offset of the transmission power is defined in advance.

At a certain time t = T ₀ , the mobile station 1 is detected as shown in FIG. 7 (a), and at time t = T ₁ (T ₀ + τ, τ> 0), the mobile station 2 is shown in FIG. 7 (b). Are detected respectively. Further, it is assumed that the random access response reception success probabilities at each time are P _D0 = 92% and P _D1 = 96%, respectively. First, when the result of measuring the delay time of the mobile station 1 at time t = T ₀ is T _{RTD, 1} = 6.8 [us], the DL CQI level is “Middle” from FIG. Is determined to be 20 dBm. Furthermore, considering the offset based on the reception success probability, the reception success probability at time t = T ₀ is P _D0 = 92%, so the offset of the transmission power is +2 dBm from FIG. 6, and the random access response of the mobile station 1 Is set to 22 dBm. Next, when the result of measuring the delay time of the mobile station 2 at time t = T ₁ after time t = T ₀ and time τ is T _{RTD, 2} = 8.7 [us], DL from FIG. It is determined that the CQI level is “Middle” and the transmission power to be set is 20 dBm. On the other hand, it can be seen that the reception success probability, which was P _D0 = 92% at time t = T ₀ , is improved to P _D1 = 96% at time t = T ₁ . Therefore, the transmission power offset is reduced from +2 dBm to +1 dBm, and the transmission power of the random access response of the mobile station 2 is set to 21 dBm. As described above, by adjusting the offset amount according to the reception success probability, more appropriate transmission power setting can be realized.

As described above, the mobile station can determine the DL CQI level without notifying the DL CQI level and set the transmission power of the random access response for each mobile station without notifying the DL CQI level. In the above embodiment, transmission power is used as a transmission parameter, but the same setting can be made for other transmission parameters such as a modulation scheme and an error correction code coding rate.

  The mobile station and base station of the present invention described above can be configured by hardware as is apparent from the above description, but can also be realized by a computer program. In this case, functions and operations similar to those of the above-described embodiment are realized by a processor that operates according to a program stored in the program memory. Note that only a part of the functions of the above-described embodiment can be realized by a computer program.

It is a block diagram for demonstrating 1st Embodiment by this invention. It is a figure for demonstrating the relationship between the delay time in 1st Embodiment by this invention, DL CQI level, and the transmission power of a random access response. It is a figure for demonstrating the delay time of the random access signal in 1st Embodiment by this invention. It is a block diagram for demonstrating 2nd Embodiment by this invention. It is a figure for demonstrating the relationship between the delay time in 2nd Embodiment by this invention, DL CQI level, and the transmission power of a random access response. It is a figure for demonstrating the definition of the offset of the transmission power according to the reception success probability of the random access response in 2nd Embodiment by this invention. It is a figure for demonstrating the delay time of the random access signal in 2nd Embodiment by this invention. It is a block diagram for demonstrating a prior art example.

Explanation of symbols

101, 201, 301 Mobile station 102, 303 Signature selection unit 103 Random access signal generation unit 104, 202, 304 Base station 105 Preamble detection unit 106 Delay time measurement unit 107 Timing control unit 108 DL CQI determination unit 109, 204 Transmission parameter control Units 110 and 304 Random access response generation unit 203 DL detection probability calculation unit 303 Transmission power control unit

Claims (16)

A communication system,
A mobile station transmitting a random access signal;
A base station that detects the mobile station by the random access signal,
The base station
A measurement unit for measuring a delay time of the random access signal;
And a setting unit configured to set a transmission parameter of a random access response to be transmitted as a response signal of the random access signal based on the measured delay time.   The said setting part determines the level of the channel quality of the downlink of the said mobile station based on the measured delay time, and controls the said transmission parameter based on this level. Communication system.   The said setting part determines the said level based on the measured delay time and the table which defined the relationship between the said delay time and the said level prepared in advance, The Claim 1 or Claim 2 characterized by the above-mentioned. The communication system described.   The setting unit calculates a reception success probability of the random access response based on a response confirmation transmitted from the mobile station in response to the random access response, and determines the transmission parameter from the reception success probability and the level. The communication system according to any one of claims 1 to 3, wherein the communication system is set. The communication system according to claim 4, wherein the setting unit determines the transmission parameter based on an offset defined according to the reception success probability and the level. A base station,
A measurement unit for measuring the delay time of the random access signal transmitted;
And a setting unit configured to set a transmission parameter of a random access response to be transmitted as a response signal of the random access signal based on the measured delay time.   The said setting part determines the level of the channel quality of the downlink of a mobile station based on the measured delay time, and controls the said transmission parameter based on this level. base station.   The said setting part determines the said level based on the measured delay time and the table which defined the relationship between the said delay time and the said level prepared beforehand, The claim 6 or Claim 7 characterized by the above-mentioned. The listed base station.   The setting unit calculates a reception success probability of the random access response based on a response confirmation transmitted in response to the random access response, and sets the transmission parameter from the reception success probability and the level. The base station according to claim 6, wherein:   The base station according to claim 9, wherein the setting unit determines the transmission parameter based on an offset defined according to the reception success probability and the level. A communication method,
A transmission step of transmitting a random access signal;
A measuring step of measuring a delay time of the random access signal;
And a setting step of setting a transmission parameter of a random access response to be transmitted as a response signal of the random access signal based on the measured delay time. The setting step includes
A determination step of determining a downlink channel quality level of the mobile station based on the measured delay time;
The communication method according to claim 11, further comprising a control step of controlling the transmission parameter based on the determined level.   12. The determination step according to claim 11, wherein the setting step includes a determination step of determining the level based on the measured delay time and a table in which a relationship between the delay time and the level is defined in advance. 12. The communication method according to 12. The setting step calculates a reception success probability of the random access response based on a response confirmation transmitted in response to the random access response;
The communication method according to any one of claims 11 to 13, further comprising a setting step of setting the transmission parameter from the calculated reception success probability and the level.   The communication method according to claim 14, wherein the setting step sets the transmission parameter based on an offset defined according to the reception success probability and the level. A program of a base station, wherein the program identifies the base station,
A measurement unit for measuring the delay time of the random access signal transmitted;
A program that functions as a setting unit that sets a transmission parameter of a random access response to be transmitted as a response signal of the random access signal based on the measured delay time.

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