Terminal device, base station device, and communication system

Abstract

This terminal device comprises: a measurement unit that measures the reception power of a signal from a base station device; a reception unit that receives threshold value information including a threshold value; and a control unit that calculates an offset value according to reference transmission power used as a reference in the calculation of the threshold value and maximum transmission power, calculates an adjusted threshold value obtained by adding the offset value to the threshold value, and controls the number of times of repeated transmission and transmission power of a first message to be transmitted at the start of a wireless connection according to the reception power and the adjusted threshold value.

Description

Terminal device, base station device, and communication system

[0001] The present invention relates to a terminal device, a base station device, and a communication system.

[0002] In current networks, traffic from mobile devices (e.g., smartphones and feature phones) accounts for the majority of wireless resources, and the traffic used by mobile devices is expected to continue to expand in the future.

[0003] In addition to traffic used by mobile devices, IoT (Internet of Things) services are being developed for use in, for example, transportation systems, smart meters, and monitoring systems for devices, etc. Therefore, networks are being required to support services with diverse requirements. In order to accommodate such diverse services, communication standards for fifth-generation mobile communications (5G or NR (New Radio)) (for example, Non-Patent Documents 11 to 28) include, for example, 4G (fourth-generation mobile communications) standard technologies (for example, Non-Patent Documents 1 to 10), as well as eMBB (Enhanced Mobile Broadband), Massive MTC (Machine Type Communications), and URLLC (Ultra-Reliable AND Low Latency Communication). The standards are being developed assuming support for many use cases classified as such.

[0004] In addition, in a working group of the 3rd Generation Partnership Project (3GPP (registered trademark)), an international standardization project, technologies for extending the above communication standards are continuously being studied and standardized.

[0005] In 3GPP, uplink synchronization is established by, for example, executing a random access procedure. The random access procedure includes, for example, a contention-based random access procedure (CBRA) and a contention-free random access procedure (CFRA). Furthermore, the random access procedure includes, for example, a two-step random access procedure and a four-step random access procedure (see Non-Patent Document 6 or 21).

[0006] In a working group of 3GPP, a technique for repetition transmission of a Physical Random Access Channel (PRACH) in a terminal device is being studied in order to improve the success rate of PRACH reception in a base station device in a random access procedure.

[0007] Techniques relating to the random access procedure are described in, for example, the following documents:

[0008] 3GPP TS 36.133 V17.10.03GPP TS 36.211 V17.3.03GPP TS 36.212 V17.1.03GPP TS 36.213 V17.5.03GPP TS 36.214 V17.0.03GPP TS 36.300 V17.4.03GPP TS 36.321 V17.5.03GPP TS 36.322 V17.0.03GPP TS 36.323 V17.2.03GPP TS 36.331 V17.4.03GPP TS 37.324 V17.0.03GPP TS 37.340 V17.5.03GPP TS 38.133 V17.10.03GPP TS 38.201 V17.0.03GPP TS 38.202 V17.3.03GPP TS 38.211 V17.5.03GPP TS 38.212 V17.5.03GPP TS 38.213 V17.6.03GPP TS 38.214 V17.6.03GPP TS 38.215 V17.3.03GPP TS 38.300 V17.5.03GPP TS 38.321 V17.5.03GPP TS 38.322 V17.3.03GPP TS 38.323 V17.5.03GPP TS 38.331 V17.5.03GPP TS 38.420 V17.2.03GPP TS 38.423 V17.5.0R1-2306069

[0009] However, details regarding the repeated transmission of the PRACH in a terminal device have not been determined. For example, increasing the number of repetitions requires corresponding radio resources, resulting in a decrease in the utilization efficiency of the radio resources. For example, if there is room to increase the transmission power of the terminal device, it may be possible to achieve a PRACH reception success rate equivalent to that of repeated transmission while suppressing a decrease in the utilization efficiency of the radio resources by increasing the transmission power of the terminal device without increasing the number of repetitions. However, a control method for the repeated transmission of the PRACH in a terminal device has not been determined, taking into account the relationship between the efficiency of radio resources and the reception success rate of the PRACH.

[0010] Therefore, one disclosure provides a terminal device, a base station device, and a communication system that perform PRACH repetitive transmission processing that efficiently uses radio resources.

[0011] The wireless communication system includes a measurement unit that measures the received power of a signal from a base station device, a receiving unit that receives threshold information including a threshold, and a control unit that calculates an offset value according to a reference transmission power used as a reference in calculating the threshold and a maximum transmission power, calculates an adjustment threshold by adding the offset value to the threshold, and controls the transmission power and the number of repeated transmissions of a first message to be sent at the start of a wireless connection according to the received power and the adjustment threshold.

[0012] One disclosure enables PRACH repetitive transmission processing that efficiently uses radio resources.

[0013] Fig. 1 is a diagram showing an example of the configuration of a wireless communication system 10. Fig. 2 is a diagram showing an example of the configuration of a base station device 200. Fig. 3 is a diagram showing an example of the configuration of a terminal device 100. Fig. 4 is a diagram showing an example of a first method of PRACH transmission control processing. Fig. 5 is a diagram showing an example of a second method of PRACH transmission control processing. Fig. 6 is a diagram showing an example of a third method of PRACH transmission control processing. Fig. 7 is a diagram showing examples of received power in the base station device 200 for each of Case 1 and Case 2. Fig. 8 is a diagram showing an example of a fourth method of PRACH transmission control processing.

[0014] [First Embodiment] A first embodiment will be described.

[0015] <Regarding the Wireless Communication System 10> FIG. 1 is a diagram illustrating an example of the configuration of the wireless communication system 10. The wireless communication system 10 includes a base station device 200 and terminal devices 100-1 and 100-2. The wireless communication system 10 is a system that controls the transmission power and number of repeated transmissions of the PRACH used in a random access procedure, for example, based on the received power of radio waves measured by the terminal devices 100-1 and 100-2. Repeated transmission of the PRACH refers to, for example, the terminal device 100-1 and / or the terminal device 100-2 transmitting the same preamble a certain number of times. Here, the certain number of times may be at least any value of 2, 4, or 8. The base station device 200 may notify the terminal device 100-1 and / or the terminal device 100-2 of the resources used for repeated transmission of the PRACH. The terminal device 100-1 and / or the terminal device 100-2 may perform repeated transmission of the PRACH using some or all of the resources used for repeated transmission of the PRACH notified by the base station device 200. Some or all of the PRACHs included in the repeated transmission of the PRACH may be transmitted using different resources in the time domain. The base station device 200 can obtain a gain by receiving some or all of the PRACHs transmitted by the repeated transmission of the PRACH from the terminal device 100-1 and / or the terminal device 100-2 and combining them (soft combining). The repeated transmission of the PRACH may be referred to as multiple PRACH transmissions. The number of repetitions may be the number of repetitions of the repeated transmission of the PRACH. Unless otherwise specified, the repeated transmission may be the repeated transmission of the PRACH.

[0016] Terminal devices 100-1 and 2 (hereinafter, sometimes referred to as terminal devices 100) are communication devices that wirelessly connect to the base station device 200 and transmit and receive data (wireless communication), and are, for example, smartphones or tablet terminals. When wirelessly connecting to the base station device 200, the terminal device 100 executes a random access procedure. In the random access procedure, the terminal device 100 transmits a PRACH to the base station device 200. The number of repeated transmissions of the PRACH and the transmission power are determined by control of the base station device 200 and / or path loss. The terminal device 100 may determine the number of repeated transmissions of the PRACH and the transmission power in accordance with the received power of a signal from the base station device 200, under the control of the base station device 200.

[0017] The base station device 200 is a device, such as an eNodeB (eNB) or a gNodeB (gNB), that is wirelessly connected to and performs wireless communication with the terminal device 100. The base station device 200 controls the transmission power and the number of repeated transmissions of the PRACH transmitted by the terminal device 100.

[0018] The base station device 200 configures a cell within which communication with the terminal device 100 is possible. In FIG. 1 , the base station device 200 configures communication ranges C1 to C3 in one or more cells. The communication range may also be referred to as coverage. The communication ranges C1 to C3 indicate the range within which wireless connection by the terminal device 100 via a random access procedure is possible (and is assumed to be successful). The boundary of each communication range is set, for example, by the received power of the signal from the base station device 200 at the terminal device 100. The received power of the terminal device 100 located within each communication range is X or more for communication range C1, Y or more for communication range C2, and Z or more for communication range C3. As a specific example, the communication range C1 is a range in which a terminal device 100 with a received power of -100 dBm or more can wirelessly connect, the communication range C2 is a range in which a terminal device 100 with a received power of -103 dBm or more can wirelessly connect, and the communication range C3 is a range in which a terminal device 100 with a received power of -106 dBm or more can wirelessly connect. The base station device 200 configures the communication range based on the received power of the terminal device 100, and controls the number of repeated PRACH transmissions and the transmission power depending on which communication range the terminal device 100 is located in. The received power may also be derived based on SSB-RSRP. The communication range may also be referred to as a cell.

[0019] 2 is a diagram showing an example of the configuration of the base station device 200. The base station device 200 includes a CPU (Central Processing Unit) 210, a storage 220, a memory 230, and a wireless communication circuit 250.

[0020] The storage 220 is an auxiliary storage device that stores programs and data, such as a flash memory, a hard disk drive (HDD), or a solid state drive (SSD). The storage 220 stores a wireless communication control program 221 and a PRACH transmission control program 222.

[0021] The memory 230 is an area into which the programs stored in the storage 220 are loaded. The memory 230 may also be used as an area in which the programs store data.

[0022] The wireless communication circuit 250 is a device that performs wireless communication with the terminal device 100. The base station device 200 transmits and receives signals (messages) to and from the terminal device 100 via the wireless communication circuit 250.

[0023] The CPU 210 is a processor that loads programs stored in the storage 220 into the memory 230, executes the loaded programs, configures each unit, and realizes each process.

[0024] The CPU 210 executes the wireless communication control program 221 to construct a notification unit and a base station control unit, and to perform wireless communication control processing. The wireless communication control processing is processing for controlling wireless communication with the terminal device 100. In the wireless communication control processing, the base station device 200 wirelessly connects to the terminal device 100 and transmits and receives signals (messages).

[0025] The CPU 210 executes the PRACH transmission control program 222 to construct a notification unit and a base station control unit, and perform PRACH transmission control processing. The PRACH transmission control processing is processing for controlling the transmission power (transmission output) and the number of repeated transmissions when the terminal device 100 transmits a PRACH of a random access procedure. In the PRACH transmission control processing, the base station device 200 transmits a threshold value of the received power of the terminal device 100, which is used to determine the transmission power and the number of repeated transmissions of the terminal device 100.

[0026] 3 is a diagram showing an example of the configuration of the terminal device 100. The terminal device 100 includes a CPU 110, a storage 120, a memory 130, and a wireless communication circuit 150.

[0027] The storage 120 is an auxiliary storage device such as a flash memory, HDD, or SSD that stores programs and data. The storage 120 stores a wireless communication program 121 and a PRACH transmission program 122.

[0028] The memory 130 is an area into which the programs stored in the storage 120 are loaded. The memory 130 may also be used as an area in which the programs store data.

[0029] The wireless communication circuit 150 is a device that performs wireless communication with the base station device 200. The terminal device 100 transmits and receives signals (messages) to and from the base station device 200 via the wireless communication circuit 150.

[0030] The CPU 110 is a processor that loads programs stored in the storage 120 into the memory 130, executes the loaded programs, configures each unit, and realizes each process.

[0031] The CPU 110 executes the wireless communication program 121 to configure a measurement unit, a receiving unit, and a control unit, and perform wireless communication processing. The wireless communication processing is processing for performing wireless communication with the base station device 200. In the wireless communication processing, the terminal device 100 wirelessly connects to the base station device 200 and transmits and receives signals (messages). In the wireless communication processing, the terminal device 100 receives, for example, a synchronization signal transmitted by the base station device 200, and measures the received power.

[0032] The CPU 110 executes the PRACH transmission program 122 to configure a receiver and a controller, and to perform PRACH transmission processing. The PRACH transmission processing is processing for transmitting a PRACH to the base station device 200 when executing a random access procedure. In the PRACH transmission processing, the terminal device 100 determines the transmission power of the PRCAH and the number of repeated transmissions under the control of the base station device 200.

[0033] <PRACH Transmission Control Processing> The base station device 200 may control the transmission power and number of repeated transmissions of the PRACH of the terminal device 100 by transmitting a threshold value of received power to the terminal device 100. Various methods of the PRACH transmission control processing will be described below. The PRACH transmission control processing is performed, for example, when the terminal device 100 transmits the PRACH once at the above-mentioned transmission power but the PRACH does not reach the base station device 200 or is expected not to reach the base station device 200. In addition, the PRACH transmission control processing is performed, for example, when the terminal device 100 is present within the communication area of ​​the base station device 200.

[0034] <PRACH Transmission Power> First, the PRACH transmission power and maximum transmission power that are the basis for each method of PRACH transmission control processing will be described.

[0035] The transmission power of the PRACH is calculated taking into consideration, for example, the maximum transmission power of the terminal device 100, the power notified from a higher layer (for example, the power required on the receiving side), and the path loss between the terminal device 100 and the base station device 200. For example, the smaller value of the maximum transmission power of the terminal device 100 or the value obtained by adding the path loss to the power notified from the higher layer is calculated as the transmission power of the PRACH. The calculation of the transmission power of the PRACH is performed, for example, by the base station device 200 or the terminal device 100.

[0036] The maximum transmission power of the terminal device 100 is the maximum value of the transmission power that the terminal device 100 can transmit, and is calculated, for example, taking into consideration the power class and MPR (Maximum Power Reduction) of the terminal device 100. For example, the maximum transmission output is calculated to be the smaller value of the maximum transmission power according to the power class of the terminal device 100 or the maximum transmission power due to MPR restrictions. The calculation of the transmission power of the PRACH is performed, for example, by the base station device 200 or the terminal device 100.

[0037] <1. First Method> A first method of PRACH transmission control processing will be described. The first method is a method in which the number of repeated transmissions is determined using a first threshold, a second threshold, and a third threshold. The base station device 200 may notify the terminal device 100 of the first threshold, the second threshold, and the third threshold at a predetermined timing. Each threshold is notified to the terminal device 100 by, for example, an SIB (System Information Block).

[0038] 4 is a diagram illustrating an example of a first method of PRACH transmission control processing. In the following diagrams, repeated transmission is referred to as "Repetition," "None" indicates that repeated transmission is not performed (transmitted once), and "x number" indicates the number of repeated transmissions. Furthermore, the received power used in the following description is, for example, the received power (SSB-RSRP) of a synchronization signal transmitted by the base station device 200. Furthermore, the terms "greater than or equal to" and "less than" used in the following description may be replaced with "greater than" and "less than or equal to."

[0039] The terminal device 100 may not perform repeated transmission when the received power is equal to or greater than the first threshold (range E1). Furthermore, the terminal device 100 may determine the number of repeated transmissions to be two when the received power is less than the first threshold and equal to or greater than the second threshold (range E2). Furthermore, the terminal device 100 may determine the number of repeated transmissions to be four when the received power is less than the second threshold and equal to or greater than the third threshold (range E3). Furthermore, the terminal device 100 may determine the number of repeated transmissions to be eight when the received power is less than the third threshold (range E4).

[0040] In the first method, the number of repetitions can be set according to the received power. On the other hand, in the first method, repeated transmission may be performed even if the transmission power of the PRACH of the terminal device 100 has not reached the maximum transmission power. Since repeated transmission uses more radio resources than single transmission, the efficiency of radio resource usage may decrease.

[0041] <Second Method> A second method of the PRACH transmission control process will be described. The second method is a method of determining the number of repeated transmissions using a second threshold and a third threshold. The base station device 200 may notify the terminal device 100 of the second threshold and the third threshold without notifying the first threshold. Each threshold is notified to the terminal device 100 by, for example, an SIB. When the first threshold is not notified, the terminal device 100 recognizes that the PRACH transmission control process will be performed using the second method.

[0042] 5 is a diagram showing an example of a second method of PRACH transmission control processing. When the received power is equal to or greater than the second threshold (range E5), the terminal device 100 performs the following processing. In the following drawings, black squares indicate received power P1 in the terminal device 100-1, and white squares indicate received power P2 in the terminal device 100-2. Unless otherwise specified, each method will be described using as an example a case where the received power P1 and the received power P2 are the same value.

[0043] When the transmission power of the PRACH is not the maximum transmission power, the terminal device 100 does not perform repeated transmission and performs processing to increase the transmission power of the PRACH. The terminal device 100 performs processing to increase the transmission power of the PRACH to the maximum transmission power, for example. Furthermore, the terminal device 100 may increase the transmission power of the PRACH by a predetermined power, may increase it in stages, or may immediately increase it to the maximum transmission power, for example.

[0044] On the other hand, when the transmission power of the PRACH is the maximum transmission power, the terminal device 100 may determine the number of repeated transmissions to be 2. When the transmission power of the PRACH is the maximum transmission power, the terminal device 100 may determine the number of repeated transmissions corresponding to range E5.

[0045] Furthermore, when the received power is less than the second threshold and equal to or greater than the third threshold (range E3), the terminal device 100 determines the number of repeated transmissions to be 4. Furthermore, when the received power is less than the third threshold (range E4), the terminal device 100 determines the number of repeated transmissions to be 8.

[0046] In the second method, there are cases where it is possible to suppress a decrease in the efficiency of use of radio resources due to repeated transmission even when the transmission power of the PRACH of the terminal device 100 has not reached the maximum transmission power. However, when the maximum transmission power of each of the multiple terminal devices 100 is different, the received power at the base station device 200 differs for each terminal device 100 even if the number of repetitions is the same.

[0047] For example, a case will be described in which the maximum transmission power of the terminal device 100-1 is 23 dBm, the PRACH transmission power is 23 dBm, and the reception power P1 falls within range E5, and the maximum transmission power of the terminal device 100-2 is 20 dBm, the PRACH transmission power is 20 dBm, and the reception power P2 falls within range E5. In this case, both the terminal device 100-1 and the terminal device 100-2 determine the number of repetitions to be two.

[0048] Since the terminal device 100-1 and the terminal device 100-2 have the same reception power, they are close in distance from the base station device 200 and can be assumed to be located in the same cell. The terminal device 100-1 and the terminal device 100-2 have the same number of repeated transmissions (2), but the transmission power of the PRACH is different, and the reception power of the PRACH at the base station device 200 is different, which may result in unfairness between the terminal devices, with the PRACH of the terminal device 100-1 being easier to reach.

[0049] <Third Method> The third method will be described. The third method is a method that adds an offset to the second method. In the third method, in order to equalize the received power at the base station device 200, for example, to reduce the difference in PRACH transmission power, the number of repetitions for the terminal device 100 with low PRACH transmission power is increased compared to the number of repetitions for the terminal device 100 with high transmission power. This increases the number of repetitions for the terminal device with low PRACH transmission power, thereby increasing the PRACH transmission power gain, and thus the received power at the base station device 200 can be increased. The theoretical value of the PRACH transmission power gain due to multiple transmissions may be, for example, approximately 3 dB for two repeated transmissions, approximately 6 dB for four repeated transmissions, and approximately 9 dB for eight repeated transmissions. Here, the PRACH transmission power gain may be the received power gain after the base station device 200 receives and combines (soft combines) the repeated PRACH transmissions transmitted from the terminal device 100. Furthermore, the gain of the transmission power of the PRACH may be the sum of the received powers after the base station device 200 receives and soft combines repeated transmissions of the PRACH transmitted from the terminal device 100 .

[0050] 6 is a diagram showing an example of a third method of PRACH transmission control processing. In the third method, the base station device 200 determines the second threshold and the third threshold using a certain transmission power of the terminal device 100 as a reference. This certain transmission power serving as a reference is called a reference transmission power. The reference transmission power may be a standard transmission power.

[0051] The terminal device 100 may acquire the reference transmission power, the second threshold, and the third threshold. The reference transmission power, the second threshold, and the third threshold are notified, for example, by SIB. Furthermore, the reference transmission power may be, for example, a value stored in advance by the terminal device 100, or may be a fixed value.

[0052] The terminal device 100 compares the maximum transmission power of the terminal device 100 with the reference transmission power and calculates an offset value. The offset value is a value obtained by subtracting the maximum transmission power from the reference transmission power. The calculated offset value is added to the second threshold and the third threshold. Processing other than adding the offset value to the threshold is assumed to be the same as, for example, the second method. Below, the processing for each will be explained using as examples a terminal device 100-1 whose maximum transmission power and reference transmission power are the same, and a terminal device 100-2 whose maximum transmission power and reference transmission power are different. It should be noted that the reference transmission power is assumed to be, for example, 23 dBm.

[0053] The terminal device 100-1 has a transmission power of 23 dBm and a maximum transmission power of 23 dBm. Since the maximum transmission power of the terminal device 100-1 is the same as the reference transmission power, the terminal device 100-1 calculates the offset value as 0 dB. In other words, the terminal device 100-1 uses the second threshold and the third threshold as they are.

[0054] The terminal device 100-1 determines the number of repeated transmissions to be two because the received power P1 is equal to or greater than the second threshold (range E5) and the transmission power is the maximum transmission power of 23 dBm.

[0055] The terminal device 100-2 has a transmission power of 20 dBm and a maximum transmission power of 20 dBm. Because the maximum transmission power of the terminal device 100-2 is 3 dB lower than the reference transmission power, the terminal device 100-2 calculates the offset value as +3 dB. Note that if the maximum transmission power is a value higher than the reference transmission power, the offset value will be a negative value. The terminal device 100-2 adds the offset value to the second threshold and the third threshold, and calculates the second threshold and the third threshold after offset adjustment.

[0056] The terminal device 100-2 determines the number of repeated transmissions to be four because the received power P2 is less than the second threshold value after offset adjustment and is equal to or greater than the third threshold value (range E3).

[0057] In the third method, as described above, the terminal device 100-1 and the terminal device 100-2 have the same reception power but different maximum transmission powers, and therefore different numbers of repeated PRACH transmissions. The terminal device 100-1 transmits once with a transmission power of 23 dBm (no repeated transmissions), while the terminal device 100-2 transmits twice with a transmission power of 20 dBm. The terminal device 100-2 transmits twice with a transmission power equivalent to 23 dBm, adding a transmission power gain of 3 dB due to the two transmissions, and can transmit the PRACH with the same transmission power as the terminal device 100-1.

[0058] In the third method, a process will be described in a case where the transmission power of the PRACH is not the maximum transmission power and the number of repeated transmissions is four or more (a case where the number is less than the second threshold). The process that can be performed by the terminal device 100 includes, for example, the following two cases.

[0059] Case 1: Repeated transmission is not performed, and the transmission power of the PRACH is increased (for example, increased to the maximum transmission power).

[0060] Case 2: According to the threshold, transmission is repeatedly performed with the PRACH transmission power unchanged.

[0061] 7 is a diagram showing examples of received power in the base station device 200 for each of Case 1 and Case 2. As a prerequisite, the first threshold is none, the second threshold is −103 dBm, and the third threshold is −106 dBm. Furthermore, the terminal device 100-1 is assumed to have received power of −100 dBm, PRACH transmission power of 22 dBm, and maximum transmission power of 23 dBm. Furthermore, the terminal device 100-2 is assumed to have received power of −105 dBm, PRACH transmission power of 27 dBm, and maximum transmission power of 29 dBm. Furthermore, in Case 1, the terminal device 100 is assumed to increase its transmission power to its maximum.

[0062] Because the received power of the terminal device 100-1 is equal to or greater than the second threshold and is not the maximum transmission power, the terminal device 100-1 increases the PRACH transmission power by 1 dB and transmits the PRACH at the maximum transmission power. In this case, the received power (estimated value or theoretical value) at the base station device 200 is −77 dBm (calculation formula: −100 + 1 + 22).

[0063] On the other hand, the terminal device 100-2 determines that the number of repeated transmissions is four, since the received power is less than the second threshold and greater than or equal to the third threshold.

[0064] In the case of processing Case 1, the terminal device 100-2 does not perform repeated transmission, but increases the PRACH transmission power by 2 dB and transmits the PRACH at the maximum transmission power. In this case, the received power (estimated value or theoretical value) at the base station device 200 is −76 dBm (calculation formula: −105 + 2 + 27).

[0065] In the processing of Case 2, the terminal device 100-2 repeats PRACH transmission four times while keeping the PRACH transmission power unchanged. These four repetitions result in a gain of +6 dB in the PRACH transmission power, and therefore the received power (estimated value or theoretical value) at the base station device 200 in this case is −72 dBm (calculation formula: −105+6+27).

[0066] Since the received power of the PRACH of the terminal device 100-1 at the base station device 200 is −77 dBm, −76 dBm in case 1 is closer to the value than −72 dBm in case 2, and therefore case 1 is preferable from the viewpoint of fairness.

[0067] In this way, for example, because the gain from four transmissions is as large as 6 dB, fairness may be more assured by increasing the transmission power as in Case 1. Therefore, unless there are other particular conditions, the terminal device 100 may prioritize increasing the transmission power over repeated transmission.

[0068] Furthermore, for example, when the maximum transmission power is large and the transmission power is a relatively small value, the gain of multiple transmissions may be smaller than the increase in transmission power. In this case, the terminal device 100 may select Case 2. In this way, the terminal device 100 may calculate the received power at the base station device 200 as shown in FIG. 7 and select Case 1 or Case 2.

[0069] When the terminal device 100 can acquire the transmission output, maximum transmission power, and received power of another terminal device 100, the terminal device 100 may calculate the received power of the other terminal device 100 at the base station device 200 and select a case that is close to that value. Alternatively, the base station device 200 may calculate the received power and notify the terminal device 100 of which case to select.

[0070] <Fourth Method> The fourth method is a method in which, when the first threshold is notified to the terminal device 100, the offset of the third method is also applied to the first threshold.

[0071] 8 is a diagram illustrating an example of a fourth method of PRACH transmission control processing. In the fourth method, the base station apparatus 200 determines the first threshold, the second threshold, and the third threshold based on the reference transmission power.

[0072] The terminal device 100 acquires the reference transmission power, the first threshold, the second threshold, and the third threshold. The reference transmission power, the first threshold, the second threshold, and the third threshold are notified, for example, by SIB. The reference transmission power may be, for example, a value stored in advance by the terminal device 100, or may be a fixed value.

[0073] The terminal device 100 compares the maximum transmission power of the terminal device 100 with the reference transmission power and calculates an offset value. The calculated offset value is added to the first threshold, the second threshold, and the third threshold. Processing other than adding the offset value to the thresholds is assumed to be the same as, for example, the first method. Below, the respective processing will be explained using as examples a terminal device 100-1 whose maximum transmission power and reference transmission power are the same, and a terminal device 100-2 whose maximum transmission power and reference transmission power are different. It should be noted that the reference transmission power is assumed to be, for example, 23 dBm.

[0074] The terminal device 100-1 has a transmission power of 23 dBm and a maximum transmission power of 23 dBm. Because the maximum transmission power of the terminal device 100-1 is the same as the reference transmission power, the terminal device 100-1 calculates the offset value as 0 dB. That is, the terminal device 100-1 uses the first threshold, the second threshold, and the third threshold as they are. Because the received power P1 of the terminal device 100-1 is less than the first threshold and greater than or equal to the second threshold (range E2), and the transmission power is the maximum transmission power of 23 dBm, the terminal device 100-1 determines that the number of repeated transmissions will be two.

[0075] The terminal device 100-2 has a transmission power of 20 dBm and a maximum transmission power of 20 dBm. Because the maximum transmission power of the terminal device 100-2 is 3 dB lower than the reference transmission power, the terminal device 100-2 calculates the offset value as +3 dB. The terminal device 100-2 adds the offset value to the first threshold, the second threshold, and the third threshold, and calculates the first threshold, the second threshold, and the third threshold after offset adjustment. Because the received power P2 of the terminal device 100-2 is less than the second threshold after offset adjustment and is equal to or greater than the third threshold (range E3), the terminal device 100-2 determines the number of repeated transmissions to be four.

[0076] In the fourth method, as described above, the terminal device 100-1 and the terminal device 100-2 have the same reception power but different maximum transmission powers, and therefore have different numbers of repeated PRACH transmissions. The terminal device 100-1 transmits twice at a transmission power of 23 dBm, and the terminal device 100-2 transmits four times at a transmission power of 20 dBm. The terminal device 100-1 transmits twice, resulting in a transmission power equivalent to 26 dBm, with a transmission power gain of 3 dB added. On the other hand, the terminal device 100-2 transmits four times, resulting in a transmission power equivalent to 26 dBm, with a transmission power gain of 6 dB added. As a result, the PRACH transmission power of the terminal device 100-1 and the terminal device 100-2 becomes equal, ensuring fairness.

[0077] [Other Embodiments] The above-described embodiments may be used in combination with each other or may be used independently. For example, the terminal device 100 and the base station device 200 may support only one of the first to fourth methods. Furthermore, for example, the terminal device 100 may execute the fourth method (or the first method) when the first threshold value is notified, and the third method (or the second method) when the first threshold value is not notified. Furthermore, the base station device 200 may notify the terminal device 100 in advance which method will be used.

[0078] In each method, when the received power is less than the second threshold and the transmission power is not the maximum transmission power, the transmission power may be increased without repeating the transmission. In this case, the number of repetitions may be reduced (for example, from four transmissions to two transmissions, or from eight transmissions to four transmissions), and the transmission power may be further increased. The number of repetitions and the transmission power may be determined, for example, according to the gain achieved by the repeated transmission.

[0079] 10: Wireless communication system 100: Terminal device 110: CPU 120: Storage 121: Wireless communication program 122: PRACH transmission program 130: Memory 150: Wireless communication circuit 200: Base station device 210: CPU 220: Storage 221: Wireless communication control program 222: PRACH transmission control program 230: Memory 250: Wireless communication circuit

Claims

1. A terminal device having a measurement unit that measures the received power of a signal from a base station device; a receiving unit that receives threshold information including a threshold; and a control unit that calculates an offset value based on a reference transmission power used as a reference in calculating the threshold and a maximum transmission power, calculates an adjustment threshold by adding the offset value to the threshold, and controls the transmission power and the number of repeated transmissions of a first message to be transmitted at the start of a wireless connection based on the received power and the adjustment threshold.

2. The terminal device of claim 1, wherein the control unit, when the threshold information does not include a first threshold and the received power is equal to or greater than a second adjustment threshold obtained by adding the offset value to a second threshold smaller than the first threshold, performs a first process of increasing the transmission power without performing the repeated transmission if the transmission power of the first message is smaller than the maximum transmission power, and performs a second process of performing the repeated transmission if the transmission power of the first message is the same as the maximum transmission power.

3. The terminal device of claim 2, wherein when the threshold information includes the first threshold, the control unit does not perform the repeated transmission when the received power is equal to or greater than a first adjustment threshold obtained by adding the offset value to the first threshold, and performs the repeated transmission when the received power is less than the first adjustment threshold.

4. The terminal device described in claim 3, wherein, when the threshold information includes the first threshold, the control unit sets the number of repeated transmissions to N (N is an integer equal to or greater than 2) when the received power is less than the first adjustment threshold and greater than or equal to the second adjustment threshold, and sets the number of repeated transmissions to M (M is an integer equal to or greater than 3) when the received power is less than the second adjustment threshold.

5. The terminal device according to claim 1, wherein the wireless connection includes a random access procedure, and the first message includes a Physical Random Access CHannel (PRACH).

6. The terminal device according to claim 1, wherein the threshold information includes the reference transmission power.

7. The terminal device according to claim 1, wherein the reference transmission power is a fixed value that is stored in advance in the terminal device and the base station device.

8. The terminal device according to claim 1, wherein the threshold information includes a first threshold, a second threshold smaller than the first threshold, and a third threshold smaller than the second threshold.

9. A base station device comprising: a base station control unit that calculates a threshold using a reference transmission power serving as a standard; and a notification unit that notifies a terminal device of threshold information including the threshold, wherein the base station control unit causes the terminal device to calculate an adjustment threshold by adding an offset value corresponding to the reference transmission power and the maximum transmission power of the terminal device to the threshold, and controls the transmission power and the number of repeated transmissions of a first message that the terminal device transmits at the start of a wireless connection according to the reception power of a signal from the base station device at the terminal device and the adjustment threshold.

10. A communication system in which a terminal device measures the received power of a signal from a base station device, the base station device calculates a threshold using a reference transmission power serving as a reference, and notifies the terminal device of threshold information including the threshold, the terminal device receives the threshold information, calculates an offset value according to the reference transmission power and a maximum transmission power, calculates an adjustment threshold by adding the offset value to the threshold, and controls the number of repeated transmissions and the transmission power of a first message to be transmitted at the start of a wireless connection according to the received power and the adjustment threshold.

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