Communication quality measurement method for wireless network, wireless network system, terminal, and program

Abstract

A method according to the present disclosure is a communication quality measurement method for a wireless network for accommodating a terminal in which a plurality of wireless paths and wireless methods can simultaneously be used. This method involves: determining a measurement interval at which communication quality of each wireless path and wireless method is measured by a terminal, the interval being determined such that, among a plurality of wireless paths and wireless methods, there is an overlap of timing at which the communication quality thereof is measured by the terminal; and, in accordance with the determined measurement interval, performing the communication quality measurement for each wireless path and wireless method by using the terminal.

Description

Wireless network communication quality measurement method, wireless network system, terminal, and program

[0001] The present disclosure relates to a technique suitable for use in measuring communication quality in a wireless network that accommodates terminals that can simultaneously use multiple wireless paths and wireless methods.

[0002] Some terminals can select or cooperate with multiple wireless paths and wireless methods depending on the communication environment and requirements. Such terminals need to continuously acquire various information, such as the connectability of each wireless path and wireless method, network information, and communication quality (channel information, available rate, delay, error rate, etc.). To acquire this information, terminals use broadcast and synchronization signals transmitted by base stations or explicitly request packet exchange from base stations to acquire communication quality information. Conventionally, this information acquisition was performed at different timings and intervals depending on the wireless method, resulting in discrepancies in the timing of communication quality measurement between wireless methods.

[0003] On the other hand, in packet division transmission using multiple wireless paths, multiple wireless methods are generally used simultaneously. In other words, the communication quality actually required is the communication quality when multiple wireless paths and wireless methods are used simultaneously, but conventional communication quality measurements are performed at different times for each wireless path and wireless method. Therefore, if there is a high temporal correlation between the time fluctuations of communication quality between wireless methods, there is a risk of a large error occurring between the estimated value and the actual value of communication quality when multiple wireless paths and wireless methods are used together.

[0004] One way to solve the above problem is to increase the frequency of measuring the communication quality of each wireless path and wireless method. However, extremely increasing the frequency of measuring communication quality is not realistic from the viewpoint of efficient use of network resources.

[0005] Examples of documents showing the state of the art in the technical field related to the present disclosure include Patent Document 1 and Non-Patent Document 1. However, the technology disclosed in either document does not solve the above-mentioned problem.

[0006] JP 2014-036261 A

[0007] Masaya Kobayashi, Tsutomu Murase, "Performance Evaluation of Adaptive Beacon Transmission Methods for High-Speed ​​Wireless LAN Communication with Mobile Vehicle APs," IEICE Technical Report, Vol. 120, No. 293, IN2020-34, pp. 7-12, December 7, 2020, Institute of Electronics, Information and Communication Engineers

[0008] The present disclosure has been made in view of the above-mentioned problems, and aims to reduce the error between the estimated value and the actual value of communication quality when multiple wireless paths and wireless methods are used in an integrated manner in a wireless network that accommodates terminals that can simultaneously use multiple wireless paths and wireless methods.

[0009] The present disclosure provides a method for achieving the above object. The method disclosed herein is a method for measuring communication quality in a wireless network that accommodates a terminal that can simultaneously use multiple wireless paths and wireless methods, and includes the following first and second steps. The first step is a step of determining a measurement interval for the communication quality of each wireless path and wireless method by the terminal so that there is overlap in the timing of measurement of communication quality by the terminal among the multiple wireless paths and wireless methods. The second step is a step of causing the terminal to measure the communication quality of each wireless path and wireless method in accordance with the determined measurement interval.

[0010] The present disclosure also provides a system for achieving the above object. The system of the present disclosure is a wireless network system accommodating a terminal capable of simultaneously using multiple wireless paths and wireless methods. The system of the present disclosure includes at least one processor and at least one memory coupled to or incorporated in the at least one processor. The at least one memory stores a plurality of instructions executable by the at least one processor. The plurality of instructions are configured to cause the at least one processor to execute the following first and second processes. The first process is a process of determining a measurement interval for the communication quality of each wireless path and wireless method by the terminal so that timings of measuring communication quality by the terminal overlap among the multiple wireless paths and wireless methods. The second process is a process of causing the terminal to measure the communication quality of each wireless path and wireless method according to the determined measurement interval.

[0011] The present disclosure also provides a terminal for achieving the above object. The terminal of the present disclosure is a terminal that can simultaneously use multiple wireless paths and wireless methods. The terminal of the present disclosure includes at least one processor and at least one memory that is coupled to the at least one processor or is built into the at least one processor. The at least one memory stores multiple instructions that are executable by the at least one processor. The multiple instructions are configured to cause the at least one processor to execute the following first and second processes. The first process is a process of determining a measurement interval for communication quality for each wireless path and wireless method so that there is overlap in the timing of measurement of communication quality among the multiple wireless paths and wireless methods. The second process is a process of measuring the communication quality of each wireless path and wireless method according to the determined measurement interval.

[0012] The present disclosure also provides a program for achieving the above object. The program of the present disclosure includes a plurality of instructions executable by at least one processor of a terminal capable of simultaneously using a plurality of wireless paths and wireless methods. The plurality of instructions are configured to cause the at least one processor to execute the following first and second processes. The first process is a process of determining a measurement interval for communication quality for each wireless path and wireless method so that timing of communication quality measurement overlaps among the plurality of wireless paths and wireless methods. The second process is a process of measuring the communication quality of each wireless path and wireless method according to the determined measurement interval. Note that the program of the present disclosure may be stored in a computer-readable non-transitory storage medium or provided via a network.

[0013] According to the technology of the present disclosure, the communication quality of each wireless route and wireless method is measured according to a measurement interval determined so that the timing of measurement of communication quality among multiple wireless routes and wireless methods overlaps, thereby suppressing variations in the timing of measurement of communication quality among wireless routes and wireless methods and reducing the error between the estimated value and the actual value of communication quality when multiple wireless routes and wireless methods are used together.

[0014] Fig. 1 is a diagram illustrating a communication quality measurement method according to an embodiment of the present disclosure in comparison with a general communication quality measurement method; Fig. 2 is a diagram illustrating a configuration of a wireless network system according to an embodiment of the present disclosure; Fig. 3 is a diagram illustrating a flow of information within the wireless network system according to an embodiment of the present disclosure; Fig. 4 is a diagram illustrating an example of a hardware configuration of a wireless network system according to an embodiment of the present disclosure; Fig. 5 is a flow diagram illustrating a flow of measurement timing synchronization control processing executed in the wireless network system according to an embodiment of the present disclosure; Fig. 6 is a flow diagram illustrating a flow of measurement timing synchronization target limitation processing executed in the wireless network system according to an embodiment of the present disclosure.

[0015] 1. Overview of the Communication Quality Measurement Method for a Wireless Network First, an overview of the communication quality measurement method for a wireless network according to an embodiment of the present disclosure will be described. FIG. 1 is a diagram illustrating the communication quality measurement method of this embodiment in comparison with a general communication quality measurement method. For simplicity of explanation, it is assumed here that the only wireless methods used by the terminal are Method A and Method B, and that different wireless paths are used for Method A and Method B. It is also assumed that only the rate is measured as the communication quality. Note that the terminal measures the communication quality of each wireless method by requesting packet switching to acquire communication quality information from a base station corresponding to each wireless method.

[0016] In a typical communication quality measurement method, communication quality measurement is performed at independent timing for each of Method A and Method B. Here, communication quality measurement is performed at a timing at which the maximum rate can be measured for each method. The rates of Method A and Method B each fluctuate over time. As shown in Figure 1, if the cycle of time fluctuation of the rates between the two methods is the same but the phases are shifted, a discrepancy will occur between the timing of communication quality measurement for Method A and the timing of communication quality measurement for Method B.

[0017] In contrast, in the communication quality measurement method of this embodiment, the communication quality measurement intervals of each of methods A and B are determined so that there is an overlap between the communication quality measurement timing of method A and the communication quality measurement timing of method B. In the example shown in Fig. 1, the communication quality measurement timing of method A and the communication quality measurement timing of method B are set to the time when the maximum rate is measured in method A. However, as long as there is an overlap between the communication quality measurement timings of the methods, the communication quality measurement timing may be set to any timing. By bringing the communication quality measurement timing of method A and the communication quality measurement timing of method B closer to each other, the error between the estimated value and the actual value of communication quality when multiple wireless methods are used together is reduced.

[0018] 2. Configuration of Wireless Network System Fig. 2 shows the configuration of a wireless network system 101 according to an embodiment of the present disclosure. The wireless network communication quality measurement method of the present disclosure is applied to the wireless network system 101. The wireless network system 101 includes multiple terminals 2, multiple base stations 3 that perform wireless communication between the terminals 2, and at least one management system 4.

[0019] Terminal 2 is a wireless terminal that can use multiple wireless paths and wireless methods in the wireless network system 101. Terminal 2 may be a portable wireless terminal such as a smartphone, a wireless terminal mounted on a drone, or a fixed wireless terminal. In this specification and drawings, when distinguishing between terminals 2, they are denoted by independent reference numerals, such as terminal 2-1, terminal 2-2, ...

[0020] A plurality of base stations 3 are provided within an area where wireless communication is performed. A wireless path is created for each combination of terminal 2 and base station 3. In this specification and drawings, when distinguishing between the base stations 3, they are denoted by independent reference symbols, such as base station 3-1, base station 3-2, base station 3-3, etc. The base stations 3 support at least one of the wireless methods available to terminal 2, such as 4G, LTE, and 5G. In the example shown in FIG. 2, different wireless methods are used for base stations 3-1, 3-2, and 3-3, but the same wireless method may be used for multiple base stations 3.

[0021] In the example shown in Figure 2, only terminal 2-1 is depicted as being connected to base stations 3-1, 3-2, and 3-3. However, in reality, terminal 2-2 and other terminals 2 are also connected to base stations 3-1, 3-2, and 3-3. In other words, one terminal 2 can be connected to multiple base stations 3 simultaneously, and one base station 3 can be connected to multiple terminals 2 simultaneously. However, each terminal 2 does not necessarily have to be connected to all base stations 3 at all times. Also, in the example shown in Figure 2, terminal 2 and base station 3 are directly connected, but they may be connected via one or more relay stations.

[0022] The management system 4 is a system that collectively manages the terminals 2 and base stations 3. The management system 4 is connected to each base station 3 by wire or wirelessly. As functions for collectively managing the terminals 2 and base stations 3, the management system 4 includes a connection information database 41, an environmental fluctuation information database 42, and a period calculation unit 43.

[0023] The connection information database 41 is a database in which network connection information relating to the connection between the terminal 2 and the wireless network via each base station 3 is registered. The environmental variation information database 42 is a database in which environmental variation information relating to environmental variations around the terminal 2, such as the movement of the terminal 2, is registered. The communication quality of each wireless method that the terminal 2 can use varies over time depending on the environmental variations around the terminal 2 and the connection status between the terminal 2 and the wireless network. Therefore, the network connection information and environmental variation information are considered to be information relating to the time variations in the communication quality of each wireless path and wireless method that the terminal 2 can use.

[0024] The period calculation unit 43 calculates a communication quality measurement interval. The communication quality measurement interval is the period from the measurement timing at which the terminal 2 actively measures the communication quality for each wireless system to the next measurement timing. Active measurement of communication quality by the terminal 2 means that the terminal 2 requests packet exchange to the base station 3 corresponding to each wireless system to acquire communication quality information.

[0025] The period calculation unit 43 calculates a communication quality measurement interval for each terminal 2 based on the network connection information and environmental variation information so that the timing of measuring communication quality overlaps between wireless methods. The communication quality measurement interval is maintained constant unless there is a change in the period of time variation of communication quality for each wireless method determined from the network connection information and environmental variation information. On the other hand, if a change in the period of time variation is expected for any wireless method, the period calculation unit 43 updates the communication quality measurement interval based on the changed period.

[0026] Furthermore, the period calculation unit 43 calculates a broadcast / synchronization signal transmission interval. The broadcast / synchronization signal transmission interval is the period from the transmission timing at which the base station 3 transmits a broadcast / synchronization signal to the terminal 2 to the next transmission timing. The broadcast / synchronization signal refers to a synchronization signal block that combines broadcast information and a synchronization signal. When a synchronization signal block is transmitted from the base station 3, the terminal 2 can measure communication quality using a reference signal included in the synchronization signal block. In this case, the timing at which the terminal 2 measures communication quality depends on the transmission timing of the synchronization signal block from each base station 3.

[0027] The period calculation unit 43 calculates the broadcast / synchronization signal transmission interval for each base station 3 based on the network connection information and environmental variation information so that the timing of measuring communication quality overlaps between wireless systems. The broadcast / synchronization signal transmission interval is maintained constant unless there is a change in the period of time variation of communication quality for each wireless system determined from the network connection information and environmental variation information. On the other hand, if a change in the period of time variation is expected for any wireless system, the period calculation unit 43 updates the broadcast / synchronization signal transmission interval based on the changed period.

[0028] 3 is a diagram illustrating the flow of information within the wireless network system 101 configured as described above. The network connection information is acquired by the base station 3. The network connection information acquired by the base station 3 is transmitted to the management system 4. The management system 4 associates the received network connection information with the base station 3 that sent it and registers it in the connection information database 41.

[0029] The environmental variation information is acquired by the terminal 2. The environmental variation information acquired by the terminal 2 is transmitted to the base station 3, and then transmitted from the base station 3 to the management system 4. The base station 3 to which the terminal 2 transmits the environmental variation information is not predetermined, and the environmental variation information may be transmitted to any base station 3. The environmental variation information may also be divided into multiple packets and transmitted to the management system 4 via multiple base stations 3. The management system 4 associates the received environmental variation information with the terminal 2 that sent it, and registers it in the environmental variation information database 42.

[0030] The management system 4 generates broadcast / synchronization signal transmission interval control information for each base station 3 based on the broadcast / synchronization signal transmission interval for each base station 3 calculated by the period calculation unit 43. The generated broadcast / synchronization signal transmission interval control information is transmitted to the base station 3. The broadcast / synchronization signal transmission interval control information is control information for controlling the base station 3 in accordance with the broadcast / synchronization signal transmission interval. For example, the base station 3 that receives this control information is controlled to repeatedly go to sleep and wake up in accordance with the broadcast / synchronization interval.

[0031] Furthermore, the management system 4 generates communication quality measurement interval control information for each terminal 2 based on the communication quality measurement interval for each terminal 2 calculated by the period calculation unit 43. The generated communication quality measurement interval control information is transmitted to the terminal 2 via the base station 3. The base station 3 that transmits the communication quality measurement interval control information to the terminal 2 is not determined, and the communication quality measurement interval control information may be transmitted from any base station 3. Furthermore, the communication quality measurement interval control information may be divided into multiple packets and transmitted to the terminal 2 via multiple base stations 3. The communication quality measurement interval control information is control information for controlling the terminal 2 in accordance with the communication quality measurement interval. For example, the terminal 2 that receives this control information is controlled to repeatedly go to sleep and wake up in accordance with the communication quality measurement interval.

[0032] In this embodiment, the management system 4 is considered to be part of the wireless network system 101, but the management system 4 itself can be considered a wireless network system in the narrow sense. Also, in Fig. 2, the management system 4 is depicted as a system independent of the terminal 2 and the base station 3, but the management system 4 may be provided in the terminal 2 or in the base station 3. In the former case, the terminal 2 integrated with the management system 4 can be considered a wireless network system in the narrow sense. In the latter case, the base station 3 integrated with the management system 4 can be considered a wireless network system in the narrow sense.

[0033] The connection information database 41, the environmental variation information database 42, and the period calculation unit 43 that constitute the management system 4 are three separate functions of the management system 4 for convenience's sake, but these may be integrated into one or two, or may be further subdivided. It is also possible for some of the functions of the management system 4 to be provided in the terminal 2 or the base station 3, or for some or all of the functions of the management system 4 to be distributed between the terminal 2 and the base station 3. For example, the function of the period calculation unit 43 to calculate the communication quality measurement interval may be provided in each terminal 2. It is also possible for the function of the period calculation unit 43 to calculate the notification / synchronization interval to be provided in each base station 3.

[0034] 3. Hardware Configuration of Wireless Network System Here, the hardware configuration of the wireless network system 101 will be described with reference to Fig. 4. As described above, the wireless network system 101 includes the terminal 2, the base station 3, and the management system 4.

[0035] The terminal 2 includes a processor 201 and a memory 202. The memory 202 stores a plurality of instructions 203 that can be executed by the processor 201. The number of each of the processors 201 and the memories 202 constituting the terminal 2 may be plural. The wireless network system 101 includes a plurality of terminals 2.

[0036] The base station 3 includes a processor 301 and a memory 302. The memory 302 stores a plurality of instructions 303 that can be executed by the processor 301. The number of each of the processors 301 and the memories 302 constituting the base station 3 may be plural. The wireless network system 101 includes a plurality of base stations 3.

[0037] The management system 4 includes a processor 401 and a memory 402. The memory 402 stores a plurality of instructions 403 executable by the processor 401. The memory 402 includes a RAM, a ROM, and a storage. The connection information database 41 and the environmental variation information database 42 described above may be provided in the memory 402. The management system 4 may include a plurality of processors 401 and a plurality of memories 402. Part or all of the hardware of the management system 4 may be integrated with the terminal 2. Furthermore, part or all of the hardware of the management system 4 may be integrated with the base station 3.

[0038] As described above, the wireless network system 101 includes a plurality of executable instructions. The plurality of instructions are executed by at least one processor included in the wireless network system 101, whereby the processing described below is performed in the wireless network system 101, and the communication quality measurement method of this embodiment is implemented. Note that a program made up of the plurality of instructions may be stored in a computer-readable non-transitory storage medium or provided via a network.

[0039] The processor included in the wireless network system 101 may be a CPU, RISC, DSP, FPGA, ASIC, PLD, or other processing unit, or may be a combination of two or more thereof, or may be a dedicated processor that operates according to the process flow described below. The processor may also be communicatively coupled to a memory or may have a built-in memory.

[0040] 4. Processing Executed in the Wireless Network System Processing executed in the wireless network system 101 includes measurement timing synchronization control processing and measurement timing synchronization target limitation processing. The measurement timing synchronization control processing is processing for synchronizing the timing of measurement of communication quality between wireless paths and between wireless methods. The measurement timing synchronization target limitation processing is processing for limiting the wireless paths and wireless methods that are targets of the measurement timing synchronization control processing. These processing will be specifically explained below using flow diagrams.

[0041] 5 is a flow diagram showing the flow of the measurement timing synchronization control process executed in the wireless network system 101. The measurement timing synchronization control process includes steps S101 to S104. Each step has a corresponding instruction. Each instruction is executed by at least one processor, particularly the processor of the management system 4, thereby performing terminal / base station control processing in the wireless network system 101.

[0042] First, in step S101, information collection for measuring communication quality is performed. Network connection information is collected from each base station 3. Environmental fluctuation information is collected from each terminal 2.

[0043] Next, in step S102, a period is determined based on the network connection information and environmental fluctuation information collected in step S101. A broadcast / synchronization signal transmission interval is determined for each base station 3. A communication quality measurement interval is determined for each terminal 2.

[0044] Next, in step S103, at least one of the control information including the broadcast / synchronization signal transmission interval determined in step S102 and the control information including the communication quality measurement interval is transmitted. The broadcast / synchronization signal transmission interval control information is transmitted to each base station 3 when communication quality measurement is performed using a reference signal included in the synchronization signal block. The communication quality measurement interval control information is transmitted to each terminal 2 when a packet switching request for acquiring communication quality information is made from the terminal 2 to the base station 3.

[0045] Then, in step S104, it is determined whether or not there has been a change in the terminal environment for each terminal 2. A change in the terminal environment means, for example, a change in topology, a connected base station, or the degree of environmental fluctuation. The determination in step S104 is repeated at regular intervals until a change in the terminal environment occurs for any terminal 2. Then, when a change in the terminal environment occurs for any terminal 2, the processes from step S101 to step S103 are executed for at least that terminal 2.

[0046] The measurement timing synchronization control process described above is executed in the wireless network system 101, thereby synchronizing the measurement timing of communication quality between wireless paths and between wireless methods. As a result, the error between the estimated value and the actual value of communication quality when multiple wireless paths and wireless methods are used in an integrated manner is reduced.

[0047] 6 is a flow diagram showing the flow of the measurement timing synchronization target limitation process executed in the wireless network system 101. The measurement timing synchronization target limitation process includes steps S201 to S203. Each step has a corresponding instruction. The measurement timing synchronization target limitation process is executed in the wireless network system 101 by executing each instruction by at least one processor, particularly the processor of the management system 4.

[0048] The measurement timing synchronization target limiting process is executed for each terminal 2. First, in step S201, for each wireless path and wireless method used by the terminal 2, the communication failure rate in communication for measuring communication quality is calculated.

[0049] In step S202, it is determined whether or not there are any wireless paths and wireless methods whose communication failure rates are greater than a predetermined threshold. If there are no wireless paths and wireless methods whose communication failure rates are greater than the threshold, step S203 is skipped and the flow returns to step S201.

[0050] If there are wireless paths and wireless systems with a communication failure rate greater than the threshold, the flow proceeds to step S203. For wireless paths and wireless systems with a high communication failure rate, the measurement period must be set excessively short. However, in order to perform measurement timing synchronization control, the measurement period must also be shortened for other wireless paths and wireless systems, which causes problems in terms of network resource utilization efficiency. Therefore, in step S203, wireless paths and wireless systems with a communication failure rate greater than the threshold are excluded from the measurement timing synchronization control.

[0051] By performing the above measurement timing synchronization target limiting process in the wireless network system 101, wireless paths and wireless methods with high communication failure rates are prevented from affecting the measurement of communication quality of other wireless paths and wireless methods.

[0052] 2 Terminal 3 Base station 4 Management system 101 Wireless network system

Claims

1. A method for measuring communication quality in a wireless network that accommodates a terminal that can simultaneously use multiple wireless routes and wireless methods, comprising: determining a measurement interval for the communication quality of each wireless route and wireless method by the terminal so that there is an overlap in the timing of measurement of communication quality by the terminal among the multiple wireless routes and wireless methods; and having the terminal measure the communication quality of each wireless route and wireless method in accordance with the determined measurement interval.

2. The method for measuring communication quality in a wireless network according to claim 1, further comprising: acquiring information relating to time fluctuations in the communication quality of each of the plurality of wireless paths and wireless methods; and determining the measurement interval based on said information.

3. A method for measuring communication quality in a wireless network as described in claim 1, further comprising: determining a transmission interval for the notification and synchronization signals by the multiple base stations corresponding to the multiple wireless paths and wireless methods so that there is an overlap in the timing of transmission of the notification and synchronization signals to the terminal from the multiple base stations; and causing the multiple base stations to transmit the notification and synchronization signals in accordance with the determined transmission interval.

4. The method for measuring communication quality of a wireless network as described in claim 3, further comprising acquiring environmental variation information relating to environmental variations around the terminal and network connection information relating to the connection between the terminal and the wireless network via each base station, and determining the transmission interval based on the environmental variation information and the network connection information.

5. A method for measuring communication quality of a wireless network as claimed in any one of claims 1 to 4, further comprising: calculating a communication failure rate for each of the plurality of wireless routes and wireless methods; and excluding wireless routes and wireless methods having a communication failure rate greater than a threshold value from targets that cause overlap in communication quality measurement timing with other wireless routes and wireless methods.

6. A wireless network system accommodating a terminal capable of simultaneously using multiple wireless paths and wireless methods, comprising: at least one processor; at least one memory coupled to the at least one processor or built into the at least one processor; and a plurality of instructions stored in the at least one memory and executable by the at least one processor, wherein the plurality of instructions are configured to cause the at least one processor to: determine a measurement interval for the communication quality of each wireless path and wireless method by the terminal so that there is an overlap in the timing of measurement of communication quality by the terminal among the multiple wireless paths and wireless methods; and cause the terminal to measure the communication quality of each wireless path and wireless method in accordance with the determined measurement interval.

7. A terminal capable of simultaneously using a plurality of wireless paths and wireless methods, comprising: at least one processor; at least one memory coupled to the at least one processor or built into the at least one processor; and a plurality of instructions stored in the at least one memory and executable by the at least one processor, wherein the plurality of instructions are configured to cause the at least one processor to: determine a measurement interval for communication quality of each wireless path and wireless method so that there is an overlap in the timing of measuring communication quality among the plurality of wireless paths and wireless methods; and measure the communication quality of each wireless path and wireless method in accordance with the determined measurement interval.

8. A program including a plurality of instructions executable by at least one processor of a terminal capable of simultaneously using a plurality of wireless paths and wireless methods, the plurality of instructions being configured to cause the at least one processor to execute the following: determining a measurement interval for the communication quality of each wireless path and wireless method so that there is an overlap in the timing of measuring the communication quality among the plurality of wireless paths and wireless methods; and measuring the communication quality of each wireless path and wireless method in accordance with the determined measurement interval.

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