JP7295424B2 - Wireless environment measuring device, wireless environment measuring system, and analysis device - Google Patents

Description

The present invention relates to a radio environment measuring device, a radio environment measuring system, and an analysis device.

In a wireless network, wireless communication is performed between a base station and a terminal device (see, for example, Patent Document 1).

JP 2014-239297 A

In such a wireless network, interference may occur in wireless communication due to the presence of interference sources, restrictions on the range of radio wave coverage of terminal devices, and the like. Therefore, it is conceivable to arrange a plurality of wireless probes and measure the wireless signals of all of the plurality of channels (frequency bands) in order to comprehensively measure the radio wave conditions at the site. However, as the number of channels increases, the number of probes becomes enormous. Therefore, it is conceivable to cause each probe to sequentially switch between measurements of a plurality of channels. However, a scan unavailable time occurs due to a control delay or the like when switching channels.

An object of the present invention is to provide a radio environment measuring device, a radio environment measuring system, and an analysis device that can measure the radio environment without interruption.

In one aspect, a radio environment measuring device includes a plurality of probes arranged in an area where a terminal device and a base station perform radio communication on a plurality of channels and classified into N (≧2) groups, One or more of the probes are arranged in each group within the radio wave reachable distance of each terminal device, the N is greater than the number of the plurality of channels, and the plurality of probes are in the same group unit The plurality of channels are synchronously switched sequentially, each channel is scanned for a scan period of t _scan , and the scan timing for the same channel is set for group i (0≤i≤N-1). An offset of _ixtoffset ( _{toffset≤tscan} ) is provided at the _scan start time, _toffset satisfies _Nxtoffset = number of channels x ( _tscan + _tinterval ), and _tinterval is when each probe is This is the time required to switch channels to be scanned.

In another aspect, a wireless environment measurement system includes the above wireless environment measurement device and an analysis device that analyzes scan results of the plurality of probes.

In another aspect, the analysis device is arranged in an area where the terminal device and the base station wirelessly communicate with a plurality of channels, and for a plurality of probes classified into N (≧2) groups, each An instruction unit that instructs the timing of scanning the radio signal of the channel, and an analysis unit that analyzes the scanning results of the plurality of probes, and within the radio wave reachability of each terminal device, one or more of the above in each group The probes are arranged, the N is larger than the number of the plurality of channels, and the instruction unit sequentially switches the plurality of channels in synchronization with the plurality of probes in the same group unit to each A channel is scanned for a scan period of t _scan , and for group i (0≦i≦N−1), an offset of i×t _offset (t _offset ≦t _scan ) is added to the scan timing for the same channel. Provided at the scan start time, t _offset satisfies N x t _offset = number of channels x (t _scan + t _interval ), where t _interval is the time required for each probe to switch channels to be scanned.

The wireless environment can be measured continuously.

FIG. 4 is a diagram illustrating placement of wireless probes; (a) and (b) are diagrams illustrating channels to be operated. FIG. 4 illustrates a multi-channel measurement; 1A is a block diagram showing the overall configuration of a radio environment measurement system according to Embodiment 1, FIG. 1B is a functional block diagram of a probe, and FIG. 1C is a functional block diagram of an analysis server; FIG. FIG. 4 is a diagram for explaining the operation of each part of the radio environment measurement system; FIG. 4 is a diagram for explaining the operation of each part of the radio environment measurement system; (a) is a flow chart showing the initial setting procedure of the wireless environment measurement system, and (b) is a diagram illustrating a table of scan start times and scan end times. FIG. 4 is a diagram illustrating scanning of each group; FIG. 4 is a diagram illustrating the arrangement of each probe; FIG. 4 illustrates overlapping reception periods in which the same channel is scanned between two groups; FIG. 4 is a diagram illustrating the arrangement of each probe; FIG. 4 is a diagram for explaining the operation of each part of the radio environment measurement system; FIG. 4 is a diagram for explaining the operation of each part of the radio environment measurement system; (a) is a block diagram illustrating the hardware configuration of a probe, (b) is a block diagram illustrating the hardware configuration of an analysis server.

In a network using wireless communication, base stations and terminals communicate wirelessly. In such a wireless network, interference may occur in wireless communication due to the presence of interference sources, restrictions on radio coverage, and the like. Packet capture, which analyzes the status of wireless communication, is effective in identifying the cause of a network failure. However, in order to analyze the position of the interference source and the reach of radio waves, it is necessary to carry a wireless probe and walk around multiple locations. In this case, an enormous amount of labor is required.

Therefore, as exemplified in FIG. 1, multiple wireless probes are placed in the network area where the base station and multiple terminal devices wirelessly communicate, and the analysis server automatically analyzes the position of the interference source, the radio wave coverage, etc. system is being developed. In particular, in networks using Wi-Fi, failures frequently occur due to multiple factors such as brought-in routers, roaming settings, channel interference, etc., making it difficult to determine the cause. Therefore, there is a strong demand for analysis and presentation of information leading to failure recovery. For example, it is desired to obtain the cause of the failure (interference source), the location of the interference source, and the like.

In failure analysis, it is desirable to measure radio signals on all channels in operation in order to comprehensively analyze radio wave conditions on site. For example, as illustrated in FIG. 2(a), in a 2.4 GHz band Wi-Fi network, three channels, channel #1, channel #6, and channel #11, are used to avoid interference between adjacent channels. be. As illustrated in FIG. 2(b), 19 channels, for example, are used in a 5 GHz band Wi-Fi network.

All radio signals of these multiple channels being used are received by any one of the radio probes. For positioning, radio signals from a terminal placed at a certain position are received by three or more radio probes.

For example, it is conceivable to increase the number of probes as the number of channels increases. However, in this method, it is required to arrange probes equal to or more than the number of channels×3 within a range (radio wave reachable range) in which a radio signal from a certain terminal device can be received. Therefore, as the number of channels increases, the number of probes becomes enormous.

Therefore, it is conceivable to cause each probe to sequentially switch between observations of a plurality of channels. For example, it is conceivable to cause each probe to cyclically switch each channel and synchronize the switching timing. For example, as illustrated in FIG. 3, during a scan period of t _scan , probes 1 and 4 scan to receive radio signals on channel #1, and probe 2 scans to receive radio signals on channel #6. , probe 3 scans for radio signals on channel #11. Then, after t _interval , for the next scan period of t _scan , probes 1 and 4 scan channel #6, probe 2 scans channel #11, and probe 3 scans channel #1. Thus, one probe scans all channels, channel #1, channel #6 and channel #11. By doing so, the number of probes can be reduced.

However, a channel switching time (t _interval ) occurs due to control delay or the like in order to switch channels in each probe. Due to this channel switching time, for example, a scan unavailable time of several hundred milliseconds occurs periodically. In this case, it becomes difficult to analyze short packet groups of several hundred ms or less, such as connection sequences. In addition, it becomes difficult to perform time-series analysis of short sections of periodically transmitted signals, such as traffic line analysis and causal relationship analysis of failures. Also, detection of CW (continuous wave) becomes difficult. From the above, it is desired that each channel can be scanned without interruption.

Therefore, in the following embodiments, a radio environment measuring device, a radio environment measuring system, and an analysis device that can continuously measure the radio environment by continuously scanning each channel will be described.

FIG. 4A is a block diagram showing the overall configuration of the radio environment measurement system 100 according to the first embodiment. FIG. 4B is a functional block diagram of the first probe 10a, the second probe 10b, the third probe 10c, and the fourth probe 10d included in the wireless environment measurement system 100. FIG. FIG. 4C is a functional block diagram of the analysis server 20 included in the wireless environment measurement system 100. As shown in FIG. In this embodiment, as an example, Wi-Fi channel #1, channel #6 and channel #11 are used.

As illustrated in FIG. 4( a ), the wireless environment measurement system 100 includes multiple probes and analysis servers 20 . In this embodiment, as an example, the plurality of probes are first probe 10a to fourth probe 10d.
These first to fourth probes 10a to 10d are arranged in a network area where wireless communication is performed between a base station and a plurality of terminal devices, as described with reference to FIG. The first probe 10a to the fourth probe 10d function as radio environment measuring devices.

As illustrated in FIG. 4(b), each of the first probe 10a to the fourth probe 10d functions as a transmitter/receiver 11, a channel switching unit 12, a capture receiver 13, a data storage unit 14, and the like. The channel switching unit 12 controls switching of channels to be scanned. The capturing receiver 13 scans the channel specified by the channel switching unit 12 for radio signals (packets), thereby capturing the packets of the channel. The data storage unit 14 stores the captured data measured by the capture receiving unit 13 . The capture data includes reception strength and the like.

As illustrated in FIG. 4C, the analysis server 20 functions as an analysis device, and functions as a start instruction unit 21, an end instruction unit 22, an analysis unit 23, and the like. The start instructing unit 21 instructs each of the first probe 10a to the fourth probe 10d to start scanning a designated channel. The end instruction unit 22 instructs the end of scanning. The start instruction section 21 and the end instruction section 22 function as instruction sections. The analysis unit 23 receives capture data from each of the first probe 10a to the fourth probe 10d, and analyzes the capture data. For example, the analysis unit 23 analyzes the radio wave reachable range of the terminal, the position of the interference source, etc., using capture data of three or more probes.

5 and 6 are diagrams for explaining the operation of each unit of wireless environment measurement system 100. FIG. The operation of each part will be described below with reference to FIGS. 4(a) to 4(c), FIGS. As exemplified in FIG. 5, when receiving the start instruction for channel #1 as the first channel from the start instruction unit 21 of the analysis server 20, the transmission/reception unit 11 of the first probe 10a transmits the scan start instruction for channel #1 to the channel. It is transmitted to the switching unit 12 . Upon receiving the scan start instruction for channel #1, the channel switching unit 12 sets channel #1 to the capture receiver 13 and transmits the scan start instruction. As a result, the capturing receiver 13 starts scanning packets on channel #1.

After that, the transmission/reception unit 11 of the first probe 10a receives a start instruction for channel #6 as the next channel from the start instruction unit 21 of the analysis server 20. FIG. As a result, the transmitting/receiving section 11 of the first probe 10 a transmits a scanning end instruction for channel # 1 to the channel switching section 12 and transmits a scanning start instruction for channel # 6 to the channel switching section 12 . When the channel switching unit 12 receives the channel #1 scan end instruction, the capturing reception unit 13 ends the channel #1 scan and stores the channel #1 capture data in the data storage unit 14 . Upon receiving the scan start instruction for channel #6, the channel switching unit 12 sets channel #6 to the capture receiver 13 and transmits the scan start instruction. As a result, the capturing receiver 13 starts scanning packets on channel #6.

After that, the transmitting/receiving unit 11 of the first probe 10 a receives a scan end instruction from the end instruction unit 22 of the analysis server 20 . As a result, the transmitting/receiving section 11 of the first probe 10 a transmits a scan end instruction for the channel #6 to the channel switching section 12 . When the channel switching unit 12 receives the scan end instruction for the channel #6, the capture reception unit 13 ends the scan for the channel #6 and stores the capture data for the channel #6 in the data storage unit 14. The channel switching unit 12 also transmits a data transmission instruction to the data storage unit 14 . Thereby, the data storage unit 14 transfers the stored capture data to the transmission/reception unit 11 . The transmission/reception unit 11 transmits the capture data transferred from the data storage unit 14 to the analysis server 20 . The analysis unit 23 of the analysis server 20 analyzes the received capture data.

As illustrated in FIG. 6, the second probe 10b is similarly scanned sequentially for each channel.

In the example of FIG. 5, scanning of only channel #1 and channel #6 is described, but it is not limited to this. In this embodiment, multiple scans are performed for all cyclically switched channels (channel #1, channel #6, and channel #11). Moreover, although only the first probe 10a and the second probe 10b are described in the examples of FIGS. 5 and 6, the present invention is not limited to this. In this embodiment, the same operation is performed for all the first probe 10a to the fourth probe 10d provided in the wireless environment measurement system 100. FIG.

Next, a procedure for initial setting of the wireless environment measurement system 100 will be described. FIG. 7(a) is a flowchart showing the initial setting procedure of the wireless environment measurement system 100. FIG. As illustrated in FIG. 7(a), the user classifies a plurality of probes provided in the wireless environment measurement system 100 into N groups (step S1). In this embodiment, as an example, the first probe 10a is classified into group 0, the second probe 10b is classified into group 1, the third probe 10c is classified into group 2, and the fourth probe 10d is classified into group 3. Classify. That is, N=4. When a large number of probes are provided, a plurality of probes may be classified into each group.

Next, the offset t _offset of the scanning period t _scan is set in consideration of the channel switching time t _interval (step S2). Specifically, N×t _offset =(number of channels)×(t _scan +t _interval ) is satisfied. Also, in group i (0≦i≦N-1), the scan timing is set to an offset of the scan period by i×t _offset (t _offset ≦t _scan ).

Next, each group is set so that the channels to be scanned are synchronized and looped (step S3). Next, each probe is installed so that one or more probes in each group are positioned within the radio wave reachability of each terminal device (step S4). Here, the radio wave reaching distance is the distance that the radio waves of the terminal device reach when there are no obstacles or sources of interference (when there is no radio interference).

The initial setting in FIG. 7A determines the scan start time and scan end time for each channel for each group. The start instructing unit 21 and the end instructing unit 22 of the analysis server 20 hold these scan start time and scan end time as a table as shown in FIG. 7(b).

FIG. 8 is a diagram illustrating scanning performed by the settings in FIG. 7(a). As illustrated in FIG. 8, the first probe 10a of group 0 scans channel #1 for a scan period of t _scan . After t _offset from the start of scanning channel #1 by the first probe 10a, the second probe 10b of group 1 scans channel #1 for a scanning period of t _scan . After t _offset from the start of scanning channel #1 by the second probe 10b, the third probe 10c of group 2 scans channel #1 for a scanning period of t _scan . After t _offset from the start of scanning channel #1 by the third probe 10c, the fourth probe 10d of group 3 scans channel #1 for the scanning period t _scan .

After finishing scanning channel #1, the first probe 10a scans channel #6 for a scanning period of t _scan after t _interval . After t _offset from the start of scanning channel #6 by the first probe 10a, the second probe 10b of group 1 scans channel #6 for a scanning period of t _scan . After t _offset from the start of scanning channel #6 by the second probe 10b, the third probe 10c of group 2 scans channel #6 for a scanning period of t _scan . After t _offset from the start of scanning channel #6 by the third probe 10c, the fourth probe 10d of group 3 scans channel #6 for the scanning period t _scan .

After finishing scanning channel #6, the first probe 10a scans channel #11 for a scanning period of t _scan after t _interval . After t _offset from the start of scanning channel #11 by the first probe 10a, the second probe 10b of group 1 scans channel #11 for a scanning period of t _scan . After t _offset from the start of scanning channel #11 by the second probe 10b, the third probe 10c of group 2 _{scans channel #11 for the scanning period t scan} . After t _offset from the start of scanning channel #11 by the third probe 10c, the fourth probe 10d of group 3 scans channel #11 during the scanning period t _scan .

In this way, the first probe 10a scans channel #1 for a scan period of t _scan , after t _{interval scans} channel #6 for a scan period of t scan, and after t _interval , _scans channel #6. , channel #11 is scanned. This operation is regarded as one set, and after one set, the first probe 10a repeats performing the next set after t _interval . The second probe 10b repeats the set after t _offset after the first probe 10a. Further, the third probe 10c repeats the set after t _offset after the second probe 10b. Furthermore, the fourth probe 10d repeats the set after t _offset after the third probe 10c.

Since t _offset is less than or equal to t _scan , either probe will scan for each channel. Therefore, even if t _interval is required for channel switching, the radio environment can be measured for all time zones regardless of the finite switching time for each channel. That is, the wireless environment can be measured without interruption.

Since t _offset is set to satisfy N×t _offset =(number of channels)×(t _scan +t _interval ), the time offset between group N−1 and group 0 is also t _offset . Since each probe is installed so that one or more probes in each group are positioned within the radio wave coverage range of each terminal device, the same scan information is obtained regardless of which area the terminal device to be scanned is located. will be obtained. Furthermore, since N>the number of channels≧2, reception is possible with three or more probes, and positioning is possible. In addition, since the number of groups N can be substantially equal to about the number of channels plus one, the number of probes to be installed can be greatly reduced.

t _interval is a control latency, for example, about 0.1 s. Therefore, it is preferable to make t _scan sufficiently larger than t _interval in order to suppress overhead due to channel switching. If the number of channels is 3, it is preferable to set N=4, t _scan to 1.5 s, and t _offset to 1.2 s. In this case, as exemplified in FIG. 9, each probe is installed so that each group is arranged in order in a square lattice, and the relationship between the radio wave reaching distance L and the inter-lattice distance d is d<√2L. It is preferable to

(Modification 1)
If the clock accuracy of each probe is low, it may be difficult to synchronize data groups observed by each probe. Therefore, as exemplified in FIG. 10, the overlapping reception period (=t _scan −t _offset ) for scanning the same channel between the two groups is set to be longer than the cycle of the packet periodically transmitted by the terminal device. . Packets that are periodically transmitted are, for example, Wi-Fi beacons (usually with a period of 102.4msms). By receiving at least one beacon packet, which is always transmitted in a Wi-Fi environment, by a plurality of probes within the overlapping reception period, data groups of these probes can be synchronized.

(Modification 2)
When a terminal to be observed moves, each probe receives packets from the terminal at different timings. If the scan period is long, each group may not be able to synchronize and loop the receive channels.

Therefore, in Modified Example 2, the radio wave reachable distance L is set by subtracting "scan period.times.moving speed". For example, as exemplified in FIG. 11, in the case of (scan period = 4.8 s), radio wave reaching distance L = 20 m, and moving speed 1 m / s, radio wave reaching range = 20 - 4.8 = 15.2 m. is preferred.

In the first embodiment, the analysis server 20 instructs each probe at each channel switching timing, but the present invention is not limited to this. Each probe may automatically switch channels. In a second embodiment, an example in which each probe automatically switches channels will be described.

12 and 13 are diagrams for explaining the operation of each part of the wireless environment measurement system 100 in the second embodiment. As illustrated in FIG. 12, when the transmitting/receiving unit 11 of the first probe 10a receives the list of each channel and the scan timing of each channel from the start instructing unit 21 of the analysis server 20, the channel switching unit 12 switches the list and Register the scan timing. Channels to be scanned are registered in order in each channel list. The scan timing includes scan start timing and scan end timing for each channel. The list of each channel and the scan timing of each channel are transmitted to the transmitting/receiving section 11 as a table as illustrated in FIG. 7(b).

Further, when receiving the scan start instruction from the start instruction unit 21 of the analysis server 20, the transmission/reception unit 11 of the first probe 10a transmits the scan start instruction of channel #1 to the channel switching unit 12 according to the order of the list. As a result, the channel switching unit 12 sets channel #1 to the capture receiving unit 13 and transmits a scan start instruction. As a result, the capturing receiver 13 starts scanning packets on channel #1.

After the channel # 1 scanning period, the channel switching unit 12 transmits a scan end instruction for the channel # 1 to the capture receiving unit 13 . As a result, the capturing reception unit 13 finishes scanning the channel #1 and saves the capture data of the channel #1 in the data saving unit 14 . Next, the channel switching unit 12 sets the channel #6 to the capture receiving unit 13 according to the order of the list, and transmits a scan start instruction. As a result, the capturing receiver 13 starts scanning packets on channel #6.

After the scanning period of channel #6, the channel switching unit 12 transmits a scanning end instruction of channel #6 to the capture receiving unit 13. FIG. As a result, the capture receiving section 13 finishes scanning the channel #6 and saves the capture data of the channel #6 in the data saving section 14 . Next, the channel switching unit 12 transmits a data transmission instruction to the data storage unit 14 . Thereby, the data storage unit 14 transfers the stored capture data to the transmission/reception unit 11 . The transmission/reception unit 11 transmits the capture data transferred from the data storage unit 14 to the analysis server 20 . The analysis unit 23 of the analysis server 20 analyzes the received capture data.

As illustrated in FIG. 13, the second probe 10b is similarly scanned sequentially for each channel.

Although the example of FIG. 12 describes scanning only channel #1 and channel #6, it is not limited to this. In this embodiment, multiple scans are performed for all cyclically switched channels (channel #1, channel #6, and channel #11). Moreover, although only the first probe 10a and the second probe 10b are described in the examples of FIGS. 12 and 13, the present invention is not limited to this. In this embodiment, the same operation is performed for all the first probe 10a to the fourth probe 10d provided in the wireless environment measurement system 100. FIG.

(probe hardware)
FIG. 14(a) is a block diagram illustrating the hardware configuration of each of the first probe 10a to the fourth probe 10d. As illustrated in FIG. 14(a), the first probe 10a to the fourth probe 10d are equipped with a CPU 101, a RAM 102, a storage device 103, a communication device 104, a receiving device 105 and the like.

A CPU (Central Processing Unit) 101 is a central processing unit. CPU 101 includes one or more cores. A RAM (Random Access Memory) 102 is a volatile memory that temporarily stores programs executed by the CPU 101, data processed by the CPU 101, and the like. The storage device 103 is a non-volatile storage device. As the storage device 103, for example, a ROM (Read Only Memory), a solid state drive (SSD) such as a flash memory, a hard disk driven by a hard disk drive, or the like can be used. The storage device 103 stores programs and the like. The communication device 104 is a device for performing wired or wireless communication with the analysis server 20 . The receiving device 105 is a device that receives radio signals transmitted from the terminal device to the base station. In this embodiment, each part of the first probe 10a to the fourth probe 10d is implemented by executing a program. For example, the communication device 104 functions as the transceiver 11 . The receiving device 105 functions as the capture receiving section 13 .

(analysis server hardware)
FIG. 14B is a block diagram illustrating the hardware configuration of the analysis server 20. As shown in FIG. As illustrated in FIG. 14B, the analysis server 20 includes a CPU 201, a RAM 202, a storage device 203, a communication device 204, and the like.

A CPU 201 is a central processing unit. CPU 201 includes one or more cores. A RAM 202 is a volatile memory that temporarily stores programs executed by the CPU 201 and data processed by the CPU 201 . Storage device 203 is a non-volatile storage device. As the storage device 203, for example, a ROM, a solid state drive such as a flash memory), a hard disk driven by a hard disk drive, or the like can be used. The storage device 203 stores programs and the like. The communication device 204 is a device for performing wireless or wired communication with the first probe 10a to the fourth probe 10d.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention described in the scope of claims. Change is possible.

REFERENCE SIGNS LIST 10 probe 11 transmission/reception unit 12 channel switching unit 13 capture reception unit 14 data storage unit 20 analysis server 21 start instruction unit 22 end instruction unit 23 analysis unit 100 wireless environment measurement system

Claims (6)

A plurality of probes arranged in an area where a terminal device and a base station perform wireless communication on a plurality of channels and classified into N (≧2) groups,
One or more of the probes are arranged in each group within the radio wave reachable distance of each terminal device,
the N is greater than the number of the plurality of channels;
The plurality of probes are synchronized in the same group unit and sequentially switch the plurality of channels , and perform scanning of radio signals for a scanning period of t _scan for each channel,
In group i (0≦i≦N−1), an offset of i×t _offset (t _offset ≦t _scan ) is provided to the scan start time for the same channel,
t _offset satisfies N x t _offset = number of channels x (t _scan + t _interval ),
A radio environment measuring apparatus, wherein t _interval is a time required for each probe to switch channels to be scanned. An overlapping reception period (t _scan - t _offset ) for scanning the same channel between two groups is set to be equal to or longer than the cycle of packets periodically transmitted by the terminal device. The wireless environment measuring device described. the number of groups is 4;
The plurality of probes are arranged so that each group is arranged in order in a square lattice,
3. The wireless environment measuring apparatus according to claim 1, wherein a relationship of d<√2L is established between a radio wave reachable distance L of the terminal device and an inter-lattice distance d of the square lattice. 2. A relationship of d<√2L′ holds when a distance obtained by subtracting (N×t _offset )×(moving speed of the terminal device) from the radio wave reaching distance L is L′. 4. The radio environment measuring device according to 3. A radio environment measuring device according to any one of claims 1 to 4;
and an analysis device that analyzes scan results of the plurality of probes. A plurality of probes classified into N (≧2) groups are arranged in an area where a terminal device and a base station perform wireless communication on a plurality of channels. an instruction unit for instructing;
and an analysis unit that analyzes the scan results of the plurality of probes,
One or more of the probes are arranged in each group within the radio wave reachable distance of each terminal device,
the N is greater than the number of the plurality of channels;
The instruction unit causes the plurality of probes to sequentially switch the plurality of channels in synchronization in the same group unit, scan each channel for a scan period of t _scan , and group i (0 ≤ i ≤ N−1), the scan timing for the same channel is provided with an offset of i×t _offset (t _offset ≤ t _scan ) at the scan start time,
t _offset satisfies N x t _offset = number of channels x (t _scan + t _interval ),
The analyzer, wherein t _interval is the time required for each probe to switch channels to be scanned.

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