JP4861920B2 - Radio frequency selection method, radio communication device, and radio communication system - Google Patents

Description

  The present invention relates to a method for selecting a frequency channel that is less affected by interference signals in order to perform high-quality wireless communication between a mobile station and a base station in a wireless communication system.

  In recent years, the use of wireless systems using 2.4G band radio frequencies has been expanding as short-range wireless communication systems. In these wireless communication systems, many standards such as IEEE802.11b / g, Bluetooth, and Zigbee exist and are used as wireless communication system standards. All of these wireless communication standards are designed on the assumption that 2.4G band radio frequencies are used, and incorporate technologies for sharing radio frequency resources with other systems.

  IEEE802.11b / g measures the electric field strength called carrier sense before transmitting a radio signal, confirms that the electric field strength is sufficiently small and there is no radio signal of its own system or other systems, and Send. As a result, the same frequency can be shared by time division.

  In Bluetooth, the 2.4G band radio frequency is divided into a plurality of frequency channels, and radio communication is performed while changing the frequency channel at high speed. This technology is called FH (Frequency Hopping), and even if signal interference with another system occurs in a certain frequency channel, stable communication is ensured by moving to another frequency channel for communication.

  In addition, the 2.4G band wireless communication system is an easy-to-use frequency band that does not require a license worldwide, and it can reduce costs and reduce development costs due to the large volume of wireless devices and parts distributed. There are an increasing number of cases where 2.4G-band wireless communication systems are applied to various fields. One of them is a CBTC (Communication Based Train Control) system that uses a radio communication system to control railway closing.

  As the application field of 2.4G band wireless communication systems expands, wireless standards originally designed for data communication between personal computers may not be able to meet the demands of new application fields. For example, CBTC has a high demand for high reliability, and in addition to the conventional interference reduction technology defined by standards such as IEEE802.11b / g, a technology for selecting a frequency channel with less interference is required.

  As such a frequency selection technique, there is, for example, Patent Document 1. In Cited Document 1, the frequency channel allocation priority is determined based on the past usage history of frequency channels. A determination is made as to whether or not the frequency channels with the highest allocation priority can be used in order. Thus, there is a technique for selecting a frequency channel with the least interference signal from the past communication history.

JP 07-222232 A

  However, as a problem of these technologies, when the interference signal is communicating intermittently, the time during which the presence or absence of the interference signal is monitored does not match the time during which the interference signal is communicating, and the interference signal is correctly There is a problem that the communication status cannot be monitored.

  In the 2.4G band wireless communication system, a communication form called a packet communication system is the mainstream, and the packet communication system has a feature that the time occupied by one data and the generation time of data are random. For this reason, when monitoring an interference signal, since it is not known when the interference signal is generated, the monitoring time zone and the time zone when the interference signal is generated can only be expected to coincide with each other. As a result, there is a problem that a situation in which monitoring cannot be performed despite the presence of an interference signal occurs, and as a result, a frequency channel in which the interference signal exists is used.

  In order to solve the above problem, in the wireless communication system according to the present invention, a plurality of first wireless devices and a plurality of second wireless devices perform wireless communication, and the first wireless device is The means for selecting one frequency channel from a plurality of frequency channels and the communication state of the selected frequency channel are monitored, and if an interference signal is recognized within the monitoring time, the monitoring time is shortened and the monitoring time is reduced. Means for extending the monitoring time when no interference signal is recognized, means for determining one frequency channel as a communication channel in accordance with the status of the interference signal from a plurality of monitored frequency channels, and the determination Means for transmitting channel information related to the frequency channel to the second radio, and the second radio transmits a frequency channel corresponding to the received channel information to a communication channel. It means for setting, characterized by further comprising a means for performing the first radio data communication with the communication channel.

  That is, in a wireless communication system having a plurality of frequency channels and selecting a frequency channel to communicate from past frequency usage conditions, one period is divided into communication time and frequency usage time monitoring time, and within the monitoring time Each frequency channel is monitored by changing the frequency channel, and the monitoring time is changed according to the result.

  The first radio device and the second radio device each include a reception system device, a transmission system device, and a radio signal processing device.

  The receiving device of the first radio unit monitors the communication state of the selected frequency channel with means for selecting one frequency channel from a plurality of frequency channels, and recognizes an interference signal within the monitoring time. If there is no interference signal within the monitoring time, the monitoring time will be shortened.If there is no interference signal, the monitoring time will be extended. Means for determining a frequency channel as a communication channel.

  The transmission device of the first radio has means for transmitting channel information regarding the determined frequency channel to the second radio.

  The receiving apparatus of the second radio has means for setting a frequency channel corresponding to the received channel information as a communication channel.

  The transmission system apparatus of the second radio has means for performing data communication with the first radio through a communication channel.

  According to the present invention, even when there is an interference source that performs intermittent wireless communication, it is possible to appropriately grasp the frequency usage state and select a frequency channel with less interference.

  A wireless communication system to which the present invention is applied will be described in detail with reference to the drawings.

<Example 1>
First, a radio communication system in which a mobile station performs radio communication with a plurality of base stations while moving on a predetermined route will be described as an example.

  FIG. 2 shows an overall configuration diagram of the wireless communication system. There is a vehicle 202 that moves on a track 201, and a mobile station 203 is mounted on the vehicle 202. Two or more mobile stations 203 may be mounted in the vehicle. Along the track 201, base stations 204, 205, and 206 are installed at arbitrary intervals. While the vehicle 201 is moving, the mobile station 203 performs wireless communication with a base station existing in the vicinity.

  FIG. 3 shows a configuration diagram of a radio 301 used in the radio communication system. Radio 301 is used as the mobile station and base station in FIG.

  The radio 301 includes an antenna 302, a changeover switch 303, a transmission system device 304, a reception system device 305, a radio signal processing device 306, a bus 307, a CPU 308, and a memory 309.

  The antenna 302 transmits and receives radio waves that are radio signals.

  The changeover switch 303 is a switch for switching between the transmission system device 304 and the reception system device 305 and sharing the antenna.

  The transmission system device 304 is for transmitting the radio signal generated by the radio signal processing device 305.

  The reception system device 305 is for sending the received signal to the wireless signal processing device 306. The reception system device 305 has a function of monitoring interference signals.

  The wireless signal processing device 306 generates and analyzes a wireless signal. The wireless signal processing device 306, the CPU 308, and the memory 309 are connected by a bus 307, and exchange communication data.

  The CPU 308 performs processing of communication data stored in the memory 309 and communication control.

  FIG. 4 shows a time chart of wireless communication between the mobile station and the base station when the base station side determines the frequency channel.

  In this description, it is assumed that the radio has four frequency channels A, B, C, and D. A mobile station and a base station have a division called a communication cycle. In the base station, the communication cycle is divided into three types of processing: interference monitoring, channel determination / notification, and data communication. In the interference monitor, the base station measures the electric field strength in each frequency channel while switching the four types of frequency channels A, B, C, and D.

  As a result of interference monitoring, the frequency channel with the lowest electric field strength is determined as the communication channel. In this description, it is assumed that the C channel is determined.

  The base station transmits information on the determined C channel to the mobile station. On the other hand, the mobile station waits for channel information communication while sequentially switching the A to D channels.

  The mobile station that has received the channel information on the C channel returns a signal for notifying the base station that reception has been successful on the C channel. When the base station receives a response to the channel notification from the mobile station, it starts data communication. By repeating the communication cycle described above, the mobile station and the base station perform wireless communication.

  Next, a detailed procedure for the base station to perform interference monitoring will be described. FIG. 5 shows a monitor table for holding the result of interference monitoring. This table is stored on the memory of the base station, for example.

  In each of the frequency channels A to D, the weight and the monitor time value are held. Using this table, an interference monitor is performed according to the procedure shown in FIG.

  The time point when the interference monitoring shown in FIG. 4 is started corresponds to Start 601 in FIG.

  602: First, the base station sets channel A, which is the first frequency channel, to the radio.

  603: Next, the monitoring time of channel A, which is the current setting channel, is acquired from the monitor table.

  604: Next, the electric field strength is measured for the monitoring time.

  605: After the monitoring time has elapsed, a new average power value is calculated by combining the value of the electric field strength as the monitoring result with the average value of the past electric field strength. The weight value of the monitor table is updated with the calculated average power value.

  606: Next, it is determined whether the value of the new electric field strength is larger than a preset threshold value. If it is larger than the predetermined threshold, the monitoring time is shortened (607). On the other hand, if it is smaller than the predetermined threshold, the monitoring time is extended (608).

  This process shortens the monitoring time for channels that can clearly be determined to have interference signals, and extends the monitoring time for channels that cannot be determined to have interference signals, thereby making it possible to determine whether interference signals are present. The goal is to be faster and more accurate.

  If the new electric field strength value is larger than a preset threshold value, it means that the number of interference signals has increased, and it can be said that the communication environment has become worse. That is, it can be estimated that there is a high possibility that an interference signal exists in the channel to be monitored.

  That is, by shortening the monitoring time of the channel where it can be clearly determined that an interference signal exists, it is possible to determine whether or not an interference signal exists earlier.

  On the other hand, the fact that the new electric field strength value is smaller than the preset threshold value means that the communication environment may have become the same or better within the range of the current monitoring time, and the interference signal could not be found by chance. There can be both possibilities.

  Therefore, by extending the monitoring time of the channel that cannot clearly determine that there is an interference signal, the time range to be measured can be increased and more information can be collected for determining the presence of the interference signal. The presence of the interference signal can be performed more accurately.

  609: Next, it is determined whether there is a channel that has not been monitored.

  If there is a channel that has not been monitored, the channel is changed (610), and the process returns to 603 to repeat the same process. When monitoring of all channels is completed, the interference monitoring is terminated (611).

  Thus, by making the monitoring time in each frequency channel variable, it is possible to more accurately determine the presence or absence of an interference signal.

  In the flowchart of FIG. 6, a value other than the electric field strength may be used as a value for determining the presence or absence of an interference signal. For example, a value representing the communication quality of the error rate may be used. Similarly, as the weight held in the monitor table, an appropriate statistical value such as a maximum value or a median value may be used in addition to the average value.

  For example, when measuring the bit error rate, if the measured bit error rate value is smaller than a predetermined threshold, the monitoring time is shortened, and if the measured bit error rate value is larger than the predetermined threshold, the monitoring time is extended. .

  Further, regarding the method for changing the monitoring time, in addition to the determination method such as the magnitude with respect to the threshold value, for example, a method of sequentially assigning small monitoring times in descending order of weights of all channels, or a method of changing the monitoring time for all channels. .

  An example of a method for determining the extension / reduction time of the monitor time will be described below. For example, consider a case where a wireless communication system using 2.4G band radio waves is set to 60 ms for each of the four frequency channels. At this time, the total time required to monitor all channels is 240 ms, and the total time cannot be changed according to the system specifications.

  In a certain monitoring cycle, the A and B channels measure the electric field strength above the threshold, and when the C and D channels are below the threshold, the monitoring time of the A and B channels is set to 20 ms in the next monitoring cycle. Set the D channel monitoring time to 100 ms. The reason for determining these monitoring times will be described.

  In the 2.4G band, wireless LAN (IEEE802.11b / g) is widespread, and can be the most significant interference source. In a wireless LAN, a base station continuously transmits a beacon signal to establish a link connection with a mobile station. Since the transmission period of this beacon signal is 100 ms, there is a possibility that the beacon signal cannot be supplemented with a monitor time within 100 ms. Therefore, accurate and quick monitoring can be performed by setting the monitoring time to 100 ms or more and increasing the probability of supplementing the beacon signal.

  FIG. 7 shows a time chart of wireless communication between the mobile station and the base station when the mobile station side determines the frequency channel.

  In this description, it is assumed that the radio has four frequency channels A, B, C, and D. A mobile station and a base station have a division called a communication cycle.

  While the mobile station performs the frequency channel search, the base station transmits UW1 that repeatedly transmits fixed pattern data and UW2 that synchronizes downlink and uplink communication times.

  While performing the frequency channel search, the mobile station receives UW1 transmitted by the base stations 204, 205, and 206 on each frequency channel while switching the four types of frequency channels A, B, C, and D, and receives the received signals. Measure the power value. As a result of the frequency channel search, the frequency channel with the largest received power value is determined as the communication channel.

  Then, UW2 is received on the frequency channel, and the timing of the reception start time of the message is synchronized. In this description, it is assumed that the C channel is determined.

  The base station transmits downlink communication data on the C channel and receives uplink communication data. Similarly, the mobile station receives downlink communication data on the C channel and transmits uplink communication data. By repeating the communication cycle described above, the mobile station and the base station perform wireless communication.

  Next, a detailed procedure for performing a frequency search by the mobile station will be described. FIG. 8 is an example of a search table for holding the frequency channel search result. This search table is stored on the memory of the base station, for example.

  In each of the frequency channels A to D, the weight and the search time value are held. Using this table, a frequency channel search is performed according to the procedure shown in FIG.

  The time point at which the frequency channel search in FIG. 7 is started corresponds to Start 901 in FIG.

  902: The mobile station sets channel A, which is the first frequency channel, to the radio.

  903: Next, the search time for channel A, which is the currently set channel, is acquired from the search table.

  904: Next, the electric field strength is measured for the search time.

  905: After the search time has elapsed, a new average power value is calculated by combining the received power value as a search result with the average value of the past received power. The search table weight value is updated with the calculated average power value.

  906: Next, it is determined whether the value of the new received power is larger than a preset threshold value. If the new received power value is larger than a preset threshold value, the search time is shortened (907). If the new received power value is smaller than the preset threshold value, the search time is extended (908).

  If the value of the new received power is larger than the preset threshold value, it is considered that the communication environment has improved due to the distance between the base station and the mobile station being shortened. By obviously reducing the monitoring time of the channel where it can be determined that a desired communication signal exists, it is possible to determine whether a communication signal exists earlier.

  On the other hand, if the value of the new received signal is smaller than the preset threshold value, it is considered that the communication environment has deteriorated due to the distance between the base station and the mobile station becoming longer. Therefore, by extending the search time of the corresponding channel, the time range to be measured can be increased and more information can be collected for determining the presence of the communication signal. Can be determined more accurately.

  This process shortens the search time for channels that can clearly be determined to have interference signals, and extends the search time for channels that cannot be determined to have interference signals, thereby making it possible to determine whether interference signals exist. The goal is to be faster and more accurate.

  909: It is determined whether there is a channel that has not been searched.

  If there is a channel that has not been searched, the channel is changed (910), and the process returns to 903 to repeat the same processing. When the search for all channels is completed, the interference search is terminated (911).

  As described above, by making the search time in each frequency channel variable, it is possible to more accurately determine the presence or absence of an interference signal.

  In the flowchart of FIG. 9, the value for determining the communication quality may be other than the received power value, for example, a value such as an error rate may be used. Similarly, as the weight held in the search table, an appropriate statistical value such as a maximum value or a median value may be used in addition to the average value.

  For example, when measuring the bit error rate, if the measured bit error rate value is smaller than a predetermined threshold, the monitoring time is shortened, and if the measured bit error rate value is larger than the predetermined threshold, the monitoring time is extended. .

  In addition to the determination method such as the magnitude of the threshold, the search time changing method may be, for example, a method in which the search times for all channels are assigned in order of increasing weight for all channels, or a method for making the search times for all channels variable. May be.

  An example of a method for determining the extension / reduction time of the search time will be described below. For example, consider a case where, in a wireless communication system using 2.4G band radio waves, the search time for each of the four frequency channels is set to 60 ms. At this time, the total time required to search all channels is 240 ms, and the total time cannot be changed according to the system specifications.

  In a certain search cycle, the A and B channels measure the electric field strength above the threshold, and when the C and D channels are below the threshold, the search time for the A and B channels is set to 20 ms in the next search cycle. The search time for the D channel is 100 ms. If the transmission cycle of the preamble signal transmitted from the base station is designed to be 20 ms, there are five chances to receive the signal when the search time is 100 ms. By receiving signals multiple times and collecting more information on received power values, link connection can be reliably performed.

  As described above, in a system in which a train traveling on a track (on a track) and a base station along the track (wire) communicate wirelessly, changes in buildings along the track (track), a new wireless system The radio wave propagation environment may change dynamically due to an increase in the number of stations. Even in such an environment, the method described in the first embodiment can quickly grasp a change in the propagation environment, select an optimal frequency channel, and perform communication.

<Example 2>
The present invention can be applied to other than the wireless communication system shown in FIG. For example, the present invention can be applied to the system configuration in the production line shown in FIG. FIG. 10 shows a system configuration in which the moving body 1002 moves on a predetermined path 1001 such as a belt conveyor.

  A mobile station 1003 is attached to the mobile body 1002, and base stations 1004, 1005, and 1006 are installed along a predetermined route 1001. Each base station performs radio communication using frequency channels F1, F2, and F3, respectively. Even when a user 1007 of another radio device 1008 is performing radio communication at the frequency F4, each base station can select a frequency that does not interfere with the interference monitoring process described above.

<Example 3>
Also, the present invention can be applied to a wireless communication system configuration as shown in FIG. FIG. 11 shows a system configuration in which a plurality of mobile stations exist in a plane with respect to one base station. Even in such a general wireless communication system, according to the present invention, appropriate interference monitoring can be performed and a frequency channel with less interference can be used.

The flowchart of this invention. 1 is a system configuration diagram of Embodiment 1. FIG. 1 is a configuration diagram of a wireless device according to a first embodiment. The time chart of Example 1 which a base station side determines a channel. The monitor table of Example 1 which a base station side determines a channel. The flowchart of Example 1 by which the base station side determines a channel. 3 is a time chart of the first embodiment in which a mobile station side determines a channel. The search table of Example 1 which a mobile station side determines a channel. 1 is a flowchart of Embodiment 1 in which a mobile station side determines a channel. The system block diagram of Example 2. FIG. FIG. 6 is a system configuration diagram of Embodiment 3.

Explanation of symbols

  201: Track, 202: Vehicle, 203: Mobile station, 204: Base station, 205: Base station, 206: Base station, 301: Radio, 302: Antenna, 303: Changeover switch, 304: Transmission system, 305: Reception system device, 306: Radio signal processing device, 307: Bus, 308: CPU, 309: Memory, 1001: Belt conveyor, 1002: Mobile body, 1003: Mobile station, 1004: Base station, 1005: Base station, 1006: Base station, 1007: Base station, 1008: Base station, 1101: Base station, 1102: Mobile station, 1103: Mobile station, 1104: Mobile station.

Claims (19)

In a wireless communication system in which a first wireless device and a second wireless device perform wireless communication,
The first radio is
Means for selecting one frequency channel from a plurality of frequency channels;
Means for monitoring the communication state of the selected frequency channel, shortening the monitoring time if an interference signal is recognized within the monitoring time, and extending the monitoring time if no interference signal is recognized within the monitoring time;
Means for determining one frequency channel as a communication channel in accordance with the state of an interference signal from a plurality of monitored frequency channels;
Means for transmitting channel information relating to the determined frequency channel to the second radio,
The second radio is
Means for setting a frequency channel corresponding to the received channel information as a communication channel;
A wireless communication system comprising: means for performing data communication with the first wireless device using the communication channel. The first radio is a base station, and the second radio is a mobile station;
The wireless communication system according to claim 1, wherein the wireless communication is performed in a communication cycle having an interference monitoring period, a channel determination and notification period, and a data communication period. The first radio is a mobile station and the second radio is a base station;
The radio communication system according to claim 1, wherein the radio communication is performed in a communication cycle having a frequency channel search period, a downlink data communication period, and an uplink data communication period. The first wireless device and the second wireless device each include a reception system device, a transmission system device, and a wireless signal processing device,
The receiving system device of the first wireless device is:
Means for selecting one frequency channel from a plurality of frequency channels;
Means for monitoring the communication state of the selected frequency channel, shortening the monitoring time if an interference signal is recognized within the monitoring time, and extending the monitoring time if no interference signal is recognized within the monitoring time;
Means for determining one frequency channel as a communication channel according to the condition of the interference signal from among the plurality of monitored frequency channels;
The transmission system device of the first radio is
Means for transmitting channel information relating to the determined frequency channel to the second radio,
The receiving system device of the second radio is
Means for setting a frequency channel corresponding to the received channel information as a communication channel;
The transmission system device of the second radio is
The wireless communication system according to claim 1, further comprising means for performing data communication with the first wireless device using the communication channel.   3. The wireless communication according to claim 2, wherein the means for determining a communication channel by the first radio unit determines a frequency channel having the smallest interference signal as a communication channel among a plurality of monitored frequency channels. system.   4. The wireless communication according to claim 3, wherein said means for determining a communication channel by said first radio unit determines a frequency channel having the smallest interference signal as a communication channel among a plurality of monitored frequency channels. system.   When the selected frequency channel is monitored, the electric field strength is measured. When the measured electric field strength value is larger than a predetermined threshold, the monitoring time is shortened. When the measured electric field strength value is smaller than the predetermined threshold value, The wireless communication system according to claim 2, wherein the monitoring time is extended.   When monitoring the selected frequency channel, the received power is measured. When the measured received power value is larger than a predetermined threshold, the monitoring time is shortened. When the measured received power value is smaller than the predetermined threshold, 4. The wireless communication system according to claim 3, wherein the monitoring time is extended.   The bit error rate is measured when monitoring the selected frequency channel, and if the measured bit error rate value is smaller than a predetermined threshold, the monitoring time is shortened, and the measured bit error rate value is smaller than the predetermined threshold value. 3. The radio communication system according to claim 2, wherein the monitoring time is extended when the time is larger.   The bit error rate is measured when monitoring the selected frequency channel, and if the measured bit error rate value is smaller than a predetermined threshold, the monitoring time is shortened, and the measured bit error rate value is smaller than the predetermined threshold value. 4. The wireless communication system according to claim 3, wherein when the time is larger, the monitoring time is extended.   The wireless communication system according to claim 2, wherein the mobile station moves on a track, and the base station is located around the track.   The wireless communication system according to claim 3, wherein the mobile station moves on a track, and the base station is located around the track.   3. The wireless communication system according to claim 2, wherein the base station has a memory for holding a table in which past frequency usage conditions are recorded.   4. The wireless communication system according to claim 3, wherein the mobile station has a memory for holding a table in which past frequency usage conditions are recorded. In a wireless device that performs wireless communication with other wireless devices,
Means for selecting one frequency channel from a plurality of frequency channels;
Means for monitoring the communication state of the selected frequency channel, shortening the monitoring time if an interference signal is recognized within the monitoring time, and extending the monitoring time if no interference signal is recognized within the monitoring time;
Means for determining one frequency channel as a communication channel in accordance with the state of an interference signal from a plurality of monitored frequency channels;
Means for transmitting channel information relating to the determined frequency channel to the other wireless device. The wireless device includes a reception system device, a transmission system device, a wireless signal processing device, and a memory,
The receiving system device monitors a communication state of the selected frequency channel with a means for selecting one frequency channel from a plurality of frequency channels, and shortens the monitoring time when an interference signal is recognized within the monitoring time. If no interference signal is recognized within the monitoring time, one frequency channel is determined as a communication channel according to the status of the interference signal from means for extending the monitoring time and a plurality of monitored frequency channels. Means,
The transmission system device has means for transmitting channel information related to the determined frequency channel to the second radio,
The wireless signal processing device has means for performing modulation / demodulation processing of a wireless signal,
16. The wireless device according to claim 15, wherein the memory holds a table in which past frequency usage conditions are recorded.   16. The wireless device according to claim 15, wherein the wireless device determines a communication channel by determining a communication channel having the smallest interference signal among a plurality of monitored frequency channels.   The wireless device according to claim 15, wherein the wireless device is a base station, and the other wireless device is a mobile station.   The wireless device according to claim 15, wherein the wireless device is a mobile station, and the other wireless device is a base station.

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