JP5759319B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system, and more particularly, to a wireless communication system in which a mobile station and a base station perform high-quality wireless communication and are less affected by interference from other systems.

[Conventional technology]
In recent years, the use of wireless communication systems using the 2.4 GHz band, which is a usable band without a license, has been expanded. The 2.4 GHz band is called an ISM (Industry-Science-Medical) band, and is a system that conforms to wireless standards such as IEEE802.11 wireless LAN (Local Area Network), Bluetooth (registered trademark), Zigbee (registered trademark), etc. In addition, it is used for various industrial equipment and medical equipment.

In such an ISM band with a high degree of freedom of use, it is necessary not only to allow interference from other than its own system, but also to minimize the amount of interference given to other systems.
However, systems such as signal systems and monitoring systems are constantly communicating, and disconnection of communication may have a great social impact. For this reason, even in the ISM band, highly reliable communication must be performed without interruption of communication.

By the way, as one of train signal systems, there is a CBTC (Communication-Based Train Control) system in which a train is controlled by communication between a mobile station mounted on a train and a base station installed on the ground.
When a mobile station moves at a high speed as in the CBTC system, the state of interference received is changing at a high speed from time to time, and it becomes more difficult to realize highly reliable communication in the ISM band.

Frequency hopping is widely used as an interference avoidance measure in the ISM band. In particular, Bluetooth (registered trademark) or the like employs a method of actively avoiding the use of frequency channels with much interference by adaptive frequency hopping.
In general, in adaptive frequency hopping, a communication quality log is acquired, information is exchanged between transmission and reception terminals, and a hopping pattern is determined by exchanging a hopping pattern based on the information.

[Related technologies]
As related prior art, Japanese Patent Laid-Open No. 2009-225135 “Frequency channel selection method and on-board radio terminal in train radio communication system” (Hitachi, Ltd.) [Patent Document 1], Japanese Patent Laid-Open No. 2009-171078 There is a publication "Radio communication system, base station and frequency channel selection method" (Hitachi, Ltd.) [Patent Document 2].

  In Patent Document 1, a front terminal and a rear terminal mounted on a train search for a transmission frequency channel during a channel search period, and while traveling in an area where both the first and second frequency channels are detected in reception strength. It is shown that downlink messages are received via different base stations by selecting different frequency channels.

  In Patent Document 2, each base station has first and second hopping tables in which frequency channels are set in advance so that interference with adjacent base stations does not occur, and hopping that is used according to the state of interference signals. Shown to select a table.

JP 2009-225135 A JP 2009-171078 A

  However, in a wireless communication system using a conventional frequency hopping method, it is necessary to acquire logs and exchange information about all channels, and further to exchange the determined hopping pattern. Since time is required and communication cannot be performed during this time, there is a problem that it is not suitable for a CBTC system or a monitoring system.

  In addition, in a conventional wireless communication system, there is a problem that communication with a mobile station moving at high speed cannot follow interference that changes at high speed with time, and may not be able to obtain sufficient communication quality. there were.

  The present invention has been made in view of the above circumstances, and is applied to train signal systems and monitoring systems such as CBTC that always perform wireless communication while considering interference with other systems, and moves that move faster. An object of the present invention is to provide a wireless communication system capable of obtaining sufficient quality through communication with a station.

  The present invention for solving the problems of the conventional example described above is a wireless communication system that performs communication using a frequency hopping method, and performs carrier sense on a plurality of channels that can be used in a superframe, and Select a channel with low interference, perform channel search for a base station that transmits a unique word multiple times using the selected channel, and a unique word transmitted multiple times from the base station, and select a channel to be used for the channel search. A mobile station that performs a carrier sense on a plurality of channels that can be used in the next superframe determined from the determined channel and transmits the result of the carrier sense to the base station as channel quality information. To do.

  According to the present invention, in the above wireless communication system, the base station performs carrier sense for a plurality of channels that can be used in the superframe, and refers to the line quality information transmitted from the mobile station, and the result of carrier sense and the line A channel with low interference is selected based on quality information.

  The present invention is characterized in that, in the wireless communication system described above, the base station stores a frequency hopping pattern including a plurality of channels that can be used in a superframe in a storage unit.

  According to the present invention, in the wireless communication system, the mobile station stores a frequency hopping pattern including a plurality of channels that can be used in a superframe in a storage unit, and the following channel is determined from the determined channel and the frequency hopping pattern. A plurality of channels that can be used in a superframe are specified.

  In the wireless communication system according to the present invention, after the base station transmits the unique word a plurality of times using the selected channel, the base station transmits a downlink message including information on a plurality of channels that can be used in the next superframe, The mobile station receives a downlink message, and identifies a plurality of channels that can be used in the next superframe from the downlink message.

  According to the present invention, the base station performs carrier sense, selects a channel with low interference by the carrier sense, transmits a unique word multiple times using the selected channel, and the mobile station transmits multiple times from the base station. A channel search is performed for the transmitted unique word, a channel used by the channel search is determined, carrier sense is performed for a plurality of channels that can be used in the next superframe obtained from the determined channel, and the carrier sense Since the result is a wireless communication system that transmits the result to the base station as channel quality information, it is possible to avoid interference from other systems, minimize interference to other systems, and improve reliability. There is.

1 is a schematic diagram of a radio communication system according to an embodiment of the present invention. It is a block diagram of the configuration of the communication device of this system. It is the schematic which shows the allocation of a channel. It is explanatory drawing of the communication operation | movement of this system. It is a figure which shows the example of a hopping pattern.

Embodiments of the present invention will be described with reference to the drawings.
[Outline of the embodiment]
The radio communication system according to the embodiment of the present invention uses a frequency hopping pattern having a plurality of frequency use candidates for each phase, and in view of the feature that communication is performed periodically in both directions, the mobile station After receiving the message from the station, only the next use frequency channel candidate is carrier sensed, the obtained interference power information is transmitted together with the message to the base station, and the base station receiving it receives the next use frequency candidate. Only the carrier sense, and the interference power information received from the mobile station is combined, the frequency channel with the lowest interference power is selected, and the next transmission is performed using that channel. In the base station communication, interference from other systems can be avoided, and interference with other systems can be minimized, improving reliability.

The outline of the operation in the radio communication system according to the embodiment of the present invention will be described. The base station transmits a unique word a plurality of times using the selected frequency channel before transmitting a message to the mobile station.
The mobile station attempts to detect a unique word while switching the frequency channel during the channel search period, and recognizes the unique word having the highest received power as the frequency channel used by the base station.

When a message is sent from the base station to the mobile station, the mobile station performs reception on the recognized frequency channel, then refers to the frequency hopping pattern, then recognizes the frequency channel that the base station may use, Carrier sense is performed for all recognized frequency channels.
Then, the interference power information of each frequency channel and the message to the base station obtained by carrier sense are transmitted on the same frequency channel as when receiving the downlink message.

The base station that has received the message from the mobile station refers to the frequency hopping pattern, recognizes the candidate for the frequency channel to be used next, and performs carrier sense for all candidates. Then, it is determined from the interference power information from the mobile station and the interference power information of the base station that the frequency channel has the best channel quality, and is selected as the frequency channel used for the next transmission.
Then, the above process is repeatedly performed to realize highly reliable communication.

In the above wireless communication system, it is not necessary to exchange the minimum necessary carrier sense instead of all channels and the interference power information immediately before communication that is not a log, and the exchange of frequency channels and hopping patterns to be used. These features make it possible to communicate with mobile stations moving at high speed with high reliability.
In addition, since the mobile station recognizes the channel by detecting a unique word, even if phase information or hopping table information is lost for some reason, the mobile station correctly recognizes the channel to be used by channel search, and the communication is normal. It is also a feature that can be performed. This point also contributes to the realization of highly reliable communication.

  In the embodiment of the present invention, the radio communication system is particularly suitable for the 2.4 GHz band, which is the ISM band, but it is also effective when used for other ISM bands and frequency bands other than the ISM band.

[Wireless communication system: Fig. 1]
A radio communication system according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of a radio communication system according to an embodiment of the present invention.
As shown in FIG. 1, a wireless communication system (this system) according to an embodiment of the present invention includes a mobile station (MT: Mobile Terminal) 101, a base station (AP: Access Point) 102, a base station, and a wired connection. It is configured by a network 103 that is connected.
The network 103 may be a closed network with respect to a certain system or an open network having a connection with the outside of the system.
For example, as one method of configuring a train signal system, there is a method of forming a base station, a mobile station, a train control system, etc. in a closed network.
Then, characteristic communication in this system is performed between the mobile station 101 and the base station 102.

[Communication device: Fig. 2]
In the present system, a communication device constituting a mobile station and a base station will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the communication apparatus of this system.
As shown in FIG. 2, the communication apparatus (mobile station and base station) includes an antenna 201, a radio reception unit 202, a radio transmission unit 203, a circulator 204, a main control unit 205, and a baseband (BB: Base). Band) signal processing unit 206, MAC (Medium Access Control) processing unit 207, hopping pattern storage unit 208, phase storage unit 209, line quality storage unit 210, frequency channel selection / storage unit 211, and received power A detection unit 212 and an interface unit 213 are provided.

[Each part of communication device]
Next, each part of the communication device will be described.
The antenna 201 inputs and outputs radio signals.
The circulator 204 has a function of outputting the radio signal received by the antenna 201 to the radio reception unit 202 and a function of outputting the transmission signal generated by the radio transmission unit 203 to the antenna 201.

The radio reception unit 202 performs reception processing such as frequency conversion from a radio frequency band to a baseband signal for the signal input from the circulator 204, and outputs the reception signal subjected to the reception processing to the main control unit 205.
Radio transmission section 203 performs transmission processing such as frequency conversion from the baseband signal to each radio frequency channel on the transmission signal input from main control section 205 and outputs the result to circulator 204.

The main control unit 205 controls the entire radio.
Specifically, the main control unit 205 controls input / output of the reception signal input from the wireless reception unit 202 to the BB signal processing unit 206 to the interface unit 213, and inputs transmission data from the above units. The output is controlled and a transmission signal is output to the wireless transmission unit 203.

  A baseband (BB) signal processing unit 206 performs pilotband addition and error correction coding processing on the transmission signal to perform baseband modulation, and performs baseband demodulation on the reception signal to perform error correction decoding. Perform processing.

The MAC processing unit 207 controls the frequency channel to be used and transmission / reception timing, adds a radio identification ID to the packet, and recognizes the transmission source radio.
The hopping pattern storage unit 208 stores a hopping pattern.
The phase storage unit 209 stores a phase used for the next transmission.
The channel quality storage unit 210 stores a history of channel quality of each frequency channel.

The frequency channel selection / storage unit 211 selects and stores a frequency channel to be used.
The reception power detection unit 212 detects interference signal power, desired signal power, and the like. In particular, the reception power detection unit 212 performs carrier sense on candidate channels to be used in the next superframe, and the result of carrier sense is displayed in the main control unit 205. Output to.
The interface unit 213 performs input / output processing of data to be wirelessly communicated.

[Operation of main control unit of base station]
The main control unit 205 of the base station acquires candidates for the next transmission phase and frequency channel from the phase storage unit 209 and the hopping pattern storage unit 208, performs carrier sense on the candidate frequency channel at the reception power detection unit 212, and performs interference. The power is detected, and the detected interference power value is stored in the channel quality storage unit 210.

The main control unit 205 of the base station causes the frequency channel selection / storage unit 211 to refer to the line quality storage unit 210 to select and store a frequency channel having a small interference power value.
Further, the main control unit 205 of the base station causes the MAC processing unit 207 and the BB signal processing unit 206 to generate a message or a unique word signal, and uses the frequency channel stored in the frequency channel selection / storage unit 211, The generated signal is transmitted from the antenna 201 to the wireless transmission unit 203.

[Operation of main control unit of mobile station]
The main control unit 205 of the mobile station uses the received power detection unit 212 to perform channel search for all 16 channels, determines the frequency channel with the highest received power, and sends the frequency channel to the frequency selection / storage unit 211. Select and memorize.
The main control unit 205 of the mobile station performs downlink message reception processing using the BB signal processing unit 206 and the MAC processing unit 207 using the frequency channel stored in the frequency selection / storage unit 211.

Further, the main control unit 205 of the mobile station refers to the phase storage unit 209 and the hopping pattern storage unit 208, recognizes candidate frequency channels that can be used in the next superframe, and receives power detection units for the frequency channels. Let 212 perform carrier sense.
Further, the main control unit 205 of the mobile station stores the channel quality information as a result of the carrier sense in the channel quality storage unit 210, and stores it in the channel quality storage unit 209 using the BB signal processing unit 206 and the MAC processing unit 207. The generated line quality information and uplink message are generated as transmission signals, and the radio transmission unit 203 performs transmission processing using the frequency channel stored in the frequency channel selection / storage unit 211.

[Channel assignment: Fig. 3]
Next, channel assignment in this system will be described with reference to FIG. FIG. 3 is a schematic diagram illustrating channel assignment.
In this embodiment, as shown in FIG. 3, the range of 2.400 GHz to 2.480 GHz is divided into 16 channels, a band of 5 MHz is assigned to each frequency channel, and CH1, CH2, CH3 are assigned in ascending order from the lowest frequency channel. , CH4, CH5, CH6, CH7, CH8, CH9, CH10, CH11, CH12, CH13, CH14, CH15, and CH16 and channel numbers are assigned.

[Communication operation: Fig. 4]
Next, a communication operation in this system will be described with reference to FIG. FIG. 4 is an explanatory diagram of the communication operation of this system.
In particular, FIG. 4 shows an operation example of communication between the mobile station 101 and the base station 102.
As shown in FIG. 4, communication between the mobile station 101 and the base station 102 is performed by time division, and a superframe is used as one unit.

The structure of the superframe related to the base station (AP) 102 includes carrier sense 1, channel selection, unique word (UW) transmission, downlink message transmission, and uplink message and mobile station interference power information (channel quality information). Consists of each period for reception.
Here, UW transmission is transmitted a plurality of times in response to a channel search in which UW detection is performed for all channels (CH1 to CH16) on the mobile station side using the selected channel (CH1 in FIG. 4).
Further, downlink message transmission and uplink message reception are also performed using the selected channel (CH1).

On the other hand, the superframe configuration relating to the mobile station (MT) 101 is composed of channel search (UW detection), downlink message reception, carrier sense 2, and each period for transmission of uplink message and its own interference power information. Is done.
By performing a channel search for CH1 to CH16 at the mobile station, the UW transmitted on the channel (CH1) selected from the base station is detected, and the channel (CH1) from which the UW has been detected is used as the channel to be used to receive the downlink message. And the upstream message is transmitted.

Carrier sense 2 senses a carrier for a channel that may be used in the next superframe, and acquires channel quality information for the sensed channel.
Specifically, a channel that may be used in the next superframe is determined in advance (when it is determined as “CH5, CH9” in FIG. 4), and carrier sense is performed for the channel.

  Further, the base station 102 performs carrier sense on the usable channels (CH5, CH9) determined in advance in the next superframe in the next superframe, and receives the channel quality information (from the mobile station side) received from the mobile station 101. Channel selection is performed based on the quality information of “CH5, CH9”) and the channel quality information carrier-sensed by the base station 102 (the quality information of “CH5, CH9” on the base station side). In this case, one of CH5 and CH9 is selected.

  The channels that can be used in the next superframe have the hopping pattern shown in FIG. 5 below, and a table of channels that can be used in the next superframe is stored in each storage unit of the base station 102 and the mobile station 101. It is stored and referred to during carrier sense, and carrier sense is performed only for the corresponding channel.

Instead of maintaining a table of channels that the base station and mobile station can use in the next superframe, the base station only maintains a table, and the mobile station can use it in the next superframe with the contents of the downlink message. You may make it notify an easy channel.
In addition, the base station and mobile station do not maintain a table, but receive notification of channels that can be used in the next superframe from the upper station of the base station, and the base station notifies the mobile station of the channel with the contents of the downlink message. You may make it do.

[Hopping pattern: Fig. 5]
Next, a hopping pattern in this system will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of a hopping pattern. The hopping pattern in FIG. 5 is determined in relation to the phase.
In this system, communication is performed using the hopping pattern of FIG. 5, and it is assumed that the phase stored in the phase storage unit 209 is “1”, and the phase is advanced by one for each superframe. To do.

  Specifically, channels (CH1, CH13) selectable for phase “1” are channels (CH5, CH9) selectable for phase “2”, channels (CH2, CH14) selectable for phase “3” are selected. ) Are channels (CH6, CH10) selectable for phase “4”, channels (CH3, CH15) selectable for phase “5”, and channels (CH7, CH11) selectable for phase “6”. Channels (CH4, CH16) that can be selected for phase “7” and channels (CH8, CH12) that can be selected for phase “8” are set.

[Specific operation processing]
First, the main control unit 205 of the base station refers to the phase storage unit 209 and the hopping pattern storage unit 208, and acquires a phase and frequency channel candidate for the next transmission.
Specifically, the phase storage unit 209 recognizes that the next transmission is the phase “1”, and the hopping pattern storage unit 208 recognizes that the frequency channel candidates are “CH1” and “CH13”.

  Based on this information, during the carrier sense 1 period, the received power detection unit 212 performs carrier sense of the CH1 and CH13 frequency channels and detects interference power. The detected interference power is stored in the channel quality storage unit 210 as channel quality information.

Subsequently, the frequency channel selection / storage unit 211 refers to the channel quality information of the candidate channels (CH1 and CH13) stored in the channel quality storage unit 210 according to the command of the main control unit 205, and selects a channel with a small interference power. The frequency channel used for the next transmission is selected and stored.
At this time, when the information regarding the interference power from the mobile station is stored in the channel quality storage unit 210, the channel quality determination information is also used, and the channel with the smallest interference power is selected. In this embodiment, CH1 is selected as a channel with low interference power and good line quality.

Then, in response to a command from the main control unit 205, the MAC processing unit 207 and the BB signal processing unit 206 generate a message or a unique word (UW) signal. Further, the signal is switched to the frequency channel stored in the frequency channel selection / storage unit 211 by the wireless transmission unit 203 and transmitted from the antenna 201.
The base station first transmits a unique word a plurality of times using the selected CH1 prior to transmission of the downlink message.

Meanwhile, the mobile station uses the received power detection unit 212 during the channel search period to detect power for all 16 channels. The channel search is performed for all channels because, at this point, the mobile station does not recognize which base station it communicates with and the phase of each base station.
Then, the frequency selection / storage unit 211 determines that the frequency channel that has detected the highest received power is the frequency channel used by the base station, and stores the frequency channel.
At the same time, the main control unit 205 recognizes the current phase by referring to the hopping pattern storage unit 208 and stores the phase in the phase storage unit 209. Then, the main control unit 205 stands by as a reception waiting state for the downlink message.

  After transmitting the unique word from the base station, the radio transmission unit 203 of the base station switches to the selected and stored frequency channel according to the command of the main control unit 205, transmits a downlink message from the antenna 201, and the mobile station performs the main control. Reception is performed according to the command of the unit 205.

Subsequently, the mobile station performs carrier sense in order to investigate surrounding interference power.
The main control unit 205 of the mobile station recognizes that the current phase is “1” by referring to the phase storage unit 209 and the hopping pattern storage unit 208, and the base station uses for transmission in the next superframe. The frequency channel (CH5, CH9) corresponding to the phase “2” is recognized.
Then, the main control unit 205 of the mobile station detects the interference power by performing carrier sense for all the recognized frequency channel candidates using the reception power detection unit 212, and the result is used as the channel quality storage unit 209 of the mobile station. To remember.

  Then, the mobile station uses the BB signal processing unit 206 and the MAC processing unit 207 in accordance with an instruction from the main control unit 205 to generate channel quality information and an uplink message stored in the channel quality storage unit 209 as a transmission signal, The radio transmission unit 203 switches to the frequency channel stored in the frequency channel selection / storage unit 211, and then transmits using the antenna 201.

In the base station, in accordance with an instruction from the main control unit 205, the radio reception unit 202, the BB signal processing unit 207, and the MAC processing unit 208 receive the uplink message and the interference power information.
The interference power information transmitted from the mobile station is stored in the channel quality storage unit 210, and the value in the phase storage unit 210 is updated to “2” which is the next phase.

  Then, the base station performs carrier sense of CH5 and CH9 which are frequency channel candidates of phase “2” by the reception power detection unit 212, selects a channel based on the channel quality information obtained from the mobile station earlier, and selects the selected channel. A unique word and a downlink message are transmitted using.

As a selection criterion for a frequency channel with the best channel quality, a channel that has the smallest packet error rate in the downlink and uplink round trips may be selected based on a packet error rate table for interference power.
Alternatively, a maximum allowable interference power threshold value may be provided, and the interference power channel may be selected randomly from the interference power channels that are equal to or lower than the threshold value.
Alternatively, the maximum interference power in each frequency channel detected by the base station and the mobile station may be used as the interference power of each frequency channel, and the frequency channel having the minimum interference power may be selected.

In the channel search in the mobile station, in the above example, a search for detecting UW is performed for all channels CH1 to CH16, but the candidate channel used in the superframe is searched first. By doing so, the detection of UW can be made faster.
Also, the candidate channel used in the superframe is searched first, and if it is equal to or greater than the threshold for UW detection, the channel search is stopped by using that channel. Good.

[Effect of the embodiment]
According to this system, the overhead required for exchanging carrier sense time and line quality can be minimized by making carrier sense not only all 16 channels but only a plurality of candidate channels according to the frequency hopping pattern, Even when the mobile station (mobile terminal) moves at high speed, it is possible to preferentially use the frequency channel with the least interference from other systems, and there is an effect that highly reliable communication can be performed.
In addition, since the frequency candidates to be used are limited by the frequency hopping pattern, many channels can be used, and there is an effect that interference with other systems can be reduced.

  The present invention is applied to a train signal system such as CBTC or a monitoring system that constantly performs radio communication while considering interference with other systems, and obtains sufficient quality by communication with a mobile station that moves at a higher speed. It is suitable for a wireless communication system capable of

  101 ... mobile station, 102 ... base station, 103 ... backbone network, 201 ... antenna, 202 ... radio receiver, 203 ... radio transmitter, 204 ... circulator, 205 ... main control unit, 206 ... BB signal processing unit, 207 ... MAC processing unit, 208 ... hopping pattern storage unit, 209 ... phase storage unit, 210 ... line quality storage unit, 211 ... Frequency channel selection / storage unit, 212 ... Received power detection unit, 213 ... Interface unit

Claims (5)

A wireless communication system that performs communication using a frequency hopping method,
A base station that performs carrier sense on a plurality of channels that can be used in a superframe, selects a channel with low interference by the carrier sense, and transmits a unique word multiple times using the selected channel;
A channel search is performed for a unique word transmitted a plurality of times from the base station, a channel used in the channel search is determined, and carrier sense is performed for a plurality of channels that can be used in the next superframe obtained from the determined channel. And a mobile station that transmits the carrier sense result as channel quality information to the base station.   The base station performs carrier sense for a plurality of channels that can be used in the superframe, and refers to the channel quality information transmitted from the mobile station, and has low interference based on the carrier sense result and the channel quality information. The wireless communication system according to claim 1, wherein a channel is selected.   3. The wireless communication system according to claim 1, wherein the base station stores a frequency hopping pattern in which a plurality of channels that can be used in a superframe are set in a storage unit.   The mobile station stores a frequency hopping pattern including a plurality of channels that can be used in a superframe in a storage unit, and determines a plurality of channels that can be used in the next superframe from the determined channel and the frequency hopping pattern. The wireless communication system according to claim 1, wherein the wireless communication system is specified. After transmitting the unique word multiple times using the selected channel, the base station transmits a downlink message including information on multiple channels that can be used in the next superframe,
The radio communication system according to any one of claims 1 to 3, wherein the mobile station receives the downlink message and specifies a plurality of channels that can be used in a next superframe from the downlink message.

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