WO2015041068A1 - 無線通信システム、及び、無線通信方法 - Google Patents
無線通信システム、及び、無線通信方法 Download PDFInfo
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- WO2015041068A1 WO2015041068A1 PCT/JP2014/073450 JP2014073450W WO2015041068A1 WO 2015041068 A1 WO2015041068 A1 WO 2015041068A1 JP 2014073450 W JP2014073450 W JP 2014073450W WO 2015041068 A1 WO2015041068 A1 WO 2015041068A1
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- 238000004891 communication Methods 0.000 title claims abstract description 81
- 238000000034 method Methods 0.000 title claims description 51
- 230000005540 biological transmission Effects 0.000 claims description 19
- 238000001514 detection method Methods 0.000 description 22
- 238000012545 processing Methods 0.000 description 15
- 238000010586 diagram Methods 0.000 description 8
- 230000004913 activation Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 230000001149 cognitive effect Effects 0.000 description 2
- 230000002452 interceptive effect Effects 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0833—Random access procedures, e.g. with 4-step access
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/02—Resource partitioning among network components, e.g. reuse partitioning
- H04W16/10—Dynamic resource partitioning
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/14—Spectrum sharing arrangements between different networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W24/00—Supervisory, monitoring or testing arrangements
- H04W24/02—Arrangements for optimising operational condition
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W48/00—Access restriction; Network selection; Access point selection
- H04W48/16—Discovering, processing access restriction or access information
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/02—Terminal devices
Definitions
- the present invention relates to a wireless communication system using a white space, and particularly to a wireless communication system and a wireless communication method capable of preventing interference between secondary usage systems that do not use a database.
- FIG. 7 is a schematic configuration diagram of a wireless communication system including a database.
- the wireless communication system using a database includes a database 1, a frequency channel management manager 2, a base station 3, and a terminal station 4.
- the database 1 stores information on frequency channels and transmission power that can be used secondarily, and the frequency management manager 2 accesses the database 1 via the Internet at the start of communication. Based on the position information (latitude and longitude information) of the base station 3 and the terminal station 4, a list of available free frequency channels (channel list) is acquired. Then, the frequency management manager 2 selects a frequency channel to be used for communication from the channel list and notifies the base station 3 of it.
- the base station 3 communicates with the terminal 4 using the frequency channel selected by the frequency management manager 2, and the terminal station 4 receives the downlink signal from the base station 3 and uses the frequency channel to communicate with the base station 3. Communicate.
- the frequency management manager 2 is required for each base station 3, and the system is enlarged.
- the Internet connection is not always possible depending on the location where the base station 3 is installed. In that case, the database 1 cannot be accessed, and usable frequency channel information cannot be obtained.
- the base station 3 and the terminal station 4 select an available frequency using a spectrum sensing technique.
- the preset enables operation of the secondary usage system without referring to the database or performing strict sensing.
- a wireless communication system using a white space is expected to be used as an emergency or agile communication means at the time of a disaster as a backup line at the time of failure.
- it is considered to install a pair of portable base stations 3 and terminal stations 4 at two points where broadband transmission is desired, and use them at Point to Point.
- the terminal station 4 of the new entry system When the terminal station 4 of the new entry system has entered the communication area of the prior use system, the terminal station 4 of the new entry system detects a wireless station of another system by sensing if possible, This should be notified to the base station 3 of the new entry system.
- the terminal station 4 of the new entry system detects a wireless station of another system by sensing if possible, This should be notified to the base station 3 of the new entry system.
- it is necessary to perform a ranging process, authentication, registration, and the like, and communication accompanying the interference is an interference for a prior use system using the same frequency.
- the terminal station 4 of the new entry system tries to connect (initialize) to the base station 3 of the preceding use system.
- the terminal station 4 determines from the BS_ID (the MAC address of the base station) included in the SCH (superframe control header) received from the base station 3 whether the source base station 3 is a partner to be connected to.
- BS_ID the MAC address of the base station
- SCH superframe control header
- Patent Document 1 describes a management device for self-coexistence using the same frequency among a plurality of secondary systems of the same type based on information of adjacent secondary systems in a wireless communication system using white space. ing.
- the base station may change the transmission time interval of the synchronization signal according to the state of the network.
- Non-Patent Document 1 describes a wireless MAC (Medium Access Control) function such as “On Demand Channel Contention” in order to coexist at the same frequency among a plurality of secondary systems of the same type.
- a wireless MAC Medium Access Control
- a wireless communication system used as a conventional secondary usage system a plurality of wireless communication systems preset with the same frequency channel are brought into the same geographical area when a database cannot be accessed, such as in a disaster. In such a case, there is a problem that the new entry system interferes with the preceding use system.
- the base station transmits a preamble at a period of n times the frame length (n is an integer of 2 or more) at the time of activation, and the terminal station detects the preamble from the received signal.
- n is an integer of 2 or more
- the frequency is changed unless a ranging signal is transmitted when a preamble is detected only at a cycle of n times the frame length, and the base station does not receive the ranging signal within a predetermined time.
- the present invention has been made in view of the above circumstances, and an object thereof is to provide a wireless communication system and a wireless communication method capable of preventing interference between secondary usage systems that do not use a database.
- the present invention for solving the problems of the above-described conventional example is a wireless communication system in which a base station and a terminal station communicate in a one-to-one correspondence using a white space, and the base station and the terminal Communicates with the station in units of a super frame consisting of a plurality of frames, and the base station selects one from a list of available frequencies stored in advance in the startup process after power-on.
- the preamble is transmitted at a period of n times the frame length (n is an integer of 2 or more), and no ranging signal is received from the corresponding terminal station within a certain time after the preamble transmission at that period is started.
- a ranging signal is received from the corresponding terminal station within a certain time, communication with the terminal station is started and a preamble is transmitted with a frame length cycle.
- the terminal station selects and sets one from a list of available frequencies stored in advance, and detects the preamble from the received signal at the set frequency. If a preamble is detected with a frame length period, the frequency is changed and set. If a preamble is not detected with a frame length period and a preamble is detected with a period n times the frame length, , A ranging signal is transmitted at a set frequency.
- the base station detects the presence / absence of the base station and the terminal station of the preceding usage system based on the received signal at the set frequency, and the base station and the terminal of the preceding usage system If there is no station, preamble transmission is started at a cycle of n times the frame length, and if there is a base station or terminal station of the preceding usage system, the frequency is changed and set.
- the present invention provides the above wireless communication system, wherein the terminal station detects the presence or absence of the terminal station of the preceding usage system, transmits a ranging signal if there is no terminal station of the preceding usage system, If it exists, it is characterized by changing the frequency.
- a wireless communication system in which a base station and a terminal station communicate with each other on a one-to-one basis using a white space, and a plurality of frames are transmitted between the base station and the terminal station.
- the base station selects and sets one from a list of available frequencies stored in advance, and is n times the frame length. If the preamble is transmitted with a period of (n is an integer of 2 or more), and the ranging signal from the corresponding terminal station is not received within a certain time after starting the preamble transmission with the period, the frequency is changed.
- a ranging signal When a ranging signal is received from a corresponding terminal station within a certain time, communication with the terminal station is started and a preamble is transmitted at a cycle of the frame length.
- select and set one from a list of available frequencies stored in advance detect the preamble from the received signal at the set frequency, and detect the preamble in the cycle of the frame length If the frequency is changed, the frequency is changed, and the preamble is not detected in the period of the frame length. If the preamble is detected in the period of n times the frame length, a ranging signal is transmitted at the set frequency.
- the terminal station it is possible to determine the existence by distinguishing the base station of the prior use system and the base station of the new entry system, and without using a database or a frequency channel management manager. With the configuration, there is an effect that communication can be realized without interfering with the prior use system.
- the base station detects the presence / absence of the base station and terminal station of the preceding usage system based on the received signal at the set frequency, and if there is no base station and terminal station of the preceding usage system. Since the above wireless communication system is configured to start preamble transmission at a cycle of n times the frame length and change the frequency if there is a base station or terminal station of the preceding usage system, There is an effect that interference can be surely prevented.
- the terminal station detects the presence or absence of the terminal station of the preceding usage system, transmits a ranging signal if there is no terminal station of the preceding usage system, and sets the frequency if there is a terminal station of the preceding usage system. Since the wireless communication system is changed and set, there is an effect that it is possible to reliably prevent interference with the prior use system in the terminal station.
- a wireless communication system is a wireless communication system in which a base station and a terminal station communicate with each other on a one-to-one basis using a white space.
- a base station and a terminal station communicate with each other on a one-to-one basis using a white space.
- a frequency channel selected from preset frequency channels, and perform preamble monitoring / ranging monitoring for a certain period of time to detect the presence of surrounding pre-use systems and detect preamble signals or ranging signals If the channel is changed, the channel is changed. If the preamble signal and the ranging signal are not detected, the operation proceeds to the following preamble transmission operation.
- the base station performs an operation of transmitting a preamble at a cycle of n times the frame length (n ⁇ 2, n is an integer) until communication with the terminal station is established.
- n is an integer
- the normal operation is started by using the frequency channel, and communication can be realized with a simple configuration and without causing interference with a prior use system without using a database or a frequency channel management manager. .
- the radio communication system when the terminal station starts up, sets a preset frequency channel, detects a preamble in the received signal, and detects a peak for each frame length. Changes the frequency on the assumption that there is a base station of a prior use system, detects a peak at a cycle of n times the frame length, and does not detect a peak at other cycles, A ranging signal is transmitted so that communication is possible, and transition to normal communication is possible. It is possible to determine the presence / absence by distinguishing the radio station of the previous use system and the base station of the new entry system, and with a simple configuration, the previous use Communication can be realized without interfering with the system.
- FIG. 1 is a configuration diagram of a radio communication system according to an embodiment of the present invention.
- the radio communication system (this system) according to the embodiment of the present invention includes a base station 30 and a terminal station 40. That is, unlike the conventional secondary usage system, the database 1 and the frequency channel management manager 2 are not provided.
- the base station is configured as a portable system and cannot be connected to the Internet in the event of a disaster. Communication between the terminal 30 and the terminal station 40 can be realized autonomously.
- the base station 30 and the terminal station 40 basically include a communication unit that performs signal processing associated with wireless communication and a control unit that controls the entire apparatus.
- a storage unit for storing various programs and parameters is provided.
- one or a plurality of usable frequency channels are preset and stored as a usable frequency channel list.
- the overall configuration is the same as that of the conventional wireless communication system shown in FIG. 7, and the base station 3 is operated without accessing the database 1 or the frequency channel management manager 2. There may be.
- the wireless communication system is substantially configured to include only the base station 3 and the terminal station 4 and autonomously constructs a communication area.
- the base station 3 and the terminal station 4 perform the same processing as the base station 30 and the terminal station 40 of the present system in addition to the conventional processing. Therefore, the processing mode indicating which processing is to be performed can be set, and the processing mode set from the outside is operated.
- FIG. 2 is an explanatory diagram showing the configuration of the radio frame of this system.
- the IEEE 802.22 radio frame has a super frame (160 ms) as a unit, and one super frame is composed of 16 frames (frame 0 to frame 15) having a period of 10 ms. .
- Each frame is composed of a downlink subframe, an uplink subframe, and a self-coexistence (coexistence) window (not essential) in this order, and includes 24 to 41 OFDM (Orthogonal Frequency Division Multiplexing) symbols.
- OFDM Orthogonal Frequency Division Multiplexing
- a preamble is arranged at the head of the downlink subframe, followed by MAP information indicating the arrangement of downlink and uplink bursts, a frame control header (FCH), and the like. Are arranged in the order of subchannels on the MAC).
- the FCH includes information such as the length of the frame and the length of the MAP information.
- the preamble is known information between radio stations (between the base station 30 and the terminal station 40), and is used for synchronization and identification between radio stations.
- a super frame preamble is provided before the preamble, and a super frame control header (SCH) is provided after the preamble.
- SCH super frame control header
- the base station transmits a preamble that is normally transmitted at a frame period in a normal n (n ⁇ 2, n is an integer) multiple period in a process at startup. This will be described later.
- FIG. 3 is a flowchart showing processing at the time of activation in the base station of the present system.
- the base station 30 of this system basically starts (initializes) as defined in “7.14.1 BS initialization” of Non-Patent Document 1, but here, for the sake of simplicity, the characteristic portion Explain and explain.
- the process of FIG. 3 is performed in the control unit of the base station 30.
- the base station 30 when the power is turned on, the base station 30 performs initial channel setting (S11).
- the channel is set by selecting one of the frequencies registered in the available frequency channel list stored in advance.
- the base station 30 checks whether a base station or a terminal of the preceding usage system exists in the vicinity as the preceding usage system detection process (S12). Specifically, the base station 30 receives a radio signal on the set channel, measures the received signal strength (RSSI; Received Signal Strength Indicator). Judge that the station exists.
- RSSI Received Signal Strength Indicator
- the preamble can be detected by calculating the cross-correlation between the received signal and the known (fixed) preamble or the auto-correlation of the received signal.
- the power of only the signal (RSSL; Received WRAN Signal Strength) can be obtained.
- RSSL Received WRAN Signal Strength
- the same time waveform is repeated 4 times (5 times including CP) in one OFDM symbol time, and in the frame preamble, it becomes a specific symbol that is repeated twice.
- an autocorrelation peak can be detected.
- Non-Patent Document 1 reception of a CBP (Co-Existence Beacon Protocol) burst preamble is also attempted.
- the base station 30 of this system can determine the presence of a base station and a terminal station of the same type system with high accuracy.
- the preamble is detected by a preamble detection circuit described later.
- the base station 30 determines whether or not there is a base station or a terminal station of the preceding usage system based on the detection of the preamble (S13). “Yes” is determined when the preamble is detected at a predetermined intensity or higher at regular 10 ms intervals (in the case of Yes), and in that case, the base station 30 proceeds to the channel change process of process S17. And set another channel. In the channel change process (S17), the base station 30 preferentially selects one unused channel from the available frequency list and sets the channel. And the base station 30 returns to process S12, and similarly performs a detection process of a prior
- the base station 30 When the base station and the terminal station of the preceding usage system are not detected in the process S13 (in the case of No), the base station 30 starts the initial operation (S14).
- the period from when the base station 30 of this system receives the ranging signal from the terminal station 40 until normal operation becomes possible is the initial operation.
- the base station 30 Transmits the preamble intermittently.
- the superframe preamble is transmitted at the head of the superframe as in the conventional case.
- the preamble transmission cycle is set to n times (n is an integer of 2 or more), for example, 3 times the frame length (here, 10 ms). That is, the base station 30 transmits a preamble at a cycle of 30 ms (once every 3 frames).
- the terminal station 40 side can distinguish and detect the base station of the prior use system and the base station 30 of the present system.
- Another preamble that is newly defined is transmitted so that the head of a frame that does not transmit a preamble is not detected by a method of detecting a null or regular preamble.
- the frame itself may not be transmitted.
- the base station 30 waits for the ranging signal (RNG-REQ) from the terminal station 40 (S15), and determines whether the ranging signal from the terminal station 40 is detected within a certain time (S16). If the base station 30 cannot detect the ranging signal from the terminal station 40 within a predetermined time (in the case of No), the base station 30 determines that the terminal station 40 cannot communicate with the currently set channel, and the process S17 Go to and change the channel.
- RNG-REQ ranging signal
- the base station 30 determines that communication with the terminal station 40 is established on the channel and starts normal operation. In normal operation, the preamble is transmitted for each frame as shown in FIG. In this way, processing at the time of activation in the base station of this system is performed.
- FIG. 4 is an explanatory diagram showing an overview of preamble detection in the terminal station 40 of this system.
- the base station 30 transmits a preamble signal at a cycle of n times (here, 3 times) the frame length only in the initial operation at the time of new entry, and when the base station 30 shifts to the normal operation, the frame length Send at periodic intervals.
- a peak appears every frame length (here, 10 ms).
- a peak occurs at a period three times the frame length.
- the terminal station 40 can obtain autocorrelation from the received preamble signal, and can determine the presence / absence of a preceding base station and the presence / absence of a new base station based on the detected peak position and size. It is.
- the terminal station 40 changes the setting channel because there is a preceding base station. And only when a peak as shown in FIG.4 (b) is detected, it becomes possible to aim at communication construction with the newly entered base station 30.
- FIG. 4 (a) or (c) a peak as shown in FIG. 4 (a) or (c) is detected.
- FIG. 5 is a flowchart showing processing at the time of activation in the terminal station 40 of the present system.
- the terminal station 40 of this system is basically activated (initialized) as defined in “7.14.2 CPE initialization” of the non-patent document. Excerpts will be explained.
- the process of FIG. 5 is performed in the control unit of the terminal station 40.
- the terminal station 40 when the power is turned on, the terminal station 40 sets a channel selected from the usable frequency channel list (S21). Then, the terminal station 40 performs a preamble detection process to detect a preamble signal from the base station of the same type system or the base station 30 of this system (S22).
- the base station of the prior use system that is already in normal operation transmits the preamble for each frame, but the base station of the newly entered system that has just started up transmits the preamble only once every three frames. Therefore, in process S22, an autocorrelation signal or the like is obtained by correlation calculation of the received signal, a preamble or a superframe preamble is detected, and the presence of a base station of the same type of a prior use system based on the detected peak period; The presence of the base station 30 of the present system can be distinguished and detected.
- the preamble detection process is performed by a preamble detection circuit described later.
- the terminal station 40 determines whether or not the preamble of the base station (preceding base station) of the preceding usage system has been detected. If the preceding base station is detected (in the case of Yes), the process proceeds to step S27 to change the channel. Process.
- the terminal station 40 attempts to detect an uplink signal (ranging signal) transmitted by the terminal station of the preceding usage system (S24).
- an uplink signal to be detected for example, RSSL detected by correlation calculation of CP or pilot subcarrier, CDMA (Code Division Multiple Access) known to be transmitted on a specific subchannel of an uplink subframe Connection) signal (up-ranging signal), CBP burst preamble, or the like.
- IEEE 802.22 stipulates that terminal stations periodically transmit ranging signals not only during initialization but also during normal operation.
- CDMA signals include bandwidth requests and detection of existing systems. These may be reported, and the terminal station 40 of the new entry system may detect these.
- the terminal station 40 determines whether or not any uplink signal is detected in step S24 (S25). If any uplink signal is detected (Yes), the terminal station 40 determines that there is a terminal station of the preceding usage system nearby. Then, the process proceeds to process S27 to change the set channel frequency.
- the terminal station 40 obtains the preamble signal of the base station 30 of the new entry system by the correlation calculation of the reception signal continued from the process S22. It is determined whether or not it has been detected (S26). If it cannot be detected (in the case of No), it is determined that there is no base station to be connected, and the process proceeds to channel change processing in step S27.
- the terminal station 40 shifts to a normal initial operation and starts transmitting an initial ranging signal (upstream ranging signal) (S28). .
- This operation is as described in “7.14.2.8.1 CDMA initial ranging and automatic adjustments” of Non-Patent Document 1, and establishes synchronization with the downlink signal from the base station 30 and performs initial ranging from the decoded US-MAP. Find information of some initial ranging codes from the interval and UCD, select one at random, send a ranging signal (RNG-REQ) when transmission opportunity comes, and shift to normal communication operation .
- the transmission power at the time of transmitting the ranging signal includes the strength of the downlink signal (RSSL) measured from the base station 30 and the transmission power (EIRP: Effective Isotropically) indicated by the DID obtained by decoding the downlink signal. Based on (Radiated Power; effective isotropic radiation power), etc., the power is set to a level that can be received by the base station 30. In other words, even if this power is obeyed, it is not guaranteed that it will not interfere with other prior use systems.
- the ranging signal is specified to include a character string in the NMEA0813 format that is a measurement result of GPS (Global Positioning System).
- GPS Global Positioning System
- FIG. 6 is a block diagram showing the configuration of the preamble detection circuit.
- the preamble detection circuit determines whether or not there is a preamble of one frame period in the input received baseband signal and outputs it, and is provided in the communication unit of the base station 30 and the terminal station 40.
- the preamble detection circuit of the base station 30 and the terminal station 40 of this system includes an autocorrelator 31, a maximum value detector 32, a delay unit 33, a comparator 34, and an averager 35. And a determiner 36.
- the autocorrelator 31 stores a known pattern of the preamble signal and calculates the autocorrelation of the received preamble signal.
- the maximum value detector 32 receives the autocorrelation result, detects the maximum value (power value) within a set specific time (usually one frame time, here 10 ms), and its time position and outputs it. Specifically, the maximum value is detected in the first one frame time, the maximum value and time (timing) are output, held inside, and the maximum value detection is continued and held for one frame time starting from that position. When a value larger than a value obtained by multiplying the maximum value by a preset coefficient is detected, the maximum value and position to be held are updated. When the maximum value is not detected, the maximum value (maximum value) is again reached in the vicinity of one frame time. It is determined whether the maximum value is detected. If the maximum value is detected, the maximum value and position are output and the maximum value and position held inside are updated.
- the comparator 34 compares the position of the previous maximum value delayed by the delay unit 33 with the position of the current maximum value, and when the interval is greatly different from an assumed one frame period, the averager 35 To reset.
- the averager 35 averages the maximum value from the maximum value detector 32 and outputs the average value to the determiner 36.
- the determiner 36 determines whether the output from the averager 35 exceeds a preset threshold value, and outputs a detection result indicating that there is a preamble if it exceeds.
- the detection period of the maximum value detector 32 may be set to n frame time.
- the base station 30 detects the preamble and detects the presence of the preceding base station and terminal station of the same type system. Further, as shown in FIG. 5, the control unit of the terminal station 40 distinguishes and recognizes the presence of the preceding base station and the new entry base station based on the preamble detection period and its size.
- the base station 30 in the wireless communication system in which the base station and the terminal station communicate one-to-one using the white space, the base station 30 However, at the time of activation, a frequency channel selected from preset frequency channels is set, the preamble is transmitted in a cycle of n times the frame length (n ⁇ 2, n is an integer), and preamble transmission in that cycle is started. Later, when ranging from the corresponding terminal station 40 is not detected within a certain time, the frequency channel is changed, and when ranging from the terminal station 40 is detected within a certain time, the frequency channel is normally used.
- the terminal station 40 When the terminal station 40 starts operation, it sets a preset frequency channel, detects a preamble in the received signal, When a peak is detected every time, the frequency is changed, and a peak is detected at a period of n times the frame length, and when no peak is detected at other periods, a ranging signal is transmitted. Therefore, on the terminal station 40 side, by detecting the preamble, it is possible to distinguish the base station 30 of the prior use system and the base station 30 of the new entry system and determine the existence, and use the database and the frequency channel management manager. In addition, there is an effect that communication can be realized with a simple configuration without causing interference to the prior use system.
- the present invention is suitable for a wireless communication system that can prevent interference between secondary usage systems that do not use a database.
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Abstract
Description
ホワイトスペースを活用した無線通信システムでは、割り当てられた周波数を使用する免許を有する既存の無線システム(一次利用システム)と、免許を持たず、一次利用システムが利用していない周波数スペクトル(ホワイトスペース)を、一次的若しくは限定された地域において利用する二次利用システムとがある。
図7に示すように、データベースを利用する無線通信システムは、データベース1と、周波数チャネル管理マネージャ2と、基地局3と、端末局4とを備えている。
そして、周波数管理マネージャ2は、チャネルリストの中から通信に使用する周波数チャネルを選定して、基地局3に通知する。
データベースを利用した無線通信システムでは、基地局3毎に周波数管理マネージャ2が必要になり、システムが肥大化する。
その場合、データベース1へアクセスすることができず、使用可能な周波数チャネル情報が得られない。
データベースを利用しないシステムでは、基地局3及び端末局4がスペクトラムセンシング技術を用いて、利用可能な周波数を選択するようにしている。
また、2次利用システムが複数存在し得る場合には、周波数が重複しないように、個々のシステムに1チャンネルずつ割り振ることも考えられる。
例えば、可搬型の一対の基地局3と端末局4とを、ブロードバンド伝送を行いたい2地点にそれぞれ設置し、Point to Pointで使用することが検討されている。
しかし、通知するためには、レンジングプロセス、認証、登録等を行う必要があり、それに伴う通信が同一周波数を使用している先行利用システムにとって干渉になる。
端末局4が、基地局3から受信したSCH(スーパーフレーム制御ヘッダ)に含まれるBS_ID(基地局のMACアドレス)から、送信元の基地局3が接続すべき相手であるか否かを判断するように設定することは可能であるが、このような設定をエンドユーザに求めることは困難であり、また、これに依存すると運用に柔軟性を欠く。
基地局は、プリアンブル送信動作として、端末局と通信確立するまではプリアンブルをフレーム長のn倍(n≧2,nは整数)周期で送信する動作を行い、新規参入システムの基地局と先行利用システムの基地局との区別を可能とし、一定時間以内に対応する端末局からのレンジングが検出されない場合には周波数チャネルを変更し、一定時間以内に端末局からのレンジングを検出した場合には、当該周波数チャネルを用いて通常運用を開始するものであり、データベースや周波数チャネル管理マネージャを用いることなく、簡易な構成で、先行利用システムに干渉を与えずに通信を実現することができるものである。
図1に示すように、本発明の実施の形態に係る無線通信システム(本システム)は、基地局30と、端末局40とを備えている。
つまり、本従来の2次利用システムのように、データベース1及び周波数チャネル管理マネージャ2は設けられておらず、例えば、可搬型のシステムとして構成され、災害時等にインターネットに接続できない場所でも基地局30と端末局40との間で自律的に通信を実現できるものである。
基地局30及び端末局40には、予め1つ又は複数の使用可能周波数チャネルがプリセットされ、使用可能周波数チャネルリストとして記憶されている。
この場合、実質的には、基地局3と、端末局4のみを備えた構成となり、自律的に通信エリアを構築する無線通信システムとなる。
基地局30及び端末局40の処理について説明する前に、IEEE 802.22 の無線フレームの構成について図2を用いて説明する。図2は、本システムの無線フレームの構成を示す説明図である。
図2に示すように、IEEE 802.22 の無線フレームは、スーパーフレーム(160ms)を単位としており、1つのスーパーフレームは、10msの周期を有する16個のフレーム(フレーム0~フレーム15)で構成される。
FCHには、フレームの長さやMAP情報の長さ等の情報が含まれる。
プリアンブルは、無線局間(基地局30と端末局40との間)において既知の情報であり、無線局間での同期や識別に用いられる。
尚、本システムの基地局30は、基本的には、非特許文献1の"7.14.1 BS initialization"に規定されるような起動(初期化)を行うが、ここでは簡単のために特徴部分を抜粋して説明する。
図3の処理は、基地局30の制御部において行われる。
具体的には、基地局30は、設定されたチャネルで無線信号を受信し、その受信信号強度(RSSI;Received Signal Strength Indicator)を測定し、一定値以上の強度であれば先行利用システムの無線局が存在すると判断する。
IEEE 802.22の場合、スーパーフレームプリアンブルでは、1OFDMシンボル時間に同じ時間波形が4回(CPも含めれば5回)繰り返され、フレームプリアンブルでは2回繰り返される特異的なシンボルとなるため、所定のタイムラグで相関演算すると、自己相関のピークが検出できる。
本システムの基地局30では、これらの方法を組み合わせることで、同種システムの基地局及び端末局の存在を高い精度で判定することができる。プリアンブルの検出は、後述するプリアンブル検出回路で行われる。
チャネル変更処理(S17)では、基地局30は、使用可能周波数リストから未使用のチャネルを優先して1つ選び、そのチャネルを設定する。
そして、基地局30は、処理S12に戻って、同様に先行利用システムの検出処理を行う。
ここでは、本システムの基地局30が端末局40からのレンジング信号を受信して通常運用が可能となるまでの期間を初期運用としており、本システムの特徴として、基地局30は、初期運用においてはプリアンブルを間欠的に送信する。
尚、スーパーフレームプリアンブルは、従来と同様にスーパーフレームの先頭で送信する。
基地局30がプリアンブルの送信周期を変更することにより、端末局40側において、先行利用システムの基地局と、本システムの基地局30とを区別して検出することができるものである。
あるいは、フレームそのものを送信しないようにしてもよい。
基地局30は、一定時間内に端末局40からのレンジング信号を検出できなかった場合(Noの場合)には、端末局40が現在設定されているチャネルでは通信できないものと判断し、処理S17に移行してチャネルを変更する。
このようにして本システムの基地局における起動時の処理が行われる。
上述したように、本システムでは、基地局30は、新規参入時の初期運用においてのみ、フレーム長のn倍(ここでは3倍)の周期でプリアンブル信号を送信し、通常運用に移行するとフレーム長周期で送信する。
また、図4(b)に示すように、端末局40の近くに新規参入した本システムの基地局30のみが存在する場合、フレーム長の3倍の周期でピークが発生する。
そして、図4(b)に示すようなピークが検出された場合のみ、新規参入の基地局30との通信構築を図ることが可能となるものである。
尚、本システムの端末局40は、基本的には、非特許文献の"7.14.2 CPE initialization"に規定されるように起動(初期化)を行うが、ここでは簡単のために特徴部分を抜粋して説明する。
図5の処理は、端末局40の制御部において行われる。
そして、端末局40は、プリアンブル検出処理を行って、同種システムの基地局、あるいは本システムの基地局30からのプリアンブル信号を検出する(S22)。
そこで、処理S22では、受信信号の相関演算により自己相関信号等を得て、プリアンブルやスーパーフレームプリアンブルを検出し、検出されたピークの周期に基づいて同種の先行利用システムの基地局の存在と、本システムの基地局30の存在を区別して検出することができるものである。
プリアンブル検出処理は、後述するプリアンブル検出回路で行われる。
検出する上り信号としては、例えば、CPやパイロットサブキャリアの相関検算で検出されるRSSL、上りサブフレームの特定のサブチャネルで送信されることが分かっているCDMA(Code Division Multiple Access;符号分割多元接続)信号(上りレンジング信号)、CBPバーストのプリアンブル等を用いることが可能である。
この動作は非特許文献1の "7.14.2.8.1 CDMA initial ranging and automatic adjustments"に記載されたとおりであり、基地局30からの下り信号と同期確立し、復号されたUS-MAPから初期レンジング間隔、UCDからいくつかの初期レンジングコードの情報をそれぞれ見つけ、コードをランダムに1つ選び、送信機会が訪れたときに、レンジング信号(RNG-REQ)を送信し、通常の通信動作に移行する。
つまり、この電力に従ったとしても他の先行利用システムへ干渉を与えないことが保証されているわけではない。
このようにして端末局40における起動時の処理が行われる。
プリアンブル検出回路は、入力された受信ベースバンド信号において、1フレーム周期のプリアンブルの有無を判定して出力するものであり、基地局30及び端末局40の通信部に設けられている。
図6に示すように、本システムの基地局30及び端末局40のプリアンブル検出回路は、自己相関器31と、最大値検出器32と、遅延器33と、比較器34と、平均化器35と、判定器36とを備えている。
最大値検出器32は、自己相関結果を入力し、設定された特定時間(通常は1フレーム時間、ここでは10ms)内の最大値(電力値)及びその時間位置を検出して出力する。
具体的には、最初の1フレーム時間で最大値を検出し、最大値及び時間(タイミング)を出力すると共に、内部に保持し、その位置から始まる1フレーム時間について最大値検出を続け、保持する最大値に予め設定された係数を乗じた値より大きなものが検出されたときには、保持する最大値及び位置を更新し、検出されないときには1フレーム時間が経過した付近で再び最大値(極大値)が検出されたかを判断し、最大値が検出されていれば、当該最大値及び位置を出力すると共に内部に保持する最大値及び位置を更新する。
平均化器35は、最大値検出器32からの最大値を平均化して判定器36に出力する。
判定器36は、平均化器35からの出力が、予め設定された閾値を超えているかどうかを判定して、超えていればプリアンブル有りを示す検出結果を出力する。
尚、nフレーム周期のプリアンブルを検出する場合には、最大値検出器32の検出期間をnフレーム時間にすればよい。
また、端末局40の制御部は、図5に示したように、プリアンブルの検出周期とその大きさとに基づいて、先行基地局及び新規参入基地局の存在を区別して認識するものである。
4,40...端末局、 31...自己相関器、 32...最大値検出器、 33...遅延器、 34...比較器、 35...平均化器、 36...判定器
Claims (8)
- ホワイトスペースを利用して、基地局と端末局とが1対1に対応して通信を行う無線通信システムであって、
前記基地局と前記端末局との間で、複数のフレームから成るスーパーフレームを単位として通信を行い、
前記基地局が、電源投入後の起動処理において、予め記憶された使用可能な周波数のリストの中から1つを選択して設定し、
前記フレーム長のn倍(nは2以上の整数)の周期でプリアンブルを送信し、
前記周期でのプリアンブル送信開始後、一定時間以内に前記対応する端末局からのレンジング信号を受信しなかった場合には、周波数を変更して設定し、前記一定時間以内に前記対応する端末局からのレンジング信号を受信した場合には、前記端末局との通信を開始して前記フレーム長の周期でプリアンブルを送信するものであり、
前記端末局が、電源投入後の起動処理において、予め記憶された使用可能な周波数のリストの中から1つを選択して設定し、
前記設定された周波数における受信信号からプリアンブルを検出し、前記フレーム長の周期でプリアンブルが検出された場合には、周波数を変更して設定し、前記フレーム長の周期ではプリアンブルが検出されず、前記フレーム長のn倍の周期でプリアンブルが検出された場合は、前記設定された周波数でレンジング信号を送信することを特徴とする無線通信システム。 - 基地局が、設定された周波数における受信信号に基づいて、先行利用システムの基地局及び端末局の有無を検出し、前記先行利用システムの基地局及び端末局がなければ、フレーム長のn倍の周期でプリアンブル送信を開始し、前記先行利用システムの基地局又は端末局があれば周波数を変更して設定することを特徴とする請求項1記載の無線通信システム。
- 端末局が、先行利用システムの端末局の有無を検出し、前記先行利用システムの端末局がなければレンジング信号を送信し、前記先行利用システムの端末局があれば周波数を変更して設定することを特徴とする請求項1記載の無線通信システム。
- 端末局が、先行利用システムの端末局の有無を検出し、前記先行利用システムの端末局がなければレンジング信号を送信し、前記先行利用システムの端末局があれば周波数を変更して設定することを特徴とする請求項2記載の無線通信システム。
- ホワイトスペースを利用して、基地局と端末局とが1対1に対応して複数のフレームから成るスーパーフレームを単位として通信を行う無線通信方法であって、
前記基地局が、電源投入後の起動処理において、予め記憶された使用可能な周波数のリストの中から1つを選択して設定するステップと、
前記基地局が、前記フレーム長のn倍(nは2以上の整数)の周期でプリアンブルを送信するステップと、
前記基地局が、前記周期でのプリアンブル送信開始後、一定時間以内に前記対応する端末局からのレンジング信号を受信しなかった場合には、周波数を変更して設定し、前記一定時間以内に前記対応する端末局からのレンジング信号を受信した場合には、前記端末局との通信を開始して前記フレーム長の周期でプリアンブルを送信するステップと、
前記端末局が、電源投入後の起動処理において、予め記憶された使用可能な周波数のリストの中から1つを選択して設定するステップと、
前記端末局が、前記設定された周波数における受信信号からプリアンブルを検出し、前記フレーム長の周期でプリアンブルが検出された場合には、周波数を変更して設定し、前記フレーム長の周期ではプリアンブルが検出されず、前記フレーム長のn倍の周期でプリアンブルが検出された場合は、前記設定された周波数でレンジング信号を送信するステップと、を有することを特徴とする無線通信方法。 - 基地局が、設定された周波数における受信信号に基づいて、先行利用システムの基地局及び端末局の有無を検出し、前記先行利用システムの基地局及び端末局がなければ、フレーム長のn倍の周期でプリアンブル送信を開始し、前記先行利用システムの基地局又は端末局があれば周波数を変更して設定するステップを有することを特徴とする請求項5記載の無線通信方法。
- 端末局が、先行利用システムの端末局の有無を検出し、前記先行利用システムの端末局がなければレンジング信号を送信し、前記先行利用システムの端末局があれば周波数を変更して設定するステップを有することを特徴とする請求項5記載の無線通信方法。
- 端末局が、先行利用システムの端末局の有無を検出し、前記先行利用システムの端末局がなければレンジング信号を送信し、前記先行利用システムの端末局があれば周波数を変更して設定するステップを有することを特徴とする請求項6記載の無線通信方法。
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