JP5771452B2 - Wireless device - Google Patents

Description

  The present invention relates to a radio apparatus used in a frequency sharing type radio communication system including a primary usage system that preferentially uses a frequency and a secondary usage system that secondary uses an empty frequency band of the primary usage system. About.

  With the recent development of wireless communication, high efficiency of frequency utilization is required. In order to use limited frequency resources more efficiently, wireless devices such as terminals and base stations have a function to recognize the surrounding radio wave conditions, and the wireless device selects the optimum frequency and method by itself for communication. A technique called cognitive radio is attracting attention (see, for example, Patent Document 1).

  The frequency sharing type wireless communication system uses a free frequency band (referred to as white space) that is not used temporally and spatially by a primary usage system that preferentially uses a frequency as another system (secondary usage system). ) Is used secondarily. The secondary usage system is required to use the vacant frequency band of the primary usage system so as not to interfere with the primary usage system as much as possible. For this reason, in the secondary usage system, it is necessary to perform sufficient spectrum sensing (signal detection) before transmitting data or during communication to confirm that the primary usage system does not use the frequency band.

JP 2011-71569 A

  However, in the prior art, since the detected bandwidth of the vacant frequency band in spectrum sensing is a fixed value, it is not possible to detect the vacant frequency band below the detected bandwidth. For this reason, even if there is a small amount of traffic in the secondary usage system and there is a free bandwidth that can be transmitted sufficiently, the transmission opportunity is lost.

  The present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide a radio apparatus capable of improving the transmission efficiency in the secondary usage system and enhancing the frequency utilization efficiency. is there.

In order to achieve the above object, a first aspect of the present invention is a radio apparatus used in a secondary usage system that secondarily uses an empty frequency band of a primary usage system that preferentially uses a frequency. Detecting means for detecting a vacant frequency band greater than or equal to a predetermined detected bandwidth by spectrum sensing; transmission means for wirelessly transmitting data with a predetermined transmission bandwidth using the detected vacant frequency band; and the secondary A determining unit that determines the detected bandwidth and the transmission bandwidth according to at least one of a traffic amount of a utilization system and a time length of a spectrum sensing section, and the detected bandwidth and the transmission determined by the determining unit based on the bandwidth, and a control means for variably controlling the transmission bandwidth of the detection target bandwidth and the transmission means of said detecting means, said transmission hand Wirelessly transmits the data, which is encoded speech, in a radio frame period corresponding to the speech encoding period, and the determining means supports the transmission bandwidth corresponding to a modulation rate at which a transmission time is within a predetermined time. and bandwidth in consideration of the roll-off rate to the symbol rate of the to be detected bandwidth and bandwidth in consideration of the guard band to the transmission bandwidth, said detecting means, said data is one line worth by said determining means When the detected bandwidth corresponding to the transmission bandwidth in the case of only a voice call is set, the free frequency band that can be used for transmission of the voice call for one line is detected. .

  According to a second aspect of the present invention, in the first aspect, the determining means sets the detected bandwidth wider as the time length of the spectrum sensing section is longer.

  That is, according to the present invention, it is possible to provide a radio apparatus capable of improving the transmission opportunity in the secondary usage system and increasing the frequency utilization efficiency.

1 is an overall view of a frequency sharing type wireless communication system. The figure which shows the structural example of a secondary usage system. The figure which shows the structural example of an IP packet. The block diagram which shows the structural example of the radio | wireless machine which concerns on one Embodiment of this invention. The figure which shows an example of a TDM-TDD frame structure. Explanatory drawing of the spectrum utilization method.

Embodiments of a wireless device according to the present invention will be described below with reference to the drawings.
FIG. 1 is an overall view of a frequency sharing type radio communication system. This system is a frequency sharing type wireless communication system including an existing system (primary use system) that preferentially uses frequencies and a secondary use system that secondarily uses a free frequency band of the existing system.

  In FIG. 1, an existing system base station 101 and an existing system terminal 102 perform wireless communication at a frequency f1. For example, when the existing system is a television broadcast, the existing system base station 101 corresponds to a transmitting station, the existing system terminal 102 corresponds to a television receiver in each home, and the communication area 103 of the existing system is a broadcasting area. The secondary usage system base station 104 and the secondary usage system terminals 105-1 to 105-3 control the transmission power and the usage frequency so as not to interfere with the existing system, and set the free frequency band (white space) to 2 Next use.

  In the example of FIG. 1, since the secondary usage system base station 104 and the secondary usage system terminals 105-1 and 105-2 are geographically separated from the existing system, transmission power control is performed so as not to cause interference. Thus, the same frequency f1 can be used. The secondary usage system terminals 105-1 and 105-2 communicate with each other by TDD (Time Division Duplex) using the frequency f1 via the secondary usage system base station 104. On the other hand, since the location of the secondary usage system terminal 105-3 is within the broadcast area 103, communication between the secondary usage system base station 104 and the terminal 105-3 does not interfere with the existing system. In addition, communication is performed using another frequency f2. The frequency f2 is a frequency that is determined to be an empty frequency as a result of spectrum sensing by the secondary usage system.

  In the secondary usage system, in order not to give interference to the existing system, it is sensed whether or not the radio signal of the existing system exists in the frequency to be used, and when it is determined that the frequency is empty, Start sending. In addition, transmission is periodically stopped during communication and spectrum sensing is executed. When a radio signal of an existing system is detected, the use of the frequency is immediately stopped and released. When it is assumed that the existing system is Japanese terrestrial digital broadcasting (ISDB-T) (when it is assumed that secondary use of the frequency for terrestrial digital broadcasting is permitted in the future), the channel bandwidth is 6 MHz. For this reason, the bandwidth of the vacant frequency to be detected is set to 6 MHz, and if the 6 MHz bandwidth of the channel or the 6 MHz × 3 bandwidth including both adjacent channels is available, it is used for secondary use. Broadband communication is possible. The idle frequency of this television broadcast is called TV white space.

  Temporary installation of a secondary usage system as a point-to-point link, for example, as a means of communication between shelters in a disaster-stricken area where existing communication infrastructure such as mobile phones cannot be used due to failure or inability to supply power when a disaster occurs Is assumed. In such applications, the demand for voice calls is higher than for broadband data communications.

  FIG. 2 shows a configuration example of the secondary usage system. In the figure, voice call information from m IP telephone terminals is transmitted point-to-point using a secondary usage system. IP telephone terminals 201-1 to 201-m and 206-1 to 206-m convert voice signals into IP packets a1-1 to a1-m and e1-1 to e1-m.

  FIG. 3 shows an ITU-T G.G. 729 (CS-ACELP) is used, and a configuration example of an IP packet when voice is packetized at a cycle of 20 msec is shown. The encoded audio data is generated at 20 bytes / 20 ms, and becomes 60 bytes / 20 msec by adding a UDP / RTP header 20 bytes and an IP header 20 bytes to it. The information speed in this case is 24 kbps, and the bandwidth required for transmission is narrower than broadband data communication (generally 500 kbps or more).

  The IP telephone terminals 201-1 to 201-m and 206-1 to 206-m are connected to the aggregation devices 202 and 205 by Ethernet (registered trademark). 1-a1-m and e1-1 to e1-m are aggregated / divided. At the time of transmission, the input IP packets for the m packets are aggregated, and the aggregated data b1 and d1 are output. At the time of reception, the received data b1 and d1 are divided into each IP packet and sent to the corresponding IP telephone terminal based on the IP address. The data b1 and d1 are transmitted to the other party by the secondary usage base station 203 and the secondary usage terminal 204.

  Regarding the connection process between the secondary usage base station 203 and the secondary usage terminal 204, control information (described later) is transmitted from the secondary usage base station 203 to the secondary usage terminal 204 after being temporarily installed in the disaster area and powered on. 5 is always received, and operates according to control parameters such as a use frequency, a bandwidth, and a frame configuration included in the control information. In the initial connection, the usage frequency, bandwidth, frame configuration and the like need to be known on the secondary usage terminal 204 side, and the following two methods are conceivable as a method for realizing it.

  As a first method, the bandwidth and frame configuration are set to predetermined settings, and the use frequency is spectrum sensing performed by the secondary use base station 203 among a plurality of candidate values, and an available free frequency is used. Send. The secondary usage terminal 204 scans and receives the candidate values of the above-mentioned several usage frequencies, recognizes a transmission signal from the secondary usage base station 203, and then starts communication.

As a second method, the bandwidth and frame configuration are set as predetermined, and another communication means (such as commercial radio) that can use the use frequency determined by spectrum sensing by the secondary use base station 203 is used. To the secondary usage terminal 204.
Next, radio devices provided in the secondary usage base station 203 and the secondary usage terminal 204 will be described. FIG. 4 is a block diagram showing a configuration example of this radio. The wireless device includes a data transmission unit 300, a bandwidth determination unit 301, a control unit 302, and a spectrum sensing unit 303, and the control unit 302 controls the other three units. The data transmission unit 300 includes an assembly / disassembly unit 304, an error correction unit 305, a modem unit 306, and a radio unit 307. The configuration of the secondary usage base station 203 and the secondary usage terminal 204 is the same except that the operations of the assembling / disassembling unit 304 in the control unit 302 and the data transmission unit 300 are different.

The assembling / disassembling unit 304 of the data transmission unit 300 performs frame assembly processing on the input data a2 from the aggregation device 202 at the time of transmission, and extracts and outputs the data a2 by disassembling the frame at the time of reception.
FIG. 5 shows a configuration example of the frame e2 assembled in the assembling / disassembling unit 304. Since communication is performed at one frequency, TDM (Time Division Multiplexing) and TDD (Time Division Duplex) systems are used. Hereinafter, each feed of the frame will be described.

In the spectrum sensing section 2000, transmission is stopped and spectrum sensing processing described later is performed. This process is executed by both the secondary usage base station 203 and the secondary usage terminal 204.
The subsequent first preamble 2001 to downlink data 2004 is a transmission section (transmission information) in the downlink direction (from the base station to the terminal).

The first preamble 2001 is used for frame synchronization, carrier recovery, clock recovery, and the like in downlink communication.
For example, the control information 2002 includes the following control parameters.
“Used frequency” is a used frequency in the current frame and the next frame determined based on the spectrum sensing result.

“Bandwidth” is the detected bandwidth and transmission bandwidth of the vacant frequency in the current frame and the next frame determined by the bandwidth determination unit 301.
“Frame configuration” is frame configuration information of the current frame, and specifies the size of each feed shown in FIG. The sizes of the downlink data 2004 and the uplink data 2006 change according to the traffic volume of the input data a2.

  The “modulation / demodulation method of the data portion” uses BPSK (Binary Phase Shift Keying) or QPSK (Quadrature Phase Shift Keying), which has strong noise resistance, because it cannot be retransmitted in the case of audio data that requires real-time performance.

“Data part error correction method” specifies no encoding (coding rate 1) or convolutional code (coding rate 1/2).
As a result of spectrum sensing at the secondary usage base station 203 or the secondary usage terminal 204, the “terminal transmission stop command” is determined that there is a signal of an existing system or the like in the usage frequency, and other free frequencies for backup are also used. If not, the secondary usage terminal 204 is instructed to stop transmission, and immediately after that, the transmission of the secondary usage base station 203 is also stopped. The procedure for restarting communication is the same as the initial connection described above.

The second preamble 2003 is provided to enable frame synchronization, carrier recovery, clock recovery, and the like in order to make the transmission bandwidth variable after this field.
Downlink data 2004 inserts downlink data (voice information) based on the frame configuration information included in the control information 2002.

The next field from the third preamble 2005 to the uplink traffic information 2008 is a transmission section (transmission information) in the uplink direction (from the terminal to the base station).
The third preamble 2005 is used for frame synchronization, carrier recovery, clock recovery and the like in uplink communication.

Uplink data 2006 inserts uplink data (voice information) based on the frame configuration information of control information 2002. Since uplink and downlink symmetric voice communication is assumed, the data amount of the downlink data 2004 and the uplink data 2006 is equal.
The spectrum sensing result 2007 is a spectrum sensing result reported from the secondary usage terminal 204.

  The uplink traffic information 2008 is the amount of uplink traffic notified from the secondary usage terminal 204, and the secondary usage base station 203 indicates the amount of uplink traffic when the secondary usage terminal 204 starts a new transmission. Information sent to recognize changes. The secondary usage base station 203 determines the transmission bandwidth by changing the other of the downlink traffic volume and the uplink traffic volume in accordance with the larger value.

  Actually, a gap time for transmission bandwidth switching is required between the control information 2002 and the second preamble 2003, and transmission / reception switching is performed between the downlink data 2004 and the third preamble 2005. The gap time is required, but the illustration is omitted.

  The error correction unit 305 performs error correction coding (convolution coding (coding rate 1/2)) on the control information 2002 in the frame e2 at the time of transmission, and the error correction method of the data part is determined by the control information 2002. When convolutional coding (coding rate 1/2) is specified, error correction coding is performed on downlink data 2004 and uplink data 2006, and a data string f2 after error correction coding is output. At the time of reception, error correction processing is performed on the demodulated reception data string f2, and a reception data string (frame) e2 after error correction is output.

  At the time of transmission, the modulation / demodulation unit 306 modulates the data of the data sequence f2 after error correction coding by the modulation method specified by the control information 2002, and outputs a modulated signal g2. At the time of reception, the baseband received signal g2 output from the wireless unit 307 is demodulated similarly using the demodulation method specified by the control information 2002, and the demodulated data f2 is output.

  Although the illustration of the internal configuration of the radio unit 307 is omitted, at the time of transmission, the transmission signal processing is performed on the modulated signal g2 based on the use frequency and bandwidth included in the control information b2 from the control unit 302. And the orthogonal modulation process which up-converts to a utilization frequency (carrier frequency) is performed, and the transmission radio wave h2 is transmitted through a power amplifier and a transmission antenna. At the time of reception, based on the use frequency and bandwidth from the control unit 302, an orthogonal demodulation process for down-converting the radio wave h2 from the partner station to the baseband frequency with respect to the signal received via the reception antenna and low noise amplifier, A reception filter process is performed and a baseband reception signal g2 is output.

  The spectrum sensing unit 303 detects the usage status of the radio wave d2 for the frequency and bandwidth included in the control information c2 from the control unit 302, and reports the presence / absence c2 of the signal as a result to the control unit 302. This process is executed in the spectrum sensing section 2000 having the frame configuration shown in FIG.

  The bandwidth determination unit 301 determines a setting value of the detection target bandwidth (detected bandwidth) of the free frequency and the transmission bandwidth setting value a3 according to the data amount of the input a2, and instructs the control unit 302 to . Based on this, the control unit 302 instructs the spectrum sensing unit 303 to set the detected bandwidth a3 determined by the bandwidth determination unit 301 as the detected bandwidth c2 of the vacant frequency. Further, it instructs the data transmission unit 300 to set the transmission bandwidth set value a3 determined by the bandwidth determination unit 301 as the transmission bandwidth by the control signal b2.

  The data transmission unit 300 operates based on the transmission bandwidth specified by the control unit 302 so as to vary the transmission bandwidth of the field after the second preamble 2003 in FIG. The detected bandwidth setting value and the transmission bandwidth setting value a3 may be configured to be switchable in several stages.

  Regarding the transmission bandwidth of the first preamble 2001 and the control information 2002 in FIG. 5, the bandwidth needs to be known on the secondary usage terminal 204 side, and the data amount of the control information 2002 depends on the traffic amount of the transmission information Therefore, a fixed bandwidth (for example, a minimum set value) is used.

  As a reference for determining the detected bandwidth setting value and the transmission bandwidth setting value a3 in the bandwidth determining unit 301, for example, in the frame configuration of FIG. 5, the transmission time of the section of the downlink data 2004 is a predetermined time. The bandwidth is obtained by modulating at a modulation speed that falls within the range, and adding the roll-off rate and guard band to the corresponding symbol rate. In this embodiment, the traffic volume of the downlink data 2004 and the uplink data 2006 are equal, and these fields have higher information transmission rates than the control information 2002, the spectrum sensing result 2007, and the uplink traffic information 2008. Traffic volume is used as a basis for bandwidth determination.

Next, a calculation example of bandwidth determination is shown. In the present embodiment, the calculation conditions are as follows.
As [Condition 1], the time length of one frame shown in FIG. 5 is set to 20 ms, and 3 ms is allocated to the downlink data section 2004.
As [Condition 2], for example, a two-line IP phone in FIG. 2 is used. As shown in FIG. 3, the traffic volume of the IP packet per line is 60 bytes / 20 ms. Therefore, the traffic amount for two lines is 120 bytes / 20 ms.
As [Condition 3], the error correction method of the data portion (downlink data 2004 and uplink data 2006) is a convolutional code (coding rate 1/2).
As [Condition 4], the modulation method of the data part is QPSK, and the roll-off rate is 0.25.

From the above [Condition 1] and [Condition 2], the transmission rate in the downlink data section is (Expression 1).
120 bytes × 8 bits / 3 ms = 320 kbps (Expression 1)
From [Condition 3], the transmission rate after error correction coding (coding rate 1/2) is (Expression 2).
320 kbps × 2 = 640 kbps (Formula 2)
From [Condition 4], the symbol speed is (Expression 3). Note that the number of bits per symbol in QPSK is “2”.
640 kbps / 2 = 320 ksymbols / s (Formula 3)
Here, the occupied bandwidth (transmission bandwidth) in the case of the roll-off rate 0.25 is (Expression 4).
320 ksymbols / s × 1.25 = 400 kHz (Formula 4)
The detected bandwidth can be obtained by (Equation 5) if the guard band is doubled.
400 kHz × 2 = 800 kHz (Formula 5)

In the above [Condition 1], as the time length of the spectrum sensing section 2000 is set longer as the distribution within one frame 20 ms, the time allocated to the downlink data section 2004 becomes shorter, and the detected bandwidth and the transmission bandwidth are Become wider. Conversely, as the time length of the spectrum sensing section 2000 is set shorter, the time allocated to the downlink data section 2004 becomes longer and the detected bandwidth and the transmission bandwidth become narrower.
Further, in the above [Condition 2], when the number of lines is increased from 2 lines to, for example, 3 lines, the traffic volume is 180 bytes / 20 ms, and the results of (Expression 1) to (Expression 5) are 1.5 times, and are detected. The bandwidth is 1.5 times.

  In the prior art, the detected bandwidth in the spectrum sensing unit and the transmission bandwidth in the data transmission unit are fixed values (determined based on the maximum number of IP telephone connections, that is, the maximum traffic volume). When the amount of voice call traffic (the information speed of the output of the aggregation device 202 in FIG. 2) is small, there are the following problems.

  As shown in FIG. 6A, if the detected bandwidth in the spectrum sensing unit is B, the bandwidth of the free frequency 604 is B or more, so that the free frequency can be detected. As shown in FIG. 6, it can be used in the secondary usage system (the portion indicated by the hatched pattern in FIG. 6B). However, when the free frequency is only the free frequency 602, the bandwidth is smaller than B, and sensing is performed including signals of surrounding frequencies, so that it is not detected as a free frequency and cannot be used in the secondary usage system. . Here, when the traffic volume of the voice call is small and the bandwidth is sufficient to transmit even the “first vacant frequency”, the transmission opportunity is lost.

  On the other hand, according to the above-described embodiment, the secondary usage system is configured by controlling the detected bandwidth in the spectrum sensing unit according to the amount of data to be transmitted and searching for the minimum free frequency necessary for transmission. Therefore, it is possible to maintain more reliable voice communication in a disaster area or the like.

  In the above embodiment, the single-carrier TDM-TDD is used as the radio access method. However, the present invention is also applicable to OFDMA (Orthogonal Frequency Division Multiplexing Access). Also, one of the aggregation devices 202 and 205 in FIG. 2 may be a non-management network such as a public network, and the aggregation devices 202 and 205 can incorporate routers and SIP server functions as appropriate.

  In short, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 101 ... Existing system base station, 102 ... Existing system terminal, 103 ... Communication area of existing system, 104 ... Secondary use system base station, 105-1 to 105-3 ... Secondary use system terminal, 106 ... Secondary use system Communication area, 201-1 to 201-m ... IP telephone terminal, 202 ... concentrator, 203 ... secondary use base station, 204 ... secondary use terminal, 205 ... concentrator, 206-1 to 206-m ... IP Telephone terminal 300... Data transmission unit 301. Bandwidth determination unit 302. Control unit 303. Spectrum sensing unit 304. Assembly / disassembly unit 305 Error correction unit 306 Modulation / demodulation unit 307 Radio unit

Claims (2)

A wireless device used in a secondary usage system that secondary uses a free frequency band of a primary usage system that preferentially uses frequencies,
Detecting means for detecting an empty frequency band equal to or greater than a predetermined detected bandwidth by spectrum sensing;
Transmission means for wirelessly transmitting data with a predetermined transmission bandwidth using the detected vacant frequency band;
Determining means for determining the detected bandwidth and the transmission bandwidth according to at least one of a traffic amount of the secondary usage system and a time length of a spectrum sensing section ;
Control means for variably controlling the detected bandwidth of the detecting means and the transmission bandwidth of the transmitting means based on the detected bandwidth and the transmission bandwidth determined by the determining means;
With
The transmission means wirelessly transmits the data that is encoded speech at a radio frame period corresponding to the speech encoding period,
Said determining means, said transmission bandwidth, transmission time is the bandwidth in consideration of the roll-off rate to the symbol rate corresponding to the modulation rate falls within a predetermined time, the guard said object detection bandwidth in the transmission bandwidth Bandwidth with band added,
If the detected bandwidth corresponding to the transmission bandwidth when the data is only a voice call for one line is set by the determining means, the detecting means transmits the voice call for the one line. A wireless device that detects the vacant frequency band that can be used in the future.   The radio apparatus according to claim 1, wherein the determination unit sets the detected bandwidth wider as the time length of the spectrum sensing section is longer.

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