JP2010171707A - Receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device having improved throughput in comparison with a conventional receiving device which stops communication during search. <P>SOLUTION: The receiver for communication in an RF band including groups of active channels and inactive channels includes: a first converter which down-converts a signal in the RF band into a signal in a low frequency band by mixing the signal in the RF band with a local oscillation signal; a demodulator which demodulates the down-converted signal of the active channel in the low frequency band corresponding to the active channel in the RF band; and a channel monitor which searches for one or more usable groups of channels in the low frequency band to search the down-converted group of inactive channels, wherein the channel monitor performs the search substantially simultaneously with demodulation by the demodulator. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a receiver that performs carrier sense.

  Since a wireless local area network (LAN) has been widely used, a new frequency band has been required. In Japan, the center frequency of the 5 GHz band that can be used for a wireless LAN was different from that in Western countries. In order to enhance convenience, the frequency was reorganized in May 2005 in consideration of compatibility with each country. At this time, four channels were added to the 5250-5350 MHz band (W53), and in January 2007, 11 channels were added to the 5470-5725 MHz band (W56).

  However, these added channels are used not only by wireless LAN but also by radar. When a wireless LAN system detects a radar interference wave (carrier sense) on a channel in use, it must stop using that channel and move to a free channel. The function of dynamically changing the channel in this way is called DFS (Dynamic Frequency Selection), and the above-mentioned 5.3 GHz band and 5.6 GHz band wireless LAN devices are required by the standard to have this function. Yes.

Patent Document 1 describes a wireless communication apparatus that searches for an empty channel by performing carrier sense.
JP 2008-72193 A

  However, in the prior art of Patent Document 1, communication is not performed while searching for an empty channel. Therefore, there is a problem that the throughput is greatly reduced.

  The present invention has been made to solve the above-described problem, and searches for an inactive channel by searching for an available channel substantially simultaneously with communication in an active channel. An object of the present invention is to provide an apparatus capable of improving throughput as compared to a conventional receiver that stops communication during a search.

  A receiver for communication in an RF band including an active channel group and an inactive channel group according to the present invention down-converts a signal in the RF band into a signal in a low band by mixing with a local oscillation signal. A converter, a demodulator for demodulating a signal corresponding to the active channel in the low band, and searching the down-converted inactive channel group for one or more available channels in the low band And the channel monitor performs the search substantially simultaneously with the demodulation by the demodulator.

  An exemplary embodiment further comprises a controller that controls a frequency of the local oscillation signal such that the active channel is changed to one of the available channels.

  An exemplary embodiment is a receiver that further comprises a storage unit, wherein if the channel monitor identifies one of the available channel groups as a result of the search, data regarding the identified channel Is stored in the storage unit, and the search is temporarily stopped.

  An exemplary embodiment is a receiver further comprising a storage unit, wherein the channel monitor continues the search until the plurality of channels of the available channel group are identified, and the plurality of identified ones. Data related to the channel group is stored in the storage unit.

  The present invention can search for an inactive channel by searching for an available channel while communicating on an active channel. This operation may improve throughput.

  A receiver according to an exemplary embodiment of the present invention can identify a plurality of available channels, select an optimal channel among them, and use it as a new active channel. As a result, it is more likely that a channel with better communication conditions can be used than a receiver that identifies only a single available channel.

  Embodiments of an apparatus according to an exemplary embodiment of the present invention will be described below with reference to the drawings. The same reference number represents the same component.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration of a receiver 100 according to a first exemplary embodiment. The receiver 100 is typically used with a transmitter to realize bidirectional wireless communication such as a wireless LAN. The receiver 100 includes a converter 110, a demodulator 120, a channel monitor 125, a controller 160, and a storage unit 170.

(Frequency conversion)
The converter 110 receives the input signal 102 in the RF band (for example, 5 GHz band), and performs conversion (down-conversion) to lower the frequency. The RF signal 102 may be band-limited by a bandpass filter (BPF) or the like before being input to the converter 110, or may not be band-limited. In this specification, the signal 102 input to the receiver 100 is referred to as an RF (Radio Frequency) signal. The signal 104 down-converted by the converter 110 is called a lower band signal. In this specification, the frequency band before being down-converted by the converter 110 is referred to as an RF band for convenience.

  Typically, the low-band signal 104 is a baseband signal (for example, 0 to 600 MHz) whose lowest frequency in the band substantially corresponds to a DC component. Alternatively, if the low-band signal 104 is on the order of 1 GHz, for example, and further down-converted later in the receiver 100, the low-band signal 104 is also referred to as an intermediate frequency (IF) signal. As used herein, the term “low band” includes both baseband and IF band as long as it is converted to a lower frequency than the input RF band signal.

  If the receiver 100 is a receiver for a wireless LAN that uses, for example, a 5 GHz band, a BPF that passes only the frequency band may be provided in front of the converter 110. The converter 110 outputs the down-converted low-band signal 104 to the demodulator 120 and the channel monitor 125 (specifically, the image rejection unit 130).

(demodulation)
The standards IEEE802.11a (W53) and IEEE802.11a (W56) allocate 4 channels and 11 channels, respectively, for 5 GHz band communication. In a communication system compliant with these standards, in an ideal situation, all of these 15 channels are usable channels without interference or the like. In this specification, a channel that is determined to have no interference in the channel and is to be used for future communication is referred to as an “available channel”.

  However, the 5 GHz band is used by weather radars and the like. Therefore, the standard prohibits the use of the channel when interference from a radar or the like is detected. In other words, if a channel is subject to radar interference, it is no longer an available channel. Therefore, when the channel currently used for communication (active channel) has to be changed due to interference, it is necessary to search for an assigned channel by searching for an available channel free from interference such as radar. It is. Such an operation is defined as DFS (Dynamic Frequency Selection) in the above standard.

  The receiver 100 performs communication using a demodulated signal 106 (for example, digital data) output by being demodulated by the demodulator 120. As will be appreciated by those skilled in the art, demodulated signal 106 may include any suitable digital data. Examples of such data include data representing audio, video (still image or moving image), text, and the like.

  An RF band channel currently used by the receiver 100 corresponding to the demodulated signal 106 is referred to as an “active channel” in this specification. On the other hand, channels in the RF band that are not used by the receiver 100 are referred to as “inactive channels”. In the aforementioned standard, for example, one channel is used for communication by the receiver 100 as an active channel, and the remaining 14 channels correspond to inactive channels. That is, the channel allocated to the RF band for communication is configured by an active channel (for example, one channel) and an inactive channel (for example, the remaining 14 channels).

  If receiver 100 has only a single demodulator 120, there is typically only one such active channel. When the active channel is changed as described below, the active channel may be temporarily absent (typically for a short period of time). In addition, when the receiver 100 is not communicating (that is, when the receiver 100 is in an idle state), the active channel may not exist.

  The demodulator 120 receives the down-converted low band signal 104 output by the converter 110. The low-band signal 104 is a signal corresponding to an active channel and an inactive channel in the RF band, and has a low-band frequency component. For example, if the signal 104 is a baseband signal, the low band signal 104 may have a frequency component between about 0-600 MHz. The demodulator 120 obtains digital data by demodulating the low-band signal 104 and outputs it as a demodulated signal 106.

(Search for available channels)
The channel monitor 125 includes an image rejection unit 130, a channel filter 140, and a signal strength detector 150. These elements are coupled in series to form a signal path for searching for available channels and searching for channels allocated within the communication band.

  The image rejection unit 130 reduces or removes image components included in the down-converted low-band signal 104, and outputs an image-suppressed signal 135. In this specification, “image suppression” includes not only the complete removal of image components, but also the reduction of image components compared to before processing. The channel filter 140 receives the image-suppressed signal 135 and selectively outputs a signal 145 having a frequency component corresponding to one of the inactive channels (hereinafter referred to as “target channel”).

  The signal strength detector 150 receives the target channel signal 145 selectively output by the channel filter 140 and outputs data 155 representing the signal strength (or corresponding to the signal strength) to the controller 160. The signal strength detector 150 can be realized by, for example, a sample and hold circuit and an A / D (analog-digital) converter. In this case, the controller 160 receives numerical data 155 corresponding to the strength of the signal 145 of the target channel. The controller 160 may store data representing the signal strength (numerical data in the above example) in the storage unit 170 together with data representing which frequency the target channel currently being searched corresponds to.

  Alternatively, for example, the signal strength detector 150 indicates “1” (indicating that the channel is an available channel) when the signal strength is smaller than a predetermined threshold, and “0” when the signal strength is equal to or higher than the predetermined threshold. It can also be realized as an electronic circuit that outputs to controller 160 (indicating that it is not an available channel). If the controller 160 stores in the storage unit 170 data indicating availability (data “1” or “0” in the above example) along with data indicating which frequency the target channel currently being searched for corresponds to. Good.

  Based on the data 155, the controller 160 determines whether there is interference from the radar or the like in the target channel (hereinafter referred to as “availability determination”). Specifically, when the intensity of the signal 145 of the target channel is larger than a predetermined threshold, it is determined that there is interference in the channel, and the channel is not used. Conversely, when the strength of the signal 145 of the target channel is smaller than a predetermined threshold, it is determined that there is no interference in that channel, and that channel is regarded as an available channel to be used for future communications.

  The controller 160 stores information on available channels in the storage unit 170. In other words, this available channel is a candidate channel to be used if the current active channel becomes unavailable.

  The channel monitor 125 and the controller 160 determine the availability of the target channel based on the intensity of the signal that has passed through the band corresponding to the target channel. It is therefore necessary to generate a band limited signal 145 from the low band signal 104 in some way.

  FIG. 2 shows an example of passband characteristics of the image rejection unit 130 and the channel filter 140. In this example, the image rejection unit 130 has a bandwidth 20 that allows the entire channels (ie, active and inactive channels) assigned for communication by the receiver 100 to pass. This bandwidth 20 is fixed. On the other hand, the channel filter 140 has a bandwidth 22 that allows only the target channel to pass. By changing the center frequency of the bandwidth 22 by the control signal 164 from the controller 160, the target channel can be sequentially selected from the inactive channels, and the availability of the target channel can be determined.

  FIG. 3 shows another example of passband characteristics of the image rejection unit 130 and the channel filter 140. The image rejection unit 130 and the channel filter 140 have bandwidths 30 and 32 that allow only the target channel to pass, respectively. By changing the center frequencies of these bandwidths 30 and 32 by control signals 163 and 164 from the controller 160, respectively, a target channel is sequentially selected from the inactive channels, and the availability determination for the target channel is performed. It can be performed.

  In the above example, it is assumed that the channel filter 140 passes a single target channel, but the present invention is not limited to this. The channel 140 may pass a band corresponding to a plurality of adjacent target channel groups.

(Overview of operation)
FIG. 4 schematically shows an operation example of the receiver 100. During the period t0 to t1, the receiver 100 is in a dormant state. From time t1, the receiver 100 starts communication at f1 given as the initial active channel.

  During the period t1 to t3, the demodulator 120 demodulates the signal of the active channel f1. The channel monitor 125 searches for an inactive channel by searching for an available channel during the period t1 to t2. Typically, the channel monitor 125 and the controller 160 identify a plurality of available channels and store data representing the identified available channels in the storage unit 170. The channel monitor 125 and the controller 160 may temporarily stop the search as soon as one available channel is found, and store data representing the channel in the storage unit 170. FIG. 4 shows an example where the search is stopped as soon as one available channel is found. In this case, for example, in the period t2 to t3, demodulation is performed for communication, but a search for an available channel is not performed.

  As a result of searching for an available channel, the channel monitor finds an available channel f2 by time t2. If the demodulator 120 has to change the active channel f1 at time t3, the demodulator 120 can demodulate the available channel f2 (eg, the local oscillator 114 shown in FIG. 6) so that it can demodulate the available channel f2. ). This frequency change can be realized by the controller 160 sending a control signal 162 to the converter 110. During the period t3 to t5, the demodulator 120 demodulates the signal of the active channel f2.

  The channel monitor 125 starts to search for an available channel by being triggered by the change of the active channel at time t3. The channel monitor 125 searches for an inactive channel by searching for an available channel during the period t3 to t4. As a result of searching for an available channel, the channel monitor finds, for example, an available channel f3 by time t4. When the demodulator 120 has to change the active channel f2 at time t5, the demodulator 120 adjusts the frequency of the local oscillator of the converter 110 so that it can demodulate the available channel f3. During the period t5 to t7, the demodulator 120 demodulates the signal of the active channel f3. Similarly, it is assumed that the channel monitor finds an available channel f4 by time t6. This available channel f4 is used for demodulation of the demodulator 120 after time t7.

  In the example shown in FIG. 4, when one available channel is identified, for example, the controller 160 temporarily stops the search. As a result, the receiver 100 can reduce power consumption while the channel monitor 125 is stopped.

  FIG. 5 schematically illustrates an alternative operation example of the receiver 100. During the period t0 to t1, the receiver 100 is in a dormant state. From time t1, the receiver 100 starts communication at f1 given as the initial active channel.

  During the period t1 to t2, the demodulator 120 demodulates the signal of the active channel f1. The channel monitor 125 searches for an inactive channel by searching for an available channel during the period t1 to t2. Typically, the channel monitor 125 and the controller 160 identify a plurality of available channels and store data representing the identified available channels in the storage unit 170. FIG. 5 shows an example in which the search by the channel monitor 125 continues until the active channel of the demodulator is changed (for example, the period t1 to t2).

  As a result of searching for an available channel, the channel monitor finds an available channel f2 by time t2. When the demodulator 120 has to change the active channel f1 at time t2, the demodulator 120 adjusts the frequency of the local oscillator of the converter 110 so that it can demodulate the available channel f2. During the period t2 to t3, the demodulator 120 demodulates the signal of the active channel f2.

  Similarly, as a result of the search in the period t2 to t3, the channel monitor 125 finds an available channel f3 by time t3. During the period t3 to t4, the demodulator 120 demodulates the signal of the available channel f3.

  In the operation of the channel monitor 125 shown in FIG. 5, multiple available channels may be found. In this case, the controller 160 may store data on all the plurality of available channels in the storage unit 170. When changing the active channel, it is necessary to select one channel from a plurality of available channels. This selection can be achieved by various methods. For example, the channel corresponding to the data obtained by the most recent availability determination can be selected. This method has the advantage that the active channel can be selected based on the latest data if the radio wave conditions change while searching for an available channel. Alternatively, as described below with reference to FIG. 17, data for all available channels can be obtained and then the optimal next active channel can be selected based on various rules.

  As shown in FIGS. 4 and 5, substantially simultaneously with demodulation by demodulator 120, channel monitor 125 searches for and searches for available channels. Specifically, in the case of FIG. 4, the search periods t1 to t2 are included in the communication periods t1 to t3. In the case of FIG. 5, the search period t1 to t2 is the same as the period t1 to t2 during which communication is performed. That is, in the present invention, the search can be performed substantially simultaneously with the communication, instead of temporarily interrupting the communication and performing the search. In other words, as long as the period of search for an available channel is included in the period of the demodulation operation by the demodulator, such operation is referred to herein as “substantially simultaneously with the demodulation by the demodulator. Is included in the “searching”.

  As a result, the demodulator 120 can continue demodulating for communication substantially continuously by switching the active channel to f1, f2, f3, f4,. In other words, the receiver 100 can check the radio wave condition of the inactive channel, for example, the presence or absence of radar interference, while performing communication on the active channel. This can improve system throughput.

  The storage unit 170 stores data regarding available channels, for example, data representing channel numbers of available channels. Alternatively, the storage unit 170 may store a flag indicating that the channel is available at an address corresponding to the available channel. Storage unit 170 may be any suitable storage medium that can store such data. For example, the storage unit 170 is a semiconductor memory.

  FIG. 6 shows details of converter 110, demodulator 120, and channel monitor 125.

(Detailed configuration of the converter)
The converter 110 includes an amplifier 111, multipliers 112 and 113, a local oscillator 114, and a phase shifter 115. The amplifier 111 receives and amplifies the input RF band signal 102. The local oscillator 114 generates a local oscillation signal and outputs it to the phase shifter 115. The local oscillator 114 receives the control signal 162 output from the controller 160 and changes the frequency of the local oscillation signal based on the control signal 162 so that a signal of a desired active channel is output to the demodulator 120. The local oscillation signal is, for example, on the order of 5 GHz, but is not limited to this.

  The phase shifter 115 outputs two signals 116 and 117 having phase differences orthogonal to each other to the multipliers 112 and 113, respectively. Therefore, the signal 117 input to the multiplier 113 has the same frequency as the signal 116 input to the multiplier 112 and has a phase substantially advanced by 90 °.

  The multiplier 112 multiplies the amplified RF band signal and the local oscillation frequency signal 116 and outputs a multiplied signal 118. The multiplier 113 multiplies the amplified RF band signal and the local oscillation frequency signal 117 and outputs a multiplied signal 119. Signal 118 at node A and signal 119 at node B are the in-phase (I) and quadrature (Q) components of the downconverted signal, respectively.

The low-band signals 118 and 119 (≧ 0) output from the multiplier 112 are expressed by Equations 1 and 2, respectively, assuming that the RF band signal is cos (ω _RF t) and the local oscillation signal is cos (ω _LO t). Is done.

cos (ω _RF t) · cos (ω _LO t) (1)
cos (ω _RF t) · sin (ω _LO t) (2)

  The local oscillator 114 used in the converter 110 is not limited to the above-described configuration as long as it can substantially generate a quadrature signal. For example, the local oscillator 114 may be a local oscillator that has a function of multiplication and division and oscillates in quadrature. The I component signal 118 and the Q component signal 119 are supplied to the demodulator 120 and the channel monitor 125.

(Detailed configuration of demodulator)
The demodulator 120 includes a BPF 122, an amplifier 124, an A / D converter 126, and a digital demodulator 128. The BPF 122 selectively passes the active channel signal necessary for the current communication by filtering the low-band signals 118 and 119. The analog signal of the active channel filtered by the BPF 122 is amplified by the amplifier 124. The A / D converter 126 receives and digitizes the amplified active channel analog signal. The digital demodulator 128 obtains digital data by demodulating the digitized signal and outputs it as a demodulated signal 106. The demodulator 120 only needs to be able to digitally demodulate only the desired frequency component from the analog signals corresponding to a plurality of channels, and the specific configuration is not limited to that described above.

(Detailed configuration of channel monitor)
The image rejection unit 130 of the channel monitor 125 receives the low band signals 118 and 119 output by the converter 110. The image rejection unit 130 includes, for example, a phase shifter 131, an adder 132, and a subtracter 133. Adder 132 outputs upper sideband signal 138, and subtractor 133 outputs lower sideband signal 139.

FIG. 7 shows the sideband components of the inactive channel. Of the non-active channel, the channel of the high frequency side of the active channel (hereinafter, "upper sideband" hereinafter) cos .omega _RF and in order from low frequency channel _{+ 1 t, cosω RF + 2} t, ..., and cos .omega _{RF + n} t, the active channel the low frequency side (hereinafter, referred to as "lower sideband") to the order from the high frequency channel _{cosω RF-1 t, cosω RF} -2 t, ..., and cosω _RF-n t. The I component signal 118 and the Q component signal 119 (≧ 0) output from the converters 112 and 113 are expressed by Expression 3 and Expression 4, respectively. Here, n is an integer of 1 or more.

cosω _{RF +} nt · cosω _LO t + cosω _RF− nt · cosω _LO t (3)
cosω _{RF +} nt · sinω _LO t + cosω _RF− nt · sinω _LO t (4)

  If the high frequency components are ignored, Equations 3 and 4 are transformed into Equations 5 and 6, respectively.

_{{Cos (ω RF + n t} -ω LO t) -cos (ω LO t-ω RF-n t)} / 2 ... (5)
_{- {sin (ω RF + n} t-ω LO t) -sin (ω LO t-ω RF-n t)} / 2 ... (6)

The phase shifter 131 substantially shifts the phase of the node B with respect to the node A by 90 °. By adding the original signal and the phase-shifted signal by the adder 132, an upper sideband signal 138 expressed as cos (ω _{RF +} nt−ω _LO t) is obtained. Similarly, by subtracting the original signal and the phase-shifted signal by the subtracter 133, a lower sideband signal 139 represented by cos (ω _LO t−ω _RF− nt) is obtained. However, there is no upper sideband when communicating on the channel with the highest frequency, and there is no lower sideband when communicating on the channel with the lowest frequency. Here, the phase shifted by the phase shifter 131 is not limited to the combination of 0 ° and 90 °, as long as each signal has a relative phase difference of 90 °. The image rejection unit 130 is not limited to a combination of a phase shifter, an adder, and a subtracter, and may use any appropriate circuit that reduces an image component.

  As described with reference to FIG. 3, the pass band of the phase shifter 131 may be changed according to the frequency of the target channel. In this case, based on the control signal 163 output by the controller 160, the phase shifter 131 sets its circuit constant so that the frequency that produces the 90 ° phase difference substantially matches the passband frequency of the channel 140. adjust. Alternatively, the phase shifter 131 may include a plurality of phase shift elements and switch the phase shift elements based on the control signal 163 so as to obtain a desired phase shift.

  The channel filter 140 receives the signal from which the image has been removed by the image rejection unit 130. The channel filter 140 has BPFs 141 and 142. The center frequencies of the passband widths of the BPFs 141 and 142 are controlled by control signals 664 and 665 from the controller 160, respectively. The control signals 664 and 665 correspond to the control signal 164 shown in FIG. By being controlled by the control signals 664 and 665, the BPFs 141 and 142 selectively output the components of the target channel from the signals 138 and 139 to the signal strength detectors 151 and 152, respectively.

FIG. 8 shows the output 138 of the adder 132 and the output 139 of the subtractor 133. In FIG. 8, the frequency (ω _{RF +} nt−ω _LO t) of the adder output 138 is ω _{IF + n,} and the output frequency (ω _LO t−ω _RF− nt) of the subtractor is ω _IF−n . Since these signals 138 and 139 are before passing through the BPFs 141 and 142, they are shown to include components corresponding to all channels assigned to the communication. Actually, when a signal exceeding a predetermined threshold (for example, a signal due to radar interference) is detected in an inactive channel, the channel cannot be an available channel.

  FIG. 9 schematically shows the bands of the BPFs 141 and 142 when a certain one of the assigned channels shown in FIG. 8 is selected by a broken line. The frequency band that the BPF passes is not limited to one channel, and may be a band corresponding to a plurality of channels.

  The signal strength detectors 151 and 152 obtain the signal strengths of the upper sideband signal 138 and the lower sideband signal 139, respectively, and output data representing the signal strength to the controller 160. As an example, the controller 160 may determine that there is interference in the target channel when at least one of the output signals of the detectors 151, 152 has a signal strength greater than a predetermined threshold.

  The BPFs 141 and 142 are realized by a BPF whose pass band is variable, for example. Such a BPF passes the frequency band corresponding to the desired target channel. However, the BPFs 141 and 142 may pass bands corresponding to a plurality of adjacent channel groups. However, when a band corresponding to an adjacent channel group is allowed to pass, it is determined that the entire channel group is not usable because only interference exists in one of the adjacent channel groups. For example, when one available channel is sandwiched between channels that are not available, it is determined that the one channel is not available. As a result, the channel usage efficiency may decrease.

  Each of the BPFs 141 and 142 may include a plurality of BPFs having different pass bands. In this case, a desired inactive channel band may be passed by using a switch that selectively outputs one of the outputs of a plurality of BPFs. FIG. 10 shows an example of the BPFs 141 and 142. Each of the BPFs 141 and 142 has a combination of a plurality of BPF groups 1010 and a switch 1020. By switching the switch 1020, a desired target channel can be selectively output. Further, each frequency band of the BPF group 1010 may be variable. In this case, a desired frequency band can be covered with a smaller number of BPFs.

  FIG. 11 shows another example of the BPFs 141 and 142. Each of the BPFs 141 and 142 can be realized by a plurality of BPFs 1140a to 1140d having different frequency bands. The signal strength detectors 1150a to 1150d receive the signals output from the BPFs 1140a to 1140d, respectively, and output data corresponding to the respective signals to the controller 160. Controller 160 receives data representing multiple target channels in parallel.

  Note that the channel filter 140 is not limited to the illustrated specific configuration as long as it can pass a desired frequency band corresponding to one channel or a plurality of channels.

FIG. 12 schematically shows the phase shifter 131 realized by the polyphase filter 1200 in the above embodiment. The input corresponding to node A in FIG. 2 is represented by Ain, and the input corresponding to node B is represented by Bin. At this time, the signals input from Ain and Bin are shifted by 90 ° with respect to node A at a frequency satisfying ω ₁ = 1 / (R1 · C1) by the _first -stage polyphase filter. Is output. When poly-phase filters are connected in m stages (m is an integer of 1 or more), ω ₁ = 1 / (R1 · C1), ω ₂ = 1 / (R2 · C2),..., Ω _m = 1 / (Rm · The phase of node B is shifted by 90 ° with respect to node A at a frequency satisfying Cm) and output. R1, R2,..., Rm and C1 so that the phase of node B is phase-shifted by 90 ° relative to node A within the frequency band including the assigned channels (ie, active channels and inactive channels). , C2,..., Cm can be adjusted to enable image rejection in all channels that may be used. The polyphase filter is not limited to a configuration in which RC (resistance / capacitance) filters are connected in multiple stages as long as the phase is shifted by 90 ° at a desired frequency.

  Alternatively, the frequency characteristic may be changed by switching the resistor R and the capacitor C constituting the polyphase filter with a switch or the like, thereby shifting the phase by 90 ° at the frequency selected by the channel filter 140.

  The phase of the signal may be shifted by 90 ° in a desired frequency band by switching a plurality of polyphase filters having different frequency characteristics with a switch.

  Polyphase filter 1200 may realize variable passband characteristic 30 shown in FIG. In this case, the passband characteristic 30 may be changed in synchronization with the passband characteristic 32 by the channel filter 140 as described above. As a result, the signal of the target channel is image-suppressed and the signal strength is detected.

  FIG. 13 shows an alternative channel monitor 425 corresponding to channel monitor 125. The channel monitor 425 includes an image rejection unit 430, a channel filter 141, and a signal strength detector 151. The image rejection unit 430 includes a phase shifter 131, an adder 132, a subtracter 133, and a switch 434. The switch 434 selectively outputs one of the output 138 of the adder 132 and the output 139 of the subtracter 133 to the channel filter 141.

  The channel monitor 125 shown in FIG. 6 has two parallel signal paths from the image rejection unit 130 to the controller 160. In contrast, channel monitor 425 has only one signal path through channel filter 141 and signal strength detector 151. Such a configuration has the advantage that a circuit can be realized with a smaller area.

  FIG. 14 shows an alternative image rejection unit 530 corresponding to the image rejection unit 130. The image rejection unit 530 includes a phase shifter 131 and an adder 132, and can extract only the upper sideband. Similar to the example of FIG. 13, the image rejection unit 530 only needs to have one signal path that passes through the channel filter 141 and the signal strength detector 151. Therefore, there is an advantage that a circuit can be realized with a smaller area.

  FIG. 15 shows an alternative image rejection unit 630 corresponding to the image rejection unit 130. The image rejection unit 630 includes a phase shifter 131 and a subtracter 133, and can extract only the lower sideband. Similar to the example of FIG. 13, the image rejection unit 630 only needs to have one signal path that passes through the channel filter 141 and the signal strength detector 151. Therefore, there is an advantage that a circuit can be realized with a smaller area.

  FIG. 16 shows an example of a receiver 1600 having a plurality of channel monitors 125a-c. In this case, the channel monitors 125a to 125c are connected in parallel, so that the availability for the three target channels can be determined separately and simultaneously. This configuration has the advantage of being able to search for available channels faster.

(Optimal channel selection method)
FIG. 17 is a schematic diagram for explaining selection of an optimum channel in a search for available channels. Channels f1 to 11 represent channels assigned to communication (for example, 11 channels in the 5 GHz band). The signal strength detector 150 detects the strongest signal strength due to active channel transmission / reception in the channel f7. In the channels f1, f2, f6, f9, and f11, the signal strength due to interference (or other interference) such as radar is detected. Channels f3-f5, f8, and f10 have zero signal strength. For example, the controller 160 stores numerical data representing the signal strength in each channel in the storage unit 170.

  If the active channel f7 cannot be used for some reason (for example, radar interference), the most desirable channel is selected as a new active channel from the channels f1 to f6 and f8 to f11 other than the active channel f7. In order to be selected as an available channel, its signal strength must be at least below a predetermined threshold. This is because the signal strength of a certain level indicates that there is radar interference in the channel. In the situation of FIG. 17, it is preferable to select a new active channel from among the channels f3 to f5, f8, and f10 having a signal strength of zero. In that sense, it can be said that all of the channels f3 to f5, f8, and f10 are usable channels.

  If there are multiple channels available, they can be prioritized according to various rules. Given that the channel change is caused by interference present in the active channel, it is generally preferable to avoid the channel immediately adjacent to the current active channel. Based on this rule, in FIG. 17, channel f8 is determined to be undesirable for the new active channel. Conversely, it may be determined that a channel away from the current active channel f7 and having a signal strength of zero is desirable. For example, it may be determined that f3 to f5 or f10 is desirable.

  In addition, if there are more than two consecutive available channels (here channels f3-f5), the central channel is generally desirable. Based on this rule, the channel f4 is determined as the most desirable channel in the example of FIG.

  As described above, the receiver 100 can select one optimum channel from a plurality of available channels and prepare for the channel change as the next active channel. As a result, the optimum channel can be selected and switched based on the overall usage of the allocated channel.

  The receiver 100 can monitor the signal strength on the inactive channel substantially simultaneously during communication on the active channel. Therefore, the receiver 100 can improve the throughput as compared with a system that interrupts communication when monitoring signal strength.

  When searching for an available channel, the active channel is typically skipped. However, as an alternative, the signal strength may be obtained for all assigned channels including the active channel, and the signal strength data for all channels may be temporarily stored in the storage unit 170. In this case, since the signal strength of the active channel is strong as shown in FIG. 17, it is not finally selected as an available channel. Alternatively, since controller 160 generally keeps track of which channel is the current active channel, it may exclude the current active channel when selecting an available channel.

(Embodiment 2)
FIG. 18 is a block diagram illustrating a configuration of a receiver 1800 according to the second exemplary embodiment. The receiver 1800 is different from the receiver 100 in that a channel filter 1840 is used instead of the channel filter 140. For the receiver 1800, the same or similar functions as those of the receiver 100 are described with reference to FIG.

  The channel filter 1840 includes multipliers 1844 and 1845, a local oscillator 1843, and BPF 1841 and 1842. Multiplier 1844 multiplies signal 138 by the local oscillation signal output by local oscillator 1843. Multiplier 1845 multiplies signal 139 by the local oscillation signal output by local oscillator 1843. BPF 1841 and 1842 extract signals of desired target channels from the outputs of multipliers 1844 and 1845, respectively. Based on the control signal 1864 from the controller 160, the local oscillator 1843 adjusts the oscillation frequency so that the signal of the desired target channel passes through the BPF 1841 and 1842.

Multipliers 1844 and 1845 receive the output signal of the adder and the output signals 138 and 139 of the subtractor of the image rejection unit 130, respectively. The signals 138 and 139 have components of ω _{IF ± 1} , ω _{IF ± 2} ,..., Ω _{IF ± n} . The multipliers 1844 and 1845 and the local oscillator 1843 output a constant monitor frequency ω _MNT by adjusting the frequency of the local oscillator 1843 in order to monitor the signal strength of the desired target channel. The BPFs 1841 and 1842 filter the input signal so as to pass the monitor frequency ω _MNT . The functions of the multipliers 1844 and 1845 and the local oscillator 1843 are frequency conversion (down conversion) by mixing with the local oscillation signal, similarly to the function of the converter 110.

FIG. 19 shows the relationship between the local oscillation signals ω _SL1 , ω _SL2 ,..., Ω _SLn generated by the local oscillator 1843 and the monitor frequency ω _MNT . In this _{case, ω IF ± 1 -ω SL1 =} ω IF ± 2 -ω SL2 = ... = ω IF ± n -ω SLn = ω MNT (≧ 0) become relevant. The broken lines in FIG. 19 schematically represent the passband widths of the BPFs 241 and 242. Alternatively, the local oscillator 1843 may generate a signal having a frequency satisfying ω _SL1 −ω _{IF ± 1} = ω _SL2 −ω _{IF ± 2} =... = Ω _SLn −ω _{IF ± n} = ω _MNT (≧ 0) Good. The local oscillator 1843 may be generated by dividing the output of the local oscillator 114 of the converter 110 with a frequency divider. The local oscillator 1843 may be generated by multiplying a signal generated by a reference oscillator (for example, a crystal oscillator) provided in the receiver 1800 with a multiplier.

  The receiver 1800 can monitor the signal strength on the inactive channel substantially simultaneously during communication on the active channel. Therefore, the receiver 1800 can improve throughput as compared with a system that interrupts communication when monitoring signal strength.

(Search algorithm)
FIG. 20 shows an algorithm 2000 that may be used to perform a search for available channels (eg, the operations of FIG. 4). The operation of FIG. 4 can be realized by a combination of hardware represented by the receiver 100 and software represented by the algorithm 2000 (hereinafter collectively referred to as “system”). In 2005, the system starts communication on the active channel given as the initial value. Before starting communication, it may first be determined whether this initial active channel is available.

  At 2010, the channel filter 140 (or In addition, the pass bandwidth of the image rejection unit 130) is adjusted. At 2020, the system determines whether the target channel is available. This determination of availability is performed, for example, in the manner described with reference to FIG.

  If the result of the determination is yes, an available channel has been specified. In 2030, data representing the target channel (for example, frequency f4 in FIG. 17) is stored in the storage unit 170. If the determination is no, control returns to 2010 to select a new target channel from the inactive channels. For example, if the previous target channel is the frequency f2 in FIG. 17, the frequency f3 can be selected as the next target channel. The target channel is sequentially scanned among the inactive channels until an available channel is identified in this way.

  At 2040, the system stops the search and proceeds to 2050. At 2050, it is determined whether the active channel should be changed. If the determination is yes, at 2060, the stored available channel (eg, channel f4) is used for communication as the active channel. If the result of the determination is no, the control returns to 2040 and the search stop is maintained.

  Control returns from 2060 to 2005 to communicate using a new active channel (eg, channel f4). Communication therefore takes place substantially continuously despite the change of the active channel. On the other hand, a search for available channels is performed substantially simultaneously with demodulation for communication. As a result, this algorithm can improve throughput.

  FIG. 21 shows an algorithm 2100 that may be used to perform a search for available channels (eg, the operations of FIG. 5). The operation of FIG. 5 may be realized by a combination of hardware represented by the receiver 100 and software represented by the algorithm 2100 (hereinafter collectively referred to as “system”). At 2105, the system starts communication on the active channel given as the initial value. Before starting communication, it may first be determined whether this initial active channel is available.

  At 2110, the channel filter 140 (or to select one target channel from inactive channels (eg, channels f1-f6, f8-f11 in FIG. 17) different from the current active channel (eg, channel f7 in FIG. 17). In addition, the pass bandwidth of the image rejection unit 130) is adjusted. At 2120, the system determines whether the target channel is available. This determination of availability is performed, for example, in the manner described with reference to FIG.

  If the result of the determination is yes, an available channel has been specified. In 2130, data representing the target channel (for example, frequency f4 in FIG. 17) is stored in the storage unit 170. If the determination is no, control returns to 2110 to select a new target channel from the inactive channels. For example, if the previous target channel is the frequency f2 in FIG. 17, the frequency f3 can be selected as the next target channel. The target channel is sequentially scanned among the inactive channels until an available channel is identified in this way.

  At 2150, it is determined whether the active channel should be changed. If the determination is yes, at 2160, one is selected from the stored available channel (s) (eg, channels f3-5, f8, f10) based on a predetermined rule, and the selected channel (eg, Channel f4) is used for communication as the active channel. If the result of the determination is no, the control returns to 2110.

  Control returns from 2160 to 2105 to communicate using a new active channel (eg, channel f4). Communication therefore takes place substantially continuously despite the change of the active channel. On the other hand, a search for available channels is performed substantially simultaneously with demodulation for communication. As a result, this algorithm can improve throughput.

  The algorithm shown in FIG. 21 continues to store data representing an available channel (group) in the storage unit 170 until the active channel is changed. Thus, the algorithm of FIG. 21 differs from the algorithm of FIG. 20 in that multiple available channels can be identified and stored. At 2160, the most desirable channel from a plurality of available channels can be selected and the selected channel can be used as an active channel for communication. The method of selecting the most desirable channel from among a plurality of available channel groups is as described with reference to FIG.

  In the example illustrated in FIG. 21, only the data of the channel determined to be an available channel in 2120 is stored in the storage unit 170. However, the present invention is not limited to this, and after data on all inactive channels are temporarily stored in the storage unit 170, as described with reference to FIG. 17, an optimal usable channel based on various rules. May be selected. In this case, the controller 160 temporarily stores data representing the signal strength in each inactive channel in the storage unit 170 without determining the availability in 2120. In other words, the controller 160 stores data corresponding to the signal intensity plot of FIG. At this time, data representing the signal strength for the active channel may be stored without skipping the active channel.

  At an appropriate timing, rules for determining availability are applied to stored inactive channel data. This allows the most desirable channel to be selected as the new active channel. The selection timing may be after the active channel needs to be changed as long as the selection can be made at a sufficient speed. In this case, the inactive channel search is repeated until the active channel is changed, and the signal strength data is always overwritten with the latest data. As a result, even when the active channel is not changed for a relatively long time, the signal strength data is not stale.

(Receiver implementation method)
The converter, demodulator, and channel monitor of the first and second embodiments can be typically realized by a circuit element group including a semiconductor element mounted on a substrate. The controller 160 and the storage unit 170 can typically be realized by digital circuits. The algorithms shown in FIGS. 20 and 21 can be typically implemented by software stored on a computer readable medium. Examples of the computer readable medium include a hard disk drive and a semiconductor memory.

  A part or all of the functional block groups of the first and second embodiments may be integrated and realized by being appropriately combined. For example, the channel monitor 125 may be realized as a hybrid IC (integrated circuit). Alternatively, all or part of converter 110, demodulator 120, channel monitor 125, and controller 160 may be implemented as a hybrid IC.

  As will be appreciated by those skilled in the art, the various functions for implementing the present invention need not be integrated solely according to the name shown (eg, “channel monitor 125”). For example, a part of the channel monitor 125 may be incorporated in a semiconductor chip constituting the controller 160.

  In other exemplary embodiments, the functional blocks of receiver 100 may be implemented using “software defined radio” technology. "Software radio" can handle communication with various frequencies, modulation methods, etc. with a single general purpose hardware. In this case, by providing an A / D converter or the like immediately after the converter 110, the software stored in the digital signal processing unit (for example, the digital signal processor) and the semiconductor memory is converted into the demodulator 120, the channel monitor 125, and Functions of the controller 160 and the like can be realized.

  Receivers according to various embodiments of the invention can be used with any suitable transmitter. For example, the controller 160 can change the transmission frequency in accordance with the change of the reception frequency by sending data representing the frequency of the active channel to the transmitter.

  The present invention is not limited to the embodiments, and can be implemented in various other forms without departing from the spirit or main features thereof. The above-described embodiments are merely examples in all respects and should not be construed as limiting. The scope of the invention should be defined by the claims, and not limited to the details described in the specification. All modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the present invention is useful for a receiver or the like that searches for an inactive channel in order to search for an empty channel.

1 is a block diagram illustrating a configuration of a receiver according to a first exemplary embodiment. FIG. It is a figure which shows the example of the pass-band characteristic of an image rejection part and a channel filter. It is a figure which shows the other example of the pass-band characteristic of an image rejection part and a channel filter. It is a figure which shows schematically the operation example of a receiver. It is a figure which shows schematically the example of an alternative operation | movement of a receiver. It is a figure which shows the detail of a converter, a demodulator, and a channel monitor. It is a figure which shows the sideband component of an inactive channel. It is a figure which shows the output of an adder, and the output of a subtractor. It is a figure which shows typically the zone | band of BPF when one channel of the allocated channels is selected with a broken line. It is a figure which shows the example of BPF. It is a figure which shows the other example of BPF. It is a figure which shows schematically the phase shifter implement | achieved by the polyphase filter. FIG. 5 is a diagram illustrating an alternative channel monitor. It is a figure which shows an alternative image rejection part. It is a figure which shows an alternative image rejection part. It is a figure which shows the example of the receiver which has several channel monitors. It is the schematic for demonstrating selection of the optimal channel in the search of an available channel. It is a block diagram which shows the structure of the receiver by 2nd exemplary embodiment. It is a figure which shows the relationship between the local oscillation signal which a local oscillator generate | occur | produces, and a monitor frequency. FIG. 5 illustrates an algorithm that may be used to perform a search for available channels (eg, the operation of FIG. 4). FIG. 6 illustrates an algorithm that may be used to perform a search for available channels (eg, the operation of FIG. 5).

100 receiver 102 RF band signal 110 converter 120 demodulator 125 channel monitor 130 image rejection unit 140 channel filter 150 signal intensity detector 160 controller 170 storage unit

Claims (14)

A receiver for communication in an RF band including active channels and inactive channels, comprising:
A first converter that down-converts the signal in the RF band to a signal in the low band by mixing with a local oscillation signal;
A demodulator that demodulates a signal corresponding to the active channel in the low band;
A channel monitor that searches the down-converted inactive channels for one or more available channels in the low band;
A receiver in which the channel monitor performs the search substantially simultaneously with demodulation by the demodulator.   The receiver of claim 1, further comprising a controller that controls a frequency of the local oscillation signal such that the active channel is changed to one of the available channels. The receiver according to claim 1, further comprising a storage unit,
As a result of the search, if the channel monitor identifies one of the available channels, the data relating to the identified channel is stored in the storage unit;
A receiver that temporarily stops the search. The receiver according to claim 1, further comprising a storage unit,
The channel monitor continues the search until a plurality of channels among the available channels are specified, and stores data related to the plurality of specified channel groups in the storage unit. The first converter includes:
A signal generator for generating two signals having phase differences orthogonal to each other;
A first multiplier for multiplying a signal in the RF band by one of the two signals generated by the signal generator;
The receiver according to claim 1, further comprising: a second multiplier that multiplies the signal in the RF band by another of the two signals generated by the signal generator. The channel monitor
An image rejection unit that suppresses an image component of the down-converted signal in the RF band and outputs an image-suppressed signal;
A channel filter for filtering the image-suppressed signal and outputting the filtered signal;
The receiver according to claim 1, further comprising: a signal strength detector that detects a strength of the filtered signal. The image rejection unit includes:
A phase shifter that relatively shifts the phases of the I component signal and the Q component signal constituting the down-converted signal by 90 °;
An adder for adding two signals output from the phase shifter;
The receiver according to claim 6, further comprising: a subtracter that subtracts one of the two signals output from the phase shifter from the other.   The receiver according to claim 7, wherein the image rejection unit includes a switch that selectively outputs one of an output of the adder and an output of the subtractor. The image rejection unit includes:
A phase shifter that relatively shifts the phases of the I component signal and the Q component signal constituting the down-converted signal by 90 °;
7. The reception of claim 6, comprising: an adder that adds two signals output from the phase shifter; and one of a subtractor that subtracts one of the two signals output from the phase shifter from the other. Machine.   The receiver according to claim 6, wherein the channel filter includes a band-pass filter that filters the image-suppressed signal and selectively passes a desired frequency component.   The channel filter includes: a second converter that converts a frequency of the image-suppressed signal and outputs the converted signal; and a band-pass filter that filters the output of the second converter. The listed receiver.   The receiver of claim 1, wherein the controller controls the first converter based on at least one frequency of the available channel.   The receiver according to claim 1, wherein the controller controls the channel filter unit based on at least one frequency of the inactive channel group being searched.   14. The receiver according to claim 13, wherein the controller controls the image rejection unit based on at least one frequency of the inactive channel group being searched.

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