Abstract:
A receiver is provided and includes a first amplifier configured to amplify, based on a first gain, a radio frequency signal to generate a first amplified signal. The radio frequency signal is received by the receiver on a first channel. A second amplifier generates, based on the first amplified signal and a second gain, a second amplified signal. An output circuit generates a baseband signal based on the second amplified signal. A first detection circuit compares the baseband signal to (i) a first threshold in response to the first gain being at a first level, and (ii) a second threshold in response to the first gain being at a second level. The first detection circuit generates a first detection signal in response to the comparison. A controller, in response to the first detection signal, (i) adjusts the second gain, or (ii) changes the receiver from the first channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent Ser. No. 12/372,858 filed on Feb. 18, 2009. This application claims the benefit of U.S. Provisional Application No. 61/060,303, filed on Jun. 10, 2008. The disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The disclosed concepts relate generally to communication apparatus and associated methods. More particularly, the disclosed concepts relate to apparatus for and associated methods for detecting and handling interference in communication apparatus and systems. 
     BACKGROUND 
     In general, there is a demand for communication systems that can accommodate an ever increasing amount of information and data transfer. Accordingly, to support such information and data transfer, communication networks of considerable complexity have become commonplace. 
     The complexity of the communication networks has further resulted in the widespread use of wireless communication systems and apparatus. By using radio frequency (RF) signals, wireless communication systems and apparatus can provide connectivity to a relatively large number of users and equipment without the use of wires and fibers. As a result, wireless communication networks have become ubiquitous. 
     SUMMARY 
     A receiver is provided and includes a first amplifier configured to amplify, based on a first gain, a radio frequency signal to generate a first amplified signal. The radio frequency signal is received by the receiver on a first channel. A second amplifier is configured to generate, based on the first amplified signal and a second gain, a second amplified signal. An output circuit is configured to generate a baseband signal based on the second amplified signal. A first detection circuit is configured to compare the baseband signal to (i) a first threshold in response to the first gain being at a first level, and (ii) a second threshold in response to the first gain being at a second level. The first detection circuit generates a first detection signal in response to the comparison. A controller is configured to, in response to the first detection signal, (i) adjust the second gain, or (ii) change the receiver from the first channel. 
     In other features, a method is provided and includes receiving a radio frequency signal on a first channel at a receiver. The radio frequency signal is amplified to generate a first amplified signal Based on a first gain. A second amplified signal is generated based on the first amplified signal and a second gain. A baseband signal is generated based on the second amplified signal. The baseband signal is compared to (i) a first threshold in response to the first gain being at a first level, and (ii) a second threshold in response to the first gain being at a second level. A first detection signal is generated in response to the comparison. In response to the first detection signal, the second gain is adjusted or the receiver is changed from the first channel. 
     One aspect of the disclosed concepts concerns the disclosed concepts apparatus and related methods for proper detection and handling of out-of-band radar signals in communication apparatus and systems that include RF apparatus. In one exemplary implementation, a communication apparatus includes a RF apparatus. The RF apparatus includes an amplifier, and a signal detection circuit. The amplifier receives RF signals and amplifies those signals. The amplifier has an adjustable gain value. The signal detection circuit detects whether a received signal is an out-of-band radar signal depending on the gain value of the amplifier and a characteristic of the received signal. 
     In another exemplary implementation, an RF receiver includes an antenna, a low noise amplifier (LNA), a received signal strength indicator (RSSI) circuit, and an out-of-band signal detector. The antenna receives an RF signal. The LNA has selectable first and second gain values. The LNA generates an amplified signal by amplifying the RF signal received by the antenna. The RSSI circuit receives an input signal derived from the amplified signal, and generates a strength indication signal for the input signal. The out-of-band signal detector generates a detection signal based on (i) whether the first gain value or the second gain value of the LNA is selected; and (ii) whether the strength indication signal exceeds a predetermined threshold. 
     In yet another exemplary implementation, a method of processing signals in a communication apparatus includes receiving RF signals, and amplifying the RF signals using an adjustable gain value. The method further includes detecting an out-of-band signal based on the gain value and a received signal indicator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended drawings illustrate only exemplary implementations and therefore should not be considered as limiting its scope. In the drawings, the same numeral designators used in more than one drawing denote the same, similar, or equivalent functionality, components, or blocks. 
         FIG. 1  illustrates a simplified block diagram of a superheterodyne receiver according to the present disclosure. 
         FIG. 2  depicts a simplified block diagram of receive-path circuitry in a superheterodyne receiver according to the present disclosure. 
         FIG. 3  shows a simplified circuit arrangement of a portion of receive path circuitry and peak detect circuitry according to the present disclosure. 
         FIG. 4  shows plots of signal strength vs. frequency in exemplary implementations according to the disclosed concepts. 
         FIG. 5  illustrates a communication system according to the present disclosure. 
         FIG. 6  depicts another communication system according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosed concepts relate generally to communication apparatus and systems and associated methods, specifically to detection and handling of interference in communication apparatus and systems. More specifically, the disclosed concepts provide apparatus and related methods for proper detection and handling of out-of-band radar signals in communication apparatus and systems that include RF apparatus. 
     In some implementations, the RF apparatus includes a superheterodyne receiver.  FIG. 1  illustrates a simplified block diagram of a superheterodyne receiver  100  according to an exemplary implementation. Superheterodyne receiver  100  includes antenna  105 , low noise amplifier (LNA)  110 , local oscillator (LO)  115 , mixer  120 , filter  125 , intermediate frequency (IF) amplifier  130 , and baseband  135 . 
     Antenna  105  receives RF signals, and provides the RF signals to LNA  110 . LNA  110  amplifies the received RF signals, and provides the resulting signals to mixer  120 . 
     LNA  110  has more than one gain value, or an adjustable or programmable gain. In one implementation, LNA  110  has two gain values—a low gain and a high gain. In other implementations, LNA  110  may have more than two gain values. 
     LO  115  provides a local oscillator signal to mixer  120 . Mixer  120  mixes, or multiplies, the amplified RF signals from LNA  110  with the output signal of LO  115 . Mixer  120  provides the mixed signals to filter  125 . 
     Filter  125  provides filtering of the signals received from mixer  120 . In one implementation, filter  125  reduces the interference or unwanted signals present in the receive path of heterodyne receiver  100 . 
     IF amplifier  130  receives filtered signals form filter  130 . IF amplifier  130  amplifies the signal at an IF frequency, and provides the resulting signals to baseband  135 . 
     Baseband  135  includes a variety of circuitry for demodulation, decoding, data processing, etc., as persons of ordinary skill in the art who have the benefit of the description of the disclosed concepts understand. For example, baseband  135  provides the function of mixing the IF signals down to baseband signals. Baseband  135  may also include various filtering and data-processing (e.g., digital signal processing, or DSP), as desired. Baseband  135  outputs processed data or signals (shown as “data out” in  FIG. 1 ). 
     In addition, and as described in detail below, baseband  135  uses a signal quality indicator, for example, a received signal strength indicator (RSSI) to properly detect and handle out-of-band or out-of-channel radar signals. The process of detecting and handling such signals entails dynamic frequency selection (DFS) based on an RSSI threshold and on the gain of LNA  110 , as described below in detail. 
       FIG. 2  depicts a simplified block diagram of receive path circuitry  200  in a superheterodyne receiver according to an exemplary embodiment. Thus, in some embodiments, one may use receive path circuitry  200  in heterodyne receiver  100  (see  FIG. 1 ). 
     Referring to  FIG. 2 , receive path circuitry  200  includes antenna  105 , LNA  110 , mixer  120 , IF filter  125 , IF amplifier  205 , complex mixer  210 , and complex filter  215 . Antenna  105 , LNA  110 , and mixer  120  may have similar structure and functionality as described above in connection with  FIG. 1 . 
     LNA  110  has adjustable, selectable, or programmable gain. More particularly, one may choose a gain for LNA  110  from among a plurality of gain values by adjusting the gain value, selecting a gain value, or programming the gain value. Signal  110 A allows the selection, adjustment, or programming of the gain of LNA  110 . Signal  110 A can be provided from a controller or programmable processor (not shown). 
     Similar to LNA  110 , IF amplifier  205  has adjustable, selectable, or programmable gain. 
     More specifically, one may choose a gain for IF amplifier  205  from among a plurality of gain values by adjusting the gain value, selecting a gain value, or programming the gain value. Signal  205 A allows the selection, adjustment, or programming of the gain of IF amplifier  205 . IF amplifier  205  provides an output signal to mixer  210  and to IF peak detect circuitry (signal  205 C; see  FIG. 3  and associated description). 
     Complex mixer  210  includes direct mixer  210 A, which mixes direct LO signal LO_I with the output signal of IF amplifier  205 . Additionally, complex mixer  210  includes quadrature mixer  210 B. Quadrature mixer  210 B mixes quadrature LO signal LO_Q with the output signal of IF amplifier  205 . Thus, complex mixer  210  provides direct and quadrature mixed signals (labeled as  210 C and  210 D, respectively) to complex filter  215 . 
     Complex filter  215  performs filtering of signals  210 C,  210 D to provide direct and quadrature filtered signals  215 A,  215 B, respectively. Complex filter  215  provides signals  215 A,  215 B to IF peak detect circuitry (see  FIG. 3  and associated description). 
     In some implementations, filter  215  may constitute a Chebyshev filter. The Chebyshev filter may have a desired or suitable order, for example, sixth order in some implementations. 
       FIG. 3  shows a simplified circuit arrangement  300  of a portion of receive path circuitry and peak detect circuitry according to an exemplary implementation. Circuit arrangement  300  includes IF amplifier  205 , mixer  210 , filter  215 , RF peak detect circuitry  305 , and IF peak detect circuitry  330 . 
     IF amplifier  205 , mixer  210 , and filter  215  may have similar structure and functionality as described above in connection with  FIG. 2 . In exemplary implementations, RF peak detect circuitry  305  constitutes wideband circuitry, whereas IF peak detect circuitry  330  constitutes narrowband circuitry. 
     RF peak detect circuitry  305  includes peak detector  310 , which accepts programmable threshold  315 . RF peak detect circuitry  305  detects whether the LNA  110  should be set to low gain (or lower gain) mode. RF signal  205 B is rectified and low passed and compared to threshold  315 . If the RF signal  205 B exceeds threshold  315 , RF peak detect signal  320  is asserted high, and is provided to automatic gain controller (AGC)  380 . Automatic gain controller  380  will assert gain adjust signal  110 A to set LNA  110  to low gain (or to a lower gain) mode to avoid saturation of the output of LNA  110 . Since the RF signal  205 B is a wide band signal (i.e., from 4.9 GHz to 5.9 GHz), RF peak detect circuitry  305  also behave as a wide band peak detector, and RF peak detect signal  320  indicates LNA  110  saturation due to any strong RF signal (i.e., from 4.9 GHz to 5.9 GHz frequency). Therefore, RF peak detect signal  320  is a wide band (i.e., 1 GHz bandwidth) peak detector. 
     One input of Automatic Gain Controller  380  is RF peak detect signal  320 , which is generated by RF peak detect circuitry  305 . Another input of Automatic Gain Controller  380  is IF peak detect signal  364 , which is generated by IF peak detect circuitry  330 . When RF peak detect signal  320  is asserted, Automatic Gain Controller  380  will assert gain adjust signal  110 A to set LNA  100  to low gain (or to a lower gain) mode. When IF peak detect signal  364  is asserted, Automatic Gain Controller  380  will assert gain adjust signal  205 A to reduce the gain of IF amplifier  205  by one step. Automatic Gain Controller  380  will wait for the IF amplifier  205  to settle to the new gain value (for example, Automatic Gain Controller  380  might wait 200 nanoseconds), and then checks whether IF peak detect signal  364  is still asserted, and will instruct the IF amplifier  205  to lower the gain one step at a time, until either the gain of IF amplifier  205  reaches the minimum gain value, or IF peak detect signal  364  is not asserted anymore. 
     As noted above, exemplary implementations of communication apparatus according to the disclosed concepts use various RSSI thresholds, depending on the gain of LNA  110 , to detect whether a radar signal constitutes an in-band or out-of-band radar signal. Depending on the results of this determination, the communication apparatus may enable DFS. 
     In some implementations, LNA  110  has a bandwidth of 4.9 GHz to 5.9 GHz (e.g., in Wi-Fi applications). Thus, LNA  110  has a sufficiently wide bandwidth so as to pass an out-of-band strong radar signal to the following stages of the RF receiver (see  FIGS. 1-3 ). 
     More specifically, the out-of-band strong radar signal saturates LNA  110 . As a result, RF peak detect circuitry  305  triggers. In response, automatic gain control in the RF receiver responds by switching LNA  110  to the low gain (or to a lower gain) mode. 
     As a consequence, the RSSI value will increase. The elevation of the RSSI value because of the changing of the gain of LNA  110  is enough to cross the DFS threshold. Crossing the DFS threshold activates DFS detection. 
     After the change of the gain of LNA  110 , the out-of-band strong radar will be attenuated quickly. Filter  125  will further attenuate the out-of-band signal. As a result, the DFS detection will false detect the out-of-band signal as a short pulse (say, with a one microsecond pulse-width), even though the out-of-band radar has a longer pulse width. 
     Furthermore, the out-of-band radar signal causes ringing and transient effects in filter  125 . The ringing and transient effects cause the activation of the peak detect circuitry. As a result, the RF receiver cannot distinguish between in-band and out-of-band radar signals (e.g., by measuring pulse-width). Thus, the out-of-band radar signals may propagate through the RF receiver. 
     To combat the phenomenon of propagation of out-of-band radar signals through the RF receiver, one may design LNA  110  with a narrower bandwidth. Alternatively, one may use more than one LNA. As yet another alternative, one may use relatively stringent filtering requirements. Doing so, however, would cause more system complexity and, hence, cost. 
     As another alternative, one may employ a heuristic solution based on the gain of LNA  110  and the RSSI. The heuristic solution allows proper detection and handling of radar signals. In other words, the heuristic solution activates DFS for in-band radar signals, but does not activate (or deactivates) DFS for out-of-band radar signals. 
       FIG. 4  shows plots  400  of RSSI vs. frequency in exemplary embodiments that employ the heuristic solution. Specifically,  FIG. 4  shows a plot  405  of RSSI as a function of frequency when LNA  110  has a low (or lower) gain value. Furthermore, plot  410  depicts RSSI as a function of frequency when LNA  110  has a high (or higher) gain value. Note that the RSSI is derived from the total gain of the RF receiver. The total gain can be estimated by the Automatic Gain Controller  380 . Since the Automatic Gain Controller  380  uses RF peak detect signal  320  and IF peak detect signal  364  to adjust the gain of LNA  110  and IF amplifier  205 , the RF peak detector  305  and the IF peak detector  330  should respond, respectively, to wideband signals (i.e., from 4.9 GHz to 5.9 GHz) or narrow band signal (i.e., approximately ±20 MHz from channel center frequency. 
     During operation of the RF receiver when LNA  110  has a low (or lower) gain value, one uses RSSI threshold  415  (labeled as “T 1 ”). Specifically, one uses threshold  415  to qualify a received signal as an in-band radar signal. 
     If RSSI exceeds threshold  415 , the signal constitutes an in-band radar signal, thus DFS is activated, and the channel is switched. On the other hand, if RSSI does not exceed threshold  415 , the signal constitutes an out-of-band signal, and DFS is not activated. 
     On the other hand, when LNA  110  has a high gain (or higher) gain value, one uses RSSI threshold  420  (labeled as “T 2 ”), i.e., a normal or nominal threshold. Thus, one uses threshold  420  to qualify a received signal as an in-band radar signal. 
     If RSSI exceeds threshold  420 , the signal constitutes an in-band radar signal, thus DFS is activated, and the channel is switched. On the other hand, if RSSI does not exceed threshold  420 , the signal constitutes an out-of-band signal, and DFS is not activated. 
     Note that threshold  420  has a lower value than does threshold  415 . The normal or nominal threshold  420  might have a value specified or prescribed by a communication standard, e.g., the −64 dBm value specified by the IEEE 802.11n standard. 
     The heuristic solution uses the RSSI thresholds  415  and  420  to properly detect and handle radar signals. More specifically, the heuristic solution uses RSSI thresholds  415  and  420 , depending on whether LNA  110  is operating in the low or high gain modes (i.e., with low (or lower) gain values, or high (or higher) gain values) to distinguish between in-band and out-of-band radar signals. 
     As persons of ordinary skill in the art who have the benefit of the description of the disclosed concepts understand, one may implement the heuristic solution using hardware blocks or circuitry. As an alternative, one may implement the heuristic solution in firmware or software. As yet another alternative, one may implement the heuristic solution using a combination of hardware, firmware, and/or software. 
     One may use receiver  100  in a variety of applications, as desired. More specifically, one may use receiver  100  in a variety of communication systems. 
       FIG. 5  illustrates a communication system  500  according to an exemplary implementation. Note that, generally, communication system  500  may have a variety of forms, as persons of ordinary skill in the art who have the benefit of the description of the disclosed concepts understand. For example, communication system  500  may constitute a wireless LAN, or a system that includes both wireless (e.g., Wi-Fi) and wireline or wired portions. In the implementation shown, communication system  500  may constitute or include a Wi-Fi network, as exemplified by the IEEE 802.1x standards. 
     Referring to  FIG. 5 , communication system  500  includes one or more access points  505 . Access point(s)  505  couples to local area network (LAN). Thus, access point(s)  505  exchange data and information with LAN  500 . Alternatively, access point(s)  505  may couple to and communicate with one or more wide area network (WAN), and/or one or more virtual network  500 , as desired. 
     Access point(s)  505  also couples to antenna  105 . Through antenna  105 , access point(s)  505  may receive and transmit RF signals from/to other devices in communication network  500 . 
     Communication system  500  may also include one or more devices or nodes  510 . Each device  510  includes antenna  105 , transceiver  520 , and data processing apparatus  515 . 
     Through antenna  105 , device(s)  510  may receive and transmit RF signals from/to other devices in communication network  500 . For example, via antenna  105 , device(s)  510  may communicate RF signals with access point(s)  505 . 
     Transceiver  520  includes receiver and transmitter circuits (although those circuits may not have individually identifiable blocks of circuits or may use common or shared circuits, as persons of ordinary skill in the art who have the benefit of the description of the disclosed concepts understand). One or more of transceivers  520  includes the circuitry in receiver  100 , as described above in detail (i.e., the heuristic solution for proper detection and handling of radar signals). 
     Data processing apparatus  515  couples to transceiver  520 . Data processing apparatus  515  may communicate data and information to transceiver  520  for further communication to other devices in communication system  500 . 
     Data processing apparatus  515  may include a variety of circuits and devices or even systems, as persons of ordinary skill in the art who have the benefit of the description of the disclosed concepts understand. For example, data processing apparatus  515  may include computer circuits or devices. As another example, data processing apparatus  515  may include industrial control or automation equipment. 
     Note that data processing apparatus  515  may couple to (or include) a variety of communication apparatus, as persons of ordinary skill in the art who have the benefit of the description of the disclosed concepts understand. For example, data processing apparatus  515  may couple to (or include) a wireless LAN, a wired LAN, a combination of the two (a hybrid LAN), or a WAN. As another example, data processing apparatus  515  may couple to (or include) Wi-Fi circuitry. In one implementation, device(s)  510  include circuitry for multiple input, multiple output (MIMO) communication, for example, as prescribed by the IEEE 802.11n standard. 
     Communication system  500  may also include one or more devices or nodes  525 . Each device  525  includes antenna  105 , receiver  100 , described above in detail, and data processing apparatus  530 . 
     Through antenna  105 , device(s)  525  may receive RF signals from other devices in communication network  500 . For example, via antenna  105 , device(s)  525  may receiver RF signals from access point(s)  505  and/or from device(s)  510 . 
     Data processing apparatus  530  couples to receiver  100 . Data processing apparatus  530  receives data and information from receiver  100 . 
     Data processing apparatus  530  may include a variety of circuits and devices or even systems, as persons of ordinary skill in the art who have the benefit of the description of the disclosed concepts understand. For example, data processing apparatus  530  may include computer circuits or devices. As another example, data processing apparatus  530  may include industrial control or automation equipment. 
     Note that data processing apparatus  530  may couple to (or include) a variety of communication apparatus—for example, data processing apparatus  530  may couple to (or include) a wireless LAN, a wired LAN, a combination of the two (a hybrid LAN), or a WAN. As another example, data processing apparatus  530  may couple to (or include) Wi-Fi circuitry. In one implementation, device(s)  530  include circuitry for multiple input, multiple output (MIMO) communication, for example, as prescribed by the IEEE 802.11n standard. 
       FIG. 6  depicts a communication system  600  according to another exemplary implementation. Unlike communication system  500  (see  FIG. 5 ), communication system  600  lacks an access point. Thus, the devices in communication system  600  act as peers, e.g., an ad hoc network. 
     Note that, generally, communication system  600  may have a variety of forms. For example, communication system  600  may constitute a wireless LAN, or a system that includes both wireless (e.g., Wi-Fi) and wireline or wired portions. In the implementation shown, communication system  600  may constitute or include a Wi-Fi network, as exemplified by the IEEE 802.1x standards. 
     Referring to  FIG. 6 , communication system  600  includes one or more devices or nodes, shown as devices  510 A- 510 B and  525 A- 525 B. Devices  510 A- 510 B may have similar structure and operation. Likewise, devices  525 A- 525 B may have similar structure and operation. Accordingly, the following describes device  510 A and device  525 A. 
     Device  510 A includes antenna  105 , transceiver  520 A, and data processing apparatus  515 A. 
     Through antenna  105 , device  510 A may receive and transmit RF signals from/to other devices in communication network  600 . For example, via antenna  105 , device  510 A may communicate RF signals with device  5106  or device  525 A. 
     Transceiver  520 A includes receiver and transmitter circuits (although those circuits may not have individually identifiable blocks of circuits or may use common or shared circuits). Transceivers  520 A includes the circuitry in receiver  100 , as described above in detail (i.e., the heuristic solution for proper detection and handling of radar signals). 
     Data processing apparatus  515 A couples to transceiver  520 A. Data processing apparatus  515 A may communicate data and information to transceiver  520 A for further communication to other devices in communication system  600 . 
     Data processing apparatus  515 A may include a variety of circuits, devices and/or systems. For example, data processing apparatus  515 A may include computer circuits or devices. As another example, data processing apparatus  515 A may include industrial control or automation equipment. 
     Note that data processing apparatus  515 A may couple to (or include) a variety of communication apparatus. For example, data processing apparatus  515 A may couple to (or include) a wireless LAN, a wired LAN, a combination of the two (a hybrid LAN), or a WAN. As another example, data processing apparatus  515 A may couple to (or include) Wi-Fi circuitry. In one implementation, device  510 A includes circuitry for multiple input, multiple output (MIMO) communication, for example, as prescribed by the IEEE 802.11n standard. 
     Device  525 A includes antenna  105 , receiver  100 A (see  FIG. 1 ), described above in detail, and data processing apparatus  530 A. 
     Through antenna  105 , device  525 A may receive RF signals from other devices in communication network  600 . For example, via antenna  105 , device  525 A may receiver RF signals from device  510 A or device  510 B. 
     Data processing apparatus  530 A couples to receiver  100 A. Data processing apparatus  530 A receives data and information from receiver  100 A. 
     Data processing apparatus  530 A may include a variety of circuits, devices and/or systems. For example, data processing apparatus  530 A may include computer circuits or devices. As another example, data processing apparatus  530 A may include industrial control or automation equipment. 
     Note that data processing apparatus  530 A may couple to (or include) a variety of communication apparatus. For example, data processing apparatus  530 A may couple to (or include) a wireless LAN, a wired LAN, a combination of the two (a hybrid LAN), or a WAN. As another example, data processing apparatus  530 A may couple to (or include) Wi-Fi circuitry. In one implementation, device  530 A includes circuitry for multiple input, multiple output (MIMO) communication, for example, as prescribed by the IEEE 802.11n standard. 
     Referring to the figures, persons of ordinary skill in the art will note that the various blocks shown might depict mainly the conceptual functions and signal flow. The actual circuit implementation might or might not contain separately identifiable hardware for the various functional blocks and might or might not use the particular circuitry shown. For example, one may combine the functionality of various blocks into one circuit block, as desired. Furthermore, one may realize the functionality of a single block in several circuit blocks, as desired. The choice of circuit implementation depends on various factors, such as particular design and performance specifications for a given implementation. Other modifications and alternative implementations in addition to those described here are possible. Accordingly, this description teaches those skilled in the art the manner of carrying out the disclosed concepts and are to be construed as illustrative only. 
     The forms and implementations shown and described should be taken as illustrative implementations. Persons skilled in the art may make various changes in the shape, size and arrangement of parts without departing from the scope of the disclosed concepts in this document. For example, persons skilled in the art may substitute equivalent elements for the elements illustrated and described here. Moreover, persons skilled in the art who have the benefit of this disclosure may use certain features of the disclosed concepts independently of the use of other features, without departing from the scope of the disclosed concepts.