Abstract:
A network apparatus for self-testing network connectivity, a method thereof, and a method of analyzing frequency spectrum. The invention includes a link mode and a diagnostic mode. In the diagnostic mode, the MAC self-tests the network apparatus for network connectivity at least in signal quality, link quality, and quality of service by generating output signals traveling from the transmitter to the receiver, thus providing a simple, low power consuming, and reliable means for troubleshooting errors. The method of analyzing frequency spectrum eliminates the need of an expensive spectrum analyzer by utilizing the transmitter to output signals detectable by the receiver, then calculating power level differences between selected channel and its adjacent channels of the channels assigned to the receiver, and comparing the calculated power level differences with a plurality of pre-determined threshold values stored in a memory controlled by the MAC in order to meet standards and specifications.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates in general to a network apparatus, and more particularly to a network apparatus for self-testing network connectivity, and a method thereof, and a method of analyzing frequency spectrum.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, testing network connectivity of a network device requires the support of an external test system.  FIG. 1  shows a system block diagram of a conventional network device. The network device  100  includes a receiver  110  (denoted as RX), a transmitter  120  (denoted as TX), a voltage controlled oscillator (VCO)  130 , a media access control (MAC) with baseband processor (BBP)  140 , a transmitter/receiver switch  150 , and an antenna  160 . The receiver  110  and the transmitter  120  are both driven by the same VCO  130  operating under a time division duplex system (TDD), in which a common carrier is shared between uplink and downlink. To transmit signals, the transmitter/receiver switch  150  connects the transmitter  120  to the antenna  160 , such that signals generated by MAC  140  can be transmitted to a network  170 ; to receive signals from the network, the transmitter/receiver switch  150  instead connects the antenna  160  to the receiver  110 .  
         [0005]     To test for network connectivity, network device  100  is connected to an external test system.  FIG. 2  shows a block diagram of an external test system. The external test system includes test controllers  210  and  240 , a spectrum analyzer  220 , a power meter  230 , power couplers  250  and  260 , an attenuator  270 , and a signal generator  280 . Test controller  210 ,, such as personal computers with test utilities, is for controlling the network device  100 , spectrum analyzer  220  and power meter  230 . Test controller  240 , such as personal computers with test utilities, is for controlling the signal generator  280 . To check for signal characteristics from the receiver  110 , the signal generator  280  generates an output signal that travels through the attenuator  270  emulating channel attenuation and eventually reaches the receiver  110  of the network device  100  under test. The couplers  250  and  260  direct the output signals to the spectrum analyzer  220  and the power meter  230 , respectively, to thereby monitor the associated signal. To test for characteristics of signals originated from the transmitter  120 , test controller  210  operates on the transmitter  120  so as to transmit output signals, which propagate in a direction that is to be measured and analyzed by the spectrum analyzer  220  and power meter  230 . The analyzed results can, for instance, then be shown on a display of test controller  210  for view by a user.  
         [0006]     To reduce the need for a bulky external test system, a built-in test system has thus been devised to incorporate the capabilities for testing network connectivity within network device  100 .  FIG. 3  shows a conventional network device with a built-in test system. As shown in the figure, the functions of the traditional test equipments in  FIG. 2 , including signal generator  280 , spectrum analyzer  220 , power meter  230 , power couplers  250  and  260 , attenuator  270 , and test controllers  210  and  220  have been embedded in the built-in test system  300  with corresponding signal generator  380 , spectrum analyzer  320 , power meter  330 , power coupler  350 , attenuator  370 , and test controller  310 , respectively, thus reducing the trouble and need for the presence of numerous test equipments.  
         [0007]     In addition to a transmitter/receiver switch  150 , the network device  300  further includes a stimulus/antenna switch  340  and a monitor/antenna switch  360 , for use in establishing connection between the two selected from the group consisting of the transmitter  120  denoted as TX, receiver  110  denoted as RX and antenna  160 . Namely, the network device  300  performs network connectivity tests during a normal transmit mode, a normal receive mode and a built-in-test mode for respective transmitter and receiver testing. During the normal receive mode, the receiver  110  is active. The transmitter/receiver switch  150  and the stimulus/antenna switch  340  are configured so as to allow signals from network  170  to reach the receiver  110 . During the normal transmit mode, the transmitter  120  is active. The transmitter/receiver switch  150  and monitor/antenna switch  360  connects the transmitter  120  to the antenna  160 , thus allowing signals, generated by transmitter  120 , to be transmitted over network  170 . During built-in-test mode, either the transmitter  120  or the receiver  110  are active; the monitor/antenna switch  360  is configured so as to allow signals transmitted from the transmitter  120  to travel through attenuator  370 , in which the signals are in turn split by power coupler  350  and received by the spectrum analyzer  320  and power meter  330  for evaluation of signal strength and other related signal qualities; also, the stimulus/antenna switch  340  is configured such that the signals generated by the signal generator  380  reaches the receiver  110 . Thus, by applying the testing scheme adapted for the network device with a built-in test system, the associated network connectivity can be tested for without the troubles accompanied with an external test system.  
         [0008]     However, while the conventional network device with a built-in test system may be applicable for use in military applications and satellite systems etc., the conventional network device has a complex architecture, which greatly reduces reliability, and is expensive and power consuming. The built-in test system also increases overall packaging size and weight of the network device, which are factors that all likely to be unsuitable for use in office and household applications.  
       SUMMARY OF THE INVENTION  
       [0009]     It is therefore an object of the invention to provide a simpler architecture for self-testing network connectivity.  
         [0010]     It is yet another object of the invention to provide a less power consuming network apparatus by self-testing network connectivity.  
         [0011]     It is yet another object of the invention to provide a more economic network apparatus.  
         [0012]     It is yet another object to the invention to provide a simpler way of analyzing frequency spectrum of signals received by the receiver.  
         [0013]     The invention achieves the above-identified objects by providing a network apparatus that includes a receiver, a transmitter, an antenna, and a media access control (MAC) with baseband processor. The invention is characterized in that the network apparatus includes a link mode and a diagnostic mode. In the link mode, the network apparatus connects to a network via the antenna. In the diagnostic mode, the media access control self-tests the network apparatus for network connectivity by generating output signals traveling from the transmitter to the receiver.  
         [0014]     The invention achieves the above-identified objects by further providing a method of self-testing network connectivity applied in a network apparatus. The network apparatus includes a receiver, a transmitter, an antenna, and a media access control (MAC) with baseband processor. The method includes: first, outputting by the transmitter a plurality of output signals to the receiver; then, optimizing transmission capability by tuning the transmitter, such that the output signals are output substantially at a predetermined maximum power level satisfying a predetermined transmitter packet error rate (PER); next, checking reception capability by tuning the transmitter, such that the output signals are output substantially at a predetermined minimum power level satisfying a predetermined receiver PER; and, double-checking crosslink capability by tuning the transmitter to output signals with a rated or an average crosslink power level to see if it satisfies a predetermined link quality indicator (LQI) and a predetermined indicator of quality of service (IQoS).  
         [0015]     The invention achieves the above-identified objects by further providing a method of analyzing frequency spectrum while optimizing transmission capability of spectrum mask fitting, applied in a network apparatus for self-testing network connectivity. The method includes: transmitting a plurality of output signals at a high-limit power level by a selected channel of the transmitter; then, receiving the output signals by the assigned channels of the receiver, the assigned channels include the selected channel of the transmitter and all its adjacent ones; next, calculating received power level differences of those adjacent channels from the selected channel; and, comparing the calculated power level differences with a plurality of pre-determined threshold values stored in a memory controlled by the media access control.  
         [0016]     Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  shows a system block diagram of a conventional network device.  
         [0018]      FIG. 2  shows a block diagram of a conventional external test system.  
         [0019]      FIG. 3  shows a conventional network device with a built-in test system.  
         [0020]      FIG. 4  illustrates a functional block diagram of the network apparatus according to the invention.  
         [0021]      FIG. 5A  illustrates a network apparatus according to a first embodiment of the invention.  
         [0022]      FIG. 5B  illustrates the mode selection table for the network apparatus  500  of  FIG. 5A  under test.  
         [0023]      FIG. 6A  illustrates a network apparatus according to a second embodiment of the invention.  
         [0024]      FIG. 6B  shows a mode selection table for the network apparatus of  FIG. 6A  under test.  
         [0025]      FIG. 7  shows a block diagram of the mutual network connectivity test between two network apparatuses according to a preferred embodiment of the invention.  
         [0026]      FIG. 8  shows a method of self-testing network connectivity applied in the network apparatus  500  according to a preferred embodiment of the invention.  
         [0027]      FIG. 9  shows the sub-steps of step  810  in optimizing uplink capability.  
         [0028]      FIG. 10  shows the sub-steps of step  820  in optimizing downlink capability.  
         [0029]      FIG. 11  shows a flow chart of the sub-steps of step  830  in optimizing crosslink capability.  
         [0030]      FIG. 12  shows a method of analyzing frequency spectrum according to a preferred embodiment of the invention.  
         [0031]     FIGS.  13 A-D illustrate plots of the outputs signals transmitted by the transmitter. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]      FIG. 4  illustrates a functional block diagram of the network apparatus according to the invention. The network apparatus  400  includes a receiver  410 , a transmitter  420 , an antenna  430 , and a media access control (MAC)  490 . For self-testing network connectivity, the network apparatus  400  operates under a full duplex system. That is, the network apparatus  400  includes a first voltage-controlled oscillator (VCO) and a second VCO for controlling the transmitter  420  and the receiver  410 , respectively. The network apparatus  400  includes a link mode and a diagnostic mode. In the link mode, the network apparatus  400  establishes connection to a network  492  via the antenna  430 . Instead of the conventional signal generator, the invention utilizes the transmitter  420  to transmit output signals generated by the MAC  490  as the stimulus for the purpose of self-testing network connectivity. In the diagnostic mode, both the transceiver and the receiver are both involved, in which the output signals transmitted from the transmitter to the receiver are analyzed. That is, in the diagnostic mode, the MAC  490  is to generate output signals that contain test signals in packets, frames or other formats, in which the output signals travel then along a signal path P from the transmitter  420  to the receiver  410  to be tested for network connectivity characteristics at least in signal quality, link quality, and quality of service (QOS).  
       First Embodiment  
       [0033]      FIG. 5A  illustrates a network apparatus according to a first embodiment of the invention. The network apparatus is a network capable device, such as a network interface card (NIC)  500 . Under the link mode, the NIC  500  further operates under a transmit mode and a receive mode. The NIC  500  includes a first switch, such as a transmitter/receiver (T/R) switch  540 , which operates under a predetermined protocol, and is configured such that the output signals from the transmitter  420  are transmitted to the network  492  in the transmit mode, and the incoming signals from the network  492  reaches the receiver  410  in the receive mode. The NIC  500  further includes a second switch, such as an antenna/transmitter (A/T) switch  550 , an attenuator  560 , and a directional coupler  570  inter-disposed on the signal path P between the transmitter  420  and the receiver  410 . The attenuator  560  is for emulating channel attenuation. The AFT switch  550  operates to connect the attenuator  560  to the receiver  410  in the diagnostic mode, and the output signals travel from the transmitter  420  to the receiver  410  via the order of passing through the directional coupler  570  and the attenuator  560 . The concept of switching is illustrated in  FIG. 5B , showing the mode selection table for the network apparatus  500  of  FIG. 5A  under test.  
         [0034]     As shown in  FIG. 5A , the T/R switch  540  can be selectively switched between position R and T, and the AFT switch  550  can be selectively switched between position A and T. The switching of the T/R switch  540  and A/Tswitch  550  depends on the modes of operation, i.e. link mode or diagnostic mode, under the control of a pre-determined protocol. That is, during the link mode, particularly, the transmit mode, the MAC  490  is to perform an uplink to the network  492  via the transmitter  420 . Hence, as shown in  FIG. 5B , transmitter  420  is active and the T/R switch  540  and the A/T switch  550  are switched to positions T and A respectively. By such arrangements, the output signals generated by the MAC  490  can be ensured to travel from the transmitter  420  to the directional coupler  570  and through the antenna  430  out to the network  492 , and not arriving at the receiver  410 .  
         [0035]     In the receive mode, the MAC  490  is to downlink signals from the network  492 . Hence, the T/R switch and the A/T switch are, switched to positions R and A, respectively, such that incoming signals from the network  492  travel via the antenna  430  to the receiver  410  and is processed by the MAC  490  accordingly. Additionally, MAC  490  can also be in a crosslink with the network  492  such that the network apparatus  500  is operating successively between the transmit mode and the receive mode.  
         [0036]     Under the diagnostic modes, as shown in  FIG. 5B , both the transmitter  420  and the receiver  410  are active, and the T/R switch and the A/T switch are switched, under the predetermined protocol, to positions R and T respectively such that signals travel on the signal path P from the transmitter  420  to the receiver  410  via passing through the directional coupler  570  and the attenuator  560 . The predetermined protocol is for preferably a link logic control (LLC).  
         [0037]     Preferably, the network apparatus  500  is applied in a device controlled by a test controller  480 , such that the device is for instance a personal computer controlled by a test utility thereof. The test controller  480  is for controlling the network apparatus  500  to monitor connection status and make configuration and encryption settings to the transmitter  420  and the receiver  410 .  
         [0038]     The diagnostic mode further includes a transmit self-test mode, a receive self-test mode, and a crosslink self-test mode for testing different network connectivity characteristics of the network apparatus  500 . There are many signal quality parameters that are indicative of the network connectivity, and the below list is not exhaustive. For signal quality, for instance, one can observe receive signal strength indicator (RSSI) and signal quality indicator in packet error rate (PER), to determine receiver maximum and minimum output powers or observe relative signal strength indicators (SSI); one can observe transmit signal strength indicator (TSSI) and signal quality indicator in packet error rate (PER) or error vector magnitude (EVM), or spectrum mask, to determine transmitter maximum and minimum output powers. For link quality, one can observe link quality indicators (LQI) in uplink/downlink throughputs or uplink/downlink packet loss rates and packet loss periods etc. For quality of service QoS, one can observe indicators of QoS (IQoS) in uplink/downlink delays and uplink/downlink jitters etc.  
         [0039]     In the transmit self-test mode, the MAC  490  is to tune the transmitter  420  such that the output signals are output substantially at a predetermined maximum power level satisfying a predetermined transmitter packet error rate (PER) such that the transmitter output power is optimized. In the receive self-test mode, the media access control (MAC)  490  is to tune the transmitter  420  such that the output signals are output substantially at a predetermined minimum power level satisfying a predetermined receiver PER, such that the receiver sensitivity is checked. In the crosslink self-test mode, the media access control (MAC)  490  is to tune the transmitter  420  such that the output signals are output at a rated or an average crosslink power level satisfying a predetermined LQI and a predetermined IQoS, such that the link quality and the quality of service are checked.  
         [0040]     Although in the first embodiment the invention has been demonstrated with the output signals being tested against a predetermined transmitter PER, in the transmit self-test mode, to optimize transmitter output power, the output signals can alternatively be tested against a predetermined transmitter EVM, or spectrum mask etc.  
       Second Embodiment  
       [0041]      FIG. 6A  illustrates a network apparatus according to a second embodiment of the invention. The second embodiment is distinguished from the first embodiment in that, the network apparatus  600  includes a directional coupler  572 , an attenuator  560 , and a second switch (such as an antenna/receiver (A/R) switch  552 ) that are inter-disposed on the signal path P between the transmitter  420  and the receiver  410 , such that when the A/R switch  552  connects the transmitter  420  to the attenuator  560  in the self-test mode, the output signals travel from the transmitter  420  to the receiver  410  instead via the order of passing through the attenuator  560  and the directional coupler  572 .  
         [0042]      FIG. 6B  shows a mode selection table for the network apparatus of  FIG. 6A  under test. The A/R switch  552  operates similar to the A/T switch  550  of  FIG. 5A . The notable distinction is that, under the diagnostic mode, the T/R switch  540  is instead switched to position T to avoid the incoming signals from the network  430  also traveling to the receiver  410 .  
         [0043]     As shown, the first and the second embodiments of the invention are cost-effective by simplifying and embedding the conventional test equipments into the network apparatus  500 . The transmitter and the receiver can be used in the diagnostic mode to check for device functionality. That is, if an apparent error has occurred from the network connectivity test, then it can be inferred that at least one of the transmitter  420  or the receiver  410  may be malfunctioning and the transmitter-receiver pair can be removed and replaced accordingly. Also, the network apparatus according to the embodiments of the invention are relatively cheaper, lighter in weight, and less power consuming, and due to less complexity, are also less prone to errors. Thus, the network apparatus according to the embodiment of the invention is especially viable commercially in that the manufacturer and even the buyer can diagnose the network apparatus in all network levels, including the PHY and MAC layers, to troubleshoot errors without expensive test equipments.  
         [0000]     Applications  
         [0044]     Additionally, the test controller  480  can utilize the network apparatus  500  to connect the device to another one of said device having another one of said network apparatus applied therein, for performing mutual network connectivity between the two network apparatuses.  FIG. 7  shows a block diagram of the mutual network connectivity test between two network apparatuses according to a preferred embodiment of the invention. The mutual network connectivity test involves network apparatuses  500 ( 1 ) and  500 ( 2 ), test controller  480 ( 1 ) and  480 ( 2 ) and an attenuator  710 . As shown in the figure, the network apparatus  500 ( 1 ), such as one shown in  FIG. 5A , is controlled by the test controller  480 ( 1 ) and used as a reference device to test network connectivity of the network apparatus  500 ( 2 ), by sending output signals that travel through the attenuator  710  emulating channel attenuation. Alternatively, the network apparatus  500 ( 2 ) can then subsequently used as the reference device to test network connectivity of the network apparatus  500 ( 1 ), i.e. the two can be used as reference devices interchangeably for mutual network connecting testing.  
         [0045]     In addition to being applied in a client station, for example a personal computer controlled by a test utility thereof, the network apparatus can also be applied in an embedded station in a basic service set (BSS), while the test controller serves as an access point (AP) in the BSS servicing the embedded station. The network apparatus can further be applied in an AP in an extended service set (ESS), while the test controller acts as a server center in the ESS servicing the AP.  
         [0046]     Additionally, a method of self-testing network connectivity applied in the network apparatus, such as network apparatus  500 , is proposed.  FIG. 8  shows a preferred embodiment of the method of self-testing network connectivity. First, in the transmit self-test mode, the transmitter  420  is tuned to optimize uplink capability, such that the output signals are output substantially at a predetermined maximum power level satisfying a predetermined transmitter packet error rate (PER), as indicated by step  810 . The predetermined transmitter PER can for instance be stored in a solid-state memory of the device in which the network apparatus is applied. Then, in the receive self-test mode, the transmitter  420  is tuned to check downlink capability, such that the output signals are output substantially at a predetermined minimum power level satisfying a predetermined receiver PER, as shown by step  820 . To simulate the typical power of uplink and downlink traffic of the network apparatus in a link mode, step  830  is performed under the crosslink self-test mode to tune the transmitter  420  such that the output signals are output at a rated or an average crosslink power level. The transmitter is checked to see if the rated or average crosslink power level satisfies a predetermined link quality indicator (LQI) and a predetermined indicator of quality of service (IQoS).  
         [0047]     The step  810  of optimizing uplink capability can include additional steps.  FIG. 9  shows the sub-steps of step  810  in optimizing uplink capability. First, step  910  is performed to read the output signals by the receiver  410  to obtain a first receiver signal quality indicator (SQI). For distant communications, it is important that the output power of the transmitter must be strong enough to ensure transfer quality. Thus, step  920  is performed to tune the transmitter  420  to output substantially at the predetermined maximum power level such that the first receiver SQI is less than or equal to a predetermined first max SQI. Since it is also important to have adequate minimum output power, such that in circumstances in which the network apparatus is, for instance, applied in a client station and is in close proximity with an AP, the transmitter  420  may be additionally tuned to output the output signals substantially at a predetermined minimum output power level such that the first receiver SQI is less than or equal to a predetermined first min SQI (step not shown). To optimize downlink capability, transmitter PER is preferably checked along with the transmitter maximum power level test of step  920 ; the two factors are trade-offs of each other, and there is a limit to the strength of the maximum output power. That is, if the output power of the transmitter  420  is increased to saturation, signals in OFDM (orthogonal frequency division multiplexing) and QAM (quadrature amplitude modulation), for instance, can become worse due to transmitter nonlinearity that the associated PER increases significantly.  
         [0048]     Consequently, step  930  is performed to read a first receiver signal strength indicator (RSSI) from the output signals. Thereafter, step  940  is performed to tune the transmitter  420  to output the output signals substantially at the predetermined transmitter PER, such that the first RSSI is within a predetermined RSSI range preferably having a lower limit of 18 dBm and an upper limit of 20 dBm. The transmitter  420  is tuned limiting the PER of the output signals within the predetermined RSSI range in order to ensure that the signal strength satisfies the associated Wi-Fi standard, EMI/FCC requirements, and other factory specifications.  
         [0049]      FIG. 10  shows the sub-steps of step  820  in checking downlink capability. In the receive self-test mode, a second receiver signal quality indicator (SQI) associated with the output signals is read from the receiver  410 , as shown in step  1010 . The transmitter  420  is then tuned to output substantially at the predetermined minimum power level such that the second receiver SQI, when read from the output signals at the receiver  410  for checking receiver sensitivity, is less than or equal to a predetermined second max SQI, as shown in step  1020 . As analogous to the transmit self-test mode, due to trade-off relationship, the receiver PER in the receive self-test mode is preferably tested jointly with the receiver sensitivity step  1020 . Consequently, a second receiver signal strength indicator (RSSI) associated with the output signals is read from the receiver  410 , as shown in step  1030 , and the transmitter is tuned to output the output signals substantially at the predetermined receiver PER such that the second RSSI is less than or equal to a predetermined maximum RSSI, as shown in step  1040 . Since it is also important to have adequate maximum input power, such that in circumstances in which the network apparatus is, for instance, applied in a client station and is in close proximity with an AP, the transmitter  420  may be additionally tuned to output the output signals substantially at a predetermined maximum input power level such that the second receiver SQI is less than or equal to a predetermined second min SQI (step not shown). That is, if the input power of the receiver  410  is increased to saturation, signals in OFDM (orthogonal frequency division multiplexing and QAM (quadrature amplitude modulation), for instance, can become worse due to receiver nonlinearity that the associated PER increases significantly.  
         [0050]      FIG. 11  shows a flow chart of the sub-steps of step  830  in checking crosslink capability. First, under the crosslink self-test mode, step  1110  is performed to read link quality indicator (LQI) associated with the output signals at the receiver  410 . The transmitter is tuned at a rated or an average power level to see if the LQI is greater than or equal to the predetermined LQI, as shown in step  1120 . In cases when the output signals contain time dependent data i.e. audio/video data, it is important to check, in addition to link quality and signal quality, for the quality of service so as to ensure no delays or jitters to the audio/video during the transfer. Thus, as shown in step  1130 , an indicator of quality of service (IQoS) associated with the output signals is read from the receiver  410 , and the transmitter is then tuned at a rated or an average power level to see if the IQoS is less than or equal to the predetermined IQoS, as shown in step  1140 .  
         [0051]     To overcome conventional needs for the presence of an expensive spectrum analyzer, which comes at the price of tens of thousands, to analyze frequency spectrum of the output signals, a novel method of analyzing frequency spectrum is proposed. The invention reconstructs the frequency spectrum by summing the output signals at the side of receiver  410 , where the output signals are transmitted from the respective channels assigned to the transmitter  420 . The channels often have reserved overlap regions; as a result, the output signals reconstructed, by combining frequency-domain mainbeam and sidelobe patterns detected from individual channels, may not appear identical to one constructed from a spectrum analyzer. However, it bears enough resemblance to be useful in determining whether the output signals reconstructed meets, for instance, the specification of an 802.11g standard, by checking the power level differences of the output signals with a plurality of predetermined threshold values.  
         [0052]      FIG. 12  shows a method of analyzing frequency spectrum according to a preferred embodiment of the invention. The method is applied in a network apparatus for self-testing network connectivity, such as one shown in  FIG. 5A . The network apparatus  500  includes a plurality of channels per each radio (transmitter or receiver). The total channel number is increased if dual-band (or tri-band; or quad-band) transmitter or receiver is used in a combo network apparatus. The total channel number is double (or triple; or quadruple) if two (or three; or four) transmitters or receivers are used in a multiple-input-multiple-output (MIMO) network apparatus. For instance and as a basic example, in an IEEE 802.11b wireless LAN system, the frequency band is divided into 11 overlapped channels of 22 megahertz (MHz) each. The transmitter  420  and the receiver  410  are assigned m and n channels of the plurality of channels, respectively, where m and n are positive integers. Generally, integers m and n are set to be equal. The method of analyzing frequency spectrum begins at step  1210 , in which the transmitter  420  transmits, by a selected channel of the m channels assigned to the transmitter  420 , a plurality of output signals at a high-limit power level. The output signals are transmitted at a high-limit power in order for the receiver  410  to be able to detect the lowest sidelobes of the frequency domain pattern formed by the output signals, which are often low in power. At step  1220 , the receiver  410  receives the output signals via the n channels assigned to the receiver  410 , for measuring corresponding power level at each channel of the n channels assigned to the receiver  410 . Then, step  1230  is performed to calculate power level differences between the received power of the channel of the n channels assigned to the receiver  410 , which corresponding to the channel of the m channels assigned to the transmitter  420 , and the received powers of the adjacent channels. At step  1240 , the calculated power level differences, collectively forming a frequency spectrum, are compared with a plurality of pre-determined threshold values of spectrum mask, stored in a memory controlled by the media access control  490 , such as the solid-state memory in the device of which the network apparatus  500  is applied. Then, step  1250  is performed to generate another set of output signals at a high-limit power level by another selected channel of the remaining m channels assigned to the transmitter  420  and step  1220  is returned. That way, by generating output signals sequentially one by one from the m channels assigned to the transmitter  420 , and then subsequently having the output signals received simultaneously by all the n channels assigned to the receiver  410 , the plurality of frequency spectra of the output signals can be constructed.  
         [0053]     The memory can store m sets of pre-determined threshold values in the form of a look-up table to correspond to the different sets of output signals outputted individually from the m channels assigned to the transmitter  420 . The reasoning can be better understood with reference to FIGS.  13 A-D. As shown in  FIG. 13A , it illustrates a couple of frequency spectra of the outputs signals transmitted by the transmitter  420 . As shown in  FIG. 13B , it illustrates the individual frequency response of the receiver channels, the receiver is shown with 11 bandpass channels with a bandwidth of 22 MHz. The channels are overlapped, and have a crossover region of 5 MHz.  FIG. 13A  illustrates frequency spectra  1310  and  1320  of the output signals transmitted from transmitter  420  as having single mainbeam and multiple sidelobes. The transmitter  420  for instance has 11 channels (m=11), with each channel being equidistant from one another, and frequency spectra  1310  and  1320  are for instance generated by channel  1  and channel  6  of the 11 channels, respectively. During the step of  1210 , the selected channel of the m channels, such as channel  1 , is to transmit the output signals with a frequency spectrum of  1310 . Due to spectral alignment, the channels assigned to the receiver  410  only receive part the frequency spectrum  1310 . Namely, suppose the spectral distribution of the channels of the transmitter and the receiver are drawn into perspective in  FIGS. 13A and 13B , then the part of the frequency spectrum  1310  to the left with respect to the Y axis is out of the range of the channels of the receiver  410 , and is therefore not detected. Consequently, the constructed frequency-domain pattern of the output signals, as received by the receiver  410 , has the shape shown in  FIG. 13C . In case of channel  6  of the m channels, on the other hand, the frequency spectrum  1320  generated therefrom is properly aligned with the n (=11) channels of the receiver  410 . Thus, the constructed frequency-domain pattern of the output signals originating from channel  6  of the transmitter has the shape as shown in  FIG. 13D . Thus, as shown, the memory may be preferable to store m sets of pre-determined threshold values to correspond to the different sets of output signals outputted individually from the m channels assigned to the transmitter  420 .  
         [0054]     Additionally, a check-result summary can be displayed according to the calculated power level differences and the pre-determined threshold values, such as in the form of a histogram, which can provide users a viewing on a display screen. The check-result summary may be used as a basis for tuning the high-limit power of the output signal such that the calculated power level differences are substantially equal to the corresponding pre-determined threshold values, thus satisfying the specification of, for instance, the Wi-Fi standard. An additional sub-step may further be included to check whether the n channels assigned to the receiver  410  have finished in receiving the output signals from all of the m channels assigned to the transmitter  420 .  
         [0055]     Accordingly, by applying the method of analyzing frequency spectrum, according to the embodiment of the invention serving the function of a conventional spectrum analyzer, costs, size and weight of the network apparatus are effectively minimized. The method can optimize the transmitter to fit the spectrum mask requirement which is particularly related to WiFi standard.  
         [0056]     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.