Abstract:
A signal generator generates amplitude noise on a selected segment of a test signal. A user interface is used for selecting a segment of the test signal and an associated power level for applying amplitude noise at a selected power level to the test signal segment. A signal processing unit compiles the selected power level of the selected segment with the test signal to generate digital data representative of the test signal with selected segments having amplitude noise. A waveform generator receives the digital data and generating a test signal output having amplitude noise at selected segments of the test signal. The method includes the steps of: selecting a segment of the test signal to add amplitude noise; selecting a power level for the amplitude noise; and applying the amplitude noise at the selected power level to the selected segment of the test signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application clams priority from Indian Provisional patent application Serial No. 1112/MUM/2007, filed Jun. 12, 2007 and incorporates by reference herein the contents of Indian Provisional patent application No. 1112/MUM/2007 as if such contents were set forth in full herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the generation of test signal and more particularly to a signal generator and user interface for adding noise to selected portions of the test signal generated by the signal generator. 
     To check the operation of an electrical circuit under test, a test signal is provided to the circuit under test. A signal generator is an apparatus that provides such at test signal for checking the operation of the circuit under test. The signal generator has controls for setting-up the test signal according to user settings. The output signal from the electrical circuit may be observed by a measurement instrument, such as an oscilloscope or the like. 
     Various manufacturers provide user interfaces for setting-up test signals. One Example is the WinIQSIM™ Simulation Software, manufactured and sold by Rohde &amp; Schwarz. The simulation software provides a user interface for setting-up digitally modulated signals and adding impairments to the signals. The user interface has a multi-carrier block diagram as shown in  FIG. 1A  having various blocks for defining parameters and setting impairments to the signal. Clicking on one of the blocks, such as the Data Source block, opens a data source dialog window as shown in  FIG. 1B  where the user can define data parameters or import a data file. Once the user has set the parameters of the data source, the user clicks the OK box and the dialog box closes. Clicking on the Modulation Setting block as shown in  FIG. 2A  opens a Modulation dialog window as shown in  FIG. 2B  where the user can set the modulation parameters of the signal. Clicking on the OK box closes the Modulation Setting dialog window. Clicking on the Noise block as shown in  FIG. 3A  and setting the Noise “On” opens a Noise dialog window as shown in  FIG. 3B  where the user can set noise levels for the signal. Clicking on the OK box closes the Noise dialog window. 
     A drawback to the above described user interface is that the noise impairment is applied to the total signal and is not to selected portions of the signal, such as the Preamble, Physical Layer Convergence Protocol (PLCP) Header, Payload or selected symbols within a WiMedia ultra wideband signal as defined by the WiMedia Alliance. Keeping selected portions of the WiMedia ultra wideband signal free of noise, such as the Preamble, allows the user to better discriminate the contribution of the added noise in the received signal, allowing the user to setup appropriate demodulation and channel equalization schemes. 
     What is needed is a user interface for use with a signal generator that allows a user to add noise to selected portions of test signal, such as pseudo random noise, additive white Gaussian noise (AWGN) and the like. The user should be able to select the location of the noise within the signal and set the level of noise to be produced. 
     SUMMARY OF THE INVENTION 
     The present invention is a signal generator and method for adding amplitude noise to a test signal. The signal generator has a user interface for selecting a segment of the test signal and an associated power level for applying amplitude noise at a selected power level to the test signal segment. A signal processing unit compiles the selected power level of the selected segment with the test signal to generate digital data representative of the test signal with the selected segment having amplitude noise. A waveform generator receives the digital data and generates a test signal output having amplitude noise at selected segments of the test signal. A memory stores the compiled digital data representative of the test signal with amplitude noise at the selected segment. 
     The user interface has a packets display element and a symbols display element with the selection of the packets radio button display element activating selectable pre-defined packet segments of the test signal with each pre-defined packet segment having an associated selectable power level box. One of the pre-defined packet segments may be selected along with a selected power level of the amplitude noise in the selected segment. The selection of the symbols radio button display element activates symbol boxes and associated selectable power level box. Beginning and ending symbol numbers of a segment of the test signal may be selected along with a selected power level of the selected segment amplitude noise. 
     The method for adding amplitude noise to a test signal has the step of: selecting a segment of the test signal to add amplitude noise; selecting a power level for the amplitude noise; and applying the amplitude noise at the selected power level to the selected segment of the test signal. The selecting of the test signal segment may include the step of selecting at least one from a plurality of packets within the test signal to apply the amplitude noise. The packet selecting step includes the step of selecting from the plurality of packets one of a pre-defined preamble, a Physical Layer Convergence Protocol (PLCP) header, and a payload packet. The selecting of the test signal segment step may alternately have the step of selecting a sequence of symbols within the test signal to apply the amplitude noise. The applying step includes compiling the amplitude noise at the selected power level of the selected segments with the test signal. The compiling step includes the step of generating an additive white Gaussian noise (AWGN), pseudo-random noise, or the like for the amplitude noise. 
     The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a Multi-carrier block diagram of an existing simulation software program for setting-up digitally modulated signals and adding impairments to the signals. 
         FIG. 1B  is a data source dialog window called using the Multi carrier block diagram. 
         FIG. 2A  is the Multi carrier block diagram with Modulation Setting block highlighted. 
         FIG. 2B  is a Modulation Setting dialog window called using the Multi carrier block diagram. 
         FIG. 3A  is the Multi carrier block diagram with Noise block highlighted. 
         FIG. 3B  is a Noise dialog window called using the Multi carrier block diagram. 
         FIG. 4  shows a signal generator having a user interface for selecting amplitude noise segments in a test signal according to the present invention. 
         FIG. 5  is a representative block diagram of a signal generator having the user interface for selecting amplitude noise segments in a test signal according to the present invention. 
         FIG. 6  is a display of the user interface for applying noise to selected portions of a test signal according to the present invention. 
         FIG. 7  is a display of test signal prior to the application of noise to selected portion of the test signal. 
         FIG. 8  is display of the signal definition user interface incorporating the user interface for applying noise to selected portions of a test signal according to the present invention. 
         FIG. 9  is a display of a test signal with amplitude noise applied to the preamble of the test signal. 
         FIG. 10  is a display of the test signal with amplitude noise applied to the header of the test signal. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 4 , there is shown a signal generator  10 , such as the AWG7102, manufactured and sold by Tektronix, Inc. Beaverton, Oreg. The signal generator  10  generates signal outputs defined by a user using front panel controls, such as buttons and knobs  12  on the front panel  14  of the signal generator  10  in conjunction with a user interface displayed on a display device  16 , such as a liquid crystal display, cathode ray tube or the like. The signal generator  10  also has a CD or DVD/CD drive for storing waveform data, executable programs and the like. 
     With reference to  FIG. 5 , there is shown a representative block diagram of the AWG7102 signal generator  10 . The signal generator  10  has a central processing unit (CPU)  20  that controls the operation of the instrument according to programs stored on a hard disk drive (HDD)  24 . A memory  22 , such as RAM memory, is used for a work area for the CPU  20  for programs read from the storage device  24 . A user can set up the signal generator via the button, knobs and the like  12  on the front panel  14  of the instrument. The display device  16  provides the user interface for visualizing the information relating to signal patterns and user settings. An external display output circuit  26  provides a video output which may be connected to an external display  28  for providing a larger display area in addition to the built-in display  16  of the signal generator. A waveform generation circuit  30  generates signal patterns based on user defined parameters. In this example, the waveform generator circuit has two channel outputs and inputs for trigger and event signals. An input/output port  32  is used for connecting an external keyboard  34 , a pointing device, such as a mouse  36 , and the like to the signal generator. The external keyboard  34  and/or mouse  36  may be included as part of the front panel controls of the signal generator. The blocks are coupled together via a signal and data bus  38 . The bus  38  of the signal generator may have a Local Area Network (LAN) interface  40  for connecting the signal generator to an external controller, such as a personal computer (PC)  42 . The LAN interface  40  allows the user interface to operate on the PC  42  as well as enabling the PC  42  to control the signal generator over a network. Alternatively, a General Purpose Interface Bus (GPIB) interface may be used for the LAN interface  40 . 
     Referring to  FIG. 6 , there is shown the gated noise user interface  50  for setting user specified power levels of amplitude noise on segments of a test signal, such as an WiMedia ultra wideband signal as defined by the WiMedia Alliance, such as displayed in  FIG. 7 . The WiMedia ultra wideband signal is shown without any amplitude noise added to the signal. The gated noise user interface  50  operates under program control of the CPU  20  with the user interface programs stored on the HDD  24 . The gated noise user interface  50  may be displayed on the display device  16  or on the external display  28 . Alternately, the gated noise user interface programs may be stored and accessed by the PC  42 . The gated noise user interface  50  is preferably activated from within a signal definition user interface  80  as shown in  FIG. 8  and described in greater detail below. Performing data entry operations is done using the front panel controls  12  of the signal generator  10  or by using the keyboard  34  and mouse  36  connected to the signal generator  10 . The gated noise user interface  50  has a “Turn on” check box  52  that is clicked to activate the gated noise user interface  50 . The user may add amplitude power noise, preferably in the form of an additive white Gaussian noise (AWGN), pseudo-random noise, or the like, to pre-defined segments of the WiMedia ultra wideband signal packets, such as Preamble, Physical Layer Convergence Protocol (PLCP) Header and Payload by clicking the on the “Packets” icon radio button display element  54 . The user may also add amplitude noise to selected symbols within the packets by clicking on the “Symbols” radio button display element  56 . Check boxes, radio buttons, icons, and the like are display elements of the gated noise user interface  50  and a signal definition user interface  80  to be described in greater detail below. 
     If the user selects “Packets”, then the user has the option of selecting one or more of the segments of the WiMedia ultra wideband test signal by clicking on the appropriate check boxes  58 ,  60 ,  62  associated with each of the signal segments. Each signal segment also has a power level data box  64 ,  66 ,  68  in which the user can set the power level of amplitude noise on the selected segment of the test signal. For example, the user may wish to add −10 dB of noise to the Preamble. The user clicks on the check box  58  associated with the Preamble and then enters −10 dB into the power level data box  64  associated with the Preamble. Each of the power level data boxes  64 ,  66  and  68  have up/down arrows which the user can click on to increase or decrease the power level of the noise. The resulting output test signal, as shown in  FIG. 9  has the prescribed amount of amplitude noise applied to the Preamble of each packet of the test signal. 
     In another example, the user wishes to add −10 dB of amplitude power noise to the PLCP Header. The user clicks on the check box  60  associated with the PLCP Header and enters −10 dB in the power level data box  66  associated with the PLCP Header. The resulting output test signal, as shown in  FIG. 10  has the prescribed amount of amplitude power noise applied to the PLCP Header of each packet of the test signal. 
     If the user selects “Symbols”, the user has the option of setting which symbols in the WiMedia ultra wideband test signal will receive the amplitude power noise. The “Symbol” area has two symbol data boxes  70  and  72  in which the user can enter the beginning and ending symbol numbers. Each of the data boxes  70  and  72  have up/down arrows which the user can click on to increase or decrease the symbol numbers. There is also included a power level data box  74  in which the user can set the level of amplitude power noise on the selected symbols. As with the other power level data boxes, the power level data box  74  has up/down arrows which the user can click on to increase or decrease the amplitude power level of the noise. When the user has set the gated noise for the test signal, the user may click on the compile button  76  to corn pile the test signal with the selected gated noise on the test signal. 
     The gated noise user interface  50  is preferably incorporated into a signal definition user interface  80 , as shown in  FIG. 8 , where a user sets parameters and data values for the WiMedia ultra wideband signal. The user interface  80  includes a Packet Group area  82  for defining Packet Groups and PPDUs in Group area  84  for defining Presentation Protocol Data Units (PPDUs). Associated with each PPDU is a frame structure interface  86  of the UWB signal. The frame structure  86  allows the user to define Presentation Protocol Data Units (PPDUs) settings  84  using front panel controls  12  of the signal generator  10  or by using a keyboard  34  and mouse  36  connected to the signal generator  10 . The user interface  80  has two mode radio buttons  88  and  90  for setting the operational modes of the WiMedia ultra wideband signal. One mode is for conformance testing and the other allows the customizing of the parameters of the WiMedia ultra wideband signal. In conformance testing, the parameters of the UWB signal are fixed as defined by the standard apart from the pull down options that are provided, such as length, scrambler init, burst mode, preamble type and the like. In the custom mode, the parameters are editable and can be modified by the user. 
     The frame structure  86  displays PPDU elements as a PLOP Preamble box  92 , a PLCP Header box  94  and a PSDU (Physical Layer Service Data Unit) box  96  which are defined in the WiMedia ultra wideband signal standard. Each of the boxes  92 ,  94 , and  96  has a smaller “±” box  98 ,  100 ,  102  that may be clicked on to display components of each of the PLCP Preamble, PLCP Header and the PSDU as shown by component boxes  104 ,  106  and  108 . The PLCP Header box and the PSDU box each has a further check box  110 ,  112  that may be clicked on and off. The PLCP Header and/or the PSDU are not provided in the WiMedia ultra wideband signal when their respective check boxes  110 ,  112  are clicked off. Selected component boxes of the PLCP Preamble, PLCP Header and the PSDU also have “±” boxes which allows the user to display detailed setting items associated with the components. 
     The user builds a test signal by first selecting between the conformance mode and the custom mode. In either mode, the user defines PPDUs by assigning a PPDU name in a Name column in a display box of the PPDUs in Group area  84 . The Name column has an associated Index column which provides indexes values to the PPDU names. The user then uses the frame structure  86  for setting the parameters for the named PPDU. In the conformance mode, the user is restricted to changing parameters that are provided in the drop down menus associated with curtain of the components and allowed by the WiMedia ultra wideband signal standard. In the custom mode, the parameters may be changed beyond the boundaries of the WiMedia ultra wideband signal standard and/or intentional error data (data impairment) may be provided to the test signal. This allows a test signal to be generated that stresses a device under test receiving the signal to determine the operating limits of the device under test and characterize the design of the device under test to secure the operational stability. 
     Assuming the user interface is set for the custom mode, the user can individually click on the “±” boxes  98 ,  100 ,  102  in the PLCP Preamble box  92 , the PLCP Header box  94  and a PSDU box  96  to display the respective components boxes  104 ,  106  and  108  of the Preamble, Header and PSDU. When a “−” symbol appears in one of the “±” boxes  98 ,  100 ,  102 , the associated component boxes  104 ,  106  and  108  of the Preamble, Header and the PSDU are displayed. When a “+” symbol appears in one of the “±” boxes  98 ,  100 ,  102 , the associated component box  104 ,  106 ,  108  is not displayed. Associated with each of the components are either drop down menus or data boxes which the user may select or enter values. Some of the component boxes  104 ,  106  and  108  also have “±” boxes, such as the Packet Sync Sequence in the Preamble component boxes  104 , the PHY Header and MAC Header in the PLCP Header component boxes  106  and the Frame Payload in the PSDU component boxes  108 . Clicking on the “±” boxes in the component boxes displays detailed setting items of the components, such as the shown by the “−” in the “±” box associated with the PHY Header component. The PHY header detailed setting items further have drop down menus and data boxes which the user may select or input values. A “Process This Packet” icon  114  is provided at the bottom of the signal definition user interface  80  for processing the entered data and parameters for each of the PLCP Preamble, PLCP Header and PSDU in the PPDU into hexadecimal codes. At this time, checking codes such as HCS, etc. are automatically generated. If the user wants to maintain the intentional modification via the user interface rather than the auto-generation, “Process Preferences”  115  provides an option to select whether the auto-generation is applied or not. 
     Once the user has set the parameters for the currently defined PPDU, the user can add a new PPDU to the PPDUs in Group area  84  by clicking the add button  116  associated with the PPDUs in Group area  84  are and assign a new PPDU name. The user then uses the frame structure  86  to set the parameters for the new PPDU. The user can define and set the parameters for any number of PPDUs by assigning new PPDU names for each of the PPDU as representatively shown by PPDU  1  through PPDU  4  in PPDUs in Group area  84 . 
     The PPDUs are grouped into Packet Groups using the Packet Group area  82 . The Packet Group area  82  has a display box that includes an Index column, a Name column, and a Repeat column. The user assigns a name to the Packet Group and set the number of times the Packet Group is to repeat. An index value is assigned to each Packet Group. An add button  118  associated with the Packet Group  82  allows a user to add new Packet Groups. The ability to associate multiple PPDUs with a Packet Group, define multiple Packet Groups and repeat the Packet Groups multiple times allows the user to develop a complex test signal for stressing a device under test. 
     Once the user has defined the test signal, the user can click on the “Interference Addition” tab  120  in the signal definition user interface  80  to add gated noise to the test signal. Clicking on the “Interference Addition” tab  120  opens the interference addition window as shown in  FIG. 6  containing the Gated Noise user interface  50 . The user adds amplitude power noise to some or all of the signal packets of the defined test signal and then clicks on the compile icon  122  at the top of the signal definition user interface  80 . The signal definition user interface program compiles the parameters and data for the test signal including the gated noise into digital data values that are stored in the memory  22  of the signal generator  10 . The waveform generation circuit  30  in the signal generator  10  receives the stored digital data representing the test signal and generates signal patterns based on user defined parameters and values set using the signal definition user interface  80  and the gated noise user interface  50 . 
     While the above gated noise user interface  50  has been described in relation to a WiMedia ultra wideband signal, the present invention may also be incorporated for use with other signal standards, such as 802.11n, 802.15.3c, WiFi, WIMAX, and WIHD standards. 
     The foregoing description of the invention has been described for the purposes of clarity and understanding. It is not intended to limit the invention to the precise form disclosed.