FSK Transmitter/Receiver Simulation Using AWR VSS

Transcription

1 FSK Transmitter/Receiver Simulation Using AWR VSS Developed using AWR Design Environment 9b This assignment uses the AWR VSS project titled TX_RX_FSK_9_91.emp which can be found on the MUSE website. It requires software version 9b or later; if you need to update your software click on Help Check for update from the main window in the AWR design environment. Instructions for obtaining a node-locked (for personal use) educational version of MWO: Go to Here you can make your own license which will be sent to you through . You will also be provided a link to the software download area. If you are already registered on the AWR website you will use that same account to get the software. If you are not previously registered the license generation will send you another with the account login information. (See end of document for step-by-step procedure.) Overview In this project you will run various simulations of a transmit-receive system that uses frequency-shiftkeyed modulation. In particular you will analyze the microwave spectrum of the transmitted and received signals, the transmitted and received bit streams, and the overall bit error rate (BER) of the system. The goal is to examine how changes in system parameters such as amplifier and antenna gain, amplifier compression, and noise affect the signal quality and system performance. The simplified system you will use is shown in the figure below. It consists of the following components, starting from the left-hand side: Signal source: o A binary digital source that generates a random bit stream, and a digital-to-analog converter (this is the information signal ) o A 5. GHz continuous wave local oscillator signal (the carrier signal ) o An FM modulator Transmitter front-end: o A power amplifier (PA) o A transmit antenna Receiver front-end: o A receive antenna (this block is also where you will specify path loss) o An additive white Gaussian noise channel, AWGN; in this block the noise is added to the spectrum o A low noise amplifier (LNA) Signal detection: 1

2 o Filter, discriminator and integrator (this combination acts on the baseband signal, so we do not need to include frequency down-conversion blocks, and demodulates the FSK signal) o An analog-to-digital converter Signal measurement: o A bit-error-rate meter o A signal aligner that insures that the original random data stream is synchronized with the demodulated data stream to facilitate the BER measurement TX Antenna TX_ANTENNA ID=S1 ANTGAIN= db NOISE=Auto RX Antenna RX_ANTENNA ID=S PATHLOSS=Path_Loss db ANTGAIN= db NOISE=Auto Binary Digital Source (RND_D) RND_D ID=A M= RATE=1e4 ID=Data D DAC ID=A3 DAC SINE ID=A5 FRQ=5. GHz AMPL= PHS= Deg CTRFRQ= SMPFRQ= A FM Modulator Tx LO 1 FM_MOD ID=A4 KF=353.5 ID=FSK PA 3 AMP_B ID=A11 GAIN=PA_GAIN db P1DB=PA_P1dB dbw IP3= IP= MEASREF= OPSAT= NF= db NOISE=Auto RFIFRQ= PA_GAIN = PA_P1dB =1 Path_Loss = -76 ID=PA_1 Channel_Noise = sweep(stepped(-84,-14,-4)) Channel_Noise = sweep(stepped(-84,-9,-4)) Channel_Noise = -14 AWGN ID=A1 PWR=Channel_Noise PWRTYP=Single-sided PSD (dbm/hz) LOSS= db ID=AWGN_1 PLSSHP ID=F1 ID=LNA_1 PLSTYP=Gaussian (BT) ALPHA=.5 PLSLN= NRMTYP=Unit Pulse Gain IMPTYP=Auto NL_AMP ID=A14 GAIN=1 db P1DB=-3 dbm IP3=7.1 dbm IPH=17.1 dbm NF=1 db NOISE=Auto AWGN RX Amplifier FM_DSCRM ID=A7 GAIN=1/353.5 IPHS= ID=Discrim NFFT= NAVG= WNDTYP=Auto SMPSYM= INTG_DMP ID=A8 N=8 INTGTYP=Sum*Time Step dt ID=INT_Dump NFFT= NAVG= WNDTYP=Auto WNDPAR= WNDWHN=Auto SLDFRC=.5 SMPSYM= MSKTYP=Pass-Symmetric ADC ID=A9 M= SMPSYM= Filter Discriminator Integrate & Dump ADC A D ID=ADC NFFT= NAVG= WNDTYP=Auto BUFSZ= ALIGN ID=A1 N= REEVAL= CORRDLY= DLYCOMP=Yes INTRPSPN= GAINCOMP=None PHSCOMP=Reversal only SMPLPTS= ALIGN (Compensate for system delay) 4 BER_EXT ID=BER1 VARNAME="Channel_Noise" VALUES= OUTFL="" BER BER Meter Figure 1. FSK transmit-receive system (BFSK system diagram). To the right of the FM modulator there is a list of variables that are assigned default values; these are enlarged below. In the procedure you will be instructed to modify these values, and sometimes to return to the default values. PA_GAIN and PA_P1dB are the gain and 1 db compression point (in db and dbw, respectively) for the power amplifier. Path_Loss is the total attenuation in db through the channel (note that it is negative, so is actually a gain). Channel_Noise is the noise added to the spectrum and is specified in terms of dbm/hz. The actual noise level you will observe in the spectrum is in dbm, and is equal to the noise density (dbm/hz) captured within the resolution bandwidth that is used for the simulation; resolution bandwidth is essentially the amount of RF spectrum processed by the simulator at each instant in time, and in this project the value is ~78 Hz. If you multiply the noise density by the resolution bandwidth you obtain the noise power in dbm. Of course, if the noise density is specified in dbm/hz you should add the db value of the bandwidth to the density. You will notice that there are three instances of the Channel_Noise variable. Two of them specify different sweep ranges, with the start, stop and step values to be used. The last one specifies a single value and is the default setting (the two sweep instances are disabled in the figure below; you enable them by right-clicking on the instance and clicking on Toggle enable). You should only have one of these

3 three instances enabled for any given simulation. In the BER block this variable is specified as a sweep variable, such that a single simulation run will generate results for multiple channel_noise values. PA_GAIN = PA_P1dB =1 Path_Loss = -76 Channel_Noise = sweep(stepped(-84,-14,-4)) Channel_Noise = sweep(stepped(-84,-9,-4)) Channel_Noise = -14 Figure. Default variable settings. For the simulations that are run in this project only the noise added to the spectrum in the AWGN block will impact the BER results. In a real system, noise is introduced from multiple sources and all will affect the BER. In particular, the receive antenna will receive not only the signal but also noise that is proportional to the background temperature (P = ktb). The signal-to-noise ratio is then further degraded by loss from the antenna to the LNA, and again by noise introduced by the LNA. Further degradation in the SNR will occur through the system but in most receivers the changes that occur past the LNA are less significant. However, since for these simulations the AWGN block determines the SNR you will not find variations in the measured BER by changing the noise figure of the LNA. For this reason the LNA noise figure is set to zero. Be sure to label all your graphs with descriptive titles, referring to the part of the procedure it corresponds to (for example: Part 13: BER with Antenna Gain = 3 db ). Project Instructions: 1. Start AWR and open the TX_RX_FSK_9_91.emp file.. Verify that the variables in the BFSK and PA Compression system diagrams are set according to Figure. For the PA Compression diagram you only need the variables that are relevant to the power amplifier. 3. Open the PA Compression system diagram. The purpose of this diagram is to verify the inputversus-output characteristics of the power amplifier. The simulation is setup to sweep the input power and the corresponding graph will display the output power versus input power. a. Click on Simulate Run/Stop System Simulators. After the simulation runs (it should take about 15 seconds to complete) open the PA Compression graph. b. Be prepared to explain the nature of the plot. You will also need to consider the PA behavior in the proceeding steps. 4. Open the BFSK system diagram. Familiarize yourself with the locations of the various test points that have been added to the diagram; in particular, those labeled Data, FSK, PA_1, AWGN_1, LNA_1, Discrim, INT_Dump and ADC. a. Open the TX Waveforms graph; it should look like Figure 3. Be prepared to explain the appearance of the data at the FSK test point. Note that the data from the FSK test point is the red curve, and it represents the phase of the signal at that point. The red curve uses the axis on the right-hand side of the plot. b. Open the RX Waveforms graph; it should look like Figure 4. Be prepared to explain the appearance of the data at the three test points. 3

4 c. Open the Spectrum graph; it should look like Figure 5. Be prepared to explain the appearance of the data at the four test points. 5. Right-click on the PA Compression tab in the Project menu and select Disable All Measurements (you won t need to have these measurements for the proceeding simulations). 6. Open the BFSK diagram. a. Enable the Channel_Noise variable instance that specifies a sweep from -84 to -9 (dbm/hz). (You will have disable the other options.) b. Run the simulation. c. Open the BER graph. Place a copy of this graph into your report, with the label BER with PA Gain = db. You will have to go to the Labels tab after you right-click on the graph and select Properties. Once there, uncheck the Default title checkbox to change the graph title. d. Repeat the process above for a PA gain of 3 db (modify the graph label accordingly). e. Repeat the process above for a PA gain of 4 db (modify the graph label accordingly). f. Be prepared to explain the variations in the three BER graphs. 7. In the BFSK diagram, reset the PA gain to db. Change the PA_P1dB variable to -1 dbw. Run the simulation and open the BER graph. Place a copy of this graph into your report, with the label BER with PA_P1dB = -1 dbw. Be prepared to explain the results. 8. In the BFSK diagram return all variables to their default settings. Enable the Channel_Noise instance in which the sweep extends to -14 (dbm/hz). You may have to make further adjustments to this vector in the following steps. 9. Set the Path_Loss to -86 db, run the simulation, and determine the noise level at which the BER is ~.3. Repeat for Path_Loss = -96 db. Be prepared to discuss/compare these two results. 1. Before proceeding to the next step, open the Spectrum graph and make note of the peak amplitude of the different curves. 11. In the BFSK diagram: a. Double-click on the RX_Antenna block and clear the entry for PATHLOSS (you may need to click on the Show Secondary button when the parameter window opens). b. Calculate the distance in meters to obtain the same amount of path loss as the last simulation (-96 db); enter this value as the DIST parameter. c. Verify your calculation by generating the spectrum and BER curves and confirm they are equivalent to the previous simulation. d. At what noise level is the BER equal to ~.3 if the distance is doubled? For your graph, adjust your sweep parameters so that the noise level corresponding to BER = ~.3 is close to the midpoint of the abscissa. 1. In the BFSK diagram return all variables to their default settings. In the RX_Antenna block, clear the DIST parameter and set PATHLOSS to Path_Loss. Note the following in Figure 5 of this report: The value -84 dbm on the bottom line is a measure of the noise floor of the system. The signal level at that same point in the system is -43 dbm. Now, use single channel noise settings of -97, -1 and -13 (dbm/hz) and run the simulation for each setting. Observe BER value in the Simulator Output panel, and record the noise floor and the signal level in the Spectrum graph. Make a table in your report for this information. Be prepared to explain the data in your table. 13. Now use the channel noise value of -1 dbm/hz. Double-click on the RX_Antenna block and change the gain from to 3 db. Record the BER, noise floor, and signal level values as in Part 1. Be prepared to explain how and why this result compares with the results of Part 1. 4

5 1.5 TX Waveforms Re(WVFM(.Data,4,1,1,,,,,)) (L) Ang(WVFM(.FSK,4,1,1,,,,,)) (R, Deg) Time (ns) Figure 3. TX Waveforms graph for first simulation. 4 RX Waveforms..1 - Re(WVFM(.Discrim,4,1,1,,,,,)) (L) Re(WVFM(.INT_Dump,4,1,1,,,,,)) (R) Re(WVFM(.ADC,4,1,,,,,,)) (L) Time (ns) -. Figure 4. RX Waveforms graph for first simulation. 5

6 5 DB(PWR_SPEC(.FSK,1,,1,,-1,,-1,1,,,,1,)) (dbm) DB(PWR_SPEC(.PA_1,1,,1,,-1,,-1,1,,4,,1,)) (dbm) DB(PWR_SPEC(.AWGN_1,1,,1,,-1,,-1,1,,4,,1,)) (dbm) DB(PWR_SPEC(.LNA_1,1,,1,,-1,,-1,1,,4,,1,)) (dbm) Spectrum 5. GHz 33.3 dbm 5.1 GHz dbm GHz dbm 5. GHz dbm Frequency (GHz) Figure 5. Spectrum graph for first simulation Report Instructions: 1. Prepare your report for the TX_RX_FSK Project including your name and the graphs noted in the steps above. Discuss the following in your report: a. Briefly describe the results of the power amplifier compression simulation. Specify the input and output power where the slope starts to change and explain why this happens where it does. b. Briefly explain the behavior of the (phase) data at the FSK test point that is shown in Figure 3. I.e. what causes the discontinuities and what is happening at these points? c. Briefly explain the behavior of the data at the three test points shown in Figure 4. d. Briefly explain the behavior of the data at the four test points shown in Figure 5. In particular, list and explain the peak values for the data from the PA_1, AWGN_1 and LNA_1 test points. e. Briefly explain the variation in the three BER graphs that correspond to PA gains of, 3 and 4 db. f. Briefly explain the BER results obtained when the PA 1-dB compression point was set to -1 dbw. Also, what is the worst BER that is possible with this system? 6

7 g. For the simulations with variable path loss, what noise levels resulted in BER values of ~.3 for the 86 and 96 db loss conditions, respectively? Briefly explain the results. h. At what distance (between the TX and RX antennas) was the path loss equal to -96 db? i. Briefly explain the change in the BER curve when the distance between the TX and RX antennas doubled. j. Briefly discuss the differences among the spectrum graphs with the channel noise settings of -14, -17 and -13 (dbm/hz). What was the BER in each case? k. Briefly explain the changes in BER, noise floor, and signal level when the antenna gain was changed from to 3 db. 7

8 9-116 Step by step guide (example from an NAU student) 1. Go to Enter NAU address, name, professor, Computer HostID, and HostID type 1) To find your hostid follow the directions from the help window (pops) 3. You should get the following Message: 1) Preferred University Registration Successful Thank you for registering with AWR. A confirmation and your 1 day demo license has been sent to username@nau.edu. 4. Log into your and retrieve your account information (Login ID and password) 5. Download the license attached to the second in a place that you will be able to find it again 6. Go to the page the second directs you to for the download: 7. Log in using the information received in the first 8. Install Version 9. from the list (first one on the list on the products tab) 9. Follow the instructions in the installer 1) You can select anything you want for the default units type since it is changeable inside of the program 1. Attempt to open AWR Design Environment where it was saved 11. Open the License Configuration window 1. Click the button "Set Location" 13. Type in the location of the license that you downloaded in step 5 (or just browse for it) 14. Hit ok 15. Close the License Configuration window 16. Open AWR Design Environment 17. Press OK 18. Read and accept the agreement 19. Press OK. Congratulate yourself for an install done right 8