+1 732-544-8700 © 2005, Spirent Communications, Inc. www.spirentcom.com/wireless

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NOTE

The procedures in this application note are intended only to confirm correct operation of a Spirent SR5500 Wireless Channel Emulator’s functions, not for verification or calibration. Please contact Spirent Communications for more information on calibration or annual support programs.

Spirent Communications’ SR5500 Wireless Channel Emulator emulates the delay, fast and slow fading, and path loss characteristics of RF mobile communication channels. Each one of these RF channel characteristics has unique properties which can cause difficulty for wireless transmission. This application note describes how to check the proper operation of the SR5500’s primary functions. All of the tests described in this application note can be completed without involving internal access to the unit. The tests are intended to check the following:

• Signal Path through the SR5500

• Output Power

• Rayleigh Fading

• Rician Fading

• Log Normal Shadowing

• Frequency Shift

• Delay Shift

• AWGN

Equipment Requirements

Equipment Requirements QTY

RF Spectrum Analyzer RF Input frequency range (800-1000 MHz Min.) Minimum Resolution BW of 10 Hz Zero Span Capability 50 Ohms Input Impedance

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RF Signal Source RF output frequency of 900 MHz (Note: You may substitute 900 MHz frequency range to that of your choice) Adjustable RF Output Power (-10 dBm) FM Modulation Capability -50 kHz dev. 50 Ohms Output Impedance

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Checking SR5500 Operation

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Test Equipment Setup

Configure the test setup as depicted in Figure 1.

• On the SR5500, connect the supplied LO cable from LO OUT to LO IN on both channels

• Connect the 10 MHz reference between the RF Signal Source, SR5500 and RF Spectrum Analyzer

• Connect the RF signal source to RF IN on the SR5500

• Connect the RF spectrum analyzer’s RF input to RF OUT of the SR5500

• Start the SR5500 TestKit software and execute “CONNECT to SR5500”

NOTE

All tests can be completed using Channel 1 or Channel 2

Figure 1. General Setup Next, perform the following steps to create a default .wce file:

1. Adjust SET: OUTPUT for channel 1 and channel 2 to 45 dBm.

2. Select FILE > SAVE SETTINGS AS.

3. Select folder to store your file.

4. Enter file name as: default.wce.

5. Select SAVE.

Checking SR5500 Operation

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Tests

Signal Path through the SR5500

This test confirms that an input signal can pass through a single, unimpaired path in the SR5500.

• Configure the test setup as depicted in Figure 1. • Configure the RF signal source as follows:

- RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = None

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = 1 MHz - Resolution Bandwidth = 10 kHz - Sweep Time = 30 msec - Reference Level = -25 dBm

STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the CHANNEL 1 tab from the Channel Emulator view.

4. Check MEASURED INPUT of channel on screen of SR5500. (Measured input = input + cable loss)

5. Check that a signal is present at the spectrum analyzer at 900 MHz and at approximately -45 dBm. See Figure 2.

Figure 2. Signal through 1 Path

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Output Power

Output power in the SR5500 is programmable from -30 to -110 dBm in 0.1 dB increments. This test confirms actual output power levels compared to the set values.

• Configure the test setup as depicted in Figure 1.

• Configure the RF signal source as follows: - RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = None

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = 1 MHz - Resolution Bandwidth = 10 kHz - Sweep Time = 30 msec - Reference Level = -20 dBm

STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the CHANNEL 1 tab from the Channel Emulator view.

4. Adjust output power in 10 dB steps from -30 to -110 dBm. (Note: The spectrum analyzer range may need adjustment for the lower output power settings)

5. Check that the peak signal level on the spectrum analyzer tracks the change specified in the channel output power field.

Rayleigh Fading

The SR5500 has the capability to emulate Rayleigh fading in each path. Rayleigh fading can be examined in either a time or frequency domain as shown in Figure 3. In the frequency domain, the power spectral density of the SR5500 will take the shape of the "Classic Rayleigh Spectrum" as shown in Figure 4. The width of the spectrum will be 2Fd, where Fd is the Doppler frequency. In the time domain, Rayleigh fading will display rapid fluctuations of power versus time. This test confirms that Rayleigh fading is functioning correctly.

• Configure the test setup as depicted in Figure 1.

• Configure the RF signal source as follows: - RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = None

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = 1 kHz - Resolution Bandwidth = 10 Hz - Sweep Time = 30 sec - Reference Level = -40 dBm

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STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the CHANNEL 1 tab from the Channel Emulator view.

4. Select PATH 1 and set MODULATION to RAYLEIGH.

5. Set the VELOCITY to 100 km/hr (DOPPLER = 83.4 Hz).

6. Execute “PLAY” within the SR5500 TestKit software.

7. Check that that the signal on the spectrum analyzer takes the shape of the "Classic Rayleigh Spectrum". See Figure 3.

8. Change the following settings on the spectrum analyzer to check Rayleigh fading in the time domain: - Span = Zero Span - Resolution Bandwidth = 100 kHz - Sweep Time = 100 msec - Scale = 7 dB/div

9. Check that the signal on the spectrum analyzer is fluctuating rapidly with deep fades that range from approximately 30 dB to 60 dB. See Figure 4.

Figure 3. Rayleigh Fading (Frequency Domain)

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-84.00

-70.00

-56.00

-42.00

-28.00

Figure 4. Rayleigh Fading (Time Domain)

Rician Fading

Rician Fading is a combination of a Rayleigh faded signal and a Line-Of-Site (LOS) signal. This test confirms that Rician fading is functioning correctly.

• Configure the test setup as depicted in Figure 1.

• Configure the RF signal source as follows: - RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = None

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = 1 kHz - Resolution Bandwidth = 10 Hz - Sweep Time = 30 sec - Reference Level = -40 dBm

STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the CHANNEL 1 tab from the Channel Emulator view.

4. Select PATH 1 and set MODULATION to RICIAN.

5. Set the VELOCITY to 100 km/hr (DOPPLER = 83.4 Hz).

6. Set the line of sight AOA to 45 degrees.

7. Execute “PLAY” within the SR5500 TestKit software.

8. Check that the signal on the spectrum analyzer takes the shape of the "Classic Rayleigh Spectrum" with a LOS signal Doppler shifted by 59 Hz. See Figure 5.

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Figure 5. Rician Fading (Frequency Domain)

Frequency Shift

The SR5500 has the capability to emulate frequency shift. This test confirms that frequency shift is functioning correctly.

• Configure the test setup as depicted in Figure 1.

• Configure the RF signal source as follows: - RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = None

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = 1 kHz - Resolution Bandwidth = 10 Hz - Sweep Time = 30 sec - Reference Level = -20 dBm

STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the CHANNEL 1 tab from the Channel Emulator view.

4. Select PATH 1 and set Frequency Shift to 241.7 Hz.

5. Execute “PLAY” within the SR5500 TestKit software.

6. Check that the signal on the spectrum analyzer is frequency shifted by approximately 241.7 Hz.

Checking SR5500 Operation

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Figure 6. Frequency Shift Signal

Log-Normal

Log-normal, (slow fading), is the slow variation of the signal envelope over time. This test confirms that Log-normal fading is functioning correctly.

• Configure the test setup as depicted in Figure 1.

• Configure the RF signal source as follows: - RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = None

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = Zero Span - Resolution Bandwidth = 100 kHz - Sweep Time = 30 sec - Reference Level = -30 dBm

STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the CHANNEL 1 tab from the Channel Emulator view.

4. Select PATH 1 and set path loss to 25 dB.

5. Set OUPUT POWER to -50 dBm.

6. Set LOG NORMAL ENABLED to YES.

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7. Set LOG NORMAL STD to 8 dB.

8. Set LOG NORMAL RATE to 0.5 Hz.

9. Execute “PLAY” within the SR5500 TestKit software.

10. Check that the signal on the spectrum analyzer is fluctuating. See Figure 7.

-80.00

-70.00

-60.00

-50.00

-40.00

-30.00

Figure 7. Log-Normal Shadowing Delay

This test confirms that delay is functioning correctly.

• Configure the test setup as depicted in Figure 1.

• Configure the RF signal source as follows: - RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = FM - Modulation Deviation = 50 kHz - Modulation Rate = 1 kHz

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = 200 kHz - Resolution Bandwidth = 3 kHz - Sweep Time = 100 msec - Reference Level = -40 dBm

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STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the CHANNEL 1 tab from the Channel Emulator view.

4. Select PATH 2. Set the Delay to 25 µsec.

5. Execute “PLAY” within the SR5500 TestKit software.

6. Check that the signal on the spectrum analyzer has notches in the band. The delta frequency between the notches should be equal to 1/delay (in this case 1/25 µsec = 40 kHz). See Figure 8.

NOTE

The notches in the band do not have to be symmetrical around the center frequency; they may be offset in the frequency domain.

Figure 8. Delay Shifted Signal

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AWGN – Additive White Gaussian Noise

This test confirms the AWGN function is performing correctly.

• Configure the test setup as depicted in Figure 1.

• Configure the RF signal source as follows: - RF Frequency = 900 MHz - RF Level = -10 dBm - Modulation = None

• Configure the RF spectrum analyzer from factory default as follows: - Center Frequency = 900 MHz - Span = 15 MHz - Resolution Bandwidth = 300 kHz - Sweep Time = Auto - Reference Level = -40 dBm

STEP PROCEDURE

1. Select the FILE function.

2. Select the File Recall sub-menu and recall default.wce.

3. Select the Interference Editor view.

4. Select Interferer state to AWGN.

5. Set Ratio to 10 dB.

6. Select AWGN Bandwidth of 6.5 MHz.

7. Set Receiver Bandwidth to 3.84 MHz.

5. Execute “PLAY” within the SR5500 TestKit software.

6. Check that the C/W signal on the spectrum analyzer is centered within the AWGN bandwidth. The peak of the signal should be approximately 20 dB above the average power of the AWGN. See Figure 9.

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Figure 9. AWGN with Carrier Signal