Setting up a 802.16 OFDM measurement

When setting up an 802.16 OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. demodulation measurement, there are several things to consider. This topic describes how to connect your signal to an 89600 VSA and successfully demodulate digital signals. The information is provided in the following order:

802.16 OFDM Measurement Setup Information

Connecting Your Signal to the VSA
Setting Input Range and Center Frequency
Configure the demodulator
1. Specify the 802.16 OFDM modulation format
2. Preset to Standard (and set nominal bandwidth)
  The VSA will configure the other signal parameters as shown in Using Standard Setups/Presets.
  These parameters can be manually adjusted or specified in the IEEE 802.16 OFDM Demod Properties dialog box.

Connecting Your Signal to the VSA

For all receiver configurations except I + jQ, connect your signal to Channel 1. In this case, the VSA assumes that your signal contains both the I and Q components (the carrier signal). If the measurement hardware has two input channels, the VSA ignores the second input channel.

If your measurement hardware has a second input channel, the raw I (In-phase) and Q (Quadrature- phase) signals can be connected. To do this, click Input > Channels > I + jQ > Single I+jQ.

Notes for I+jQ input:

Selecting an I+jQ configuration enables DC coupling.
Use User Correction to correct for any offset or gain imbalance between the I and Q signals.
Range is set independently for the I and Q inputs, but can be coupled by selecting the Couple Paired Channels parameter.

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Input range

The Input Range must be set correctly to obtain accurate measurements. Input ranges that are too low overload the VSA's ADC Analog-to-Digital Converter. Input ranges that are too high increase noise, which increases errors reported in error summary data, such as EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format..

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Center Frequency

The VSA's center frequency should be set to within approximately ±500 kHz kiloHertz: A radio frequency measurement (one kilohertz = one thousand cycles per second). of the transmitted carrier frequency or the VSA may not be able to lock onto your signal.

The VSA center frequency must be within 2 * Subcarrier Spacing (625 kHz for 802.11a or HIPERLAN/2) to lock properly.

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