Bandwidth Ratio (802.16 OFDMA)

Default: 8/7 or 28/25 (See OFDMA Standard Presets Table).

Range: 1 to 2

The BW Ratio is defined as the ratio between the OFDMA FFT Fast Fourier Transform: A mathematical operation performed on a time-domain signal to yield the individual spectral components that constitute the signal. See Spectrum. sample rate and the nominal channel bandwidth. The 802.16 Standard specifies the Bandwidth Ratio be set to 8/7 or 28/25 depending on the Nominal Bandwidth (see Legacy BW Ratio Implentation for more information).

is only available when the Restrict bandwidth to standard values checkbox on the tab is cleared.

When the Restrict bandwidth to standard values checkbox is selected, the BW Ratio is set automatically. When this checkbox is cleared, one of the standard Bandwidth Ratios can be selected or an arbitrary value specified using Other. The value is entered as a decimal fraction between 1 and 2 and returned as an equivalent rational fraction.

The OFDMA standard refers to the Bandwidth Ratio as the Sampling Factor "n". The Sampling Factor in conjunction with the nominal bandwidth and number of used subcarriers "Nused" determines the OFDMA useful subcarrier spacing and the useful symbol time.

Legacy Bandwidth Ratio Implementation

The IEEE Institute of Electrical and Electronics Engineers. A US-based membership organisation that includes engineers, scientists, and students in electronics and related fields. The IEEE developed the 802 series wired and wireless LAN standards. Visit the IEEE at http://www.ieee.org 802.16 OFDMA default Bandwidth Ratio has been changed to match the P802.16-2004/Cor1/D5 draft standard, which matches the ratified IEEE Std 802.16e-2005 standard. This is default Bandwidth Ratio when the Restrict bandwidth to standard values checkbox is selected. As an example, the "IEEE 802.16 OFDMA (e10MHz)" Preset to Standard will default the Bandwidth Ratio to 28/25, while the "TTA Telecommunications Technology Association (Korea): A telecommunications standards setting body in Korea.-Phase2 (WiBro)" Preset to Standard uses a default Bandwidth Ratio of 8/7. Consult the IEEE 802.16 OFDMA standard for a complete description of how BW and default Bandwidth Ratio are coupled. In pre-D5 draft standards (and in some early releases of the 89600A OFDMA measurement software) 8/7 was always the default value.

If measurements of the legacy 8/7 Bandwidth Ratio are needed, the the following format tab parameters must be changed:

Clear the the Restrict bandwidth to standard values checkbox on the Advanced tab.
Specify the floor-function compensated BW value (i.e. 9.996MHz for the 10MHz example, see the "Nominal Bandwidth" help topic).
Specify an 8/7 Bandwidth Ratio.