Preamble, pilots and data (802.16 OFDMA)

Default: Selected (See OFDMA Standard Presets Table.)

(applies to Downlink only)

The equalizer is trained by analyzing the entire OFDMA burst, including the Channel Estimation Sequence (contained in the preamble), the Data symbols, and Pilot symbols. This type of training generally gives a more accurate estimate of the true response of the transmission channel.

When demodulating 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 signal, the VSA uses an equalizer to correct for linear impairments in the signal path, such as, multi-path. Switching between the different equalizer training methods can help isolate problems contributing to increased 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./RCE Relative Constellation Error is the RMS level of the Error Vector Magnitude, averaged over all subcarriers and all detected OFDM symbols..

When demodulating a Downlink Subframe Type which uses Matrix A or Matrix B coding, the Preamble, pilots, and data training mode is not valid when the matrix decoder is disabled (cleared). This is because the data subcarriers may not be valid due to coupling between transmitters. In this situation, the VSA will use Preamble and pilots training mode instead

The advantages of using the Preamble, pilots and data method of equalization include the following:

The equalizer coefficients typically reflect the linear channel impairment with greater accuracy, as the data set used to train the equalizer is larger and is less affected by turn-on transient effects in the burst.
The EVM/RCE is typically lower because the equalizer is less impacted by noise and other forms of distortion. EVM/RCE represents the error due to noise, non-linear distortion, spurious and residual linear distortion.)

The disadvantages of usingthe Preamble, pilots and data method of equalization include the following:

It is less likely to accurately reflect the performance of a typical OFDMA receiver. This type of equalizer computation is less likely to be used in practical receivers because it is more complicated and therefore more expensive to implement.
The reduced robustness of the channel estimation to impairments. Since the reference data symbols are used to help estimate the channel, impairments large enough to cause incorrect data decisions may incorrectly bias a data-aided channel estimate.