Tài liệu Complex Disturbance Models for OFDM-based Systems

In the consideration above, an on–off error model is defined describing the availability of
a transmission channel. However, if a disturbance impulse occurs, it can affect a variable
number of OFDM subcarrier frequencies depending on its characteristics, spectral power,
origin, and so on. Therefore, the disturbances have to be modeled not only in the time
domain (duration and interarrival time of impulses) but also in the frequency domain,
specifying how many and which subcarriers are affected by a disturbance impulse.
Furthermore, in the simple on–off disturbance model, an OFDM subcarrier can be only
in two hard defined states: On – available for the transmission, or Off – not available. On
the other hand, an OFDM system can apply bit loading (Sec. 4.2.1) to provide variable data
rates of a subcarrier according to its quality, which depends on the noise behavior on the
subcarrier frequency. To model an OFDM system using bit loading, the on–off disturbance
model is extended to include several states between “channel is Off” (transmission not
possible) and “channel is On” (full data rate is possible) as is presented in Tab. 3.7.
The states between “Off” and “On” represent the situations when a subcarrier is affected
by the disturbance impulse, but is still able to transmit the data.