As previously discussed with regards to FIG. 4 herein, an exemplary OFDM frame comprises a preamble sequence 402, channel learning sequences 404 (typically to be used for channel estimation), and data symbols 408. Pilot tones 406 are typically assumed to be intermingled with data tones. The preamble and CIR (Channel Impulse Response) learning sequences are typically larger compared to the pilot tones within the data part, and are also deterministic. In most cases, the preamble and CIR learning field of the entire spectral usage can be calculated or determined (as opposed to the data fields, of which, only the pilot tones are easily determined).
Consequently, interference cancellation can be efficiently distributed by time-shifting the preamble 402 and CIR learning sequence 404 fields of the interfering BS; in one variant, these are shifted to maximally coincide with the same time interval as the data part 408 of the BS transmitting the useful data symbol as shown in FIGS. 8A and 8B. Specifically, the complete overlap should be the objective if the frame structure allows for it. If not (as it is the case in FIG. 8A), the level of overlap should be maximized and the delay should be adapted correspondingly. In practice, a perfect overlap (FIG. 8B) is rarely possible and in most cases, the overlap with learning sequences is only a partial overlap. In such cases, two types of interference reduction strategies are applied: i) full interference reduction over preamble part, ii) partial interference reduction over part with useful data, typically exploiting a priori knowledge on pilot tones.
