Function ofdm_sync 

pub fn ofdm_sync(
    iq: &[Complex32],
    fs: f32,
    preamble: &OfdmPreamble,
    search_start: usize,
    search_end: usize,
) -> Vec<OfdmSyncResult>

Searches iq[search_start..search_end) for a repeated-segment preamble match, returning candidates sorted by descending score.

search_end is clamped so every candidate start has room for the full preamble (2 * repeat_len samples for the correlation window, extended across all num_repeats segments). Returns an empty Vec if the search range is too short to hold a full preamble.