| 摘要 |
An frame structure for an OFDM system (eg. DVB) includes preamble and payload symbols (Fig. 5). The preamble symbols include overhead signalling. In order to achieve frame detection/synchronisation a signature sequence 208 is added 212 to each of the sub-carriers of the OFDM symbol 200-204. The sum of the two signals is then inverse Fourier transformed 214 and transmitted 218. The two signals may be power scaled 206/210 to maintain constant signal power. The signature sequence may be an m-sequence, a Gold code or a CAZAC sequence. Detection of the signature sequence may use matched filters. The preamble symbol may also include pilot symbols on some sub-carriers for coarse frequency offset detection/correction (Fig. 17). The number of pilot symbols may be selected to be insufficient for channel impulse response estimation. |
