| 摘要 |
A frame structure for an orthogonal frequency division multiplexed (OFDM) system (e.g. DVB) comprises preamble and payload symbols, with the preamble symbols including overhead signalling. To achieve frame detection/synchronisation, a signature sequence 1302, 1303 is added to each of the sub-carriers of the preamble symbols 1301. The two signals may be power scaled 1002, 1006 to ensure their combination maintains constant power. The signature sequence may be selected from a set of sequences with the selection providing a message, for example, an early warning signal (EWS). A guard interval (GI) is formed from a part of the signature sequence and prefixed to the preamble so that a receiver can detect the EWS from the guard interval. Combining another part (the remainder) of the signature sequence with the preamble increases the channel impulse response that can be estimated. The guard interval may be made up solely from the signature sequence 1403, 1404 so as to increase the likelihood of signature sequence detection. A post-fix to the preamble may also be formed from the signature sequence. |
