DTMB Single Frequency Network (SFN) Adaptor
Advantages of SFN over MFN
- Higher bandwidth efficiency - For the same coverage, MFN requires three different frequency bands or more, while in SFN only one frequency band is needed.
- Lower transmission power
- Re-modulating identical information onto different transmitters can be avoided.
- More reliable reception and better coverage - A receiver in SFN can achieve potential diversity gain.
Spectrum Efficiency - SFN vs. MFN
Synchronization is a Key Function of SFN Adaptor
Transmitters shall radiate:
- over the same frequency band
- at the same time
- the same signals.
Solution of SFN Adaptor
- Frequency Synchronization
- Same working frequency from each transmitter
- Same frequency for each carrier in multi-carrier system
- Can be achieved by using common reference frequency (GPS10M for example) to control the modulation
- Time Synchronization
- Use GPS as reference timing (1pps, 10M)
- Achieved through SFN Adaptor
- Guard Interval (GI)
- The length of GI determines the maximum delay spread the system can manage - the longer the GI, the longer the allowed distance among the transmitters, but the lower the transmission efficiency.