What is single frequency network technology?
A single frequency network (SFN: Single Frequency Network) is a synchronous radio station in multiple locations that transmits the same signal at the same time and frequency to achieve reliable coverage of a certain service area.
What are the advantages of single frequency network technology?
The first advantage of a single frequency network is that it facilitates frequency planning. In the case of limited spectrum resources in China,
Can greatly save precious frequency resources and improve spectrum utilization.
Secondly, due to the characteristics of the radio signal itself, in a city full of tall buildings, no matter how much the transmission power of a single digital TV transmission site, there will be many areas that cannot be covered by the signal. These areas that are not covered are called coverage blind areas or Blind spot, single frequency network can solve the problem of coverage blind area through multi-point co-frequency transmission, and obtain better coverage.
Third, the single frequency network technology can also reduce the cost of transmitter equipment; by optimizing and adjusting the single frequency network transmission network (number of base stations, distribution, height of transmitting antennas, transmitting power, etc.), multiple smaller power transmitters can be used instead A high-power transmitter can reduce signal radiation, reduce electromagnetic wave pollution, enhance coverage uniformity, and can also change coverage intent as needed.
What are the difficulties in implementing a single frequency network?
To achieve a single frequency network, the biggest difficulty at the transmitter is that multiple transmitters simultaneously broadcast the same program. The biggest technical difficulty at the receiving end is how the receiver can reliably receive the transmitted signal in the cross coverage area covered by multiple transmitting sites. In addition to using multi-frequency networks, the American ATSC standard also uses a co-channel repeater to expand the service area; the repeater receives the signal from the transmitting station and performs simple processing to forward the signal out. In such a repeating relay system The forwarding point often uses directional antennas. Because the signals transmitted by different repeaters are not synchronized, just like the relaying of analog TV, this structure is not strictly a single frequency network.
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