External factors

Written on 3:09 PM by ooe

The external factors that need to be taken into account include radio frequency interference (RFI) – typically originating from high power broadcast transmitters; and impulse noise interference – typically originating from transport systems, home appliances and of course the weather. There is nothing that can be done to eliminate these external factors, and VDSL systems must therefore be designed to withstand their influence to operate reliably. Key enablers being robust error protection techniques, and ensuring that the systems are deployed with adequate head-room above the noise – known as the noise margin.

Determining the appropriate noise margin is critical but it is also non-trivial because it requires the network operator to acquire intimate technical knowledge of both modem performance and network performance. This technical knowledge must then be combined with knowledge of the business opportunity to engineer the noise margin for a given service capability. Excessive margin, and fewer customers will be reached, undermining the business case. Insufficient margin, and systems will be unreliable in service due to varying noise and cable conditions.