Vectoring could allow BT to achieve 100 Mbps download and 40 Mbps upload speeds
Read our follow-up articles:
While BT’s Fibre-to-the-Cabinet (FTTC service) currently offers download connection speeds of up to 80 Mbps, many premises generally get speeds significantly lower than this. Vectoring is an advanced digital signal processing technology that would enable BT to deliver speeds of 100 Mbps (and above) to a substantial number of premises. BT will test vectoring in summer 2013.
While FTTC is often cheaper than FTTP to deploy, proponents of FTTP (and critics of FTTC) are often keen to point out that the biggest weakness of FTTC is its dependence on copper cables. FTTC service rely on copper cables to carry broadband signals between premises and the street cabinet and these signals are susceptible to:
- signal attenuation (resulting in decreasing speeds the further premises are from the street cabinet)
- crosstalk, which is interference caused from broadband signals in surrounding cables.
Currently, BT’s FTTC service offers download connection speeds up to 80 Mbps, and yet only a proportion of premises are able to achieve the maximum speed.
As described in our recent blog post Chart of BT FTTC (VDSL2) speed against distance from the cabinet, the speed achieved by FTTC generally falls with distance from the street cabinet. Crosstalk introduces a degree of uncertainty in speeds since some copper cables may be subject to increased interference from other cables.
Vectoring will significantly improve download speeds, allowing BT to deliver 100 Mbps downloads at up to 500 metres from the street cabinet
The term ‘vectoring’ refers to advanced digital signal processing aimed at cancelling crosstalk interference to significantly improve performance and provide much more consistent speeds. Vectoring is being strongly promoted by manufacturers of FTTC equipment, such as Alcatel Lucent.
Without vectoring, VDSL2 has the potential of delivering 100 Mbps speeds but not at any practical distance from the street cabinet. Currently, BT limits the maximum connection speed to 80 Mbps as very few would be able to benefit from higher speeds without vectoring.
In September 2012, Dr Stefaan Vanhastel and Jan Verlinden published the results of customer trials:
The authors claimed that 17 VDSL2 vectoring trials demonstrated that 100 Mbps is achievable over copper at 400 metres – and even up to 500 metres – from the street cabinet. Their results suggest that vectoring could allow BT to increase its maximum FTTC data rate to 100 Mbps and confidently deliver this date rate to a substantial proportion of users.
In addition to overall broadband speed increases, vectoring allows the speed variations achieved with FTTC to be significantly evened out. For example, in a particular Alcatel-Lucent test, downstream bit rates exhibited a significant spread – from 57 Mbps to 88 Mbps – at a distance of 350 metres from the street cabinet. With vectoring, all lines consistently reached download speeds of between 101 Mbps and 107 Mbps.
Vectoring significantly improves upload too, and could allow BT to offer upstream speeds of up to 40 Mbps
Vectoring is also able to successfully cancel crosstalk interference in the upstream direction. Without vectoring, FTTC systems generally reduce the transmit powers from users close to the street cabinet so that they don’t interfere with weaker signals from premises further away. By cancelling crosstalk interference, vectoring allows transmit powers to be increased enabling maximum upstream data rates to be substantially increased.
Currently, BT’s FTTC service offers upstream connection rates up to 20 Mbps. Vectoring could allow BT to offer upstream data rates of 30–40 Mbps.
BT will test vectoring during summer 2013
BT Openreach is planning to test vectoring during summer 2013. This will help it to decide if, and when, it will implement vectoring in its FTTC network.
Read our follow-up articles: