For several years, the cost-effectiveness of copper-based transmission systems has been the pillar of broadband internet access for domestic and corporate markets. Digital Subscriber Line (DSL), a family of technologies that provides broadband access over the telephone infrastructure, has continuously evolved aiming at providing faster and more stable services reusing the existing copper network. Its low investment requirements, great coverage and high data rates and stability make DSL a very attractive physical platform for supporting and offering services that demand high data rates.
The evolution of copper networks has been demarked by the necessity of counteracting two issues that limit their capacity: attenuation and crosstalk interference. Long loops, very common in former telephone networks to cover large territories, exhibit high attenuation of the transmitted signals, which reduces the Signal to Noise Ratio (SNR) at the receiver side and consequently, its capacity. This problem is aggravated by the usage of wide spectrum in new DSL systems that intends to add capacity in high frequency carriers to increase data rates; the attenuation levels are so high that high frequency carriers cannot carry any bit. On the other hand, the copper network is an end-to-end network that groups lines in an electromagnetically coupled medium: the cable-binder. Thus, services operating within the same cable-binder interfere with each other, mutually limiting their achievable data rates. This interference is known as crosstalk.
Vectoring mitigates crosstalk and obtains single line performance
DSL operators have transformed their copper network replacing long copper segments by optical fiber links. Thus, operators’ access system so called DSL Access Multiplexer (DSLAM) is installed at locations closer to the Customer Premise Equipment (CPE), reducing the signal attenuation and the number of mutually interfering services. Additionally, manufacturers have introduced techniques that allow DSLAMs and CPEs to compensate the crosstalk interference. This novel technique is known as Vectoring and uses Multiple-Input Multiple-Output signal processing to mitigate crosstalk and obtain single line performance. Therefore, transmission systems are not any longer seen as independent entities interfered by and interfering with coexisting counterparts. Instead, they are treated as collaborative entities that constructively use their mutual interaction, i.e. interference, to maximize their performance.