Thesis Open Access
Magesacher, Thomas; Ödling, Per; Börjesson, Per Ola
The whole society is digitalizing, filled with streaming services, cloud computing and an ambition of ubiquitous connectivity. To address the data demand, ultra-fast broadband, at the speeds of 1Gbps and more, is developed and deployed. Optical fibers have been long viewed as a future-proof carrier for the ultra-fast broadband. However, the physical deployment of fiber networks, including digging, burying, rewiring, drilling, etc., is still an expensive and disruptive process. The economic concern repeatedly defers the delivery of end-to-end fiber connections to every premise while the 5G development cannot wait any longer. This dilemma motivates the industry to use the readily in-place copper-based network to deliver the last-mile communication which is the most expensive segment for fiber roll-outs. The challenge is: are the copper cables capable of offering a fiber-like experience?
This thesis supports the answer: Yes.
Focusing on the network side, where centralized cooperative processing is available, the potential of copper networks is explored in three subparts: evolution, maintenance and extension.
The first subpart, devoted to DSL evolution, continues extracting available resources to increase network capacity. The main concept of the 4GBB is to further broaden bandwidth over shorter cables for loading more data. However, its effectiveness gets saturated after around 200MHz due to severe data channel attenuation and strong interference level. To cut this Gordian knot, a new precoding scheme combining beamforming and crosstalk mitigation is presented, improving the bit-loading capability at high frequencies via constructive crosstalk from adjacent twisted pairs.
The second subpart addresses a newly observed disruption of the evolved broadband network to maintain the stability of services. The disruption, caused by sudden termination changes at user premises, significantly degrades performances at high frequencies, which are the key for the DSL evolution. A low-cost precoder updating procedure is proposed and applied to two types of common-used precoders. It enables quick retrieving of the normal operation state without the end-users experiencing any impairment on the quality of service.
The third subpart extends the application from providing fixed access to fronthauling 4G and 5G mobile networks. In order to coordinate power and spectrum usage, the mobile network has its baseband unit (BBU) centralized, while pushing the radio unit (RU) closer to end-users with fronthaul links connected in between. Those links are then normally served by the fixed access network. In this regard, this thesis firstly sketches and analyzes the feasibility of an LTE-over-copper system considering the crosstalk issue. When it comes to 5G where the number of antennas scales up to be "massive", strategies of beneficial functional split are discussed to lessen the dramatically growing traffic on the fronthaul links.