Scientists from the Eindhoven University of Technology and Genexis, a fiber broadband equipment supplier, have devised data transmission methods that increase the data transmission capacity of prevalent fiber-to-the-home connections by two, or even three, times.
In order to make the most of this increase in data transmission capacity, prevalent modems have to be upgraded. However, one can obtain a higher data capacity even if only their neighbors upgrade their modem.
The methods are applicable to passive optical networks (PONs). This type of connection has been in use in approximately 80% of fiber-to-the-home connections across the globe. PONs, in general, connect 16–64 households to one fiber lain in the street or district. However, not all the households have similar connection quality. Specifically, the homes located further apart from the central data station, or the central office, have a lower signal quality. Prevalent networks are over-dimensioned as providers want to ensure connectivity for everyone, resulting in unused capacity.
The Dutch scientists discovered certain intelligent and cost-effective methods to utilize this extra capacity, based on the actual signal quality for each user, with the help of established technology from ADSL/VDSL, coax, and wireless communication.
A normal signal consists of two states: a bit is either a one or a zero. We have increased the number of states to four or even eight levels. A higher number of levels implies more information. This way we can transfer twice or even three times as much.
Robbert van der Linden
For more enhanced performance, these levels can be transmitted with unequal distances between them. Since the levels located further away can be easily distinguished and hence easily decoded, they do not need higher signal quality. Hence, levels located further apart are assigned to users located further apart, and the levels located closer together are used by the users nearby the local station. This effectively results in an additional performance gain.
A third enhancement was achieved with the help of multiple clock rates for different users. This ensures shorter time intervals between the transmitted symbols, thereby increasing the throughput. The attainable increase is based on the particular network layout. “We have demonstrated that by using only three different clock rates, already an increase in throughput of 180 percent can be achieved,” stated Van der Linden.
The extra capacity made available by these methods is offered by the high-quality connections close to the central data station. However, once their capacity increases, they need less time to communicate. This indicates that there is more time for the users located further apart on the same PON, thus also enhancing their connection capacity.
The scientists and their partners are now making efforts to create chips that combine the innovative methodologies. The central data stations and also the modems of the users have to be equipped with these chips. It is most probable that new users, who purchase a new modem, will profit first from the innovative methodologies. However, even if only one’s neighbors become part of the same PON upgrade, one’s own capacity will probably also increase. The enhanced methodologies will reduce the timeslots needed by the upgraded users for data transfer, making more time for the other users to obtain their share of data.
Robbert van der Linden defended his Ph.D. thesis titled “Adaptive Modulation Techniques for Passive Optical Networks” at the Eindhoven University of Technology on Tuesday, April 17, 2018.