Pushing the limits of copper: Paving the road to FTTH

Abstract

The ever growing demand for higher data rate is pushing existing electrical broadband communication systems, using coax or twisted pair cabling, to the limit. While optical access systems inherently have a much higher transmission capacity, upgrading the access network entirely to fiber remains a costly and time-consuming effort. Therefore, many operators deploy fiber gradually closer to the end user, while bridging the remaining distance through copper technologies such as VDSL2. In the next step of this evolutionary path, fiber is brought to distribution points that are in the range of no more than 200 m from the end user, with a copper access technology called G.fast delivering data rates of 500 Mb/s to 1 Gb/s over the remaining copper stretch. In this paper, we give an overview of the G.fast technology that is currently being standardized in ITU. We show the feasibility of its main technical requirements, namely i) powering of the access equipment through the customer premises modem, ii) high transmission efficiency for orthogonal frequency division multiplexing over short copper loops and iii) offering high net data rates to end users.

Investigation of phantom circuit benefits for next generation xDSL systems

“…However, this whole frequency band will be optionally notched on frequencies used for standard AM and FM radio broadcasting (approx. The value of Shannon gap capacity Γ = 10.75 dB, which is typical for today's xDSL systems, will be probably used for upcoming G.fast system as well, and it already includes a 6-dB noise margin [4]. These frequencies were also notched in all the following estimations.…”

“…87.5 to 108 MHz) and also separated frequencies occupied by emergency and communication systems and digital DBA [23]. The transmission efficiency describes the ratio between coding overhead and transmitted user data, and in case of G.fast, its value is η = 78.5% [4]. The subchannel (subcarrier) spacing of both G.fast types (with 106-and 212-MHz upper frequencies) is currently being considered as 51.75 kHz [8], which results in approximately 1689 subchannels in the case of the 106-MHz G.fast version and 3702 subcarriers for the 212-MHz G.fast type, when notching is applied.…”

“…The main motivation is to achieve transmission rates in hundreds of Mbps for very short existing metallic loops not exceeding 200 m to provide high-speed Ethernet connection [5]. New G.fast system will be partially based on previous xDSL principles; moreover, it will include several upgrades and innovations to achieve higher transmission rates [4]. The frequency bands used by G.fast will be extended up to 106 or 212 MHz, which results in using 2048 or 4096 subchannels assuming subcarrier spacing of 51.75 kHz [6].…”

“…Next, the simulations and modeling of attenuation and FEXT characteristics were evaluated, and these results were further used for estimations of potential transmission rates of next generation G.fast systems in both 106-and 212-MHz frequency bands [4]. In all following estimations, two bonding scenarios are assumed.…”

Capacity analysis of G.fast systems via time-domain simulations

“…To evaluate the ISI caused by insufficient cyclic prefix length, a time-domain simulation is required. In this study, capacity results are simulated with different cyclic prefix lengths and different loop topologies via this timedomain simulator, improving upon the theoretical derivations in [4], [5]. The required cyclic prefix lengths are also evaluated for different loop topologies from a capacity maximization point of view.…”