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Waldemar WÓJCIK, Zbigniew LACH, Andrzej SMOLARZ, Tomasz ZYSKA Lublin University of Technology, Department of Electronics Power supply via optical fibre in home telematic networks Abstract. The article shows a concept of development of full optical home networks. Forecasts of development of supporting technologies has been done as well as scenarios of development of systems based on technology in question. The article also marks some goals to be achieved in order to make the technology market available. Streszczenie. W artykule pokazano koncepcję w pełni optycznych sieci domowych. Wykonano prognozy dotyczące wspierających technologii a także opracowano możliwe scenariusze rozwoju systemów opartych na tych technologiach. W artykule pokazano również cele, które powinny zostać osiągnięta aby technologia ta stała się dostępna na rynku. (Optyczne zasilanie sieci domowych). Keywords: home network, optical fiber, photovoltaic cell. Słowa kluczowe: sieć domowa, światłowód, ogniwo fotowoltaiczne. Optical power supply in home telematic networks The principle of the remote powering technology consists in emission, basically from some central device, of high power continuous optical signal through a fibre-optic link and its conversion, by means of a photovoltaic module, into electrical power that can be used to supply the electronic components. One drawback of the idea of transmitting optical power via a telecom fiber is that fibers introduce distortions to the transmitted signals at high power values. Consequently, one can expect limitations to practical realization of supplying optically electronic appliances. In order to identify, whether this limits constitute a real bottleneck a survey of electronic appliances and typical network communication devices was performed. The results are summarized in the following. Table 1. Trends in ICs’ development Year Parameter Layer thickness [μ] Wafer size [mm] Min. supply voltage [V] Max power dissipation [W] Clock frequency [MHz] DRAM capacity [GB] 1997 2001 2003 2012 2020 0.25 0.15 0.13 0.05 <10 200 300 300 450 Molec./ Biolog. 1,82,5 1,21,5 1,21,5 0,50,6 <0,001 70 110 130 175 600 750 1500 2100 10 0.256 2.0 4.0 256 5 –5 >5⋅10 5 > 1000 0,1 0,09 power consumption per megahertz of processor clock linear trend power per unitary frequency [W/MHz] Introduction Looking from the present perspective it seems that in the future most of the home management and/or control services will be integrated in one device located inside the home. Such solutions already exist in very fragmented form. There are several systems that allow simple management tasks being sold under the name “intelligent building”. After the launching of several modalities of the so called set-top boxes including the „Livebox” which generally are capable to centralize all the telecom and multimedia services in the home, maybe we have to think about extending its capabilities with other home services like management and control of the home. Adding the module of home security management is the simplest and justified step. In the future such device may become a centre of home management. Nowadays we basically use two transmission media types in home networks – copper and air. The first one offers quite resonable bandwidth of tens of megabits per second and the second one brings the flexibility of location. Both of them are reaching limits of their technological capabilities. Now let us assume that the future home networks are entirely optical. There is no problem with passive devices, but active devices have to be supplied with electrical energy. It can be done using a local mains or battery supply. However, such solution is marked by a series of disadvantages like for example constraint of location, unknown reliability, difficult maintenance or (still) high cost. In the case of fiber optic networks the remote optical powering can be the method which avoids the use of a local power supply via a power line and/or batteries to power and monitor active components. 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0 1995 2000 2005 year 2010 2015 Fig. 1. Schematic diagram of measurement setup As we look at the table 1 and the figure 1 we can see that there is a decreasing ratio of power consumption to both clock frequency and memory capacity. It allows us to forecast that capacity of optical power supply can meet the power demand of the consumer’s devices in future. Nevertheless, we are not sure if such gross estimation is sufficient, so first we have to group the devices in dependence on foreseen power consumption. 1. Low power consumption • passive intrusion sensors, • fire, smoke, gas and other detectors, • coders, selectors, small displays • local modems 2. medium power consumption PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 84 NR 3/2008 277 • switches, multiplexers, • filters, attenuators, • signalling devices 3. high power consumption • sound and video converters and processors, Table 2. Trends in ICs’ development Component electrical power Low power consumption intrusion detection 0 fire detection 1mW smoke detection 1mW movement 5mW detection Communication 10mW circuits Telemetry 1mW SFC – signal forming circuit Medium power consumption Telephone 50mW High power consumption TV & Radio over 1W IP Decoder TV & Radio 1W analogue Decoder Optical signalling Simple video 0.5 to converters (Icams, 1W small displays) optical power *0 (+SFC) *0 (+SFC) *0 (+SFC) 10mW Remarks Passive 20mW 1mW considered below 100mW Maximally simplified 2W /? 2W /? 1W 1 to 2W If it comes to communication devices, the currently available USB devices have a natural limitations of 2.5 W. It is much far beyond the limit that optical power transmitted via a telecom fiber can afford. If we consider Gigabit Ethernet we also see that currently available 1Gb link ICs are quite power consuming. For example RTL8139 series consume at least 900 mW at 3.3 V power supply, according to the manufacturer (Realtek). It results in about 2 W of optical power needed for each device when typical value of 40% PPC efficiency is considered. As it can be seen the „conventional” solutions are not valid. FPGA based Xilinx solutions may be better for the second approach – they need about 200 mW. Another factor that has to be considered is that the continuous operation is not always needed. Usually modems transmits in “bursts” which ecourages to exploit an idea of accumulation of energy in the power supply device. According to the idea, energy is accumulated over certain time before it is used. One can expect that the practical minimum of the supply power for a device, which operate in burst mode with very low cycle, can limited by the consumption of electronic driving circuitry in the power supply device itself. Let us consider an example of optically powered phone. According to G.711u [1] – 64 kbps band is needed. In the GPON [2] network the link time coefficient is then about –4 5⋅10 and adding some extra margin for initialization and –4 termination it can be estimated to about 6⋅10 . The power consumption during transmission is estimated to be 500mW. Taking into account the efficiency of light to electrical energy conversion and efficiency of accumulation we get that the energy needed is about 1mWs. It means that we do not need so much optical power if we can accumulate energy. This concept may be extended to “full-speed” transceivers provided two conditions are satisfied. First that we operate in a TDM mode. For example, in the case of 278 a complete typical TDM PON (64 users) an individual user th has a chance to transmit every 64 time slot. It is the central control unit (OLT) that controls the transmission so if the traffic control protocol is aware of the power accumulating transceivers it can arrange the schedule in such way which allows recovery of the charge. The second condition is that the network is complete because in the sparse network timeslots can be assigned more frequently so there may be not enough time to recover the energy status of the transceiver. Considering the above results and discussion we propose a concept of introducing optical supply to the appliances which can be connected to a fiber optic home network. Being conscious of limitations of contemporarily available technology, we suggest two system evolution scenarios depending on technology and market state of the art and the customer necessities. The first one may be the first step in introducing photonics into the home telecom appliances. It basically consists in expanding the existing functionality of the set-top box with the optical remote powering and optically powered user terminals. A sort of modular approach. The second one supposes remote optical powering of the set-top box. It is contemplated as photonic solution with some electrical add-ons. It is meant to be a future oriented solution; new technologies need to be developed as well as new power optimized specialized ICs with advanced power saving functionality. Solution 1 It assumes modular set-top box with remote optical powering and local electrical power supply. The minimum requirement for the set-top box is, the device should be equipped with optically powered phone. There are following advantages of such solution: • Phone service fully protected against mains failures (independence on external power supply • Full control of the service from the central office to the receiver, • Electrical powering of modem allows alleviation of central office even in case of increasing service capability, • Easier distribution of optical supplying power, • It is possible to power optically more consuming devices like detectors, TV decoders or advanced phone. There is one disadvantage for this solution. It is: • In case of failure in supply of electrical energy most of “Livebox” extensions cease to operate. It is assumed that “emergency” phone is optically supplied in its basic functionality so the problem reporting is possible. Solution 2 It assumes remote optical powering of the entire Livebox. The requirements include: optically powered phone and optically powered modem for basic data connection. According to these requirements the two services: phone and data will persist even in case of local power failure (we allow data link to slow-down in this case). Other devices may be connected later in dependence on each technology (basically after decrease in power consumption). The main advantages of this solution are as follows: • Independence on external power supply • Full control of the service from the central office to the receiver. The solution has also few disadvantages, which can be briefly listed: • Low efficiency of currently available PPCs. • Transmission of high optical power is necessary PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 84 NR 3/2008 • Application of separate optical power supply fibre may be necessary. • Advanced technologies of optical user safety are required (e.g. in case of breaking the fibre), • Fire safety is unknown, • Aggregation of functionality is necessary e.g. DVB decoder integrated in DVD recorder allows avoiding necessity to power the decoder in optical way. Conclusions Supplying optically a terminal and other devices, which can be connected to them, practically cannot be solved at present. For the purpose of structuring possible development actions we propose to distinguish separate classes of optically supplied devices: • 1st class, which contains the analogue part of a terminal; the 1-st class would be obligatory supplied optically • 2nd class, which contains blocks of the slowest transmission speed (it may include POTS-to-network interface and possibly a Bluetooth modem); it could be supplied optically in the next stage of development • 3rd class; which contains other devices; the devices belonging to this class as well as their interfaces to the network would be supplied externally. We also suggest to start a research on a low-power moderate speed interface to optical network (transmission convergence block). The possibility to realize such interface, and possibility for including it into the optically supplied class 1, may be of primary interest of future operators of PONs, for some services should be offered without restrictions from the availability of local supply. The key for supplying power to a transceiver via fibre is the minimization of power consumption of many blocks, which at present consume watts or hundreds of milliwats. One can reject idea of supplying optically lots of terminals from a central site like in favour of supplying them (if necessary) from a local optical source. The USB-like network can be one candidate solution. Acknowledgments: The core of this research was financed by France Telecom. REFERENCES [1] ITU-T, “G.711 -” (03/2003) [2] ITU-T, “G.984.1 - Gigabit-capable Passive Optical Networks (GPON): General characteristics” (03/2003) [3] Lach Z., Smolarz A., Wójcik W., Tymecki A., Experimental validation of an optical supply for an electrooptic switch, Przeglad Elektrotechniczny, 84 (2008), nr.3, 259-261 Authors: dr hab. inż. Waldemar Wójcik, prof. PL; dr inż. Zbigniew Lach; dr inż. Andrzej Smolarz; mgr inż. Tomasz Zyska; University of Technology, Department of Electronics, Nadbystrzycka 38a, 20-680 Lublin, Poland; E-mail: wal;[email protected]; E-mail: [email protected]; E-mail: [email protected]; PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 84 NR 3/2008 279