1. Field of the Invention
The present invention relates generally to hybrid fiber cable network systems and more specifically, to a tap device for the distribution of hybrid fiber cable network signals to the drop cable.
2. Discussion of the Related Art
Hybrid fiber cable network distribution systems (HFC) such as cable television networks (CATV) generally comprise five major parts: 1) the headend; 2) the trunk cable; 3) the feeder cable; 4) the drop cable to the home and 5) the subscriber's equipment. The distribution cable runs past homes of subscribers. Taps are devices located at various points along the distribution cable. A tap connects the distribution cable to the drop cable. Subscribers are typically connected to the drop cable, which is about 25-150 feet long. Known tap devices receive the RF signal from the distribution cable and pass the signal forward to subscribers. The known tap typically splits the signal to two or more subscribers through the use of a splitter device. The tap that divides the signal among the outgoing CATV network subscribers must provide several important performance characteristics. The most important characteristic concerns transmission and distribution of a signal having a bandwidth spanning a wide range of frequencies. Currently, a standard CATV signal has a typical bandwidth ranging from about 5 MHz to about 860 MHz. At frequencies above 860 MHz conventional tap devices do not perform. In addition, successful protocols for broadband data transfer over hybrid fiber coax (HFC) networks such as DOCSIS cannot be used as an alternative to existing data and telephony services because the currently available HFC networks do not provide sufficient spectrum especially in the upstream direction where out of 5-42 MHz less than 20 MHz is usable, thus providing only 60 Mbps of upstream transmission speed. There is therefore a need for tap devices capable of providing to subscribers CATV system signal at frequencies above 860 MHz and up to 3 GHz or above.
One aspect of the present invention regards a hybrid fiber cable network tap device for the receiving and distribution of a wideband signal of about 5 MHz to about 3000 MHz through at least one line output port and at least two tap output ports. The hybrid fiber cable network tap device comprises an input port for the reception of the wideband signal, a first diplexer device for separating the wideband signal into a low frequency signal of about 5 MHz to about 860 MHz, an AC power signal, and a high frequency signal of about 1000 MHz to about 3000 MHz, an AC power bypass comprising an RF choke for separating the AC power signal from the low frequency signal, a second diplexer device for re-combining the low frequency signal, and the high frequency signal and the AC power signal and to feed the re-combined signal to the at least one line output port, a third diplexer device for re-combining the high frequency signal, and the low frequency signal and for feeding the re-combined signal, a first splitter device for receiving the low frequency signal and for dividing the low frequency signal, and a second splitter device for receiving the high frequency signal and for dividing the high frequency signal.
A second aspect of the present invention regards a hybrid fiber cable network tap device for the receiving and distribution of a wideband signal of about 5 MHz to about 3000 MHz through at least one line output port an at least two tap output ports. The hybrid fiber cable network tap device comprises an input port for the reception of the wideband signal, a first diplexer device for separating the wideband signal into a low frequency signal of about 5 MHz to about 860 MHz, an AC power signal, and a high frequency signal of about 1000 MHz to about 3000 MHz, an AC power bypass comprising an RF choke for separating the AC power signal from the low frequency signal, a second diplexer device for re-combining the low frequency signal, and the high frequency signal and the AC power signal and to feed the re-combined signal to the at least one line output port, a third diplexer device for re-combining the high frequency signal, and the low frequency signal and for feeding the re-combined signal, a first directional coupler device for unequal division of the low frequency signal, and a second directional coupler device for receiving the high frequency signal and for unequal division of the high frequency signal.
A third aspect of the present invention regards a method operating in a hybrid fiber cable network system for the receiving and distribution of a wideband signal of about 5 MHz to about 3000 MHz through a tap device and at least one line output port an at least two tap output ports. The method comprises receiving at an input port the wideband signal, separating at a first diplexer the wideband signal into a low frequency signal of about 5 MHz to about 860 MHz, an AC power signal, and a high frequency signal of about 1000 MHz to about 3000 MHz, separating at an RF choke the AC power signal from the low frequency signal, dividing at a first splitter the low frequency signal, dividing at a second splitter the high frequency signal, re-combining at a second diplexer the low frequency signal, the high frequency signal and the AC power signal and feeding the re-combined signal to the at least one line output port, and re-combining at a third diplexer the high frequency signal and the low frequency signal,
A fourth aspect of the present invention regards a method operating in a hybrid fiber cable network system for the receiving and distribution of a wideband signal of about 5 MHz to about 3000 MHz through a tap device and at least one line output port an at least two tap output ports. The method comprises receiving at an input port the wideband signal, separating at a first diplexer the wideband signal into a low frequency signal of about 5 MHz to about 860 MHz, an AC power signal, and a high frequency signal of about 1000 MHz to about 3000 MHz, separating at an RF choke the AC power signal from the low frequency signal, dividing at a first directional coupler the low frequency signal, to a second diplexer device and a third diplexer device, the signal is divided in unequal signal levels, dividing at a second directional coupler the high frequency signal to the second diplexer device and the third diplexer device, the signal is divided in unequal signal levels, re-combining at a second diplexer the low frequency signal, the high frequency signal and the AC power signal and feeding the re-combined signal to the at least one line output port, re-combining at a third diplexer the high frequency signal, and the low frequency signal and feeding the re-combined signal, and receiving at the splitter device from the third diplexer device the combined low frequency signal and high frequency signal and dividing the combined signal to the least two tap output ports, the at least two tap output ports receiving the divided combined signal comprising of the low frequency signal and the high frequency signal and feeding the divided signal to a drop cable.
All the above aspects of the present invention provide for the division of a RF signal having a substantially extended bandwidth with a frequency range of about 5 MHz to 3 GHz and above.
All the above aspects of the present invention provide for complete AC current power-passing capabilities.
All the above aspects of the present invention provide for superior power loss, output return loss and output isolation values.
The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:
The present application is a continuation-in-part of co-pending PCT application serial no. PCT/IL02/00342 entitled A WIDEBAND CATV SIGNAL SPLITTER DEVICE, filed 7 May 2002, and is also related to co-pending PCT Patent application serial no. PCT/IL00/00655 entitled SYSTEM AND METHOD FOR EXPANDING THE OPERATIONAL BANDWIDTH OF A COMMUNICATION SYSTEM, filed 16 Nov. 2000, which are incorporated herein by reference.
A new and novel wideband hybrid fiber cable network such as cable television network (Community Access Television or CATV) tap device is disclosed. The tap device is located on various points along the distribution cable. The tap device is the connection point between the distribution cable and the drop cable, the latter being connected on the far end to subscribers' devices of the CATV system. The AC power signal is preferably bypassed by the tap device to the forward side of the distribution line. As a result of transmitting high RF frequency signal, at least above 1 GHz, over the distribution cable, a new and novel tap device is provided in order to enable the tap device to pass the AC power signal and the low frequency signal, of between about 5 MHz and 860 MHz, while still providing the complete wideband RF signal (about 5 MHz-3000 MHz) to the drop cable at a proper carrier-to-noise ratio (CNR) and also to allow the forward signal to pass to the downstream distribution line. The present invention overcomes the inabilities of previous tap devices by providing diplexers for band splitting the legacy (or now used) signal frequency of about 5-860 MHz and the high frequency band signal of about 1000-3000 MHz. Once the signal has been divided the low frequency signal is passed through a splitter while the AC power signal is bypassed using an RF Choke. The high frequency signal is also split and both low and high frequency signals are then combined. After the signals are combined the combined signal of about 5 MHz to 3000 MHz is sent towards the output port of the distribution line and the tap output ports leading to the drop cable and from there to subscribers of the CATV system. The combined signal directed towards the tap output ports leading to the drop cable may be split again once or more to provide signal to more than one drop cables while maintaining acceptable CNR reduction. The tap device of the present invention is operative both in the upstream and in the downstream direction. Signal entering the tap device in the upstream direction travels from the tap output port to the line in port in a return course as described above. The tap device is designed to allow both downstream and upstream transmissions.
The low pass filter of diplexer located adjacent to the line in port of the tap device is used as a high impedance device for the RF choke at frequencies above the legacy frequencies of up to about 860 MHz. Thus, the tap device of the present invention is enabled to transfer the AC power signal from the distribution line and still enable the transfer of RF frequencies above 1000 MHz both in the forward direction to the drop cable and the distribution cable and in the upstream the head end. The structure of the tap device is necessary to allow the high frequency signal (above 1 GHz) to send downstream and upstream RF signal in excess of 860 MHz.
In addition, one non-limiting and exemplary application of the present invention is the use of the DOCSIS protocol as described below. In the upstream direction the tap device of the present invention provides additional spectrum that allows DOCSIS to be used to serve increasing needs of subscribers including those of businesses. In one embodiment of the present invention the combined signal may be divided into a 700 MHz in the downstream and in the upstream directions enabling about 100 channels at 6 MHz with QAM 64 (30 Mbps per channel) in the downstream which enables data transfer speed in excess of 3000 Mbps. In the upstream about 100 channels at 3.2 MHz with QAM 16 (5 Mbps per channel) can be returned thus enabling data transfer speeds in excess of 1000 Mbps. Persons skilled in the art will appreciate that various other divisions of the combined signal are readily available to the HFC network operator and are contemplated by the present invention. Persons skilled in the art will appreciate that the tap device of the present invention can be used as a replacement for legacy tap devices so as to enable the transfer of RF frequencies above 1000 MHz along the distribution line and to subscribers.
Referring to
As the wideband signal transmission is operative in both the upstream and the downstream from the subscriber devices 18, 20, 22, 24 subscriber-specific signals are passed upstream from the through cable transmission drop line segments 17, 19, 21, and 23 respectively back to the tap device 16. The tap device 16 effects the combining of the separate subscriber-specific signals and consequently the combined signal is passed upstream through the transmission distribution line segment 15 to the CATV node 12 and head end 10.
Note should be taken that although in the drawing under discussion only a limited number of hub units, line splitters, drop tap devices, and subscriber devices are shown in a realistic configuration the CATV system would include a plurality of hubs, splitters, amplifiers, tap devices and subscribers.
Referring now to
A combined signal of about 5-3000 MHz carrying information content is transmitted from and to the CATV head-end 10 of
The third diplexer 127 output port is connected to a wideband splitter 135. The wideband splitter includes an RF matching transformer device and a splitter device. An exemplary RF Matching Transformer device is an RF Transformer Device, Component Number B78408A1227A from Epcos AG of Munich, Germany. An exemplary RF Splitter device is an RF Splitter Device, Component Number B78408A1226A from Epcos AG of Munich, Germany. The wideband splitter 135 provides two output ports 130, 131. Each of the two output ports 130, 131 output a signal about 7 dB lower relative to the signal power at the input port 106. The signal level is dependant upon the number of diplexers and splitters the signal has passed through in the tap device 100. The signal thus applied to the second and third output ports 130, 131 is fed to the subscribers serviced by the tap device.
Note should be taken that the AC current is passed by the low pass filter only. The signal output level is relative to the input level of the signal and that the various output ports share in identical signal levels. The output levels described above and below serve as examples and it will be appreciated that various other levels can be implemented in different networks and configurations that are clearly contemplated by the present invention.
Wideband splitters, such as wideband splitter 135 may be combined to provide additional tap output ports in the drop cable direction. Each leg of a wideband splitter is connected to the output of another two-way wideband splitter as long as more wideband signal splitting is required and is plausible given the cable to noise (CNR) ratio of the output signal after splitting. In the exemplary embodiment shown in association with
Signal splitting that diverts a pre-defined portion of the signal to a side port is referred to a directional coupling and the electronic units affecting unequal dividing of the signal are called directional couplers.
The low frequency (legacy) bandwidth range of about 5-860 MHz is fed into the low frequency coupler 150 that divides the signal into two. The two portions are fed respectively to the low pass filter section 116 of the second diplexer 117 and to the low pass filter section 128 of the third diplexer 127. The high frequency bandwidth range of about 1000-3000 MHz is fed into the high frequency coupler 152 that divides the signal into two. The two portions are fed respectively to the high pass filter section 118 of the second diplexer 117 and to the high pass filter section 126 of the third diplexer 127.
The low frequency bandwidth range of the signal, the high frequency bandwidth range component of the signal and the AC component are re-combined by the diplexer 116 and are passed together to the output port 120. The power of the signal at output port is about 2-3 dB lower relative to the signal power at the input port 106. The signal arriving at the output port 120 is passed to the continuance of the distribution cable. The third diplexer 127 output port is connected to the first tap output port 131 and the second tap output port 120 of the two-way wideband signal splitter device 135. The third diplexer 127 re-combines the low frequency bandwidth signal and the high frequency bandwidth signal. AC power signal does is not passed by the tap towards the drop cable and is only bypassed towards the forward distribution line via the AC bypass and RF Choke 104 via line output 120. The signal level at the first and second tap output ports 131, 130 is about −13 dB relative the signal level at the input port 106. The difference in signal output level is a result of the low and high frequency directional couplers side and output port signal division. As illustrated in association with
In an alternative embodiment the high frequency splitter 122 as well as the directional coupler 152 are implemented also as a distributed element as part of a low loss printed circuit board, or alternatively can be substituted by a wide band drop device eliminating the need for a low loss printed circuit board by using a low cost FR-4 drop device. In such case the tap 100 can be assembled on a PCB which is identical for various taps and tap outputs (the same PCB can be implemented in association with the devices shown in
Referring now to
While the respective portions of the device are identified for convenience as input, and output although the tap device is also functional as a signal combiner and as such, the terms input and output indicate relative positioning and are not to be construed to require that signal processing and handling occurs in a particular direction in the device. In the preferred embodiment of the invention, the tap device is utilized in a CATV system or in another signal distribution network and the like. It would be easily perceived by one with ordinary skill in the art that in other preferred embodiments of the invention the tap device could be utilized in diverse other computing and communications environments such as a satellite communications network, a high-speed data transmission network, a telephone network, and the like.
The description of the preferred embodiment of the present invention is not meant to be limiting to other possible embodiments already contemplated of the present invention. For example in the future the substantially expended bandwidth of the signal could reach frequencies in the excess of 3 GHz. Any number of output ports could be associated with the proposed tap device while allowing reasonable signal level drop. The relative output power levels achieved could be diverse and could be suitably adjusted according to the differing requirements. The HFC network of the present invention may be a hybrid fiber cable network or a cable only or a fiber only networks transporting signals including RF signals which may carry television broadcast and data.
It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims, which follow.
Number | Date | Country | Kind |
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157285 | Aug 2003 | IL | national |
The present application is generally related to co-pending PCT application No. PCT/IL00/00655 entitled SYSTEM AND METHOD FOR EXPANDING THE OPERATIONAL BANDWIDTH OF A COMMUNICATION SYSTEM, filed 16 Nov. 2000 and is a continuation-in-part in-part of co-pending PCT application No. PCT/IL02/00342 entitled A WIDEBAND CATV SIGNAL SPLITTER DEVICE, filed 7 May 2002, which are incorporated herein by reference.