MXPA98001288A - Path filter of controlled return of high-end terminal to reduce noise entry on cable systems bidirection - Google Patents

Abstract

The present invention relates to a device for selectively passing RF energy in a CATV communication path from a higher setting terminal to an input end, comprising: monitoring means for monitoring a selected bandwidth within the communication path, detection means having a unique address, responsive to the monitoring means, for detecting a valid communication signal transmitted from the upper adjustment terminal within at least a portion of the bandwidth, wherein the signal valid communication includes the unique address of the detection means, and controllable filter means, which respond to the detection means, to pass RF energy in the portion of the bandwidth when a valid communication signal has been detected and blocks all RF energy within the bandwidth portion with a bypass filter when u A valid communication signal has not been detected

Description

PATH FILM OF CONTROLLED RETURN OF SUPERIOR ASSEMBLY TERMINAL TO REDUCE THE NOISE ENTRY ON CABLE SYSTEMS BIDIRECTIONAL BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates generally to cable television communication systems. More partarly, the invention relates to a system that reduces the ingress of noise into the return communication path of a bidirectional cable television communication system.

DESCRIPTION OF THE RELATED TECHNIQUE Cable television communication networks (CATV) have increased their use for applications that require two-way data transmission. Bidirectional CATV networks have become commonplace as the diversity of services has grown. Many CATV operators now provide networks that support interactive applications, including home banking and home shopping, or life safety applications, such as medical alert and alarm services. CATV operators have even begun to challenge regional ring operators (RBOC) by offering telephone services over CATV networks. Although bidirectional CATV networks have become commonplace, there are several problems that continue to plague CATV operators by offering interactive services. One of the main problems has been the entry of noise, which refers to unwanted external signals that enter the CATV network at weak points in the network such as roof discontinuities, defective connectors and in a consumer's home through upper assembly terminals. The noise input presents an interference signal on the CATV network, thereby degrading or even eliminating the valid signals transmitted on the CATV network. Noise input is partarly undesirable in bidirectional CATV systems since bidirectional systems are significantly more susceptible to noise. In the upstream communication path, noise from any point in the CATV network is propagated, aggregated and amplified in the upstream direction. As the signal travels to the head end of the system, each line in the CATV system is amplified and added. It is extremely difft at the head end, if not impossible, to detect the input of noise from valid signals sent from higher set terminals. One method to reduce the noise input from the upper assembly terminals is to place a filter at each derivation location corresponding to homes where no upstream communication equipment is present. This limits the sources of noise input to the derivation locations corresponding to households that use the upstream communication path. Because many of the services offered by CATV providers are interactive, almost every household uses an upstream communication path. Therefore, this method to reduce the noise income has decreased the benefits. Attempts have been made in the prior art to overcome the problems caused by the entry of unwanted noise. For example, U.S. Patent No. 5,235,619; and the related Patents Nos. 5,225,902; 5,155,590 and 5,142,690 disclose a bidirectional CATV communication system that compensates for unwanted noise input by communicating each message from the upper set terminals to the head end over a plurality of frequencies and time slots. The head end receives and compares the redundant transmissions to confirm the transmitted message. This system requires that high-speed hardware be located both at the head end and at each upper assembly terminal, resulting in a system that is efficient and costly. Accordingly, there is a need for a system to improve bidirectional CATV communication systems by reducing the input of unwanted noise into the upstream communication path.

BRIEF DESCRIPTION OF THE INVENTION The present invention comprises a device that eliminates the input of noise introduced in each derivation location or at any point within the CATV communication network preventing it from entering the communication network in the communication path upstream. The device includes a filter with a bandwidth equal to the bandwidth of the upstream communication path that isolates the energy from the input noise at the bypass location. The device monitors the communication path upstream and detects when a valid communication signal is being transmitted. After detection of a valid signal, the filter is disconnected from the upstream communication path to allow the valid transmission to be sent. When the end of the valid signal is detected, the filter is again disconnected to block all transmissions upstream in that bandwidth.

Accordingly, an object of the present invention is to provide a method for improving bidirectional CATV communication systems by decreasing the amount of upstream noise input. Other objects and advantages of the present invention will be apparent to those skilled in the art after reading the detailed description of a currently preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a CATV transmission network including the present invention; Figure 2 is a simplified block diagram of the communication path between a subscriber and the head end; Figure 3 is the preferred embodiment of the input noise reduction device of the present invention modalized in the subscriber derivation; Figure 4 is the device of Figure 3 included within an environment-tight housing; Figure 5 is the secondary return path filter (SRPF) according to the present invention; Figure 6 is an alternative mode of the SRPF using CD signaling; Figure 7 is a second alternative of the SRPF that - supports multiple frequency bands; Figure 8 is the signaling preamble used with a plurality of detectors; Y; Figure 9 is a plurality of detectors for segmenting the upstream bandwidth.

DETAILED DESCRIPTION OF THE MODALI DAD PREFERI DA The detailed description of the preferred embodiment will be described with reference to the figures in which similar numbers represent similar elements throughout. Figure 1 shows a bidirectional CATV network including the input noise reduction device of the present invention. The CATV network 118 is configured in a "branch and tree configuration". The head end 64 is in the upper part of the shaft and the upper assembly terminals 57 are located along the entire length of the trunk and the branches. The CATV signals that originate the head end 64 are sent to the plurality of terminals 2-57 of the upper set and the transmissions from each terminal 2-57 of the upper subscriber set are received at the head end 64. The network 118 It begins with a plurality of coaxial or fiber optic trunk lines 82 coupled to the head end 64. At points where the coaxial transmission cable is divided, signal splitters / combiners 58 are installed. The line dividers 62 and bidirectional signal amplifiers 90 are distributed throughout the CATV network 118 to propagate the transmitted signals and maintain the nominal signal strength levels. The descent lines 98, branch lines 60, 88 and trunk lines 82 provide the bidirectional transport means. The upper set terminal 57 includes a tuner 11 7, data receiver 110, to receive communication from the head end 64, and a data transmitter 112, to allow a subscriber to communicate with the head end 64. The data receiver 110 and the data transmitter 112 can be fixed or agile in frequency, depending on the requirements of the system. The head end 64 includes at least one frequency agile RF data transmitter / receiver 68 for transmitting data to, and receiving data from, the plurality of higher set terminals 2-57. In Figure 2 a simplified block diagram of the communication path between a subscriber facility 113 and the head end 64 according to the present invention is shown. At least one transceiver 68 transmits video and audio programs (either analogue or digital), and data from the head end 64 to a subscriber facility 113 typically comprising a top set terminal 57 and a television set 116 or a VCR (not shown). As is well known to those skilled in the art, the transceiver 68 transmits programming over a plurality of CATV transmission channels allocated by the CATV network operator. Additionally, data only channels can be provided for interactive communications. The plurality of transmission and data channels are combined by a combiner (not shown) for transmission over the CATV network 118. Although only one terminal 57 of the upper assembly is shown in Figure 2, it should be understood that thousands of upper assembly terminals 57 can communicate with an individual head end 64. The CATV network 118 is capable of supporting a bandwidth of about 5 MHz to more than 750 MHz. The bandwidth above 50 MHz is typically used to transmit signals in the downstream direction from the head end 64 to terminal 57 of the upper assembly. The bandwidth below 40 MHz is typically reserved for transmitting signals in the upstream address communication path from the upper set terminal 57 to the head end 64. A guard band between 40 and 50 MHz can be used to separate the Bandwidths upstream and downstream, although this is not required.

The head end 64 includes a central processor 122 which originates all data communications at the head end 64 such as account statements, information of interest to the community or notifications of special events. Additionally, the central processor 122 retransmits communications received by the head end 64 from external service providers such as bank network or shopping services. The upper set terminal 57 receives video and audio transmissions from the head end 64 via a conventional tuner 117 and the data transmissions via the data receiver 110. The video and audio programs are processed and sent to the television set 116 to be seen and heard by the subscriber in a manner that is well known to those skilled in the art. In the bidirectional CATV communication system of the present invention, the upper set terminal 57 also includes the data transmitter 112 which enables the upper set terminal 57 to transmit communications to the head end 64 on the upstream communication path. It should be evident that all the components within the CATV network 118 are bidirectional. With reference to Figure 3, the preferred embodiment of the present invention is shown modalized in a subscriber branch 132. Subscriber branch 132 includes an entry port 134, an exit port 136 and 4 subscriber derivation ports 138. The input port 134 is coupled to a directional coupler 146 which passes the CATV signal to both the output gate 136 and the subscriber derivation ports 138. The signal is fractionated again with the fractionators 142, 143, 145 depending on the number of bypass gates 138. As will be described in more detail below, a secondary return path filter (SRPF) 144 is preferably coupled between signal splitters 143, 145 and each subscriber bypass gate 138. Alternatively, the SRPF 144 may be located between the signal splitter 142 and the signal splitters 143, 145 or between the signal splitter 142 and the directional coupler 146. These alternative locations reduce the cost since there is less SRPF 144 per gate 138 bypass. However, the benefits of using SRPF 144 will be slightly decreased if it is used in alternative locations. As shown in Figure 4, the subscriber branch 132 preferably includes an environmentally-friendly housing having the entry and exit doors 134, 136 and a plurality of subscriber derivation doors 138. The preferred embodiment of the SRPF 146 according to the present invention is shown in more detail in Figure 5.

The SRPF 146 comprises the input and output ports 148, 149, a controllable filter 150, a downstream bandpass filter 151, a signal splitter 152, a sampling bandpass filter 154, a bypass filter 155 and a detector 156. The downstream bandpass filter 151 allows communications from the head end 64 to pass through the SRPF 146 without interruption to the upper set terminal 57. The controllable filter 150 comprises two filters: a return path block filter 157 and a return path return filter 158. The block filter 157 allows a control signal from the upper set terminal 57 to reach the sampling filter 154 when the bypass filter 155 is activated, as will be explained in the following with details. The through filter 158 allows communications from the upper set terminal 57 to pass through the SRPF 146 to the head end 64 without interruption. The bypass filter 155 filters all of the RF energy in the bandwidth of the upstream communication path, thereby blocking any unwanted noise ingress preventing it from entering the CATV network 118 from the upper set terminal 57. The signal splitter 152 receives transmissions from the upper set terminal 57 and directs a portion of the RF energy to the sampling filter 154. Preferably, the sampling filter 154 has a bandwidth equal to the bandwidth of the upstream communication path. The output of the sampling filter 154 is fed to the detector 156. The detector 156 will detect both the RF noise input and the valid transmissions from the upper set terminal 57. However, the amplitude of a valid transmission will typically be several orders of magnitude greater than the input of RF noise. When the detector 156 detects RF energy above a predetermined or relative threshold, it performs two functions. First, the detector 156 deactivates the bypass filter 155, thereby removing the bypass filter 155 from the upstream communication path. Second, the detector 156 changes the block filter 157 out of the communication path and changes the passage filter 158 in the upstream communication path. In a standby operation, when the upper set terminal 57 is not transmitting an upstream signal, the block filter 157 is normally within the upstream communication path. The bypass filter 155 blocks all of the RF energy downstream of the SRPF 146 by preventing it from entering the upstream communication path by shortening all frequencies within a selected bandwidth to ground. In the active operation, when the subscriber wishes to send an upstream transmission, the transmission is sent in the upstream communication path to the head end 64. The fractionator 152 directs a portion of the RF energy from the upstream communication path to the sampling filter 154 and the detector 156. Although the bypass filter 155 shortens all frequencies within a selected bandwidth to ground, the block filter 157 allows transmissions from the upper set terminal 57 to reach the filter 154 Of sampling. The specific operation of all filters is well known to those skilled in the art and a detailed discussion of these filters is beyond the scope of the present invention. The upstream transmission from the upper set terminal 57 is passed through the sampling filter 154 and is detected by the detector 156. The detector 156 deactivates the bypass filter 155 and causes the controllable filter 150 to change the filter 157 of block out of the communication path upstream and changes the filter 158 to the upstream communication path. Additionally, the detector 156 deactivates the bypass filter 155 for the duration of the valid transmission. The upstream transmission from the upper set terminal 57 will pass through the input port 148, the controllable filter 150 and the output port 149 to the head end 64. Once the valid transmission ceases and a predetermined period has elapsed since then, the detector 156 activates the bypass filter 155 which will block all additional RF transmissions in the upstream direction. The detector 156 also causes the controllable filter 150 to change the pass filter 158 out of the upstream communication path and the block filter 157 to the upstream communication path. To prevent any data from being lost during transmission in the upstream communication path, the upper set terminal 57 preferably transmits a preamble tone or sequence for detection by the detector 156. This avoids data loss and there is a short time delay by deactivating the bypass filter 155. If a specific preamble tone or signal is used, the detector 156 is preferably calibrated to detect the signal. The power for the SRPF 146 is supplied from a power inserter on the CATV network 118, or from the upper set terminal 57. Alternatively, the power for the SRPF 146 can be derived from the RF energy that is being transmitted by the upper set terminal 57 using a very high gain switch, such as a MOSFET. In an alternative embodiment, shown in Figure 6, the upper set terminal 57 may apply a DC voltage to activate or deactivate the SRPF 146 when a transmission in the upstream communication path is desired. The CD block 161 prevents the CD signal from proceeding upstream. The detector 163 detects the DC current or voltage and activates the trap filter 155 as required. Although SRPF 146 has been described as being located upstream of subscriber lead 138, those skilled in the art will clearly recognize that SRPF 146 can also be located between lead 138 and the subscriber's home, within the home of the subscriber or even integrated as part of the upper set terminal 57. The SRPF 146 can also be located at any point between the subscriber and the head end 64 on the CATV network 118. In a second alternative embodiment, shown in Figure 7, SRPF 158 supports multiple frequency bands with multiple detectors 156, 256 and multiple sampling filters 154, 254. The upstream communication path may be split between several pieces of equipment at the subscriber's premises that may desire upstream communication path access, but not related to each other. When splitting the bandwidth, a class of service suffers no degradation of noise revenue due to the presence of other classes of service. For example, if the cable telephone equipment uses the return bandwidth of 15-30 MHz and the CATV services use the 8-12 MHz bandwidth, the SRPF 158 comprises two units 147, 246, each comprising a sampling filter 154, 254, a detector 156, 256, a deflection filter 155, 255 and a controllable filter 150, 250. The first deflection filter 155 grounds the bandwidth of 8-12 MHz. The second deflection filter 255 grounds the bandwidth of 15-30 MHz. The units 147, 246 can be used individually, where only a type of service is present, or cascading when both services are present. The upstream communication path can be divided into small bandwidths, or the order of hundreds of kHz or less, each of which is controlled by a different SRPF. The activation or deactivation of a particular SRPF can be effected in many different ways. For example, the preamble for a valid transmission may include a stopwatch signal as shown in Figure 8 to be used with the mode having a plurality of detectors as shown in Figure 9. In this embodiment, in order of activating the detector D1, the signal S1 is transmitted in the preamble. Detector D1 will detect two separate pulses by a duration of 1T. After detection of this signal sequence the detector 1 T deactivates the corresponding trap filter F1 and activates the corresponding return path step filter P1. Several P1 -PN pass filters can be activated in parallel using a plurality of corresponding detectors D1 -DN and filters F1-FN to simultaneously support multiple services. In this way, small segments of the upstream bandwidth can be used selectively. Those skilled in the art will clearly recognize that a different signaling scheme such as multiple level signaling can be used. Additionally, each detector may have a unique address and the preamble of a valid transmission may include the specific address of the detector corresponding to the desired portion of the upstream bandwidth to be used for the transmission. Although the invention has been described in part with detailed reference to the preferred embodiment, the detail is intended to be instructive rather than restrictive. Those skilled in the art will appreciate that many variations can be made in the structure and mode of operation without departing from the spirit and scope of the invention as described in the teachings therein.

Claims (14)

1. CLAIMS 1 . A device for selectively passing RF energy into a CATV communication path, characterized in that it comprises: monitoring means for monitoring a selected bandwidth within the communication path; detection means, responsive to the monitoring means, for detecting a valid communication signal transmitted within the selected bandwidth; and filter means, in response to the detection means, for selectively passing RF energy when a valid communication signal has been detected within at least a portion of the selected bandwidth.
2. 2. The device, in accordance with the claim 1, characterized in that the filter means further comprise a controllable filter having means for passing RF energy and means for blocking the RF energy.
3. 3. The device, in accordance with the claim 2, characterized in that the filter means further comprise a deflection filter to block all the RF energy within the selected bandwidth.
4. 4. The device, according to claim 1, further characterized in that it comprises a bandpass filter to allow the uninterrupted transmission of RF signals over a second selected bandwidth.
5. 5. The device according to claim 2, characterized in that the monitoring means monitors the selected bandwidth for a CD signal and the detection means detects the CD signal.
6. 6. The device, according to claim 5, characterized in that the filter means further comprise: a deflection filter to block all the RF energy within the selected bandwidth; and a CD signaling block.
7. 7. The device, according to claim 1, characterized in that the RF energy comprises the valid communication signal.
8. 8. The device according to claim 4, wherein the communication path is divided into a plurality of subbands and the monitoring means monitors a first selected subband within the communication band; the device, further characterized in that it comprises: second monitoring means for monitoring a second selected sub-band within the communication path; second detection means, in response to the second monitoring means, for detecting a valid communication signal transmitted within the second selected sub-band; and second filter means, in response to the second detection means, for selectively passing RF energy when a valid communication signal has been detected within at least a portion of the second selected subband.
9. 9. The device, according to claim 8, characterized in that each of the detection means further includes a unique address; and wherein the valid communication signal includes a header having a unique address corresponding to one of the detection means.
10. 10. A device for selectively passing RF energy over a CATV communication path, having a plurality of subbands, characterized in that it comprises: a plurality of monitoring means, each for monitoring a different sub-band selected within the communication path; a plurality of detection means, each in response to one of the monitoring means, for detecting a valid communication signal transmitted within the selected sub-band; and a plurality of filter means, each in response to one of the detection means, to selectively pass RF energy when over the selected subband when a valid communication signal has been detected within the selected subband. . eleven .
11. The device according to claim 10, characterized in that each of the filter means further comprises a controllable filter having means for passing RF energy and means for blocking the RF energy.
12. 12. The device, according to claim 11, characterized in that each of the filter means further comprises a deflection filter to block all the RF energy within the selected subband.
13. 13. The device according to claim 10, characterized in that each of the monitoring means monitors the selected bandwidth for a CD signal and each of the detection means detects the CD signal.
14. 14. The device, according to claim 13, characterized in that each of the filter means further comprises: a deflection filter to block all the RF energy within the selected bandwidth; and a CD signaling block.