HK1188344B - Cable modem with dual automatic attenuation and method thereof - Google Patents

Description

Cable modem with dual automatic attenuation and method therefor

Technical Field

The invention relates to a wireless communication system and fading management. More particularly, the present invention relates to a system for automatic control

Enhanced protocols and algorithms for cable modem attenuation.

Background

As technology continues to evolve and electronic devices become more advanced, one problem that continues to plague system designers is the inevitable signal loss, known as attenuation, that exists across the span of the cable. For all cables (e.g., coaxial cable, which is a cable that provides signals to a cable modem), attenuation is a very important indicator that affects signal propagation to upstream and downstream electronic circuits. This is a significant problem for the cable and telecommunications industry, where thousands of miles of cable are routed to provide services to subscribers. The basic function of coaxial cable is to act as a conduit for the transmission of RF (radio frequency) signals from a source to a recipient, for example from a cable plant to an end user. In the perfect world, the amount of power used to exit the coaxial cable should be equal to the amount of power entering the coaxial cable. In the real world, however, this is not the case, and there is a possibility that some power will be lost along the length of the RF cable, resulting in less power reaching the user than initially entering the RF cable. Cable and telecommunications companies often employ a variety of strategies to address this problem. These policies may include: placing amplifiers on the line and using low loss cables. As is well known, attenuation varies depending on the type of cable and is generally directly related to the length of a particular cable. Unfortunately, cable and telecommunications companies are reluctant to use lower loss cables because such cables tend to be more expensive. Table 1 provides an overview and compares the different coaxial cable signal losses.

TABLE 1

Attenuation is defined in terms of decibels per unit length at a given frequency (the longer the cable the greater the loss), where the loss is also frequency dependent and generally increases with frequency. However, other factors may also affect the attenuation value of the cable. For example, at a frequency of 1GHz, the loss of an RF cable, which typically exhibits a 10dB loss, may increase by 1dB or more when physically bent. Other factors, including temperature and weather, may also affect wear. Typically, 75 Ω coaxial cable is used almost exclusively for TV and VHF FM applications. But 50 omega coaxial cable has been adopted as a standard for commercial, amateur and CB applications.

The reasons for the above power loss are many. The first cause of power loss is radiation loss. Since most cables typically radiate only a very small amount of power, radiation losses are usually the least significant cause. However, very inexpensive coaxial cables may have a very poor outer covering braid, in which case the radiation loss may appear to be a significant loss factor. As described in the following paragraphs, most of the losses can be attributed to resistive and dielectric losses inside the coaxial cable.

The second loss cause is resistive loss inside the coaxial cable. Resistive losses arise from the fundamental resistance of the conductor (e.g., copper wire inside the cable), and the current flowing through the conductor can result in the dissipation of heat. The actual area of current flow through the conductor is limited by skin effects, which become increasingly more pronounced as the frequency increases. Since the stranded conductor has a lower resistance than a solid conductor, by using the stranded conductor, power loss due to the resistance can be reduced. To reduce the level of power loss in a coaxial cable, the conductor area must be increased, thereby resulting in a lower loss coaxial cable being larger (and heavier) than a higher loss cable. It is also possible that the resistive losses increase with the square root of the frequency, which means that resistive losses will generally dominate at lower frequencies.

A third cause for losses is dielectric losses. Dielectric losses represent the dominant losses in most coaxial cables. Like resistive losses, power losses, which are dielectric losses, are dissipated as heat. Dielectric losses are generally independent of RF cable size, but increase linearly with frequency. Thus, in the case where the resistive loss increases with the square root of the frequency, the dielectric loss increases linearly, thereby causing the dielectric loss to dominate at higher frequencies.

To cope with such power losses, cable and/or telecommunications companies often install spaced apart power amplifiers throughout the cable network ("cable plant"). Such amplifiers are adjusted at the time of installation of the cable plant and are adjusted again each time an additional tap is installed or removed from the cable plant. Furthermore, the cable installer typically overpowers each cable strand ("hot" cable) to some degree in order to ensure adequate signal strength on each tap. At each tap, the power is typically attenuated to an appropriate level to avoid damage to downstream circuitry. This attenuation is accomplished by installing a physical attenuator on each tap and/or coiling an extra length of cable until the correct power level is achieved. This strategy is problematic because the attenuator must be changed and/or the cable rewound whenever the power propagating through the cable plant changes.

Currently, cable companies use splice closures to set downstream ratings. The drop box, which may or may not be power amplified, is typically located on a service line in a street or roadway (e.g., a distribution line carrying signals from a cable plant) and provides a connection for individual users. The tap box effectively acts as a "T-connection" in that the service line carrying the high power signal (e.g., -20 to 52 dBmV) from the cable plant can continue to the next residence, while the power of the signal tapped to each subscriber is reduced until the desired target downstream level is reached. Such tap boxes are well known in the industry and typically only set the downstream power, tapping off a small portion of the power and feeding it to the user. Relevant examples can be found in U.S. patent No.3,989,333 to Jack Vauldwell and U.S. patent No.4,691,976 to Judith a. Both the caudwell and Cowen patents teach cable tap connectors that divert signals from a cable service line to a subscriber without interrupting the flow of the service line to the next subscriber. In some cases, the cable company may insert a physical attenuator plug in the tap box.

Since RF signals typically travel from the service line to the subscriber over long distance cables (e.g., 150-200 feet), in which case the loss incurred by standard RF cables is greater at high frequencies than at low frequencies, the downstream attenuation may be large, while the upstream attenuation may be small. The present invention is designed to take into account this highly unbalanced condition between downstream and upstream attenuation. For example, upstream may have a low frequency range of about 5-100MHz, while downstream may have a range of about 100 to about 800 MHz. Currently, at least in the United states, a typical DOCSIS modem is capable of transmitting upstream signals in the 5-54MHz (although this range may be extended upward) band while being capable of receiving cable or data channels in the range of approximately 88-750 MHz.

Therefore, there is a need for an effective strategy to handle cable power fluctuations on the tap to avoid the necessity for cable/telecom personnel service visits.

Furthermore, it is worth mentioning that cable modem chips such as manufactured by Texas Instruments or Broadcom are designed to be optimized specifically for the above defined device. Cable companies define the working range of these devices directly attached to the cable plant by fitting closely to the chip manufacturer and must themselves meet stringent requirements with respect to out-of-band and in-band noise. These specifications are described in detail in "Data Over Cable System Interface Specification" of CableLabs and encompass PHY (physical), MAC (media Access control), DLC (Data Link control), networking protocol layers, and other aspects of Cable modem operation in the plant. It is believed that these specifications are optimized to address the operational requirements of the hundreds of millions of cable modems installed and operating throughout the world.

These cable modems are optimized to address the operational needs of the home users, and as previously mentioned, these needs are for the location of most cable modems after experiencing significant downstream attenuation caused by the 150 and 200 feet of high loss cable connecting the plant to each home.

However, the class and actual operating requirements for equipment located directly at the cable plant are different from the millions of home cable modems. More specifically, in addition to the higher downstream levels, cable modems installed directly attached to the plant must accept very high (typically up to +35dBmV, but possibly up to +45 dBmV) input signals. As mentioned above, such high levels require considerable downstream attenuation. However, it has not been described that these cable modems require a minimum level of spurious emissions to be injected into the plant. All cable modems use output level control, which is defined in the DOCSIS (cable data service interface) specification as +8dBmV to +54dBmV (some devices may be slightly higher or lower). This wide range of output levels is achieved by a DAC (digital to analog converter) in the cable modem performing level adjustment on the upstream signal, where the DAC is typically a 14-bit DAC. A CMTS (cable modem termination system) located in the cable operator facility controls the output level of the cable modem and will adjust the upstream level of the cable modem to achieve an acceptable input level.

Most cable modems installed in the home will have a significant amount of downstream attenuation due to the 150-200 foot cable arrangement and as a result, the CMTS need not adjust the upstream level too low. For example, if a 200 foot RG58 were installed, the downstream attenuation would be at least 10dBi once the connector loss is included. This means that the CMTS will set the upstream signal level to a value, for example +35dBmV, so that the upstream signal falls within the desired range of the CMTS. However, if the same cable modem is installed that is directly connected to the cable plant, then the downstream is increased by 10dB, and the CMTS sets the upstream level down by 10dB, or in this case +25dBmV within the operating range of the cable modem, when adjusted using a fixed attenuator as usual.

Plant engineers, i.e. the technical team managing the levels of the core infrastructure of the plant, have important rules regarding permitted and not permitted levels. Since the inherent signal-to-noise ratio (SNR) rating of a cable modem is relatively high when transmitting at +8dBmV instead of +48dBmV, plant engineers can know that a cable modem should never transmit at a low level. This is understandable because the SNR is a function of the number of bits in the DAC and since each bit provides 6dB of gain, a +8dBmV signal will use 5 bits for signal level shifting, thereby reducing the SNR. Plant engineers require a minimum level between +45dBmV and +52dBmV, thereby maximizing the DAC level of the cable modem and reducing the noise injected into the plant. They rely on the separation of external filters, i.e. by using a fixed downstream filter and a fixed upstream dedicated filter in an attempt to achieve the desired level. A static attenuator is installed that is not changed, thereby allowing the CMTS to automatically adjust the upstream level to the desired range.

The present invention "cable modem with dual automatic attenuation" provides a control algorithm that enables the cable modem to operate with maximum SNR while also addressing the synchronization level adjustment of the CMTS. In the presence of autotuning from the CMTS to control the upstream level, the present invention autotunes the downstream and upstream attenuation levels independently. The present application achieves an optimal downstream class to minimize BER and simultaneously adjust the upstream class to enable the cable modem to operate at maximum SNR while ensuring that the absolute class of the cable modem is within a specified tolerance, which is not defined by the CAbleLabs DOCSIS standard, but rather is defined by the plant engineer's experience.

Disclosure of Invention

The present invention is directed to a cable modem automatic attenuation system and other automatic attenuation systems.

It is an object of the present application to dynamically sense downstream received signal strength by implementing an algorithm at or near the cable modem and adjust the attenuation on the upstream and downstream links until a desired target signal strength is achieved, thereby reducing or eliminating unnecessary costs as described above.

To avoid high losses (typically in 150 to 200 feet RF cable), embodiments of the present invention are preferably designed to connect directly to a cable service line and to be able to automatically and/or manually attenuate the signal delivered to the cable modem installed in a strand-mounted device (e.g., a BelAir100S strand-mounted wireless access point), by way of example. The attenuation structure and function may be located inside the cable modem, installed in the device between the cable and the modem, or some combination of the two may be used. If installed in a modem, the attenuation can typically be performed by software running on one or more of the microprocessors/signal processors/DSPs/ASICS/… … already present in the modem. Similar structures/software may be used if the attenuation is performed by one or more devices located outside the modem. Preferably, the attenuation is performed inside the modem, for example in BelAir 100S.

According to a first aspect of the invention, an apparatus for automatically attenuating upstream modem signals comprises: a duplexer for separating an upstream signal and a downstream signal; an upstream attenuator capable of attenuating an upstream signal; and a control processor running software configured to (i) sense an upstream signal level, and (ii) adjust the upstream attenuator until a desired target signal strength is reached.

According to a second aspect of the invention, an apparatus for automatically attenuating downstream modem signals from a CMTS comprises: a duplexer for separating an upstream signal and a downstream signal; a downstream attenuator capable of attenuating a downstream signal; and a controller capable of monitoring receive error rate (BER or CER) information from the received downstream signal and containing one or more processors for running software configured to (i) sense a downstream signal level, and (ii) adjust the downstream attenuator until a desired target signal strength is reached.

According to a third aspect of the invention, an apparatus for automatically attenuating downstream and upstream modem signals comprises: a duplexer for separating an upstream signal and a downstream signal; a downstream attenuator capable of attenuating a downstream signal; an upstream attenuator capable of attenuating an upstream signal; and a controller capable of monitoring reception error rate (BER or CER) information from a received downstream signal and containing one or more processors for running software configured to: (i) sensing an upstream signal level, (ii) adjusting the upstream attenuator until a desired target signal strength is reached, (iii) sensing a downstream signal level, and (iv) adjusting the downstream attenuator until a desired target signal strength is reached.

According to a fourth aspect of the invention, an apparatus for automatically attenuating downstream and upstream modem signals comprises: a duplexer for separating an upstream signal and a downstream signal; a combined upstream/downstream attenuator capable of attenuating downstream and upstream signals; an upstream attenuator capable of attenuating an upstream signal; and a controller capable of monitoring reception error rate (BER or CER) information from a received downstream signal and containing one or more processors for running software configured to: (i) sensing an upstream signal level, (ii) adjusting the upstream attenuator until a desired target signal strength is reached; (iii) (iii) sensing a downstream signal level, and (iv) adjusting the downstream attenuator until a desired target signal strength is reached.

According to a fifth aspect of the invention, an apparatus for automatically attenuating downstream and upstream modem signals comprises: a duplexer for separating an upstream signal and a downstream signal; a combined upstream/downstream attenuator capable of attenuating downstream and upstream signals; a downstream attenuator capable of attenuating the upstream signal; and a controller capable of monitoring reception error rate (BER or CER) information from a received downstream signal and containing one or more processors for running software configured to: (i) sensing an upstream signal level, (ii) adjusting the upstream attenuator until a desired target signal strength is reached; (iii) (iii) sensing a downstream signal level, and (iv) adjusting the downstream attenuator until a desired target signal strength is reached.

According to a sixth aspect of the invention, an apparatus for automatically attenuating downstream and upstream modem signals comprises: a duplexer for separating an upstream signal and a downstream signal; a combined upstream/downstream attenuator capable of attenuating downstream and upstream signals; an upstream attenuator capable of attenuating an upstream signal; and a controller capable of monitoring reception error rate (BER or CER) information from a received downstream signal and containing one or more processors for running software configured to: (i) sensing an upstream signal level, (ii) adjusting the upstream attenuator until a desired target signal strength is reached; (iii) (iii) sensing a downstream signal level, and (iv) adjusting the downstream attenuator until a desired target signal strength is reached, wherein the upstream or downstream signal may be comprised of a plurality of frequency separated signals.

In certain embodiments, the controller of the foregoing embodiments may be a cable broadband controller and/or connected to a cable plant through a cable interface. Furthermore, the upstream and/or downstream signals may be constituted by a plurality of frequency separated signals.

According to a seventh aspect of the present invention, a cable modem is taught that is capable of automatically attenuating upstream and downstream modem signals. The cable modem may include: a duplexer for separating the signal into an upstream signal and a downstream signal; an upstream attenuator capable of attenuating an upstream signal; a downstream attenuator capable of attenuating a downstream signal; and one or more processors for running software configured to sense the downstream signal strength and adjust the upstream attenuator and the downstream attenuator until a desired target signal strength is reached.

In some embodiments, the signal may be provided to the modem via a cable or wirelessly. In another embodiment, the one or more processors for running software may be configured to adjust the upstream attenuator and the downstream attenuator independently or simultaneously.

According to an eighth aspect of the present invention, a method for automatically attenuating at least one signal is taught. The method comprises the following steps: (i) sensing a downstream signal strength; and (ii) adjusting the upstream attenuation and the downstream attenuation until a desired target signal strength is achieved.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention.

Various steps, methods and solutions are described herein that can be used to greatly improve attenuation control of RF signals propagating through a cable. The preferred embodiment relates to a DOCSIS cable modem automatic attenuation system ("autoattenuation system"), but may be applied to any signal transmission system. The automatic attenuation system is capable of acquiring high power signals from the cable plant service line, reducing the power level to a usable level, and providing the signals to the Cable Modem (CM) while eliminating the need for the stringent specifications typically required for conventional cable modems. In some embodiments, the automatic attenuation system may be integrated into a stand-alone device connected (wired or wirelessly) between the modem and the cable company service line, and may be configured to handle Upstream (US) and Downstream (DS) attenuation separately or in combination. Alternatively, the automatic attenuation system may be integrated with the cable modem itself. In practice, the automatic attenuation system may also be integrated with tap box functionality, according to the preference of the application or designer. In a typical cable system, the upstream and downstream signals may be carried on a single coaxial cable separate from the service line on a box, commonly referred to as a breakout box. Since the tap box may have some insertion loss (e.g., 1 to 1.5 dB), cable companies typically install the tap directly on the service line.

An example of an automatic attenuation system for a cable modem is described using a strand mounted radio, such as the BelAir100S described above. The messenger is typically bundled between the posts and/or support structures to provide structural integration with the system while providing a source of ground. The service lines for carrying high power signals from the cable plant are bundled in a substantially parallel manner to the suspension wires and may be connected and/or bound to the suspension wires at certain intervals. To minimize signal loss, the service line may also include amplifiers disposed at certain intervals (e.g., every mile). These amplifiers may be bidirectional amplifiers with downstream and upstream duality, thereby allowing each signal to be amplified independently. The main role of the service line is to deliver high power signals from the cable plant to different users or neighbors. For example, when a subscriber requests cable service, a breakout box will be used to shunt signals to the subscriber's residence. In previous systems, 150 and 200 feet of cable had to be bundled from the tap box to the customer premises. However, rather than using an unnecessary length of wire to carry the signal from the tap box to the user, the automatic attenuation system uses only a short RF cable (e.g., 1 to 4 feet) to carry the signal from the tap box to the strand mounted radios. The strand mounted radios are typically mounted on a messenger and wirelessly transmit signals to the subscriber premises while avoiding any potential loss in the 150 and 200 foot cables currently in use. In some embodiments, the amplifier may be integrated with a tap box or an automatic attenuation system device.

The strand mounted radio is capable of receiving high power RF signals from the service line and/or tap and is capable of wirelessly communicating RF signals via the access antenna and/or the backhaul antenna. The strand mounted radio may include a dual radio unit having an access radio and/or a backhaul radio coupled with an access antenna and a backhaul antenna. In addition, the strand mounted radios may also include a power supply (e.g., a 40-87VAC-5VDC supply), a power and protection module, and a cable modem (e.g., a DOCSIS cable modem).

In a preferred cable modem architecture equipped to operate an automatic attenuation system, an RF signal from the service line is provided to an input, which provides the signal to a duplexer, which duplexes the incoming RF signal into transmit (upstream) and receive (downstream) signal paths. The downstream signal then proceeds to a digital DS attenuator, which adjusts the signal to a desired range before sending it to a tuner (e.g., a cable tuner). The downstream signals from the tuner go to a control processor (e.g., a signal ASIC with a central processor, media address controller, and physical layer functions plus typical a/D and I/O structures). The control processor may also communicate with SDRAM and/or ROM for short and long term memory/data storage. The downstream signals may be passed to the peripheral device via an ethernet connection using the ethernet physical layer and/or using USB or other functionality provided by the control processor. Upstream signals may also be communicated from the peripheral device to the control processor using the ethernet physical layer via an ethernet connection and/or using USB or other functionality. The control processor may pass the upstream signal to a filter and a digital upstream attenuator. The digital upstream attenuator conditions the signal to a desired range before returning the signal to the duplexer 304.

The DOCSIS modem of an autodamping system has two attenuators that can independently control downstream and upstream attenuations. These attenuators may be 0-31dB attenuators with a usable range of about 0-20dB and step size of 1 dB. Downstream and upstream control may run independently in software (e.g., downstream control is not dependent on upstream control, and vice versa). The attenuator may be controlled by a cable modem (e.g. a Hitron modem) by means of software commands. The automatic attenuation algorithm is implemented by means of software commands in the modem for controlling the level of the attenuator.

The cable modem system may also include a hard-wired power supply and/or a battery at the power supply input. When using a hard-wired power source, 120VAC power from the consumer's home or other source may be reduced and converted to DC using an AC/DC converter (e.g., a typical wall adapter). The DC current may then be connected (e.g., via a plug) on the power input and may be increased/decreased using a DC/DC converter as needed. Preferably, the AC power is provided through a coaxial cable and is split from the RF signal at a splitter, which is mounted anywhere between the tap and the cable modem, and is typically inside the housing containing the automatic attenuation system. In one variant, an US/DS attenuator is placed between the input and the duplexer. As a result, only a single attenuator (e.g., a single US or DS attenuator) is required between the duplexer and the CPU.

The automatic attenuation system may be enabled to measure the received power and automatically adjust the upstream and/or downstream gains to ensure proper performance (e.g., by maintaining the level near a predetermined target range and/or above/below a predetermined threshold, where the range and/or threshold may be adjusted automatically or manually). The automatic damping system performs automatic adjustments, whereby a technician does not need to calibrate the system at installation and, if adjustments are needed later, the automatic damping system can automatically perform later adjustments. The present application is unique and highly advantageous.

The main goal of the automatic attenuation system algorithm is to monitor the downstream and upstream levels to and/or from the cable modem. In doing so, the automatic attenuation system algorithm will bring the downstream and upstream levels to a target range (e.g., a target +/-range window) by adjusting each attenuator. Generally, the downstream and upstream attenuator state machines are independently operable; however, they may also be run synchronously. The automatic attenuation system algorithm may also be used to maintain the downstream and upstream power levels within a target range by monitoring the downstream and upstream levels and adjusting one or both attenuators for out-of-range or out-of-sync conditions. In some cases, the automatic attenuation system may include a mechanism that can alarm when certain conditions (e.g., maximum or minimum attenuator settings are reached, out of synchronization, and/or out of range) occur. The cable modem may also alert downstream and/or upstream algorithms if the cable modem cannot achieve synchronization because the attenuator is operating out of range (e.g., outside of a minimum/maximum attenuation range).

The basic automatic attenuation algorithm state for a cable modem indicates that once the modem is initialized, the system (e.g., a processor in the cable modem) will automatically make a determination to indicate whether the cable modem is in-range, out-of-sync, or out-of-range based on (i) target parameters, (ii) range, and (iii) the connection status between the cable modem and the Cable Modem Termination System (CMTS). Assuming no condition change has occurred since the last initialization, the initialized modem can speed up the synchronization time by implementing the last attenuation value. These final attenuation values may be stored in the modem (e.g., in RAM or ROM). However, if the conditions change significantly, the modem may need to search between maximum and minimum attenuation for downstream in order to achieve synchronization. If the upstream conditions change significantly, the cable modem can use a minimum attenuation setting and can rely on a large upstream dynamic range to achieve an effective US state.

For example, if the cable modem in operation is not synchronized with the CMTS for data exchange, the cable modem is in an unsynchronized state. In the non-synchronized state, the cable modem is capable of communication, but at an undesirable level (e.g., a low level of-35 dBmv). This condition is not ideal because if there are too many cable modems with low transmit power, the transmit power will not be full power and thus may be attenuated too much, thereby introducing additional wideband noise. Thus, while this arrangement works physically, it is far from optimal because when many modems are operating at this level, the noise threshold on the service line will be exceeded, compromising signal quality.

If the cable modem synchronizes and exchanges data with the CMTS, the cable modem is considered to be in range (e.g., upstream and downstream levels are in optimal range). If the cable modem synchronizes and exchanges data with the CMTS, but the upstream and/or downstream levels are out of the optimal range (optimal range IL-to IL +, described below), then the cable modem is out of range. This narrower window-in-range/optimum range will allow the cable plant to lag without the risk of falling into an unsynchronized state. This is very important because the cable plant and/or service line is actually "breathing" in accordance with factors such as weather and/or temperature. For example, a change of 3, 4 or 5dB can be considered as a cable plant or service line warming (e.g., during the day or summer), thereby increasing synchronization, while a cable plant or service line cooling (e.g., during the night or cooler months) decreases synchronization.

Table 2 describes the non-synchronized, out-of-range, and in-range states.

The state is as follows:	downstream	Upstream of
			Asynchronous	Non-downstream synchronization	Change range/synchronization has not been performed

Out of range	Downstream synchronization	Change range/synchronization has been completed
			Within the range of	IL-<Downstream RF level<IL+	IL-<Upstream RF level<IL+

TABLE 2

The algorithm takes into account a number of settable algorithm parameters. These parameters are typically set by the cable company in accordance with its desired signal power and the amount of acceptable deviation from the desired signal power (i.e., the optimal range/range IL-to-IL +). Input parameters to the algorithm may include, for example, IL +/- (in-range window), OOR +/- (out-of-range window-accounting for hysteresis or fluctuation), and target signal power. However, the target signal power need not be at the center of the range. These settable algorithm parameters are typically separate values for the upstream and downstream signals, but the user may use the same values for the upstream and downstream signals if desired.

The cable modem can change states based on whether the cable modem is in-range or out-of-range and active or inactive. The cable modem has active status while synchronized with the CMTS; the cable modem has an inactive status when not synchronized with the CMTS. The cable modem is in range when the algorithm adjusts the upstream and/or downstream attenuators so that the upstream and/or downstream signals are within an optimal range (e.g., between IL-and IL +). Similarly, the cable modem is out of range when the upstream and/or downstream signals are outside of the optimal range (e.g., IL- > signal > IL +). The algorithm typically has input parameters such as the current cable modem status (including any status changes), downstream and/or upstream power measurements of the cable modem, and target values based on parameters set by the cable company. These input parameters are used to generate outputs such as one or more downstream and/or upstream attenuation settings, downstream and/or upstream algorithm states, and any desired alarms (e.g., when the cable modems are not synchronized).

The cable modem basic automatic attenuation algorithm state further includes a manual state. The automatic damping system algorithm can have two types of control. If manual setup is enabled, the automatic state machine is disabled and some attenuation determined by the service technician may be applied to the upstream and/or downstream signals. The manual state may be enabled regardless of the current state (e.g., regardless of being out-of-sync, out-of-range, and/or in-range). Thus, the manual mode may override the automatic mode when triggered.

The automatic damping system can also be adjusted or controlled remotely (e.g., in a manual mode, or adjusted for certain parameters). For example, if the cable company determines that the attenuation needs to be adjusted, the cable plant may simply send a signal (e.g., a CLI command) down the cable strand (e.g., via telnet) to the modem processor to trigger the desired attenuation adjustment.

Once requested, the cable company can monitor and view the current measurement values on a certain cable modem. An exemplary command window is described in table 3.

Once initialized, DS and US attenuations are set manually, but the US power is out of range.

The DS attenuation is manually adjusted to 14dB, while the US is set to automatic mode.

After the passage of time, the US attenuation will automatically increase, whereby the US is now in range.

The adjustment for the US attenuation may be performed automatically in order to keep the attenuated US power within the set range until it is switched to manual mode, for example.

TABLE 3

In some embodiments, if the cable modem is not synchronized and the timer expires (e.g., after a preset number of seconds or a preset number of synchronization attempts), the upstream and/or downstream attenuators may be automatically set to a minimum value during the attempts to synchronize with the CMTS. Once the minimum value is set, the cable modem may return to the unsynchronized state and a determination may be made as to whether the cable modem is now synchronized.

As shown, the algorithm may use one or more timers to trigger certain operations (e.g., end a loop or change state). The one or more timers typically have separate values for the upstream and downstream signals, but they may also be the same. For example, the algorithm may include three preset timers: timer 1 (T1) may be set to trigger the wait time for out-of-range/sync state; timer 2 (T2) may be set to trigger a wait time for an in-range state or state update; and timer 3 (T3) may be set to a wait time that triggers an unsynchronized state.

The states of the cable modem's basic automatic attenuation algorithm further include a manual state and additional attenuation control. If the cable modem is not synchronized and the timer expires (e.g., after a preset number of seconds or a preset number of synchronization attempts), the upstream and/or downstream attenuators may be automatically switched between the minimum and maximum values using the timer during the attempts to synchronize with the CMTS. The cable modem can cycle back from this to the unsynchronized state, out-of-range state, and/or in-range state based on whether the cable modem is now in-range, out-of-range, active, or inactive.

Once the cable modem has established the downstream signal and received data and/or information from the CMTS, the CMTS may send a message to the cable modem to increase or decrease power as much as possible in an attempt to establish the upstream signal. If the upstream signal cannot be established, the cable modem will begin switching between the minimum and maximum values.

Preferably, the algorithm is designed to allow connection to the cable plant in the event the class is too hot to allow easy recovery of the cable modem. The algorithm is initiated by scanning for cable plant signals and if no available channels are found within a certain time period (which may depend on such factors as mixed mode, DOCSIS in europe, DOCSIS in north america, and/or DOCSIS in japan), the attenuator is quickly adjusted to a higher attenuation level (e.g., 20 dB) and the scanning process is repeated. Once the cable modem is synchronized, it establishes a downstream signal that allows the cable modem to receive data and information from the CMTS. Since the entire system is static, the only possible variations are the cable and the transmit power. The signal between the CMTS and the cable modem will adjust the transmit power at the cable modem, thereby allowing the CMTS to receive the target signal level. On a typical cable modem, the CMTS may increase or decrease the upstream level in dB increments. In some embodiments, the automatic attenuation system algorithm may need to provide an unsynchronized search (e.g., if there are no downstream channels that can be synchronized, the algorithm may need to cycle through some attenuator settings until synchronization is achieved).

At the downstream end, the cable modem may process an input of-15 to +15 dBmV. Thus, assuming a minimum insertion loss of 3dB, an input node at 0dB attenuation would have a range of-12 to +18dBmV and a range of +8 to +38dBmB at 20dB attenuation. Therefore, to detect downstream signals, the cable modem may need to periodically switch between attenuation levels of 0dB and 20dB to ensure that synchronization can be achieved. At the upstream end, the cable modem may output +8 to +55 dBmV. Thus, assuming a minimum insertion loss of 3dB at the output node, if the attenuation is 0dB, a range of +5 to +52dBmV will result, while an attenuation of 20dB will result in-15 to +22 dBmV. Once downstream synchronization is achieved and a change in range is attempted, the modem can be started with 0dB attenuation while occasionally switching to 20dB attenuation in order to obtain a valid upstream power measurement. This processing may only be necessary if the required output level < +5 dBmV; thus, the cable modem does not necessarily need to cycle the upstream attenuator when the upstream state is inactive.

For the non-synchronized state, the functions are preferably performed by one or more processors (with the required memory) in the cable modem, but may also be performed by structures other than the modem, or by a combination of structures internal to the modem and external to the modem. The one or more cable modem processors begin by determining the current state (as described above). If the cable modem is synchronized with the CMTS (status active), the cable modem will go out-of-range. If the cable modem is not synchronized with the CMTS (status invalid), then the attenuation alternates between the minimum and maximum attenuation values until a timer (T3) expires or the cable modem changes status.

For the out-of-range state, the cable modem begins by determining the current state. If the cable modem is not synchronized (state invalid) with the CMTS, the cable modem will go out of sync. If the cable modem is synchronized with the CMTS (status active), then the cable modem determines if the upstream and downstream classes are within an optimal range (range). If the cable modem is determined to be in-range, the cable modem will change to an in-range state. If it is determined that the cable modem is not within range, the cable modem determines the change in attenuation (delta attenuation) by subtracting the target value from the current downstream power. If the current attenuation is equal to the maximum (minimum) attenuation and the amount of attenuation is greater (less) than 0, an alarm is generated. Otherwise, the alarm is cleared. After the alarm operation, the attenuation is set to be the current attenuation plus delta _ attenuation. The cable modem restarts until a timer (T1) expires or the cable modem changes state.

For the in-range state, the cable modem begins by determining the current state. If the cable modem is not synchronized (state invalid) with the CMTS, the cable modem becomes non-synchronized. If the cable modem is synchronized with the CMTS (status active), then the algorithm determines if the upstream and downstream levels are out of optimum range (out of range). If the cable modem is out of range, the cable modem will become out of range. If the cable modem is not out of range (i.e., in range), the cable modem may restart until a timer (T2) expires or the cable modem changes state.

If the cable modem fails to achieve synchronization because the attenuators are operating out of range (e.g., outside of the minimum and maximum attenuation ranges), the cable modem may alert downstream and/or upstream algorithms.

Thus, a preferred inventive embodiment for providing simple and efficient signal attenuation processing supplied to a modem is described herein. While the description thus far has been directed to coaxial cables, it will be clear to those skilled in the art that the description is equally applicable to other cable systems including, for example, balanced differential twisted pairs.

The patents and patent publications cited above are hereby incorporated by reference in their entirety for the purpose of providing additional background information that may be considered relevant to the present application. Although various embodiments have been described herein with reference to particular arrangements of parts, features and the like, these embodiments are not intended to exhaust all possible arrangements or features, and indeed many other embodiments, modifications and variations will be apparent to those of skill in the art. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein.

Claims (17)

1. A system for automatically synchronizing the exchange of data signals from a remote Cable Modem (CM) to a Cable Modem Termination System (CMTS) and from the cable modem termination system to the cable modem, respectively, comprising:

a diplexer configured to separate the data signal into an upstream signal from the cable modem to the cable modem termination system and a downstream signal from the cable modem termination system to the cable modem;

an upstream attenuator configured to adjustably attenuate an upstream signal;

a downstream attenuator configured to adjustably attenuate a downstream signal; and

one or more processors for running software, the software configured to: (i) sensing an asynchronous state between the cable modem termination system and a cable modem; (ii) sensing a power level of the upstream signal; (iii) sensing a power level of the downstream signal; (iv) sensing an out-of-target-range condition when the power level of the upstream signal is not within a predetermined upstream power target range or the power level of the downstream signal is not within a predetermined downstream power target range; (v) upon sensing a non-synchronous condition, adjusting the upstream attenuator to a predetermined maximum or minimum attenuation value, and/or adjusting the downstream attenuator to a predetermined maximum or minimum attenuation value; and (vi) upon sensing an out-of-target range condition, adjusting the upstream attenuator until the upstream signal power level is within a predetermined upstream power target range, and/or adjusting the downstream attenuator until the downstream signal power level is within a predetermined downstream power target range.

2. The system for automatically synchronizing exchange of data signals according to claim 1, wherein the one or more processors include a cable broadband controller.

3. A system for automatically synchronizing exchange of data signals according to claim 2, wherein the controller is connected to the cable modem termination system through a cable interface.

4. A system for automatically synchronizing the exchange of data signals according to claim 2 or 3, wherein the controller is configured to monitor reception error rate information from downstream signals.

5. The system for automatically synchronizing the exchange of data signals according to claim 1, integrated within a Cable Modem (CM).

6. A system for automatically synchronizing the exchange of data signals according to claim 1, wherein the upstream or downstream signal is comprised of a plurality of frequency separated signals.

7. A system for automatically synchronizing the exchange of data signals according to claim 1, wherein the upstream attenuator and/or the downstream attenuator is a combined upstream/downstream attenuator configured to attenuate downstream and upstream signals.

8. The system for automatically synchronizing the exchange of data signals according to claim 1, wherein the data signals are exchanged over a cable.

9. The system for automatically synchronizing exchange of data signals according to claim 1, wherein the one or more processors are to run software configured to independently adjust the upstream attenuator and the downstream attenuator.

10. The system for automatically synchronizing exchange of data signals according to claim 1, wherein the one or more processors are for running software configured to adjust the upstream attenuator and the downstream attenuator simultaneously.

11. A method for automatically synchronizing the exchange of data signals from a remote Cable Modem (CM) to a Cable Modem Termination System (CMTS) and from the cable modem termination system to the cable modem, respectively, comprising the steps of:

separating the data signal into an upstream signal from the cable modem to the cable modem termination system and a downstream signal from the cable modem termination system to the cable modem;

automatically performing: (i) sensing when an asynchronous state exists between the cable modem termination system and a cable modem to stop an exchange of data signals; (ii) sensing a power level of the upstream signal; (iii) sensing a power level of the downstream signal; (iv) sensing when the power level of the upstream signal is not within a predetermined upstream power target range or when the power level of the downstream signal is not within a predetermined downstream power target range; (v) attenuating the upstream signal and/or the downstream signal by a predetermined maximum or minimum upstream attenuation value and/or a predetermined maximum or minimum downstream attenuation value, respectively, upon sensing the non-synchronization; and (vi) attenuating the upstream signal and/or the downstream signal when the power level of the upstream signal or the downstream signal is not within the respective predetermined upstream power target range or predetermined downstream power target range until the upstream signal power level is within the predetermined upstream power target range and/or until the downstream signal power level is within the predetermined downstream power target range.

12. The method of claim 11, wherein upstream attenuation and downstream attenuation are independently adjusted.

13. The method of claim 11, wherein upstream attenuation and downstream attenuation are adjusted simultaneously.

14. The method according to any of claims 11-13, wherein the method is performed inside a Cable Modem (CM).

15. The method of claim 11, wherein the method is performed inside a strand-mounted radio.

16. The method of claim 11, wherein the method is performed between a tap box and a Cable Modem (CM).

17. The method of claim 11, wherein the method is performed in a device wirelessly coupled between a tap box and a Cable Modem (CM).