HK1198081A - Communication system with proactive network maintenance and methods for use therewith - Google Patents

Abstract

The present invention is directed to a communication system with proactive network maintenance and methods for use therewith. A transmitter for use in a cable modem termination system includes a data processing module that generates a plurality of OFDM symbols from a data packet. A probe symbol generator generates a probe symbol, as one of a plurality of probe symbol types. The probe symbol is selectively inserted within the plurality of OFDM symbols, at a pre-defined probe symbol interval.

Description

Communication system with active network maintenance and method of use thereof

Technical Field

The present disclosure relates generally to communication systems and, more particularly, to single point to multipoint communication systems such as wired modem systems.

Background

In a conventional single point to multi-point communication system, a network supports bidirectional data communication between a central entity and a plurality of Customer Premises Equipment (CPE). For example, single point to multipoint communication systems include wired modem systems, fixed wireless systems, and satellite communication systems. In various systems, the communication path from the central entity to a CPE is generally referred to as downstream, while the communication path from the CPE to the central entity is generally referred to as upstream.

A cable modem system is a type of single-point to multi-point system that typically includes a headend capable of communicating with multiple CPEs and provides cable modem functionality. In a cable modem system, for example, the CPE may be a cable modem, a set-top box, or a cable gateway.

DOCSIS (data over cable service interface specification) refers to a set of specifications promulgated by CableLabs that define industry standards for cable head ends and cable modem equipment. To some extent, DOCSIS sets the requirements and objectives for various aspects of cable modem systems, including the operational support system, management, data interface, and network layers, the data link layer, and the physical layer used to transmit data over the cable system. The DOCSIS specification of Release 2.0 and the DOCSIS Radio Frequency Interface (RFI) specification SP-RFIV2.0-I03-021218 (hereinafter the "DOCSIS RFI specification") are incorporated herein by reference.

DOCSIS2.0 supports the ITU-T j.83b (hereinafter "annex B") standard for the downstream Physical (PHY) layer for transmission from the head-end to the cable modems. Advances in communication technology require more and more bandwidth, which can result in insufficient channel capacity, particularly for downstream transmissions. For example, even cable groups operating at 750MHz may be challenged by insufficient capacity due to increased demand for video-on-demand (VOD), High Definition Television (HDTV), digital services, and expanded analog channel lineups. Many schemes have been proposed to reduce the downstream bandwidth problem, including analog spectral correction and advanced video coding techniques. The DOCSIS3.0 specification supported in conjunction with channels and the DOCSIS3.1 project that has been propagated have been in use for many years.

Disclosure of Invention

The present invention provides a transmitter for use in a cable modem termination system, the cable modem termination system communicating with a cable modem via a cable group, the transmitter comprising: a data processing module configured to generate a plurality of orthogonal frequency division multiplexing, OFDM, symbols from a data packet; a probe symbol generator configured to generate a probe symbol that is one of a plurality of probe symbol types; a multiplexer coupled to the data processing module and the probe symbol generator and configured to selectively insert the probe symbols within the plurality of OFDM symbols at predetermined probe symbol positions to form a symbol stream for transmission via the cable constellation.

The transmitter further includes: a pause control generator coupled to the data processing module, the pause control generator generating a pause signal; wherein the data processing module suspends generation of the plurality of OFDM symbols in response to the suspension signal; and wherein the multiplexer selectively multiplexes the probe symbols with the plurality of OFDM symbols in response to the pause signal.

In the above transmitter, the plurality of probe symbol types include active probe symbols and static probe symbols.

In the transmitter above, the plurality of probe symbol types includes symbols for locating leaks in the cable cluster.

In the above transmitter, the plurality of OFDM symbols includes at least one pilot tone for locating leakage in the cable cluster.

In the transmitter above, the at least one pilot tone is a carrier pilot that is phase continuous over the plurality of OFDM symbols.

In the above transmitter, the plurality of OFDM symbols includes at least one pilot tone for phase noise test and subcarrier spacing detection.

The invention provides a method, comprising the following steps: generating a plurality of orthogonal frequency division multiplexing, OFDM, symbols from the data packet; generating a probe symbol as one of a plurality of probe symbol types; selectively inserting the probe symbols within the plurality of OFDM symbols at predetermined probe symbol positions to form a symbol stream for transmission via cable aggregation.

The method further comprises the following steps: generating a pause signal; and suspending generation of the OFDM symbols in response to the suspension signal, wherein the probe symbols are selectively inserted into the plurality of OFDM symbols in response to the suspension signal.

In the above method, the plurality of probe symbol types include active probe symbols and static probe symbols.

In the above method, the plurality of probe symbol types includes probe symbols for locating leaks in the cable cluster.

In the above method, the plurality of OFDM symbols includes at least one pilot tone for locating leakage in the cable cluster.

In the above method, the at least one pilot tone is a carrier pilot that is phase continuous over the plurality of OFDM symbols.

In the above method, the plurality of OFDM symbols includes at least one pilot tone for phase noise test and subcarrier spacing detection.

The present invention provides a system comprising: a Cable Modem Termination System (CMTS) that generates a downstream OFDM symbol stream for communication with a cable modem via a cable cluster and receives an upstream OFDM symbol stream from the cable modem via the cable cluster, wherein at least one of the upstream OFDM symbol stream and the downstream OFDM symbol stream includes a plurality of probe symbol transmissions that include a plurality of probe symbol types; the cable modem generating the upstream OFDM symbol stream for communication with the CMTS via the cable cluster and receiving the downstream OFDM symbol stream from the CMTS via the cable cluster; and a network analyzer configured to communicate active network maintenance data with the cable modem and the CMTS to provide a plurality of active network maintenance functions via the plurality of probe symbol transmissions.

In the above system, the plurality of probe symbol types include active probe symbols and static probe symbols.

In the above system, the plurality of active probe symbols comprises at least one of: full spectrum probe symbols, narrow band probe symbols, and notch spectrum probe symbols.

In the above system, the plurality of active network maintenance functions includes at least one vector signal analyzer function.

In the above system, the plurality of active network maintenance functions includes at least one spectrum analyzer function.

In the above system, the plurality of active network maintenance functions comprises at least one of: forward error correction statics and impulse noise statics.

Drawings

Fig. 1 shows an embodiment 100 of a communication system.

Fig. 2 shows an embodiment 200 of OFDM (orthogonal frequency division multiplexing).

Fig. 3 illustrates an embodiment 300 of a communication system.

Fig. 4 shows an embodiment 400 of a transmitter and a receiver performing signal transmission.

Fig. 5 illustrates an embodiment 500 of an OFDM symbol stream with probe symbol insertion.

Fig. 6 shows an embodiment 600 of stationary probe symbols.

Fig. 7 shows an embodiment 700 of an active probe symbol.

Fig. 8 shows an embodiment 800 of an active probe symbol.

Fig. 9 shows an embodiment 900 of an active probe symbol.

Fig. 10 shows an embodiment 1000 of an OFDM symbol stream with probe symbol insertion.

Fig. 11 illustrates an embodiment of a network analyzer 1100.

Fig. 12 illustrates an embodiment of a trigger information block 1200.

Fig. 13 illustrates an embodiment 1300 of a cable group (plant) with a drain-source 1302.

Fig. 14 shows an embodiment 1400 of a cable group with a leakage source 1402.

Fig. 15 shows an embodiment 1500 of a leakage receiver 1525 and a central terminal 1535.

Fig. 16 illustrates an embodiment 1600 of the location of a leak source via a plurality of leak check data.

Fig. 17 illustrates an embodiment 1700 of locations of leakage sources mapped according to cable groupings.

Fig. 18 illustrates an embodiment of a baseband processor or other data processing element 440'.

Fig. 19 shows another embodiment of a leak receiver 1404.

FIG. 20 illustrates an embodiment of a method.

FIG. 21 illustrates an embodiment of a method.

Detailed Description

Fig. 1 shows an embodiment 100 of a communication system. In particular, the communication system 100 is a communication channel 199 that communicatively couples a communication device 110 (including a transmitter 112 having an encoder 114 and including a receiver 116 having a decoder 118) located at one end of the communication channel 199 to another communication device 120 (including a transmitter 126 having an encoder 128 and including a receiver 122 having a decoder 124) located at the other end of the communication channel 199. The respective devices 110 and 120 send and/or receive probe symbol transmissions for the purposes of characterizing channel 199, determining group leakage, and performing other functions including active network maintenance (proactive network maintenance, active network maintenance) and optimization.

In some embodiments, either of the communication devices 110 and 120 includes only a transmitter or a receiver. The communication channel 199 may be implemented by several different types of media (e.g., a satellite communication channel 130 using satellite dishes 132 and 134, a wireless communication channel 140 using towers 142 and 144 and/or local antennas 152 and 154, a wired communication channel 150, and/or a fiber optic communication channel 160 using an electrical-to-optical interface (E/O) 162 and an optical-to-electrical interface (O/E) 164). In addition, multiple types of media may be implemented and connected together to form communication channel 199.

It is noted that such communication devices 110 and/or 120 may be stationary or mobile without departing from the scope and spirit of the present disclosure. For example, communication devices 110 and/or 120 may be implemented in fixed locations, or communication devices 110 and/or 120 may be mobile communication devices capable of associating with and/or communicating with more than one network access point (e.g., various Access Points (APs) in the context of a mobile communication system including one or more Wireless Local Area Networks (WLANs), various different satellites in the context of a mobile communication system including one or more satellites, or generally various different network access points in the context of a mobile communication system including one or more network access points through which communications may be implemented using communication devices 110 and/or 120). A variety of different types of encoding may be employed in any of the desired communication systems (e.g., including those variations described with reference to fig. 1), any of the information storage devices (e.g., Hard Disk Drives (HDDs), network information storage devices and/or servers, etc.), or applications in which encoding and/or decoding of information is desired.

Fig. 2 shows an embodiment 200 of OFDM (orthogonal frequency division multiplexing). In particular, an OFDM modulation scheme is presented that uses a connection over communication channel 199 via devices 110 and 120. Modulation of OFDM may be viewed as dividing the available spectrum 202 into multiple narrowband subcarriers (e.g., lower data rate carriers). Typically, the frequency responses of the subcarriers overlap and are orthogonal. The individual subcarriers may be modulated using various modulation code techniques.

OFDM modulation operates by performing simultaneous transmission of a large number of narrowband carriers (or tone multi-tones). Often times, a Guard Interval (GI) or guard distance is also used between the various OFDM symbols in an attempt to minimize the effects of ISI (inter-symbol interference) that may be caused by multipath effects within the communication system, which is particularly important in wireless communication systems. In addition, CP (cyclic prefix) may also be employed within the guard interval to allow for flipping time (when hopping to the new band) and to help maintain orthogonality of the OFDM symbols. In general, OFDM system design is based on an expected delay spread within a communication system (e.g., an expected delay spread of a communication channel).

Fig. 3 shows an embodiment 300 of a communication system. The embodiment of the communication system 100 is presented as a cable system 300 providing bi-directional communication between a CMTS (cable modem termination system) 305 and a plurality of cable modems 320 via a cable group 310 (a particular embodiment of the devices 110, 120 and channels in a connection shown in fig. 1). In this embodiment, the CMTS305 and cable modem 320 operate according to DOCSIS protocol or other cable modem protocol employing OFDM modulation in the downlink from the CMTS305 to the cable modem 320 and further from the cable modem 320 to the CMTS 305.

As discussed in connection with fig. 3, the CMTS305 and cable modem 320 send and/or receive probe symbol transmissions that include probe symbols 302 for purposes of characterizing cable groups 310, performing network maintenance and optimization, or other purposes. Specifically, while the current DOCSIS2.0/3.0 is provided for quiet time during upstream of a measured noise floor, in an embodiment, quiet probe symbols are inserted into upstream and/or downstream transmissions to provide sensitive measurement data such as thermal noise, inbound (ingress), CPD (common path distortion), CSO (composite quadratic), CTB (composite triple beat frequency), products from laser and amplifier clipping (clipping), range of previous OFDM symbols to quiet time including echo over the length of the cyclic prefix, and optionally other measured quantities. In addition, active probe symbols may be inserted in either the upstream or downstream transmission to describe the transfer function of the cable group 310. In particular, the active probe symbols can be used to determine the complex frequency response (amplitude and group delay), the non-linear response including amplifier compression, laser clipping, diode detection effects, non-linear components via histogram techniques, and other cable group 310 characteristics and/or characteristics of the CMTS305 and individual transmitters and receivers of each cable modem 320.

In an embodiment, the actual data-carrying symbol may be used to implement the functionality of the active probe symbol 302. To make the above function more efficient, the content of the data-carrying symbols is acquired in the transmitter and can thus be used to compare with the received samples in order to describe the transfer function of the cable group 310. The data symbol having known content is herein equivalent to a probe symbol and is used as the probe symbol 302. The probe symbols described herein are in all cases actual data symbols that can be used for this purpose.

In addition, the CMTS305 and cable modem 320 send and/or receive command data 304 and feedback data 306 related to instructions for performing analysis, and the analysis results include MIB (management information base) data and other data and instructions.

The present disclosure includes, for example, various embodiments of system 300. For example, the transmitter includes a data processing module that generates a plurality of OFDM symbols from a data packet. The probe symbol generator generates 302 a probe symbol as one of a plurality of probe symbol types. The probe symbols 302 thereof are inserted in the plurality of OFDM symbols selectively at predetermined probe symbol interval times. The probe symbols may be data symbols, in which case no special probe insertion is required, as the normal data carrying symbols are used to implement the functionality of the active probe symbols. Rather, the content of the data symbols is acquired by the transmitter and later compared with samples also acquired by the receiver. Synchronization is required to ensure that the same symbol is acquired at the transmitter and receiver. This synchronization may be provided by the trigger information depicted in the connection shown in fig. 12.

In another embodiment, the network analyzer is configured to communicate active network maintenance data with the cable modem 320 and the CMTS305 to provide active network maintenance functions including transmitting test upstream and downstream parameters via the probe symbols.

In a further example, the CMTS305 or cable modem 320 includes a transmitter that generates a plurality of OFDM symbols for transmission over the cable group 310, wherein the plurality of OFDM symbols includes at least one pilot tone for cable group leakage check, phase noise testing, subcarrier space detection, and/or other testing and measurement purposes.

In yet another example, a transmitter used in the CMTS305 generates a plurality of OFDM symbols for transmission over a cable group, wherein the plurality of OFDM symbols includes at least one pilot tone for locating leakage in the cable group 310 associated with the CMTS305, wherein the at least one pilot tone is a carrier pilot that is phase continuous across the plurality of OFDM symbols.

In yet another example, a transmitter used in a CMTS305 includes a probe symbol generator that generates probe symbols 302 used to locate leaked probe symbols in a cable group 310 associated with the CMTS 305. The multiplexer selectively multiplexes a plurality of OFDM symbols for transmission via the cable group 310.

In yet another example, a transmitter for use in a CMTS305 includes a data processing module that generates a plurality of OFDM symbols from a data packet, wherein the data processing module suspends generation of the OFDM symbols in response to a suspension signal. The probe symbol generator generates a probe symbol 302. The pause control generator generates a pause signal. The multiplexer selectively multiplexes the probe symbol 302 having the plurality of OFDM symbols according to a pause signal.

With respect to further embodiments of the transmission, the receipt and analysis of the probe symbols 302, command data 304, and feedback data 306 includes several optional functions and features described in connection with the subsequent fig. 4-21.

Fig. 4 shows an embodiment 400 of a transmitter and a receiver performing signal transmission. Specifically, the transmitter 480/receiver 490 pair is used in a connection communication channel 199 between devices 110 and 120, or specifically the CMTS305 and cable modem 320 communicate via cable group 310, and embodiments of the communication channel 199 or other communication systems communicate via OFDM symbols. The incoming packet 420 (which includes the command data 304 and other data) is processed by a baseband processor or other data processing element 440 to produce a plurality of OFDM symbols. The baseband processor 440 as shown includes functional modules that implement MAC and mid-layer 402, FEC (forward error correction) coding 404, IFFT (inverse fast fourier transform) 406, cyclic prefix insertion 408, and interleaver 410. The OFDM symbols 422 are selectively multiplexed with probe symbol inputs 424 (e.g., probe symbols 302) from a probe symbol generator 416. In particular embodiments, the pause control generator 418 generates a transmit enable/pause signal 425 that is operable to pause the generation of non-probe OFDM symbols 422 and optionally to insert probe symbol inputs 424 into the OFDM output of the multiplexer 412 via the baseband processor 440. The OFDM symbol stream is modulated and amplified via modulator 414 into a radio frequency signal 426 that is incoming over cable group 310. In addition, the input probe symbols are input to one of a plurality of modules of the data processing element 440, such as the MAC and the mid layer 402, FEC (forward error correction) coding 404, IFFT (inverse fast fourier transform) 406, cyclic prefix insertion 408, and interleaver 410 or other modules not explicitly shown.

In receiver 490, the radio frequency signal 428 is generated by transmission of radio frequency signal 426 via communication channel 199, amplified and demodulated via demodulator 464 and demultiplexing 462 to separate the OFDM symbol 430 from probe symbol output 432. The OFDM symbols 430 are processed by the baseband processor 442 into output data packets 464 that include the recovery command data 204. As shown, the baseband processor or other data processing element 442 includes functional modules that implement MAC and mid-layer 452, FEC (forward error correction) decoding 454, FFT (fast fourier transform) 456, cyclic prefix removal 458, and de-interleaver 460. The OFDM symbol 430 is selectively demultiplexed from the probe symbol output 432.

In particular embodiments, pause control generator 468, synchronized with pause control generator 418 based on a common time scheme, generates a transmit enable/pause signal 435 that when executed is capable of pausing reception of OFDM symbols 430 by baseband processor 442 and selectively routing probe symbol outputs 432 into PNM (active network management) sample buffer 466, where PNM sample buffer 466 is further processed by, for example, a PNM server or other analyzer 475 operating under control of command data 204, to analyze the probe symbol outputs to generate feedback data 306, and as previously discussed, identify characteristics of cable group 310 and/or provide other metrics. In addition, the analyzer 475 operates based on other data from the demodulator 464, one or more modules from the data processor 442, and/or other portions of the receiver 490, and generates the feedback data 306 based on the probe symbol transmissions or other previously discussed metrics that characterize and/or provide other control and management information for the cable group 310 or other communication channel 199.

The feedback data 306 may be retransmitted from a transmitter associated with the receiver 490 to a receiver associated with the transmitter 480 via the cable group 310 or other communication channel 199. In this manner, the CMTS305 may send probe symbols 302 and command data 304 to the multiple CMs 320 and receive feedback data 306 based entirely or in part on the probe symbol transmissions. In another mode of operation, the CM320 may send probe symbols 302 and command data 304 to the CMTS305 and receive feedback data 306 based entirely or in part on the probe symbol transmissions.

The optional use of transmit and receive enable/suspend signals 425 and 435 on the data processing elements allows existing functional blocks to be implemented with minimal changes. In operation, the system will not recognize that a pause has occurred when the data processing is paused. For example, since the interleaving process is also suspended, the suspension does not require refreshing (flush) the interleaver. The only processing of the baseband processors 440 and 442 is concerned with suspending in real time, such as time interpolation across pilots, smoothing buffers, etc. The system may have a minimum delay impact (e.g., only 40-80 millionths of a second). The transmit and receive enable/pause signals 425 and 435 may be periodic signals to simplify the synchronization process. For example, the pause function may have a period of 1 second to 10 minutes, or the function may be turned off if not required. In particular, short periods such as 1 second may be used in fast data acquisition when performing a troubleshooting mode operation at the time of troubleshooting of a node. A longer period of time, for example 10 minutes, can be used in the normal operating mode during the recording of background data information.

The data processing elements 440 and 442 and the analyzer 475 may each be implemented by a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, microcontroller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. The processing module, processing circuit, and/or processing unit may have associated memory and/or integrated storage elements, which may be a single storage device, multiple storage devices, and/or embedded circuitry of the processing module, processing circuit, and/or processing unit. Such a memory device may be read-only memory (ROM), random-access memory (RAM), volatile memory, non-volatile memory, a state machine, dynamic memory, flash memory, high-speed memory, and/or any device that stores digital information. Note that if the processing module, processing circuitry, and/or processing unit includes multiple processing devices, the processing devices may be centrally located (e.g., directly coupled together via a wired and/or wireless bus structure) or may be distributed (e.g., via cloud computing coupled indirectly via a local area network and/or a wide area network). It should be further noted that if the processing module, processing circuit, and/or processing unit implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory and/or storage elements storing the corresponding operational instructions may be embedded within or external to the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. It is still further noted that the memory components may store and the processing modules, processing circuits, and/or processing units execute hard-coded and/or operational instructions that correspond to at least some of the steps and/or functions set forth in one or more of the figures. Such storage devices or storage elements may be included in an article of manufacture.

The pause control generators 418 and 468 may be implemented by timers, counters, or other groups (sets of lines) that generate corresponding transmit enable/pause signals 425 and receive enable/pause signals 435.

As described above, the channel estimation block analyzes samples of the probe symbol output to identify characteristics of the cable group 310 or other communication channels 199 and/or to provide other metrics as previously discussed. Examples of channel qualification techniques and probe symbols 302 supporting the techniques are provided below.

Example 1-Pilot estimation

The technique operates by subtracting the values of the scattered pilots using smoothed channel estimates. The result is a noise floor estimate for the pilot that moves across the entire band. The noise layer includes irregular noise and spurs. This technique can give performance 5-10dB stronger than the required QAM SNR (over 40 dB). While this approach works as an enhancement to other receiver designs, it can even be used in a corrupted channel when only PLC (physical layer link channel) can be received by CM 320. The CM320 may also have to report measurement data through the corrupted group condition via the uplink. This may allow troubleshooting of the damaged group.

In this example, the noise estimation works as follows. The symbols received within the scattered pilots are Y = H X + N, where H is the channel response on the Scattered Pilots (SP), X is the SP symbols transmitted, and N is noise, all in the frequency domain. If the receiver channel estimates h (ce) are sufficiently filtered, then n (est) of n (est) = Y-h (ce) × is the noise estimate at its pilot location. The noise power may be averaged over time to obtain better accuracy. N (est) includes inherent noise, spurs, implementation loss, etc. of the receiver. The scattered pilot positions may be flipped over the full range (bin). In this manner, noise estimates may be generated over all ranges in conventional reception over time. Discontinuous CTB/CSO will be easily detected when a large noise power is present in the known CTB/CSO frequency.

Example 2 stationary Pilot Probe

In the extremely narrow band, a single tone signal or several tones are swept across the band with a zero modulation sweep. This is similar to having additional scattered pilots with zero (static or null) modulation. This approach can cause minimal disruption to current system designs. This provides better performance than using the existing pilot of example 1, since the channel estimate does not need to subtract the pilot value because the pilot value is null. Considering the DOCSIS3.1 implementation, the time and frequency interleaver 410 may place null input subcarriers at random subcarrier locations across multiple frequency bands and across multiple OFDM symbols equal to the interleaver depth. Thus, interleaver 410 provides null subcarrier measurement data in random (but in complete) groups of subcarriers across multiple transmitted symbols.

EXAMPLE 3 Wide Band (WB) stationary Probe

In an extremely wide frequency band, the downstream OFDM symbol stream is paused every 1 second to 10 minutes and quiet symbols are inserted across the entire 192MHz band. This would be the most sensitive measurement, but would require modification when applied in PHY and MAC designs. An example of this approach is presented in connection with fig. 5.

Example 4 Noise Power Ratio (NPR) Probe

In this approach, less than the full frequency band may be quieted. For example, a narrow band of 6MHz continuous tone tones may be quiet. This creates a notch that can be swept across the full band. The notch may be filled with intermodulation products if there is a non-linearity in the group. It is a challenge how to distinguish the group noise floor from the intermodulation products. However, widening the notch may help to determine intermodulation products. The inverse non-linearity in the receiver can be adjusted until the notch (notch) is maximally open, in which process the LMS algorithm is used as much as possible for adjustment. The histogram technique works well for inferring the non-linearity of groups. Estimates may be used to assist the NPR method. An example of this approach is presented in connection with fig. 9.

Example 5 data carrying Probe symbols

As discussed in connection with fig. 3, the actual data-carrying symbol may be used to implement the functionality of the active probe symbol 302. In particular, symbols of any data type can be used for the above purpose. To make this function most effective, the content of the data-carrying symbols is acquired at the transmitter so that its content can be compared to the received samples in order to characterize the transfer function of the cable group 310 or to support other active network management functions as described herein. When the probe symbol is a data symbol, no special probe insertion is required. Rather, the content of the data symbols is acquired by the transmitter and later compared with samples also acquired by the receiver. Synchronization is required to ensure that the same symbol is acquired at the transmitter and receiver. This synchronization may be provided in connection with the trigger information described in fig. 12.

Example 6 reverse interleaver method

In this example a stationary (broad band or narrow band) probe is inserted. In particular, null QAM values are inserted into the interleaver at the input. These values are spread in a particular "reverse interleaving" pattern so that its interleaving function can reassemble these values into successive tone tones across a single OFDM symbol. From the transmit enable/pause signal 425, the non-insertable data value may then know that the QAM slot is unavailable by virtue of the blocks of the interleaver. This may avoid the problem of suspending MAC and TC blocks, as opportunities may be interspersed rather than grouped in a normal data flow. The PHY may still determine missing symbols or partial symbols. A state machine associated with processing module 440 may be used for reverse interleaving mapping and companion control.

In an embodiment, the interleaver 410 comprises a convolutional interleaver for subcarriers in consecutive OFDM symbols, so the interleaving is not tied to block boundaries to "pause" between interleaver blocks. However, the fact that for an interleaving depth of N, adjacent subcarriers in an OFDM symbol are successively delayed by one symbol to N successive subcarriers and then reset and repeated (modulo N) until the end of the OFDM symbol may be used to "pre-interleave". The method may pre-interleave null subcarriers across N consecutive OFDM symbols in a reverse interleaving mode. In this manner, all null subcarriers are generated at the output of the time interleaver for the same OFDM symbol entering the channel (i.e., a single symbol with all null subcarriers). Subsequent frequency interleaving can randomize the subcarrier order in the symbol but this is a known pattern for reordering at the receiver. The method can also work in the uplink with the proposed small slot offset to reduce the depth of interleaving by using adjacent small slots instead of subcarriers. This is similar to predistortion, precorrection or precoding. Pre-interleaving provides a solution that skillfully solves the static channel measurements.

In addition to the above example, example 5 would be used to transmit a wideband probe in a single OFDM symbol with either downlink convolutional interleaving or uplink mini-slot tilted interleaving. The OFDM symbol builder takes the incoming bit stream and inserts test QAM subcarriers (null values of 0+ j0 or probe sequence values like PRBS BPSK values, complex sequence values, etc.) into the IFFT for use with a state machine synchronized with the commutator stage of the convolutional interleaver, mapping the data into the appropriate QAM symbols. This is only slightly more complex than a simple divider. When triggered (e.g., according to the "pause"), the test QAM subcarrier is inserted (null at 0+ j0 or probe sequence values like PRBS BPSK value, complex sequence value, etc.) into the first symbol of the most delayed path, the next QAM test symbol is inserted into the second symbol of the second most delayed path, and the process is performed until the nth symbol for the interleaver with depth N of the first non-delayed path. The state machine can be triggered at any time to generate channel measurements without requiring any frames and can start the above procedure just synchronized with the interleaver stage. The output of the interleaver resulting from pre-interleaving the OFDM symbol sequence may be a single null or a probe symbol across all subcarriers. The CP is considered in advance, and the IFFT modulates and transmits the symbols into the channel. At the receiving end, the receiver searches for a test OFDM symbol having a flag, a timestamp, a MAC message, etc. that can avoid increasing the complexity of the upper layer protocol. The FFT may recover test OFDM symbols with either full QAM test or null subcarriers. The just identified symbol is null data detected by the demodulator. The FFT may be a separate processor for the full band capture front end. I.e., performing the desired processing includes or removing the CP, then averaging, windowing, calculating MER, etc.

In an embodiment, the symbol constellation (constellation) comprises null symbols. The interleaver and other blocks may have additional bits representing null values for null carriers. For example, this is similar to having 257QAM instead of the conventional 256QAM, where the 257 th point is cartesian zero, at the origin of the constellation (0 + j 0). A still symbol is like any other symbol except that the QAM constellation point is a digital 0+ j 0. The last constellation point (zero) may be modulated over all carriers. RF muting may be better accomplished if the RF is turned off completely. This is difficult to do, however, when no additional time is provided for the RF circuitry to settle. Noise-reducing individual subcarriers by zero symbol modulation for digitization is more practical in some cases.

In an embodiment, the pilots are turned off during the stationary probe symbol. The receiver algorithm operates in the same case when a symbol is missing, e.g. during a noise pulse in the channel. Further RF automatic gain control may be frozen (suspended) during the quiescent symbol, for example by receiving an enable/suspend control signal 435, the arrival of which is known a priori and indicated. In addition, the absence of energy in an OFDM symbol may be detectable in some cases and with some delay. Furthermore, the probe symbols may be generated without being completely stationary but with only some tones stationary. The total power of the probe symbols may be selected as the normal power of the OFDM symbols.

In an embodiment, there is a gap in PLC narrowband acquisition. In particular DOCSIS3.1 is designed to operate with a gap. A stationary symbol may be placed within the gap without affecting the PLC.

While the delay through the Epoc PHY in DOCSIS implementations may be generally constant, occasional missing (quiescent) symbols may be compensated using FIFO smoothing the flow and synthesizing the FIFO input and output rates using a rational NCO. For example, if the OFDM symbol of 1/1000 is stationary, two clocks with a ratio of 999/1000 are synthesized. Another approach is to use it only on DOCSIS3.1 without burdening Epoc with silent probe issues.

In a cable system embodiment, a system with inputs and outputs for a cable group would allow the use of "system identification" techniques. This includes models with groups including non-linearity and filtering effects. One such model is:

low pass filter amplifier with compression function low pass filter.

The parameters of the model may be adjusted such that the error between the model and the actual data is minimized. In order for the model to work, samples are taken from the inputs and outputs of the group. The output samples in the receiver may be provided to the channel estimation block, e.g. of a PNM server for processing. The samples input into the group, e.g., transmitted, (a) may be by re-modulating any corrected FEC subcarriers at the receiver, or (b) by utilizing the head-end to save samples of the regular OFDM symbols transmitted. In summary, input and output samples of the channel may be obtained. For method (b), a specification (spec) at the CMTS305 transmitter may capture samples of a specified OFDM symbol. For method (a), the specification at the receiver may provide the information necessary for the remodulation process.

As previously discussed, the probe symbols 302 may occupy all of the OFDM tone-tones or only a partial number of the tone-tones in the symbol. In one example, only a portion of the probe symbol 302 may be stationary. The total power may be a regular power that does not affect the analog AGC. This may allow for tone studies on the tone from 200-. Another embodiment may also leave the pilot in the probing process.

In an embodiment, if there is a set of problems with a fault situation that is indistinguishable using only spectral data, histograms may be employed at different points (up and/or down) to provide useful, mutually perpendicular information for spectral acquisition. In model-based linearization, the nonlinearity of the amplifier is modeled digitally with some parameters P1, P2, P3, etc. The mathematical model may include memory if the non-linearity is a function of voltage history and not just instantaneous voltage. The model utilizes some parameter inversions relating to the parameter P, Q1, Q2, Q3, etc. One approach is to invert the remote non-linearity using a local inversion block and local observation. For example, assume that there are several non-linear amplifiers in a group, each with some power series description. The concatenation will also have a power series description. If the waveform of the incoming de-reconstructed transmit waveform has been observed and related to previous information, the parameters P and Q may be estimated and non-linearly inverted. The above procedure can be simpler if the transmission signal statistics are known. Monitoring can identify a damaged amplifier in many paths. There are also enhanced cable modems embedded in the cable group called DMON (downstream monitoring). These methods can also be used to capture histograms.

In an embodiment, a counter method may be employed to optionally suspend the transmit and receive functions. The mode of operation of the counter method may be described in connection with the following similarities. Assuming you are watching a movie, you can pause the DVD player to get up to rest for a while and then can start again when you come back. Fluency with respect to the image on the counter DVD player display; when started again the images continue from where they stopped previously and there is no glitch and the frame sequence of this movie is of course not affected by the pause time. However, if a DVD player tries to use real-time to render its image frames after an interruption, its player must subtract the time of the interruption from the counter, which makes the overall process more complicated. By using a counter that is suspended with the content, all images are smooth and the DVD player is hardly aware of the occurrence of the interruption. The idea of the pause button in the downstream is therefore that the MAC does not need to change anything but to use a virtual counter instead of a real time counter.

These techniques may be applied to processing block 440 as follows. Assume that there are 3840 subcarriers in the system and that the FEC encoder 404 terminates on subcarrier 500. In the conventional case without stationary probes, the FEC encoder 404 starts on subcarrier 1900 of OFDM symbol n and terminates on subcarrier 500 of OFDM symbol n + 1. Thus, SCs 1900-3840 of symbol n may be occupied, as well as SCs 1-500 of symbol n + 1. In the case where a stationary probe is inserted, the FEC encoder 404 may occupy the SCs 1900-3840 for symbol n, and the SCs 1-500 for symbol n + 2. The symbol n may be stationary. From another point of view, the suspend function implies notionally maintaining binary counters, respectively: real-time symbol counters and virtual symbol counters. The virtual counter does not count stationary probe symbols and therefore there is no gap in its sequence of computation. The virtual counter may be used by FEC or the like.

The operation of the transmitter 480 and receiver 490 in connection with the generation and transmission of the probe symbols 302, command data 304, and feedback data 306 may be described in connection with the following accompanying examples.

The probe symbols 302 facilitate allowing measurement of the cable group 310 or other communication channel 199, and in particular the cable group response including potential noise and collisions. The linear and nonlinear responses of the cable group 310 may be measured. Analysis of the response may provide a broadband, short duration view of the cable group 310 or other communication channel 199. For example, a transmitter 480 operating in the CMTS305, transmits downstream probe symbols 302 at predetermined intervals designed to be in the range of 1 second to 10 minutes. The probe symbol 302 includes the following patterns:

(a)standard mode frequency domain probe.For example 16 or some other number of standard test patterns are employed. These standard test patterns include predetermined patterns defined by frequency domain values corresponding to subcarrier QAM modulation values. The CMTS305 inserts these samples at the input of the IFFT406 or multiplexer 412. The CMTS305 inserts a cyclic prefix. In particular, the baseband processor 440 accepts control from the probe symbol generator 416 with or without pilot insertion. When a probe symbol is inserted in this manner, the baseband processor 440 does not perform interleaving or FEC on the probe symbol.

(b)Any time domain probe.The CMTS305 accepts a sequence of time domain samples. The CMTS305 inserts these samples, which are input at modulator 414 via multiplexer 412 as a substitute for the entire OFDM symbol. In an embodiment, the CMTS305 does not perform pilot insertion, CP insertion, interleaving, or FEC encoding on the probe symbols.

(c)Noise Power Ratio (NPR) probe.The CMTS305 accepts values for a notch start frequency and a notch end frequency. The CMTS305 sends a known test pattern in all subcarriers except the notched subcarriers. The CMTS305 sends a zero bit value (zero RF or substantially zero RF) in the notched sub-carriers. The CMTS305 inserts a cyclic prefix. The CMTS305 may choose not to perform pilot insertion, interleaving, or FEC coding on the probe symbols.

(d)The probe is stationary.The CMTS305 sends all zero samples during all OFDM symbols(zero RF or substantially zero RF). In an embodiment, some active subcarriers whose total symbol power is maintained at a normal energy level are reserved in order to avoid completely stationary symbols.

According to the example described above, the receiver 490, e.g., CM320, takes the received probe symbols 302 and performs the following processes via analyzer 475 to generate the feedback data 306.

(a)Time domain sample acquisition.The CM320 acquires time domain (I and Q) samples corresponding to the probe symbols. The CM320 also takes additional samples of 1/8 for the symbol before the probe symbol and 1/8 for the symbol after the probe symbol from a total of 1.25 probe durations. The CM320 may send the acquired samples as required by the CMTS305 via the command data 304, such as by the feedback data 306.

(b)Frequency spectrumThe CM320 calculates the FFT power spectrum of the probe symbol using the same FFT size as used for data reception. The CM320 may apply a window to the spectrum. For example, it is equivalent to having the sequence [ -1/4,1/2, -1/4 ] in the frequency domain]The cosine square window of the deconvolution may be employed. Other windows may be similarly employed. The CM320 may perform true power averaging of multiple probe spectra, for example, using a drain integrator with a hysteresis coefficient averaging in the range of 1 to 128. The CM320 may accept command data 304 from the CMTS305 to restart spectrum averaging. The CM320 may provide the feedback data 306 in the form of a maximum preserved spectrum, showing the maximum power values for the various ranges since the last reset. The CM320 may send feedback data 306 indicating the latest average spectrum and/or the largest retained spectrum to the CMTS305 via command data 304 as required.

In an embodiment, the analyzer 475 or CM320 processing each probe symbol 302 produces the following example of feedback data 306.

(a)Standard mode frequency domain probe.The CM320 may make measurements on the probe symbol. Examples include the power of each subcarrier and RxMER (receiver modulation error ratio), and the total received power, etc. RxMER can be used to makeCalculated using the known probe pattern constellation points.

(b)Any time domain probe.The CM320 may make measurements on the probe symbol. Examples include total received power, etc.

(c)Noise Power Ratio (NPR) probe.The CM320 may make measurements on the probe symbol. Examples include: the ratio of the average power outside and within the notch (excluding 4 bins at the range of the respective notch edge and excluding the outer bins by 10dB or more above average); power and RxMER for each subcarrier; total received power, etc.

In a further example, the CMTS305 and CM320 may cooperate to synchronize probes in multiple OFDM bands. In particular, such a configuration allows for the viewing of tones or other effects in one frequency band while providing excitation in another frequency band. The CMTS305 transmits an active probe in the 200MHz band, and a stationary probe when in another band, such as the 3rd tone 600 MHz. CM320 acquires and processes the probe in a quiescent frequency band and provides a spectrum, rough sample, etc. so that the tone can be observed and analyzed. Providing some time penalty in synchronizing the two probes. This error can be removed during post-processing of the sample. The CMTS305 in operation includes the ability to transmit probe symbols to two OFDM bands simultaneously. Its CMTS305 can desynchronize the probe in both bands exactly +/-10OFDM FFT clock cycles.

In a further example, the CMTS305 and CM320 may cooperatively share band measurements. In particular, such a configuration allows for measurement of intermittent noise and interference and/or provides a long time view of the narrowband and a portion of the channel. The exclusion band is employed as a programmable contiguous set of subcarriers with zero modulation (zero RF). The CM320 traverses a series of start-stop frequency ranges received via the command data 304 that receive the spectral definition to the 16-band. The frequency bands may or may not overlap. The CM320 provides measurement-derived feedback data 206 for each defined frequency band. Examples include: time averaged power; a maximum holding power; a time-averaged frequency spectrum; a maximum preserved spectrum; power averaged when taken during an interval when energy or no energy is present (when power in a frequency band is above/below a defined threshold), etc.

In a further example, the CMTS305 and CM320 may cooperatively share a broadband spectrum display. In particular, this configuration provides a broadband spectrum analyzer function in the CM320 that can be reported via the feedback data 206. CM320 provides wideband spectrum analysis capability for each DOCSIS spectrum analysis MIB that exists via analyzer 475. The CM320 may provide, for example, a spectral analysis bandwidth of 192MHz or greater. The CM320 optionally provides spectral analysis bandwidth that covers the entire downstream spectrum of the cable group 310 or other communication channel 199.

In another example, the CM320 may be based on CMTS305 values from the CMTS305 requesting equalization equipment providing the CM via feedback data 306 via command data 304.

In further examples, the CMTS305 and CM320 may cooperate to share FEC statistics or monitor link quality by maintaining FEC error event statistics. The CM320 may measure FEC statistics shared via the feedback data 306. Examples include the total number of whistles, the number of whistles passing parity, the number of whistles failing parity, error seconds since the last challenge, and the calculation of error for an interval of 1 second to 10 minutes since the last challenge. The feedback data 306 may provide details such as LDPC, BCH, codeword length, conventional classification of errors to shortened codewords, and the like.

In a further example, the CMTS305 and CM320 may cooperate to generate a received channel estimate that is computed by the receiver as part of its normal operation based on the pilot. The CM320 generates the receive channel estimates and sends feedback data 306 to the CMTS305 via command data 304 as required.

In a further example, the CMTS305 and CM320 may cooperatively share each subcarrier RxMER and power measurements scheduled by the receiver. This allows frequency dependence of the overall performance of the observed channel. The intention is to use the granularity already provided in the system, which is pre-subcarrier, pre-mini-slot, etc. RxMER measurements per subcarrier, and/or Rx power measurements per subcarrier, are made while the CM320 is in operation. The CM320 may be provided on all non-zero subcarriers, on zero RF subcarriers, on pilots. And an average measurement of RxMER and Rx power on the data subcarriers via feedback data 306. The averaging process may be performed at real power and may be done in a drain integrator filter with a programmable hysteresis factor of 1 second to 1 minute, or no averaging process is performed. The CM320 may send these measurement data to the CMTS305 via feedback data 306 as required via command data 304.

In further examples, the CMTS305 and CM320 may cooperatively share QAM constellations for observation and analysis. In an embodiment, because the amount of data may be large, records of reduced size may be stored and sent to the CMTS305 via the feedback data 306. The CM320 may capture the received constellation when the CMTS305 issues a command via command data 304. Various modes can be used including:

(a)all constellations.The soft decision data may be shared from up to 10OFDM symbols. The size may be up to 8K × 10=80K complex, with 12 bits each for I and Q, for a total = greater than 2 Mbit.

(b)The constellation is quantized.The soft decision data may be quantized to 1/8 distances between constellation points, i.e., may be summarized as a 2-dimensional histogram. The respective ranges may be recorded as 1-bit values, for example. The effect is that the copy is removed, giving a value of 1 once the location is "hit" and still retaining the value 1 if hit again. The maximum value of the number of dots may be 4096 × 8 × 8=256 Kbits. The constellation may be aggregated for a programmable number of OFDM symbols.

(c)A compressed constellation.The pattern includes, for example, up to 4096 patterns having the mean and standard deviation of the respective interior pointsConstellationDots, and adding straightTo 100 soft decision samples that fall outside the boundary line of the constellation. The size may be 4096 × 2 × 12+100 × 2 × 12= about 100 Kbits.

(d)An error constellation.The pattern may capture the difference between the soft decision and the correct or nearby constellation point. This may be done by a single OFDM symbol. The maximum size may be 8192 × 2 × 12= about200Kbits. The error constellation is mostly accurate when the data is known, e.g., pilot or zero RF subcarrier, or for probe symbols with known data pattern, because no decision error occurs with known data.

(e)Compressed error constellation.This pattern can capture the difference between the soft decision and the correct or nearby constellation point and report only the mean and standard deviation of the error, plus an error sample equivalent to 100 falling outside the decision. Total range =2 × 12+100 × 2 × 12= about 2.5KBit。

In a further example, the CMTS305 and CM320 may cooperatively share impulse/burst noise (time scale, duration, level versus FEC error) measurement data. The CM320 may detect burst/impulse noise events at programmable thresholds and may time stamp the events using a small slot counter, where the counter has a resolution of 1 sample per OFDM FFT clock. The CM320 may measure the duration of an event at a resolution of 1 sample per OFDM FFT clock, and may further measure the true average power of the samples during the duration of the event. The CM320 will also time stamp the FEC block containing the error to compare it to the time stamp of the burst/impulse noise event. Any or all of this data may be provided through feedback data 306.

In another example, the CMTS305 and CM320 may cooperate to share a histogram of wideband samples, such as to provide a view of non-linear effects in the channel, such as amplifier compression and laser clipping. For example, it allows detection of laser trimming which causes the end of the histogram to be cut and replaced by a burr spike. The CM320 may capture a histogram of time-domain samples at the wideband front end of the receiver and share the histogram information via the feedback data 306. The histogram may have a resolution of at least 256 bin. The histogram may be two-sided, i.e. including the maximum negative and maximum positive values of the sample. The histogram may be aggregated over a programmable period, such as 1 second to 1 minute, or until reset based on command data 304.

Fig. 5 illustrates an embodiment 500 of an OFDM symbol stream. In particular, OFDM symbol stream 510 is graphically illustrated in time and frequency. In the illustrated embodiment, a frequency range of 192MHz may be employed, however other ranges may be used in other embodiments. Enabling the pause control 506, e.g., receiving enable/pause signal 425 or transmitting enable/pause signal 435, as shown in the figure, indicates the time at which the probe symbols 502 and 504 are inserted in the OFDM symbol stream 510. In the illustrated embodiment, the start/pause control 506 is a periodic signal.

In operation, the baseband processor disables the OFDM divider for one OFDM symbol based on the enable/disable control 506 inserted for each probe symbol. For stationary probe symbols, the transmitter of the CMTS305, CM320, or other device sends a silent silence (zero) for this time period. A number of samples are obtained at the receiver of the CMTS305 or CM320, such as 4K + or 8K + samples including a cyclic prefix and surrounding samples during the symbol period. These samples are buffered via the buffered samples and sent to a PNM server or other processor to measure and characterize the noise floor of the communication channel 199, such as cable group 310. For active probe symbols, the transmitter of the CMTS305, CM320, or other device sends a probe signal. A number of samples are obtained at the receiver of the CMTS305 or CM320, such as 4K + or 8K + samples including a cyclic prefix and surrounding samples during the symbol period. These samples are buffered via the buffered samples and sent to a PNM server or other processor to measure and characterize the transfer function of the communication channel 199, such as cable group 310.

Fig. 6 shows an embodiment 600 of a stationary probe symbol. The stationary symbols as previously discussed may be generated by not transmitting RF or substantially not transmitting RF. During the quiet detector symbol 610, the receiver takes PNM sample decimated/interfered samples by taking PNM sample from the end of the previous OFDM data symbol 606 to the beginning of the next OFDM data symbol 608 during the PNM sample capture window 612. The processing of these PNM samples allows for measurements outside of CP interval 620 and CP interval 620, such as echo echoes within CP622 and echo echoes outside of CP 624. The processing of these PNM samples also allows for the measurement of a pre-ringing alert (pre-ringing) 626 to the end of the stationary probe symbol 610 as well as the measurement of other parameters such as noise floor.

Fig. 7 shows an embodiment 700 of an active probe symbol. While the example presented in connection with fig. 6 presents a stationary probe symbol, non-stationary or active probe symbols may be equally employed. In particular, the active probe symbols can be used to characterize the transfer function of the cable assembly, including complex frequency response (amplitude and group delay), and nonlinear response including amplifier compression, laser trimming, diode detection effects, and/or other effects generated via histogram techniques or other methods. These active symbols may use some or all of the subcarriers for each OFDM probe symbol time.

In operation, the transmitter 480 may be inserted into any desired RF sample during a probe symbol time. For example, a frequency domain probe that is wideband may be generated using all subcarriers, or some subcarriers may be muted to observe harmonics and intermodulation (intermediate) products from active subcarriers. In another example, a time domain probe may be employed. In particular, portions of some probe signals may be muted in time to observe ringing of the channel. The cyclic prefix may or may not be subsumed in the probe symbol. In particular, CP can be included where the probe symbols are intended to be demodulated into data signals by a receiver.

In the illustrated example, a broadband probe symbol is generated. When the spectrum of the OFDM probe signal is substantially flat before transmission over the cable group 310 or other communication channel 199, the channel introduces micro-reflections that can alter the spectrum after the channel.

Fig. 8 shows an embodiment 800 of an active probe symbol. In the illustrated example, a narrowband probe symbol is generated. As shown in the figure, the cable group 310 or other communication channel 199 introduces a 40db distortion term in the third harmonic of the transmitted signal.

Fig. 9 shows an embodiment 900 of an active probe symbol. In the illustrated example, a broadband probe symbol having a notch is produced. In operation, the notch is filled with intermodulation products and/or other tones generated through the channel. As shown, the cable group 310 or other communication channel 199 introduces a 40db distortion term in the notch frequency. The notch frequency may be swept to determine the result in different frequencies. Generally, any combination of a stationary frequency band and an active probe symbol may be employed. In particular, the transmitter may schedule stationary probe symbols on one or more OFDM bands at the same time as active probe symbols on one or more other OFDM bands via a common time reference synchronization, or via other synchronization controls. Received samples taken in the quiet band, along with the active probe symbols from which the samples were generated, may be used to analyze the damage-induced tone.

Figure 10 illustrates one embodiment of probe symbol insertion. As discussed in connection with fig. 4, the (wide band or narrow band) probes may be interleaved before the interleaved probe symbols 1000 are inserted. In particular, null QAM values may be inserted at the input into interleaver 410 of fig. 4. These values are spread in a particular "reverse interleaving" map 1005 so that the interleaving function of interleaver 410 can reassemble these values into successive probe symbols 1002 having successive tones tonetone that traverse a single OFDM symbol. In response to sending enable/pause signal 425, the block relying on (feed) interleaver 410 may know that these QAM slots are unavailable and that data values cannot be inserted into them. This may avoid the problem of suspending MAC and TC blocks, as opportunities may be interspersed rather than grouped in a normal data flow. The PHY may still determine missing symbols or partial symbols. A state machine associated with processing module 440 may be used for reverse interleaving mapping 1005 and companion control.

Fig. 11 illustrates an embodiment of a network analyzer 1100. In particular, the network analyzer 1100 is presented for operation with a system, such as the system 300 described in connection with FIG. 3, including at least one CMTS305, a cable group 310, and a plurality of cable modems 320. While the CMTS305 and CM320 are shown separate from the cable group 310, it is noted that the entire system 300 can be considered a cable group. In particular, cable group 310 may correspond to a cable group that is partially separated from CMTS305 and CM 320. It should also be noted that while described as a cable group or DOCSIS3.1 compatible cable system, various embodiments may be employed with other cable systems including CMTS305 and CM 320. Likewise, the techniques described herein may be equally applied to other wired or wireless systems, and in particular may be employed by other network components and user equipment for such systems.

In operation, the network analyzer 1100 monitors, tests, analyzes the performance of the system 300 as a component under test (DUT), and generates test results in the form of reports and other test data. In an embodiment, any of the active and passive probe symbol delivery types described in connection with fig. 1-10 may be used in this embodiment, however other tests may also be employed in embodiments thereof.

The operation of the network analyzer 1100 and system 300 may provide Proactive Network Maintenance (PNM). In particular, a plurality of active functional network maintenance functions such as the spectrum analyzer function 1102, the vector signal analyzer function 1104 and other test point functions 1106 of the CMTS305 and cable modem 320 to enable measurement and network condition reporting so that undesirable effects such as fixed equipment and cable faults and interference and ingress from other systems can be detected and measured. From this information cable network the operator can make the modifications necessary to improve the conditions and detect network trends to detect when the network needs improvement. In one example, the system 300 may operate in accordance with the DOCSIS3.1PHY specification.

Fig. 11 as shown provides the components, test points, and management capabilities of active network maintenance and interfaces with network analyzer 1100 to monitor, test, and analyze the performance of the system 300. The CMTS305 and CM320 contain test points including a spectral analyzer 1102, a Vector Signal Analyzer (VSA) 1104, and other test points 1106 used in connection with the network analyzer 1100. The aim is to be able to describe, maintain and repair obstacles quickly and accurately to upstream and downstream cable groups in order to guarantee the highest flow and reliability of service. The spectrum analyzer function 1102 may include full spectrum, narrow spectrum, notch spectrum, or other triggered or unstriggered spectral analysis. The VSA functions 1104 may include determining pre-equalizer and equalization equipment, constellation display, and RxMER vs. subcarrier measurements for DS and/or US. Other test point functions 1106 include FEC statistics, impulse noise statistics, and/or histogram histograms. Additional functions performed by the CMTS305, CM320, and network analyzer 1110 are presented in connection with the examples that follow.

The following downstream PNM behaviors define CMTS305 and CM320 functions for obtaining and buffering symbol samples, triggering collection of upstream spectral condition information, providing broadband spectral analysis, employing additional subcarriers as spectral notches, providing equalization device values, providing QAM constellation points for display, obtaining and reporting receiver MER measurement data, obtaining and reporting forward error correction statistics, and reporting signal histograms for downstream channels.

As discussed in connection with fig. 3, the actual data-carrying symbol may be used to implement the functionality of the active probe symbol 302. In particular, symbols of any data type can be used for the above purpose. To make this function most effective, the content of the data-carrying symbols is acquired at the transmitter so that its content can be compared to the received samples in order to characterize the transfer function of the cable group 310 or to support other active network management functions as described herein. When the probe symbol is a data symbol, no special probe insertion is required. Rather, the content of the data symbols is acquired by the transmitter and later compared with samples also acquired by the receiver. The above process requires synchronization to ensure that the same symbol is acquired at the transmitter and receiver. This synchronization may be provided by the trigger information described in fig. 12.

Downlink symbol capture

The purpose of the downstream symbol capture is to provide part of the functionality of the network analyzer 1100 to analyze the response of the cable group. In the CMTS305, the frequency domain modulation values of all OFDM symbols before IFFT are obtained and effectively analyzed. The values thereof include I and Q modulation values in all subcarriers including data subcarriers, pilots, PLC header symbols, and additional subcarriers. This acquisition may result in many data points equal to the FFT length in use (e.g., 4096 or 8192), and 16 bits may be used as the width of each of I and Q with LSBs filled with zeros, if necessary.

In CM320, the received all OFDM symbol I and Q time domain samples before FFT do not include a guard interval and are acquired and effectively analyzed at 204.8mhz FFT sample density. This acquisition process may produce a number of data points equal to the length of the FFT in use (4096 or 8192), 16 bits in the width of each of I and Q with LSBs padded with zeros as necessary. The acquisition may include a point indication if a receiver window effect is present in the data.

Taking the inputs and outputs of the cable groups amounts to a broadband sweep over the channel broadband that allows a complete description of the linear and nonlinear responses of the downstream groups. The MAC provides signals via PLC triggers to ensure that the same symbols are acquired in the CMTS305 and CM 320. In an embodiment, the CMTS305 may be able to obtain modulation values for all downstream symbols for analysis. In an embodiment, the CM320 is capable of locating and obtaining time domain samples of all downlink symbols for analysis.

Downstream wide band spectrum acquisition

In an embodiment, downstream broadband spectrum acquisition provides a downstream broadband spectrum analyzer function in DOCSIS 3.1. Where the capabilities of CM320 are similar to those provided in DOCSIS 3.0. In an embodiment, the CM320 may provide downstream broadband spectrum acquisition and analysis capabilities. The CM320 may also provide the ability to acquire and analyze the entire downstream band of the cable group.

Downlink Noise Power Ratio (NPR) measurement

The purpose of the downstream NPR measurement is to observe the noise, interference and intermodulation products that are hidden in a portion of the OFDM signal. The CMTS305 defines a dedicated band of zero-valued subcarriers that form a spectral notch in the downstream OFDM signal. The CM320 provides a conventional spectral capture measurement function showing the notch depth. The limiting notch width may be chosen to be a value that does not exceed 10MHz in the normal case. One possible use case is to observe LTE interference occurring within the OFDM band; another possible use case is to observe intermodulation products generated from signal level calibration problems.

In an embodiment, the CMTS305 is capable of accepting start-stop subcarrier indices that define dedicated frequency bands (notches). The CMTS305 may also set the modulation values of all subcarriers in the notch to zero (no energy).

Downlink equalization equipment

The purpose of the equalization device is to provide access to the downstream adaptive equalizer coefficients that describe the linear response of the cable group. The OSSI specification may be defined as a summary metric to avoid having to send all equalization devices at the time of each inquiry. In an embodiment, the CM320 may report its downlink adaptive equalizer coefficients (in full or in summary) for any single OFDM block as required.

Downlink constellation display

The downlink constellation display provides received QAM constellation points for display. Equalized soft decisions (I and Q) at the segment inputs are collected over time, with optional subsamples of reduced complexity, and are available for analysis. The start-stop index defines the range of subcarriers included in the measurement. In an embodiment, only data-bearing subcarriers having specified properties and QAM constellations are sampled; pilots and additional subcarriers within the range may be used. 8192 samples are provided for each query, although larger or fewer samples may be used; additional queries may be added to the sample graph. In an embodiment, the CM320 is capable of acquiring and reporting received soft decision samples for a single selected configuration, a single constellation, and a range of subcarriers within a selectable single OFDM block.

Downstream received modulation error ratio per subcarrier (RxMER)

The downstream received modulation error ratio per subcarrier (RxMER) provides a measure of the received modulation error ratio for each subcarrier. CM320 measures the RxMER using pilot and zero-valued subcarriers that are not classified as symbol errors as data subcarriers may be classified as symbol errors. Since scattered pilots access all data subcarriers and zero-valued subcarriers are located at defined locations including the dedicated band, rxmers for all subcarriers in the active OFDM band may be measured over time. The scattered pilot pattern overlays the PLC header symbols, which are used for measurements as if they were pilots.

In an embodiment, only those zero-valued subcarriers processed by the CM320 receiver are measured. For the purposes of this measurement, RxMER is defined as the ratio of the average power of the balanced QAM constellation to the average error-vector power. For pilots, the error vector is the difference between the balanced received pilot value and the known correct pilot value. For zero-valued subcarriers, the error vector is the unbalanced received value itself, since the correction value is zero, and no reliable channel estimation for the excluded subcarrier locations performs balancing with it. Using this definition, a noise measurement for a zero-valued subcarrier is termed an equivalent RxMER value using average QAM mean power as a reference.

In an example of operation, for an ideal AWGN channel, a mixed OFDM block containing QAM symbology includes some zero-valued subcarriers, along with 35dB CNR on the QAM subcarriers, a nominal 35dB RxMER measurement for all subcarrier locations including zero-valued subcarriers may be obtained. In an embodiment, CM320 can use pilot, PLC header symbols, and/or zero-valued subcarriers for measurements, providing measurements of RxMER for all subcarrier locations for a single OFDM block. The CM320 may omit measurement of some zero valued subcarriers.

Signal-to-noise ratio (SNR) margin of candidate contours

The purpose of this feature is to provide an estimate of the SNR margin available on the downlink data channel according to the candidate modulation profile. The following calculation steps may be used to calculate this estimate. The CM320 performs this calculation only as required. The same calculations are done for the NCP channel.

And (3) an algorithm:

(1) CM320 measures RxMER values for each data subcarrier as detailed above.

(2) From these measurements, it calculates an average RxMER, MER1 per data subcarrier.

(3) Which is the average MER per subcarrier, MER2 required for candidate contour acceptance as input.

(4) The SNR margin is defined as MER1-MER2, where all numbers are in dB.

For example, if CM320 measures MER1=33dB, and the candidate profile requires MER2=30dB, CM320 reports a 3dB SNR margin. In addition, CM320 reports the number of subcarriers whose rxmers are at least x dB below a threshold of CER =1e-5 for a given QAM order, where x is a configurable parameter with, for example, a default value = 3.

Downlink FEC statistics

The purpose of FEC statistics is to monitor downlink quality via FEC and related statistics. The inner LDPC code and outer BCH code are calculated, statistics are applied on FEC codeword error events and are placed on each OFDM channel and for each profile received by the CM 320. The measurement may be marked with a timestamp, for example, using bits 21-52 of a 64-bit extended timestamp, where bit 0 is the LSB, which is provided with a resolution of 0.4msec and a 32-bit timestamp value in the range of 20 days. Time stamping may be performed with a nominal accuracy of 100msec or better. In an embodiment, the codeword count and codeword error count may comprise only full length codewords, i.e., LDPC codewords having a size of 16, 200 bits. Similar statistics can be used on NCP, again using only full length codewords, and on PLC. The MAC packet statistics are not profile based, but are computed over all packets sent to CM 320.

The CM320 can provide the following downlink performance specifications:

uncorrectable full length codeword: the number of full length codewords for which the BCH decoding fails.

Modifiable full length codeword: predecoding the number of full length codewords that fail LDPC failure checks and convey BCH decoding failures.

Unreliable full length NCP codeword: number of full length NCP codewords that fail LDPC post-decoding failure checking.

Unreliable PLC codeword: number of PLC codewords that failed LDPC post-decoding failure check.

NCP full length CRC failure: the number of full length NCP codewords that fail the CRC check.

MAC CRC failure: the MAC RC checks the number of failed packets.

Total number of full length FEC codewords.

Total number of full length NCP codewords.

Total number of PLC codewords.

The total number of MAC packets.

The start and stop times of the analysis cycle.

CM320 can provide the following downlink FEC profile on each OFDM channel for each profile received by CM 320.

Full length codeword error ratio vs. time (sec): the ratio of the number of full lengths of codewords that cannot be corrected to the total number of full length codewords in each one-second interval of a rolling 10-minute period (600 values).

Full length codeword error ratio vs. time (min): the ratio of the number of full length codewords that cannot be corrected to the total number of full length codewords in each one-minute interval of a rolling 24-hour period (1440 values).

The end time of the roll period.

Red/yellow/green summary link status (color defined in FLD 1).

CM320 may provide two sets and reporting methods for each error count metric:

and (5) long-term statistics. The CM320 collects the specifications for each profile all the time in the background. The code words (or packets) and error counters are automatically reset every hour. When the counters are reset due to suspension, the previous value of each counter is saved so that a full hour of reads is always available in a steady state environment.

Short termAnd (6) counting. CM320 utilizes two configuration parameters N_eAnd N_cA measurement is performed that is completed once. When N is present_eOccurrence of an error or N_cThe CM320 reports the result when any one of the first occurrences of the codeword has been processed. This measurement is particularly useful for down-line profile performance measurements.

Down histogram

The purpose of the down histogram is to provide a measure of non-linear effects in the channel, such as amplifier compression and laser clipping. For example, laser clipping causes one end of the histogram to be truncated and replaced with a spike. The CM320 captures a histogram of the time-domain samples at the wideband front end of the receiver. The histogram may be bilateral, i.e. it comprises sampled values from far negative to far positive values.

In an embodiment, the CM320 is capable of capturing a histogram of time-domain samples at the wideband front end of the receiver. The histogram may have a programmable accumulation period of 1 second to 1 minute and a minimum resolution of, for example, 255bins (bins).

Down profile performance specification

The following measurements are used for PNM diagnostics and for performance testing of the downstream modulation profile. The data format used to report a given measurement may be different for both purposes.

Uncorrectable full length codewords

Corrected full length codewords

MAC CRC codeword error

NCP LDPC full length codeword error

NCP full Length CRC failure

Total number of full length FEC codewords

The total number of full length NCP codewords.

RxMER per subcarrier

RxMER measurement type per subcarrier

SNR margin of candidate data outline

SNR margin of candidate NCP contour

The following upstream PNM behavior sets forth the following CMTS305 and CM320 functions: for obtaining and buffering symbol samples, providing broadband spectral analysis, obtaining and reporting noise power measurements and statistics, providing equalizer coefficient values, obtaining and reporting forward error correction statistics, and reporting signal histograms for uplink channels.

Quiet period uplink capture and probe symbol

The purpose of the capture is to observe potential noise and measure device response by capturing one or more OFDM symbols during a scheduled quiet period or probe. The quiet period provides a potential opportunity for observation when no communication is sent in the OFDM band. The upstream probe provides part of the functionality of the network analyser as the input is known and the output is captured. This allows a complete description of the linear and nonlinear response of the upstream cable cluster. A list of excluded subcarriers is also provided to fully define the transmitted waveform. The indicator of the beginning sampling used by the receiver for its FFT is also reported. In an embodiment, during an upstream quiet period or probing, the CMTS305 can capture samples of one upstream OFDM symbol (including guard time) and make them available for analysis.

Uplink triggered spectrum capture

Upstream triggered spectrum capture provides a broadband spectrum analyzer function in the CMTS305 that can be triggered to check for desired upstream transmissions and potential noise/interference during quiet periods. Capture capabilities herein include OFDM as well as pre-DOCSIS-3.1 upstream channels that may be present in the upstream spectrum.

In an embodiment, CMTS305 may provide broadband spectral analysis capabilities. The CMTS305 can provide a spectrum analysis range covering up to the full upstream spectrum of a cable cluster. The CMTS305 may provide the ability to trigger spectrum sample capture using the following modes:

free running

SID (service identifier) -based triggering

Triggering during quiet periods

Triggered based on the small slot count.

Up pulse noise statistics

The upstream impulse noise statistics collect statistics of the burst/impulse noise that occurs in the selected narrow frequency band. In an embodiment, the band pass filter is placed in the idle upstream band. A threshold is set, energy exceeding the threshold triggers measurement of an event, and energy falling below the threshold ends the event. The threshold may be set to zero, in which case the average power in the band may be measured. The measurements are time stamped using, for example: the D3.0 region of the 64-bit extended timestamp (bits 9-40, where bit 0 is the LSB) provides a resolution of 98ns and a 7 minute range.

In an embodiment, CMTS305 may provide the ability to capture the following statistics in selected bands up to 5.12MHz wide:

time stamping of events

Duration of event

Average power of event

In an embodiment, the CMTS305 may provide a time history buffer of up to 1024 events.

Uplink equalizer coefficients

The upstream balancer coefficients provide access to the CM320 upstream pre-balancer coefficients and the CMTS305 upstream adaptive balancer (post-balancer) coefficients, which together describe the linear response of the upstream cable cluster for a given CM 320. The OSSI specification may define a profile specification to avoid having to send all balancer coefficients for each query.

In an embodiment, CM320 may provide the ability to report its upstream pre-balancer coefficients (full or summary) as required. In an embodiment, the CMTS305 may provide the ability to report its upstream adaptive balancer coefficients associated with a given CM320 on demand.

Uplink FEC statistics

Uplink FEC statistics are provided for monitoring uplink quality via FEC and related statistics. Statistics may be employed on codeword error events. The measurements are time-stamped, for example, using bits 21-52 of the extended time stamp. LDPC codewords that fail post-decoding failure checking may be marked as "unreliable," but the data portion of the codeword may contain no bit errors; so the "unreliable codeword" count may tend to be disadvantageous. All codewords, whether full length or shortened, are included in the measurement.

In an embodiment, CMTS305 can provide the following FEC statistics for any single upstream user:

pre-FEC error-free codeword: the number of codewords that pass the predecode failure check.

Unreliable codeword: the number of codewords for which the post-decoding failure check failed.

Correcting the code word: the number of codewords that failed the pre-decoding failure check, but passed the post-decoding failure check.

MAC CRC failure: the MAC RC checks the number of failed packets.

Total number of FEC codewords.

The total number of MAC packets.

The start and stop times of the analysis cycle.

In an embodiment, CMTS305 can provide the following FEC summary for any single upstream user over a period of up to 10 minutes:

the total number of seconds.

Number of erroneous seconds (seconds during which at least one unreliable codeword occurs).

A count of codeword errors (unreliable codewords) in each 1 second interval.

Start and stop times of the summary period.

Red/yellow/green summary link status (color defined in FLD 1).

Histogram of the data

The purpose of the histogram is to provide a measure of non-linear effects in the upstream channel, such as amplifier compression and laser clipping. For example, laser clipping causes one end of the histogram to be truncated and replaced with a spike. The CMTS305 captures a histogram of the time domain samples at the wideband front end of the receiver. The histogram is bilateral, i.e. it comprises sampled values from far negative to far positive values.

In an embodiment, the CMTS305 can capture a histogram of time domain samples at the wideband front end of the receiver. The histogram may have a programmable accumulation period of 1 second to 1 minute and a minimum resolution of 255 bins.

Fig. 12 illustrates an embodiment of a trigger message block 1200. An example format of a trigger Message Block (MB) is shown for use in connection with one or more of the functions and features described in connection with fig. 1-11.

In one mode of operation, the trigger MB1200 provides a mechanism for synchronizing events between the CMTS305 and the CM320, such as the CM320 and the CMTS305, via command data 304 or other data exchange. In particular, the trigger message block 1200 may be used to trigger the execution of one or more pre-described PNM features. According to this example, the CMTS305 inserts TR MB into the PLC and performs an action at a particular time with PLC frame alignment. When CM320 detects TR MB, CM320 performs an action at the same relatively specified time that is aligned with the PLC frame that is received at CM 320. As discussed in connection with fig. 3, when the probe symbols are data symbols, synchronization is required to ensure that the same symbols are captured at the transceiver. Such synchronization may be provided by the trigger MB1200, e.g., via a symbol selection function.

The area of the trigger message block 1200 is shown in the following table according to an embodiment.

In this embodiment, the trigger type area identifies the type of measurement to be performed. The value is an unsigned integer from 0 to 15, its default value (default) = 1. The service identifier field is incremented by one on each trigger message sent, and toggled at value 255. The values are unsigned integers from 0 to 255. The trigger group area identifies which groups of CMs may respond to the trigger message.

In an example of operation, if CM320 has been configured to enable triggers and CM320 has components in a specified trigger group, CM320 responds to the trigger message. If CM320 is not configured to enable triggering, CM320 does not respond to the trigger message. The frame delay region tells the CM320 how many frames to wait before performing the specified action. Frame delay (FrameDelay) =1 (not allowed) may indicate that an action is performed in the next PLC frame after the frame containing TR MB; frame Delay) =2 indicates that an action is performed in the second PLC Frame after TR MB; and so on. The values are unsigned integers from 2 to 31, default value (default) = 2. The values 0 and 1 are not allowed because they may not give the CM320 sufficient time for a preparatory action.

The symbol selection area tells the CM320 which symbols in the designated PLC frame to perform an action. Symbol Select (Symbol Select) =0 denotes performing an action at the OFDM Symbol aligned with the first PLC header Symbol; symbol Select (Symbol Select) =1 denotes performing an action at an OFDM Symbol aligned with a second PLC header Symbol; symbol Select) =8 denotes performing an action on an OFDM Symbol aligned with a first Symbol after utilizing a PLC header, the OFDM Symbol corresponding to a first PLC data Symbol; and so on. The values are unsigned integers from 0 to 127, the default value (default) = 1. In addition to selecting a symbol, this parameter conventionally points to a point in time at the beginning of the selected symbol. (Note that, in contrast, DOCSIS PHY3.1 numbers the first PLC data symbol as symbol 0 because it only numbers the data field, except for the header.)

When a managed object commands to do so, the CMTS305 may insert a single TR MB into the PLC. The CMTS305 may place the trigger MB in the PLC frame immediately preceding the time stamp MB, but before any EM MB, and before the MC MB. The CMTS305 may increase the service ID field in each successive TR MB it transmits. When the trigger is enabled via the management object, CM320 may detect TR MB.

For example, for downstream symbol capture measurements, the following CMTS305 requirements apply:

the CMTS305 may set Trigger Type (Trigger Type) = 1.

The CMTS305 may capture and report the downstream symbols specified in the TR MB.

The CMTS305 may report the time stamp from what the PLC frame is directed through a trigger message.

The CMTS305 may report a service ID.

For example, for downlink symbol capture measurements, the following CM320 requirements apply:

when it is enabled for triggering and the composition of the trigger group is specified in the TR MB, the CM320 may capture and report the downlink symbols specified in the TR MB.

CM320 may report the service ID.

Application of trigger message block

This TR MB message 1200 may be used according to the following example. In order for the CM320 to respond to the TR MB, the CM320 is first evoked if the CM320 is in sleep mode. CM320 is configured to initiate a trigger. CM320 is configured to belong to a trigger group. The CMTS305 inserts a single trigger message per measurement that includes trigger group parameters associated with the group of CMs that are intended to perform the measurement. Messages only act upon those CMs, which are enabled to trigger and exist in the appropriate trigger group; unicast, multicast and broadcast groups are supported.

In one mode of operation, the TR MB is used to initiate downlink symbol acquisition measurements. The purpose of this measurement is to capture the same OFDM symbol at the CMTS305 and CM 320. The captured symbols are conventional symbols (not special test symbols or altered in any way) carrying downstream QAM data traffic. The entire OFDM symbol is captured at the CMTS305 and CM320 in I and Q samples at all subcarriers. The PLC frame is used merely as a timing mechanism to define the location of the desired symbol in the downstream OFDM symbol stream. For downlink symbol capture, the Trigger Type (Trigger Type) parameter is set to 1.

An OSS management station, such as network analyzer 1100 or other OSS device, initiates measurements via a despot to CMTS management object. The CMTS305 inserts TR MBs in the PLC channel of the designated OFDM downlink channel, waits for the number of PLC frames defined by the Frame Delay (Frame Delay) parameter, and captures the OFDM symbols designated by the Symbol Select (Symbol Select) parameter. This capture may cause many frequency domain data points equal to the FFT length in use (e.g., 4096 or 8192), each I & Q being 16 bits wide and the LSBs padded with zeros if needed.

The Trigger enabled CM320 addressed by the Trigger Group (Trigger Group) parameter detects the presence of TR MB in the PLC, waits for the number of PLC frames defined by the Frame Delay (Frame Delay) parameter, and captures the OFDM Symbol specified by the Symbol Select (Symbol Select) parameter. This capture will cause many time domain data points equal to the FFT length in use (e.g., 4096 or 8192), each I & Q is 16 bits wide, and the LSBs are padded with zeros if needed.

The CMTS305 captures the 8-byte spread timestamp value present in the PLC frame where the OFDM symbol was captured, and the CMTS305 returns the 8-byte spread timestamp value with the captured OFDM symbol samples to the management station; this helps identify the captured data and allows the capture time to be compared to other time-stamped events (e.g., burst noise and FEC errors). Both the CMTS305 and/or CM320 return the service ID along with the captured data; this provides a mechanism for grouping CMTS and CM data from the same symbol for analysis and for detecting missing captures. That condition (along with the service ID if available) is reported to the management station in place of the data if no data was successfully captured by the CMTS305 and/or CM 320. Data may be stored locally in the CMTS305 and CM320 and returned to the management station based on commands issued by the management station to management objects in the CMTS305 and CM 320.

In an embodiment, the OSSI specification may limit how many trigger messages can be sent before the OSS reads the captured data from the CM320 in order to limit CM storage requirements. The recommended initial default value is a maximum value captured one at a time in a given CM 320. If a new trigger message arrives before reading out the previously captured data, the CM320 can optionally ignore the new trigger and report that condition.

In an embodiment, the PNM system described herein synchronizes upstream quiet time capture with CMTS downstream symbol capture. The reason is to measure the Common Path Distortion (CPD), i.e. for example the non-linearity of the corroded connector, which constitutes a diode, causing the downstream signal to be modulated into the upstream.

In one mode of operation, the uplink and downlink measurements are synchronized based on the timestamp value. For example, a PNM station (e.g., network analyzer 1100 or other OSS management station) sends a command to CMTS305 to trigger two traps. The MIB may request a capture during quiet time or upstream user transmission, and the CMTS305 may convert the capture into a timestamp value. In an embodiment, a DOCSIS3.0 timestamp (bits 9-40 representing a DOCSIS3.1 extended timestamp) may be used in this regard.

For example, the planner plans a quiet period in the upstream of any future mini-slot and knows that the timestamp/mini-slot snapshot is out of alignment, the timestamp value t1 corresponding to the symbol in the middle of the quiet period is known. When PLC timestamp = t1, CMTS305 captures OFDM symbol periods in both upstream and downstream. In this manner, the CMTS305 can capture downstream symbols at predetermined times as dictated by known future PLC timestamp values.

In an operational mode, the CMTS software is operable to determine how the time stamp translates to a particular symbol on the PLC channel for the downstream and enters a particular small slot count for the upstream. In particular, the CMTS software separately configures the downstream and upstream capture functions so that they are calibrated. In this example, the CMTS and CM capture hardware in downstream does not have to know the timestamp values — these can still look for "symbol X after PLC frame Y". In this example, the CM320 sender may set a trigger message related to a timestamp to initiate the synchronization.

In an example, CMTS305 provides synchronization of US symbol capture by providing a unique allocation of quiet time for CM320 and CMTS 305. In particular, the CMTS305 may use P-MAP (rather than mini-slots) with capture markers or special SIDs to specify the symbols used.

In various embodiments, the burst receiver in the uplink channel captures more than one OFDM symbol (ideally, this extra capture length may provide a margin to account for any offset in time alignment between the uplink and downlink symbol boundaries and to ensure that the period of interest of the particular OFDM symbol in synchronization is captured for analysis.

Fig. 13 illustrates an embodiment 1300 of a cable cluster with a leakage source 1302. While the previous discussion focused on a number of functions including active network maintenance and network optimization on probe symbol transmission, probe symbols and other OFDM symbols could be inserted for detecting and/or locating leakage sources 1302 in communication channels 199, such as cable clusters 310. The leakage source 1302 may be a source of RF leakage from an amplifier enclosure, connectors, improper cable splices or connections, forcibly inserted cables, unterminated cables, or other cables such as the cable cluster 310 or other channels 199. In particular, the leakage source 1302 is part of the transmission system where the OFDM probe symbols are transmitted. The leakage receiver 1304 operates by detecting these OFDM probe symbol transmissions.

In embodiments, the probe symbol may be a broadband probe symbol, such as any of the active probe symbols described in connection with fig. 7-9. The leakage receiver 1304 includes a matched filter that is matched to the active probe symbols or other signal processing that detects the probe symbol transmissions. In one mode of operation, the leak receiver 1304 uses the received signal strength of the probe symbols to detect and locate the leak source. The leak receiver 1304 may optionally include a directional antenna for identifying the direction from the leak receiver 1304 to the leak source 1302 to further assist in locating the leak source 1302.

Consider, for example, a probe symbol occupying the full 192MHz OFDM bandwidth for a 1OFDM symbol of 20 microseconds in length. The format of the probe symbols may be received coherently in a matched filter. Which in conventional OFDM transmission are equal to 3800QAM values, each with 40dBSNR inside the cable. Allowing a 15dB SNR to reliably detect a signal present in a leak detector provides a processing gain of 40dB-15dB +10 × log10 (3800) =61dB to overcome leakage path loss.

In another mode of operation, the leakage receiver 1304 analyzes the leakage signal from the leakage source 1302 as a function of frequency. This takes advantage of the uncorrelated nature of LTE band leakage and low frequency (aeronautical band) leakage. Also, the frequency content helps to represent the mechanism that causes leakage, such as different sized apertures (cracks, weak connectors, etc.) corresponding to different wavelengths of RF leakage energy. It may be noted that the leak receiver 1304 may be a single purpose device, or incorporated into an accessory device that may be coupled to a smart phone, desktop computer, laptop computer, or other portable device, or otherwise incorporated into a smart phone, desktop computer, laptop computer, self-contained receiver, or other portable device.

Fig. 14 shows an embodiment 1400 of a cable cluster with a leakage source 1402. As with the leakage source 1302, the leakage source 1402 may be a source of RF leakage from an amplifier enclosure, connectors, improper cable splices or connections, force-on cables, unterminated cables, or other cables from, for example, a cable cluster 310 or other channel 199. In particular, the leakage source 1402 is part of the transmission system where the OFDM probe symbol is transmitted. Leak receivers 1404, 1406, 1408, and 1410 operate by detecting OFDM probe symbol transmissions.

In embodiments, the probe symbol may be a broadband probe symbol, such as any of the active probe symbols described in connection with fig. 7-9. The leakage receivers 1404, 1406, 1408, and 1410 include matched filters that are matched to the active probe symbols or other signal processing that detects the probe symbol transmissions.

In addition or as an alternative to operating as the leak receiver 1304, each leak receiver 1404, 1406, 1408, and 1410 includes a GPS receiver that provides a stable time base and GPS location of the receiver. When the leak receivers detect the probe symbol, a time of arrival (TOA) is calculated at each receiver and used in conjunction with the position of each receiver to pinpoint the position of the leak source 1402. Leak data from each leak receiver 1404, 1406, 1408, and 1410, which is used to calculate the location of the leak source 1402, is collected by a central terminal 1420, such as a master station, fixed station, or other receiver. In particular, the central terminal employs similar techniques as GPS location-but has TOA data from multiple receivers as opposed to TOA data at receivers from multiple sources.

Fig. 15 shows an embodiment 1500 of a leak receiver 1525 and a central terminal 1535. In particular, the central terminal 1535 is an example of the central terminal 1420 and the leakage receiver 1525, and 1525' represents two examples of two leakage receivers 1404, 1406, 1408 and 1410.

The leakage receivers 1525 and 1525' each include a leakage check receiver 1504 having a matched filter 1508, the matched filter 1508 being matched to the active probe symbols to detect probe symbol transmissions in the leakage signal 1512. In addition, the leak receivers 1525 and 1525' also include a GPS receiver 1502 that provides a stable time base for TOA calculations, as well as processes the GPS signal 1510 to generate GPS location data corresponding to the receiver location.

When the leak check receiver 1504 detects a probe symbol, a time of arrival (TOA) is calculated at each receiver via the TOA processor 1506. The TOA data and corresponding GPS location are incorporated in leak check data 1520 and 1520' that is transmitted to a central terminal 1535 via a wireless transceiver 1514. As shown, central terminal 1535 includes a wireless transceiver 1528 for coordinating the receipt of leak check data 1520 and 1520 ', and receiving leak check data 1520 and 1520'. Although a wired interface is described in connection with wireless reception, such as a universal serial bus interface, an ethernet interface, an internet connection, or other interface, either wired or wireless may alternatively be used.

The central terminal 1535 also includes a processing unit that executes a leak location application 1530, and a display device 1532 that provides a graphical user interface and helps a user of the central terminal 1535 identify the location of a leak source, such as the leak source 1402. In operation, the leak location application 1530 operates based on leak check data from 2, 3, 4, or more leak receivers at a plurality of locations to pinpoint the location of the leak source 1402. The leak location application 1530 uses the leak data from each of the leak receivers 1404, 1406, 1408, and 1410 to calculate the location of the leak source 1402. In particular, the leak location application 1530 employs similar techniques as the GPS location-but with TOA data from multiple receivers and GPS coordinates as opposed to TOA data at receivers from multiple sources.

Fig. 16 illustrates an embodiment 1600 of the location of a leak source via multiple leak check data. In this example, X1, X2, X3, and X4 represent coordinate locations of four leak receivers, e.g., 1404, 1406, 1408, and 1410. As discussed in connection with fig. 14 and 15, these coordinate locations may be generated by the GPS receiver of each leak receiver. The dashed circles according to each coordinate position (X1, X2, X3, X4) represent distances from each coordinate derived from TOA data generated by the corresponding leak receiver and the corresponding velocity of signal transmission in air. Although the TOA data itself is non-directional, the leak location application 1530 combines the leak check data from all four leak receivers to calculate the location Y of the leak source 1302. As shown, the location Y of the leakage source 1302 corresponds to the intersection of the four dashed circles. As one skilled in the art will appreciate, although the presence of errors in the GPS coordinate locations (X1, X2, X3, X4) and the corresponding TOA data from each leak receiver may indicate that there may not be an accurate intersection, the identification of the intersection region and its midpoint may be used to estimate the location Y and further provide a method of measuring the accuracy of the estimate.

Fig. 17 illustrates an embodiment 1700 of a leakage source location according to a cable cluster map. In particular, the locations of certain components of a cable cluster, such as cable cluster 310, overlap on the layout drawing. In the illustrated example, the dark lines represent buried or overhead cables, and other symbols are used to represent known sources of possible RF signal leakage. In particular, the squares represent connectors and the triangles represent amplifier housings. The cable cluster plan map may be used in conjunction with the leak location application 1530 to help identify and locate the leak source 1402.

In one example of operation, a cable cluster plan is displayed on the display 1532 of the central terminal 1535 to assist a user of the central terminal in locating the leak source 1402. In the illustrated example, the computed position Y is superimposed on the cable cluster plan map. The user may see that the calculated position Y is close to the amplifier housing which may be the source of the leak. In another example, the leak location application 1530 automatically identifies similar sources of leaks that are proximate to the calculated location Y and, as applicable, highlights the similar source or sources to the user.

Returning again to fig. 14, in another embodiment, an egress monitoring signal, such as any of the active probe symbols described in connection with fig. 7-9, is inserted in the downstream and/or upstream transmissions. The leakage receiver 1404 includes a matched filter that is matched to the active probe symbols or other signal processing to detect probe symbol transmissions. In one mode of operation, the leak receiver 1404 uses the received signal strength of the probe symbols to detect and locate the source of the leak. The leak receiver 1404 may optionally include a directional antenna that is used to identify the direction from the leak receiver 1404 to the leak source 1402 to further assist in locating the leak source 1402.

Consider, for example, a probe symbol occupying the full 192mhz OFDM bandwidth for a 1OFDM symbol of 20 microseconds in length. The format of the probe symbols may be received coherently in a matched filter. Which in conventional OFDM transmission are equal to 3800QAM values, each with 40dBSNR inside the cable. Allowing a 15dB SNR to reliably detect a signal present in a leak detector provides a processing gain of 40dB-15dB +10 × log10 (3800) =61dB to overcome leakage path loss.

In another mode of operation, the leak receiver 1404 analyzes the leak signal from the leak source 1402 as a function of frequency. This takes advantage of the uncorrelated nature of LTE band leakage and low frequency (aeronautical band) leakage. Also, the frequency content helps to represent the mechanism that causes leakage, such as different sized apertures (cracks, weak connectors, etc.) corresponding to different wavelengths of RF leakage energy. It may be noted that leak receiver 1404 may be a single purpose device, or incorporated into an accessory device that may be coupled to a smart phone, desktop computer, laptop computer, or other portable device, or otherwise incorporated into a smart phone, desktop computer, laptop computer, self-contained receiver, or other portable device.

Consider another embodiment where multiple phase continuous OFDM pilot tones are inserted in either the uplink or downlink transmission in addition to or as an alternative to active probe symbols. In particular, pilot tones, such as continuous wave pilots, may be generated for egress monitoring, phase noise measurement, subcarrier spacing detection, and/or for other testing and measurement purposes.

A continual pilot tone in the band can be generated which, if properly chosen in frequency, causes a true CW or substantially true CW, even in the presence of a cyclic prefix. For example, the pilot symbols may be true CW (unmodulated), i.e. they may be considered as spectral lines when viewed on a spectrum analyzer. The CW pilot may also be used as an OFDM pilot for acquisition and tracking, as the phase may be known. The CW pilot may remain orthogonal to another OFDM tone. For egress testing, link loss (leakage from the cable, plus path loss) may be the limiting factor, rather than the transmission SNR of the CW tone. The pilot tones in the band can optionally be implemented without guard bands. The leaky receiver 1404 can clearly detect the pilot tones in these bands, which are time-averaged over thousands of OFDM symbols.

In an embodiment, the CMTS305 or CM320 allocates a number of OFDM tones (e.g., 5 to 10) in either the upstream or downstream as Carrier (CW) pilots to be sent continuously across all symbols. Each CW pilot may be identical to any other continuous pilot except for the continuous phase constraint on the OFDM symbol. Because the cyclic prefix (and/or guard interval) in each OFDM symbol adds a phase shift due to its duty cycle, the CW pilot can account for this extra phase shift and start with the correct phase in the next OFDM symbol.

This form of pilot may be coherently received via a matched filter that detects the presence of these RFCW tones in order to measure device leakage. The leakage receiver 1404 may use time averaging in the detection to up-tune the tone to the OFDM-away background noise. In yet another embodiment, the leak receiver 1404 may be synchronized to an OFDM frame and the CW pilot tone may be detected based on its orthogonality with other OFDM symbols. In this case, time averaging may not be required.

Consider the application of such CW pilots to a CMTS305 and/or CM320 operating in accordance with DOCSIS 3.1. Conventional sniffer devices in DOCSIS3.0 insert tones in the cable constellation that have a spectral density about 9dB lower than and between the QAM signals, when measured in a 50kHz BW. In one mode of operation, the continual pilots are raised 6dB above the OFDM data subcarriers. If the OFDM and legacy QAM spectral densities are about equal, the continuous phase CW pilot may be 9+6=15dB stronger than the legacy sniffer tone. This can be very effective for leak checking-even in the presence of LTE band leakage and low frequency (airband) leakage.

It can be noted that placing the egress monitoring signal in the upstream (e.g., CW tone at a known frequency or an upstream full band probe) and in the downstream transmission allows for rapid discovery and repair of leaks. The uplink transmission can be tracked to a given location because only one uplink Tx is transmitting the full-band probe at a time. This is better for finding the problem, where the signal is sent to all users, than downstream.

Some modulation may be used in addition to the use of unmodulated pilot tones. For example, a constant such as a point taken from QAM averaging, AM, BPSK, or other modulation techniques may be used to modulate the subcarriers. In one mode of operation, a large value of the semblance may be used. In another mode of operation, the modulation may be selectable among a set of programmable modulation values.

Although the above discussion focuses on in-band pilots, the transmitter may employ one or more enunciators to provide OFDM band tones and/or OFDM band edge tones. For example, a CW generator using 2, 3, 4, …, such as a Numerically Controlled Oscillator (NCO), or other enunciator that may be used to generate the pilot tone. If these pilot tones are generated at 50kHz or 25kHz centers, or otherwise, the OFDM FFT bin spacing is matched, then the pilot tones may be orthogonal to the OFDM symbols.

Consider the case where two or three pilot tones are generated. By selecting the amplitude and phase of these tones, an AM signal can be generated that can be easily received, demodulated, and identified by a site device, such as leak receiver 1304. With the CMTS305 locked to a stable reference, such as a DTI server and/or GPS, AM signals can be easily acquired with few frequency searches. The use of such signals for export monitoring facilitates easy reception and measurement by means of simple, standard field equipment.

In addition to the use of such CP pilots discussed above for leak detection or other egress monitoring, CW pilot tones may be employed in conjunction with the CMTS305 and CM320 in upstream and/or downstream transmissions for phase noise testing, subcarrier spacing detection, and/or other testing purposes. For phase noise testing, one CW generator may be sufficient to generate a single tone for measurement on a phase noise testing apparatus or other device. For measuring the OFDM subcarrier spacing, two tones may be generated with the subcarrier frequency spacing. The frequency difference can be measured using standard test equipment.

Fig. 18 illustrates an embodiment of a baseband processor or other data processing element 440'. In particular, the baseband processor or other data processing element 440' includes similar functionality and features described in connection with fig. 4, which are referenced by common reference numerals.

In particular, IFFT406 and/or pilot insertion block 1800 generates and inserts OFDM pilot tones in OFDM symbol stream 422' for transmission. For example, the IFFT406 may operate to insert CW pilot tones in the band. The IFFT406 generates many OFDM tones (e.g., 5 to 10) as Carrier (CW) pilots in the downlink to continuously transmit through all symbols. Each CW pilot is generated identically to the other continuous pilots except for the continuous phase constraint on the OFDM symbol. Because the cyclic prefix in each OFDM symbol adds a phase shift due to its duty cycle, the IFFT406 or pilot insertion block 1800 can account for this extra phase shift and start the CW pilot at the correct phase in each OFDM symbol for phase coherence of the OFDM symbol sequence.

In one embodiment, the baseband processor or other data processing element 440' optionally reacts to the transmission initiation/pause control 425 to pause processing to insert probe symbols in the OFDM symbol stream. When such probe symbols are performed, the CW pilots may or may not be included.

Consider the manner of operation in which tones are generated by transmitting a +1 through IFFT406 for each subcarrier, located at (in the complex baseband) 0Hz and at a multiple of Nfft/CP in the band. To double the number of possible valid positions for the insertion tones, BPSK equalization may be employed, and alternating values (+ 1 and-1) may be used.

Considering the manner of operation of egress monitoring, here CW pilots are inserted in the middle of OFDM data subcarriers via IFFT 406-optionally with no guard band around the pilots. In this application, time averaging may be applied in the leakage receiver 1304. Consider the example: 4K IFFT, CP =256, and Window) =128, and 15 continual pilots are inserted with 2X pilot boosting; 8 continuous pilots at positive frequencies are set on the subcarriers generating the CW tone, and 7 continuous pilots at negative frequencies are set to the subcarriers ending with 180 degree inversion from symbol to symbol. The pilot is modulated in the frequency direction by a BPSK sequence, but the pilot is static in the time direction. Simulation results for a power spectral density of 1600FFT symbol periods with a 50KHz RBW (note: 1600 × (4096 + 256) close to 7 million complex samples at 204.8 MHz) indicate that the pilot shows a higher than nominal +6dB spike at positive frequencies and higher than nominal +3dB at negative frequencies. This means that CW pilots may not be used with guard bands and will be clearly detectable by receivers with time averaging of more than thousands of OFDM symbols. Although described above without guard bands, guard bands may equally be implemented that include some number of subcarriers around each CW pilot.

In another mode of operation, the IFFT406 generates modulated tones that are modulated at the IFFT output to either [ +1, -1, +1, -1 … ] or [1, 1, 1, 1, … ] at 204.8MHz, which creates tones at either Fc +102.4MHz or Fc after being up-converted to the carrier frequency Fc. This scheme may be well suited for phase noise testing.

Optional pilot insertion block 1800 may include one or more NCO's for generating one or more out OFDM band tones and/or OFDM band edge tones that are added to the OFDM stream and added to the output of IFFT406 after cyclic prefix insertion. The combined stream including the extra tones is modulated for transmission via a modulator, such as modulator 414 described in connection with fig. 4. Although pilot insertion block 1800 is schematically shown subsequent to CP insertion 408 and interleaver 410, other orderings are equally possible. For example, pilot insertion block 1800 includes 4 complex NCO, running at 204.8MHz clock, added to the output of the IFFT (after CP insertion). This can be used to test phase noise and exit monitoring. BSK modulation (+ 1, -1) can be applied to tones or DC (no modulation).

Whether tones are generated in-band as OFDM band or OFDM band edge tones via IFFT406 or by optional pilot insertion block 1800, these tones may be used for cable cluster leakage check, phase noise test, subcarrier spacing detection, and/or other test purposes.

Fig. 19 shows an embodiment of leak receiver 1404. The leakage receiver 1404 includes a plurality of matched filters 1908, the matched filters 1908 being matched to the active probe symbols and/or CW pilot tones to detect probe symbol transmissions in the leakage signal 1912. Consider the example discussed in connection with fig. 14, where the active probe symbols take the form of phase continuations of a number of OFDM pilots in the downlink transmission. The matched filter detects the presence of these RF CW tones to measure device leakage. The leakage receiver 1404 may use time averaging in the detection to up-tune the tone to the OFDM-away background noise. In further embodiments, the leaky receiver 1404 may be synchronized to the OFDM frame via an optional frame synchronizer 1900, which optional frame synchronizer 1900 operates in a similar manner to the corresponding part of the receiver 490 described in connection with fig. 4. In this case, the CW pilot tone may be detected based on orthogonality of the CW pilot tone with other OFDM symbols. In this case, time averaging may not be required.

Consider the situation discussed in connection with fig. 14 where two or three pilot tones are generated. By selecting the amplitude and phase of these tones, an AM signal may be generated that may be received, demodulated, and identified by leak receiver 1404 via AM detector 1910. With the CMTS305 locked to a stable reference, such as a DTI server and/or GPS, AM signals can be easily acquired with few frequency searches. The use of such signals for export monitoring facilitates easy reception and measurement by means of simple, standard field equipment.

As discussed in connection with fig. 18, CW pilots may be inserted in the middle of OFDM data subcarriers via IFFT 406-optionally with no guard bands around the pilots. Consider the situation: 4KIFFT, CP =256, and Window =128, and 15 continual pilots are inserted with 2X pilot boosting; 8 continuous pilots at positive frequencies are set on the subcarriers generating the CW tone, and 7 continuous pilots at negative frequencies are set to the subcarriers ending with 180 degree inversion from symbol to symbol. The pilot is modulated in the frequency direction by a BPSK sequence, but the pilot is static in the time direction. In this application, time averaging may be applied in the leaky receiver 1404 in conjunction with a matched filter 1908, the matched filter 1908 tuned to the frequency of the inserted tone. Additionally, conventional FFT techniques can be used to detect the presence of pilot tones in the received signal spectrum.

Fig. 20 illustrates an embodiment of a method. In particular, methods are presented for use with one or more of the functions and features described in connection with fig. 1-19. Step 2000 includes generating a plurality of orthogonal frequency division multiple access (OFDM) symbols from the data packet. Step 2002 includes generating a probe symbol, such as one of a plurality of probe symbol types. Step 2004 includes selectively inserting the probe symbols at predetermined probe symbol positions within the plurality of OFDM symbols to form a symbol stream for transmission via cable aggregation.

In an embodiment, the plurality of probe symbol types includes one or more types of active probe symbols and/or quiet probe symbols. The plurality of probe symbol types may include probe symbols for locating leaks in a cable cluster. The plurality of OFDM symbols includes at least one pilot tone for locating leakage in a cable cluster associated with the CMTS. The at least one pilot tone may be a carrier pilot that is phase continuous over the plurality of OFDM symbols. The plurality of OFDM symbols may include at least one pilot tone for phase noise testing and subcarrier spacing detection.

Fig. 21 illustrates an embodiment of a method. In particular, methods are presented for use with one or more of the functions and features described in conjunction with fig. 1-20. Step 2100 includes generating a pause signal. Step 2102 comprises suspending said generating of said OFDM symbols responsive to said suspension signal, wherein said probe symbols are selectively inserted in said plurality of OFDM symbols responsive to said suspension signal.

It should be noted that as used herein, specialized terms such as bitstreams, streams, signal sequences and the like (or their equivalents) have been used interchangeably to describe digital information whose content corresponds to any of a number of desired types (e.g., data, video, voice, audio and the like, any of which may be referred to collectively as "data").

It should be noted that specialized words such as bitstreams, streams, signal sequences and the like (or their equivalents), which may be used herein, have been used interchangeably to describe digital information whose content corresponds to any of a number of desired types (e.g., data, video, voice, audio and the like, any of which may be referred to collectively as "data").

As may be used herein, the terms "substantially" and "approximately" provide an industry-recognized tolerance for relativity between the terms and/or objects to which it corresponds. Such industry-accepted tolerances range from less than one percent to fifty percent and correspond to, but are not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between objects ranges from a few percent difference to a large number of differences. As also used herein, the terms "configured to," "operatively coupled to," "coupled to," and/or "coupled to" include direct coupling between objects and/or indirect coupling between objects via an intervening item (e.g., an item that includes, but is not limited to, a component, element, circuit, and/or module), where for the example of indirect coupling, the intervening item does not modify the information of a signal, but may adjust its current level, voltage level, and/or power level. As also used herein, coupled inferentially (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two objects in the same manner as "coupled". As may be further used herein, the terms "configured to," "operatively coupled to," "coupled to," or "operatively coupled to" mean that the article includes one or more electrical connections, inputs, outputs, etc., that when activated, perform one or more of its corresponding functions, and may further include inferentially coupling to one or more other objects. As may be used further herein, the term "associated with" includes a separate object embedded within another object and/or a direct and/or indirect coupling of one object.

As used herein, the term "compares favorably", indicates that a comparison between two or more objects, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a smooth comparison may be achieved when the magnitude of signal 1 is greater than signal 2 or when the magnitude of signal 2 is less than signal 1. As used herein, the term "compares favorably", indicates that a comparison between two or more objects, signals, etc., does not provide a desired relationship.

As also used herein, the terms "processing module," "data processing circuit," "processor," and/or "processing unit" may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, microcontroller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. The processing module, data processing circuit and/or processing unit may be or further comprise a memory and/or integrated memory element, which may be a single memory device, a plurality of memory devices and/or embedded circuitry of another processing module, data processing circuit and/or processing unit. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. It should be noted that if the processing module, data processing circuit, and/or processing unit includes more than one processing device, the processing devices may be centrally located (e.g., directly coupled together via a wired and/or wireless bus structure) or may be distributed (e.g., cloud computing indirectly coupled via a local area network and/or a wide area network). It should further be noted that if the processing module, data processing circuit, and/or processing unit implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory and/or storage elements storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. It is further noted that the memory elements may store, and the processing modules, data processing circuits and/or processing units execute, hard-coded and/or operational instructions corresponding to at least some of the steps and/or functions illustrated in the figures. Such a memory device or memory element may be classified as an article of manufacture.

One or more embodiments are described above with the aid of method steps illustrating the performance of specified functions and relationships there between. The boundaries and sequence of these functional building blocks and method steps have been arbitrarily defined herein for the convenience of the description. Alternate boundaries and sequences may be defined so long as the specified functions and relationships are appropriately performed. Any such alternate boundaries or sequences are therefore within the scope and spirit of the claims. Furthermore, for the sake of convenience of description, the boundaries of these functional building blocks have been arbitrarily defined. Alternate boundaries can be defined so long as certain significant functions are appropriately performed. Similarly, flow diagram blocks may also be arbitrarily defined herein to illustrate certain significant functions.

To the extent used, additional flow diagram block boundaries and sequences may have been defined and still perform some significant functions. Such alternative definitions of functional building blocks and flow diagram blocks and sequences are therefore within the scope and spirit of the present claims. One of ordinary skill in the art will also recognize that the functional building blocks and other illustrative blocks, modules, and components herein can be implemented as shown, or by discrete components, application specific integrated circuits, processors executing appropriate software, etc., or any combination thereof.

Further, the flow chart may include a "start" and/or "continue" indication. The "start" and "continue" indications reflect that the described steps may alternatively be used in conjunction with other routines or in addition to other routines. In this regard, "start" means the beginning of the first step described and may precede other activities not specifically shown. Further, the "continue" indication reflects that the described step may be performed multiple times and/or may continue through other actions not specifically shown. Moreover, although a flowchart shows a particular order of steps, other orderings are equally possible as long as the principles of causality are retained.

The one or more implementations are used herein to illustrate one or more aspects, one or more features, one or more concepts, and/or one or more examples. Physical embodiments of an apparatus, article, machine, and/or process may include one or more aspects, features, concepts, examples, etc. described with reference to one or more of the embodiments discussed herein. Furthermore, from figure to figure, embodiments may incorporate the same or similarly named functions, steps, modules, etc. that may use the same or different reference numbers, and thus the functions, steps, modules, etc. may be the same or similar functions, steps, modules, etc. or different.

In the drawings of any of the figures presented herein, analog or digital, continuous-time or discrete-time, and single-ended differential. For example, if the signal path is shown as a single ended path, it also behaves as a differential signal path. Similarly, if the signal path is shown as a differential path, it also represents a single-ended signal path. Although one or more particular architectures are described herein, other architectures can be implemented as well, using an average level of non-expressive illustration of one or more data buses, direct connectivity between elements, and/or indirect coupling between other elements, as would be known by one of ordinary skill in the art.

The term "module" is used in the description of one or more embodiments. A module implements one or more functions via a device, such as a processor, or other processing device, or may include memory storing operational instructions, or other hardware that operates in conjunction with the memory storing operational instructions. Modules may operate alone and/or in conjunction with software and/or firmware. As also used herein, a module may contain one or more sub-modules, each of which may be one or more modules.

Although specific combinations of features and characteristics are described herein for one or more embodiments, other combinations of features and functions are equally possible. The present disclosure is not limited by the specific examples disclosed herein, and is expressly incorporated in such other combinations.

Claims (10)

1. A transmitter for use in a cable modem termination system, the cable modem termination system communicating with a cable modem via a cable group, the transmitter comprising:

a data processing module configured to generate a plurality of orthogonal frequency division multiplexing, OFDM, symbols from a data packet;

a probe symbol generator configured to generate a probe symbol that is one of a plurality of probe symbol types;

a multiplexer coupled to the data processing module and the probe symbol generator and configured to selectively insert the probe symbols within the plurality of OFDM symbols at predetermined probe symbol positions to form a symbol stream for transmission via the cable constellation.

2. The transmitter of claim 1, further comprising:

a pause control generator coupled to the data processing module, the pause control generator generating a pause signal;

wherein the data processing module suspends generation of the plurality of OFDM symbols in response to the suspension signal; and

wherein the multiplexer selectively multiplexes the probe symbols with the plurality of OFDM symbols in response to the pause signal.

3. The transmitter of claim 1, wherein the plurality of probe symbol types includes active probe symbols and static probe symbols.

4. The transmitter of claim 1, wherein the plurality of probe symbol types includes symbols for locating leaks in the cable cluster.

5. The transmitter of claim 1, wherein the plurality of OFDM symbols include at least one pilot tone for locating leakage in the cable cluster.

6. The transmitter of claim 5, wherein the at least one pilot tone is a carrier pilot that is phase continuous over the plurality of OFDM symbols.

7. The transmitter of claim 1, wherein the plurality of OFDM symbols include at least one pilot tone for phase noise testing and subcarrier spacing detection.

8. A method, comprising:

generating a plurality of orthogonal frequency division multiplexing, OFDM, symbols from the data packet;

generating a probe symbol as one of a plurality of probe symbol types;

selectively inserting the probe symbols within the plurality of OFDM symbols at predetermined probe symbol positions to form a symbol stream for transmission via cable aggregation.

9. The method of claim 8, further comprising:

generating a pause signal; and

suspending generation of the OFDM symbol in response to the suspension signal, wherein the probe symbol is selectively inserted into the plurality of OFDM symbols in response to the suspension signal.

10. A system, comprising:

a Cable Modem Termination System (CMTS) that generates a downstream OFDM symbol stream for communication with a cable modem via a cable cluster and receives an upstream OFDM symbol stream from the cable modem via the cable cluster, wherein at least one of the upstream OFDM symbol stream and the downstream OFDM symbol stream includes a plurality of probe symbol transmissions that include a plurality of probe symbol types;

the cable modem generating the upstream OFDM symbol stream for communication with the CMTS via the cable cluster and receiving the downstream OFDM symbol stream from the CMTS via the cable cluster; and

a network analyzer configured to communicate active network maintenance data with the cable modem and the CMTS to provide a plurality of active network maintenance functions via the plurality of probe symbol transmissions.