Patent Publication Number: US-2020304170-A1

Title: Proactive echo cancellation (ec) training

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to echo cancellation. 
     BACKGROUND 
     A Hybrid Fiber-Coaxial (HFC) network is a broadband network that combines optical fiber and coaxial cable. It has been commonly employed globally by cable television operators. In a HFC cable network, television channels are sent from a cable system&#39;s distribution facility to local communities through optical fiber trunk lines. At the local community, a box translates the signal from a light beam to electrical signal, and sends it over cable lines for distribution to subscriber residences. The optical fiber trunk lines provide adequate bandwidth to allow future expansion and new bandwidth-intensive services. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate various embodiments of the present disclosure. In the drawings: 
         FIG. 1  is a block diagram of a system for providing proactive Echo Cancellation (EC) training; 
         FIG. 2  is a flow chart of a method for providing proactive EC training; 
         FIG. 3  illustrates Explicit Echo Cancellation Training Opportunity (EECTO) scheduling; 
         FIG. 4  illustrates Implicit Echo Cancellation Training Opportunity (IECTO) scheduling; and 
         FIG. 5  is a block diagram of a computing device. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     Proactive Echo Cancellation (EC) training may be provided. First, a plurality of Echo Cancellation Training Opportunities (ECTOs) may be identified in an upstream bandwidth allocation. Identifying the ECTOs may comprise identifying a corresponding plurality of mini-slots in a two dimensional time frequency space designated as not to be used for Upstream (US) traffic. Then Echo Cancellation Training (ECT) may be conducted for each of the plurality of ECTOs. 
     Both the foregoing overview and the following example embodiments are examples and explanatory only, and should not be considered to restrict the disclosure&#39;s scope, as described and claimed. Furthermore, features and/or variations may be provided in addition to those described. For example, embodiments of the disclosure may be directed to various feature combinations and sub-combinations described in the example embodiments. 
     Example Embodiments 
     The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar elements. While embodiments of the disclosure may be described, modifications, adaptations, and other implementations are possible. For example, substitutions, additions, or modifications may be made to the elements illustrated in the drawings, and the methods described herein may be modified by substituting, reordering, or adding stages to the disclosed methods. Accordingly, the following detailed description does not limit the disclosure. Instead, the proper scope of the disclosure is defined by the appended claims. 
     Multiple-system operators (MSOs) are operators of multiple cable or direct-broadcast satellite television systems. These systems may include HFC networks. To amplify upstream (US) signals and downstream (DS) signals in the HFC network, MSOs may use nodes deployed within the HFC. In the HFC network, a node may comprise a container that may house optical and electrical circuitry. An optical fiber cable or a coaxial cable may be connected to an input side of the node and a plurality of coaxial cables may be connected to a output side of the node. The input side of the node may be connect to a headend in the HFC network and the DS side of the node may be connected to Customer Premises Equipment (CPE) of subscribers to the HFC. Amplifiers may be used in the node to amplify upstream (US) signals and downstream (DS) signals. Embodiments of the disclosure may provide an echo cancellation (EC) process that may support full duplex (FDX) Data Over Cable Service Interface Specification (DOCSIS) operation. 
       FIG. 1  is a block diagram of a system  100  for providing proactive Echo Cancellation (EC) training consistent with embodiments of the disclosure. System  100  may comprise a Distributed Access Architecture (DAA). As shown in  FIG. 1 , system  100  may comprise a core  105 , a remote PHY device (RPD)  110 , and a plurality of Customer Premises Equipment (CPE)  115 . Core  105  may comprise a Converged Cable Access Platform (CCAP) core and may include a Cable Modem Termination System (CMTS)  120  that may include a scheduler  125 . RPD  110  may comprise an echo canceler  130 . Plurality of CPE  115  may comprise a first CPE  135  and a second CPE  140 . 
     CMTS  120  may comprise a device located in a service provider&#39;s (e.g., a cable company&#39;s) headend (i.e., core  105 ) that may be used to provide high speed data services, such as cable Internet or Voice-Over-Internet Protocol, to subscribers. Remote physical layer (i.e., RPHY) may comprise shifting or distributing the physical layer (i.e., PHY) of a conventional cable headend CMTS to fiber nodes (e.g., RPD nodes) in a network. RPD  110  may comprise circuity to implement the physical layer of the CMTS. First CPE  135  and second CPE  140  may comprise, but are not limited to, a Cable Modem (CM), a cellular base station, a tablet device, a mobile device, a smart phone, a telephone, a remote control device, a set-top box, a digital video recorder, a personal computer, a network computer, a mainframe, a router, or other similar microcomputer-based device. 
     RPD  110  may comprise a node in an HFC network. RPD  110  may comprise a container that may house optical and electrical circuitry. An optical fiber cable  145  may be connected to one side of RPD  110  and a plurality of coaxial cables  150  may be connected to the other side of RPD  110 . Optical fiber cable  145  may be connected to CMTS  120  in core  105  in the HFC network. Plurality of coaxial cables  150  may be connected to plurality of CPE  115  of subscribers to the HFC. As such, RPD  110  may facilitate communications between core  105  and plurality of CPE  115 . 
     Elements described above of system  100  (e.g., RPD  110 , CMTS  120 , scheduler  125 , echo canceler  130 , first CPE  135 , and second CPE  140 ) may be practiced in hardware and/or in software (including firmware, resident software, micro-code, etc.) or in any other circuits or systems. Elements of system  100  may be practiced in electrical circuits comprising discrete electronic elements, packaged or integrated electronic chips containing logic gates, a circuit utilizing a microprocessor, or on a single chip containing electronic elements or microprocessors. Elements of system  100  may also be practiced using other technologies capable of performing logical operations such as, for example, AND, OR, and NOT, including but not limited to, mechanical, optical, fluidic, and quantum technologies. As described in greater detail below with respect to  FIG. 5 , elements of system  100  may be practiced in a computing device  500 . 
     Consistent with embodiments of the disclosure, system  100  may support FDX DOCSIS operation. Echoes may occur in FDX DOCSIS operations. Echo Cancellation (EC) (e.g., via echo canceler  130 ) may be implemented for suppressing self-interference (e.g., from a transmitter in RPD  110  to a receiver in RPD  110 ) to enable FDX operations. CMTS  120  may ensure proper Echo Cancellation Training (ECT) for echo canceler  130  to observe and characterize the echoes, in order to derive EC coefficients. 
     ECT may be done during a “quiet period” during which there may be no Upstream (US) transmissions, so the received US signal may contain the echoes of the transmitted Downstream (DS) signal and the channel noise. Such a quiet period may be referred to as an ECT opportunity. Per the FDX DOCSIS 3.1 specification, an ECT opportunity may cover an entire 96 MHz upstream channel and may last one or multiple Orthogonal Frequency Division Multiple Access (OFDMA) frames. Because the magnitude and phase of the echoes may change over time (i.e., time varying channel), periodic ECT may be used to maintain sufficient convergence of the EC. However, because no US transmission may be permitted in an ECT opportunity, frequent ECT incurs high bandwidth cost. 
     The FDX DOCSIS 3.1 specification defines reactive ECT scheduling, where a CMTS schedules ECTs at a size and interval based on the ECT requests from an echo canceler. In the DAA, the CMTS US scheduler is located at the CCAP core, separated from the echo canceler at the RPD over a Converged Interconnect Network (CIN). Round Trip Time (RTT) over the CIN, may be in the order of multiple milliseconds, causing delayed ECT training opportunities that may result in echo cancellation divergence. This may be problematic in cases where the channel experiences rapid changes (e.g., wind blowing, heavy truck parking close to cable pedestal, etc.). Consequently, there may be a need for frequent and always-on ECT opportunities at a low bandwidth cost. 
     Embodiments of the disclosure may provide a proactive Echo Cancellation Training (ECT) process that may provide always-on ECTs and at low bandwidth cost. CMTS  120  may proactively schedule Echo Cancellation Training Opportunities (ECTOs) without waiting for ECT requests from echo canceler  130 . ECTOs may be formed explicitly with dedicated mini-slots, or implicitly when a grant is not used or is partially used. For explicit ECTOs, CMTS  120  may restrict an ECTO to one or a few mini-slots at low bandwidth cost. For example, a one-mini-slot ECT may take 0.42% of the spectrum of a 96 MHz FDX US channel. 
     CMTS  120  may achieve channel level ECT, for example, by allocating mini-slot level ECTOs in nearly every frame with different mini-slot offsets relative to the start of the channel spectrum. Echo canceler  130  at RPD  110  may detect ECTOs in time and frequency for constant EC training. 
       FIG. 2  is a flow chart setting forth the general stages involved in a method  200  consistent with an embodiment of the disclosure for providing proactive Echo Cancellation (EC) training. Method  200  may be implemented using echo canceler  130  as described in more detail above with respect to  FIG. 1 . Ways to implement the stages of method  200  will be described in greater detail below. 
     Method  200  may begin at starting block  205  and proceed to stage  210  where a plurality of Echo Cancellation Training Opportunities (ECTOs) may be established. For example, ECTOs may comprise Explicit Echo Cancellation Training Opportunity (EECTOs) and Implicit Echo Cancellation Training Opportunity (IECTOs). 
       FIG. 3  illustrates EECTO scheduling. As shown in  FIG. 3 , an EECTOs may comprise one or more mini-slots reserved for EC training. Mini-slots included in an EECTO may be assigned, for example, to NULL Service Flow Identifier (SID) or a designated SID not used for any US transmissions. 
     CMTS  120  may limit the spectrum overhead by controlling the number of mini-slots included in an EECTO. For example, a 1 mini-slot per frame EECTO may be equivalent to 1/237 (i.e., 0.42%) of an 96 MHz FDX US channel bandwidth (a channel may have 237 mini-slots). EECTOs may be placed at different mini-slots, for example, over consecutive frames. The time to cover a channel may be referred to as an ECT cycle duration. 
     Under fast interference changing conditions, the ECT cycle duration may be reduced with slight increase of the spectrum cost. For example, at a 400 μs frame size, the ECT cycle duration may comprise 94.8 ms (i.e., 400 μs×237) with 1 mini-slot for EECTO per frame (i.e., spectrum overhead=0.42%). However, an ECT cycle duration may comprise 9.48 ms with 10 mini-slots for EECTO per frame (i.e., spectrum overhead=4.2%). 
       FIG. 4  illustrates IECTO scheduling. As shown in  FIG. 4 , an IECTO may comprise an “accidental” ECTO, created whenever there may be a gap between grants or when a grant is not fully used. This may include: i) contention regions in an upstream bandwidth allocation map provided to RPD  110  from scheduler  125 ; ii) guard time for routine DOCSIS operations such as Upstream Channel Descriptor (UCD) change, sounding, and Proactive Network Maintenance (PNM) functions; and iii) unused or partially used data grants when the grant size is bigger than a packet queue size at the CPE. FDX DOCSIS may require a per CPE (e.g., Cable Modem (CM)) grant size to be greater than a minimum grant bandwidth to meet fidelity requirements. Predictive granting for low-latency service may result in frequently unused grants. 
     Consistent with embodiments of the disclosure, IECTOs may complement EECTOs and my provide additional EC training at no extra spectrum overhead cost. Furthermore, CMTS  120  may shift the grant locations, such that the subsequent grants end at different mini-slot offsets in order to cover an entire channel frequency spectrum over time. The potentially unused mini-slots may comprise the remaining mini-slots at the end of a grant after a queue is served. 
     From stage  210 , where the plurality of ECTOs are established, method  200  may advance to stage  220  where echo canceler  130  may identify the plurality of ECTOs. For example, the ECTOs may be referred to as “silent windows” or “quiet periods”. There may be several ways that RPD  110  (e.g., echo canceler  130  in RPD  110 ) may detect silent windows. One way to detect silent windows may be via a special SID. For example, scheduler  125  at CMTS  120  may assign a special SID to mini-slots that may be designated as a silent windows for ECT in the upstream bandwidth allocation map that scheduler  125  may provide to RPD  110 . RPD  110  may parse the upstream bandwidth allocation map to determine where the silent windows are ahead of time. This can be used to identify EECTOs as described above with respect to  FIG. 3 . 
     Another way to detect silent windows may be via power detection. For example, RPD  110  may detect the power of mini-slots at each frame, and based on the detected power, it may determine that there are US signals at the mini-slot. This may be used to identify either EECTOs or IECTOs. 
     Silent window detection via power detection may be described as follows. Echo Cancellation (EC) coefficients, for example, may be determined in the frequency domain for each and every subcarrier (i.e., frequency domain EC). Echoes may be characterized by echo canceler  130  with echo cancellation turned on. For example, echo cancellation may be on once US traffic on the FDX band is turned on. Thus, the EC coefficients may be determined as changes (i.e., deltas) except, for example, in the initial stage where the EC coefficients may be set to zero. 
     For each subcarrier, embodiments of the disclosure may determine the symbol power as follows:
         p=sum(abs(si){circumflex over ( )}2), where si is the symbol level on the subcarrier i, where i=1, 2, . . . N, where N is the frame length.
 
If p&gt;p0i, this subcarrier may be skipped, if &lt;p0i, this may be an empty subcarrier, so its EC coefficients may be determined and updated. Consistent with embodiments of the disclosure, p0i may comprise a pre-determined threshold, for example, for subcarrier i.
       

     With echo cancellation turned on at echo canceler  130 , the Signal-to-Noise (SNR) of the US signal may, for example, be &gt;25 dB, and may, for example, at least be &gt;10 dB. Accordingly, there may be a minimum 10 dB power jump after EC is turned on when there is an US signal. Embodiments of the disclosure may set p0i as the middle value of the average US signal power observed after EC on subc i:
         P0i=N/2*P_ave_i; where P_ave_i is the average US power observed after EC on subc i. N is the frame length.       

     To improve the robustness of silent window detection, the detection may be done on a per mini-slot base. For each mini-slot, embodiments of the disclosure may determine symbol power as follows:
         p1=sum(abs(sij){circumflex over ( )}2), sij is the symbol level on subcarrier i and on symbol j; i=1,2, . . . N,N is the frame length, j=1,2, . . . , M, M is the mini-slot width If p1&gt;p10, skip all the subcarrier in this mini-slot, if p1&lt;p10, this is an empty mini-slot, the EC coefficient may be computed and updated on every subcarrier within this MS. Embodiments of the disclosure may set p10=N/2*P_ave_ms_i′, where P_ave_ms_i′ is the average US power observed after EC on mini-slot i′.
 
Accordingly, silent window detection may involve power detection with minimum overhead.
       

     Compared to the special SID approach, the power detection approach may have many benefits. For example, contention regions may be utilized for ECT. Contention regions may be planned for collision avoidance and low latency, thus the capacity may largely be under-utilized, and most of time the contention regions may have no signals. The power detection approach may detect if there are contention signals, and if not, it may be utilized for ECT. As another example, un-used mini-slots may be utilized for ECT. Some mini-slots may be assigned to an SID (CM), but they may not be used for various reasons (e.g., dropped MAP, scheduler does not schedule them, CM may have no US data, etc.). Those un-used mini-slots may be detected via power detection and used for ECT. As yet another example, power detection approach may be used for both FDX RDP and FDX amplifier. FDX amplifier may not have the capability to parse an upstream bandwidth allocation map. The power detection approach may be feasible for FDX amplifiers. 
     Once echo canceler  130  identifies the plurality of ECTOs in stage  220 , method  200  may continue to stage  230  where echo canceler  130  may conduct Echo Cancellation Training (ECT) for each of the identified ECTOs. For example, EC coefficients may be determined for each subcarrier in a mini-slot within a silent window as coefficient changes (i.e., deltas). Once they are determined, the EC coefficients changes may be used to update EC coefficients used by echo canceler  130  through a rolling or a synchronizing process. With the rolling process, for each mini-slot, once its EC coefficient changes are obtained, embodiments of the disclosure may use them to update the current EC coefficients, and apply the new EC coefficients by echo canceler  130  in the next frame. However, with the synchronizing process, embodiments of the disclosure may wait until the EC coefficients of all the mini-slots have been updated, and apply the new EC coefficients of all the subcarrier at once by echo canceler  130 . The synchronizing approach may reduce data interruptions. After echo canceler  130  conducts ECT for each of the identified ECTOs in stage  230 , method  200  may then end at stage  240 . 
     For FDX systems, embodiments of the disclosure may provide echo cancellation performed in the frequency domain on each subcarrier on each active mini-slot. Embodiments of the disclosure may comprise an echo cancellation training scheme that uses, in an FDX system, EECTOs that may comprise a pattern of mini-slots in two dimension time-frequency space in which the pattern of mini-slots may have equal or close to equal coverage of each active mini-slots and where the pattern of mini-slots may be dynamically adjusted based on channel conditions and per request. 
     In addition, embodiments of the disclosure may comprise an echo cancellation training scheme that uses, in an FDX system, IECTOs that may comprise mini-slots that may be assigned for US traffic, but may not be used by CPEs for US traffic. The IECTOs may include contention regions, un-used mini-slots, and un-assigned mini-slots. Scheduler  125  may schedule US allocation in such a way that these IECTOs may have equal or close to equal coverage of each active mini-slots. 
     Embodiments of the disclosure my provide, for an FDX system, echo canceler  130  that may parse an upstream bandwidth allocation map provided by scheduler  125 , identify EECTOs, and conduct ECT on the identified EECTOs. In addition, embodiments of the disclosure my provide, for an FDX system, echo canceler  130  that may detect the US power of the each subcarrier, tag the subcarrier as an IECTO when the detected power is less than a pre-determined threshold, and conduct ECT on the identified ECT opportunities. Moreover, embodiments of the disclosure my provide, for an FDX system, echo canceler  130  that may detect the US power of each mini-slot, tag the mini-slot as an IECTO when the detected power is less than the pre-determined threshold, and conduct ECT on the identified ECT opportunities. 
       FIG. 5  shows computing device  500 . As shown in  FIG. 5 , computing device  500  may include a processing unit  510  and a memory unit  515 . Memory unit  515  may include a software module  520  and a database  525 . While executing on processing unit  510 , software module  520  may perform, for example, processes for providing proactive Echo Cancellation (EC) training, including for example, any one or more of the stages from method  200  described above with respect to  FIG. 2 . Computing device  500 , for example, may provide an operating environment for RPD  110 , CMTS  120 , scheduler  125 , echo canceler  130 , first CPE  135 , and second CPE  140 . RPD  110 , CMTS  120 , scheduler  125 , echo canceler  130 , first CPE  135 , and second CPE  140  may operate in other environments and is not limited to computing device  500 . 
     Computing device  500  may be implemented using a Wireless Fidelity (Wi-Fi) access point, a cellular base station, a tablet device, a mobile device, a smart phone, a telephone, a remote control device, a set-top box, a digital video recorder, a cable modem, a personal computer, a network computer, a mainframe, a router, a switch, a server cluster, a smart TV-like device, a network storage device, a network relay devices, or other similar microcomputer-based device. Computing device  500  may comprise any computer operating environment, such as hand-held devices, multiprocessor systems, microprocessor-based or programmable sender electronic devices, minicomputers, mainframe computers, and the like. Computing device  500  may also be practiced in distributed computing environments where tasks are performed by remote processing devices. The aforementioned systems and devices are examples and computing device  500  may comprise other systems or devices. 
     Embodiments of the disclosure, for example, may be implemented as a computer process (method), a computing system, or as an article of manufacture, such as a computer program product or computer readable media. The computer program product may be a computer storage media readable by a computer system and encoding a computer program of instructions for executing a computer process. The computer program product may also be a propagated signal on a carrier readable by a computing system and encoding a computer program of instructions for executing a computer process. Accordingly, the present disclosure may be embodied in hardware and/or in software (including firmware, resident software, micro-code, etc.). In other words, embodiments of the present disclosure may take the form of a computer program product on a computer-usable or computer-readable storage medium having computer-usable or computer-readable program code embodied in the medium for use by or in connection with an instruction execution system. A computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. 
     The computer-usable or computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific computer-readable medium examples (a non-exhaustive list), the computer-readable medium may include the following: an electrical connection having one or more wires, a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CD-ROM). Note that the computer-usable or computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory. 
     While certain embodiments of the disclosure have been described, other embodiments may exist. Furthermore, although embodiments of the present disclosure have been described as being associated with data stored in memory and other storage mediums, data can also be stored on or read from other types of computer-readable media, such as secondary storage devices, like hard disks, floppy disks, or a CD-ROM, a carrier wave from the Internet, or other forms of RAM or ROM. Further, the disclosed methods&#39; stages may be modified in any manner, including by reordering stages and/or inserting or deleting stages, without departing from the disclosure. 
     Furthermore, embodiments of the disclosure may be practiced in an electrical circuit comprising discrete electronic elements, packaged or integrated electronic chips containing logic gates, a circuit utilizing a microprocessor, or on a single chip containing electronic elements or microprocessors. Embodiments of the disclosure may also be practiced using other technologies capable of performing logical operations such as, for example, AND, OR, and NOT, including but not limited to, mechanical, optical, fluidic, and quantum technologies. In addition, embodiments of the disclosure may be practiced within a general purpose computer or in any other circuits or systems. 
     Embodiments of the disclosure may be practiced via a system-on-a-chip (SOC) where each or many of the components illustrated in  FIG. 1  may be integrated onto a single integrated circuit. Such an SOC device may include one or more processing units, graphics units, communications units, system virtualization units and various application functionality all of which may be integrated (or “burned”) onto the chip substrate as a single integrated circuit. When operating via an SOC, the functionality described herein with respect to embodiments of the disclosure, may be performed via application-specific logic integrated with other components of computing device  500  on the single integrated circuit (chip). 
     Embodiments of the present disclosure, for example, are described above with reference to block diagrams and/or operational illustrations of methods, systems, and computer program products according to embodiments of the disclosure. The functions/acts noted in the blocks may occur out of the order as shown in any flowchart. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     While the specification includes examples, the disclosure&#39;s scope is indicated by the following claims. Furthermore, while the specification has been described in language specific to structural features and/or methodological acts, the claims are not limited to the features or acts described above. Rather, the specific features and acts described above are disclosed as example for embodiments of the disclosure.