WO2020069646A1

WO2020069646A1 - Computing cyclic prefix length and receiver windowing length using ingress conditions in an ofdm system

Info

Publication number: WO2020069646A1
Application number: PCT/CN2019/092177
Authority: WO
Inventors: Syed Rahman; Sanjay Gupta
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2018-10-03
Filing date: 2019-06-21
Publication date: 2020-04-09

Abstract

The disclosure relates to technology for selecting a cyclic prefix length and a downstream receiver window length in an OFDM signal of a cable modem termination system (CMTS). The CMTS receives ingress statistics for one or more ingress signals collected by one or more cable modems. A cyclic prefix length for downstream signal transmissions to the one or more cable modems is selected based on the collected ingress statistics, and an OFDM signal is transmitted to the one or more cable modems using the selected cyclic prefix length.

Description

COMPUTING CYCLIC PREFIX LENGTH AND RECEIVER WINDOWING LENGTH USING INGRESS CONDITIONS IN AN OFDM SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefit of U.S. Provisional Application No. 62/740,786, filed on October 3, 2018, entitled “Computing Cyclic Prefix Length and Receiver Windowing length Using Ingress Conditions in an OFDM System, ” which application is hereby incorporated by reference.

FIELD

The disclosure generally relates to detection of signal ingress in a cable network, and in particular, to determining a cyclic prefix and windowing length based on the signal ingress in a cable network.

BACKGROUND

Operators of cable television systems, also known as Multiple Service Operators (MSOs) , continuously make attempts to offer faster service to meet customer demand and competition for better service, yielding higher peak rates year after year. Data Over Cable Service Interface Specification (DOCSIS) is a cable communication standard developed to permit the addition of high-bandwidth data transfers to an existing cable television (CATV) system. It is employed internationally by many cable television operators to provide, for example, internet access over existing infrastructures, such as a hybrid fiber-coaxial (HFC) infrastructure.

The DOCSIS standard uses conventional modems to provide gateway access to the internet. In the latest version of the standard, DOCSIS 3.1 purports to support capacities of at least 10 Gbit/sdownstream and 1 Gbit/supstream using 4096 quadrature amplitude modulation (QAM) . The new standard uses 6 and 8 MHz wide channel spacing and instead uses smaller (25-50 kHz wide) orthogonal frequency-division multiplexing (OFDM) subcarriers. The OFDM subcarrier can be bonded inside a block spectrum that can be about 200 MHz wide.

BRIEF SUMMARY

According to one aspect of the present disclosure, there is provided a method of selecting a cyclic prefix length and a downstream receiver window length in an OFDM signal of a cable modem termination system (CMTS) , comprising the CMTS receiving ingress statistics for one or more ingress signals collected by one or more cable modems; the CMTS selecting the cyclic prefix length for downstream signal transmissions to the one or more cable modems based on the collected ingress statistics; and the CMTS transmitting the OFDM signal to the one or more cable modems using the selected cyclic prefix length.

Optionally, in any of the preceding aspects, the method further includes the CMTS calculating the downstream receiver window length based on the collected ingress statistics, wherein the selecting the cyclic prefix length for downstream signal transmissions includes the CMTS calculating the cyclic prefix length based on the downstream receiver window length.

Optionally, in any of the preceding aspects, selecting the cyclic prefix length is based on collected channel impulse responses, egress statistics and ingress statistics.

Optionally, in any of the preceding aspects, a power spectrum encompassing expected ingress signal power levels is sub-divided into a series of power bins for classifying power levels of ingress signal occurrences.

Optionally, in any of the preceding aspects, the collection of the ingress statistics by the one or more cable modems comprises recording a power level of each ingress signal at the one or more cable modems with respect to an average signal power level; and classifying an ingress signal of the one or more ingress signals into a corresponding power bin of a series of power bins based on a recorded power level for the ingress signal, wherein a power spectrum encompassing expected ingress signal power levels is sub-divided into the series of power bins for classifying power levels of ingress signal occurrences.

Optionally, in any of the preceding aspects, the method further comprising the CMTS discarding each of the ingress statistics having a power level outside of the power bin ranges.

Optionally, in any of the preceding aspects, the method further comprising the CMTS requesting the ingress statistics collected by the one or more cable modems, and the CMTS sending the downstream receiver window length to the one or more cable modems.

Optionally, in any of the preceding aspects, the ingress statistics are determined based on collected ingress signal occurrences in each bin of the series of power bins.

Optionally, in any of the preceding aspects, the method further comprising the CMTS generating a histogram using the classified ingress signals in each power bin to calculate an average ingress power level and a number of ingress signals for each of the power bins.

Optionally, in any of the preceding aspects, the method further comprising the CMTS calculating the receiver window length for the downstream includes the CMTS determining a number of ingress signals, the CMTS determining a power level of each of the ingress signals, and the CMTS determining a signal-to-noise ratio in the one or more cable modems.

Optionally, in any of the preceding aspects, the method further comprising the CMTS computing an upstream receiver window length and an upstream cyclic prefix length using the ingress statistics.

According to still one other aspect of the present disclosure, there is a device for selecting a cyclic prefix length and receiver window length in an OFDM signal, comprising a non-transitory memory storage comprising instructions; and one or more processors in communication with the memory, wherein the one or more processors execute the instructions to receive ingress statistics for one or more ingress signals collected by one or more cable modems; select the cyclic prefix length for downstream signal transmissions to the one or more cable modems based on the collected ingress statistics; and transmit the OFDM signal to the one or more cable modems using the selected cyclic prefix length.

According to still one other aspect of the present disclosure, there is a non-transitory computer-readable medium storing computer instructions for selecting a cyclic prefix length and receiver window length in an OFDM signal, that when executed by one or more processors, cause the one or more processors to perform the steps of receiving ingress statistics for one or more ingress signals collected by one or more cable modems; selecting the cyclic prefix length for downstream signal transmissions to the one or more cable modems based on the collected ingress statistics; and transmitting the OFDM signal to the one or more cable modems using the selected cyclic prefix length.

According to still one other aspect of the present disclosure, there is method of selecting a cyclic prefix length and receiver window length in an OFDM signal of a cable modem termination system (CMTS) , comprising receiving ingress statistics for one or more ingress signals collected by the CMTS; and computing an upstream receiver window length and an upstream cyclic prefix length using the ingress statistics.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the Background.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are illustrated by way of example and are not limited by the accompanying figures for which like references indicate elements.

FIG. 1 illustrates an example communications system.

FIG. 2 illustrates an example cable modem termination system (CMTS) .

FIG. 3 is a block diagram of an example transmitter of a conventional OFDM system using a windowing and overlap scheme.

FIG. 4A illustrates a signal experiencing micro-reflection at a receiver. Cyclic prefix (CP) and windowing may be applied in the upstream transmission.

FIGS. 4B and 4C illustrate generation and placement of a cyclic prefix (CP) in an OFDM symbol.

FIG. 5A illustrates a table of cyclic prefix values converted into a number of samples.

FIG. 5B illustrates a table of roll-off period values.

FIG. 6A illustrates a block diagram for constructing a histogram according to an example embodiment.

FIG. 6B illustrates ingress statistics grouped into buckets.

FIG. 7 is a flowchart of a process to select a cyclic prefix and receiver window length.

FIG. 8 is a block diagram of a network processing device that can be used to implement various embodiments of a CMTS in accordance with the present technology.

DETAILED DESCRIPTION

The present disclosure will now be described with reference to the figures, which in general relate to selection of a cyclic prefix (CP) length and receiver window length in an OFDM communication system.

In telecommunications, the term cyclic prefix (CP) refers to the prefixing of a symbol which acts as a buffer region (or guard interval) to protect an OFDM signal from and eliminate both inter-symbol interference (ISI) and inter-carrier interference (ICI) . In eliminating ISI and ICI, the cyclic prefix compensates for the effect of multi-path dispersion, but also consumes scarce spectrum and power resources. Conventional OFDM systems use a fixed (or variable) and large cyclic prefix length that takes into consideration worst-case channel conditions. This causes a loss in bandwidth efficiency and consumes more transmitter energy. Accordingly, in order to optimize system capacity and improve overall system performance, an optimal cyclic prefix should be selected. In the disclosed technology, a mechanism collects ingress signal leakage or noise, referred to herein as ingress statistics. These ingress statistics may be based on, for example, some or all of a random selection of a number of ingress occurrences (e.g., an integer from 1 to 48) , power levels of the ingresses (e.g., an integer from -3 to +20 dBc) , a width (or time duration) of the ingresses (e.g., an integer from 1 OFDM subcarrier to 6 OFDM subcarriers) , or system signal-to-noise ratio (SNR) (e.g., an integer from 25 to 45 dB) . The ingress statistics may be collected in a predefined format in the upstream or downstream transmissions of a communications system (e.g., using a series of power bins, which can be represented as a histogram, for example) . An optimal cyclic prefix length and/or receiver window length may then be calculated based on the collected ingress statistics.

It is understood that the present embodiments of the disclosure may be implemented in many different forms and that claim scope should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the inventive embodiment concepts to those skilled in the art. Indeed, the disclosure is intended to cover alternatives, modifications and equivalents of these embodiments, which are included within the scope and spirit of the disclosure as defined by the appended claims. Furthermore, in the following detailed description of the present embodiments of the disclosure, numerous specific details are set forth in order to provide a thorough understanding. However, it will be clear to those of ordinary skill in the art that the present embodiments of the disclosure may be practiced without such specific details.

As introduced in DOCSIS 3.1, orthogonal frequency division multiple access (OFDMA) is a manner of encoding digital data on multiple carrier frequencies, i.e., a plurality of subcarriers. The available bandwidth of an OFDMA channel may be divided into many narrow bands for transmitting data on these bands (subcarriers) in parallel, where the signals transmitted are mathematically orthogonal. Data is carried over the subcarriers by varying the phase or amplitude of each subcarrier (e.g., QPSK, 4-QAM, 16-QAM, 64-QAM, etc. ) .

OFDMA may be used in any data transmission, including applications such as digital television and audio broadcasting, Digital Subscriber Line (DSL) internet access, wireless networks, and 4G mobile communications. OFDMA is useful for many solutions, including, by way of example but not limited to, asymmetric digital subscriber loop (ADSL) and very high speed digital subscriber line (VDSL) broadband access via plain old telephone service (POTS) or public switched telephone network (PSTN) copper wiring, digital video broadcasting-cable (DVB-C) , e.g., DVB-C2, power line communication (PLC) , International Telecommunications Union (ITU) Telecommunications Standardization Sector (ITU-T) implementations, e.g., ITU-T G. hn high speed local area networking, Multimedia over Coax Alliance (MOCA) , DOCSIS, and others.

A typical DOCSIS architecture includes a cable modem (CM) located at the customer premises and a cable modem termination system (CMTS) located at the CATV headend. A more detailed description of such a system is described below with reference to FIG. 1. DOCSIS provides a variety of options available at Open Systems Interconnection (OSI) layers 1 and 2, the physical layer, and the data link layer. A DOCSIS physical layer may include the basic networking hardware transmission technologies of a network. A DOCSIS physical layer defines the means of transmitting raw bits rather than logical data elements over a physical link connecting network nodes. The bit stream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a hardware transmission medium. The modulation schemes available for use and similar low-level parameters are defined by the DOCSIS scheme.

The evolving DOCSIS 3.1 platform employs OFDM and OFDMA subcarriers for RF transmission, as noted above, where the frequency-division multiplexing (FDM) scheme is used as a multi-carrier modulation method using multiple subcarrier signals that are orthogonal to each other. For example, a large number of closely spaced orthogonal subcarriers may be used to carry data on several parallel data streams or channels. Using orthogonal subcarriers minimizes or eliminates cross-talk between the sub-channels and inter-guard bands are not required i.e., the separate filter for each sub-channel is not required as it is in frequency division multiplexing (FDM) .

OFDM is used by most modern terrestrial transmission methods (mobile radio and terrestrial TV) , and is a complex modulation method that uses a number of narrowband subcarriers. All subcarriers are transmitted simultaneously, called the OFDM symbol. The OFDM symbols are broken up with a guard interval, known as the afore-mentioned cyclic prefix (CP) . The transmit signal is the sum of a number of digitally modulated carriers. Compared to the single carrier modulation, the subcarriers are transmitted with a relatively long symbol duration (FFT duration) . In OFDM, a single user transmits on all subcarriers at any given time. To support multiple users, time and/or frequency division access techniques may be employed. OFDMA, on the other hand, allows multiple users to transmit simultaneously on different sub-carriers per OFDM symbol.

Generally in DOCSIS 3.1, OFDMA is used in the upstream (US) and OFDM is used in the downstream (DS) . For the DS, OFDM subcarriers in a channel are generated in a single transmitter, which makes the generation of orthogonal subcarriers relatively simple. For the US, different CMs serving as transmitters each generate a subset of the subcarriers for an OFDM symbol. The subsets are not combined into a complete OFDM until they reach the receiver input at the CMTS. This is known as OFDMA. The individual CMs are frequency synchronized, as the individual carriers would otherwise lose their orthogonality.

The latest version DOCSIS 3.1 provides a leap in technology to offer larger bandwidth and faster data rates in both the US (upstream) and DS (downstream) transmissions. A cable modem US transmission uses OFDMA for data transmission, which allows a high volume of users to share the whole band at the same time. Each user occupies a set of sub-carriers for the US data transmission.

FIG. 1 illustrates an example communication system 100. The communication system 100, such as a cable television system, provides one or more of commercial TV services, Internet data services, and voice services, e.g., Voice-over-Internet Protocol (VoIP) to one or more customer locations (i.e., end users) in a given geographic area. The communications system 100 may include a cable headend transmitter 110 that provides service to a set-top box (STB) 120 or cable modem CM1-CMn 132 via cable network segment (CNS) 130. The STB 120 provides output to a display device (or display capable device) 135, such as a television, smart phone, tablet, augmented or virtual reality device, etc. Similarly, the cable modems CM1-CMn 132 may also provide output to a user device, such as a television, smart phone, tablet, augmented or virtual reality device, etc. The cable headend transmitter 110 can support any of a number of service flows such as audio, video, local access channels, as well as any other service of cable systems. For example, the cable headend transmitter 110 can provide media (e.g., video and/or audio) to the display device 135.

The cable headend transmitter 110 may provide operation of a cable modem termination system (CMTS) 125. For example, the cable headend transmitter 110 may perform such CMTS functionality. In one embodiment, the CMTS 125 may be implemented separately from the cable headend transmitter 110. The CMTS 125 can provide network service (e.g., Internet, other network access, etc. ) to any number of cable modems CM1, CM 2 to CMn 132 via the CNS 130 (which may also serve as a cable modem network segment, as part of the CNS or separately) . In one embodiment, the CNS 130 couples the cable modems CM1-CMn 132 to the CMTS 125. Such a cable system (e.g., CNS 130) may generally be referred to as a cable plant and may be implemented, at least in part, as a hybrid fiber-coaxial (HFC) network (e.g., including various wired and/or optical fiber communication segments, light sources, light or photo detection complements, etc. ) .

Although the disclosed embodiment discusses cable modems, other network elements may also be employed in the system. For example, other network elements (not shown) may include set top boxes (shown as STB 120) , televisions equipped with set top boxes, data over cable service interface specification (DOCSIS) terminal devices, media terminal adapters (MTA) , and the like. Thus, where reference is made to a cable modem, the concepts also apply more broadly to alternate types of network elements. Moreover, in the disclosed embodiment, the CMTS 125 and cable modems CM1-CMn 132 operate in accordance with a DOCSIS protocol or other cable modem protocol that employs OFDM modulation on the downstream link from the CMTS 125 and the cable modems CM1-CMn 132 and further the upstream link from the cable modems CM1-CMn 132 to the CMTS 125.

The CMTS 125 is a component that exchanges digital signals with cable modems CM1-CMn 132 on the CNS 130. Each of the cable modems 132 is coupled to the CNS 130. In one embodiment, a number of elements may be included within the CNS 130, such as routers, splitters, couplers, relays, and amplifiers. Generally speaking, when information is being communicated, downstream (DS) information may be viewed as data that flows from the CMTS 125 to the connected cable modems CM1-CMn 132 and upstream (US) information as data that flows from the cable modems 132 to the CMTS 125.

The CMTS 125 forms an interface to IP-based networks over the Internet, and modulates the data from the Internet (downstream modulator) for transmission to homes and receives the upstream data from homes (upstream demodulator) . The CMTS additionally manages the load balancing, error correction parameters and the class of service (CoS) . The CoS management makes it possible to assign higher priority to specific CMs. It should be noted that there are multiple embodiments of a CMTS architecture, such as a CMTS with a physical (PHY) layer and a MAC layer. The MAC layer is software responsible for arranging the signal transmission sequence, setting parameters (e.g., cyclic prefix) length and programmable logic. The PHY layer is responsible for modulating the transmitted data, demodulating the received data and other logic built in the hardware.

The cable modems CM1-CMn 132 may be connected through the network 130 to the CMTS 125. The cable modems CM1-CMn 132 convert signals received from the CMTS 125 carried over fiber and/or coaxial lines in the network. In the upstream direction, the cable modems CM1-CMn 132 may convert digital data to a modulated RF signal for upstream transmission. In the downstream direction, the cable modems CM1-CMn 132 may convert received downstream RF signals to digital form. For example, in the downstream, the cable modems CM1-CMn 132 demodulate the downstream RF signal and feed the digital data to the IPTV server 116, for example. On the return path, in the upstream direction, digital data is fed to the cable modem CM1-CMn 132, which converts it to a modulated RF signal for upstream transmission. Once the CMTS 125 receives the upstream RF signal, it demodulates it and transmits the digital data to its eventual destination.

To provide the above noted services, such as commercial TV services, Internet data service and voice services, the cable headend transmitter 110 may be communicatively coupled via the CDN 115 to one or more content providers 105, an IPTV server 116, and/or a public switched telephone network (PSTN) 117. In one embodiment, the content providers 105 may be the source of media content (e.g., movies, television channels, etc. ) .

The content delivery network 115 may be a cable data network such as an all-coaxial or a hybrid-fiber/coax (HFC) network. Of course, other broadband access networks such as xDSL (e.g., ADSL, ADLS2, ADSL2+, VDSL, and VDSL2) and satellite systems may also be employed. In embodiments, the content delivery network 115 comprises, for example, a packet-switched network that is capable of delivering IP packets or data elements from an IPTV Server 116 to CM1-CMn 132, using, for example, a cable data network, a passive optical network (PON) , or the like. Examples of a content delivery network 115 include networks comprising, for example, managed origin and edge servers or edge cache/streaming servers.

The cable headend transmitter 110 may be communicatively coupled to the IPTV server 116 and the PSTN 117 via the CDN 115, e.g., the Internet, for providing Internet and telephony services (e.g., to and from CM1-CMn 132) via the CMTS 125. The CMTS 125, in an embodiment, is a general-purpose computing device or application-specific integrated circuit (ASIC) that converts downstream digital data to a modulated RF signal, which is carried over the fiber and coaxial lines in the communication system 100 to one or more cable modems CM1-CMn 132.

FIG. 2 illustrates an example Cable Modem Termination System (CMTS) 125. The CMTS 125 may be include a variety of different modules or components, for example, a routing module 220, a forwarding module 222, DOCSIS control 224, and a line card 226. In example embodiment, the routing module 220 and the DOCSIS control 224 may be part of a control plane, while the forwarding module 222 and the line card 226 may be part of a data plane.

The routing module 220 may implement routing or forwarding operations, and may be configured to provide layer one, layer two, layer three, and layer four functionality, as well as quality of service (QoS) functionality. In one embodiment, routing module 220 may be configured as a processor-based routing system including functionality incorporated within a typical router. For example, as shown, routing module 220 includes a processor (s) 230 and memory (not shown) . In another embodiment, the routing module 220 may construct and load routing tables used by the forwarding module 222.

Routing module 220 may also perform configuration management functions, and communicate with neighboring peers, standby, and/or backup routers to exchange protocol data units used to construct the routing tables in accordance with routing algorithms. Additionally, other memory types, including various computer readable media, may be used for storing and executing program instructions pertaining to the operation of routing module 220.

The forwarding module 222 may comprise a processor (s) 234 and memory (not shown) for handling transport layer and network layer functionality. Forwarding module 222 may also provide packet-forwarding operations, as well as provide transaction compacting functionality, data parcel tunneling functionality, data transmission functionality, etc.

Line card 226 may implement a DOCSIS functionality, such as, for example, a DOCSIS MAC functionality. In an embodiment, DOCSIS control 224 may send timing and frequency requirements to line card 226. DOCSIS control 224 may also include a processor 232 and memory (not shown) . In one embodiment, as shown, line card 226 may provide functions on several network layers, including a physical layer and a MAC layer. The physical layer may be responsible for receiving and transmitting radio frequency (RF) signals. Hardware portions of the physical layer may include at least one upstream PHY, such as upstream PHY 240 and/or at least one downstream PHY, such as downstream PHY 242. The physical layer may also include software for driving the hardware components of the physical layer.

In an embodiment, upstream optical data signals (traffic) arriving via an optical fiber node are converted to electrical signals and then demodulated by upstream PHY 240. The demodulated information is then passed to the MAC layer. In one example, the MAC layer includes both a MAC hardware portion and a MAC software portion for upstream MAC 236 and downstream MAC 238. The MAC layer software portion may include software relating to DOCSIS MAC functionality. The MAC layer hardware and software portions can operate together to provide the DOCSIS MAC functionality.

In an embodiment, the MAC layer (MAC 236 and 238) may encapsulate, with MAC headers, downstream packets at downstream MAC 238 and decapsulate, the MAC headers, upstream packets at upstream MAC 236. The encapsulation and decapsulation processes may proceed for transmission of data or other information. The MAC headers may include addresses to specific modems (if sent downstream) , or to the CMTS (if sent upstream) . In other embodiments, cable modems, such as CM1-CMn (FIG. 1) may also include MAC addressing components. In the cable modems CM1-CMn, these components may encapsulate upstream data with a header containing the MAC address of the CMTS 125.

Upstream MAC 236 may pass the traffic to backplane 228. Backplane 28 may include the appropriate hardware and/or software for converting data formats received at the line card 226 to a suitable protocol format for transmission from the line card 226 to forwarding module 222. In the disclosed embodiment, backplane 228 is shown as coupled to the respective interface circuitry of line card 226 and forwarding module 222. For example, backplane 228 may pass traffic to downstream MAC 238 from forwarding module 222.

Downstream MAC 238 transmits information to downstream PHY 242. Downstream PHY 42 takes the traffic (or other information) in a packet structure and converts it to modulated downstream frames on the downstream carrier using, for example, QAM64 modulation. Other methods of modulation may also be used, for example, QAM256 modulation, Code Division Multiple Access (CDMA) , Orthogonal Frequency Division Multiplexing (OFDM) , FREQ Shift Keying (FSK) , etc. The return data is likewise modulated using, for example, QAM16 or QSPK. According to one embodiment, the modulated data is converted from intermediate frequency (IF) electrical signals to radio frequency (RF) electrical signals (or vice-versa) using one or more electrical signal converters (not shown) .

Additionally, line card 226 may include an upstream scheduler 244 that arbitrates bandwidth requirements among multiple cable modems CM1-CMn 132, and a map builder 246 to transmit a bandwidth allocation map containing upstream slot specifications and grant specifications to cable modems.

Although not depicted in the figure, line card 226 may also include a central hardware block including one or more processors and memory. These hardware components interact with software and other hardware portions of the various layers within the line card 226 to provide general purpose computing power for much of the software. The memory may include, for example, I/O memory (e.g., buffers) , program memory, shared memory, etc. One or more data structures used for implementing the technique of the present disclosure may reside in such memory. In one embodiment, the software entities are implemented as part of a network operating system running on hardware. In one embodiment, at least part of the functionality of the various embodiments are implemented in software as part of the operating system.

FIG. 3 is a block diagram of an example transmitter of a conventional OFDM system using a windowing and overlap scheme. Typically, and as noted above, conventional communication systems use OFDM or OFDMA based modulation techniques to multiplex signal traffic from mobile stations, in both the frequency and time domains. Each OFDM symbol may comprise an inverse fast Fourier transform (IFFT) symbol, which is the result of an IFFT operation on a modulation data sequence. The OFDM symbol may also comprise a cyclic prefix (CP) , which is typically a repetition of the last portion of the associated IFFT symbol, and is typically inserted before the IFFT symbol. The OFDM symbol may also comprise windowing sections, to shape the modulation pulse such that the radio spectrum of the transmitted signal meets emission mask requirement set forth by a radio regulatory body, such as the Federal Communication Commission (FCC) .

In an exemplary communications system, such as communication system 100, a fixed cyclic prefix having a length N _CP, is prepended to a symbol of N samples. The CP serves as a guard interval that reduces or eliminates inter-symbol interference (ISI) and facilitates modeling linear convolution of a frequency-selective multipath channel as circular convolution, which in turn may be transformed to the frequency domain using a discrete Fourier transform. Since the CP includes redundant data, the transmission of the CP consumes bandwidth, which reduces a realizable data rate for the communications system. Thus, the choice of length for the CP is a compromise between efficiency and performance (e.g., bit error rate) of the communications system.

In conventional communications system, the length of the CP may be determined prior to system implementation, based on a predicted channel length and a target data rate. Once the system is deployed, the length of the CP is fixed. However, an approximation for a length of the actual channel that provides target performance may be shorter than the predicted fixed channel length, making a fixed CP length longer than necessary, which unnecessarily reduces the data rate. A technique to increase throughput over particular channels includes implementing a variable CP length. A CP length is selected according to actual channel conditions, which allows reduction of the CP length from a maximum length. A continued description of CP and windowing may be found below with reference to FIGS. 4A and 4B.

Turning to the illustration, a transmitter 300 is disclosed according to an embodiment. When information bits 302 are received at the transmitter 300, the information bits 302 are passed to a channel coding module 304 configured to implement channel coding. A symbol mapping module 306 maps the encoded bits (received from the channel coding module 304) to constellation points, e.g., the symbol mapping module 306 maps encoded bits to transmission symbols according to a suitable modulation scheme such as binary phase shift keying (BPSK) , quadrature amplitude modulation (QAM) , etc. The resulting constellation points are provided from the symbol mapping module 306 to a serial-to-parallel module 308 that parses the constellation points to different inputs of an IDFT module 310. The IDFT module 310 performs an Inverse Discrete Fourier Transform (IDFT) , e.g., an inverse fast Fourier transform (IFFT) . The different inputs of the IDFT module 310 correspond to different OFDM sub-channels.

An output of the IDFT module 310 is provided to a parallel-to-serial module 312 that generates a time-domain signal. The output of the parallel-to-serial module 312 is provided to a cyclic prefix module 314 which adds a CP to the time-domain signal. The output of the cyclic prefix module 314 is provided to a windowing module 316. A windowing function is applied by the windowing module 316 and provided to a DAC 318. An analog representation of the OFDM symbol is generated by a digital-to-analog converter (DAC) 318. The output OFDM symbol 320 may then be transmitted by transmitter 300, wherein the transmitter 300 comprises a component included in any of the devices in communication system 100 of FIG. 1, for example.

In one embodiment, since the windowing function is applied in the time domain (e.g., after the IFFT) , in such a conventional system, the windowing function is the same for all the subcarriers in the time domain signal. In other words, the transition period corresponding to the windowing function is the same for all the subcarriers in the time domain signal.

FIG. 4A illustrates a signal experiencing micro-reflection at a receiver. CP and windowing may be applied in the upstream transmission. As depicted by the upper signal in the figure, the CP is constructed by repeating an end of the OFDM symbol 320 and adding it to the front of each symbol to form a guard interval. The lower signal in the figure represents an echo in the upper signal. A portion of an echo from a previous signal is called inter-symbol interference (ISI) . The CP is added in order to enable to receiver to overcome the effects of the ISI that is caused by micro-reflections in the channel between the transmitter and receiver. An example of a transmitter and receiver may be found in FIG. 3, as described above. Windowing is applied in order to maximize channel capacity by sharpening the edges of the spectrum of the OFDM signal. Spectral edges occur at the two ends of the spectrum of the OFDM symbol 320, as well as at the ends of internal exclusion bands.

When micro-reflection is present in the transmission medium, the received signal (the lower signal in the figure) is the sum of the main signal and the delayed (T) and attenuated micro-signal. As long as the delay (t) is less than the time duration of the cyclic prefix T _CP, the CMTS 125 (FIGS. 1 and 2) receiver can trigger the FFT to avoid any ISI or ICI due to the micro-reflection. If the delay (t) of the micro-reflection exceeds the length of the CP, the ISI resulting from the micro-reflection is:

where t is the delay introduced by the micro-reflection, T _CP is the CP length in μs, A is the relative amplitude of the micro-reflection, and T _U is the FFT duration. The ICI introduced by the micro-reflection is of the same order as the ISI, where the cable modems CM1-CMn and the CMTS 125 support the CP values defined in FIG. 5A, described below.

FIGS. 4B and 4C illustrate generation and placement of a cyclic prefix (CP) in an OFDM symbol. FIG. 4B shows the received OFDM symbol after demodulation, as an N-point IDFT output 420. As explained above, an OFDM modulation scheme having an available spectrum is divided into a plurality of narrowband sub-carriers (e.g., lower data rate carriers) . Typically, the frequency responses of these sub-carriers are overlapping and orthogonal. Each sub-carrier may be modulated using any of a variety of modulation coding techniques.

OFDM modulation operates by performing simultaneous transmission of a larger number of narrowband carriers (or multi-tones) . Oftentimes a guard interval or guard space is also employed between the various OFDM symbols to try to minimize the effects of ISI that may be caused by the effects of multi-path within the communication system (which can be particularly of concern in wireless communication systems) . In addition, a CP may also be employed within the guard interval to allow switching time (when jumping to a new band) and to help maintain orthogonality of the OFDM symbols.

In DOCSIS 3.1, in order to generate and place the CP in the OFDM symbol, each of the symbols of the downstream OFDM sub-layers include a CP for synchronization and mitigation of signal artifacts (such as multipath and micro-reflections) that may arise for example due to slight impedance mismatches at locations along a cable distribution system. The CP, as illustrated, is added to each symbol near the end of the transmission process, after the payload portion of a symbol has been converted to a time-domain sequence of N (e.g., 4096 or 8192) samples by the IDFT 310 (FIG. 3) . The last N _CP samples of each symbol are copied and inserted before the first sample of that symbol payload, as the CP (see arrow in the lower representation) . The N-point IDFT output420 is now of length N + N _CP, where N _CP is not of a predetermined, fixed length. This CP provides a degree of redundancy in the transmitted signal from which correct symbol reception can be determined.

To optionally allow for windowing, which reduces the out-of-band spectrum occupied by the OFDM signal, as defined by the DOCSIS 3.1 specification, a number of samples N _RP may be copied. The samples N _RP are copied from the beginning of each symbol and appended after the last sample of that symbol, as shown in FIG. 4C. This is referred to as the roll-off period, and is explained further below with reference to FIG. 5B.

In FIG. 5A, the CP is converted into a number of samples (N _RP) using a sample rate of 102.4 Msamples/s, and windowing is then applied in the time domain by tapering (or rolling-off) the edges using a raised cosine function. The cable modems CM1-CMn 132 and the CMTS 125 support the roll-off period values defined in FIG. 5B. Additionally, the CMTS 125 allows a configuration in which the roll-off period value is smaller than the CP value (N _RP<N _CP) , except for initial ranging transmissions. As illustrated, the roll-off period is provided in μs and in a number of samples using the sample rate of 102.4 Msamples/s. This allows some of the CP to be retained after windowing, to aid in synchronization and mitigation of multipath effects. In fact, the amount by which N _CP exceeds N _RP determines the range of received multipath that can be mitigated based upon the maximum time differential. This is a trade-off against throughput efficiency of the data stream, wherein the throughput efficiency is reduced by increasing the value of N _CP (thereby increasing a total symbol length) . This is why the cable system operator is given a range of values for these parameters, to be able to adjust throughput efficiency in relation to an acceptable multipath mitigation effect. In an embodiment, zero is a permitted option for the roll-off period.

FIG. 6A is a block diagram for constructing a histogram according to an example embodiment. A histogram (or empirical cumulative distribution) is a graphical representation of a distribution of data samples. That is, a histogram may graphically represent an estimated result size for a particular query of a database. For example, to estimate the result size of a predicate having a range, an estimation routine can be employed to identify “buckets” or “bins” (i.e., histogram components) having boundaries that intersect with that range. Then, using any number of known approximation formulas, the routine estimates the number of values in each identified bucket or bin that satisfy the range predicate, along with the frequency of each such value. These frequencies are summed over the identified buckets or bins to yield the estimate of the result size.

In one embodiment, the histogram may be constructed by CMTS 125 by creating a single histogram using histograms created and reported by individual CMs CM1-CMn 132. This single histogram may be, in one example, an average of all the histograms reported by the CMs CM1-CMn 132. In one other embodiment, the single histogram may be an average of histograms from one or more CMs 132, representing the cases of severe ingress statistics. In one other embodiment, the CMTS 125 may compute a separate receiver windowing length based upon the histogram of each of the CMs CM1-CMn 132. The CMTS 125 may compute a single windowing length based on an averaging or software processing of the windowing lengths of all the CMs 132. For example, a mean averaging or a weighted averaging with different weights for each CM CM1-CMn 132 may be used, such that the sum of the weights will be equal to one.

Construction of a histogram can include, for example, sampling attributes in a column of a database on a server, and then determining a bucket or bin set for the histogram based on a number of buckets or bins that represent a distribution of the attributes with minimum error. Each of the buckets or bins in the bucket or bin set include boundaries and an approximation of a count of attributes falling within the boundaries. In one embodiment, construction further includes determining a precision for encoding the approximation, such that the histogram having the bucket or bin set fits within a storage limit, e.g. for storage on a tangible computer-readable medium. In this regard, the histogram can then be stored for the database on a tangible computer-readable medium by encoding the approximation with the precision. Once constructed, a histogram can be stored for use in query-related operations. For example, a database system catalog can include one or more histograms constructed from tables in the database. The histogram can be reconstructed or otherwise updated to reflect changes in database.

In the embodiment illustrated in FIG. 6A, a histogram analysis and creator 602 collects ingress statistics, such as number of ingress occurrences (or ingress signals) and the power and width of each ingress. Ingress statistics may be caused by one or more sources including, but not limited to, analog TV sync signals, power line ingress, and RF ingress entering a cable through a delaminated cable shielding. For example, in cable shielding, the detection of flaws may be achieved through detection of the signal carried by the cable transmission system that has leaked into the environment, essentially by being broadcast from the shield flaw.

In one embodiment, ingress statistics (i.e., noise or leakage) may be detected using a monitoring device (not shown) that is coupled to a location or device that is receiving the signal. As signals are detected, the monitoring device may determine spectral and repetitious properties of ingress statistics, for example. The monitoring device may be part of the histogram analysis and creator 602, or otherwise may comprise a part of any system component that receives and/or transmits an ingress signal. For example, the monitoring device may be located in the CMTS 125 or within any one or more of the CMs CM1-CMn 132. The monitoring device may, for example, monitor and detect ingress signals using a signal processor, such as a digital signal processor (DSP) , along with RF detectors. For example, received ingress signals may be monitored according to set parameters, either in the time domain, such as amplitude and pulse shape analysis, or in the frequency domain, such as FFT spectrum analysis technique, and compared to threshold data to determine various ingress noise.

In another embodiment, the threshold data may be determined based on well-known general characteristics of an ingress occurrence type, the specific characteristics of an ingress for the specific cable plant, or a combination of the two. Such thresholds may change over the course of time, depending on the characteristics of the cable plant and the services in place. The monitored ingress signals, in one embodiment, may be stored in an ingress database (not shown) to compare against the threshold data as an indication of unacceptable levels of noise. Additionally, historical ingress data that has been previously collected may be used to determine the threshold or may be used in combination with the aforementioned techniques.

In one embodiment, the power level at each ingress is recorded in dBc by the histogram analysis and creator 602 with respect to an average signal power level (which may also be used as a threshold) . For example, the ingress power level may be monitored to determine whether the ingress power level equals or exceeds the average signal power level or remains less than the average power level. As explained above, the collected ingress statistics may be grouped into pre-defined ingress signal power level buckets or bins, based upon the power level of an ingress signal, and further defined using edges of the buckets or bins. Pre-defined ingress signal power level buckets or bins refers to the manner in which the collected ingress statistics are grouped. For example, in the context of measuring the ingress power level, the buckets or bins may be pre-defined such that each of the buckets/bins is defined by a range (i.e., a first bucket/bin stores measured ingress power levels between 0-5 dBc, a second bucket/bin stores measured ingress power levels between 6-10 dBc, etc. ) . More broadly, buckets and bins may be pre-defined to store a specific type of ingress statistic, such as a power level or shape and pulse of the ingress signal. In this instance, measured power levels are stored in one bucket/bin, whereas shape and pulse of ingress statistics are stored in another bucket/bin.

In one embodiment, the edges of the power buckets or bins may be pre-defined in DOCSIS or may be communicated dynamically by the CMTS 125 to the CMs CM1-CMn 132. The edges of the buckets or bins in one embodiment refer to the upper and lower boundaries of the ingress statistics stored in a particular bucket or bin, which may be graphically represented as a histogram, as shown in FIG. 6B. The horizontal axis represents ingress occurrence power, and is divided into a series of power bins 1-n. The vertical axis of the histogram represents the number of ingress occurrences (and may represent occurrences over a time period, for example) . Therefore, after classification of ingress occurrences into appropriate power bins, the histogram comprises a visual representation of the characteristics of the ingress occurrences. In addition, the resulting histogram (or histograms) can be stored and/or processed in order to understand and quantify the characteristics and numbers of such ingress occurrences. For example, and as illustrated in FIG. 6B, the collected ingress statistics (e.g., power ratio of a signal to a carrier signal) may be measured over a period of time as [-10, 0, 3, 6, 9, 12, 18, 21, 24, 27, ∞] dBc. The ingress statistics may then be grouped into buckets or bins, which are defined by predetermined bin sizes and/or predetermined edges or boundary values. In this example, bin#1 includes ingress statistics ranging from -10 dBc to 0 dBc, bin#2 includes ingress statistics ranging from 0 dBc to 3 dBc and bin#n includes ingress statistics ranging from upper lower 27 dBc to upper edge ∞ dBc.

Following the above example, and for the ingress statistics (e.g., power level and edges of power bins) recorded in each bucket or bin, the number of ingress signals 612 and the average power of the ingress signals 608 is recorded by, and output from, the histogram analysis and creator 602. A count represents the number of ingress statistics recorded within a bucket or bin. Ingress statistics that do not affect the receiver windowing length (in this example, statistics below -10 dBc) may be discarded or ignored. In one embodiment, the average width in the number of subcarriers 610 is additionally recorded and output from the histogram analysis and creator 602. This additional information may be used, for example, to monitor the health of the network, diagnostics, etc.

FIG. 7 illustrates a flowchart of a process 700 to select a cyclic prefix (CP) and receiver window length. The process illustrated in the figure may be performed, in one embodiment, by the CMTS 125. However, it is appreciated that implementation is not limited to such an embodiment.

At 702, the CMTS 125 may optionally request the ingress statistics that are being collected (or have been previously collected) by one or more of the CMs CM1-CMn 132. It is appreciated that the CMTS 125 may also request additional information (or be provided such information) from the CMs CM1-CMn 132, such as channel impulse response and egress statistics.

Upon receipt of the requested ingress statistics from the CMs 132 at 704, the CMTS 125 may select a CP length for the downstream transmission based at least in part on the received ingress statistics. In one embodiment, the ingress statistics are collected, recorded and/or classified by the CMTS 125. In one embodiment, the CMTS 125 selects the CP based on channel impulse response, egress statistics (upstream noise or leakage) and/or ingress statistics (e.g., downstream noise or leakage) . As detailed in the DOCSIS specification, the CMTS 125 collects downstream channel impulse response from the CMs CM1-CMn 132, and is also responsible for selecting the downstream transmit window length.

At 704A, to further assist in selection of the CP, the CMTS 125 calculates the window length (either upstream or downstream window length, such as the window length at a receiver device) . The receiver window length may be an optimal length that is calculated to aid in selecting the best CP so as to avoid performance degradation. Determination of the r window length is a three dimensional problem involving: 1) the number of ingress signals, 2) the power level of each of the ingress signals and 3) the system signal-to-noise ratio (SNR) . Within this context, system SNR is referred to as the average modulation error ratio (MER) (in the absence of ingress noise) . In one embodiment, computation of the length of the receiver window is based upon the measured ingress statistics and the system SNR. The ingress statistics, as discussed above, includes the number of ingress signals and the power level of each of the ingress signals.

In one embodiment, the receiver window does not mitigate the actual ingress signal, as it contains leakage of the ingress into the adjacent subcarriers. Accordingly, the width of the ingress occurrence does not affect the length of the receiver windowing. However, the MER and the system capacity (directly proportional to the SNR) does decrease with an increase in ingress width. Nevertheless, while the capacity is dependent on the ingress width, the length of the receiver window is independent of the ingress width. Hence, the ingress width may be ignored in determining the length of the receiver window, in the example embodiment.

As will become evident from the equations below, in one other embodiment, the length of the receiver window linearly increases with a linear increase in the number of ingress signals, the length of the receiver window linearly increases with a linear increase in ingress power (in dBc) , and the length of the receiver window linearly increases with a linear increase in system SNR (in dBs) .

Based upon the linear relationship between the number of ingress signals and the length of the receiver window, the length of the receiver windowing is modeled as:

where N is the number of ingress occurrences, w _n is the optimal length of the receiver windowing due to n ^th ingress, and w is the optimal length of the receiver windowing due to the N ingresses.

In another embodiment, the length of the receiver window is linearly proportional to the power of the ingress. Thus w _n can be modeled as:

w _n ∝ mp _n (2)

where p _n =power of n ^th ingress in dBc, and m = slope.

In still another embodiment, the length of the receiver window is linearly proportional to the system SNR. Since the system SNR is independent of the ingress, Equation (2) can be modified to include the effect of system SNR as:

w _n =mp _n +C (3)

Equation (3) is a slope-intercept form of a linear equation, where C is the intercept and C is a constant that is proportional to the system SNR. Thus, if w _n<0, then w _n is set to zero. The CMTS 125 may then make a selection for the slope m, and the intercept C.

After creating a single histogram, as described above, the CMTS can consider each bin to represent a single ingress occurrence, with a power of the bin given by the product of number of ingresses in the bin and the average ingress power of the bin, where power of an n ^th bin, w _n is given as:

w _n= (Number of ingresses in the bin) * (Average power of the bin) (4)

In one other embodiment, the receiver window length may be computed based upon total ingress power due to all ingresses. In this case, the receiver window length is given as:

w=m2* (Total ingress power) (5)

where m2 is a constant.

Once the receiver window length has been determined at 704A, then at 706 the CMTS 125 may select the CP length for downstream signal transmissions to the CMs CM1-CMn 132 based on the collected ingress statistics and/or the length of the receiver window. Selection of the CP is considered a key OFDM parameter, as it is used to eliminate ISI and ICI, as long as the CP length is greater than the channel delay spread. As explained above, by eliminating ISI and ICI, the CP compensates for the effect of the multi-path dispersion. However, compensating in this manner also consumes a considerable amount of spectrum and power. By selecting the CP based on the ingress statistics (and optionally in addition to other parameters such as channel impulse response and egress leakage) , the CP length optimizes the system capacity and improves overall system performance. Moreover, the CP can be dynamically selected and re-selected over time in order to optimize system capacity and performance as system performance changes, based on changes in the ingress statistics.

The CP may be calculated at 706A, as explained above, based on the collected ingress statistics and/or the receiver window length for the downstream signal transmissions. The receiver window length for the downstream may be determined based on a number of ingresses (or number of ingress occurrences) , a power level of each of the ingresses, and a signal-to-noise ratio in the CM receiver. Optionally, the CP may be calculated based on the channel impulse response and the detected egress leakage.

In one embodiment, at 706B, the collection of the ingress statistics, as explained above, includes recording a power level of each ingress signal occurrence (with respect to an average signal power level) at the CMs CM1-CMn 132. In one other embodiment, the recorded power levels may be used to group the collected ingress statistics into power bins at 706C. A power spectrum encompassing the expected ingress signal power levels is sub-divided into a series of power bins for classifying power levels of ingress signal occurrences. Each power bin includes a predetermined range of power levels. The bins are substantially non-overlapping in some embodiments. Additionally, any ingress statistics that do not fall within a specific power level of the power bin ranges may be discarded. Based on the power levels of each ingress and the edges of each of the power bins, a histogram may be generated to calculate an average ingress power level and a number of ingresses for each of the power bins.

Upon selecting the CP at 706, the OFDM signal may then be transmitted at 708 to the CMs CM1-CMn 132 using the selected cyclic prefix. In one embodiment, the CMTS 125 may optionally compute an upstream receiver window length and an upstream cyclic prefix length using the ingress statistics collected by the CMTS at 710 and send them to the CMs CM1-CMn 132.

FIG. 8 is a block diagram of a network processing device 801 that can be used to implement various embodiments of a CMTS in accordance with the present technology. Specific network processing devices may utilize all of the components shown, or only a subset of the components, and levels of integration may vary from device to device. Furthermore, the network processing device 801 may contain multiple instances of a component, such as multiple processing units, processors, memories, transmitters, receivers, etc. The network processing device 801 may be equipped with one or more input/output devices, such as network interfaces, storage interfaces, and the like. The processing unit 801 may include a central processing unit (CPU) 810, a memory 820, a mass storage device 830, and an I/O interface 860 connected to a bus 870. The bus 870 may be one or more of any type of several bus architectures including a memory bus or memory controller, a peripheral bus or the like.

The CPU 810 may comprise any type of electronic data processor. The memory 820 may comprise any type of system memory such as static random access memory (SRAM) , dynamic random access memory (DRAM) , synchronous DRAM (SDRAM) , read-only memory (ROM) , a combination thereof, or the like. In an embodiment, the memory 820 may include ROM for use at boot-up, and DRAM for program and data storage for use while executing programs. In embodiments, the memory 820 is non-transitory. In one embodiment, the memory 820 includes a receive module 820A receiving ingress statistics for one or more ingress signals collected by one or more cable modems in the CMTS, a select module 820B selecting the cyclic prefix length for downstream signal transmissions to the one or more cable modems 132 based on the collected ingress statistics, a transmit module 820C transmitting the OFDM signal to the one or more cable modems 132 using the selected cyclic prefix, a calculate module 820D calculating the receiver window length for downstream signal transmissions based on the collected ingress statistics, a record module 820E recording a power level of each ingress signal with respect to an average signal power level at the one or more cable modems, and a classification module 820F classifying each of the ingress signals into power bins based on the recorded power level for each of the ingress signals.

The mass storage device 830 may comprise any type of storage device configured to store data, programs, and other information and to make the data, programs, and other information accessible via the bus 870. The mass storage device 830 may comprise, for example, one or more of a solid state drive, hard disk drive, a magnetic disk drive, an optical disk drive, or the like.

The processing unit 801 also includes one or more network interfaces 850, which may comprise wired links, such as an Ethernet cable or the like, and/or wireless links to access nodes or one or more networks 880. The network interface 850 allows the processing unit 801 to communicate with remote units via the networks 880. For example, the network interface 850 may provide wireless communication via one or more transmitters/transmit antennas and one or more receivers/receive antennas. In an embodiment, the processing unit 801 is coupled to a local-area network or a wide-area network for data processing and communications with remote devices, such as other processing units, the Internet, remote storage facilities, or the like.

In an example embodiment, the network processing device 801 includes a statistics reception module receiving ingress statistics for one or more ingress signals collected by one or more cable modems, a selection module selecting the cyclic prefix length for downstream signal transmissions to the one or more cable modems based on the collected ingress statistics, and a transmission module transmitting the OFDM signal to the one or more cable modems using the selected cyclic prefix length. In some embodiments, the network processing device 801 may include other or additional modules for performing any one of or combination of steps described in the embodiments. Further, any of the additional or alternative embodiments or aspects of the method, as shown in any of the figures or recited in any of the claims, are also contemplated to include similar modules.

It is understood that the present subject matter may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this subject matter will be thorough and complete and will fully convey the disclosure to those skilled in the art. Indeed, the subject matter is intended to cover alternatives, modifications and equivalents of these embodiments, which are included within the scope and spirit of the subject matter as defined by the appended claims. Furthermore, in the following detailed description of the present subject matter, numerous specific details are set forth in order to provide a thorough understanding of the present subject matter. However, it will be clear to those of ordinary skill in the art that the present subject matter may be practiced without such specific details.

Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable instruction execution apparatus, create a mechanism for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The computer-readable non-transitory media includes all types of computer readable media, including magnetic storage media, optical storage media, and solid state storage media and specifically excludes signals. It should be understood that the software can be installed in and sold with the device. Alternatively the software can be obtained and loaded into the device, including obtaining the software via a disc medium or from any manner of network or distribution system, including, for example, from a server owned by the software creator or from a server not owned but used by the software creator. The software can be stored on a server for distribution over the Internet, for example.

Computer-readable storage media (medium) exclude (excludes) propagated signals per se, can be accessed by a computer and/or processor (s) , and include volatile and non-volatile internal and/or external media that is removable and/or non-removable. For the computer, the various types of storage media accommodate the storage of data in any suitable digital format. It should be appreciated by those skilled in the art that other types of computer readable medium can be employed such as zip drives, solid state drives, magnetic tape, flash memory cards, flash drives, cartridges, and the like, for storing computer executable instructions for performing the novel methods (acts) of the disclosed architecture.

The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a" , "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising, " when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The aspects of the disclosure herein were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure with various modifications as are suited to the particular use contemplated.

For purposes of this document, each process associated with the disclosed technology may be performed continuously and by one or more computing devices. Each step in a process may be performed by the same or different computing devices as those used in other steps, and each step need not necessarily be performed by a single computing device.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A method of selecting a cyclic prefix length and a downstream receiver window length in an OFDM signal of a cable modem termination system (CMTS) , comprising:

the CMTS receiving ingress statistics for one or more ingress signals collected by one or more cable modems;

the CMTS selecting the cyclic prefix length for downstream signal transmissions to the one or more cable modems based on the collected ingress statistics; and

the CMTS transmitting the OFDM signal to the one or more cable modems using the selected cyclic prefix length.
The method of claim 1, further comprising:

the CMTS calculating the downstream receiver window length based on the collected ingress statistics,

wherein the selecting the cyclic prefix length for downstream signal transmissions includes the CMTS calculating the cyclic prefix length based on the downstream receiver window length.
The method of any of claims 1-2, wherein selecting the cyclic prefix length is based on collected channel impulse responses, egress statistics and ingress statistics.
The method of any of claims 1-3, wherein a power spectrum encompassing expected ingress signal power levels is sub-divided into a series of power bins for classifying power levels of ingress signal occurrences.
The method of claim 4, wherein the collection of the ingress statistics by the one or more cable modems comprises:

recording a power level of each ingress signal at the one or more cable modems with respect to an average signal power level; and

classifying an ingress signal of the one or more ingress signals into a corresponding power bin of a series of power bins based on a recorded power level for the ingress signal, wherein a power spectrum encompassing expected ingress signal power levels is sub-divided into the series of power bins for classifying power levels of ingress signal occurrences.
The method of any of claims 1-5, further comprising the CMTS discarding each of the ingress statistics having a power level outside of the power bin ranges.
The method of any of claims 1-6, further comprising:

the CMTS requesting the ingress statistics collected by the one or more cable modems, and

the CMTS sending the downstream receiver window length to the one or more cable modems.
The method of any of claims 1-7, wherein the ingress statistics are determined based on collected ingress signal occurrences in each bin of the series of power bins.
The method of any of claims 1-8, further comprising the CMTS generating a histogram using the classified ingress signals in each power bin to calculate an average ingress power level and a number of ingress signals for each of the power bins.
The method of any of claims 1-9, wherein the CMTS calculating the receiver window length for the downstream includes the CMTS determining a number of ingress signals, the CMTS determining a power level of each of the ingress signals, and the CMTS determining a signal-to-noise ratio in the one or more cable modems.
The method of any of claims 1-10, further comprising the CMTS computing an upstream receiver window length and an upstream cyclic prefix length using the ingress statistics.
A device for selecting a cyclic prefix length and receiver window length in an OFDM signal, comprising:

a non-transitory memory storage comprising instructions; and

one or more processors in communication with the memory, wherein the one or more processors execute the instructions to:

receive ingress statistics for one or more ingress signals collected by one or more cable modems;

select the cyclic prefix length for downstream signal transmissions to the one or more cable modems based on the collected ingress statistics; and

transmit the OFDM signal to the one or more cable modems using the selected cyclic prefix length.
The device of claim 12, wherein the one or more processors further execute the instructions to:

calculate the downstream receiver window length based on the collected ingress statistics,

wherein the selecting the cyclic prefix length for downstream signal transmissions includes calculating the cyclic prefix length based on the downstream receiver window length.
The method of any of claims 12-13, wherein a power spectrum encompassing expected ingress signal power levels is sub-divided into a series of power bins for classifying power levels of ingress signal occurrences.
The device of any of claims 12-14, wherein the collection of the ingress statistics causes the one or more processors to further execute the instructions to:

record a power level of each ingress signal at the one or more cable modems with respect to an average signal power level; and

classify an ingress signal of the one or more ingress signals into a corresponding power bin of a series of power bins based on a recorded power level for the ingress signal, wherein a power spectrum encompassing expected ingress signal power levels is sub-divided into the series of power bins for classifying power levels of ingress signal occurrences.
The device of any of claims 12-15, wherein the one or more processors further execute the instructions to:

record a power level of each ingress signal at the one or more cable modems with respect to an average signal power level;

classify an ingress signal of the one or more ingress signals into a corresponding power bin of a series of power bins based on a recorded power level for the ingress signal, wherein a power spectrum encompassing expected ingress signal power levels is sub-divided into the series of power bins for classifying power levels of ingress signal occurrences; and

generate a histogram using the classified ingress signals in each power bin to calculate an average ingress power level and a number of ingress signals for each of the power bins.
The device of any of claims 12-16, wherein calculating the downstream receiver window length includes determining a number of ingress signals, a power level of each of the ingress signals, and a signal-to-noise ratio.
The device of any of claims 12-17, wherein the one or more processors further execute the instructions to compute an upstream receiver window length and an upstream cyclic prefix length using the ingress statistics.
A non-transitory computer-readable medium storing computer instructions for selecting a cyclic prefix length and receiver window length in an OFDM signal, that when executed by one or more processors, cause the one or more processors to perform the steps of:

receiving ingress statistics for one or more ingress signals collected by one or more cable modems;

selecting the cyclic prefix length for downstream signal transmissions to the one or more cable modems based on the collected ingress statistics; and

transmitting the OFDM signal to the one or more cable modems using the selected cyclic prefix length.
The non-transitory computer-readable medium of claim 19, wherein the one or more processors further perform the steps of:

calculating the downstream receiver window length based on the collected ingress statistics,

wherein the selecting the cyclic prefix length for downstream signal transmissions includes calculating the cyclic prefix length based on the downstream receiver window length.
A method of selecting a cyclic prefix length and receiver window length in an OFDM signal of a cable modem termination system (CMTS) , comprising:

receiving ingress statistics for one or more ingress signals collected by the CMTS; and

computing an upstream receiver window length and an upstream cyclic prefix length using the ingress statistics.