Abstract:
A cable modem termination system measures signal qualities of upstream transmissions associated with one or more cable modems. The system monitors the measured upstream signal qualities, and selectively commands at least one of the one or more cable modems to switch between upstream channels based on the signal quality monitoring.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The instant application is a continuation of U.S. patent application Ser. No. 10/659,739, filed Sep. 11, 2003, which claims priority from U.S. Provisional Application No. 60/409,982, filed Sep. 12, 2002, the disclosures of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to cable modem systems and, more particularly, to systems and methods for improving bandwidth efficiency in cable modem systems. 
     2. Description of Related Art 
     In conventional cable modem systems, a cable modem termination system (CMTS) at the headend typically services multiple cable modems (CMs). The CMTS transmits data and messages to the CMs on a downstream frequency and receives data bursts from the CMs on different upstream frequencies. Conventionally, CMTSs&#39; upstream receivers are set to receive upstream signals from the CMs based on the capabilities of the lowest performing CM. Thus, even though some CMs may have higher performance capabilities, all CMs will be set to transmit at the settings of the least capable CM. With all CMs set to transmit at the settings of the least capable CM, the available upstream bandwidth is used inefficiently. The CMs with higher performance capabilities will use more bandwidth than if they transmitted using their higher performance capabilities. Conventional cable modem systems, thus, inefficiently use available upstream bandwidth. 
     Therefore, there is a need in the art to more efficiently use upstream bandwidth in cable modem systems. 
     SUMMARY OF THE INVENTION 
     Systems and methods consistent with the principles of the invention address this and other needs by altering transmission characteristics of modems of a cable modem system to improve bandwidth utilization. Systems and methods consistent with the principles of the invention may monitor upstream transmission quality and command cable modems to alter their transmission characteristics to improve transmission rate and, thus, increase bandwidth utilization. For example, altering the modulation scheme a modem uses (e.g., QPSK to 16QAM) may substantially improve the modem&#39;s transmission rate. By “moving” one or more modems from under performing transmission settings to better performing transmission settings, available bandwidth of the cable modem system may be used more efficiently. 
     In accordance with one aspect of the invention as embodied and broadly described herein, a method of altering modem transmission characteristics includes setting a modem to transmit on a first upstream channel using first transmission characteristics. The method further includes monitoring a quality of the modem upstream transmissions on the first upstream channel. The method also includes setting the modem to transmit on a second upstream virtual channel using second transmission characteristics based on the monitored quality. 
     In another implementation consistent with principles of the invention, a method of controlling transmission characteristics of cable modems includes monitoring upstream transmission quality of one or more cable modems. The method further includes commanding at least one of the one or more cable modems to change its transmission characteristics based on the monitored quality. 
     In still another implementation consistent with principles of the invention, a method of changing virtual upstream channels in a cable modem system includes monitoring upstream signal qualities associated with one or more cable modems. The method further includes selectively switching at least one of the one or more cable modems between virtual upstream channels based on the signal quality monitoring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, explain the invention. In the drawings, 
         FIG. 1  is a diagram of an exemplary network in which systems and methods consistent with the principles of invention may be implemented; 
         FIG. 2  is a diagram of an exemplary cable modem termination system (CMTS) according to an implementation consistent with the principles of invention; 
         FIG. 3  is a diagram of an exemplary cable modem (CM) according to an implementation consistent with the principles of invention; 
         FIG. 4  is a diagram of exemplary upstream/downstream communications between a CMTS and multiple cable modems according to an implementation consistent with the principles of invention; 
         FIG. 5  is a diagram of an exemplary upstream channel descriptor according to an implementation consistent with the principles of the invention; 
         FIG. 6  is a flow chart illustrating an exemplary CMTS upstream transmission quality monitoring process according to an implementation consistent with the principles of the invention; and 
         FIG. 7  is a flowchart illustrating an exemplary CM transmission characteristic parameter alteration process according to an implementation consistent with the principles of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the invention refers to the accompanying drawings. The same reference numbers may be used in different drawings to identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents. 
     Systems and methods consistent with the principles of the invention implement mechanisms for moving cable modems in a cable modem system from under performing transmission settings to better performing transmission settings to improve upstream bandwidth utilization. Different cable modems of the system may, thus, transmit using different transmission characteristics, such as, for example, a different modulation or symbol rate. A CMTS, consistent with the principles of the invention, may monitor transmission quality from each of the modems of the cable modem system to ensure that the transmissions from each cable modem maintain a sufficient level of quality. If transmissions from any one cable modem does not meet an expected level of quality, or sufficiently exceeds the expected level of quality, the CMTS may command the cable modem to change its transmission characteristics to either improve the transmission quality or improve the cable modem&#39;s performance (e.g., transmission rate), respectively. 
     Exemplary Network 
       FIG. 1  is a diagram of an exemplary network  100  in which systems and methods consistent with the principles of the invention may be implemented. Network  100  may include sub-network  105  and cable sub-network  110  interconnected via a CMTS  115 . Host(s)  120  and server(s)  125  may connect with sub-network  105  via any type of link, such as, for example, wired, wireless or optical connection links. Sub-network  105  can include one or more networks of any type, including a Public Land Mobile Network (PLMN), Public Switched Telephone Network (PSTN), local area network (LAN), metropolitan area network (MAN), wide area network (WAN), Internet, or Intranet. The one or more networks may alternatively include packet-switched sub-networks, such as, for example, General Packet Radio Service (GPRS), Cellular Digital Packet Data (CDPD), and Mobile IP sub-networks. 
     Cable sub-network  110  may include a coaxial or hybrid optical fiber/coaxial (HFC) cable network. Cable modems  130 - 1  through  130 -N may interconnect with cable sub-network  110  via coaxial cable/optical fiber. Each cable modem  130  couples with a respective Customer Premises Equipment (CPE)  135 . Each CPE  135  may include a television, a computer, a telephone, or any other type of equipment that can receive and/or send data via cable network  110 . 
     CMTS  115  may transmit data received from host(s)  120  or server(s)  125  on one or more downstream channels via cable network  110  to cable modems  130 . Cable modems  130  may receive the downstream transmissions and pass the demodulated transmissions on to respective CPEs  135 . Cable modems  130  may further receive data from respective CPEs  135 , modulate the data, and transmit the data on one or more upstream channels to CMTS  115  via cable network  110 . CMTS  115  may forward the data, via network  105 , to host(s)  120  or server(s)  125 . 
     It will be appreciated that the number of components illustrated in  FIG. 1  is provided for explanatory purposes only. A typical network may include more or fewer components than are illustrated in  FIG. 1 . 
     Exemplary Cable Modem Termination System 
       FIG. 2  illustrates a diagram of an exemplary CMTS  115  according to an implementation consistent with the principles of the invention. CMTS  115  may include one or more processing units  205 , a memory  210 , a communication interface  215 , an upstream/downstream communication interface  220 , and a bus  225 . 
     Processing unit  205  may perform data processing functions for data transmitted/received via communication interface  215  to/from sub-network  105 , and data transmitted/received via upstream/downstream communication interface  220  to/from cable network  110 . Memory  210  may include Random Access Memory (RAM) that provides temporary working storage of data and instructions for use by processing unit  205  in performing control and processing functions. Memory  210  may additionally include Read Only Memory (ROM) that provides permanent or semi-permanent storage of data and instructions for use by processing unit  205 . Memory  210  can also include large-capacity storage devices, such as a magnetic and/or optical recording medium and its corresponding drive. 
     Communication interface  215  may include conventional circuitry well known to one skilled in the art for transmitting data to, or receiving data from, sub-network  105 . Upstream/downstream communication interface  220  may include transceiver circuitry well known to one skilled in the art for transmitting data bursts on downstream channels, and receiving data bursts on upstream channels, via cable sub-network  110 . Such transceiver circuitry may include amplifiers, filters, modulators/demodulators, interleavers, error correction circuitry, and other conventional circuitry used to convert data into radio frequency (RF) signals for transmission via cable network  110 , or to interpret data bursts received from cable modems  130  via cable network  110  as data symbols. 
     Bus  225  interconnects the various components of CMTS  115  to permit the components to communicate with one another. 
     Exemplary Cable Modem 
       FIG. 3  illustrates a diagram of an exemplary CM  130  according to an implementation consistent with the principles of the invention. CM  130  may include a processing unit  305 , a memory  310 , a CPE interface  315 , an upstream transmitter  320 , a downstream receiver  325 , and a bus  330 . 
     Processing unit  305  may perform data processing functions for data received via downstream receiver  325  and data transmitted via upstream transmitter  320 . Memory  310  may include RAM that provides temporary working storage of data and instructions for use by processing unit  305  in performing control and processing functions. Memory  310  may additionally include ROM that provides permanent or semi-permanent storage of data and instructions for use by processing unit  305 . Memory  310  can also include large-capacity storage devices, such as a magnetic and/or optical recording medium and its corresponding drive. 
     CPE interface  315  may include circuitry well known to one skilled in the art for interfacing with a CPE  135 . Upstream transmitter  320  may include circuitry well known in the art for transmitting on an upstream channel. For example, upstream transmitter  320  may include amplifiers, filters, modulators, interleavers, error correction circuitry, and other conventional circuitry used to convert data into RF signals for transmission via cable sub-network  110 . Downstream receiver  325  may include circuitry well known to one skilled in the art for receiving data bursts on a downstream channel. For example, downstream receiver  325  may include amplifiers, filters, demodulators and other conventional circuitry used to interpret data bursts received from CMTS  115  as data symbols. 
     Bus  330  interconnects the various components of CM  130  to permit the components to communicate with one another. 
     Exemplary Downstream/Upstream Communication 
       FIG. 4  illustrates exemplary upstream and downstream communication between a CMTS  115  and multiple CMs  130  according to an implementation consistent with the principles of the invention. As illustrated in  FIG. 4 , CMTS  115  and CMs  130 - 1  through  130 -N interconnect via downstream RF channels  405  and upstream RF channels  410  of cable network  110 . Each downstream channel  405  and upstream channel  410  may include a different frequency. CMTS  115  may transmit messages and data to each CM  130  on a downstream channel  405  and may receive transmission from each CM  130  via an upstream channel  410 . Each upstream channel  410  may include multiple “virtual” channels. Each virtual upstream channel may include a time division multiplexed (TDM) timeslot of the upstream channel frequency. Each virtual upstream channel may further be associated with different transmission characteristics of cable modems  130 . Such different transmission characteristics may include a different channel profile, such as different TDM timeslot size, symbol rate, frequency, pre-amble pattern, and/or burst profile. The different burst profile may include a different modulation, pre-amble length, data block size (e.g., Reed-Solomon block size), error correction (e.g., Reed-Solomon error correction), scrambling or encryption, encoding (e.g., differential encoding), maximum burst size, and/or guard time size. 
     Upstream channels  410  from cable modems  130 - 1  through  130 -N may, thus, include frequency bandwidth divided into multiple channels, with each channel possibly further time division multiplexed into multiple virtual upstream channels. CMTS  115  may monitor a quality of the transmissions from each CM  130  on upstream channels  410 . Based on this monitoring, CMTS  115  may command one or more CMs  130  to change their transmission characteristics, such as changing their channel and/or burst profile. For example, CMTS  115  may command CM  130 - 1  to increase its performance (i.e., bit rate) by changing from quadrature phase shift keying (QPSK) modulation to 16 quadrature amplitude modulation (16QAM) (or to 8QAM, 32QAM or 64QAM). Such a change may increase CM  130 - 1 &#39;s transmission rate from, for example, approximately 2 Mbps to approximately 10 Mbps. In other implementations, for example, CMTS  115  may command CM  130 - 1  to change from 8QAM to 32 QAM, from 16QAM to 64QAM, etc. to increase CM  130 - 1 &#39;s performance. As another example, CMTS  115  may command CM  130 -N to increase its symbol rate. Thus, if CM  130 -N is using QPSK and transmitting at approximately 2 Mbps, increasing the symbol rate may increase the bit rate. 
     CMTS  115  may issue commands to CMs  130  to instruct them to select one of multiple upstream channel descriptors (UCDs). The multiple UCDs each may describe different upstream transmission characteristics that are to be used by CMs  130  for transmitting on an upstream channel  410 . 
     Exemplary Upstream Channel Descriptor 
       FIG. 5  illustrates an exemplary upstream channel descriptor (UCD)  500 , one or more of which may be periodically transmitted from CMTS  115  to CMs  130 , according to an implementation consistent with the principles of the invention. UCD  500  may include a header  505  and a message payload  510 . Header  505  may include conventional overhead data for the use of any type of medium access control protocol. 
     Message payload  510  may include an upstream channel identifier  515 , a configuration change count  520 , a time-slot size  525 , a downstream channel identifier  520  and channel/burst descriptors  535 . Upstream channel identifier  515  may identify the upstream channel that is associated with this UCD  500 . Configuration change count  520  may indicate when any values of this UCD  500  change. If the value of count  520  remains the same, a receiving CM  130  can conclude that the fields of UCD  500  have not changed, and may disregard the remainder of the message. Time-slot size  525  may indicate the size T of the time-slot for the upstream channel identified by upstream channel identifier  515 . T may include integer multiples of 2 (e.g., T=2M). 
     Downstream channel identifier  530  may indicate the downstream channel on which UCD  500  has been transmitted. Burst/channel descriptors  535  may indicate channel and burst profiles for CM transmission on the channel identified by upstream channel identifier  515 . The channel profile may include symbol rate, frequency and pre-amble pattern. The burst profile may include modulation (e.g., QPSK, 16AM, 8QAM, 32QAM, 64QAM), pre-amble length, data block size, error correction, scrambling or encryption, encoding, maximum burst size, and guard time size. 
     Exemplary CM Transmission Quality Monitoring Process 
       FIG. 6  illustrates an exemplary process for monitoring CM transmission quality in a manner consistent with the principles of the invention. As one skilled in the art will appreciate, the method exemplified by  FIG. 6  can be implemented as a sequence of instructions and stored in memory  210  of CMTS  115  for execution by processing unit(s)  205 . 
     The exemplary process may begin with CMTS  115  periodically broadcasting multiple UCDs on one or more downstream channels  405 , with each of the multiple UCDs describing different upstream transmission characteristics [act  605 ]. For example, each UCD  500  may include a different upstream channel identifier  515 . Each UCD may further include different channel/burst descriptors  535 . CMTS  115  may also transmit a bandwidth allocation message for each upstream channel  410  [act  610 ]. Each bandwidth allocation message may define transmission opportunities on an associated upstream channel  410 , such as, for example, available time slots over which a CM  130  may transmit. 
     CMTS  115  may then monitor the transmission quality of each upstream transmission from a corresponding CM  130  [act  615 ]. CMTS  115  may monitor quality parameters, such as, for example, bit-error-rate or signal-to-noise ratio, using well-known circuitry within upstream/downstream communication interface  220 . 
     CMTS  115  may determine whether the upstream transmission quality of any CM  130  is inadequate [act  620 ]. Transmission quality measurements for each upstream channel may be compared with a single upstream quality parameter to determine whether the measured transmission quality does not meet the quality requirements. Alternatively, transmission quality measurements for each upstream channel may be compared with different upstream quality parameters associated with each channel. If the upstream quality of any CM(s)  130  is inadequate, CM(s)  130  with the inadequate upstream transmission quality may be commanded to use a selected UCD that include more robust transmission characteristics [act  625 ]. For example, one UCD may include a burst profile with modulation set to QPSK, whereas another UCD may include a channel profile with modulation set to 16QAM, 8QAM, 32QAM or 64QAM. CMTS  115  may command CM  130  to select a specific UCD that includes a description of more robust QPSK modulation. 
     If the upstream transmission quality of any CM  130  is sufficiently adequate, CMTS  115  may further determine whether the upstream transmission quality of a CM  130  is greater than a pre-selected quality threshold [act  630 ]. If not, the exemplary process may return to act  605  above. If the upstream transmission quality of any CM  130  is greater than the quality threshold, then the appropriate CM(s)  130  may be commanded to use a selected UCD with higher performance transmission characteristics [act  635 ]. For example, if a monitored CM  130  has a bit error rate less than a pre-selected maximum bit error rate, than CMTS  115  may command that CM  130  to use a UCD that includes channel/burst descriptors  535  that specify, for example, 16QAM modulation instead of the CM  130 ′s current QPSK modulation. The exemplary process of acts  605 - 635  may be selectively repeated to, for example, maximize the performance of any CM  130  (e.g., maximize bit rate) while maintaining adequate upstream signal quality. 
     Exemplary CM Transmission Characteristic Alteration Process 
       FIG. 7  illustrates an exemplary cable modem transmission characteristic alteration process according to an implementation consistent with the principles of the invention. As one skilled in the art will appreciate, the process exemplified by  FIG. 7  can be implemented as a sequence of instructions and stored in memory  310  of CM  130  for execution by processing unit  305 . 
     The exemplary process may begin with a CM  130  either being newly connected to cable sub-network  110 , or being re-booted. CM  130  may periodically receive multiple UCDs  500  on a downstream channel  405  [act  705 ]. Each UCD  500  may specify different transmission characteristics for CM  130 , such as, for example, different channel/burst descriptors  535 . Each UCD  500  may further specify a different upstream virtual channel via upstream channel identifier  515 . CM  130  may also receive bandwidth allocation messages corresponding to each of the received UCDs [act  710 ]. One of the UCDs may be selected and CM  130  may then transmit on an upstream channel  410  using transmission characteristics identified by the selected UCD [act  715 ]. CM  130  may select one of the multiple UCDs randomly or according to any other criteria. 
     A determination may be made whether a “change transmission characteristics” command has been received from CMTS  115  on a downstream channel  405  [act  720 ]. If not, the exemplary process may return to act  705  above. If a change transmission characteristics command has been received, then CM  130  may select a UCD  500 , as commanded by CMTS  115 , from the multiple received UCDs [act  725 ]. The multiple UCDs  500  may be received periodically from CMTS  115  and, thus, CM  130  may select a UCD commanded by CMTS  115  from the most recently received UCDs  500 . 
     CM  130  may transmit on an upstream channel  410  using transmission characteristics identified by the selected UCD [act  730 ]. The selected UCD may include a different channel and/or burst profile in channel/burst descriptors  535 . The different channel and/or burst profile may specify, for example, a different modulation scheme or a different symbol rate that increases the transmission rate of CM  130 . For example, the selected UCD may change CM  130  from QPSK to 16QAM modulation, thus, increasing the transmission rate from, for example, approximately 2 Mbps to approximately 10 Mbps. The exemplary process of  FIG. 7  may be selectively repeated by CMs  130 - 1  through  130 -N so that as many CMs  130  as possible can move to better performing (i.e., higher transmission rate) transmission characteristics. Bandwidth utilization, thus, may be improved using the exemplary processes of  FIGS. 6-7  consistent with the principles of the invention. 
     CONCLUSION 
     Consistent with the principles of the present invention, processes may be implemented that selectively alter the transmission characteristics of one or more modems of a cable modem system to improve bandwidth utilization. Systems and methods consistent with the principles of the invention may monitor upstream transmission quality and command cable modems to alter their transmission characteristics to improve transmission rate and, thus, increase bandwidth utilization. For example, altering the modulation scheme a modem uses (e.g., QPSK to 16QAM, QPSK to 32QAM, etc.) may substantially improve the modem&#39;s bit rate. By “moving” one or more modems from under performing transmission settings to better performing transmission settings, available bandwidth of the cable modem system may be utilized more efficiently. 
     The foregoing description of embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. For example, certain portions of the invention have been described as executed as instructions by one or more processing units. However, implementations, other then software implementations, may be used with the present invention, including, for example, hardware implementations such as application specific integrated circuits, field programmable gate arrays, or combinations of hardware and software. Furthermore, instead of, or in addition to, channels being time division multiplexed into multiple virtual upstream channels, channels that include portions of a frequency bandwidth may be code division multiplexed (e.g., CDMA) into multiple virtual upstream channels. While series of acts has been described in  FIGS. 6 and 7 , the order of the acts may vary in other implementations consistent with the present invention. Also, non-dependent acts may be performed in parallel. 
     No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used. The scope of the invention is defined by the claims and their equivalents.