Abstract:
Systems and methods for reducing the latency and for increasing throughput for MoCA devices that are connected via a coax network are provided. One method according to the invention includes, in a network having a plurality of network modules, each of the plurality of network modules being connected to a coax backbone, communicating over the coax backbone between the plurality of network modules. The method further includes a requesting the use of short burst messages. The method further includes responding to the requesting by constructing a short burst message with a single channel equalization section and reducing the number of bits per hertz in the transmission constellation. The resulting messages can be received with an acceptable error rate while making more efficient use of the MoCA network.

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application No. 61/140,054, filed Dec. 22, 2008, entitled “MoCA 2.0 Short Preamble”, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The present invention relates generally to information networks and specifically to transmitting information such as media information over communication lines such as coaxial cable (hereinafter “coax”), thereby to form a communications network. 
       BACKGROUND OF THE INVENTION 
       [0003]    Network technologies using coax are generally known. The Multimedia over Coax Alliance (MoCA™), at its website mocalliance.org, provides an example of a suitable specification for networking of digital video and entertainment through existing coaxial cable in the home which has been distributed to an open membership. The MoCA 1.1 specification is incorporated by reference herein in its entirety. 
         [0004]    Home networking over coax taps into the vast amounts of unused bandwidth available on the in-home coax. More than 70% of homes in the United States have coax already installed in the home infrastructure. Many have existing coax in one or more primary entertainment consumption locations such as family rooms, media rooms, master bedrooms and other locations. Home networking technology allows homeowners to utilize this infrastructure as a networking system and to deliver other entertainment and information programming with high Quality of Service (QoS). 
         [0005]    The technology underlying home networking over coax provides high speed (270 mbps), high QoS, and the innate security of a shielded, wired connection combined with packet-level encryption. Coax may allow for the carrying of high bandwidth video. Today, it is regularly used to securely deliver millions of dollars of pay per view and premium video content on a daily basis. Home networking over coax can also be used as a backbone for multiple wireless access points used to extend the reach of wireless network throughout a consumer&#39;s entire home. 
         [0006]    Home networking over coax provides a consistent, high throughput, high quality connection through the existing coaxial cables to the places where the video devices currently reside in the home. Home networking over coax provides a primary link for digital entertainment, and may also act in concert with other wired and wireless networks to extend the entertainment experience throughout the home. 
         [0007]    Currently, home networking over coax works with access technologies, such as Asynchronous Digital Subscriber Line (ADSL) and Very high bit rate Digital Subscriber Line (VDSL) services or Fiber to the Home (FTTH), that typically enter the home on a twisted pair or on an optical fiber, operating in a frequency band from a few hundred kilohertz to 8.5 MHz for ADSL and 12 Mhz for VDSL. As services reach the home via unknown Digital Subscriber Line (xDSL) or FTTH, they may be routed via home networking over coax technology and the in-home coax to the video devices. Cable functionalities, such as video, voice and Internet access, may be provided to homes, via coaxial cable, by cable operators, and use coaxial cables running within the homes to reach individual cable service consuming devices locating in various rooms within the home. Typically, home networking over coax type functionalities run in parallel with the cable functionalities, on different frequencies. 
         [0008]    It would be desirable to reduce latency and/or improve throughput with MoCA devices connected by a MoCA network. 
       SUMMARY OF THE INVENTION 
       [0009]    A system and/or method for reducing latency with MoCA devices connected by a MoCA network with or without improving throughput in the network. The system and/or method may also improve the throughput of MoCA devices connected by a MoCA network with or without reducing latency in the network. The method or system may be implemented substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
           [0011]      FIG. 1  shows a message with an typical preamble; 
           [0012]      FIG. 2  shows a message with a short burst preamble according to the invention; and 
           [0013]      FIG. 3  shows a chip module according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    In the following description of the various embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope and spirit of the present invention. 
         [0015]    As will be appreciated by one of skill in the art upon reading the following disclosure, various aspects described herein may be embodied as a method, a data processing system, or a computer program product. Accordingly, those aspects may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, such aspects may take the form of a computer program product stored by one or more computer-readable storage media having computer-readable program code, or instructions, embodied in or on the storage media. Any suitable computer readable storage media may be utilized, including hard disks, CD-ROMs, optical storage devices, magnetic storage devices, and/or any combination thereof. 
         [0016]    In addition, various signals representing data or events as described herein may be transferred between a source and a destination in the form of electromagnetic waves traveling through signal-conducting media such as metal wires, optical fibers, wave guides, and/or wireless transmission media (e.g., air and/or space). 
         [0017]    For ease of reference, the following glossary provides definitions for the various abbreviations and notations used in this patent application:
   ACK TCP Acknowledge Signal message   ADSL Asynchronous Digital Subscriber Line   CE Channel Equalization   CP Cycle Prefix   EN MoCA Existing Node (the term “node” may be referred to alternatively herein as a “module”)   FTTH Fiber To The Home   IFG Inter-Frame Gap   MAC Media Access Control   MAP Media Access Plan   NC MoCA Network Controller   OFDM Orthogonal Frequency Division Multiplexing   PHY Communications layer for the grouping of messages and transmission over the physical medium   RR Reservation Request Message   SC Sub-Carriers of the OFDM system   SNR Signal to Noise Ratio   STB Set Top Box   TCP Transmission Control Protocol   QoS Quality of Service   VDSL Very high bit rate Digital Subscriber Line   xDSL unknown Digital Subscriber Line   
 
         [0038]    The specification describes a method to achieve reduced latency and/or improved throughput with MoCA devices which have been modified according to the invention. The MoCA devices may be nodes on a MoCA network. The MoCA network may be constructed using a collection of coaxial cables to connect a plurality of network nodes. Each node in the network may be configured to request messages constructed according to the invention. There are many types of messages that can be used in the MoCA network. 
         [0039]    Typical messages in the MoCA network include a payload section and a preamble section. The payload section includes data which is to be transferred via the network. The preamble section may include one or more symbols that the receiver may use to adjust one or more receiver parameters in a manner that may improve the reception of the message. 
         [0040]    Some of the messages in a MoCA network are called short burst messages. These messages are so short that the overhead used to send the message, in particular the preamble of these messages, are overly burdensome and become a source of inefficiency in the MoCA network. 
         [0041]    The MoCA network is an OFDM network that utilizes a number of constellations that are set forth in the MoCA specification. Each constellation may be interpreted as a matrix of “points.” Each point may allow the transmission of a certain number of bits. All bits used in the MoCA specification are transmitted via these points. A MoCA device may include a receiver that interprets the points of the constellation, and adjusts its parameters according the channel adjustment symbols in the preamble. A MoCA device may also include a transmitter that responds to receiver requests. 
         [0042]    The systems and/or methods of the invention may provide for the transmission and reception of reduced-size preambles for short burst messages. The systems and/or methods may reduce the preamble size while optionally changing the interpretation of the constellation used to modulate the signals in the MoCA network. The constellation may be reduced by reducing the number of bits interpreted from some or all of the points. The shortened preamble and if requested, the reduced constellation, may be sent/used when the receiver requests (i.e. indicates the ability to receive) the shortened preamble. 
         [0043]    Nodes communicate using several types of message. Messages are constructed from OFDM symbols and typically begin with the preamble section. Every OFDM symbol may include a cyclic prefix that includes a specifically constructed bit pattern so that the orthogonality of channels in the OFDM constellation can be improved by the receiver. The preamble may be used for adjusting the receiver parameters that control bit reception accuracy. 
         [0044]    Two CE symbols are typically included in the MoCA preamble. The CE symbol is another specifically designed group of bits. A receiver may use the reception of the a CE symbol to improve the accuracy filters that extract OFDM constellation bits. The typical preamble size scales with the number of SC in the OFDM system and can be a significant overhead burden particularly when the message payload is small. 
         [0045]    Certain message types belong to the category of short burst messages e.g., RR, ACK etc. Short burst messages are less than 200 bytes (2000 bits) in length (including overhead) while excluding the MAC overhead. The MoCA network uses OFDM symbols to transmit collections of bits. Each OFDM symbol includes approximately 4000 bits. 
         [0046]      FIG. 1  shows a typical short burst message  100  using a typical preamble  110 . The short burst message  100  includes a typical preamble  110  and a payload section  120 . The typical preamble  110  includes an optional short series section  111  designated by “S”, a larger cycle prefix section  112  designated by “CP0”, a first CE section  113  and a second CE section  114  each designated by “CE.” The CP0 is the cyclic prefix for the first CE symbol. The second CE symbol does not have a CP. The optional short series section has a typical length of 64 samples but may be larger or smaller size. The larger cycle prefix section has a length of 160 samples and each CE section has a length of 512 samples producing a total length for the typical preamble of between 1184-1248 samples. 
         [0047]    The payload section  120  includes a cycle prefix section  121  and an OFDM data section  122  which together form one OFDM symbol. The CP section has a length of 60 samples and the OFDM data section  122  has a length of 512 samples producing a total length for the payload section  120  of 572 samples. The length of a complete short burst message including the typical preamble  110  is between 1756-1820 samples, which in sum are less than 50% of the capacity of an ordinary OFDM symbol used by the MoCA network. The typical short burst message  100  contains three OFDM symbols without the optional short series section  111 . 
         [0048]      FIG. 2  shows a short burst message  200  using an embodiment of a short preamble  210  according to the principles of the invention. The short burst message  200  includes a short preamble  210  and a payload section  220 . The short preamble  210  includes an optional short series preamble section  211  designated by “S”, a larger cyclic prefix section  212  designated by “CP0” and a CE section  213  designated by “CE.” The CP0 is the cyclic prefix for the for CE symbol The optional short series section has a typical length of 64 samples but may be larger or smaller size. The larger cycle prefix section has a length of 160 samples and the CE section has a length of about 512 samples producing an approximate length for the short preamble  210  varying between 672-736 samples. 
         [0049]    The payload section  220  includes a CP section  221  and an OFDM data section  222 . The CP section has a length of about 60 samples and the OFDM data section  222  has a length of about 512 samples producing an approximate length for the payload section  220  of 572 samples. The approximate length of the complete short burst message  200  including a short preamble  210  according to the invention varies between 1244-1308 samples which are less than 50% of the capacity of the ordinary OFDM symbol used by the MoCA network. The short burst message  200  contains two OFDM symbols without the optional short series section  111 , thus improving the bandwidth utilization of short burst messages. 
         [0050]    The use of a single CE section  213  included in the short preamble  210  instead of the two CE sections  113 ,  114  included in the typical preamble  110  reduces the quality of the received signal to noise ratio in the MoCA network. The shorter bit sequence, of the single CE symbol, results in a less accurate adjustment channel estimation. When a receiver chooses to receive a short preamble  210  it may be desirable to compensate for the loss of channel equalization. Therefore, the receiver may also request the use of a reduced constellation when the short preamble  210  is requested. The reduced constellation reduces the number of bits per hertz at some or all of the points in the constellation. The reduction bits may achieve an improvement in the noise margin of up to 6 dB in signal to noise ratio (SNR) for the transmission of a short burst message. This improved SNR margin may compensate for the missing CE section in the short preamble  210 . 
         [0051]    The reduction of bits per hertz in the constellation reduces the number bits in an exemplary OFDM symbol to about 3000 bits. Since an exemplary short burst message is less than 2000 bits in length the reduction in the number of available bits does not reduce the efficiency of the transmission. 
         [0052]      FIG. 3  shows a single or multi-core module  330  according to the invention, which can be one or more integrated circuits, in an illustrative data processing system  300  according to the invention. Data processing system  300  may include one or more of the following components: I/O circuitry  320 , peripheral devices  310 , processor  340  and memory  350 . These components may be coupled together by a system bus or other interconnections  360  and are disposed on a circuit board  370  in an end-user system that may be in communication with a coax medium via an interface. 
         [0053]    Thus, systems and methods for providing a MoCA short burst preamble have been described. 
         [0054]    Aspects of the invention have been described in terms of illustrative embodiments thereof. A person having ordinary skill in the art will appreciate that numerous additional embodiments, modifications, and variations may exist that remain within the scope and spirit of the appended claims. For example, one of ordinary skill in the art will appreciate that the steps illustrated in the figures may be performed in other than the recited order and that one or more steps illustrated may be optional. The methods and systems of the above-referenced embodiments may also include other additional elements, steps, computer-executable instructions, or computer-readable data structures. In this regard, other embodiments are disclosed herein as well that can be partially or wholly implemented on a computer-readable medium, for example, by storing computer-executable instructions or modules or by utilizing computer-readable data structures.