Abstract:
A method of generating a transmission schedule for a network device of a home network includes ensuring that strongly interfering nodes of different domains do not transmit simultaneously while enabling other non interfering nodes of the different domains to transmit simultaneously. A domain master for a home network includes a receiver and a scheduler. The receiver receives at least one transmission from at least one node of its domain indicating at least one node of at least one neighboring domain whose transmissions are interfering. The scheduler schedules transmissions of said nodes of its domain in coordination with a domain master of said neighboring domain according to inter-domain node interference.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit from U.S. Provisional Patent Application No. 61/365,969, filed Jul. 20, 2010, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to mitigation of neighboring interference in networks generally and to a signaling protocol for mitigation of interference from neighboring networks in particular. 
       BACKGROUND OF THE INVENTION 
       [0003]    Neighboring networks (domains), in which signals are transmitted over shared media (such as powerline, coax, twisted pair etc), are known to be problematic due to interference from concurrently transmitting nodes within these domains whose signals may interfere with other nodes, not of their domain. Current solutions include having domain specific seeds for encoding the preambles of transmissions in one domain, using orthogonal preambles which encode the preambles using codes which are mathematically orthogonal to one another and thus, should not interfere with one another, and TDMA (Time Division Multiple Access) methods which allocate time slots or transmission opportunities (TXOPs) of a Medium Access Cycle (MAC) and which divide the MAC cycle among the interfering neighboring domains such that each domain receives only a portion of the MAC cycle. 
       SUMMARY OF THE INVENTION 
       [0004]    There is therefore provided, in accordance with a preferred embodiment of the present invention, a domain master for a home network. The domain master includes a receiver and a scheduler. The receiver receives at least one transmission from at least one node of its domain indicating at least one node of at least one neighboring domain whose transmissions are interfering. The scheduler schedules transmissions of the nodes of its domain in coordination with a domain master of the neighboring domain according to inter-domain node interference. 
         [0005]    Moreover, in accordance with a preferred embodiment of the present invention, the scheduler includes an interference evaluator to determine the level of interference, a planner to plan the transmissions according to the level of interference between nodes of two or more different domains and inter domain coordinator to communicate with the neighboring domain masters. 
         [0006]    Additionally, in accordance with a preferred embodiment of the present invention, the scheduler includes a unit to instruct the nodes of its domain to periodically transmit a media access plan with default parameters to enable the detection of interfering nodes. 
         [0007]    Further, in accordance with a preferred embodiment of the present invention, the scheduler includes a unit to produce a media access plan having zones allocated to nodes with allocations dependent on the level of interference between neighboring nodes. Each node includes a neighbor transmission detector which not only detects the media access plan with default parameters sent by its neighbors but all transmissions sent with default preambles. 
         [0008]    Still further, in accordance with a preferred embodiment of the present invention, the planner includes an allocator to provide allocations to nodes with inter-domain node interference below a predefined level in at least one orthogonal preamble zone. 
         [0009]    Moreover, in accordance with a preferred embodiment of the present invention, the planner includes an allocator to provide allocations to nodes with inter-domain node interference above a predefined level in protected zones of the media access plan separate from protected zones of media access plans allocated for interfering nodes of neighboring domains. 
         [0010]    Further, in accordance with a preferred embodiment of the present invention, the inter domain coordinator includes unit to negotiate the locations of the protected zones with inter domain coordinators of the neighboring domains. 
         [0011]    Still further, in accordance with a preferred embodiment of the present invention, the scheduler includes an aligner to align MAC cycles when the protected zones are needed. 
         [0012]    Additionally, in accordance with a preferred embodiment of the present invention, the planner includes unit for allocating contention based transmission opportunities for coordinated domains in which transmissions are to be transmitted with a default preamble. 
         [0013]    Moreover, in accordance with a preferred embodiment of the present invention, the scheduler also includes unit to release at least one transmission opportunity to the domain master of the neighboring domain if the traffic services required by the neighboring domain master are of higher priority. 
         [0014]    There is also provided, in accordance with a preferred embodiment of the present invention, a method of generating a transmission schedule for a network device of a home network. The method includes receiving at least one transmission from at least one node of its domain indicating at least one node of at least one neighboring domain whose transmissions are interfering and scheduling nodes which experience strong interference from nodes of neighboring domains not to transmit simultaneous with the strongly interfering nodes while enabling other nodes to transmit simultaneously with other nodes of the other domains. 
         [0015]    Moreover, in accordance with a preferred embodiment of the present invention, the method also includes evaluating interference to determine the level of interference; planning the transmissions according to the level of interference between nodes of two or more different domains and communicating between neighboring domain masters to coordinate the transmissions according to inter-domain node interference. 
         [0016]    Further, in accordance with a preferred embodiment of the present invention, the method also includes instructing the nodes of its domain to periodically transmit a media access plan with default parameters to enable the detection of interfering nodes. 
         [0017]    Still further, in accordance with a preferred embodiment of the present invention, the method also includes producing a media access plan having zones allocated to nodes with allocations dependent on the level of interference between neighboring nodes. 
         [0018]    Additionally, in accordance with a preferred embodiment of the present invention, the method also includes providing allocations to nodes with inter-domain node interference below a predefined level in at least one orthogonal preamble zone. 
         [0019]    Further, in accordance with a preferred embodiment of the present invention, the method also includes providing allocations to nodes with inter-domain node interference above a predefined level in protected zones of the media access plan separate from protected zones of media access plans allocated for interfering nodes of neighboring domains. 
         [0020]    Moreover, in accordance with a preferred embodiment of the present invention, the method also includes negotiating the locations of the protected zones with inter domain coordinators of the neighboring domains. 
         [0021]    Further, in accordance with a preferred embodiment of the present invention, the method also includes aligning MAC cycles when the protected zones are needed. 
         [0022]    Still further, in accordance with a preferred embodiment of the present invention, the method also includes allocating contention based transmission opportunities of coordinated domains concurrently in which transmissions are to be transmitted with a default preamble. 
         [0023]    Finally, in accordance with a preferred embodiment of the present invention, the method also includes releasing at least one transmission opportunity to the domain master of the neighboring domain if the traffic services required by the neighboring domain master are of higher priority. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
           [0025]      FIG. 1  is a schematic illustration of three neighboring domains transmitting over a powerline; 
           [0026]      FIG. 2  is a schematic illustration of the three neighboring domains of  FIG. 1  and the interference between nodes thereof. 
           [0027]      FIG. 3  is a schematic illustration of partial transmission schedules for domains X, Y and Z, for nodes which have low interference and for those which have high interference, respectively; 
           [0028]      FIG. 4  is a schematic illustration of a domain master; and 
           [0029]      FIGS. 5A and 5B  are schematic illustrations of the alignment of transmission schedules for domains Y and Z. 
           [0030]    It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. 
         [0032]    It is often the case that within powerline networks a single signal within a domain can easily be picked up by nodes in neighboring domains. Applicant has realized that since not all nodes are exposed to interference from neighboring nodes, division of the MAC cycle by domain is neither necessary nor efficient. Therefore a solution is only required for those nodes with a high probability of interference with each other. 
         [0033]    Reference is now made to  FIG. 1  which illustrates three neighboring domains X, Y and Z all using the same power line  10 , each comprising individual nodes. It will be appreciated that at peak user times, there may be some form of inter-domain node interference between node  2  (domain Z) and node B as (domain Y) as demonstrated by the single solid line. It will be further appreciated that there may be a higher level of inter-domain node interference between node  1  (domain Z) and node A (domain Y) as demonstrated by the double line, such as may be due to their close proximity. However, as Applicant has realized, the remaining nodes, such as node  3  (domain Z) and node Q (domain X), don&#39;t interfere with each other and can be allowed to transmit constantly and regularly, such as by using regular preambles. 
         [0034]    In accordance with a preferred embodiment of the current invention, each domain may comprise a domain master  20 ,  30  or  40  as illustrated in  FIG. 2 . Domain masters  20 ,  30  and  40  may schedule transmissions for domains X, Y and Z, respectively, through advertisement of the schedule in a media access plan (MAP). In accordance with a preferred embodiment of the present invention, domain masters  20 ,  30  and  40  may not only schedule transmissions for their own domains but may also work together to schedule transmissions for nodes across each other&#39;s domains. 
         [0035]    When a node detects neighbor interference, it may decode the source node, destination node and domain number of the interfering transmitter and may convey this information, as well as the strength of the interference, to its domain master as demonstrated by the dotted lines in the case of nodes  1  and A. Using this information, each domain master may work with its interfering neighbor domain masters to produce transmission schedules which enable all nodes to transmit without interference. 
         [0036]    In a preferred embodiment of the current invention, domain master  30 , for example, may distinguish between low and high interference caused by neighboring domain nodes through updated information reports from its domain nodes. When interference is low, domain master  30  may decide that it is sufficient to avoid detection of the preambles of the neighbor domain frames by using orthogonal preambles (i.e. preambles to transmissions which are designed not to interfere with each other). The domain master may allocate a dedicated transmission period for using orthogonal preambles for nodes that have low interference. 
         [0037]    On the other hand, when interference is high, as illustrated in  FIG. 1  by nodes  1  and A, domain master  30  may coordinate the media resources between interfering nodes  1  and A using a TDMA based technique, discussed in detail hereinbelow, together with domain master  40 . The communication between the domain masters is performed in a special TXOP used for neighboring network coordination (NNTXOP) also discussed hereinbelow. 
         [0038]    Reference is now made to  FIG. 3  which illustrates partial transmission schedules for domains X, Y and Z which may be produced by domain masters  20 ,  30  and  40  to avoid interference. In accordance with a preferred embodiment of the present invention, since nodes  1  (domain Z) and A (domain Y) cannot transmit concurrently due to their high level of interference (as illustrated in  FIG. 1 ), the domain masters may coordinate their transmission schedules to have separate, protected transmission zones for interfering nodes. Domain master  40  may instruct node  1  to transmit only during time slot ts 1  within a protected zone to allow node A (domain Y) to transmit during time slot ts 2 , allocated to domain master  30 . Since there is only high interference between nodes  1  and A, when node A is transmitting, other nodes from domain Y (such as  2  and  3 ) may transmit freely. 
         [0039]    At the same time, for low interfering nodes, such as nodes  2  (domain Z) and B (domain Y), each domain master may instruct its low interfering nodes to use orthogonal preambles during their transmissions. Finally, for other nodes, such as node  3  (domain Z) and all nodes in domain X where no interference is expected, the domain masters may allow these nodes to transmit either using regular or orthogonal preambles according to the TXOP attributes along the entire MAC cycle. In these cases, for low or no interference, the domain masters may either allocate specific TXOPs, as in full TDMA, or may define a section of the MAC cycle in which transmissions may be done using collision avoidance/carrier sensing media access (CA/CSMA) methods of any type. For example, one type may be that disclosed in U.S. patent application Ser. No. 11/218,708 entitled ‘Collision Avoidance Media Access Method for Shared Networks’, filed Sep. 6, 2005 and assigned to the common assignee of the present invention, which application is incorporated herein by reference. The method disclosed in the application employs a media access plan (MAP) having sub-burst slots. Each sub-burst slot has a very short duration (e.g., 8-32 μsecs), is associated with a particular one or group of network participants, and represents an opportunity for the initiation of a data transmission by its associated network participants. When a participant utilizes a sub-burst slot allocated to it, the participant expands the slot until the transmission ends or the section of the MAC cycle has ended. 
         [0040]    In order to enable one domain to study its neighbor&#39;s domain (e.g. its MAC cycle duration and start time, the location of its NNTXOP, etc.), each domain master may periodically transmit a default MAP, known as MAP-D, described in detail in U.S. Ser. No. 12/814,512, filed Jun. 14, 2010, assigned to the common assignee of the present invention and incorporated herein by reference. Each domain master may also periodically and randomly instruct all nodes in its domain to repeat the MAP-D. MAP-D is a MAP sent with default PHY parameters so all nodes in all domains are able to receive it. MAP-Ds are transmitted (by the domain master and by any node that repeats it) using default preambles so their signals may be interpreted by other nodes. 
         [0041]    Each node has a neighbor transmission detector that detects not only the MAP-Ds sent by its neighbors but all transmissions performed with the default preamble. 
         [0042]    Reference is now made to  FIG. 4  which details domain masters  30  and  40  and their inter domain communication. Each domain master may comprise a receiver  50 , a scheduler  60 , a planner  70 , an interference evaluator  80 , an aligner  90  and an inter domain coordinator  100 . Receiver  50  may receive information from one of the nodes of the domain when the node detects or receives a MAP-D of a neighboring node with a signal level that is higher than a predefined level (such as node  1  (domain Z). Interference evaluator  80  may then determine the level of interference detected (low vs. high as defined by a threshold). Scheduler  60  may then start TDMA-based NN (neighboring node) coordination and may indicate to inter domain coordinator  100  to inform the inter domain coordinator  100  of the other domain master, such as domain master  40 , that protected zones are required for the strongly interfering nodes. 
         [0043]    According to the information interpreted by interference evaluator  80 , aligner  90  may determine which MAC cycles from which domains need to be aligned, as described in more detail hereinbelow. Once the MAC cycles have been aligned, planner  60  may generate the MAP for the upcoming MAC cycle using the information of interference evaluator  80  about which nodes have which levels of interference. 
         [0044]    Reference is now made to  FIGS. 5A and 5B .  FIG. 5A  illustrates the MAC cycles of domains X and Y before alignment. At this point, there is no coordination between the domains and domain masters  30  and  40  may instruct their nodes to transmit according to their separate MAPs. Therefore there is a high probability of neighboring nodes transmitting concurrently and thus, possibly interfering with each other. 
         [0045]    Reference is now made to  FIG. 5B  where domain master  30  may align its MAC cycle offset to the MAC cycle offset of domain master  40  using information received from the MAP of domain master  40 . Thus, in  FIG. 5B , the first time slot for node A becomes aligned with the time slot for node  3  as are all the other time slots. 
         [0046]    The alignment process uses the fact that the domain master (or the MAP repeater) stamps each MAP with its current time, known as NTR (Network Time Reference). Each node in the domain is synchronized with its domain master time, by adjusting its local time with the domain master time according to the NTR in the MAPs. When a node decodes a MAP from a neighboring domain, the node can decode the current time in the neighbor domain of sending the MAP, via the NTR specified in the neighbor&#39;s MAP, hence it can calculate the offset from its own local time to get the neighbor MAC cycle start time within the timing of its own domain. Accordingly, the reception time (RXtime) of the neighbor&#39;s MAP (which is in the local node time) minus the NTR in the neighbor MAP is the offset that has to be added/subtracted from the MAC cycle start (CYCSTART) specified in the neighbor MAP to know where the neighbor MAC cycle will start in terms of the local time at the node. 
         [0047]    In mathematical terms: 
         [0000]      Neighbor MAC cycle start= RX time of neighbor MAP+neighbor CYSTART−neighbor NTR
 
         [0048]    As mentioned hereinbelow, inter domain coordinator  100 Y may request protected zones from inter domain coordinator  100 Z during the MAC cycle to enable strongly interfering nodes, such as nodes  1  and A, to communicate (transmit or receive) without collisions. This way, domain master  40  may schedule nodes that are not interfering to transmit during these requested protected zones. 
         [0049]    Alternatively, the domain masters may use silent TXOPs, where no node is allowed to transmit. This method allows allocation of silent TXOPs only when it is really necessary (i.e. no non-interfering nodes can be assigned for transmission there). 
         [0050]    Domain master  40  may reply to the protected bandwidth request from domain master  30  with a confirmation message that specifies the confirmed protected zones and may suggest other positions for the denied protected zones. In addition, based on information about priority levels of the traffic transmitted by its nodes, domain master  40  may be forced to release some of its TXOPs to free time for domain master  30  in case the traffic services required by domain master  30  are of higher priority. 
         [0051]    When a new domain is initiated and it detects neighboring domains with high interference, it may coordinate with them by MAC cycle alignment, NNTXOP allocation and requesting a protected TXOP zone for its MAP. 
         [0052]    Contention based transmission opportunities (CBTXOPs) of coordinated domains may also be allocated concurrently to use carrier sense multiple access (CSMA) bandwidth sharing by using the default preamble in such TXOPs. 
         [0053]    It will be appreciated that in general, for multiple domains such as is illustrated in  FIG. 1 , the domain master which is coordinated with the least number of neighboring domains may start the coordination procedure. If both domains are coordinated with the same number of domains, the domain that contains the least number of detected interfering nodes may start the coordination procedure. 
         [0054]    As soon as an interfering node (such as node A (domain Y)) which is transmitting in a protected TXOP has finished its transmissions, domain master  30  may inform domain master  40  that transmission has ended in order to release bandwidth for other nodes to transmit. 
         [0055]    Embodiments of the present invention may include apparatus for performing the operations herein. This apparatus may be specially constructed for the desired purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but not limited to, any type of disk, including floppy disks, optical disks, magnetic-optical disks, read-only memories (ROMs), compact disc read-only memories (CD-ROMs), random access memories (RAMs), electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories. (EEPROMs), magnetic or optical cards, Flash memory, or any other type of media suitable for storing electronic instructions and capable of being coupled to a computer system bus. 
         [0056]    While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.