Patent ID: 12255799

DETAILED DESCRIPTION

When many LNs attempt to join the network ofFIG.1simultaneously, they will all contend during the single STRS, and the INs use the STRS to relay the association requests and responses. The present work has recognized that these factors can disadvantageously result in high latencies and high power consumption during association due to the contention for the STRS, and because all nodes consume power during the STRS. Every node awakes for the STRS, actively contends for access to the STRS if transmission is desired, and then transmits if contention is successful. Also, if transmission is not desired, or if contention is not successful, the node still listens in the active receive state. The latency and power consumption problems will be further exacerbated by the aforementioned use of the STRS for communication of network maintenance information and traffic routing information.

The present work has also recognized that the aforementioned latency and power consumption problems might be addressed by providing additional STRSs. However, simply increasing the number of STRSs would significantly increase power consumption because, as indicated above, all nodes would need to be awake in each STRS.

Example embodiments of the present work apply strategic solutions to the latency and power consumption problems encountered as TSCH networks experience increased demand of nodes attempting to join the network. These solutions exploit factors such as: INs (which have relatively large batteries or power-harvesting capabilities) are typically less power-constrained than LNs (which have relatively small batteries); INs at higher levels of the hierarchy experience more traffic than INs at lower levels; the operating profile of an LN changes after it becomes associated with the network; and the post-association operating profile of the LN typically requires more uplink communication (to the RN) than downlink communication (from the RN). As described in detail below, the RN uses messages such as beacon packets and association responses to implement solutions according to example embodiments of the present work.

To alleviate the latency and power consumption problems, an RN according to example embodiments of the present work allocates for LN association contention a suitably-sized plurality of STRSs to help accommodate a large LN association contention load. The RN transmits a beacon message (beacon packet) that advertises the number of STRSs allocated for LNs to use in contending for association. All nodes desiring network association may then contend for association in each of the advertised STRSs.

In some embodiments, when the RN responds to a successful association request, its association response (transmitted across network hops in STRSs) re-defines the plurality of shared slots available to the newly associated LN, such that the shared slots comport with the post-association operating profile of the LN and provide for reduced LN power consumption. For example, LNs in sensor applications typically use uplink extensively for data transfer. Accordingly, some embodiments re-define the plurality of STRSs such that: at least one STRS is changed to a shared receive-only slot (SROS) in which the LN may only receive communications; and the rest (a majority) of the STRSs are changed to shared transmit-only slots (STOSs) in which the LN may only transmit communications. A SROS always requires power consumption for listening in the active receive state, whereas an STOS requires power consumption only when the node has information to transmit, in which case the node contends for the STOS and, if the contention is successful, transmits the information. Because the re-definition of the STRSs results in allocation of mostly STOSs to the LN, it comports with the LN's post-association operating profile (mostly uplink transmissions). Because the re-definition is complete, i.e., it retains none of the STRSs, it avoids unnecessary LN power consumption. In some embodiments, the re-definition changes only one STRS to an SROS, and changes the rest of the STRSs to STOSs. In some embodiments, the re-definition adds one or more further STOSs such that the LN is actually allocated a total number of SROS(s) and STOSs that is larger than the total number of STRSs that were initially available to the LN for contending to join the network.

Because INs also experience increased traffic as large numbers of LNs attempt to join the network, in some embodiments, the RN allocates a relatively large number of STRSs to an IN. The RN's association response to a joining IN is used in some embodiments to communicate this allocation of STRSs. In some embodiments, the number of STRSs allocated to an IN exceeds the number of STRSs advertised for use by LNs contending for network association. Because a IN is typically less power-constrained than a LN, the added power-consumption required by the relatively large number of STRSs allocated to the INs will generally be acceptable. Furthermore, because a higher level IN (e.g., Level 1 IN ofFIG.1) handles more traffic than an associated lower level IN (e.g., Level 2 IN ofFIG.1), more STRSs may be allocated for a higher level IN than for an associated lower level IN. Note that the RN knows the hierarchical level of a joining IN by inspecting the hop count conventionally provided in the association request received from the IN. The hop count is incremented at each hop traversed by the association request.

As network conditions change, it may be helpful to provide one or more INs with more network communication capacity. For example, as the number of LNs in the network increases, one or more INs may require more uplink capacity to accommodate increased uplink traffic from the LNs. In some embodiments, when the RN detects that the number of LNs in the network exceeds a predetermined threshold, it transmits a beacon message to add one or more STOSs (and/or one or more SROSs) to the shared slot allocation of each of one or more INs. Some embodiments limit the number of STOSs/SROSs added for an IN such that its resulting total allocation of STOSs and SROSs and STRSs does not exceed the number of STRSs allocated to any associated IN at the next higher level of the hierarchical topology.

In some embodiments, the aforementioned messages (i.e., beacon messages and association responses) used to implement solutions according to the present work employ payload information elements (IEs) that are conventionally available in those messages. The payload IEs are suitably formatted to indicate the location of the shared slots, how many shared slots are STOS, how many shared slots are SROS, and how many shared slots are STRS. In the instances where a beacon message advertises STRSs for association contention, the payload IE contains a predetermined broadcast identifier such that all potentially joining nodes are informed. In the other above-described instances of shared slot re-definition and shared slot allocation, the payload IE (whether in a beacon message or an association request) contains information that identifies the node to which the payload IE is directed.

FIGS.2A and2Billustrate operations described above that can be performed in a network such as shown inFIG.1according to example embodiments of the present work. The illustrated operations are performed by the RN. When an association request is received from an IN at21inFIG.2A, the hop count in the request is inspected at22. If the hop count=1, then the IN is joining at Level 1 (see alsoFIG.1), so a total of A STRSs are allocated to the IN at23. If the hop count=2, then the IN is joining at Level 2, so a total of B (B<A) STRSs are allocated at24.

At25and26inFIG.2B, there is illustrated the allocation of one or more STOSs (and/or one or more SROSs) to each of one or more INs, in response to detection of a predetermined condition in the network. In the example ofFIG.2B, the predetermined condition is the number of LNs in the network exceeding a threshold TH, as shown at25. If the condition at25is satisfied, the aforementioned allocation of one or more STOSs (and/or one or more SROSs) to each of one or more INs occurs as shown at26.

At27inFIG.2B, there is illustrated advertisement of C (C<B) STRSs for LNs to use in contending for network association. If a LN association request is received at28, the C STRSs advertised at27are changed for the new LN at29, to become D SROS(s) and E STOSs, where D+E=C and D<E. As noted above, the re-definition at29may also include addition of one or more further STOSs (not explicitly shown inFIG.2B). After the re-definition at29, operations may proceed to check for the network condition at25, unless that condition was already detected previously, in which case operations proceed to27as shown by broken line inFIG.2B.

In some embodiments, the value of threshold TH is updated (increased) in response to a “yes” decision at25inFIG.2B, thus providing for the possible allocation of further STOSs/SROSs (at26) as the network grows. In such case, the broken line path from29to27inFIG.2Bwould be omitted.

FIGS.3and4show bar graphs that illustrate example allocations of shared slots to a Level I IN, a Level 2 IN and a LN according to example embodiments of the present work.FIG.3shows allocations existing before the LN has joined the network, andFIG.4shows allocations after the LN joins.FIG.3shows A, B and C STRSs allocated for use by the Level I IN, the Level 2 IN and the LN, respectively, with A>B>C.FIG.4shows post-association shared slot re-definition for the LN such that the STRSs previously allocated to the LN (seeFIG.3) for association contention are changed to D SROS(s) and E STOSs, with D<E and D+E=C.FIG.4also shows, in broken line, F STOSs added to the shared slot allocation of an IN (Level 2 IN in this example) in response to detection of a predetermined condition in the network. As one particular illustrative example, some embodiments have A=10, B=6, C=4, D=1, E=3 and F=4. As another particular example, the LN's shared slot re-definition in some embodiments (not shown inFIG.4) adds two further STOSs for the LN, resulting in a total of E+2 (e.g., 3+2=5) STOSs and C+2 total shared slots for the LN, with C+2<B<A.

FIG.5diagrammatically illustrates an apparatus for use as a RN in a TSCH wireless communication network such as shown inFIG.1according to example embodiments of the present work. Various conventional structures and functions not necessary for understanding the present work may be omitted. The apparatus ofFIG.5is capable of performing operations described above and shown inFIGS.2-4. A slot allocator51is coupled for communication with a node association interface53and a beacon generator55. In some embodiments, the slot allocator51, the node association interface53and the beacon generator55are collectively implemented by a suitably programmed data processor. As indicated diagrammatically by the broken line at57, the node association interface53receives incoming association requests from nodes that are associating with the network, and outputs corresponding association responses for transmission through the network to the associating nodes. In some embodiments, the node association interface53uses conventional techniques to analyze each incoming association request, and then forwards to the slot allocator51pertinent information from the association request. For example, in some embodiments, the node association interface53forwards to the slot allocator51information such as the type of node (LN or IN) that sent the incoming association request, and the hop count contained in the association request. The slot allocator51determines the shared slot allocation for the associating node based on the association request information received from the node association interface53, and forwards the determined shared slot allocation to the node association interface53. The node association interface53prepares for the associating node an association response that contains the determined shared slot allocation, and then outputs the association response at57for transmission through the network to the associating node.

The beacon generator55receives shared slot allocation information from the slot allocator51, prepares a beacon message that contains the received shared slot allocation information, and outputs the beacon message at59for transmission through the network. As described above, beacon messages are used to advertise STRSs allocated by the slot allocator51for use by nodes contending to associate with the network. As also described above, beacon messages are used to inform INs that STOSs and/or SROSs (allocated by slot allocator51) are added to their shared slot allocations. In some embodiments, the slot allocator51maintains a count of the number of LNs in the network, and compares this count with a threshold to determine when to add STOSs/SROSs to the shared slot allocations of INs (see also25and26inFIG.2).

Although example embodiments of the present work are described above in detail, this does not limit the scope of the present work, which may be practiced in a variety of embodiments.