Patent Application
20220256503
The field of the invention is multicast communication, such as for use in intra-vehicular wireless sensor networks, Internet of Things, home automation, and low-power devices, for example.
The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Currently, there is an increasing demand for new applications of wireless sensor networks (WSNs). One exemplary area of application concerns in-vehicle communications, especially for aircrafts. As aircraft systems are becoming more and more connected, additional sensors are being employed in the aircraft to determine a status and health of seats, electronic equipment, and other components. With these increasing demands for new applications, it is useful to connect WSNs to the Internet via an Internet Protocol (IP) addressing, and specifically via Internet Protocol version 6 (IPv6) and future protocols, to achieve all-IP communication and thus, achieve interoperability.
However, current standards including Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 do not natively support multicast. Instead, algorithms have been developed that utilize link layer unicast transmission or link layer broadcast transmission to achieve IP multicast. While link layer unicast transmissions offer high reliability due to the re-transmissions based on acknowledgment, they have poor end-to-end latency as individual transmissions are required to each of the multicast subscribers and require high energy consumption. In contrast, broadcast transmissions have low end-to-end latency and low energy consumption due to a single transmission to all multicast subscribers, but there is lower reliability because of the lack of re-transmissions and acknowledgements.
Thus, while various techniques have been developed to attempt to address the problems identified above, each has its own problems.
For example, the IEEE 802.11aa standard identifies various mechanisms for multicast transmission. A study of the standard can be found in “A study of IEEE 802.11aa,” by B. T. Vijay and B. Malarkodi, published in the 2017 8th International Conference on Computing, Communication and Networking Technologies (ICCCNT), Delhi, in 2017. The standard addresses methods of transmission of stream (e.g., voice, audio, and video) over multicast communication.
Using this standard, the coordination between multiple access points (APs) can be improved by adding new control messages and mechanisms. In addition, wireless network performance can be better assessed with interferences more likely avoided with better channel selection. Load sharing can also be accomplished among APs, through additional ways to schedule and add broadcast transmission opportunities between APs. Using a Group Cast with Retries (GCR) service, multicast frames are sent several times without awaiting any acknowledgement, which leads to increased delivery probability.
However, the 802.11aa standard is a non-deterministic scheme based on CSMA and the GCR service adds overhead depending on the number of retries and becomes inefficient and unnecessary when the link quality is good.
As another example, the TRM-MAC protocol can be used to manage available slots to a current node density. In case of a low node density, minimum slots can be used. For a large node density, additional slots can be added. The TRM-MAC protocol can result in a higher successful transmission rate with a minimum delay, by providing a trade-off between energy and delay. Additional details about the protocol can be found in the article “TRM-MAC: A TDMA-based reliable multicast MAC protocol for WSNs with flexibility to trade-off between latency and reliability” by Bhatia and Hansdah, published in 2016 in Computer Networks. As shown in
The channel access mechanism employed in the CFP1 of the MAC-frame is TDMA, and it is used by the internal nodes to relay multicast data. The slot-size in this portion is typically equal to the time required to transmit multicast data (at the current data rate, tdata). The number of slots in the CFP1 portion depends upon the number of internal nodes in the Multicast Spanning Tree (MST) and the algorithm used to perform the TDMA slot-scheduling for the internal nodes.
The channel access mechanism employed in the CFP2 of the MAC-frame is also TDMA and is used by the leaf nodes using ACK-based approach to transmit their acknowledgement (ACK) messages. The slot size in this portion is typically equal to the time required to transmit an ACK message (tack) and is usually smaller than the slot size in CFP1. The number of slots in this portion again depends upon the number of leaf nodes using ACK-based approach in the MST and the algorithm used to perform the TDMA slot-scheduling.
The channel access mechanism employed in the CAP portion of the MAC-frame is prioritized-CSMA, in which a child node with local id, j, using NACK-based approach transmits a NACK message in the CAP portion of MAC-frame, provided (a) it finds the channel idle for a duration defined by j−1−nRouters−nACK)*tcca and (b) it has not received the data. The tcca is the time required to perform clear channel assessment (CCA) by any sensor node to ensure that no other node is already transmitting, and n Routers is the number of internal-child nodes of its parent. The value of tcca is usually smaller than tdata, tack and tnack. The reason for calling this mechanism as prioritized-CSMA is that the nodes with smaller local ID value have higher priority to access the channel as compared to the nodes with larger local ID value. The length of this portion would be (α−1)*tcca+tnack, where α is the maximum number of leaf-child nodes using NACK-based approach at any internal node, in the network.
TRM-MAC can be disadvantageous because it does not propose a way to optimize slots allocation in the CFP. In addition, the CCA operation may fail in the presence of hidden nodes, and therefore, the proposed prioritized-CSMA channel access mechanism does not completely avoid the collision between NACK messages.
As another example, optimization-based rate allocation and scheduling in TDMA-based wireless mesh networks can be used which is further described in the article “Optimization based rate allocation and scheduling in TDMA based wireless mesh networks” by Wang, Mutka, and Torng, published in the 2008 IEEE International Conference on Network Protocols. In this article, the authors worked to optimize the multicast and unicast communications of a TDMA protocol considering delay and throughput. To accomplish this result, they introduced a multi-transfer rate scheduling algorithm based on the construction of a perfect graph. It first constructs a spanning tree rooted at the gateway, then prunes the tree to accommodate all sessions to achieve the perfect graph.
Unfortunately, the algorithm uses broadcast slots for its multicast transmission, which is unreliable. It requires centralized control and can reduce special reuse. In addition, the algorithm is quite complex to put in place and requires some computational power. The algorithm may also require bigger timeslots adding latency to the overall slot frame.
All publications identified herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Thus, there is still a need for reducing end-to-end latency in unicast transmissions.
The inventive subject matter provides apparatus, systems and methods for reducing end-to-end latency in a low-power wireless personal area network (6LoWPAN) using a link layer unicast mode. In such networks, the protocol in the link layer (L2) is typically IEEE 802.15.4, and the protocol in the network layer (L3) adopts IPv6.
IEEE 802.15.4 provides a low-power energy-efficient protocol. The IEEE 802.15.4 protocol has a broad scope of applications including, for example, home automation, factory automation, predictive maintenance as well as live monitoring. IEEE 802.15.4 can also become deterministic when using one of its Time Division Multiple Access (TDMA) modes, where the communication between nodes is divided into timeslots and scheduled on a super frame (SF). However, any TDMA based protocol could be used.
It should to be understood that, while the systems and methods disclosed herein are described in connection with the IEEE 802.15.4 protocol, it is contemplated that the systems and methods disclosed herein could be used with later-developed protocols where reallocation of transmissions to subscribers of a multicast group can reduce end-to-end latency.
Latency in such networks can be reduced by shifting timeslots in the super frame when in one of the TDMA modes. The reallocation of timeslots is preferably based on membership to a multicast group, such that transmission to each of the multicast subscribers of a group occupies adjacent timeslots. This can advantageously result in an optimized timeslot allocation and improvement of the end-to-end latency for multicast communication.
The inventive subject matter described herein has various applications. In an aircraft setting, for example, in-vehicle sensors could be divided into separate multicast groups. In such an environment, galleys could form a first multicast group, each seat class could form separate multicast groups, and on-board trolleys could be formed as separate multicast groups.
Multicast groups could also be formed based on applications. For example, oxygen mask release at the passenger service unit could form a separate group.
Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
Throughout the following discussion, references may be made regarding access points, routers, servers, services, interfaces, portals, platforms, or other systems formed from computing devices. It should be appreciated that the use of such terms is deemed to represent one or more computing devices having at least one processor configured to execute software instructions stored on a computer readable tangible, non-transitory medium. For example, an access point can be configured to fulfill preprogrammed roles, responsibilities, or functions.
The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
If the packet was received from a preferred parent, it is checked whether the multicast group is listed in the routing table. If so, the packet is forwarded downward using a link layer unicast or broadcast transmission based on the number of children and then it is checked whether the node (node and mote are used interchangeably herein to represent devices in the wireless sensor network) is a member of the multicast group. If the multicast group is not listed in the routing table, the packet is not forwarded, and it is checked whether the mote is a member of the multicast group.
If the mote is a member of the multicast group, the packet is delivered up the network stack and the packet is accepted. If not, the packet is dropped.
If the packet was not received from a preferred parent, it is checked whether the packet arrived from below in the RPL tree (i.e. received from a link layer unicast transmission). If yes, it is checked whether the multicast group is listed in the routing table. If not, the packet is dropped.
If the multicast group is listed in the routing table, the packet is forwarded downward using link layer unicast, except to the child from which the packet was received. It is then checked whether the mote is the RPL root. If so, it is checked if the mote is a member of the multicast group. If not, the packet is forwarded upward to the preferred parent.
If the mote is a member of the multicast group, the packet is delivered up the network stack and the packet is accepted. If not, the packet is dropped.
Because all the mote (sensors) in the network are aware of the topology, a multicast source can be anywhere within the network. The processor can determine whether to utilize unicast or broadcast at the link layer based on the number of interested children and the duty cycle rate.
To improve the reliability of messages being received during broadcast transmissions, time slotted channel hopping (TSCH) can be used to provide for broadcast retransmissions. As shown in
For unicast transmission, as the number of subscribers increases, the number of radio transmissions increase due to the individual transmission of packets to every subscriber as well as the acknowledgements being sent back. Because the timeslots for multicast communication can be spread across the super frame, end-to-end latency can be increased.
This is at least partly caused by the inherent delay introduced due to the TDMA mode. For example,
To reduce such latency, preferred systems and methods shift the timeslots in the Super Frame based on membership to a multicast group. In this manner, all the multicast subscribers can occupy adjacent timeslots, which results in an optimization of the allocation of slots and reduces the end-to-end latency for multicast communications.
An example of this is shown in
In step 620, timeslots of a time division multiple access (TDMA) super frame can be dynamically allocated by the router for transmission to and acknowledgements from a set of motes. The set of motes can comprise a plurality of motes that includes a first motes, a second motes, and a third motes. Transmission to each of the motes from mote A can thereby be allocated a distinct timeslot.
In step 630, the router or other component can determine whether any of the motes of the set are members of a multicast group.
If determined that the second mote is a member of the same multicast group as the first mote, the timeslot allocated for transmission to the second mote can be shifted or reallocated in step 640 such that the timeslots for transmission to the first and second motes are adjacent.
If determined that the third mote is also a member of the same multicast group as the first mote, the timeslot assigned for transmission to the third mote can be shifted or reallocated in step 650 such that the timeslots for transmission to the second and third motes are adjacent.
In one aspect, a system for reducing end-to-end latency in in link layer unicast transmissions using the IEEE 802.15.4 protocol comprise a router having a processor and a control thread stored on a non-transitory computer readable medium. It is contemplated that the processor and control thread can enable a transceiver module at a beginning of a timeslot of a TDMA super frame. Although IEEE 802.15.4 protocol is mentioned above, any TDMA based protocol could be used.
The processor can be configured to dynamically allocate a timeslot for transmission to each of a set of motes. The processor can then determine if each of the motes of the set is a member of a first multicast group. If a mote of the set is a member of the first multicast group, the router can shift the timeslot for transmission to that mote, such that the shifted timeslot is adjacent to another of the timeslots allocated for transmission to a subscriber of the first multicast group. This process can continue until timeslots allocated for transmission to all the motes of the set that are members of the first multicast group are adjacent to another of those timeslots.
In some contemplated embodiments, the processor can be configured to determine whether each of the motes of the set is a member of a second multicast group. The processor can then shift timeslots collocated for transmission to each mote that is a member of the second multicast group, so that each timeslot for transmission to each of the members of the second multicast group are shifted to be adjacent to another of the timeslots allocated for transmission to members of the second multicast group.
Preferably, the processor defines a structure of the super frame based on IEEE 802.15.4 according to a topology of a wireless sensor network comprising the set of motes.
The systems and methods described herein can be further embodied in a program stored in non-transitory computer-readable storage medium. Preferred programs are configured to execute a set of operations for multicast communication over an IP network when the program is executed by one or more processors of a router.
Contemplated operations include dynamically allocating timeslots of a TDMA super frame for transmission from a first mote to a second mote and from the first mote to a third mote, where each transmission is allocated a distinct timeslot. For example, a transmission from the first mote to the second mote can be allocated a first timeslot.
Another operation can determine if the third mote is a member of the same multicast group as the second mote. If so, a timeslot allocated for transmission to the third mote can be relocated or shifted based on a membership of the third mote to the multicast group, such that the reallocated second timeslot is adjacent to the first timeslot.
Similarly, a third timeslot of the TDMA super frame can be dynamically allocated for transmission from the first mote to a fourth mote.
Another operation can determine if the fourth mote is a member of the same multicast group as the second mote. If so, a timeslot allocated for transmission to the fourth mote can be relocated or shifted based on a membership of the fourth mote to the multicast group, such that the reallocated third timeslot is adjacent to the second timeslot.
Preferably, the motes wirelessly communicate over a low-power wireless personal area network using the IEEE 802.15.4 protocol.
Although a central entity can distribute a fixed schedule (i.e., a list of timeslots of the super frame) to each node within the network to improve determinism, the inventive concepts described herein address timeslot allocation in environments where timeslots are dynamically allocated by the nodes based on their distance between each other. In such environments, timeslots may be allocated randomly, and may not be optimized for end-to-end communication, and more specifically, for multicast communication where the nodes use 802.15.4 unicast transmission to send multicast packets.
As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously.
In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.
As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value with a range is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
This application claims priority to U.S. provisional patent application having Ser. No. 62/880,355 filed on Jul. 30, 2019. This and all other referenced extrinsic materials are incorporated herein by reference in their entirety. Where a definition or use of a term in a reference that is incorporated by reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein is deemed to be controlling.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US20/44340 | 7/30/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62880355 | Jul 2019 | US |
