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Energy Profiling of Bluetooth Mesh Nodes in Wireless Sensor Networks

This example shows energy profiling in a Bluetooth mesh network using the Communications Toolbox™ Library for the Bluetooth® Protocol. One of the fundamental features of a Bluetooth mesh is its suitability for the low power and energy-constrained nodes. This example models the energy profiling of Low Power, battery operated Bluetooth mesh nodes that implement an energy saving feature called Friendship. Energy is computed based on the time profiled at various states (transmission, listen, sleep and idle) of each node in the mesh network. The derived results show that the Low Power nodes always consume less energy by spending more time in sleep state, thus resulting in energy conservation and increased lifetime.

Bluetooth Mesh Stack

The Bluetooth Core Specification [ 1 ] includes a low energy version for low-rate wireless personal area networks, referred to as Bluetooth Low Energy (BLE) or Bluetooth Smart. The BLE stack consists of the: Generic Attribute Profile (GATT), Attribute Protocol (ATT), Security Manager Protocol (SMP), Logical Link Control and Adaptation Protocol (L2CAP), Link layer (LL) and Physical layer. BLE was added to the standard for low energy devices generating small amounts of data, such as the notification alerts used in applications like home automation, health-care, fitness, and Internet of Things (IoT).

The Bluetooth mesh profile [ 2 ] defines the fundamental requirements to implement mesh networking solutions for BLE. The mesh stack is located on top of the BLE core specification and consists of the: Model Layer, Foundation Model Layer, Access Layer, Upper Transport Layer, Lower Transport Layer, Network Layer and Bearer Layer. Bluetooth mesh networking enables end-to-end communication in large-scale device networks to support applications like smart lighting, industrial automation, sensor networking, asset tracking, and many other IoT solutions.

Mesh Stack:

The figure below shows the Bluetooth mesh stack over the advertising bearer.

  • Model Layer: This layer defines the models, messages and states required for user scenarios. For example, to change the state of a light to On or Off, Generic OnOff Set message from the Generic OnOff model is used. This example supports only two models, Generic OnOff and Light Lightness with set and status messages.

  • Foundation Model Layer: This layer defines the models, messages and states required to configure and manage the mesh network. This layer is used to configure element, publish and subscription addresses. This example assumes that the node is configured with all addresses.

  • Access Layer: This layer defines the interface to the upper transport layer and the format of the application data. It also controls the encryption and decryption of the application data in the upper transport layer. This example supports retransmissions and acknowledgments at this layer. You can configure the access layer using helperBLEMeshAccessLayer.

  • Upper Transport Layer: The functionality of upper transport layer includes encryption, decryption and authentication of the application data and is designed to provide confidentiality of access messages. This layer is also responsible for generation of transport control messages (Friendship and heartbeat) internally and transmits those messages to a peer upper transport layer. These messages are encrypted and authenticated at the network layer. In this example encryption, decryption, authentication and heartbeat messages are not supported.

  • Lower Transport Layer: The functionality of lower transport layer includes segmentation and reassembly of upper transport layer messages into multiple lower transport layer messages to deliver large upper transport layer messages to other nodes. This layer also defines the friend queue used by the Friend node to store the lower transport layer messages for a Low Power node. In this example, segmentation and reassembly is not supported. In this example, both the upper and the lower transport layers are implemented as a single transport layer object helperBLEMeshTransportLayer.

  • Network Layer: This layer defines encryption, decryption and authentication of the lower transport layer messages. It transmits the lower transport layer messages over the bearer layer and relays the mesh messages when 'Relay' feature is enabled. It also defines the message cache containing all the recently seen network messages. If the received message is found to be in the cache, then it is discarded. The message cache is used by the relay nodes (nodes in which the 'Relay' feature is enabled). In this example encryption, decryption and authentication is not supported. You can configure the network layer using helperBLEMeshNetworkLayer.

  • Bearer Layer: This layer is an interface between the Bluetooth mesh stack and the BLE core specification. It is also responsible for creating a mesh network by provisioning the mesh nodes. This example assumes all the nodes are already provisioned into a mesh network. The two types of bearers supported by the Bluetooth mesh are advertising bearer and GATT bearer. This example considers only the advertising bearer.

BLE Core Stack:

  • Generic Access Profile: This profile defines advertising data (AD) types for carrying mesh messages over the advertising bearer. This example supports "Mesh message" AD type and it is used for exchanging network layer messages between mesh nodes.

  • Link Layer: This layer defines Broadcaster and Observer roles for message exchange between the nodes within the Bluetooth mesh network. In a Broadcaster role, a node always advertises whereas in an Observer role the node always scans for the advertisers. Each node in the mesh network switches between these two roles to serve as a Bluetooth mesh node. You can configure the Link Layer using helperBLEMeshLLGAPBearer.

Friendship in Bluetooth Mesh

Wireless Sensor Network (WSN) is known to be a highly resource constrained class of networks where energy consumption is one of the fundamental concerns. Most of the sensors are battery powered devices. In WSNs, sensor nodes are deployed in large scale and thus it is impractical to replace the batteries of sensor nodes. Therefore, each sensor node must use energy efficiently to survive for long time. The Bluetooth mesh defines the Friendship functionality for the energy constrained devices. The transport layer (upper and lower) in the Bluetooth mesh stack is mainly responsible for the Friendship functionality. It defines two types of nodes.

  • Low Power node: Low Power node has a limited power source and operates at reduced receiver duty cycles. This node switches to ON state only to receive data packets.

  • Friend node: Friend node enables the Friend feature and stores the messages destined for Low Power nodes. This node transmits the messages only when the Low Power nodes explicitly requests. This example supports Friendship between one Friend and one Low Power node.

Friendship:

Friendship is established between Friend and Low Power nodes. The Low Power node initiates the Friendship as soon as it is provisioned into the Bluetooth mesh network. This example assumes that, Friendship is already established between Friend and Low Power nodes. After the Friendship is established, the Friend node stores the messages on behalf of a Low Power node in the friend queue. A polling mechanism is used for optimizing the energy consumption at the Low Power nodes. The Bluetooth mesh message exchange between the Low Power node and the Friend node is illustrated in this figure:

The timing parameters used in Friendship are:

  • Receive delay: This parameter specifies the time between Low Power node sending a request and listening for a response from the Friend node. Low Power node is in sleep state for the complete duration of the receive delay.

  • Receive window: This parameter specifies the time for which Low Power node listens for a response from the Friend node. Low Power node is in the scanning state for the complete duration of receive window.

  • Poll timeout: This parameter specifies the maximum time between two consecutive requests from a Low Power node. Within the poll timeout, if the Friend node or the Low Power node fails to receive request or response from the other node, Friendship is terminated.

Periodically, Low Power nodes polls Friend nodes for any data messages stored in the friend queue. After polling the Friend node, Low Power nodes enter the sleep state for the duration of receive delay. The Friend node uses the receive delay to prepare the response for the Low Power node. After the receive delay, the Friend node responds to the Low Power node before the sum of receive delay and receive window.

Check for Support Package Installation

% Check if the 'Communications Toolbox Library for the Bluetooth Protocol'
% support package is installed or not.
commSupportPackageCheck('BLUETOOTH');

Bluetooth Mesh Energy Profiling Simulation

This example allows you to create and configure a Bluetooth mesh network with different types of nodes such as End nodes, Relay nodes, Friend nodes, Low Power nodes. This example initiates and relays a sample mesh message from a configured source node to the configured destination node. If the same source node is transmitting the mesh messages to multiple destination nodes, then all the destination nodes form a group and the mesh message is transmitted to the group address. So, all the nodes in that group will receive the mesh message. Along with the mesh messages originated at the source node, Friendship messages are also exchanged between configured Friend and Low Power nodes. While the simulation is running, each node calculates the time spent in various states (transmission, listen, idle and sleep) of the node. This helps in calculating the lifetime of a node within the network.

Goals:

  1. Create and configure a mesh network

  2. Visualize message flooding

  3. Analyze the behavior of Friendship in the Bluetooth mesh network

  4. Profile the energy consumed by each node in the Bluetooth mesh network

Configuration:

  1. Source and destination node pairs

  2. TTL value for packet originated at each source

  3. Friend and Low Power node pairs

  4. Receive window and poll timeout value for each Friend and Low Power node pairs

  5. Relay nodes

Results:

  • Time spent in various states (transmission, listen, sleep and idle) by each node within the Bluetooth mesh network

  • Average time spent by each type (Relay, End, Friend and Low Power node) of node at various states

Create and configure mesh network:

You can use helperBLEMeshNode and helperBLEMeshVisualizeNetwork for creating and visualizing the mesh network respectively. In helperBLEMeshVisualizeNetwork , NumberOfNodes specify the total number of nodes in the network, whereas Positions specify the respective node positions. The default value for NodePositionType is 'Grid'. You can also specify your own network by configuring the value of NodePositionType to 'UserInput' and node positions to Positions.

% Reset the random number generator seed
sprev = rng('default');

% Number of nodes in the Bluetooth mesh network
totalNodes = 55;

% Initialize "meshNodes" with an object of type helperBLEMeshNode
meshNodes(1, totalNodes) = helperBLEMeshNode();
for nodeIdx = 1:totalNodes
    % Create an object for a mesh node
    meshNode = helperBLEMeshNode();
    % Unique identifier for a mesh node
    meshNode.Identifier = nodeIdx;

    meshNodes(nodeIdx) = meshNode;
end

% Load node positions
load('bleMeshNodesPositions.mat');

% Visualization object for Bluetooth mesh network
meshNetworkGraph = helperBLEMeshVisualizeNetwork();
meshNetworkGraph.NumberOfNodes = totalNodes;
meshNetworkGraph.NodePositionType = 'UserInput';
meshNetworkGraph.Positions = bleMeshNodesPositions;
meshNetworkGraph.VicinityRange = 25;
meshNetworkGraph.Title = 'Energy Profiling: Bluetooth Mesh Network';

Configure simulation parameters: You can specify the number of source and destination pairs in the network using sourceDestinationPairs. You can specify the number of Friend and Low Power node pairs in the network using friendLowPowerPairs. The number of relay nodes in the network are specified using relayNodeIDs. The mesh node objects pertaining to each mesh node are specified in meshNodes. The paths obtained for source and destination pairs are stored in paths.

% Simulation time, in milliseconds
simulationTime = 6000;

% Enable/disable visualization
enableVisualization = true;

% Enable/disable the animation in the visualization. If the
% "enableVisualization" is set to false, "enableAnimation" is not
% considered.
enableAnimation = false;

% Source destination pairs - sample mesh message originates at the source
% node and delivered to the destination node
sourceDestinationPairs = [1 52; 1 17; 12 7; 6 53; 54 51; 9 33; 18 52; ...
    29 52; 31 7; 12 9; 54 53; 55 1; 9 17; 18 35];

% Time to live (TTL) value for each source and destination pair in the
% range [0 127]
ttl = [20 23 35 21 23 30 22 20 23 35 21 23 30 22];

% Friend Low Power pairs - assuming that Friendship is established between
% the configured Friend and Low Power node pairs
friendLowPowerPairs = [16 52];

% Receive window (in milliseconds) for each Friend and Low Power node pairs
% (>= 120 milliseconds and <= 255 milliseconds)
receiveWindow = 180;

% Poll timeout (in seconds) for each Friend and Low Power node pairs
% (>= 2 seconds and <= 95.9 hours)
pollTimeout = 20;

% Relay nodes
relayNodeIDs = [3 4 5 8 10 11 15 19 20 21 23 25 28 30 32 34 36 37 38 39 41 ...
    42 43 44 45 46 47 48 49 26 2 16 13 27];

% Simulate the Bluetooth mesh network with the above configuration
[meshNodes, paths] = helperBLEMeshSimulation(meshNodes, totalNodes, meshNetworkGraph, ...
    simulationTime, sourceDestinationPairs, ttl, friendLowPowerPairs, receiveWindow, ...
    pollTimeout, relayNodeIDs, enableVisualization, enableAnimation);

% Restore the previous setting of random number generation
rng(sprev);

Statistics at Each Node

The statistics captured at each node are:

  • Time spent in transmission state

  • Time spent in listening state

  • Time spent in sleep state

  • Time spent in idle state

  • Number of messages transmitted from the node

  • Number of messages received by the node

  • Number of messages relayed by the node

  • Number of messages dropped at the node

  • Number of messages received with CRC failures

The workspace variable statisticsAtEachNode contains cumulative network statistics of all the nodes in the network. However, for a given simulation run, You can see the network statistics for a maximum of first five nodes. The network statistics for the first five nodes in the network are:

% Statistics of each node
statisticsAtEachNode = helperBLEMeshNodesStatistics(meshNodes);
statisticsForFirstFiveNodes = statisticsAtEachNode(1:min(totalNodes, 5), :)
statisticsForFirstFiveNodes =

  5x14 table

              NodeType    TransmittedMsgs    ReceivedMsgs    ReceivedMsgsFromLPN    ReceivedApplicationMsgs    RelayedMsgs    DroppedMsgs    CRCFailedMsgs    TotalTransmittedBytes    TotalReceivedBytes    SleepTime (milliseconds)    IdleTime (milliseconds)    ListenTime (milliseconds)    TransmissionTime (milliseconds)
              ________    _______________    ____________    ___________________    _______________________    ___________    ___________    _____________    _____________________    __________________    ________________________    _______________________    _________________________    _______________________________

    Node_1     End               6                10                  0                        1                    0              9               0                   171                    284                       0                         123.5                        5871                           1.368             
    Node_2     Relay            15                 6                  0                        0                    5              1               0                   426                    170                       0                           187                        5800                           3.408             
    Node_3     Relay            15                24                  0                        0                    5             19               0                   426                    685                       0                           178                        5809                           3.408             
    Node_4     Relay            12                20                  0                        0                    4             14               2                   339                    566                       0                           168                      5821.5                           2.712             
    Node_5     Relay            12                10                  0                        0                    4              4               2                   339                    285                       0                           168                      5821.5                           2.712             

The average time spent by each type of node at different states is calculated and plotted below. The results conclude that the Low Power nodes spend most of the time in sleep state, resulting in energy conservation and increased lifetime.

fprintf('Average time statistics of different Bluetooth mesh nodes are:\n');
meshNodesAvgStats = helperBLEMeshNodeAverageTime(meshNodes)
Average time statistics of different Bluetooth mesh nodes are:

meshNodesAvgStats =

  4x5 table

    Type of Bluetooth mesh node    Transmission time (milliseconds)    Listen time (milliseconds)    Idle time (milliseconds)    Sleep time (milliseconds)
    ___________________________    ________________________________    __________________________    ________________________    _________________________

          Low Power node                         2.304                              720                         103                       5166.5          
          Friend node                            6.192                           5771.5                       205.5                            0          
          Relay node                            3.3869                           5801.4                       185.7                            0          
          End node                              0.4836                           5907.4                        90.3                            0          

This example models a single message transmission from the source node to the destination node. However, you can configure the application traffic at the source node by calling the pushModelMessage function periodically. The transmission time at the End node depends upon the application traffic. Similarly, the transmission time at the Low Power node is influenced by the configured value of the poll timeout.

Further Exploration

Calculate Lifetime of Low Power Node:

You can use helperBLEMeshNodeLifetime to calculate the lifetime of a node in the Bluetooth mesh network at the end of simulation. The mesh node object of type helperBLEMeshNode is given as an input to helperBLEMeshNodeLifetime along with simulationTime to compute the node lifetime. The energy parameters are hardware dependent which are used to calculate the node lifetime. You can update the respective hardware parameters in the function helperBLEMeshNodeLifetime.

% Fetch one of the Low Power nodes for calculating the lifetime
meshNode = meshNodes(52);
lifeTime = helperBLEMeshNodeLifetime(meshNode, simulationTime);
fprintf('Lifetime of the node %d is: %.4f days.\n', meshNode.Identifier, lifeTime);
Configured hardware parameters for the battery capacity of 1200 mAh are:

hardwareParameters =

  7x2 table

       Hardware parameters        Configured values (mA)
    __________________________    ______________________

    Self-discharge                      0.0013699       
    Transmission on channel 37               7.57       
    Transmission on channel 38               7.77       
    Transmission on channel 39                7.7       
    Listening                                10.3       
    Sleep                                     0.2       
    Idle                                     1.19       

Statistics at node "52" are:

statisticsAtNode =

  4x2 table

     Time variables      Time (ms)
    _________________    _________

    Transmission time      2.304  
    Listen time              720  
    Sleep time            5166.5  
    Idle time                103  

Lifetime of the node 52 is: 34.8927 days.

Lifetime of Low Power Node by Varying Poll Timeout

The lifetime of a Low Power node depends on the time for which the node is in listen state. Most of the time, a Low Power node is in listen or sleep state for a given poll timeout. The time for which the node is in listen state is determined by the receive window for every poll request made by the Low Power node. The Low Power node spends the remaining time in sleep, idle and transmission state. However, the time spent in transmission state is negligible.

This result shows the plot of lifetime of Low Power node as a function of poll timeout for receive window values 120 milliseconds, 200 milliseconds and 255 milliseconds.

The results in the derived plot conclude that the lifetime of Low Power node is directly proportional to the poll timeout. This plot can be reproduced using the script helperBLEMeshLPNLifetimeVSPolltimeout.

This example shows how to create and configure a multi-node Bluetooth mesh network and then analyze the mesh message exchange through the statistics collected at each node within the network. This example also enables you to analyze the behavior and the advantages of the Friendship. The Bluetooth mesh network is simulated with multiple Friend and Low Power node pairs to calculate the time spent by each node on different states. The derived plot of the average time spent by each node in different states show that the Low Power nodes always consume less energy by spending more time in sleep state. Furthermore, you can also experiment by varying different configurations such as the receive window and poll timeout values as shown in the 'Low Power Node: Lifetime vs Poll Timeout' plot.

Appendix

The example uses these features:

The example uses these helpers:

Selected Bibliography

  1. Bluetooth Special Interest Group (SIG). "Bluetooth Core Specification". Version 5.0. https://www.bluetooth.com/.

  2. Bluetooth Special Interest Group (SIG). "Bluetooth Mesh Profile". Version 1.0. https://www.bluetooth.com/.

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