GSOC2015LrWpanMac

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802.15.4 realistic MAC and Energy Model

  • Abstract: The IEEE 802.15.4 standard defines the physical and media access control layers for LR-WPANs (Low-Rate Wireless Personal Area Networks), and is one of the enabling technologies for Wireless Sensor Networks as well as the emerging Internet of Things applications. The ns-3 network simulator currently offers support for simulating LR-WPANs as specified by the IEEE standard 802.15.4 (2006). The current MAC implementation however, lacks sleep features. The radio is assumed to be always active, which is not true for nodes deployed in the field which usually employ some sort of sleep/wake mechanism in order to conserve energy. The goal of this project is therefore to develop a realistic MAC model and link it with the energy model in order to simulate realistic scenarios where a node’s energy can get depleted resulting in changes in the network topology. Most of WSN research is focused on developing energy efficient protocols at each level of the protocol stack and hence this project, along with allowing for more realistic simulations would also help researchers to test the energy efficiency of their protocols running on top of 802.15.4 nodes.
  • About me: I’m currently in the final year of B.E. (Electrical and Electronics) at BITS Pilani, India. My main research interest is in networked embedded systems, specifically WSNs and IoT.

Approach

Deliverables

  • 802.15.4 Energy Model:

Development of LrWpan Radio Energy model that models the energy consumption of 802.15.4 nodes.

  • 802.15.4 Phy layer support for duty cycling MAC protocols:

Modifications to the LrWpanPhy model in order to support linking with the LrWpan Radio Energy model.

  • RDC layer for the 802.15.4 MAC:

RDC layer for testing the newly developed Energy model - development of the ContikiMAC Radio Duty Cycling Protocol is planned.

  • Linking the RDC layer with the 802.15.4 Energy Model

Integration of the 802.15.4 Energy Model and the new 802.15.4 MAC Model.

Researchers can test their own protocols by developing their own models and linking with the developed 802.15.4 Energy Model.

Schedule

  • Week1
* Define the various classes. Implement the energy model.
  • Week2-3
* Modify the Phy model. Define and implement the PhyListener for the energy model. 
* Define the energy model test class for testing the energy model. Test and document.
  • Week4-5
* New Mac layer implementation.
  • Week6-7
* Thoroughly test the working of the newly developed MAC model and check the flow of outgoing and incoming packets. 
* Debug any issues that may arise. Document.
  • Week8-9
* Start development of the ContikiMAC model. 
* Test the working of ContikiMAC. Document.
  • Week10-11
* Integration of the energy module and the Mac module. Thoroughly test the basic implementation of ContikiMAC, along with the energy model. 
* Simulate, analyze, debug, document.
  • Week12
* Define scope for future work. Optimizations. Buffer period.

Energy Model

The energy model consists of 2 major components:

  • Energy source.
  • Device energy model.

The Device energy model is used to represent the energy consumed by a specific device on a node (eg. a LrWpan radio device). The LrWpanRadioEnergyModel class (derived from DeviceEnergyModel class) will model the energy consumption due to the LrWpan radio device.


LrWpanMac.jpg


LrWpanRadioEnergyModel

Radio state machine:

States.jpg

The node's energy consumption is modeled as a function of the three main states of the radio transceiver:

  • Transceiver disabled (TRX_OFF)
  • Transmitter enabled (TX_ON)
  • Receiver enabled (RX_ON)

For most radios, there is no difference between *_ON and BUSY_* states with respect to the radio transceiver circuitry. Hence, the energy consumed in these states is approximately the same.

The amount of energy consumed by the radio depends on the current draw of the state and the time spent in that state. The current draw for various states can be found in the datasheets of radio transceivers. For example, for CC2420:

  • TRX_OFF (sleep): 426 uA
  • TX_ON (transmit): 17.4 mA @ 0 dBm
  • RX_ON (recv/idle): 18.8 mA

The EnergySource is updated periodically or after each transition, using the formula stateDuration * stateCurrent * supplyVoltage

Note: The transient energy when switching from one mode to another also impacts the total power consumption. Hence, it is important to precisely characterize the transition time between transceiver states. In the Three States Model described, six different transitions are possible:

  • TRX_OFF -> TX_ON and TX_ON -> TRX_OFF
  • TRX_OFF -> RX_ON and RX_ON -> TRX_OFF
  • TX_ON -> RX_ON and RX_ON -> TX_ON

The state transition energy is evaluated by multiplying the transition time by the power in the arrival state.

Weekly Progress

Week 1 (May 25, 2015 - May 31, 2015)

  • Implemented and tested LrWpanRadioEnergyModel with the four basic states.
  • Linked the LrWpanPhy with the LrWpanRadioEnergyModel and tested energy source update after each PHY transition.

Classes added/modified:

  1. LrWpanRadioEnergyModel (extends DeviceEnergyModel and LrWpanPhyListener)
  2. LrWpanPhyListener
  3. LrWpanPhy

References

  • Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (WPANs) [1]
  • The ContikiMAC Radio Duty Cycling Protocol [2]
  • An Energy Framework for the Network Simulator 3 (ns-3) [3]
  • Energy efficiency of the IEEE 802.15.4 standard in dense wireless microsensor networks: modeling and improvement perspectives [4]