Case Study: WSN Term Project at IIT-M with NetSim

Wireless Sensor Networks (WSN) is an active area of research and given below is a case study of a WSN term project done at Indian Institute of Technology (IIT) Madras using NetSim, titled “Estimation of Carrier Sense Range and its effect on IEEE 802.15.4 Sensor Networks”

Challenge

  • Building probability models: The attenuation of IEEE 802.15.4 signals was to be observed and probability models for decoding range and carrier sense range were to be developed.
  • Estimating decoding range: This is the threshold below which packets sent from the transmitter are always received, and was to be estimated in terms of the probability that two devices separated by a distance are in decoding range.
         
Use Case
  • Developing custom code: Source C files, Sensor.c, CheckRoute.c and CCA.c of NetSim WSN library were modified. These codes were linked and debugged using NetSim’s project work environment.
  • Modeling network configurations: Custom Sensor network configurations were created using NetSim’s XML based network configuration files
  • Generating performance metrics: Packet and event traces were used for analyzing network performance metrics such as Throughput, Probability of packet discard, Average service rate and Mean Backoff duration
Results
  • Creating dependency graphs

  • These are directed graphs representing the probability of link establishment between sensors.These graphs were generated by sampling the probability model for each link.
  • Statistically analyzing performance: Variation in network performance, from simulation, for different dependency graphs were plotted for the 10 most likely and 10 least likely DG’s
  • Establishing confidence interval: This provides the probability that a network will operate in a corresponding range. The confidence interval for operation of the 802.15.4 Wireless Sensor network with limits of performance, i.e. throughput and packet failure probability, was established.
The complete report (1.3 Mb) is available at http://tetcos.com/WSN_Project_Report_IITM.pdf

Simulation of 802.22 Cognitive Radio Networks with NetSim

IEEE 802.22 Wireless Regional Area Networks (WRANs) are designed to provide broadband access to data networks. The WRAN systems will use vacant channels in the VHF and UHF bands allocated to the Television Broadcasting Service in the frequency range between 54 MHz and 862 MHz while avoiding interference to the broadcast incumbents in these bands.

NetSim v7, expected to be released in April, covers simulation of 802.22 WRAN based cognitive radio networks featuring: MAC layer model containing Super frame, DS-MAP, US-MAP, BW request, Quiet period and Normal mode operation

  1. PHY layer operating through OFDMA.
  2. CR Base station with interfaces to connect with Switch or Router and CPE’s  with a Max 512 CPE’s in each BS
  3. UGS, nrtPS, rtPS and BE QoS classes
  4. Incumbent model, Incumbent detection and channel switching
  5. Connection establishment via CID consisting of a 9-bit station ID (SID) and a 3-bit flow ID (FID).
  6. The cognitive plane consisting of Spectrum Manager, Spectrum Sensing Function, Spectrum Sensing Automaton, Channel Model.


802.22 Primitives with source C Code
The following protocol functionalities are available with source C code for extending existing algorithms: Transmit_SCH, Transmit_FCH, Transmit_DS_MAP, Transmit_US_MAP, Request_BW, Access_Phy_OFDMA, Spectrum_Manager, Spectrum_Sensing_Fn, Spectrum_Sensing_Automation, apart from various Channel_models

Metrics
Network metrics such as Network Throughput, Packet Delay plus CR specific metrics such as throughputs for each QoS class, incumbent detection rate, channel switching rate etc are available.
Packet Trace & Event Trace for CR simulations are also available for performance validation, statistical analysis and custom code de-bugging.