Given below are some important points users should keep in mind when running 802.22 cognitive radio simulations

  • CR BS allocates max one symbol per CPE. If the generation rate is more than the data filled in one symbol then allocation fails and it results in zero throughput.
  • The first symbol is reserved for CR control frames or any broadcast PDU
  • Operational frequency: It is the frequency band at which the incumbent operates. It ranges from 54 MHz to 862 MHz.
  • Operational interval(s): It is the time gap between two successive incumbent operations. It ranges from 0-10.
  • Operational time(s): It is the active period of the incumbent. i.e. If the operational interval is set to 5s, then incumbent operates with an  interval of every 5s. If the operational interval is set to 0s, then the incumbent remains active.

For Operational Time(s) = 4, Operational interval=9

 

The timing diagram is as follows:

Incumbent --- 0s to 10s (OFF), 10s to 14s (ON), 14s to 24s (OFF), 24s to 28s (ON) ... and so on.


NetSim outputs App layer throughput which is lesser than that of MAC layer throughput because of

  • TCP connection establishment
  • ARP set-up
  • Service flow creation CPE-BS and BS-CPE
  • BW request

To avoid the above effects

  • Generate custom traffic
  • Set DL/UL Ratio as 1:1 so that the BS transmits whatever it receives
  • Run UDP in transport layer
  • Use static ARP
  •  Run Simulation for more than 100 sec