Effect of Downlink Uplink Ratio

The Cognitive Radio network you model from the example configuration file meets the following specifications:

  • A network with 1 base station, 1 router, 1 Wired node and 2 CR CPEs, and a unicast application running on one of the CR CPEs.

NetSim uses the following defaults for this example:

  • The unicast application transmits data at a constant bit-rate from CR_CPE_2 to Wired_Node_5.
  • Simulation runs for 30 seconds.

To simulate the example Effect of Downlink-Uplink Ratio for Cognitive Radio, in NetSim:

Open NetSim and Select Examples > Cognitive Radio Networks > Effect of DL UL Ratiothen click on the tile in the middle panel to load the example as shown in below screenshot

Figure4-9

The following network diagram illustrates what the NetSim UI displays when you open theexample configuration file Figure 4-10.

Figure4-10

  1. See that by default, NetSim has set a grid length of 500m X 500m.
  2. See that by default, NetSim has set the Uplink to Downlink ratio to 1:1. To do so:
    a. Right-click Base_Station_1 and click Properties. The Cr_Bs pop-up window appears.
    b. Click INTERFACE_1 (COGNITIVE_RADIO) in the left area.
    c. Click PHYSICAL_LAYER in the right area see Figure 4-11.
    d. DL_UL_Ratio drop-down list is set to 1:1.
    e. Click OK. The following figure illustrates the CR_Bs pop-up window and the default settings.

    Figure4-11

  3. See that by default, NetSim has not enabled Path Loss for the wireless links between the Base Station and the CR_CPEs. To do so:
    a. Right-click the wireless link between Base_Station_1 and CR_CPE_2 and click Properties. The Link Properties pop-up window appears.
    b. Channel_Characteristics drop-down list is set to NO_PATHLOSS.
    c. Click OK.

  4. Right click on the Application icon present in the top ribbon/toolbar and select Properties.
    a. A CBR Application is generated from CR-CPE-2 i.e., Source to Wireless Node 5 i.e. Destination with Packet Size remaining 1460Bytes and Inter Arrival Time remaining 10000µs. Transport Protocol is set to UDP instead of TCP.
  5. In NetSim GUI Plots are Enabled.
  6. Simulate the Effect of Downlink-Uplink Ratio for Cognitive Radio example. To do so:
    a. Click the Run icon located on the toolbar. The Run Simulation pop-up window appears.
    b. Retain the default settings in the Simulation Configuration tab (Simulation Time = 30)
    c. Click OK. After NetSim simulates the Effect of Downlink-Uplink Ratio for Cognitive Radio example, NetSim displays the Simulation Results window.
  7. Interpret the results. To do so, see the value in the Throughput (Mbps) column, in the Application_Metrics_Table window see Figure 4-12. You will see a value of 0.8218 Mbps. The following figure illustrates step (6) Figure4-12
  8. Simulate the Effect of Downlink-Uplink Ratio for Cognitive Radio example with the following Uplink to Downlink ratios: 1:2,1:3, and 1:4. You should see the following values of throughput for the different Uplink to Downlink ratios see Table 4-1
Sl No DL: UL Ratio Throughput (Mbps)
1 1:1 0.8218
2 1:2 0.9571
3 1:3 0.9575
4 1:4 1.001

You will see that the throughput for #2 is lesser than that for #3 because, 3 subframes are allocated for upstream and only 1 subframe for downstream. This means more data can be transmitted through the uplink.