Tactical vehicular radio network with multiple vehicles

• Simulation environment: 50 km * 50 km
• Application Traffic (HQ communicating with two vehicular Reece detachments)
  • Situational-awareness – 79 Byte packet sent every 1s
  • Data_Files – 0.5 MB file sent every 20s
  • Video – 0.6 Mbps streaming video
• Type of Devices: UHF MANET Radios
• Network Layer: MANET AODV Protocol
• PHY Layer
  • Transmitter Power: 20 Watts
  • Receiver Sensitivity: -113 dbm
  • Modulation Technique: QPSK

• Datalink Layer
  • Protocol: DTDMA (Dynamic TDMA) with demand-based slot allocation
  • Slot Duration: 2 ms, Frame Duration: 12 s
  • Guard Interval: 100 μs
  • Bits per slot: 3600 bits, Overhead per slot: 600 bits
• RF Propagation:
  • Path Loss Model: Log distance
  • Fading Model: Rayleigh, Shadowing Model: Log Normal
• Simulation time - 100 sec

Case 1: One vehicle transmitting data to HQ

Case 2: Two vehicles transmitting data to HQ

Throughput vs time plot (FTP Application)

Throughput vs time plot (Application - FTP_1)

Throughput vs time plot (Video Application)

Throughput vs time plot (Application - Video_1)

Throughput vs Time Plot (Link)

Throughput vs Time Plot (Link_1)

Conclusions - Case 1

The FILE_RECEE application starts at 5 s. Its Throughput vs Time plot shows that the file transfer starts at 5 s, with a throughput of about 1.1 Mbps. The file size is 562500 B (4.5 Mbit). At 1.1 Mbps, the transfer takes about 4.5 s, so the throughput drops at about 9.5 s.

The file inter-arrival time is 20 s. The application therefore generates the second file at 25 s (5 s + 20 s). This transfer also takes about 4.5 s and completes at about 29.5 s. The cycle repeats.

The Video application starts at 0 s with a throughput of about 600 Kbps. This matches the generation rate, so the network has enough capacity for the video. When the FTP application starts at 5 s, it gets transmission priority, and the video throughput drops to 0.

When the FTP transfer completes at 10 s, the video transmission continues. The throughput increases to about 1.2 Mbps while the vehicle sends the buffered video frames. By 18 s, the buffer is empty, and the video throughput returns to the generation rate of 600 Kbps.

The link capacity is 1.5 Mbps. At first, the link occupancy is about 600 Kbps. When the FTP application starts, the occupancy increases to 1.2 Mbps. After the file transfer, only video uses the link, and the occupancy decreases.

Conclusions - Case 2

Case 2 has simultaneous transmission by two vehicles. Case 1 has transmission by one vehicle.

At 0 s, both vehicles start their video transmissions. In case 1, the video throughput is about 600 Kbps. In case 2, each video gets 600 Kbps at first, for a total system throughput of 1.2 Mbps. The link PHY capacity is 1.5 Mbps, so the link can carry both videos.

FILE_RECEE_1 starts at 5 s, and FILE_RECEE_2 starts at 10 s. Each application sends a 4.5 Mbit file every 20 s, which gives an average FTP generation rate of 225 Kbps. When FILE_RECEE_1 starts in Vehicle 1, it gets priority over the video from the same vehicle. The Video_1 throughput therefore drops at once.

In case 1, the FTP application got an instantaneous throughput of about 1.1 Mbps. In case 2, it gets only about 710 Kbps, because some of the link slots go to the Video_2 application. The 4.5 Mbit file therefore takes about 6.3 s to transfer, against 4.5 s in case 1. The buffered Video_1 frames start to go out only at about 11.3 s (5 s + 6.3 s). In case 1, they started at 9.5 s.

The second vehicle shows a similar pattern. Its video starts at 0 s and gets 600 Kbps until 5 s. Then FTP_1 starts, and Video_2 drops slightly, because the DTDMA protocol assigns more slots to FTP_1. FTP_2 starts at 10 s and gets priority over Video_2, because both come from the same vehicle. The Video_2 throughput therefore drops to zero.

FTP_2 also gets about 710 Kbps, so each of its files also takes about 6.3 s to transfer. After each transfer, Video_2 gets about 750 Kbps. This is more than the 600 Kbps generation rate, because the vehicle buffers video packets during the file transfer and sends them afterwards. The cycle repeats.

In case 1, the link was not fully occupied. In case 2, the link is fully used, at 1.5 Mbps. The combined generation rate of the two FTP and two video applications is more than 1.5 Mbps. For this reason, the situational awareness application sees a latency of 9.3 s, against 8.78 ms in case 1.