This application note covers the following path loss information:
In ACE Studio, simulated radios communicate when they are in-tune and in-range. Path loss effects are used to simulate radio degradation due to weather effects, terrain, time-of-day, etc. The radio receiver finds in-tune radios and then sends out a PDU request to the server for each in-tune radio. The server returns a response packet and the radio applies the amount of path loss to the radio calculation.
The path loss interface feature is a separately purchased software option. If your Target has the Path Loss Interface Software Package it is displayed on the RMS "Options File" page as the "Prop. Loss I/F" option.
The general operation of the path loss interface is as follows:
The packet is in a DIS-like format. The packet is formatted as follows:
RXpathPDU = record PDUheader : record ProtocolVer : byte; ExerciseID : byte; PDUtype : byte; PDUfamily : byte; TimeStamp : Unsigned_32bit; Length : Unsigned_16bit; Pad1 : Unsigned_16bit; end; RXEntityID : record Site : Unsigned_16bit; Application/Host : Unsigned_16bit; Entity : Unsigned_16bit; end; RXDeviceID : Unsigned_16bit; TXEntityID : record Site : Unsigned_16bit; Application/Host : Unsigned_16bit; Entity : Unsigned_16bit; end; TXDeviceID : Unsigned_16bit; PathFactor : IEEE_float_32bit; LocationRX : record X : IEEE_float_64bit; Y : IEEE_float_64bit; Z : IEEE_float_64bit; end; LocationTX : record X : IEEE_float_64bit; Y : IEEE_float_64bit; Z : IEEE_float_64bit; end; FrequencyMSW : Unsigned_32bit; FrequencyLSW : Unsigned_32bit; end;
All PDUs are delivered in network byte order (Big Endian). Path factor loss is of the range 0.0 - 1.0 with 1.0 indicating no loss at all (0dB) and 0.0 indicating complete loss (-300dB).
If the path loss interface shares the same Ethernet interface (for example eth0) as the host interface, it is highly recommended that the port numbers are set to different numbers.
Packets are transmitted to the host address and port number specified in the DIS Gateway. Upon reception of a packet containing path loss PDUs, the host computer must perform the following operations:
It is important that the reply packet contains all of the ID numbers in the original request packet. The host should not modify any field except as described above.
As a simple example, if line-of-sight occulting was being used:
If the host has a more sophisticated model, which takes into account frequency, the frequency of the transmitter/receiver pair is provided in the PDU.
There is not a global path loss enable for a radio. Instead, each of the radio’s mode/waveform/rxgain combinations must be configured to ensure the radio issues the path loss requests in those modes.
The path loss interface also has a set of parameters that control when a radio should send a path loss request. These parameters are set in the Parameters.ini file located inside the Domain. These settings help control timeouts, default values, and allow the radio to send path loss requests even if it is located at the center of the earth. The default file is included below:
The Path Periodic Timeout occurs once a radio has already received a path loss response and is stationary. This is similar to the normal timeout used by radios. The default is 60,000 milliseconds.
path_periodic_timeout = 60000
The Path Moving Timeout occurs if either the transmitter or receiver are moving. It is similar to the moving timeout used by radios. If the path moving timeout occurs, a new request is sent by the receiver. The default is 2000 milliseconds.
path_moving_timeout = 2000
If the transmitter or the receiver move more than the Path Moving Threshold before the Path Moving Timeout occurs, a new path loss request is sent out. The default is 500 meters.
path_moving_threshold = 500
The Path Request Timeout is used whenever a request is sent. It is the amount of time the receiver will wait before sending another request. If any of the above timeouts or thresholds are triggered and a path loss request is sent, the receiver will always use this timeout until hearing back from the server. The default is 2500 milliseconds.
path_request_timeout = 2500
The Path Timeout Count is the number of Path Request Timeouts that must occur before using the Path Timeout Factor.
path_timeout_count = 2
The Timeout Path Factor is the number the radio will use for path loss after reaching the Path Timeout Count. The default is 1.0 which is the same as if no path factor or additional attenuation were present.
path_timeout_factor = 1.0
The Initial Path Factor is the number used by the radio before a response is received from the server. The default value is 0, which is the same as a completely blocked path.
path_initial_factor = 0.0
The Force Path Request option allows radios that are in tune with a transmitter located at the center of the earth to still send out path loss requests. The default value is 0. To enable, set the value to 1.
path_force_request = 0
Also in the Target command line type:
tcpdump -i eth0 udp port 55001
Double-click the radio to open a detailed radio page.
At the bottom of the radio details page you should see a valid range and a path factor between 0-1. Note that this value will not be directly from the server and will include any additional propagation that is applied by ACE.