Radio

Radio Model

Radio Calculation

An adapted Friis transmission formula is used to determine the radio signal strength:

$$RSSI = P_{t} + G_{t}(r) + G_{r}(t) + 20 * log_{10}(\frac{\lambda}{4 \pi d}) + Trace_{LoS} + Trace_{Fresnel}$$

$RSSI$ - The received signal strength at the receiver, measured in $dBm$.

$P_{t}$ - Transmitter power in $dBm$.

$G_{r}(t)$ - Gain of the receiver antenna in the direction of the transmitter, in $dBm$.

$G_{t}(r)$ - Gain of the transmitter antenna in the direction of the receiver, in $dBm$.

$\lambda$ - Wavelength in meters.

$d$ - Distance between transmitter and receiver in meters.

$Trace_{LoS}$ - Attenuation due to physical obstacles on the line of sight between receiver and transmitter, in $dBm$ (a negative value if obstacles are present, or $0$ if there are none). This parameter also includes rain. The attenuation intensity depends on frequency (higher frequencies are more easily blocked by obstacles).

$Trace_{Fresnel}$ - Attenuation due to obstacles in the Fresnel zone, in $dBm$. Typically ranges from $0$ to $-10$, and the intensity depends on frequency.

Link quality is defined as follows:

$$LQ = \frac{RSSI + CG — I}{SNR}$$

$$0\% <= LQ <= 100\%$$

$LQ$ — Link quality as a percentage, usually indicating the ratio of received packets to sent packets.

$CG$ — Computational gain in $dBm$.

$I$ — Interference level in $dBm$. This takes into account the strongest signal among all others or the background thermal noise in the absence of any signals.

$SNR$ — Signal-to-noise ratio (SNR), including computational gain, relative to interference, required to achieve $100\%$ link quality.

Note

In practice, $CG$ and $SNR$ are abstract parameters used to regulate the range of link quality.

List of Accepted Radio Parameters

• Control transmitter gain: +15.
• Control transmitter power gain: +32.
• Control receiver gain: 0.
• Control frequency: 900MHz.
• Control SNR: 18.
• Control beamwidth: 60 degrees.
• Video transmitter gain: +5.
• Maximum video transmitter power: 2.5 watts (+34 dBm)
• Video receiver gain: +15.
• Video frequency: 5.6GHz.
• Video SNR: 25.
• Video beamwidth: 60 degrees
• Fresnel zone is independent of distance and frequency.
• Obstacle interference depends on frequency.
• Signal loss over distance is calculated using FSPL (Friis formula).
• Background noise in the absence of jamming is slightly above the thermal noise level.
• Default antenna height: 5 meters.
• Earth curvature is not considered.
• Antenna polarization is not considered.
• Trees are not considered unless present.
• Signals are not cumulative. Two EW signals at -60 dBm do not combine into a -57 dBm noise level.

List of Interference Sources

Power refers to the specific power per channel. It is assumed that the source must affect all potential channels equally due to the use of FHSS (Frequency Hopping Spread Spectrum).

Name	Directionality	Control	Video	Satellite Navigation
Stationary EW	+15dBm	9.0W	3W	4W
Trench EW	+0dBm	1.5W	---	1W
Tank EW	+0dBm	1.5W	---	1W
SuperCam EW	+0dBm	1.0W	---	0.5W