FREQUENCY
PLANNING

The Fresnel zone clearance requirement grows with distance and decreases with frequency. At 300 MHz over ten kilometers, the first zone has a 50-meter midpoint clearance requirement — meaning obstacles within fifty meters of the direct path between transmitter and receiver will degrade signal quality even without physically blocking the path. This physical constraint drives the entire deployment strategy for elevated mesh nodes across the brigade area.

Digital Elevation Model Integration

Lisa 26 loads Copernicus DEM (30-meter resolution, freely available from the European Space Agency) for the area of operations. The DEM provides ground elevation at every 30-meter grid cell. From this data, Lisa 26 calculates line-of-sight between every pair of MANET nodes by checking whether any terrain cell along the direct path rises above the Fresnel zone clearance envelope. A single hill that intrudes into 60 percent or more of the first Fresnel zone reduces signal strength by 6-20 dB — potentially the difference between a reliable link and a dead zone.

The radio planning computation runs for a full brigade network of 84 nodes in under 2 seconds on the battalion laptop. The output is a color-coded coverage map overlaid on the tactical map: green links have 20+ dB margin (reliable in all conditions), yellow links have 5-20 dB margin (work in clear weather but degrade in rain or heavy vegetation), red links have negative margin (no reliable communication possible without a relay). Fischer 26 at 300 m AGL turns most red links green by providing a relay path that clears all ground-level terrain obstacles.

Dynamic Replanning During Operations

Units move. The radio plan that was valid at the operations order becomes invalid when the battalion advances 2 km behind a ridgeline. Lisa 26 receives position updates from all MANET nodes every 2 seconds and recalculates the coverage map continuously. When a unit moves into a predicted dead zone, Lisa 26 alerts the signals officer: "Battalion HQ lost direct link to Company 2 — recommend Fischer 26 orbit shift 1.5 km west to provide relay." If Fischer 26 is under autonomous Lisa 26 control, it repositions automatically without human intervention.

The signals officer sees the electromagnetic picture on the same COP that shows the tactical picture. This integration is critical — radio planning cannot be separated from tactical planning. A company commander who plans a flanking movement through a valley must see that the valley is a radio dead zone BEFORE committing forces, not after they lose communication mid-movement. Lisa 26 provides this visibility.

Integration with Mission Planning

Radio coverage analysis feeds directly into mission planning. Before issuing an operations order, the company commander views the radio coverage overlay on the Lisa 26 COP alongside the tactical plan. If the planned axis of advance passes through a radio dead zone (red on the coverage map), the commander has three options: modify the route to maintain connectivity, pre-position a ground relay on the high ground overlooking the dead zone, or accept the communications gap and plan for temporary autonomy during the transit. This integration prevents the surprise discovery of dead zones during execution — when the cost of lost communication is measured in lives, not minutes of troubleshooting.

Try the interactive Link Budget Calculator →

Open the interactive Mission Planner →

Open the interactive Link Budget Calculator →

← Del av Platoon Integration

Radio Planning with Terrain Analysis

The radio planning tool in Lisa 26 loads digital elevation models (Copernicus DEM, 30-meter resolution, free) and calculates line-of-sight and Fresnel zone clearance between every pair of MANET nodes. The radio planning output shows coverage quality on a map: green indicates reliable links, yellow indicates marginal links requiring relay support, and red indicates dead zones where ground-to-ground communication fails. Fischer 26 at 200 meters altitude closes most red zones by providing an elevated relay above terrain obstacles.

Dynamic Radio Planning During Operations

During active operations, radio planning updates continuously as units move. When a battalion advances behind a ridge and loses direct MANET connectivity, Lisa 26 automatically recalculates coverage and recommends either repositioning a ground relay or adjusting Fischer 26 orbit to maintain the communication backbone. The radio planning algorithm runs in under two seconds for a full brigade network of eighty-four nodes, enabling real-time adaptation to changing tactical geometry.

Implementation

# pip install numpy
# Radio Coverage Planner — Fresnel Zone + LOS Analysis
import numpy as np
import math

def radio_coverage(tx_pos, tx_height_m, rx_positions, freq_mhz,
                   dem_data=None):
    """Calculate radio coverage from transmitter to multiple receivers."""
    results = []
    
    for rx_pos in rx_positions:
        distance_km = haversine_km(tx_pos, rx_pos)
        
        # Free space path loss
        fspl = 20*math.log10(distance_km) + 20*math.log10(freq_mhz) + 32.44
        
        # Fresnel zone radius at midpoint
        wavelength = 300 / freq_mhz
        f1_radius = math.sqrt(wavelength * distance_km * 1000 / 4)
        
        # Line of sight (simplified, flat earth + height)
        los_clear = tx_height_m > f1_radius * 0.6  # 60% Fresnel clearance
        
        # Link budget
        rx_power = 33 + 2 + 2 - fspl  # tx_dbm + tx_gain + rx_gain - fspl
        margin = rx_power - (-110) - 10  # noise floor - required SNR
        
        results.append({
            "position": rx_pos,
            "distance_km": distance_km,
            "fspl_db": fspl,
            "fresnel_radius_m": f1_radius,
            "los_clear": los_clear,
            "margin_db": margin,
            "link_ok": margin > 0 and los_clear
        })
    
    return results

def haversine_km(pos1, pos2):
    R = 6371
    dlat = math.radians(pos2[0] - pos1[0])
    dlon = math.radians(pos2[1] - pos1[1])
    a = math.sin(dlat/2)**2 + math.cos(math.radians(pos1[0])) * math.cos(math.radians(pos2[0])) * math.sin(dlon/2)**2
    return R * 2 * math.asin(math.sqrt(a))

# Fischer 26 at 300 m AGL, checking coverage to 10 ground nodes
tx = (65.8, 17.5)  # Norrbotten
nodes = [(65.8 + i*0.05, 17.5 + i*0.02) for i in range(10)]
coverage = radio_coverage(tx, 200, nodes, 300)
for c in coverage:
    print(f"  {c['distance_km']:.1f}km: margin={c['margin_db']:.0f}dB {'✓' if c['link_ok'] else '❌'}")

Related Chapters

Sources

ArduPilot docs. Silvus Technologies. NATO STANAG 4609 Ed. 4 and 4671. Ukrainian operational experience as documented by Watling & Reynolds, RUSI (2023) and ISW daily assessments. Swedish Armed Forces public publications (specific documents cited in sections above where applicable).