Calculate complete link budgets including all gains and losses
Apply the link success criterion to determine if wireless links will work
Compare protocol ranges for indoor, urban, and rural environments
Design BLE beacon deployments with proper coverage overlap
Plan LoRa gateway placement for urban and rural scenarios
635.2 Introduction
Link budget calculation determines if a wireless link will work by accounting for all gains and losses between transmitter and receiver. This chapter provides worked examples for designing IoT wireless coverage.
Time: ~20 min | Difficulty: Intermediate | P07.C15.U05c
635.3 Link Budget Calculation
Link Budget determines if a wireless link will work by accounting for all gains and losses.
Transmit power: +14.0 dBm
TX antenna gain: +2.0 dBi
TX cable loss: -0.5 dB
---------
Effective TX power: +15.5 dBm
Free space path loss: -113.66 dB
Environmental loss: -7.4 dB
Fade margin: -10.0 dB
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Total path loss: -131.06 dB
RX antenna gain: +6.0 dBi
RX cable loss: -2.0 dB
---------
Effective RX gain: +4.0 dBi
===================================
RECEIVED POWER: -111.56 dBm
SENSITIVITY: -137.00 dBm
-----------------------------------
LINK MARGIN: +25.44 dB (check)
===================================
Conclusion: Link works! With 25.4 dB margin, the connection is reliable even with additional fading, rain, or foliage growth.
Show code
{const container =document.getElementById('kc-net-6');if (container &&typeof InlineKnowledgeCheck !=='undefined') { container.innerHTML=''; container.appendChild(InlineKnowledgeCheck.create({question:"A LoRa gateway has receiver sensitivity of -137 dBm and a sensor transmits at 14 dBm with a 2 dBi antenna. The calculated path loss to a sensor location is 145 dB. An engineer proposes upgrading the gateway antenna from 3 dBi to 9 dBi. Will this make the link work?",options: [ {text:"No - the 6 dB gain improvement is insufficient",correct:false,feedback:"Let's calculate: Current link budget = 14 (TX) + 2 (TX ant) + 3 (RX ant) - 145 (path) = -126 dBm. With 9 dBi RX antenna: 14 + 2 + 9 - 145 = -120 dBm. Both exceed -137 dBm sensitivity! The original 3 dBi antenna already works."}, {text:"Yes - the 6 dB gain provides adequate margin",correct:false,feedback:"The link already works! With original 3 dBi: received = 14 + 2 + 3 - 145 = -126 dBm, which is 11 dB above -137 dBm sensitivity. The upgrade adds margin but isn't required to make it work."}, {text:"Yes, but the original antenna already provides a working link",correct:true,feedback:"Correct! Original: 14 + 2 + 3 - 145 = -126 dBm (11 dB margin above -137 dBm). Upgraded: 14 + 2 + 9 - 145 = -120 dBm (17 dB margin). Both work! The engineer should verify the actual problem isn't elsewhere (interference, obstacles, etc.) before spending on antenna upgrades."}, {text:"Cannot determine without knowing the frequency",correct:false,feedback:"Frequency affects path loss calculation, but the problem already gives us the calculated path loss (145 dB). With this value, we can determine link viability: 14 + 2 + 3 - 145 = -126 dBm, which exceeds -137 dBm sensitivity."} ],difficulty:"hard",topic:"Link Budget" })); }}
635.5 Protocol Range Comparison
Using link budget and propagation models, we can compare realistic ranges for different IoT protocols:
635.5.3 Rural Open Field (n=2.2, minimal obstacles)
Protocol
Frequency
TX Power
Sensitivity
Maximum Range
Application
LoRaWAN
868/915 MHz
14 dBm
-137 dBm
10-15 km
Farm sensors
Sigfox
868/915 MHz
14 dBm
-142 dBm
15-30 km
Remote monitoring
NB-IoT
700-2100 MHz
23 dBm
-140 dBm
10-35 km
Agricultural IoT
635.6 BLE Beacon Placement Example
Scenario: Retail store wants to deploy BLE beacons for customer proximity detection. Store is 50m x 30m with concrete walls, metal shelving, and merchandise.
Requirements: - Detect customers within 3-5 meter radius of beacon - Coverage for entire store - Minimize beacon count (cost)
Link Budget Analysis:
Beacon specifications:
- TX power: 0 dBm (1 mW - typical iBeacon)
- Antenna: 0 dBi (chip antenna)
- Frequency: 2.4 GHz
Smartphone receiver:
- Sensitivity: -95 dBm (typical)
- Antenna: 0 dBi
Environment: Indoor retail (n = 3.5, metal shelving)
Required detection distance: 5 meters
FSPL at 5m, 2.4 GHz:
L_FSPL = 20 log(5) + 20 log(2400) + 32.45 = 60.4 dB
Environmental excess loss (n=3.5 vs n=2.0):
L_env = 10(3.5 - 2.0) log(5) = 10.5 dB
Total path loss: 60.4 + 10.5 = 70.9 dB
Received power: 0 dBm - 70.9 dB = -70.9 dBm
Sensitivity: -95 dBm
Margin: -70.9 - (-95) = 24.1 dB (check) (good!)
Figure 635.1: Retail store BLE beacon placement with six 5-meter coverage zones
{fig-alt=“BLE beacon placement diagram showing retail store floor plan with six beacons positioned to provide overlapping 5-meter coverage zones across electronics, clothing, home goods, groceries, checkout, and entrance areas”}
Beacon Spacing Calculation:
Coverage radius per beacon: 5 meters (conservative, accounting for obstacles)
Coverage area per beacon: pi x 5 squared = 78.5 sq m
Store area: 50 x 30 = 1500 sq m
Minimum beacons needed: 1500 / 78.5 = 19.1 -> 20 beacons
With 30% overlap for handoff: 20 x 1.3 = 26 beacons
Recommended deployment: 24-26 beacons in grid pattern with 8-10 meter spacing.
635.7 LoRa Urban vs Rural Coverage Comparison
635.7.1 Urban Deployment (Dense City, n=4.0)
Gateway location: Rooftop, 30m height
Sensor location: Street level, 2m height
Frequency: 915 MHz
TX power: 14 dBm
RX sensitivity: -137 dBm (SF12)
Urban path loss model:
L(d) = L_0 + 10(4.0) log(d/d_0) + 15 dB (building penetration)
At 2 km distance:
L = 58 + 40 log(2000) + 15 = 58 + 132.0 + 15 = 205 dB
Link budget:
TX: 14 dBm
Path loss: -205 dB
RX: 14 - 205 = -191 dBm
Sensitivity: -137 dBm
Margin: -191 - (-137) = -54 dB (X) LINK FAILS!
Urban realistic range: 1-2 km
635.7.2 Rural Deployment (Open Field, n=2.2)
Gateway location: 10m mast
Sensor location: Ground level
Frequency: 915 MHz
TX power: 14 dBm
RX sensitivity: -137 dBm (SF12)
Rural path loss model:
L(d) = L_0 + 10(2.2) log(d/d_0) + 5 dB (foliage/ground reflection)
At 10 km distance:
L = 58 + 22 log(10000) + 5 = 58 + 88.0 + 5 = 151 dB
Link budget:
TX: 14 dBm
Path loss: -151 dB
RX: 14 - 151 = -137 dBm
Sensitivity: -137 dBm
Margin: 0 dB (marginal, but works)
Rural realistic range: 10-15 km
Figure 635.2: LoRaWAN urban vs rural coverage showing 5-10x range difference
{fig-alt=“Comparison diagram showing LoRaWAN coverage in urban versus rural environments, with urban gateway reaching 1-2 km through buildings versus rural gateway achieving 10-15 km over open terrain, illustrating significant range difference based on propagation environment”}
Key Insight: Same hardware, 5-10x range difference based purely on propagation environment!
TipAlternative View: Link Budget Waterfall
This variant shows the same propagation concepts as a link budget waterfall diagram - how signal strength diminishes step-by-step from transmitter to receiver.
Figure 635.3: Link Budget Waterfall - Shows how signal power changes from transmitter through path losses to receiver
Reading the Waterfall: Start at +14 dBm TX power, add antenna gains (green), subtract all losses (orange), and check if received signal exceeds sensitivity. Positive link margin = reliable link.
635.8 Summary
Link budget calculation accounts for all gains (antennas) and losses (path, cables, obstacles) to predict if a link works
Link success criterion: Received power must exceed receiver sensitivity
Urban vs rural coverage differs by 5-10x for the same LoRa hardware due to path loss exponent differences
BLE beacon deployments require 20-30% coverage overlap for reliable handoffs
Protocol selection depends on environment - LoRa excels in rural, NB-IoT in urban building penetration