Wireless coverage is simultaneously WiFi's greatest advantage and its most complex challenge. Unlike wired networks where performance is predictable and consistent, wireless performance varies moment-to-moment based on distance, obstacles, interference, and even the weather.

Effective WiFi deployment requires understanding radio propagation physics, environmental attenuation sources, and the interplay between coverage and capacity. Under-provisioning creates dead zones and frustrated users. Over-provisioning wastes budget and can paradoxically degrade performance through excessive interference.

This page examines range from multiple perspectives: the physics governing signal propagation, environmental factors that attenuate coverage, practical planning methodologies, and optimization techniques for maximizing effective range.

A link budget accounts for all gains and losses between transmitter and receiver. If the received signal exceeds the receiver's sensitivity threshold, communication is possible. The margin between received power and sensitivity determines reliability.

Link Budget Equation:

Received Power (dBm) = Tx Power (dBm) + Tx Antenna Gain (dBi) - Path Loss (dB) 
                       - Environmental Losses (dB) + Rx Antenna Gain (dBi)

Required Condition:

Received Power ≥ Receiver Sensitivity + Fade Margin

Typical Values:

Parameter	Access Point	Client Device
Transmit Power	17-23 dBm (50-200 mW)	10-20 dBm (10-100 mW)
Antenna Gain	2-6 dBi (internal), 6-15 dBi (external)	0-3 dBi
Receiver Sensitivity	-90 to -95 dBm @ low rates, -65 to -75 dBm @ high rates	Similar

Understanding Receiver Sensitivity:

Receiver sensitivity varies dramatically with data rate. Higher MCS values require stronger signals:

Data Rate / MCS	Typical Sensitivity	Use Case
MCS 0 (BPSK 1/2)	-90 to -93 dBm	Maximum range, minimum speed
MCS 4 (16-QAM 3/4)	-80 to -83 dBm	Good range, moderate speed
MCS 7 (64-QAM 5/6)	-70 to -75 dBm	Moderate range, good speed
MCS 9 (256-QAM 5/6)	-60 to -65 dBm	Close range, maximum speed
MCS 11 (1024-QAM 5/6)	-55 to -60 dBm	Very close range

Example Link Budget Calculation:

Scenario: 802.11ac AP to laptop, 5 GHz, indoor office

Transmit Side (AP):

• Tx Power: 20 dBm (100 mW)
• Antenna Gain: 4 dBi (internal antenna)
• EIRP: 24 dBm

Path Losses:

• Free Space Path Loss (20m at 5.5 GHz): 74.3 dB
• Two interior walls: 10 dB (5 dB each)
• Furniture/clutter: 3 dB
• Total Path Loss: 87.3 dB

Receive Side (Laptop):

• Antenna Gain: 2 dBi

Received Power:

Rx Power = 24 dBm - 87.3 dB + 2 dBi = -61.3 dBm

Analysis:

• MCS 0 sensitivity: -90 dBm → Margin: 28.7 dB ✓ (excellent)
• MCS 7 sensitivity: -72 dBm → Margin: 10.7 dB ✓ (acceptable)
• MCS 9 sensitivity: -62 dBm → Margin: 0.7 dB ✗ (unreliable)

This client can reliably achieve MCS 7 (~65 Mbps) but cannot sustain MCS 9.

Real-world coverage differs dramatically from free-space calculations due to material attenuation, reflection, and absorption. Understanding common attenuators enables accurate coverage predictions.

Common Building Materials:

Floor and Ceiling Penetration:

Multi-story buildings require special consideration:

Construction Type	2.4 GHz Loss	5 GHz Loss	Notes
Suspended ceiling	2-4 dB	3-6 dB	Acoustic tile, minimal plenum
Concrete floor/ceiling	15-25 dB	25-35 dB	Standard construction
Post-tension concrete	25-40 dB	35-50 dB	Rebar mesh, very dense
Steel deck + concrete	30-50 dB	40-60+ dB	Industrial/commercial

Rule of thumb: Plan separate APs per floor unless explicitly verified otherwise. Even 'thin' floors typically attenuate signals enough to make floor-to-floor coverage unreliable.

Human Body Attenuation:

People absorb and block radio signals, especially at higher frequencies:

• Single person (torso): 3-6 dB attenuation
• Crowd (dense): 10-25 dB cumulative attenuation
• Higher frequencies affected more than lower

Implications:

• Conference rooms full of people perform worse than empty rooms
• Lecture halls need more margin than calculated for empty space
• Standing desks vs. seated affects signal paths
• Plan for worst-case occupancy, not empty-building surveys

Environmental Reflections and Multipath:

Not all environmental interaction is attenuation. Reflections create multipath propagation:

Multipath Effects:

• Metal surfaces reflect signals strongly
• Reflections can reach areas without line-of-sight
• Multiple paths can constructively interfere (stronger signal)
• Multiple paths can destructively interfere (signal nulls)
• MIMO systems actually benefit from moderate multipath

Fast Fading: In indoor environments, moving just a few centimeters can change received power by 10-20 dB due to changing interference patterns. This 'fast fading' is why fixed measurements don't capture real-world variability.

WiFi design falls into two fundamental approaches:

Coverage-Based Design:

• Goal: Ensure usable signal everywhere in the deployment area
• Metric: RSSI ≥ threshold everywhere (e.g., -70 dBm)
• Approach: Minimum APs to achieve coverage
• Typical: Small offices, warehouses, guest networks

Capacity-Based Design:

• Goal: Ensure sufficient bandwidth for all users
• Metric: Throughput per user ≥ requirement (e.g., 10 Mbps each)
• Approach: More APs for smaller cells, lower contention
• Typical: High-density venues, enterprises, classrooms

Capacity Calculation Example:

Scenario: Lecture hall with 300 students, video streaming requirement (5 Mbps each)

Required Capacity: 300 users × 5 Mbps = 1,500 Mbps aggregate demand

Per-AP Capacity (802.11ac, 80 MHz, reasonable conditions):

• Practical throughput: ~400 Mbps per radio
• With contention (50+ clients): ~250 Mbps usable
• Per-user if evenly distributed: 250 Mbps ÷ 50 clients = 5 Mbps each

Required APs:

• 300 users ÷ 50 users/AP = 6 APs minimum
• With redundancy margin: 8-10 APs recommended

Coverage Check: Does 8-10 APs provide overlapping coverage? For a lecture hall, likely yes—but coverage alone might have suggested 2-3 APs.

Cell Sizing and Power Control:

In capacity-based design, reducing transmit power is often beneficial:

Benefits of Smaller Cells:

1. More channel reuse (same channel used more times across space)
2. Fewer clients per AP (less contention)
3. Higher MCS achieved (clients closer to AP)
4. Less co-channel interference between APs
5. Better OFDMA/MU-MIMO effectiveness

Power Reduction Guidelines:

Deployment Type	Typical Tx Power	Cell Radius (indoor)
Coverage-focused	17-20 dBm	25-40 meters
Standard enterprise	11-14 dBm	15-25 meters
High-density	5-11 dBm	8-15 meters
Very high-density	2-8 dBm	5-10 meters

Professional WiFi deployment involves systematic site surveying—either predictive (modeling) or active (on-site measurement).

Predictive Survey:

Uses software to model coverage based on floor plans and material properties:

1. Import floor plan to survey software
2. Define wall types and materials (assign attenuation values)
3. Place virtual APs at proposed locations
4. Software calculates coverage heat map
5. Iterate placement until requirements met

Advantages:

• No on-site time required for initial design
• Easy to test multiple configurations
• Documentation for procurement

Limitations:

• Requires accurate material data (often estimated)
• Can't detect interference sources
• Real-world often differs from predictions

Active Survey (AP-on-a-Stick):

Physically places a test AP at each proposed location and measures actual coverage:

Procedure:

1. Configure test AP to match production settings (power, channel width, etc.)
2. Mount at proposed location (use tripod for ceiling heights)
3. Walk the coverage area with survey tool
4. Capture RSSI, SNR, data rates at each point
5. Repeat for each AP location
6. Combine for complete coverage picture

Advantages:

• Actual propagation data, not estimates
• Captures real interference environment
• More accurate than predictive alone

Limitations:

• Time-consuming for large spaces
• Empty building differs from occupied
• Interference changes over time

Survey Data Collection:

Key metrics to capture during active survey:

Metric	Target Value	Notes
RSSI (signal)	≥ -67 dBm	For high-rate traffic
	≥ -70 dBm	For general data
	≥ -80 dBm	For voice
SNR	≥ 25 dB	For reliable high MCS
	≥ 20 dB	For moderate performance
Channel utilization	< 50%	To allow growth
Retry rate	< 10%	Indicator of environmental issues
AP overlap	15-20%	For roaming support

Post-Deployment Validation:

After installation, validate actual coverage against design:

• Walk-test with production configuration
• Test during typical usage hours
• Verify roaming between APs
• Document any dead zones for remediation

When coverage requirements exceed practical AP placement, several techniques can extend effective range:

1. Antenna Selection:

External antennas trade omnidirectional coverage for increased range in specific directions:

Antenna Type	Gain	Pattern	Use Case
Omni (internal)	2-4 dBi	360° horizontal	Standard indoor
Omni (external)	5-8 dBi	360° horizontal, narrower vertical	Warehouses, open spaces
Patch/Panel	8-12 dBi	~60-90° beam	Hallways, specific areas
Sector	10-16 dBi	~60-120° beam	Large venues, outdoor
Directional/Yagi	12-18 dBi	~30-45° beam	Point-to-point, long corridors

Antenna Gain Math:

• Each 3 dB gain approximately doubles range (in free space)
• 6 dBi vs. 2 dBi internal = ~1.5× range improvement
• But: regulatory EIRP limits may require reducing Tx power

2. AP Placement Optimization:

AP location significantly impacts coverage:

Height Considerations:

• Higher mounting reduces furniture obstruction
• But excessive height (>15 feet) reduces direct-path signal to desks
• Optimal: 8-12 feet for most office environments
• Warehouses: mount at mezzanine level if possible

Orientation:

• Most internal antennas are optimized for horizontal radiation
• Vertical mounting often degrades horizontal coverage
• Some APs have orientation-specific antenna patterns

Positioning:

• Avoid corners—wastes coverage in walls
• Prefer center placement for omnidirectional coverage
• Place outside interference sources (microwave, Bluetooth, etc.)
• Consider cable path requirements

3. Frequency Band Selection:

For maximum range, 2.4 GHz outperforms 5 GHz and 6 GHz:

Band	Relative Range	Best For
2.4 GHz	100% (baseline)	Legacy devices, maximum coverage
5 GHz	60-75%	Capacity + reasonable coverage
6 GHz	50-65%	Capacity in smaller cells

Strategy: Use 2.4 GHz as coverage underlayer with 5 GHz for capacity overlay. Band steering keeps capable devices on 5 GHz while 2.4 GHz catches edge-of-coverage clients.

4. Mesh/Repeater Architectures:

When wired backhaul isn't available, mesh extends coverage at the cost of capacity:

Dedicated Backhaul Mesh:

• Separate radio for backhaul (often 5 GHz)
• Client traffic on 2.4 GHz or another 5 GHz radio
• ~50-60% of wired AP throughput

Shared Radio Mesh:

• Same radio serves clients and backhaul
• ~25-40% of wired AP throughput
• Each hop approximately halves available capacity

Mesh Limitations:

• Not suitable for high-density or bandwidth-sensitive deployments
• Latency increases with each hop (10-30 ms per hop typical)
• Best for coverage extension, not capacity augmentation

While every environment differs, these guidelines provide starting points for planning:

Indoor Coverage Radius (Typical Office Construction):

Square Footage Guidelines (Enterprise Office):

Design Approach	2.4 GHz Coverage	5 GHz Coverage
Coverage-focused	3,000-5,000 sq ft/AP	2,000-3,500 sq ft/AP
Balanced	2,000-3,500 sq ft/AP	1,500-2,500 sq ft/AP
Capacity-focused	1,000-2,000 sq ft/AP	800-1,500 sq ft/AP
High-density	500-1,000 sq ft/AP	400-800 sq ft/AP

Environment-Specific Considerations:

Open Office:

• Fewer obstructions, larger coverage per AP
• But: more clients visible to each AP (capacity limited)
• Strategy: Moderate density, capacity-based design

Private Offices:

• Walls attenuate signals, smaller effective coverage
• Fewer clients per AP (easier capacity)
• Strategy: Coverage-based design, 1 AP per 4-6 offices

Conference Rooms:

• High density when in use, empty otherwise
• Critical for reliability (meetings, presentations)
• Strategy: Dedicated AP per large conference room

Warehouses/Industrial:

• Large open spaces favor 2.4 GHz
• Metal racks create challenging multipath
• Mounting height critical for coverage patterns
• Strategy: High-mount omnis, coverage-focused