Indoor propagation models (any two)

Indoor propagation differs from outdoor because distances are short, the transmitter power is low, and walls, floors, furniture and people strongly affect the signal. Indoor channels are classified as line-of-sight (LOS) or obstructed (OBS). Two widely used models are described below.

1. Partition losses (same floor) model

Buildings have many internal partitions (walls, office cubicles, doors). Each partition between transmitter and receiver adds a measured loss.

• Hard partitions are part of the building structure (brick, concrete walls).
• Soft partitions are movable and do not reach the ceiling (cubicle walls, cloth office dividers).

Path loss is the free-space or reference loss plus the sum of losses of all partitions crossed:

PL(d) = PL(d₀) + 10 n log(d/d₀) + Σ PAF  (dB)

Typical measured partition losses: cloth office partition ≈ 1.4 dB, double plasterboard wall ≈ 3.4 dB, concrete block wall ≈ 13 dB, all-metal wall ≈ 26 dB.

2. Partition losses between floors (floor attenuation factor) model

Losses between floors depend on the building material, the floor type and the windows. The floor attenuation factor (FAF) is the extra loss for each floor between transmitter and receiver. The first floor gives the largest loss; additional floors add less.

           Floor 3   Rx
           ─────────────   FAF ≈ 6–10 dB
           Floor 2
           ─────────────   FAF ≈ 13–16 dB
           Floor 1   Tx

Typical values: about 13 dB for one floor, 18.7 dB for two floors, 24.4 dB for three floors (office building measurements).

3. Log-distance path loss model (with variants)

Many indoor measurements fit the log-normal form:

PL(dB) = PL(d₀) + 10 n log(d/d₀) + X_σ

• n = path loss exponent depending on building and surroundings (about 1.6–1.8 in an open LOS corridor, 2 to 3 in offices, up to 4–6 in obstructed paths).
• X_σ = zero-mean Gaussian random variable (dB) with standard deviation σ, which models shadowing.

The attenuation factor model (Seidel) combines both ideas:

PL(d) = PL(d₀) + 10 n_SF log(d/d₀) + FAF + Σ PAF

where n_SF is the exponent measured on the same floor.

Use

These models are used to plan Wi-Fi access points, femtocells and in-building DAS systems, for example to decide how many access points a three-storey office needs.