Concept 4E Building Entry

Concept 4E is a bounded analysis for the question: “What is the estimated signal immediately inside a representative building facade?” It is available at 2.6 GHz and 28 GHz. It does not turn the building dataset into an indoor radio map, a floor/room model, or a whole-building coverage claim. The 140 GHz research_sub_thz profile remains outside this concept.

Boundary and no-double-counting rule

Concept 4E evaluates a two-stage link:

1. Use the Concept 4D urban_short_range UMa outdoor LOS/NLOS median baseline from the serving cell to a representative facade point.
2. Subtract one standard O2I external-wall entry term at a receiver placed at zero indoor depth immediately inside that facade.

The facade target is not treated as an outdoor wall event. Outdoor-to-outdoor NLOS already uses the Concept 4D empirical NLOS formula, so Concept 4E does not add the legacy per-wall loss to that outdoor baseline. The response reports outdoor_wall_loss_db: 0 for this reason. The entry term is applied once, separately, as low_loss and high_loss scenarios.

There is no interior-room, floor, interior-wall, reflection, fast-fading, building-height, or whole-building inference. The receiver height is the configured per-cell receiver height. The result is one deterministic estimate per selected building, served by the strongest eligible cell under the low-loss scenario; the response retains both scenario powers.

Standard-derived loss model

The reference is 3GPP TR 38.901 V19.4.0, §7.4.3.1, “O2I building penetration loss.” The standard writes the O2I path loss as:

PL = PL_b + PL_tw + PL_in + X_sigma

where PL_b is the basic outdoor path loss, PL_tw is external-wall loss, PL_in is depth-dependent indoor loss, and X_sigma is penetration shadowing. Concept 4E uses the deterministic median (X_sigma = 0) and sets d2D-in = 0 m, so PL_in = 0 dB. Its implemented link budget is therefore:

P_outdoor_facade = Concept 4D UMa LOS/NLOS received power
P_low_inside     = P_outdoor_facade - PL_tw_low
P_high_inside    = P_outdoor_facade - PL_tw_high

For 28 GHz, the standard material terms are evaluated with f in GHz:

L_glass     = 2 + 0.2 f
L_IRRglass = 25.4 + 0.11 f
L_concrete = 5 + 4 f

The two reference compositions are:

PL_tw_low  = 5 - 10 log10(0.3 * 10^(-L_glass/10)
                           + 0.7 * 10^(-L_concrete/10))
PL_tw_high = 5 - 10 log10(0.7 * 10^(-L_IRRglass/10)
                           + 0.3 * 10^(-L_concrete/10))

At 28 GHz these evaluate to 17.8287874527 dB and 35.0290195972 dB. At 2.6 GHz the implementation uses the standard’s UMa/UMi single-frequency backward-compatibility value from Table 7.4.3-3: PL_tw = 20 dB and PL_in = 0.5 * d2D-in. Because Concept 4E fixes indoor depth at zero, its low/high API scenarios are equal at 2.6 GHz (20 dB each). The standard’s reference sigmas are exposed as metadata, but no random draw is sampled.

The standard’s material composition is a simulation parameter dependent on metal-coated glass, regional market, and deployment scenario. A.T.O.M. does not invent that mapping from a generic OSM building type. Known tags are returned as optional evidence only; they never select one profile automatically. If material evidence is absent or not defensibly mapped, both profiles remain in the response and selected_entry_profile is unknown.

Geometry and deterministic selection

The backend evaluates one HTTP request containing the selected cell RF profiles and the building filter. It then:

• sorts cells and footprints by stable ID;
• selects footprints inside the effective per-cell radius union, unless an explicit building_ids filter is supplied;
• obtains a representative interior point from the polygon centroid when it is inside, then a vertex average, then a deterministic 15×15 interior grid;
• finds the first true outside-to-inside crossing from the cell to that point;
• rejects invalid polygons, tangent-only contacts, boundary-only points, and unclassifiable outdoor paths;
• classifies blockers before the target facade as outdoor LOS/NLOS and excludes the target building from the blocker test;
• evaluates the Concept 4D outdoor baseline and applies the two entry losses.

The response identifies the point sources and includes the facade coordinate, outdoor LOS state, outdoor received power, both entry losses, both just-inside powers, serviceability flags, material evidence, and limitations for each building. The -100 dBm building-service threshold and each cell’s receiver sensitivity are reported separately; they are not interchangeable.

Geometry regression fixtures cover rectangular, concave, multipart/decomposed, centroid-outside, invalid, and tangent cases. GeoJSON holes are not inferred as interior rooms: the existing runtime footprint representation uses outer rings, and Concept 4E makes no claim beyond the selected representative facade point.

API

POST /api/building-entry-analysis accepts the network-shaped RF defaults and one to six selected cells. The request is batched; it does not issue one HTTP request per building.

{
  "towers": [
    {
      "id": "cell-28-a",
      "tower_lon": 32.8541,
      "tower_lat": 39.9208,
      "azimuth": 45,
      "rf_profile": {
        "schema_version": 1,
        "network_tech": "5g",
        "propagation_model": "urban_short_range",
        "frequency_ghz": 28,
        "band": "n257",
        "bandwidth_mhz": 100,
        "channel_id": "NR-634666",
        "duplex_mode": "tdd",
        "tx_power_dbm": 30,
        "antenna_gain_dbi": 17,
        "system_loss_db": 2,
        "radius_m": 400,
        "beam_width": 120,
        "antenna_height_m": 25,
        "receiver_height_m": 1.5,
        "receiver_sensitivity_dbm": -115
      }
    }
  ],
  "rays": 72,
  "radius_m": 400,
  "frequency_ghz": 28,
  "tx_power_dbm": 30,
  "beam_width": 120,
  "calibration_offset_db": 0,
  "residential_only": false,
  "building_ids": []
}

The endpoint returns model, applicability, summary, per-building results, per-cell summaries, effective profiles, rf_contract, and diagnostics. diagnostics.http_requests_required is 1; the frontend stores the response under an RF-derived source key containing effective cell profiles, coordinates, azimuths, dataset revision, and filters.

Concept 4E results are invalidated when frequency, power, beam, antenna/RF profile, azimuth, selected cells, tower inventory, or dataset revision changes. Optimization priorities alone do not invalidate them because they do not change the RF payload. A successful azimuth/network optimization does invalidate the prior entry result because it changes effective RF state. The analysis is diagnostic/reporting output only; it is not an optimizer objective, constraint, score term, or candidate-site coupling.

Data audit

The active Ankara Open Planning Dataset is version 2026.07. Its manifest contains 451 towers and 161,626 building GeoJSON features; the runtime index contains 161,784 outer-ring footprints after multipart decomposition. Dataset validation reported zero invalid, repaired, or dropped building geometries.

The material audit scans building:material, facade:material, material, and roof:material. The canonical Ankara pack contains no usable material metadata in those fields, so Concept 4E reports 0 known and 100% unknown for that pack. Building type and residential/demand attributes remain useful for filtering and weighting, but they do not become material composition.

Canonical six-cell Ankara audit

The gated regression fixture uses the existing six-cell 28 GHz Ankara network scenario, with deterministic repeated execution and the active dataset. The following values are from the measured run on 17 September 2026. The analyzed building domain is summary.relevant_buildings, which includes all selected relevant footprints. summary.relevant_residential_buildings is a subset used for residential reporting; it is not the denominator for the all-building service rows. A service numerator includes only buildings with an applicable, valid facade estimate that meets the relevant threshold; unsupported buildings remain in the denominator but cannot enter the numerator.

Unsupported reason breakdown

The unsupported count is derived from the implementation applicability status, not from a free-text interpretation. The canonical breakdown is:

There were no invalid_geometry records in this run. The dominant status is an intentional aggregate result for buildings where no selected cell produced a valid eligible facade baseline under the configured radius/beam contract; it is not evidence that invalid geometry or a propagation-model fallback was hidden.

Representative ledger rows from the same run:

No known-material row or both-scenarios-fail row occurred among the selected canonical targets; those are intentionally reported as absent rather than fabricated examples. Repeating the fixture produced identical summaries, results, and cell summaries.

The complete low-loss-pass/high-loss-fail ledger for feature-101294 is:

Scope of future refinement

The current contract intentionally stops at a representative facade entry estimate. A later concept could add explicit floor/room geometry, material survey evidence, interior depth distributions, or calibrated regional composition parameters. Those additions would require a new model contract; they must not be inferred by silently extending Concept 4E.