"Small cell" spans a range of low-power nodes below the macro. They differ by coverage, power, capacity and where they sit. Samsung's units map onto this spectrum: femto for homes, enterprise/pico indoors (CB1000), mmWave for dense capacity (LTM), and metro/outdoor for the street (FRMM).
| Class | Typical power | Range | Users | Where | Samsung |
|---|---|---|---|---|---|
| Femto | 10–100 mW | 10–50 m | ~8–16 | Home / SOHO | Home sFemto · sFemto2 |
| Enterprise / Pico | 100 mW–1 W | 50–200 m | ~32–64 | Offices / venues | CB1000 · LAA eFemto |
| mmWave | low (FR2) | tens of m | high-capacity | Dense indoor | LTM |
| Metro / Outdoor | 1–10 W | 100–300 m | ~128+ | Street / hot-spot | FRMM |
Small cells fill the gaps the macro leaves: deep indoor, ultra-dense capacity, outdoor hot-spots and homes. Each sits under the macro umbrella — which is exactly why macro↔small-cell interference, PCI and power are the first things you tune.
| Product | Class | Environment | Access | Role |
|---|---|---|---|---|
| CB1000 (Link Cell) | Enterprise | Indoor · enterprise | Open | In-building coverage & capacity for offices / venues |
| LTM | mmWave | Indoor · mmWave | Open | Ultra-high-capacity mmWave (n257 / n258 / n261) |
| FRMM | Metro | Outdoor | Open | Outdoor small cell / street-level densification |
| Home sFemto | Femto | Residential indoor | Closed / Hybrid | FSR 5.4.0 home coverage |
| sFemto2 | Femto | Residential / SOHO | Closed / Hybrid | FSR 5.4.0 home coverage (2nd gen) |
| LAA eFemto | Femto | Enterprise indoor | Open / Hybrid | FSR 5.4.0 enterprise femto with LAA (5 GHz) + Wi-Fi coexistence |
Most mobile traffic is indoors, where the macro signal is weakest (building penetration loss). Two ways to fix it: a Distributed Antenna System (DAS) — one shared radio feeding many passive antennas — or small cells like CB1000, each a self-contained cell. Small cells add capacity (each is its own cell); DAS mainly adds coverage (one cell, many antennas).
The LTM runs FR2 mmWave — enormous bandwidth for dense indoor capacity, but short range and easily blocked by walls/bodies, so it lives indoors close to users. FR2 is beam-based (up to 64 SSB beams) with wider sub-carrier spacing (120 kHz) and very short slots.
| Band | Frequency range | Duplex | Common name |
|---|---|---|---|
n257 | 26.5 – 29.5 GHz | TDD | 28 GHz |
n258 | 24.25 – 27.5 GHz | TDD | 26 GHz |
n261 | 27.5 – 28.35 GHz | TDD | 28 GHz (US) |
The LAA eFemto uses Licensed-Assisted Access: a licensed anchor carrier plus a 5 GHz unlicensed secondary carrier — the same U-NII spectrum Wi-Fi uses. To coexist fairly it runs Listen-Before-Talk (LBT): sense the channel's energy; if it's below the detection threshold after a random back-off, transmit for a bounded occupancy time. LAA is the LTE mechanism (Rel-13); NR-U is its 5G successor (Rel-16).
| LBT category | Behaviour | Used for |
|---|---|---|
| Cat 1 | No LBT (immediate, within an acquired TXOP) | short control after gap |
| Cat 2 | LBT without random back-off (fixed ~25 µs sense) | short signals / DRS |
| Cat 3 | LBT with random back-off, fixed contention window | — |
| Cat 4 | LBT with random back-off, variable contention window | data (Wi-Fi-fair) |
A femto/enterprise cell decides who may camp on it. This is the Closed Subscriber Group (CSG) model — critical for home femtos so a neighbour's phone doesn't hog your cell.
The macro must recognise small cells to treat their mobility differently. These are actual managed-object leaves from the Samsung Parameter Description (small-cell-pci-config): small cells carry a longer node ID (Home-eNB-ID 28-bit vs Macro 20-bit) and are matched by PCI range, so the gNB can register them as neighbours and apply small-cell mobility (e.g. redirection-only).
| Leaf | Range | Default | What it sets |
|---|---|---|---|
| small-cell-enb-id-length | macro(20) / home(28) | home(28) | E-UTRA small-cell eNB ID length (Home-eNB = 28-bit) |
| small-cell-gnb-id-length | 22 … 32 | per model | NR small-cell gNB ID length |
| register-nr-small-cell-as-neighbor | true / false | false | Register an NR small cell as a neighbour |
| register-eutra-small-cell-as-neighbor | true / false | false | Register an E-UTRA small cell as a neighbour |
| eutra-small-cell-pci · index | 0 … 15 | — | Index into the small-cell PCI-range list |
| small-cell-pci-range-index | −1 … 15 | −1 | Which PCI range marks a cell as "small" (−1 = none) |
| redirection-only-mode | true / false | false | Handle small-cell measurement reports by redirection only |
When a small cell shares the macro's channel, they interfere. 3GPP HetNet tools manage it: CRE (Cell Range Expansion) adds a bias so the small cell offloads more users; eICIC then protects those cell-edge users with ABS (Almost Blank Subframes) — the macro blanks subframes so the small-cell edge is interference-free.
Small cells are dense and often installed by non-experts, so they lean on SON (Self-Organizing Networks). Samsung's Smart SON automates the plug-and-play: pick a non-colliding PCI, learn neighbours via ANR, and set power/tilt so the new cell slots under the macro without manual planning.
Small cells need transport back to the core/CU. Options: fibre (best, for enterprise/metro), Ethernet over building LAN (femto/enterprise), or wireless backhaul for hard-to-cable outdoor sites. Femtos typically use the subscriber's broadband with IPsec back to a security gateway.
Small cells add capacity — if they don't hurt the macro.
Femto to metro, indoor mmWave to outdoor, LAA in unlicensed, CSG access, real PCI/ID config, eICIC and SON — the whole game is layering them under the macro cleanly. Next in 1.1: the 3GPP band map that ties every radio and cell to its spectrum.