Radio access in a city centre. A city centre with a macro site on the tallest roof and small cells at four junctions. The red map is the SINR the radios give the street.

Layers

Scenario

A city centre with a macro site on the tallest roof and small cells at four junctions. The red map is the SINR the radios give the street.

01/08

n78 3.5 GHz: 3.30–3.80 GHz · λ 84.4 mm · Main 5G capacity layer, massive MIMO · 3GPP TS 38.101-1

Network scenes

Radio access in a city centre

A three-sector macro site on the tallest roof and small cells on street poles: their coverage, interference and beams computed over the streets and buildings of the drawing.

The place: City centre

In this scene

Macro gNB, three sectors

Three 64-element active antenna units on the tallest roof, one per 120° sector, carrying the 3.5 GHz capacity layer and the 700 MHz coverage layer. (3GPP TS 38.104 (wide area BS), 3GPP TS 38.211)
Scene input: 73 dBm EIRP per n78 sector, 8° downtilt · Array: 8 × 8 elements, λ/2 spacing

Small cell on a street pole

Street-level capacity at about 11 m on existing poles: n78 today, a 26 GHz mmWave radio where the street is busy. (3GPP TS 38.104 (local area BS), 3GPP TR 38.901 UMi)
Scene input: 46 dBm EIRP at n78, 60 dBm at n258

Small cell

Small cell

Small cell

Exchange: baseband hub and edge

The street-level radios terminate here on dark fibre; baseband for the small cells runs on pooled servers next to the edge cache. (3GPP TS 38.401, O-RAN.WG4.CUS.0)

Links and interfaces

Fronthaul fibre

Dark fibre in the street ducts from each small cell to the exchange; the one-way delay is read from its routed length. (O-RAN.WG4.CUS.0 (split 7.2x), eCPRI 2.0)

Backhaul

The macro site reaches the exchange over fibre; from there the core network is in the operator cloud. (3GPP TS 38.410 (NG))

Computed for this scenario

Outdoor area at SINR ≥ 10 dB

55 %

Median SINR

11.4 dB

Shannon bound at median, 100 MHz

390 Mbit/s

Cell edge (5th percentile)

0.1 dB · 101 Mbit/s

SSB beams per burst (TS 38.213)

8

User beams steered

5

Array gain, 64 elements

18.1 dB

Beamwidth, azimuth

12.8°

Fronthaul fibre

139 m · 0.7 µs one way

Fronthaul fibre

629 m · 3.1 µs one way

Backhaul

755 m · 3.7 µs one way

Scenarios

Normal

All macro sectors and small cells on air at 3.5 GHz.

Sector A off

Macro sector A is off for maintenance; neighbouring sectors and the small cells carry its streets.

Interference

A co-channel transmitter switches on in the north-east block; SINR collapses around it.

26 GHz layer

The small cells switch to their 26 GHz radios: much more bandwidth, but only where the street gives line of sight.

Crowd

An event fills the streets; the macro steers a beam to each busy group.

Tour transcript

1. A city centre with a macro site on the tallest roof and small cells at four junctions. The red map is the SINR the radios give the street.
2. Three sectors of 64-element antennas. The lobes are the TR 38.901 pattern; the arcs are the wavefronts leaving each sector.
3. An SSB burst sweeps eight beams across the sector; then the panel steers one beam to each user it serves.
4. A small cell on a street pole fills the street canyon the macro cannot see into.
5. Switch sector A off: its streets fall back to the other sectors and the small cells.
6. A co-channel interferer: SINR, not signal strength, decides what a user can do.
7. At 26 GHz the small cells reach only the streets in their line of sight.
8. Fronthaul fibre runs in the street ducts to the exchange; its length sets the delay.

How the numbers are computed

Coverage is the strongest carrier at 1.5 m above the street on a 72 × 72 grid. Path loss follows 3GPP TR 38.901 (UMa for the macro, UMi street canyon for the small cells), with line of sight tested against the drawn buildings; the macro pattern is the TR 38.901 sector element with an 8° downtilt; SINR sums every co-channel transmitter and thermal noise (−174 dBm/Hz plus a 7 dB noise figure). The beams are the array factor of an 8 × 8 panel steered to each user; the SSB burst has 8 beams at 3.5 GHz (TS 38.213).