# Cells, coverage and capacity

A cell is the area served by one base station sector. Every device in it shares the cell's radio capacity and spectrum. Full bars show a strong signal, not free capacity or a clean signal. Capacity is shared, and interference is a quality problem rather than a coverage problem.

- A cell is one radio coverage area served by a base station sector; every attached device shares its capacity.

- Reuse lets several cells use the same frequencies, and the co-channel cells interfere with each other.

- RSRP measures strength; RSRQ and SINR measure quality, including interference.

- Adding cells adds capacity only when they reuse spectrum or add spectrum; it does not create spectrum.

## A cell is a shared resource

A cell is the area served by one base station sector. Every device in that area shares the sector's radio resources, its scheduling and its backhaul. The cell does not give each device a private channel; it decides, many times per second, which device transmits and how much.
Capacity arithmetic is simple and easy to misread. If a cell serves 100 active devices and each needs 5 Mbps, the aggregate demand is 500 Mbps. That figure is illustrative, not a rating: the radio, the band width and the signal quality set the ceiling, and the ceiling falls as the signal worsens or the interference rises.
Full bars describe strength at the device. They do not describe how much capacity is left, how many devices are active or how clean the signal is. A device can show five bars in a cell that is saturated, and a saturated cell can still be a small distance from the antenna.
Coverage is not a circle. Buildings, terrain and antenna patterns make the edge uneven, so a device can be close to a site and still sit in a null or behind a wall. That is why a map drawn as a smooth ring and a reading taken on site disagree, and why the reading should win.

### Reuse the same frequencies in different cells

The teaching model shows N=1 and N=3. In N=1 every cell uses the same channel; in N=3 the pattern repeats every third cell. Cells with the same label are co-channel and interfere.

Alt: A seven-cell reuse model with two states. In N=1 all cells carry the same channel label; in N=3 the labels repeat every third cell.

The model shows seven cells. At N=1 all seven use the same frequency, so every neighbor is co-channel. At N=3 the pattern repeats after three cells, and the cells with the same label share the channel. Reuse buys capacity by spacing co-channel cells, in exchange for fewer channels per cell. This is a teaching model, not a network plan; real plans use other factors and the local terrain.

| Item | Value | Note |
| --- | --- | --- |
| N = 1 · 1 | Cell | f1 |
| N = 1 · 2 | Cell | f1 |
| N = 1 · 3 | Cell | f1 |
| N = 1 · 4 | Cell | f1 |
| N = 1 · 5 | Cell | f1 |
| N = 1 · 6 | Cell | f1 |
| N = 1 · 7 | Cell | f1 |
| N = 3 · 1 | Cell | f1 |
| N = 3 · 2 | Cell | f2 |
| N = 3 · 3 | Cell | f3 |
| N = 3 · 4 | Cell | f1 |
| N = 3 · 5 | Cell | f2 |
| N = 3 · 6 | Cell | f3 |
| N = 3 · 7 | Cell | f1 |

Source: Our teaching model; measurement definitions in 3GPP TS 36.214 (https://www.3gpp.org/ftp/Specs/archive/36_series/36.214/)

## Reuse buys capacity; it does not create spectrum

Spectrum is a fixed range assigned by a regulator. Reuse divides that range across space: the same channel serves one cell, then another cell far enough away. A tight pattern such as N=1 gives every cell the whole channel and accepts more interference. A looser pattern such as N=3, N=4 or N=7 spaces the co-channel cells and reduces interference, but each cell gets less of the channel.
Adding cells does not add spectrum. It adds capacity only when the new cells reuse the existing spectrum with less interference, or when the operator adds spectrum or wider channels. A new site that overlaps an existing one without a plan can raise interference and leave the user experience unchanged.
The band sets the room available. A wide mid-band channel carries more capacity than a narrow low-band channel, which is why cities use mid band for traffic and low band for reach. A device that supports only one of those bands cannot use the other, however good the network is.

### Shared capacity, illustrative arithmetic

100 users at 5 Mbps each is 500 Mbps of aggregate demand. The arithmetic is illustrative; the radio, the band width and the signal set the real ceiling.

Alt: A capacity scale showing 100 users per cell, 5 Mbps per user and 500 Mbps of aggregate demand.

The scale multiplies the number of active users by the average rate per user to show aggregate demand. With 100 users at 5 Mbps, the cell would need 500 Mbps of shared capacity to give every user that rate at the same moment. The model does not claim a real cell delivers that rate; it shows why the rate per user falls as more devices share the same cell.

| Item | Value | Note |
| --- | --- | --- |
| Users per cell | 100 |  |
| Rate per user | 5 Mbps |  |
| Shared capacity | 500 Mbps |  |

Source: Our illustrative model; capacity depends on band, radio and load (https://www.gsma.com/connectivity-for-good/spectrum/5g-spectrum-guide-2/)

## Strength is not quality

RSRP measures how much reference signal arrived. RSRQ compares that signal with the noise and interference around it. SINR compares the wanted signal with the interference. A strong RSRP with a poor RSRQ or SINR is a quality problem, and it produces the same symptom as a weak signal: a slow or unstable session.
Five bars with slow pages points to one of three causes. The cell may be congested, so the scheduler gives each device a small share. The signal may be interfered with, so retransmissions eat the capacity. The backhaul may be saturated, so the radio is fine and the path behind it is not. Measure all three before you change the radio plan.
Distance is a strength problem. Interference is a quality problem. A device at the cell edge can have a weak signal and a clean one; a device near the antenna can have a strong signal and a dirty one. The two need different fixes: more sites or a lower band for distance, and tighter reuse, antenna adjustment or more sectors for interference.
Measure at the busy hour, not at noon on a quiet day. Capacity problems appear when the most devices are active, and a reading taken outside that window can look healthy. Note the time with the reading so the next person can compare like with like.

The scenario fills RSRP and the technology. Enter RSRQ and SINR from the field to see the quality grade. Readings stay in the browser.

[Open the tool](/en/tools/signal/?src=learn-cells-coverage-and-capacity&scenario=field-rsrp&rsrp=-95&tech=lte)

## What to measure and what to change

Ask for five items: RSRP, RSRQ, SINR, the cell identifier and the time. Add the band and the number of active devices if the operator has them. Without the cell identifier, two readings from different cells look like one inconsistent measurement.
Change the cheapest thing first. Antenna tilt and azimuth, a new sector, a small cell or more backhaul can solve a local problem without a new spectrum license. Carrier aggregation helps when the device and the network share more than one band. None of these creates spectrum; each uses the existing spectrum better or relieves a bottleneck behind the radio.
Ask the operator to separate coverage from capacity in its answer. "We have coverage there" is a statement about signal. "We have capacity there" needs a band, a channel width, a cell count and a busy-hour measurement. The two claims answer different questions.
Keep the before-and-after readings with the change ticket. If a new sector or a tilt adjustment does not move RSRQ or SINR, the change did not address the cause. A measurement that is not repeated cannot show whether the fix worked.

### Five bars means good service

Myth: five bars means the cell has capacity for one more device.
Fact: bars show signal strength. Capacity depends on the band, the channel width, the number of devices and the interference. A five-bar cell can be full.

### Check your understanding

**Five bars, slow pages: what do you measure?**

Measure RSRQ and SINR for quality, then the cell load and the backhaul. A strong RSRP with poor quality points to interference or congestion, not coverage.

**Why does adding cells not add spectrum?**

Spectrum is a fixed range set by the regulator. A new cell reuses the same frequencies; it does not create new ones. It adds capacity only if it reuses them with less interference or if new spectrum is added.

**Which reading tells you interference rather than distance?**

SINR and RSRQ. RSRP falls with distance; SINR and RSRQ fall when the wanted signal is weak relative to interference or noise.

## FAQ

**Can a cell be full with five bars?**

Yes. Bars measure signal strength, not available capacity. A cell with a strong signal can still have many active devices or high interference.

**What is a reuse factor?**

The number of cells after which the same frequency group repeats. A larger factor spaces co-channel cells further apart and reduces interference, in exchange for fewer channels per cell.

**Is more RSRP always better?**

More RSRP means a stronger signal. It does not mean more throughput if the cell is congested or the signal is interfered with.

## Sources

- [3GPP TS 36.214: physical layer measurements (RSRP, RSRQ, RS-SINR)](https://www.3gpp.org/ftp/Specs/archive/36_series/36.214/) — Accessed: 2026-10-19
- [3GPP TS 36.133: requirements for support of radio resource management (reporting ranges)](https://www.3gpp.org/ftp/Specs/archive/36_series/36.133/) — Accessed: 2026-10-19
- [GSMA 5G Spectrum Guide: low, mid and high band capacity](https://www.gsma.com/connectivity-for-good/spectrum/5g-spectrum-guide-2/) — Accessed: 2026-10-19
- [ITU-R IMT-2020: 5G usage scenarios and spectrum](https://www.itu.int/en/ITU-R/study-groups/rsg5/rwp5d/imt-2020/Pages/default.aspx) — Accessed: 2026-10-19

Updated: 2026-10-19