Cells, coverage and capacity

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 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.

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.

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.