Summary
In brief: a base station contains cells; a cell contains sectors; each sector can host multiple radio carriers; and each radio carrier includes multiple channel elements.
Overview
A cell is a logical concept, while base station, sector, and radio carrier are physical concepts. Typically one base station corresponds to one cell, though a base station can be divided into multiple cells. If there are multiple sectors, there are multiple cells. The number of radio carriers per sector is determined by traffic demand.
Base Station
A base station is the outdoor tower or pole with mounted equipment and an equipment room, and can be classified as a macro site, microcell site, or indoor distributed antenna system (DAS). It is composed of antenna and feeder systems, RRU, BBU, and other modules.
A base station can be located at the center of a hexagonal cell using an omnidirectional antenna, referred to as center excitation, or at a vertex of the hexagon using 120-degree or 60-degree directional antennas, referred to as vertex excitation. When traffic in a cell increases significantly, the cell can be split into smaller cells (cell splitting), sometimes called micro-cells.
For CDMA base transceiver stations (BTS), the base station is usually omnidirectional and is itself a single cell without the concept of sectors. A CDMA BTS can support one or multiple radio carriers. Neighboring cells may use the same carrier frequency distinguished by different codes.
Cell
A cell generally refers to the coverage area centered on a base station and is identified by a cellId. For large macro sites, the coverage can be divided into several cells; in that case a cell corresponds to a sector (one or more carriers per sector), such as 3-sector or 6-sector configurations. When a base station contains multiple cells, those cells correspond to the station's sectors.
Sector
A sector is a physical concept describing the directional coverage provided by a base station antenna. Each sector covers a geographic area and uses one or more radio carriers (radiocarriers) operating at specific frequency points. Sectors and radio carriers together form the minimum service unit that provides user equipment (UE) access, i.e., the cell.
Omnidirectional base stations are used for low-traffic coverage and use an omnidirectional transceiver to cover a 360 degree circular area. In this case, a cell is a single sector and a base station equals one cell.
Directional base stations split the 360 degree area into sectors as traffic increases, forming 3-sector or 6-sector configurations. Each directional antenna covers an angular sector—for example, 3-sector sites typically use 120 degree coverage per antenna, and 6-sector sites use 60 degree coverage per antenna. In practice, sector beamwidths overlap slightly to ensure coverage continuity.
The number of cells a base station supports is determined by "number of sectors × carriers per sector." For example, a typical 3x2 configuration divides the full circle into three sectors (Sector0/1/2), each sector using two carriers, yielding six cells in total.
Radio Carrier
A radio carrier (carrier frequency) is a physical concept: a specific radio frequency in hertz used to carry information. In wireless systems, baseband information is modulated onto a high-frequency carrier for over-the-air transmission and reception.
In this context, a radio carrier refers to a hardware function within the base station responsible for modulation and demodulation. In communication systems, TRX denotes the transceiver unit and is typically considered a carrier. TRU (transmission receiver unit) is a generic hardware term for a carrier unit. A TRX specifically denotes the transmit/receive unit and is part of the TRU. Typically one TRX card supports one carrier, although there are higher-density TRX cards that support two carriers per unit.
TRX uses a modular structure that includes baseband processing and RF processing units. The TRX receives signals from mobile stations via the antenna, demodulates them to extract signaling and voice data, and forwards these to higher layers. Downlink signaling and voice are processed by the TRX and then sent to the antenna for over-the-air transmission. TRXs also receive management and configuration information from network modules and report status and alarms. Typical components include the baseband processing unit (TBPU) and RF processing unit (RPU).
Thus, a radio carrier is the fundamental front-end unit in wireless communication, responsible for receiving mobile signals and transmitting network signals.
Channel Element
A channel element (CE) is an abstraction on the baseband board of a base station capable of handling the equivalent of one voice channel.
