Shulou(Shulou.com)11/24 Report--

Introduction: Readers often ask about the difference between cells and sectors, as well as the difference between carrier frequencies and carriers. Today, Xiao Zaojun will explain in detail.

Cell, sector, carrier and carrier frequency are concepts related to mobile communication base stations.

Let's start with base stations.

Base Station, or BaseStation, for short. It is an important part of wireless access network in mobile communication network.

The main functions of the base station are signal modulation and demodulation, radio frequency transmission and reception (see here for details: baseband, radio frequency, what is it used for?).

In the 4G era, the main hardware components of the base station are BBU (baseband processing unit), RRU (radio frequency remote unit) and antenna feed (antenna, feeder) system. In the 5G era, hardware has changed, passive antennas have become active antennas, that is, AAU (Active Antenna Unit).

In real life, we often see base stations. For example:

In fact, strictly speaking, the above picture is a tower of a physical site (or station,"station", site). Hanging from the tower are many antennas of the base station.

Complete composition of a base station (4G)

Usually, a site has not only one base station, but several base stations.

For example, mobile, telecommunications, Unicom and other operators, they all have their own base stations, are installed in the same site.

Moreover, even if it is an operator, it is likely that there are base stations with different network standards such as 2G, 3G, 4G and 5G, all of which are located at this site.

When I introduced antennas before, I mentioned that antennas have omnidirectional antennas and directional antennas. Omnidirectional antenna (usually whip, cylindrical), is to transmit signals in all directions. A directional antenna (usually a plate) transmits signals in a specified direction.

For some areas with wide field of view and low user density, omni-directional antenna is used, and the signal with lower frequency (longer wavelength, good diffraction ability and long coverage distance) covers a large area around. This is called "central motivation."

For complex areas and areas with high user density, directional antennas can be used to improve signal coverage.

Experts have calculated that the three antennas (each covering 120°) have the highest cost performance and the best effect. Therefore, there is a design of 3 coverage areas of a base station.

As can be seen from the figure below, base stations are located at the three vertices of each cell hexagon, and each base station uses three directional antennas covering one third of each of the three adjacent cells.

The above method is called "vertex excitation" method.

It can be seen that the coverage of directional antennas is more flexible and can effectively eliminate the impact of obstacles in the cell.

Of course, in addition to 3 antennas, other coverage methods can also be used, such as 6 antennas, each antenna covering 60°.

Whether it's 60° or 30°, the coverage area looks like a fan. This wireless coverage area is called a sector. Sectors, like base stations, are physical concepts that actually exist.

On the network optimization tool interface, the sector industries you see generally have the names of S and O base stations. S stands for Sectorized, Directional, Sectorized Site. O means omni-directional.

So, what is a neighborhood? A base station is a cell? Or is a sector a cell?

The answer is: not necessarily.

Before introducing cells, I need to introduce two concepts-carrier and carrier frequency.

Carrier, English name carrier, is also a physical concept. Generally speaking, it refers to modulated wireless electromagnetic waves carrying audio and video information. Each carrier occupies a certain range of frequencies.

The carrier frequency is the carrier frequency. The carrier frequency has many references, sometimes referring to the frequency value, sometimes referring to the associated hardware. The value of the center frequency of the carrier wave is the center frequency point.

A sector, if there is only one carrier, may not have enough capacity. In this case, multiple carriers are configured.

A sector is a physical concept, while a cell is a logical concept. Different network standards have different definitions of cells.

In 2G GSM, cell = sector.

2G GSM is a narrowband system with small single carrier capacity. Therefore, multiple carriers are "bundled" together to form a "cell."

For example, S2/2/2 means that the site has 3 cells (sectors), each with 2 carriers.

In 3G WCDMA, 4G LTE, 5G, cell = carrier.

3G WCDMA is wideband CDMA, 4G LTE single carrier bandwidth is larger. For a sector, 1-2 carriers are enough.

If it is an S 1/1/1 configuration with 3 sectors and only 1 carrier per sector, then there are 3 cells in total. (Between cells, scrambling codes are used to distinguish, for example, scrambling codes are 1, 2, 3).

For an S 2/2/2 configuration with 3 sectors and 2 carriers per sector, that makes a total of 3×2=6 cells. (The number of cells that can be configured in a single sector is related to hardware capabilities.)

We can also simply remember that the bandwidth is small, the number of carriers is large, and multiple carriers are configured as one cell. The frequency is wide, the number of carriers is small, and one carrier is one cell.

To sum up:

A wireless coverage area identified by a Base Station Identity Code (BSIC) or a Cell Global Identifier (CGI) is called a cell.

A cell is the smallest service area unit that provides terminal access. It is virtual and logical. The system defines it, and then engineers can configure and manage it as an object.

The key to distinguishing cells is whether they can provide independent services.

GSM has multiple carriers in a cell, but only one broadcast BCCH (broadcast control channel), so a cell is a combination of multiple carriers to provide cell service.

WCDMA and LTE have pilot signals between different carriers, which are independent. Therefore, a carrier is the concept of a cell.

All right, everybody get it?

This article comes from Weixin Official Accounts: Fresh Jujube Class (ID: xzclasscom), Author: Xiaozaojun

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