Cellular Networks

- Cellular Networks

A cellular network is a telecommunications network that allows wireless communication between mobile devices. It's also known as a mobile network. 

Cellular networks are made up of smaller cells, each served by a base station. The base stations and public telephone network are connected so that data and calls can be routed between cells. When a mobile phone is turned on, it scans the airwaves for a signal from a base station. 

Cellular networks are the most common connectivity method for most cell phones, smartphones, and dial-up devices. They provide high-capacity coverage over a wide area. 

Cellular networks offer protocol translation, data filtering, security, and local processing capabilities. 

- Mobile Phone Networks

The most common example of a cellular network is a mobile phone (cell phone) network. A mobile phone is a portable telephone which receives or makes calls through a cell site (base station), or transmitting tower. Radio waves are used to transfer signals to and from the cell phone. 

Modern mobile phone networks use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets change frequency under computer control and use low power transmitters so that the usually limited number of radio frequencies can be simultaneously used by many callers with less interference.

A cellular network is used by the mobile phone operator to achieve both coverage and capacity for their subscribers. Large geographic areas are split into smaller cells to avoid line-of-sight signal loss and to support a large number of active phones in that area. All of the cell sites are connected to telephone exchanges (or switches), which in turn connect to the public telephone network. 

In cities, each cell site may have a range of up to approximately 1⁄2 mile (0.80 km), while in rural areas, the range could be as much as 5 miles (8.0 km). It is possible that in clear open areas, a user may receive signals from a cell site 25 miles (40 km) away.

As the phone user moves from one cell area to another cell while a call is in progress, the mobile station will search for a new channel to attach to in order not to drop the call. Once a new channel is found, the network will command the mobile unit to switch to the new channel and at the same time switch the call onto the new channel.

[A Typical Cellular Network - ITU]

- Channels in Cellular Systems

In cellular, each cell phone communicates with its base station. Usually, this is done over two channels, one downstream and one upstream. 

Or sometimes the system uses "time division duplexing" (TDD), which shares one channel for up and down. 

And, multiple users in each cell can share the down and up links, with digital protocols such as TDMA (time division), CDMA (code division), or OFDMA and FBMC. 

If the two users are on the same cell system, they usually will not be in the same cell. Cells are small. Say, something like 1 or 2 km square, depending. Some can be a lot smaller, especially as we go to 4G and then 5G. Whatever the case may be, cell phones communicate only to base stations, in the normal case. 

So, whether cell system users are in the same cellular network or not, most of the time a so-called "backhaul network" becomes involved. The fixed, cabled or wireless network, which ties together the cells and ties the cellular system to the telephone system.

- Structure of the Mobile Phone Cellular Network

A simple view of the cellular mobile-radio network consists of the following:

• A network of radio base stations forming the base station subsystem.
• The core circuit switched network for handling voice calls and text
• A packet switched network for handling mobile data
• The public switched telephone network to connect subscribers to the wider telephony network

There are a number of ways to provide mobile cellular network but it is generally broken down into two main terms, macrocell and small cell. Both provide radio coverage but in very different ways making each more effective in different situations.

Despite their similarities, what differentiates the outdoor small cells is that microcells are for capacity and macrocells are for coverage. This is why in urban areas that are densely populated, such as New York City’s Wall Street, you will commonly find microcells used to create a cellular network that can cope with the high demand that macrocells cannot cope with. 

There are still challenges as macrocells can overpower microcells because they are more dominant which causes interference. To stop this from happening power needs to be carefully set so not to overpower neighbouring microcells. This needs to be reviewed every time more microcells are deployed as this changes the power balance.

[More to come ...]