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Wireless Cell Technology

Tokyo_Japan_052917A
(Tokyo City, Japan - Hsi-Pin Ma)
 

 

Wireless Cellular Networks

 

[Wikipedia]: "A cellular network or mobile network is a communication network where the last link is wireless. The network is distributed over land areas called cells, each served by at least one fixed-location transceiver, but more normally three cell sites or base transceiver stations. These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell. When joined together, these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, tablets and laptops equipped with mobile broadband modems, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission.

In a cellular radio system, a land area to be supplied with radio service is divided into cells, in a pattern which depends on terrain and reception characteristics but which can consist of roughly hexagonal, square, circular or some other regular shapes, although hexagonal cells are conventional. Each of these cells is assigned with multiple frequencies (f1 – f6) which have corresponding radio base stations. The group of frequencies can be reused in other cells, provided that the same frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference.

The first commercial cellular network, the 1G generation, was launched in Japan by Nippon Telegraph and Telephone (NTT) in 1979, initially in the metropolitan area of Tokyo. Within five years, the NTT network had been expanded to cover the whole population of Japan and became the first nationwide 1G network." 

 

Mobile Phone Network


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.

 

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 London’s Oxford 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.

 

Macrocell

 

The term macrocell is used to describe the widest range of cell sizes. A macrocell or macrosite is a cell in a mobile phone network that provides radio coverage served by a high power cell site (tower, antenna or mast). Generally, macrocells provide coverage larger than microcell. The antennas for macrocells are mounted on ground-based masts, rooftops and other existing structures, at a height that provides a clear view over the surrounding buildings and terrain. Macrocells are found in rural areas or along highways. They can provide cellular network coverage for a large area which can span a large town. Macrocell base stations have power outputs of typically tens of watts. Macrocell performance can be increased by increasing the efficiency of the transreciever.

Fewer new macrocell sites are being built, with larger numbers of small cells recognized as an important method of increasing cellular network capacity, quality and resilience with a growing focus using LTE Advanced. 

 

Small Cell

 

Small cells are low-powered cellular radio access nodes that operate in licensed and unlicensed spectrum that have a range of 10 meters to a few kilometers. They are "small" compared to a mobile macrocell, partly because they have a shorter range and partly because they typically handle fewer concurrent calls or sessions. They make best use of available spectrum by re-using the same frequencies many times within a geographical area. Small cells can be used to provide in-building and outdoor wireless service. Mobile operators use them to extend their service coverage and/or increase network capacity.

Small cells, which have a smaller coverage area than base stations, are categorized as follows: Microcell (less than 2 kilometres), Picocell (less than 200 metres), Femtocell (around 10 metres). Small-cell networks can also be realized by means of distributed radio technology using centralized baseband units and remote radio heads. Beamforming technology (focusing a radio signal on a very specific area) can further enhance or focus small cell coverage. These approaches to small cells all feature central management by mobile network operators. 

Over a smaller cell area, a microcell is used in a densely populated urban area. Picocells are used for areas smaller than microcells, such as a large office, a mall, or train station. Currently the smallest area of coverage that can be implemented with a femtocell is a home or small office.

 

 

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