Deployment of Antennas – Spatial Coverage
Cellular communication is based on geographic division of the communication coverage area into cells. This technology was aimed at providing solutions for a large number of users simultaneously. Cellular communication antennas are the element that emits radiofrequency radiation in order to conduct cellular wireless communication. The antennas are deployed spatially in the form of cells, according to the required communication coverage. The size of the cells varies with population density (and consequently with the number of users) of each area covered. In rural areas there are fewer users, and the cells usually cover a wider area (cell radius up to 15 km), while in cities each cell covers a much smaller area.
The communication channels in a cell are divided into designated frequency bands, where each frequency in a specific band may cover a different number of users. Cells located close to one another use different frequencies in order to avoid intercellular interference For example, a particular cell uses 'set A' of frequencies, cells close to it will use 'sets B, C, or D' of frequencies, and more distant cells may go back to using 'set A' (this is called frequency reuse).
- The cellular network and communications technology
- Cellular base stations and the cellular network
- Comparison of the radiation intensity between a large cell (rural area) and a small cell (urban area)
- Radiation exposure in conversation compared with data transmission through the cellular network
The cellular network and communication technologies
Every cellular network operates through one of the existing communication technologies, and some of the networks allow communication through a number of parallel technologies. Each technology is characterized by its range of frequencies and the method of managing phone conversations, messages, data transfer or multimedia.
In the cellular communication networks, mobile phones operate at in specific radiofrequency ranges, for example, 900/1800 MHz (GSM), 800/900 MHz (WCDMA), 1800 MHz (LTE) and 2100 MHz (UTMS).
Cellular antennas at base stations and in the cellular network
In each cell there is a base station, and all phones and mobile devices in the same cell communicate with the base station in their area. The base station relays the transmitted information (conversation, message, data, etc.) to base stations in other cells through wireless communication, or through a cable network, or through a combination of wireless and cables. Each cell is divided into three zones and in each zone a transmission antenna and a reception antenna operating at that cell's frequencies are used. The division of the cell into zones enhances the quality of communication provided by the cell on the one hand, and reduces radiation intensity on the other.
Comparison of radiation intensity between a large cell (rural area) and a small cell (urban area)
The illustration below shows the effect of dense deployment of an array of antennas as opposed to low-density deployment. The bigger the cell, the higher the transmission power required, both for mobile devices and/or base stations. This could lead to greater radiation exposure, especially from mobile devices held close to the user's body (head or hand). Dense deployment reduces the radiated power of each antenna. In urban areas where antennas are densely arrayed, the power required to be received by each cellular device decreases sharply (more than the distance squared). For example, a two-fold decrease in the radius of the cell may reduce the required power four-fold or more. Therefore, the use of a large number of antennas to serve a densely populated area does not lead to greater radiation exposure, but in fact reduces it (see illustration).
This may be demonstrated as follows: For example, for a cell with a radius of 90 meters,a certain power is required between the base station and the mobile device at the edge of the cell in order to ensure adequate cellular communication,. If a number of smaller cells (7-9) with a radius of up to 30 meters are packed into the cell area, a much lower power is required, which could be as low as one-ninth of the previous power. The total overall power of the smaller cells is thus close to the radiation power of the large cell. This means that radiation exposure may be reduced up to nine-fold in the smaller cells compared with the single large one. Communication will still be adequate and maybe even enhanced. The conclusion is that an increase in the number of transmission cells covered by a communication area, through an increase in the number of antennas of lower intensity, will result in a reduction in the level of exposure to cellular radiation.
Increased density of transmission sources in cellular communication coverage reduces radiation intensity in the area
Radiation exposure during speech communication compared with data transfer through a cellular network
Radiation intensity differs when using a communication device as a phone (at low transmission power) and using it for data transfer through the internet (when not through a Wi-Fi connection). In this situation the transmission power is higher (up to 600 milliwatts when transmitting a photo/video from a mobile phone). Although for this purpose the device is not held close to the head but at some distance, exposure to the user's body exists and may be relatively higher. This is due to the relatively higher power, and because the device is still close to the body, usually the user's hands or legs.
References
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Ian Poole, Cellular Communications Explained: From Basics to 3G, March 31, 2006, ISBN-13: 978-0750664356.
