Planning site selection
Equipment is installed at the location
The location of the telephony services requires a place from which the administration of the system can be done, preferably an office or some other centrally located place. It also requires finding somewhere to install the BTS, which can be in the same physical location as where the administration happens or can be somewhere else altogether. However, it is important to take into account some technical and safety considerations when deciding where to put equipment. To find out more about the equipment that is needed for each installation, visit the Lista de componentes para la instalación del Sistema.
For more more information about the installation visit Diagramas y Ensamblaje del Sistema.
A Safe Place
The place where equipment is installed must be safe both for the equipment and for the people near the equipment and site. As far as the safety of the equipment is concerned, we are mainly talking about finding a place where it will be safe from robbery or vandalism, as well as protected from environmental hazards, such as lightening or other problems like electrical surges. Don't forget, the equipment is not cheap and in many cases are the collective property of the community, so it's important the community provides a safe place that is reasonably accessible in order to ensure the safety and security of the equipment.
It is important that the equipment be protected from environmental risks, particularly lightening, and so it is important that the installation site be properly grounded and protected.
For more information on this, please visit this external link:
In order to protect against current variations and spikes, we recommend installing a No Break or UPS, which is a voltage regulator with a battery included.
When it comes to the safety of people in the vicinity of the equipment, it is first necessary to make known to the general population that cellular equipment emits radiation. Although transmission equipment is usually installed at a reasonable distance from where people circulate, it is nevertheless a good idea to let people know about the effects of radiation close to the site and to maintain as much distance as they can from the transmission antennas.
The IFETEL in Mexico is developing their ruling for radiation safety in Mexico, for for information you can go to their website:
For information on FCC Policy on Human Exposure to Radio frequency Electromagnetic Fields go to the following link:
GSM technology has a built-in overage limit of 32 kilometers, nevertheless, the equipment used and documented on this wiki has a smaller range of coverage. Coverage depends on various factors: topography and geographic location of the BTS and the user handset, as well as atmospheric conditions, foliage and other possible environmental factors that effect the propagation of radio signals.
When speaking about topography, it is important to keep in mind that GSM signals propagate depending on the type of antenna used. We generally use omnidirectional antennas that spread the signal more or less evenly over a 360 degree horizontal plane. This type of antenna is recommended when installing in the center of a community or population.
We also use directional antennas that focus the energy of the BTS in a particular direction, depending on where they are pointed and the specs of the antenna. The back of the antenna will also emit and receive signal, but with little or no gain. This type of antenna is useful when installing in the edges of the community pointing at the town.
GSM signals are most easily thought of as being line-of-site, in other words, if there is a clear path between the antenna and the mobile handset, within the coverage area, there should not be any reception problems. GSM does penetrate most building materials, which allows for coverage indoors. It is unlikely that it will penetrate through dense foliage or through mountains or other geographic obstacles. If you imagine a lighthouse, the shadow or part where light can't reach because something is in the way will be places without coverage.
This is why it is a good idea to install the BTS and antennas in a high place, in order to transmit and receive over physical objects that might obstruct the signal path and create poor reception and call quality.
The ideal location of the Basic Radio (BTS) will have to be in the highest part of the community. If it used an omnidirectional antenna, the ideal geographic location for the antenna should be more or less in the centre of the community. If the location will be in a peripheral area of the community, the ideal will be to use a directional antenna aiming to the community.
Due to possible negative effects on coverage from topographic and geographic realities, it is necessary to do a site survey before installing equipment and towers to find the optimum location in terms of coverage, safety and accessibility. For example if potential site needs a WiFi connection between the BSC and BTS, there must be line of site between the two locations.
In theory, GSM signals should not be affected by climate or weather conditions, however in practice we have heard reports of this happening, specifically during heavy rains and fog, when coverage is seemingly affected. This is most likely caused by high levels of humidity that blocks or refracts the signal.
When looking for an installation site, accessibility is a key factor. The installation must be safe from easy theft and vandalism so neither too easily accessible or too isolated, but also accessible enough for technical repairs and maintenance to be done easily. The easiest thing is also for the site to have an electrical connection (of course properly grounded and protected from voltage spikes and lightening).
If the installation site chosen is on the roof of a building, ensure that access to the site or roof is restricted to protect people from radiation and the equipment itself from theft or damage.
If instead a tower site has been chosen, it is imperative that the tower be properly installed and grounded to avoid accidents and damage to equipment.
There are some basic preconditions that, if unmet, will result in the equipment not working properly.
1. There must be a standard 120v AC electrical connection with physical ground. This connection should be for the exclusive use of the equipment 2. In case a WiFi link is needed, there must be line of site between where the BTS will be installed and the location of the BSC, otherwise the WiFi links will not work properly.
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Signal amplifiers, antennas and repeaters
In some rural areas it is not uncommon to find fixed wireless terminals with high gain antennas or repeaters that are able to communicate and amplify very low and distant GSM signals that are not heard by normal mobile handsets. In many cases, the presence of these devices can create interoperability issues with community cellular installations. If there are many of these devices present or the community has invested in a signal repeater, these issues can potentially create conflict as this pre-existing service may be affected by the presence of the community cellular network.
This is how they work:
Fixed wireless terminals with high-gain directional (Yagi) antenna
These are essentially the same as mobile phones, except stationary and with the possibility of installing an external antenna. They use SIM cards and connect to the GSM network same as a normal mobile phone. In many cases, especially at the extreme limits of coverage of an existing GSM networks, these phone are connected to high-gain directional antennas. When a community network is installed close by, the receiver on these fixed wireless terminals can be "deafened" due to the very high gain antenna and the relatively high power of the newly installed signal, which means the phone no longer is able to receive the signal it once did from afar, even if the two networks are on different frequencies. The same thing can happen with repeaters. In Mexico, this problem is most common with Telcel fixed wireless terminals.
The phone has a directional Yagi antenna attached to it and installed on the roof or a mast:
The antenna amplifies the power of the signal going in to the receiver of the telephone, making it possible to community with very weak GSM signals. In many instances, the fixed terminal phone will then simply hop over the stronger signal (local community network) automatically. This can cause conflicts with those that already receive signal from afar as they lose their ability to connect to that signal when the community network is installed. In order to avoid these conflicts, Rhizomatica strongly prefers not to install in places where these types of phones are present. It is important that the community meet about this issue first, before communicating with us about installation plans.
N.B. Existen teléfonos "fijos" que se parecen mucho a los terminales celulares fijos, pero no utilizan frecuencias de GSM y por lo tanto, no hay interferencia. Normalmente, se puede encontrar información sobre la frecuencia que utiliza el teléfono en la parte trasera o debajo de la pila. Asimismo, las antenas son más cortas y cuentan con menos elementos perpendiculares.
En algunas comunidades se han realizado instalaciones de equipos que toman la señal de alguna compañía telefónica celular y la retransmiten. Estos equipos se llaman repetidoras. En algunas comunidades lejanas se han instalado repetidoras para poder tomar la señal de una compañía telefónica y poder contar con el servicio.
Estos equipos captan la señal telefónica a su alcance, sin embargo, en algunas ocasiones estas repetidoras no tienen la capacidad de quedarse fijas en una frecuencia y brincarán a la frecuencia que les llegue con más potencia, muy similar a la situación con los equipos fijos arriba mencionados. Cuando se realiza la instalación de la telefonía comunitaria, es posible que la repetidora brinque a la señal de la telefonía comunitaria, ya que tendrá una señal más fuerte y nítida que opacará a la señal previa más lejana. Esto interferirá con el servicio previo, de modo que Rhizomatica prefiere no realizar instalaciones en donde exista el servicio de repetidoras para no interferir con este.
Estos servicios son instalados por un particular o tercero, no necesariamente por la compañía que genera la señal original, de modo que estas repetidoras no cuentan con los estándares ni permisos de retransmisión. Por lo tanto, la compañía que proporciona la señal no se hace responsable de corregir el problema.
La forma en que funciona este servicio se describe abajo (tomada del sitio de ventas de estos equipos):
Con una antena Yagi recibes la señal en ese punto de montaña, cima, o loma donde si llega la señal, esa antena amplifica la señal y la manda al amplificador, el equipo la vuelve a amplificar y la manda a la segunda antena yagi, esa segunda antena yagi debe estar alejada 15mts de la otra antena y así podrá reenviar la señal hacia donde la apuntes con esa segunda antena yagi.
N.B. No todas las repetidoras usan antenas yagis.