GSM Cell

The number of cells in any geographic area is determined by the number of MS

subscribers who will be operating in that area, and the geographic layout of the area

(hills, lakes, buildings etc).

The maximum cell size for GSM is approximately 70 km in diameter, but this is

dependent on the terrain the cell is covering and the power class of the MS. In GSM, the

MS can be transmitting anything up to 8 Watts; obviously, the higher the power output of

the MS the larger the cell size. If the cell site is on top of a hill, with no obstructions for

miles, then the radio waves will travel much further than if the cell site was in the middle

of a city, with many high-rise buildings blocking the path of the radio waves.

Generally large cells are employed in:

_ Remote areas.

_ Coastal regions.

_ Areas with few subscribers.

_ Large areas which need to be covered with the minimum number of cell sites.

Small cells are used where there is a requirement to support a large number of MSs, in a

small geographic region, or where a low transmission power may be required to reduce

the effects of interference. Small cells currently cover 200 m and upwards.

Typical uses of small cells:

_ Urban areas.

_ Low transmission power required.

_ High number of MSs.

There is no right answer when choosing the type of cell to use. Network providers would

like to use large cells to reduce installation and maintenance cost, but realize that to

provide a quality service to their customers, they have to consider many factors, such as

terrain, transmission power required, number of MSs etc. This inevitably leads to a

mixture of both large and small cells.

 

 

Frequency Re-use

Standard GSM has a total of 124 frequencies available for use in a network. Most

network providers are unlikely to be able to use all of these frequencies and are generally

allocated a small subset of the 124.

We will take an example here suppose a network provider has been allocated 48 frequencies to provide coverage over a large area, let us take for example Great Britain.As we have already seen, the maximum cell size is approximately 70 km in diameter,thus our 48 frequencies would not be able to cover the whole of Britain.

To overcome this limitation the network provider must re-use the same frequencies over and over again, in what is termed a “frequency re-use pattern”. When planning the frequency re-use pattern the network planner must take into account how often to use the same frequencies and determine how close together the cells are, otherwise co-channel and/or adjacent channel interference may occur. The network provider will also take into account the nature of the area to be covered. This may range from a densely populated city (high frequency re-use, small cells, high capacity) to a sparsely populated rural expanse (large omni cells, low re-use, low capacity).

Principles of Cellular Telecommunications

A cellular telephone system links mobile station (MS) subscribers into the public

Telephone system or to another cellular system’s MS subscriber.

Information sent between the MS subscriber and the cellular network uses radio

Communication. This removes the necessity for the fixed wiring used in a traditional

telephone installation. Due to this, the MS subscriber is able to move around and become fully mobile, perhaps traveling  in a vehicle or on foot.

Cellular networks have many advantages over the existing “land” telephone networks.There are advantages for the network provider as well as the mobile subscriber.

Network Components :

GSM networks are made up of Mobile services Switching Centres (MSC), Base Station Systems (BSS)and Mobile Stations (MS). These three entities can be broken down further into smaller entities; such as, within the BSS we have Base Station Controllers, Base Transceiver Stations and Transcoders. These smaller network elements, as they are referred to, will be discussed later in the course. For now we will use the three major

entities. With the MSC, BSS and MS we can make calls, receive calls, perform billing etc, as any normal PSTN network would be able to do. The only problem for the MS is that all the calls made or received are from other MSs. Therefore, it is also necessary to connect the GSM network to the PSTN. Mobile Stations within the cellular network are located in “cells”, these cells are provided by the BSSs. Each BSS can provide one or more cells, dependent on the manufacturers equipment.The cells are normally drawn as hexagonal, but in practice they are irregularly shaped, this is as a result of the influence of the surrounding terrain, or of design by the network

planners.

Frequency Spectrum :

The frequency spectrum is very congested, with only narrow slots of bandwidth allocated for cellular communications. The list opposite shows the number of frequencies and spectrum allocated for GSM, Extended GSM 900 (EGSM), GSM 1800 (DCS1800) and PCS1900. A single Absolute Radio Frequency Channel Number (ARFCN) or RF carrier is actually a pair of frequencies, one used in each direction (transmit and receive). This allows information to be passed in both directions. For GSM900 and EGSM900 the paired frequencies are separated by 45 MHz, for DCS1800 the separation is 95 MHz and for PCS1900 separation is 80 MHz. For each cell in a GSM network at least one ARFCN must be allocated, and more may be allocated to provide greater capacity. The RF carrier in GSM can support up to eight Time Division Multiple Access (TDMA) timeslots. That is, in theory, each RF carrier is capable of supporting up to eight simultaneous telephone calls, but as we will see later in this course although this is possible, network signalling and messaging may reduce the overall number  from eight timeslots per RF carrier to six or seven timeslots per RF carrier, therefore reducing the number of mobiles that can be supported. Unlike a PSTN network, where every telephone is linked to the land network by a air of fixed wires, each MS only connects to the network over the radio interface when required. Therefore, it is possible for a single RF carrier to support many more mobile stations than its eight TDMA timeslots would lead us to believe. Using statistics, it has been found that a typical RF carrier can support up to 15, 20 or even 25 MSs. Obviously, not all of these MS subscribers could make a call at the same time, but it is also unlikely that all the MS subscribers would want to make a call at the same time. Therefore, without knowing it, MSs share the same physical resources, but at different times.

Composition of low-voltage systems

Structured cabling systems greatly simplify and optimize the management of various cable systems, since the installation of SCS allows you to combine them into a single information space. SCS include information, telephone, security and fire protection and so on. network, various switchgears, cables, control panels, necessary equipment, etc.
Design by SCS at the stage of construction. This requirement will create a literate project distribution of communications and connectivity for all cable systems to a single hardware node - the control center structured cabling system.
Local-area networks provide the following: resource sharing networks (modems, printers, files, and so on.) Reserve funds and storage of different information, the ability to quickly access the necessary information in the network information is protected from hacking, to work with modern means of enhancing the effectiveness of working process (electronic document management system, receiving and sending faxes, online databases, uninterrupted Internet access).

Automatic telephone stations are used to create a rapid and reliable telephone communications between departments and offices of the company. On the design and installation of ATS should also be approached intelligently. You must select a telephone station, to carry out programming and configuration of equipment and trained personnel to use the telephone station.

The system-clockwise and radio include: basic elements - the master clock and the secondary clock (interior, street, etc.); tuner - radio receiver, the receiver wire broadcasting, switching (jumper) equipment, aerial devices, line equipment.
This system provides indexing lap, Moscow and Greenwich Time; indication of the number, day of week, month and year, the alarm went off at the scheduled time, input signals a single time in a synchronized hardware. System indexes the level of background radiation.
World total time is measured ultra-precise atomic clocks that transmit signals to a satellite global positioning system (GPS), where the radio signal is received which were in connection with the master clock. Master clock, in turn, combined with the secondary clock (digital, switch, etc.), making the whole system shows the exact time.
Thus, low-voltage systems are designed to satisfy the most diverse aspects of modern life. Thanks slabotochke, our lives become more convenient, comfortable and safe. Home and office we are doing chores, relax and socialize, do not hesitate to organize the points needed to optimize the residential and commercial spheres of human activity. Modern equipment running smoothly, thanks to low-voltage systems, controls the situation in the home or office. And all that is required of us - is to learn to use new, accessible to every opportunity for his own benefit.

Designing low-power networks

The problem of designing "slabotochki" should be approached with understanding of its special importance, because the low-voltage systems will operate without problems only if well-designed project of installation. Ask for help is a professional design engineers. The project should be conceived not only in terms of literacy to accommodate objects of different sites (low-current flap, sockets, switches and so on.) Wire harnesses on the risers, but in accordance with established norms and standards, which are governed by SNIP 083-98.

Total regulatory documentation to be followed is as follows: GOST 21.101-97 "Basic requirements for design and documentation; RD 78.36.002-99" Technical means of security objects. Graphical symbols of system elements; SEP 7, "Electrical Code"; RD 78.145-93 "systems and systems security, fire and burglar alarms. Rules of production and acceptance of work; SNIP 3.05.06-85 "Building Regulations. Electrical devices; NPB 105-03 "Determination of categories of rooms, buildings and outdoor facilities for the explosion and fire hazard."

Of course, do not forget about the designer design room, where all the attributes of low-voltage systems must seamlessly fit.

To compile the project engineer to the Terms of Reference, which reflected the following aspects: the technical conditions for connection, the plan of the building design project facilities, the plan adjacent protected areas. Also need to pre-departure of the expert on the subject.